SURFACE HARDENED STEEL AND SURFACE HARDENING METHOD OF STEEL

PURPOSE:To produce easily a surface hardened steel having high hardness by bringing a steel contg. nitride forming metallic elements into contact with a cathode in a nitrogen ion atmosphere, impressing a specified voltage between the cathode and anode and executing intermittently electric discharge. CONSTITUTION:The steel contg. nitride forming metallic elements of >=1 kinds of Cr, Al, etc. except Fe is brought into contact with the cathode and is thus homopolarized. A gaseous mixture contg. gaseous nitrogen is introduced into a reaction vessel and the specified voltage is substantially intermittently im pressed between the above-mentioned cathode and anode in the above-mentioned reaction vessel to execute intermittently the electric discharge between the two electrodes. The nitride layer in which the nitrogen concn. in the surface is as high as 0.1-10wt% and that the decreasing gradient ¦DELTAc/DELTAt¦ of the nitrogen concn. (t; thickness mu, c; nitrogen concn. %) from the surface toward the inside is as small as =0.01mm thickness is formed on the steel surface. The surface hardened steel having the high hardness is thus easily and quickly obtd.