12Cr/30Cr2Ni4MoV异种转子钢焊接接头微区冲击韧性研究

Research on Impact Toughness in Microzones of 12Cr/30Cr2Ni4MoV Dissimilar Rotor Steel Welded Joint

采用窄间隙钨极氩弧焊(Narrow-gap tungsten inert gas,NG-TIG)和窄间隙埋弧焊(Narrow-gap submerged arc welding,NG-SAW)组合焊接技术制造了带有过渡层的异种转子钢焊接接头(12Cr/30Cr2Ni4MoV)。采用微剪切试验获得了接头微区的剪切强度,通过分区测试法获得了微区韧脆转变温度FATT50,研究了显微组织对微区硬度、强度和韧性的影响。研究结果表明,焊接接头的硬度和剪切强度分布特征基本一致,热影响区力学性能梯度分布,熔合线界面两侧力学性能不匹配;过渡层存在局部弱化区,显微硬度为227 HV,为整个焊接接头最为薄弱的区域;由母材12Cr过渡至30Cr2Ni4MoV,接头微区脆韧转变温度FATT50逐渐降低;20℃下,母材30Cr2Ni4MoV及其热影响区冲击韧性优异,裂纹萌生于基体/第二相界面,通过微孔聚集发生韧性断裂,其余微区均发生准解理断裂,焊缝冲击韧性最差。

The dissimilar rotor steel welded joint(12Cr/30Cr2Ni4MoV) with buttering layer is fabricated by using the combined welding technology of narrow-gap tungsten inert gas(NG-TIG) and narrow-gap submerged arc welding(NG-SAW). The shear strength of joint microzone is obtained by microshear test, and the ductile-brittle transition temperature FATT50 of microzones is obtained by partition test. The influence of microstructure on hardness, strength and toughness of microzones is investigated. The results indicate that the distribution characteristics of hardness and shear strength in welded joint are basically the same. The mechanical properties of HAZs exhibit gradient distribution, and interface mechanical properties mismatch on both sides of the fusion line. There is a local weakening area in buttering layer, and the micro-hardness value is 227 HV, which is the weakest area of the whole welded joint. From base metal 12Cr to 30Cr2Ni4MoV, the ductile-brittle transition temperature FATT50 of joint microzones gradually decreases. At 20℃, the impact toughness of 30Cr2Ni4MoV and its heat affected zone is excellent, with generation of cracks at the interface between matrix and second phase, ductile fracture occurs through the aggregation of micropores. Quasi-cleavage fracture occurs in all the other microrzones, and the impact toughness of welded metal is the weakest.