A method for producing a machine component excellent in pitting resistance characteristics and toughness includes a carburizing step, performed on a steel material containing 0.13-0.30% C and 0.90-2.00% Cr in mass % and at least one of Si, Mn, Ni, Mo, Nb, V, Ti, B, Al, and N, balance Fe and unavoidable impurities; heating the material to 850-1030 C. to attain carbon concentration in a surface of 0.8-1.5%; cooling the material at an average rate of 5 C./sec or lower from a temperature higher than the A.sub.cm point of a surface layer to a cooling end temperature that is at least 50 C. lower than the A.sub.1 point to cause the surface layer to have a pearlite or bainite structure with dispersion; spheroidizing annealing at a temperature not higher than the A.sub.cm point at the surface layer; heating the material to not higher than the A.sub.cm point at the surface layer; and performing tempering.

A steel alloy includes about 1.65 to about 2 percent by weight nickel (Ni), about 0.7 to about 0.9 percent by weight chromium (Cr), about 0.6 to about 0.9 percent by weight manganese (Mn), about 0.58 to about 0.63 percent by weight carbon (C), about 0.25 to about 0.35 percent by weight niobium (Nb), about 0.15 to about 0.35 percent by weight silicon (Si), about 0.2 to about 0.3 percent by weight molybdenum (Mo), about 0.005 to about 0.01 percent by weight boron (B), and iron (Fe).

A steel alloy includes about 1.65 to about 2 percent by weight nickel (Ni), about 0.7 to about 0.9 percent by weight chromium (Cr), about 0.6 to about 0.9 percent by weight manganese (Mn), about 0.58 to about 0.63 percent by weight carbon (C), about 0.25 to about 0.35 percent by weight niobium (Nb), about 0.15 to about 0.35 percent by weight silicon (Si), about 0.2 to about 0.3 percent by weight molybdenum (Mo), about 0.005 to about 0.01 percent by weight boron (B), and iron (Fe).

A gear manufacturing method includes a step of preparing a gear blank; a step (teeth cutting step) of cutting the gear blank to form a half-finished gear having a plurality of gear teeth; a step (heat treatment step) of heat-treating the half-finished gear having the gear teeth; and a step (form rolling step) of rolling the half-finished gear which is subjected to the heat treatment, in which the gear teeth of the half-finished gear which is subjected to the teeth cutting step is formed with protuberances on both sides in a circumferential direction, and at the form rolling step, the protuberances are pressed by a rolling die, so that the half-finished gear becomes a gear.

A gear manufacturing method includes a step of preparing a gear blank; a step (teeth cutting step) of cutting the gear blank to form a half-finished gear having a plurality of gear teeth; a step (heat treatment step) of heat-treating the half-finished gear having the gear teeth; and a step (form rolling step) of rolling the half-finished gear which is subjected to the heat treatment, in which the gear teeth of the half-finished gear which is subjected to the teeth cutting step is formed with protuberances on both sides in a circumferential direction, and at the form rolling step, the protuberances are pressed by a rolling die, so that the half-finished gear becomes a gear.

The invention relates mainly to an assembly comprising: a combustion engine ring gear having a plurality of teeth, the said ring gear being defined by a modulus and a pressure angle, a starter comprising a pinion (31) able to engage with the said ring gear of the said combustion engine, the said pinion (31) having a plurality of teeth (42) is defined by a modulus (Mp) and a pressure angle (alpha_p), characterized in that a pinion product which is the product of the modulus (Mp) of the said pinion (31) and the cosine of the pressure angle (alpha_p) of the said pinion (31) is greater than a ring-gear product equal to the product of the modulus of the said ring gear and the cosine of the pressure angle of the said ring gear.

A method for producing a steel member includes carburizing the steel member, pearlitizing austenite, and performing quenching. The pearlitizing of the austenite includes performing a first pearlite precipitation treatment of cooling the steel member to a first temperature lower than an austenite transformation start temperature and higher than 680 C. and holding the steel member at the first temperature to pearlitize a part of the austenite formed in the carburizing of the steel member, and performing a second pearlite precipitation treatment of further cooling the steel member to a second temperature equal to or lower than 680 C. and higher than a nose temperature and holding the steel member at the second temperature to pearlitize the austenite retained in the first pearlite precipitation treatment.

A method for producing a steel member includes carburizing the steel member, pearlitizing austenite, and performing quenching. The pearlitizing of the austenite includes performing a first pearlite precipitation treatment of cooling the steel member to a first temperature lower than an austenite transformation start temperature and higher than 680 C. and holding the steel member at the first temperature to pearlitize a part of the austenite formed in the carburizing of the steel member, and performing a second pearlite precipitation treatment of further cooling the steel member to a second temperature equal to or lower than 680 C. and higher than a nose temperature and holding the steel member at the second temperature to pearlitize the austenite retained in the first pearlite precipitation treatment.

The present invention relates to a steel composition comprising, in percentages by weight of the total composition: Carbon: 0.06-0.20 preferably 0.08-0.18; Chromium: 2.5-5.0, preferably 3.0-4.5; Molybdenum: 4.0-6.0; Tungsten: 0.01-3.0; Vanadium: 1.0-3.0, preferably 1.5-2.5; Nickel: 2.0-4.0; Cobalt: 9.0-12.5, preferably 9.5-11.0; Iron: remainder
as well as the inevitable impurities,
optionally further comprising one or more of the following elements: Niobium: 2.0; Nitrogen: 0.50, preferably 0.20; Silicon: 0.70, preferably 0.05-0.50; Manganese: 0.70, preferably 0.05-0.50; Aluminum: 0.15, preferably 0.10;
the combined niobium+vanadium content being in the range 1.0-3.5; and the carbon+nitrogen content being in the range 0.06-0.50.

It further relates to method of manufacture thereof, the steel blank obtained and a mechanical device or an injection system comprising same.

The present invention relates to a steel composition comprising, in percentages by weight of the total composition: Carbon: 0.06-0.20 preferably 0.08-0.18; Chromium: 2.5-5.0, preferably 3.0-4.5; Molybdenum: 4.0-6.0; Tungsten: 0.01-3.0; Vanadium: 1.0-3.0, preferably 1.5-2.5; Nickel: 2.0-4.0; Cobalt: 9.0-12.5, preferably 9.5-11.0; Iron: remainder
as well as the inevitable impurities,
optionally further comprising one or more of the following elements: Niobium: 2.0; Nitrogen: 0.50, preferably 0.20; Silicon: 0.70, preferably 0.05-0.50; Manganese: 0.70, preferably 0.05-0.50; Aluminum: 0.15, preferably 0.10;
the combined niobium+vanadium content being in the range 1.0-3.5; and the carbon+nitrogen content being in the range 0.06-0.50.

It further relates to method of manufacture thereof, the steel blank obtained and a mechanical device or an injection system comprising same.