JPH0711392A - Stainless steel for supporting nb3sn superconductor excellent in cryogenic characteristic and its production - Google Patents

Abstract

PURPOSE:To obtain stainless steel for supporting an Nb3Sn superconductor excellent in cryogenic characteristics by specifying the compsn. constituted of C, Si, Mn, Cr, Ni, Nb, Al, N and iron and precipitating NbC or NbN. CONSTITUTION:In steel contg., by weight, <=0.02% C, 0.01 to 2.O% Si, 1 to 8% Mn, 12 to 25% Cr, 5 to 20% Ni, 0.01 to 0.2% Nb, 0.001 to 0.l0% Al and 0.05 to 0.3% 'N, furthermore contg., at need, 0.5 to 3% Mo and moreover contg. 0.0005 to 0.01% Ca, and the balance iron with inevitable impurities, NbC and/or NbN are 1 precipitated. The precipitation of the NbC and NbN executed by subjecting a steel ingot or slab having the same componental compsn. to hot rolling by the conventional method, thereafter executing heating to 1000 to 1200 deg.C for <=0.5min, holding it between 950 to 800 deg. for 1 to 30min at the time of cooling and subsequently executing cooling. in this way, the stainless steel for supporting an Nb3Sn superconductor excellent in strength and toughness at an extremely low temp. can be obtd. at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel having excellent strength and toughness at cryogenic temperature for a conduit tube of Nb ₃ Sn superconducting coil used in a superconducting generator and the like and a method for producing the same. Since Nb ₃ Sn superconductors are very brittle, they are manufactured by heat treating these materials into a coil shape using a metal support. This support is used as a strength member as it is while it is cooled to the superconducting temperature and is in operation.

[0002]

2. Description of the Related Art Conduit tubes of Nb ₃ Sn superconducting coils are heated at 600 to 750 ° C. for a long time during the production of superconductors, and are required to have high strength and excellent toughness in an extremely low temperature range of superconducting temperature. Since it is in contact with the superconducting coil, it is indispensable that it is non-magnetic and that there is no weld cracking from the viewpoint of making a conduit tube.

Conventionally, for this application, austenitic stainless steel in which C is reduced as much as possible and N is added in a large amount to secure low temperature strength and stabilize the γ phase has been used. But,
Even with such low C austenitic stainless steel,
It has been recognized that Cr nitrides are formed at grain boundaries by long-term heating at 600 to 850 ° C., and the toughness at extremely low temperatures deteriorates. On the other hand, Japanese Patent Laid-Open No. 58-193347 discloses a method of adding V. However, not only the addition of expensive elements is required, but also high N is effective in order to improve strength. Is not always clear. Further, Japanese Patent Application Laid-Open No. 63-134627 discloses a method of reheating to a temperature range higher than the heat treatment temperature for Nb ₃ Sn formation after solution heat treatment. This method cannot prevent an increase in cost because the process becomes complicated.

Conventionally, the influence of the components has been studied aiming at improving the characteristics in the extremely low temperature range. As a result, it has been recognized that the addition of a large amount of Ni suppresses the deterioration of the characteristics in the extremely low temperature range. Therefore, application of a high Ni alloy such as incoloy has been attempted. However, this method is expensive
It was necessary to add a large amount of i, and it was difficult to apply it widely in terms of cost.

As described above, there has been no low-cost material or a countermeasure for the conduit tube of the Nb ₃ Sn superconducting coil which can secure the strength and toughness in the cryogenic temperature range.

[0006]

SUMMARY OF THE INVENTION The present invention is based on Nb ₃ Sn
Disclosed is a low-cost austenitic stainless steel capable of ensuring high strength with little deterioration of toughness even at a low temperature even when heat treatment is carried out during manufacturing of Nb ₃ Sn in a superconducting coil conduit tube, and a method for manufacturing the same. .

[0007]

[Means for Solving the Problems] In a high-strength austenitic stainless steel containing a large amount of N, which is used for Nb ₃ Sn superconducting conduit tubes, deterioration of toughness at cryogenic temperatures due to heat treatment during Nb ₃ Sn production does not occur. It has been considered that this is because a large amount of Cr carbonitride precipitates at the grain boundaries during this heat treatment. Therefore, aiming at the suppression of precipitation of grain boundary Cr carbonitrides by this heat treatment, a method of precipitating carbonitrides other than Cr, which easily precipitates in the grains, and a method of optimizing alloy elements have been investigated. However, since it is usually an austenitic stainless steel with a large amount of N added for the purpose of high strength, it is extremely difficult to suppress the precipitation of Cr carbonitrides, and even if some suppression is possible, it is uncertain. I found out.

Therefore, the present inventors have aimed not to suppress the precipitation of Cr carbonitride, but to control it so that it does not harm the toughness in the extremely low temperature region even if it is deposited. did. That is, the reason why the precipitated carbonitride deteriorates the toughness at an extremely low temperature is that it precipitates at the grain boundary, and it is considered that its adverse effect is small as long as it precipitates within the grain. Therefore, it was aimed to guide the precipitation site of Cr carbonitride into the grain by some method.

The present inventors have investigated the origin of precipitation of Cr carbonitrides in various alloys in detail, and found that the tendency of using fine Nb carbonitrides as precipitation nuclei was observed. The present invention has constituted the inventions of the following gist based on this finding. 1)% by weight, C: 0.02% or less, Si: 0.01%
Or more and 2.0% or less, Mn: 1% or more and 8% or less, Cr: 1
2% to 25%, Ni: 5% to 20%, N
b: 0.01% to 0.2%, Al: 0.001%
Cryogenically characterized by containing not less than 0.10% and not more than 0.10%, N: not less than 0.05% and not more than 0.3%, balance iron and unavoidable impurities, and precipitating NbC and / or NbN in steel. Nb ₃ Sn superconductor supporting stainless steel with excellent characteristics.

Furthermore, in order to improve the strength in the extremely low temperature range, M
As an embodiment of steel to which o is added, 2)% by weight, C: 0.02% or less, Si: 0.01%
Or more and 2.0% or less, Mn: 1% or more and 8% or less, Cr: 1
2% to 25%, Ni: 5% to 20%, M
o: 0.5% to 3%, Nb: 0.01% to 0.
2% or less, Al: 0.001% or more and 0.10% or less,
And N: 0.05% or more and 0.3% or less, with the remainder being iron and inevitable impurities, excellent Nb ₃ Sn cryogenic properties, characterized in that to NbC and / absence to precipitate NbN in steel Stainless steel for supporting superconductors.

Further, as an embodiment of steel in which Ca is added in order to improve hot workability, 3)% by weight, C: 0.02% or less, Si: 0.01%
Or more and 2.0% or less, Mn: 1% or more and 8% or less, Cr: 1
2% to 25%, Ni: 5% to 20%, N
b: 0.01% to 0.2%, Al: 0.001%
Or more and 0.10% or less, N: 0.05% or more and 0.3% or less, Ca: 0.0005% or more and 0.01% or less, and the balance iron and inevitable impurities, and NbC in the steel.
And / or NbN is precipitated, which is a stainless steel for supporting Nb ₃ Sn superconductor having excellent cryogenic characteristics. And 4) wt%, C: 0.02% or less, Si: 0.01%
Or more and 2.0% or less, Mn: 1% or more and 8% or less, Cr: 1
2% to 25%, Ni: 5% to 20%, M
o: 0.5% to 3%, Nb: 0.01% to 0.
2% or less, Al: 0.001% or more and 0.10% or less,
N: 0.05% to 0.3%, Ca: 0.0005
% Or more to 0.01% or less and the balance of iron and inevitable impurities, excellent Nb ₃ Sn cryogenic properties, characterized in that to NbC and / absence to precipitate NbN in steel
Stainless steel for supporting superconductors.

In the present invention, in order to limit the precipitation nuclei of Cr carbonitrides to Nb carbonitrides, it is necessary that the total amount of precipitated Cr carbonitrides is small. That is, when a large amount of Cr carbonitride is precipitated, the precipitation from the portion other than the carbonitride of Nb which is likely to be precipitated, that is, the grain boundary is increased,
The intended purpose cannot be achieved. Therefore, it is necessary to limit the amount of C added to an extremely low level.

The steel of the present invention cannot be achieved by matching the alloy components. That is, it is important that fine Nb carbonitrides serving as precipitation nuclei of Cr carbonitrides are scattered in the grains. For this purpose, various manufacturing methods are possible. As a method for this purpose, it is proposed that after solutionizing various carbonitrides once, Nb carbonitrides are deposited but Cr carbonitrides are not deposited by gradually cooling or maintaining the same temperature range. did. Therefore, in the present invention, the Nb carbonitride precipitates but the Cr carbonitride does not precipitate during the cooling after heating in the solution heat treatment, and the specific temperature range is gradually cooled.

Conventionally, it is common knowledge that the solution treatment is rapidly cooled in order to ensure the intended effect. But,
In the present invention, even if a steel having the same composition as that of the steel of the present invention is used, C and N will be completely solutionized by rapid cooling according to the conventional wisdom. In that case, the Cr carbonitride precipitates at the grain boundaries due to the absence of precipitation nuclei in the grains during the subsequent heat treatment during the production of Nb ₃ Sn, and the toughness at cryogenic temperatures deteriorates. Can't expect. Nb carbonitrides are also precipitated in the solution treatment, but they do not function as precipitation nuclei of Cr carbonitrides because they are precipitated almost simultaneously with Cr carbonitrides.

Based on the above findings, the invention of the following gist was constructed. 5)% by weight, C: 0.02% or less, Si: 0.01%
Or more and 2.0% or less, Mn: 1% or more and 8% or less, Cr: 1
2% to 25%, Ni: 5% to 20%, N
b: 0.01% to 0.2%, Al: 0.001%
Or more and 0.10% or less, N: 0.05% or more and 0.3% or less, and the steel ingot or slab containing the balance iron and unavoidable impurities is hot-rolled by a conventional method, and then 1000 ° C or more and 1200 ° C. The steel is characterized in that it is heated below for 0.5 minutes or more, and when cooled, the temperature between 950 and 800 ° C. is held for 1 minute or more and 30 minutes or less, followed by cooling NbC and / or
To Nb ₃ S with excellent cryogenic properties
n A method for manufacturing stainless steel for supporting a superconductor.

6)% by weight, C: 0.02% or less, S
i: 0.01% to 2.0%, Mn: 1% to 8%
Below, Cr: 12% or more and 25% or less, Ni: 5% or more 2
0% or less, Mo: 0.5% or more and 3% or less, Nb: 0.0
1% to 0.2%, Al: 0.001% to 0.1
0% or less, N: contains 0.05% or more and 0.3% or less,
A steel ingot or a steel slab containing the balance iron and unavoidable impurities is hot-rolled by a conventional method, and then 1000 ° C. or more 1200
It is heated to below ℃ for 0.5 minutes or more, and at the time of cooling, it is 950 to 8
NbC and / or Nb in steel characterized in that the temperature is held between 00 ° C for 1 minute or more and 30 minutes or less and then cooled.
A method for producing Nb ₃ Sn superconductor-supporting stainless steel having excellent cryogenic properties, in which N is precipitated.

7)% by weight, C: 0.02% or less, S
i: 0.01% to 2.0%, Mn: 1% to 8%
Below, Cr: 12% or more and 25% or less, Ni: 5% or more 2
0% or less, Nb: 0.01% or more and 0.2% or less, Al:
Steel ingot containing 0.001% or more and 0.10% or less, N: 0.05% or more and 0.3% or less, Ca: 0.0005% or more and 0.01% or less, and the balance iron and unavoidable impurities Hot rolling a billet by a conventional method, then 1000 ° C
It is heated to 1200 ° C or lower for 0.5 minutes or longer, and the temperature is kept at 950 to 800 ° C for 1 minute to 30 minutes during cooling.
Nb ₃ and / or NbN precipitated in steel, which is characterized by being cooled thereafter, and having excellent cryogenic properties, Nb ₃
A manufacturing method of stainless steel for supporting an Sn superconductor. 8) C: 0.02% or less, Si: 0.01% by weight
Or more and 2.0% or less, Mn: 1% or more and 8% or less, Cr: 1
2% to 25%, Ni: 5% to 20%, M
o: 0.5% to 3%, Nb: 0.01% to 0.
2% or less, Al: 0.001% or more and 0.10% or less,
N: 0.05% to 0.3%, Ca: 0.0005
% Or more and 0.01% or less and the steel ingot or slab containing the balance iron and unavoidable impurities is hot-rolled by a conventional method, then heated to 1000 ° C. or more and 1200 ° C. or less for 0.5 minutes or more, and then cooled. sometimes 950-800 and retention less than 30 minutes 1 minute between ° C., excellent Nb ₃ Sn superconductors supporting cryogenic properties to precipitate NbN to NbC and / absence in the steel, characterized by thereafter cooled For manufacturing stainless steel for automobiles.

Next, the limiting conditions of the present invention will be described. When C is added in a large amount, the strength at cryogenic temperature is improved, but in addition to the intragranular precipitation of Nb carbonitride of Cr carbonitride, which is the aim of the present invention, as precipitation nuclei, a large amount of C is also precipitated at grain boundaries. Therefore, the toughness at cryogenic temperature deteriorates and the intended purpose cannot be achieved, so 0.02% was made the upper limit.

If the Si content is less than 0.01%, the cleanliness of the steel becomes poor and the toughness deteriorates, so 0.01% was made the lower limit. However, if it exceeds 2.0%, the cold workability deteriorates,
Since it is difficult to manufacture a conduit pipe, 2.0% was made the upper limit. Mn is an element that is positively added in order not only to promote the stabilization of the austenite phase but also to expand the solid solution limit of N to enable strengthening. However, if it is less than 1%, this effect is small. Therefore, the lower limit is 1%, and if it exceeds 8%, the toughness of the base material deteriorates at extremely low temperatures. Therefore, the upper limit is 8%.

Cr is required to be 12% or more in order to secure high temperature strength and corrosion resistance during heat treatment for producing Nb ₃ Sn, but if it exceeds 25%, a brittle σ phase is formed to deteriorate toughness. Therefore, 25% was made the upper limit. Ni is an element that stabilizes the austenite phase and improves the strength, toughness and ductility at cryogenic temperatures, but if it is less than 5%, the effect of stabilizing the austenite phase is insufficient, so the lower limit was made 5%. However, since it is an extremely expensive element, from the viewpoint of cost, the upper limit was 20% at which the austenite stabilizing effect was saturated.

Nb is an indispensable element for forming the precipitation starting point of the Cr carbonitride of the present invention. If it is less than 0.01%, the effect is not recognized, and if it exceeds 0.2%, a large amount of Nb carbonitrides consumes the strengthening element N to reduce the strength at cryogenic temperature. _The Nb content was limited to 0.01 to 0.2% in order to form Fe ₂ Nb during the heat treatment for the production of ₃ Sn and conversely deteriorate the toughness at extremely low temperatures.

Al is an element that improves the cleanliness of steel as a deoxidizer. However, if it is less than 0.001%, this effect does not exist, and if it exceeds 0.10%, the hot workability deteriorates, so the Al content is limited to 0.001 to 0.10%. N
Is an extremely effective element for stabilizing the austenite phase and ensuring strength at extremely low temperatures. But 0.0
If it is less than 5%, the effect is small, and if it exceeds 0.3%, the weldability is remarkably deteriorated and weld cracks and blowholes frequently occur, so the N content is limited to 0.05 to 0.3%.

The above are the basic components of the steel of the present invention. In the present invention, in addition to the above basic components, Mo is added to secure the strength, and Ca is added to improve the hot workability.
It can be added alone or in combination. If the addition of Mo is less than 0.5%, the strength improving effect is small, and if it exceeds 3%, Fe ₂ Mo is formed and the toughness at cryogenic temperature is deteriorated, so the Mo content is limited to 0.5 to 3%. . If the addition of Ca is less than 0.0005%, there is no hot workability improving effect, and if it exceeds 0.01%, the Ca content is limited to 0.0005 to 0.01% in order to impair cleanliness.

In each of the methods for producing the steel of the present invention as defined in claims 5 to 8, after hot rolling by a conventional method, 1000
The heating is limited to 0.5 to 1200 ° C. for 0.5 minutes or more, and then the temperature is kept at 950 to 800 ° C. for 1 to 30 minutes, and then cooled. After hot rolling, it is necessary to solution heat various carbonitrides once.
If the temperature exceeds 200 ° C., the austenite crystal grains are coarsened and the strength is lowered.
Limited to 0 ° C.

A suitable temperature range for precipitating Nb carbonitride without precipitating Cr carbonitride is 950 to 800 ° C. The cooling rate is not limited in the present invention because the temperature range exceeding 950 ° C. is a solution state regardless of the cooling rate. 950 to 800 [deg.] C. is a temperature range where intragranular fine precipitation of Nb carbonitride occurs. Therefore, in the present invention, it is a limiting requirement to gradually cool or retain this temperature range. N
b In-grain microprecipitation of carbonitrides should occur in this temperature range for more than 1 minute 3
It is necessary to hold it for 0 minutes or less and then cool it, or gradually cool this temperature range over 1 minute or more. But 3
The retention or gradual cooling for more than 0 minutes was excluded in the present invention because the precipitation of Nb carbonitride is almost completed and the subsequent retention or gradual cooling becomes meaningless.

[0026]

In the steel of the present invention, Nb finely precipitated in the grains
To serve as precipitation nuclei of Cr carbonitrides carbonitride precipitates during the heat treatment for Nb ₃ Sn production, C of the grain boundaries
Precipitation of r-carbonitride is reduced, and excellent toughness can be secured at extremely low temperatures. Further, without quenching immediately after solution heat treatment, Cr carbonitrides do not precipitate, but Nb carbonitrides are finely precipitated in grains by gradually cooling or retaining the temperature range in which Nb carbonitrides precipitate. This makes it possible to easily manufacture the steel of the present invention.

[0027]

[Example] The steels shown in Table 1 were melt-cast and hot-rolled.
Thus, a hot rolled sheet having a thickness of 3 mm was manufactured. This hot rolled steel sheet 1
Heating to 050 ° C and cooling under the cooling conditions shown in Table 2
Body treatment was carried out. Then, the precipitate of the solution heat treated material
Investigation of precipitation state and Nb ₃Corresponds to Sn formation heat treatment
Adjustment of the deposition state of the deposit after air-cooling treatment at 700 ° C-200h
And the strength and toughness at 4K were evaluated, and the results are shown in Table 2.
It is also shown. In addition, strength is a tensile test and toughness is charpy.
-Evaluated by impact value.

In the steel of the present invention produced by the method of the present invention, fine Nb carbonitrides are precipitated in the grains in the solution treated material, and Nb ₃ Sn
After the heat treatment equivalent to formation, Cr carbonitride was precipitated mainly in the grains, and it was confirmed that the strength at 4K was high and the toughness was excellent. On the other hand, in the steel containing no Nb, no precipitate was observed after the solution treatment even after the heat treatment limited by the method of the present invention, and Cr carbonitride was precipitated at the grain boundary after the heat treatment corresponding to Nb ₃ Sn formation. The toughness was poor. The large amount of the added steel with Nb Conversely, solution treatment after precipitates when implementing the heat treatment is limited in the present invention a method is a large amount was observed, including grain boundary, Nb ₃
After heat treatment equivalent to Sn generation, Cr carbonitride was precipitated at the grain boundaries, and the toughness was also inferior. Further, in the case of steel containing a large amount of C, when the heat treatment limited by the method of the present invention is carried out, fine Nb carbonitrides precipitate in the grains in the solution treated material, but Nb ₃ S
After the heat treatment corresponding to n generation, a large amount of Cr carbonitride was precipitated not only in the grains but also at the grain boundaries, and the toughness was also inferior.

In the steel of the present invention to which Ca was added, it was confirmed that the flaws during hot working were significantly reduced and the hot workability was improved. Of course, no effect on precipitates and strength toughness was observed, and the toughness at 4K was also excellent.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

As described above, according to the present invention, Nb ₃
It is possible to obtain austenitic stainless steel excellent in strength and toughness at cryogenic temperatures, which is used for a conduit tube of an Sn superconducting coil, at low cost. Conventionally, since the toughness of the conduit pipe is deteriorated, the Nb ₃ Sn formation reaction cannot be set to an appropriate condition. For this reason, a large superconducting coil had to be manufactured in order to pass a large current as the superconducting coil. However, the present invention makes it possible to appropriately set the heat treatment conditions for producing Nb ₃ Sn, and a device using superconductivity. Can be promoted. Furthermore, as a result, a large amount of energy can be saved, and industrial and social effects are great.

Claims (8)

[Claims] 1. C: 0.02% or less by weight%, Si:
0.01% to 2.0%, Mn: 1% to 8%, Cr: 12% to 25%, Ni: 5% to 20
% Or less, Nb: 0.01% or more and 0.2% or less, Al:
Characterized by containing 0.001% or more and 0.10% or less, N: 0.05% or more and 0.3% or less, and consisting of balance iron and unavoidable impurities, and precipitating NbC and / or NbN in steel. A stainless steel for supporting Nb ₃ Sn superconductor with excellent cryogenic properties. 2. C: 0.02% or less, Si:
0.01% to 2.0%, Mn: 1% to 8%, Cr: 12% to 25%, Ni: 5% to 20
% Or less, Mo: 0.5% or more and 3% or less, Nb: 0.01
% To 0.2%, Al: 0.001% to 0.10
% Or less, N: 0.05% or more and 0.3% or less, consisting of balance iron and unavoidable impurities, and characterized by precipitating NbC and / or NbN in the steel, excellent in cryogenic characteristics nb ₃ Sn superconductors supporting stainless steel. 3. By weight%, C: 0.02% or less, Si:
0.01% to 2.0%, Mn: 1% to 8%, Cr: 12% to 25%, Ni: 5% to 20
% Or less, Nb: 0.01% or more and 0.2% or less, Al:
0.001% or more and 0.10% or less, N: 0.05% or more and 0.3% or less, Ca: 0.0005% or more and 0.01% or less, and the balance iron and unavoidable impurities. Nb ₃ Sn superconductor-supporting stainless steel having excellent cryogenic characteristics, characterized in that NbC and / or NbN is precipitated in the. 4. By weight%, C: 0.02% or less, Si:
0.01% to 2.0%, Mn: 1% to 8%, Cr: 12% to 25%, Ni: 5% to 20
% Or less, Mo: 0.5% or more and 3% or less, Nb: 0.01
% To 0.2%, Al: 0.001% to 0.10
% Or less, N: 0.05% or more and 0.3% or less, Ca: 0.
It contains 0005% or more and 0.01% or less, the balance is iron and unavoidable impurities, and NbC and / or N is contained in the steel.
Stainless steel for supporting Nb ₃ Sn superconductors, which has excellent cryogenic characteristics and is characterized by depositing bN. 5. By weight%, C: 0.02% or less, Si:
0.01% to 2.0%, Mn: 1% to 8%, Cr: 12% to 25%, Ni: 5% to 20
% Or less, Nb: 0.01% or more and 0.2% or less, Al:
A steel ingot or billet containing 0.001% or more and 0.10% or less and N: 0.05% or more and 0.3% or less, and the balance iron and unavoidable impurities is hot-rolled by a conventional method, and then 1000 Heat above ℃ to 1200 ℃ below 0.5 minutes,
During cooling, the temperature between 950 and 800 ° C. is held for 1 minute or more and 30 minutes or less, and then the steel is cooled.
A method for producing Nb ₃ Sn superconductor-supporting stainless steel excellent in cryogenic properties, wherein bC and / or NbN is deposited. 6. C: 0.02% or less, Si:
0.01% to 2.0%, Mn: 1% to 8%, Cr: 12% to 25%, Ni: 5% to 20
% Or less, Mo: 0.5% or more and 3% or less, Nb: 0.01
% To 0.2%, Al: 0.001% to 0.10
% Or less, N: 0.05% or more and 0.3% or less, and a steel ingot or a steel slab containing the balance iron and unavoidable impurities is hot-rolled by a conventional method, and then 1000 ° C. or more and 1200 ° C.
Heat to below for 0.5 minutes or more, and 950-80 at the time of cooling
NbC and / or NbN in steel characterized by holding at 0 ° C for 1 minute to 30 minutes and then cooling
A process for producing Nb ₃ Sn superconductor-supporting stainless steel having excellent cryogenic properties, which is obtained by precipitating. 7. In weight%, C: 0.02% or less, Si:
0.01% to 2.0%, Mn: 1% to 8%, Cr: 12% to 25%, Ni: 5% to 20
% Or less, Nb: 0.01% or more and 0.2% or less, Al:
Steel ingot containing 0.001% or more and 0.10% or less, N: 0.05% or more and 0.3% or less, Ca: 0.0005% or more and 0.01% or less, and the balance iron and unavoidable impurities Hot rolling a billet by a conventional method, then 1000 ° C
It is heated to 1200 ° C or lower for 0.5 minutes or longer, and the temperature is kept at 950 to 800 ° C for 1 minute to 30 minutes during cooling.
Nb ₃ and / or NbN precipitated in steel, which is characterized by being cooled thereafter, and having excellent cryogenic properties, Nb ₃
A manufacturing method of stainless steel for supporting an Sn superconductor. 8. In weight%, C: 0.02% or less, Si:
0.01% to 2.0%, Mn: 1% to 8%, Cr: 12% to 25%, Ni: 5% to 20
% Or less, Mo: 0.5% or more and 3% or less, Nb: 0.01
% To 0.2%, Al: 0.001% to 0.10
% Or less, N: 0.05% or more and 0.3% or less, Ca: 0.
A steel ingot or a slab containing 0005% or more and 0.01% or less and the balance of iron and unavoidable impurities is hot-rolled by a conventional method, and then heated to 1000 ° C or more and 1200 ° C or less.
A cryogenic property of NbC and / or NbN precipitated in steel characterized by heating for 5 minutes or more, holding at 950 to 800 ° C. for 1 minute to 30 minutes during cooling, and then cooling. An excellent method for producing stainless steel for supporting Nb ₃ Sn superconductor.