JP3249389B2 - High-strength non-magnetic steel for fastening linear motor car superconducting coils - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-magnetic material used for fastening a structure used in a strong magnetic field, which is used for fastening parts of a superconducting coil used for levitation or propulsion of a linear motor car. The present invention relates to a steel, and more particularly to a manufacturing method for ensuring non-magnetic properties of the component and at the same time improving corrosion resistance and strength.

[0002]

2. Description of the Related Art Materials of structures exposed to a strong magnetic field, such as a linear motor car and a nuclear magnetic resonance apparatus, are required to be non-magnetic in order to prevent heat generation due to induction and the accompanying deterioration of characteristics. Is done. Particularly for those requiring corrosion resistance, austenitic stainless steels represented by SUS304, SUS316, etc. are used, and a method of manufacturing a non-magnetic steel part by performing a solution treatment after molding is generally performed. ing. In addition, as a material of a structure particularly requiring strength, a high Mn nonmagnetic steel in which an austenite phase is stabilized by adding N is used.

[0003] In recent years, structural components used for the above-mentioned applications have corrosion resistance comparable to austenitic stainless steel equivalent to SUS304 in terms of material reliability,
At the same time as the required strength level of tempered mechanical structural steel, manufacturing cost is an important factor. In such a case, Japanese Unexamined Patent Application Publication No.
High Mn with reduced amount of expensive Ni such as -102318
High N non-magnetic steel has been proposed. However, these non-magnetic steels have poor cold workability, and are usually disclosed in Japanese Patent Application Laid-Open No. 7-2430.
After hot forging as in the case of No. 01, it is used in a solid solution state, or as in JP-A-7-102318, the final working is formed by warm forging, so it can be used for post-processing such as descaling or cold working. Compared to final forming by cold working, there is a problem in that the size system is poor and final finishing by machining is required, and the number of steps is increased and the cost is high.

[0004]

Conventionally used materials are ordinary austenitic stainless steels, which have a magnetic permeability of 1.1 or less due to solution treatment and have relatively good non-magnetism and corrosion resistance. It is impossible to guarantee high strength. As a material having both high strength level and corrosion resistance, there is a precipitation hardening stainless steel such as SUS631. However, with this material, it is difficult to control the composition and amount of the precipitate and the matrix phase, and it is difficult to stably guarantee nonmagnetic properties.

[0005] However, the characteristics required of the non-magnetic steel for fastening aimed by the present invention are specifically described as follows. 0.2% proof stress: 650 N / mm ² or more tensile strength: 800 N / mm ² or more corrosion resistance: salt spray test (JIS Z 2371)
Does not rust even after 100 hours. Permeability: 1.05 or less Other: Low cost

Among these required characteristics, 0.2% proof stress and tensile strength are important characteristics for securing static strength and fatigue strength as a fastening material.

In addition, low cost means that not only alloy components used but also manufacturing process costs occupy a large proportion.

[0008] However, conventional materials cannot satisfy all of them, and it is necessary to realize a non-magnetic steel having all the properties. In the present invention, by selecting components that are appropriate not only for their properties but also for their chemical components, and using cold working and cold forming in all member forming, the process cost is lower than that of hot or warm working. It is intended for reduction. Therefore, in the present invention, as a material which can meet the above-mentioned objects, has good cold workability and can have high strength, and has good corrosion resistance and non-magnetic properties, it is disclosed in Japanese Patent Application Laid-Open No.
M having component balance as disclosed in Japanese Patent No. 70701
A stainless steel containing n, Ni, Cu, and N was used. Therefore, the present invention is directed to Japanese Patent Application Laid-Open No. 7-70701.
Based on the invention disclosed in the gazette, it is an object of the present invention to research and develop a manufacturing process capable of satisfying all of the above strength characteristics, corrosion resistance, and non-magnetic properties, and to provide a corrosion-resistant high-strength non-magnetic steel part. .

[0009]

According to the present invention, as a means for solving the above-mentioned problems, according to the first aspect of the present invention, the chemical component is 0.1% by weight or less, C: 0.12% or less, and Si: 0.05 to
1.00%, Mn: 5.0 to 8.5%, P:. 045%
Hereinafter, S: 0.015% or less, Ni: 4.0 to 9.0.
%, Cr: 16.0-21.0%, Cu: 1.0-4.
0%, N: 0.15 to 0.30%, O: 0.0040%
Hereinafter, B: 0.0015 to 0.0040%, C + N: 0.20 to 0.35%, the balance being Fe and unavoidable impurities, and conditional expression: 53
0-410 [C] -350 [N] -10 [Mn] -15
[Cr] -30 [Ni + Cu] -10 [Mo] ≤-80
Is subjected to cold working at a working rate of 10 to 20%, and then cold forging or header working is performed in a temperature range of 60 to 150 ° C., and further , 300 to 5 in a salt bath .
By holding for 15 minutes or more in the range of 50 ° C, 0.2
% Proof stress of 650 N / mm ² or more and tensile strength of 800 N /
This is a high-strength non-magnetic steel for fastening a linear motor car superconducting coil having a diameter of not less than mm ² and a permeability of not more than 1.05. In the conditional expression, [] means weight% of each element.

[0010] According to the invention of claim 2, in the chemical component of the means of claim 1, Nb: 0.05 to 0.2.
0% or V: one or more of 0.05 to 0.50%
The high-strength non-magnetic steel for fastening a superconducting coil of a linear motor car according to the means of claim 1, wherein at least one kind is added.

The present invention has been found to be constituted by combining steel having an appropriate chemical composition with appropriate manufacturing conditions as described above, whereby a high-strength non-magnetic steel part having desired properties can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In showing the embodiments of the present invention, the reasons for limiting the components of steel, which are requirements, will first be described. The details are described in Japanese Unexamined Patent Publication No. 7-70701. Things will be described. In addition, each of the following elements is% by weight.

C + N: For 0.2 to 0.35%, C
And N are necessary to obtain high strength as a solid solution strengthening element in the form of C + N, but if the total amount is less than 0.20%, the strength used as the steel will be insufficient.
The lower limit was set to 0.02%. However, if the content exceeds 0.35%, hot workability and cold workability are impaired.
5%.

For Mn: 5.0 to 8.5%, Mn is very effective as a deoxidizing material and an austenite-forming element, and replaces expensive Ni which suppresses the formation of a martensite phase during cold working. Element. It also hinders the formation of chromium nitride, which impairs corrosion resistance because it increases the solubility of N in the austenitic phase. When the content is less than 5.0%, these effects are small, so the lower limit is set to 5.0%. If the content exceeds 8.5%, deterioration of corrosion resistance due to solid solution Mn and deterioration of cold and hot workability are caused.
5%.

Ni: 4.0-9.0%, Ni
Is a basic element in austenitic stainless steel, is a strong austenite-forming element, and is an element that improves corrosion resistance and suppresses martensite generation after cold working. However, since Ni is expensive, it is desirable to substitute Mn, Cu, N, etc., as far as these performances can be ensured, and to reduce as much as possible. That is, if it is less than 4.0%, it is difficult to secure the performance, and if it is added more than 9.0%, there is almost no effect of improving the corrosion resistance which is regarded as important in the use of the steel, so that 4.0 to 9 0.0%.

Cr: 16.0 to 21.0%, C
r is a basic element in austenitic stainless steel together with Ni, and imparts corrosion resistance. When it is 16.0% or more, sufficient weather resistance can be obtained. However, when it exceeds 21.0%, a ferrite phase is easily generated, so 16.0 to 21.0%
And

Cu: 1.0-4.0%, Cu
Is an austenite-forming element and stabilizes the austenite phase. Further, similarly to Ni, the formation of a martensite phase due to processing is suppressed. In particular, Cu lowers the work hardening index of the matrix, so that ductility during cold working can be maintained, and thus has an effect of suppressing the occurrence of cracks.
Since 1.0% or more is required to exhibit the effect, the lower limit is set to 1.0%. However, when the content exceeds 4.0%, the hot workability is significantly deteriorated, so the upper limit is set to 4.0%.

B: For 0.0015 to 0.0040%, B is an element that improves hot workability.
If the content is less than 0015%, the effect is small, so the lower limit is set to 0.1%.
0015%. On the other hand, if the content exceeds 0.0040%, a B compound is generated, which deteriorates hot workability. Therefore, the upper limit is made 0.0040%.

Nb: For 0.05 to 0.20%, N
When b is contained and subjected to a precipitation hardening heat treatment, carbonitrides are formed, crystal grains are refined, and the ductility after cold working increases with the increase in strength. In the present invention, especially when ductility after cold working is required, it is added. In this case, the effect cannot be obtained if the content is less than 0.05%, so the lower limit is set to 0.05%. If the content exceeds 0.20%, the cold workability is impaired, so the upper limit was made 0.20%.

V: 0.05 to 0.50%, V
In the case where Nb is contained as in Nb, a carbonitride is formed when a precipitation hardening heat treatment is performed, and the same effect is obtained.
Since the effect cannot be obtained if the content is less than 0.05%, the lower limit is set to 0.05%. If the content exceeds 0.50%, the cold workability deteriorates, so the upper limit was made 0.50%. Conditional expression: 530-410 [C] -350 [N] -10
[Mn] -15 [Cr] -30 [Ni + Cu] -10
For [Mo] ≦ −80, the basic chemical composition of the steel used in the present invention is as described above, and the balance is composed of Fe and unavoidable impurities, but it is necessary to further satisfy the above conditional expression. . In the conditional expressions, [] means weight% of each element. The above conditional expression relates to the generation of work-induced martensite during cold working. From FIG. 1 showing the relationship between the value of the conditional expression and the magnetic permeability after 50% cold working, this conditional expression Indicates that the magnetic permeability after cold working can be predicted. The steel is usually partially subjected to a cold working rate of 40% or more depending on the final shape. Therefore, it is necessary to set an appropriate component balance in the present conditional expression in order to secure non-magnetic properties. Conditional expression value is -8
If it exceeds 0, the magnetic permeability exceeds 1.05 and non-magnetic properties cannot be maintained, so the upper limit was set to -80. Further, if the value is -80 or less, the stability of austenite to processing is sufficient, so no particular lower limit is set.

Next, the working process of the present invention will be described.
Even if steel of the above-defined range of components is formed into parts such as bolts by hot forging or direct cutting, the corrosion resistance and non-magnetic properties are satisfied, but the required strength of 0.2%
Yield strength: 650 N / mm ² or more, tensile strength: 800 N / m
it is impossible to obtain m ² or more strength. Further, if only the entire part is formed by cold forging or cold forming such as a header, there is a difference in workability depending on the portion, and it is difficult to satisfy the above-mentioned strength in all portions depending on the shape.

Therefore, in the present invention, the relationship between the increase in strength due to cold working and the cold workability of the next step such as cold forging or a header is studied, and the forming is performed before cold forming. It has been found that cold forming in a temperature range enables cold forming without deteriorating the strength characteristics improved by the cold working.

For cold working at a working ratio of 10 to 20%, the cold working ratio is an important factor for determining the initial strength, but in the present invention, steel having a chemical composition range of less than 10% is used. Since the working ratio does not satisfy the strength characteristics, the lower limit is 10
%. Originally, the upper limit of the working ratio is not particularly limited in terms of strength, but if the working ratio here is too high, the deformation resistance at the time of cold forming such as cold forging or header in the next process is high. Since problems such as lack of lubrication, seizure, and die cracking occur, the upper limit is set to 20%. FIG. 2 shows an appropriate cold working range and its limiting factor.

For cold forging or header working in the temperature range of 60 to 150 ° C., the cold-worked steel has high strength and is difficult to form by ordinary methods at room temperature.
Therefore, the relationship between the temperature during forming and the deformation resistance was studied, and a temperature range in which the strength after cold forming was not affected and cold forming was sufficiently possible was found. FIG.
Fig. 2 shows the changes in temperature and deformation resistance during cold forming. As a result, if the temperature at the time of cold forming is 60 ° C. or more, the deformation resistance is greatly reduced as compared with the normal temperature, and the forming process becomes possible.
However, when the temperature is 150 ° C. or higher, the temperature begins to soften significantly and the strength after cold forming decreases, so the temperature range during cold forming is limited to 60 to 150 ° C.

With respect to holding at a temperature in the range of 300 to 550 ° C. for 15 minutes or more, a lubricating material such as molybdenum disulfide is used for lubrication with a mold in ordinary cold forming, but a lubricating film remains. Then, since the corrosion resistance deteriorates, it is necessary to remove this lubricating film in order to obtain a product. In this type of lubricating film removal, removal treatment is generally performed at around room temperature using a combination of an alkaline solution and an acid solution. As a result of research on removal conditions, removal of the film by treatment using a salt bath was performed. It was also found that by appropriately controlling the temperature during the film removal treatment using a salt bath, it was possible to increase the strength without impairing the corrosion resistance and non-magnetism. When the temperature at the time of the salt bath treatment is about 300 ° C. or less, there is no effect of increasing the strength, and as shown in FIG. 4, the strength, particularly the proof strength, greatly increases in the temperature range of 300 ° C. to 550 ° C. However, at higher temperatures, softening begins. So, in order to guarantee the required strength,
The temperature range was 300 to 550 ° C. Although the treatment time is about 10 minutes, the effect of increasing the strength is obtained, but it is 15 minutes or more in order to achieve the removal of the film. In addition, since the outer surface finish cutting / grinding or polishing is performed after the forming process, when the lubricating film removing process is omitted, the process may be performed in the above-mentioned temperature range by using a device such as a heating furnace or a constant temperature bath.

[0026]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples do not limit the present invention. It is included in the technical scope of the invention.

Now, an embodiment will be described. The target performance as a criterion was set as follows. That is, 0.2% proof stress: 650 N / mm ² or more tensile strength: 800 N / mm ² or more corrosion resistance: salt spray test (JIS Z 2371)
No rusting after 100 hours. Permeability: 1.05 or less.

[0028]

[Table 1]

Table 1 shows examples of chemical components of steel used in the practice of the present invention. Steels having these chemical components were melted in a vacuum induction furnace, and then hot-rolled into bar steel having an outer diameter of 35 mm. After keeping the steel bar at 1050 ° C. × 20 minutes, a solution treatment was performed by water cooling, and the outer diameter was 34.5 by machining.
mm, 32.5 mm and 31 mm, and cold worked to an outer diameter of 30 mm by cold drawing. At this time, the processing degrees (area reduction rates) are 24.4%, 14.8% and 6.4%, respectively. Using these steel bars after cold drawing, the working temperature was set to 1 at room temperature, 100 ° C and 200 ° C, respectively.
00 bolts were cold formed and the cold formability was evaluated. The evaluation was performed based on the occurrence of defects such as seizure or galling, the presence or absence of cracks in the material, cracks in the dies and dies, and the presence or absence of breakage. . Those that could be cold-formed were heat-treated at 100 ° C., 450 ° C., and 620 ° C., respectively, and then evaluated for strength by a tensile test, permeability measurement by a low permeability meter, and corrosion resistance by a salt spray test. .

[0030]

[Table 2]

Table 2 shows the results of evaluating the characteristics of the present invention, and Table 3 shows the results of evaluating the characteristics of the comparative steel. In the steel of the present invention, the deformation resistance was high when the cold forming temperature was normal temperature at any cold working degree, and seizure and cracks in the material occurred, and forming was impossible. Molding was possible at all cold working ratios, but because of softening, there was no strength increasing effect in the subsequent heat treatment, and all were insufficient in strength.

[0032]

[Table 3]

Molding at 100 ° C. has a cold working degree of 6.4.
% And 14.8% were possible. However, when the degree of cold working was 6.4%, it was not hardened sufficiently, and the strength could not be satisfied even after the post heat treatment. That is, only the case where the degree of cold working: 14.8%, the cold forming temperature: 100 ° C., and the heat treatment temperature: 450 ° C., which correspond to the process range of the present invention, could satisfy the strength as the target performance. In addition, all of the inventive steels that could be cold formed satisfy the target performance in both magnetic permeability and corrosion resistance.

As shown in Table 3, in the case of SUS304, which is generally widely used, cold forming is possible when the cold working ratio is low. Is satisfied, the strength is insufficient. On the other hand, when the degree of cold work is increased to, for example, 24.4%, the cold workability is deteriorated along with the hardening due to martensitic transformation, and cold forming becomes impossible.

As described above, in producing the steel, as shown in the present invention, a steel produced by appropriate component control, an appropriately controlled degree of cold working, cold forming temperature and It can be seen that only the combination of the heat treatment is possible.

[0036]

As described above, according to the present invention, it is possible to apply cold working to all forming processes, which was not satisfactory with conventional austenitic stainless steels or precipitation-hardening stainless steels, and at the same time, it has corrosion resistance. It has become possible to obtain a relatively inexpensive high-strength non-magnetic steel for fastening a linear motor car superconducting coil having excellent strength, sufficient strength, and good non-magnetism.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a value calculated by a conditional expression of the present invention and a magnetic permeability after 50% cold working.

FIG. 2 is a diagram showing a range of a cold working degree and a limiting factor thereof.

FIG. 3 is a diagram showing changes in temperature and deformation resistance during cold forming.

FIG. 4 is a diagram showing changes in mechanical properties due to heat treatment after cold working.

Continuation of front page (56) References JP-A-7-70701 (JP, A) JP-A-64-99740 (JP, A) JP-A-6-79389 (JP, A) JP-A-4-359662 (JP) JP-A-64-89403 (JP, A) JP-A-7-11392 (JP, A) JP-A-4-141557 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) C22C 38/00-38/60 C21D 8/00 H01F 5/08 B21J 5/00

Claims (2)

(57) [Claims] 1. A chemical component in weight%, C: 0.12% or less, Si: 0.05 to 1.00%, Mn: 5.0 to 8.0.
5%, P:. 045% or less, S: 0.015% or less, N
i: 4.0 to 9.0%, Cr: 16.0 to 21.0%,
Cu: 1.0 to 4.0%, N: 0.15 to 0.30%,
O: 0.0040% or less, B: 0.0015 to 0.00
40%, C + N: 0.20 to 0.35%
With the balance being Fe and unavoidable impurities, and the conditional expression: 530-410 [C] -350 [N]
-10 [Mn] -15 [Cr] -30 [Ni + Cu]-
Stainless steel satisfying 10 [Mo] ≦ −80
After cold working at a working rate of ~ 20%, 60 ~ 150
Cold forging or header processing in the temperature range of 300 ° C., and holding in a salt bath in the range of 300 to 550 ° C. for 15 minutes or more, the 0.2% proof stress is 650 N / mm ² or more,
The tensile strength is 800 N / mm ² or more, and the magnetic permeability is 1.
High-strength non-magnetic steel for fastening linear motor car superconducting coils of less than 05. In the conditional expressions, [] means% by weight of each element. 2. The composition of claim 1, further comprising:
Nb: 0.05 to 0.20% or V: 0.05 to
The high-strength non-magnetic steel for fastening a linear motor car superconducting coil according to claim 1, wherein one or more kinds of 0.50% are added.