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通过正火球铁表面滚压、软氮化后疲劳裂纹萌生、扩展的试验研究及电镜断口分析得出:表面软氮化、表面滚压均能有效地提高球铁的疲劳强度;滚压强化既能有效地阻止裂纹的萌生,又能大幅度地降低裂纹扩展速率;由于滚压强化层较深,有利的残余压应力分布层也深,故对原始态具有短裂纹的试样,滚压效果也很显著;滚压强化后其名义门坎值有大幅度提高,达▽K_(th名义)=66公斤/毫米~(3/2);软氮化及滚压强化后断口源区和早期扩展的特点为细质点、亚结构和不连续的分割条纹,使疲劳裂纹萌生抗力提高,裂纹扩展速率降低。
The results show that the surface nitrocarburizing and surface rolling can both effectively improve the fatigue strength of ductile iron. The rolling strengthening Can effectively prevent the crack initiation, but also greatly reduce the crack growth rate; due to the deep rolling strengthening layer, the depth of the residual compressive stress is also deep, so the original state with a short crack specimens, rolling effect Is also significant. After roll strengthening, the nominal threshold value is greatly increased up to ▽ K th (nominal) = 66 kg / mm ~ (3/2). After soft nitriding and rolling strengthening, the source region and early extension of fracture Is characterized by fine spots, sub-structures and discontinuous stripes, which increase the resistance to fatigue crack initiation and reduce the crack propagation rate.