Hot-rolled steel sheet and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-11208702-B2
Application number	US-201916263457-A
Country	US
Kind code	B2
Filing date	Jan 31, 2019
Priority date	May 14, 2013
Publication date	Dec 28, 2021
Grant date	Dec 28, 2021

Abstract

There is provided a hot-rolled steel sheet in which a composition contains: in mass %, C: 0.01% to 0.2%; Si: 2.5% or less; Mn: 4.0% or less; P: 0.10% or less; S: 0.03% or less; Al: 0.001% to 2.0%; N: 0.01% or less; O: 0.01% or less; Ti: 0.01 to 0.30%; and the balance being composed of iron and impurities and a structure is composed of by volume fraction, 90% or more of tempered martensite with an average aspect ratio of 2 or less, or 90% or more in total of both tempered martensite and lower bainite.

First claim

The invention claimed is:

1. A manufacturing method of a hot-rolled steel sheet, comprising:
smelting a steel having a composition containing:
in mass %,
C: 0.01 to 0.2%;
Si: 2.5% or less (not including “0” (zero));
Mn: 4.0% or less (not including “0” (zero));
P: 0.10% or less;
S: 0.03% or less;
Al: 0.001 to 2.0%;
N: 0.01% or less (not including “0” (zero));
O: 0.01% or less (not including “0” (zero));
Ti: 0.03 to 0.30%;
Nb: “0” (zero) to 0.30%;
Cu: “0” (zero) to 2.0%;
Ni: “0” (zero) to 2.0%;
Mo: “0” (zero) to 1.0%;
V: “0” (zero) to 0.3%;
Cr: “0” (zero) to 2.0%;
Mg: “0” (zero) to 0.01%;
Ca: “0” (zero) to 0.01%;
REM: “0” (zero) to 0.1%;
B: “0” (zero) to 0.01%; and
the balance being composed of iron and impurities and casting the steel into a slab, and then directly heating the cast slab to 1200° C. or higher or once cooling the cast slab and then heating the cast slab to 1200° C. or higher;
performing hot rolling in which a reduction ratio of rolling at the final stage of rough rolling is set to 25% or more and a rolling temperature is set to lower than 1100° C. and the rough rolling is completed, an obtained rough-rolled piece is heated by 10° C. or higher before finish rolling, and a finishing temperature of finish rolling to be performed subsequently is set to 900° C. or higher; and
performing cooling at an average cooling rate of 50° C./sec or more from the finishing temperature of the finish rolling to 400° C. and performing coiling at 100° C. to 390° C.

2. The manufacturing method of the hot-rolled steel sheet according is claim 1 , further comprising:
performing a galvanizing treatment or a galvanealed treatment after the coiling.

3. The manufacturing method of the hot-rolled steel sheet according to claim 1 , wherein said coiling is performed at a temperature of 100° C. to 380° C.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Sakakibara Akifumi
• Yokoi Tatsuo
• Shuto Hiroshi
• KANZAWA Yuuki
• Azuma Masafumi

Classifications

• C22C38/32

  with boron · CPC title

• C22C38/26

  with niobium or tantalum · CPC title

• C22C38/08

  containing nickel {(C22C38/105 takes precedence)} · CPC title

• C23C2/40

  Plates; Strips · CPC title

• B21B3/02

  Rolling special iron alloys {, e.g. stainless steel} · CPC title