JP3362315B2 - Method for producing ultrafine wire of austenitic stainless steel and ultrafine wire - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an austenitic stainless steel.
Relates to the production method and the same ultra-fine line of less steel fine wire, in particular,
When the wire diameter is 500 μm or less, it has high strength and excellent sag property, and members and parts that require good workability, such as wire springs for communication equipment, computer-related equipment, precision electronic equipment, office equipment or electric equipment, etc. A method for manufacturing austenitic stainless steel ultrafine wire suitable for mini ropes, etc.
And the same ultrafine wire .

[0002]

2. Description of the Related Art In recent years, as the weight and downsizing of equipment have been developed, the diameter of ultrafine wire is inevitably becoming thinner. From this point of view, high strength and high sag resistance are required. On the other hand, from the standpoint of product molding, bending and twisting are often performed, and ensuring the workability of high-strength ultrafine wires is also an important required characteristic.

Conventionally, general-purpose austenitic stainless steel such as SUS301 or SUS304 has been used for the stainless steel ultrafine wire for the above-mentioned members, but it has become difficult to meet the above-mentioned strict requirements, and oxide-based materials together with the basic components have been used. A non-metallic inclusion is proposed (for example, JP-A-62-290848). However, adjustment of the composition of the oxide-based non-metallic inclusions is sensitive to the composition of raw materials or the operating conditions, and therefore requires an extremely fine control technique. As a result, there is a drawback of causing quality instability, and it has not been widely used. Therefore, development of an austenitic stainless steel ultrafine wire having good wire drawability and more stable quality is strongly desired.

[0004]

DISCLOSURE OF THE INVENTION In order to meet the strong demands of the industry, the present invention has been made by the present inventors as a result of earnest studies in view of the problems of conventional austenitic stainless steel ultrafine wires, and as a result, the chemical composition was properly adjusted. It was clarified that all the conventional problems can be solved by adjusting and controlling the materials and the composition of non-metallic inclusions and an appropriate heat treatment after wire drawing, and the present invention has been completed. And has as its object a good drawability to fine wire, formability of products excellent, yet the production of very good austenitic stainless steel fine wire of sag resistance at high intensity in product performance Method and
The same ultrafine wire is provided.

[0005]

The subject matter of the present invention is as follows.

(1) In weight%, C: 0.05 to 0.15%, S ≦ 0.005%, Al ≦ 0.005%, N: 0.02 to 0.10%, O ≦ 0. The content of non-metallic inclusions in steel is adjusted to 1 wt% by adjusting the content of S to Al to satisfy the formula (1).
% Of S or more oxysulfide formed austenitic stainless steel is rolled into a wire rod, followed by annealing / drawing to produce ultrafine wire, followed by heat treatment, before the heat treatment. Area reduction of wire drawing of 50
% Or more, followed by heat treatment 100 ° C or more, 600 ° C
The method is performed at the following temperature and for a short time of 30 seconds or less under the condition that the k value represented by the formula (2) satisfies 6.5 or more and 13.5 or less. And a method for producing an austenitic stainless steel ultrafine wire.

[S] ≧ [Al] / 2 (1) Here, [S]; S content in steel (wt%) [Al]; Al content in steel (wt%) k = T × ( logt + 20) × 10 ⁻³ (2) where k: heating coefficient T; heating temperature (K) t; heating time (Hr)

(2) By weight%, C: 0.05 to 0.15%, Si: 0.2 to 3%, Mn: 0.2 to 3%, S ≦ 0.005%, Ni: 6. 5 to 12%, Cr: 16 to 20%, Al ≤ 0.005%, N: 0.02 to 0.10%, O ≤ 0.005%, and the relationship between S and Al content is (1 ) The composition is adjusted to satisfy the formula, and the total composition of non-metallic inclusions in steel is 1 wt.
% Of S or more oxysulfide formed austenitic stainless steel is rolled into a wire rod, followed by annealing / drawing to produce ultrafine wires, followed by heat treatment when the heat treatment is performed. Area reduction of the previous wire drawing process is 5
0% or more, followed by heat treatment at 100 ℃ or more, 600
At a temperature of ℃ or less, and the k value represented by the formula (2) is 6.5.
Short time of 30 seconds or less under the condition that 13.5 or less is satisfied
A method for producing an austenitic stainless steel ultrafine wire, which is characterized by being applied for a period of time .

[S] ≧ [Al] / 2 (1) where [S]; S content in steel (wt%) [Al]; Al content in steel (wt%) k = T × ( logt + 20) × 10 ⁻³ (2) where k: heating coefficient T; heating temperature (K) t; heating time (Hr)

(3) In weight%, C: 0.05 to 0.15%, Si: 0.2 to 3%, Mn: 0.2 to 3%, S ≦ 0.005%, Ni: 6. 5 to 12%, Cr: 16 to 20%, Al ≤ 0.005%, N: 0.02 to 0.10%, O ≤ 0.005%, and the relationship between S and Al content is (1 ) Satisfies the formula,
The composition of non-metallic inclusions in steel is oxysulfide containing 1 wt% or more of S in total, and the spring limit value is 70.
An austenitic stainless steel ultrafine wire characterized by having a weight of at least kgf / mm ² .

[0011]     [S] ≧ [Al] / 2 (1) Here, [S]; S content in steel (wt%) [Al]; Al content in steel (wt%)

That is, the inventors of the present invention have made detailed studies on the influential factors that affect the workability, formability, mechanical properties, etc. of austenitic stainless steel ultrafine wires. On the other hand, it was clarified that the mechanical properties (deterioration resistance, strength) of steel are greatly influenced by the quality of steel and heat treatment. Based on this finding, it is effective to reduce the amount of non-metallic inclusions as much as possible and then control the composition in order to make them finer and more dispersed during processing. It is clarified that adjustment is important, and that it is effective to set the wire drawing rate within an appropriate range and then perform appropriate heat treatment for sag resistance. The present invention has been achieved by combining them.

[0013]

The function of the austenitic stainless steel ultrafine wire according to the present invention will be described. (1) High workability and high formability In order to enable wire drawing with high strength and to improve the formability of stainless steel extra fine wire with high strength, it is necessary to reduce the hard non-metallic inclusions that are the starting points of fracture. Required.

Conventionally, as a method for reducing the harmfulness of hard non-metallic inclusions, the amount of oxide non-metallic inclusions has been reduced by ultra-low oxygen, and the amount of Al has been reduced to reduce the amount of alumina (Al).
Attempts have been made to reduce the amount of ₂ O ₃ ) -based oxides, or to control the composition of oxide-based inclusions to a low-melting-point SiO ₂ —MnO—Al ₂ O ₃ system. The present inventors have conducted detailed studies on the generation behavior of non-metallic inclusions or the deformation behavior during processing, and as a result, when the oxygen content is extremely low, a hard oxide remains despite the extremely low Al content. It turned out to be the starting point of the crack. This depends on the concentration of Al ₂ O ₃ in the oxide, which indicates that it is not easy to control the composition of oxide inclusions, which has been conventionally said. That is, oxide-based inclusions are converted to low melting point SiO ₂ --MnO--Al
Controlling to ₂ O ₃ system is to control alloy components (Al, Si, M
n and O) balance or refining conditions (temperature, time, slag composition, etc.) need to be controlled in detail, and the temperature is about 1200 ° C when the melting point is lowered, so the quality is practically stable. It was found that there are many problems in industrial production.

Therefore, as a result of further intensive studies, if the morphology of the non-metallic inclusions is controlled to oxysulfide containing S in the oxide, it can be easily drawn by hot rolling and then finely drawn by wire drawing. The present invention has been completed by finding that it does not become a starting point of fracture because it is divided into two parts, and that the morphology of oxysulfide can be controlled only by adjusting the alloy components (S, Al and O).

(2) Sag resistance and high strength Sag resistance is improved by releasing the strain accumulated by wire drawing. The present inventors have a temperature of 100 ° C. or higher , 600
Low temperature below ℃ and short time heat treatment below 30 seconds (Table 2 and
And Table 3) , the strength is increased and the sag resistance (spring limit value) is improved. On the other hand, when using a stainless steel ultrafine wire as a spring, high strength and high toughness are important subjects, and the present invention also takes these points into consideration.

That is, high strength and high toughness are caused by the action of solid solution strengthening of C and N which are interstitial elements and strain caused by heat treatment after wire drawing, which effectively utilizes dislocations accumulated by wire drawing of strength. This is due to the overlapping effect of age hardening.
Here, the strength is increased by alloying a large amount of C and N having a strong solid solution hardening action, but on the other hand, addition of a large amount of C and N causes deterioration of toughness. Therefore, it is important to select an appropriate value thereof. is there. Further, since the degree of solid solution strengthening and the degree of deterioration of toughness are different between C and N, optimal C and N contents exist from the balance of strength and toughness.

It should be noted that after the stainless steel wire rod is drawn 40
A so-called bluing treatment, in which low-temperature annealing is performed at 0 to 500 ° C for 10 to 30 minutes, is generally known. However, the present inventors provide 100 ° C if wire drawing with a strength of 50% or more is applied.
As described above, at a low temperature of 600 ° C. or less, as shown in Tables 2 and 3, 3
Sufficient strain aging only by heat treatment for a short time of 0 seconds or less
It has been found that (the spring limit value is remarkably improved) , and the heat treatment after the wire drawing in the present invention is performed by controlling the composition of the non-metallic inclusions and appropriately increasing the strength of C and N. This is an important requirement for the construction of the invention as well as ensuring the line workability, and is essentially different from the conventional bluing treatment.

Next, the reasons for limiting the numerical values of the composition component ratios and the heat treatment conditions in the method for producing an austenitic stainless steel ultrafine wire and the same ultrafine wire of the present invention will be described. (1) C C has an action of interstitial solid solution in steel to strengthen it, and is the most effective and necessary element in the steel of the present invention. If the content is less than 0.05 wt%, this effect is small, and
If the content exceeds 0.15 wt% and is excessive, Cr carbide precipitates at the grain boundaries to lower the ductility, deteriorating the wire drawability and formability, and lowering the corrosion resistance. Therefore, C is set to 0.05 to 0.15 wt%.

(2) Si Si is added as a deoxidizing agent and is contained for the purpose of actively reducing oxide-based non-metallic inclusions and controlling the formation of Al ₂ O ₃ -based non-metallic inclusions. To do. That is, the composition of the non-metallic inclusions that is the base in the present invention is adjusted. If the content is less than 0.2 wt%, the composition of the non-metallic inclusions is mainly Al ₂ O ₃ and the effect is small. However, if it is contained excessively in excess of 3 wt %, a δ-ferrite phase is likely to be formed and the hot rolling property is deteriorated. Therefore, S
The content of i was 0.2 to 3 wt%.

(3) Mn Mn combines with S to form MnS, and combines with O to form MnO.
And is an important element for producing oxysulfide in the present invention, and 0.2 wt% or more is necessary to exert this effect. However, if contained in a large amount, it becomes difficult to form an effective oxysulfide, which deteriorates corrosion resistance and toughness, so the upper limit is 3 w.
It was set to t%. Therefore, the Mn content is 0.2 to 3 wt%
And

(4) S S is an important element in the present invention in order to form an oxysulfide having so-called plasticity, which is stretched in hot working and divided in subsequent cold working.
However, if it is contained excessively, the hot workability deteriorates and the corrosion resistance of the product also deteriorates. Therefore, the upper limit of S is 0.00
It was set to 5 wt%.

Here, a proper amount of S is required to form oxysulfide. The present inventors have conducted various studies on the deformation behavior of non-metallic inclusions and found that the S content in non-metallic inclusions is closely related to the Al content, as shown in FIG. FIG. 2 shows 0.07 wt% C, 0.
50 wt% Si, 1.2 wt% Mn, 0.020 wt%
P, 0.003 wt% S, 8.7 wt% Ni, 18.7
5 wt% Cr, 0.038 wt% N, 0.0008 wt
9 kinds of austenitic stainless steel wire rods with 6% as a basic component and varying the balance of S and Al amount (6 mm
φ) was manufactured, and further drawn to 2 mmφ, and the behavior of non-metallic inclusions was investigated. Here, the composition analysis of the non-metallic inclusions was performed mainly with a wire rod having a diameter of 6 mm, and for some of them, a wire having a diameter of 2 mm was used. The size of the non-metallic inclusion was determined by a 2 mmφ line.

As a result, the composition of the non-metallic inclusions stretched and divided during hot working and / or cold working (wire drawing) has a low Al ₂ O ₃ concentration and contains 1 wt% or more of S (the present invention). In oxysulfide). O amount to 0.0050 wt% or less and Al amount to 0.0050
If it is less than wt%, this tendency and the effect are remarkable.

Therefore, formation of oxysulfide is indispensable in order to make non-metallic inclusions fine and dispersed and harmless to workability. For effective formation of oxysulfide, the amount of S represented by the following formula can be used. Securing is important. [S] ≧ [Al] / 2 (1) That is, by satisfying the expression (1), the S concentration in the non-metallic inclusion becomes 1 wt% or more, and the non-metallic inclusion is oxysulfide having plasticity. Become.

(5) Ni Ni is a basic component of austenitic stainless steel and is an extremely effective element for stably obtaining an austenitic phase at room temperature. It is also an important element for ensuring the toughness of steel and wire drawing workability and formability, and 6.5 wt% or more is necessary to effectively exhibit these effects. On the other hand, the content of Ni in excess of 12 wt% only lowers the strength. Therefore, the content of Ni is set to 6.5 to 12 wt%.

(6) Cr Cr is a basic component for stably obtaining an austenite phase in a proper balance with the amount of Ni and ensuring good corrosion resistance. Further, the steel of the present invention improves the strength and Young's modulus of the steel. If the content is less than 16 wt%, the above effect is small, and if the content of Cr exceeds 20 wt%, δ ferrite is formed, the hot workability is deteriorated, and product defects after rolling frequently occur. Therefore, the Cr content is 16 to 2
It was set to 0 wt%.

(7) Al Al is added as a deoxidizing agent. That is, if proper deoxidation with Al is not performed, hard Cr ₂ O ₃ , SiO ₂ ,
SiO ₂ —MnO or a composite oxide of these is formed,
It causes deterioration of workability. Therefore, the basic oxide of oxysulfide in the present invention is SiO ₂ —MnO—A.
A proper amount is necessary for the formation of the l ₂ O ₃ -based oxide.
However, excessive addition is not preferable because it forms a hard Al ₂ O ₃ -based oxide and has an adverse effect. Therefore, as an appropriate amount of Al to make the above effect effective, 0.005
It was set to be wt% or less.

(8) N N is an austenite-forming element similar to C, and is an important element in the present invention for strongly strengthening the austenite phase as an interstitial solid solution effect in steel. Is less than 0.02 wt%, the desired effect cannot be obtained. On the other hand, if the content exceeds 0.10 wt% and is excessive, the toughness or ductility is extremely reduced, and it becomes difficult to perform drawing work on ultrafine wires and a problem occurs in product formability. Therefore, the N content is set to 0.02 to 0.10 wt%.

(9) O 2 O is preferable because it forms oxide inclusions.
However, the extreme reduction is disadvantageous in terms of steel manufacturing cost. On the other hand, the upper limit of the amount of O is 0.0050 wt% for stable formation of oxysulfide in the present invention. Therefore, the content of O is set to 0.0050 wt% or less.

Next, the reason for limiting the heat treatment conditions after wire drawing, which is an important requirement for improving the sag resistance in the present invention, will be described in detail. The sag resistance is generally represented by a plastic deformation strain amount or a spring limit value. That is, in terms of the spring limit value, the higher this value, the better the sag resistance and the higher the performance of the spring and the like.

Therefore, one example of the chemical component of the present invention is
0.08wt% C, 0.52wt% Si, 0.85wt
% Mn, 0.020 wt% P, 0.003 wt% S,
8.7 wt% Ni, 18.90 wt% Cr, 0.002
0 wt% Al, 0.0010 wt% O, 0.052 wt
150% for wire rod rolling by melting and casting austenitic stainless steel with% N and the balance unavoidable impurities
The following experiment was conducted after manufacturing a billet of mm □.

That is, the billet was heated at 1200 ° C. and then hot rolled to obtain a wire rod having a diameter of 6 mm. Then, after pickling and descaling, wire drawing is performed up to a diameter of 2 mm, followed by bright annealing and wire drawing to obtain a diameter of 1 mm.
An ultrafine wire of 50 μmφ was used. The ultrafine wire was heat-treated at various temperatures and times to measure the spring limit value. The result is shown in FIG. In the figure, k is a factor of the heating temperature and the heating time and is expressed by the equation (2).

K = T × (logt + 20) × 10 ⁻³ (2) where k: heating coefficient T; heating temperature (K), t; heating time (Hr)

As is apparent from FIG. 3, the spring limit value is improved by increasing the k value of the heat treatment condition. It can be seen that this effect is remarkable when the k value is 6.5 or more. As a result of the above, from the viewpoint of sag resistance, k expressed by the equation (2)
The value was set to 6.5 or more. By the way, the k value is a factor of heating temperature and time, and if the temperature is low, it requires a long time. The lower limit was set to 100 ° C. as the industrially stable production time. On the other hand, the higher the temperature, the shorter time the purpose can be achieved, but if the temperature exceeds 600 ° C., there is a tendency to soften, scale formation and carbide precipitation occur, and toughness decreases. Therefore, the heating temperature is set to 100 to 600 ° C.

FIG. 1 shows the influence of the area reduction ratio of the wire drawing process before the heat treatment for obtaining a high spring limit value. As is clear from this figure, if the wire drawing area reduction ratio before heat treatment is 50% or more, the required spring limit value can be obtained. Therefore, in consideration of industrial productivity, the area reduction ratio of the wire drawing process before the heat treatment is limited to 50% or more. On the other hand, the heating coefficient k is 13.
If it exceeds 5, it becomes a softening annealing region, and No. Shown in 34
As the spring limit value decreases, the upper limit of the k value is set to 1
It was set to 3.5. This effect is exhibited whether the heat treatment atmosphere is air, reducing or non-oxidizing, but air treatment is preferable from the viewpoint of equipment and productivity. However, depending on the processing conditions, the surface may be discolored due to oxidation. On the other hand, in a nitrogen atmosphere, nitriding enhances strength.
This is effective because a high spring limit value can be obtained, but the toughness may decrease depending on the processing conditions. Therefore, the heat treatment atmosphere should be selected according to the production scale, equipment, etc., and is not particularly limited.

[0037]

EXAMPLES The features of the high-strength, high-toughness austenitic stainless steel ultrafine wire according to the present invention, which is excellent in sag resistance, will be described with reference to examples. Austenitic stainless steel having the chemical composition shown in Table 1 was melted in a vacuum melting furnace, and the steel ingot obtained by ingot casting was heated and hot-rolled at 1200 ° C. to obtain a wire rod having a diameter of 6 mmφ. Pickling the obtained wire rod
After annealing, after drawing wire to make 2mmφ intermediate wire,
Degreasing, bright annealing, and subsequent wire drawing are performed to produce ultrafine wires with a wire diameter of 150 μmφ.
After heat treatment of the ultrafine wire under various conditions, various mechanical properties (spring limit value, tensile strength, elongation, bending workability, etc.) were investigated. Here, the evaluation of the non-metallic inclusions was performed using an energy dispersive analyzer and an image analyzer. Also,
The evaluation of the wire drawability was carried out by the presence or absence of disconnection in the wire drawing from 2 mmφ to 150 μmφ.

Table 1 is an example in which the relationship between non-metallic inclusions and wire drawability was first observed. Material numbers 1 to 7 shown in Table 1 are steels of the present invention, and numbers 8, 9 and 10 are comparative steels. Since all of the chemical components of the steel of the present invention are adjusted, the non-metallic inclusions observed in the 2 mmφ intermediate wire are fine, and therefore have good wire drawability. On the other hand, since the No. 8 steel contains an extremely large amount of Al of 0.006 wt%, large inclusions due to the hard Al ₂ O ₃ based oxide remain, and Oxysulfide is not formed in the steel because the S content is low, and the hard composite oxide remains. Further, since the No. 10 steel has an excessive amount of O, a large amount of oxide remains and the number is large. Therefore, all of the steel Nos. 8 to 10 are broken by wire drawing.

Table 2 shows that the wire drawing area reduction rate is constant (99.4).
%) Shows the relationship between the sag resistance (spring limit value) and the heat treatment. Among them, the steels Nos. 21 to 29 are the steels of the present invention, and the steels 30 to 34 are the comparative steels. Reduction of wire drawing
When the surface ratio is 50% or more, the k value is 6.5 or more , 13.5.
All of the steels of the present invention which have been heat-treated as described below have a spring limit value of 70 kgf / mm ² or more. this is,
It is significantly higher than the conventional one. On the other hand, if the heat treatment is not performed or the heat treatment is insufficient (k value is less than 6.5), the spring limit value is low, and the heat treatment temperature is higher than 650 ° C (high number). Three
4 steel) and the spring limit value decreases. From the above examples, it is clear that the steel of the present invention has extremely good sag resistance.

Table 3 is an example showing the relationship between the spring limit value and the area reduction ratio of wire drawing. Steel Nos. 35 to 38 are steels of the present invention having a wire drawing reduction ratio of 50% or more, and Steels Nos. 39 and 40 are comparative steels. The Nos. 35 and 36 steels have wire drawing area reductions of 60% and 70.3%, so that the spring limit value exceeds 70 kgf / mm ² . On the other hand, although the No. 39 steel has a high k value of 8.1, it has a reduced wire drawing work.
Since the surface ratio is as low as 45.7%, the spring limit value is low.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

As described above, according to the present invention, it is possible to easily produce austenitic stainless steel extra fine wire which is stable, has high strength and good workability by the existing melting and refining technology. In addition, the product has outstanding sag resistance and excellent molding processability, and can provide austenitic stainless steel extra fine wires suitable as members for precision equipment, including extra fine wires for springs. There is one that results in a very large effect on the industry.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a wire drawing area reduction rate and a spring limit value after heat treatment.

FIG. 2 is a diagram showing a region where a good oxysulfide is obtained from the relationship between the amount of Al and the amount of S in steel.

FIG. 3 is a diagram showing a relationship between a heating coefficient (k) and a spring limit value.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hidehiko Sumitomo 3434 Shimada, Hikaru City, Yamaguchi Prefecture Nippon Steel Co., Ltd. Komatsu Works (56) Reference JP 62-290848 (JP, A) (58) ) Fields surveyed (Int.Cl. ⁷ , DB name) C21D 8/06 C21D 9/52 103 C22C 38/00 302 B21C 1/00

Claims (3)

(57) [Claims] 1. By weight%, C: 0.05 to 0.15% , S ≤ 0.005%, Al ≤ 0.005%, N: 0.02 to 0.10% O ≤ 0.005% Is added and the composition of S and Al is adjusted to satisfy the formula (1), and the total composition of the non-metallic inclusions in the steel is 1 wt.
% Of S or more oxysulfide formed austenitic stainless steel is rolled into a wire rod, followed by annealing / drawing to produce ultrafine wire, followed by heat treatment, before the heat treatment. Area reduction of wire drawing of 50
% Or more, followed by heat treatment 100 ° C or more, 600 ° C
The method is performed at the following temperature and for a short time of 30 seconds or less under the condition that the k value represented by the formula (2) satisfies 6.5 or more and 13.5 or less. And a method for producing an austenitic stainless steel ultrafine wire. [S] ≧ [Al] / 2 (1) where [S]; S amount in steel (wt%) [Al]; Al amount in steel (wt%) k = T × (logt + 20) × 10 ⁻³ (2) where k: heating coefficient T; heating temperature (K) t: heating time (Hr) 2. By weight%, C: 0.05 to 0.15%, Si: 0.2 to 3%, Mn: 0.2 to 3%, S ≦ 0.005%, Ni: 6.5. ~12%, Cr: 16~20%, Al ≦ 0.005%, N: 0.02~0.10%, containing O ≦ 0.005%, and the relationship between S and Al amount (1) The composition is adjusted to satisfy the formula, and the total composition of non-metallic inclusions in steel is 1 wt.
% Of S or more oxysulfide formed austenitic stainless steel is rolled into a wire rod, followed by annealing / drawing to produce ultrafine wires, followed by heat treatment when the heat treatment is performed. Area reduction of the previous wire drawing process is 5
0% or more, followed by heat treatment at 100 ℃ or more, 600
At a temperature of ℃ or less, and the k value represented by the formula (2) is 6.5.
Short time of 30 seconds or less under the condition that 13.5 or less is satisfied
A method for producing an austenitic stainless steel ultrafine wire, which is characterized by being applied for a period of time . [S] ≧ [Al] / 2 (1) where [S]; S amount in steel (wt%) [Al]; Al amount in steel (wt%) k = T × (logt + 20) × 10 ⁻³ (2) where k: heating coefficient T; heating temperature (K) t: heating time (Hr) 3. By weight%, C: 0.05 to 0.15%, Si: 0.2 to 3%, Mn: 0.2 to 3%, S ≦ 0.005%, Ni: 6.5. ~12%, Cr: 16~20%, Al ≦ 0.005%, N: 0.02~0.10%, containing O ≦ 0.005%, and the relationship between S and Al amount (1) Satisfy the formula,
The composition of non-metallic inclusions in steel is oxysulfide containing 1 wt% or more of S in total, and the spring limit value is 70.
An austenitic stainless steel ultrafine wire characterized by having a weight of at least kgf / mm ² . [S] ≧ [Al] / 2 (1) where [S]; S content in steel (wt%) [Al]; Al content in steel (wt%)