Process for manufacturing iron-carbon-maganese austenitic steel sheet with excellent resistance to delayed cracking

Patent metadata

Field	Value
Publication number	US-10006099-B2
Application number	US-201514858276-A
Country	US
Kind code	B2
Filing date	Sep 18, 2015
Priority date	Jul 11, 2006
Publication date	Jun 26, 2018
Grant date	Jun 26, 2018

Abstract

A process for fabricating a steel sheet is provided. The process includes soaking a steel sheet. The steel has a composition including iron, carbon, manganese, silicon, aluminum, sulfur, phosphorus and nitrogen and at least one metallic element X chosen among vanadium, titanium, niobium, molybdenum, and chromium. A quantity X p of metallic element under the form of carbides, nitrides or carbonitrides is, by weight:

0.030%≤V p ≤0.40%;

0.030%≤Ti p ≤0.50%;

0.040%≤Nb p ≤0.40%;

0.14%≤Mo p ≤0.44%; or

0.070%≤Cr p ≤0.6%.

The soaking step occurs under a pure nitrogen or argon atmosphere with a dew point lower than −30° C. at a soaking temperature θ between 250 and 900° C. and with a dynamic circulation of a regenerated atmosphere.

First claim

What is claimed is:

1. A process for fabricating a steel sheet, comprising:
soaking a steel sheet, comprising a steel with a composition comprising Fe, and by weight:
0.35%≤C≤1.05%;

15%≤Mn≤26%;

Si≤3%;

Al≤0.050%;

S≤0.030%;

P≤0.080%;

N≤0.1%;

at least one metallic element X chosen among vanadium, titanium, niobium, molybdenum, and chromium, in a percentage as follows:
0.050%≤V≤0.50%,

0.040%≤Ti≤0.50%,

0.070%≤Nb≤0.50%,

0.14%≤Mo≤2%; and

0.070%≤Cr≤2%;

wherein a quantity X p of metallic element under the form of carbides, nitrides or carbonitrides is, by weight:
0.030%≤V p ≤0.40%

0.030%≤Ti p ≤0.50%

0.040%≤Nb p ≤0.40%

0.14%≤Mo p ≤0.44%

0.070%≤Cr p ≤0.6%,

under a pure nitrogen or argon atmosphere with a dew point lower than −30° C. at a soaking temperature θ comprised between 250 and 900° C., with a dynamic circulation of a regenerated atmosphere and wherein the soaking temperature θ is below a recrystallization temperature.

2. The process of claim 1 , wherein the steel sheet comprises a Zn or Zn—Y alloy coating, wherein element Y is at least one element selected from the group consisting of consisting of Ni, Cr, and Mg and wherein the temperature and time of the soaking satisfy θ(° C.)Ln(t(s))≥2200.

3. The process of claim 2 , wherein θ (° C.)Ln(t(s))≥2450.

4. The process of claim 2 , wherein θ (° C.)Ln(t(s))≥2750.

5. The process of claim 1 , wherein the soaking is performed by continuous annealing.

6. The process of claim 1 , wherein the soaking is performed by batch annealing.

7. The process of claim 6 , wherein the soaking is performed by open coil annealing.

8. The process of claim 1 , wherein the soaking is performed by induction heating.

9. The process of claim 6 , wherein the soaking is performed with transversal electromagnetic field.

10. The process of claim 1 , further comprising the step of:
cold forming the steel sheet to obtain a part,
the soaking step being performed before or after the cold forming step.

11. The process of claim 1 , wherein the steel includes 0.70%<C≤1.05%.

12. The process of claim 1 , wherein the steel includes 0.35%≤C<0.50%.

13. The process of claim 1 , wherein the steel includes boron.

14. The process of claim 1 , wherein the steel comprises hydrogen and the sheet has a hydrogen content, H max , designating the maximal hydrogen content that can be measured from a series of at least five specimens, and a quantity X p , by weight, such that:

1000
⁢

H
max

X
p

≤

3.3
.

15. The process of claim 1 , wherein the steel comprises hydrogen and the sheet has a hydrogen content, H max , designating the maximal hydrogen content that can be measured from a series of at least five specimens, and a quantity X p , by weight, such that:

1000
⁢

H
max

X
p

≤

2.5
.

16. The process of claim 14 , wherein

2.5
≤

1000
⁢

H
max

X
p

≤

3.3
.

17. The process of claim 1 , further comprising at least one element selected from the group consisting of boron, nickel, and copper, in a percentage as follows:
0.0005%≤B≤0.010%;

Ni≤2%; and

Cu≤5%.

Assignees

• Arcelormittal
• Thyssenkrupp Steel Europe Ag

Inventors

• Scott Colin
• Cugy Philippe
• Allely Christian

Classifications

• C21D8/02 Primary

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C21D6/001

  containing Ni (C21D6/004 takes precedence) · CPC title

• C22C38/08

  containing nickel {(C22C38/105 takes precedence)} · CPC title

• C21D6/004

  containing Cr and Ni · CPC title

• C23C28/021

  including at least one metal alloy layer · CPC title