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对一种新型70Si3Mn Cr Mo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。
A new type of 70Si3Mn Cr Mo steel was subjected to isothermal and continuous cooling bainite transformation heat treatment. Tensile and impact tests were used to study the mechanical behavior of the test steel. The phase composition and microstructure of the test steel were observed by XRD, SEM and TEM. The results show that the optimum mechanical properties of the test steel after isothermal bainitic transformation appear in the tempering at 200 ℃, and the strong plastic product is 26.4 GPa ·%. After continuous cooling bainite transformation, the best comprehensive mechanical properties appear at 300 ℃ tempering, strong plastic product reached 28.6 GPa ·%. In the case of a low tempering temperature, the heat-treated structure is a carbide-free bainite structure composed of bainitic ferrite and retained austenite. This carbide-free bainite consists of ultrafine bainite Ferrite slats and get ultra-high strength, by a certain amount of high carbon residual austenite to ensure high ductility and toughness. The continuous cooling of the test steel bainite phase transformation, the bainitic ferrite slab superfine subunit appears, and the retained austenite was thin and two kinds of billets distributed in bainitic ferrite Between the laths, the stability of these two forms of retained austenite is different. The retained austenite in the tensile specimen during the deformation continues the TRIP effect until all the retained austenite is transformed into strain-induced martensite so as to make the steel get a better combination of strong and plastic properties and show a very excellent Comprehensive performance.