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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.
Using different austenitizing temperature and cooling rate, the carbon steel with the mass fraction of 0.54% was heat-treated to obtain samples with different grain size and pearlite interlaminar microstructure.At the temperature of -120 ~ 20 ℃, Tensile specimens of different microstructures and three-point bending (3PB) notched specimens were tested. The stress distribution before notch of three-point bending notched specimen was calculated by two-dimensional plane strain finite element method. The fracture of 3PB specimen was observed by scanning electron microscope Observe and measure the position of cleavage initiation source and determine the cleavage fracture stress of wheel steel specimens with different microstructure.With the extended control fracture mechanism, the microstructure has obvious influence on the cleavage and fracture stress of wheel steel, the grain size and The smaller the pearlite spacing, the higher the cleavage fracture stress.The grain refinement reduces the feature length of the unexpanded microcracks, and the refinement of the pearlite sheet spacing helps to increase the effective surface energy of the pearlite, resulting in a cleavage fracture Increased stress.