Hot-press formed product and method for manufacturing same

Patent metadata

Field	Value
Publication number	US-9850554-B2
Application number	US-201314373965-A
Country	US
Kind code	B2
Filing date	Mar 15, 2013
Priority date	Mar 15, 2012
Publication date	Dec 26, 2017
Grant date	Dec 26, 2017

Abstract

A hot-press formed product can be achieved which has regions corresponding to a shock resistant portion and an energy absorption portion within a single formed product without applying a welding method and achieves the balance of high strength and elongation with a high level according to each region by means of having a first forming region exhibiting a metal structure containing martensite: 80-97 area % and retained austenite: 3-20 area % respectively, the remaining structure being 5 area % or less, and a second forming region exhibiting a metal structure containing annealed martensite or annealed bainite: 30-97 area %, martensite as quenched: 0-67 area %, and retained austenite: 3-20 area %.

First claim

The invention claimed is:

1. A hot-press formed steel product, comprising:
a first forming region exhibiting a metal structure containing martensite of 80-97 area %, retained austenite of 3-20 area %, and other structure of 5 area % or less, and
a second forming region exhibiting a metal structure containing annealed martensite or annealed bainite of 30-97 area %, martensite as quenched of 0-67 area %, and retained austenite of 3-20 area %.

2. The hot-press formed steel product according to claim 1 , wherein
the first forming region and the second forming region have the same chemical component composition, and
steel of each forming region comprises:
C: 0.1-0.3;
Si: 0.5-3 mass %;
Mn: 0.5-2 mass %;
P: 0.05 mass % or less, excluding 0 mass %;
S: 0.05 mass % or less, excluding 0 mass %;
Al: 0.01-0.1 mass %;
N: 0.001-0.01 mass %; and
iron.

3. The hot-press formed steel product according to claim 2 , wherein the steel further comprises:
B: 0.01 mass % or less, excluding 0 mass %; and
Ti: 0.1 mass % or less, excluding 0 mass %.

4. The hot-press formed steel product according to claim 2 , wherein the steel further comprises:
at least one element selected from the group consisting of Cu, Ni, Cr and Mo in a total amount of 1 mass % or less, excluding 0 mass %.

5. The hot-press formed steel product according to claim 2 , wherein the steel further comprises:
at least one of V and Nb in a total amount of 0.1 mass % or less, excluding 0 mass %.

6. A method for manufacturing the hot-press formed steel product according to claim 1 , the method comprising:
heating a steel sheet separated into at least two regions and comprising a metal structure having 80 area % or more of martensite or bainite so as to simultaneously execute a plurality of heating treatments including a first heating treatment for heating the first forming region to a temperature of AC3 transformation point or above and 1,000° C. or below and a second heating treatment for heating the second forming region to Ac 1 transformation point or above and a temperature equivalent to A or below wherein A=Ac 1 transformation point×0.2+Ac 3 transformation point×0.8;
thereafter cooling with an average cooling rate of 20° C./s or more and forming by pressing jointly using a tool at least for the first forming region and the second forming region; and finishing forming at a temperature lower than the martensitic transformation starting point Ms by at least 50° C.

7. A method for manufacturing the hot-press formed steel product according to claim 1 , the method comprising:
heating a steel sheet separated into at least two regions so as to simultaneously execute a plurality of heating treatments including a first heating treatment for heating the first forming region to a temperature of Ac 3 transformation point or above and 1,000° C. or below and a second heating treatment for heating the second forming region to Ac 1 transformation point or above and a temperature equivalent to A or below wherein A=Ac 1 transformation point×0.2+Ac 3 transformation point×0.8;
thereafter cooling with an average cooling rate of 20° C./s or more and forming by pressing jointly using a tool at least for the first forming region and the second forming region; and finishing forming at a temperature lower than the martensitic transformation starting point Ms by at least 50° C.

8. The hot-pressed formed steel product according to claim 1 , wherein the first forming region has a tensile strength of 1,470 MPa or more and a total elongation of 10% or more.

9. The hot-pressed formed steel product according to claim 1 , wherein the second forming region has a tensile strength of 980 MPa or more and a total elongation of 15% or more.

10. The hot-pressed formed steel product according to claim 2 , wherein the steel of each forming region comprises Si: 1.15-3 mass %.

11. The method according to claim 6 , wherein, for the first forming region, the cooling comprises a first stage cooling with an average cooling rate of 20° C./s or more to a temperature of (Ms-50)° C. and a subsequent second stage cooling with an average cooling rate of less than 20° C./s to a temperature of 200° C. or below.

12. The method according to claim 6 , wherein, for the second forming region, the finish forming is carried out at a temperature of 200° C. or below.

13. The method according to claim 7 , wherein, for the first forming region, the cooling comprises a first stage cooling with an average cooling rate of 20° C./s or more to a temperature of (Ms-50)° C. and a subsequent second stage cooling with an average cooling rate of less than 20° C./s to a temperature of 200° C. or below.

14. The method according to claim 7 , wherein, for the second forming region, the finish forming is carried out at a temperature of 200° C. or below.

Assignees

• Kobe Steel Ltd

Inventors

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

Classifications

• C21D8/00

  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

• C22C38/28

  with titanium or zirconium · CPC title

• C21D1/673 Primary

  for die quenching · CPC title

• C21D8/005

  Chemistry & Metallurgy · mapped topic

• C21D2221/00

  Treating localised areas of an article · CPC title