Abstract: PURPOSE:To improve hardness without degrading fatigue strength and impact resistance strength by subjecting spheroidal graphite cast iron of specific components to an austempering treatment of specific conditions then to shot peening. CONSTITUTION:Spheroidal graphite cast iron parts consisting, by weight, of 2.6- 4% C, 1.5-3.5% Si, 0.1-1% Mn, 0.02-0.1% Mg, 0.3-1.5% Cu, 0.03-0.09% Mo, 0.1-0.5% W and the balance Fe are heated to 850-950 deg.C and are held at this temps. within 4hr, whereby the ground is austenitized. Thence, they are subjected to an austempering treatment of quickly coolig these to 220-270 deg.C and holding these at these temps. for 30min or above to make the structure to bainite. These parts are next subjected to shot peening.

Abstract: PURPOSE:To improve at the same time the fatique strength and the abration resistance of a machined part of ductile cast iron, by machining a stock of ductile cast iron followed by carbonitriding and austempering treatments. CONSTITUTION:After ductile cast iron is cast into a gear of an automobile or the like, it is machined into a prescribed shape. Then it is heated in an electric furnace at 850-950 deg.C for 0.5-6hr in a carbonitriding atmosphere so that it is austenitized and nitrogen is diffused. Subsequently it is introduced in a salt bath to be quenched to 220-360 deg.C, and is held at this temperature for 0.5- 8hr so that it is austempered. Thus, a gear of ductile cast iron excellent in the fatigue strength and the abrasion resistace can be produced in which the inside has a bainite matrix structure and it has a hardened top layer with a thickness >=50mu and a Vickers hardness >=750 that has a fine bainite structure wherein nitrogen is diffused and at solid solution.

Abstract: PURPOSE:To obtain mechanical parts such as gears having deep surface hardened layers, hard core parts and small strains by heating steel to perfect austenitization temp., subjecting the same to a soft nitriding austempering treatment in a salt bath of high temp., then cooling the same. CONSTITUTION:Steel parts such as gears are heated to perfect austenitization temp. higher by about 30-50 deg.C than the A3 transformation point. These are immersed into a salt bath for soft nitriding treatment of about 500-650 deg.C whereby they are subjected to austempering and soft nitriding simultaneously, thence they are cooled. By this treatment, the nitrided and hardened layers of about 0.15-0.25 depths are formed, and the mechanical parts of the stable isothermal transformation structure in the core parts and about >=250Hv hardness are obtained.

Abstract: PURPOSE:To obtain the titled steel forming a surface hardened layer and a core having an isothermally transformed sturcture by soft-nitriding and austempering by adding adequate amounts of C, Si, Mn, Cr and Al. CONSTITUTION:This steel consists of 0.52-0.75% C, 0.15-0.45% Si, 0.85-1.75% Mn, 0.3-1.7% Cr, 0.1-0.6% Al and the valance Fe. 0.1-0.4% Mo and/or 0.15- 0.35% V may be optionally contained besides said essential components.

Abstract: PURPOSE:To obtain mechanical properties equal to those of steel made gears subjected to carburizing hardening by subjecting a blank material to soft nitriding to form a soft nitrided layer deeper than specified depth in a surface layer part, heating and holding the same to austenitize the base, quenching the same down to specific temps. and applying an austempering treatment. CONSTITUTION:A gear blank material made of ductile cast iron is subjected to a soft nitriding treatment for 1-30hr at 500-650 deg.C, whereby a soft nitride layer of >=4mu depths is formed on the surface layer. Thence, this gear blank material is held for 5-6hr at 850-950 deg.C to austenitize the base. Thereafter, it is subjected to an austempering treatment of cooling quickly to 220-360 deg.C and holding for 1-8hr at these temps, whereby bainite structure is obtained.