回火工艺对65Mn钢疲劳裂纹扩展行为的影响

Effects of tempering process on fatigue crack propagation behavior of 65Mn spring steels

采用中温回火和高温回火对65Mn钢进行热处理,测试其拉伸性能,并对其疲劳裂纹扩展行为进行研究,探索其疲劳断裂机制.结果表明,两种回火方案对应的裂纹扩展速率的m值相差不大,而C值差异较大,反映出在稳定扩展区的疲劳裂纹扩展对其微观组织不敏感,塑性变形消耗了裂纹扩展的能量,使裂纹扩展速率下降;随着回火温度的升高,实验钢的疲劳断裂特征由脆性逐渐变为韧性,高温回火提高了其裂纹扩展的门槛值,降低了疲劳裂纹扩展速率,65Mn钢经高温回火后有较优的综合力学性能和疲劳性能.

65Mn spring steels were heat treated by medium-temperature tempering and high-temperature tempering. Its tensile properties were tested, and the fatigue crack propagation behavior as well as fatigue fracture mechanism were investigated. Results show that the crack growth rate m is different but the C-value is less difference after two kinds of tempering scheme, which reflects that the fatigue crack propagation is not sensitive to the microstructure in the region of stable crack propagation and the crack propagation rate decreases due to plastic deformation consume energy of crack propagation. With the tempering temperature increases, the characteristic of fatigue fracture transforms from brittle to ductile gradually, high-temperature tempering treatment improves the fatigue crack propagation threshold and reduces the fatigue crack growth rate. After high temperature tempered, the steel has better comprehensive mechanical property and fatigue property.