Motor vehicle component and a method of manufacturing thereof

Abstract

A motor vehicle component and a method of manufacturing thereof is disclosed having at least regionally high-strength and at the same time ductile properties, including providing a sheet metal blank composed of a hardenable steel alloy with at least 0.25% carbon fraction, at least partially heating the sheet metal blank to above austenitizing temperature, in less than 20 seconds, hot-forming and press-hardening the sheet metal blank, in the process, setting a tensile strength Rm of greater than 1800 MPa and an elongation at break A20 of greater than 6%.

Claims

1. A method of manufacturing a motor vehicle component, the method comprising: providing a sheet metal blank comprising a hardenable steel alloy with greater than 0.35% carbon fraction in weight; heating the sheet metal blank at a heating rate greater than 100° C./s at least partially to above austenitizing temperature; holding, during the heating, the sheet metal blank at the heating temperature; transferring from the heating into a hot-forming and press-hardening tool; and hot-forming and press-hardening the sheet metal blank in the hot forming and press-hardening tool to obtain the motor vehicle component having an elongation at break A20 of greater than 6%, wherein the press-hardening is performed to obtain the motor vehicle component having a tensile strength Rm of greater than 1900 MPa, and the heating, holding, and transferring are performed in less than 30 seconds.

2. The method of claim 1, wherein said press-hardening is performed to obtain the motor vehicle component having the tensile strength Rm of greater than 2000 MPa.

3. The method of claim 1, wherein said press-hardening is performed to obtain the motor vehicle component having an elongation at break A20 of greater than 8%.

4. The method of claim 1, wherein the heating is performed in less than 10 seconds.

5. The method of claim 1, wherein, in the heating, the holding time of the heated sheet metal blank at the heating temperature is less than 20 seconds.

6. The method of claim 5, wherein the transferring time from the heating into the hot-forming and press-hardening tool is in less than 10 seconds.

7. The method of claim 1, wherein a martensitic material microstructure with 5.0% to 20.0% bainite in weight is achieved in the motor vehicle component during the press hardening.

8. The method of claim 1, wherein the heating is contact heating.

9. The method of claim 1, wherein the heating comprises heating the sheet metal blank completely.

10. The method of claim 9, wherein the press-hardening comprises hardening the motor vehicle component only in regions where anticipated loads are high.

11. The method of claim 10, further comprising at least partial thermal after-treatment of the motor vehicle component.

12. The method of claim 1, further comprising preforming the sheet metal blank before the heating.

13. The method of claim 12, wherein the sheet metal blank is multi-ply having a centrally located ply comprising the hardenable steel alloy, and two outer plies comprising a stainless steel alloy.

14. The method of claim 1, wherein said press-hardening is performed to obtain the motor vehicle component having an elongation at break A20 of greater than 10%.

15. The method of claim 1, wherein, in said heating, a first region of the sheet metal blank is heated to a temperature higher than the austenitizing temperature, and a second region of the sheet metal blank is not heated, or is heated to a temperature lower than the austenitizing temperature.

16. A method of manufacturing a motor vehicle component, the method comprising: providing a sheet metal blank comprising a hardenable steel alloy with at least 0.25% carbon fraction in weight; heating the sheet metal blank at least partially to above austenitizing temperature; hot-forming and press-hardening the sheet metal blank to obtain the motor vehicle component having an elongation at break A20 of greater than 6%; and edge decarburizing the motor vehicle component after it is manufactured.

17. The method of claim 16, wherein the edge decarburizing is performed in an edge zone at 5 to 150 μm, measured from a surface of the motor vehicle component.

18. A motor vehicle component manufactured using the method of claim 1, wherein the motor vehicle component has the tensile strength Rm of greater than 1900 MPa and the elongation at break A20 of greater than 6%, and the motor vehicle component comprises the hardenable steel alloy having the carbon fraction of greater than 0.35% in weight and has a substantially martensitic material microstructure with a bainite fraction of 5.0% to 20.0% in weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic representation of a manufacturing line for manufacturing the vehicle component in accordance with one embodiment;

(3) FIG. 2 is a sectional view of a multi-ply sheet metal blank; and,

(4) FIG. 3 is a graph representation of time versus temperature illustrating the heat-up phase, the hold phase, and the press-hardening phase.

(5) In the figures, the same reference designations are used for identical or similar components, even if a repeated description is omitted for reasons of simplicity.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

(6) FIG. 1 illustrates a manufacturing line 1 where, as the first step, a sheet metal blank 2 is provided to be inserted into a contact heating station 4. The sheet metal blank is at least partially heated to above austenitizing temperature. Once the sheet metal blank is heated, it is next transferred to a forming station 5, where it will be subjected to hot forming and press hardening to form a motor vehicle component 6. The sheet metal blank 3 may optionally first be subjected to preforming, for example, cold preforming, illustrated by preform metal blank 9. In that case, it is the preform blank 9 that is heated and further hot-formed and press-hardened in accordance with the process.

(7) FIG. 2 illustrates a three-ply sheet metal blank 2 having a center ply 7 made of a hardenable steel alloy which includes a carbon fraction of at least 0.25%, expressed in weight percent. The two outer plies 8, in contrast, are made of a noncorroding or rust-free steel alloy, and more specifically, made from a stainless steel alloy.

(8) FIG. 3 illustrates a time-temperature diagram. The temperature is plotted on the Y-axis, and the time is plotted on the X-axis. As can be seen, in a heat-up time from time S0 to time S1, the sheet metal blank is heated to more than AC3 temperature, preferably in less than 10 seconds. In a hold time from time S1 to S2, the heating temperature is then maintained. The hold phase is preferably less than 5 seconds and may in particular also be nearly 0 second. Additionally, a transfer phase is depicted from time S2 to time S3, in which the heated sheet metal blank is transferred from the heating station into the hot-forming and press-hardening tool.

(9) This procedure is preferably carried out in less than 10 seconds, and more particularly in less than 5 seconds. The forming takes place in the range starting from time S3. When forming has taken place, quench-hardening is carried out, so that the temperature drops sharply again from time S3 to S4. The duration of S0 to S3, i.e., heating, optional holding, and transfer time, is preferably accomplished in less than 30 seconds, more particularly in less than 20 seconds.

(10) The foregoing description of some embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The specifically described embodiments explain the principles and practical applications to enable one ordinarily skilled in the art to utilize various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. Further, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as described by the appended claims.