Stainless steel narrow line, stainless steel extra-narrow line and production methods of them

Abstract

To provide a stainless steel extra-narrow line whose surface is a highly hard surface and which is excellent in intensity / ductility balance, and a stainless steel narrow line being the material of the same, at low costs.SOLUTION: There is provided a stainless steel extra-narrow line which has high intensity / ductility, in which the stainless steel extra-narrow line includes a prescribed component and is configured so that the component is adjusted so that Md30 expressed by a formula (A) becomes -90 to 30, average nitrogen concentration in the cross section of the stainless steel extra-narrow line is 0.12 to 0.50%, a difference of (front layer nitrogen concentration)-(center part nitrogen concentration) is 0.01 to 0.25%, namely the difference has an inclined concentration distribution, the average crystal grain diameter of the front layer is greater than 0.1 μm and 2.0 μm or smaller, a surface hardness Hv index expressed by a formula (B) is 300 to 550, tensile strength is 1300 MPa or more, and breaking extension is 7% or greater. There is also provided a stainless steel narrow line which has the similar component and the nitrogen concentration distribution as the stainless steel extra-narrow line.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a high-strength and high-ductility stainless steel ultra-fine wire that is surface-nitrogen-enriched and surface-hardened and used for a screen printing mesh excellent in corrosion resistance and durability, a stainless steel fine wire that is a material thereof, and a method for manufacturing them.

Background Art

[0002] Conventionally, stainless steel ultra-fine wires have been used for wire meshes such as meshes used for screen printing. With the progress of high-tech technologies, there has been an increasing demand for high strength, high durability, and thinning of the mesh. In addition, with the increase in strength, high precision of the mesh is required, and high strength and high ductility are required for the stainless steel ultra-fine wire as a material for precise mesh manufacturing properties (for example, Patent Document 1).

[0003] For high strength and high ductility of ultra-fine wires, high nitrogen content of the stainless steel constituting the ultra-fine wire is also effective, and in Patent Document 2, a nitrogen additive of 0.1% or more has been proposed for SUS304. Recently, an increase in the number of uses due to high durability by improving the wear resistance of the mesh for screen printing has also been required, and high nitrogen content contributing to high strength is considered effective.

[0004] For high nitrogen content, there is a method of adding N in the melting stage, but a solid-phase nitrogen absorption method at the steel wire stage has also been proposed (Patent Document 3). In particular, the solid-phase nitrogen absorption method is advantageous for surface high hardness and is effective for high durability due to the wear resistance of the mesh. However, if the nitrogen concentration of the ultra-fine wire is simply increased, the strength becomes too high, the surface hardness also becomes too high, the ductility decreases, and the mesh manufacturing property deteriorates.

[0005] However, in the case of ultra-fine wires for wire meshes such as highly corrosion-resistant meshes made of stainless steel with excellent conventional durability, the balance between high strength and ductility is insufficient, and no stainless steel ultra-fine wire excellent in durability and mesh manufacturing property has been proposed. In particular, there is no finding regarding functional improvement such as control of the nitrogen concentration and crystal grain size in the fine wire cross section. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6491983 [Patent Document 2] Patent No. 4068216 [Patent Document 3] Patent No. 5963355 Summary of the Invention [Problem to be solved by the invention]

[0007] To achieve both durability (wear resistance) and mesh-making properties, it is effective to increase the strength and ductility of the matrix of the ultrafine wires that make up the mesh, and to control the surface hardness of the ultrafine wires. For example, to achieve high mesh durability, it is effective for the ultrafine wires to have a tensile strength of 1300 MPa or more and a surface hardness of 300 Hv or more, and a total elongation of 7% or more is required for precise mesh-making properties.

[0008] The problem to be solved by the present invention is to provide a high-strength stainless steel ultra-fine wire having a highly hardened surface and an excellent balance of strength and ductility, and the stainless steel fine wire that is the raw material for the wire, as well as a method for producing the same, at low cost, thereby contributing to improving the durability of wire mesh such as screen printing mesh. [Means for solving the problem]

[0009] As a result of various studies to solve the above problems, the present inventors have arrived at the following present invention. As a component composition, an austenitic stainless steel fine wire whose austenite structure stability is adjusted by components is used. In the stainless steel fine wire as the material, the average nitrogen concentration is set to 0.15 to 0.50% by solid-phase nitrogen absorption, and the nitrogen concentration gradient is controlled so that the nitrogen concentration difference of (surface layer nitrogen concentration) - (central part nitrogen concentration) becomes 0.01% to 0.2% for nitriding. Then, using the stainless steel fine wire as a material, an ultra-fine wire with the average crystal grain size of the steel wire surface layer refined and strengthened to φ0.1 to 3.0 μm is obtained by combining wire drawing with a reduction ratio of 95% or more and short-time heat treatment. As a result, it has been found that an ultra-fine wire with a hardened surface and excellent strength-ductility balance of 1300 MPa or more and elongation at break of 7% or more can be obtained. The present invention has been made based on the above findings, and the gist thereof is as follows.

[0010] [1] By mass, C: More than 0.06% and 0.15% or less, Si: 0.1 to 2.0%, Mn: 0.1 to 3.0%, P: 0.05% or less, S: 0.01% or less, Ni: 7.0 to 12.0%, Cr: 16.0 to 21.0% It contains, with the balance being Fe, nitrogen and impurities, and the component is adjusted so that Md30 represented by the following formula (A) becomes -90 to 30, the average nitrogen concentration in the cross section is 0.12 to 0.50%, and the difference of (surface layer nitrogen concentration) - (central part nitrogen concentration) is 0.01 to 0.25% to form a gradient concentration distribution. A stainless steel fine wire characterized by this. Md30 (°C) = 551 - 462C - 9.2Si - 8.1Mn - 29 (Ni + Cu) - 13.7Cr - 18.5Mo ··· (A) In formula (A), the element symbol means the content (mass%) of the element in the steel. [2] Instead of a part of the Fe, further by mass, Cu: 3.5% or less Mo: 3.5% or less, W: 3.5% or less, The stainless steel fine wire according to [1], characterized by containing one or more kinds within 0.01% or less of B.

[0011] The ultra-fine stainless steel wire having the component and nitrogen concentration distribution according to [3], [1] or [2], wherein the average crystal grain size of the surface layer of the steel ultra-fine wire is more than 0.1 μm and 2.0 μm or less, the surface hardness Hv index represented by the following formula (B) is 300 to 550, the tensile strength is 1300 MPa or more, and the elongation at break is 7% or more. A high-strength and high-ductility ultra-fine stainless steel wire. Hv index = 150 + 400 × Nh 0.5 ×(1.5D) -0.5 ····(B) In the formula (B), Nh: nitrogen concentration of the surface layer (%), D: average crystal grain size of the surface layer (μm)

[0012] The method for manufacturing the stainless steel fine wire according to [1] or [2], characterized by performing a solid-phase nitrogen absorption treatment on the stainless steel wire having the component according to [4], [1] or [2] in an atmosphere containing nitrogen gas with a nitrogen partial pressure of 0.002 to 0.05 MPa at 1000 to 1300 °C for 10 to 500 minutes. The method for manufacturing the high-strength and high-ductility ultra-fine stainless steel wire according to [3], characterized by subjecting the stainless steel fine wire according to [5], [1] or [2] to wire drawing to a wire diameter of 50 μm or less with a reduction ratio of 95% or more and then performing strand annealing at 700 to 950 °C for 5 seconds or less.

[0013] The high-strength and high-ductility ultra-fine stainless steel wire according to [3], characterized by being used for wire meshes such as screen printing meshes. The stainless steel fine wire according to [1] or [2], characterized by being a material for manufacturing the ultra-fine stainless steel wire for wire meshes such as screen printing meshes.

Advantages of the Invention

[0014] The high-strength stainless steel ultra-fine wire with surface nitriding and refined crystal grains of the present invention has high strength and excellent ductility, so that it can be accurately processed into a screen printing mesh, and also has excellent durability of the mesh because the surface is hardened.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0016] The stainless steel fine wire and the high-strength and high-ductility stainless steel ultra-fine wire of the present invention contain C: more than 0.06% and 0.15% or less, Si: 0.1 to 2.0%, Mn: 0.1 to 3.0%, P: 0.05% or less, S: 0.01% or less, Ni: 7.0 to 12.0%, Cr: 16.0 to 21.0%, and the balance is Fe, nitrogen and inevitable impurities, and the Md30 represented by formula (A) is adjusted to -90 to 30, and the average nitrogen concentration in the cross section is 0.12 to 0.50%, and the difference between (surface layer nitrogen concentration) - (central part nitrogen concentration) is 0.01 to 0.2% to form a gradient concentration distribution. The stainless steel fine wire controlled in this way is a suitable material for imparting the characteristics of high strength, high ductility and high surface hardness of the final product, the stainless steel ultra-fine wire.

[0017] Hereinafter, the chemical components of the stainless steel fine wire and the stainless steel ultra-fine wire will be described. "%" for the chemical composition of steel means mass%. In addition, the numerical range represented by using "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. In addition, when "more than" or "less than" is attached to the numerical values described before and after "~", the numerical range means a range not including these numerical values as the lower limit value or the upper limit value.

[0018] First, the reasons for limiting the chemical composition and the like of the stainless steel fine wire and the stainless steel ultra-fine wire of the present invention will be described below.

[0019] C is added in an amount exceeding 0.06% in order to ensure that the strength of the ultra-fine wire product after final annealing is 1300 MPa or more and the elongation is 7% or more. However, when added in an amount exceeding 0.15%, coarse Cr carbonitrides are formed, deteriorating the drawability. Therefore, the upper limit of C is set to 0.15%. The preferred range of C is 0.08 to 0.13%.

[0020] Si is added in an amount of 0.1% or more in order to perform deoxidation and ensure drawability. However, when added in an amount exceeding 2.0%, not only does the effect saturate, but the ductility deteriorates and the drawability deteriorates, so the upper limit is set to 2.0%. The preferred range of Si is 0.3 to 1.0%.

[0021] Mn is added in an amount of 0.1% or more in order to perform deoxidation and ensure drawability. However, when added in an amount exceeding 3.0%, surface oxidation becomes intense during strand annealing during wire drawing, deteriorating the drawability, so the upper limit is set to 3.0%. The preferred range of Mn is 0.2 to 2.0%.

[0022] P is limited to 0.05% or less because it deteriorates the drawability of the ultra-fine wire. The preferred range of P is 0.035% or less.

[0023] S is limited to 0.01% or less because it generates sulfides or segregates at the grain boundaries, deteriorating the drawability during the production of ultra-fine wires. The preferred range of S is 0.005% or less.

[0024] Ni is added in an amount of 7.0% or more in order to stabilize the austenite phase, improve the ductility, and ensure drawability. However, when added in an amount exceeding 12.0%, the strength of the ultra-fine wire product decreases, so the upper limit is set to 12.0%. The preferred range is 8.0 to 11.0%.

[0025] Cr is added in an amount of 16.0% or more to stabilize the austenite phase, improve ductility, and ensure drawability. However, if the addition exceeds 21.0%, the ductility of the ultra-fine wire product will decrease, so the upper limit is set at 21.0%. The preferred range is 17.0% - 20.0%.

[0026] The stainless steel fine wire and ultra-fine wire of the present invention contain the above components, and the balance consists of Fe, nitrogen, and impurities. Nitrogen will be described below.

[0027] The Md30 in the formula (A) is known as an index representing the amount of strain-induced martensite after processing of stainless steel. Since the value of Md30 calculated by the formula (A) affects the stability of the austenite phase together with the average nitrogen concentration in the cross-section, the component adjustment is made to be 30 or less to make the generation amount of strain-induced martensite during the final heavy drawing process 80 vol.% or less to ensure heavy drawability. However, if it is less than -90, the strain-induced martensite during the final wire drawing will be less than 10%, and the reverse-transformed austenite from the strain-induced martensite will decrease during the final annealing, making it difficult to ensure high ductility due to excessive refinement of the overall crystal grain size. Therefore, the lower limit is set at -90. The preferred range is in the range of -50 to 20. In the present invention, since nitrogen is added at a gradient concentration in the cross-section of the steel wire by subsequent solid-phase nitrogen absorption treatment, it is controlled by the value obtained by excluding the term of N from Md30.

[0028] Next, the reasons for limiting the nitrogen concentration distribution in the cross-section of the stainless steel fine wire and ultra-fine wire of the present invention will be described. The average nitrogen concentration in the cross-section is made to be 0.12% or more to stabilize the austenite phase and ensure the strength-ductility balance of the ultra-fine wire product manufactured by heavy drawing and annealing. However, if it exceeds 0.50%, the drawability to the ultra-fine wire will decrease, so the upper limit is set at 0.50%. The preferred range is 0.15 - 0.35%. In the present invention, as will be described later, since the nitrogen gradient concentration in the cross-section is controlled, nitrogen is added by the solid-phase nitrogen absorption method.

[0029] Applying an appropriate gradient to the nitrogen concentration of the surface layer and the central part contributes to improving the durability of the mesh, which is an ultrafine wire product, while maintaining the ductility of the ultrafine wire. That is, while maintaining the average cross-sectional nitrogen concentration, by applying a gradient to the nitrogen concentration in the radial direction so that (surface layer nitrogen concentration) - (central part nitrogen concentration) is 0.01% or more, it is possible to effectively increase the surface hardness that contributes to the durability of the mesh while maintaining the ductility of the ultrafine wire. However, if the concentration difference exceeds 0.25%, the drawability of the ultrafine wire decreases, so the upper limit of the concentration difference is set to 0.25%. Preferably, it is in the range of 0.02 to 0.20%. Here, the surface layer nitrogen concentration indicates the average nitrogen concentration in the region of 1 / 8 from the surface layer where the cross-section of the steel wire is equally divided into eight parts by radius, and the central part nitrogen concentration indicates the average nitrogen concentration in the region from 7 / 8 to the center.

[0030] Fig. 1 shows an example of the EPMA analysis result of the nitrogen concentration of the cross-section of a stainless steel fine wire. Fig. 1 contains more than 0.06% and 0.15% or less of C, 0.1 to 2.0% of Si, 0.1 to 3.0% of Mn, 0.05% or less of P, 0.01% or less of S, 7.0 to 12.0% of Ni, 16.0 to 21.0% of Cr, with the balance being Fe, nitrogen, and impurities. The Md30 represented by formula (A) is adjusted to be -90 to 30, the average nitrogen concentration in the cross-section is 0.12 to 0.50%, and the difference between (surface layer nitrogen concentration) - (central part nitrogen concentration) is in a gradient concentration distribution of 0.01 to 0.2%. It can be seen that the nitrogen concentration continuously decreases from the surface layer to the center. The stainless steel fine wire controlled in this way is suitable for imparting the characteristics of high strength, high ductility, and high surface hardness to the ultrafine wire product.

[0031] Next, the reasons for limiting the chemical components that can be selectively contained in place of a part of the Fe in the stainless steel fine wire and the stainless steel ultrafine wire of the present invention will be explained.

[0032] Cu is added as necessary to improve the drawability. However, if it is added in excess of 3.5%, conversely, the hot manufacturability deteriorates and product processing becomes impossible, so the upper limit is set to 3.5%. Preferably, it is 3.0% or less.

[0033] Mo and W are added as necessary to improve the corrosion resistance of the ultra-fine wire products. However, if each is added in excess of 3.5%, the drawability deteriorates, so the upper limit is set at 3.5%. Preferably, it is 2.5% or less.

[0034] B is added as necessary to improve the drawability. However, if it is added in excess of 0.01%, the drawability deteriorates conversely due to the formation of B-based precipitates, so the upper limit is set at 0.01%. Preferably, it is 0.006% or less.

[0035] Note that the impurities in the above component composition are those mixed from raw materials such as scrap and alloys during the melting of stainless steel, or element additives that do not affect the essential effects of the present invention even if intentionally added. For example, Al: 0.01% or less, Ti: 0.1% or less, Nb: 0.1% or less, V: 0.2% or less, Ta: 0.2% or less, Co: 0.5%, Bi: 0.01% or less, Pb: 0.01% or less, Se: 0.01%, Te: 0.01% or less, REM: 0.01% or less, O: 0.015% or less, etc.

[0036] Next, the reasons for limiting the crystal grain size and material properties defined in the stainless steel ultra-fine wire of the present invention will be explained. The average crystal grain size (diameter) D of the ultra-fine wire surface layer affects the hardening of the surface layer by crystal grain refinement together with the surface nitrogen concentration Nh according to formula (B).

[0037] It is difficult to directly measure the surface hardness of the ultra-fine wire. On the other hand, from the relationship between the nitrogen concentration, crystal grain size, and micro-hardness by nano-indentation, based on the surface layer nitrogen concentration Nh (%) and crystal grain size D (μm), the actual hardness Hv can be predicted and calculated using the Hv index represented by the above formula (B). Generally, the strength of steel is proportional to the square root of the N content for solid solution strengthening and proportional to the square root of the reciprocal of the crystal grain size according to the Hall-Petch law. That is, the surface hardness Hv of the ultra-fine wire is greatly dominated by the solid solution strengthening of nitrogen on the surface and the strengthening of crystal grain refinement. A constant is determined from the measured value examples of other steel materials in this component system, and the influence on the surface hardness can be represented by the Hv index of the formula (B). The surface hardening can be controlled by the nitrogen concentration and crystal grain size in the surface layer.

[0038] For improving the durability of the mesh, the higher the surface hardness, the more preferable it is. If the Hv index of the formula (B) is 300 or more, it is confirmed that the surface hardness required for the stainless steel ultra-fine wire of the present invention can be ensured. Furthermore, it is preferably 350 or more. However, when the Hv index exceeds 550, the total elongation of the ultra-fine wire decreases and the mesh-making property deteriorates, so the upper limit is limited to 550. Preferably, it is in the range of 350 to 500.

[0039] Figure 2 is a diagram showing an example of the metal structure by a transmission electron microscope in the vicinity of the surface layer (region with a depth of 3 μm from the surface layer) of an ultra-fine wire with high strength, high ductility, and surface hardening (surface grain refinement) made from a stainless steel fine wire having a nitrogen concentration gradient characteristic treated by solid-phase nitrogen absorption. A group of fine crystal grain sizes of about 0.2 to 1 μm can be confirmed. For example, in cross-section a, the average crystal grain size (diameter) is 0.3 μm, and in cross-section b, it is 0.2 μm.

[0040] As shown in Figure 2, by refining the crystal grains on the surface layer of the ultra-fine wire, the strengthening of crystal grain refinement can be utilized, and it becomes possible to harden the surface while ensuring the ductility of the stainless steel ultra-fine wire. Therefore, in the stainless steel ultra-fine wire of the present invention, the crystal grain size of the surface layer is limited to 2.0 μm or less. However, when the crystal grain size becomes excessively ultra-fine to be 0.1 μm or less, the surface is hardened too much and the ductility of the stainless steel ultra-fine wire decreases. Therefore, the lower limit is set to exceed 0.1 μm. The preferable range is in the range of 0.3 to 1.5 μm.

[0041] The material of the stainless steel ultra-fine wire is such that the durability of a mesh or the like is improved to the extent that it has high strength and high surface hardness, and precision wire mesh processing is possible to the extent that it has high ductility. As market requirements, if the strength is a tensile strength of 1300 MPa or more, the ductility is an elongation at break of 7% or more, and the surface hardness is in the range of 300 to 550 in terms of the Hv index, a remarkable effect can be exerted from the viewpoints of durability and wire mesh manufacturability as compared with conventional materials.

[0042] Next, the reasons for limiting the manufacturing method of the stainless steel fine wire of the present invention will be described. The stainless steel fine wire of the present invention is a material for manufacturing a stainless steel ultra-fine wire. In order to manufacture a high-strength and high-ductility stainless steel ultra-fine wire with surface hardening, it is characterized by having a predetermined average nitrogen concentration and a nitrogen concentration gradient within the cross-section. Therefore, it is effective to perform a solid-phase nitrogen absorption treatment for 10 minutes or more in an atmosphere having nitrogen gas with a nitrogen partial pressure of 0.002 MPa or more at 1000 °C or higher. However, if the treatment temperature exceeds 1300 °C and the treatment time exceeds 500 minutes, not only will the predetermined nitrogen concentration gradient between the surface layer and the central part not be obtained because nitrogen diffuses sufficiently, but other adverse effects such as the shape of the stainless steel fine wire cannot be maintained due to the high temperature and long time, and subsequent processing cannot be performed will also become apparent. Also, when the nitrogen partial pressure increases, the nitrogen concentration within the cross-section becomes excessively high and the ductility of the ultra-fine wire cannot be ensured. Therefore, the upper limits of the nitrogen partial pressure, treatment temperature, and treatment time are limited to 0.05 MPa, 1300 °C, and 500 minutes, respectively. Preferably, the conditions are in the range of 0.005 to 0.03 MPa, 1050 to 1250 °C, and 30 to 400 minutes. Note that these conditions are examples of the conditions for obtaining the stainless steel fine wire of the present invention, and do not exclude performing the nitrogen absorption treatment under other conditions or improvement means.

[0043] In order to obtain a nitrogen concentration gradient within a predetermined cross-section by the above-mentioned solid-phase nitrogen absorption treatment, it is preferable that the wire diameter (diameter) of the stainless steel fine wire during the solid-phase nitrogen absorption treatment is 0.5 mm or more. If the wire diameter is less than 0.5 mm, not only is it difficult to obtain a predetermined concentration gradient because nitrogen cannot diffuse sufficiently to the center, but other adverse effects such as the shape of the stainless steel fine wire not being maintainable will become apparent. On the other hand, if the wire diameter exceeds 6 mm, nitrogen cannot diffuse sufficiently to the center of the stainless steel fine wire, making it difficult to achieve a predetermined concentration distribution. Therefore, for industrial stable production, the wire diameter during the solid-phase nitrogen absorption treatment is preferably in the range of 0.5 to 6 mm, and more preferably in the range of 2 to 4.0 mm. The stainless steel fine wire of the present invention means a stainless steel fine wire with a diameter of 0.5 to 6 mm. Also, for the solid-phase nitrogen absorption treatment, in order to stably maintain the shape and surface properties of the stainless steel fine wire, it is preferable to perform the solid-phase nitrogen treatment in a large furnace that can create a nitrogen atmosphere in a batch furnace.

[0044] Next, the reasons for limiting the manufacturing method of the stainless steel ultra-fine wire of the present invention will be described. The stainless steel ultra-fine wire of the present invention is characterized in that the nitrogen concentration in the surface layer is high, and the crystal grains in the surface layer are refined and the surface layer is hardened. The stainless steel fine wire of the present invention having a nitrogen concentration gradient in the cross-section is severely processed, and annealing is performed at a low temperature for a short time while suppressing the diffusion of nitrogen to maintain the nitrogen concentration gradient, so that fine crystal grains with an average crystal grain size exceeding 0.1 μm and not exceeding 2.0 μm are formed in the surface layer. In order to obtain surface fine grains, it is necessary to perform severe wire drawing with a reduction ratio of 95% or more without annealing in the middle and then perform final annealing. Although the upper limit of the reduction ratio is not defined, if it exceeds 99.95%, wire breakage frequently occurs at the wire drawing limit, so the upper limit is preferably 99.95% as required for industrial stable production.

[0045] After the above-mentioned drawing and wire drawing processes, in order to obtain a predetermined high strength and high ductility using a stainless steel ultra-fine wire, it is necessary to recrystallize and recover the heavily worked structure by annealing at a low temperature for a short time to form fine crystal grains on the surface layer. Therefore, short-time annealing at 700 °C or higher is performed. However, if the annealing temperature exceeds 950 °C, the crystal grains on the surface layer will coarsen, so the upper limit is set at 950 °C. In addition, in order to maintain the crystal grains in a fine state, the in-furnace time (annealing time) of annealing is preferably limited to 5 seconds or less as required. Therefore, it is preferable to perform annealing in this process by strand annealing, and the annealing temperature and annealing time are preferably in the ranges of 750 to 850 °C and 0.5 to 2 seconds, respectively.

[0046] Here, if the wire diameter of the stainless steel ultra-fine wire after wire drawing exceeds 50 μm, heat will not reach the central part during the final short-time annealing, resulting in insufficient uniform recrystallization and recovery treatment, making it difficult to satisfy the high strength and high ductility as a stainless steel ultra-fine wire. On the other hand, if it is less than 8 μm, wire breakage frequently occurs due to the wire drawing processing limit. Therefore, if necessary, the wire diameter of the ultra-fine wire after wire drawing is preferably limited to 8 to 50 μm, and more preferably in the range of 10 to 30 μm. The stainless steel ultra-fine wire of the present invention means a stainless steel ultra-fine wire with a diameter of 8 to 50 μm.

[0047] Next, the reasons for limiting the uses of the stainless steel ultra-fine wire and the stainless steel fine wire will be described. The stainless steel fine wire having a nitrogen concentration gradient within the cross-section of the present invention is essential as a material for manufacturing a stainless steel ultra-fine wire with high strength, high ductility, and surface hardening. By applying the stainless steel ultra-fine wire particularly to wire meshes such as meshes for screen printing, it exhibits a remarkable effect of improving the wire mesh manufacturing property and durability. Therefore, if necessary, it is preferable to limit the stainless steel ultra-fine wire of the present invention to be used for wire meshes and meshes. Also, it is preferable to limit the stainless steel fine wire of the present invention as its material.

[0048] As described above, the stainless steel fine wire of the present invention is manufactured by controlling the nitrogen concentration gradient in the cross section by the solid-phase nitrogen absorption method, and the stainless steel ultra-fine wire with high strength, high ductility, and high surface hardness is manufactured by controlling the wire drawing ratio, wire diameter, and final heat treatment conditions from the fine wire. Then, it is precision processed into a wire mesh such as a mesh for screen printing to achieve high durability of a mesh with a precise shape.

Example

[0049] In order to confirm the effects of the present invention, the following examples were carried out. Note that this example shows one example of the present invention and is not limited to the following configuration. This example can adopt various conditions as long as it does not deviate from the gist of the present invention and achieves the object of the present invention. Note that in each of the following tables, the underlines in the table indicate those outside the scope of the present invention. Table 1 shows the chemical compositions of the stainless steel fine wire and the stainless steel ultra-fine wire of the examples.

[0050]

Table 1

[0051] 《Manufacture of wire rod》 The steel with the chemical composition shown in Table 1 was melted at 1600 °C in a 150 kg vacuum melting furnace, then cast into a mold with a diameter of 170 mm, and the cast slab was hot-rolled into a wire rod with a diameter of 8.0 mm. Subsequently, it was heat-treated at 1050 °C for 30 minutes and pickled to obtain a wire rod.

[0052] 《Example 1》 Thereafter, for the above wire rod, normal wire drawing and strand annealing at 1050 °C (which is a solution treatment of general stainless steel fine wire and is treated in an atmosphere of hydrogen, nitrogen, Ar, etc. or a mixed gas thereof for about several minutes) were repeated to obtain a stainless steel fine wire with a diameter of 4 mm. For each of these steel wires, a solid-phase nitrogen absorption treatment was performed at 1250 °C with a nitrogen partial pressure of 0.15 atm (0.015 MPa) for 200 minutes to create a stainless steel fine wire having a nitrogen gradient in the cross section of the steel wire. Then, for the steel fine wire, the average nitrogen concentration of the cross-section was measured by instrumental analysis (ON analysis) of the steel wire, and the nitrogen concentration distributions in the surface layer and the central part within the cross-section were measured by EMPA analysis. Subsequently, the stainless steel fine wire was continuously subjected to normal wire drawing and strand annealing at 1050 °C to prototype a stainless steel fine wire with a wire diameter of 0.5 mm.

[0053] Thereafter, using the prototyped stainless steel fine wire as a material, a final high-strength and high-ductility wire drawing with a cross-sectional area reduction rate of 99.8% was performed, and a low-temperature short-time strand annealing at 800 °C for 1 second in the furnace was carried out to prototype a product of an ultra-fine wire with a wire diameter of 25 μm. For the ultra-fine wire product, the tensile strength and elongation at break were measured by a tensile test. Also, the average crystal grain size of the surface layer of the stainless steel ultra-fine wire product was measured by preparing a thin film sample for a transmission electron microscope and observing the metallographic structure by transmission electron microscope observation. As shown in Fig. 2, the average crystal grain size was measured by the cutting method (length of the straight line in the measurement part / number of intersections of the straight line with the crystal grain boundaries). Note that the crystal grain boundaries in the thin film electron image were counted at the parts showing clear linear contrast. The average nitrogen concentration within the cross-section of the steel fine wire, the nitrogen concentration of the surface layer, and the nitrogen concentration difference between the surface layer and the central part, the tensile strength, elongation at break, and crystal grain size of the surface layer of the stainless steel ultra-fine wire, and the Hv index according to formula (B) are shown in Table 2. Note that the average nitrogen concentration within the cross-section of the stainless steel ultra-fine wire, the nitrogen concentration of the surface layer, and the nitrogen concentration difference between the surface layer and the central part were almost equivalent to the values of the stainless steel fine wire in the same example.

[0054]

Table 2

[0055] In steels 16 to 33 outside the component range of the present invention, not only can the target high strength and high ductility not be obtained in the stainless steel ultra-fine wire product, but also processing (wire rod rolling, high-strength and high-ductility wire drawing) into a stainless steel ultra-fine wire that can exhibit predetermined characteristics cannot be performed. On the one hand, the ultra-fine stainless steel wire of the present invention trial-produced using the ultra-fine stainless steel wire of the present invention having the chemical components of Steel 1 to Steel 15 within the component range of the present invention and subjected to solid-phase nitrogen absorption treatment has a surface high hardness (Hv index), high strength, and high ductility suitable for precision meshes and the like, and the superiority of the present invention is obvious.

[0056] 《Example 2》 Next, in order to confirm the effects of the area reduction rate during wire drawing, the wire diameter of the ultra-fine wire, and the conditions of strand annealing when manufacturing the ultra-fine stainless steel wire of the present invention using the stainless steel fine wire as a raw material, the following Example 2 was conducted on the steel having the chemical components of Steel 1 shown in Table 1. Using the φ8 mm wire shown in 《Manufacture of Wire Rod》, normal wire drawing and strand annealing were repeated to obtain a stainless steel fine wire with a diameter of 2 mm. Then, a solid-phase nitrogen absorption treatment was performed in a furnace for 7 to 550 minutes in an atmosphere having nitrogen gas with a nitrogen partial pressure changed from 0.01 to 0.6 atm (0.001 to 0.06 MPa) at 975 to 1320 °C as shown in Table 3 to produce a stainless steel fine wire having a nitrogen gradient in the cross-section of the steel wire. For this steel fine wire, the average nitrogen concentration of the cross-section of the steel wire was measured by instrumental analysis (ON analysis) of the steel wire, and the nitrogen concentration distributions of the surface layer and the central part in the cross-section were measured by EMPA analysis. After that, the stainless steel wire was continuously subjected to normal wire drawing and strand annealing at 1050 °C to trial-produce a stainless steel fine wire.

[0057] Using this fine wire as a raw material, a final severe wire drawing process with an area reduction rate of 93.8 to 99.97% was performed, and a low-temperature and short-time strand annealing at 680 to 960 °C for 6 seconds or less in the furnace was performed to trial-produce a product of an ultra-fine stainless steel wire with a wire diameter of 7 to 60 μm. The wire diameter of the stainless steel fine wire was determined so that the wire diameter of the ultra-fine stainless steel wire of each example could be obtained by processing with the area reduction rate of each example.

[0058] After that, for the ultra-fine wire product, the tensile strength and elongation (total elongation) were measured by a tensile test. Also, the crystal grain size of the surface layer of the ultra-fine wire product was measured by observing the metal structure by transmission electron microscope observation after preparing a thin film sample for transmission electron microscope.

[0059] The average nitrogen concentration of the stainless steel fine wire, the nitrogen concentrations of the surface layer and the core, the nitrogen concentration difference between the surface layer and the core, the tensile strength of the ultra-fine wire, the elongation at break, the crystal grain size of the surface layer, and the Hv index are shown in Table 3 together with the manufacturing conditions.

[0060]

Table 3

[0061] In Comparative Examples Nos. 19 to 31, not only the target high strength, high ductility, and high surface hardness cannot be obtained in the ultra-fine wire products, but also the stainless steel ultra-fine wire that can exhibit predetermined characteristics cannot be processed (wire rolling, patenting). On the other hand, the ultra-fine wires of Invention Examples Nos. 16 to 25 produced by the manufacturing method of the present invention using the stainless steel fine wire having the components of Steel 1 have high surface hardness (Hv index), high strength, and high ductility suitable for precision meshes and the like, and the superiority of the manufacturing method and products of the present invention is clear. In addition, in the ultra-fine wires of Invention Examples Nos. 21 and 22, since the area reduction rate was higher than the suitable range, wire breakage frequently occurred during wire drawing, but the ultra-fine wires could be evaluated.

Industrial Applicability

[0062] As is clear from the above examples, according to the present invention, it is possible to stably provide a stainless steel fine wire having a nitrogen concentration gradient in the cross section and an ultra-fine wire having high strength and high ductility with surface crystal grain refinement and surface hardening, and it is possible to significantly improve the precision wire manufacturing property and durability of precision wire meshes such as meshes for screen printing, which is extremely useful industrially.

Claims

1. By mass percentage, C: exceeding 0.06% and not exceeding 0.15%, Si: 0.1 - 2.0%, Mn: 0.1 - 3.0%, P: not exceeding 0.05%, S: not exceeding 0.01%, Ni: 7.0 - 12.0%, Cr: 16.0 - 21.0% are contained, with the balance being Fe, nitrogen and impurities, and the component adjustment is made such that Md30 represented by the following formula (A) is -90 to 30, the average nitrogen concentration in the cross-section is 0.12 - 0.50%, and the difference between (surface layer nitrogen concentration) - (central part nitrogen concentration) is 0.01 - 0.25% to form a gradient concentration distribution. A stainless steel fine wire is characterized by this. Md30 (°C) = 551 - 462C - 9.2Si - 8.1Mn - 29(Ni + Cu) - 13.7Cr - 18.5Mo... (A) In formula (A), the element symbol means the content (mass percentage) of the element in the steel.

2. Instead of a part of the Fe, further by mass percentage, Cu: not exceeding 3.5% Mo: not exceeding 3.5%, W: not exceeding 3.5%, Among B not exceeding 0.01%, one or more are contained. The stainless steel fine wire according to Claim 1 is characterized by this.

3. A stainless steel ultra-fine wire having the components and nitrogen concentration distribution according to Claim 1 or Claim 2, wherein the average crystal grain size of the surface layer of the ultra-fine wire exceeds 0.1 μm and does not exceed 2.0 μm, the surface hardness Hv index represented by the following formula (B) is 300 - 550, the tensile strength is 1300 MPa or more, and the elongation at break is 7% or more. A high-strength and high-ductility stainless steel ultra-fine wire is characterized by this. Hv index = 150 + 400 × Nh ０．５ × (1.5D) －０．５ ・・・・(B) In formula (B), Nh: surface layer nitrogen concentration (%), D: average crystal grain size of the surface layer (μm)

4. A method for manufacturing the stainless steel fine wire according to Claim 1 or Claim 2, characterized in that a solid-phase nitrogen absorption treatment is performed at 1000 - 1300 °C for 10 - 500 minutes in an atmosphere containing nitrogen gas with a nitrogen partial pressure of 0.002 - 0.05 MPa on the stainless steel wire having the components according to Claim 1 or Claim 2.

5. A method for manufacturing the high-strength and high-ductility stainless steel ultra-fine wire according to Claim 3, characterized in that after wire drawing the stainless steel fine wire according to Claim 1 or Claim 2 to a wire diameter of 50 μm or less with a reduction ratio of 95% or more, strand annealing is performed at 700 - 950 °C for 5 seconds or less.

6. The high-strength and high-ductility stainless steel ultra-fine wire according to Claim 3, characterized in that it is for wire meshes such as screen printing meshes.

7. The stainless steel fine wire according to claim 1 or claim 2, characterized in that it is a material for manufacturing extremely fine stainless steel wires for wire meshes such as screen printing meshes.

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