SURFACE HARDENING METHOD OF IRON OR IRON ALLOY AND APPARATUS OF THE SAME, AND SURFACE HARDENING STRUCTURE OF IRON OR IRON ALLOY

摘要

PROBLEM TO BE SOLVED: To provide a surface hardening method of iron or an iron alloy, which can provide a part from a cheap steel material such as carbon steel with a sufficient surface hardness and a small degree of thermal strain, and a small degree of dimensional change, a surface hardening apparatus of the iron or rion alloy, and a surface hardening structure of the iron or iron alloy obtained thereof.;SOLUTION: A process of forming a two-layer structure of Fe₁₆ N₂ and nitrogen martensite on an object to be treated includes the following steps: the object to be treated is transported to a heating room where ammonia gas is supplied; a temperature of the heating room is set to the temperature of a mixed phase region of austenite and iron nitride (Fe₄ N) in an iron-nitrogen phase equilibrium diagram so that the object to be treated is nitrided such that a surface nitrogen concentration of the object to be treated becomes a nitrogen concentration of Fe₁₆ N₂; and the object to be treated is rapidly cooled and heated again.;COPYRIGHT: (C)2015,JPO&INPIT