Heat- treated steel and heat treatment method for steel
AssigneeTokyo Rope Mfg. Co., Ltd.
InventorKazuhiro ISHIMOTO
Life of this patent
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Abstract
To provide a heat-treated steel excellent in both tensile strength and toughness. A heat-treated steel contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, wherein an average crystal grain size at a grain boundary setting angle of 15° is 10×C+7 (μm) or less (wherein, C represents a carbon content (%)).
Claims13
A heat-treated steel which contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, characterized in that:
- an average crystal grain size at a grain boundary setting angle of 15° is 10×C+7 (μm) or less (wherein C represents a carbon content (%)).
A heat-treated steel which contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, characterized in that:
- (the number of crystal grains at a grain boundary setting angle of 5°)/(the number of crystal grains at a grain boundary setting angle of 15°) is 5.4×C−0.95 or less (wherein C represents a carbon content (%)).
A heat-treated steel which contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, characterized in that:
- (the number of crystal grains at a grain boundary setting angle of 2°)/(the number of crystal grains at a grain boundary setting angle of 15°) is 9.8×C−1.9 or less (wherein C represents a carbon content (%)).
A heat-treated steel which contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, characterized in that:
- a GOS value at a grain boundary setting angle of 15° is 11×(C−0.42)+5.3 or less (wherein C represents a carbon content (%)).
A heat-treated steel which contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, characterized in that:
- a cumulative frequency of a GOS value in a range of 0° to 10° at a grain boundary setting angle of 15° is −0.1C3−1.3C2+1.1C+0.7 or more (wherein C represents a carbon content (%)).
A heat-treated steel which contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, characterized in that:
- when a structure is observed with a backscattered electron (BSE) image, in a layered structure of ferrite and an iron carbide, an area fraction of the branched, bent, or curved iron carbide is 9% or more in a field of view.
A heat-treated steel which contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, characterized in that:
- when a structure is observed with a scanning electron microscope (SEM), in a layered structure of ferrite and an iron carbide, a spherical protrusion is observed on a surface of the iron carbide.
A heat-treated steel which contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, characterized in that:
- when a structure is observed with a scanning electron microscope (SEM), in a layered structure of ferrite and an iron carbide, a surface of the iron carbide has unevenness, and a rod-shaped or plate-shaped relatively isotropic iron carbide, which is three-dimensionally comb-shaped or mesh-shaped, is produced.
A heat-treated steel which contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, characterized in that:
- when a tensile strength is TS (MPa), a reduction of area is −0.000064TS2+0.09TS+46 (%) or more.
A heat-treated steel which contains 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities, characterized in that:
- a difference in proof stress obtained by subtracting a 0.2% proof stress obtained in a S-S curve from a 0.4% proof stress obtained in the S-S curve is 45×C−3 (MPa) or less (wherein C represents a carbon content (%)).
A heat treatment method for a steel, characterized by comprising the steps of:
- preparing s steel containing 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities;
- causing the steel itself to generate heat to directly heat the steel;
- and
- passing the heated steel through a bath in which a cooling medium capable of isothermal transformation is stored to cool the steel, wherein
- a temperature gradient in a final stage of heating of the heating step is the largest, and the heated steel is allowed to enter the cooling medium immediately after the steel reaches a predetermined maximum heating temperature in the final stage of heating of the heating step to start the cooling without maintaining the predetermined maximum heating temperature.
A heat treatment method for a steel, comprising:
- heating a steel from room temperature to 820° C. or more within a few seconds, and cooling the heated steel to 620° C. or less within a few seconds without maintaining a maximum heating temperature, the steel containing 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities.
Dependencies are inferred from the claim text.