Steel Material For Hot Stamp Forming, Hot Stamp Forming Process And Hot Stamp Formed Member

• US 20190309385A1
• Filed: 09/08/2016
• Published: 10/10/2019
• Est. Priority Date: 07/08/2016
• Status: Active Grant

• Current Assignee: Northeastern University, Bengang Steel Plates Company Limited (Province of Liaoning (Liaoning))
• Original Assignee: Northeastern University, Bengang Steel Plates Company Limited (Province of Liaoning (Liaoning))
• Inventors: Yi, Hongliang, Liu, Hongliang, Chang, Zhiyuan, Wu, Di, Huang, Jian, Wang, Guodong
• Granted Patent: US 11,377,703 B2
• Time in Patent Office: Days
• CPC Class Codes: C21D 8/00 Modifying the physical properties by deformation combined with, or followed by, heat treatment hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02
• CPC Class Codes: C21D 8/02 during manufacturing of plates or strips C21D8/12 takes precedence
• CPC Class Codes: C21D 8/04 to produce plates or strips for deep-drawing
• CPC Class Codes: C21D 8/0405 of ferrous alloys
• CPC Class Codes: C21D 8/0421 characterised by the working steps
• CPC Class Codes: C22C 38/00 Ferrous alloys, e.g. steel alloys cast-iron alloys C22C37/00
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/12 containing tungsten, tantalum, molybdenum, vanadium, or niobium
• CPC Class Codes: C22C 38/24 with vanadium
• CPC Class Codes: C22C 38/26 with niobium or tantalum
• CPC Class Codes: C22C 38/28 with titanium or zirconium
• CPC Class Codes: C22C 38/32 with boron
• CPC Class Codes: C22C 38/38 with more than 1.5% by weight of manganese
• CPC Class Codes: C22C 38/46 with vanadium
• CPC Class Codes: C23C 2/06 Zinc or cadmium or alloys based thereon
• CPC Class Codes: C23C 2/12 Aluminium or alloys based thereon

Abstract

The present invention relates to a steel material for hot stamp forming with ultra-fine grains and a process of making the same, a hot stamp forming process and a hot stamp formed member. The steel material for hot stamp forming comprises the following components by weight: 0.27 to 0.40% of C; 0.2 to 3.0% of Mn; 0.11 to 0.4% of V; 0 to 0.8% of Si; 0 to 0.5% of Al; 0 to 2% of Cr; 0 to 0.15% of Ti; 0 to 0.15% of Nb; 0 to 0.004% B; a total of less than 2% of Mo, Ni, Cu and other alloying elements that are beneficial to improving the hardenability, and other impurity elements. After hot stamp forming or equivalent heat treatment, the steel material or the formed member of the present invention can achieve a yield strength of 1300 MPa to 1700 MPa, a tensile strength of 1800 to 2200 MPa, and an elongation of 6 to 9% after direct hot stamping quenching and without tempering, which properties cannot be achieved by a material with a composition in the prior art in the situation of direct quenching (no tempering). After the tempering treatment of the present invention, preferably 1500 MPa-1900 MPa-8%, and 1600 MPa-2100 MPa-7% can be reached.

Claims

1. A steel material for hot stamp forming, wherein the steel material for hot stamp forming comprises the following components by weight:

0.27 to 0.40% of C;

0.2 to 3.0% of Mn;

0.11 to 0.4% of V;

0 to 0.8% of Si;

0 to 0.5% of Al;

0 to 2% of Cr;

0 to 0.15% of Ti;

0 to 0.15 of Nb;

0 to 0.004% of B;

a total of less than 2% of Mo, Ni, Cu; and

inevitable impurity elements.

2. The steel material for hot stamp forming according to claim 1, wherein the steel material for hot stamp forming has a heating temperature range of 800 to 920°

C. during a hot stamp forming process, and has a carbide of VC and/or composited carbide of V with Ti, Nb at an austenite grain boundary during an austenitizing process.

3. The steel material for hot stamp forming according to claim 2, wherein in the austenitizing process of the steel material for hot stamp forming, a precipitated particle size of the carbide of VC and/or composited carbide of V with Ti, Nb at the austenite grain boundary is from 1 to 80 nm.

4. The steel material for hot stamp forming according to claim 1, wherein in the hot stamping process, the steel material for hot stamp forming precipitates a certain amount of the carbide of VC and/or composited carbide of V with Ti, Nb in an austenite crystal including a grain boundary during a cooling process after austenitizing, and a carbide particle size in the austenite crystal is 0.1 to 20 nm.

5. The steel material for hot stamp forming according to claim 1, wherein a volume fraction of the carbide of VC and/or composited carbide of V with Ti, Nb in the steel material for hot stamp forming is more than 0.1%.

6. The steel material for hot stamp forming according claim 1, wherein after the hot stamp forming, the steel material for hot stamp forming achieves a yield strength of 1300 MPa to 1700 MPa, a tensile strength of 1800 to 2200 MPa, and an elongation of 6 to 9% without tempering;

and achieves a yield strength of 1350 to 1800 MPa, a tensile strength of 1700 to 2150 MPa, and an elongation of 7 to 10% after tempering heat treatment.

7. The steel plate according to claim 1, wherein the steel material includes a hot-rolled steel plate, a hot-rolled pickled steel plate, a cold-rolled steel plate, or a steel plate with a coating layer.

8. The steel plate according to claim 7, wherein the steel plate with a coating layer is a zinc-coated steel plate which is a hot-rolled steel plate or a cold-rolled steel plate on which a metal zinc layer is formed, wherein the zinc-coated steel plate includes at least one selected from hot-dip galvanizing, galvanizing annealing, zinc plating, or zinc-iron plating.

9. The steel plate according to claim 7, wherein the steel plate with a coating layer is a hot-rolled steel plate or a cold-rolled steel plate on which an aluminum-silicon layer is formed, or a steel plate with an organic coating layer.

10. A hot stamp forming process, comprising the following procedures:

(a) steel material austenitizing;

providing a steel material for hot stamp forming according to claim 1 or a preformed member thereof, heating it to 800 to 920°

C. and maintaining the temperature for 1 to 10000 s;

(b) steel material transferring;

transferring the above heated steel material to a die for hot stamp forming while ensuring that the steel material has a temperature of above 550°

C. when being transferred to the die;

(c) hot stamp forming;

setting a reasonable press tonnage according to the above-mentioned steel blank size, the stamping pressure being 1 to 40 MPa, determining a dwell time according to a thickness of the plate, which is controlled at 4 to 40 s, and controlling a die surface temperature below 200°

C. through a cooling system of the die, so that the steel material in the die is rapidly cooled to below 250°

C. at an average cooling rate of not less than 10°

C./s.

11. The hot stamp forming process according to claim 10, wherein a heating method in the procedure (a) comprises a roller-type heating furnace, a box-type heating furnace, induction heating, and resistance heating.

12. A tempering process, comprising the steps of:

(a) obtaining a formed member by the hot stamp forming process of claim 10;

(b) during a coating process, heating the formed member to 150 to 200°

C. and maintaining the temperature for 10 to 40 minutes;

or heating the formed member to 150 to 280°

C. at a heating rate of 0.001 to 100°

C./s and maintaining the temperature for 0.5 to 120 minutes, and then cooling it in any way.

13. A hot stamp formed member, wherein the hot stamp formed member is produced by the steel material according to claim 1 through the hot stamp forming process according to claim 10, and properties thereof reach a yield strength of 1300 MPa to 1700 MPa, a tensile strength of 1800 to 2200 MPa, and an elongation of 6 to 9%.

14. The hot stamp formed member according to claim 13, treated by the tempering process according to claim 12, wherein properties thereof reach a yield strength of 1300 MPa to 1800 MPa, a tensile strength of 1700 to 2150 MPa, and an elongation of 7 to 10%.

15. The hot stamp formed member according to claim 13, wherein the hot stamp formed member can be used for automotive high-strength members including an A-pillar, a B-pillar, a bumper, a roof frame, an underbody frame, and a door bumper bar of an automobile.