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用透射电镜研究了20Cr3Mo2V二次硬化钢的组织,发现这是一种比通常所谓的“上、下贝氏体”更复杂的贝氏体结构。贝氏体中“S—形”残留奥氏体的存在,可能是钢具有高韧性的原因。当回火温度低于400℃,贝氏体的组织是稳定的;超过500℃,残留奥氏体分解,渗碳体原位转变,并在基体中析出弥散的VC和亚稳Mo_2C,于是钢呈现二次硬化效应。由于贝氏体中渗碳体粗,位错密度比马氏体中低,使合金碳化物的析出和长大动力学受限制,因而贝氏体二次硬化钢的组织稳定性和热强性比直接淬成马氏体后回火的优越。
The microstructure of 20Cr3Mo2V secondary hardened steel was investigated by transmission electron microscopy and found to be a more complex bainitic structure than the so-called “upper and lower bainite”. The presence of “S-shaped” retained austenite in bainite may be responsible for the high toughness of the steel. When the tempering temperature is below 400 ℃, the microstructure of bainite is stable. When the temperature exceeds 500 ℃, the retained austenite decomposes and the cementite changes in situ, and VC and metastable Mo_2C are precipitated in the matrix. Showing secondary hardening effect. Due to the coarse bainite cementite, dislocation density lower than the martensite, carbide precipitation and growth kinetics are limited, so bainitic hardened steel tissue stability and thermal strength Than the direct quenching martensite after the tempering superior.