Brittle fracture of large forging equipment usually leads to catastrophic consequences. To avoid this kind of accident, the brittle fracture behaviors of a large die holder were studied by simulating the practical application. The die holder is used on the large die forging press, and it is made of 55NiCrMoV7 hot-work tool steel. Detailed investigations including mechanical properties analysis, metallographic observation, fractography, transmission electron microscope (TEM) analysis and selected area electron diffraction (SAED) were conducted. The results reveal that the material generated a large quantity of large size polyhedral M 23 C 6 (M: Fe and Cr mainly) and elongated M 3 C (M: Fe mainly) carbides along the martensitic lath boundaries when the die holder was recurrently tempered and water-cooled at 250 °C during the service. The large size carbides lead to the material embrittlement and impact toughness degradation, and further resulted in the brittle fracture of the die holder. Therefore, the operation specification must be emphasized to avoid the die holder being cooled by using water, which is aimed at accelerating the cooling.
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机译：大型锻造设备的脆性断裂通常会导致灾难性的后果。为避免此类事故，通过模拟实际应用研究了大型模具夹具的脆性断裂行为。模架用于大型模锻压力机，由55NiCrMoV7热作工具钢制成。进行了详细的研究，包括力学性能分析，金相观察，分形学，透射电子显微镜（TEM）分析和选择区域电子衍射（SAED）。结果表明，当对模具座进行回火时，该材料沿马氏体板条边界生成了大量的大尺寸多面体M 23 C 6（M：主要为Fe和Cr）和细长的M 3 C（M：主要为Fe）碳化物。在维修期间将其水冷至250°C。大尺寸的碳化物导致材料脆化和冲击韧性降低，并且进一步导致模具保持器的脆性断裂。因此，必须强调操作规范以避免模具座被水冷却，目的是加速冷却。
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