METHOD FOR PRODUCING COATED STEEL SHEET, GALVANIZED STEEL SHEET (EMBODIMENTS) AND APPLICATION OF GALVANIZED STEEL SHEET Russian patent published in 2023 - IPC C21D1/28 C21D1/78 C21D8/02 C22C38/12 C22C38/32 C23C2/06 C23C2/12 C23C2/26 B82B3/00 

FIELD: metallurgy.

SUBSTANCE: invention relates to a method for producing a coated steel sheet on which a zinc-based coating is applied, to a galvanized steel sheet produced by this method and the use of this sheet. The method comprises: A) providing a steel sheet having the following chemical composition in wt.%: 0.01≤ Al≤ 1.0, 0.07≤ C≤ 0.50, 0.3≤ Mn≤ 5.0, V< 0.2, 0.01≤ Si≤ 2.45, 0.35≤ Si+Al≤ 3.5, N≤ 0.01, P< 0.02, S≤ 0.01 and optionally at least one of the following elements in wt.%: B≤ 0.004, Co≤ 0.1, Cu≤ 0.5, 0.001≤ Cr≤ 1.00, 0.001≤ Mo≤ 0.5, Nb≤ 0.1,Ni≤ 1.0, Ti≤ 0.1, the rest of the composition consists of iron and inevitable impurities, B) annealing of said steel sheet, including: i) a preheating step in which said steel sheet is heated from room temperature to a temperature T₁ between 550°C and Ac1+50°C, ii) a heating step in which said steel sheet is heated from a temperature T₁ to a recrystallization temperature T₂ 720-1000° C in an atmosphere of A₁, including 0.1-15 vol.% H₂, with a residue consisting of inert gas, H₂O, O₂ and inevitable impurities, having a dew point DP₁ of -10°C to +30°C, iii) a holding stage in which said steel sheet is held at said recrystallization temperature T₂ in an atmosphere A₂ comprising 0.1-15 vol.% H₂, with a residue consisting of inert gas, H₂ O, O₂ and inevitable impurities, having a dew point DP₂ between -30°C and 0°C, wherein said dew point DP₁ is higher than said dew point DP₂, and iv) a cooling step, C) coating the steel sheet with a zinc-based coating. The galvanized steel sheet comprises a main part of steel (18), a partially decarburized layer (17) having a thickness of 20-40 microns, and also having a wt.% carbon that differs from the wt.% carbon of the main part of steel by 5-20%, and having a microstructure comprising at least 50% ferrite and at least one of the following components: bainite, martensite and/or retained austenite, a decarburized layer (16) having a thickness of 5-40 mcm, and also having such wt.% carbon, which differs from the wt.% carbon of the main part of the steel by less than 5%, and having a microstructure comprising at least 90% ferrite, and the upper part of the specified decarburized layer (16) comprises an inner oxide layer (15) with a thickness of 2-12 mcm and comprises oxides of the elements Mn, Si, Al and Cr, and mixed oxides of Mn, Si, Al and Cr, an inhibitory layer (14) with a thickness of 100-500 nm, and a coating layer (13) based on zinc with a thickness of 3-30 mcm.

EFFECT: improved resistance to liquid metal embrittlement (LME) along with target mechanical properties.

16 cl, 3 tbl, 15 dwg