Steel sheet for heat treatment

Patent metadata

Field	Value
Publication number	US-10822680-B2
Application number	US-201615563986-A
Country	US
Kind code	B2
Filing date	Apr 7, 2016
Priority date	Apr 8, 2015
Publication date	Nov 3, 2020
Grant date	Nov 3, 2020

Abstract

A steel sheet for heat treatment having a chemical composition including, by mass %: C: 0.05 to 0.50%; Si: 0.50 to 5.0%; Mn; 1.5 to 4.0%; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ti: 0.01 to 0.10%; B: 0.0005 to 0.010%; Cr: 0 to 1.0%; Ni: 0 to 2.0%; Cu: 0 to 1.0%; Mo: 0 to 1.0%; V: 0 to 1.0%; Ca: 0 to 0.01%; Al: 0 to 1.0%; Nb: 0 to 1.0%; REM: 0 to 0.1%; and the balance: Fe and impurities, wherein a maximum height roughness Rz on a surface of the steel sheet is 3.0 to 10.0 μm, and a number density of carbide being present in the steel sheet and having circle-equivalent diameters of 0.1 μm or larger is 8.0×103/mm2 or lower.

First claim

What is claimed is:

1. A steel sheet for heat treatment having a chemical composition comprising, by mass %:
C: 0.05 to 0.50%;
Si: 0.50 to 5.0%;
Mn: 1.5 to 4.0%;
P: 0.05% or less;
S: 0.05% or less;
N: 0.01% or less;
Ti: 0.01 to 0.10%;
B: 0.0005 to 0.010%;
Cr: 0 to 1.0%;
Ni: 0 to 2.0%;
Cu: 0 to 1.0%;
Mo: 0 to 1.0%;
V: 0 to 1.0%;
Ca: 0 to 0.01%;
Al: 0 to 1.0%;
Nb: 0 to 1.0%;
REM: 0 to 0.1%; and
the balance: Fe and impurities, wherein
a maximum height roughness Rz on a surface of the steel sheet is 3.0 to 10.0 μm,
carbides are present in the steel sheet, and a number density of the carbides, each having a circle-equivalent diameter of 0.1 μm or larger, is 8.0×10 3 /mm 2 or lower, and
a Mn segregation degree α expressed by a following formula (1) is 1.6 or lower:
α=[Maximum Mn concentration (mass %) at sheet-thickness center portion]/[Average Mn concentration (mass %) in ¼ sheet-thickness depth position from surface]  (i).

2. The steel sheet for heat treatment according to claim 1 , wherein the chemical composition contains, by mass %, one or more elements selected from:
Cr: 0.01 to 1.0%;
Ni: 0.1 to 2.0%;
Cu: 0.1 to 1.0%;
Mo: 0.1 to 1.0%;
V: 0.1 to 1.0%;
Ca: 0.001 to 0.01%;
Al: 0.01 to 1.0%;
Nb: 0.01 to 1.0%; and
REM: 0.001 to 0.1%.

3. The steel sheet for heat treatment according to claim 1 , wherein an index of cleanliness of steel specified in JIS G 0555(2003) is 0.10% or lower.

4. The steel sheet for heat treatment according to claim 2 , wherein an index of cleanliness of steel specified in JIS G 0555(2003) is 0.10% or lower.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Suwa Yoshihiro
• Tabata Shinichiro
• Azuma Masafumi
• Hikida Kazuo

Classifications

• C22C38/58 Primary

  with more than 1.5% by weight of manganese · CPC title

• C22C38/00

  Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00) · CPC title

• C21D8/04 Primary

  to produce plates or strips for drawing, e.g. for deep-drawing · CPC title

• B22D11/001

  of specific alloys · CPC title

• B22D11/00

  Continuous casting of metals, i.e. casting in indefinite lengths (metal drawing, metal extruding B21C) · CPC title