Steel sheet for soft-nitriding and method for manufacturing the same

Patent metadata

Field	Value
Publication number	US-10077485-B2
Application number	US-201214409549-A
Country	US
Kind code	B2
Filing date	Jun 27, 2012
Priority date	Jun 27, 2012
Publication date	Sep 18, 2018
Grant date	Sep 18, 2018

Abstract

A steel sheet for soft-nitriding has a composition containing: C: 0.05% or more to 0.10% or less; Si: 0.5% or less; Mn: 0.7% or more to 1.5% or less; P: 0.05% or less; S: 0.01% or less; Al: 0.01% or more to 0.06% or less; Cr: 0.5% or more to 1.5% or less; V: 0.03% or more to 0.30% or less; and N: 0.005% or less, on a mass percent basis, wherein a ratio of amount of solute V to the V content (amount of solute V/V content) is more than 0.50, and balance comprises Fe and incidental impurities, and a complex-phase microstructure containing ferrite and pearlite.

First claim

The invention claimed is:

1. A steel sheet for soft-nitriding, having:
a chemical composition containing:
C: 0.05% or more to 0.10% or less;
Si: 0.5% or less;
Mn: 0.7% or more to 1.5% or less;
P: 0.05% or less;
S: 0.01% or less;
Al: 0.03% or more to 0.06% or less;
Cr: 0.5% or more to 1.5% or less;
Ti: 0% or more to 0.005% or less;
V: 0.03% or more to 0.30% or less; and
N: 0.003% or less, on a mass percent basis,

wherein a ratio of amount of solute V on a mass percent basis to the V content on a mass percent basis is more than 0.50, and balance comprises Fe and incidental impurities, and
a complex-phase microstructure containing ferrite and pearlite.

2. The steel sheet for soft-nitriding according to claim 1 , wherein the chemical composition further contains
Nb of 0.005% or more to 0.025% or less by mass %.

3. A method for manufacturing a steel sheet for soft-nitriding, including:
heating a steel slab;
performing hot rolling that includes rough rolling and finish rolling; and
after the finish rolling, cooling and coiling the steel sheet to produce a hot-rolled steel sheet, wherein
the steel slab has a chemical composition containing:
C: 0.05% or more to 0.10% or less;
Si: 0.6% or less;
Mn; 0.7% or more to 1.4% or less;
P; 0.05% or less;
S: 0.01% or less;
At: 0.03% or more to 0.06% or less;
Cr 0.5% or more to 1.5% or less;
Ti: 0% or more to 0.005% or less;
V: 0.03% or more to 0.30% or less; and
N: 0.005% or less, on a mass percent basis,

wherein balance comprises Fe and incidental impurities, and
setting a heating temperature of the hot rolling from 1100° C. or more to 1300° C. or less,
setting a finishing temperature of the finish rolling from an Ar 3 transformation point or more to (Ar 3 transformation point+100° C.) or less,
setting an average cooling rate of the cooling to 30° C./s or more, and
setting a coiling temperature of the coiling from 500° C. or more to 600° C. or less, such that the steel sheet of claim 1 is formed.

4. The method for manufacturing the steel sheet for soft-nitriding according to claim 3 , wherein the chemical composition further contains
Nb of 0.005% or more to 0.025% or less by mass %.

Assignees

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

Inventors

• Kobayashi Takashi
• Nakamura Nobuyuki
• Funakawa Yoshimasa

Classifications

• C22C38/02

  containing silicon · CPC title

• C21D9/46 Primary

  for sheet metals · CPC title

• C21D6/005

  containing Mn · CPC title

• C22C38/04

  containing manganese · CPC title

• C21D2211/005

  Ferrite · CPC title