回火热处理对低屈强比高强钢组织与性能的影响

Influence of tempering heat treatment on microstructure and mechanical properties of a high strength steel with low yield ratio

利用力学性能测试、光学显微镜、透射电镜观察等方法,阐明了回火热处理对低屈强比高强度钢组织与力学性能的影响规律。研究表明,回火温度对低屈强比高强度钢的组织和力学性能具有决定性影响。回火前,试验钢显微组织主要由细小板条状和粒状贝氏体组成,还含有少量铁素体及一些M/A岛。随回火温度提升,板条贝氏体逐渐合并长大,板条宽度增加,M/A岛分解,抗拉强度和冲击韧性下降,而屈服强度保持稳定,导致屈强比升高。M/A岛以块状和链条状形态存在,位于板条之间或贝氏体/铁素体边界。较低的回火温度可获得高强度、高韧性和低屈强比钢,这主要归功于其细小的板条组织和稳定的M/A岛。

Influence of tempering heat treatment on microstructure and mechanical properties of a high strength steel with low yield ratio was analyzed by means of mechanical property test and microstructure observation with optical microscope and transmission electron microscopy. The results show that tempering temperature has a decisive influence on the microstructure and properties of the steel with low yield ratio. Before tempering,the microstructure of the tested steel is composed of fine lath and granular bainite,small fraction of ferrite and some M/A constituent. With increase of the tempering temperature,bainite laths merge gradually,lath width increases,M/A constituent is decomposed,and the tensile strength and impact toughness decrease,while the yield strength remains stable,so the yield ratio increases. The M/A constituent between laths or at the bainite/ferrite boundary exists in the form of lump and stringer. The high strength steel with good toughness and low yield ratio is obtained at lower tempering temperature,and this is mainly attributed to the fine lath-type microstructure and stable M/A constituent.