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本文研究了18Cr2Ni4WA钢的疲劳性能与组织结构之间的关系。通过空冷和油冷两种不同介质的淬火,其后进行不同温度的回火,获得不同的组织结构。测定了各种状态下的疲劳门坎值⊿K_(th);裂缝第二阶段扩展速率da/dN=C(⊿K)~m;并对疲劳裂缝萌生和扩展阶段的断口进行了电镜观察。试验表明:18Cr2Ni4WA钢的疲劳裂缝萌生阶段出现羽毛状的台阶花样由空冷或油冷形成的不同的组织结构,对材料的疲劳门坎值⊿K_(th)和第二阶段裂缝扩展速率产生规律性的影响,空淬后,疲劳门坎值⊿K_(th)随回火温度的降低而升高,油淬后,疲劳门坎值⊿K_(th)随回火温度的降低而下降。无论何种淬火状态,其裂缝扩展速率da/dN=C(⊿K)~m都随回火温度降低而降低,并且发现在低应力强度因子幅度阶段,组织结构的影响较为显著,当应力强度因子幅度升高时,裂缝扩展速率da/d_N=C(⊿K)~m趋于一致。空冷+低温回火,组织为低碳马氏体和部分上贝氏体,具有较高的σ_(0.2)和疲劳门坎值⊿K_(th)(在应力比R=1/3时,⊿K_(th)=20.23kg/mm~(3/2)),和较低的疲劳裂缝扩展速率,是所研究的热处理工艺中的最佳工艺。
This paper studies the relationship between the fatigue properties and microstructure of 18Cr2Ni4WA steels. Through air-cooled and oil-cooled quenching of two different media, followed by tempering at different temperatures, to obtain a different organizational structure. The fatigue threshold value ⊿K_ (th) under various conditions was measured. The second stage expansion rate da / dN = C (⊿K) ~ m. The fracture of the initiation and propagation of fatigue crack was observed under electron microscope. The experimental results show that the feather-shaped step patterns of 18Cr2Ni4WA steels have different microstructures formed by air cooling or oil cooling, and the regularity of the fatigue threshold value ⊿K_ (th) and the second-stage crack propagation rate After quenching, the fatigue threshold value ⊿K_ (th) increases with decreasing tempering temperature. After oil quenching, the fatigue threshold value ⊿K_ (th) decreases with decreasing tempering temperature. No matter what kind of quenching state, the crack propagation rate da / dN = C (⊿K) ~ m decreases with the decrease of tempering temperature, and it is found that the influence of the microstructure is significant at the low stress intensity factor amplitude stage. When the factor amplitude is increased, the crack propagation rate da / d_N = C (⊿K) ~ m tends to be consistent. Air-cooled + low-temperature tempering, the organization of low-carbon martensite and bainite, with high σ_ (0.2) and fatigue threshold value ⊿ K_ (th) (stress ratio R = 1/3, (th) = 20.23 kg / mm ~ (3/2)), and the lower rate of fatigue crack propagation is the best in the heat treatment process studied.