Austenitic stainless steel and production method therefor
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 [Mo SS /Mo≥0.98] (Mo SS : Mo amount dissolved in the steel).
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.