Determination of Critical Temperatures in Hot Rolling of a Nb-Microalloyed Steel Sheet  

作　　者：Daavood Mirahmadi Khaki Vahid Alizaadeh Otaaghvar 

机构地区：[1]Department of Materials Engineering,Shahid Rajaee Teacher Training University,Tehran,Iran [2]School of Mechanical Engineering,Islamic Azad University,Tehran,Iran

出　　处：《Journal of Iron and Steel Research International》2011年第S1期585-589,共5页

摘　　要：To design the controlled hot rolling and thermomechanical processes of microalloyed steels,it is essential to know the various critical transformation temperatures like the grain coarsening temperature (T gc),the non-recrystallization temperature (T nr),the start of austenite-to-ferrite transformation (A r3),and the finish of the austenite-to-ferrite transformation (A r1).In this work,the heat treatment and continuous cooling compression (CCC) testing were performed to determine the critical temperatures of a Nb-microalloyed steel.Results obtained from the CCC testing on the strain-stress curves were confirmed by metallographic tests.To carry out the CCC testing,T nr equals 960℃;A r3 equals 830℃ and A r1 equals 665℃ were determined.In addition,to specify the grain coarsening temperature that it usually occurs during reheating the slabs,seven different reheating temperatures between 1000 to 1300℃ with 50℃ increments for the soaking treatment were chosen.By soaking the specimens in furnace,the grain coarsening temperature (T gc) was obtained about the temperature of 1250 ℃.Moreover,it was observed that increasing the reheating temperatures causes more decline of the precipitates percentage.Therefore,the temperature range of 1200 to 1250℃ is recommended to reheat these types of steels.To design the controlled hot rolling and thermomechanical processes of microalloyed steels,it is essential to know the various critical transformation temperatures like the grain coarsening temperature (T gc),the non-recrystallization temperature (T nr),the start of austenite-to-ferrite transformation (A r3),and the finish of the austenite-to-ferrite transformation (A r1).In this work,the heat treatment and continuous cooling compression (CCC) testing were performed to determine the critical temperatures of a Nb-microalloyed steel.Results obtained from the CCC testing on the strain-stress curves were confirmed by metallographic tests.To carry out the CCC testing,T nr equals 960℃;A r3 equals 830℃ and A r1 equals 665℃ were determined.In addition,to specify the grain coarsening temperature that it usually occurs during reheating the slabs,seven different reheating temperatures between 1000 to 1300℃ with 50℃ increments for the soaking treatment were chosen.By soaking the specimens in furnace,the grain coarsening temperature (T gc) was obtained about the temperature of 1250 ℃.Moreover,it was observed that increasing the reheating temperatures causes more decline of the precipitates percentage.Therefore,the temperature range of 1200 to 1250℃ is recommended to reheat these types of steels.

关 键 词：Nb-microalloyed steel continuous cooling compression testing critical temperatures MICROSTRUCTURE 

分 类 号：TG335.55[金属学及工艺—金属压力加工]