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利用CO2激光器对X80管线钢焊接接头进行表面热处理,通过拉伸疲劳对比试验,用罗卡提法求出激光热处理前后X80管线钢焊接接头的疲劳极限。采用扫描电镜和金相显微镜分析激光热处理前后X80管线钢焊接接头的组织与断口形貌,通过X射线衍射仪分析了激光热处理前后X80管线钢焊接接头的残余应力及残留奥氏体,并对激光热处理提高抗疲劳断裂机理进行了探讨。结果表明,激光热处理在试样表面形成强化层,使X80管线钢焊接接头疲劳强度由542 MPa提高到604 MPa,提高了11.4%;原始状态下试样疲劳裂纹源起始于试样表面,经激光热处理后试样疲劳裂纹源转移至次表层;残留奥氏体增加、强化层晶粒细化和残余压应力场是提高疲劳强度的主要机制。
X80 pipeline steel welded joints were heat-treated by CO2 laser, and the fatigue limit of X80 pipeline steel welded joints before and after laser heat treatment was obtained by the comparison of tensile fatigue tests and Rocard’s method. The microstructure and fracture morphology of X80 pipeline steel before and after laser heat treatment were analyzed by scanning electron microscopy (SEM) and optical microscope. The residual stress and residual austenite of X80 pipeline steel welded joints before and after laser heat treatment were analyzed by X-ray diffraction. Heat treatment to improve anti-fatigue fracture mechanism were discussed. The results show that the laser heat treatment forms a strengthening layer on the surface of the sample to increase the fatigue strength of X80 pipeline welded joints from 542 MPa to 604 MPa, an increase of 11.4%. In the initial state, the fatigue crack source of the sample starts from the surface of the sample. After the laser heat treatment, the fatigue crack source transferred to the subsurface; residual austenite increases, grain refinement and residual compressive stress fields are the main mechanisms to improve the fatigue strength.