PURPOSE: To obtain a stainless steel having high surface hardness and sufficient wear resistance, base material hardness and toughness by forming a nitride layer on a ferrite alloy surface of a specific compsn. consisting of Cr, Ni, Al, Zr, etc., and Ti and Fe.
CONSTITUTION: An Fe-Cr-Ni-Al ferrite alloy is set as cathode in a reduced pressure atmosphere contg. nitrogen where this alloy is heated to and held at 400 to 700°C to induce a glow discharge and the nitride layer is formed on the surface of the alloy. The compsn. of this ferrite alloy is composed of 20 to 40wt.% Cr, 2 to 30% Ni, 2 to 15.0% Al, 0.05 to 3.0% 1 kinds among Zr, Y, Hf, Ce, La, Nd and Gd, 0 to 0.5% Ti and the balance Fe. This alloy is preferably subjected to a heat treatment consisting of holding at 1250 to 1350°C for a prescribed period of time in a non-oxidative atmosphere, then rapid cooling at a rate of ≥10°C/sec prior to the nitriding treatment. The nitrogen in the reduced pressure atmosphere mentioned above is preferably obtd. by introduction of a gaseous mixture composed of N2 and H2 or gaseous NH3.
YAMADA SHUJI
HAMADA TADASHI
NAKADA KAZUHIRO
