Duplex stainless steel, seamless steel pipe or tube, and a method of manufacturing the duplex stainless steel

Patent metadata

Field	Value
Publication number	US-12344910-B2
Application number	US-201917426245-A
Country	US
Kind code	B2
Filing date	Nov 14, 2019
Priority date	Jan 30, 2019
Publication date	Jul 1, 2025
Grant date	Jul 1, 2025

Abstract

Provided is duplex stainless steel which has high strength and high toughness and can be subjected to hot working during manufacturing processes, the duplex stainless steel having a predetermined chemical composition and a microstructure containing an austenite phase in a volume fraction of 20% to 70% and a ferrite phase in a volume fraction of 30% to 80%, and mechanical properties such that a yield strength is 862 MPa or more and an absorption energy in a Charpy impact test at −10° C., vE −10 , is 40 J or more.

First claim

The invention claimed is:

1. Duplex stainless steel comprising:
a chemical composition containing, in mass %,
C: 0.03% or less,
Si: 1.0% or less,
Mn: 0.10% to 1.5%,
P: 0.030% or less,
S: 0.005% or less,
Cr: 20.0% to 30.0%,
Ni: 5.0% to 10.0%,
Mo: 2.0% to 5.0%,
Cu: 1.0% or more and less than 2.0%, and
N: less than 0.075%,

with a balance being Fe and inevitable impurities,
a microstructure containing:
an austenite phase in a volume fraction of 30% to 70%; and
a ferrite phase in a volume fraction of 30% to 70%; and

mechanical properties such that a yield strength YS is 862 MPa or more and an absorption energy in a Charpy impact test at −10° C., vE −10 , is 40 J or more.

2. The duplex stainless steel according to claim 1 , wherein the chemical composition further contains, in mass %, at least one of the group consisting of
a) W: 1.5% or less,
b) V: 0.20% or less,
c) at least one of Zr: 0.50% or less and B: 0.0030% or less,
d) at least one selected from the group consisting of REM: 0.005% or less, Ca: 0.005% or less, Sn: 0.20% or less, and Mg: 0.01% or less,
e) at least one selected from the group consisting of Ta: 0.1% or less, Co: 1.0% or less, and Sb: 1.0% or less, and
f) at least one selected from the group consisting of Al: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less.

3. The duplex stainless steel according to claim 1 , wherein the chemical composition contains, in mass %, Cr: 21.0% to 30.0%.

4. A seamless steel pipe or tube made of the duplex stainless steel according to claim 1 .

5. A seamless steel pipe or tube made of the duplex stainless steel according to claim 2 .

6. A method of manufacturing the duplex stainless steel according to claim 1 , the method comprising:
subjecting a steel raw material having the chemical composition according to claim 1 to solution treatment whereby the steel raw material is heated to a heating temperature of 1000° C. or higher; then, cooled at an average cooling rate of 1° C./s or more to a cooling stop temperature of 300° C. or lower,
subjecting the steel raw material after the solution treatment to cold working with a rolling reduction in a thickness direction of 5% to 10%, and
subjecting the steel raw material after the cold working to aging heat treatment whereby the steel raw material is heated to a heating temperature of 350° C. to 600° C., held at the heating temperature for a holding time of 5 minutes or more and 100 minutes or less, and subsequently cooled.

7. A method of manufacturing the duplex stainless steel according to claim 2 , the method comprising:
subjecting a steel raw material having the chemical composition according to claim 2 to solution treatment whereby the steel raw material is heated to a heating temperature of 1000° C. or higher; then, cooled at an average cooling rate of 1° C./s or more to a cooling stop temperature of 300° C. or lower,
subjecting the steel raw material after the solution treatment to cold working with a rolling reduction in a thickness direction of 5% to 10%, and
subjecting the steel raw material after the cold working to aging heat treatment whereby the steel raw material is heated to a heating temperature of 350° C. to 600° C., held at the heating temperature for a holding time of 5 minutes or more and 100 minutes or less, and subsequently cooled.

Assignees

• Jfe Steel Corp

Inventors

• Yoshimura Yusuke
• Sasaki Shunsuke
• Kamo Yuichi

Classifications

• C21D8/10

  during manufacturing of tubular bodies · CPC title

• C22C38/54

  with boron · CPC title

• C22C38/50

  with titanium or zirconium · CPC title

• C22C38/48

  with niobium or tantalum · CPC title

• C22C38/46

  with vanadium · CPC title