Heat treatment furnace and method for heat treatment of a pre-coated steel sheet blank and method for production of a motor vehicle part

Patent metadata

Field	Value
Publication number	US-10526677-B2
Application number	US-201615385835-A
Country	US
Kind code	B2
Filing date	Dec 20, 2016
Priority date	Dec 23, 2015
Publication date	Jan 7, 2020
Grant date	Jan 7, 2020

Abstract

A heat treatment furnace and a method for heat treatment of a steel sheet blank is disclosed having at least one furnace chamber and a transport system for conveying the steel sheet blanks through the furnace chamber. A preheating chamber, a metallurgical bonding path and a cooling chamber, wherein the steel sheet blank can be heated in the preheating chamber to a temperature of above 200° C. A method for the production of a hot-formed and press-quenched motor-vehicle part is also disclosed.

First claim

The invention claimed is:

1. Method for heat treatment of a pre-coated steel sheet blank, in which a pre-coating is provided on a steel sheet blank, the method comprising:
preheating the pre-coated steel sheet blank to a preheat temperature between 200° C. and 450° C.,
then heating the preheated, pre-coated steel sheet blank to a metallurgical bonding temperature above an austenizing temperature, such that the pre-coating is metallurgically bonded to the steel sheet blank to form a coating,
then cooling the metallurgically bonded steel sheet blank to a cooling temperature of less than 450° C. at a cooling rate of greater than 30 s per millimeter of sheet thickness of the steel sheet blank, and
then hot-forming and press-hardening the cooled, metallurgically bonded steel sheet blank,
wherein the metallurgically bonded steel sheet blank has, in at least one region, a fraction of atomic hydrogen below 0.5 ppm.

2. Method according to claim 1 , wherein
the preheat temperature is between 250° C. to 450° C., and/or
the cooling temperature is between 450° C. and 300° C.

3. Method according to claim 1 , wherein
the heating to the metallurgical bonding temperature is performed as rapid heating at a heating rate of less than 20 s per mm of sheet thickness of the steel sheet blank to be heated.

4. Method according to claim 1 , wherein
a thickness of the coating is between 0.6 μm and 0.15 μm and/or
the fraction of atomic hydrogen is below 0.3 ppm.

5. Method according to claim 1 , wherein
the steel sheet blank is of a quenchable steel alloy,
the pre-coating is of an Al—Si alloy, and
at least an intermetallic phase of Fe—Al is formed when the pre-coating is metallurgically bonded to the steel sheet blank.

6. Method according to claim 1 , wherein
heat radiation of metallurgically bonded steel sheet blanks that are guided through a cooling path during the cooling is used to preheat other, pre-coated steel sheet blanks that are guided through a preheating path during the preheating.

7. Method according to claim 1 , wherein
the heating to metallurgical bonding temperature is performed as rapid heating at a heating rate of less than 5 s per mm of sheet thickness of the steel sheet blank to be heated.

8. Method according to claim 1 , wherein
the cooling temperature is between 450° C. and 300° C., and
the method further comprises a further cooling process to cool the metallurgically bonded steel sheet blank to a temperature of less than 300° C.

9. Method for producing a hot-formed and press-quenched motor vehicle part, the method comprising:
preheating a pre-coated steel sheet blank, in which a pre-coating is provided on a steel sheet blank, to a preheat temperature between 200° C. and 450° C.,
then heating the preheated, pre-coated steel sheet blank to a metallurgical bonding temperature above an austenizing temperature, such that the pre-coating is metallurgically bonded to the steel sheet blank to form a coating,
then cooling the metallurgically bonded steel sheet blank to a cooling temperature of less than 450° C. at a cooling rate of greater than 30s per millimeter of sheet thickness of the steel sheet blank,
then reheating the cooled, metallurgically bonded steel sheet blank at least partially, in a time of less than 20 s, to a temperature greater than or equal to the austenizing temperature, and
then hot-forming and press-quenching the reheated, metallurgically bonded steel sheet blank into the hot-formed and press-quenched motor vehicle part,
wherein the metallurgically bonded steel sheet blank has, in at least one region, a fraction of atomic hydrogen below 0.5 ppm.

10. Method according to claim 9 , wherein
in the reheating, the cooled, metallurgically bonded steel sheet blank is reheated from the cooling temperature, or from room temperature.

11. Method according to claim 9 , wherein
the produced motor vehicle part has, in at least one region, a tensile strength Rm of greater than 1250 MPa, and/or
the fraction of atomic hydrogen is below 0.3 ppm.

12. Method according to claim 11 , wherein
the tensile strength Rm is greater than 1450 MPa.

13. Method according to claim 1 , wherein
the heating to the metallurgical bonding temperature is performed as rapid heating at a heating rate of less than 10 s per mm of sheet thickness of the steel sheet blank to be heated.

Assignees

• Benteler Automobiltechnik Gmbh

Inventors

• Frost Georg
• Kettler Markus
• Bake Karsten

Classifications

• C21D6/00

  Heat treatment of ferrous alloys · CPC title

• F27D13/00

  Apparatus for preheating charges; Arrangements for preheating charges · CPC title

• C21D9/0056

  Furnaces through which the charge is moved in a horizontal straight path (C21D9/0043 takes precedence) · CPC title

• F27D2009/0075

  in direct contact with the charge · CPC title

• F27D9/00

  Cooling of furnaces or of charges therein (casings, linings, walls or roofs incorporating cooling arrangements F27D1/12) · CPC title