开轧温度对铌微合金化热成型钢氢致延迟开裂性能的影响

Effect of initial rolling temperature on the hydrogen-induced delayed fracture of Nb alloyed hot stamping steel

通过动态充氢恒载荷、氢渗透等实验研究轧制工艺对铌合金化热成型钢的氢致延迟开裂性能的影响.随着开轧温度从1000℃降低到950℃,热成型钢的氢扩散系数降低,氢致延迟开裂性能提高,耐腐蚀性能下降.透射电镜观察发现开轧温度为1000℃时MX型析出相尺寸为30 nm;开轧温度为950℃时热成型钢的MX型析出相尺寸为5 nm左右,可以观察到直径为50 nm Cr2C3析出相.作为氢陷阱的纳米析出相是提高实验钢氢致延迟开裂性能的主要因素.析出相不同的原因是开轧温度为1000℃时MX型析出相发生熟化现象,进一步抑制Cr2C3的析出.

The effect of initial rolling temperature on the hydrogen-induced delayed fracture resistance of Nb alloyed hot stamping steel was studied by the constant load test and the electrochemical hydrogen permeation method. When the initial rolling temperature drops from 1000 ℃ to 950 ℃,the hydrogen diffusion coefficient and the corrosion resistance of the steel decrease,but the hydrogen-induced delayed fracture resistance increases. TEM test shows that when the initial rolling temperature is 1000 ℃,the MX precipitated phase has an average size of 30 nm,and the Cr2C3 precipitated phase can be observed with an average size of 100 nm; when the initial rolling temperature is 950 ℃,the MX precipitated phase has an average size of 5 nm. The main reason leading to the improvement of delayed fracture resistance is the hydrogen trapping effect of the MX precipitated phase. The reason for the difference of precipitated phases is that a higher rolling start temperature will prompt the coarsening of the MX precipitated phase,which will suppress the precipitation of the Cr2C3 phase.