Free-cutting steel and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-12404573-B2
Application number	US-202017757601-A
Country	US
Kind code	B2
Filing date	Dec 23, 2020
Priority date	Dec 23, 2019
Publication date	Sep 2, 2025
Grant date	Sep 2, 2025

Abstract

Free-cutting steel includes a specific composition, with an A value defined by a following formula (1) satisfying 4.0 or more and 20.0 or less, and remainder having Fe and an unavoidable impurity; and texture with 1000 or more sulfide particles with an equivalent circle diameter of less than 1 μm per mm 2 , 500 or more sulfide particles with an equivalent circle diameter of 1 μm or more and 5 μm or less per mm 2 , and 1000 or more Pb particles with an equivalent circle diameter of 1 μm or less per mm 2 , wherein

A value=(Mn+5Cr)/S  (1)
here, symbols of elements in the formula indicate contents (% by mass) of the elements.

First claim

The invention claimed is:

1. A free-cutting steel comprising:
a composition of, in % by mass,
0.15% or less of C,
0.5% or more and 2.0% or less of Mn,
0.200% or more and 0.650% or less of S,
more than 0.01% and 0.05% or less of O,
0.05% or more and 2.00% or less of Cr,
0.02% or more and less than 0.10% of Pb,
0.005% or more and 0.015% or less of N,
with an A value defined by a following formula (1) satisfying 4.0 or more and 20.0 or less, and
a remainder being Fe and unavoidable impurities; and
a microstructure with 1000 or more sulfide particles with an equivalent circle diameter of less than 1 μm per mm 2 , 500 or more sulfide particles with an equivalent circle diameter of 1 μm or more and 5 μm or less per mm 2 , and 1000 or more Pb particles with an equivalent circle diameter of 1 μm or less per mm 2 ,
wherein
A value=(Mn+5Cr)/S  (1)

here, symbols of elements in the formula (1) indicate contents, in % by mass, of the elements.

2. The free-cutting steel according to claim 1 , wherein the composition further contains, in % by mass, any one or more of:
0.10% or less of Si;
0.01% or more and 0.15% or less of P; and
0.010% or less of Al.

3. The free-cutting steel according to claim 1 , wherein the composition further contains, in % by mass, any one or more of:
0.0010% or less of Ca;
0.30% or less of Se;
0.15% or less of Te;
0.20% or less of Bi;
0.020% or less of Sn;
0.025% or less of Sb;
0.010% or less of B;
0.50% or less of Cu;
0.50% or less of Ni;
0.100% or less of Ti;
0.20% or less of V;
0.050% or less of Zr; and
0.0050% or less of Mg.

4. The free-cutting steel according to claim 2 , wherein the composition further contains, in % by mass, any one or more of:
0.0010% or less of Ca;
0.30% or less of Se;
0.15% or less of Te;
0.20% or less of Bi;
0.020% or less of Sn;
0.025% or less of Sb;
0.010% or less of B;
0.50% or less of Cu;
0.50% or less of Ni;
0.100% or less of Ti;
0.20% or less of V;
0.050% or less of Zr; and
0.0050% or less of Mg.

Assignees

• Jfe Steel Corp

Inventors

• Kasai Masayuki
• Fukuoka Kazuaki
• Nishimura Kimihiro

Classifications

• C22C38/38 Primary

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

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title

• C22C38/001

  containing N · CPC title

• C21D8/0226

  Hot rolling · CPC title

• B21B2001/022

  Blooms or billets · CPC title