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

Abstract

This report reveals gigacycle fatigue properties for a modified-ausformed V-added steel with the chemical composition of 0.3 C-0.3 Si-1.0 Cr-0.7 Mo-0.3 V in mass %. Modifiedausformed 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 oilquenched 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 × 10 9 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 10 6 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 10 6 cycles.

Suppression of Hydrogen-Assisted Fatigue Crack Growth in Carbon Steels

“…8,9) Hirukawa et al 10) investigated the giga-cycle fatigue properties of a modified-ausformed, vanadium-added, low-alloy steel (0.30C0.30Si0.31Mn 1.00Cr0.70Mo0.35V; mass%) at room temperature in air. Giga-cycle fatigue is a phenomenon that occurs in highstrength steels.…”

“…They proposed that the sum of the ODA width and the inclusion diameter should be used as the size of the initial defect that reduces the fatigue strength. Hirukawa et al 10) suggested that ODAs in modified-ausformed, vanadium-added, low-alloy steels were smaller than those in quenched and tempered steels, and that the giga-cycle fatigue strength of modifiedausformed steels was higher than that of quenched and tempered steels. From these results, it can be concluded that the giga-cycle fatigue strength of high-strength steels can be increased by refining martensite blocks through modifiedausforming and tempering and by precipitating fine VCs.…”