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对一种新型70Si3MnCrMo钢进行了等温和连续冷却贝氏体相变热处理.利用拉伸和冲击试验研究试验钢的力学行为,利用XRD、SEM和TEM等方法对试验钢进行了相组成分析和微观组织形貌观察.研究结果表明,试验钢经等温贝氏体相变,其最佳综合力学性能出现在200℃回火,强塑积为26.4 GPa·％.经连续冷却贝氏体相变,其最佳综合力学性能出现在300℃回火,强塑积达到28.6 GPa·％.回火温度较低的情况下,热处理后的组织为由贝氏体铁素体和残余奥氏体组成的无碳化物贝氏体组织,这种无碳化物贝氏体由超细贝氏体铁素体板条而获得超高强度,由一定量的高碳残余奥氏体来保证较高的塑性和韧性.试验钢经连续冷却贝氏体相变,其贝氏体铁素体板条中出现了超细亚单元,并且残余奥氏体呈薄膜状和小块状两种形态分布于贝氏体铁素体板条之间,这两种形态残余奥氏体的稳定性不同.拉伸试样在变形过程中残余奥氏体持续发生TRIP效应,直至全部残余奥氏体都发生转变生成应变诱发马氏体,从而使钢得到更好的强、塑性配合,表现出十分优异的综合性能.

The 70Si3MnCrMo steel was treated by austempering and continuous cooling treatment to obtain bainite microstmcture.Mechanical properties of the steel were detected via tensile test and impact test experiments.The phase composition and microstructure morphology of the steel were analyzed by XRD,SEM and TEM.Results show that for austempering treatment,the best comprehensive mechanical properties of the steel were obtained when the tempering temperature was 200 ℃,with a product of strength and ductility of 26.4 GPa· ％.For continuous cooling treatment,the best comprehensive mechanical properties were obtained when the tempering temperature was 300 ℃,with a product of strength and ductility of 28.6 GPa-％.A carbide-free bainite microstructure composed of bainite ferrite and retained austenite formed in the steel at a relatively low tempering temperature.The ultra-fine bainitic ferrite plate had a ultra-high strength,and the stable residual austenite guaranteed the high plasticity and toughness.Observations show that there were ultra-fine subunits in the bainitic ferrite plate in the steel treated by continuous cooling process.Retained austenites were in shape of film and block possessing different stability,and distributed among the bainitic ferrite plate.The retained austenite gradually transformed to martensite during the tensile process,which made a good combination of strength and toughness,and presented an excellent comprehensive properties.