芯棒淬裂的原因分析与改进措施

Reason Analysis and Improving Measures for Core Rod Quenching Crack

对芯棒渗硼后开裂的原因进行了分析。结果表明:开裂的原因有三。一是组织粗大且出现魏氏组织,导致力学性能降低;二是未淬透,导致过渡区轴向相变应力与热应力叠加,存在叠加应力;三是盲孔底部处于过渡区,叠加应力与孔底表面拉应力再次叠加,且在底部产生应力集中诱发裂纹。改进措施:芯棒渗硼后,增加正火处理;盲孔填充堵塞后,采用双液淬火代替单液淬火。

Crack reasons of core rod after boronizing and direct quenching were analyzed.The results show that there are three reasons for producing quenching crack of the core rod.The first is：the bigger grain and the widmanstatten structure result in low mechanical properties; the second is：no through quenching results in a considerable overlap between the thermal stress and the phrase transition stress in the direction of axis in transition region,and produces overlap stress; the third is：at the bottom of the blind hole in transition region,stress concentration breaks out,and leads to quenching crack,as a result of overlap between overlap stress and tensile stress from the blind hole’s surface.Taking measures：after boronizing,normalizing treatment; and with the blind hole being filled up and plugged up,double liquid quenching comes into use instead of single liquid quenching.