Q960E热影响粗晶区疲劳寿命与ΔK_(th)值的关系分析

Research on relationship between ΔK_(th) and fatigue life of heat-affected coarse grain zone in Q960E

基于模拟焊接热循环试验及疲劳裂纹扩展试验,对动载结构用高强钢Q960E热影响粗晶区进行了多种应力幅值作用下的疲劳寿命研究.通过得到Paris方程建立了不同焊接热模拟工艺下疲劳裂纹扩展门槛值(ΔKth)随不同交变载荷下疲劳寿命值的近似线性关系.利用场发射扫描电镜中背散射衍射功能(EBSD)对疲劳裂纹扩展试样中的裂纹尖端进行了晶体学取向分析及扩展机制讨论.结果表明,在应力幅值ΔP固化后,疲劳寿命N随ΔKth的增大而增加,其延寿微观机理在于组织中的亚结构取向存在差异,所形成的大角度晶界(≥15°)可有效迫使裂纹转向,从而提高材料的疲劳寿命.

Based on the simulation of welding thermal cycle test and fatigue crack propagation test,the fatigue life on coarse grain heat affect zone of high strength steel Q960E,which acted as dynamic load structure,were investigated.The approximate linear relationship between fatigue crack propagation threshold value (ΔK_(th))by Paris equation under different welding thermal simulation technique and fatigue life under different cyclic loading were obtained.The crystallographic orientation analysis and expansion mechanism of the crack tip in the fatigue crack propagation specimen were discussed by using the electron backscatter diffraction(EBSD)in scanning electric mirror.The results showed that if stress amplitudeΔP was fixed,the fatigue life N increased with the growth of ΔK_(th).Its working micro-mechanism of prolonging life was due to the orientation differences of substructure,resulting in the formation of large Angle grain boundaries(≥15°),which effectively forced the crack to swerve,so as to improve the fatigue life of materials.