Hot press-formed product and process for producing same

Patent metadata

Field	Value
Publication number	US-9475112-B2
Application number	US-201214113771-A
Country	US
Kind code	B2
Filing date	Jun 8, 2012
Priority date	Jun 10, 2011
Publication date	Oct 25, 2016
Grant date	Oct 25, 2016

Abstract

There is provided a hot press-formed product, including a thin steel sheet formed by a hot press-forming method, and having a metallic structure that contains bainitic ferrite at 70% to 97% by area, martensite at 27% by area or lower, and retained austenite at 3% to 20% by area, the remainder structure of which is at 5% by area or lower, whereby balance between strength and elongation can be controlled in a proper range and high ductility can be achieved.

First claim

The invention claimed is:

1. A hot press-formed product, comprising a thin steel sheet formed by a hot press-forming method, and having a metallic structure that contains bainitic ferrite at 70% to 97% by area, as-quenched martensite at 5% to 27% by area, and retained austenite at 3% to 20% by area, the remainder structure of which is at 5% by area or lower, having the following chemical element composition:
C at 0.15% to 0.4% (where “%” means “% by mass”, and the same applies to the below with respect to the chemical element composition);
Si at 0.5% to 3%;
Mn at 0.5% to 2%;
P at 0.05% or lower (not including 0%);
S at 0.05% or lower (not including 0%);
Al at 0.01% to 0.1%;
Cr at 0.01% to 1%;
B at 0.0002% to 0.01%;
Ti at (N content)×4% to 0.1%; and
N at 0.001% to 0.01%,
and the remainder consisting of iron and unavoidable impurities.

2. The hot press-formed product according to claim 1 , further comprising, as additional elements, one or more selected from the group consisting of Cu, Ni, and Mo at 1% or lower (not including 0%) in total.

3. The hot press-formed product according to claim 1 , further comprising, as additional elements, V and/or Nb at 0.1% or lower (not including 0%) in total.

4. A process for producing a hot press-formed product as set forth in claim 1 , comprising:
heating a thin steel sheet to a temperature not lower than Ac 3 transformation point and not higher than 1000° C.; and then
starting the forming of the thin steel sheet with a press tool to produce the hot press-formed product, during which forming an average cooling rate of 20° C./sec or higher is kept in the press tool and the thin steel sheet is cooled to a temperature range of not lower than martensite transformation starting temperature (Ms), and which forming is finished after retention in the temperature range for 10 seconds or longer.

Assignees

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

Inventors

• Naitou Junya
• Murakami Toshio
• Ikeda Shushi
• Okita Keisuke

Classifications

• C22C38/04

  containing manganese · CPC title

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title

• C22C38/20

  with copper · CPC title

• C22C38/02

  containing silicon · CPC title

• C21D2211/008

  Martensite · CPC title