Method for manufacturing press-formed product and press-formed product

Patent metadata

Field	Value
Publication number	US-9938597-B2
Application number	US-201314382139-A
Country	US
Kind code	B2
Filing date	Feb 28, 2013
Priority date	Mar 9, 2012
Publication date	Apr 10, 2018
Grant date	Apr 10, 2018

Abstract

In the present invention, a press-formed product is manufactured by heating a steel sheet for hot pressing use to a temperature of 900° C. or above and 1,100° C. or below, the steel sheet for hot pressing use having a predetermined chemical component composition, some of Ti-containing precipitates contained in the steel sheet, each of which having an equivalent circle diameter of 30 nm or less, having an average equivalent circle diameter of 6 nm or less, and the precipitated Ti amount and the total Ti amount in the steel fulfilling the relationship represented by formula (1) shown below, thereafter starting press-forming, and holding at the bottom dead point and cooling to a temperature lower than the martensite transformation starting temperature Ms while securing the average cooling rate of 20° C./s or more within a tool.

Precipitated Ti amount(mass %)−3.4[N]<0.5×[total Ti amount (mass %)−3.4[N]]  (1)

(In the formula (1), [N] represents the content (mass %) of N in the steel.).

First claim

The invention claimed is:

1. A method for manufacturing a press-formed product, the method comprising
winding a steel sheet at a winding temperature of from 200° C. to 500° C.,
heating the steel sheet to a temperature of from 900° C. to 1,100° C., thus forming a heated steel sheet, and
press-forming the heated steel sheet to form the press-formed product by holding the heated steel sheet at a bottom dead point and cooling to a cooling finish temperature of lower than martensite transformation starting temperature Ms at an average cooling rate of 20° C./s or more,
wherein
the steel sheet comprises: by mass %,
iron;
C: 0.15-0.5%;
Si: 0.2-3%;
Mn: 0.5-3%;
P: a positive amount of 0.05% or less;
S: a positive amount of 0.05% or less;
Al: 0.01-1%;
B: 0.0002-0.01%;
N: 0.001-0.01%; and
Ti: 3.4[N]+0.01% or more and 3.4[N]+0.1% or less, where [N] is an amount of N in the steel sheet by mass %,

an average equivalent circle diameter of fine Ti-containing precipitates in the steel sheet is 6 nm or less, the fine Ti-containing precipitates in the steel sheet being Ti-containing precipitates that have an equivalent circle diameter of 30 nm or less, and
a precipitated Ti amount by mass % represented by [Ti] precipitated , an amount of N by mass % represented by [N], and a total Ti amount by mass % represented by [Ti] in the steel sheet satisfy formula (1):
[Ti] precipitated −3.4[N]<0.5×([Ti]−3.4[N])  (1).

2. The method according to claim 1 , wherein the steel sheet further comprises, by mass %, at least one of
(a) at least one element selected from the group consisting of V, Nb, and Zr in a total positive amount of 0.1% or less;
(b) at least one element selected from the group consisting of Cu, Ni, Cr, and Mo in a total positive amount of 1% or less; and
(c) at least one element selected from the group consisting of Mg, Ca, and REM in a total positive amount of 0.01% or less.

3. The method according to claim 1 , wherein the steel sheet comprises Al, by mass %, of from 0.4% to 1%.

4. The method according to claim 1 , wherein the precipitated Ti amount [Ti] precipitated , the amount of N [N] and the total Ti amount [Ti] in the steel sheet satisfy:
[Ti] precipitated −3.4[N]<0.4×([Ti]−3.4[N]).

5. The method according to claim 1 , wherein the precipitated Ti amount [Ti] precipitated , the amount of N [N], and the total Ti amount [Ti] in the steel sheet satisfy:
[Ti] precipitated −3.4[N]<0.3×([Ti]−3.4[N]).

6. The method according to claim 1 , wherein the average equivalent circle diameter of the fine Ti-containing precipitates in the steel sheet is 5 nm or less.

7. The method according to claim 1 , wherein the average equivalent circle diameter of the fine Ti-containing precipitates in the steel sheet is 3 nm or less.

8. The method according to claim 1 , further comprising:
cooling from the cooling finish temperature to room temperature at an average cooling rate ranging from 1° C./s to 100° C./s.

Assignees

• Kobe Steel Ltd

Inventors

• Murakami Toshio
• Hata Hideo
• Naitou Junya
• Okita Keisuke
• 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

• C22C38/54

  with boron · CPC title

• C22C38/50

  with titanium or zirconium · CPC title

• C22C38/42

  with copper · CPC title

• C22C38/26

  with niobium or tantalum · CPC title