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采用四点弯曲腐蚀疲劳试验测定4340钢在人造海水中的△Kth,研究加载条件对测定△Kth的影响,并对门槛值附近裂纹扩展的形态进行观察。用降载法测得的△Kth值比升载法所测值低;门槛值附近裂纹扩展主要受机械应力控制,裂纹扩展形态以穿晶解理为主;阴极保护电位使条件门槛值△Kth稍有提高。在升载情况下,起始载荷越大,△Kth随之越高。合理选择初始临界应力强度因子范围是较精确地测得△Kth值的关键。
The △ Kth of 4340 steel in artificial seawater was measured by four-point bending corrosion fatigue test. The influence of loading conditions on the determination of △ Kth was studied. The crack growth morphology near the threshold was observed. The △ Kth value measured by the load-down method is lower than that measured by the lift method. The crack growth near the threshold value is mainly controlled by mechanical stress, and the crack propagation morphology is dominated by transgranular cleavage. The cathodic protection potential makes the conditional threshold △ Kth Slightly improved. Under load, the larger the initial load, the higher ΔKth. Reasonable selection of the initial critical stress intensity factor is more accurate measurement △ Kth value of the key.