Case hardening steel e.g. for transmission components of helicopters, competition vehicles and heat engines

摘要

A case hardening steel, with specified contents of nickel, manganese, copper, cobalt, chromium, molybdenum and vanadium, is new. A novel case hardening steel has the composition (by wt.) 0.06-0.18% C, 0.5-1.5% Si, 0.2-1.5% Cr, 1-3.5% Ni, 1.1-3.5% Mo, } 1.6% Mn, } 0.4% V, } 2% Cu, } 4% Co, balance Fe and impurities, with the proviso that Ni + Mn + 1.5 Cu + 0.5 Co = 2.5 to 5 wt. % and Cr + Mo + V = 2.4 to 3.7 wt. %. Independent claims are also included for the following: (i) production of case hardened parts by producing the above steel in an arc furnace, subjecting cast ingots to reheating and hot working, carrying out a homogenization and grain refining heat treatment, case hardening and heat treating according to use; (ii) a steel part having the above composition; and (iii) a steel part made by the above process. Preferred Features: The steel has the composition 0.09-0.16 % C, 0.7-1.3 % Si, 0.5-1.2% Cr, 2-3 % Ni, 1.5-2.5% Mo, 0.2-0.7 % Mn, 0.15-0.35 % V, 0.3-1.1 % Cu, } 1.5 % Co, } 0.020 % P, }0.010 % S, }0.1 % each of Al, Ce, Ti, Zr, Ca and Nb, balance Fe and impurities. Arc furnace melting may be carried out by vacuum induction melting and may be followed by consumable electrode remelting. The homogenization and grain refining heat treatment step comprises normalizing at above the Ac3 point, air cooling and soft tempering at below the Ac1 point. Case hardening is carried out at low pressure and is followed by cooling to ambient temperature, reheating to 900 -1050 deg C, oil or gas quenching and tempering at up to 350 deg C.