Patent ID: 10633733

Abstract:
Nitrogen (N) absorption and diffusion treatments are performed for the inner and/or outer surfaces of austenite stainless steel pipe materials in N gas atmosphere at temperatures near 1,100° C. to obtain nitrided stainless steel pipe materials having 0.25˜1.7% (mass) of solid solution nitrogen (N) including a gradient structure formed within the pipe wall in which the concentration of solid solution N continuously decreases gradually from the surface. The solid solution N present in the gradient structure promotes short range ordering (SRO) of substitutional alloying elements leading to homogenization of distribution of alloying elements in the austenite phase, generating an extremely high proof strength (yield strength) about 3 times as high as that of conventional austenite stainless steel pipe materials and enhancing characteristic of anti-hydrogen gas embrittlement (anti-HGE) so as to be suitable for use in a high pressure hydrogen tank utilized in hydrogen cell vehicle (FCV) and a liquid hydrogen tank.