Effect of plastic strain and recovery rate on thermal fatigue behavior in high heat-resistant ferritic stainless steel SUS444

Ferritic stainless steels are used for automobile exhaust parts because of their high heat and corrosion resistances. Among them, parts located upstream near engine, so-called hot-end parts, for example, exhaust manifolds, are required to show excellent heat resistance. Since thermal fatigue is induced by repeating heating and cooling with strain restriction, thermal fatigue resistance is one of the most important properties for upstream exhaust-parts materials. In this study, the effect of plastic strain and recovery rate on thermal fatigue behavior was investigated for high heat-resistant ferritic stainless steel SUS444 which has been used for automobile exhaust parts. In the case of a maximum temperature at 973 K, cracking occurred without necking. On the other hand, in the case of a maximum temperature at and above 1073 K, failure with necking was predominant. To improve the thermal fatigue resistance of SUS444 in a higher-temperature exhaust gas atmosphere, high-temperature strengthening would be more favorable.