铁素体不锈钢的疲劳裂纹扩展

Fatigue Crack Propagation of Ferritic Stainless Steels

本文用线弹性断裂力学法研究了 AISI409与18Cr—Nb 铁素体不锈钢在 25～649℃ (77～1200°F) 空气环境下的疲劳裂纹扩展 (FCP) 行为。疲劳裂纹扩展速率 (da)/(dN) 满足 Paris 关系:(da)/(dN)=C(⊿k)~n。室温下应力比 (R) 对(da)/(dN)的影响在低⊿k下较为敏感。(da)/(dN)随温度的提高和加载频率的减小而增加,但对18Cr—Nb,475℃(885°F)下的(da)/(dN)却高于538℃(1000°F)下的(da)/(dN),这与含Cr量高于15％时的475℃脆性有关。文中还测定了室温与高温下的材料常数c与n值。并对疲劳裂纹扩展机理进行了探讨。

Lineal elastic fracture mechanics technigues are used to characterite the fatigue crack propagation (FCP) behavior of AISI409 and 18Cr—Nb ferritic stainless steels in the air medium at the temperature range from 25 to 649℃ (77—1200 F). The crack growth rate de/dN follows the parise Law da/dN=C(△k)The effect of stress ratio R on the FCP is more sensitive at a low stress intensity range △k at the room teperature. The FCP rate increases as the test temperature is raised and the cyclic loading frequency is decreased, but, the FCP rate at a temperature of 475℃(885°F) is more rapid than at a tempera- ture of 538℃(1000℃) for 18Cr—Nb. This phenomenon is considered to be associated with 475℃ embrittlement for the steel containing more than 15% Cr. The constants (C,N) at the room and elevated temperatures are examined. Also. tbe FCP mechanism is discussed.