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

• US 10,526,677 B2
• Filed: 12/20/2016
• Issued: 01/07/2020
• Est. Priority Date: 12/23/2015
• Status: Active Grant

• Current Assignee: Benteler Automobiltechnik GmbH (Benteler International AG)
• Original Assignee: Benteler Automobiltechnik GmbH (Benteler International AG)
• Inventors: Frost, Georg, Kettler, Markus, Bake, Karsten
• Primary Examiner(s): Nguyen, Cam N.
• Application Number:
  US15/385,835
• Publication Number:
  US 20170183754A1
• Time in Patent Office: 1,113 Days
• CPC Class Codes: C21D 6/00 Heat treatment of ferrous alloys
• CPC Class Codes: C21D 9/005 Furnaces in which the charge is moving up or down for wire, strip C21D9/54
• CPC Class Codes: C21D 9/0056 Furnaces through which the charge is moved in a horizontal straight path C21D9/0043 takes precedence
• CPC Class Codes: C21D 9/0062 Heat-treating apparatus with a cooling or quenching zone
• CPC Class Codes: C21D 9/46 for sheet metals
• CPC Class Codes: F27D 13/00 Apparatus for preheating charges; Arrangements for preheating charges
• CPC Class Codes: F27D 2003/0075 Charging or discharging vertically, e.g. through a bottom opening
• CPC Class Codes: F27D 2009/0075 in direct contact with the charge
• CPC Class Codes: F27D 3/0024 of metallic workpieces
• CPC Class Codes: F27D 9/00 Cooling of furnaces or of charges therein F27D1/00, F27D3/00 take precedence

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.

Claims

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 μ

m and 0.15 μ

m 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.

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.

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.