Gigacycle Fatigue Properties of V-Added Steel with an Application of Modified Ausforming

This report reveals gigacycle fatigue properties for a modified-ausformed V-added steel with the chemical composition of 0.3C-0.3Si-1.0Cr-0.7Mo-0.3V in mass %. Modified-ausformed and oil-quenched steels were prepared for fatigue tests, followed by tempering at 400°C and 600°C. The tensile strengths of the 600°C tempered steels were almost equal to those of the 400°C tempered versions because of secondary hardening due to fine precipitation of vanadium carbides. The fatigue properties of the 600°C tempered version of oil-quenched steel (QT600) showed little difference from the 400°C tempered version (QT400) in spite of the fine precipitation of vanadium carbides. The modified-ausformed steels (AF400 and AF600) revealed higher fatigue limits at 5× 10⁹ cycles than the oil-quenched versions (QT400 and QT600), although the difference between AF400 and AF600 was small. The remarkable difference between AF400 and AF600 was fatigue strengths at around 10⁶ cycles, i.e. the fatigue strength of AF600 at those cycles was higher than that of AF400. Based on the above results, the effect of the fine precipitation of vanadium carbides was small on the gigacycle fatigue properties, while modified-ausforming could improve those properties. On the other hand, the multiple effects of the fine precipitation and modified-ausforming was large on the fatigue strength at around 10⁶ cycles.