【摘要】 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。更多还原

【Abstract】 The rules of changes in mechanical properties of 406 steel during tempering have been studied.The fine structure of martensite and the type, morphology, distribution of carbide precipitates havebeen examined under a transmission electron microscope. The inter-relation between the mechanicalbehavior and the martensite substructure has also been studied. The results indicated that 406 steelpossesses high strength and high toughness after quenching and tempering at 300℃. The fine struc-ture is, lath martensite with high dislocation density. The majority of fine needle-like precipitateswithin martentite has been indentified to be ε-carbide which is highly coherent with the matrix, byelectron diffraction pattern analysis. Thin films of 2-3% retained austenite in net form have been dis-tributed between martensite laths. This steel contains 1.5% silicon and 0.5% molybdenum, so that thestability of ε-carbide and retained austenite can be maintained to a higher temperature, thereby de-laying and retarding the embrittlement trough of tempered martensite and improving the fracture ap-pearance. In addition, the temper embrittlement at about 360-500℃ is due to the precipitation of ce-mentite in interlath surface and the segregation of impurities at grain boundaries.更多还原