??????????????????Ч????

 通过断口分析、低倍检验、高倍组织以及模拟热处理人工断口观察等实验对模具钢在热处理裂纹成因进行了分析。分析表明，模具钢裂纹是在淬火过程中扩展形成的，钢中的白点缺陷和超尺寸夹杂物是引发淬火扩展裂纹的主要原因。由于钢模块在缺陷和裂纹形成后又经历了不同的热处理阶段并在室外放置了较长时间，原始实物断口不可避免的发生一些破坏给断口分析带来一定的困难。本文采用模拟热处理人工断口的方法，即在与钢模块类似的热处理制度下加热人工断口，观察加热温度对断口花样钝化的影响，并与实物断口进行比较，由此判断白点裂纹和淬火扩展裂纹的形成阶段。这种实验分析方法针对工件裂纹受到高温作用影响而使断面发生损坏的裂纹成因失效分析具有一定的推广应用价值。

Failure Analysis of Heat Treatment Fracture for Large Scale Die Steel

The cause for heat treatment crack of die steel was analyzed by the experiments of fracture surface analysis,macroscopic examination,metallographic structure analysis and observation of simulating heat treatment artificial fracture.The analysis shows that cracks of die steel are formed during quenching.White spot defects and super size inclusion of steel are the main reason causing quenching cracks.Since the steel experienced different stages of heat treatments after the formation of defects and cracks and was placed outside for a long time,unavoidable damages of original fracture bring certain difficulties to analyze the fracture.The method of simulating heat treatment artificial fracture was adopted.That is,the artificial fracture is heated under heat treatment system,which is similar to steel modular,the influence on fracture texture passivation of heating temperature is observed to judge the formation stage of white point cracks and quenching cracks with the comparison of the original fracture.The experimental method has certain application value on failure analysis of cracks affected by high temperature.