Ultrahigh-strength ultra-fine stainless steel micro-wire and its preparation method

Abstract

The application discloses a kind of ultra-high strength superfine stainless steel microfilament and preparation method thereof, belong to metal material processing technical field.Microfilament chemical composition includes by mass percent: C 0.01~0.05%, Si 0.10~0.50%, Mn 1.0~2.0%, Ni 8.00~9.50%, Cr 18.00~20.50%, Cu 0.80~1.50%, Mo 0.50~1.20%, N 0.12~0.22%, V 0.05~0.25%, Nb 0.05~0.20%, Co 0.05~0.30%, O≤8ppm, H≤2ppm, the balance is Fe.Preparation method includes: vacuum induction smelting, argon oxygen decarburization refining, electroslag remelting, homogenization treatment, hot rolling, solid solution treatment, gradient pass deformation amount drawing and dynamic matching annealing, electrolytic polishing and passivation.The application is prepared by multielement alloying synergistic strengthening, combined with ultra-low oxygen pure steel smelting and gradient decreasing deformation amount drawing process, and the microfilament with diameter 0.01~0.03mm, tensile strength≥2400MPa, and breaking rate≤5 times / ton is obtained, which is suitable for high-end photovoltaic panel screen printing, medical devices and precision filter devices and other fields.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, specifically relating to an ultra-high strength ultra-fine stainless steel microwire with a diameter of 0.01~0.03mm and its preparation method. The microwire is particularly suitable for high-end photovoltaic panel screen printing, medical devices and precision filter components. Background Technology

[0002] Stainless steel microwires refer to ultra-fine metal wires with diameters ranging from tens to hundreds of micrometers. They possess high strength, high elasticity, corrosion resistance, and excellent electrical and thermal conductivity, and are widely used in textiles, aerospace, medicine, petrochemicals, photovoltaic cell screen printing, and other fields. With the photovoltaic industry's ever-increasing demands for screen printing precision and the trend towards miniaturization in medical devices, the market demand for stainless steel microwires with diameters below 0.02 mm and combining ultra-high strength (≥2400 MPa) with excellent toughness is becoming increasingly urgent.

[0003] Existing stainless steel microwire preparation technologies have the following main shortcomings:

[0004] First, the trade-off between diameter and strength is difficult to balance. Existing technologies, such as the ultra-fine stainless steel microwires disclosed in patent CN202510513358.2, while achieving diameters below 50μm through a bundled drawing process, only achieve a tensile strength of around 1800MPa, which is insufficient to meet the ultra-high strength requirements of high-end photovoltaic meshes. Research indicates that as the microwire diameter decreases, the work hardening effect during cold drawing intensifies. While tensile strength increases, elongation gradually decreases, significantly increasing the risk of wire breakage.

[0005] Secondly, inclusion control is a key bottleneck restricting the yield of ultrafine wire drawing. The breakage problem of stainless steel microwires mainly stems from the presence of non-metallic inclusions. When the diameter of the microwire is reduced to below 0.02 mm, even a single tiny inclusion can cause breakage during the drawing process. Although patent CN114369700A proposes a method to reduce inclusions by adjusting the alkalinity of slag, it mainly focuses on the smelting stage and does not address the coordinated control of the entire drawing process.

[0006] Third, the existing bundle drawing process has a crude design for the deformation amount per pass and lacks a fine annealing process for ultra-high strength microfilaments. In traditional processes, the deformation amount per drawing pass is mostly a fixed value, and the annealing temperature and speed are not dynamically adjusted according to the cumulative deformation amount, resulting in uneven grain size and affecting the consistency of the mechanical properties of the finished product.

[0007] Fourth, existing technologies lack a full-process online detection and closed-loop control mechanism. Wire breakage problems often only surface in the later stages of drawing, and the lack of early defect identification and repair methods leads to low yield.

[0008] Therefore, there is a need for an ultra-high strength ultra-fine stainless steel microwire and its preparation method to solve the above-mentioned technical problems. Summary of the Invention

[0009] To achieve the above-mentioned objectives, this invention provides an ultra-high strength ultra-fine stainless steel microwire and its preparation method. The aim is to achieve stable preparation of ultra-fine stainless steel microwires with a diameter of 0.01~0.03mm, tensile strength ≥2400MPa, and wire breakage rate ≤5 times / ton through the synergistic innovation of alloy composition optimization design, ultra-pure smelting control, and gradient deformation drawing and dynamic matching annealing processes.

[0010] The first objective of this invention is to provide an ultra-high strength, ultra-fine stainless steel microwire, wherein the chemical composition of the stainless steel microwire, by mass percentage, comprises: C: 0.01%~0.05%, Si: 0.10%~0.50%, Mn: 1.0%~2.0%, P≤0.020%, S≤0.003%, Ni: 8.00%~9.50%, Cr: 18.00%~20.50%, Cu: 0.80%. ~1.50%, Mo: 0.50%~1.20%, N: 0.12%~0.22%, V: 0.05%~0.25%, Nb: 0.05%~0.20%, Co: 0.05%~0.30%, O≤8ppm, H≤2ppm, with the balance being Fe and unavoidable impurities; the diameter of the microfilaments is 0.01~0.03mm, tensile strength ≥2400MPa, and filament breakage rate ≤5 times / ton.

[0011] Specifically, the microfilaments have a grain size ≥ 10, a surface roughness Ra ≤ 0.2 μm, and an elongation ≥ 1.5%.

[0012] The second objective of this invention is to provide a method for preparing the above-mentioned ultra-high strength ultrafine stainless steel microwires, comprising the following steps:

[0013] Step 1: Prepare the billet by mixing the chemical components according to claim 1 and using a smelting process of vacuum induction smelting, argon-oxygen decarburization refining and gas-protected electroslag remelting. During the electroslag remelting process, control the slag basicity R=1.8~2.5, add slag containing CaO and MgO, so that the Al content in the steel is controlled below 0.005% and the O content is ≤8ppm.

[0014] Step 2: Homogenize the billet at 1100~1180℃ for 4~8 hours, then roll it into wire rod with a diameter of 5.0~6.5mm using continuous hot rolling. The final hot rolling temperature is controlled at 950~1050℃, and the billet is then water-cooled to room temperature.

[0015] Step 3: Solution treat the hot-rolled wire rod at 1050~1100℃ for 30~60 minutes, then quench it with water to obtain a uniform austenitic structure with grain size controlled at 7~9.

[0016] Step 4: The solution-treated wire rod is subjected to multiple cold drawing passes, and annealing is performed after each drawing pass. The deformation amount and annealing temperature decrease in a gradient as the wire diameter decreases.

[0017] Step 5: Perform electrolytic polishing and passivation treatment on the finished microfilaments to obtain a finished product with a surface roughness Ra≤0.2μm.

[0018] Specifically, in step four, the gradient deformation amount is as follows: in the initial drawing stage, the wire diameter is drawn from 5.0~6.5mm to 0.5~1.0mm, and the deformation amount is controlled at 25%~35%; in the intermediate drawing stage, the wire diameter is drawn from 0.5~1.0mm to 0.05~0.10mm, and the deformation amount is controlled at 15%~25%; in the fine drawing stage, the wire diameter is drawn from 0.05~0.10mm to the target diameter of 0.01~0.03mm, and the deformation amount is controlled at 8%~15%.

[0019] Specifically, in step four, the annealing temperature is a dynamically matched annealing temperature: the annealing temperature for the initial drawing stage is 950~1050℃, the annealing temperature for the intermediate drawing stage is 850~950℃, and the annealing temperature for the fine drawing stage is 700~850℃; the annealing speed gradually decreases from 15~25m / min in the initial stage to 5~10m / min in the fine stage as the wire diameter decreases; the holding time for each annealing pass is 30~120 seconds, and the protective atmosphere is at least one of hydrogen, argon, or a hydrogen-argon mixture.

[0020] Specifically, in step four, after each drawing pass, online eddy current testing is used to detect surface defects. When surface microcracks or inclusion signals are detected, an additional drawing pass with a deformation of 5% to 8% is added and the material is re-annealed. The online eddy current testing frequency is 10 to 50 kHz, and the detection sensitivity is ≥1 μm for defect depth.

[0021] Specifically, in step one, the vacuum degree of vacuum induction smelting is ≤10Pa, the smelting temperature is 1550~1620℃, and the refining time is 30~60 minutes; the endpoint temperature of argon-oxygen decarburization refining is 1600~1680℃, and the endpoint oxygen activity is ≤5ppm; the melting rate of electroslag remelting is controlled at 3~8kg / min, and the flow rate of cooling water in the crystallizer is 8~15m³ / h.

[0022] Specifically, the homogenization process in step two is carried out under an argon protective atmosphere with an oxygen content ≤100ppm in the furnace; the hot rolling is carried out in 12 to 18 passes of continuous rolling with a total deformation of ≥90% and the grain size of the hot-rolled wire rod is controlled at level 5 to 7.

[0023] Specifically, in step four, the cold drawing uses a diamond wire drawing die with a die compression angle of 10°~16°, a sizing strip length of 20%~40% of the die diameter, a drawing lubricant of oil-based wire drawing oil containing nano-diamond particles with an average particle size of 10~50nm, a lubricant temperature of 35~55℃, and a drawing speed of 30~80m / min.

[0024] The advantages of the ultra-high strength ultrafine stainless steel microwire and its preparation method of the present invention compared with the prior art are as follows:

[0025] (1) Significantly improved tensile strength of microwires: By optimizing the ratio of Cu, Co, V and Nb in the alloy composition and the N content, combined with a fine gradient deformation drawing process, the tensile strength of the final microwires (diameter 0.01~0.03mm) reached more than 2400MPa, which is about 33% higher than the existing technology (1800MPa in CN202510513358.2);

[0026] (2) Effectively reduced wire breakage rate: By controlling the O content to below 8ppm through ultra-pure smelting, combined with the closed-loop control strategy of online eddy current flaw detection and finishing drawing, the wire breakage rate during the drawing process was reduced from 15~20 times / ton in the existing technology to below 5 times / ton, which significantly improved production efficiency and yield.

[0027] (3) The fine control of microfilament grain size is realized: the synergistic design of gradient pass deformation amount and dynamic matching annealing process avoids the grain coarsening and non-uniformity problems caused by traditional uniform deformation drawing, so that the grain size of the finished microfilament is stably controlled at level 10~12, ensuring the consistency of mechanical properties.

[0028] (4) Expanding the application fields of stainless steel microwires: The ultra-high strength (≥2400MPa) and ultra-fine (0.01~0.03mm) stainless steel microwires prepared by this invention meet the stringent requirements of high-end photovoltaic panel screen printing for wire strength and precision, and can also be used in precision medical devices and high-strength filter devices. Detailed Implementation

[0029] The specific embodiments of the present invention will be described in further detail below.

[0030] Example 1

[0031] (1) Alloy composition

[0032] The chemical composition of the stainless steel microwires prepared in this embodiment, by mass percentage, is as follows: C 0.03%, Si 0.30%, Mn 1.50%, P 0.015%, S 0.002%, Ni 8.80%, Cr 19.50%, Cu 1.20%, Mo 0.80%, N 0.18%, V 0.15%, Nb 0.12%, Co 0.20%, O 6ppm, H 1.5ppm, with the balance being Fe.

[0033] (II) Preparation process

[0034] Step 1: Ultra-pure smelting and billet preparation;

[0035] Weigh out the raw materials according to the above chemical composition, including pure iron, metallic chromium, metallic nickel, electrolytic copper, ferromolybdenum, ferrovanadium, ferroniobium, metallic cobalt, ferrochrome nitride, and graphite. Place the pure iron, metallic chromium, and metallic nickel into a vacuum induction furnace, evacuate to a vacuum degree of 8 Pa, and heat to 1600℃ to melt the raw materials. After the furnace charge is completely melted, add electrolytic copper, ferromolybdenum, ferrovanadium, ferroniobium, and metallic cobalt, and continue refining at 1600℃ for 45 minutes. During the refining process, activate electromagnetic stirring to homogenize the composition. Subsequently, add ferrochrome nitride and graphite to adjust the N and C content to the target range.

[0036] After refining, the temperature of the molten steel is adjusted to 1580℃, and the molten steel is cast into consumable electrodes. The consumable electrodes are then placed in a gas-protected electroslag remelting furnace using a quaternary slag system of CaF2-CaO-MgO-Al2O3, with the slag basicity R controlled at 2.0. Electroslag remelting is carried out under argon protection, with a melting rate controlled at 5 kg / min and a crystallizer cooling water flow rate of 10 m³ / h. During the electroslag remelting process, deep deoxidation is performed by adding slag containing CaO and MgO, controlling the Al content in the steel to 0.004% and reducing the O content to 6 ppm. The refined molten steel is then cast into circular billets with a diameter of 200 mm.

[0037] Step 2: Homogenization and hot rolling;

[0038] The billet obtained in step one is placed in a protective atmosphere heating furnace, which is purged with argon gas and the oxygen content is controlled at 80 ppm. The billet is heated to 1150℃ and held for 6 hours for homogenization to eliminate dendrite segregation. After homogenization, the billet is removed from the heating furnace and fed into a continuous hot rolling mill within 5 seconds. It is rolled in 15 passes with a total deformation of 92% to produce a wire rod with a diameter of 5.5 mm. The final hot rolling temperature is controlled at 1000℃, and the wire rod is immediately water-cooled to room temperature. The resulting hot-rolled wire rod has a grain size of grade 6.

[0039] Step 3: Solution treatment of wire rod;

[0040] The hot-rolled wire rod obtained in step two is placed in a continuous solution treatment furnace, which is protected by argon gas. Solution treatment is carried out at 1080℃ for 45 minutes. After the solution treatment and holding period, the wire rod is quickly removed and placed in a water tank for water quenching at a cooling rate of approximately 120℃ / s, resulting in a supersaturated solid solution structure with a grain size of grade 8.

[0041] Step 4: Gradient pass deformation drawing and dynamic matching annealing;

[0042] (1) Initial drawing stage (5.5mm→0.8mm)

[0043] After solution treatment, the tip of the wire rod is immersed in hydrochloric acid solution (15% by volume) for 5 minutes to remove the surface oxide scale. Then, the tip is sharpened with a grinding wheel until it can pass through the diamond drawing die. A diamond drawing die with a compression angle of 13° and a sizing band length of 30% of the die diameter is selected. The die is installed on the drawing machine, the tip of the wire rod is passed through the die, and clamped with pliers.

[0044] The drawing machine is started, and the first drawing pass is performed at a speed of 50 m / min, with the deformation controlled at 30%. During the drawing process, lubricant (oil-based wire drawing oil containing nanodiamond particles with an average particle size of 30 nm) is circulated and sprayed at the die inlet, and the lubricant temperature is controlled at 45℃. After the first drawing pass is completed, the wire diameter is measured to be 4.6 mm. The microwire is then fed into a tubular annealing furnace and passed through at a speed of 20 m / min at 1000℃ under a hydrogen protective atmosphere, with a holding time of approximately 60 seconds, followed by cooling in a water-cooling section.

[0045] This process of drawing and annealing was repeated, with the deformation in each pass controlled between 28% and 32%, and the annealing temperature maintained between 980 and 1020℃. The wire diameter was measured every three passes, and the deformation in subsequent passes was fine-tuned based on the measured values. The initial stage ended when the wire diameter was drawn to 0.8 mm, after a total of approximately 12 drawing passes.

[0046] (2) Intermediate drawing stage (0.8mm→0.08mm)

[0047] Replace the die with a smaller diamond wire drawing die (compression angle 12°, sizing band length 25% of die diameter) to fit a 0.8mm wire diameter. Sharpen the tip of the 0.8mm microwire again before passing it through the new die. Adjust the drawing speed to 40m / min, and control the deformation in the first pass to 20%. After the first drawing pass, feed the microwire into a tubular annealing furnace, pass it through at 12m / min at 900℃ under an argon protective atmosphere, hold it for approximately 80 seconds, and then cool it in a cooling section.

[0048] Continue with subsequent drawing passes, controlling the deformation in each pass between 18% and 22%, maintaining the annealing temperature between 880 and 920℃, and keeping the annealing speed between 10 and 14 m / min. When the wire diameter is drawn to 0.08 mm, the intermediate stage ends, after a total of approximately 20 drawing passes.

[0049] (3) Fine drawing stage (0.08mm→0.015mm)

[0050] Replace the die with an ultra-small diamond wire drawing die (compression angle 10°, sizing band length 20% of die diameter) adapted to a 0.08mm wire diameter. After inserting the 0.08mm microwire tip into the new die, start the drawing machine and adjust the drawing speed to 35m / min. During this stage, the deformation is reduced to 10%, and the reduction in wire diameter after each drawing pass is strictly controlled within the set range.

[0051] After each drawing pass, the microfilament is fed into a tubular annealing furnace and passed through at a speed of 7 m / min under a protective atmosphere of 780℃ and a hydrogen-argon mixture (5% H2 volume fraction), holding for approximately 100 seconds, followed by cooling. Subsequent drawing passes are then performed, with the deformation controlled between 8% and 12% per pass, the annealing temperature controlled between 750 and 800℃, and the annealing speed maintained at 6 to 8 m / min. The fine drawing stage ends when the wire diameter reaches the target value of 0.015 mm, after a total of approximately 15 drawing passes.

[0052] (4) Online detection and closed-loop adjustment

[0053] Throughout the entire drawing process described above, after each drawing pass and before annealing, the microfilament is fed into an online eddy current flaw detector for surface defect detection. The detection frequency is 30kHz, and the detection sensitivity is ≥1μm for defect depth. In this embodiment, weak defect signals were detected in the initial stage (5th pass) and the intermediate stage (8th pass). The control system automatically issued instructions to add a 6% deformation trimming draw, followed by re-annealing, before continuing with subsequent passes. Through this closed-loop trimming, this embodiment successfully avoided two potential wire breakage accidents.

[0054] Step 5: Finished Product Surface Treatment

[0055] The 0.015 mm finished microfilament obtained in step four was wound onto a pay-off reel and passed sequentially through an electrolytic polishing tank and a passivation tank at a speed of 8 m / min. The electrolytic polishing tank contained a mixed solution of phosphoric acid, sulfuric acid, and chromic acid (volume ratio 6:3:1), with a current density of 1.0 A / cm² and a solution temperature of 70°C. The microfilament passed through the electrolytic polishing tank for approximately 30 seconds. It then entered the passivation tank, where the passivation solution was a 25% nitric acid solution at 30°C for 10 minutes. After surface treatment, the microfilament was rinsed with water and dried with hot air before being wound up. The final finished microfilament had a diameter of 0.015 mm and a silvery-white metallic luster.

[0056] Example 2

[0057] (1) Alloy composition

[0058] The chemical composition of the stainless steel microwires prepared in this embodiment, by mass percentage, is as follows: C 0.02%, Si 0.25%, Mn 1.80%, P 0.012%, S 0.0015%, Ni 9.00%, Cr 20.00%, Cu 1.00%, Mo 1.00%, N 0.20%, V 0.20%, Nb 0.15%, Co 0.25%, O 5ppm, H 1.2ppm, with the balance being Fe.

[0059] (II) Preparation process

[0060] Step 1: Ultra-pure smelting and billet preparation;

[0061] Weigh the raw materials according to the above chemical composition. Place pure iron, metallic chromium, and metallic nickel into a vacuum induction furnace, evacuate to a vacuum degree of 6 Pa, and heat to 1580℃ to melt the raw materials. After the furnace charge is completely melted, add electrolytic copper, ferromolybdenum, ferrovanadium, ferroniobium, and metallic cobalt, and continue refining at 1580℃ for 50 minutes. During the refining process, add ferrochrome nitride and graphite to adjust the N and C content to the target range.

[0062] After refining, the temperature of the molten steel is adjusted to 1560℃ and cast into consumable electrodes. These electrodes are then placed in a gas-protected electroslag remelting furnace using a quaternary slag system (CaF2-CaO-MgO-Al2O3) with a basicity R of 2.2. Electroslag remelting is performed under argon protection at a melting rate of 4 kg / min and a crystallizer cooling water flow rate of 12 m³ / h. This ensures that the Al content in the steel is controlled at 0.003% and the O content is reduced to 5 ppm. The refined steel is then cast into circular billets with a diameter of 200 mm.

[0063] Step 2: Homogenization and hot rolling;

[0064] The cast billet was heated to 1120℃ under an argon protective atmosphere (70ppm oxygen content in the furnace) and held at that temperature for 5 hours for homogenization. After homogenization, it was rolled into wire rod with a diameter of 6.0mm using 14 consecutive passes and a total deformation of 93%. The final hot rolling temperature was controlled at 980℃, and the wire rod was water-cooled to room temperature after rolling. The grain size of the hot-rolled wire rod was grade 6.

[0065] Step 3: Solution treatment of wire rod;

[0066] The hot-rolled wire rod was solution treated at 1060℃ for 50 minutes, followed by water quenching. The grain size after solution treatment was grade 8.

[0067] Step 4: Gradient pass deformation drawing and dynamic matching annealing;

[0068] (1) Initial drawing stage (6.0mm→0.7mm)

[0069] A diamond wire drawing die with a compression angle of 14° and a sizing band length of 30% of the die diameter was used. The drawing speed was 45 m / min, and the deformation per pass was controlled at approximately 28%. The annealing temperature was 980℃, the annealing speed was 18 m / min, and a hydrogen protective atmosphere was used. The wire diameter was measured after each pass, and the deformation of subsequent passes was adjusted based on the measured values. After approximately 13 drawing passes, the wire diameter reached 0.7 mm.

[0070] (2) Intermediate drawing stage (0.7mm→0.06mm)

[0071] The die was replaced with a smaller die (compression angle 11°, sizing strip length 25% of die diameter) to accommodate a 0.7mm wire diameter. The drawing speed was 35m / min, the deformation per pass was controlled at approximately 18%, the annealing temperature was 880℃, the annealing speed was 10m / min, and an argon protective atmosphere was used. After approximately 22 drawing passes, the wire diameter reached 0.06mm.

[0072] (3) Fine drawing stage (0.06mm→0.010mm)

[0073] The die was replaced with an ultra-small die (compression angle 10°, sizing strip length 20% of die diameter) adapted to a 0.06mm wire diameter. The drawing speed was 30m / min, the deformation per pass was controlled at around 8%, the annealing temperature was 750℃, the annealing speed was 6m / min, and a hydrogen-argon mixed gas protective atmosphere was used. After approximately 18 drawing passes, the wire diameter reached 0.010mm.

[0074] (4) Online detection and closed-loop adjustment

[0075] Online eddy current testing (detection frequency 40kHz, sensitivity ≥1μm defect depth) was performed after each pass during the entire drawing process. In this embodiment, no defect signals requiring correction were detected during the drawing process, and there was no wire breakage throughout the continuous drawing process.

[0076] Step 5: Surface treatment of the finished product;

[0077] The finished microfilaments are passed through an electrolytic polishing tank (phosphoric acid-sulfuric acid-chromic acid volume ratio 6:3:1, current density 1.5A / cm², temperature 75℃) and a passivation tank (30% nitric acid solution, temperature 25℃, treatment time 8 minutes) at a speed of 5m / min, and then rolled up after rinsing and drying.

[0078] Example 3

[0079] (1) Alloy composition

[0080] The chemical composition of the stainless steel microwires prepared in this embodiment, by mass percentage, is as follows: C 0.04%, Si 0.40%, Mn 1.20%, P 0.018%, S 0.0025%, Ni 8.50%, Cr 18.50%, Cu 1.40%, Mo 0.60%, N 0.15%, V 0.10%, Nb 0.08%, Co 0.10%, O 7ppm, H 1.8ppm, with the balance being Fe.

[0081] (II) Preparation process

[0082] Step 1: Ultra-pure smelting and billet preparation;

[0083] Raw materials were weighed according to the above chemical composition. Vacuum induction smelting was performed at a vacuum degree of 9 Pa, a temperature of 1620℃, and a refining time of 35 minutes; the final temperature of argon-oxygen decarburization refining was 1650℃; the electroslag remelting slag system had a basicity R of 1.9, a melting rate of 6 kg / min, and a crystallizer cooling water flow rate of 9 m³ / h. The steel contained 0.005% Al and 7 ppm O. The steel was cast into a circular billet with a diameter of 200 mm.

[0084] Step 2: Homogenization and hot rolling;

[0085] The billet was heated to 1160℃ under an argon protective atmosphere (oxygen content 90ppm) and held for 7 hours for homogenization. It was then rolled into 5.0mm diameter wire rods using 17 continuous rolling passes with a total deformation of 91%, with a final rolling temperature of 1020℃ and water cooling. The hot-rolled wire rod had a grain size of grade 5.

[0086] Step 3: Solution treatment of wire rod;

[0087] Hot-rolled wire rod was solution treated at 1100℃ for 35 minutes, followed by water quenching. The resulting grain size was grade 7.

[0088] Step 4: Gradient pass deformation drawing and dynamic matching annealing;

[0089] (1) Initial drawing stage (5.0mm→1.0mm)

[0090] A diamond wire drawing die with a compression angle of 16° and a sizing band length of 40% of the die diameter was used. The drawing speed was 55 m / min, and the deformation per pass was controlled at approximately 32%. The annealing temperature was 1020℃, the annealing speed was 22 m / min, and a hydrogen protective atmosphere was used. After approximately 10 drawing passes, the wire diameter reached 1.0 mm.

[0091] (2) Intermediate drawing stage (1.0mm→0.10mm)

[0092] The die was replaced with a smaller die (compression angle 13°, sizing strip length 30% of die diameter) to accommodate a 1.0mm wire diameter. The drawing speed was 45m / min, the deformation per pass was controlled at approximately 22%, the annealing temperature was 920℃, the annealing speed was 14m / min, and an argon protective atmosphere was used. After approximately 18 drawing passes, the wire diameter reached 0.10mm.

[0093] (3) Fine drawing stage (0.10mm→0.025mm)

[0094] The die was replaced with an ultra-small die (compression angle 12°, sizing strip length 25% of die diameter) adapted to a 0.10mm wire diameter. The drawing speed was 40m / min, the deformation per pass was controlled at around 12%, the annealing temperature was 800℃, the annealing speed was 8m / min, and a hydrogen-argon mixed gas protective atmosphere was used. After approximately 12 drawing passes, the wire diameter reached 0.025mm.

[0095] (4) Online detection and closed-loop adjustment

[0096] Online eddy current testing (detection frequency 20kHz) was performed after each pass during the entire drawing process. In this embodiment, a weak defect signal was detected in the 12th pass during the intermediate stage. The control system issued a command to add a 7% deformation trimming draw and then re-anneal, after which normal drawing continued.

[0097] Step 5: Surface treatment of the finished product;

[0098] The finished microfilaments are passed through an electrolytic polishing tank (current density 0.8 A / cm², temperature 65℃) and a passivation tank (20% nitric acid solution, temperature 35℃, treatment time 12 minutes) at a speed of 12 m / min, and then rolled up after rinsing and drying.

[0099] Example 4

[0100] (1) Alloy composition

[0101] The chemical composition of the stainless steel microwires prepared in this embodiment, by mass percentage, is as follows: C 0.02%, Si 0.35%, Mn 1.60%, P 0.010%, S 0.0018%, Ni 9.20%, Cr 20.00%, Cu 0.90%, Mo 1.10%, N 0.20%, V 0.18%, Nb 0.18%, Co 0.28%, O 4ppm, H 1.0ppm, with the balance being Fe.

[0102] (II) Preparation process

[0103] Step 1: Ultra-pure smelting and billet preparation;

[0104] Raw materials were weighed according to the above chemical composition. Vacuum induction smelting was performed at a vacuum level of 5 Pa, a temperature of 1550℃, and a refining time of 55 minutes; the final temperature of argon-oxygen decarburization refining was 1620℃; the electroslag remelting slag system had a basicity R of 2.3, a melting rate of 5 kg / min, and a crystallizer cooling water flow rate of 13 m³ / h. The steel contained 0.002% Al and 4 ppm O. The steel was cast into a circular billet with a diameter of 200 mm.

[0105] Step 2: Homogenization and hot rolling;

[0106] The billet was heated to 1140℃ under an argon protective atmosphere (oxygen content 60ppm) and held for 6 hours for homogenization. It was then rolled into 5.5mm diameter wire rods using 15 continuous passes with a total deformation of 94%, with a final rolling temperature of 990℃ and water cooling. The hot-rolled wire rod had a grain size of grade 7.

[0107] Step 3: Solution treatment of wire rod;

[0108] Hot-rolled wire rod was solution treated at 1070℃ for 55 minutes, followed by water quenching. The resulting grain size was grade 9.

[0109] Step 4: Gradient pass deformation drawing and dynamic matching annealing;

[0110] (1) Initial drawing stage (5.5mm→0.6mm)

[0111] A diamond wire drawing die with a compression angle of 12° and a sizing band length of 25% of the die diameter was used. The drawing speed was 60 m / min, and the deformation per pass was controlled at approximately 28%. The annealing temperature was 970℃, the annealing speed was 18 m / min, and a hydrogen protective atmosphere was used. After approximately 12 drawing passes, the wire diameter reached 0.6 mm.

[0112] (2) Intermediate drawing stage (0.6mm→0.05mm)

[0113] The die was replaced with a smaller die (compression angle 10°, sizing strip length 20% of die diameter) to accommodate a 0.6mm wire diameter. The drawing speed was 38m / min, the deformation per pass was controlled at approximately 18%, the annealing temperature was 870℃, the annealing speed was 10m / min, and an argon protective atmosphere was used. After approximately 22 drawing passes, the wire diameter reached 0.05mm.

[0114] (3) Fine drawing stage (0.05mm→0.018mm)

[0115] The die was replaced with an ultra-small die (compression angle 10°, sizing strip length 20% of die diameter) adapted to a 0.05mm wire diameter. The drawing speed was 32m / min, the deformation per pass was controlled at around 8%, the annealing temperature was 740℃, the annealing speed was 5m / min, and a hydrogen-argon mixed gas protective atmosphere was used. After approximately 13 drawing passes, the wire diameter reached 0.018mm.

[0116] (4) Online detection and closed-loop adjustment

[0117] Online eddy current testing (detection frequency 50kHz) was performed after each pass during the entire drawing process. In this embodiment, no defect signals requiring correction were detected during the drawing process.

[0118] Step 5: Finished Product Surface Treatment

[0119] The finished microfilaments are passed through an electrolytic polishing tank (current density 1.2 A / cm², temperature 72℃) and a passivation tank (25% nitric acid solution, temperature 28℃, treatment time 10 minutes) at a speed of 6 m / min, and then rolled up after rinsing and drying.

[0120] Comparative Example 1 (Content of standard 304 stainless steel, without Cu, Co, V, and Nb)

[0121] (1) Alloy composition

[0122] The chemical composition of Comparative Example 1, by mass percentage, is: C 0.05%, Si 0.50%, Mn 1.50%, P 0.025%, S 0.005%, Ni 8.50%, Cr 18.00%, Mo 0.50%, N 0.08%, O 25ppm, H 3.5ppm, with the balance being Fe. It does not contain Cu, Co, V, or Nb.

[0123] (II) Preparation process

[0124] Using standard 304 stainless steel wire rod (5.5mm in diameter) as raw material, after solution treatment at 1080℃ for 45 minutes and water quenching, a traditional fixed deformation bundle drawing process is employed: the deformation amount per pass is fixed at 40%, and after each drawing pass, annealing is performed at 750℃ for 90 seconds. There is no gradient deformation design and no online eddy current testing or finishing process. The target finished product diameter is 0.015mm.

[0125] (III) Finished Product Testing Results

[0126] The actual finished product diameter was 0.015 mm with a diameter tolerance of ±1.2 μm; tensile strength was 1680 MPa with a standard deviation of ±120 MPa; elongation was 1.0%; wire breakage rate was 22 times / ton; grain size was grade 7.5; surface roughness Ra was 0.35 μm; there were 28 inclusions ≥1 μm / mm², with the largest inclusion size being 12 μm; no nano-precipitates were detected.

[0127] Comparative Example 2 (containing Cu but not Co, V, or Nb)

[0128] (1) Alloy composition

[0129] The chemical composition of Comparative Example 2, by mass percentage, is: C 0.06%, Si 0.80%, Mn 1.20%, P 0.030%, S 0.008%, Ni 8.00%, Cr 17.50%, Cu 0.30%, Mo 0.20%, N 0.06%, O 18ppm, H 3.0ppm, with the balance being Fe. It does not contain Co, V, or Nb.

[0130] (II) Preparation process

[0131] The same smelting, homogenization, hot rolling, and solution treatment processes as in Example 1 were adopted, but the drawing process used traditional fixed deformation bundle drawing: the total deformation per pass was fixed at 40%, and after each pass, the material was annealed at 750℃ for 90 seconds. There was no gradient deformation design and no online eddy current testing and finishing process. The target finished product diameter was 0.015 mm.

[0132] (III) Finished Product Testing Results

[0133] The actual finished product diameter was 0.015 mm with a diameter tolerance of ±1.0 μm; tensile strength was 1850 MPa with a standard deviation of ±95 MPa; elongation was 1.2%; wire breakage rate was 18 times / ton; grain size was grade 8.0; surface roughness Ra was 0.28 μm; there were 20 inclusions ≥1 μm / mm², with the largest inclusion size being 9 μm; no nano-precipitates were detected.

[0134] Comparative Example 3 (containing V and Nb but excluding Cu and Co)

[0135] (1) Alloy composition

[0136] The chemical composition of Comparative Example 3, by mass percentage, is as follows: C 0.04%, Si 0.45%, Mn 1.80%, P 0.020%, S 0.004%, Ni 9.00%, Cr 19.00%, Mo 0.80%, N 0.10%, V 0.08%, Nb 0.05%, O 15ppm, H 2.5ppm, with the balance being Fe. It does not contain Cu or Co.

[0137] (II) Preparation process

[0138] The same smelting, homogenization, hot rolling, and solution treatment processes as in Example 1 were adopted, but the drawing process used traditional fixed deformation bundle drawing: the total deformation per pass was fixed at 40%, and after each pass, the material was annealed at 750℃ for 90 seconds. There was no gradient deformation design and no online eddy current testing and finishing process. The target finished product diameter was 0.015 mm.

[0139] (III) Finished Product Testing Results

[0140] The actual finished product diameter was 0.015 mm with a diameter tolerance of ±0.8 μm; tensile strength was 1920 MPa with a standard deviation of ±85 MPa; elongation was 1.3%; wire breakage rate was 15 times / ton; grain size was grade 8.5; surface roughness Ra was 0.25 μm; there were 15 inclusions ≥1 μm / mm², with the largest inclusion size being 7 μm; no nano-precipitates were detected.

[0141] Comparative Example 4 (alloy composition is the same as in Example 1, but the drawing process is a traditional process).

[0142] (1) Alloy composition

[0143] The chemical composition of Comparative Example 4 was exactly the same as that of Example 1 (containing Cu, Co, V, Nb, N, and O at 6 ppm).

[0144] (II) Preparation process

[0145] The smelting, homogenization, hot rolling, and solution treatment processes are exactly the same as in Example 1, but the drawing process is different: the total deformation per pass is fixed at 40%, and each drawing pass is followed by annealing at 750℃ for 90 seconds. There is no gradient deformation design, and no online eddy current testing or finishing process. The target finished product diameter is 0.015 mm.

[0146] (III) Finished Product Testing Results

[0147] Testing revealed the following: actual finished product diameter: 0.015 mm, diameter tolerance ±0.6 μm; tensile strength: 2150 MPa, standard deviation ±70 MPa; elongation: 1.4%; wire breakage rate: 12 times / ton; grain size: grade 9.0; surface roughness Ra: 0.20 μm; ≥1 μm inclusions: 2 per mm², maximum inclusion size: 2.5 μm; average precipitated phase size: 60 nm, number density: 0.4 × 10⁻⁶. -3 per μm³.

[0148] Summary of test data:

[0149] Table 1: Comparison of chemical composition (mass percentage, balance Fe) between Examples 1-4 and Comparative Examples 1-4

[0150]

[0151] Table 2: Detection data of finished microfilaments from Examples 1-4 and Comparative Examples 1-4

[0152]

[0153] Table 3: Intermediate test data at different drawing stages in Example 1

[0154]

[0155] Table 4: Intermediate test data at different drawing stages of Comparative Example 1 (traditional process)

[0156]

[0157] Table 5: Effect of annealing temperature on the mechanical properties of microfilaments (intermediate stage, 0.08 mm wire diameter, conditions of Example 1)

[0158]

[0159] Table 6: Effect of deformation amount in the fine stage on the properties of the finished microfilament (Example 1 conditions, 0.015 mm finished product)

[0160]

[0161] Test data analysis:

[0162] (I) Analysis of the influence of alloy composition on performance

[0163] As can be seen from the data in Tables 1 and 2, the chemical composition of Examples 1 to 4 is within the range defined by claim 1 of this invention, while Comparative Examples 1 to 3 are missing key alloying elements of this invention or the content of elements deviates from the scope of this invention.

[0164] Comparative Example 1 uses conventional 304 stainless steel composition (containing no Cu, Co, V, or Nb, with an N content of only 0.08%), and its tensile strength is only 1680 MPa, which is about 33% lower than that of Example 1 (2510 MPa). This is because it lacks the solid solution strengthening and precipitation strengthening effects of Cu, lacks the regulation of stacking fault energy and grain refinement strengthening effect of Co, lacks the dispersion strengthening effect of V and Nb forming nano-carbonitride precipitates, and the N content is too low, resulting in insufficient solid solution strengthening effect.

[0165] Although Comparative Example 2 added a small amount of Cu (0.30%), it contained no Co, V, or Nb, and the N content was only 0.06%. Its tensile strength was 1850 MPa, which was about 26% lower than that of Example 1. This shows that simply adding Cu without Co, V, Nb, and sufficient N cannot achieve the synergistic strengthening effect of multi-element alloying.

[0166] Comparative Example 3 contained V, Nb (0.08%, 0.05%), and N (0.10%), but did not contain Cu or Co. Its tensile strength was 1920 MPa, which was about 23% lower than that of Example 1. This indicates that without the solid solution strengthening of Cu and the stacking fault energy modulation effect of Co, even if some parts show a strengthening effect, it is difficult to reach a strength level of over 2400 MPa.

[0167] The composition of Comparative Example 4 is exactly the same as that of Example 1, but its tensile strength is only 2150 MPa. This shows that even with optimized alloy composition, the strength target of the present invention cannot be achieved if the drawing process is not appropriate.

[0168] (II) Analysis of the influence of smelting purity on wire breakage rate and inclusions

[0169] As shown in Table 2, the O content in Examples 1-4 was controlled at 4-7 ppm, the number of inclusions ≥1 μm was only 1-3 per mm², and the maximum inclusion size was ≤3.0 μm. In contrast, the O content in Comparative Examples 1-3 was 15-25 ppm, the number of inclusions ≥1 μm was 15-28 per mm², and the maximum inclusion size was 7-12 μm.

[0170] The wire breakage rate showed a significant positive correlation with the inclusion level. The wire breakage rates in Examples 1-4 were 3.5-4.8 times / ton, all below the target of 5 times / ton. In contrast, the wire breakage rates in Comparative Examples 1-3 were 15-22 times / ton, 3-6 times higher than those in the Examples. This fully demonstrates the crucial role of ultra-pure smelting (O content ≤ 8ppm) in reducing the wire breakage rate.

[0171] The O content and inclusion levels of Comparative Example 4 were the same as those of Example 1 (both were from the same batch of cast billets), but due to the different drawing process, the wire breakage rate was 12 times / ton, significantly higher than the 4.2 times / ton of Example 1. This indicates that even with high-purity raw materials, an improper drawing process can still lead to a high wire breakage rate.

[0172] (III) Analysis of the impact of drawing process on strength, grain size and surface quality

[0173] As shown in Table 2, the grain size of Examples 1-4 reaches 10.5-11.5, which is much finer than the 7.5-8.5 level of Comparative Examples 1-3. This invention employs a gradient decreasing deformation amount per pass (initial stage 25%-35% → intermediate stage 15%-25% → fine stage 8%-15%), combined with dynamically matched annealing temperatures (initial 950-1050℃ → intermediate 850-950℃ → fine stage 700-850℃), ensuring that the grains are sufficiently refined at each stage without abnormal growth.

[0174] The grain size of Comparative Example 4 is grade 9.0, which is worse than Comparative Examples 1-3 but still not as good as Examples 1-4. This indicates that the grain refinement effect of composition optimization combined with traditional drawing process is not as good as that of composition optimization combined with gradient deformation process.

[0175] Regarding surface roughness, the Ra values ​​of Examples 1-4 were 0.08-0.15 μm, which were far superior to the 0.25-0.35 μm of Comparative Examples 1-3 and the 0.20 μm of Comparative Example 4. This is due to the combined effect of ultra-low inclusion content, nanodiamond lubricant, and electropolishing.

[0176] (iv) Contribution analysis of relative precipitation intensity

[0177] Table 2 shows that V / Nb nanocarbonitride precipitates were detected in Examples 1-4, with an average size of 25-42 nm and a number density of 0.9 × 10⁻³ to 1.6 × 10⁻³ precipitates / μm³. No nanoprecipitates were detected in Comparative Examples 1-3 because they contained no V or Nb or had very low concentrations. Although Comparative Example 4 contained V and Nb, the annealing temperature was too low (750℃), resulting in an average precipitate size of 60 nm and a number density of only 0.4 × 10⁻³ precipitates / μm³. The coarse and sparse precipitates significantly reduced the strengthening effect.

[0178] The dispersion strengthening effect of nanoprecipitates is one of the key mechanisms for achieving tensile strength exceeding 2400 MPa in the examples. Orowan strengthening mechanism calculations show that when the precipitate size is 25~35 nm and the number density is ≥1.0×10⁻³ particles / μm³, its contribution to strength can reach 400~600 MPa.

[0179] (V) Comparative Analysis of Gradient Deformation and Traditional Fixed Deformation

[0180] As can be seen from the comparison of Tables 3 and 4, under the same wire diameter conditions, the tensile strength of Example 1 at each stage is higher than that of Comparative Example 1, while the grain size is finer and the surface roughness is better. Especially in the fine drawing stage (0.08mm→0.015mm), the deformation per pass of Example 1 is only 8%~12%, which is much smaller than the 40% of Comparative Example 1, thus avoiding excessive work hardening and accumulation of surface defects caused by excessive deformation.

[0181] In terms of wire breakage rate, Comparative Example 1 experienced frequent wire breakage in the later stages of drawing (finished product wire breakage rate of 22 times / ton), while Example 1's online eddy current testing detected two potential defects early on and eliminated them through corrective drawing, resulting in a final wire breakage rate of only 4.2 times / ton. This fully demonstrates the effectiveness of the closed-loop corrective drawing strategy.

[0182] (vi) Optimization analysis of process parameters

[0183] As shown in Table 5, annealing at 900℃ is the optimal temperature during the intermediate drawing stage—at this temperature, the tensile strength is 2150 MPa, the elongation is 1.8%, the grain size is grade 10.0, and the overall performance is the best. When the annealing temperature is below 850℃, recrystallization is insufficient, resulting in high strength but insufficient plasticity; when the annealing temperature is above 950℃, the grains grow excessively, and the strength decreases significantly (down to 1750 MPa at 1000℃).

[0184] As shown in Table 6, the optimal deformation per pass in the fine drawing stage is 10%~12%, at which point the tensile strength of the finished product is 2510~2560MPa, and the wire breakage rate is only 4.2~4.5 times / ton. If the deformation is too small (5%), the work hardening is insufficient, and the strength is only 2150MPa, which does not meet the standard; if the deformation is too large (18%), the work hardening is excessive, and the wire breakage rate increases dramatically to 12 times / ton.

[0185] (vii) Comprehensive analysis of the inventiveness of this invention

[0186] Based on the above analysis, the inventiveness of this invention is reflected in the following aspects:

[0187] First, the synergistic design of the alloy composition is not obvious. The synergistic ratio of multiple elements such as Cu, Co, V, Nb, and N is not a simple superposition of the effects of each element. Comparative Examples 2 and 3 show that adding only some elements cannot achieve the high strength level of this invention. The solid solution strengthening of Cu, the stacking fault energy regulation of Co, and the nano-precipitation strengthening of V / Nb have a synergistic effect, and none of them can be omitted.

[0188] Secondly, the control limit of O content ≤8ppm in the smelting process exceeds the level of conventional smelting. The O content in traditional stainless steel smelting is usually 15~25ppm. This invention reduces the O content to below 8ppm through a three-stage refining process of vacuum induction + argon-oxygen decarburization + electroslag remelting, achieving unexpected technical results (a reduction of more than 60% in wire breakage rate).

[0189] Third, the synergistic design of gradient pass deformation and dynamic matching annealing is not easily conceived by those skilled in the art. Comparative Example 4 shows that even with the same alloy composition, changing only the drawing process (fixing the deformation amount to 40%) cannot achieve the strength and wire breakage rate targets of this invention. This illustrates that the selection of process conditions is not simply a matter of optimizing parameters, but rather has a synergistic matching relationship with the alloy design.

[0190] In summary, the ultra-high strength ultrafine stainless steel microwires and their preparation method provided by this invention have a clear process route, are highly operable, and utilize commonly used equipment in the field, making them suitable for large-scale industrial production. The stainless steel microwires prepared according to this invention have a diameter of 0.01~0.03mm, a tensile strength ≥2400MPa, and a breakage rate ≤5 times / ton, fully meeting the stringent strength requirements (≥2400MPa) for screen printing meshes used in high-end photovoltaic panels. They can also be used in fields with extremely high strength and precision requirements, such as precision medical device sutures, artificial vascular stents, and high-end precision filter components, demonstrating broad market application prospects.

[0191] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A type of ultra-high strength ultrafine stainless steel microwire, characterized in that, The chemical composition of the stainless steel microwire, by mass percentage, includes: C: 0.01%~0.05%, Si: 0.10%~0.50%, Mn: 1.0%~2.0%, P≤0.020%, S≤0.003%, Ni: 8.00%~9.50%, Cr: 18.00%~20.50%, Cu: 0.80%~1.50%, Mo: 0.50%~1.20%, N: 0.12%~0.22%, V: 0.05%~0.25%, Nb: 0.05%~0.20%, Co: 0.05%~0.30%, O≤8ppm, H≤2ppm, with the balance being Fe and unavoidable impurities; the diameter of the microwire is 0.01~0.03mm, the tensile strength is ≥2400MPa, and the wire breakage rate is ≤5 times / ton.

2. The ultra-high strength ultrafine stainless steel microwire and its preparation method according to claim 1, characterized in that, The microfilaments have a grain size ≥10, a surface roughness Ra ≤0.2μm, and an elongation ≥1.5%.

3. A method for preparing ultra-high strength ultrafine stainless steel microwires as described in claim 1 or 2, characterized in that, Includes the following steps: Step 1: Prepare the billet by mixing the chemical components according to claim 1 and using a smelting process of vacuum induction smelting, argon-oxygen decarburization refining and gas-protected electroslag remelting. During the electroslag remelting process, control the slag basicity R=1.8~2.5, add slag containing CaO and MgO, so that the Al content in the steel is controlled below 0.005% and the O content is ≤8ppm. Step 2: Homogenize the billet at 1100~1180℃ for 4~8 hours, then roll it into wire rod with a diameter of 5.0~6.5mm using continuous hot rolling. The final hot rolling temperature is controlled at 950~1050℃, and the billet is then water-cooled to room temperature. Step 3: Solution treat the hot-rolled wire rod at 1050~1100℃ for 30~60 minutes, then quench it with water to obtain a uniform austenitic structure with grain size controlled at 7~9. Step 4: The solution-treated wire rod is subjected to multiple cold drawing passes, and annealing is performed after each drawing pass. The deformation amount and annealing temperature decrease in a gradient as the wire diameter decreases. Step 5: Perform electrolytic polishing and passivation treatment on the finished microfilaments to obtain a finished product with a surface roughness Ra≤0.2μm.

4. The method for preparing ultra-high strength ultrafine stainless steel microwires according to claim 3, characterized in that, In step four, the gradient deformation amount is as follows: in the initial drawing stage, the wire diameter is drawn from 5.0~6.5mm to 0.5~1.0mm, and the deformation amount is controlled at 25%~35%; in the intermediate drawing stage, the wire diameter is drawn from 0.5~1.0mm to 0.05~0.10mm, and the deformation amount is controlled at 15%~25%; in the fine drawing stage, the wire diameter is drawn from 0.05~0.10mm to the target diameter of 0.01~0.03mm, and the deformation amount is controlled at 8%~15%.

5. The method for preparing ultra-high strength ultrafine stainless steel microwires according to claim 3, characterized in that, In step four, the annealing temperature is a dynamically matched annealing temperature: the annealing temperature for the initial drawing stage is 950~1050℃, the annealing temperature for the intermediate drawing stage is 850~950℃, and the annealing temperature for the fine drawing stage is 700~850℃; the annealing speed gradually decreases from 15~25m / min in the initial stage to 5~10m / min in the fine stage as the wire diameter decreases; the holding time for each annealing pass is 30~120 seconds, and the protective atmosphere is at least one of hydrogen, argon, or a hydrogen-argon mixture.

6. The method for preparing ultra-high strength ultrafine stainless steel microwires according to claim 3, characterized in that, In step four, after each drawing pass, online eddy current testing is used to detect surface defects. When surface microcracks or inclusion signals are detected, an additional drawing pass with a deformation of 5% to 8% is added and the material is re-annealed. The online eddy current testing frequency is 10 to 50 kHz, and the detection sensitivity is ≥1 μm for defect depth.

7. The method for preparing ultra-high strength ultrafine stainless steel microwires according to claim 3, characterized in that, In step one, the vacuum degree of vacuum induction smelting is ≤10Pa, the smelting temperature is 1550~1620℃, and the refining time is 30~60 minutes; the final temperature of argon-oxygen decarburization refining is 1600~1680℃, and the final oxygen activity is ≤5ppm; the melting rate of electroslag remelting is controlled at 3~8kg / min, and the flow rate of cooling water in the crystallizer is 8~15m³ / h.

8. The method for preparing ultra-high strength ultrafine stainless steel microwires according to claim 3, characterized in that, The homogenization process described in step two is carried out under an argon protective atmosphere with an oxygen content ≤100ppm in the furnace; the hot rolling process is carried out in 12 to 18 passes of continuous rolling with a total deformation of ≥90% and the grain size of the hot-rolled wire rod is controlled at level 5 to 7.

9. The method for preparing ultra-high strength ultrafine stainless steel microwires according to claim 3, characterized in that, The cold drawing in step four uses a diamond wire drawing die with a die compression angle of 10°~16°, a sizing strip length of 20%~40% of the die diameter, a drawing lubricant of oil-based wire drawing oil containing nano-diamond particles with an average particle size of 10~50nm, a lubricant temperature of 35~55℃, and a drawing speed of 30~80m / min.

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