正火对建筑用热轧20MnV钢组织与性能的影响

Effect ofnormalizing on microstructure and properties of hot rolled 20MnV steel for construction

采用光学显微镜、扫描电镜和透射电镜等手段,研究了正火温度和时间对20MnV钢显微组织、拉伸性能和低温冲击性能的影响。结果表明,热轧态20MnV钢的显微组织为铁素体+珠光体条带,具有较高的强塑性和较低的低温冲击性能;当正火温度从770℃升高至1000℃过程中,20MnV钢中条带状组织逐渐消失,晶粒呈现等轴化趋势,铁素体晶粒有所粗化,组织均匀化升高;830℃及以上正火处理后,(Fe,Mn)3C相回溶至基体,晶内弥散析出了纳米级VC相;随着正火温度的升高,20MnV钢的抗拉强度和规定塑性延伸强度都表现为先减小而后增加的特征,断口伸长率、-25℃和-45℃冲击吸收能量则先增大而后减小;当正火保温时间从20min增加至80min时,20MnV钢的强度变化幅度较小,而断后伸长率、-25℃和-45℃冲击吸收能量都呈现先增加而后减小的特征,在正火温度为920℃、正火保温时间为60 min时,20MnV钢具有最佳的强塑性和低温冲击性能。

The effects of normalizing temperature and time on the microstructures,tensile properties and low temperature impact properties of 20 Mn V steel were studied by means of optical microscopy,scanning electron microscopy and transmission electron microscopy,etc.The results show that the microstructure of the hot rolled 20 Mn V steel is banded ferrite and pearlite,which has high strength,plasticity and low impact toughness at low temperature.When the normalizing temperature rises from 770℃to 1000℃,the banded microstructure disappears gradually,the grains show equiaxed tendency,the ferrite grains are coarsened and the microstructure is homogeneous.With the increase of normalizing temperature,the(Fe,Mn)3 C phase dissolves back to the matrix,and nano-sized VC phase disperses in the grains;the tensile strength and yield strength of the 20 Mn V steel decrease first and then increase,while the elongation and the impact energies at-25℃and-45℃increase first and then decrease.When the normalizing holding time increases from 20 min to 80 min,the strength of the 20 Mn V steel changes slightly,while the elongation and the impact absorbed energy at-25℃and-45℃increase first and then decrease.When the normalizing temperature is 920℃and the normalizing holding time is 60 min,the 20 Mn V steel has the best strength,plasticity,and low temperature impact toughness.