The effect of grain size and aging on hydrogen embrittlement of a maraging steel

Abstract

Notched tensile tests were conducted under a slow displacement rate to evaluate the influences of grain size and aging on hydrogen embrittlement (HE) of T-200 maraging steel. In addition, an electrochemical permeation method was employed to measure the effective diffusivity (Deff) and apparent solubility (Capp) for hydrogen of various heat-treated specimens. The results indicated that the aged (482 °C/4 h) specimens comprised of numerous precipitates led to a raised Capp and a decreased hydrogen diffusivity as compared to those of the solution-treated ones. The solution-treated specimens were resistant to gaseous HE, whereas aged specimens were susceptible to it, implying the strength level was the controlling factor to affect the HE susceptibility of the specimens. Nevertheless, all specimens suffered from sulfide stress corrosion cracking (SSCC) severely but to different degrees. The aged specimens were more likely to form intergranular (IG) fractures in H2S but quasi-cleavage (QC) in H2. For the solution-treated specimens, a fine-grained structure was susceptible to HE in H2S and revealed mainly QC that differed from the IG fracture of the coarse-grained one. The fracture mode of the specimens could also be related to the transport path and / or the supply of hydrogen to the plastic zone of notched specimens in hydrogen-containing environments.