A method of heat treating a cold rolled steel strip includes soaking a cold rolled steel strip having a specific composition above (Ac3−60)° C. for a certain duration thereby obtaining a cold rolled strip having a partially austenitic microstructure; cooling of the resulting soaked steel strip to a temperature below Ms; heating and heat treating the cooled steel strip in the temperature range of Bs-Ms; and cooling the heat treated steel strip to ambient temperature.

The present invention relates to an iron-based alloy powder wherein the alloy comprises the elements Fe (iron), Cr (chrome) and Mo (molybdenum) and the iron-based alloy powder is produced by an ultra-high liquid atomization process comprising at least two stages as defined below.

This hot-rolled steel sheet has a predetermined chemical composition, the microstructure includes, by volume percentage, 70% or more of martensite, tempered martensite, and bainite in total and 5% to 20% of residual austenite, in a surface layer region that is a range from a surface to a position at 1/10 of a sheet thickness, a sum of an average pole density of an orientation group consisting of {211}<111> to {111}<112> and a pole density of a crystal orientation of {110}<001> is 6.0 or less, a concentration of solid solution carbon in the residual austenite is 0.5 mass % or more, and a tensile strength is 980 MPa or more.

This hot-rolled steel sheet has a predetermined chemical composition, the microstructure includes, by volume percentage, 70% or more of martensite, tempered martensite, and bainite in total and 5% to 20% of residual austenite, in a surface layer region that is a range from a surface to a position at 1/10 of a sheet thickness, a sum of an average pole density of an orientation group consisting of {211}<111> to {111}<112> and a pole density of a crystal orientation of {110}<001> is 6.0 or less, a concentration of solid solution carbon in the residual austenite is 0.5 mass % or more, and a tensile strength is 980 MPa or more.

Provided is a steel reinforcement including an amount of 0.07 to 0.43 wt % of carbon (C), an amount of 0.5 to 2.0 wt % of manganese (Mn), an amount of 0.05 to 0.5 wt % of silicon (Si), an amount greater than 0 and less than or equal to 0.5 wt % of chromium (Cr), an amount greater than 0 and less than or equal to 4.5 wt % of copper (Cu), an amount greater than 0 and less than or equal to 0.003 wt % of boron (B), an amount greater than 0 and less than or equal to 0.25 wt % of vanadium (V), an amount greater than 0 and less than or equal to 0.012 wt % of nitrogen (N), an amount greater than 0 and less than or equal to 0.03 wt % of phosphorus (P), an amount greater than 0 and less than or equal to 0.03 wt % of sulfur (S), an amount of 0.01 to 0.5 wt % of the sum of one or more of nickel (Ni), niobium (Nb) and titanium (Ti), the balance of iron (Fe), and other inevitable impurities. A final microstructure includes ferrite, bainite, pearlite, retained austenite, and precipitates comprising copper.

Provided is a steel reinforcement including an amount of 0.07 to 0.43 wt % of carbon (C), an amount of 0.5 to 2.0 wt % of manganese (Mn), an amount of 0.05 to 0.5 wt % of silicon (Si), an amount greater than 0 and less than or equal to 0.5 wt % of chromium (Cr), an amount greater than 0 and less than or equal to 4.5 wt % of copper (Cu), an amount greater than 0 and less than or equal to 0.003 wt % of boron (B), an amount greater than 0 and less than or equal to 0.25 wt % of vanadium (V), an amount greater than 0 and less than or equal to 0.012 wt % of nitrogen (N), an amount greater than 0 and less than or equal to 0.03 wt % of phosphorus (P), an amount greater than 0 and less than or equal to 0.03 wt % of sulfur (S), an amount of 0.01 to 0.5 wt % of the sum of one or more of nickel (Ni), niobium (Nb) and titanium (Ti), the balance of iron (Fe), and other inevitable impurities. A final microstructure includes ferrite, bainite, pearlite, retained austenite, and precipitates comprising copper.

A section steel according to an exemplary embodiment of the present invention is characterized in that it includes an amount of 0.08 to 0.17% by weight of carbon (C), an amount of 0.50 to 1.60% by weight of manganese (Mn), an amount of 0.10 to 0.50% by weight of silicon (Si), an amount of 0.10 to 0.70% by weight of chromium (Cr), an amount greater than 0 and 0.5% by weight or less of copper (Cu), an amount of 0.30 to 0.70% by weight of molybdenum (Mo), an amount greater than 0 and 0.02% by weight or less of phosphorus (P), an amount greater than 0 and 0.01% by weight or less of sulfur (S), an amount greater than 0 and 0.012% by weight or less of nitrogen (N), an amount greater than 0 and 0.003% by weight or less of boron (B), an amount of 0.01 to 0.5% by weight of the sum of at least one or more of nickel (Ni), vanadium (V), niobium (Nb), and titanium (Ti), and the remainder of iron (Fe) and other unavoidable impurities, and has a tensile strength of 490 to 620 MPa, a yield strength of 355 MPa or greater, and a yield ratio of 0.8 or less at room temperature, and a high-temperature yield strength of 273 MPa or greater at a temperature of 600° C.

A section steel according to an exemplary embodiment of the present invention is characterized in that it includes an amount of 0.08 to 0.17% by weight of carbon (C), an amount of 0.50 to 1.60% by weight of manganese (Mn), an amount of 0.10 to 0.50% by weight of silicon (Si), an amount of 0.10 to 0.70% by weight of chromium (Cr), an amount greater than 0 and 0.5% by weight or less of copper (Cu), an amount of 0.30 to 0.70% by weight of molybdenum (Mo), an amount greater than 0 and 0.02% by weight or less of phosphorus (P), an amount greater than 0 and 0.01% by weight or less of sulfur (S), an amount greater than 0 and 0.012% by weight or less of nitrogen (N), an amount greater than 0 and 0.003% by weight or less of boron (B), an amount of 0.01 to 0.5% by weight of the sum of at least one or more of nickel (Ni), vanadium (V), niobium (Nb), and titanium (Ti), and the remainder of iron (Fe) and other unavoidable impurities, and has a tensile strength of 490 to 620 MPa, a yield strength of 355 MPa or greater, and a yield ratio of 0.8 or less at room temperature, and a high-temperature yield strength of 273 MPa or greater at a temperature of 600° C.

The present invention has as its object the provision of a coated steel member and coated steel sheet excellent in hydrogen embrittlement resistance in a corrosive environment and methods for manufacturing the same. The coated steel member of the present invention is provided on its surface with an Al—Fe-based coating containing Cu and one or more of Mo, Ni, Mn, and Cr in a total by mass % of 0.12% or more by heating, cooling, and manufacturing a coated steel sheet having a layer containing Cu on its surface under predetermined conditions.

There is provided a carburized bearing that is excellent in rolling contact fatigue life with a change in structure under a hydrogen-generating environment. In the carburized bearing, a chemical composition of a core portion consists of, in mass %, C: 0.25 to 0.45%, Si: 0.10 to 0.50 %, Mn: 0.40 to 0.70 %, P: 0.015% or less, S: 0.005% or less, Cr: 0.80 to 1.50%, Mo: 0.17 to 0.30%, V: 0.24 to 0.40%. Al: 0.005 to 0.100%, N: 0.0300% or less, O: 0.0015% or less, and the balance being Fe and impurities, and satisfies Formula (1) to Formula (4) described in the present specification. A proportion of a total area of CaO—CaS—MgO—Al.sub.2O.sub.3 composite oxides with respect to a total area of oxides in the carburized leaping is 30.0% or more, and a number density of oxides having an equivalent circle diameter of 20.0 μm or more is 15.0 pieces/mm.sup.2or less.