Duplex stainless steel and production method therefor

Patent metadata

Field	Value
Publication number	US-9771628-B2
Application number	US-201213984314-A
Country	US
Kind code	B2
Filing date	Feb 10, 2012
Priority date	Feb 14, 2011
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

Provided is a duplex stainless steel having a high strength and a high toughness. A stainless steel according to the present invention includes: a chemical composition containing, in mass percent, C: at most 0.030%, Si: 0.20 to 1.00%, Mn: at most 8.00%, P: at most 0.040%, S: at most 0.0100%, Cu: more than 2.00% and at most 4.00%, Ni: 4.00 to 8.00%, Cr: 20.0 to 30.0%, Mo: at least 0.50% and less than 2.00%, N: 0.100 to 0.350%, and sol. Al: at most 0.040%, the balance being Fe and impurities; and a structure, wherein a rate of ferrite in the structure is 30 to 70%, and a hardness of the ferrite in the structure is at least 300 Hv 10gf .

First claim

The invention claimed is:

1. A production method for a duplex stainless steel material, comprising the steps of:
producing a hot worked product made of a duplex stainless steel material having a chemical composition containing, in mass percent, C: at most 0.030%, Si: 0.20 to 1.00%, Mn: at most 8.00%, P: at most 0.040%, S: at most 0.0100%, Cu: more than 2.00% and at most 4.00%, Ni: 4.00 to 8.00%, Cr: 20.0 to 30.0%, Mo: at least 0.50% and less than 2.00%, N: 0.100 to 0.350%, and sol. Al: at most 0.040%, the balance being Fe and impurities;
performing solution treatment on the produced hot worked product at 980 to 1,200° C.; and
performing aging heat treatment on the hot worked product that has been subjected to the solution treatment, at a temperature of more than 480 and at most 600° C. for a soaking time of 2 to 30 minutes,
wherein the hot worked product after the aging heat treatment has:
a structure, wherein a rate of ferrite in the structure is 43 to 55%, and a hardness of the ferrite in the structure is more than 315 Hv 10gf , a yield strength of 580MPa or more, and
an absorbed energy vE 0 obtained in a Charpy impact test at 0° C. with full-size V notch specimen specified in JIS Z2242 of 150 J or more.

2. A hot worked product made of a duplex stainless steel comprising:
a chemical composition containing, in mass percent, C: at most 0.030%, Si: 0.20to 1.00%, Mn: at most 8.00%, P: at most 0.040%, S: at most 0.0100%, Cu: more than 2.00% and at most 4.00%, Ni: 4.00 to 8.00%, Cr: 20.0 to 30.0%, Mo: at least 0.50% and less than 2.00%, N: 0.100 to 0.350%, and sol. Al: at most 0.040%, the balance being Fe and impurities; and
a structure, wherein a rate of ferrite in the structure is 43 to 55%, and a hardness of the ferrite in the structure is more than 315 Hv 10gf ,
wherein the hot worked product has a yield strength of 580 MPa or more, and the hot worked product has an absorbed energy vE 0 obtained in a Charpy impact test at 0° C. with full-size V notch specimen specified in JIS Z2242 of 150 J or more.

3. The hot worked product made of a duplex stainless steel according to claim 2 , wherein the chemical composition further contains, in mass percent, V: at most 1.50%.

4. The hot worked product made of a duplex stainless steel according to claim 3 , wherein the chemical composition further contains, in mass percent, at least one type selected from the group consisting of Ca: at most 0.0200%, Mg: at most 0.02%, and B: at most 0.0200%.

5. The hot worked product made of a duplex stainless steel according to claim 4 , wherein the chemical composition further contains, in mass percent, rare earth metal: at most 0.2000%.

6. The hot worked product made of a duplex stainless steel according to claim 3 , wherein the chemical composition further contains, in mass percent, rare earth metal: at most 0.2000%.

7. The hot worked product made of a duplex stainless steel according to claim 2 , wherein the chemical composition further contains, in mass percent, at least one type selected from the group consisting of Ca: at most 0.0200%, Mg: at most 0.02%, and B: at most 0.0200%.

8. The hot worked product made of a duplex stainless steel according to claim 7 , wherein the chemical composition further contains, in mass percent, rare earth metal: at most 0.2000%.

9. The hot worked product made of a duplex stainless steel according to claim 2 , wherein the chemical composition further contains, in mass percent, rare earth metal: at most 0.2000%.

Assignees

• Motoya Daisuke
• Hamada Masahiko
• Amaya Hisashi
• Nagayama Hiroyuki
• Yamada Kenta
• Nippon Steel & Sumitomo Metal Corp

Inventors

• Motoya Daisuke
• Hamada Masahiko
• Amaya Hisashi
• Nagayama Hiroyuki
• Yamada Kenta

Classifications

• C21D6/005 Primary

  containing Mn · CPC title

• C22C38/42

  with copper · CPC title

• C21D6/004

  containing Cr and Ni · CPC title

• C22C1/02

  by melting {(C22C1/1036 takes precedence)} · CPC title

• C22C38/005

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