纯铁晶粒粗化与均匀化的热处理工艺研究

STUDY ON HEAT TREATMENT PROCESS OF GRAIN COARSENING AND HOMOGENIZATION OF PURE IRON

通过对XGM6-1铜包钢丝用钢显微组织的观察实验,研究了纯铁在不同加热温度、保温时间和冷却方式下晶粒形貌的变化规律。结果表明:在加热温度为840℃且保温时间较短时,冷却方式对晶粒形貌无本质影响,随保温时间延长至90 min,采用随炉冷却方式,试样发生二次再结晶;当加热温度提高至870℃,保温时间30 min并采用炉冷时,试验钢发生了充分再结晶,得到细小均匀的铁素体晶粒,继续延长保温时间,采用冷却速率较快的空冷方式,发生了二次再结晶,产生异常长大晶粒。在930~1030℃加热保温时,随保温时间延长和加热温度的提高,试验钢晶粒越来越粗大,但长大到一定程度后,晶粒尺寸基本不发生变化;在该温度区间加热保温后,水冷试样较炉冷试样显微组织不均匀性严重,水冷试样小尺寸晶粒较多。冷变形试样在840℃退火处理时,冷拔减面率为20.38%的试样得到粗大均匀的铁素体组织,之后,随冷拔减面率增加,晶粒逐渐细化。

By observing the microstructure of XGM6-1 copper clad steel,the change of grain morphology of pure iron under different heating temperature,holding time and cooling mode was studied.The results show that:when the heating temperature is 840℃and the holding time is short,the cooling method has no essential effect on the grain morphology;while the holding time extended to 90 min,the sample is recrystallized again with furnace cooling;when the heating temperature is increased to 870℃and the holding time is 30 min,the test steel fully recrystallized with furnace cooling;and fine and uniform ferrite grains are obtained;prolonging the holding time and adopting the air cooling method with faster cooling rate,secondary recrystallization occurred and abnormal grain growth was produced.When heated at 930~1030℃,with the prolongation of holding time and the increasing of heating temperature,the grain size of test steel becomes coarser and coarser,but after it grows to a certain extent,the grain size basically does not change;after heating and holding in this temperature range,the microstructure heterogeneity of water-cooled sample is more serious than that of furnace cooling sample,and the water-cooled sample has more smaller grain.When the cold deformation sample is annealed at 840℃,the coarse and uniform ferrite structure is obtained with 20.38%cold drawing reduction rate.Then,with the increasing of cold drawing reduction rate,the grain size is gradually refined.