滚压对中碳钢疲劳强度的影响及强化机理

Effect of Rolling for Fatigue Strength of Midium Carbon Steel and Strengthening Mechanism

本文研究了滚压对不同热处理状态的45Cr钢三点弯曲、不对称循环下疲劳强度的影响,井用x射线衍射法测定了残余应力的分布及半高宽,用电镜观察了断口形貌和断裂特征。结果表明,滚压影响疲劳强度的主要因素是组织结构的变化和残余应力,其作用的大小与原始组织和工作应力有关。对高温回火试样,滚压可同时造成组织强化和损伤,组织强化和残余压应力是提高疲劳强度的主要因素,但当残余应力衰减较剧时,组织损伤可引起疲劳强度的下降。对低温回火试样,滚压可显著地提高其疲劳强度,其原因除表层有较高的残余压应力外,滚压使表层回火马氏体内的微观应力均匀化也是一个重要因素。

The effect of rolling on the fatigue strength of the 45 Cr steel in the different heat-treatment states, were studied in this paper. The 3-point bending fatigue test was carried out; the distribution of the residual stresses and the half-high-width were measured by the x-ray diffraction, the fracture surfaces were observed by the electrical microscope. The results show that the change in the micro-structure and the residual stresses are the main factors which have effect on the fatigue strength after rolling, their effects are relative to the original structures and the loading stresses. For the high-temperature tempered specimens rolling can make the microstructure streugthen and harm. The strengthening of the microstructure and the residual compressive stresses are the main factors for increasing the fatigue strength, but when the residual stresses are severely reduced, the harm in the microstructure will cause to decrease the fatigue strength, For the low-temperature tempered specimens. the fatigue strength can be remarkably increased after rolling, the reason is that there are the high residual compressive stresses in the surface stories; except that, the homogenizing of the microscopic stresses in the tempered martensite is an important factor.