High-strength hot-rolled steel sheet and method for manufacturing high-strength hot-rolled steel sheet

Patent metadata

Field	Value
Publication number	US-2024254584-A1
Application number	US-202218289601-A
Country	US
Kind code	A1
Filing date	May 13, 2022
Priority date	May 17, 2021
Publication date	Aug 1, 2024
Grant date	—

Abstract

A high-strength hot-rolled steel sheet according to the present invention has a specific chemical composition and a steel microstructure including, as main phases, 80% to 100% of martensite and bainite in terms of total area fraction. An entire area fraction of the martensite dispersed in the bainite is 2% to 20%. Among the martensite dispersed in the bainite, an area fraction of martensite each having an orientation difference of less than 15° between a crystal orientation of the martensite and a crystal orientation of at least one of bainite adjacent to the martensite is 50% or more relative to the whole martensite dispersed in the bainite.

First claim

1 . A high-strength hot-rolled steel sheet comprising:
a chemical composition containing, by mass %, C: 0.04% to 0.18%, Si: 0.1% to 3.0%, Mn: 0.5% to 3.5%, P: more than 0% and 0.100% or less, S: more than 0% and 0.020% or less, and Al: more than 0% and 1.5% or less, and further containing one or two or more selected from Cr: 0.005% to 2.0%, Ti: 0.005% to 0.20%, Nb: 0.005% to 0.20%, Mo: 0.005% to 2.0%, and V: 0.005% to 1.0%, the balance being Fe and incidental impurities; and a steel microstructure including, as main phases, 80% to 100% of martensite and bainite in terms of total area fraction, wherein an entire area fraction of the martensite dispersed in the bainite is 2% to 20%, and among the martensite dispersed in the bainite, an area fraction of the martensite each having an orientation difference of less than 15° between a crystal orientation of the martensite and a crystal orientation of at least one of the bainite adjacent to the martensite is 50% or more relative to the whole martensite dispersed in the bainite.

2 . The high-strength hot-rolled steel sheet according to claim 1 , comprising:
in addition to the chemical composition, by mass %, one or two or more selected from: Cu: 0.05% to 4.0%, Ni: 0.005% to 2.0%, B: 0.0002% to 0.0050%, Ca: 0.0001% to 0.0050%, REM: 0.0001% to 0.0050%, Sb: 0.0010% to 0.10%, and Sn: 0.0010% to 0.50%.

3 . A method for manufacturing a high-strength hot-rolled steel sheet according to claim 1 , the method comprising:
heating a slab having the chemical composition; and subsequently subjecting the slab to hot rolling, wherein the hot rolling includes performing rough rolling, at 1,100° C. or higher, in 3 passes or more and at a rolling reduction of 15% or more per pass, performing finish rolling under conditions in which a total rolling reduction at 1,000° C. or lower is 50% or more, and a total number of passes at 1,000° C. or lower is 3 times or more, subsequently performing natural cooling for 1.0 s or more, subsequently performing cooling under a condition in which an average cooling rate from a cooling start temperature to 550° C. is 50° C./s or more, and subsequently performing coiling at a coiling temperature of (Ms temperature—50° C.) to 550° C.

4 . A method for manufacturing a high-strength hot-rolled steel sheet according to claim 2 , the method comprising:
heating a slab having the chemical composition; and subsequently subjecting the slab to hot rolling, wherein the hot rolling includes performing rough rolling, at 1,100° C. or higher, in 3 passes or more and at a rolling reduction of 15% or more per pass, performing finish rolling under conditions in which a total rolling reduction at 1,000° C. or lower is 50% or more, and a total number of passes at 1,000° C. or lower is 3 times or more, subsequently performing natural cooling for 1.0 s or more, subsequently performing cooling under a condition in which an average cooling rate from a cooling start temperature to 550° C. is 50° C./s or more, and subsequently performing coiling at a coiling temperature of (Ms temperature—50)° C. to 550° C.

Assignees

• Jfe Steel Corp

Inventors

• Hasegawa Hiroshi
• Kimura Hideyuki

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C22C38/06

  containing aluminium · CPC title

• C22C38/04

  containing manganese · CPC title

• C22C38/02

  containing silicon · CPC title

• C22C38/002

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