The NiCrMoV rotor steel used in the steam turbine was welded by narrow gap submerged arc welding(SAW)process based on multi-pass and multi-layer techniques.The microstructures,tensile property at room and elevated temperature,bending property and impact property of the welded joint were investigated.The fracture morphology of the tensile specimens and impact specimens taken from the welded center were observed by scanning electron microscope (SEM).The results showed that the yield strength(YS)and tensile strength(TS)of welded joints at room temperature(RT)were about 730 MPa and 790 MPa,respectively.The YS and TS decreased with the temperature increasing,but tended to became stable when the temperature was higher than 200 ℃.All of the specimens exhibited the ductile fracture characteristic and fractured in the center of the welded seam.The bending test revealed that the bending property of welded joint was accordance to the design requirement.The ductile-brittle transition temperature(FATT)of the weld center was about -1 7 ℃.In addition,with the decrease of temperature,the impact property of the welded center declined,which could be attributed to the fracture mode transition from ductile fracture to quasi-cleavage fracture,and to final cleavage fracture.At room temperature,the base metal exhibited the best impact properties,and the average impact absorb energies of the base metal,weld center and the 1 /4 weld were about 250 J,97 J and 44 J,respectively.The impact absorbing energy of the heat affected zone had a large dispersion and ranged from 56 J to 293 J,which resulted from the various crack growth and propagated paths.%采用基于多层多道焊技术的埋弧焊(SAW)方法对汽轮机用NiCrMoV转子钢进行窄间隙焊接,研究了焊接接头的组织、常温及高温拉伸性能、抗弯性能及冲击性能.通过扫描电子显微镜(SEM)对拉伸断口及焊缝中心冲击断口的形貌进行观察.结果表明,焊接接头在常温下的屈服强度和抗拉强度约730和790 MPa,随着试验温度的升高,屈服强度和抗拉强度逐渐减小,当温度高于200 ℃时逐渐趋于稳定.各温度下拉伸试样断裂类型均为韧性断裂,且均断裂在焊缝中心.焊接接头的抗弯性能符合设计要求.焊缝中心处的韧脆转变温度为-17 ℃,其冲击吸收能量随温度的降低而减小,这主要是断裂方式由韧性断裂转变为准解理断裂最后变为解理断裂造成的.室温下母材的冲击性能最好,其冲击吸收能量均值约250 J,焊缝中心和1/4处的冲击吸收能量均值分别约97和44 J.热影响区的冲击吸收能量在56 ~293 J内波动,其数值发散的原因主要是由裂纹扩展路径不同导致的.
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