转向架用SMA490BW钢焊接接头超高周疲劳性能的影响因素

Influence Factors for Very High Cycle Fatigue Performance of SMA490BW Steel Welded Joint for Bogie

对转向架用SMA490BW钢焊接试样,采用冲击电流为1.5A、冲击时间分别为5,10,15或20min的超声冲击、低温热处理、机械打磨(磨平焊缝余高、打磨焊趾)的处理方法,通过残余应力测试和超声疲劳试验,对比分析应力集中、晶粒细化、残余应力等因素单独作用时对焊接接头超高周疲劳性能的影响程度,并借助扫描电镜观察疲劳断口,分析焊接接头超声冲击前后的裂纹萌生位置变化及失效模式。结果表明:经超声冲击或机械打磨后,焊接试样的疲劳寿命均得到不同程度的提高;磨平焊缝余高对提高焊接接头疲劳寿命最为显著,较原始焊接试样其疲劳寿命可提高约86.4倍;改善应力集中、细化表层晶粒、引入残余压应力对延长焊接接头寿命的贡献比分别约为59%,28%和13%;焊态及冲击态试样的疲劳裂纹大多萌生于焊趾表面,部分冲击态试样的裂纹转而从表面的机械加工的缺陷处萌生,少数从材料内部缺陷处萌生并扩展至断裂失效。

SMA490 BW steel welded specimen for bogie was treated by means of ultrasonic impact,low temperature heat treatment and mechanical grinding method（smoothing weld reinforcement and grinding weld toe）under the impact current of 1.5 A,and the impact time of 5,10,15,and 20 min,respectively.The influence degree of such factors as stress concentration,grain refinement and residual stress on the very high cycle fatigue performance of welded joint was analyzed and compared respectively through residual stress measurement and ultrasonic fatigue test.The changes of crack initiation location and the failure mode of the welded joint before and after the ultrasonic impact were studied with the aid of the scanning electron microscope observation of fatigue fracture.Results show that the fatigue life of welded specimen has been improved to some extent by ultrasonic impact or mechanical grinding.The effect of smoothing weld reinforcement on increasing the fatigue life of welded joint is the most remarkable,which can be improved by about 86.4 times than that of the original welded specimen.The contribution ratio of improving the fatigue life of the welded specimen is about 59%,28% and 13% respectively by means of decreasing the stress concentration,refining the surface grain and introducing residual compressive stress.Most fatigue cracks initiate on the weld toe surface both for as-welded and ultrasonic treated specimens.Some cracks of ultrasonic treated specimen initiate on the surface of machining defects,a small number of cracks initiate at the defects inside the material and propagate to fracture failure.