超细晶粒钢HAZ晶粒长大的规律

研究了低碳钢、普通市售Ｘ６５钢和高洁净度Ｘ６５钢三种超细晶粒钢焊接ＨＡＺ的晶粒长大倾向。试验结果表明，这些超细晶粒钢都具有严重的晶粒长大倾向；低碳超细晶粒钢比Ｘ６５超细晶粒钢有更为严重的晶粒长大，这是因为前者不含有能阻碍晶粒长大的稳定碳、氮化物形成元素Ｎｂ和Ｔｉ，而后者中含有这些元素；高洁净度Ｘ６５超细晶粒钢的ＨＡＺ晶粒长大倾向小于普通市售Ｘ６５超细晶粒钢。这是因为钢中杂质元素含量越多，α→γ转变温度越低，即Ａｃ３点越低，在同样的焊接热循环条件下，普通市售Ｘ６５超细晶粒钢中的γ晶粒在高温停留时间就越长，晶粒长大的程度也就越大。

Grain Growth in HAZ of Ultra-fine Grain Steels

In this paper,the grain growth in the HAZ of three kinds of ultra - fine grain steels such as low carbon steel,commercial X65 steel and high purity X65 steel were evaluated. Experimental results show that these ultra -- fine grain steels are prone to serious grain coarsening. The low carbon ultra -- fine grain steel has more serious grain growth in its HAZ than the ultra - fine grain X65 steels. It is because that the low carbon ultra -- fine grain steel doesnt contain niobium and titanium, while ultra -- fine grain X65 steels contain these elements. The high purity ultra - fine X65 steel has less grain growth tan commercial ultra -- fine grain X65 steel. It is because that the higher the ultra -- fine gain X65 steel's purity is,the higher the phase transformation temperature from a to r i,,that is to say, the lower Ac3 is. As a result, under the same condition, the shorter the time of the r phase in the commercial X65 steel staying in high temperature is,the bigger the grain growth in its HAZ is.