超声冲击对SMA490BW钢焊接接头超高周疲劳性能的影响

采用超声冲击工艺对转向架用SMA490BW钢对接接头焊趾表面进行冲击处理,研究了超声冲击对接头超高周疲劳性能的影响。借助金相显微镜、SEM和TEM研究了冲击层金相组织、冲击前后焊趾处的形貌及表层金属晶粒细化程度。运用有限元软件计算焊接接头的应力分布,采用X射线应力仪对冲击前后焊趾表层的应力进行了测量和分析。结果表明,在5×10~6循环周次下,冲击态接头和焊态接头的疲劳强度分别为206 MPa和153 MPa,经冲击处理后疲劳强度提高了34.6%。在1×10~8循环周次下,冲击态接头的疲劳强度为195 MPa,与焊态接头的141 MPa相比提高了38.3%。在240 MPa的应力水平下,焊接接头经超声冲击处理后的疲劳寿命提高了7倍。经冲击处理的焊趾部位的应力集中系数下降了19.1%,其表面的残余拉应力得到消除,并转变为有益的残余压缩应力,焊趾表层组织得到明显细化,这3个方面均对提高焊接接头疲劳性能起到了积极贡献。

Influence of UIT on VHCF Performance of SMA490BW Steel Welded Joints

The welded toe surface of SMA490BW steel used to making bogie frame was treated using ultrasonic impact treatment (UIT) technology. The effect of UIT on the very high cycle fatigue(VHCF) properties of the welded joints were investigated. The microstructure of treated layer, geometrical morphology of weld toe before and after UIT, and grain refinement were analyzed by means of metallographic microscope, SEM and TEM. The stress distribution of the welded joint was calculated using finite element software, and the residual stress of weld toe surface area before and after UIT were measured and analyzed using X-ray stress tester. Results show that under the condition of 5×10⁶ cycles, the fatigue strength of treated and as-welded joint is 206 and 153 MPa, respectively. The fatigue strength is increased by 34.6%. Under the condition of 1×10⁸ cycles, the fatigue strength of treated joint is 195 MPa, and the fatigue strength is increased by 38.3% compared to 141MPa of as-welded joint. Under the stress level of 240 MPa, the fatigue life of treated joint is enhanced to 7 times than that of as-welded. After UIT, the stress concentration factor of weld toe is decreased by 19.1%, and the residual tensile stress in the surface of the weld toe is eliminated, and it changes into the beneficial residual compressive stress, the surface microstructure is refined. The three aspects of stress concentration of the weld toe, residual stress distribution and surface grain refinement have played a positive contribution to improve the fatigue performance of welded joint.