焊接接头低周疲劳性能薄弱区转移

Weak zone shift in welded joints for low cycle fatigue

研究汽轮机焊接转子接头低周疲劳性能薄弱区对转子的安全运行具有重要意义。该文测试了汽轮机低压焊接转子用25Cr2Ni2MoV耐热钢焊接接头低周疲劳性能,统计分析焊接接头低周疲劳性能薄弱区与应变幅之间的关系,采用显微硬度测试和有限元模拟分析薄弱区转移原因。结果表明:低周疲劳试验中宏观裂纹出现于焊缝和热影响区的回火区,当外加应变载荷由大变小时,焊接接头低周疲劳性能薄弱区由焊缝中心区域转移至热影响区的回火区。在大应变外加载荷条件下,热影响区的回火区塑性变形受较大约束,焊接接头整体的塑性应变向焊缝区转移;在小应变外加载荷条件下,焊缝区域始终处于弹性状态,热影响区的回火区大硬度梯度的软硬夹层结构加剧了应变集中程度。

Weak zones in welded joints due to low cycle fatigue can affect the safety of welded steam turbine rotors. This study analyzes the low cycle fatigue strength of welded 25Cr2Ni2MoV refractory steel steam turbine rotor joints. The strains in the weak zones of the welded joints are modeled statistically. The reason for the weak zone shift is studied using hardness tests and finite element analyses. The experimental results show that cracks develop in the weld and in tempered regions of the heat affected zone. The weak zone shifts from the weld to tempered regions with decreasing strain. With large strains, the plastic strain concentrates in the weld while with low strains, the weld stays in the elastic range. The large hardness gradient in the tempered region with sandwich construction increases the strain concentration.