Method for producing a precoated steel sheet and associated sheet

Patent metadata

Field	Value
Publication number	US-11786993-B2
Application number	US-201816757451-A
Country	US
Kind code	B2
Filing date	Oct 19, 2018
Priority date	Oct 20, 2017
Publication date	Oct 17, 2023
Grant date	Oct 17, 2023

Abstract

A method for producing a precoated steel sheet (1) includes providing a precoated steel strip comprising a steel substrate (3) having, on at least one of its main faces, a precoating comprising an intermetallic alloy layer and a metallic alloy layer. The metallic alloy layer is a layer of aluminum, a layer of aluminum alloy or a layer of aluminum-based alloy. The method also includes laser cutting said precoated steel strip so as to obtain at least one precoated steel sheet (1) comprising a cut edge surface (13) resulting from the cutting operation. The cut edge surface (13) includes a substrate region (14) and a precoating region (15) and the thickness of the precoated steel sheet (1) is comprised between 0.8 mm and 5 mm. The laser cutting is carried out such that it results directly in a corrosion-improved zone (19) of the cut edge surface (13). The surface fraction of aluminum on the substrate region (14) of the corrosion-improved zone (19) is greater than or equal to 9% and the surface fraction of aluminum on the bottom half of the substrate region (14) of the corrosion-improved zone (19) is greater than or equal to 0.5%.

First claim

What is claimed is:

1. A method for producing a precoated steel sheet comprising the successive steps of:
providing a precoated steel strip comprising a steel substrate having, on at least one main face thereof, a precoating, the precoating comprising an intermetallic alloy layer and a metallic alloy layer extending atop the intermetallic alloy layer, the metallic alloy layer being a layer of aluminum, a layer of aluminum alloy or a layer of aluminum-based alloy;
laser cutting the precoated steel strip so as to obtain at least one precoated steel sheet, the precoated steel sheet comprising a cut edge surface resulting from the cutting operation, the cut edge surface comprising a substrate region and a precoating region and a thickness of the precoated steel sheet being between 0.8 mm and 5 mm, the cut edge surface further comprising solidification striations,
the laser cutting being carried out such that the laser cutting results directly in a corrosion-improved zone of the cut edge surface, extending over an entire height of the cut edge surface and over a length smaller than or equal to a length of the cut edge surface, a surface fraction of aluminum on the substrate region of the corrosion-improved zone of the cut edge surface directly resulting from the laser cutting operation being greater than or equal to 9% and a surface fraction of aluminum on a bottom half of the substrate region of the corrosion-improved zone of the cut edge surface directly resulting from the laser cutting operation being greater than or equal to 0.5%.

2. The method according to claim 1 , wherein the laser cutting is carried out such that, in the corrosion-improved zone of the cut edge surface, the surface fraction of aluminum on the substrate region directly resulting from the laser cutting operation is between 9% and 70%.

3. The method according to claim 1 , wherein the laser cutting step is performed using an inert gas as an assist gas.

4. The method according to claim 3 , wherein the assist gas is chosen among argon, helium, nitrogen and mixtures of these gases.

5. The method according to claim 3 , wherein the laser cutting step is performed using a CO 2 laser.

6. The method according to claim 5 , wherein, in order to obtain the corrosion-improved zone, the laser cutting is performed using a laser cutting linear energy E between 0.18 kJ/cm and 0.29 kJ/cm and an assist gas pressure P between P min =54.5×E−7.8 bars and P max , whereby P max is equal to 14 bars for E≤0.24 KJ/cm and P max is equal to −80×E+33.2 bars for E>0.24 KJ/cm.

7. The method according to claim 1 , wherein the laser cutting step is performed using a solid state laser.

8. The method according to claim 7 , wherein the solid state laser is an Nd:YAG laser, a fiber laser, a disk laser or a diode laser.

9. The method according to claim 7 , wherein, in order to obtain the corrosion-improved zone, the laser cutting is performed using a laser cutting linear energy E between 0.08 kJ/cm and 0.34 kJ/cm and an assist gas pressure P between P min and P max , whereby P min =64.3×E−3.9 bars when E>0.2 KJ/cm and P min =9 bars when E≤ 0.2 KJ/cm and P max is equal to 28.6×E+8.3 bars.

10. The method according to claim 1 , wherein the laser cutting is carried out such that the surface fraction of aluminum directly resulting from the laser cutting operation on the bottom half of the substrate region of the cut edge surface is greater than or equal to 1.5%.

11. The method according to claim 10 , wherein, in order to obtain the corrosion-improved zone, the laser cutting is performed using a CO 2 laser and using a laser cutting linear energy E between 0.18 kJ/cm and 0.29 kJ/cm and an assist gas pressure P between P min =72.7×E−11.1 bars and P max , whereby P max is equal to 14 bars for E≤0.24 KJ/cm and P max is equal to −80×E+33.2 bars for E>0.24 KJ/cm.

12. The method according to claim 10 , wherein the laser cutting is further carried out such that, in the corrosion-improved zone, a ratio of the surface fraction of aluminum on the substrate region divided by the surface fraction of aluminum in the bottom half of the substrate region is smaller than or equal to 5.5 and the surface fraction of aluminum on the substrate region of the cut edge surface of the precoated steel sheet directly resulting from the laser cutting operation is greater than or equal to 11%.

13. The method according to claim 12 , wherein, in order to obtain the corrosion-improved zone, the laser cutting is performed using a CO 2 laser and a laser cutting linear energy E between 0.18 kJ/cm and 0.24 kJ/cm and an assist gas pressure between P min =200×E−34 bars and P max =14 bars.

14. The method according to claim 1 , wherein the thickness of the precoated steel sheet is between 1.0 mm and 1.8 mm.

15. The method according to claim 14 , wherein the thickness of the precoated steel sheet is between 1.0 and 1.5 mm.

16. The method according to claim 1 , wherein the corrosion-improved zone forms a first section of the cut edge surface extending over only a fraction of the length of the cut edge surface and wherein the laser cutting is further carried out such that, in a second section of the cut edge surface, extending over the entire height of the cut edge surface and over only a fraction of the length of the cut edge surface, the surface fraction of aluminum on the substrate region directly resulting from the laser cutting operation is between 0.3% and 6%.

17. The method according to claim 16 , wherein, in order to obtain the second section of the cut edge surface, laser cutting is performed over the second section using a laser cutting linear energy greater than or equal to 0.6 kJ/cm.

18. The method according to claim 17 , wherein the pressure of the assist gas is between 2 and 18 bars.

19. A method for manufacturing a welded blank, comprising the steps of:
producing a first and a second precoated steel sheet, at least one among the first and the second precoated steel sheets being produced using the method according to claim 16 ; and
butt welding the first and the second steel precoated steel sheets so as to create a weld joint between the first and second precoated steel sheets and thus obtain a welded blank, the butt welding step including arranging the first and second precoated steel sheets in such a manner that the second section of at least one of the precoated steel sheets faces an edge.

20. The method according to claim 19 , wherein the welding is a laser welding operation.

21. The method according to claim 19 , further comprising, prior to the butt welding step, a step of removing, for each of the first and second steel sheets, the metallic alloy layer in a removal zone adjacent to the second section of the respective precoated steel sheet and wherein, during the butt welding step, the precoated steel sheets are welded at their edges where the metallic alloy layer has been removed.

22. The method according to claim 21 , wherein the removing of the metallic alloy layer is performed using a laser beam.

23. The method according to claim 21 , wherein, during the removing step, the intermetallic alloy layer is left in the removal zone over at least a portion of a height of the intermetallic alloy layer.

24. The method according to claim 19 , wherein the welding is performed using a filler wire or a powder addition.

25. The method according to claim 24 , wherein the filler wire or powder contains austenite-forming alloying ele

Assignees

• Arcelormittal

Inventors

• Schmit Francis
• Bernardi Quentin

Classifications

• B23K26/322 Primary

  involving coated metal parts (using absorbing layers on the workpiece B23K26/18) · CPC title

• B23K26/362

  Laser etching · CPC title

• B23K26/40

  taking account of the properties of the material involved · CPC title

• B32B15/012

  one layer being formed of an iron alloy or steel, another layer being formed of aluminium or an aluminium alloy · CPC title

• C21D9/50

  for welded joints · CPC title