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Mathematical Modeling of the Hot Strip Rolling of Microalloyed Nb,Multiply-Alloyed Cr-Mo,and Plain C-Mn Steels FULVIO SICILIANO,Jr.and JOHN J.JONASIndustrial mill logs from seven different hot strip mills(HSMs)were analyzed in order to calculatethe mean flow stresses(MFSs)developed in each stand.The schedules were typical of the processingof microalloyed Nb,multiply-alloyed Cr-Mo,and plain C-Mn steels.The calculations,based on theSims analysis,take into account work roll flattening,redundant strain,and the forward slip ratio.Themeasured stresses are then compared to the predictions of a model based on an improved MisakaMFS equation,in which solute effects,strain accumulation,and the kinetics of static recrystallization(SRX)and metadynamic recrystallization(MDRX)are fully accounted for.Good agreement betweenthe measured and predicted MFSs is obtained over the whole range of rolling temperatures.Theevolution of grain size and the fractional softening are also predicted by the model during all stagesof strip rolling.Special attention was paid to the Nb steels,in which the occurrence of Nb(C,N)precipitation strongly influences the rolling behavior,preventing softening between passes.The presentstudy leads to the conclusion that Mn addition retards the strain-induced precipitation of Nb;bycontrast,Si addition has an accelerating effect.The critical strain for the onset of dynamic recrystalliza-tion(DRX)in Nb steels is derived,and it is shown that the critical strain/peak strain ratio decreaseswith increasing Nb content;furthermore,Mn and Si have marginal but opposite effects.It is demon-strated that DRX followed by MDRX occurs under most conditions of hot strip rolling;during theinitial passes,it is due to high strains,low strain rates,and high temperatures,and,in the final passes,it is a consequence of strain accumulation.I.INTRODUCTION been achieved.The goal of the present research was,there-fore,to characterize strip rolling in terms of softening mecha-T HE metallurgical features of plate rolling are now nism,strain accumulation,grain size,and precipitation.Also,largely understood.[1–10]The long interpass times allow com-the rolling behavior of microalloyed Nb,plain C-Mn,andsome Cr-Mo grades will be considered and compared. plete static recrystallization(SRX)to take place if the steelAnother important point that arose from this study is that is being rolled above the interpass recrystallization stopthe levels of Mn and Si present in the steel appear to influence temperature(T nr),i.e.,in the absence of carbonitride precipi-the precipitation behavior during strip rolling.The occur-tation.Plate rolling below T nr leads to austenite pancaking,rence of precipitation changes the rolling load and must, because strain-induced precipitation prevents any furthertherefore,be accurately predicted.SRX from occurring.By contrast,during the very shortHodgson[15]has carried out an excellent analysis of the interpass times involved in rod rolling,neither SRX nordifferent types of mathematical models and has supplied a precipitation can take place,[11–14]and,in contrast to platelist of the advantages associated with the application of a rolling,the strain accumulation that takes place leads toparticular model to a given practical situation.According dynamic recrystallization(DRX)followed by metadynamicto this author,the main advantages are(1)a reduction in recrystallization(MDRX).Thus,the metallurgical character-the number of mill trials,(2)an evaluation of hardware istics of plate rolling,on the one hand,and of rod rolling,modifications,(3)the prediction of variables that cannot on the other hand,are now fairly clear.be measured,(4)an estimation of the effect of interactions, From the point of view of interpass time,strip rolling(5)the potential for performance enhancement,and(6) falls between the two processes discussed previously.Duringinexpensive research costs.the initial passes,when the interpass times are still relativelyThe applicability of any model must be intensively tested long,the metallurgical behavior is similar to plate rolling.in advance,preferably with industrial data.That is the As the interpass intervals become shorter,the characteristicsapproach that was employed here.After an improved accu-approach those of rod rolling.Because the classification of racy in predicting the operational parameters has been dem-strip rolling as being like plate rolling,on the one hand,or onstrated,the model can then be applied to production. like rod rolling,on the other,depends on chemistry and The analysis of mean flow stress(MFS)behavior as a rolling schedule as well as pass number,a relatively simple function of inverse absolute temperature permits identifica-and generally accepted analysis of this process has not yet tion of the main microstructural changes taking place duringrolling.These include SRX,DRX followed by MDRX,strainaccumulation,and phase transformation.Figure1illustratesthese phenomena schematically in the form of an MFS vs FULVIO SICILIANO,Jr.,Research Associate,and JOHN J.JONAS,1/T curve for a hypothetical five-pass schedule.Beginning Professor,are with the Department of Metallurgical Engineering,McGillat the first pass(on the left-hand,or high-temperature side), University,Montreal,PQ,Canada H3A2B2.Manuscript submitted March22,1999.there is a low-slope region,within which SRX occurs.The(a )Fig.1—Schematic representation of the evolution of MFS as a function of the inverse absolute temperature.Each characteristic slope is associated with a distinct metallurgical phenomenon.high temperature permits full softening to take place during the interpass interval.After pass 2,the lower temperature does not permit full softening,leading to strain accumula-tion.This accumulation then leads to the onset of DRX (as long as there is no precipitation),which is followed by MDRX between passes 3and 4.The analysis of MFS curves as described previously was first proposed by Boratto et al.[1]for determination of the (b )three critical temperatures of steel rolling (Ar3,Ar1,and Tnr ).[2,3,4]This technique has also been used to deduce that DRX occurs in seamless tube rolling [16,17]as well as in hot strip mills (HSMs).[18,19]Sarmento and Evans [19]came to similar conclusions in their analysis of industrial data from two HSMs.The main types of controlled rolling considered here are listed in the following paragraphs.Recrystallization-Controlled Rolling .In the schedules considered subsequently,as long as strip rolling is carried out above T nr ,SRX is considered to take place.Conversely,below T nr ,there is strain accumulation.Conventional-Controlled Rolling .Here,finishing is employed to flatten or “pancake”the austenite grains at temperatures below T nr .In this case,the particle pinning (c )resulting from the precipitation of Nb(C,N)retards or even Fig.2—Temperature-time diagrams comparing three rolling approaches:prevents the occurrence of recrystallization.In the absence (a )recrystallization controlled rolling,(b )conventional controlled rolling,of precipitation,as long as rolling is carried out below T nr and (c )dynamic recrystallization controlled rolling.for static recrystallization,the strain accumulation that takes place can trigger DRX followed by MDRX,leading to rapid softening between passes.In terms of mathematical model-ing,if there is no precipitation and the accumulated strain exceeds the critical strain,DRX is initiated,often causing caused by DRX when high strain rates are employed and large strains are applied (this corresponds to single-peak full and fast softening.This is usually associated with unpre-dictable load drops in the final passes.[20]behavior in the stress-strain curve).Circumstantial evidence for the occurrence of DRX in seamless tube rolling [16,17]and Dynamic Recrystallization-Controlled Rolling .This type of process consists of inducing DRX in one or more passes HSMs [18,19,21,22]can be found in the literature.Figure 2illustrates schematically the three different rolling during the rolling schedule.This can be done either by applying large single strains to the material or via strain paradigms described previously for a hypothetical five-pass schedule.The conditions associated with each type of rolling accumulation.Both methods allow the total strain to exceed the critical strain for the initiation of DRX.Some of the are displayed in Table I.Knowledge of the rolling parameters and process limitations associated with each method makesbenefits of this approach involve the intense grain refinementTable I.Mechanistic Conditions Pertaining to the Three Controlled Rolling TechniquesRole of Relation betweenType of T Range with Strain-Induced Precipitation andProcess Respect to T nr Precipitation RecrystallizationRCR above absence required SRX before precipitationCCR below presence required precipitation before SRX or DRX DRCR below absence required no SRX;DRX before precipitation possible the design of rolling schedules to fit the needs and B.Analysis of Mill Log Dataconstraints of each case.Logged data were collected from the following fiveHSMs:Dofasco seven-stand HSM(Hamilton,Canada), II EXPERIMENTAL PROCEDURE Algoma six-stand–2.69-m-wide HSM(Sault Ste.Marie,Canada),Sumitomo seven-stand HSM(Kashima,Japan), The present work combines the use of models developedSumitomo seven-stand HSM(Wakayama,Japan),and BHP from hot torsion test data and from the analysis of industrialsix-stand HSM(Port Kembla,Australia).Data from two mill logs.other HSMs were taken from the literature.[19]One is fromthe Usiminas six-stand HSM in Brazil,and the other is an A.Materials unidentified seven-stand HSM referred to here as“Davy.”Some1300logs were made available for analysis,of Various materials were tested and were divided into threewhich about300were examined in detail.The data that groups:microalloyed Nb(group A),multiply alloyed Cr-were employed consisted of interstand distances,work roll Mo(group B),and plain C-Mn(group C)steels.Tables IIdiameters,and pyrometer locations.For each strip,the fol-and III list the grades studied here.In group A(Table II),lowing data were used:chemical composition,strip width, some steels have low Si contents,with the same base compo-strip thicknesses before and after all passes(H and h,respec-sition(e.g.,AD5and AD6and AD7and AD8).Other typestively),work roll rotational speeds,roll forces,and tempera-have different Mn contents,with the same base compositiontures(mean values)for each pass,according to a model or (e.g.,AD9and AD10and AD2,AD3,and AD4).Theseto entry and exit temperatures.grades are used to study the influences of Mn and Si on theThe previous parameters were then employed to calculate precipitation of Nb(C,N)and on the critical strain/peakthe true strains,strain rates,interpass times,and MFSs, strain ratio.Table III gives the chemical compositions ofaccording to the Sims formulation.[4,23]The corrections for some of the multiply alloyed Cr-Mo and plain C-Mn gradesroll flattening,[24,25]redundant strain,and forward slip studied here.The steels used for the torsion tests are markedwith“TT.”between roll and strip[25]were taken into account in theseTable II.Chemical Compositions of the Niobium Steels Investigated(Group A)Steel Plant C Mn Si Nb Ti N*Al P S AA1TT Algoma0.050.350.0100.035—0.0040.0430.0080.006 AA2Algoma0.050.700.1000.053—0.0050.0450.0070.004 AA3Algoma0.060.700.1100.058—0.0050.0450.0080.004 AS1TT Sumitomo0.07 1.120.0500.0230.0160.0000.0290.0190.002 AS2TT Sumitomo0.09 1.330.0600.0360.0160.0030.0190.0170.020 AB BHP0.11 1.050.0100.031—0.0030.0400.0120.012 AD1Dofasco0.060.650.2250.020—0.0040.0350.0080.005 AD2Dofasco0.140.650.2250.020—0.0040.0350.0080.005 AD3Dofasco0.120.850.2250.020—0.0040.0350.0080.005 AD4Dofasco0.12 1.000.2250.020—0.0040.0350.0080.005 AD5Dofasco0.060.650.1150.030—0.0040.0350.0080.005 AD6Dofasco0.060.650.0100.030—0.0040.0350.0080.005 AD7Dofasco0.060.650.1150.045—0.0040.0350.0080.005 AD8Dofasco0.060.650.0100.045—0.0040.0350.0080.005 AD9Dofasco0.060.450.0100.008—0.0040.0350.0080.005 AD10Dofasco0.060.650.0100.008—0.0040.0350.0080.005 AD11Dofasco0.06 1.250.3250.0750.0240.0040.0350.0080.005 AD12Dofasco0.06 1.250.3250.080—0.0040.0350.0080.005 AM1“Davy”0.060.700.0700.050—0.0040.0510.0180.013 AM2“Davy”0.050.450.0200.020—0.0050.0470.0140.008 AU Usiminas0.110.540.0020.018—0.0040.0570.0140.008 *For the Dofasco grades,a mean value of40ppm N is listed here.The actual values are taken into account in the spreadsheets.Table III.Chemical Compositions of the Multiply-Alloyed and Plain C-Mn SteelsGroup Steel Plant C Mn Si Nb Ti Cr Mo V Ni N Al P S B BCM Sumitomo 0.280.520.220——0.830.15——0.0050.0260.0160.004BCMV Sumitomo 0.410.630.280—0.015 1.380.600.270.020.0060.0460.0130.001BCMVN Sumitomo 0.470.660.1700.0160.0160.980.970.120.460.0040.0420.0160.004CCA TT Algoma 0.030.270.010——————0.0040.0420.0080.010CS1TT Sumitomo 0.10 1.080.060——————0.0030.0200.0170.003CS2Sumitomo 0.450.760.210——————0.0050.0040.0170.004CD Dofasco 0.060.270.000——————0.0040.0350.0070.005CM “Davy”0.030.240.020——————0.0040.0420.0090.006CUUsiminas0.050.240.002——————0.0040.0300.0160.010calculations and were organized using MICROSOFT [1];here,the MFS (␴M )is a function of the strain,strain rate,temperature,and carbon content in weight percent.EXCEL*spreadsheet software.Some typical spreadsheet*MICROSOFT and EXCEL are trademarks of the Microsoft Corpora-␴M ϭexp ΂0.126Ϫ1.75C ϩ0.594C 2[1]tion,Redmond,WA.inputs and outputs are shown in Table IV .The same spread-sheet was used for the microalloyed Nb,multiply alloyed ϩ2851ϩ2968C Ϫ1120C 2T΃␧0.21␧˙0.13Cr-Mo,and plain C-Mn grades;this is because it does not consider microstructure but only mechanical parameters.According to the present method,the Sims formulation is employed to calculate and plot the MFS vs 1000/T for several bars.Because strip rolling reductions are applied at III.THE SUBMODELS APPLIED TO HOTSTRIP ROLLING various strains and strain rates,all the derived MFSs are“normalized”to ␧ϭ0.4and ␧˙ϭ5s Ϫ1.[27,28]An example of this approach for grade D5is illustrated A.The MFS Modelin Figure 3.It can be seen that Misaka’s equation overpre-dicts the MFSs obtained from the mill logs for this 0.03pct Improvement of the Misaka equationMisaka’s equation [26]has often been employed to specify Nb steel.On the other hand,it underpredicts the MFSs for some higher Nb grades.[28]The trend of the Misaka equation the MFS for C-Mn steels during hot strip rolling.It will be used here as the basis for a modified equation that takes fits the mill log values reasonably well in the region where the slope is quite shallow (i.e.,at low 1/T or high T values).into account the effects of different alloying elements,such as Mn,Nb,and Ti.The Misaka equation is displayed in Eq.This indicates that full SRX is occurring between the passesTable IV .Example of the Spreadsheet Calculations Carried Out Using the Mill DataInputs:Data from mill logsRoll Radius Roll Speed Width Gage TemperatureRoll Force Pass (mm)(rpm)(mm)(mm)(ЊC)(Tonne)————30.60——F139433.9126417.339872157F239154.5126410.799512223F338179.212647.429152116F4365119.01264 5.109071691F5363147.11264 3.908961357F6376167.21264 3.148841264F7378172.012642.618721627Outputs Hitchcock Forward Nominal Total Strain Rate Interpass 1000/T Sims MFS Pass R Ј(mm)Slip Factor Strain Strain*(s Ϫ1)Time (s)(K Ϫ1)(MPa)F1403 1.100.660.7512.9 3.480.79116F2412 1.090.550.6125.2 2.140.82151F3416 1.080.430.4841.3 1.480.84179F4402 1.080.430.4772.7 1.010.85151F5428 1.060.310.3494.20.790.86178F6472 1.050.250.271150.630.86185F75611.040.210.23131—0.87250*Includes the redundant strain.effects of the other elements are considered to be linear over their concentration intervals.**Comparison of Tables II and III indicates that the Eq.[2](group A)steels (Table II)have only half the average Si levels (about 0.11)compared to the Eq.[4](group B)steels of Table III (about 0.22pct Si).At the time this analysis was carried out,no account was taken of the Si levels on the MFS and,therefore,on the rolling load.In retrospect,however,this would have been desirable,as it appears from a study of the previous relations that the introduction of such a term may have permitted the use of a single set of coefficients.B.Modeling of Grain Size and Fractional SofteningDuring a particular pass of a rolling schedule,the sum ofFig.3—Comparison of Misaka’s equation and the present equation (MFS*)the retained and applied strains will determine which soften-based on chemical composition and fitted to the mill (Sims)data in the ing mechanism (SRX or DRX ϩMDRX)will operate.SRX region.Here,the mill data for grade AD5(0.03pct Nb)are corrected Depending on the type of softening,different equations are to a constant strain of 0.4and a constant strain rate of 5s Ϫ1.then employed to specify the grain size and fractional soften-ing.In this section,a method is described that can be used to follow the microstructural evolution during multipass roll-in this region.A solution-strengthening factor can,therefore,ing.For now,no attention is paid to the exact onset of DRX,be added that allows Misaka’s equation to fit all grades.For and the critical strain is simply taken as a fixed fraction of compositions AS1,AS2,and AB,for example,a correction the peak strain.The example given subsequently involves for solute strengthening due to the high Mn content (1.12,modeling microstructural evolution in a plain C-Mn grade,1.33,and 1.08,respectively),allows Misaka’s equation to and the critical strain is considered to be 0.8␧p .The onset fit the mill values.[28]Another correction is still required for of DRX in Nb steels is discussed in the next section,IIIC.the occurrence of strain accumulation and DRX,which leads During rolling,the temperature decreases continuously.to departures from Misaka-type behavior at high values of Thus,the temperature adopted for each interpass interval 1/T (i.e.,low T ).For this purpose,the model by Yada and is taken as the average of the prior and subsequent pass Senuma [29,30,31]was adapted and tested.[25,27,29]This pro-temperatures.This assumption is employed because the pres-duced the following final MFS equation:ent equations were derived for isothermal conditions and the interpass times are short enough to allow the use of a MFS ϩNbϭ(MFS Misaka (0.768ϩ0.51Nb ϩ0.137Mn [2]single temperature value.In the present work,the recrystallization and grain-size ϩ4.217Ti))ϫ(1ϪX dyn )ϩK ␴ss X dynrelations described subsequently were incorporated into the Here,X dyn is the softening attributable to DRX,␴ss is theMICROSOFT EXCEL spreadsheet software,as shown in steady-state stress,and K ϭ1.14is a parameter that converts more detail in Section IV .The submodels involved here flow stress to MFS.were assembled by following a method developed for rod Equation [2]is valid over the following concentration rolling.[11]The recrystallization kinetics equations used here ranges:0.020to 0.080pct Nb,0.35to 1.33pct Mn,and 0are adaptations of the Avrami–Johnson–Mehl–Kolmogorov to 0.024pct Ti.This approach has been used successfully equation,with parameters that were selected to fit the mill to calculate the MFSs in plain C-Mn [25,27]as well as in Cr-data.Mo steels,[27,32]and the respective equations are displayed 1.Softening between passesin Eqs.[3]and [4],respectivelyA softening model uses parameters such as strain,strain MFS ϩC-Mn ϭ(MFS Misaka (0.768ϩ0.137Mn))[3]rate,initial grain size,and temperature to decide upon the mechanism and calculate the extent of softening.In an HSM,ϫ(1ϪX dyn )ϩK ␴ss X dynthe softening between passes can be calculated with the aid of an MFS equation and temperature corrections.In the The Mn concentrations studied ranged from 0.27to 1.08present work,the microstructural evolution equations were pct.For the multiply alloyed steels,the following relation tested directly using the spreadsheet for the three groups of is applicable:[27,32]steels.The t 0.5equation selected for each group is shown in MFS ϩCr-Moϭ(MFS Misaka (0.835ϩ0.51Nb ϩ0.098Mn Table V .Note that Eq.[6]is the only one available for the DRX ϩ0.128Cr 0.8ϩ0.144Mo 0.3ϩ0.175V [4]kinetics of Nb steels.A similar expression is employed for ϩ0.01Ni))ϫ(1ϪX dyn )ϩK ␴ss X dynthe multiply alloyed grades,as derived in a recent study.[32]For the C-Mn steels,several equations are available;how-Equation [4]is considered to apply to the following composi-ever,the one developed by Hodgson et al.[33,36]provided the tion ranges:0.52to 0.66pct Mn,0to 0.08pct Nb,0.83tobest fit to the mill logs.1.38pct Cr,0to 0.46pct Ni,0.15to 0.97pct Mo,and 0to 0.27pct V .Due to the high maximum concentrations of Cr2.Strain accumulation between passesPartial recrystallization between passes results in retained and Mo,the solution effects approached “saturation;”this is why exponents are employed in this expression.Thestrain,which must be added to the strain applied in theTable V .Equations Describing the Softening KineticsGroup Type EquationReferenceASRX t SRX 0.5ϭ(Ϫ5.24ϩ550[Nb])ϫ10Ϫ18␧(Ϫ4.0ϩ77[Nb])d 20exp (330,000/R T )[5]33DRXt MDRX 0.5ϭ4.42ϫ10Ϫ7␧˙(Ϫ0.59)exp (153,000/R T )[6]34,35B SRX32t 0.5ϭ1.57ϫ10Ϫ14иd 20и␧Ϫ2.9exp ΂271,000R T ΃[7]DRX32t 0.5ϭ1.84ϫͫ␧˙иexp ΂330,000R T΃ͬϪ0.86exp΂271,000R T΃[8]C SRX32,36t SRX0.5ϭ2.3ϫ10Ϫ15␧Ϫ2.5d 20exp΂230,000R T ΃[9]DRX14t MDRX 0.5ϭ0.4΂␧˙иexp ΂300,000R T΃΃Ϫ0.8exp΂240,000R T΃[10]subsequent stand.The accumulated strain in pass i (i Ͼ1)is small,d 0i ϩ1will be close to the original grain size,d 0i ;in the latter case,the grains only change their shapes because then becomes [37]of the applied strain.[11]␧a i ϭ␧i ϩK acc (1ϪX i Ϫ1)␧i Ϫ1[11]b.Grain growth after recrystallizationwhere X is the fractional softening and K acc is a constant.After complete recrystallization,the microstructure is sub-The value of K acc was reported in the literature as falling jected to grain growth;this is driven by the decrease in free between 0.5and 1.[11,37]The parameter K acc can be related energy associated with the grain boundaries.For the group to the rate of recovery.High rates of recovery result in less A and B steels,one single equation (Eq.[19])was employed accumulated strain.This is clear from the work of Gibbs et to describe grain growth:al.,[37]where longer interpass times led to K acc ϭ0.5and shorter interpass times (less recovery)to K acc ϭ1.In the present hot strip model,the K acc constant is assumed to be d 4.5ϭd 4.50ϩ4.1ϫ1023ϫt ip[19]1and the accumulated strain is used in all the calculations.The latter is considered to represent the average strain pres-ϫexp (Ϫ435,000/R T )ent within the material.3.Grain-size evolutionAlthough the previous equation was derived for Nb steels,a.Recrystallized grain sizeit is used here to describe grain growth in the multiply This calculation simply takes into account the initial grain alloyed steels as well.This is due to the lack of an equation size,strain,and/or strain rate.The grain size after SRX is for the multiply alloyed grades,and because the alloying well known to be strongly dependent on the prior strain and elements present in the group B grades make it more rea-only depends on the strain rate to a minor extent.On the other sonable to adopt an equation derived for Nb steels than hand,the grain sizes after MDRX are strongly dependent on one derived for C-Mn grades.The grain-growth kinetics the strain rate.[14,15,34–36,38–41]The equations used here are in Nb and multiply alloyed steels are,of course,expected listed in Table VI.to be slower than in plain C-Mn compositions due to solute The grain size pertaining to the entrance of a given pass drag.For the group C (C-Mn)steels,however,a group of is considered to be the “initial”grain size (d 0).Note that equations is available to describe grain growth.The the equations used to model the recrystallized grain sizes method used here was proposed by Hodgson et al.[11,36,44]for the steels pertaining to groups A and B are the same;and is a “pragmatic”one,based on both laboratory [44]and this is due to the lack of appropriate equations for the multi-industrial [11]observations.ply alloyed steels.It should be noted that there is a large difference between In the case of incomplete recrystallization,the initial grain the rate of growth during the first second of the interpass size for the following pass (d 0i ϩ1)can be calculated using interval and the remaining time.This difference may arise the following relation,[11,33,43]which specifies a kind of because of the large driving force for grain growth present “average”derived from the freshly formed and original in the initially fine-grained structure.Another possible effect grain sizes:concerns the presence of “deformation”vacancies immedi-ately after rolling,which could accelerate growth.[45]This d 0i ϩ1ϭd rex i ϫX 4/3i ϩd 0i (1ϪX i )2[18]transition was handled by adopting different grain-growth exponents for each stage [11]and by using the following With this formulation,when X i is close to 1,the initial grainsize for the following pass is d rex i .On the other hand,if X iequations.Table VI.Equations Describing the Recrystallized Grain SizeGroup Type Equation Ref.A SRX d SRXϭ1.1иd0.670и␧Ϫ0.67[12]42DRX34d MDRXϭ1370ϫ␧Ϫ0.13exp΂Ϫ45,000R T΃[13]B SRX d SRXϭ1.1иd0.670и␧Ϫ0.67[14]41DRX35d MDRXϭ1370ϫ␧Ϫ0.13exp΂Ϫ45,000R T΃[15]C SRX33,36d SRXϭ343иd0.40и␧Ϫ0.5exp΂Ϫ45,000R T΃[16]DRX33,36d MDRXϭ2.6ϫ104и΂␧˙иexp΂300,000R T΃΃Ϫ0.23[17]SRX,t ipϽ1s[20]Eq.[3],based on the Misaka equation.The observed andpredicted MFSs are compared in Table VIII,where the differ-ences between the three sets of MFSs are also shown(in d2ϭd2SRXϩ4.0ϫ107(t ipϪ4.32t0.5)exp΂Ϫ113,000R T΃percentage).The“basic”version of the prediction spreadsheet MDRX,t ipϽ1s[21]described previously,allowing for strain accumulation andDRXϩMDRX,is considered to be fully applicable to the d2ϭd2MDRXϩ1.2ϫ107(t ipϪ2.65t0.5)exp΂Ϫ113,000R T΃group C(C-Mn)grades.However,for Nb steels,the criticalstrain for the initiation of DRX must be accurately known,and agreement regarding this quantity is lacking in the litera-SRX,t ipϾ1s[22]ture.The actual precipitation start time during hot strip roll-ing is also an unknown quantity.In the next two sections d7ϭd7SRXϩ1.5ϫ1027(t ipϪ4.32t0.5)exp΂Ϫ400,000R T΃(C and D),some improved methods for the estimation ofthese two parameters will,therefore,be proposed anddescribed for the Nb grades.MDRX,t ipϾ1s[23]d7ϭd7MDRXϩ8.2ϫ1025(t ipϪ2.65t0.5)exp΂Ϫ400,000R T΃ C.Critical Strain for the Initiation of DRX4.Design of the microstructural-predictionThe critical strain for the onset of DRX is an important spreadsheet parameter employed in the mathematical modeling of micro-The previous equations describing the microstructuralstructural evolution and of rolling load.Knowledge of the events can now be organized into a spreadsheet.Basically,critical strain for the initiation of DRX is a requirement for the spreadsheet parameters displayed in Table VII are usedprediction of the operating softening mechanisms in hot as input data to simulate the microstructural changes taking working processes.place during hot rolling,in a pass-by-pass analysis.TheFor the present purpose,it is useful to express the critical starting grain size(after roughing and before strip rolling)strain for the initiation of DRX(␧c)as a function of the is adopted as100␮m for the C-Mn grades and as80␮mpeak strain(␧p),as determined from a stress-strain curve. for the others.The subsequent grain sizes are calculated This is because several equations are available to specify after recrystallization and grain growth,and the results con-the peak strain as a function of initial grain size,temperature, stitute the input data for the next pass.Both the accumulated and strain rate for Nb steels.The␧c/␧p ratio often lies strain as well as the redundant strain are employed through-between0.67and0.86[46]and is generally considered to be out the calculations.Some typical inputs and outputs of the0.8for plain C-Mn steels.Previous workers have reportedvalues for Nb steels as low as0.65.[34]The effects of Nb, microstructural-evolution spreadsheet are given in Table VII.The following example uses data from the Dofasco HSM,Mn,and Si were taken into account in a recent investiga-grade CD.tion,[47]and a fit was found for the␧c/␧p ratio.The method In C-Mn steels,mechanisms such as carbonitride precipi-used was to test several possible values of␧c/␧p and then tation followed by strain accumulation do not take place,soto select the ratio that provides the best fit to the Sims MFS only SRX as well as DRXϩMDRX effects are considered curve.This procedure,thus,specifies the conditions underwhich DRX will occur.Over100mill logs were tested in here.The observed MFS is calculated using the Sims formu-lation(from the mill data).Then,predictions are made using this way using the grades listed in Table I.The resulting。

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Rev Account Stud(2010)15:915–953DOI10.1007/s11142-009-9111-xManagement’s tone change,post earnings announcement drift and accrualsRonen FeldmanÆSuresh GovindarajÆJoshua LivnatÆBenjamin SegalPublished online:20August2009ÓSpringer Science+Business Media,LLC2009Abstract This study explores whether the management discussion and analysis (MD&A)section of Forms10-Q and10-K has incremental information content beyondfinancial measures such as earnings surprises and accruals.It uses a clas-sification scheme of words into positive and negative categories to measure the tone change in the MD&A section relative to prior periodic SECfilings.Our results indicate that short window market reactions around the SECfiling are significantly associated with the tone change of the MD&A section,even after controlling for accruals and earnings surprises.We show that management’s tone change adds significantly to portfolio drift returns in the window of2days after the SECfiling date through1day after the subsequent quarter’s preliminary earnings announce-ment,beyondfinancial information conveyed by accruals and earnings surprises. The drift returns are affected by the ability of the tone change signals to help predict the subsequent quarter’s earnings surprise but cannot be completely attributed to R.FeldmanData&Text Mining Laboratory,Jerusalem School of Business Administration,Hebrew University,Jerusalem91905,Israele-mail:Ronen.Feldman@huji.ac.ilindarajRutgers Business School,Newark and New Brunswick,Department of Accounting,Business Ethics,and Information Systems,Ackerson Hall,Room302B,180University Avenue,Newark,NJ07102-1897,USAe-mail:sureshg@J.Livnat(&)Stern School of Business Administration,New York University,10-76K-MEC Hall,44W.4th St.,New York City,NY10012,USAe-mail:jlivnat@B.SegalAccounting and Control Group,INSEAD,Boulevard de Constance,Fontainebleau77305,Francee-mail:Benjamin.Segal@916R.Feldman et al. this ability.We alsofind that the incremental information of management’s tone change depends on the strength of thefirm’s information environment. Keywords Textual analysisÁEarnings driftÁAccrualsÁEarnings surprisesÁManagement tone changeÁMD&AJEL Classification G12ÁG14ÁM411IntroductionThere is a substantial body of literature infinancial economics and accounting that examines the value relevance and information content of conventional quantitative factors in the pricing of stocks,using economic and statistical tools that have become increasingly sophisticated over the years.While there is no doubt that these studies have contributed to our understanding of the structure and characteristics of financial markets,they have also led to the growing realization that incorporating information conveyed by quantitative factors alone may not be adequate to explain the movement of stock prices.As early examples of this growing realization in the finance literature,Shiller(1981),Roll(1988)and Cutler et al.(1989),demonstrate that stock prices cannot be explained by quantitative measures offirm fundamentals alone.In the accounting literature,Lev and Thiagarajan(1993)and Amir and Lev (1996)are two early examples of research that has shown the inadequacy of conventional quantitativefinancial measures in pricing afirm’s stock.There are many more recent papers in accounting andfinance that make the same point.1 It is not difficult to understand why prior research has primarily focused on quantitative factors to study the formation and movement of stock prices. Quantitative data is easily available,is more objective,and certainly less controversial to incorporate than qualitative data.However,there is no reason to expect that market participants communicate solely through quantitative informa-tion.Firms and even the federal government(Boukus and Rosenberg2006) routinely provide qualitative information to investors through explanatory state-ments,disclosures,elaborations,clarifications etc.,in different forums and media. Such disclosures have become even more frequent in recent years with transparency and good governance assuming high importance.Clearlyfinancial market participants would be expected to process and analyze these pieces of information (in addition to the quantitative data)provided to them while making their decisions. Consequently,analyzing the impact of these qualitative communications can only enhance our current understanding of thefinancial markets.The obvious difficulty in studying the role and impact of qualitative communi-cations in thefinancial markets is tofind an objective quantitative measure of the information being conveyed.However,given recent developments in otherfields of research that face similar problems(such as computer science,linguistics,psychology, and statistics),there are specific methods and tools available now that can be used to 1We discuss prior work relevant to our paper in our literature review below.Management’s tone change,earnings drift and accruals917 quantify the information content of verbal communications in a relatively objective fashion.Tetlock(2007)is,arguably,among the best known works to use these recently developed tools to quantify qualitative information and provide persuasive evidence on the incremental predictive content of qualitative verbal information.2He shows that the depth of pessimism expressed in a daily news column from The Wall Street Journal (titled Abreast of the Market and covering the stock market activity on the previous day)exerts a significant downward(temporary)pressure on prices of the stock indices.3In a follow up,using similar tools for quantifying qualitative communica-tions,Tetlock et al.(2008)show that increases in the negative words used in The Wall Street Journal and the Dow Jones News Service columns about S&P500firms relative to prior stories predict larger negative shocks to future earnings.Furthermore,they also provide evidence that potential profits could be made by trading on negative words from Dow Jones News Service—a timely news service.4From a methodological viewpoint,the Tetlock(2007)and Tetlock et al.(2008) papers are the main motivators for our work.5However,by focusing on news stories in the media,their work is more concerned with the information content of verbal communications by outsiders(media-persons).While these papers make a strong case for the predictive value of pessimism expressed by outsiders on stock prices and future earnings,they may not completely capture the views of mangers(or insiders),who are required to express their views in Securities and Exchange Commission(SEC)filings. It can be argued that managers are better informed than outsiders,and assuming that they truthfully report their views(under SEC scrutiny and penalty of litigation),their statements may have higher predictive ability than outsiders’reports.6 Our study investigates the information content of the‘‘tone change’’conveyed through management discussion and analysis(MD&A)disclosures for a large sample offirms.By‘‘tone change,’’we mean the optimism or pessimism of the information embedded in qualitative verbal disclosures by managers in the MD&A section offirms’periodic SECfilings as compared with prior periodicfilings of the samefirm.We focus on the effects of management’s tone change on immediate and delayed stock returns beyond what is captured by preliminary earnings surprises and accruals,the two accounting variables best known to be informative about the future stock performance of thefirm.72The history of research trying to assess the information content of qualitative information is long.Our literature review below discusses earlier and contemporaneous works.3We discuss the specificfindings of Tetlock(2007)in some detail in our literature review.4The authors acknowledge that these profits could be wiped out by transactions costs from high frequency trading.5We emphasize that while the Tetlock papers motivated our methodology in our paper,there are a number of other papers discussed later that are also related to our work.6Kothari and Short(2003)is probably thefirst paper to recognize this and examine the information content of MD&A disclosures in addition to the information content of analysts’forecasts and media reports using a methodology similar to Tetlock(2007)and Tetlock et al.(2008).However,they focus on the effects of the MD&A’s sentiment on thefirm’s cost of capital and risk(stock price volatility),not on their ability to predict future stock prices and earnings.7In an earlier version of this paper,we had also controlled for operating cashflows(OCF)with similar results to those obtained here.We have dropped the OCF in this version of the paper at the suggestion of an anonymous reviewer who pointed out that OCF and Accruals are correlated.918R.Feldman et al.Wefind that the change in tone of the MD&A section of the SECfilings from prior periodicfilings,in fact,contains significant information beyond accruals and earnings surprises.We show by regression analysis and by construction of buy-and-hold portfolio strategies,that the optimism,pessimism,and the differential optimistic tone change measure(the change in optimism net of pessimism)yield excess average stock returns over the short window surrounding thefiling of the MD&As but also that returns continue to drift for longer periods that extend until after the subsequent quarter’s preliminary earnings announcement.As can be expected,the change in MD&A tone is incrementally more informative when the information environment surrounding thefirm(as measured by size and analyst following)is weaker.The tone change is also a weaker signal for valuefirms,which are typically more mature and easier to understand.We alsofind the tone change signal to have stronger implications forfirms with positive earnings surprises;this may be because these are cases where investors need additional information beyond quantitative disclosures.The implication is that the qualitative tone change expressed in MD&As can be potentially exploited to earn significant excess returns over and above those associated with well known trading strategies based on accruals and earnings surprises alone.It should be emphasized,though,that consistent with most of the literature to date,the incremental contributions of using qualitative information beyond quantitative signals are not large when compared with the total unexplained variation in returns(that is,the incremental contribution to R2is statistically significant,but the level of the R2still remains low).This implies that either the potential of qualitative information is low or that the tools we currently have to quantify qualitative information are too crude.Our results contribute in general to research on the information content and value relevance of SECfilings and mandated disclosures.Specifically,our paper contributes to the value relevance of disclosures in the MD&A statements.To the best of our knowledge,this is thefirst paper to measure and show that the tone change expressed by management through words(qualitative communications)in MD&A is associated with immediate market reactions and can also predict future stock prices beyond well-known measures of company performance.Ourfindings should be relevant to academics who are interested in such issues as market efficiency and how well public(especially qualitative)information is captured in security prices and to those academics who are concerned with the effects of the information environment on the associations between public information and security returns.The results of our study should also be of interest to policy-makers, because they show the incremental valuation relevance of required qualitative information.Since the tone change in SECfilings(which arefiled regularly)can be used to improve portfolio performance beyond quantitative variables,our results should interest practitioners as well.8The rest of the paper is organized as follows:the next section reviews the relevant literature and motivates our research hypotheses.Section3describes the 8The set-up costs required for analyzing the tone change of qualitative disclosure may favor professional investors.Management’s tone change,earnings drift and accruals919 sample defines and describes the variables used in our paper.Section4presents our results,and Sect.5concludes.2Prior research and research questions2.1Prior researchBroadly speaking,there are two kinds of research relating to the valuation of corporate disclosures in the accounting literature,namely,the voluminous body of work that has examined the value relevance(or information content)offinancial disclosures9and the relatively smaller set of research papers that have studied the valuation of nonfinancial disclosures.Within the set of studies of value relevance of nonfinancial data there are two major subsets,namely,those that focus on quantifiable data and those that examine qualitative verbal expositions that elaborate and explain quantitative disclosures.Our research examines the information content of narratives from MD&A and so is related to the latter stream of research,that is, the value relevance of nonfinancial,nonquantitative disclosures.However,in examining the incremental value relevance of MD&A disclosures,we also control for the value relevance of otherfinancial variables that have been extensively documented by prior studies.We cite two papers that examine the incremental information content of quantitative non-financial information.10Using a large sample offirms from1974 through1988,Lev and Thiagarajan(1993)show that certain non-audited quantitative information,such as order backlogs and the strength of their labor force,provide information for company valuation beyond the traditionalfinancial accounting information.Amir and Lev(1996)build on this theme by studying the value relevance offinancial and nonfinancial data for a sample of wireless communicationfirms andfind thatfinancial data alone show very little value relevance,but if combined with quantitative nonfinancial data(specifically,proxies for potential customers)the value relevance of thesefinancial variables is considerably enhanced.Some of the early research relating to MD&A is mostly descriptive.Bagby et al. (1988)provide a historical review of MD&A and the social usefulness of qualitative disclosures within a broader framework of federally mandated disclosures using a critical examination of legal cases relating to mandated disclosures.Dieter and Sandefur(1989)outline the MD&A requirements mandated by the SEC and suggest guidelines on drafting an MD&A that would satisfy these regulations in form and substance.Shroeder and Gibson(1990)is among the earliest papers to try and quantify the readability quotient of the exposition in the MD&A and also the president’s letter. Borrowing techniques from the psychology literature,they construct the so-called9We refer the interested reader to the book by Beaver(1997)for a discussion and analysis of the value relevance offinancial disclosures.10These papers provide citations for the interested reader.920R.Feldman et al. Flesch Index scores(a measure of reading ease)using a standard formula based on the word length and sentence length and by also examining the general tenor of the language used(active vs.passive voice in sentence constructions),they conclude that MD&A statements are,in general,less than readable.One of the earliest papers in the accounting literature that use linguistic techniques to analyze narrative disclosures is Frazier et al.(1984).Using a computer program called WORDS to identify the most important words(or factors)that could be reasonably interpreted as positive or negative narrative themes for a sample of74 annual reports offirms in1978,they show that there are no significant differences in managerial narratives across the ownership structure of thesefirms.They also provide evidence to support their hypothesis that the positive and negative factors (and the associated themes)can predict the cumulative abnormal annual returns for the next year(1979).11Pava and Epstein(1993)study the MD&A disclosures of25randomly selected firms during1989andfind that while the disclosures provided adequate details of historical events,they did a better job of predictingfirm-specific,industry-specific, and economy-specific good news than predicting bad news for1990.They conclude that managers may be withholding disclosures related to bad news.In1989,the SEC issued guidelines to clarify what was expected in MD&A disclosures in an attempt to make them more informative.Hooks and Moon(1993) attempt to measure the differences between the actual and expected frequency of MD&A disclosures across a spectrum of disclosures that they classify as mandated to those that are classified as voluntary and show that these differences have decreased for certain items after the SEC MD&A guideline release in1989, indicatingfirms provide more disclosure in their MD&A after1989.While these studies are related to our work,their samples are small and limited to specific early years prior to revised SEC’s guidelines on MD&A and the availability of SECfilings on the Electronic Data Gathering,Analysis,and Retrieval(EDGAR) system.The small sizes and limited analysis of data is these early studies is understandable,given that they were constrained by the available computing power, data sets,and data analysis techniques available to them in those years.One of the more recent papers by Li(2008a)vividly illustrates the contrast between earlier studies and the current state of the art.Motivated by the SEC requirements thatfirms provide easy to read and plain disclosures,Li examines whether the readability and the writing style of annual corporate reports(including the MD&A section)of a large sample offirms during the years1993–2003can predict futurefirm earnings and ing measures from linguistics for readability and writing styles,Li concludes thatfirms with poor performance put out hard-to-read reports and that profitablefirms with more complicated reports have a lower persistence of earnings butfinds that these measures do not correlate with future stock returns.Li(2008b) examines the tone and content of forward looking statements extracted from the MD&A section of a large sample of10-Ks and10-Qsfiled with the SEC between 1994and2007using a computer intensive Bayesian learning algorithm(rather than the dictionary approach used by Tetlock and others including our paper)and shows 11The paper also discusses other applications of WORDS infinance and accounting.Management’s tone change,earnings drift and accruals921 that tone of the forward looking statements has significant predictive power for future earnings and liquidity.He also shows thatfirms with better current performance,lower accruals,smaller size,lower market-to-book ratio,and less return volatility tend to have more positive forward-looking statements in MD&As.12Bryan(1997)examines if the specific accounting related narratives from MD&A have incremental information content beyond quantitativefinancial statement information regarding futurefinancial variables such as the directions of changes in future sales,future earnings per share,future operating cashflows,and future capital ing a sample of MD&A disclosures by250firms in1990(a year after clearer guidelines were issued by the SEC),hefinds that there is a strong association between MD&A disclosures and the direction of changes in the aforementioned futurefinancial variables3years into the future.In addition,he demonstrates that MD&A disclosures,especially the disclosure relating to capital expenditures,are significantly associated withfinancial analyst forecasts and stock returns around the release date of MD&As.Bryan’s paper differs from our work in that we are interested in the predictive ability of the overall tone change of the MD&A rather than the contents of individual MD&A disclosures.He does not examine if abnormal stock returns can be earned or study the issue of post-announcement drift in stock prices.Furthermore,the content analysis by Bryan is subjective as opposed to the more objective tone change index used here and by Tetlock(2007)and Tetlock et al.(2008).Finally,our sample size is much larger and is drawn from years when the legal and disclosure environments are substantially different.There are few papers that examine the relationship between MD&A disclosures and analyst forecasts.One such paper is by Barron and Kile(1999).Using a large sample offirms drawn from1987through1989MD&A disclosures of26different industries and after controlling for quantitativefinancial factors,they show a strong association between the accuracy of analysts’forecasts and the quality of MD&A disclosures(as measured by scores assigned by personnel at the SEC),especially disclosures relating to capital expenditures.Clarkson et al.(1999)document that MD&A disclosures are found to be useful to sell-side analysts who are members of the Toronto Society of Financial Analysts based on33responses to questionnaires. In addition,using a sample of55firms on the Toronto Stock Exchange in1991and 1992,they show that the levels and the changes in the quality of various sub-sections of the MD&A disclosures(where the quality of disclosures is a score provided by the Toronto Analysts)are generally determined by expectedfirm performance,financing activities(mainly increased equityfinancing),firm size, independent press reports,and majorfirm related events.Cole and Jones(2004)use MD&A disclosures from a sample of150firms for the period1996through1999from the retail industry to show that certain types of quantifiable disclosures,(namely sales growth,store openings and closings and 12Interestingly,Li(2008b)alsofinds that the information content of MD&As has not changed significantly after the passage of the Sarbanes-Oxley Act.This may partially contradict thefindings of Loughran and McDonald(2008),whofind fewer strong modal words relative to weak ones after the passage of this act.922R.Feldman et al. capital expenditures),can predict future profitability and are associated with contemporaneous stock returns.Sun(2007)examines the MD&A disclosures explaining inventory increases between1998and2002for568manufacturingfirms and shows that favorable explanations are associated with future profitability and sales growth and thatfirms in growth industries and competitive industries tend to disclose more.Kothari and Short(2003)is perhaps thefirst accounting work to have used the General Inquirer classification(which is one of two word lists that we use in this study)to assess the effects of the tone(as opposed to tone change used in our paper) expressed in MD&A disclosures on thefirm’s cost of capital.13They extend the work of Botosan(1997)by studying the effect of the positive and negative sentiments expressed in MD&A,analyst reports,and thefinancial press between 1996and2001on the cost of capital and risk(stock price volatility)for a sample of 887firms from four industries(technology,telecommunications,pharmaceutical, andfinancial).Theyfind that aggregated(across all three sources)positive (favorable)disclosures decreased the cost of capital and the stock return volatility of thefirm,while negative(unfavorable)disclosures had the opposite effects. However,when disclosures are analyzed by sources,theyfind that positive sentiments expressed in corporate MD&As do not have an effect on the cost of capital,while negative sentiments significantly increase it.They attribute this to skepticism on the part of investors regarding positive disclosures(that is,they are viewed more as self serving)butfind negative sentiments credible because management would not normally reveal bad news.Disclosures relating to analysts’sentiments seem to have no effect on the cost of capital,and this is attributed to the lack of credibility.They attribute this to the fact that analysts are seen to be reporting their sentiments after the market has already absorbed them.Finally,they find that positive media stories and disclosures seem to decrease the cost of capital and negative disclosures increase it.14Related to this line of enquiry is Li(2006), who examines whether the risk sentiments and change in risk sentiments expressed in annual reports are associated with futurefirm performance and future stock ing a large sample of annual reports from1994to2005,Li constructs an intuitive quantitative measure of levels and changes in risk sentiments extracted from the text of these reports andfinds large increases in risk sentiments to be associated with lower future earnings and significantly lower stock returns.We note that our paper differs from Kothari and Short(2003)in that we are not interested in analyzing the effects of soft disclosures on thefirm’s cost of capital or the variability of stock returns.We are also different from Li(2006),who is interested in the incremental effects of the subjective measures of references to risk changes in annual reports(including the MD&As)on future stock prices and 13Since managers usually use prior MD&As as a blueprint for producing a new and incremental MD&A, there could be considerable similarities in MD&As that are close in years.This suggests that our tone change measure may be a better measure of information content than the tone level measure used by Kothari and Short(2003).14This supports thefindings of Tetlock(2007),who shows similar results for a market index(Dow Jones).That is,when the media reports are pessimistic,the stock index price drops and market volatility increases.Management’s tone change,earnings drift and accruals923 earnings.We are not concerned with any measure of risk but rather with the incremental effects of general tone changes in MD&As on immediate and future stock returns.There are other differences between the Li(2006)paper and our work as well.He searches corporate disclosures for any mention of the word‘‘risk’’or related terms that are usually scattered throughout the periodic reports and does not restrict his search to MD&A section.We are solely concerned with MD&As. Furthermore,terms referring to risk may or may not have positive or negative content as we(and others such as Tetlock)define tone.While there may be some overlap in the words in Li’s set and ours,we use a much more comprehensive word list than Li.Finally,Li’smeasure of changes in risk sentiments is different from our tone change metric.15As mentioned before,the two papers that motivated our study are by Tetlock (2007)and Tetlock et al.(2008).They do not focus on pessimism and predictive content of MD&As but on news columns and releases.Tetlock(2007)uses the General Inquirer text analysis computer program to assess the negative quotient of The Wall Street Journal daily column Abreast of the Market from1984to1999and finds results consistent with pessimistic articles putting temporary downward pressures on market prices(Dow Jones stock index)and increasing trading volume in the New York Stock Exchange(NYSE).The increased volume of trade is consistent with microstructure theory that predicts high absolute values of pessimism should lead to a group of liquidity traders trading more and refutes the suggestion that the pessimism factor is a proxy for transaction costs(Tetlock 2007).16It is important to note that Tetlock(2007)finds that higher pessimism leads to higher volatility(risk)for the Dow Jones portfolio of stocks.This contradicts the intuition that higher pessimism should lead to lower returns,or equivalently,lower risk,suggesting that the pessimism factor captured by negative words may be distinct from risk.This is further corroborated by the fact that the effects of pessimism seem to be temporary and future stock returns reverse.17Continuing this line of research,Tetlock et al.(2008)examine the ability of media pessimism measured by the proportion of negative words in the real time stories news from Dow Jones News Service and daily news stories in The Wall Street Journal from 1984to2004relating to S&P500firms to predict future earnings and returns.They show that the change in the proportion of negative words(especially those relating tofirm fundamentals)in these news releases does convey information aboutfirm future earnings.They alsofind that the proportion of negative words in the timely news releases from Dow Jones News Service leads to lower stock returns the following trading day and that this trend persists over the next10days.These results remain robust even after controlling for other sources like analysts’forecasts, 15Li measures changes in risk sentiments simply as a change across consecutive years in the(log of)the numbers of occurrences of risk-related words rather than the standardized measure of tone change used in our paper,by Tetlock(2007)and by Tetlock et al.(2008).Tetlock et al.(2008)discusses the merits of using standardized metrics to measure changes in sentiments.16If the pessimism factor were a proxy for transactions costs,then higher levels of pessimism should lead to lower volumes of trading on the following periods(see Tetlock2007).17This reversal seems to be slower for smallfirms’stocks relative to stocks of bigfirms when the tests are run on stocks other than those in the Dow Jones Index.。

MySQL中⽂分词原理⼀，⾸先我们来了解⼀下其他⼏个知识点：1. Mysql的索引意义？索引是加快访问表内容的基本⼿段，尤其是在涉及多个表的关联查询⾥。

当然，索引可以加快检索速度，但是它也同时降低了索引列的插⼊，删除和更新值的速度。

换通俗的话来讲：mysql中的索引就是⼀个特殊的平衡⼆叉树，当在平衡⼆叉树中搜索某⼀条值的时候，上亿条的数据可以在⼗多次内可以塞选出来。

所以，每个数据表⾥⾯有多少个索引就有多少个对应的索引表。

当然，⼀个表⾥⾯的索引越多写⼊速度会越慢，但读去速度会越。

mysql的索引类型：唯⼀索引。

常规索引。

fulltext索引spatial索引hash索引2. 什么fulltext索引？fulltext索引也叫做全⽂本索引,MySQL具备全⽂搜索的能⼒，它可以让你在不使⽤模板匹配操作的情况下进⾏单词或短语的查找。

ps：(个⼈理解)1. mysql的全⽂本索引是针对与英⽂⽂本的索引(毕竟是别⼈国外⼈开发的mysql)，我们知道在⼀篇英⽂⽂章中可以发现⼀个特点，每个单词与每个单词都是以空格隔开的。

如果我们把每个单词看做⼀个数据，按照单词的⼤⼩来进⾏前后排列，也可以形成⼀个⼆叉树。

2. 有规律可循，有⼆叉树，我们就可以对其快速搜索，并可以对应进⾏封装成索引，也就是我们所说的全⽂本索引————fulltext索引。

3. 注意————fulltext索引只能搜索英⽂。

⼆，使⽤FULLTEXT搜索1. 全⽂搜索的特性(重点)全⽂搜索基于fulltext索引。

fulltext索引，只能出现在char varchar text这⼏种类型的表字段⾥⾯。

全⽂搜索会忽略那些常见词：常见词，指的是⾄少⼀半的⾏⾥都出现过，超过50%的词，都为常见词；有些为内建的常⽤单词：也叫停⽤词，⽐如：the／after，other⽐较短的单词也会被停⽤。

单词的定义：它们是由字母，数字，撇号和下划线，构造⽽成的字符串。

(英⽂单词完全符合，但是中⽂不⾏)可以为⼀个字段(列)创建fulltext索引，也可以为多个字段(列)创建⼀个fulltext索引。

fulltext字段英文处理English Answer:Fulltext Search of English Text.Introduction.Fulltext searching is a powerful technique for finding relevant information within a large body of text. In the context of English language processing, fulltext search can be used to retrieve documents that contain specific words or phrases, even if those words or phrases appear in different forms or are misspelled.Tokenization and Normalization.The first step in fulltext search is to tokenize the text into individual words or phrases. This can be done using a variety of techniques, such as whitespace splitting or regular expressions. Once the text has been tokenized,the tokens are normalized to remove common variations such as case, punctuation, and stemming.Stemming.Stemming is a process of reducing words to their root form. This can be done using a variety of algorithms, such as the Porter stemmer or the Lancaster stemmer. Stemming can help to improve the recall of fulltext search queries by matching words that have different suffixes.Stop Words.Stop words are common words that do not add significant meaning to a query. Examples of stop words include "the", "and", and "of". Stop words can be removed from queries to improve efficiency and reduce noise.Indexing.Once the text has been tokenized, normalized, and stemmed, it is indexed. An index is a data structure thatmaps words or phrases to the documents in which they appear. This allows for fast and efficient searching.Querying.To perform a fulltext search, a user submits a query. The query is typically a string of words or phrases that represent the information the user is seeking. The query is then processed using the same techniques as the text, and the results are ranked based on their relevance to the query.Relevance Ranking.There are a number of factors that can be used to determine the relevance of a document to a query. These factors include:Term frequency: The number of times a term appears ina document.Document frequency: The number of documents in thecorpus that contain a term.Inverse document frequency: A measure of how common a term is in the corpus.Proximity: The distance between terms in a document.Boosting: A way to give certain terms or documents more weight in the ranking.Applications.Fulltext search has a wide range of applications, including:Document retrieval: Finding documents that contain specific keywords or phrases.Web search: Searching the web for information.E-commerce: Searching for products on an e-commerce website.Spam filtering: Identifying and blocking spam emails.Machine translation: Translating text from one language to another.中文回答：全文搜索对英文文本的处理。

mysql全⽂索引：fulltext
fulltext全⽂索引
要使⽤全⽂索引，不仅需要把某个字段的索引类型设置为fulltext，还需要修改mysql配置⽂件：[mysqld]
ft_wordlist_charset #表⽰词典的字符集
ft_wordlist_file #词表⽂件，每⾏⼀个词及其词频
ft_stopword_file #过滤掉不索引的词表，⼀⾏⼀个
ft_min_word_len #加⼊索引的词的最⼩长度，默认为4，为了⽀持中⽂单字故可设置为2
如果创建好全⽂索引之后，我们的表有问题，可以修复⼀下：
repair table 表名称 quick
SQL中怎么查询？
select*from product where match(name) against('php') limit 0,20;
匹配name字段，这个字段的索引必须是fulltext。

这就是mysql中全⽂搜索的简单介绍。

注意这只适合数据量很⼩的项⽬。

实际开发中，推荐使⽤第三⽅如 Sphinx（中⽂版coreseek）或者ElasticSearch
mysql的全⽂索引full text和sphinx的区别
1）sphinx可以提供⽐数据库本⾝更专业的搜索功能，使得应⽤程序更容易实现专业化的全⽂检索
2）sphinx是⼀个独⽴的服务器，具有很多mysql⾃⾝不具备的扩展功能，性能更⾼，更好的缓解数据库的压⼒等。

J Appl Electrochem (2009) 39:577-582DOI 10.1007/s10800-008-9695-zORIGINAL PAPERElectrochemical treatment of pharmaceutical azo dye amaranthfrom waste waterRajeev Jain . Nidhi Sharma . Keisham RadhapyariReceived: 25 February 2008/Accepted: 13 0ctober 2008/Published online: I November 2008@ Springer Science+Business Media B.V. 2008Abstract The electrochemical behavior of pharmaceuti-cal azo dye amaranth has been investigated in distilledwater and Britton-Robinson buffer. One well-definedirreversible cathodic peak is observed. This may beattributed to the reduction of the -N=N- group. Calculationof the number of electrons transferred in the reductionprocess has been performed and a reduction mechanismproposed. Results indicate that the electrode process isdiffusion controlled. The cathodic peak in the case of controlled potential electrolysis is found to reduce substantially with a decrease in color and absorbance. The reaction has first order kinetics with k value 5.75 x10-2 abs min-l. The effciency of different electrode materials (platinum and steel) for decolorisation is compared. Chemical oxygen demand (COD) decreases substan-tially from 2,680 t0 96 ppm at platinum and t0 142 ppm atsteel. This translates t0 97% COD removal at platinum and95% at steel.Keywords Electrochemical treatment . AmaranthAzo dye . Industrial effluents . CV, CODI IntroductionAzo dyes continue to be a source of pollution fromindustrial processes which employ dyes to color paper,R. Jain . N. Sharma . K. RadhapyariSchool of Studies in Chemistry, Jiwaji UniversityGwalior 474011, Indiae-mail: raj eevj ain54 @ yahoo.co.inplastics, foodstuffs, pharmaceutical products, and naturaland artificial fibers [1, 2]. It is reported that approximately5 tonnes of dye discharge from dye and coloration industriesevery year [3]. The release of such compounds into theenvironment is of great concern due to their toxicity,mutagenicity, carcinogenicity, and bio-transformationproducts [4-6]. Hence. much research has focused onmethods of azo dye destruction. Many treatment processeshave been investigated extensively to treat wastewaters suchas chemical precipitation [7], adsorption [8], biologicaltreatment [9], photocatalytic degradation [10, 11], electro-catalytic oxidation [12], ozonation [13], Fentons' reaction[14], and electrochemical methods [15-19]. Electrochemi-cal techniques are an attractive methodology for thetreatment of dye wastewaters. This technique has significantadvantages viz., wide application, simple equipment, easyoperation, lower temperature requirements. and no sludgeformation [20-24].Amaranth (Fig.1) [trisodium salt of l-(4-sulpho-l-naphthylazo)-2-naphthol-3, 6-disulphonic acid] is an acidicmonoazo dye used as food and pharmaceutical colorant.Only a few analytical methods, such as square waveadsorptive stripping voltammetry (SWAdSV) and spec-trophotometry are available for determination of amaranthin soft drink samples [25]. Degradation of amaranth fromenvironmental samples has been studied on activated car-bon fiber (ACF) electrodes [26,27]. The amaranth azo dyehas electroactive groups. However. its electrochemicalbehavior and treatment have not been investigated.Therefore, cyclic voltammetric and differential pulsepolarographic studies have been undertaken in the presentwork for understanding the electrochemical behavior ofamaranth. Results have been analyzed employing the cri-terion of complete decolorisation of the dye-containingsolutions.Springer578J Appl Electrochem (2009) 39:577-582Na07SOH S03NaFig. 1 Structure of amaranth2 Experimental2.1 InstrumentationO,NaCyclic voltammetric (CV) studies were carried out on an EGand G potentiostat (Princeton Applied Research) integratedwith applied electrochemistry software. The working elec-trode potential was cycled between -1.2 and +1.2 V atdifferent sweep rates (50-2.000 mV s-1). The electrochemical cell consisted of three electrodes (in close proximity) immersed in the solution to be electrolyzed. The voltammetric behavior was studied using platinum as working electrode, SCE as reference, and platinum wire as counter electrode. Controlled potential electrolysis was carried out using a cyclic voltammograph coupled to a digital electronic 2000 0mnigraph x-y/t recorder. The working electrodes used for controlled potential electrolysis (CPE) were platinum foil (3 x 3 cm2)and steel foil (4.5 x 3.5 cm2), Ag/AgCI as reference elec-trode and platinum wire as counter electrode.Differential pulse polarographic (DPP) measurementswere carried out on an Elico pulse polarograph model CL 90 connected with Polarocord recorder model LR-108.Triple distilled mercury was used for the DME. The capillary had a flow rate of 3.02 mg s-l together with a drop time of 3 s. The pH measurements were made on a Hach digital EC-40 Benchtop pH/ISE meter. The absorption spectra of samples were recorded using an Elico SL 159 UV-Visible spectrophotometer. The chemical oxygen demand (COD) was determined using the open reflux method using COD digester apparatus (Spectralab 2015-S).The synthetic azo dye amaranth was obtained from Aldrich USA. All chemicals used were AR grade. Readymade silica gel G plate for TLC, having fine coating on alumina sheet. was obtained from E-Merck.2.2 Reagents and materialsStock solution of amaranth (2 x l0-3 M) was prepared in doubly distilled water. In order to evaluate the effect of varying pH, BR buffers in the pH range 2.5-12.0 were prepared as per a literature method[,. ]. The supportingSpringerelectrolyte was l.0 M KCI.For the COD experiments reagents were prepared in accordance with standard methods (APHA. 1995) [29].2.3 ProcedureThe CV and DPP studies were carried out by mixing l.0 mL of potassium chloride, 1.0 mL stock solution, and 8.0 mL of appropriate BR buffer/distilled water. Solutions of different concentrations were prepared. Dissolved oxygen was removed from the solution by passing nitrogen gas for about 15 min. The polarograms and cyclic voltammograms were then recorded. The redox behavior was studied at varying pH (2.5-12.0), concentrations and sweep rates (100-2,000mV s-l). Controlled potential electrolysis of the dye solution was performed at slightly more negative potential than the peak potential of the respective peak. Absorbance of the olution was measured at different time intervals at 520 nm.The value of the rate constant k was calculated from the l091(absorbance) vs time plots. The number of electrons transferred was calculated from the decrease in current with time during electrolysis. Controlled potential coulometry was also carried out at different pH values. The progress of electrolysis was monitored by recording cyclic voltammograms at regular intervals of time. The end products of electrolysis were identified by TLC. For COD studies. The experiments were carried out as per standard methods.2.4 CoulometryFor the coulometric determination of number of electrons "n" consumed in the reduction. a solution of depolarizer,potassium chloride, and buffer/distilled water was mixed in the same ratio as that for CV and DPP studies. The solution was de-aerated by passing nitrogen gas for 15 min and cyclic voltammograms were recorded at slightly more negative potential than the peak potential. With the progress of electrolysis the color of the solution gradually faded and finally a colorless solution was obtained. The number of electrons "n" transferred at the platinum electrodewas determined from the formula Q = nFN.3 Results and discussion3.1 Cyclic voltammetric (CV) studiesThe cyclic voltammogram of amaranth in distilled water (2 x 10-4 M) exhibits reduction peak at -0.872 V and corresponding oxidation peak at -0.779 V at scan rate of 100 mV s-l. The cathodic peak can be safely assigned to the reduction of the azo (-N=N-) group. The separation between cathodic and anodic peak potentials is more than 60 mV. indicating the irreversible nature of the electrode process [30]. As the scan rate (v) is increased. the reduction peak potential shows negative shift and the oxidation peakpotential shows positive shift. At higher scan rate of1,000 mV s-1 the reduction peak appears at -1.0 V andthe oxidation peak at -0.697 V. The peak potential separation (AEp) increases gradually from 0.093 t0 0.306 V asthe scan rate is increased from 100 to 1,000 mV s-l suggesting the irreversible nature of the electrode process.The plot of ip,c vs 1/2 in the 6.5 pH solution is a straight line passing through the origin indicating the diffusion controlled nature of the electrode process (Fig. 2 (I)) This proportionality may be attributed to the fact that a steeper concentration gradient is established thereby increasing the rate of diffusion at faster scan rates. Reduced species will diffuse away from the electrode faster as the scan rate is increased [31,32]. A similar plot for the dye solution in neutral aqueous medium and at pH 8.8 is,once again, a linear behavior, however, not passing through the origin. This indicates adsorption effects contributing to diffusion current. In such a case an adsorbed species may undergo electron transfer.3.2 Effect of pHWell-defined cathodic peaks in the acidic pH range are obtained with both platinum and glassy carbon electrodes.With increase in pH the cathodic peak shifts negatively and the anodic peak positively with increasing pH, which indicates that proton transfer occurs as a step consecutive to an irreversible electrode process [33]. The plot of Ep.c vs pH is linear up to pH 6.5 as also above 6.5.However. the two linear segments have different slopes.The value of pH 6.5, is in accord with the pKa value.Above pH 6.5, the Ep,c becomes practically independent of pH. This indicates the reduction of unprotonated species34]. These results are presented in Table .3.3 Differential pulse polarographic studiesA single four-electron irreversible reduction peak is observed in the pH range 2.5 t0 12.0 at the mercury electrode. This may be attributed to reduction of the azo group(-N=N-). A shift in Ep,c towards more cathodic potentialwith pH, along with a break at pH 6.5, is observed. Beyondthis there is near constancy in Ep,c (Fig.3). This suggestsparticipation of protons in the rate determinatiAnalysisofthepeakEd.e.vs log刍）- O;,at4m, lo[rt]Xtand shifting of the peak potential towards more negativevalue with concentration suggests the irreversible nature ofthe electrode process [35,36]. The results of DPP studies arethus in close agreement with those of the CV studies.3.4 Controlled potential coulometric studiesBy using controlled potential coulometry, the number ofelectrons transferred "n" at platinum electrode werecalculated and this lies in the range 2土0.2 (Table ..). Thevalue of "n" lies in the range 4 + 0.2 at the steel electrode.Controlled potential electrolysis of amaranth (2 x 10-4 M)at platinum and steel electrodes was carried out at -1.20 V.Bench scale electrochemical treatment was carried out.Electrolysis results in complete disappearance of colorwhich is fairly faster in case of platinum where the solutionis decolorized within 10 min of electrolysis leading to thecomplete disappearance of the cathodic peak current. Withsteel. the colored solution took 80 min for complete colorremoval. The data are summarized in Table '_ . A compara-tive overlay of the dye solution of pH 8.8 before and afterelectrochemical treatment is presented as Fig. i.3.5 Spectral studiesUV-visible spectra of amaranth (2 x 10-4 M) in distilledwater were recorded at Amax = 532.5 nm. The progress of 有错controlled potential electrolysis was monitored by record-ing spectral changes at different time intervals. AtAnax = 532.5 nm, absorbance decreases systematically 有错with the progress of electrolysis. The kinetic measurementswere conducted at steel electrodes. The observed rateconstant, k= 5.75 x 10-2 a s min-l was determinedfrom the first-order kinetics plot of log absorbance vs time3.6 COD removalThe electrolyzed solution shows a substantial decrease inCOD from an initial value of 2,680 ppm to a final value of96 ppm at platinum and t0 142 ppm at steel.3.7 Proposed mechanismOn the basis of the coulometry, controlled potential elec-trolysis, chromatographic and spectral analysis, tworeduction mechanisms are proposed. One is the two elec-tron reduction to hydrazo compound at platinum (Fig. ).A four electron reduction at steel (Fig. ) may be favoredby the presence of the strong electron releasing substituent,the -OH group [37].In Fig.6, amaranth undergoes 2e- reduction in acidic aswell as alkaline medium. The reduction process proceedsby the protonation of the polarized molecule resulting in the formation of (B). In the second step, which is slow and rate determining, (B) accepts 2e- and a proton and results in the formation of stable hydrazo (-NH-NH-) form (C).In Fig.7, 4e- reduction takes place at the steel foil electrode. The I and II steps of reduction proceed in the same way as described in Fig. . In step III. (c) the hydrazo moiety undergoes a further two electron reduction resulting into two products (D) and (E).4 ConclusionThe newly developed electrochemical method gives satis- factory and promising results. The electrochemical reduction of amaranth under the experimental conditions described in this work is an irreversible process controlled by diffusion. Both platinum and steel electrodes exhibit great stability and resistance to redox and acidic/basic environments showing no deactivation. During the elec- trochemical degradation process, the COD decreases by approximately 97u/o at the platinum electrode and by 95% at the steel foil electrode with complete color removal. The electrochemical treatment developed achieves higher de- coloration and COD removal than that reported previously through the ACF electrode treatment method [26] which gives only 60% COD removal. Hence, the present elec- trochemical procedure is a better alternative approach for wastewater treatment resulting in significant lowering of toxicity.。

文章主题：全文索引 fulltext全文索引 fulltext 是一种用于数据库中文本字段的索引技术，它可以加速文本搜索的速度，提高数据库查询性能。

在本文中，我们将介绍全文索引的基本概念、原理和使用方法，以及它在实际应用中的优缺点和注意事项。

一、全文索引的概念全文索引是指对文本字段进行索引，使其成为可被快速搜索的对象。

与传统的索引方法只能对单个词语进行匹配不同，全文索引可以进行词组、部分词语的模糊匹配，大大提高了搜索的灵活性和效率。

全文索引的实现原理与传统索引有所不同，它使用了特殊的数据结构和算法来对文本进行分词、建立索引，并提供高效的搜索接口。

常见的全文索引技术包括倒排索引、Trie树、n-gram等。

二、全文索引的使用方法在数据库中使用全文索引，通常需要先对相关文本字段进行创建索引的操作。

具体的创建方法和语法取决于所使用的数据库产品和版本，一般可以通过创建索引的SQL语句来实现。

在创建全文索引时，需要注意选择合适的分词器和配置索引参数，以便提高搜索的准确性和效率。

另外，还可以对全文索引进行优化和调优，以适应不同的查询模式和负载情况。

在使用全文索引进行搜索时，可以使用全文搜索的SQL语法进行查询，常见的语法包括MATCH、AG本人NST等。

使用全文索引搜索可以实现对文本的快速匹配和检索，适用于各种数据库查询场景。

三、全文索引的优缺点全文索引具有以下优点：1. 提高搜索的速度和效率，适用于大规模文本的查询和检索。

2. 支持模糊匹配、词组匹配等多种搜索模式，提供更灵活的搜索功能。

3. 可以对搜索结果进行相关度排序，提高搜索结果的质量和准确性。

但全文索引也存在一些缺点：1. 需要消耗较大的存储空间和索引维护成本，对数据库性能有一定影响。

2. 在处理特殊字符、多语言文本等方面需要一定的技术支持和适配工作。

3. 在高并发、大数据量情况下，全文搜索可能出现性能瓶颈，需要进一步优化和扩展。

四、全文索引的注意事项在使用全文索引时，需要注意以下几点：1. 合理选择全文索引的字段和范围，避免过多地索引无关字段，浪费存储和性能。