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通过断口形貌观察、金相检验和硬度检测等试验,确定了轴的断裂性质及断裂原因。结果表明:从动轴的断裂形式是中心为一次性的过载断裂,边缘为疲劳断裂,疲劳源区在次表层。从动轴的断裂原因是由于轴中心存在原始缺陷,在使用中扩展为一条长约140 mm的大裂纹,裂纹源从大裂纹的边缘沿横向扩展,断口形貌复杂,断裂形式多样;从动轴材料心部组织为铁素体+珠光体,有魏氏组织倾向,按YB31-64标准评级为C列1级,晶粒大小不均匀,有混晶现象。从动轴表面热处理工艺控制不当,使得表面硬度不高,未达到调质处理的组织。
Through the fracture surface morphology observation, metallographic examination and hardness testing, the fracture properties and fracture causes of the shaft were confirmed. The results show that the driven shaft is in the form of a one-time over-break at the center, the edge is fatigue fracture, and the fatigue source is at the subsurface. The reason of the driven shaft fracture is that due to the original defects in the shaft center, it expands to a large crack of about 140 mm in length. The crack source extends transversely from the edge of the large crack, the fracture surface is complex and the fractures are diverse. The core material of the shaft material is ferrite + pearlite, and has the tendency of Widman’s organization. According to the standard of YB31-64, it is rated as C-rank 1, the grain size is not uniform and mixed crystal phenomenon occurs. Slave shaft surface heat treatment process is not properly controlled, making the surface hardness is not high, did not reach the quenched and tempered organizations.