Austenitic stainless steel and production method therefor

Patent metadata

Field	Value
Publication number	US-11041232-B2
Application number	US-201716091126-A
Country	US
Kind code	B2
Filing date	Apr 6, 2017
Priority date	Apr 6, 2016
Publication date	Jun 22, 2021
Grant date	Jun 22, 2021

Abstract

An austenitic stainless steel is provided which has a chemical composition that consists, by mass %, of: C: 0.015% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.05% or less, S: 0.030% or less, Cr: 16.0% or more and less than 22.0%, Ni: 11.0 to 16.0%, Mo: 2.5 to 5.0%, N: 0.07% or more and less than 0.15%, Nb: 0.20 to 0.50%, Al: 0.005 to 0.040%, Sn: 0 to 0.080%, Zn: 0 to 0.0060%, Pb: 0 to 0.030%, and the balance: Fe and impurities, and that satisfies the formula [MoSS/Mo≥0.98] (MoSS: Mo amount dissolved in the steel).

First claim

The invention claimed is:

1. An austenitic stainless steel having a chemical composition consisting, by mass percent, of:
C: 0.015% or less,
Si: 1.00% or less,
Mn: 2.00% or less,
P: 0.05% or less,
S: 0.030% or less,
Cr: 16.0% or more and less than 22.0%,
Ni: 11.0 to 16.0%,
Mo: 2.5 to 5.0%,
N: 0.07% or more and less than 0.15%,
Nb: 0.20 to 0.50%,
Al: 0.005 to 0.040%,
Sn: 0 to 0.080%,
Zn: 0 to 0.0060%,
Pb: 0 to 0.030%, and
the balance: Fe and impurities,
and satisfying formula (i) below:
Mo SS /Mo≥0.98  (i)

where, Mo in formula (i) represents a content (mass %) of Mo contained in the steel, and Mo SS represents an Mo content (mass %) that is dissolved in the steel.

2. The austenitic stainless steel according to claim 1 , wherein:
in the chemical composition, R 1 value defined by formula (ii) below satisfies formula (iii) below:
R 1 =0.25Ni+0.2Cr+(Mo×(Mo SS /Mo)) 1.45   (ii)

R 1 ≥10.2  (iii)

where, each symbol of an element in formula (ii) represents a content (mass %) of the corresponding element that is contained in the steel, and Mo SS represents an Mo content (mass %) that is dissolved in the steel.

3. The austenitic stainless steel according to claim 2 , wherein the austenitic stainless steel has a steel micro-structure in which a grain size number with respect to inside of the steel is 7.0 or more.

4. The austenitic stainless steel according to claim 2 , wherein:
the chemical composition contains, by mass %, one or more elements selected from:
Sn: 0.002 to 0.080%,
Zn: 0.0002 to 0.0060%, and
Pb: 0.0005 to 0.030%,
and an L value defined by formula (iv) below satisfies formula (v) below:
L=7.6Sn 0.18 +9.5Pb 0.18 +12.8Zn 0.2   (iv)

1.8≤L≤13.9  (v)

where, each symbol of an element in formula (iv) represents a content (mass %) of the corresponding element that is contained in the steel.

5. The austenitic stainless steel according to claim 4 , wherein the austenitic stainless steel has a steel micro-structure in which a grain size number with respect to inside of the steel is 7.0 or more.

6. The austenitic stainless steel according to claim 4 , wherein:
in the chemical composition, R 2 value defined by formula (vi) below satisfies formula (vii) below:
R 2 =R 1 +(L−5.1)/3  (vi)

R 2 ≥12.0  (vii)

where, R 1 in formula (vi) is a value defined by formula (ii) above, and L in formula (vi) is a value defined by formula (iv) above.

7. The austenitic stainless steel according to claim 6 , wherein the austenitic stainless steel has a steel micro-structure in which a grain size number with respect to inside of the steel is 7.0 or more.

8. The austenitic stainless steel according to claim 1 , wherein:
the chemical composition contains, by mass %, one or more elements selected from:
Sn: 0.002 to 0.080%,
Zn: 0.0002 to 0.0060%, and
Pb: 0.0005 to 0.030%,
and an L value defined by formula (iv) below satisfies formula (v) below:
L=7.6Sn 0.18 +9.5Pb 0.18 +12.8Zn 0.2   (iv)

1.8≤L≤13.9  (v)

where, each symbol of an element in formula (iv) represents a content (mass %) of the corresponding element that is contained in the steel.

9. The austenitic stainless steel according to claim 8 , wherein the austenitic stainless steel has a steel micro-structure in which a grain size number with respect to inside of the steel is 7.0 or more.

10. The austenitic stainless steel according to claim 1 , wherein the austenitic stainless steel has a steel micro-structure in which a grain size number with respect to inside of the steel is 7.0 or more.

11. An austenitic stainless steel material that includes an austenitic stainless steel according to claim 1 .

12. An austenitic stainless steel pipe that includes the austenitic stainless steel according to claim 1 .

13. An austenitic stainless steel plate that includes the austenitic stainless steel according to claim 1 .

14. An austenitic stainless steel bar that includes the austenitic stainless steel according to claim 1 .

15. An austenitic stainless wire rod that includes the austenitic stainless steel according to claim 1 .

16. An austenitic stainless forged steel that includes the austenitic stainless steel according claim 1 .

17. An austenitic stainless valve that includes the austenitic stainless steel according to claim 1 .

18. An austenitic stainless joint that includes the austenitic stainless steel according to claim 1 .

19. An austenitic stainless welding material that includes the austenitic stainless steel according to claim 1 .

20. A method for producing an austenitic stainless steel, comprising:
a heat treatment step of heating a steel having a chemical composition according to claim 1 for 8 hours or more in a temperature range of more than 1260° C. to not more than 1370° C.;
a hot working step of subjecting the steel to hot working such that a finishing temperature is in a range of 960 to 1150° C.; and
a finishing heat treatment step of heating the steel for 3 minutes or more in a temperature range of 1000 to 1100° C.

21. The method for producing an austenitic stainless steel according to claim 20 , further comprising:
a cold working step of performing cold working under conditions such that a reduction of area is 30% or more.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Seto Masahiro
• Sagara Masayuki
• Yamada Kenta
• Osuki Takahiro

Classifications

• C21D8/10

  during manufacturing of tubular bodies · CPC title

• C21D8/06

  during manufacturing of rods or wires · CPC title

• C21D8/02

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

• C21D7/13

  by hot working · CPC title

• B23K2103/06

  Cast-iron alloys · CPC title