Low density press-hardening steel having enhanced mechanical properties

Patent metadata

Field	Value
Publication number	US-11612926-B2
Application number	US-201817251655-A
Country	US
Kind code	B2
Filing date	Jun 19, 2018
Priority date	Jun 19, 2018
Publication date	Mar 28, 2023
Grant date	Mar 28, 2023

Abstract

A method of forming a shaped steel object is provided. The method includes cutting a blank from an alloy composition including 0.05-0.5 wt. % carbon, 4-12 wt. % manganese, 1-8 wt. % aluminum, 0-0.4 wt. % vanadium, and a remainder balance of iron. The method also includes heating the blank until the blank is austenitized to form a heated blank, transferring the heated blank to a press, forming the heating blank into a predetermined shape to form a stamped object, and decreasing the temperature of the stamped object to a temperature between a martensite start (Ms) temperature of the alloy composition and a martensite final (Mf) temperature of the alloy composition to form a shaped steel object comprising martensite and retained austenite.

First claim

What is claimed is:

1. A method of forming a shaped steel object, the method comprising:
cutting a blank from an alloy composition, the alloy composition comprising:
carbon (C) at a concentration of greater than or equal to about 0.05 wt. % to less than or equal to about 0.5 wt. % of the alloy composition,
manganese (Mn) at a concentration of greater than or equal to about 4 wt. % to less than or equal to about 12 wt. % of the alloy composition,
aluminum (Al) at a concentration of greater than or equal to 2 wt. % to less than or equal to about 8 wt. % of the alloy composition,
vanadium (V) at a concentration of greater than 0 wt. % to less than or equal to about 0.4 wt. % of the alloy composition, and
a balance of the alloy composition being iron (Fe);

heating the blank until the blank is austenitized;
transferring the heated blank to a press;
forming the heated blank into a predetermined shape defined by the press to generate a stamped object; and
decreasing the temperature of the stamped object to a temperature between a martensite start (Ms) temperature of the alloy composition and a martensite final (Mf) temperature of the alloy composition to form a shaped steel object comprising martensite and retained austenite.

2. The method according to claim 1 , wherein the alloy composition further comprises:
zirconium (Zr) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. % of the alloy composition.

3. The method according to claim 2 , wherein the alloy composition further comprises at least one of:
nickel (Ni) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. % of the alloy composition,
molybdenum (Mo) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. % of the alloy composition,
niobium (Nb) at a concentration of greater than 0 wt. % to less than or equal to about 0.2 wt. % of the alloy composition,
copper (Cu) at a concentration of greater than 0 wt. % to less than or equal to about 3 wt. % of the alloy composition,
titanium (Ti) at a concentration of greater than 0 wt. % to less than or equal to about 0.1 wt. % of the alloy composition,
nitrogen (N) at a concentration of greater than 0 wt. % to less than or equal to about 0.01 wt. % of the alloy composition, and
boron (B) at a concentration of greater than 0 wt. % to less than or equal to about 0.005 wt. % of the alloy composition.

4. The method according to claim 1 , wherein the Mn is at a concentration of greater than or equal to about 6 wt. % to less than or equal to about 10 wt. % and the Al is at a concentration of greater than or equal to 2 wt. % to less than or equal to about 5 wt. %.

5. The method according to claim 1 , wherein the C is at a concentration of greater than or equal to about 0.1 wt. % to less than or equal to about 0.45 wt. %.

6. The method according to claim 1 , wherein the alloy composition is in coil form.

7. The method according to claim 1 , wherein the heating the blank comprises heating the blank to a temperature of greater than or equal to about 900° C. to less than or equal to about 950° C. for a time period of greater than or equal to about 1 minute to less than or equal to about 60 minutes.

8. The method according to claim 1 , wherein the temperature between the Ms temperature of the alloy composition and the Mf temperature of the alloy composition is ambient temperature.

9. The method according to claim 1 , wherein the decreasing the temperature comprises decreasing the temperature at a rate of greater than or equal to about 5 degrees Celsius per second to less than or equal to about 300 degrees Celsius per second.

10. The method according to claim 1 , further comprising, prior to the heating the blank until the blank is austenitized:
preoxidizing the alloy composition by heating the alloy composition to a temperature of greater than or equal to about 500° C. to less than or equal to about 600° C. for a time period of greater than or equal to about 1 minute to less than or equal to about 60 minutes.

11. The method according to claim 1 , further comprising, after the decreasing the temperature:
tempering the shaped steel object.

12. The method according to claim 11 , wherein the tempering the shaped steel object comprises:
heating the shaped steel object to a temperature greater than or equal to about 150° C. to less than or equal to about 300° C. for a time period of greater than or equal to about 1 minute to less than or equal to about 120 minutes, and
cooling the shaped steel object to ambient temperature.

13. The method according to claim 1 , wherein the shaped steel object has a higher strength and a lower weight relative to an equivalent shaped steel object formed from 22MnB5.

Assignees

• Gm Global Tech Operations Llc

Inventors

• Pang Jiachen
• Lu Qi
• Wang Jianfeng

Classifications

• C22C38/14 Primary

  containing titanium or zirconium · CPC title

• C22C38/12

  containing tungsten, tantalum, molybdenum, vanadium, or niobium · CPC title

• C22C38/06

  containing aluminium · CPC title

• C22C38/04

  containing manganese · CPC title

• C21D2211/008

  Martensite · CPC title