A high-strength galvanized steel sheet of the present invention includes a steel sheet having a chemical composition containing a predetermined component element, and a steel structure in which an average grain size of inclusions containing at least one of Al, Si, Mg, and Ca and existing in an area extending from a surface to a position of ⅓ of a sheet thickness is 50 μm or less, and an average nearest distance between ones of the inclusions is 20 μm or more; and a galvanized layer provided on a surface of the steel sheet and having a coating weight per one surface of 20 g/m.sup.2 or more and 120 g/m.sup.2 or less, in which an amount of diffusible hydrogen contained in the steel is less than 0.25 mass ppm, and a tensile strength is 1100 MPa or more.

The present invention relates to a flat steel product which has good deep-drawing ability, low edge-crack sensitivity and good bending behaviour. To this end, the flat steel product contains a steel which consists of (in wt %) 0.1-0.5% C, 1.0-3.0% Mn, 0.9-1.5% Si, up to 1.5% Al, up to 0.008% N, up to 0.020% P, up to 0.005% S, 0.01-1% Cr and optionally one or more of the following elements: up to 0.2% Mo, up to 0.01% B, up to 0.5% Cu, up to 0.5% Ni and optionally a total of 0.005-0.2% microalloying elements, the remainder being iron and unavoidable impurities, wherein 75<(Mn2+55*Cr)/Cr<3000 where Mn is the Mn content of the steel in wt % and Cr is the Cr content of the steel in wt %. The steel has a structure which consists of at least 80 area % martensite, of which at least 75 area % is tempered martensite and at most 25 area % is non-tempered martensite, at least 5 volume % residual austenite, 0.5 to 10 area % ferrite and at most 5 area % bainite, wherein in the region of the phase boundary between tempered martensite and residual austenite there is a low-Mn ferrite seam which has a width of at least 4 nm and at most 12 nm and the Mn content of which is at most 50% of the average Mn content of the flat steel product. The flat steel product contains carbides with a length of less than or equal to 250 nm. The invention also relates to a method for producing a flat steel product according to the invention, in which method the structural characteristics of the flat steel product according to the invention are set by suitable heat treatment.

A coated metal sheet includes a steel substrate and a coating on at least one surface of the steel substrate. The coating includes between 0.2 and 0.7% by weight of Al, with a remainder of the metal coating being Zn and inevitable impurities. The coated metal sheet was subjected to a skin pass operation after coating. An outer surface of the metal coating has a waviness Wa.sub.0.8 of less than or equal to 0.55 μm.

A steel sheet for the manufacture of a press hardened part is provided, having a composition of: 0.15%≤C≤0.22%, 3.5%≤Mn<4.2%, 0.001%≤Si≤1.5%, 0.020%≤Al≤0.9%, 0.001%≤Cr≤1%, 0.001%≤Mo≤0.3%, 0.001%≤Ti≤0.040%, 0.0003%≤B≤0.004%, 0.001%≤Nb≤0.060%, 0.001%≤N≤0.009%, 0.0005%≤S≤0.003%, 0.001%≤P≤0.020%. A microstructure has less than 50% ferrite, 1% to 20% retained austenite, cementite, such that the surface density of cementite particles larger than 60 nm is lower than 10{circumflex over ( )}7/mm.sup.2, and a complement of bainite and/or martensite, the retained austenite having an average Mn content of at least 1.1*Mn %. Press-hardened steel part obtained by hot forming the steel sheet, and manufacturing methods thereof.

In accordance with one aspect of the present disclosure, there is provided a steel material for a tailor-welded blank, including 0.04 to 0.06 wt % of carbon (C), 1.2 to 1.5 wt % of manganese (Mn), 0.01 to 0.10 wt % of titanium (Ti), 0.01 to 0.10 wt % of niobium (Nb), and the balance of iron (Fe) and inevitable impurities; having a tensile strength (TS) of 550 MPa or greater, a yield strength (YS) of 300 MPa or greater, and an elongation (EL) of 20% or greater; and having a dual-phase structure of ferrite and martensite.

The steel plate has a specific chemical composition, and a microstructure where a volume fraction of martensite at a depth of 1 mm from a surface of the steel plate is 95% or more, and at a depth of 1 mm from a surface of the steel plate, a Vickers hardness at 400° C. is 288 or more, and a Brinell hardness at 25° C. is 360 HBW10/3000 to 490 HBW10/3000.

A steel sheet has a specific chemical composition and has a structure represented by, by area ratio, ferrite: 5 to 60%, and bainite: 40 to 95%. When a region that is surrounded by a grain boundary having a misorientation of 15° or more and has a circle-equivalent diameter of 0.3 μm or more is defined as a crystal grain, the proportion of crystal grains each having an intragranular misorientation of 5 to 14° to all crystal grains is 20 to 100% by area ratio. A precipitate density of Ti(C,N) and Nb(C,N) each having a circle-equivalent diameter of 10 nm or less is 10.sup.10 precipitates/mm.sup.3 or more. A ratio (Hvs/Hvc) of a hardness at 20 μm in depth from a surface (Hvs) to a hardness of the center of a sheet thickness (Hvc) is 0.85 or more.

The high-strength hot-dip galvanized steel sheet, which includes a hot-dip galvanized coating layer on a surface of the steel sheet, has a component composition containing, in mass %, C: 0.07% to 0.20%, Si: 0.1% to 2.0%, Mn: 2.0% to 3.5%, P: 0.05% or less, S: 0.05% or less, and sol. Al: 0.005% to 0.1%, with the balance being Fe and incidental impurities; and has a steel microstructure containing, in area fraction, 60% or less of ferrite, 40% or more of tempered martensite, and 10% or less of fresh martensite and having a void number density of 1,500/mm.sup.2 or less in a bent portion in the VDA bending test.

A steel sheet for the manufacture of a press hardened part is provided, having a composition of: 0.15%≤C≤0.22%, 3.5%≤Mn<4.2%, 0.001%≤Si≤1.5%, 0.020%≤Al≤0.9%, 0.001%≤Cr≤1%, 0.001%≤Mo≤0.3%, 0.001%≤Ti≤0.040%, 0.0003%≤B≤0.004%, 0.001%≤Nb≤0.060%, 0.001%≤N≤0.009%, 0.0005%≤S≤0.003%, 0.001%≤P≤0.020%. A microstructure has less than 50% ferrite, 1% to 20% retained austenite, cementite, such that the surface density of cementite particles larger than 60 nm is lower than 10{circumflex over ( )}7/mm.sup.2, and a complement of bainite and/or martensite, the retained austenite having an average Mn content of at least 1.1*Mn %. Press-hardened steel part obtained by hot forming the steel sheet, and manufacturing methods thereof.

A method for controlling or regulating the temperature of a steel strip in hot forming in a hot strip mill. A superordinate open-loop or closed-loop controller has a process model that predetermines the temperature development of the hot strip. The target values of the individual units are adjusted based on this predetermined temperature development.