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通过宏观形貌观察、扫描电镜分析、能谱分析和显微组织分析等手段对落球疲劳试验时耐磨钢球冲击疲劳强度偏低的原因进行了研究。结果表明:断口平直较规则,无明显塑性变形;裂纹源处呈现“冰糖块”形貌,且部分晶粒尺寸超过100μm,为典型的沿晶界脆性断裂;断口附近存在少量的屈氏体组织,且沿着原奥氏体晶界分布;钢球近表面到断口处的晶粒尺寸明显不均匀,而且断口附近的晶粒较粗大。结合钢球生产工艺分析可知,钢球冲击疲劳强度偏低的主要原因是淬火组织粗大,另一重要原因是回火工序没有有效降低淬火内应力。
The causes of the low impact fatigue strength of the wear-resistant ball were investigated by macroscopic observation, scanning electron microscopy, energy spectrum analysis and microstructure analysis. The results show that the fractures are flat and regular without any obvious plastic deformation. The cracked source shows a “rock mass” morphology with a part of grain size over 100μm, which is a typical brittle fracture along the grain boundary. And distributed along the original austenite grain boundaries. The grain size near the fracture surface of the steel ball is obviously uneven, and the grains near the fracture are coarse. Combined with the ball production process analysis shows that the ball impact fatigue strength is mainly due to the quenched tissue coarse, another important reason is that the tempering process does not effectively reduce the quenching stress.