Provided is a method for producing a Ni- or Ti-based alloy product, the method capable of locally increasing the cooling rate and effectively cooling. The method includes the steps: preliminarily processing a hot working material of a Ni- or Ti-based alloy after hot working into a predetermined shape; heating and holding the material at a solution treatment temperature to obtain a material held in a heated state; and cooling the material held in a heated state to obtain a solution-treated material. The cooling step includes placing a flow path-forming member having a space for forming a flow path for a fluid on a surface of the material held in a heated state to form a fluid flow path defined by the surface of the material held in a heated state and an inner surface of the space of the flow path-forming member; and allowing a fluid to flow in the fluid flow path so that the fluid in the flow path locally cools a part of the surface of the material held in a heated state.

A steel sheet has a predetermined chemical composition, in which a microstructure in a ¼ width portion, a microstructure in a ½ width portion, and a microstructure in a ¾ width portion, include, by area %, ferrite: 80% or more, martensite: 2% or less, and residual austenite: 2% or less, in which a proportion of unrecrystallized ferrite in the ferrite is 5% to 60%, an average grain size of carbonitrides is 6.0 nm to 30.0 nm, and Expressions (2) to (5) are satisfied.

Δ.sub.SF/μ.sub.SF≤0.10  (2)

Δ.sub.dF/μ.sub.dF≤0.20  (3)

Δ.sub.SUF≤20  (4)

Δ.sub.dC/μ.sub.dC≤0.50  (5)

A cold-rolled high-strength steel plate having excellent phosphating performance and formability and a manufacturing method therefor. The chemical composition of the steel plate is, in percentage by weight, C 0.01-0.20%, Si 1.50-2.50%, Mn 1.50-2.50%, P≤0.02%, S≤0.02%, Al 0.03-0.06%, N≤0.01%, the remainder being Fe and impurities. The surface layer of the steel plate has an inner oxide layer with a thickness of 1-5 μm, and there is no enrichment of Si and Mn on the surface of the steel plate. The steel plate has tensile strength of ≥980 MPa and an elongation of ≥20%. The structure at the room temperature contains retained austenite, ferrite, and martensite and/or bainite.

The invention relates to a method for producing a hot-rolled strip composed of a bainitic multi-phase steel and having a Zn—Mg—Al coating, comprising the following steps: melting a steel melt containing (in weight percent): C: 0.04-0.11, Si: <=0.7, Mn: 1.4-2.2, Mo: 0.05-0.5, Al: 0.015-0.1, P: up to 0.02, S: up to 0.01, B: up to 0.006, and at least one element from the group Nb, V, Ti in accordance with the following condition: 0.02<=Nb+V+Ti<=0.20, the remainder being iron including unavoidable steel-accompanying elements resulting from the melting process, casting the steel melt into a preliminary material, in particular a slab or a block or a thin slab, hot rolling the preliminary material into a hot-rolled strip having a final rolling temperature in the range of 800 to 950° C., cooling the hot-rolled strip to a winding temperature less than 650° C., winding the hot-rolled strip at a winding temperature less than 650° C., cooling the wound hot-rolled strip to room temperature in still air, wherein the microstructure of the wound hot-rolled strip then has a bainite fraction greater than 50% after the hot rolling, heating the hot-rolled strip to a temperature greater than 650° C. and less than Ac3, in particular less than Ac1+50° C., cooling the hot-rolled strip to zinc bath temperature, hot-dip coating the heated hot-rolled strip in a zinc alloy molten bath containing (in weight percent): Al: 1.0-2.0, Mg: 1.0-2.0, the remainder being zinc and unavoidable impurities. The invention further relates to the hot-rolled strip produced in accordance with the method above and to shaped, dynamically highly loadable components, in particular motor vehicle parts, that are produced from said hot-roiled strip and that are resistant to corrosive and abrasive influences.

Provided is a hot rolled steel sheet comprising a predetermined composition wherein the hot rolled steel sheet comprises ferrite with an average orientation difference in the same grain of 0.5 to 5.0° in 30 to 70 vol %, the ferrite and martensite in a total of 90 vol % or more, and a balance microstructure of 10 vol % or less, has an average grain size of the ferrite of 0.5 to 5.0 μm, and has an average grain size of the martensite and the balance microstructure of 1.0 to 10 μm. Provided is a method for producing a hot rolled steel sheet comprising rolling where two or more consecutive passes of rolling including a final pass are performed under conditions of a rolling temperature: A point or more and less than Ae.sub.3 point, a strain rate: 1.0 to 50/sec, and a time between passes: within 10 seconds and where a total strain amount of all passes satisfying the conditions is 1.4 to 4.0, cooling by a 20° C./sec or more average cooling rate, and coiling the steel sheet at room temperature or more and less than 300° C.

The steel sheet of the present invention has a steel microstructure containing, in area fraction, martensite: from 20% to 100%, ferrite: from 0% to 80%, and another metal phase: 5% or less, and in which a ratio of a dislocation density in metal phases on a surface of the steel sheet to a dislocation density in the metal phases in a thicknesswise central portion of the steel sheet is from 30% to 80%. The maximum amount of warpage of the steel sheet when the steel sheet is sheared to a length of 1 m in a rolling direction is 15 mm or less.

An electric resistance welded steel pipe includes a base metal zone and an electric resistance welded zone. The base metal zone has a predetermined chemical composition and a microstructure including, by volume, ferrite: more than 30%, and bainite: 10% or more. The total volume fraction of the ferrite and the bainite is 70% or more and 95% or less. The balance being one or two or more phases selected from pearlite, martensite, and austenite. Further, when regions surrounded by boundaries between adjacent crystals having a misorientation of 15° or more are defined as crystal grains, the average size of the crystal grains is less than 7.0 μm, and the volume fraction of crystal grains having a size of 40.0 μm or more is 30% or less. A compressive residual stress generated in the inner and outer surfaces of the steel pipe in the axial direction is 250 MPa or less.

Provided are high-strength steel plate having excellent low-temperature impact toughness and method of manufacturing the same. The present disclosure relates to a high-strength steel plate comprising, by weight %, carbon (C): 0.04-0.12%, silicon (Si): 0.1-0.5%, manganese (Mn): 1.2-2.5%, phosphorus (P): 0.01% or less, sulfur (S): 0.01% or less, aluminum (Al): 0.01-0.08%, niobium (Nb): 0.01-0.08%, chromium (Cr): 0.01-0.5%, nickel (Ni): 0.4-1.0%, copper (Cu): 0.5% or less, molybdenum (Mo): 0.01-0.5%, vanadium (V): 0.05% or less, titanium (Ti): 0.005-0.02%, boron (B): 0.001-0.0025%, nitrogen (N): 0.002-0.01%, the balance Fe and inevitable impurities, a Ceq value being less than 0.55.

A spot welded joint of at least two steel sheets is provided. At least one of the steel sheets presents yield strength above or equal to 600 MPa, an ultimate tensile strength above or equal to 1000 MPa, uniform elongation above or equal to 15%. The base metal chemical composition includes 0.05≤C≤0.21%, 4.0≤Mn≤7.0%, 0.5≤Al≤3.5%, Si≤2.0%, Ti≤0.2%, V≤0.2%, Nb≤0.2%, P≤0.025%, B≤0.0035%, and the spot welded joint contains a molten zone microstructure containing more than 0.5% of Al and containing a surface fraction of segregated areas lower than 1%, said segregated areas being zones larger than 20 μm.sup.2 and containing more than the steel nominal phosphorus content.

A cold-rolled and heat treated steel sheet, has a composition comprising 0.1%≤C≤0.4%, 3.5%≤Mn≤8.0%, 0.1%≤Si≤1.5%, Al≤3%, Mo≤0.5%, Cr≤1%, Nb≤0.1%, Ti≤0.1%, V≤0.2%, B≤0.004%, 0.002%≤N≤0.013%, S≤0.003%, P≤0.015%. The structure consists of, in surface fraction: between 8 and 50% of retained austenite, at most 80% of intercritical ferrite, the ferrite grains, if any, having an average size of at most 1.5 μm, and at most 1% of cementite, the cementite particles having an average size lower than 50 nm, martensite and/or bainite.