A new approach to the powder metallurgical production of high nitrogen steels by integrated diffusion alloying in a hot isostatic press

Abstract

Alloying with nitrogen in stainless steels, with nitrogen being dissolved interstitially, results in improved mechanical properties and higher resistance to local corrosion phenomena. However, the positive effect cannot be arbitrarily scaled to higher nitrogen contents, mainly due to the limited nitrogen solubility in the liquid phase. This paper presents a powder metallurgical approach to the production of a high nitrogen variant of the austenitic stainless steel X2CrNi18-9, in which a powder mixture of steel and Si3N4 powder is hot isostatically pressed and integrally cooled by uniform rapid quenching (URQ®). This procedure, known as diffusion alloying, allows nitrogen to dissociate from Si3N4 and dissolve into the solid austenitic phase, which provides a nitrogen solubility greater than 0.5 mass% under HIP conditions. With this approach, about 0.38 mass% N could be interstitially dissolved in the steel, which, however, can be further increased in the future by adjustments discussed here.