Effect of tempering duration on hydrogen embrittlement of vanadium-added tempered martensitic steel

Abstract This paper presents a quantification of the effect of tempering duration tTEM on hydrogen embrittlement (HE) resistance of vanadium-added tempered martensitic steel. High-carbon steel containing 0.3 wt% vanadium was tempered at 570 °C for durations 1 ≤ tTEM ≤ 16 h. With increasing tTEM, hardness and strength were well maintained up to tTEM = 4 h, then decreased afterwards at tTEM > 4 h. The notch-fracture strength of hydrogen charged specimen, a measure of HE resistance, followed the same trend as those of strength and hardness. Thermal desorption analysis indicated that tTEM = 4 h resulted in the maximum hydrogen-trapping capability, accompanied by a slight increase in the peak temperature. A hydrogen permeation test also revealed that hydrogen diffusivity was the lowest at tTEM = 4 h. Our results indicate that HE resistance of tempered martensitic steel is greatly affected by the characteristics of V-carbide such as the degree of precipitation-hardening, and that the HE resistance is greatest at the peak aging condition.