High carbon thin steel sheet and method for producing same

Patent metadata

Field	Value
Publication number	US-9394595-B2
Application number	US-201214117757-A
Country	US
Kind code	B2
Filing date	May 16, 2012
Priority date	May 18, 2011
Publication date	Jul 19, 2016
Grant date	Jul 19, 2016

Abstract

A high carbon steel sheet having a chemical composition containing C: 0.20% to 0.50%, Si: 1.0% or less, Mn: 2.0% or less, P: 0.03% or less, S: 0.02% or less, sol. Al: 0.08% or less, N: 0.02% or less, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, and a microstructure composed of ferrite and cementite, wherein the fraction of pro-eutectoid ferrite, among the ferrite, in the whole steel microstructure is 20% or more and less than 50%, the average grain size dc of the cementite in the region from the position at one-quarter of the sheet thickness of the steel sheet to the sheet thickness center is 0.50 to 1.5 μm, and the average grain size ds of the cementite in the region from the surface of the steel sheet to the position at one-quarter of the sheet thickness satisfies ds/dc≦0.8.

First claim

The invention claimed is:

1. A high carbon steel sheet having a chemical composition containing C: 0.20% to 0.50%, Si: 1.0% or less, Mn: 2.0% or less, P: 0.03% or less, S: 0.02% or less, sol.Al: 0.08% or less, N: 0.02% or less, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, and a microstructure composed of ferrite and cementite, wherein the fraction of pro-eutectoid ferrite, among the ferrite, in the whole steel microstructure is 20% or more and less than 50%, the average grain size dc of the cementite in the region from the position at one-quarter of the sheet thickness of the steel sheet to the sheet thickness center is 0.50 to 1.5 μm, and the average grain size ds of the cementite in the region from the surface of the steel sheet to the position at one-quarter of the sheet thickness satisfies ds/dc≦0.8.

2. The high carbon steel sheet according to claim 1 , further comprising at least one selected from the group consisting of Cr: 0.1% to 1.5%, Mo: 0.1% to 0.5%, Ni: 0.1% to 1.0%, Ti: 0.01% to 0.05%, Nb: 0.01% to 0.05%, V: 0.01% to 0.05%, and B: 0.0005% to 0.0050% on a percent by mass basis.

3. The high carbon steel sheet according to claim 1 , wherein the Si content is 0.1% or more and 0.5% or less.

4. The high carbon steel sheet according to claim 1 , wherein the Mn content is 0.2% or more and 1.0% or less.

5. The high carbon steel sheet according to claim 1 , wherein the ds/dc is 0.7 or more and 0.8 or less.

6. The high carbon steel sheet according to claim 1 , wherein a Rockwell hardness in HRB after annealing is 85 or less.

7. The high carbon steel sheet according to claim 1 , wherein a Rockwell hardness in HRC after induction hardening is 40 or more.

Assignees

• Kobayashi Takashi
• Nakamura Nobuyuki
• Funakawa Yoshimasa
• Jfe Steel Corp

Inventors

• Kobayashi Takashi
• Nakamura Nobuyuki
• Funakawa Yoshimasa

Classifications

• C22C38/18

  containing chromium · CPC title

• C22C38/44 Primary

  with molybdenum or tungsten · CPC title

• C21D1/42

  Induction heating · CPC title

• C21D2211/005

  Ferrite · CPC title

• C21D2211/003

  Cementite · CPC title