Patent ID: 11884987
Assignee: ARCELORMITTAL
Field: Materials, metallurgy (Chemistry)
Classification: CPC C  B | IPC B  C

Claim 0:
1. A method for manufacturing a galvannealed steel sheet, the 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%,
Al≤0.20%,
V<0.005%,
0≤P<0.04%,
0≤Nb≤0.05%,
0≤B≤0.003%,
0≤Mo≤0.020%,
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 H2 and an inert gas with a dew point DP1 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% H2 by volume and an inert gas with a dew point DP3 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% H2 by volume and an inert gas with a dew point DP4 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.