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本文叙述了以中碳低合金钢经油淬及强烈风冷两种不同冷却方式,得到单一回火马氏体组织及在马氏体(M)中存在铁素体(F)或贝氏体(B)复合组织。应用断裂力学方法研究了不同显微组织对疲劳裂纹扩展速率dα/dN的影响。采用金相技术对裂纹扩展路径观察,应用扫描电镜对疲劳扩展不同阶段进行了断口分析。试验结果表明,单一回火马氏体具有较高的强度,但同时具有较高的dα/dN;M/F复合组织虽具有较低的dα/dN,但其强度及疲劳裂纹萌生期N_o也显著降低;M/B复合组织可保持较高强度的同时显著提高裂纹韧性W/A,降低dα/dN及提高缺口试样N_o及疲劳寿命N_f。本文还初步探讨了不同显微组织的疲劳断口的微观特征。
In this paper, we present a single tempered martensite structure and the presence of ferrite (F) or bainite in martensite (M) by means of two different cooling methods of oil quenching and intense air cooling of medium carbon low alloy steels. (B) Complex tissue. The effect of different microstructures on fatigue crack growth rate dα / dN was studied by fracture mechanics. Using the metallographic technique to observe the propagation path of the crack, the fracture analysis was carried out using scanning electron microscopy in different stages of fatigue propagation. The results show that the single tempered martensite has higher strength, but higher dα / dN at the same time. The M / F composite microstructure has lower dα / dN but its strength and fatigue crack initiation N_o M / B composite structure can maintain higher strength and significantly improve the crack toughness W / A, reduce dα / dN and improve the notch N_o and fatigue life N_f. In this paper, the microscopic features of fatigue fracture of different microstructures are also discussed.