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

Patent metadata

Field	Value
Publication number	US-10077489-B2
Application number	US-201214408662-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; Nb: 0.005% or more to 0.025% or less; and N: 0.005% or less, on a mass percent basis, such that C and Nb satisfy 0.10≤Nb/C≤0.30 (where C and Nb are respective contents of the elements (by mass %)), wherein balance comprises Fe and incidental impurities, and a microstructure that is a complex-phase microstructure containing ferrite and pearlite, and the microstructure having a ratio of a microstructure other than the ferrite and the pearlite of 1% or less, and the microstructure having a ratio of polygonal ferrite in the ferrite of less than 50%.

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: 0.01% or more to 0.06% or less;
Cr: 0.5% or more to 1.5% or less;
Nb: 0.005% or more to 0.025% or less; and
N: 0.005% or less, on a mass percent basis, such that C and Nb satisfy the formula 0.10≤Nb/C≤0.30, where C and Nb are respective contents of the elements (by mass %),
wherein balance comprises Fe and incidental impurities, and

a microstructure that is a complex-phase microstructure containing ferrite and pearlite, the microstructure having a ratio of a microstructure other than the ferrite and the pearlite of 1% or less, the microstructure having a ratio of polygonal ferrite in the ferrite of less than 50%.

2. 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: 0.5% 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;
Nb: 0.005% or more to 0.025% or less; and
N: 0.005% or less, on a mass percent basis, such that C and Nb satisfy the formula 0.10≤Nb/C≤0.30, where C and Nb are respective contents of the elements (by mass %),
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 to 500° C. or more to 650° C. or less.

Assignees

• Kobayashi Takashi
• Nakamura Nobuyuki
• Mega Tetsuya
• Jfe Steel Corp

Inventors

• Kobayashi Takashi
• Nakamura Nobuyuki
• Mega Tetsuya

Classifications

• C21D8/0263

  following hot rolling · CPC title

• C21D6/008

  containing Si · CPC title

• C21D6/005

  containing Mn · CPC title

• C21D6/002

  containing Cr (C21D6/004 takes precedence) · CPC title

• C22C38/00

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