Method of producing a phosphatable part from a sheet coated with an aluminum-based coating and a zinc coating

Patent metadata

Field	Value
Publication number	US-2018044774-A1
Application number	US-201615552135-A
Country	US
Kind code	A1
Filing date	Jan 22, 2016
Priority date	Feb 19, 2015
Publication date	Feb 15, 2018
Grant date	—

Abstract

A steel sheet coated with an aluminum-based coating and a second zinc coating having a thickness less than or equal to 1.1 μm is provided. A method for preparing the coated steel sheet, a method for preparing a press-hardened part from the steel sheet, a press-hardened part, and the use of the press-hardened part are also provided.

First claim

What is claimed is:

1 - 21 . (canceled)

22 . A steel sheet for press hardening comprising:
an aluminum-based coating; and a zinc coating having a thickness less than or equal to 1.1 μm.

23 . The steel sheet according to claim 22 , wherein the thickness of the zinc coating is less than or equal to 1.0 μm.

24 . The steel sheet according to claim 23 , wherein the thickness of the zinc coating is less than or equal to 0.7 μm.

25 . The steel sheet according to claim 22 , wherein the aluminum-based coating comprises up to 3% iron and from 9% to 12% silicon, a balance being aluminum.

26 . The steel sheet according to claim 22 , wherein the steel sheet is coated on at least one side with the aluminum-based coating having a thickness between 5 μm and 50 μm.

27 . The steel sheet according to claim 22 , wherein the aluminum-based coating is directly in contact with the zinc coating.

28 . The steel sheet according to claim 22 , wherein the product of a thickness of the aluminum-based coating and the thickness of the zinc coating is between 2 and 25.

29 . The steel sheet according to claim 22 , having a weight composition as follows:
0.20%≦C≦0.25%, 0.15%≦Si≦0.35%, 1.10%≦Mn≦1.40%, 0%≦Cr≦0.30%, 0%≦Mo≦0.35%, 0%≦P≦0.025%, 0%≦S≦0.005%, 0.020%≦Ti≦0.060%, 0.020%≦Al≦0.060%, and 0.002%≦B≦0.004%, a balance of the composition being iron and unavoidable impurities resulting from the process.

30 . The steel sheet according to claim 22 , having a weight composition as follows:
0.24%≦C≦0.38%, 0.40%≦Mn≦3%, 0.10%≦Si≦0.70%, 0.015%≦Al≦0.070%, 0%≦Cr≦2%, 0.25%≦Ni≦2%, 0.020%≦Ti≦0.10%, 0%≦Nb≦0.060%, 0.0005%≦B≦0.0040%, 0.003%≦N≦0.010%, 0.0001%≦S≦0.005%, and 0.0001%≦P≦0.025%, amounts of titanium and nitrogen satisfying Ti/N>3.42, and amounts of carbon, manganese, chrome, and silicon satisfying

2.6

C

+

Mn
5.3

+

Cr
13

+

Si
15

≥

1.1



%

,

a balance of the composition being iron and unavoidable impurities resulting from the process.

31 . The steel sheet according to claim 30 , further comprising one or more of the following elements by weight:
0.05%≦Mo≦0.65%, 0.001%≦W≦0.30%, and 0.0005%≦Ca≦0.005%.

32 . A method for preparing a steel sheet according to any of claim 22 , wherein the zinc coating is performed by cementation, by electroplating, or by sonic jet vapor deposition under vacuum.

33 . The method according to claim 32 wherein when the zinc coating is deposited by cementation or electroplating, said zinc coating being directly deposited on the aluminum-based coating.

34 . The method according to claim 33 , wherein the zinc coating deposited by cementation is carried out by immersion or by spraying.

35 . The method according to claim 33 , wherein when the zinc coating is deposited under vacuum by sonic jet vapor, a thin layer of stainless steel is deposited between the aluminum-based coating and the zinc coating.

36 . A method for preparing a press-hardened part coated with a phosphatable coating comprising the sequential steps of:
A) providing a steel sheet for press-hardening according to claim 22 ; B) cutting the sheet obtained in step A) to obtain a blank; then C) heating the blank at a temperature T 1 in a range from 840° C. to 950° C. to obtain a completely austenitic structure in the steel; D) transferring the blank to a press; E) hot-pressing the blank to obtain a part; F) cooling the part obtained in step E) to obtain a martensitic or a martensitic-bainitic structure in the steel composed of at least 75%≦equiaxed iron, an amount of martensite greater than or equal to 5% and less than or equal to 20%, an amount of bainite less than or equal to 10%.

37 . The method according to claim 36 , wherein step C) is implemented for a time t 1 from 3 to 12 minutes in an inert atmosphere or an atmosphere comprising air.

38 . The method according to claim 36 , wherein during step E), hot-pressing is carried out at a temperature T 2 ranging from 600° C. to 830° C.

39 . A hardened part capable of being obtained by a method according to claim 36 , comprising:
a ZnO layer; and a phosphate crystal layer on the ZnO layer obtained after an additional phosphatation step G).

40 . The hardened part according to claim 39 , wherein a degree of phosphate crystal coverage on the surface of the part is greater than or equal to 90%.

41 . The hardened part according to claim 40 , wherein the degree of phosphate crystal coverage on the surface of the part is greater than or equal to 99%.

42 . The hardened part according to claim 39 , further comprising a cataphoresis layer on the phosphate crystal layer.

43 . A motor vehicle comprising:
a press-hardened part according to claim 39 .

44 . A method of manufacturing motor vehicle parts comprising:
preparing a press hardened part according to claim 36 .

Assignees

• Arcelormittal

Inventors

• Allely Christian
• Jacqueson Eric
• Chaleix Daniel

Classifications

• C25D5/52

  by brightening or burnishing · CPC title

• C21D9/46

  for sheet metals · CPC title

• C21D2211/008

  Martensite · CPC title

• C25D13/20

  Pretreatment · CPC title

• C21D8/0221

  characterised by the working steps · CPC title