Duplex stainless steel and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-11512374-B2
Application number	US-201816498725-A
Country	US
Kind code	B2
Filing date	Mar 30, 2018
Priority date	Mar 30, 2017
Publication date	Nov 29, 2022
Grant date	Nov 29, 2022

Abstract

A duplex stainless steel and method of manufacturing the same, said steel having an amount of Cr in an extraction residue [Cr] of 0.005 to 0.050% and an amount of Nb in an extraction residue [Nb] of 0.001 to 0.080%, the [Nb]/[Cr] ratio being 0.2 or more. By slow cooling down to 800° C., then fast cooling down to 600° C., it is possible to control the precipitation of chromium nitrides and niobium nitrides, and by making the ratio [Nb]/[Cr] 0.2 or more, it is possible to raise the corrosion resistance. Further, by reducing Mn to less than 2.0% and N to 0.25% or less, then adding a trace amount of Nb, the effect of raising the critical pitting temperature CPT is obtained.

First claim

The invention claimed is:

1. Duplex stainless steel comprising, by mass %,
C: 0.001 to 0.03%,
Si: 0.05 to 1.5%,
Mn: 0.1 to 1.5%,
Cr: 20.0 to 26.0%,
Ni: 2.0 to 7.0%,
Mo: 0.5 to 3.0%,
N: 0.10 to 0.25%,
Nb: 0.005 to 0.10%, and
Al: 0.003 to 0.05%,
further comprising one or more of
W: 0.01 to 1%,
Co: 0.01 to 1.0%,
Cu: 0.01 to 2.0%,
V: 0.01 to 0.3%,
Ti: 0.001 to 0.03%, and
B: 0.0001 to 0.0050%,
having a balance of Fe and unavoidable impurities, and
in impurities, restricting
O: 0.006% or less,
P: 0.05% or less, and
S: 0.003% or less,
said steel having
an amount of Cr in an extraction residue [Cr] of 0.005 to 0.050 mass %,
an amount of Nb in an extraction residue [Nb] of 0.001 to 0.080 mass %, and
an [Nb]/[Cr] ratio being 0.2 or more.

2. Duplex stainless steel comprising, by mass %,
C: 0.001 to 0.03%,
Si: 0.05 to 1.5%,
Mn: 0.1 to 1.5%,
Cr: 20.0 to 26.0%,
Ni: 2.0 to 7.0%,
Mo: 0.5 to 3.0%,
N: 0.10 to 0.25%,
Nb: 0.005 to 0.10%,
Al: 0.003 to 0.05%,
Ca: 0.0005 to 0.005%, and
Mg: 0.0001 to 0.003%,
further comprising one or more of,
W: 0.01% to 1%,
Co: 0.01 to 1.0%,
Cu: 0.01 to 2.0%,
V: 0.01 to 0.3%,
Ti: 0.001 to 0.03%,
B: 0.0001 to 0.0050%, and
REM: 0.005 to 0.10%,
having a balance of Fe and unavoidable impurities,
in impurities, restricting
O: 0.006% or less,
P: 0.05% or less, and
S: 0.003% or less,
said steel having
an amount of Cr in an extraction residue [Cr] of 0.005 to 0.050 mass %,
an amount of Nb in an extraction residue [Nb] of 0.001 to 0.080 mass %, and
an [Nb]/[Cr] ratio being 0.2 or more.

3. The duplex stainless steel according to claim 1 , wherein an actual critical pitting temperature (CPT measured value), in ° C., of the duplex stainless steel is greater than or equal to a CPT calculated value in ° C. obtained by equation 1:
CPT calculated value=2.86(Cr+3.3(Mo+0.5W)+16N—Mn)−45  (equation 1)

wherein Cr, Mo, W, N, and Mn in equation 1 represent the content in mass % of the corresponding elements in the duplex stainless steel.

4. The duplex stainless steel according to claim 2 , wherein an actual critical pitting temperature (CPT measured value), in ° C., of the duplex stainless steel is greater than or equal to a CPT calculated value in ° C. obtained by equation 1:
CPT calculated value=2.86(Cr+3.3(Mo+0.5W)+16N—Mn)−45  (equation 1)

wherein Cr, Mo, W, N, and Mn in equation 1 represent the content in mass % of the corresponding elements in the duplex stainless steel.

5. A method of manufacturing the duplex stainless steel of claim 1 , said method comprising
heating to a temperature of a temperature region of 940 to 1150° C., wherein the steel has a composition comprising, by mass %,
C: 0.001 to 0.03%,
Si: 0.05 to 1.5%,
Mn: 0.1 to 1.5%,
Cr: 20.0 to 26.0%,
Ni: 2.0 to 7.0%,
Mo: 0.5 to 3.0%,
N: 0.10 to 0.25%,
Nb: 0.005 to 0.10%, and
Al: 0.003 to 0.05%,
further comprising one or more of
W: 0.01% to 1%,
Co: 0.01 to 1.0%,
Cu: 0.01 to 2.0%,
V: 0.01 to 0.3%,
Ti: 0.001 to 0.03%, and
B: 0.0001 to 0.0050%,
having a balance of Fe and unavoidable impurities,
in impurities, restricting
O: 0.006% or less,
P: 0.05% or less, and
S: 0.003% or less,
then cooling the steel by an average cooling rate of less than 5° C./s until a temperature of said steel becomes a temperature of 1080° C. to 800° C., then cooling the steel so that an average cooling rate from 800° C. to 600° C. in temperature of the steel becomes 3° C./s or more.

6. A method of manufacturing the duplex stainless steel of claim 2 , said method comprising
heating to a temperature of a temperature region of 940 to 1150° C., wherein the steel has a composition comprising, by mass %,
C: 0.001 to 0.03%,
Si: 0.05 to 1.5%,
Mn: 0.1 to 1.5%,
Cr: 20.0 to 26.0%,
Ni: 2.0 to 7.0%,
Mo: 0.5 to 3.0%,
N: 0.10 to 0.25%,
Nb: 0.005 to 0.10%,
Al: 0.003 to 0.05%,
Ca: 0.0005 to 0.005%, and
Mg: 0.0001 to 0.003%,
further comprising one or more of
W: 0.01% to 1%,
Co: 0.01 to 1.0%,
Cu: 0.01 to 2.0%,
V: 0.01 to 0.3%,
Ti: 0.001 to 0.03%,
B: 0.0001 to 0.0050%, and
REM: 0.005 to 0.10%,
having a balance of Fe and unavoidable impurities,
in impurities, restricting
O: 0.006% or less,
P: 0.05% or less, and
S: 0.003% or less,
then cooling the steel by an average cooling rate of less than 5° C./s until a temperature of said steel becomes a temperature of 1080° C. to 800° C., then cooling the steel so that an average cooling rate from 800° C. to 600° C. in temperature of the steel becomes 3° C./s or more.

Assignees

• Nippon Steel Stainless Steel Corp

Inventors

• Tsuge Shinji
• Oikawa Yuusuke

Classifications

• C21D8/02

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

• C22C38/005

  containing rare earths, i.e. Sc, Y, Lanthanides · CPC title

• C22C38/48

  with niobium or tantalum · CPC title

• C21D6/04

  Hardening by cooling below 0 degrees Celsius · CPC title

• C22C38/58

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