Method for the manufacture of a coated steel sheet including the following successive steps A. the provision of an annealed steel sheet having the following chemical composition in weight: 0.10<C<0.40%, 1.5<Mn<3.0%, 0.7<Si<2.0%, 0.05<Al<1.0%, 0.75<(Si+Al)<3.0%, and on a purely optional basis, one or more elements such as Nb0.5%, B0.005%, Cr1.0%, Mo0.50%, Ni1.0%, Ti0.5%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, such steel sheet being annealed at a temperature between 600 to 1200 C., B. the coating of the steel sheet obtained in step A) with a first coating including nickel, such first coating not including iron, and having a thickness equal or above 0.5 m and C. the coating of the steel sheet obtained in step B) with a second coating based on zinc. A steel sheet, a spot welded joint and further uses of the steel sheet are also provided.

Low-density hot dip galvanized steel, comprising a steel substrate (1) located at a core portion and a coating layer (3) located on the surface. An interface layer is disposed between the steel substrate (1) and the coating layer (3), the interface layer comprises an iron particle layer (4), iron particles dispersed on the steel substrate (1) and covering the steel substrate (1) are disposed in the iron particle layer (4), and the iron particles are covered by a first inhibition layer (5). The low-density hot dip galvanized steel contains element Al in a mass percentage of 3.0% to 7.0%. Correspondingly, the present invention also comprises a manufacturing method for the low-density hot dip galvanized steel. The low-density hot dip galvanized steel has a low density, a high strength and high galvanizability and coating layer adhesion.

[Object] What is provided is a manufacturing method of a galvannealed steel sheet capable of further promoting alloying of zinc plating with the steel sheet.

[Resolution Means] A manufacturing method of a galvannealed steel sheet, including: forming on a surface of a steel sheet after hot rolling and pickling which contains, by mass %, C: 0.001% to 0.350%, Si: 0.001% to 2.500% or P: 0.001% to 0.100%, or combination thereof, Mn: 0.10% to 3.00%, S: 0.001% to 0.010%, N: 0.0010% to 0.0065%, and sol. Al: 0.001% to 0.800% with a remainder being Fe and impurities, grooves having an opening surface width of 10 m to 25 m and a depth of 10 m to 30 m at intervals of 20 m to 500 m; cold rolling the steel sheet at a rolling reduction of 30% or more; reduction annealing the steel sheet after the cold rolling; immersing the steel sheet in a hot-dip galvanizing bath containing 0.10 mass % to 0.20 mass % of Al with a remainder consisting of Zn and optional components, and adhering a hot-dip galvanized layer to the surface of the steel sheet; and heating the steel sheet to which the hot-dip galvanized layer is adhered, and alloying the steel sheet with the hot-dip galvanized layer.

A high strength galvanized steel sheet having excellent surface qualities, plating adhesion, and formability is provided, wherein a galvanized layer is formed on a cold-rolled steel sheet comprising 0.1-0.3 wt % of C, 1-2.5 wt % of Si, 2.5-8 wt % of Mn, 0.001-0.5 wt % of sol. Al, at most 0.04 wt % of P, at most 0.015 wt % of S, at most 0.02 wt % of N (excluding 0 wt %), 0.1-0.7 wt % of Cr, at most 0.1 wt % of Mo, (48/14)*[N] to 0.1 wt % of Ti, 0.005-0.5 wt % of Ni, 0.01-0.07 wt % of Sb, at most 0.1 wt % of Nb, and at most 0.005 wt % of B, with the remainder being Fe and other inevitable impurities.

Provided is a method for producing a galvannealed steel sheet. When the steel sheet passing through the soaking zone is a type of steel containing 0.2 mass % or more of Si, both dry gas and humidified gas are supplied to the soaking zone, where the humidified gas is supplied only from the humidified gas supply port positioned in a latter part of the soaking zone among a plurality of humidified gas supply ports, where the latter part of the soaking zone is determined considering a sheet passing speed V and a target temperature T on the exit side of the soaking zone.

A steel part includes a steel sheet substrate and a coating on at least one surface of the steel sheet 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 steel sheet substrate and the coating have at least one deformation. An outer surface of the coating has a waviness Wa.sub.0.8 of less than or equal to 0.43 m.

A method of producing a galvannealed steel sheet includes: annealing a steel strip by conveying the steel strip through a heating zone including a direct fired furnace, a soaking zone, and a cooling zone in this order in an annealing furnace; hot-dip galvanizing the steel strip discharged from the cooling zone; and heat-alloying a galvanized coating formed on the steel strip. Mixed gas of humidified gas and dry gas is supplied into the soaking zone from at least one gas supply port located in a region of lower of the soaking zone in a height direction so that a dew point measured in a region of upper of the soaking zone in the height direction and a dew point measured in a region of lower of the soaking zone in the height direction are both 20 C. or more and 0 C. or less.

Provided are an austenite-based molten aluminum-plated steel sheet comprising: a steel plate which contains, by weight %, 0.3 to 0.9% of C, 12 to 25% of Mn, 0.5 to 2.5% of Si, 0.3 to 3.0% of Al, 0.01 to 0.5% of Ti, 0.05 to 0.5% of V, 0.01-0.5% of Mo, 0.01-0.2% of Sn, 0.001-0.1% of Co, and 0.001-0.1% of W, the remainder being Fe and unavoidable impurities; and a molten aluminum-based plated layer formed on a surface of the steel plate, and a method for producing the same.

The invention relates to an ultrahigh strength multiphase steel having a minimum tensile strength of 980 MPa containing (in wt. %): C0.075 to 0.115; Si0.400 to 0.500; Mn1.900 to 2.350; Cr0.250 to 0.400; Al0.010 to 0.060; N0.0020 to 0.0120; P0.020; S0.0020; Ti0.005 to 0.060; Nb0.005 to 0.060; V0.005 to 0.020; B0.0005 to 0.0010; Mo0.200 to 0.300; Ca0.0010 to 0.0060; Cu0.050; Ni0.050; Sn0.040; H0.0010; and residual iron, including customary steel-accompanying smelting-related impurities, wherein the total content of Mn+Si+Cr is 1.750 to 2.250 wt. % with a view to a processing window which is as wide as possible during the annealing process, in particular during the continuous annealing process, of cold strips of said steel.

The present invention provides a method for manufacturing a metal sheet. In this method, at least one of the following equations is satisfied: $\begin{array}{cc}\frac{Z}{d}+18\ln \left(\frac{Z}{d}\right)<8\ln \left(\frac{P}{V}\right)-27.52& \left(A\right)\\ f{O}_2<\frac{2.304.Math.{10}^{-3}}{{(27.52+\frac{Z}{d}+8\ln (}^{}}\end{array}$