Method for manufacturing press-molded article, and press-molded article

Patent metadata

Field	Value
Publication number	US-2016222483-A1
Application number	US-201314917845-A
Country	US
Kind code	A1
Filing date	Sep 10, 2013
Priority date	Sep 10, 2013
Publication date	Aug 4, 2016
Grant date	—

Abstract

A method for manufacturing a press-formed article includes: heating a specific steel sheet for hot-pressing at 900° C. or more and 1,100° C. or less; starting press forming of the steel sheet which has been heated; and then, cooling the steel sheet to a temperature equal to or less than a temperature 100° C. below a bainite transformation starting temperature Bs and equal to or more than a martensite transformation starting temperature Ms, while ensuring an average cooling rate of 20° C./sec or more in a mold during forming and after the completion of forming; and further cooling the steel sheet, which has been cooled, to 200° C. or less at an average cooling rate of less than 20° C./sec.

First claim

1 . A method for manufacturing a press-formed article, the method comprising:
heating a steel sheet for hot-pressing at 900° C. or more and 1,100° C. or less, to obtain a heated steel sheet; beginning press forming of the heated steel sheet; cooling the steel sheet to a temperature equal to or less than a temperature 100° C. below a bainite transformation starting temperature (Bs) and equal to or more than a martensite transformation starting temperature (Ms), while ensuring an average cooling rate of 20° C./sec or more in a mold during the press forming and after completion of the press forming to obtain a cooled steel sheet; and further cooling the cooled steel sheet to 200° C. or less at the average cooling rate of less than 20° C./sec, wherein the steel sheet comprises
C: from 0.15 to 0.5% by mass,
Si: from 0.2 to 3% by mass,
Mn: from 0.5 to 3% by mass,
P: 0.05% by mass or less (exclusive of 0%),
S: 0.05% by mass or less (exclusive of 0%),
Al: from 0.01 to 1% by mass,
B: from 0.0002 to 0.01% by mass.
Ti: equal to or more than 3.4[N]+0.01% by mass and equal to or less than 3.4[N]+0.1% by mass, wherein [N] indicates a content (mass %) of N,
N: from 0.001 to 0.01%, iron, and
unavoidable impurities;
an average equivalent-circle diameter of a Ti-containing precipitate having an equivalent-circle diameter of 30 nm or less among Ti-containing precipitates contained in the steel sheet is 6 nm or less; and a precipitated Ti amount and a total Ti amount in a steel of the steel sheet satisfies formula (1):
Precipitated Ti amount (mass %)−3.4[N]<0.5×[total Ti amount (mass %)−3.4[N]]  (1)

2 . The method according to claim 1 , wherein the steel sheet for hot-pressing further comprises, as the other element(s), at least one of the following (a) to (c):
(a) at least one selected from the group consisting of V, Nb and Zr, in an amount of 0.1% or less (exclusive of 0%) in total; (b) at least one selected from the group consisting of Cu, Ni, Cr and Mo, in an amount of 1% or less (exclusive of 0%) in total; and (c) at least one selected from the group consisting of Mg, Ca and REM, in an amount of 0.01% or less (exclusive of 0%) in total.

3 . A press-formed article of a steel sheet comprising:
C: from 0.15 to 0.5% by mass; Si: from 0.2 to 3% by mass; Mn: from 0.5 to 3% by mass; P: 0.05% by mass or less (exclusive of 0%); S: 0.05% by mass or less (exclusive of 0%); Al: from 0.01 to 1% by mass; B: from 0.0002 to 0.01% by mass; Ti: equal to or more than 3.4[N]+0.01% by mass and equal to or less than 3.4[N]+0.1% by mass, wherein [N] indicates a content (mass %) of N; from 0.001 to 0.01%; iron; and unavoidable impurities, wherein: a metal microstructure of the press-formed article includes bainitic ferrite: from 60 to 97 area %, martensite: 37 area % or less, retained austenite: from 3 to 20 area %, and remainder microstructure: 5 area % or less; an average equivalent-circle diameter of Ti-containing precipitate having an equivalent-circle diameter of 30 nm or less among Ti-containing precipitates contained in the press-formed article is 10 nm or less; and a precipitated Ti amount and a total Ti amount in a steel of the steel sheet satisfies formula (1):
Precipitated Ti amount (mass %)−3.4[N]<0.5×[total Ti amount (mass %)−3.4[N]]  (1)

4 . A press-formed article of a steel sheet comprising:
C: from 0.15 to 0.5% by mass; Si: from 0.2 to 3% by mass; Mn: from 0.5 to 3% by mass; P: 0.05% by mass or less (exclusive of 0%); S: 0.05% by mass or less (exclusive of 0%); Al: from 0.01 to 1% by mass; B: from 0.0002 to 0.01% by mass; Ti: equal to or more than 3.4[N]+0.01% by mass and equal to or less than 3.4[N]+0.1% by mass, wherein [N] indicates a content (mass %) of N; N: from 0.001 to 0.01%; iron; and unavoidable impurities, wherein: the steel sheet for hot-pressing further comprises, as the other element(s), at least one of the following (a) to (c): (a) at least one selected from the group consisting of V, Nb and Zr, in an amount of 0.1% or less (exclusive of 0%) in total; (b) at least one selected from the group consisting of Cu, Ni, Cr and Mo, in an amount of 1% or less (exclusive of 0%) in total; and (c) at least one selected from the group consisting of Mg, Ca and REM, in an amount of 0.01% or less (exclusive of 0%) in total; a metal microstructure of the press-formed article includes bainitic ferrite: from 60 to 97 area %, martensite: 37 area % or less, retained austenite: from 3 to 20 area %, and remainder microstructure: 5 area % or less; an average equivalent-circle diameter of Ti-containing precipitate having an equivalent-circle diameter of 30 nm or less among Ti-containing precipitates contained in the press-formed article is 10 nm or less; and a precipitated Ti amount and a total Ti amount in a steel of the steel sheet satisfies formula (1):
Precipitated Ti amount (mass %)−34[N]<0.5×[total Ti amount (mass %)−3.4[N]]  (1).

Assignees

• Kk Kobe Seiko Sho(Kobe Steel Ltd )
• Kobe Steel Ltd

Inventors

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

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

• C22C38/06

  containing aluminium · CPC title

• C22C38/005

  containing rare earths, i.e. Sc, Y, Lanthanides · CPC title

• C22C38/002

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

• C21D1/20

  Isothermal quenching, e.g. bainitic hardening · CPC title