	US 12,378,627 B2
	Galvannealed steel sheet
David Zapico Alvarez, Metz (FR); Florence Bertrand, Scy-Chazelles (FR); and Joris Giroux, Metz (FR)
Assigned to ArcelorMittal, Luxembourg (LU)
Filed by ArcelorMittal, Luxembourg (LU)
Filed on Dec. 13, 2023, as Appl. No. 18/538,254.
Application 18/538,254 is a division of application No. 16/760,399, granted, now 11,884,987, previously published as PCT/IB2018/058141, filed on Oct. 19, 2018.
Claims priority of application No. PCT/IB2017/001343 (WO), filed on Nov. 8, 2017.
Prior Publication US 2024/0110257 A1, Apr. 4, 2024
Int. Cl. C21D 9/46 (2006.01); B32B 15/01 (2006.01); C21D 1/26 (2006.01); C21D 1/76 (2006.01); C21D 6/00 (2006.01); C21D 9/00 (2006.01); C21D 9/56 (2006.01); C21D 9/573 (2006.01); C22C 18/04 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/06 (2006.01); C22C 38/14 (2006.01); C22C 38/38 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C22C 38/54 (2006.01); C22C 38/58 (2006.01); C23C 2/00 (2006.01); C23C 2/02 (2006.01); C23C 2/04 (2006.01); C23C 2/06 (2006.01); C23C 2/26 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01); C21D 1/74 (2006.01); C23C 28/00 (2006.01)

CPC C21D 9/46 (2013.01) [B32B 15/013 (2013.01); C21D 1/26 (2013.01); C21D 1/76 (2013.01); C21D 6/002 (2013.01); C21D 6/004 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 9/0062 (2013.01); C21D 9/561 (2013.01); C21D 9/573 (2013.01); C22C 18/04 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/06 (2013.01); C22C 38/14 (2013.01); C22C 38/38 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C22C 38/54 (2013.01); C22C 38/58 (2013.01); C23C 2/0038 (2022.08); C23C 2/02 (2013.01); C23C 2/0224 (2022.08); C23C 2/024 (2022.08); C23C 2/04 (2013.01); C23C 2/06 (2013.01); C23C 2/261 (2022.08); C23C 2/28 (2013.01); C23C 2/40 (2013.01); C21D 1/74 (2013.01); C21D 2201/02 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/004 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01); C23C 28/321 (2013.01); C23C 28/345 (2013.01)]

18 Claims

1. A galvannealed steel sheet obtainable by a method comprising:

A. providing a steel sheet having the following chemical composition in weight percent:

0.05≤C≤0.20%,

1.5≤Mn≤3.0%,

0.10≤Si≤0.45%,

0.10≤Cr≤0.60%,

0≤Al≤0.20%,

0≤V<0.005%,

0≤P<0.04%,

0≤Nb≤0.05%,

0≤B≤0.003%,

0≤Mo≤0.20%,

0≤Ni≤0.1%,

0≤Ti≤0.06%,

0≤S≤0.01%

0≤Cu≤0.1%,

0≤Co≤0.1%,

0≤N≤0.01%,

a remainder of the composition being made of iron and inevitable impurities resulting from processing;

B. recrystallization annealing the steel sheet in a full radiant tube furnace comprising a heating section, a soaking section, and a cooling section, and optionally an equalizing section, the recrystallization annealing including the following sub-steps:

i. heating the steel sheet from ambient temperature to a temperature T1 between 700 and 900° C. in the heating section having an atmosphere A1 including from 0.1 to 15% by volume of H₂and an inert gas with a dew point DP1 is between −18° C. and +8° C.,

ii. soaking the steel sheet from T1 to a temperature T2 between 700 and 900° C. in the soaking section having an atmosphere A2 identical to A1 with a dew point DP2 equal to DP1, and

iii. cooling the steel sheet from T2 to T3 between 400 and 700° C. in the cooling section having an atmosphere A3 including from 1 to 30% H₂by volume and an inert gas with a dew point DP3 is below or equal to −30° C., and

iv. optionally, equalizing the steel sheet from a temperature T3 to a temperature T4 between 400 and 700° C. in the equalizing section having an atmosphere A4 including from 1 to 30% H₂by volume and an inert gas with a dew point DP4 is below or equal to −30° C.,

C. hot-dip galvanizing of the annealed steel sheet in a zinc bath; and

D. alloying the galvanized annealed steel sheet, the alloying performed at a temperature T5 between 460 and 600° C. during a time t5 between 1 and 45 seconds;

wherein the zinc coating is alloyed through diffusion of the iron from the steel sheet such that the zinc coating includes from 5 to 15% by weight of Fe, oxides including FeO, Mn₂SiO₄and MnO, the balance being zinc, the steel sheet including internal oxides including FeO, Mn₂SiO₄and MnO in the steel sheet.