Press-formed product and method for producing same

Patent metadata

Field	Value
Publication number	US-9315876-B2
Application number	US-201113876832-A
Country	US
Kind code	B2
Filing date	Sep 30, 2011
Priority date	Sep 30, 2010
Publication date	Apr 19, 2016
Grant date	Apr 19, 2016

Abstract

There is provided a useful method for producing a press-formed product without causing disadvantages such as hardness variation, which product has favorable formability in a level so as to be able to be produced by deep drawing, and which method is carried out by heating a thin steel sheet to a temperature not lower than an Ac 3 transformation point thereof; and then cooling the thin steel sheet at a rate not lower than a critical cooling rate, during which the thin steel sheet is formed into the press-formed product, wherein the forming is started from a temperature higher than a martensitic transformation start temperature Ms thereof, the cooling rate is kept to be 10° C./sec. or higher during the forming, and the forming is finished in a temperature range not higher than the martensitic transformation start temperature Ms.

First claim

The invention claimed is:

1. A method for producing a formed product by press-forming a thin steel sheet with a punch and a die, comprising:
heating the thin steel sheet to a temperature not lower than an Ac 3 transformation point thereof; and then cooling the thin steel sheet at a rate not lower than a critical cooling rate; and thereafter starting forming a thin steel sheet into the formed product,
wherein the forming is started from a temperature higher than a martensitic transformation start temperature Ms thereof, the cooling rate is kept to be 10° C./sec. or higher during the forming, and the forming is finished in a temperature range not higher than the martensitic transformation start temperature Ms.

2. The production method according to claim 1 , wherein the thin steel sheet is gas-jet cooled before the start of the forming.

3. The production method according to claim 1 , wherein the thin steel sheet is brought into contact with a cooled metal roll before the start of the forming.

4. The production method according to claim 1 , wherein the cooling rate before the start of the forming is 25° C./sec. or higher.

5. The production method according to claim 1 , wherein the cooling rate during the forming is 30° C./sec. or higher.

6. The production method according to claim 1 , wherein the forming is finished at a temperature higher than a martensitic transformation finish temperature Mf thereof.

7. The production method according to claim 1 , wherein the forming is carried out by drawing with a blank holder.

8. A press-formed product obtained by a production method as set forth in claim 1 , having a Vickers hardness Hv of 450 or higher.

Assignees

• Okita Keisuke
• Naitou Junya
• Ikeda Shushi
• Kobe Steel Ltd

Inventors

• Okita Keisuke
• Naitou Junya
• Ikeda Shushi

Classifications

• C21D8/00 Primary

  Modifying the physical properties of ferrous metals or ferrous alloys 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 title

• C21D9/48

  deep-drawing sheets · CPC title

• C21D1/18

  Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) · CPC title

• C21D8/005 Primary

  Chemistry & Metallurgy · mapped topic

• C21D1/673

  for die quenching · CPC title