回火温度对低碳马氏体高强钢组织和性能的影响

Effect of tempering temperature on microstructure and properties of low carbon martensitic high strength steel

采用光学显微镜、扫描电镜、电子背散射衍射和拉伸及冲击试验等研究了回火温度对离线再加热淬火(RQ)与在线直接淬火(DQ)低碳马氏体高强钢组织和性能的影响。结果表明:两种淬火态试验钢组织均为板条马氏体,其中RQ钢中原奥氏体晶粒及板条束呈等轴状,而DQ钢中呈扁平状;随着回火温度升高,马氏体板条发生合并、粗化,并逐渐消失,形成多边形铁素体;碳化物析出并聚集长大、球化。在同一回火温度下,RQ钢的屈服和抗拉强度均较DQ钢低,但伸长率较DQ钢高。同时,RQ钢比DQ钢具有更高的冲击吸收能量和更低的韧脆转变温度(DBTT);随着回火温度升高,RQ和DQ钢的伸长率和屈强比上升,屈服强度和抗拉强度下降,DBTT先升高后降低;RQ和DQ钢在200℃或500~600℃回火时具有优良的综合力学性能。

Effect of tempering temperature on microstructure and properties of off-line reheat quenching(RQ)and on-line direct quenching(DQ)low carbon martensitic high strength steel was studied by means of optical microscope,scanning electron microscopy,electron backscatter diffraction technique and tensile and impact tests.The results show that the microstructure of the steel under two quenched state is lath martensite.The prior austenite grains and packet in the RQ steel are equiaxed,while those in the DQ steel are flat.With the increase of tempering temperature,martensite laths merge,coarsen and gradually disappear to form polygonal ferrite,and the carbides precipitate,aggregate,grow and spheroidize.At the same tempering temperature,the yield and tensile strength of the RQ steel are lower than DQ steel,but the elongation is higher than DQ steel.At the same time,the RQ steel has higher impact absorbed energy and lower ductile-to-brittle transition temperature(DBTT)than DQ steel.With the increase of tempering temperature,the elongation and yield strength ratio of the RQ and DQ steel increase,the yield strength and tensile strength decrease,and DBTT first increases and then decreases.The RQ and DQ steel has excellent comprehensive mechanical properties when tempered at 200℃or 500-600℃.