Method for manufacturing hot-press formed steel-member, and the hot-press formed steel-member

Patent metadata

Field	Value
Publication number	US-10029294-B2
Application number	US-201314380180-A
Country	US
Kind code	B2
Filing date	Mar 29, 2013
Priority date	Mar 30, 2012
Publication date	Jul 24, 2018
Grant date	Jul 24, 2018

Abstract

Provided is a method for manufacturing a hot-press formed steel-member that is capable of reducing LME without causing cracking of a galvanized steel sheet. The method includes using a galvanized steel sheet, as a base steel, having a prescribed chemical composition, heating the galvanized steel sheet to not lower than an Ac3 transformation-point, and executing hot-press forming at least twice after the heating. Every hot-press forming in is executed so that to satisfy the following expression (1): (R/t)>√(a·(T−b)), where “R” is a curvature radius (mm) of a shoulder of a tool used in the hot-press forming, “t” is a thickness (mm) of the galvanized steel sheet, “T” is a forming-start temperature (° C.) of the hot-press forming, “a” is a constant 0.2984, and “b” is a constant 590.

First claim

The invention claimed is:

1. A method for manufacturing a hot-press formed steel-member, the method comprising:
providing a galvanized steel sheet comprising a base steel having a chemical composition comprising
from 0.010 mass % to 0.35 mass % of C,
from 1.0 mass % to 3.5 mass % of Mn,
from 0.1 mass % to 2.5 mass % of Si, and
from greater than 0 mass % to 0.5 mass % of Al,
with the balance being iron and unavoidable impurities;
heating the galvanized steel sheet to not lower than an Ac 3 transformation-point; and
executing hot-press forming at least twice after the heating,
wherein every hot-press forming is executed so as to satisfy the following expression (1):

R
t

>

a
·

(

T
-
b

)

,

(
1
)

wherein
“R” is a curvature radius (mm) of a shoulder of a tool used in the hot-press forming,
“t” is a thickness (mm) of the galvanized steel sheet,
“T” is a forming-start temperature (° C.) of the hot-press forming,
“a” is a constant 0.2984, and
“b” is a constant 590.

2. The method for manufacturing a hot-press formed steel-member, according to claim 1 , wherein a curvature of radius for the shoulder of the tool used in the latter hot-press forming is smaller than that of the tool used in the previous hot-press forming.

3. The method for manufacturing a hot-press formed steel-member, according to claim 1 , wherein the base steel of the galvanized steel sheet comprises the Si-content not less than 0.5%.

4. The method for manufacturing a hot-press formed steel-member, according to claim 1 , wherein the base steel of the galvanized steel sheet further comprises from greater that 0 mass % to 0.005 mass % of B.

5. The method for manufacturing a hot-press formed steel-member, according to claim 1 , wherein the base steel of the galvanized steel sheet further comprises from greater that 0 mass % to 0.10 mass % of Ti and/or Nb.

6. The method for manufacturing a hot-press formed steel-member, according to claim 1 , wherein the base steel of the galvanized steel sheet further comprises from greater that 0 mass % to 0.5 mass % of Ni and/or Cu.

7. The method for manufacturing a hot-press formed steel-member, according to claim 1 , wherein the base steel of the galvanized steel sheet further comprises from greater that 0 mass % to 3.5 mass % of Cr and/or Mo.

8. The method for manufacturing a hot-press formed steel-member, according to claim 1 , wherein the galvanized steel sheets is obtained by applying a hot-dip galvanizing coating (GI) or a hot-clip galvannealing coating (GA) to base steel sheet.

9. The method for manufacturing a hot-press formed steel-member, according to claim 8 , wherein a coating weight of the hot-dip galvanizing coating (GI) is from 70 g/m 2 to 100 g/m 2 .

10. The method for manufacturing a hot-press formed steel-member, according to claim 1 , wherein the forming-start temperature is from 550 to 750° C.

11. The method for manufacturing a hot-press formed steel-member, according to claim 1 , wherein the curvature radius of a shoulder of a tool is form 2.5 to 15 mm.

12. The method for manufacturing a hot-press formed steel-member, according to claim 1 , comprising executing hot-press forming at least three times after the heating.

13. The method for manufacturing a hot-press formed steel-member, according to claim 1 , wherein a heating time is from 3 to 6 minutes.

Assignees

• Kobe Steel Ltd

Inventors

• Yamano Takayuki
• Jimbo Noriyuki
• Asai Tatsuya

Classifications

• C22C38/001

  containing N · CPC title

• C22C38/58

  with more than 1.5% by weight of manganese · CPC title

• Y10T428/1241

  Nonplanar uniform thickness or nonlinear uniform diameter [e.g., L-shape] · CPC title

• C22C38/38

  with more than 1.5% by weight of manganese · CPC title

• C22C38/14

  containing titanium or zirconium · CPC title