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 cause of low impact fatigue strength in grinding balls for mining was studied by means of macroscop-ic morphology observation,scanning electron microscopy analysis,energy dispersive spectrum analysis,micro-structure analysis,etc.The results show that the morphology of fracture zone is straight and regular,no obvious plastic deformation is found.The rock candy-shaped morphologies are found on the location of crack origin,and the sizes of some grains exceed 100μm,which are the typical intergranular brittle fracture.A small amount of the troosite structures are found nearby the fracture zone along the original austenite grain boundaries.The grain size of the grinding ball from near surface to fracture zone are not uniform obviously,and the grain size is coarse near the fracture zone.Combined steel ball production process,quenching structure coarsening is the primary reason for low impact fatigue strength of grinding ball.Internal stress is reduced ineffectively during tempering process which may be one of the important reasons leading to the low impact fatigue strength.
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