Method for the manufacture of a galvannealed steel sheet

Patent metadata

Field	Value
Publication number	US-2020283868-A1
Application number	US-201816754589-A
Country	US
Kind code	A1
Filing date	Oct 19, 2018
Priority date	Oct 24, 2017
Publication date	Sep 10, 2020
Grant date	—

Abstract

Method for the manufacture of a galvannealed steel sheet includes the following steps: A) the provision of a pre-coated steel sheet coated with a first coating comprising iron and nickel, such steel sheet having the following chemical composition in weight percent 0.10<C<0.40%, 1.5<Mn<3.0%, 0.7<Si<2.0%, 0.05<Al<1.0%, 0.75<(Si+Al)<3.0% and on a purely optional basis, one or more elements such as Nb≤0.5%, B≤0.005%, Cr≤1.0%, Mo≤0.50%, Ni≤1.0%, Ti≤0.5%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, B) the thermal treatment of such pre-coated steel sheet at a temperature between 600 to 1000° C., C) the hot-dip coating of the steel sheet obtained in step B) with a second coating based on zinc and D) an alloying treatment to form a galvannealed steel sheet.

First claim

What is claimed is:

1 - 31 . (canceled)

32 : A method for the manufacture of a galvannealed steel sheet comprising the following steps:
providing a pre-coated steel sheet coated with a first coating comprising iron and nickel, such steel sheet having the following chemical composition in weight percent:
0.10<C<0.40%,
1.5<Mn<3.0%,
0.7<Si<2.0%,
0.05<Al<1.0%
0.75<(Si+Al)<3.0%
and on a purely optional basis, one or more elements such as
Nb≤0.5%,
B≤0.005%,
Cr≤1.0%,
Mo≤0.50%,
Ni≤1.0%,
Ti≤0.5%,

a remainder of the composition making up of iron and inevitable impurities resulting from processing;
thermally treating the pre-coated steel sheet at a temperature between 600 to 1000° C.;
hot-dip coating of the steel sheet obtained by the thermally treating step with a second coating based on zinc; and
providing an alloying treatment to form a galvannealed steel sheet.

33 : The method as recited in claim 32 wherein the first coating includes from 10% to 75% by weight of iron.

34 : The method as recited in claim 33 wherein the first coating includes from 25.0 to 65.0% by weight of iron.

35 : The method as recited in claim 34 wherein the first coating includes from 40 to 60% of weight of iron.

36 : The method as recited in claim 32 wherein the first coating includes from 25 to 90% by weight of nickel.

37 : The method as recited in claim 36 wherein the first coating includes comprises from 35 to 75% by weight of nickel.

38 : The method as recited in claim 37 wherein the first coating includes from 40 to 60% by weight of nickel.

39 : The method as recited in claim 32 wherein the first coating consists of iron and nickel.

40 : The method as recited in claim 32 wherein the first coating has a thickness equal or above 0.5 μm.

41 : The method as recited in claim 40 wherein the first coating has a thickness between 0.8 and 5.0 μm.

42 : The method as recited in claim 41 wherein the first coating has a thickness between 1.0 and 2.0 μm.

43 : The method as recited in claim 32 wherein the second coating includes above 70% of zinc.

44 : The method as recited in claim 43 wherein the second coating includes above 80% of zinc.

45 : The method as recited in claim 44 wherein the second coating includes above 85% of zinc.

46 : The method as recited in claim 32 wherein the second coating consists of zinc.

47 : The method as recited in claim 32 wherein the thermally treating step is a continuous annealing.

48 : The method as recited in claim 32 wherein the thermally treating step is performed in an atmosphere comprising from 1 to 10% of H 2 at a dew point between −30 and −60° C.

49 : The method as recited in claim 32 wherein the alloying treatment is performed by heating the coated steel sheet obtained after the thermally treating step at a temperature between 460 and 550° C.

50 : A galvannealed steel sheet obtainable from the method as recited in claim 32 , the galvannealed steel sheet comprising: a steel substrate coated with a first layer comprising iron and nickel directly topped by a second layer based on zinc, the first and second layers being alloyed through diffusion such that the second alloy layer includes from 5 to 15 wt. % of iron, from 0 to 15 wt. % of nickel, a balance being zinc.

51 : The galvannealed steel sheet as recited in claim 50 wherein the second alloy layer includes from 1 to 15% by weight of nickel.

52 : The galvannealed steel sheet as recited in claim 50 wherein a microstructure of the steel substrate includes from 1 to 50% of residual austenite, from 1 to 60% of martensite and optionally at least one element chosen from: bainite, ferrite, cementite and pearlite.

53 : The galvannealed steel sheet as recited in claim 52 wherein the microstructure includes from 5 to 25% of residual austenite.

54 : The galvannealed steel sheet as recited in claim 52 wherein the microstructure includes from 1 to 60% of tempered martensite.

55 : The galvannealed steel sheet as recited in claim 52 wherein the microstructure includes from 10 to 40% of bainite.

56 : The galvannealed steel sheet as recited in claim 52 wherein the microstructure includes from 1 to 25% of ferrite.

57 : The galvannealed steel sheet as recited in claim 52 wherein the microstructure includes from 1 to 15% of untempered martensite.

58 : A spot welded joint comprising:
at least two metal sheets including a first metal sheet being the galvannealed steel sheet as recited in claim 50 , the joint containing less than 3 cracks having a size above 100 μm and wherein the longest crack has a length below 400 μm.

59 : The spot welded joint as recited in claim 58 wherein a second metal sheet of the metal sheets is a steel sheet or an aluminum sheet.

60 : The spot welded joint as recited in claim 58 wherein a second metal sheet of the metal sheets is a galvannealed steel sheet including a second steel substrate coated with a further first layer comprising iron and nickel directly topped by a further second layer based on zinc, the further first and further second layers being alloyed through diffusion such that the further second alloy layer includes from 5 to 15 wt. % of iron, from 0 to 15 wt. % of nickel, a balance being zinc.

61 : The spot welded joint as recited in claim 58 wherein the at least two metals sheets include a third metal sheet being a steel sheet or an aluminum sheet.

62 : A spot welded joint comprising:
at least two metal sheets including a first metal sheet being a steel sheet obtained from the method as recited in claim 32 , the joint containing less than 3 cracks having a size above 100 μm and wherein the longest crack has a length below 400 μm.

63 : An automotive vehicle part comprising the steel sheet as recited in claim 50 .

64 : An automotive vehicle part comprising a steel sheet obtained by the method as recited in claim 32 .

Assignees

• Arcelormittal

Inventors

• Chakraborty Anirban
• Ghassemi-Armaki Hassan

Classifications

• C23C2/06 Primary

  Zinc or cadmium or alloys based thereon · CPC title

• C23C2/0224

  Two or more thermal pretreatments · CPC title

• C21D1/76

  Adjusting the composition of the atmosphere · CPC title

• C23C2/29

  Cooling or quenching · CPC title

• C21D9/46 Primary

  for sheet metals · CPC title