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通过透射电镜观察和鉴别了406钢在回火过程中的力学性能变化规律和马氏体精细结构特征,碳化物种类、形态、分布及它们之间的关系。结果表明:406钢淬火并300℃回火后具有较高的强度和韧性,是高位错密度的板条马氏体和马氏体内大量的与基体高度共格的ε-碳化物弥散析出,及马氏体板条周围2～3％的残留奥氏体网状薄膜的贡献。同时钢中含有1.5％Si和0.5％Mo,提高了ε-碳化物和残留奥氏体的稳定性,从而推迟并减缓了马氏体回火脆性凹,改善了断裂形貌。360～500℃回火脆性是由于渗碳体在板条边界析出和杂质元素在晶界偏聚的结果。
Transmission electron microscopy was used to observe and identify the mechanical properties of 406 steel during tempering and the fine structure characteristics of martensite, carbide species, morphology, distribution and their relationship. The results show that 406 steel has high strength and toughness after being quenched and tempered at 300 ℃. It is a large amount of ε-carbides dispersed highly in matrix martensite and martensite with high dislocation densities. Contribution of 2-3% residual austenite reticular film around martensite laths. At the same time, the steel contains 1.5% Si and 0.5% Mo, which improves the stability of ε-carbides and retained austenite, thus postponing and slowing the martensite temper embrittlement and improving the fracture morphology. Temper embrittlement at 360 ~ 500 ℃ is the result of cementite precipitation at the slab boundary and segregation of impurity elements at grain boundaries.