某规格为M16的螺母及锥形垫圈组合件在现场装配过程中断裂，采用宏观观察、化学成分分析、扫描电镜分析、金相检验、硬度测试等方法分析了垫圈断裂的原因。结果表明：由于锥形垫圈在热处理过程中的回火温度小于350℃，属于第一类回火脆性温度区（200~350℃），导致垫圈产生了回火脆性；垫圈表面存在的微裂纹沿晶界扩展，经380℃保温2 h、油冷、回火后，垫圈脆性消除。

Cracking failure occurred in a nut and conical washer assembly of M16 in the field assembly process. The causes of washer cracking were analyzed by means of macroscopic observation, chemical composition analysis, scanning electron microscope analysis, metallographic examination and hardness test. The results show that the tempering temperature of the conical washer was less than 350℃ during the heat treatment process, which was the first type of tempering brittleness temperature zone (200~350℃), resulting in the tempering brittleness of the washer. The micro-cracks on the surface of the gasket propagated along the grain boundary, and the brittleness of the gasket was eliminated after holding at 380℃ for 2 h, oil cooling and tempering.