Abstract:

The fatigue crack growth properties were important to the welded rotor in nuclear turbine. The fitting relations between the fatigue crack growth rate and stress intensity factor range for submerged arc weld metal of 25Cr2Ni2MoV simulating product of nuclear power low pressure turbine rotors were researched. The critical points between stable and near-threshold fatigue crack propagation were different in different specimens and their locations were determined by the method of backward inference. After the observation of the microstructure around the critical points, a good correspondence between the size of prior austenite and the maximum size of monotonic plastic zone on the crack tip was confirmed. The differences of the critical points between different specimens are caused by the heterogeneous microstructures in the multi-pass and multi-layer weld metal, and become an important reason for the dispersion of the experimental threshold values.

Key words: fatigue crack propagation, critical point, microstructure heterogeneity, prior austenite, monotonic plastic zone

摘要：

研究了25Cr2Ni2MoV核电汽轮机低压焊接转子模拟件埋弧焊焊缝金属疲劳裂纹扩展速率和应力强度因子幅关系曲线，发现了不同试样疲劳裂纹稳定扩展区和近门槛区临界点对应的应力强度因子幅不同的现象。使用逆推法在金相中确定了临界点位置，并进一步研究了临界点处的原奥氏体晶粒尺寸，发现其与裂纹尖端单向塑性区最大尺寸有较好的对应关系。而模拟件多层多道焊焊缝金属组织不均匀性带来的临界点位置的差异是造成门槛值测试结果分散的重要原因之一。

关键词: 疲劳裂纹扩展, 临界点, 组织不均匀性, 原奥氏体尺寸, 单向塑性区