JP2582919B2 - Austenitic stainless steel ultrafine wire manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing ultrafine stainless wires used in industrial fields such as high-precision filters or high-performance printing meshes.

[Prior art] Ultrafine stainless steel wires having a wire diameter of 60 μmφ or less are used in large quantities in the chemical industry, the aviation industry, the electronic equipment industry, and the like as raw materials for composite materials, industrial filters or meshes for IC printing.

The ultrafine stainless steel wire used for this purpose is required to have good drawability and corrosion resistance, and to have a perfect circular cross-sectional shape. Conventionally, using a SUS316 or SUS304 wire material as a material, wire drawing and annealing are repeated to obtain a required wire diameter, and then a final product heat treatment is performed to produce a desired ultrafine stainless steel wire.

Here, the final product heat treatment is intended to improve the ductility by softening the mesh in order to impart the woven workability. Generally, the tensile strength 70~80kgf / mm ^2, elongation 25
However, in recent years, the usefulness of stainless steel ultrafine wires has been recognized, and a dramatic expansion of the application field is expected. However, the product performance required in these industrial fields is required to be high in strength, rich in ductility, and excellent in rust resistance, because of high wire diameter accuracy and the severer application environment. The conventional ultrafine stainless steel wire has low strength and poor rust resistance, and cannot satisfy the above-mentioned required characteristics.

In order to solve this problem, it is necessary to increase the strength (target tensile strength is 100 kgf / mm ² or more) and ensure high rust resistance without reducing the ductility of the ultrafine stainless steel wire. However, in general, when the strength is increased, the fine wire drawability deteriorates,
Since it becomes difficult to stably draw the ultrafine stainless steel wire, it is necessary to soften the strand.

The method of lowering the annealing temperature of the final product is effective for increasing the strength of ultrafine stainless steel wires. However, if the heat treatment temperature is low, the recovery of ductility is not sufficient, and problems such as disconnection and poor weaving during mesh processing occur. . Further, the solid solution of the carbide becomes insufficient, and the carbide remains to deteriorate the rust resistance.

[Problems to be Solved by the Invention] An object of the present invention is to provide a material for an ultrafine wire with excellent drawability, and to obtain a final product with high strength, high ductility and excellent rust resistance. I do.

Means and Action for Solving the Problems In order to realize high strength without deteriorating the ultrafine wire drawing workability, the present inventors adjusted the steel substrate to a relatively soft composition, and made it sufficiently ductile. In the final product annealing after drawing to ultrafine stainless steel wire, by taking advantage of the fact that it is an ultrafine wire, by performing appropriate surface nitriding at the same time as annealing the final product, high strength can be achieved. It has succeeded in achieving high rust resistance at the same time.

The present invention has been made based on the above findings,
The gist is: 1. In the process of drawing an austenitic stainless steel wire to produce an ultrafine stainless steel wire, the C + N
To a concentration of 0.04 to 0.15% by weight, and the fine wire of stainless steel after the final wire drawing is processed. Nitrogen concentration: 30 to 80 vol.% Oxygen concentration: 0.003 vol.% Or less The balance is substantially hydrogen gas. Dew point: -40 ° C The method is characterized in that the final product is annealed at a temperature of 900 ° C. or more and 1100 ° C. or less in a mixed gas controlled as described below, and the C + N content of the ultra-thin stainless steel wire after annealing is set to 0.05 to 0.20%. .

 The reasons for limiting the components in the present invention are as follows.

First, the improvement of the fine wire drawability of the strand will be described. Austenitic stainless steel undergoes work hardening by cold working. Because ultra-fine wire drawing is cold working with high area reduction,
Softness and high ductility are indispensable to ensure extra fine wire drawing.
However, if the steel composition is designed to be an alloy that is advantageous for ultrafine wire drawing, it will be difficult to obtain sufficient strength in the heat treatment of the final product, and it will be necessary to set the heat treatment temperature low. However, when the heat treatment temperature is lowered, a sufficient recrystallized structure cannot be obtained, so that the ductility of the product is reduced. For this reason, the weaving processability deteriorates.

As a result of repeated experiments on various components, the present inventors have found that the use of solution hardening is effective as a means for softening the steel composition and increasing the strength of the product after heat treatment. As this means, we focused on C and N and examined the wire component.

As a result, when C and N are added to the austenitic stainless steel, the strength is increased, but the ductility is reduced and the ultrafine wire drawing is reduced. Therefore, it is desirable that C and N are low in consideration of ultrafine drawing.

However, if C and N are too low, the initial steel quality becomes soft and the ductility also increases, but the austenite phase becomes unstable, and the generation of a work-induced martensite phase accompanying the progress of wire drawing becomes remarkable. . For this reason, the ultrafine wire drawing workability is rather deteriorated due to a decrease in ductility due to an increase in work hardening. Further, the strength of the ultrafine stainless steel wire after annealing of the final product cannot be satisfied.

From the above, in the ultra-fine wire drawing, the decrease in ductility due to work hardening is relatively small, and has a good ultra-fine wire drawing property,
The lower limit of the amount of C + N in the strand was set to 0.04% in order to increase the strength of the ultrafine stainless steel wire after annealing the final product.

If C and N are too low, a δ ferrite phase is formed during solidification, and the hot workability is reduced. Therefore, surface flaws are generated in wire rolling, and the fine wire drawability is deteriorated.

On the other hand, when the C + N content of the strand is increased, the strength of the strand is increased and the ductility is decreased due to solid solution hardening, so that the ultrafine drawability is decreased. Furthermore, when the strength is high, the die wear is severe at the time of extra fine wire drawing, which results in an increase in die cost, a decrease in productivity due to frequent die replacement, and instability of quality. For this reason, the upper limit of the amount of C + N is set to 0.15%.

Therefore, the amount of C + N of the strand for making the above-mentioned action effective and obtaining good ultrafine drawability as a stainless fine wire is
0.04 to 0.15%.

The present invention adjusts the steel composition as described above, after drawing a stainless steel ultrafine wire, in order to obtain high strength and high rust resistance, in the final product annealing treatment step, the furnace atmosphere,
It can be obtained by strictly adjusting the dew point and temperature.

 Next, these operations and means will be described.

The present inventors, by weight%, C: 0.07%, N: 0.0535%, Ni: 10.
Ultrafine stainless steel wires with a main composition of 87%, Cr: 18.85% and Mo: 0.95% were manufactured, and the influence of annealing of the final product on rust resistance was studied for various factors.

FIG. 1 and FIG. 2 summarize the results of this study. From the research results, the reasons for limiting the annealing conditions in the present invention are as follows.

Furnace atmosphere: The aim of the present invention is to increase the strength by adjusting the furnace atmosphere to cause nitriding of the ultrafine stainless steel wire, and to improve the rust resistance of the coating on the surface of the ultrafine stainless steel wire formed by heat treatment. Control of the composition.

Therefore, a nitriding gas is required to make the nitriding action effective, while a reducing gas is needed to control the coating composition to be effective for rust resistance. Therefore, the atmosphere used was limited to a mixed gas of hydrogen and nitrogen in order to make these effects simultaneous and effective.

In order to increase the strength by nitriding, it is preferable to increase the mixing ratio of nitrogen, and the fine wire drawability is good.In a steel composition, the amount of nitrogen in the atmosphere gas for achieving the target strength is 30 vol. % Or more is sufficient. However, when the ratio of nitrogen is increased, the ductility of the ultrafine stainless steel wire product is reduced due to the formation of nitride, and the rust resistance is deteriorated.

In order to improve the rust resistance, it is important that the coating composition on the surface of the ultrafine stainless steel wire after the heat treatment is mainly composed of Cr ₂ O ₃ . To this end, it is effective to mix an appropriate amount of hydrogen having a reducing action into the mixed gas. As shown in FIG. 1, the rust resistance is remarkably improved when the amount of hydrogen is 20 vol.% (The amount of nitrogen is 80 vol.%) Or more. Therefore, the nitrogen concentration in the mixed gas is set as a range that satisfies both the strength and the rust resistance.
The volume was 30 to 80 (hydrogen concentration 70 to 20%) vol.%, And the remainder was hydrogen.

Dew point: The dew point affects the composition of the film formed during heat treatment. If the dew point is high, a thick oxide film mainly composed of Fe-based oxide is formed. As described above, in order to obtain a highly stable rust resistance, it is essential to stably form the Cr ₂ O ₃ coating, and therefore, the dew point is set to −40 ° C. or less.

Oxygen concentration: Strict control is required because the trace oxygen concentration in the furnace also affects the coating composition on the surface of the ultrafine stainless steel wire formed during heat treatment. That is, as the oxygen concentration increases, the composition of the coating becomes richer in Fe-based oxides, and the coating itself becomes thicker, deteriorating rust resistance. In order to stably form a film mainly composed of Cr ₂ O ₃ , the oxygen concentration in the furnace must be
It must be 0.003 vol.% Or less.

Heat treatment temperature: This heat treatment is an annealing treatment for restoring the ductility of the ultrafine stainless steel wire strengthened by wire drawing and imparting the workability of the final product.
25% or more and a yield ratio of 60% or less are required. Therefore, in the present invention, the above mechanical properties are set as the target values of ductility.

As the heat treatment temperature is higher, the drawing stress is removed and the ductility is increased. A heat treatment temperature of 900 ° C. or higher is required to completely transform the metal structure into a recrystallized structure and restore the above ductility. However, when the heat treatment temperature exceeds 1100 ° C., the strength is extremely reduced. Therefore, the heat treatment temperature range for realizing the target high strength was set to 900 to 1100 ° C.

[Examples] In the present invention, target quality is as follows, and examples are shown below.

・ Extremely fine drawability: 1 break or less after drawing 10kgf ・ Tensile strength> 100kgf / mm ²・ Yield ratio <0.60 ・ Elongation> 25% ・ Rust resistance: Within rust resistance rank C Examples in Table 1 The chemical composition of the austenitic stainless steel subjected to the above was shown.

These steels were smelted by vacuum melting and electron beam melting to produce wire rod billets. The billet was heated in a billet heating furnace and then rolled into a 5.5 mmφ wire.
The rolled wire rod was annealed and pickled, then repeatedly subjected to wire drawing and bright annealing to obtain a stainless steel ultrafine wire having a wire diameter of 30 μm.

The drawn ultrafine stainless steel wire was continuously annealed at a line speed of 100 m / min in a bright annealing furnace with an adjusted atmosphere. The annealing time of the stainless fine wire in the furnace is 1.5 seconds.

Table 2 shows the ultrafine drawability and mechanical properties of the ultrafine stainless steel wires shown in Table 1.

The ultrafine drawability is good when the C + N content of the strand is in the range of 0.04 to 0.15%, while the C + N content is less than 0.04% (No.
7) and more than 0.15% of C + N (No.9, No.10), there are many disconnections.

 The final product annealing conditions are as follows.

・ Stainless steel extra fine wire diameter: 40μmφ ・ Annealing temperature: 1050 ℃ ・ Atmosphere: 20% H ₂ + 80% N ₂・ O ₂ concentration: 0.0005vol.% ・ Line speed: 100m / min. High C + N amount after final annealing Then, the higher the ratio of the amount of N, the higher the strength and the lower the ductility. However, the steels of the present invention Nos. 1 to 6 sufficiently satisfy the target mechanical properties.

On the other hand, No. 7 steel and No. 8 steel have insufficient strength due to low C + N, while No. 9 steel and No. 10 steel have C + N.
The ductility is low because N is too high.

 FIG. 3 shows the relationship between the annealing temperature and the tensile properties.

Conventional steel (SUS316) needs to be treated at a temperature of 950 ° C. or less in order to obtain a tensile strength of 100 kg / mm ² or more. However, in this case, it is difficult to stably obtain a sufficient recrystallized structure, and the ductility is low. In contrast, the steel of the present invention (No.
5) has high strength, high ductility, and low yield ratio over a wide range from 950 ° C to 1100 ° C. On the other hand, the comparative steel (No. 9) has high strength but high ductility due to high N and high C + N.

FIG. 4 illustrates the relationship between the C + N content and the mechanical properties after product annealing shown in Table 2.

C + N (substantially N) is 70-
It is about 100 ppm higher.

The target strength characteristics can be obtained with a C + N amount of 0.05 to 0.2% after the final product annealing.

Table 3 shows the results of the rust resistance test. Here, the rust resistance test method and conditions are as follows.

Test method: An ultrafine stainless steel wire was set in a test apparatus so that the test piece length was 1 m, and a spray test was performed under the following test conditions. After the test, the entire surface of the ultrafine stainless steel wire was observed for rust using a stereoscopic microscope.

・ Solution: 5% NoCl + 0.2% H ₂ O ₂・ Test temperature: 35 ° C ・ Test time: 24hours As a result, the present invention in which the dew point, H ₂ concentration, and O ₂ concentration in the heat treatment atmosphere were adjusted to appropriate ranges It can be seen that the No. 11 to 17 steels of the examples show good rust resistance. No.18
Steel is a high dew point, No.19 because the steel has a low concentration of H _2, also No.
Both 20 and 21 steels have poor oxygen resistance because of their high oxygen concentration.

[Effects of the Invention] As described above, the austenitic stainless steel ultrafine wire having excellent rust resistance and workability, high strength, and low yield ratio manufactured by the present invention can be easily and inexpensively manufactured by the existing technology. It can be applied to high-precision filters for high-precision IC printing or high-grade composite fiber raw materials, such as high-performance filters in the chemical industry, food and medical equipment industries, etc., and promises the rapid expansion of the next industry. Contribution is extremely large.

[Brief description of the drawings]

FIG. 1 shows the relationship between the oxygen concentration in the annealing atmosphere and the rust resistance rank, FIG. 2 shows the relationship between the dew point of the annealing atmosphere and the rust resistance rank, and FIG. 3 shows the final product annealing temperature. Fig. 4 shows the relationship between the mechanical properties of the stainless steel extra fine wire and the stainless steel extra fine wire.
It is a figure showing the relation between quantity and mechanical properties.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hidehiko Sumitomo 3434 Shimada, Hikari-shi, Yamaguchi Prefecture Inside Nippon Steel Corporation Hikari Works

Claims (1)

(57) [Claims] (1) In the step of drawing an austenitic stainless steel wire rod to produce a stainless fine wire, the C + N of the strand is adjusted to 0.04 to 0.15% by weight, and the stainless fine wire after the final drawing is subjected to nitrogen. Concentration: 30 to 80 vol.% Oxygen concentration: 0.003 vol.% Or less The balance is substantially hydrogen gas. Dew point: The final product at a temperature of 900 ° C or higher and 1100 ° C or lower in a mixed gas controlled to -40 ° C or lower. A method for producing an austenitic stainless steel ultrafine wire, wherein annealing is performed and the C + N content of the ultrafine stainless steel wire after annealing is set to 0.05 to 0.20%.