JPH08165543A - Non-magnetic steel material and production thereof - Google Patents

Abstract

PURPOSE: To produce a non-magnetic steel material for prestressed concrete, excellent in mechanical properties and delayed fracture characteristic, by subjecting a steel material, having specific Mn and Ni contents, to wire drawing at specific reduction of area and then to heating treatment. CONSTITUTION: The non-magnetic steel material has a composition consisting of, by weight, <=0.15% C, <=2.0% Si, 1.0-15.0% Mn, 2.0-15.0% Ni, 15.0-20.0% Cr, 0.1-0.5% N, and the balance essentially Fe and satisfying Ni+Mn=10 to 18%. The steel material with this composition is wire-drawn at a draft of 50-70% reduction of area and heated at 300-700 deg.C, preferably at 500-600 deg.C. By this method, the non-magnetic steel material, having <=1.01 magnetic permeability, >=1600N/mm<2> fracture strength, and >=3.5% elongation, can be obtained. This material is suitably used for prestressed concrete (PC). Further, the amount of martensite is regulated to 2-10% in this steel material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel material suitable for prestressed concrete (hereinafter referred to as PC) in a structure requiring non-magnetism and a method for producing the steel material.

[0002]

2. Description of the Related Art Conventionally, carbon steel is a steel material based on carbon steel. Since these are all magnetically ferromagnetic, they cannot be used in places where non-magnetism of structures is required, such as guideways for linear motor cars. In addition, Mn is 1 as a steel material that realizes non-magnetism.
High Mn steels and austenitic stainless steels containing about 5% or more have been conventionally known (Japanese Patent Laid-Open No. 4-1549).
38, JP-A-4-141557, JP-A-4-139934, JP-A-4-143252 and JP-B-6-4891).

[0003]

However, the high Mn steel is M
Since a large amount of n is contained, delayed fracture characteristics are deteriorated, which is not desirable for PC steel. Austenitic stainless steels such as SUS304 and SUS316 are both used, but the cold working increases the magnetic permeability, impairs non-magnetism, and PC.
There is a problem in that mechanical properties such as tensile strength, proportional limit, yield strength, elongation and relaxation required for steel cannot be satisfied. Therefore, the object of the present invention is to
It is an object of the present invention to provide a method for producing a non-magnetic steel material which satisfies the mechanical properties (tensile strength, proportional limit, yield strength, elongation, relaxation) of PC steel and is excellent in delayed fracture properties.

[0004]

In order to achieve this object, the first constitution of the present invention is such that, in% by weight, C: 0.15% or less, Si: 2.0% or less, Mn: 1.0-. 15.0%,
Ni: 2.0 to 15.0%, Cr: 15.0 to 20.0
%, N: 0.1 to 0.5%, the balance being a non-magnetic steel material consisting essentially of Fe, Ni + Mn: 10 to 18%, magnetic permeability of 1.01 or less, tensile strength of 1600 N / mm ² or more, The elongation is 3.5% or more. Here, the amount of Mn is 1.0 to 5.0% by weight, and the amount of Ni is 10.0 to 1
It is preferably 5.0% by weight. The manufacturing method is characterized in that a steel material having the same composition is drawn at a working ratio of 50% or more and 70% or less in cross-section reduction and heated to 300 ° C to 700 ° C, preferably 500 ° C to 600 ° C. And

The second constitution is C: 0.1% by weight.
5% or less, Si: 2.0% or less, Mn: 1.0 to 15.
0%, Ni: 2.0 to 15.0%, Cr: 15.0 to 2
0.0%, N: 0.1 to 0.5%, the balance being substantially Fe
A non-magnetic steel material consisting of Ni + Mn: 10 to 18% and a relaxation value of 1.5% or less. Here, it is preferable that the amount of Mn is 1.0 to 5.0% by weight and the amount of Ni is 10.0 to 15.0% by weight. And the manufacturing method is characterized in that after cold working a steel material having the same composition, it is heated to a temperature of 200 ° C. to 700 ° C. to give a tensile force less than the breaking load of the steel material.

The third structure is such that, in weight%, C: 0.15% or less, Si: 2.0% or less, Mn: 1.0 to 5.0%, N.
i: 10.0 to 13.0%, Cr: 15.0 to 20.0
%, N: 0.1 to 0.5%, the balance being a steel material consisting essentially of Fe, characterized in that at least one of the following three conditions is satisfied. The amount of martensite is 2 to 10% by volume. The full width at half maximum of fcc (220) in X-ray analysis is 0.65 or more, more preferably 0.7 or more. Carbides of 100 nm or less are dispersed.

[0007] In such a steel material manufacturing method, C: 0.15% or less, Si: 2.0% or less, and Mn: 1.
0 to 5.0%, Ni: 10.0 to 13.0%, Cr: 1
5.0 to 20.0%, N: 0.1 to 0.5%, the balance being at least one of the following conditions when heat-treated after wire-drawing a steel material consisting essentially of Fe Is characterized by. Wire drawing processing is 0 to 100 ° C, more preferably 0 to 60 ° C
In the temperature range of. The cross-section reduction rate of wire drawing is set to 50 to 70%. The heat treatment condition is 300 to 600 ° C., more preferably 50.
It is 10 to 60 minutes at 0 to 600 ° C.

The reasons for limiting the components and manufacturing conditions in this way are as follows. C stabilizes austenite,
In addition, it is an element that contributes to the strength improvement by solid solution strengthening and is a very important element. However, if the content is more than 0.15% by weight, carbides precipitate and delayed fracture characteristics deteriorate, and ductility decreases, so the content was made 0.15% or less. Si
Is an element required in production as a deoxidizer. However, since it is a stabilizing element of ferrite on the one hand, 2.
This is because if the content exceeds 0%, ferrite may be generated and the non-magnetism may be impaired. Mn is a strong austenite stabilizing element, and is an element necessary for ensuring non-magnetism after cold working. However, a content of less than 1.0% is not sufficient, and a content of more than 15% not only deteriorates the wire drawability but also deteriorates the delayed fracture property. Considering delayed fracture characteristics,
The Mn content is preferably 1.0 to 5.0%.

Ni, like Mn, is an austenite stabilizing element and is an element effective for ensuring the non-magnetism of the steel material. If less than 2.0%, the effect is insufficient, 15%
This is because there is no further effect even if the above is exceeded, and only the cost is increased. Practically, 10.0 to 13.0% is preferable. Further, both Mn and Ni are austenite stabilizing elements, and in order to make the steel material nonmagnetic surely, Mn
The amount of + Ni must be 10% or more. On the other hand, if the amount is too large, the cost increases, so 18% or less is preferable. C
r is an element that improves the corrosion resistance of the steel material and contributes to the stabilization of austenite by the addition of an appropriate amount, but when it is contained in excess, it promotes the formation of ferrite. Therefore, the content of 15% or more is required to ensure the corrosion resistance, but it is necessary to be 20% or less in order to suppress the generation of ferrite and to secure the nonmagnetic property. N, like C, contributes to austenite stabilization and is an element necessary for securing strength by solid solution strengthening. If it is less than 0.1%, its effect is small, and if it exceeds 0.5%, a large amount of bubbles are generated during steel making, which impairs hot workability and further deteriorates delayed fracture characteristics.

The heat treatment temperature of the steel material having such a composition after wire drawing is set to 300 ° C. or more and 700 ° C. or less because the steel material sufficiently satisfies the tensile strength and elongation required for the non-magnetic PC steel. Is to get. Furthermore, the temperature conditions when applying a tensile force less than the breaking load to 200 ° C. to 700 ° C. after cold working the steel material having the above composition are the mechanical properties, the proportional limit, and the yield limit. Greatly improved,
This is to keep the relaxation low. Japanese Patent Publication No. 61-53408 proposes a heat treatment similar to the heat treatment of the present invention, but basically the composition of the target steel material is different. In particular, regarding the content of C, the invention described in the publication is 0.2% or more, whereas that of the present application is 0.
It is as low as 15% or less, which is a big difference in that it aims to improve the proportional limit and the yield strength in low C steel.

Further, by setting the drawing processing temperature to 0 to 60 ° C., the amount of martensite after drawing is set to 2 to 10% by volume, and the half width of fcc (220) is set to 0.65 or more. You can If the amount of martensite exceeds 10%,
The magnetic permeability of the steel material is significantly increased, which deviates from the condition that the magnetic permeability is 1.01 or less, which is generally said to be non-magnetic. On the other hand, if the amount of martensite is less than 2%, the strength required as a PC steel material cannot be satisfied. Similarly, if the full width at half maximum of fcc (220) is less than 0.65, the strength required as a PC steel material cannot be satisfied. When the half-value width is 0.70 or more, the strength improving effect is particularly large.

The heat treatment temperature after wire drawing is set to 300 to 700.
As described above, limiting the temperature to ° C contributes to the improvement of tensile strength and elongation. This heat treatment condition is 300 to 600 ° C.
More preferably, the temperature is 500 to 600 ° C., and the heating time is 10 to 6
By limiting the time to 0 minutes, the tensile strength and delayed fracture characteristics can be further improved. That is, by this heat treatment,
By dispersing fine carbide of 100 nm or less in the steel material, it is possible to obtain sufficient strength as a PC steel material. Heating time 6
If it exceeds 0 minutes or if the heating temperature exceeds 600 ° C., the carbide becomes larger than 100 nm, and the delayed fracture property is inferior even if the strength is obtained. On the other hand, if the heating time is less than 10 minutes or the heating temperature is less than 300 ° C., the precipitation of carbide is insufficient and it is difficult to obtain a high-strength material.

[0013]

Embodiments of the present invention will be described below. (Example 1) A steel material having a composition shown in Table 1 was subjected to hot treatment to obtain a wire rod having a diameter of 7 mm. After the solution treatment, they were drawn and heat-treated under each condition. 1 heat treatment for each temperature
It hold | maintained for 0 minute and water-cooled. After that, magnetic permeability, tensile strength, elongation at break, yield strength, proportional limit, relaxation and delayed fracture characteristics were investigated. The results are shown in Table 2 and FIG.

[0014]

[Table 1]

[0015]

[Table 2]

Table 2 shows the results of the mechanical properties of a wire rod which was subjected to wire drawing with a cross-section reduction rate of 55%, heated and held at 350 ° C. for 10 minutes, and water-cooled.
The delayed fracture characteristic is ammonium thiocyanate (NH ₄ S
In the (CN) solution, a load of 70% of the tensile strength was applied, and the time until breakage was maintained for 200 hours or more. As can be seen from Table 2, the examples show stable magnetic characteristics even after cold working, and the magnetic permeability is very small. The tensile strength and elongation at break also show higher values than those of the comparative examples. On the other hand, FIG. 1 shows the influence of the heating temperature in the heat treatment after cold working on the sample D in Table 1. As shown in the figure, it was confirmed that the tensile strength was significantly improved by heating to a temperature of 300 ° C. or higher and 700 ° C. or lower (particularly 500 to 600 ° C.).

(Example 2) Using sample D shown in Table 1, a wire rod having a diameter of 7 mm was produced by hot rolling. After that, solution treatment was performed, wire drawing was performed at a cross-sectional reduction rate of 55%, heating was performed at each temperature, and the yield strength, proportional limit, and relaxation of the material subjected to 50% of the breaking load were examined. Table 3 shows the results.

[0018]

[Table 3]

As shown in Table 3, above 200 ° C. and 700 ° C.
By applying a load in the following temperature range, the yield strength and proportional limit are greatly improved, and the relaxation is very small. Therefore, it was confirmed that it was extremely excellent as a PC steel material.

(Example 3) Further, using sample D shown in Table 1, processing was performed at each cross-section reduction rate, and 350 ° C x 10
The strength and elongation of the wire which was heat treated for a minute were measured. The relationship between the cross-section reduction rate and these mechanical properties is shown in the graph of FIG. As shown in the figure, when the cross-section reduction rate is high, the tensile strength is high, but the elongation tends to be small. When the cross-section reduction rate is 50 to 70%, a wire having excellent strength and toughness can be obtained. I understand.

(Example 4) A steel material having the composition shown in Table 4 (same as Sample D in Table 1) was hot-rolled to give a diameter of 7 mmφ.
I got the wire. After the solution treatment, they were subjected to wire drawing with a cross-section reduction rate of 56.5% at each processing temperature. Then 52
Hold at 5 ℃ for 10 minutes and cool with water to obtain tensile strength, magnetic permeability,
Amount of martensite by X-ray analysis, fcc by X-ray analysis
The full width at half maximum of the (220) peak was measured. The processing temperature was the temperature of the wire material at the die exit in the wire drawing process.

[0022]

[Table 4]

The results are shown in FIGS. As shown in each figure, as the processing temperature decreases, the amount of martensite / fcc
Full width at half maximum of (220) peak (amount of strain in austenite phase)
It can be seen that the tensile strength is increased and the tensile strength can be improved. Although a tensile strength of 1600 N / mm ² can be obtained even at a processing temperature of about 100 ° C., a wire material having a higher strength can be obtained particularly by wire drawing at 60 ° C. or less. However, when the processing temperature is lower than 0 ° C., the magnetic permeability increases with the increase in the amount of martensite, which is not preferable as a nonmagnetic material.

Example 5 A steel material having the composition shown in Table 4 was hot-rolled to obtain a wire rod having a diameter of 7 mm. After subjecting them to solution treatment, wire drawing was carried out at 50 to 55 ° C. at a cross-section reduction rate of 56.5%. After that, heat treatment is performed under various conditions to obtain tensile strength
The state of carbide precipitation and delayed fracture characteristics were evaluated. The delayed fracture property was tested by using 0.1N HCl solution as a corrosive liquid at a load of 80% of the breaking load, and the test time was 200 hours at maximum. In Example 1, the delayed fracture characteristics mainly due to H were investigated, but in this example, the delayed fracture characteristics due to Cl ⁻ corrosion was also investigated. The results are shown in Table 5.

[0025]

[Table 5]

As shown in the table, the heating temperature is 300 to 7
It can be seen that a tensile strength of 1600 N / mm ² or more is obtained in the range of 00 ° C. In particular, the heating temperature is 500-60
When the temperature is 0 ° C., fine carbides are precipitated and the tensile strength is remarkably improved. Moreover, when the heating time was set to 10 to 60 minutes, a wire rod having high tensile strength and excellent delayed fracture characteristics could be obtained. If the heating temperature is too high or the heating time is too long, the precipitated carbides will be large, and the delayed fracture property will be poor even if the tensile strength is high.

Example 6 A steel material having the composition shown in Table 6 was hot-rolled to obtain a wire rod having a diameter of 7 mm. After the solution treatment, they were subjected to wire drawing with a cross-section reduction rate of 56.5% at each processing temperature. Then, hold at 525 ° C for 10 minutes and cool with water,
The delayed fracture characteristics of the obtained wire rod were evaluated. The evaluation was performed in the same manner as in Example 5. The results are shown in Table 7. As is clear from the table, it can be seen that the examples show extremely excellent delayed fracture characteristics as compared with the reference examples.

[0028]

[Table 6]

[0029]

[Table 7]

[0030]

As described above, according to the present invention, it is possible to obtain a steel material which satisfies the mechanical properties required for non-magnetic PC steel. Particularly, the steel material according to claim 1 is excellent in magnetic permeability, tensile strength, elongation and delayed fracture. The steel material according to claim 3 is excellent in yield strength, proportional limit and relaxation in addition to these mechanical properties. Further, the steel materials according to claims 7 to 9 are also excellent in tensile strength and can realize low magnetic permeability. In particular, the steel material according to claim 9 is excellent in delayed fracture characteristics. Therefore, it can be used as PC steel in a structure requiring non-magnetism such as a guideway of a linear motor car and a nuclear magnetic resonance tomography chamber.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between heat treatment temperature and tensile strength.

FIG. 2 is a graph showing a relationship between a cross-section reduction rate and mechanical properties.

FIG. 3 is a graph showing the relationship between drawing processing temperature and tensile strength.

FIG. 4 is a graph showing the relationship between drawing processing temperature and magnetic permeability.

FIG. 5 is a graph showing the relationship between the drawing processing temperature and the amount of martensite.

FIG. 6 is a graph showing the relationship between the drawing processing temperature and the fcc (220) peak.

Claims (13)

[Claims] 1. C: 0.15% or less by weight%, Si:
2.0% or less, Mn: 1.0 to 15.0%, Ni: 2.
0 to 15.0%, Cr: 15.0 to 20.0%, N:
0.1 to 0.5%, the balance consisting essentially of Fe, Ni
+ Mn: 10-18%, a magnetic permeability of 1.01 or less, a breaking strength of 1600 N / mm ² or more, and an elongation of 3.5% or more, a non-magnetic steel material. 2. C: 0.15% or less by weight%, Si:
2.0% or less, Mn: 1.0 to 15.0%, Ni: 2.
0 to 15.0%, Cr: 15.0 to 20.0%, N:
0.1 to 0.5%, the balance consisting essentially of Fe, Ni
+ Mn: Steel material of 10 to 18% is subjected to wire drawing at a working ratio of 50% or more and 70% or less in cross-section reduction, and 300 ° C or more and 700
A method for producing a non-magnetic steel material, which comprises heating to below ℃. 3. C: 0.15% or less by weight%, Si:
2.0% or less, Mn: 1.0 to 15.0%, Ni: 2.
0 to 15.0%, Cr: 15.0 to 20.0%, N:
0.1 to 0.5%, the balance consisting essentially of Fe, Ni
+ Mn: 10 to 18%, relaxation value is 1.5
% Or less, a non-magnetic steel material. 4. C: 0.15% or less by weight%, Si:
2.0% or less, Mn: 1.0 to 15.0%, Ni: 2.
0 to 15.0%, Cr: 15.0 to 20.0%, N:
0.1 to 0.5%, the balance consisting essentially of Fe, Ni
+ Mn: 10 to 18% of steel, after cold working, 2
A method for producing a non-magnetic steel material, which comprises heating to a temperature of 00 ° C to 700 ° C and applying a tensile force less than a breaking load of the steel material. 5. Among the chemical components of steel, Mn is 1.0 to 5.
The non-magnetic steel material according to claim 1 or 3, wherein 0 wt% and Ni are 10.0 to 13.0 wt%. 6. The chemical composition of a steel material, wherein Mn is 1.0 to 5.
The non-magnetic manufacturing method according to claim 2 or 4, wherein 0 wt% and Ni are 10.0 to 13.0 wt%. 7. C: 0.15% or less by weight%, Si:
2.0% or less, Mn: 1.0 to 5.0%, Ni: 10.
0 to 13.0%, Cr: 15.0 to 20.0%, N:
0.1 to 0.5%, the balance substantially consisting of Fe, and the amount of martensite in volume% is 2 to 10%, a non-magnetic material. 8. C: 0.15% or less by weight%, Si:
2.0% or less, Mn: 1.0 to 5.0%, Ni: 10.
0 to 13.0%, Cr: 15.0 to 20.0%, N:
0.1 to 0.5%, the balance being substantially Fe, and a half-value width of fcc (220) in X-ray analysis of 0.65 or more. 9. C: 0.15% or less by weight%, Si:
2.0% or less, Mn: 1.0 to 5.0%, Ni: 10.
0 to 13.0%, Cr: 15.0 to 20.0%, N:
0.1 to 0.5%, the balance consisting essentially of Fe, 10
A non-magnetic steel material in which carbides of 0 nm or less are dispersed. 10. C: 0.15% or less by weight%, Si:
2.0% or less, Mn: 1.0 to 5.0%, Ni: 10.
0 to 13.0%, Cr: 15.0 to 20.0%, N:
A method for producing a non-magnetic steel material, which comprises subjecting a steel material, which is 0.1 to 0.5% and the balance being substantially Fe, to a wire drawing process in a temperature range of 0 to 100 ° C. 11. The drawing workability is a cross-section reduction rate of 50 to 70.
%, The method for producing a non-magnetic steel material according to claim 10. 12. C: 0.15% or less by weight%, Si:
2.0% or less, Mn: 1.0 to 5.0%, Ni: 10.
0 to 13.0%, Cr: 15.0 to 20.0%, N:
0.1 to 0.5%, the balance being steel made of substantially Fe, drawn in a temperature range of 500 to 600 ° C. for 10 to 60
A method for producing a non-magnetic steel material, which comprises heating for a minute. 13. The method for producing a non-magnetic steel material according to claim 12, wherein the drawing process is performed in a temperature range of 0 to 100 ° C.