Duplex stainless steel and method for manufacturing same, and duplex stainless steel pipe

Patent metadata

Field	Value
Publication number	US-12264376-B2
Application number	US-202017613316-A
Country	US
Kind code	B2
Filing date	Apr 9, 2020
Priority date	May 29, 2019
Publication date	Apr 1, 2025
Grant date	Apr 1, 2025

Abstract

The invention is intended to provide a duplex stainless steel and a method for manufacturing same. A duplex stainless steel pipe is also provided. A duplex stainless steel of the present invention has a specific composition, and has a microstructure containing an austenitic phase and a ferrite phase. The duplex stainless steel satisfies the following contents for C, Si, Mn, Cr, Mo, Ni, N, Cu, and W in the formula (1) below, and has a yield strength YS of 655 MPa or more, and an absorption energy vE −10 of 40 J or more as measured by a Charpy impact test at a test temperature of −10° C.

0.55[% C]−0.056[% Si]+0.018[% Mn]−0.020[% Cr]−0.087[% Mo]+0.16[% Ni]+0.28[% N]−0.506[% Cu]−0.035[% W]+[% Cu*F]≤0.94  (1)

First claim

The invention claimed is:

1. A duplex stainless steel having a composition comprising, in mass %,
C: 0.03% or less,
Si: 1.0% or less,
Mn: 0.10 to 1.5%,
P: 0.040% or less,
S: 0.01% or less,
Cr: 20.0 to 28.0%,
Ni: 2.0 to 10.0%,
Mo: 2.0 to 5.0%,
Cu: 2.0 to 6.0%,
Al: 0.001 to 0.05%, and
N: less than 0.070%,
and in which the balance is Fe and incidental impurities,
the duplex stainless steel having a microstructure containing an austenitic phase and a ferrite phase, and satisfying the following contents for C, Si, Mn, Cr, Mo, Ni, N, Cu, and W in the formula (1) below,
the duplex stainless steel having a yield strength YS of 655 MPa or more, and an absorption energy vE −10 of 40 J or more as measured by a Charpy impact test at a test temperature of −10° C.,
0.55[% C]−0.056[% Si]+0.018[% Mn]−0.020[% Cr]−0.087[% Mo]+0.16[% Ni]+0.28[% N]−0.506[% Cu]−0.035[% W]+[% Cu*F]≤0.94  (1),

wherein [% symbol of elements] represents the content (mass %) of the element in the steel, [% symbol of elements *F] represents the content (mass %) of the element in the ferrite phase, and the contents are zero for elements that are not contained.

2. The duplex stainless steel according to claim 1 , wherein the composition further comprises, in mass %, one or two or more groups selected from the following groups A to E,
group A: W: 1.5% or less,
group B: V: 0.20% or less,
group C: one or two selected from Zr: 0.50% or less, and B: 0.0030% or less,
group D: one or two or more selected from REM: 0.005% or less, Ca: 0.005% or less, Sn: 0.20% or less, and Mg: 0.01% or less,
group E: one or two or more selected from Ta: 0.1% or less, Co: 1.0% or less, and Sb: 1.0% or less.

3. A duplex stainless steel pipe using the duplex stainless steel of claim 1 .

4. The duplex stainless steel pipe according to claim 3 , wherein the composition of the duplex stainless steel further comprises, in mass %, one or two or more groups selected from the following groups A to E,
group A: W: 1.5% or less,
group B: V: 0.20% or less,
group C: one or two selected from Zr: 0.50% or less, and B: 0.0030% or less,
group D: one or two or more selected from REM: 0.005% or less, Ca: 0.005% or less, Sn: 0.20% or less, and Mg: 0.01% or less,
group E: one or two or more selected from Ta: 0.1% or less, Co: 1.0% or less, and Sb: 1.0% or less.

5. A method for manufacturing a duplex stainless steel, comprising subjecting a steel material of the composition of claim 1 to
a σ-phase precipitation treatment that heats the steel material to a temperature of 700° C. or more and 950° C. or less, and cools the heated steel material to a temperature of 300° C. or less at an average cooling rate of air cooling or faster,
a solution heat treatment that heats the steel material to a temperature of 1,000° C. or more, and cools the heated steel material to a temperature of 300° C. or less at an average cooling rate of air cooling or faster, and an aging heat treatment that heats the steel material to a temperature of 350 to 600° C., and cools the heated steel material.

6. The method for manufacturing a duplex stainless steel according to claim 5 , wherein the composition further comprises, in mass %, one or two or more groups selected from the following groups A to E,
group A: W: 1.5% or less,
group B: V: 0.20% or less,
group C: one or two selected from Zr: 0.50% or less, and B: 0.0030% or less,
group D: one or two or more selected from REM: 0.005% or less, Ca: 0.005% or less, Sn: 0.20% or less, and Mg: 0.01% or less,
group E: one or two or more selected from Ta: 0.1% or less, Co: 1.0% or less, and Sb: 1.0% or less.

Assignees

• Jfe Steel Corp

Inventors

• Fujimura Kazuki
• Eguchi Kenichiro
• Yoshimura Yusuke
• Yuga Masao

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C21D8/10

  during manufacturing of tubular bodies · CPC title

• C22C38/58

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

• C22C38/54

  with boron · CPC title

• C22C38/52

  with cobalt · CPC title