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 文章以5CrNiMo钢小型热锻模的开裂为例，具体分析了其化学成分、洛氏硬度、冶金质量、断口形态和显微组织等，特别针对调质后的显微组织对性能的影响进行了相关分析和讨论。最终认为：由于在调质过程中淬火冷却速度较慢，模具未完全淬成马氏体，心部存在一定量的中温转变组织，它导致了模具强度和热稳定性的下降，该模具在刚上模热锻时就发生开裂，这与热处理的目标组织存在差异有密切关系。

Analysis on Fracture of 5CrNiMo Steel for Hot-forging Die

Based on the fracture of 5CrNiMo steel for hot-forging die, the composition, fracture feature, Rockwell hardness and microstructure of the die have been investigated; the influence of microstructure on the die quality also have been discussed. Then it is suggested that the cooling rate of quenching during the heat treatment is very slow,therefore the martensite reaction cannot be complete, there are some retained bainite in the die, and it cause decrement both in the strength and in hot stability. These factors induce the fracture of the die.