微观组织对高速车轮钢解理断裂应力的影响

利用不同奥氏体化温度和冷却速率对碳质量分数为0.54%高速车轮钢进行热处理,得到具有不同晶粒尺寸和珠光体片间距微观组织的试样.在-120~20℃温度下对具有不同微观组织的拉伸试样和三点弯曲（3PB）缺口试样进行测试;采用二维平面应变有限元计算三点弯曲缺口试样缺口前的应力分布;利用扫描电镜对3PB试样断口进行观察并测量解理起裂源的位置;测定不同微观组织车轮钢试样的解理断裂应力.在扩展控制断裂机制下,微观组织对车轮钢的解理断裂应力具有明显影响,晶粒尺寸和珠光体片间距越小解理断裂应力越高.细化晶粒使未扩展微裂纹的特征长度减小,细化珠光体片间距有助于提高珠光体的有效表面能,从而使得解理断裂应力提高. 

Effect of microstructure on the cleavage fracture stress of high-speed railway wheel steel

The microstructures with different grain sizes and pearlite interlamellar spacings of high-speed railway wheel steel with a carbon mass fraction of 0.54% were achieved by heat treatment at different austenitizing temperatures and cooling rates. Notched 3-point bending(3PB) bars and tensile specimens with different microstructures were tested at temperatures from -120 ℃ to 20 ℃. The stress distribution ahead of the notch tip was calculated by a two-dimensional plane strain finite element method. The fracture surfaces of the 3PB specimens were observed by scanning electron microscopy and the cleavage initiation site was located. The cleavage fracture stress of specimens with different microstructures was measured. It is shown that the cleavage fracture stress depends on the microstructure when the cleavage critical event is propagation-controlled. The characteristic size of un-propagated microcracks decreases by grain refinement,the decrease of pearlite interlameller spacing is be propitious to increase the effective surface energy of the pearlite microstructure,so the cleavage fracture stress increases with decreasing grain size and pearlite interlameller spacing.