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Vacuum73(2004)643–648

Amechanicalaspectofboridesformedonthe

AISI440Cstainless-steel

IbrahimOzbeka,SadumanSena,MedihaIpeka,CumaBindala,

SakinZeytina,A.HikmetUcisikb,*

aDepartmentofMetallurgyandMaterialsEngineering,EngineeringFaculty,SakaryaUniversity,54187EsentepeCampus,Sakarya,TurkeybBogaziciUniversity,DepartmentofProstheses,MaterialsandArtificialOrgans,InstituteofBiomedicalEngineering,Bebek-Istanbul80815,Turkey

Abstract

Inthepresentstudy,somepropertiesofboridesformedonAISI440Cstainless-steelhavebeeninvestigated.BoronizingwascarriedoutinasolidmediumconsistingofEKaborspowderatatemperatureof950󰀁Cfor2–8h.Thepresenceofboridese.g.FeB,Fe2B,CrB,Cr2B,Mn2BandMnBwererevealedbymeansofX-raydiffractometry,scanningelectronmicroscopy,andopticalmicroscopy.Thehardnessofborideswhichwasover1500VHNandboridelayerthicknessweremeasuredanditwasobservedthat,thethicknessesoftheboridelayerswerestronglydependentontheprocesstime,andchemicalcompositionofthesubstratematerials.Itwasalsofoundthatthelongerboronizingtimeresultsinanincreaseinthicknesslayer;thethicknessofboridelayersrangedfrom10to50mm.OpticalmicroscopyexaminationsoftheboridesformedonthesurfaceofAISI440Cstainless-steelsubstraterevealedasmoothandcompactmorphology.TodeterminedistributionofalloyingelementsfromsurfacetotheinteriorenergydispersiveX-rayspectroscopywasused.r2004ElsevierLtd.Allrightsreserved.

Keywords:Boronizing;Stainless-steel;Microstructureofboridedzone;Indentation

1.Introduction

Boronizingisathermochemicaldiffusionsur-

facetreatmentinwhichboronatomsarediffused

intothesurfaceofworkpiecetoformhardborides

withthebasematerial[1–4]anditisaprominentchoiceforawiderangeoftribologicalapplications

wherethecontroloffrictionandwearisof

primaryconcern[5].Boronizingcanbeapplied

toawiderangeofsteelalloysincludingcarbon-

steel,lowalloy-steel,tool-steelandstainless-steel.

Inaddition,materialssuchasnickelbasedalloys,

cobaltbasedalloys,molybdenumandtitanium

canbeboronizedtoobtainveryhighhardnessand

wearresistantontheirsurfaces[6–11].Inparti-

cular,boronizingcanincreasetheresistanceof

lowalloysteeltoacidssuchassulfuric,phosphoric

andhydrochloricacids.Inaddition,boronized*Correspondingauthor.BogaziciUniversity,DepartmentofProstheses,MaterialsandArtificialOrgans,InstituteofBiomedicalEngineering,Bebek-Istanbul80815,Turkey.Fax:+90-212-227-79-34.E-mailaddress:hucisik@hotmail.com(A.HikmetUcisik).

0042-207X/$-seefrontmatterr2004ElsevierLtd.Allrightsreserved.doi:10.1016/j.vacuum.2003.12.083austeniticstainless-steelhasexcellentresistanceto

hydrochloricacid[2,12–14].Inthisstudy,we

investigatedsomepropertiesofboridesformed

onAS440Cstainless-steelwhichisextensively

usedforball-bearingsandraces,seats,pump

parts,surgicaltools,implantmaterialandcutlery.

AISI440Cstainless-steelshasalsohighcarbon

andchromiumcontentandtherefore,itmaybe

hardenedandtemperedtoincreasewearresis-

tance.

Atpresentstudy,weattempttoelucidatesome

propertiesofboronizedAISI440Cstainless-steel,

e.g.distributionofalloyingelements,microstruc-

tureofboridedzoneetc.Specifically,weuseda

Vickersindenterandanopticalmicroscopeto

determinehardnessandmicrostructuresofbor-

onizedAISI440Cstainless-steel.Todetermine

distributionofalloyingelementsfromthesurface

totheinteriorenergydispersiveX-rayspectro-

scopy(EDS)wasused.

2.Experimentaldetails

2.1.Substratematerials

Thesubstratematerialusedinthisstudywas

AS440Cstainless-steelwithchemicalcomposi-

tiongiveninTable1.ThetestpiecesofAISI440C

stainless-steelhadadimensionof15mmÂ

15mmÂ3mm.

2.2.Boronizing

Boronizingwascarriedoutinasolidmedium

consistingofEKabor2spowders(BorTec

GmbH).Testsamplestobeboronizedwereplaced

incontactwithEKabor2spowdersandthen

placedinelectricalresistancefurnace.Thetest

sampleswereheatedtoatemperatureof950󰀁C

underatmosphericpressureandholdforapredeterminedamountoftime(about2–8h).This

isfollowedbyquenchinginair.

2.3.Filmcharacterization

Thestructureandtypeofboridesformedon

AS440Cstainless-steeliscloselyrelatedtothe

chemicalcompositionofAISI440Cstainless-steel

substrateusedinthisstudy.Thepresenceof

boridesformedincoatinglayerwasconfirmedby

meansofX-raydiffractometry(XRD),andoptical

microscopy.APhillipshighresolutiondiffract-

ometerwasemployedforXRDanalysisofthe

boridesformedonAISI440Cstainless-steel

surfaces.ACoKaradiationwithawavelengthof

1.790(Awasusedovera2yrangeof20󰀁–90󰀁.

OlympusBHM-313opticalmicroscopewasalso

utilizedforexaminingmicrostructures.Thedis-

tributionofalloyingelementswasconfirmedvia

EDSfromsurfacetointerior.

2.4.Hardnessandthicknessofcoatinglayer

Themicrohardnessofborideswasmeasuredby

usingaVickersmicrohardnesstesterandaloadof

0.5N.Atleastfiveindentationsweremadeoneach

coatingfilmundereachexperimentalconditionto

checkreproducibilityofthehardnessdata.The

thicknessesofthecoatinglayerweremeasuredby