Galvannealed steel sheet

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 T 1 between 700 and 900° C. in the heating section having an atmosphere A 1 including from 0.1 to 15% by volume of H 2 and an inert gas with a dew point DP 1 between −18° C. and +8° C.,

ii. soaking the steel sheet from T 1 to a temperature T 2 between 700 and 900° C. in the soaking section having an atmosphere A 2 identical to A 1 with a dew point DP 2 equal to DP 1 , and

iii. cooling the steel sheet from T 2 to T 3 between 400 and 700° C. in the cooling section having an atmosphere A 3 including from 1 to 30% H 2 by volume and an inert gas with a dew point DP 3 below or equal to −30° C., and

iv. optionally, equalizing the steel sheet from a temperature T 3 to a temperature T 4 between 400 and 700° C. in the equalizing section having an atmosphere A 4 including from 1 to 30% H 2 by volume and an inert gas with a dew point DP 4 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 T 5 between 460 and 600° C. during a time t 5 between 1 and 45 seconds.

2. The method as recited in claim 1 wherein in step A), the steel sheet includes less than 0.30% by weight of Si.

3. The method as recited in claim 1 wherein in step A), the steel sheet includes above 0.0001% by weight of V.

4. The method as recited in claim 1 wherein in steps B.i) and B.ii), A 1 includes between 1 and 10% by volume of H 2 .

5. The method as recited in claim 1 wherein in steps B.i) and B.ii), DP 1 is between −15° C. and +5° C.

6. The method as recited in claim 1 wherein in step B.ii), T 2 is equal to T 1 .

7. The method as recited in claim 1 wherein in steps B.i) and B.ii), T 1 and T 2 are between 750 and 850° C.

8. The method as recited in claim 1 wherein in steps B.iii) and the optional sub-step B.iv), A 3 is identical to A 4 , DP 4 being equal to DP 3 .

9. The method as recited in claim 1 wherein in steps B.i), B.ii) and B.iii) and the optional sub-step B.iv), the inert gas is chosen from the group consisting of: N 2 , Ar, He and Xe.

10. The method as recited in claim 1 wherein the zinc-based coating includes between 0.01 and 0.4% by weight of Al, the balance being Zn.

11. The method as recited in claim 1 wherein in step D), T 5 is between 470 and 570° C.

12. The method as recited in claim 1 wherein in step D), t 5 is between 1 and 35 seconds.

13. The method as recited in claim 1 wherein the chemical composition of the steel does not include Bismuth (Bi).

14. The method as recited in claim 1 wherein the equalizing sub-step is performed.

15. The method as recited in claim 1 , wherein the galvannealed steel sheet has a microstructure comprising bainite, martensite and ferrite.

16. The method as recited in claim 15 , wherein the galvannealed steel sheet has a microstructure comprising from 1 to 45% of martensite, from 1 to 60% of bainite, the balance being austenite.

17. The method as recited in claim 1 , wherein wherein the galvannealed steel sheet has a microstructure comprising from 1 to 25% of fresh martensite, from 1 to 10% of ferrite, from 35 to 95% of martensite and lower bainite and less than 10% of austenite.

18. The method as recited in claim 1 , wherein the steel sheet comprises a Dual Phase steel having a ferritic-martensitic microstructure.

19. A method for manufacturing part of an automotive vehicle comprising the method for manufacturing a galvannealed steel sheet as recited in claim 1 .