Abstract The martensite-austenite constituents are known to deteriorate the impact toughness of alloyed steel. In order to reduce this adverse effect, the pre-tempering process at low temperatures was introduced before the tempering of intercritical heat treatment process of a MnNiMo bainitic steel. The effects of pre-tempering temperature on the decomposition of martensite-austenite constituents and impact toughness properties of the pre-tempered specimens were investigated. The results of instrumented Charpy V-notch impact testing show that the impact toughness of the materials can be significantly improved by the pre-tempering process, especially for the condition of pre-tempering at 400 °C. After pre-tempering at 400 °C, more martensite-austenite constituents are decomposed into ferrite and small carbides, resulting in the reduction of microcracks nucleation sites. The residual martensite-austenite constituents become mainly the island-like, which can effectively hinder the propagation of secondary cracks. In addition, the pre-tempering at 400 °C increases the fraction of high-angle grain boundaries and refines the size of blocks, which can effectively prevent or deflect the propagation of microcracks. All of those microstructure changes are beneficial to the crack propagation energy. The results suggest that the application of the pre-tempering process is a feasible method to enhance the impact toughness of the studied alloyed steel.

中文翻译：

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马氏体-奥氏体成分对预回火MnNiMo贝氏体钢冲击韧性的影响

摘要 已知马氏体-奥氏体成分会降低合金钢的冲击韧性。为了减少这种不利影响，在MnNiMo贝氏体钢的临界间热处理工艺回火之前引入了低温预回火工艺。研究了预回火温度对马氏体-奥氏体成分分解和预回火试样冲击韧性的影响。仪器化夏比V型缺口冲击试验结果表明，预回火工艺可以显着提高材料的冲击韧性，尤其是在400℃预回火条件下。400℃预回火后，更多的马氏体-奥氏体成分分解为铁素体和细小的碳化物，导致微裂纹成核位点的减少。残余马氏体-奥氏体成分以岛状为主，可有效阻碍二次裂纹的扩展。此外，400℃的预回火增加了大角度晶界的比例，细化了块体的尺寸，可以有效地阻止或偏转微裂纹的扩展。所有这些微观结构的变化都有利于裂纹扩展能量。结果表明，采用预回火工艺是提高所研究合金钢冲击韧性的一种可行方法。400℃的预回火增加了大角度晶界的比例，细化了块体的尺寸，可以有效地阻止或偏转微裂纹的扩展。所有这些微观结构的变化都有利于裂纹扩展能量。结果表明，采用预回火工艺是提高所研究合金钢冲击韧性的可行方法。400℃的预回火增加了大角度晶界的比例，细化了块体的尺寸，可以有效地阻止或偏转微裂纹的扩展。所有这些微观结构的变化都有利于裂纹扩展能量。结果表明，采用预回火工艺是提高所研究合金钢冲击韧性的一种可行方法。