轧后冷速对Q500GJE钢组织和拉伸性能的影响

为了开发Q500GJE高性能超高层建筑用钢,利用Gleeble热/力学模拟、扫描电镜、透射电镜、背散射电子衍射、着色腐蚀金相等方法研究了轧后控冷冷速对TMCP交货低屈强比(≤0.80)Q500GJE钢组织和拉伸性能的影响。结果表明:试验钢在冷速5~25℃/s的范围内,形成由针状铁素体、粒状贝氏体以及M-A岛构成的混合组织。随着轧后冷速的提高,针状铁素体数量减少,粒状贝氏体数量增多,晶粒发生细化,位错密度升高,屈服强度和抗拉强度升高;随着轧后冷速的适当降低,硬相M-A岛的含量增加,尺寸增大,屈强比下降,应变硬化量增加。拉伸性能满足低屈强比Q500GJE钢要求的轧后控冷冷速是15~20℃/s。

Effect of post-roll cooling rate on microstructure and tensile properties of Q500E-class steel for high-rise building

The effect of the post-roll cooling rate on the microstructure and tensile properties ofa Q500E-class building steel under TMCP delivery is investigated using the Gleeble thermo-mechanical simulator together with SEM, TEM, EBSD and coloring metallography. The results indicate that as the Cooling rate increases from 5℃/s to 25℃/s, the amount of granular bainite increases at the expense of acicular ferrite, along with the grain refinement and increase of dislocation density, leading to the enhancement of the yield strength and the tensile strength. When decreasing the cooling rate moderately, the M-A constituents become larger and increase significantly in the amount, resulting to the decreased yield ratio and the increased strain hardening capacity. The optimum cooling rate required for the tensile properties of the low yield ratio Q500E-class building steel is determined ranging from 15℃/s to 20 ℃/s.