Nb对低碳Si-Mn钢连续冷却转变的影响

Effect of Nb on Low-Carbon Si-Mn Steel During Continuous Cooling Transformation

利用Gleeble 1500对含Nb与不含Nb两种低碳Si-Mn钢进行了连续冷却转变实验,并绘制了未变形及变形条件下的CCT曲线.结果表明:在未变形条件下,Nb的添加降低了铁素体相变温度(Ar3),使未变形CCT曲线下移;在变形条件下,应变诱导析出的Nb(C,N)等析出物使铁素体的转变温度上升并降低了贝氏体的转变冷速,从而使Ar3提高,CCT曲线上移;在变形条件下,Nb使铁素体晶粒明显细化,进而使实验钢的硬度明显提高.

The continuous cooling transformation（CCT） tests of low-carbon Si-Mn steel were conducted on Gleeble 1500 thermal simulator with and without Nb addition, and the relevant curves were plotted under deformed and undeformed conditions. The results showed that the undeformed CCT curves mostly go down due to the effect of Nb addition that lowers the phase transformation temperature of ferrite（Ar3 ）, while the deformed CCT curves go up due to the effect of strain-induced precipitates as Nb（C, N）, which raises Ar3 hence lowers the starting cooling rate in banite transformation. Moreover, ferrite grains were refined obviously with the addition of Nb under deformed conditions, thus hardening greatly the tested steel.