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1、奈米級析出物強化熱軋汽車用鋼開發TheDevelopmentofNano-PrecipitationStrengthenedHot-RolledAutomobileSteels1212黃慶淵■顏鴻威■潘永村■楊哲人C.Y.Huang,H.W.Yen,Y.T.Pan,J.R.Yang為了節省能源消耗與兼顧乘車安全Tosavetheenergyandincreasethepassengersafety,性,汽車用鋼材使用的強度等級愈來愈therequiredstrengthlevelofautomobilesteelshasbecome高。過
2、去高強度鋼通常採用麻田散鐵或higherandhigher.Traditionally,themicrostructureofthe變韌鐵為主要顯微組織的相變態強化設highstrengthsteelsismainlycomposedofmartensiteor計,然而此類鋼材加工成形性不夠好。bainiteforgettingthetransformationstrengtheningeffect,為了得到優良強度與加工性組合,本研butthesesteelsusuallyexhibitpoorformability.Toreach究採
3、用高鈦(>0.08wt%)複合添加釩之合thedemandofhighstrengthandformabilitybalance,the金設計配合熱軋軋延參數之精緻控制,steelswithcompositionofhighTicontent(>0.08wt%)and利用肥粒鐵晶粒細化及奈米析出複合強minorVadditionundergoingcarefulcontrolofhotrolling化機構來產製高強度熱軋汽車用鋼。其parametersareusedtogetthegrainrefinementandnano-冶金機制是利
4、用高溫時非常穩定之TiNprecipitationcoupledstrengtheningmechanismsforthe來抑制熱軋製程再加熱時沃斯田鐵晶粒productionofhighstrengthautomobilesteel.Thestable成長,並於熱軋製程上控制完軋溫度盡TiNprecipitatesinhibitthegraingrowthduringreheating可能接近Ar3來大幅增加肥粒鐵成核位treatment.Inaddition,thepropercontrolofthefinish置,配合採用快速冷卻模
5、式來防止於高rollingtemperaturenearbytheAr3temperaturepromotes溫產生肥粒鐵相變化,以避免肥粒鐵晶alotofferritenucleationsitesontheprioraustenite粒粗化。另外再藉由熱軋盤捲溫度的適grainboundaries.Duringthesubsequentcoolingstage,當控制,使奈米尺寸的(Ti,V)C界面析fastcoolingisappliedtofurtherpreventtheoccurrence出物(<10nm)持續於肥粒鐵相變化過
6、程offerritetransformationandcorrespondingcoarsening中析出,而得到大量均勻散布於肥粒鐵offerritegrainsize.Additionally,bycontrollingthe晶粒中之析出物,充分發揮良好的析出coilingtemperatureofthestrip,lotsofnano-sized(<10強化效果。本研究藉由微米級(<3μm)nm)(Ti,V)Cinterfaceprecipitatesareconsecutively細晶肥粒鐵中奈米級析出物之大量產appearedd
7、uringtheslowcoolingperiod.Theultrafine生,使得熱軋後之鋼材不需再經過任grainedrefinementandnano-precipitationtechnologies何熱處理,其抗拉強度可以穩定達到ensurethestrengthofsteelhigherthan780MPa,and>780MPa的超高強度,而且伸長率還可theelongationofthesteelbetterthan18%,sparingthe達到18%的水準。此鋼材超高強度與良commonstrengtheningbyhe
8、attreatment.Thissteelhas好加工成形性,已經被廣泛應用於卡車beenappliedinseveralpartsofautomobile,suchastruck大樑及汽車之