Dual-phase stainless steel, and method of production thereof

Patent metadata

Field	Value
Publication number	US-11566301-B2
Application number	US-201716325572-A
Country	US
Kind code	B2
Filing date	Aug 22, 2017
Priority date	Sep 2, 2016
Publication date	Jan 31, 2023
Grant date	Jan 31, 2023

Abstract

Provided herein is a dual-phase stainless steel having excellent carbon dioxide corrosion resistance, excellent sulfide stress corrosion cracking resistance, and excellent sulfide stress cracking resistance. The dual-phase stainless steel contains, 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: 2.0 to 6.0%, N: less than 0.07%, and the balance Fe and unavoidable impurities, and has a structure that is 20 to 70% austenite phase, and 30 to 80% ferrite phase in terms of a volume fraction.

First claim

The invention claimed is:

1. A dual-phase stainless steel of a composition consisting of, 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: 2.0 to 6.0%, N: 0.03% or less, and optionally including at least one group selected from the groups A to D consisting of:
Group A: W: 0.02 to 1.5%,
Group B: at least one selected from Zr: 0.50% or less, and B: 0.0030% or less,
Group C: at least one selected from REM: 0.005% or less, Ca: 0.005% or less, Sn: 0.20% or less, and Mg: 0.0002 to 0.01%,
Group D: at least one selected from Ta: 0.01 to 0.1%, Co: 0.01 to 1.0%, and Sb: 0.01 to 1.0%,
with the balance Fe and unavoidable impurities,
the dual-phase stainless steel having a structure that is 20 to 70% austenite phase and 30 to 80% ferrite phase in terms of a volume fraction, 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.

2. The dual-phase stainless steel according to claim 1 , wherein the stainless steel is a seamless steel pipe and wherein the structure has a GSI value of 176 or more at a central portion in a wall thickness of the steel pipe, the GSI value being defined as a number of ferrite-austenite grain boundaries that are present per unit length of 1 mm of a line segment drawn in a wall thickness direction.

3. A method for producing a dual-phase stainless steel having a structure that is 20 to 70% austenite phase and 30 to 80% ferrite phase in terms of volume fraction, 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.,
the method comprising subjecting a stainless steel of a composition consisting of, 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: 2.0 to 6.0%, N: 0.03% or less, and optionally including at least one group selected from the groups A to D consisting of:
Group A: W: 0.02 to 1.5%,
Group B: at least one selected from Zr: 0.50% or less, and B: 0.0030% or less,
Group C: at least one selected from REM: 0.005% or less, Ca: 0.005% or less, Sn: 0.20% or less, and Mg: 0.0002 to 0.01%,
Group D: at least one selected from Ta: 0.01 to 0.1%, Co: 0.01 to 1.0%, and Sb: 0.01 to 1.0%,
with the balance Fe and unavoidable impurities to the following:
a solution heat treatment in which the stainless steel is heated to a heating temperature of 1,000° C. or more, and cooled to a temperature of 300° C. or less at an average cooling rate of air cooling or faster; and
an aging heat treatment in which the stainless steel is heated to a temperature of 350° C. to 600° C., and cooled.

4. The method according to claim 3 , wherein the stainless steel is a seamless steel pipe made from a steel material of the composition by heating and hot working the steel material to prepare a steel pipe material, heating the steel pipe material, forming a steel pipe out of the steel pipe material, and shaping the steel pipe, followed by cooling of air cooling or faster, the hot working involving a total reduction of 30% or more and 50% or less in a temperature range of 1,200° C. to 1,000° C.

Assignees

• Jfe Steel Corp

Inventors

• Yoshimura Yusuke
• Ota Hiroki
• Yuga Masao
• Kamo Yuichi
• Eguchi Kenichiro

Classifications

• C21D2211/005

  Ferrite · CPC title

• C22C38/46

  with vanadium · CPC title

• C21D2211/001

  Austenite · CPC title

• C22C38/52

  with cobalt · CPC title

• C22C38/004

  Very low carbon steels, i.e. having a carbon content of less than 0,01% · CPC title