A packaging sheet metal product from a cold-rolled steel sheet with a thickness of less than 0.6 mm has a specified composition. The packaging sheet metal product during biaxial deformation in a bulge test has a lower yield strength (Sb.sub.eL) of more than 300 MPa and a corresponding elongation at break (Ab) of more than 10% and in the plastic region between the Lüders elongation (Ab.sub.e) and an upper (plastic) elongation limit of ε.sub.max=0.5.Math.Ab.Math.(Sb.sub.eL/Sb.sub.m) has a biaxial stress/strain diagram σ.sub.B(ε) that can be represented by a function ε.sub.B=b.Math.ε.sup.n, with: σ.sub.B is the true biaxial stress in MPa; ε is the amount of true elongation in the thickness direction in %; Sb.sub.m is the absolute strength; b is a proportionality factor; and n is a strain-hardening exponent. A strengthening of the packaging sheet product in the thickness direction is characterized by a strain-hardening exponent of n≥0.353-5.1.Math.Sb.sub.eL/10.sup.4 MPa.

A zinc-plated steel sheet for hot stamping according to an aspect of the present invention includes a steel substrate and a plated layer provided on a surface of the steel substrate, in which the steel substrate contains, in % by mass, C: 0.10 to 0.5%, Si: 0.7 to 2.5%, Mn: 1.0 to 3%, and Al: 0.01 to 0.5%, with the balance being iron and inevitable impurities, and the steel substrate has, in the inside thereof, an internal oxide layer consists of an oxide containing at least one of Si and Mn having a thickness of 1 μm or more, and a decarburized layer having a thickness of 20 μm or less from an interface with the plated layer toward an internal direction of the steel substrate.

A method for producing a steel sheet for packaging includes: cold-rolling a hot-rolled steel sheet made from a steel having a carbon content of 10 to 1000 ppm by weight, the steel of the hot-rolled steel sheet having a predetermined recrystallization temperature (T.sub.R); heating the cold-rolled steel sheet to a predetermined heating temperature (T.sub.E), where T.sub.R≤T.sub.E, the heating performed at least partially in the presence of a nitrogen donor at least until T.sub.R is reached such that when the cold-rolled steel sheet is heated, nitrogen from the nitrogen donor is diffused at least into a near-surface region of the cold-rolled sheet steel and incorporated in the near-surface region, as a result of which the T.sub.R in the near-surface region is increased by a value ΔT, where T.sub.E<T.sub.R+ΔT. Using this method, high-strength steel sheets having a multilayer microstructure can be produced.

A cold-rolled sheet is provided. The cold-rolled sheet includes a steel substrate with a carbon content C.sub.0 between 0.07% and 0.5%, expressed by weight, and a metal pre-coating on at least the two principal faces of the steel substrate. The substrate has a decarburized area on the surface of each of the two principal faces. The depth p.sub.50% of the decarburized area is between 6 and 30 micrometers, and p.sub.50% is the depth at which the carbon content is equal to 50% of the content C.sub.0. The sheet does not contain a layer of iron oxide between the substrate and the metal pre-coating.

A nitrided packaging steel in the form of a flat steel product and method for producing a nitrided packaging steel with a carbon content of 10-1000 ppm and uncombined nitrogen, dissolved in the steel, of more than 100 ppm. The nitriding is performed in two stages: a first stage, in which a molten steel is nitrided to a nitrogen content of at most 160 ppm by introducing a nitrogen-containing gas and/or a nitrogen-containing solid into the molten steel, and a second stage, in which a flat steel product produced from the nitrided molten steel by cold rolling is treated with a nitrogen-containing gas in order to increase further the amount of uncombined nitrogen in the flat steel product. The second stage is performed in an annealing furnace, in which the flat steel product is at the same time annealed in a recrystallizing manner. The packaging steels produced are distinguished by great strength, in excess of 600 MPa, and good elongation to fracture, regularly in excess of 5%, as well as by good forming properties.

A high-strength cold-rolled steel sheet having excellent bending workability includes, by weight %, 0.13-0.25% of carbon (C), 1.0-2.0% of silicon (Si), 1.5-3.0% of manganese (Mn), 0.08-1.5% of aluminum (Al)+chromium (Cr)+molybdenum (Mo), 0.1% or less of phosphorus (P), 0.01% or less of sulfur (S), 0.01% or less of nitrogen (N), the remainder of Fe and inevitable impurities, and comprises, by area fraction, 3-25% of ferrite, 20-40% of martensite, and 5-20% of retained austenite, in which a nickel-rich layer formed of nickel (Ni) introduced from the outside is provided on a surface layer portion, and the concentration of nickel (Ni) at a depth of 1 μm from the surface may be greater than or equal to 0.15 wt %.

Provided is a low-cost cold rolled steel sheet for zirconium-based chemical conversion treatment that contains Si and Mn and has excellent zirconium-based chemical convertibility even when a relatively large amount of Si-based oxide and Si—Mn-based oxide exists on the steel sheet surface. A cold rolled steel sheet for zirconium-based chemical conversion treatment comprises a chemical composition containing, in mass %, C: 0.05% to 0.30%, Si: 0.01% to 1.4%, Mn: 0.14% to 3.2%, P: 0.10% or less, and S: 0.01% or less, with a balance consisting of Fe and inevitable impurities, wherein a Si/Mn mass ratio in steel is 0.10 to 0.7, and a surface coating ratio of steel sheet surface layer oxides having Si content of 10 mass % or more is 40% or less.

A cold rolled and heat-treated steel sheet, the steel including, in weight percentage, 0.17%≤carbon≤0.25%, 2%≤manganese≤3%, 0.9%≤silicon≤2%, 0%≤aluminum≤0.09%, 0.01%≤molybdenum≤0.2%, 0%≤phosphorus≤0.02%, 0%≤sulfur≤0.03%, 0%≤nitrogen≤0.09%, and optionally one or more of the following elements 0%≤chromium≤0.3%, 0%≤niobium≤0.06%, 0%≤titanium≤0.06%, 0%≤vanadium≤0.1%, 0%≤calcium≤0.005%, 0%≤boron≤0.010%, 0%≤Magnesium≤0.05%, 0%≤Zirconium≤0.05%, 0%≤Cerium≤0.1%, and the balance including iron and unavoidable impurities, the steel sheet having a microstructure of—50% to 80% of Bainite, 10% to 30% of residual austenite, 15% to 50% of Partitioned martensite, 0% to 10% of ferrite and 0% to 5% fresh martensite in area fractions, and a ferrite-enriched layer extending up to 50 microns from both surfaces of the steel sheet, such ferrite-enriched layer having a mean ferrite content from 55% to 80% in area fraction.

The present invention provides: a plated steel sheet for hot press forming having excellent impact properties after hot press forming; a hot press formed member manufactured using the plated steel sheet for hot press forming; and manufacturing methods thereof. The plated steel sheet comprises: a base steel sheet containing, by weight, 0.15-0.4% of C, 0.1-1% of Si, 0.6-8% of Mn, 0.001-0.05% of P, 0.0001-0.02% of S, 0.01-0.1% of Al, 0.001-0.02% of N, and 0.01-0.5% of Cr, with the remainder comprising Fe and miscellaneous impurities; and a plating layer formed on the surface of the base steel sheet and composed of zinc, aluminum, or an alloy containing zinc and aluminum, wherein the ratio (C S/C B) of the content (C S) of C in a surface layer to the content (C B) of C in the base steel sheet is 0.6 or less, and the ratio ((Mn S+Cr S)/(Mn B+Cr B)) of the total content (Mn S+Cr S) of Mn and Cr in the surface layer to the total content (Mn B+Cr B) of Mn and Cr in the base steel sheet is 0.8 or more.

A high strength steel sheet comprising a center part of sheet thickness and a surface soft part formed at one side or two sides of the center part of sheet thickness, having metal structures of the center part of sheet thickness comprising, by area ratio, tempered martensite: 85% or more, one or more of ferrite, bainite, pearlite, and retained austenite: total of less than 15%, and as-quenched martensite: less than 5%, and additionally having metal structures of the surface soft part comprising, by area ratio, ferrite: 65% or more, pearlite: 5% or more and less than 20%, one or more of tempered martensite, bainite, and retained austenite: total of less than 10%, and as-quenched martensite: less than 5%, wherein a Vickers hardness (Hc) of the center part of sheet thickness and a Vickers hardness (Hs) of the surface soft part satisfy 0.50≤Hs/Hc≤0.75.