1Cr11Ni2W2MoV不锈钢螺栓脆性断裂故障失效分析

Failure Analysis for Brittle Fragile Fracture of 1Cr11Ni2W2MoV Stainless Steel Bolt

针对某型航空发动机在整机装配过程中发生的1Cr11Ni2W2MoV不锈钢螺栓断裂故障,按照零件失效分析的一般方法,进行了故障件理化检测和批次零件制造质量检查,包括对故障件进行断口宏观与显微SEM检查,对零件热处理工艺参数与材料标准、热处理执行标准参数进行比照,并对存在质疑的回火脆性问题开展了不同回火温度与冷却速度下的验证试验。结果表明:故障件断口主要由扩展区与瞬断区组成,主要特征为沿晶+准解理,失效模式为一次性大应力脆断;致使零件脆性的原因在于回火温度640℃处于第2类回火脆性区间;回火后快速冷却可缓解脆性,但无法消除。避免回火脆性是解决螺栓装配断裂的根本途径,因此要求螺栓零件选择回火温度时应避开脆性区间,冷却时快速通过该区间。

In order to solve the problem of fracture failure of 1Cr11Ni2W2MoV stainless steel bolts during aeroengine assembly,examination of the failed parts and quality investigation of lot production process were carried out according to the general failure analysis procedure,including fracture surface macro and SEM examination,comparison of the heat treatment process parameters with parameters from material standards and implemented heat treatment standards,and verification tests of different tempering temperatures and cooling rates for the suspicious temper embrittlement problem. The results show that the fracture surface is mainly composed of stretch zone and final fast overload,the fracture characteristics are intergranular & quasi cleavage,and the failure mode is quick overlord brittle fracture. The reason for the brittleness is that the tempering temperature 640 ℃ is in the type Ⅱ temper brittleness region. Rapid cooling after tempering relieves brittleness but does not eliminate it. Avoiding temper embrittlement is the approach to fundamentally solve the problem,so it is required that bolt parts should avoid the brittleness region when choosing tempering temperature,and pass through the region quickly when cooling.