EFFECTS OF MINOR ALLOYING ELEMENTS ON INH ERENT CREEP STRENGTH PROPERTIES OF FERRITIC STEELS

Creep rupture strength properties of carbon steel have been analyzed f rom a viewpoint of inherent creep strength, and the effects of minor a lloying elements on inherent creep strength have been investigated. In herent creep strength, which is a new concept proposed by the authors, is an essential strength property independent of both microstructural morphology and time, and the governing factor of long-term creep stre ngth property. Large heat-to-heat Variation of inherent creep strength observed for the carbon steel has been cleared to be caused by a rema rkable improving effect of Mo on that, However, strengthening effect o f Mo has been speculated to saturate at a slight amounts of about 0.03 mass%. It has been concluded that an inherent creep strength of ferrit ic steel is governed by solid solution strengthening effect due to suc h as C and Mo, and the maximum inherent creep strength is obtained by the addition of C and about 0.03mass% of Mo. Moreover, it has been sug gested that the inherent creep strength of many ferritic heat resistan t steels are maximum level for ferritic steels, consequently, creep ru pture strength of those converges to an almost same level at the long- term region.