Abstract
In order to improve the susceptibility of ultrahigh strength maraging steel to hydrogen gas environment embrittlement, the effect of aluminum coating prepared by ion-plating on the susceptibility has been studied.
When ion-plating was carried out at a lower specimen temperature, a diffused layer between the coated layer and the steel that could be detected by EPMA was not formed, and the notch tensile strength of the coated specimen in hydrogen gas was higher than that of the steel itself, and the coated layer suppressed the hydrogen embrittlement.
When the specimen temperature was increased during ion-plating up to a high temperature at which the maraging steel was overaged, a thick diffused layer identified as intermetallic compounds of aluminum and the alloying elements of the steel was formed in the coated layer. This diffused layer was very brittle, so that many cracks were initiated at the coated layer in the early stage of loading both in hydrogen gas and in vacuum. The notch tensile strength in vacuum was not lowered by the existence of the cracks. However, that in hydrogen gas was extremely lower than that of the steel itself, and the existence of the coated layer promoted hydrogen embrittlement.
