The invention relates to a hot-rolled steel sheet having a tensile strength of greater than 1200 MPa, an R.sub.e/R.sub.m ratio of less than 0.75 and an elongation at break of greater than 10%, the composition of which contains, the contents being expressed by weight: 0.10%≦C≦0.25%; 1%≦Mn≦3%; Al≧0.015%; Si≦1.985%; Mo≦0.30%; Cr≦1.5%; S≦0.015%; P≦0.1%; Co≦1.5%; B≦0.005%; it being understood that 1%≦Si+Al≦2%; Cr +(3×Mo)≦0.3%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting, the microstructure of the steel consisting of at least 75% bainite, residual austenite in an amount equal to or greater than 5% and martensite in an amount equal to or greater than 2%.

The invention relates to a hot-rolled steel sheet having a tensile strength of greater than 1200 MPa, an R.sub.e/R.sub.m ratio of less than 0.75 and an elongation at break of greater than 10%, the composition of which contains, the contents being expressed by weight: 0.10%≦C≦0.25%; 1%≦Mn≦3%; Al≧0.015%; Si≦1.985%; Mo≦0.30%; Cr≦1.5%; S≦0.015%; P≦0.1%; Co≦1.5%; B≦0.005%; it being understood that 1%≦Si+Al≦2%; Cr +(3×Mo)≦0.3%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting, the microstructure of the steel consisting of at least 75% bainite, residual austenite in an amount equal to or greater than 5% and martensite in an amount equal to or greater than 2%.

An induction heating device for heating a metal article includes a support plate with an upper surface for receiving the metal article, and a plurality of induction coils, which are arranged concentrically around an axis and are provided at an underside of the support plate. Each induction coil is connected to and selectively powered by a generator, and at least one temperature probe is disposeable on the metal article during heating in order to monitor and control the heating of the article.

A case hardening steel having excellent fatigue resistance is provided at relatively low production cost. A case hardening steel has a chemical composition containing C: 0.10% to 0.30%, Si: 0.10% to 1.20%, Mn: 0.30% to 1.50%, S: 0.010% to 0.030%, Cr: 0.10% to 1.00%, B: 0.0005% to 0.0050%, Sb: 0.005% to 0.020%, and N: 0.0150% or less in a predetermined range, and further containing Al: 0.010%≤Al≤0.120% in the case where B−(10.8/14)N≥0.0003%, and 27/14[N−(14/10.8)B+0.030]≤Al≤0.120% in the case where B−(10.8/14)N<0.0003%.

A case hardening steel having excellent fatigue resistance is provided at relatively low production cost. A case hardening steel has a chemical composition containing C: 0.10% to 0.30%, Si: 0.10% to 1.20%, Mn: 0.30% to 1.50%, S: 0.010% to 0.030%, Cr: 0.10% to 1.00%, B: 0.0005% to 0.0050%, Sb: 0.005% to 0.020%, and N: 0.0150% or less in a predetermined range, and further containing Al: 0.010%≤Al≤0.120% in the case where B−(10.8/14)N≥0.0003%, and 27/14[N−(14/10.8)B+0.030]≤Al≤0.120% in the case where B−(10.8/14)N<0.0003%.

A method of manufacturing a hypoid gear includes face hobbing a gear blank and forming a green hypoid gear with gear teeth, heat treating the green hypoid gear to form a heat treated hypoid gear with heat treated gear teeth, and hard hobbing the heat treated gear teeth to form a hard finished hypoid gear. Critical non-tooth features on the heat treated hypoid gear are hard finished. Also, the critical non-tooth features on the heat treated hypoid gear can be hard finished prior to hard hobbing the heat treated gear teeth. The heat treating includes at least one of carburizing and induction hardening the green hypoid gear, a surface of the heat treated gear teeth has a hardness greater than or equal to 58 HRC, and the hard hobbing removes heat distortion from the heat treated gear teeth.

A method of manufacturing a hypoid gear includes face hobbing a gear blank and forming a green hypoid gear with gear teeth, heat treating the green hypoid gear to form a heat treated hypoid gear with heat treated gear teeth, and hard hobbing the heat treated gear teeth to form a hard finished hypoid gear. Critical non-tooth features on the heat treated hypoid gear are hard finished. Also, the critical non-tooth features on the heat treated hypoid gear can be hard finished prior to hard hobbing the heat treated gear teeth. The heat treating includes at least one of carburizing and induction hardening the green hypoid gear, a surface of the heat treated gear teeth has a hardness greater than or equal to 58 HRC, and the hard hobbing removes heat distortion from the heat treated gear teeth.

The present invention discloses a method for manufacturing a manual tool, comprising: performing dual-frequency induction quenching on a first surface of a moment output part or a moment transmission part of the manual tool such that a quench-hardened layer is formed within a first depth range from the first surface of the moment output part to the interior of the moment output part or within a first depth range from the first surface of the moment transmission part to the interior of the moment transmission part, the hardness of the quench-hardened layer being higher than that of the body of the moment output part or the moment transmission part; the dual-frequency induction quenching being configured to simultaneously feed or introduce a high-frequency current and an intermediate-frequency current to the same induction coil to simultaneously heat the first surface of the moment output part or the first surface of the moment transmission part by the high-frequency current and the intermediate-frequency current, and then the moment output part or the moment transmission part being cooled and quenched. The present invention also discloses a manual tool manufactured by the above method. The manual tool subjected to double-frequency induction quenching according to the present invention has good abrasion resistance.

The present invention discloses a method for manufacturing a manual tool, comprising: performing dual-frequency induction quenching on a first surface of a moment output part or a moment transmission part of the manual tool such that a quench-hardened layer is formed within a first depth range from the first surface of the moment output part to the interior of the moment output part or within a first depth range from the first surface of the moment transmission part to the interior of the moment transmission part, the hardness of the quench-hardened layer being higher than that of the body of the moment output part or the moment transmission part; the dual-frequency induction quenching being configured to simultaneously feed or introduce a high-frequency current and an intermediate-frequency current to the same induction coil to simultaneously heat the first surface of the moment output part or the first surface of the moment transmission part by the high-frequency current and the intermediate-frequency current, and then the moment output part or the moment transmission part being cooled and quenched. The present invention also discloses a manual tool manufactured by the above method. The manual tool subjected to double-frequency induction quenching according to the present invention has good abrasion resistance.

A method of making a forged, martensitic, stainless steel alloy is provided. The alloy is a forged preform of martensitic, pitting corrosion resistant stainless steel alloy comprising, by weight: 12.0 to 16.0 percent chromium; greater than 16.0 to 20.0 percent cobalt, 6.0 to 8.0 percent molybdenum, 1.0 to 3.0 percent nickel, 0.02 to 0.04 percent carbon; and the balance iron and incidental impurities. The alloy has a microstructure that comprises a retained austenite phase less than or equal to 2 percent by volume of the microstructure. The method heats the preform to a solutionizing temperature to form a solutionized microstructure. The preform is cooled with a liquid to room temperature. The preform is immersed in a cryo-liquid to transform the retained austenite phase in the microstructure to martensite. The preform is heated to a temperature of less than 600° F. for a time sufficient to form a tempered forged preform.