A process for the manufacture of a pre-painted sheet. The process includes supplying a steel substrate, depositing a metallic coating on at least one face by hot-dipping of the substrate in a bath including 4.4% to 5.25% by weight aluminum and 0.3% to 0.56% by weight magnesium. The rest of the bath includes exclusively zinc, unavoidable impurities resulting from the process and optionally one or more additional elements including Si, Ti, Ca, Mn, La, Ce and Bi. The content by weight of each additional element in the metallic coating is less than 0.3% and the presence of nickel is excluded. The process further includes solidifying the metallic coating, surface preparation of the metallic coating and painting of the metallic coating. The present invention further provides a pre-painted sheet.

A process for the manufacture of a pre-painted sheet. The process includes supplying a steel substrate, depositing a metallic coating on at least one face by hot-dipping of the substrate in a bath including 4.4% to 5.25% by weight aluminum and 0.3% to 0.56% by weight magnesium. The rest of the bath includes exclusively zinc, unavoidable impurities resulting from the process and optionally one or more additional elements including Si, Ti, Ca, Mn, La, Ce and Bi. The content by weight of each additional element in the metallic coating is less than 0.3% and the presence of nickel is excluded. The process further includes solidifying the metallic coating, surface preparation of the metallic coating and painting of the metallic coating. The present invention further provides a pre-painted sheet.

There is provided a coated steel product having a steel product and a coating layer including a Zn—Al—Mg alloy layer disposed on a surface of the steel product, in which the Zn—Al—Mg alloy layer has a Zn phase, the Zn phase contains a Mg—Sn intermetallic compound phase, and the coating layer consists of Zn: more than 65.0%, Al: from more than 5.0% to less than 25.0%, Mg: from more than 3.0% to less than 12.5%, Sn: 0.1% to 20.0% in terms of percent (%) by mass, given amounts of optional elements, and impurities, and has a chemical composition that satisfies the following Formulas 1 to 5:
Bi+In<Sn  Formula 1:
Y+La+Ce≤Ca  Formula 2:
Si<Sn  Formula 3:
0≤Cr+Ti+Ni+Co+V+Nb+Cu+Mn<0.25  Formula 4:
0≤Sr+Sb+Pb+B<0.5.  Formula 5:

A method for manufacturing a high strength galvanized steel sheet and a high strength galvanized steel sheet are provided. A base steel sheet having a chemical composition comprising C: 0.03% to 0.35%, Si: 0.01% to 0.50%, Mn: 3.6% to 8.0%, Al: 0.001% to 1.000%, P0.10%, S0.010%, and the balance comprising Fe and incidental impurities, on a percent by mass basis, is subjected to annealing and galvanization treatment, wherein the maximum steel sheet temperature in an annealing furnace is 600 C. or higher and 700 C. or lower, the steel sheet transit time in a temperature region of the maximum steel sheet temperature of 600 C. or higher and 700 C. or lower is specified to be 30 seconds or more and 10 minutes or less, and the dew point in an atmosphere is specified to be 45 C. or lower.

A method for manufacturing a high strength galvanized steel sheet and a high strength galvanized steel sheet are provided. A base steel sheet having a chemical composition comprising C: 0.03% to 0.35%, Si: 0.01% to 0.50%, Mn: 3.6% to 8.0%, Al: 0.001% to 1.000%, P0.10%, S0.010%, and the balance comprising Fe and incidental impurities, on a percent by mass basis, is subjected to annealing and galvanization treatment, wherein the maximum steel sheet temperature in an annealing furnace is 600 C. or higher and 700 C. or lower, the steel sheet transit time in a temperature region of the maximum steel sheet temperature of 600 C. or higher and 700 C. or lower is specified to be 30 seconds or more and 10 minutes or less, and the dew point in an atmosphere is specified to be 45 C. or lower.

By first fluxing a steel long product with novel specific flux compositions, it is possible to continuously produce, more uniform, smoother and void-free galvanized coatings on such steel long products in a single hot dip galvanization step making use of zinc-aluminum alloys or zinc-aluminum-magnesium alloys with less than 95 wt. % zinc. This is achieved by providing potassium and sodium chlorides in a KCl/NaCl weight ratio of at least 2.0 in a flux composition comprising (a) more than 40 and less than 70 weight % zinc chloride, (b) from 10 to 30 weight % ammonium chloride, (c) more than 6 and less than 30 weight % of a set of at least two alkali metal chlorides.

By first fluxing a steel long product with novel specific flux compositions, it is possible to continuously produce, more uniform, smoother and void-free galvanized coatings on such steel long products in a single hot dip galvanization step making use of zinc-aluminum alloys or zinc-aluminum-magnesium alloys with less than 95 wt. % zinc. This is achieved by providing potassium and sodium chlorides in a KCl/NaCl weight ratio of at least 2.0 in a flux composition comprising (a) more than 40 and less than 70 weight % zinc chloride, (b) from 10 to 30 weight % ammonium chloride, (c) more than 6 and less than 30 weight % of a set of at least two alkali metal chlorides.

By first fluxing a steel long product with novel specific flux compositions, it is possible to continuously produce, more uniform, smoother and void-free galvanized coatings on such steel long products in a single hot dip galvanization step making use of zinc-aluminum alloys or zinc-aluminum-magnesium alloys with less than 95 wt. % zinc. This is achieved by providing specific amounts of lead chloride and tin chloride in a flux composition comprising (a) more than 40 and less than 70 weight % zinc chloride, (b) from 10 to 30 weight % ammonium chloride, (c) more than 6 and less than 30 weight % of a set of at least two alkali or alkaline earth metal chlorides.

By first fluxing a steel long product with novel specific flux compositions, it is possible to continuously produce, more uniform, smoother and void-free galvanized coatings on such steel long products in a single hot dip galvanization step making use of zinc-aluminum alloys or zinc-aluminum-magnesium alloys with less than 95 wt. % zinc. This is achieved by providing specific amounts of lead chloride and tin chloride in a flux composition comprising (a) more than 40 and less than 70 weight % zinc chloride, (b) from 10 to 30 weight % ammonium chloride, (c) more than 6 and less than 30 weight % of a set of at least two alkali or alkaline earth metal chlorides.

A zinc-coated steel may be produced by performing a pre-alloying heat treatment after galvannealing the steel and prior to the hot stamping the steel. The pre-alloying heat treatment is conducted at a temperature between about 850 F. and about 950 F. in an open coil annealing process. The pre-alloying heat treatment allows for shorter time at the austenitization temperature to form a desired -Fe phase in the coating by increasing the concentration of iron. This also decreases the loss of zinc, and a more adherent oxide exists after hot stamping.