A method for producing a cold-rolled steel strip with a yield ratio Re/Rm of at least 0.7, the cold-rolled steel product including iron, unavoidable impurities and (in wt. %) C: 0.05-0.20%, Si: 0.25-1.00%, Mn: 1.0-3.0%, Al: 0.02-1.5%, Cr: 0.1-1.5%, N: <0.Q2%, P: <0.03%, S: <0.05% and optionally one or more of Ti, Mo, Nb, V, and B, Ti: up to 0.15%, Mo: <2%, Nb: <0.1%, V: <0.12%, and B: 0.0005-0.003%. The cold-rolled flat steel product undergoes heat treatment for 4.5-24 hours at a temperature of 150-400 C. Also, a cold rolled flat steel product discussed above having a structure including at least two phases, selected from (in vol. %) at least 10% tempered martensite, <10% bainite, <10% residual austenite and remainder ferrite, a yield ratio of at least 0.7, a tensile strength of 750 MPa and a hole expansion of at least 18%.

Disclosed is a steel composition for hot stamping that comprises carbon (C) in an amount of about 0.22 to about 0.25 wt %, silicon (Si) in an amount of about 0.2 to about 0.3 wt %, manganese (Mn) in an amount of about 1.2 to about 1.4 wt %, titanium (Ti) in an amount of about 0.02 to about 0.05 wt %, chromium (Cr) in an amount of about 0.11 to about 0.2 wt %, boron (B) in an amount of about 0.005 to about 0.01 wt %, zinc (Zr) in an amount of about 0.005 to about 0.02 wt %, niobium (Nb) in an amount of about 0.01 to about 0.05 wt %, tungsten (W) in an amount of about 0.1 to about 0.5 wt %, iron (Fe) constituting the remaining balance of the steel composition, all the wt % based on the total amount of the steel composition.

The present disclosure relates to a high-strength hot-dip galvannealed steel sheet excellent in bake hardenability and bendability and having a component composition containing, in mass %, C: from 0.05 to 030%, Si: from 0.5 to 3.0%, Mn: from 0.2 to 3.0%, P: from 0 to 0.10%, S: from 0 to 0.010%, N: form 0 to 0.010%, and Al: from 0.001 to 0.10%, with the remainder being iron and unavoidable impurities. The steel sheet has a steel structure containing, in terms of area percentage, martensite: form 50 to 85% and ferrite: 0% or more and less than 5%, with the remainder being bainite. The steel sheet has a dislocation density of 5.010.sup.15 m.sup.2 or more, a solute carbon amount of 0.08 mass % or more and a tensile strength of 1180 MPa or more.

Disclosed is a continuous processing line for processing a non-magnetic metal strip 1 and specifically to an induction heating apparatus 14 and method intended for heating the non-magnetic metal strip travelling through the continuous processing line, including a coating section 20, the apparatus being installed downstream from the coating section in the direction of travel of the strip, the apparatus making it possible to raise the temperature of the strip across the entire width thereof to the level required to obtain the sought development of the coating thereof, the heating apparatus including at least one cross-flow inductor 15.

Disclosed in the present invention a cold rolled steel plate for a galvanized steel plate, containing Fe and inevitable impurities, and also containing the following chemical elements, in mass percent: 0.18-0.25% of C, 1.5-2.0% of Si, 1.5-2.3% of Mn, and 0.01-0.06% of Nb. The microstructure of the cold rolled steel plate is bainite+tempered martensite+residual austenite, wherein the volume fraction of bainite and tempered martensite is great than or equal to 95%. Accordingly, also disclosed in the present invention is a manufacturing method for the galvanized steel plate, comprising the steps: (1) smelting and casting to obtain a steel billet; (2) hot rolling; (3) cold rolling; (4) annealing: the annealing soaking temperature is 890-920 C., the soaking and heat preservation time is 80-150 s, and then cooling is performed at a cooling rate of 30-100 C./s to reach 270-350 C.; (5) overaging: the overaging temperature is 450-475 C., and the overaging time is 40-60 s; (6) entering a zinc pot for galvanizing; (7) alloying; and (8) leveling.

A steel sheet, a member, and methods for manufacturing both are disclosed. The steel sheet has a chemical composition satisfying a carbon equivalent of 0.46% or more and a specific steel microstructure. In the steel sheet, an average crystal grain size of ferrite is 25 m or less, coefficient of variation of ferrite grain sizecarbon equivalent is 0.28 or less, when the steel sheet is bent by 90 in a rolling direction with a width direction as an axis at radius of curvature/sheet thickness: 4.2 and then unbent to be flattened again, the ratio of ferrite grains having a void at an interface to all ferrite grains is 15% or less in an L section in a region extending by 0 to 50 m from a steel sheet surface on a compressive-tensile deformation side, and a tensile strength is 780 MPa or more.

Provided are a dehydrogenation apparatus, a steel sheet production system, and a method of producing a steel sheet capable of producing a steel sheet having excellent hydrogen embrittlement resistance without changing mechanical properties of the steel sheet. The dehydrogenation apparatus includes a housing that accommodates a steel sheet coil of a steel strip coiled into a coil shape, and a magnetic field applying apparatus that applies a steady magnetic field along the sheet transverse direction of the steel sheet coil in the housing.

This cold-rolled steel sheet has a predetermined chemical composition, in which a metallographic structure of a t/4 portion, which is at a position of a sheet thickness t from a surface of the cold-rolled steel sheet in a sheet thickness direction has a predetermined structure, and in both an edge portion, which is an end portion of the cold-rolled steel sheet, and a center portion of the cold-rolled steel sheet, in the width direction, a metallographic structure of a 20 m portion, which is at a position 20 m from the surface in the sheet thickness direction, includes, by volume percentage, ferrite and bainite: 75.0% or more and 100.0% or less in total, and a metallographic structure of a 75 m portion, includes ferrite and bainite: 0.0% or more and 15.0% or less in total.

A method for producing a high-strength hot-dip galvanized steel sheet is disclosed. In the method, in a direct-fired furnace, in an early stage, a steel sheet is heated to a temperature of not less than 400 C. and not more than 670 C. in an atmosphere containing 1000 ppm by volume or more of O.sub.2 and 1000 ppm by volume or more of H.sub.2O, and in a later stage, the steel sheet is heated to a temperature of not less than 600 C. and not more than 700 C. in an atmosphere containing 500 ppm by volume or less of O.sub.2, and in an annealing furnace including a radiant tube-type heating and holding furnace, the steel sheet is held at a temperature of not less than 650 C. and not more than 900 C. for at least 90 seconds in an atmosphere which satisfies certain conditions.

Disclosed in the present invention are a hot-stamped component having high cold-bending performance and high strength, and a manufacturing method therefor. The method comprises: (1) manufacturing a steel plate for hot stamping; (2) preprocessing a component; (3) heat treatment, transfer and stamping of the component: placing a semi-finished product of the component into a heat treatment furnace, controlling a heat treatment temperature to be 750 C.-960 C., and controlling the total time of heat treatment to be 1.5-10 min and the time for the heat treatment temperature above 880 C. not to be less than 1.2 min; transferring the heat-treated semi-finished product into a mold for mold-closed stamping, and the temperature of the semi-finished product when leaving the heat treatment furnace not being lower than 900 C.; when the thickness of the steel plate forming the component is less than or equal to 1.5 mm, controlling transfer time to be 11 s-20 s, and when the thickness of the steel plate forming the component is greater than 1.5 mm, controlling the transfer time to be 13 s-25 s; and (4) stamping posttreatment: performing thermal insulation homogenization on the component, then performing machining to obtain a finished product. Accordingly, a component having a product of strength and elongation of 10 GPa.Math.%, a cold-bending angle of 60 degrees, and a three-point bending maximum load of 13 KN can be prepared by using the method.