20Mn2钢圆环链脆性断裂原因分析

Analysis on Brittle Fracture of 20Mn2 Steel Ring Chains

针对20Mn2结构钢圆环链拉伸试验时出现脆性断口的现象,经断口宏微观观察、金相分析后,认为圆环链的断裂性质为沿晶脆性断裂。分析认为,出现沿晶脆断是由于回火温度过高,且圆环链加工现场受场地限制,热处理后的成品链堆放在一起,造成内部圆环链冷却速率较慢,致使Si、Mn、P等元素在奥氏体晶界偏聚富集,形成高温回火脆性。利用合金结构钢高温回火脆性的可逆性,该批圆环链经670℃保温1 h重新回火后,用油快速冷却,消除了高温回火脆性,经检验完全合格。

Brittle fracture occurred to the ring chains made of 20Mn2 structure steel during tensile tests. The fracture cause was analyzed by macro and micro inspection and metallographic analysis. The results show that the fracture mode is intercrystalline brittle fracture. Because of high temper temperature and slow cooling rate, the elements such as Si, Mn and P gathered and were enriched along austenite grain boundaries, which resulted in high temperature temper brittleness. As a result, abnormal brittle fracture occurred to the ring chains. According to the reversibility of the high-temperature temper brittleness of structural alloy steels, these ring chains were tempered at 670 % for 1 h and then rapidly cooled down in oil, and thus the high-temperature temper brittleness was eliminated.