回火温度对铁素体/粒状贝氏体钢显微组织及力学性能的影响

Effects of tempering on microstructure and mechanical properties of fine grain ferrite/granular bainite dual phase steel

采用Gleeble 1500热模拟试验机对成分为0. 12C-1. 46Mn-0. 83Si-0. 70Al-0. 34Mo-0. 01Nb的低碳钢进行多道次连续压缩后并空冷处理,得到了细晶铁素体+粒状贝氏体复相组织。采用扫描电镜和透射电镜研究了复相组织在600℃以下不同温度回火后的组织,并研究了实验钢回火后的室温拉伸性能。结果表明:该复相组织钢具有较好的强度及塑性,室温拉伸时屈服强度大于500 MPa,伸长率超过20%,屈强比为0. 65;同时该复相组织具有较好的回火稳定性,300~400℃较低温度回火3 h后不会引起马奥(M-A)岛的分解,500℃回火3 h后有少量马奥岛发生了分解,等轴铁素体内仍然存在高密度位错,600℃回火3 h后仍能保持一定量的马奥岛,贝氏体铁素体板条间及等轴铁素体晶界等处有碳化物粒子析出;随回火温度提高,实验钢的屈服强度和伸长率均呈现先增加后降低的趋势,400℃回火后屈服强度和伸长率达到峰值,600℃回火后的屈服强度仍高于未回火状态,伸长率与未回火态基本相当,但抗拉强度下降,屈强比增大。

The low carbon steel with composition of 0. 12 C-1. 46 Mn-0. 83 Si-0. 70 Al-0. 34 Mo-0. 01 Nb was subjected to multi-pass continuous compression and air cooling treatment with Gleeble 1500 thermal simulation tester,and the fine-grain ferrite/granular bainite multiphase microstructure was obtained. The microstructure of the steel with multiphase microstructure tempered at different temperatures( below 600 ℃) was studied by means of scanning electron microscopy( SEM) and transmission electron microscopy( TEM),and the tensile properties of the steel at room temperature after tempering were also studied. The results show that the multiphase microstructure steel has good strength and plasticity,the room temperature yield strength is more than 500 MPa,the elongation is more than 20%,and the yield strength ratio is 0. 65. At the same time,the multiphase microstructure steel has good tempering stability,the M-A island of the steel after tempering at 300-400 ℃ for 3 h will not decompose. A small amount of M-A island will decompose after tempering at 500 ℃ for3 h,and high density dislocations still exist in equiaxed ferrite. After tempering at 600 ℃ for 3 h,a certain amount of M-A island is observed,and carbide particles are precipitated between the bainitic ferrite laths and the equiaxed ferrite grain boundaries. With the increase of tempering temperature,the yield strength and elongation of the steel increase at first and then decrease. The yield strength and elongation reach the peak value after tempering at 400 ℃,the yield strength after tempering at 600 ℃ is still higher than that of the untempered state,and the elongation is basically the same as that of the un-tempered state,but the tensile strength decreases and the yield strength ratio increases.