JPS5970751A - Superconductive material - Google Patents

Abstract

PURPOSE:To obtain a low-cost superconductive material having a relatively high critical temp., by preparing a ferritic-austenitic two-phase steel having a specified composition contg. Cr, Ni, etc. CONSTITUTION:This superconductive material is an alloy having a structure in wich sigma phase is present between alternate phases of a ferritic-austenitic two- phase steel contg. <0.20% C, 0.2-3.0% Si and/or Mn, 15.0-30.0% Cr, 2.5-20.0% Ni, <10.0% Mo and <0.2% N. In the composition, 20<=Cr equiv. <=35 and 5<=Ni equiv. <=15 are satisfied when Cr equiv. and Ni equiv. are expressed by Cr equiv. =Cr%+Mo%+1.5XSi% and Ni equiv. =Ni%+0.5XMn%+30XC%+25X N%. The superconductive material is less expensive than other superconductive material, and the critical temp. for superconductivity is relatively high.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superconducting material that has a relatively high critical temperature and is inexpensive.

Conventionally, Nb-Zr has been used as a material exhibiting superconducting properties.

Nb-Ti, Nb-Zr-Ti, or Nb-Zr
-Alloys such as Ta, Nb3Sn, V3Ga,
Nb3 (AM o, 5Geo2) + Nbs G
Intermetallic compounds such as e+ or Nb5AU are known, and many studies have been conducted with the aim of commercializing □ superconducting magnets using these materials.

However, the critical temperature of alloy-based materials is extremely low, at most 10°, which is extremely disadvantageous as a practical superconducting material.On the other hand, the critical temperature of intermetallic compound-based materials is 17~17°C. 21', but all of them were extremely brittle and extremely difficult to process into wire by ordinary plastic working techniques.

Under these circumstances, in order to effectively utilize the excellent superconducting properties of intermetallic compounds, for example, intermetallic compounds with predetermined properties may be embedded in a base material with good ductility, or tape-shaped base materials may be used. A thin film of an intermetallic compound is precipitated and adhered to the material by a vapor deposition method or a vapor phase reduction method, or a single metal powder that forms an intermetallic compound is mixed and filled in a base material tube and then processed into a predetermined shape. Through a complex process that involves the generation of intermetallic compounds through subsequent heat treatment, tape-shaped or wire-shaped superconducting materials are produced in which appropriate compounds are retained in a strong base material. However, these methods not only have a complicated manufacturing process but also have a poor material yield, which inevitably leads to high costs.

From the above-mentioned viewpoints, the present inventors have continued to strive to obtain a superconducting material that can obtain a desired shape without requiring complicated and expensive processes and has good properties such as a high critical temperature. In the course of research from various aspects, it was discovered that the alpha phase, which appears during the heat treatment cycle of rust-resistant steels such as high chromium steel, and which was disliked because it adversely affects the preparation properties, exhibits excellent superconducting properties. I discovered that I have it. Therefore, the present inventors conducted further research in order to utilize the alpha phase of and as a practical superconducting phase. (a) Even among rust-resistant steels, duplex stainless steels in particular (b) In duplex stainless steel, the α phase precipitates at the interface between the α phase and the γ phase, so it cannot be easily formed by processing such as rolling or drawing. , if the γ phase existing in the form of islands is elongated in advance, subsequent heat treatment such as aging treatment can be avoided.
(C) It is possible to precipitate a dimensionally connected α phase;
A duplex steel with a structure in which γ phase) and α phase are present at the interface exhibits excellent superconducting properties.''2.It also has good mechanical properties such as workability and toughness. Therefore, we have come to the knowledge shown in (al~(C)).

This invention was made based on the above findings, and the superconducting material has the following properties: C: 0.20% or less (hereinafter referred to as "multiple band width").

One type of Sl and Mn plate 2.02-3.0%.

Cr: 15.0-30.0%.

Ni: 2.5-20.0%.

Mo: 10.0% or less.

N, 02% or less.

and the formula, Creq=Cr(%)+MO
(%) + 1.58i (%), and N1eq = NN%)
-4-0,5Mn(%)+30C(%)+25N(%
), Creq and N1eq are respectively composed of two-phase steels of ferrite and austenite whose component compositions (in weight percent) satisfy the following formula: 20≦Creq≦35゜5≦Ni, eq≦15゜. By being composed of a structure in which the ferrite phase and austenite phase are alternately layered and an α phase is present at the interface between them, it has both excellent superconducting properties and mechanical properties. It has the following characteristics.

Next, in this invention, the reason why the content of each chemical component constituting the superconducting material is limited as described above will be explained.

■ When C 0 min exceeds 0.20%, Cr, Fe, M
With metal elements such as o (Cr + 'e + MO)
23 The formation of C6 carbides becomes significant, reducing the effective amount of Cr and MO necessary for the formation of the α phase, and suppressing the formation of the α phase, which has properties as a superconducting material. The amount was set at 0.20% or less. C
It goes without saying that the lower the content, the better the content, but if the content is less than 0.003%, industrial production becomes extremely difficult, and from this point of view it becomes impractical.

■Si and Mn 51 and Mn components act as deoxidizing agents during melting of steel, but if the combined content of Si and Mn is 0.2
If it is less than 3.%, the desired effect cannot be obtained.
Even if the content exceeds 0%, not only will no special effect for α phase generation be obtained, but it will also be disadvantageous in terms of cost.
The content of Si+Mn) was determined to be 02 to 3.0%.

(2) Cr, Ni These components are necessary to facilitate precipitation of the α phase and to form a two-dimensional structure of ferrite and austenite near room temperature.

That is, Cr and N1 components are elements necessary to generate α phase and r phase respectively to form an α/γ structure, and in order to obtain a 2-degree structure, the Cr content should be 15.0 to 30.0. It is necessary to contain Ni in the range of 2.5 to 20.0%. Outside this range, it becomes difficult to obtain a desired structure.

■ MO The Mo component is also Cr-? Like Ni, it is an element necessary to precipitate the α phase and realize a 2-dimensional structure, but since it is disadvantageous in terms of cost to contain more than 10.0, the content is reduced to 10. .0% or less. and,
In order to obtain a significant addition effect, and also from the viewpoint of manufacturing difficulties, it is preferable that the content is 0.01% or more.

■N N, like C, has the effect of forming nitrides such as (Cr, Mo) 2 N and suppressing the precipitation of α phase, and when its content is 0. Since this problem becomes particularly noticeable when the content exceeds 2%, the N content was set at 0.2% or less.

In addition, the above-mentioned lii component proxies pKMn, C, and N
The same effect can be obtained by adding , but the above-mentioned 7).

For reasons such as those described in Section 0, it is necessary to limit the amount added.

Furthermore, KMo + Si may be increased in place of Cr, but increasing Cr is more cost-effective than increasing MO, and if the Sl content exceeds 3.0 Ti,
It is suitable for α-phase forming that is exceptional compared to anything smaller than that.”
If the two effects do not appear, it will cause a significant decrease in toughness, so it is necessary to limit the amount added.

For the same reason as limiting the content of Cr component and N1 component, Cr(%l+Mo(%):i-,
Cr equivalent (Creq) expressed in 5si (%) and N
1(%H-0,5Mn(%)"-300(%l+25N
The N1 equivalent (N1eq) expressed in (%) is 20≦Creq≦35. and 5≦N i e q
It is necessary to limit it to ≦15. That is, outside this range, it becomes extremely difficult to obtain the desired structure.

The superconducting material of the present invention may contain AQ, V, Tj, Nb, T in addition to these components, as long as each of the above components satisfies their respective composition ranges.
a.

It goes without saying that the present invention is also intended for duplex steels further containing components such as W, Re, Cu, and CO.

Next, a method for manufacturing the superconducting material of the present invention will be explained.

In manufacturing superconducting materials, first, a predetermined set Di (
A dual-phase steel of D ferrite and austenite is melted and forged, held at 1000 to 1300°C for about 30 minutes, and then the amount of ferrite and austenite in the steel structure is adjusted. Note that the ratio between the amount of ferrite and the amount of austenite at this time is preferably about 1:1.

This is then hot- or cold-processed to achieve the target product dimensions. This process involves elongating the ferrite grains and austenite grains to form layers of the ferrite phase and austenite phase, respectively. It is something. For this reason, the higher the degree of processing, the better, preferably 70 to 90%.
It is.

Following this processing, strain relief annealing is performed at around 1000°C. The purpose of this treatment is to prevent the α phase from precipitating in the ferrite phase and to properly precipitate the α phase in a layered manner at the α interface between the ferrite phase, the austenite phase, and the α phase. This strain relief annealing may be omitted, but if omitted, the α phase may precipitate finely and the layered shape may not be formed, so it is preferable not to omit it if possible.

After strain relief annealing, this steel was heated to 600-1000℃ and 7%
An aging treatment consisting of holding at a temperature of 00 to 900°C is performed to precipitate a layered σ phase at the interface between the ferrite phase and the austenite phase. The holding time at this time varies depending on the composition of the steel, and may range from several minutes to several hundred minutes, but from an economic standpoint, it is economical to choose a duplex steel with a composition that will last 200 minutes or less. .

In particular, the aging temperature of steel is set to 600 to 1000°C.
Even if the temperature is lower than 600°C or 1000°C twice, precipitation of the σ phase does not occur, or even if it does occur, it is extremely slow (103-10
This is because it lacks practicality.

In this way, the amount of σ phase precipitated is determined by aging treatment, and if a large amount is precipitated, the toughness will deteriorate, and conversely, if the amount of precipitation is too small, the σ phase will be scattered instead of layered. As a result, the material no longer functions as a superconducting material, so the conditions must be carefully selected.

FIG. 1 is a process diagram showing an example of the method for producing a superconducting material according to the present invention more simply.

Figure 2 is a schematic diagram showing an example of the structure of a longitudinal section of a duplex steel before and after the final aging treatment process, and shows the composition ratio of ferrite and austenite depending on the chemical composition and solution treatment conditions. Dual-phase steel material with adjusted austenite phase shape by plastic processing such as wire drawing [
When the aging treatment is applied to the ferrite phase near the interface between the ferrite phase and the austenite phase, a part of the austenite phase and a layered σ phase precipitate out [Figure 2 (a)].
b) This is an explanation of the situation.

Next, the present invention will be explained using examples and comparing with comparative examples.

Examples First, by a normal method using a high frequency furnace, steels A to A, which are subject to the present invention and have chemical compositions as shown in Table 1, were prepared.
Comparative steels J to K, whose chemical compositions are outside the scope of the present invention in terms of the points indicated by * in Table 1, were melted and steel ingots weighing 20 kg were obtained.

Next, these steel ingots were hot-forged into round bars with a diameter of 30 mm, and the wire diameter after drawing was 1, +IIj.
It was hot-rolled to a size such that a predetermined working degree could be obtained when +l was determined, and then solution treatment was performed.

Some of these are subjected to cold drawing after solution treatment, followed by a pickling process, and others are directly machined after solution treatment, each with a diameter of 1. Manufactured Moe's wire rod.

Following these processing treatments, the wires were subjected to strain relief annealing and further subjected to aging treatment to obtain paulownia materials 1 to 18 of the present invention as shown in Table 2. and comparative material]g~20 was obtained. The specific manufacturing conditions for each of the conductive materials 1 to 20 manufactured as described above were as shown in Table 2.

Note that the * mark in Table 2 indicates steel whose chemical composition is outside the scope of the present invention, and the ☆ mark indicates that cold drawing was performed after solution treatment, pickling, and cold drawing. , and the ☆☆ mark indicates that machining was performed directly after solution treatment.

When the microscopic structure of each of the conductive materials 1 to 20 thus obtained was observed, the monthly yield was 1 to 1.
In contrast, in the case of No. 8, a structure as shown in Fig. 2(b) was observed, in which ferrite phases and austenite (layers) were alternately layered and a σ phase was present at the interface between them.
In materials 19 and 20, no precipitation of σ phase could be observed.

Furthermore, Table 2 also shows the results of examining the critical temperatures at which these materials exhibit superconducting properties.

From the results shown in Table 2, it is clear that the inventive material has excellent superconducting properties that are comparable to or even better than conventionally known intermetallic compound-based superconducting materials. It is.

In addition, it goes without saying that the paulownia wood of the present invention had excellent mechanical properties that were almost close to those of duplex steel used as ordinary steel.

According to this invention, a superconducting material with excellent superconducting properties and mechanical properties and low cost can be obtained, and it can be used in the power field such as DC machines, turbine generators, electric cables, plasma equipment, etc. Alternatively, the application of superconducting technology to fields such as memory elements, amplifiers, communication cables, electronics and communication fields, and magnetic levitation transport systems can be further expanded, resulting in useful industrial effects. It is possible.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing an example of the method for manufacturing a superconducting material of the present invention, and FIG. 2 is a schematic diagram showing an example of the microstructure of a duplex steel before and after an aging treatment step. Figure 2(b) shows the structure before aging treatment, and Figure 2(b) shows the structure after aging treatment. Applicant Sumitomo Metal Industries Co., Ltd. Agent Tomi 1) Kazuo and one other person 1 Figure 1 □- --■ 260 Figure 2 (a) (1))

Claims (1)

[Claims] C: 0.20% or less. One or more of Sl and Mn: 0.2 to 3.0%. Cr: 15.0-30.0%. Ni: 2.5-20.0%. Mo: 10.0% or less. N: 0.2% or less. If it contains, the formula, Creq=:Cr(%)+M
o (%) + 1.5Si (%), and N1eq = Ni (%
) +0.5Mn (%) + 30 C (%n+25
C19q and N1eq, represented by N (%), are made of two-phase steel of ferrite and austenite, each of which has a composition (in weight %) that satisfies the formula: 20≦Cr6q≦35゜5≦N1eq≦15゜, A superconducting material characterized by having a structure in which the ferrite phase and the austenite phase are alternately layered and a σ phase is present at the interface between them.