Free-cutting steel and method for manufacturing same

Patent metadata

Field	Value
Publication number	US-12522906-B2
Application number	US-202117906975-A
Country	US
Kind code	B2
Filing date	Mar 31, 2021
Priority date	Mar 31, 2020
Publication date	Jan 13, 2026
Grant date	Jan 13, 2026

Abstract

Free-cutting steel that has the same or better machinability compared to low-carbon sulfur-lead composite free-cutting steel, despite of no-addition of Pb, is provided. Free-cutting steel contains, in mass %, C: 0.08% or less, Mn: 0.50 to 1.50%, P: 0.100% or less, S: 0.250 to 0.500%, N: 0.0050 to 0.0150%, O: more than 0.0100% and 0.0500% or less, Cr: 0.50 to 1.50%, at least one of Si, Al, or Ti: 0.050 to 0.500% in total, with the balance being Fe and inevitable impurities, with an A value defined by formula (1) satisfying 0.40 to 2.00, and with a B value defined by formula (2) satisfying 1.10×10 −3 to 1.50×10 −2 ; and a steel microstructure with distributed 3000 or more sulfide particles with an equivalent circular diameter of 5 μm or less per mm 2 .

First claim

The invention claimed is:

1 . Free-cutting steel comprising:
a chemical composition containing, in mass %, C: 0.08% or less, Mn: 0.50 to 1.50%, P: 0.100% or less, S: 0.250 to 0.500%, N: 0.0050 to 0.0150%, O: more than 0.0100% and 0.0500% or less, Cr: 0.70 to 1.50%, and a total amount of at least one element selected from a group consisting of Si, Al, and Ti of 0.050 to 0.500%, wherein a content of Ti is 0.010% or less, with the balance being Fe and inevitable impurities, with an A value defined by a following formula (1) satisfying 0.40 to 2.00, and with a B value defined by a following formula (2) satisfying 1.10×10 −3 to 1.50×10 −2 ; and a steel microstructure with distributed 3000 or more sulfide particles with an equivalent circular diameter of 5 μm or less per mm 2 , wherein
A value=[Mn]/[Cr]  (1)

B value=(2[Si]+2+[Ti])×[O]  (2)

where [M] indicates a content in mass % of an element M described in [ ].

2 . The free-cutting steel according to claim 1 , wherein the chemical composition further contains, in mass %, at least one selected from the group consisting of:
Ca: 0.0010% or less; Se: 0.30% or less; Te: 0.15% or less; Bi: 0.20% or less; Sn: 0.020% or less; Sb: 0.025% or less; B: 0.010% or less; Cu: 0.50% or less; Ni: 0.50% or less; V: 0.20% or less; Zr: 0.050% or less; Nb: 0.100% or less; and Mg: 0.0050% or less.

3 . The free-cutting steel according to claim 1 , wherein the sulfide is in a Mn—Cr—S system.

4 . A method for manufacturing the free-cutting steel according to claim 1 , comprising:
rolling a rectangular cast steel into a billet at a heating temperature of 1120° C. or more and an area reduction rate of 60% or more, the cast steel having a cross section perpendicular to a longitudinal direction with a side length of 250 mm or more, the cast steel having a chemical composition containing, in mass %, C: 0.08% or less, Mn: 0.50% to 1.50%, P: 0.100% or less, S: 0.250% to 0.500%, N: 0.0050% to 0.0150%, O: more than 0.0100% and 0.0500% or less, Cr: 0.70% to 1.50%, and a total amount of at least one element selected from a group consisting of Si, Al, and Ti of 0.050 to 0.500%, wherein a content of Ti is 0.010% or less, with the balance being Fe and inevitable impurities, with an A value defined by a following formula (1) satisfying 0.40 to 2.00, and with a B value defined by a following formula (2) satisfying 1.10×10 −3 to 1.50×10 −2 ; and hot-working the billet at a heating temperature of 1050° C. or more and an area reduction rate of 95% or more, wherein
A value=[Mn]/[Cr]  (1)

B value=(2[Si]+2[Al]+[Ti])×[O]  (2)

where [M] indicates a content in mass % of an element M described in [ ].

5 . The method for manufacturing free-cutting steel according to claim 4 , wherein the chemical composition further contains, in mass %, at least one selected from the group consisting of:
Ca: 0.0010% or less; Se: 0.30% or less; Te: 0.15% or less; Bi: 0.20% or less; Sn: 0.020% or less; Sb: 0.025% or less; B: 0.010% or less; Cu: 0.50% or less; Ni: 0.50% or less; V: 0.20% or less; Zr: 0.050% or less; Nb: 0.100% or less; and Mg: 0.0050% or less.

Assignees

• Jfe Steel Corp

Inventors

• Kasai Masayuki
• Fukuoka Kazuaki
• Nishimura Kimihiro

Classifications

• C22C38/18

  containing chromium · CPC title

• C22C38/04

  containing 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