Fatigue crack growth in 15KH2MFA steel subjected to aging in high-temperature hydrogen

We study the influence of high-temperature aging in gaseous hydrogen on the cyclic crack-growth resistance of 15Kh2MFA steel by taking into account the effect of fatigue crack closure. We show that aging in hydrogen promotes the intense pulverization and homogenization of the structural components. Changes in the structure of steel and a decrease in the effective fatigue threshold ΔK _{th eff} on holding in hydrogen are caused primarily by the action of hydrogen and the load is an additional factor accelerating this process. We discovered that the effect of internal hydrogen on the effective fatigue threshold is ambiguous depending on the level of stresses in the process of holding in hydrogen. Thus, ΔK _{th eff} increases on holding at σ=120 MPa as compared with the degassed metal but decreases on holding at σ=240 MPa. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 4, pp. 121–126, July–August, 1997.