锻造及热处理工艺对MC5冷轧辊坯缺陷与组织性能的影响

工程硕士学位论文锻造及热处理工艺对MC5冷轧辊坯缺陷与组织性能的影响EFFECTSOFFORGINGANDHEATTREATMENTPROCESSOFMC5COLDROLLBLANKDEFECTSANDSTRUCTUREPROPERTY徐咏梅哈尔滨工业大学2014年6月国内图书分类号：TG146.2+2学校代码：10213国际图书分类号：679密级：公开工程硕士学位论文锻造及热处理工艺对MC5冷轧辊坯缺陷与组织性能的影响硕士研究生：徐咏梅导师：杜之明教授申请学位：工程硕士学科、专业：材料工程所在单位：北满特殊钢有限责任公司答辩日期：2014年6月授予学位单位：哈尔滨工业大学ClassifiedIndex:TG146.2+2U.D.C:679DissertationfortheMasterDegreeinEngineeringEFFECTSOFFORGINGANDHEATTREATMENTPROCESSOFMC5COLDROLLBLANKDEFECTSANDSTRUCTUREPROPERTYCandidate：XuYongmeiSupervisor：Prof.DuZhimingAcademicDegreeAppliedfor：MasterofEngineeringSpeciality：MaterialsEngineeringAffiliation：BeimanSpecialSteelCo.,Ltd.DateofDefence：June,2014Degree-Conferring-Institution：：HarbinInstituteofTechnology哈尔滨工业大学工程硕士学位论文I摘要随着钢铁工业的快速发展，现代化轧机对性能要求逐渐提高，辊坯对不同规格、质量等级、材质的要求不断增加。而在各种轧辊类产品中冷轧工作辊是质量要求最高的，因而也是对材质要求极高、制造工艺较为复杂的高技术产品。随着工艺的发展，锻钢冷轧辊的材质逐渐向高铬方向发展，由最初冷轧辊只含1.5%Cr，经过多年发展已经达到含5%Cr，现今的研究方向是在5%Cr的基础上采用微合金化技术进行改进。但是，由于Cr5钢中含有大量的合金元素且碳含量较高，使钢锭凝固时更容易产生成分偏析，产生块状或共晶骨骼状液析碳化物，这种碳化物硬度高，脆性大，当存在于轧辊辊身表层时，在轧制载荷的作用下，往往成为疲劳裂纹源而引起浅层或大块剥落。针对上述问题，本文对MC5电渣钢辊坯进行了试验研究，对辊坯的缺陷及缺陷的产生原因进行分析，并根据缺陷产生的原因设计试验方案，以期达到消除或改善辊坯产生的缺陷。通过质点偏析区过烧试验、高温均质化试验以及不同锻造比的锻造试验，分析锻造工艺对辊坯性能及碳化物的影响。根据质点偏析区过烧试验，质点偏析特别严重的区域，其过烧温度接近1200℃，为了防止质点过烧，锻造温度要低于1200℃；根据高温均质化试验，随着高温均质化试验温度及保温时间的提高，辊坯内碳化物液析等级降低，一般采用1190℃进行长时间高温扩散，保温时间一般为14-36小时；根据不同锻造比的锻造试验，随着锻造比的增加，硬度及延伸率变化不明显，屈服强度、抗拉强度随着锻造比的增加而增加，但增长幅度不明显，冲击功随着锻造比的增加而显著增加。通过在不同的温度和保温时间，锻后热处理，研究锻后热处理等各工序对网状碳化物和带状碳化物的影响。通过对球化退火工艺的研究得出，球化退火的加热温度范围很宽，在820℃-900℃区间，球化退火等温温度应在700℃-740℃之间。对于硬度要求低的，等温温度应该高一些。辊坯的预备热处理工艺应该选择在淬火910℃-930℃，回火690℃-720℃对后续的最终热处理最为有利。最终淬火温度在930℃-950℃之间，MC5钢选0.5mm/s的速度作为轧辊双频感应淬火下降速度。关键词：MC5冷轧辊坯；碳化物偏析；锻造工艺；锻后热处理工艺哈尔滨工业大学工程硕士学位论文IIAbstractWiththerapiddevelopmentofsteelindustry,modernizedrollingmillisinacontinuousimprovement,whichresultsinincreasinglyhighrequirementsonthematerialsandqualityofrolling.Coldrollblankhasthehighestqualityrequirementamongawiderangeofrollproducts,thusitisahightechnologyproductwithextremelyhighrequirementonthematerialsandcomplicatedmanufacturingprocess.Thematerialsofforgedsteelcoldrolldeveloptowardhigh-contentchromedirectioninaprogressivewaythankstothedevelopmentofcraftsmanship,increasingfromonly1.5%Crintheinitialcoldrollto5%Craftergettingthroughmanyyears’development.Today,thestudyfocusesontheimprovementthroughtheapplicationofmicro-alloyingtechnologybasedon5%Cr.However,asalargenumberofalloyelementsexistinCr5steelandcarboncontentisrelativelyhigh,whichcausestoeasilyproducecompositionsegregationwhensteelingotsolidifies,blockoreutecticskeleton-shapeliquationcarbidewillbeproduced.Suchcarbidehashighhardnessandtremendousbrittleness,anditwillusuallybecomefatiguesourceofcrackorleadspeelinginthesuperficiallayerorinlargeareaundertherollingloadinthesteelrollingprocesswhenitexistsinthesurfaceofrollbarrel.Inviewoftheabovequestions,thispaperconductsacollectionofexperimentalresearchesonMC5electroslagsteelrollblankandanalyzesthedefectsofrollandtheircauses.Basedonabovecauses,theexperimentalplanisdesignedwithaimtoeradicateorimprovethosedefectsarisingfromtherollblank.Basedontheparticleoverburningexperiment,hightemperaturehomogenizationexperimentandforgingexperimentsofdifferentforgingratios,analyzetheimpactofforgingprocessonrollperformanceandcarbide.Accordiontotheparticleoverburningexperiment,theareawhereconfrontswithsevereparticlesegregationhasatemperatureapproximating1200℃,whichshallnotbeexceedinordertopreventfromparticleoverburning;accordingtothehightemperaturehomogenizationexperiment,theliquationlevelofcarbidewithintherolldecreaseswiththeincreaseofhightemperaturehomogenizationexperimentaltemperatureandheatpreservationtime,generally,long-timehightemperaturediffusionisappliedunder1190℃withtheheatpreservationtimeofrangingfrom14to36hours;accordingtotheforgingexperimentsofdifferentforgingratios,nosignificantchangeoccursinthehardnessandductility哈尔滨工业大学工程硕士学位论文IIIwiththeincreaseofforgingratio,buttheyieldstrengthandtensilestrengthincreasesaccordinglyinainsignificantrange,theimpacthasadramaticincreasealongwiththeincreaseofforgingratio.Underdifferenttemperature，heatpreservationtimeandheattreatmentafterforging，researchtheimpactsofpost-forgingheattreatmentonthecarbideandband-typecarbide.Thestudyonthespheroidizingannealingprocessrevealsthattheheatingtemperatureofspheroidizingannealinghasawiderange(820℃-900℃).Thespheroidizingannealingisothermyshallbebetween700℃and740℃andtheisothermytemperatureshouldbehighinthecaseoflowhardnessrequirement.Theprocessofhardeningandtemperingisappliedforquenchingunder910℃to930℃,withappropriatetemperingtemperatureunder690℃to720℃.Inductionhardeningensuresthepowerfrequencyandintermediatefrequencyoutlettemperaturefallsintothecategorybetween930℃and950℃inadecreasingspeedof0.5mm/sforroll.Keywords:MC5coldrollblank;carbidesegregation;forgingprocess;AfterForgedHeatTreatmentProcess哈尔滨工业大学工程硕士学位论文IV目录摘要...................................................................................................................................IAbstract....................................................................................