退火工艺对强塑性变形珠光体钢丝组织和性能的影响

第27卷　第5期2006年　10月材　料　热　处　理　学　报TRANS ACTIONS OF M ATERIA LS AND HE AT TRE AT ME NTV ol .27　N o .5October2006退火工艺对强塑性变形珠光体钢丝组织和性能的影响涂益友1,　刘响亮1,　蒋建清1,　蔡　磊2,　卞建春2(1.东南大学材料科学与工程系,江苏南京　210096;2.江苏法尔胜集团公司,江苏江阴　214433)摘　要:用TE M 、XRD 研究了强塑性变形(ε=2160)SWRH72A 钢丝经不同温度(100-400℃)退火处理后的微观结构变化。

XRD 分析显示强塑性变形引起SWRH72A 钢丝中渗碳体回溶,部分碳原子溶入铁素体形成过饱和铁素体,过饱和铁素体中含碳量约0134at %。

由TE M 分析可知强塑性变形钢丝经200-300℃退火,由于渗碳体颗粒的弥散析出,钢丝强度升高到2400MPa 。

退火温度进一步升高到400℃,渗碳体片开始球化,钢丝强度大幅降低,但塑性显著增加。

关键词:珠光体钢;　强塑性变形;　渗碳体回溶;　退火中图分类号:TG 11515;　TG 15612 文献标识码:A 文章编号:100926264(2006)0520043203收稿日期:　2005211223;　修订日期:　2006206206基金项目:　江苏省科技成果转化专项资金项目(BA2004019)作者简介:　涂益友(1978—),男,博士研究生。

通讯作者:　蒋建清(1963—),男,教授,jqjiang @ 珠光体钢的强塑性变形可获得非常优异的应变强化而一直被广泛应用于钢帘线、钢丝绳和大桥缆索等领域。

高强度钢丝制品一般采用共析点附近的高碳钢作为生产原料,铅浴等温淬火后高碳盘条获得片层细小的珠光体组织,再进行剧烈冷拉拔变形,钢丝强度随应变量的增大而急剧上升,金属制品发达国家已在实验室中研制出强度超过5000MPa 的钢丝绳。

国外研究者采用高分辨电子显微镜(HRE M ,TE M )[1,2,5210]、穆斯堡尔谱(M ssbauer )[3,4]、原子探针(APFI M 、S DAP )[2],X 衍射分析[6,8,10]等分析手段研究了强塑性变形珠光体钢中渗碳体随着应变的增大而溶解的问题。

目前对强塑性变形引起珠光体钢中渗碳体溶解这一现象已达成共识,但对于冷拔冷变形珠光体在不同温度退火过程中的微观结构和性能变化并无系统研究。

本文对强塑性变形珠光体钢丝及其不同温度退火后力学性能和微观组织结构特征进行研究,以期为更高强度钢丝的开发提供技术依据。

1　试验材料和方法试验材料为斯太尔摩高速轧制线控轧控冷生产的SWRH72A 钢盘条,规格<5150mm ,热轧供货态。

在某钢丝绳厂拉制成钢丝,最终尺寸<1150mm ,拉拔应变ε=ln (A 0ΠA n )=216(A 0,A n 分别为变形前后钢丝截面积),拉拔速度10m Πs ,化学成分见表1。

表1　SWRH 72A 钢盘条化学成分(质量分数,%)T able 1　Chemical composition of SWRH 72A steel(w t %)C S i Mn SPFe 0.70-0.720.17-0.370.50-0.80≤0.04≤0.04Bal.变形后钢丝分别在100,200,300,400℃下退火30min ,退火后在Instron 25569型电子拉力试验机上以1mm Πs 的速度,室温下进行钢丝力学性能测试。

为保证性能测试的准确性实验结果取5个相同工艺处理试样测试的平均值,并进行了2次平行试验验证试验结果的可靠性。

显微组织在J E M2000EX 透射电镜上观察,TE M观察用薄膜试样先机械减薄至100μm ,再在5%高氯酸2酒精溶液中进行双喷电解减薄,电解电压为50V ,温度253K 。

钢丝变形前后及不同温度退火处理后α2Fe 点阵常数的变化采用XRD 精确测量的方法进行测试,实验在X D 23A X 射线衍射仪上进行,实验参数:Cu 靶,管电压40kV ,管电流30mA ,并采用旋转样品法以减弱应力对晶面间距测量的影响。

对高角峰α2Fe (211)峰进行窄区慢扫描,扫描范围80-85°,并用标准硅粉对测试角度进行准确度校正。

2　试验结果和分析211　钢丝力学性能分析图1示出钢丝在不同温度退火30min 后的力学性能的变化规律。

可以看出冷拉高碳钢丝强度约图1　钢丝强度和伸长率与退火温度的关系Fig 11　T ensile strength and elongation of steel wireannealed at different temperatures for 30min2250MPa ,伸长率为510%;100℃低温退火处理对钢丝性能影响较小,300℃退火时,钢丝强度明显升高达到2400MPa ,比拉拔态钢丝高了7%左右;退火温度进一步升高,钢丝强度骤然下降,400℃退火30min 后钢丝强度仅为1950MPa ,相应的钢丝伸长率明显升高,达到6%左右。

图2　冷拉拔及不同温度退火处理的SWRH72A 钢丝纵截面珠光体组织形貌Fig 12　TE M images showing the m orphology of pearlite in SWRH72A steel wire (a )as 2drawn by ε=2160,bright field image and the dark field images of cementite annealed at different temperatures for 30min :(b )100℃;(c )200℃;(d )300℃;(e )400℃212　显微组织分析图2为SWRH72A 钢拉拔变形及不同温度退火后钢丝纵截面微观组织TE M 形貌。

由于钢丝承受了强塑性变形,珠光体片层间距减小至50nm 左右(图2a )。

由渗碳体的暗场像可见,强塑性变形钢丝经100℃退火微观组织基本无变化(图2b )。

随着退火温度升高到200℃,在铁素体片层中析出少量渗碳体颗粒,颗粒尺寸在纳米级(图2c )。

退火温度进一步升高到300℃,渗碳体颗粒大量析出,从图2d 可见纳 米颗粒在渗碳体片层附近的铁素体中较多(如图2d中箭头所示),而铁素体片中心部位较少。

从400℃退火钢丝TE M 照片中(如图2e )可以看到渗碳体片层开始球化,铁素体片层中渗碳体颗粒急剧增加。

213　XR D 分析图3示出变形前后及不同温度退火SWRH72A 钢丝的α2Fe (211)衍射峰的变化。

从图可以看出强塑性变形后α2Fe (211)衍射峰向小角区漂移了011°左右,说明强塑性变形后铁素体点阵常数变大了。

此外,强塑性变形后衍射峰宽度明显宽化,这可能是由于强塑性变形细化α2Fe 晶粒尺寸和残余微观应力所致。

强塑性变形钢丝经100℃退火处理衍射峰位基本与冷变形态一致,但400℃退火处理后发现α2Fe (211)衍射峰位已基本回复到变形前位置。

不同温度退火后,冷拉钢丝的铁素体点阵常数如表2所示。

图3　变形前后及不同温度退火处理后XRD 分析谱图Fig 13　X 2ray diffraction patterns in the initial state ,as 2drawn and after annealing at different temperatures44材　料　热　处　理　学　报第27卷表2　铁素体点阵常数的变化T able 2　Ch anges of ferrite lattice constantS tate Before drawnAs 2drawnAnnealed at different tem perature 100℃200℃300℃400℃Lattice constant Πnm0.287280.287570.287550.287310.287300.287303　讨论在强塑性变形高碳钢丝中渗碳体是不稳定的,冷拉拔过程中一部分渗碳体回溶了,渗碳体中的碳原子溶解到铁素体片层中。

Nam [3]等用M ssbauer 谱方法测定高碳钢中渗碳体的体积分数随拉拔应变的变化关系。

假设在相同冷拉拔应变下,根据他们的实验结果,回溶的渗碳体的量是相同的,那么冷拉拔应变为2160时,约有1Π4的渗碳体溶解。

假设渗碳体溶解后,碳原子均匀分布到铁素体中,那么经应变量为2160的拉拔变形后铁素体中的平均碳含量为01595at %。

然而渗碳体回溶后碳原子有三种存在形式:成为过饱和铁素体中间隙碳原子[1,2,6]、存在于塑性变形产生的高密度位错中或晶界中[3,8]。

由表1的试验结果,根据Fasiska 和Wagemblast [11]提出经验公式,铁素体点阵常数与其间隙碳含量的关系:Δa =(8.4±0.8)×10-4Δx (nm )式中:Δa 为点阵常数变化量;Δx 为间隙碳含量。

计算得知,SWRH72A 钢强塑性变形后形成了含碳量约为0134%at 的过饱和铁素体,少于根据Nam等人试验结果的计算值。

因此猜测SWRH72A 钢丝强塑性变形过程中渗碳体回溶释放的碳原子部分以间隙碳形式固溶于铁素体片层中,其余的分散于位错和晶界上。

XRD 测试结果显示,低温退火(≤100℃)对点阵常数影响较小,退火后铁素体点阵常数和冷拉拔态的相近。

当退火温度超过200℃时,铁素体点阵常数显著降低,基本恢复到变形前状态。

与之对应,铁素体片层中开始弥散析出大量渗碳体颗粒。

根据文献[1]珠光体钢强塑性变形后有部分碎化渗碳体以尺寸极小(仅几十个原子层)的原子团形式游离于铁素体中。

退火过程中以这些原子团为形核核心,渗碳体颗粒在铁素体中弥散析出。

而由于渗碳体颗粒的弥散强化作用,钢丝强度亦随之升高。

4　结论不同温度退火处理对冷拉拔强塑性变形(ε=216)SWRH72A 钢丝力学性能有显著影响。

XRD 分析结果显示由于强塑性变形引起渗碳体回溶,释放出碳原子,钢丝中形成了过饱和铁素体,SWRH72A 钢丝α2Fe 点阵常数变大。

200-300℃退火后,过饱和铁素体中碳原子脱溶,析出弥散分布的渗碳体颗粒,α2Fe 点阵常数恢复至变形前大小,钢丝强度随之上升了7%,达2400MPa 。

400℃退火后渗碳体片层开始球化,钢丝强度降至1900MPa ,但伸长率提高了20%。

参考文献[1]　Languillaume J ,K apelski G,Baudelet B.Cemnetite diss olution in heavily cold drawn pearlitic steel wires[J ].Acta M ater ,1997,45:1201-1212.[2]　H ono K,Ohnuma M ,Murayama M ,et al.Cementite decom position in heavily drawn pearlite steel wire[J ].Scripta M ater ,2001,44:977-983.[3]　Nam W J ,Bae C M ,Oh SJ ,et al.E ffect of interlamellar spacing on cementite diss olution during wire drawing of pearlitic steel wires[J ].Scripta M ater ,2000,42:457-463.[4]　G avriljuk V G.C omment on “E ffect of interlamellar spacing on cementite diss olution during wire drawing of pearlitic steel wires ”[J ].Scripta M ater ,2001,45:1469-1472.[5]　Ivanisenko Y,Lojkowski W ,Valiev R Z.The mechanism of formation of nanostructure and diss olution of cementite in a pearlite steel during high pressuretorsion[J ].Acta M aterialia ,2003,51:5555-5570.[6]　Lojkowski W ,Djahanbakhsh M ,Burkle G,et al.Nanostructure formation on the surface of railway tracks[J ].M aterials Science and Engineering ,2001,A303:197-208.[7]　Xu Y,Umem oto M ,Tsuchiya K.C om paris on of the characteristics of nanocrystalline ferrite in Fe 20.82C steels with pearlite and spheroidite structure produceby ball milling[J ].M ater T rans ,2002,43:2205-2212.[8]　K orznikov A V ,Dimitrov O ,K orznikova G F ,et al.Nanocrystalline structure and phase trans formation of the intermetallic com pound T iAl processed by severeplastic deformation[J ].Nano S tructured M aterials ,1999,11(1):17-23.[9]　许晓嫦,刘志义,党　朋,等.研究强塑性变形过程中第二相回溶现象的现状及发展趋势[J ].金属热处理,2005,30(4):1-6.[10]　孙淑华,熊　毅,傅万堂,等.共析珠光体钢在冷轧过程中的组织变化[J ].金属学报,2005,41(3):267-270.[11]　Fasiska E J ,W agenblast H.Dilation of alpha iron by carbon[J ].T ransactions of the M etallurgical S ociety of AIME ,1967,239:1818-1820.54第5期涂益友等:退火工艺对强塑性变形珠光体钢丝组织和性能的影响transmission election microscopy and an images analysis approach. The results show that the addition of Mn and S i obviously restrains the growth of cementite particles in the severely cold2rolled pearlite during subsequent annealing,and improves the distribution evenness of spheroidized cementite particle sizes.The addition of Mn is m ore effective to refine the cementite particles than that of S i.The coarsening kinetics equations of cementite particles for the alloys of Fe2018C,Fe2018C21S i and Fe2018C21Mn are d=18614t01195,d= 9015t0.205and d=85.9t0.166in turn.K ey w ords:alloying element;pearlite;cementite;cold rolling; annealingE ffect of annealing process on microstructure and mech anical properties of severe plastic deform ation pearlitic steel wireT U Y i2y ou1,LI U X iang2liang1,J I ANG Jian2qing1,C AI Lei2,BI AN Jian2chun2(1.Department of Material Science and Engineering, S outheast University,Nanjing210096,China; 2.Jiangsu Fasten G roup,Jiangyin214433,China)T rans Mater Heat T reat,2006,27(5):43～45,figs3,tabs2,refs11. Abstract:E ffect of annealing process on microstructure of SWRH72A steel wire under severe plastic deformation were investigated by TE M and XRD.The XRD analysis shows that severe plastic deformation causes partial of cementite decomposition and diss olution of carbon into ferrite up to0134at%.Cementites form which distribute dispersively in matrix when the annealing temperature reachs200-300℃, resulting in increasing the strength of wire.Annealing temperature reachs400℃,the strength of wire decreases sharply,but the plasticity enhances significantly.K ey w ords:pearlitic steel;severe plastic deformation;cementite re2 diss olution;annealingI nvestigation on dynamic recrystallization of FGH96powder metallurgy superalloyLI U Jian2tao1,ZH ANG Y i2wen1,T AO Y u1,LI U G uo2quan2,H U Ben2fu2(1.High T emperature Material Institute,Central Iron and S teel Research Institute,Beijing100081,China;2.School of Material Science and Engineering,University of Science and T echnology Beijing,Beijing100083,China)T rans Mater Heat T reat,2006,27(5):46～50,figs8,tabs0,refs6. Abstract:The dynamic recrystallization(DRX)behaviour of as2HIP FG H96PΠM superalloy at1070℃～1170℃with strain rate at5×10-4s-1～2×10-1s-1was studied by means of is othermal compression test on a G leeble21500thermal mechanical simulator.The experiment results show that curves of true stress(σ)2true strain(ε) at higher strain rate(ε≥2×10-2s-1)are the type of dynamic recrystallization and are the type of dynamic recovery at lower stain rate(ε≤2×10-3s-1).Although temperature,strain rate and strain are important factors which affect grain refining during hot deformation,grain size during DRX is mainly determined by strain rate to s ome degree.The grain size( D)and Z ener2H ollm on parameter (Z)during DRX process obey the following equation:ln D=71617-010134ln Z.By means of w orking hardening rate2strain curves deduced from the stress2strain curves,the steady strain(εs)is determined,and als o the diagram of DRX for FG H96PΠM superalloy is given.K ey w ords:FG H96PΠM superalloy;hot deformation;dynamic recrystallizationPrecipitation of microalloyed carbonitride and its strengthening mech anism in low carbon steels containing Nb and MoC AO Jian2chun1,2,Y ONG Qi2long2,LI U Qing2y ou2,S UN X in2jun2(1.Department of Materials and Metallurgy Engineering,K unming University of Science and T echnology,K unming650093,China;2. Institute of S tructural Materials,Central Iron and S teel Research Institute,Beijing100081,China)T rans Mater Heat T reat,2006,27(5):51～55,figs3,tabs7,refs12. Abstract:The distribution,m orphology,composition,crystal structure and particle size of microalloyed carbonitride precipitates in hot rolled Nb2M o steels were examined by XRD,TE M and E DS.The results reveal that the fine and uniformly distributed MC type carbonitrides containing M o and Nb with NaCl type structure precipitate in the steels,in which the atomic ratios of M o to Nb in01081Nb20114M o steel and0117Nb20112M o steel are0141and0122,respectively. Meanwhile,the mass percent of the fine particles(<10nm)in the tw o Nb2M o steels is5814%and6611%,respectively,and the corresponding yield strength increments reach to17913MPa and 25717MPa.The mechanism of the precipitation is discussed.K ey w ords:microalloying carbonitride;niobium;m olybdenum; precipitation;precipitation strengtheningMicrostructures and high2temperature properties of a new Ni2 b ased superalloy after long2term agingC UI T ong1,W ANG Ji2jie2,W ANG Lei1,Y ANG H ong2cai1,ZH AO G uang2pu3(1.C ollege of Materials and Metallurgy,N ortheastern University,Shenyang110006,China; 2.Department of Materials Engineering,Shenyang Institute of Aeronautical Engineering, Shenyang110034,China; 3.Central Iron and S teel Research Institute,Beijing100081,China)T rans Mater Heat T reat,2006,27(5):56～59,figs3,tabs3,refs9. Abstract:The relationship between high2temperature stress2rupture properties and microstructure of a Ni2base alloy used in spacecrafts was investigated after long2term aging at temperatures of750℃, 800℃and850℃,respectively.The microstructure and stress2rupture fractographs were als o analyzed by means of SE M.The results indicate that T CP(T opologically Close2Packed)phase,a harm ful phase to Ni2 base alloy,precipitated during aging at temperatures from750℃to 800℃,and its quantities and sizes increase with the aging time increasing that make the strength of matrix of alloy decrease and the stress2rupture behavior be changed from grain boundary rupture to grain interior.750℃Π510MPa stress2rupture strength of the alloy aged at temperatures of800℃and850℃for1000h was the lowest, respectively because of the changes ofγ′phase size.The higher of aging temperature is,the lower of750℃Π510MPa stress2ruptureⅢ第5期M AI N T OPICS,ABSTRACTS&KEY W ORDS。