# US 11,306,378 B2 · Duplex stainless steel

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- Number: US 11,306,378 B2
- Document ID: US11306378B2
- Status: Granted
- Kind: B2
- Application number: 16/969,711
- Filed: 2019-02-14
- Published: 2021-01-07
- Granted: 2022-04-19
- Earliest claimed: 2018-02-15
- Assignees: Sandvik Intellectual Property AB
- Applicants: Sandvik Intellectual Property AB
- Inventors: Tomas Antonsson; Lars Nylöf
- Web page: https://patentgrep.com/patent/US11306378B2

## CPC

- C22C 38/004: {Very low carbon steels, i.e. having a carbon content of less than 0,01%}
- C22C 38/58: with more than 1.5% by weight of manganese
- C21D 6/004: {containing Cr and Ni}
- C21D 6/005: {containing Mn}
- C21D 6/02: Hardening by precipitation
- C21D 8/00: Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02)
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/06: during manufacturing of rods or wires
- C21D 8/10: during manufacturing of tubular bodies
- C21D 9/08: for tubular bodies or pipes
- C21D 9/46: for sheet metals
- C21D 9/525: {for wire, for rods (C21D9/54 takes precedence)}
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- C22C 38/001: {containing N}
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/42: with copper
- C22C 38/44: with molybdenum or tungsten
- C21D 2211/001: Austenite
- C21D 2211/005: Ferrite
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)

## Abstract

The present disclosure relates to a duplex stainless steel comprising in weight % (wt %): C less than 0.03; Si less than 0.60; Mn 0.40 to 2.00; P less than 0.04; S less than or equal to 0.01; Cr more than 30.00 to 33.00; Ni 6.00 to 10.00; Mo 1.30 to 2.90; N 0.15 to 0.28; Cu 0.60 to 2.20; Al less than 0.05; balance Fe and unavoidable impurities. The present disclosure also relates to a component or a construction material comprising the duplex stainless steel. Additionally, the present disclosure also relates to a process for manufacturing a component comprising said duplex stainless steel.

## Claims

### Claim 1

A duplex stainless steel comprising in weight % (wt %):
C
less than 0.03;
Si
less than 0.60;
Mn
0.40 to 2.00;
P
less than 0.04;
S
less than or equal to 0.01;
Cr
more than 30.00 to 33.00;
Ni
6.00 to 10.00;
Mo
1.30 to 2.90;
N
0.15 to 0.28;
Cu
0.60 to 2.20;
Al
less than 0.05;
balance Fe and unavoidable impurities,
wherein said duplex stainless steel has a ferrite content of from 40 to 70 vol % and a balance is austenite,
wherein said duplex stainless steel has a CPT of greater than or equal to 50° C. and equal to or less than 65° C., where CPT is determined according to the G48A method, and
wherein said duplex stainless steel has a yield strength Rp0.2 of greater than 610 MPa determined by ASTM A-370.

### Claim 2 (depends on 1)

The duplex stainless steel according to claim 1, wherein said duplex stainless steel has a PRE, which is greater than or equal to 36 and wherein PRE=wt % Cr+3.3*wt % Mo.

### Claim 3 (depends on 1)

The duplex stainless steel according to claim 1, wherein the content of Al is less than 0.03 wt %.

### Claim 4 (depends on 1)

The duplex stainless steel according to claim 1, wherein the content of Si is less than 0.30 wt %.

### Claim 5 (depends on 1)

The duplex stainless steel according to claim 1, wherein the content of Mn is 0.60-1.80 wt %.

### Claim 6 (depends on 1)

The duplex stainless steel according to claim 1, wherein the content of Ni is 6.50-9.50 wt %.

### Claim 7 (depends on 1)

The duplex stainless steel according to claim 1, wherein the content of Cu is 1.10-1.90 wt %.

### Claim 8 (depends on 1)

The duplex stainless steel according to claim 1, wherein the content of N is 0.17-0.25 wt %.

### Claim 9 (depends on 1)

The duplex stainless steel according to claim 1, wherein the content of Cr is 30.50-32.50 wt %.

### Claim 10 (depends on 1)

The duplex stainless steel according to claim 1, wherein the content of Mo is 1.35-2.90 wt %.

### Claim 11 (depends on 1)

A method for manufacturing a component comprising a duplex stainless steel according to claim 1, the method comprising the following steps:
providing a melt comprising an alloy composition, including in weight % (wt %):
C
less than 0.03,
Si
less than 0.60,
Mn
0.40 to 2.00,
P
less than 0.04,
S
less than or equal to 0.01,
Cr
more than 30.00 to 33.00,
Ni
6.00 to 10.00,
Mo
1.30 to 2.90,
N
0.15 to 0.28,
Cu
0.60 to 2.20,
Al
less than 0.05,
balance Fe and unavoidable impurities;
casting the melt to an object;
optionally heat-treating the object;
hot working the object to a component;
heat-treating the component;
optionally cold working the component; and
optionally heat-treating the component;
wherein the heat treatment between the hot working and the optional cold working is a solution heat treatment.

### Claim 12 (depends on 1)

A component comprising a duplex stainless steel according to claim 1.

### Claim 13 (depends on 12)

The component according to claim 12, wherein the component is a forging, a bar, a rod, a plate, a wire, a sheet, a tube or a pipe.

### Claim 14 (depends on 1)

A construction material comprising a duplex stainless steel according to claim 1.

### Claim 15 (depends on 1)

The duplex stainless steel according to claim 1, wherein the content of Mo is 1.40-2.80 wt %.

### Claim 16 (depends on 1)

The duplex stainless steel according to claim 1, wherein said duplex stainless steel has a value for PRE of greater than or equal to 36 and equal to or less than 37, where PRE=wt % Cr+3.3*wt % Mo.

### Claim 17 (depends on 1)

The duplex stainless steel according to claim 1, wherein said duplex stainless steel has a vol. % of intermetallic phases of equal to or less than 25 vol. %, where the vol. % of intermetallic phases are determined during isothermal heating at a temperature of 900° C. for 3 hours.

### Claim 18 (depends on 1)

The duplex stainless steel according to claim 1, wherein said duplex stainless steel has an impact toughness equal to or greater than 130 J, where the impact toughness is determined on notched Charpy-V samples with dimensions of 10×10×55 mm at a test temperature of −50° C.

### Claim 19 (depends on 1)

The duplex stainless steel according to claim 1, wherein said duplex stainless steel has a value for PRE of greater than or equal to 36 and equal to or less than 37, where PRE=wt % Cr+3.3*wt % Mo,
wherein said duplex stainless steel has a vol. % of intermetallic phases of equal to or less than 25 vol. %, where the vol. % of intermetallic phases are determined during isothermal heating at a temperature of 900° C. for 3 hours, and
wherein said duplex stainless steel has an impact toughness equal to or greater than 130 J, where the impact toughness is determined on notched Charpy-V samples with dimensions of 10×10×55 mm at a test temperature of −50° C.

### Claim 20 (depends on 19)

The duplex stainless steel according to claim 19, wherein the vol. % of intermetallic phases is equal to or greater than 5 and equal to or less than 24 vol. %,
wherein the yield strength Rp0.2 is greater than 618 MPa and equal to or less than 624 MPa, and
wherein the impact toughness is equal to or greater than 146 J and equal to or less than 227 J.

### Claim 21

A duplex stainless steel comprising in weight % (wt %):
C
less than 0.03;
Si
less than 0.60;
Mn
0.60 to 1.80;
P
less than 0.04;
S
less than or equal to 0.01;
Cr
more than 30.00 to 32.50;
Ni
6.50 to 9.50;
Mo
1.40 to 2.80;
N
0.17 to 0.25;
Cu
0.60 to 1.90;
Al
less than 0.03;
balance Fe and unavoidable impurities,
wherein said duplex stainless steel has a ferrite content of from 40 to 70 vol % and a balance is austenite,
wherein said duplex stainless steel has a CPT of greater than or equal to 50° C. and equal to or less than 65° C., where CPT is determined according to the G48A method, and
wherein said duplex stainless steel has a yield strength Rp0.2 of greater than 610 MPa determined by ASTM A-370.

### Claim 22 (depends on 21)

The duplex stainless steel according to claim 21, wherein said duplex stainless steel has a value for PRE of greater than or equal to 36 and equal to or less than 37, where PRE=wt % Cr+3.3*wt % Mo.

### Claim 23 (depends on 21)

The duplex stainless steel according to claim 21, wherein said duplex stainless steel has a vol. % of intermetallic phases of equal to or less than 25 vol. %, where the vol. % of intermetallic phases are determined during isothermal heating at a temperature of 900° C. for 3 hours.

### Claim 24 (depends on 21)

The duplex stainless steel according to claim 21, wherein said duplex stainless steel has an impact toughness equal to or greater than 130 J, where the impact toughness is determined on notched Charpy-V samples with dimensions of 10×10×55 mm at a test temperature of −50° C.

### Claim 25 (depends on 21)

The duplex stainless steel according to claim 21, wherein said duplex stainless steel has a value for PRE of greater than or equal to 36 and equal to or less than 37, where PRE=wt % Cr+3.3*wt % Mo,
wherein said duplex stainless steel has a vol. % of intermetallic phases of equal to or less than 25 vol. %, where the vol. % of intermetallic phases are determined during isothermal heating at a temperature of 900° C. for 3 hours, and
wherein said duplex stainless steel has an impact toughness equal to or greater than 130 J, where the impact toughness is determined on notched Charpy-V samples with dimensions of 10×10×55 mm at a test temperature of −50° C.

### Claim 26 (depends on 25)

The duplex stainless steel according to claim 25, wherein the vol. % of intermetallic phases is equal to or greater than 5 and equal to or less than 24 vol. %,
wherein the yield strength Rp0.2 is greater than 618 MPa and equal to or less than 624 MPa, and
wherein the impact toughness is equal to or greater than 146 J and equal to or less than 227 J.