A hot-dip galvanized steel sheet having a base steel sheet and a hot-dip galvanized layer, a ferrite phase is, by volume fraction, 50% or less in a range of ? thickness to ? thickness centered at a position of ? thickness from the surface of the base steel sheet, a hard structure is 50% or more, wherein the hot-dip galvanized steel sheet has the hot-dip galvanized layer in which Fe is 5.0% or less and Al is 1.0% or less, and columnar grains formed of a ? phase is 20% or more in an entire interface between the plated layer and the base steel sheet. On the surface of the base steel sheet, a volume fraction of a residual austenite is 3% or less.

To provide a galvanized steel sheet for hot pressing which can achieve heating for suppressing the occurrence of LME cracks in a short time during a hot pressing process, and a method of manufacturing a hot press-formed product obtained by performing hot pressing using the galvanized steel sheet. Disclosed is a galvanized steel sheet for use in hot pressing, including a galvanized layer and a base steel sheet, wherein internal oxide is present on a side of the base steel sheet from an interface between the galvanized layer and the base steel sheet, the base steel sheet including defined C, Si, Mn, and Cr, with the balance being iron and inevitable impurities, wherein the base steel sheet satisfies the following formula (1):

(2?[Si]/28.1+[Mn]/54.9+1.5?[Cr]/52.0)?0.05(1)

wherein, in the formula (1), [Si] represents a Si content in mass % of the base steel sheet, [Mn] represents a Mn content in mass % of the base steel sheet, and [Cr] represents a Cr content in mass % of the base steel sheet.

This disclosure describes methods for improving the performance and consistency of steels by closely controlling the initial homogenization of steel compositions prior to hot working. Experimental data is provided illustrating that the traditional austenitization techniques do not take into account diffusion of the various components within a steel composition and, as such, may not completely homogenize the steel composition. In the methods described in this disclosure, the initial step of austenitizing the steel ingot is altered to achieve a more homogenous distribution of the different components throughout the ingot. The improved method includes heating the steel composition to a temperature within the upper half of the pure austenitic phase temperature range and maintaining the steel composition at that temperature for a period of time determined based on the diffusivity in the austenitic phase of the steel composition of at least one constituent of the steel.

A hot-pressed member includes a steel sheet, a Ni-diffusion region present in a surface layer of the steel sheet, and an intermetallic compound layer and a ZnO layer which are provided in order on the Ni-diffusion region, the intermetallic compound layer corresponding to a phase present in a phase equilibrium diagram of a ZnNi alloy, wherein a spontaneous immersion potential indicated in a 0.5 M NaCl aqueous air-saturated solution at 25 C.5 C. is 600 to 360 mV based on a standard hydrogen electrode.

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 flat steel product for hot forming, a formed shaped sheet metal part and methods of production of the same. The flat steel product and the shaped sheet metal part have improved properties, especially in conjunction with an aluminum-based anticorrosion coating.

A cold-rolled sheet is provided. The cold-rolled sheet is annealed and pre-coated for the fabrication of press hardened parts, composed of a steel substrate for heat treatment 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 comprises 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. Processes are also provided.

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 m from the surface may be greater than or equal to 0.15 wt %.

A method for producing a steel sheet having a two-layer recrystallization structure includes: providing a cold-rolled steel sheet made of a steel with a carbon content of 10 to 1000 ppm, based on the weight, and a specified recrystallization temperature; applying a barrier layer which is at least partly impermeable to nitrogen onto a first face; and heating the steel sheet to a heating temperature. The heating is carried out at least temporarily in a nitrogenizing gas atmosphere at least until the recrystallization temperature is reached, whereby nitrogen from the gas atmosphere is diffused at least in a region near the surface on a second face of the steel sheet upon heating and is stored in the region, whereby the recrystallization temperature of the steel is raised in the region. The heating temperature is higher than or equal to the specified recrystallization temperature and lower than the raised recrystallization temperature.

Provided is a method of manufacturing a cold-rolled steel sheet. The method includes: cold-rolling a steel material; applying nickel (Ni) powder on a surface of the cold-rolled steel material in a coating amount of 300 mg/m.sup.2; heating the steel material to completely transform the steel material to austenite; slowly cooling the heated steel material at a cooling rate of 5-12 C./s to a slow cooling termination temperature of 630-670 C., and maintaining the steel material at the slow cooling termination temperature for 10-90 seconds; rapidly cooling the slowly cooled and maintained steel material at a cooling rate of 7-30 C./s to a temperature range of a martensitic transformation termination temperature or higher and a martensitic transformation initiation temperature or lower; and maintaining the rapidly cooled steel material at a temperature higher than the martensitic transformation initiation temperature and the bainite transformation initiation temperature or lower for 300-600 seconds and partitioning the steel material.