New manufacturing process of nickel-free austenitic stainless steel with nitrogen absorption treatment

Ingots of ferritic stainless steels, Fe-24Cr and Fe-24Cr-2Mo in mass%, were worked to various dimensions for test specimens. Nitrogen was absorbed by the specimens in a furnace filled with nitrogen gas with a pressure of 101.3 kPa at 1473 K to develop a simple and convenient manufacturing process of nickel-free austenitic stainless steels. Changes in the mechanical properties of the alloys with nitrogen absorption treatment are discussed on the basis of the resultant microstructure. Ferritic Fe-24Cr and Fe-24Cr-2Mo were austenitized with nitrogen absorption to a 2-mm depth from the surface. The hardness, tensile strength, 0.2% proof stress, and elongation to fracture increased, and the reduction of area decreased in Fe-24Cr and Fe-24Cr-2Mo by austenitization due to nitrogen absorption. The tensile strength and 0.2% proof stress of these alloys with nitrogen absorption for 129.6 ks were much larger than those of 316L steel, while the elongation to fracture was much smaller than that of 316L steel. Therefore, small devices and parts with a maximum thickness or diameter of 4 mm were manufactured with this process in this study.