Method for coating steel sheets or steel strips and method for producing press-hardened components therefrom

Patent metadata

Field	Value
Publication number	US-2020232057-A1
Application number	US-201816487004-A
Country	US
Kind code	A1
Filing date	Feb 14, 2018
Priority date	Feb 21, 2017
Publication date	Jul 23, 2020
Grant date	—

Abstract

The invention relates to a method for coating a steel sheet or steel strip to which an aluminium-based coating is applied in a dip-coating process and the surface of the coating is freed of a naturally occurring aluminium oxide layer. In order to provide a low-cost method for coating steel sheets or steel strips that makes the steel sheets or steel strips outstandingly suitable for the production of components by means of press hardening and for the further processing thereof, it is proposed that transition metals or transition metal compounds are subsequently deposited on the freed surface of the coating to form a top layer. The invention also relates to a method for producing press-hardened components from the aforementioned steel sheets or steel strips with an aluminium-based coating.

First claim

What is claimed is:

1 .- 21 . (canceled)

22 . A method for coating a steel sheet or steel strip, comprising:
applying an aluminium-based coat on the steel sheet or steel strip in a hot-dipping process; freeing a surface of the aluminium-based coat of a naturally occurring aluminium oxide layer; depositing transition metals or transition metal compounds on the freed surface of the coat to thereby form a top layer as a planar deposit with a layer weight, based on iron, in a range of 7 to 25 mg/m 2 .

23 . The method of claim 22 , wherein the layer weight is 10 to 15 mg/m 2 .

24 . The method of claim 22 , wherein the transition metals or transition metal compounds comprise at least a chemical element selected from the group consisting of titanium, vanadium, chromium, manganese, iron, and compounds thereof.

25 . The method of claim 22 , wherein the transition metals or the transition metal compounds comprise predominantly or almost completely iron or compounds thereof.

26 . The method of claim 22 , wherein the transition metals or the transition metal compounds are deposited in the presence of at least one further chemical element selected from the group consisting of cobalt, molybdenum, tungsten, and compounds thereof.

27 . The method of claim 22 , wherein the transition metals or the transition metal compounds are deposited by chemical deposition.

28 . The method of claim 27 , wherein the chemical deposition includes spraying, dipping or rolling application.

29 . The method of claim 27 , further comprising removing atmospherically occurring, natural oxide layer and the chemical deposition in a single process step.

30 . The method of claim 29 , wherein the removal of the atmospherically occurring, natural oxide layer and the chemical deposition are performed in a continuously operating coating installation which is located downstream of a hot-dip coating installation or is separate from the hot-dip coating installation.

31 . The method of claim 22 , wherein the transition metals or the transition metal compounds are deposited electrolytically.

32 . The method of claim 31 , wherein the transition metals or transition metal compounds are applied electrolytically in an aqueous medium as an electrolyte at an electrolyte temperature of 25° C. to 85° C., at current densities between 0.05 and 150 A/dm 2 .

33 . The method of claim 22 , wherein an aluminium oxide layer with mixed oxides from the top layer is formed on the coat with the top layer when exposed to an oxygen atmosphere or when exposed to steam.

34 . The method of claim 33 , wherein the aluminium oxide layer is formed with the mixed oxides in a furnace at a temperature >750° C., preferably 850 to 950° C., and a furnace dwell time >90 s, preferably 120 to 180 s.

35 . The method of claim 33 , wherein self-limitation of a layer growth of the aluminium oxide is avoided by formation of the mixed oxides.

36 . The method of claim 33 , wherein corundum, eskolaite, haematite, karelianite, tistarite, ilmenite, perowskite and/or spinels are formed as the mixed oxides.

37 . The method of claim 22 , wherein the aluminium-based coat includes aluminium, aluminium-silicon (AS) or aluminium-zinc-silicon (AZ) with optional incorporation of an additional element selected from the group consisting of. magnesium, manganese, titanium, and rare earth.

38 . A method for producing a press-hardened component from a steel sheet or steel strip, comprising:
applying an aluminium-based coat on the steel sheet or steel strip in a hot-dipping process, with a surface of the aluminium-based coat being freed of a naturally occurring aluminium oxide layer and transition metals or transition metal compounds being deposited on the freed surface of the coat in order to form a top layer as a planar deposit with a layer weight, based on iron, in a range of 7 to 25 mg/m 2 ; heating at least a region of the steel sheet or steel strip to a temperature above Ac3; forming the steel sheet or steel strip at said temperature; cooling the steel sheet or steel strip such as to harden at least a region of the steel sheet or steel strip at a rate which is above a critical cooling rate.

39 . The method of claim 38 , wherein the steel sheet or steel strip is made of a steel which is hardenable by heat treatment.

40 . The method of claim 39 , wherein the steel is alloyed with manganese and boron.

41 . The method of claim 40 , wherein the steel is a 22MnB5 steel.

Assignees

• Salzgitter Flachstahl Gmbh

Inventors

• Beier Frank
• Körner Kerstin
• Debeaux Marc

Classifications

• C21D1/06 Primary

  Surface hardening · CPC title

• C25D5/48

  After-treatment of electroplated surfaces · CPC title

• C21D1/673

  for die quenching · CPC title

• C25D5/44

  Aluminium · CPC title

• C25D5/50

  by heat-treatment · CPC title