Method of producing a motor vehicle component from a high-strength steel alloy having ductile properties and motor vehicle component

Patent metadata

Field	Value
Publication number	US-2019366407-A1
Application number	US-201916425386-A
Country	US
Kind code	A1
Filing date	May 29, 2019
Priority date	May 30, 2018
Publication date	Dec 5, 2019
Grant date	—

Abstract

The present invention relates to a method of producing a motor vehicle component and to a motor vehicle component. Said motor vehicle component is produced by means of hot forming and press hardening. A blank is heated in a continuous furnace with supply of nitrogen. This produces a skin-decarburized layer on the blank that achieves ductility in a motor vehicle component produced with ultrahigh strength.

First claim

1 . A method of producing a motor vehicle component having a tensile strength Rm greater than 1700 MPa, the method comprising:
heating a blank of a hardenable carbon-containing steel alloy having a carbon content of not less than 0.3 percent by mass in a continuous furnace to a temperature not less than an AC3 temperature of the steel alloy, while supplying nitrogen to the continuous furnace under closed-loop control to establish an oxygen content of 0.5% to 15% by volume in a furnace atmosphere in the continuous furnace; removing the blank from the continuous furnace; and hot forming and press hardening the blank, in a hot forming and press hardening mold, into the motor vehicle component having a bending angle greater than 50°.

2 . The method as claimed in claim 1 , wherein, in the supplying nitrogen to the continuous furnace, the oxygen content is controlled to be between 0.5% and 10% by volume.

3 . The method as claimed in claim 1 , wherein, in the supplying nitrogen to the continuous furnace, a nitrogen volume flow rate has a value per hour between two and four times a furnace volume of the continuous furnace.

4 . The method as claimed in claim 1 , wherein, in the supplying nitrogen to the continuous furnace, the nitrogen, based on a spatial direction, is introduced into the continuous furnace above the blank being heated.

5 . The method as claimed in claim 1 , wherein the blank is a tailored blank.

6 . The method as claimed in claim 1 , wherein, in the heating of the blank, the blank is guided through the continuous furnace within a period of 2 to 10 min.

7 . The method as claimed in claim 1 , wherein, in the heating of the blank, a temperature is between 910 and 980° C. in the continuous furnace.

8 . The method as claimed in claim 1 , wherein the steel alloy includes iron, melting-related impurities, and alloy elements, the alloy elements including
0.3-0.4% by mass of C (carbon), 0.15-1% by mass of Si (silicon), 0.5-2% by mass of Mn (manganese), max 0.05% by mass of P (phosphorus), max 0.01% by mass of S (sulfur), max 0.01% by mass of N (nitrogen), 0.05-1% by mass of Cr (chromium), max 0.3% by mass of Ni (nickel), max 0.1% by mass of Cu (copper), max 0.5% by mass of Mo (molybdenum), max 0.1% by mass of Al (aluminum), 0.02-0.1% by mass of Nb (niobium), max 0.06% by mass of V (vanadium), max 0.1% by mass of Ti (titanium), and 0.001-0.01% by mass of B (boron).

9 . A motor vehicle component, comprising:
a hot-formed press-hardened steel alloy having a carbon content not less than 0.3% by mass, wherein the motor vehicle component has
a tensile strength Rm greater than 1700 MPa,
at a surface of the motor vehicle component, a skin-decarburized layer having a layer thickness of 10 to 70 μm, and
a bending angle greater than 50°.

10 . The motor vehicle component as claimed in claim 9 , further comprising:
a middle layer, wherein the skin-decarburized layer has a carbon content at or less than 50% of the carbon content in the middle layer.

11 . The method as claimed in claim 1 , further comprising:
cathodic dip painting causing the motor vehicle component to have a yield strength Rp0,2 greater than 1300 MPa.

12 . The method as claimed in claim 1 , wherein, in the supplying nitrogen to the continuous furnace, the oxygen content is controlled to be between 0.5% and 5% by volume.

13 . The method as claimed in claim 1 , wherein, in the supplying nitrogen to the continuous furnace, the oxygen content is controlled to be between 0.5% and 3% by volume.

14 . The method as claimed in claim 1 , wherein, in the supplying nitrogen to the continuous furnace, a nitrogen volume flow rate has a value per hour between 2.5 and 3.5 times a furnace volume of the continuous furnace.

15 . The method as claimed in claim 1 , wherein, in the supplying nitrogen to the continuous furnace, a nitrogen volume flow rate has a value per hour three times a furnace volume of the continuous furnace.

16 . The method as claimed in claim 1 , further comprising, after the hot forming and press hardening, coating the motor vehicle component.

17 . The method as claimed in claim 1 , wherein, in the heating of the blank, the blank is guided through the continuous furnace within a period of 120 to 360 sec.

18 . The method as claimed in claim 1 , wherein, in the heating of the blank, the temperature within the continuous furnace is more than 5% higher than the AC3 temperature of the steel alloy.

19 . The motor vehicle component as claimed in claim 9 , wherein the motor vehicle component has
the tensile strength Rm greater than 1900 MPa, the skin-decarburized layer having the layer thickness of 20 to 40 μm, and the bending angle greater than 60°.

20 . The motor vehicle component as claimed in claim 9 , wherein the steel alloy includes iron, melting-related impurities, and alloy elements, the alloy elements including
0.3-0.4% by mass of C (carbon), 0.15-1% by mass of Si (silicon), 0.5-2% by mass of Mn (manganese), max 0.05% by mass of P (phosphorus), max 0.01% by mass of S (sulfur), max 0.01% by mass of N (nitrogen), 0.05-1% by mass of Cr (chromium), max 0.3% by mass of Ni (nickel), max 0.1% by mass of Cu (copper), max 0.5% by mass of Mo (molybdenum), max 0.1% by mass of Al (aluminum), 0.02-0.1% by mass of Nb (niobium), max 0.06% by mass of V (vanadium), max 0.1% by mass of Ti (titanium), and 0.001-0.01% by mass of B (boron).

Assignees

• Benteler Automobiltechnik Gmbh

Inventors

• Holzweissig Martin
• Kettler Markus
• Bake Karsten
• Frost Georg
• Frehn Andreas

Classifications

• C22C38/44

  with molybdenum or tungsten · CPC title

• C22C38/02

  containing silicon · CPC title

• C21D1/76

  Adjusting the composition of the atmosphere · CPC title

• C22C38/50

  with titanium or zirconium · CPC title

• C22C38/42

  with copper · CPC title