Hot-formed previously welded steel part with very high mechanical resistance and production method

• US 10,919,117 B2
• Filed: 07/23/2012
• Issued: 02/16/2021
• Est. Priority Date: 07/26/2011
• Status: Active Grant

• Current Assignee: Arcelormittal Investigacion Y Desarrollo, S.l. (ArcelorMittal SA)
• Original Assignee: Arcelormittal Investigacion Y Desarrollo, S.l. (ArcelorMittal SA)
• Inventors: Cretteur, Laurent, Yin, Qingdong, Schmit, Francis, Ehling, Wolfram
• Primary Examiner(s): Schleis, Daniel J.
• Application Number:
  US14/235,420
• Publication Number:
  US 20150030382A1
• Time in Patent Office: 3,130 Days
• Field of Search: None
• CPC Class Codes: B23K 2101/34 Coated articles , e.g. plated or painted; Surface treated articles
• CPC Class Codes: B23K 2103/08 Non-ferrous metals or alloys
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 26/32 taking account of the properties of the material involved
• CPC Class Codes: B23K 26/60 Preliminary treatment
• CPC Class Codes: B23K 31/02 relating to soldering or welding dip or wave soldering in the manufacture of printed circuits H05K3/34
• CPC Class Codes: B23K 35/0261 Rods, electrodes, wires
• CPC Class Codes: B23K 35/3053 Fe as the principal constituent
• CPC Class Codes: B23K 35/3073 with Mn as next major constituent
• CPC Class Codes: B23K 35/383 mainly containing noble gases or nitrogen
• CPC Class Codes: B32B 15/012 one layer being formed of an iron alloy or steel, another layer being formed of aluminium or an aluminium alloy
• CPC Class Codes: C21D 1/673 for die quenching
• CPC Class Codes: C21D 2211/001 Austenite
• CPC Class Codes: C21D 2211/008 Martensite
• CPC Class Codes: C21D 2221/01 End parts (e.g. leading, trailing end)
• CPC Class Codes: C21D 2221/02 Edge parts
• CPC Class Codes: C21D 2251/02 Clad material
• CPC Class Codes: C21D 9/48 deep-drawing sheets
• CPC Class Codes: C21D 9/50 for welded joints
• CPC Class Codes: C21D 9/505 Cooling thereof
• CPC Class Codes: C22C 38/04 : containing manganese
• CPC Class Codes: C22C 38/18 : containing chromium
• CPC Class Codes: C23C 28/021 : including at least one metal alloy layer
• CPC Class Codes: C23C 28/023 : only coatings of metal elements only

Abstract

The invention relates principally to a welded steel part with a very high mechanical strength characteristics obtained by heating followed by hot forming, then cooling of at least one welded blank obtained by butt welding of at least one first and one second sheet consisting at least in part of a steel substrate and a pre-coating which is constituted by an intermetallic alloy layer in contact with the steel substrate, topped by a metal alloy layer of aluminum or aluminum-based alloy.

This welded steel part claimed by the invention is essentially characterized in that the metal alloy layer (19, 20) has been removed from the edges (36) in direct proximity to the weld metal zone (35), while the intermetallic alloy layer (17, 18) has been left in place, and in that over at least a portion of the length of the weld metal zone (35), the ratio between the carbon content of the weld metal zone (35) and the carbon content of the substrate (25, 26) of either the first or the second sheet (11, 12) having the higher carbon content (Cmax) is between 1.27 and 1.59.

The invention likewise relates to a method for the fabrication of a welded steel part as well as the use of this welded steel part for the fabrication of structural or safety parts for automotive vehicles.

Claims

1. A welded steel part obtained by heating in the austenitic range followed by hot forming, then cooling, of at least one welded blank obtained by a butt welding of at least a first and a second sheet comprising:

a steel substrate; and

a pre-coating including an intermetallic alloy layer and a metal alloy layer of an aluminum or aluminum-base alloy, the intermetallic alloy layer contacting the steel substrate, the metal alloy layer topping the intermetallic alloy layer;

a weld metal zone resulting from the welding operation and forming a bond between the first and second sheets;

the metal alloy layer being removed from edges peripheral to the weld metal zone while the intermetallic alloy layer remains;

over at least a portion of the weld metal zone, a ratio between a carbon content of the weld metal zone and a carbon content of the steel substrate of the first or second sheet having a higher carbon content Cmax, is between 1.27 and 1.59;

a composition of the steel substrate of at least the first or the second sheet, comprises the following elements, expressed in percent by weight;

0.10%≤

C≤

0.5%

0.5%≤

Mn≤

3%

0.1%≤

Si≤

1%

0.01%≤

Cr≤

1%

Ti≤

0.2%

Al≤

0.1%

S≤

0.05%

P≤

0.1%

0.0002%≤

B≤

0.010%,

the balance being iron and unavoidable impurities from processing.

2. The steel part as recited in claim 1, wherein the ratio between the hardness of the welded metal zone and the hardness of the substrate of one of the first or second sheets having a higher carbon content is greater than 1.029+(0.36 Cmax), whereby Cmax is expressed in percent by weight.

3. The steel part as recited in claim 1, wherein the composition of the steel substrate of at least the first or second sheet includes the following elements, expressed in percent by weight:

0.15%≤

C≤

0.4%

0.8%≤

Mn≤

2.3%

0.1%≤

Si≤

0.35%

0.1%≤

Cr≤

1%

Ti≤

0.1%

Al≤

0.1%

S≤

0.03%

P≤

0.05%

0.0005%≤

B≤

0.010%,

the balance being iron and unavoidable impurities from processing.

4. The steel part as recited in claim 1, wherein the composition of the steel substrate of at least the first or second sheet includes the following elements, expressed in percent by weight:

0.15%≤

C≤

0.25%

0.8%≤

Mn≤

1.8%

0.1%≤

Si≤

0.35%

0.01%≤

Cr≤

0.5%

Ti≤

0.1%

Al≤

0.1%

S≤

0.05%

P≤

0.1%

0.0002%≤

B≤

0.005%,

the balance being iron and unavoidable impurities from processing.

5. The steel part as recited in claim 1, wherein the carbon content of the weld metal zone is less than or equal to 0.35% by weight.

6. The steel part as recited in claim 1, wherein the metal alloy layer of the pre-coating includes, expressed in percent by weight, between 8 and 11% silicon and between 2 and 4% iron, the remainder of the metal ahoy layer composition consisting of aluminum and unavoidable impurities.

7. The steel part as recited claim 1, wherein a microstructure of the weld metal zone includes no ferrite.

8. The steel part as recited in claim 1, wherein a microstructure of the weld metal zone is martensitic.

9. The steel part as recited in claim 1, wherein hot forming of the welded blank is performed by a hot stamping operation.

10. The steel part as recited in claim 1, wherein the aluminum or aluminum alloy of the metal alloy layer is removed from respective cut edges of peripheral edges of the first and second sheets destined to undergo the welding operation.

11. The steel part as recited in claim 1, wherein the welded steel part includes a mechanical strength greater than 1230 MPa.