Titanium microalloying high-purity 50 # cold-rolled steel strip special for precision measuring tape rack and preparation process of titanium microalloying high-purity 50 # cold-rolled steel strip

Abstract

The invention discloses a titanium microalloying high-purity 50 # cold-rolled steel strip special for a precision measuring tape rack and a preparation technology of the titanium microalloying high-purity 50 # cold-rolled steel strip, and belongs to the technical field of metal pressure machining and special steel strip preparation. Through converter-LF-RH triple smelting and calcium treatment, the inclusion content is reduced, and the fatigue life is prolonged by about 67%; the precise control of the thickness tolerance of + / -0.01 mm is realized by adopting a six-roller CVC rolling mill and laser thickness measurement closed-loop control, and the problem of wire jumping is solved; through optimized gradient heat treatment, the hardness fluctuation is smaller than or equal to 5 HB, the tensile strength fluctuation is smaller than or equal to 10 MPa, and the performance uniformity is guaranteed; the friction coefficient of the tooth surface is reduced to 0.20-0.25 from 0.35-0.40 through the zinc-manganese phosphating film, so that the meshing reliability is effectively improved; the whole process is optimized, so that the cold rolling pass is reduced, the annealing time is shortened, the comprehensive cost is reduced by about 25%, and the unification of high quality and high benefit is realized.

Description

Technical Field

[0001] This invention belongs to the field of metal pressure processing and special steel strip preparation technology, specifically relating to a 50# cold-rolled steel strip for titanium microalloyed high-purity precision measuring tape racks and its preparation process. Background Technology

[0002] As a precision measuring tool used in construction engineering, interior decoration, and daily household applications, the accuracy of steel tape measures and their long-term reliability fundamentally depend on the comprehensive performance of their core transmission component—the tape measure rack. This rack is typically made of 50# cold-rolled steel strip through precision stamping or milling. Therefore, the material quality and manufacturing process of the steel strip directly determine the final performance of the rack.

[0003] Currently, the industry faces a series of interconnected technical challenges in producing such specialized cold-rolled steel strips using traditional processes. Firstly, regarding material purity, mainstream smelting processes largely remain at the "converter-LF refining" stage, lacking efficient vacuum degassing (such as RH) steps. This results in incomplete removal of gaseous impurities such as oxygen, nitrogen, and hydrogen, as well as various non-metallic inclusions, from the molten steel. These residual inclusions become the origin of microcracks during subsequent processing and use, significantly reducing the material's fatigue strength. Consequently, the final racks are prone to premature fracture during frequent bending cycles, impacting the product's service life.

[0004] Secondly, in terms of dimensional accuracy control, the traditional cold rolling process suffers from relatively outdated strip shape control technology, resulting in significant fluctuations in steel strip thickness tolerance. When using steel strips with uneven thickness to process tooth profiles, it directly causes significant deviations in tooth pitch. This deviation can easily lead to meshing failure of the rack and gear during the tape measure's pulling and retracting process, a common phenomenon known as "slipping," which severely disrupts measurement consistency and user experience.

[0005] Furthermore, the uniformity of steel strip performance is also a pain point in the industry. Due to the rough control of hot rolling and subsequent heat treatment process parameters, the hardness and tensile strength of the same coil of steel strip fluctuate significantly along its length. This non-uniformity of performance is transmitted to the rack, resulting in significant differences in wear resistance and fatigue resistance in different sections, leading to large fluctuations in product life and making it difficult to guarantee batch quality consistency.

[0006] Furthermore, surface quality defects and heat treatment deformation are equally prominent issues. From surface flaws in continuously cast billets to residual iron oxide scale from hot rolling, these can all form defects such as pitting and scratches on the surface of the cold-rolled steel strip, affecting the surface finish and lubrication of the gear teeth. At the same time, traditional quenching and tempering heat treatment, due to insufficient temperature control precision, is prone to uneven microstructure transformation and residual stress concentration, leading to deformation of the gear rack after heat treatment, making it difficult to meet the high-precision assembly requirements.

[0007] To address these challenges, existing technological solutions still have significant limitations. For example, while high-carbon, high-alloy designs can improve strength, they often come at the cost of sacrificing toughness and significantly increasing material and processing costs. Furthermore, optimization of traditional 50 steel often fails to comprehensively improve hardness, precision, or wear resistance due to inadequate steel composition design and process routes. More critically, existing solutions primarily focus on localized improvements to single processes, lacking comprehensive and systematic process coordination and quality control across smelting, rolling, heat treatment, and surface treatment. Consequently, they struggle to fundamentally achieve a stable leap in the overall performance of the product.

[0008] Therefore, developing a special cold-rolled steel strip with high purity, high dimensional accuracy, excellent performance uniformity, good surface condition, and controllable cost, as well as its entire manufacturing process, has become an urgent need to promote the performance upgrade of high-end tape measure racks and solve common technical problems in the industry. Summary of the Invention

[0009] This invention discloses a 50# cold-rolled steel strip for high-purity precision measuring tape racks made of titanium microalloyed, and its preparation process. It is particularly suitable for solving technical problems in the manufacturing of high-end measuring tape racks, such as wire skipping, breakage, and assembly accuracy defects caused by insufficient steel strip purity, large dimensional fluctuations, and high surface friction coefficients.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, this invention provides a method for preparing titanium-containing 50# cold-rolled steel strip for high-uniformity anti-slip toothed measuring tape racks, comprising the following steps: (1) Set the Si / Mn ratio in the molten steel to Si=0.35%-0.45% and Mn=0.8%-0.9%, and introduce the microalloying element Ti, controlling its content at 0.015%-0.025%; (2) The smelting process is carried out by a converter-LF refining-RH vacuum degassing triple process; during the RH vacuum degassing process, the vacuum degree is controlled to be ≤67 Pa and the degassing time is ≥25 min; and calcium treatment is carried out to obtain steel billets; (3) The obtained steel billet is hot rolled, and the final rolling temperature is controlled at 830-870℃ and the coiling temperature is 620-670℃; (4) The obtained hot-rolled steel strip is subjected to six-roll cold rolling with a cold rolling rate of 60%-65%. The thickness tolerance of the cold-rolled steel strip is controlled within ±0.01mm, and the thickness of the cold-rolled steel strip is 0.77-0.80mm. (5) The cold-rolled steel strip is subjected to quenching and tempering treatment using dual-furnace temperature control technology; (6) The steel strip after step (4) is subjected to zinc-manganese phosphate treatment, and the free acidity of the phosphate solution is controlled to be 10-15 points and the total acidity is 80-100 points, so as to form a phosphate film with a thickness of 2-3 μm on the surface of the steel strip.

[0011] In step (1), the chemical composition of the molten steel used in the smelting is as follows by mass percentage: C: 0.50-0.51%, Si: 0.35-0.45%, Mn: 0.8-0.9%, Ti: 0.015-0.025%, Al: 0.025-0.030%, P≤0.015%, S≤0.010%, with the balance being Fe.

[0012] In step (2), the amount of calcium treatment agent added in the calcium treatment is 0.8-1.0 kg / t steel.

[0013] In step (6), the chemical composition of the zinc-manganese phosphating solution used is as follows by mass percentage: ZnO 2-3%, Mn(H2PO4)2 8-10%, H3PO4 5-7%, NaNO2 0.3-0.5%, citric acid 0.2-0.4%, and the remainder is deionized water.

[0014] To achieve a balance between strength and toughness in steel strip, this invention carefully adjusts the chemical composition. The Si / Mn ratio is set to Si = 0.35%-0.45% and Mn = 0.8%-0.9%. Through solid solution strengthening, sufficient strength is ensured while maintaining good toughness, resulting in an elongation ≥18%. Furthermore, the microalloying element Ti is introduced, with its content controlled at 0.015%-0.025%. Ti can combine with N and C to form TiN and TiC fine particles. These particles effectively inhibit grain growth and refine the grain structure during the solidification and heating process of the steel. Simultaneously, they improve the morphology of inclusions, reducing the harm caused by inclusions as crack initiation sites, thereby enhancing the overall performance of the steel strip.

[0015] In the smelting process, a three-stage smelting process of "converter-LF refining-RH vacuum degassing" is adopted. This process achieves efficient removal of gaseous impurities and inclusions by strictly controlling key parameters. During RH vacuum degassing, the vacuum degree is controlled at ≤67Pa and the degassing time is ≥25min. Under these conditions, gaseous impurities such as oxygen (O), nitrogen (N), and hydrogen (H) in the molten steel can fully escape, significantly reducing their content in the steel. Simultaneously, calcium treatment is performed, and the amount of calcium treatment agent added is precisely controlled to make inclusions such as MnS spherically distributed, effectively improving the morphology and distribution of inclusions, reducing the inclusion rating from level 2.0 in traditional processes to ≤1.0, significantly improving the purity of the steel strip and extending its fatigue life. The cold rolling stage is crucial for ensuring the dimensional accuracy of the steel strip. This invention employs a six-roll CVC mill combined with a laser thickness measurement closed-loop control system to achieve precise control of the steel strip thickness, strictly controlling the thickness tolerance within ±0.01mm, while ensuring a flatness of ≤5I units. Furthermore, an online surface inspection system with a resolution of 0.01mm is introduced to monitor the surface quality of the steel strip in real time. Any steel strip with surface defects is immediately rejected, effectively improving the product yield to over 98%, ensuring that all steel strips entering subsequent processing stages possess excellent dimensional accuracy and surface quality.

[0016] Preferably, step (4) further includes the step of using an online surface inspection system to monitor the surface quality of cold-rolled steel strip in real time and remove defective steel strips, wherein the resolution of the online surface inspection system is not less than 0.01 mm.

[0017] To achieve a uniform martensitic transformation and reduce residual stress, this invention optimizes the heat treatment process. During the quenching and tempering process, a dual-furnace temperature control technology is employed, achieving a temperature control accuracy of ±5℃. Specifically, the steel strip is first austenitized at 860±5℃ and held for 30 minutes to ensure full austenitization. Then, it is tempered at 480±5℃ for 60 minutes. Through precise temperature and time control, a uniform martensitic transformation is achieved, reducing residual stress by up to 60%. Subsequently, the tempered steel strip undergoes low-temperature annealing at 550±10℃ for 2 hours. This process effectively eliminates work hardening generated during cold rolling while maintaining a hardness of 290-330 HV0.5, meeting subsequent application requirements.

[0018] To address the meshing characteristics of measuring tape racks, this invention employs a zinc-manganese phosphating process to treat the steel strip surface. Strict control of phosphating process parameters is maintained, with free acidity at 10-15 and total acidity at 80-100, forming a phosphating film with a thickness of 2-3 μm on the steel strip surface. This phosphating film effectively reduces the tooth surface friction coefficient from 0.35-0.40 in traditional processes to 0.20-0.25, significantly reducing the occurrence of wire skipping, improving the meshing reliability of the rack and gear, and reducing the probability of meshing failure to <1%.

[0019] Through the comprehensive application of a series of technical measures, including chemical composition optimization, full-process purity control, high-precision rolling process, gradient heat treatment, and surface functionalization, the No. 50 cold-rolled steel strip of this invention has achieved significant improvements in purity, dimensional accuracy, performance uniformity, and surface quality. At the same time, it has reduced production costs, reduced the number of cold rolling passes by 30%, shortened the annealing time by 40%, and reduced the overall cost by 25%. It meets the precision manufacturing requirements of high-end tape measure racks and has important industrial application value and market competitiveness.

[0020] In a second aspect, the present invention provides a titanium-containing 50# cold-rolled steel strip for a high-uniformity anti-slip toothed measuring tape rack prepared by the above method, wherein the cold-rolled steel strip simultaneously meets the following performance indicators: a) Thickness is 0.77-0.80 mm, with a thickness tolerance of ±0.01 mm; b) Non-metallic inclusions are rated ≤1.0, with oxygen content ≤0.0025% and nitrogen content ≤0.008%; c) The surface is covered with a zinc-manganese phosphate film with a thickness of 2-3 μm, and the tooth surface friction coefficient based on this phosphate film is 0.20-0.25; d) Its metallographic structure is uniform tempered sorbite with a hardness of 290-330 HV0.5 and a hardness fluctuation of ≤5 HB; e) The tensile strength is 770-800 MPa, and the tensile strength fluctuation is ≤10 MPa; f) Surface defect control requirements: pitting depth < 0.01 mm, scratch incidence rate < 0.5 scratches / meter.

[0021] In a third aspect, the present invention provides the application of the above-mentioned high-uniformity anti-slip tape measure toothed rack with titanium-containing 50# cold-rolled steel strip in the manufacture of high-precision tape measure toothed racks.

[0022] Preferably, the tooth pitch deviation of the high-precision measuring tape rack is ≤ ±0.02 mm.

[0023] The beneficial effects of this invention are: 1. This invention utilizes a three-stage smelting process of "converter-LF refining-RH vacuum degassing" and calcium treatment to significantly reduce the content of gaseous impurities in steel (O≤0.0025%, N≤0.008%), lowering the inclusion rating from 2.0 in traditional processes to ≤1.0, and resulting in a spherical distribution of MnS inclusions. This significantly reduces internal defects in the steel strip and extends the fatigue crack initiation period to 5×10⁻⁶. 5 Next, compared to traditional processes (3×10) 5 The speed improvement is approximately 67%, significantly enhancing the service life and reliability of the rack under repeated bending conditions.

[0024] 2. This invention employs a six-roll CVC mill combined with laser thickness measurement closed-loop control to achieve high-precision control of cold-rolled steel strip thickness tolerance to ±0.01mm and flatness ≤5I units. Based on this steel strip, the tooth pitch deviation of the measuring tape rack can be controlled within ±0.015mm, fully meeting the ISO13920 precision rack processing standard. This fundamentally solves the problem of wire skipping caused by thickness fluctuations, ensuring the consistency and accuracy of measuring tape measurements.

[0025] 3. This invention achieves uniform martensitic transformation and reduces residual stress by 60% through an optimized gradient heat treatment process (dual-furnace temperature control ±5℃). The final steel strip hardness fluctuation is ≤5HB, tensile strength fluctuation is ≤10MPa, and the wear resistance difference between different parts of the rack is less than 5%. This high performance uniformity ensures consistent overall performance of the rack during use, avoiding premature local wear or breakage.

[0026] 4. This invention combines zinc-manganese phosphate surface treatment, resulting in a steel strip surface pit depth of <0.01mm, a scratch incidence rate of <0.5 scratches / meter, and 100% phosphate film coverage. The phosphate film thickness is 2-3μm, reducing the tooth surface friction coefficient from the traditional 0.35-0.40 to 0.20-0.25, a reduction of 40%, improving meshing reliability by 90%, and effectively eliminating wire skipping.

[0027] 5. This invention, through full-process system integration and process parameter optimization, reduces the number of cold rolling passes from 5 to 3, shortens the annealing time from 6 hours to 3.5 hours, and reduces overall energy consumption by 22%. While achieving higher performance indicators, production costs are reduced by approximately 25%, achieving a balance between high quality and low cost, and possessing outstanding market competitiveness and industrial application value. Attached Figure Description

[0028] Figure 1 The present invention provides a flow chart of the cold-rolled steel strip manufacturing process.

[0029] Figure 2 This is a metallographic image of the hot-rolled steel strip used as the base material in Example 1 of the present invention, with a scale of 50 μm.

[0030] Figure 3 This is a metallographic image of the cold-rolled annealed steel strip in Embodiment 1 of the present invention, with a scale of 20 μm.

[0031] Figure 4 This is a metallographic image of the quenched and tempered steel strip in Example 1 of the present invention, with a scale of 20 μm. Detailed Implementation

[0032] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0033] Addressing the key technical problems commonly found in existing 50# cold-rolled steel strips used for measuring tape toothed racks, such as low purity, insufficient dimensional accuracy, uneven strip performance, and susceptibility to wire skipping defects, this invention aims to provide a 50# cold-rolled steel strip with optimized chemical composition and a method for manufacturing it that implements coordinated control throughout the entire process of smelting, rolling, heat treatment, and surface treatment. The core objective of this invention is to optimize production costs while improving overall product performance through systematic technological innovation, specifically pursuing the following goals: 1) High purity: Reduces gaseous impurities (O≤0.0025%, N≤0.008%) and inclusions (rating ≤1.0), increasing fatigue life by 50%; 2) High precision: thickness tolerance ±0.01mm, tooth pitch deviation ≤±0.02mm, meeting the requirements for precision rack machining; 3) Anti-spinning: Through surface phosphating treatment and dimensional accuracy control, the coefficient of friction of the tooth surface is reduced to 0.20-0.25, and the probability of meshing failure is <1%; 4) Uniform performance of the rack: tensile strength fluctuation ≤10MPa, hardness fluctuation ≤5HB, and consistency of all parts of the rack improved by 80%; 5) Low-cost process: Cold rolling passes are reduced by 30%, annealing time is shortened by 40%, and overall cost is reduced by 25%.

[0034] To achieve the above objectives, the present invention employs the following key technical solutions that support and synergistically complement each other: First, the chemical composition was optimized at the material design level. This invention breaks through the traditional Si and Mn element ratio range of 50 steel (Si=0.2%-0.3%, Mn=0.6%-0.7%), setting the Si content to 0.35%-0.45% and the Mn content to 0.8%-0.9%. This ratio effectively improves the strength of the steel strip through solid solution strengthening mechanism, while also taking into account good toughness, ensuring an elongation of ≥18%. In addition, 0.015%-0.025% of the microalloying element titanium (Ti) was creatively introduced. Titanium can form fine TiN and TiC precipitates in steel. These particles can effectively inhibit the growth of austenite grains during heating, playing a role in refining the final grain structure. At the same time, it can also improve the morphology of inclusions, reduce their harmfulness, and lay the microstructure foundation for obtaining uniform high performance.

[0035] Secondly, a complete purity control process system was constructed. In the smelting stage, this invention abandons the traditional single or dual-process approach and innovatively adopts a three-stage high-efficiency smelting process: "converter primary smelting - LF furnace refining - RH vacuum degassing". During this process, by strictly controlling the vacuum degree of RH vacuum degassing to ≤67Pa and ensuring a degassing time of no less than 25 minutes, efficient and deep removal of gaseous impurities such as oxygen (O), nitrogen (N), and hydrogen (H) from the molten steel is achieved. Simultaneously, a precise calcium treatment process is implemented. By controlling the amount of calcium treatment agent added, the main plastic inclusions in the steel, such as MnS, are transformed into spherical or near-spherical shapes, thereby significantly improving the morphology and distribution of inclusions. The overall inclusion rating is drastically reduced from level 2.0 in traditional processes to ≤1.0, greatly improving the purity of the steel.

[0036] Third, it integrates high-precision rolling and inspection technologies. In the cold rolling stage, which determines the final dimensional accuracy of the product, this invention employs a six-roll CVC mill with advanced shape control capabilities and integrates a laser thickness gauge to form a closed-loop thickness control system. This achieves millimeter-level precise control of the strip thickness during rolling, ultimately stabilizing the finished product thickness tolerance at ±0.01mm and controlling the strip flatness to ≤5I units. To further ensure surface quality, an online surface inspection system with a resolution of up to 0.01mm is introduced to perform real-time, full inspection of the steel strip surface. This system can instantly identify and remove sections with defects such as pitting and scratches, thereby increasing the overall product yield to over 98%.

[0037] Fourth, a gradient-based precision heat treatment process was developed. To address the challenges of performance uniformity and residual stress, this invention features a refined design for the heat treatment regime. In the quenching and tempering stage, a dual-furnace system with a temperature control accuracy of ±5℃ is employed. First, austenitization is performed at 860±5℃ and held for 30 minutes, followed by tempering at 480±5℃ for 60 minutes. This precise gradient temperature control process ensures a uniform transformation of the martensitic structure, reducing residual stress after heat treatment by 60%. Subsequently, the quenched and tempered steel strip undergoes low-temperature annealing at 550±10℃ and held for 2 hours. This process effectively eliminates work hardening caused by cold rolling and maintains the steel strip within the ideal hardness range of 290-330 HV0.5, perfectly matching the dual requirements of hardness and machinability for gear racks.

[0038] Fifth, targeted surface functionalization treatment was implemented. Addressing the tribological characteristics of the measuring tape rack meshing pair, this invention specifically employs zinc-manganese phosphating surface treatment technology. By precisely controlling the free acidity (10-15 points) and total acidity (80-100 points) in the phosphating solution, a uniform, dense, and strongly adherent phosphating film is prepared on the steel strip surface, with a film thickness controlled at 2-3 μm. This phosphating film significantly reduces the coefficient of friction of the tooth surface, drastically decreasing it from 0.35-0.40 in the traditional untreated or ordinary treated state to 0.20-0.25, a reduction of up to 40%. This fundamentally reduces resistance and the risk of jamming during meshing, making it a key surface technology measure for solving the problem of wire skipping.

[0039] Through the organic combination and full-process implementation of the above five technical measures, the No. 50 cold-rolled steel strip and the toothed racks manufactured by this invention have achieved significant invention effects: in terms of purity, the actual oxygen content can be as low as 0.0021%, the nitrogen content is 0.0072%, the inclusion rating is 1.0, and the fatigue crack initiation cycle is extended to 5×10 5 In terms of precision, the thickness tolerance is ±0.01mm and the pitch deviation is only ±0.015mm; in terms of uniformity, the tensile strength fluctuation is about 8MPa and the hardness fluctuation is about 4HB; in terms of surface and meshing performance, the pitting depth is <0.01mm, the phosphating film coverage is 100%, and the meshing reliability is improved by 90%; in terms of process economy, the number of cold rolling passes has been successfully reduced from 5 to 3, the annealing time has been shortened from 6 hours to 3.5 hours, and the overall production cost has been reduced by about 25%.

[0040] The specific embodiments of the present invention will be described in further detail below with reference to examples. The following detailed descriptions are illustrative and intended to provide further explanation of this application, rather than limiting the scope of the invention.

[0041] The performance testing indicators in the examples are all based on the corresponding national standards, among which: Purity: According to GB / T 10561-2005 "Standard Rating Chart Microscopic Examination Method for Determination of Non-metallic Inclusion Content in Steel"; Thickness tolerance: in accordance with GB / T 708-2016 "Dimensions, shape, weight and permissible deviations of cold-rolled steel sheets and strips"; Tooth pitch deviation: in accordance with ISO 13920:2015 "Technical conditions for delivery of steel for welded structures"; Tensile strength: According to GB / T 228.1-2010 "Metallic materials, tensile testing - Part 1: Test at room temperature"; Hardness: According to GB / T 4340.1-2009 "Metallic materials - Vickers hardness test - Part 1: Test method"; Pitting depth: According to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test"; Coefficient of friction: According to GB / T 10006-1988 "Determination of coefficient of friction of plastic films and sheets".

[0042] Example 1 1. Chemical composition of molten steel (mass percentage) Chemical composition (wt%): C=0.50, Si=0.40, Mn=0.85, P=0.012, S=0.008, Ti=0.020, Al=0.025, balance Fe.

[0043] 2. Preparation process: Smelting: A 150-ton converter is used for primary smelting. After tapping the steel from the converter, it is refined by LF for 40 minutes and degassed by RH vacuum for 30 minutes (vacuum degree 50Pa, degassed time 30 minutes). After degassed, calcium treatment is carried out with a calcium treatment agent addition of 0.8 kg / t steel. After treatment, steel billets are obtained.

[0044] Hot rolling: The steel billet is heated to 1100℃, the initial rolling temperature is 1050℃, the final rolling temperature is 850℃, and the coiling temperature is 650℃ to obtain hot-rolled steel coils. Cold rolling: Hot-rolled steel coils are cold rolled using a six-roll CVC mill with a cold rolling rate of 60%, and the thickness is rolled from 2.0mm to 0.8mm. The online thickness measurement accuracy is ±0.005mm. During the rolling process, a laser thickness gauge is integrated for closed-loop thickness control, and an online surface inspection system with a resolution of 0.01mm is used for real-time monitoring. Heat treatment: Performed on a dual-furnace continuous heat treatment line. First, austenitization is carried out in the 860℃ furnace section, held for 30 minutes, and then quenched. Subsequently, tempering is performed in the 480℃ furnace section, held for 60 minutes. After quenching and tempering, it is held in a low-temperature annealing furnace at 550℃ for 2 hours, followed by air cooling.

[0045] Phosphating treatment: A zinc-manganese phosphating solution is used for treatment. The phosphating solution temperature is 55℃, the free acidity is 12 points, the total acidity is 90 points, and the treatment time is 15 minutes, forming a uniform phosphating film with a thickness of 2.5μm on the steel strip surface. The zinc-manganese phosphating solution formulation (mass percentage): ZnO 2.5%, Mn(H2PO4) 29%, H3PO4 6%, NaNO2 0.4%, citric acid 0.3%, and the balance is deionized water.

[0046] 3. Performance Indicators: Purity: O=0.0023%, N=0.0075%, inclusion rating 1.0; Dimensional accuracy: thickness tolerance ±0.008mm, tooth pitch deviation ±0.012mm; Mechanical properties: tensile strength 780MPa (fluctuation 8MPa), hardness 295HV0.5 (fluctuation 4HB); Surface quality: pitting depth 0.005mm, coefficient of friction 0.22, skip rate 0.8%; Processing efficiency: 3 cold rolling passes.

[0047] Example 2: 1. Chemical composition of molten steel (mass percentage) Chemical composition (wt%): C=0.51, Si=0.42, Mn=0.88, P=0.010, S=0.006, Ti=0.022, Al=0.028, balance Fe.

[0048] 2. Preparation process: Smelting: A 150-ton converter is used for primary smelting, with RH vacuum degassing time of 35 minutes (vacuum degree 40 Pa, degassing time 35 minutes). After degassing, calcium treatment is carried out, with calcium treatment agent added at a rate of 1.0 kg / t steel. After treatment, steel billets are obtained.

[0049] Hot rolling: The billet is heated to 1100℃, the initial rolling temperature is 1050℃, the final rolling temperature is 830℃, and the coiling temperature is 630℃. Cold rolling: Hot-rolled steel coils are cold rolled using a six-roll CVC mill with a cold rolling rate of 65%, and the thickness is rolled from 2.2mm to 0.77mm. The online thickness measurement accuracy is ±0.005mm. During the rolling process, a laser thickness gauge is integrated for closed-loop thickness control, and an online surface inspection system with a resolution of 0.01mm is used for real-time monitoring. Heat treatment: Performed on a dual-furnace continuous heat treatment line. First, austenitization is carried out in the 855℃ furnace section, held for 35 minutes, and then quenched. Subsequently, tempering is carried out in the 485℃ furnace section, held for 55 minutes. After quenching and tempering, it is held in a low-temperature annealing furnace at 550℃ for 2 hours, followed by air cooling.

[0050] Phosphating treatment: A zinc-manganese phosphating solution is used for treatment. The phosphating solution temperature is 55℃, the free acidity is 12 points, the total acidity is 100 points, and the treatment time is 12 minutes, forming a uniform phosphating film with a thickness of 2.8μm on the steel strip surface. The zinc-manganese phosphating solution formulation (mass percentage): ZnO 3%, Mn(H2PO4)2 10%, H3PO4 7%, NaNO2 0.5%, citric acid 0.4%, and the balance is deionized water.

[0051] 3. Performance Indicators: Purity: O=0.0021%, N=0.0070%, inclusion rating: 0.8; Dimensional accuracy: thickness tolerance ±0.009mm, tooth pitch deviation ±0.015mm; Mechanical properties: tensile strength 795MPa (fluctuation 7MPa), hardness 305HV0.5 (fluctuation 3HB); Surface quality: coefficient of friction 0.21, skip rate 0.6%; Processing efficiency: 3 cold rolling passes.

[0052] Comparative Example 1: RH-free vacuum degassing process This comparative example uses a process of "converter → LF furnace refining" followed by direct calcium treatment and continuous casting, omitting the RH process. Except for the elimination of the RH vacuum degassing process, the chemical composition and smelting process are consistent with those of Example 2.

[0053] Performance testing: The gas content in the steel is significantly increased, with O content at 0.0040% and N content at 0.013%. The number of inclusions has increased, resulting in a rating of 2.0.

[0054] Comparative Example 2: Optimization of Chemical Composition of Molten Steel The Si and Mn content in the molten steel of this comparative example is in the conventional ratio (Si=0.25%, Mn=0.65%), without the addition of Ti, and the remaining chemical composition and smelting process are consistent with those of Example 2.

[0055] Performance results: The strength-toughness match of the steel strip is poor. Although the tensile strength reaches 760MPa, the tensile strength fluctuates by 38MPa, and the hardness of the strip fluctuates by 14HB.

[0056] Comparative Example 3: Traditional Heat Treatment Process This comparative example uses the same chemical composition and smelting and rolling process as Example 2, but the heat treatment method is changed. After cold rolling, a conventional one-time annealing process is used, holding at 720°C for 6 hours. The quenching and tempering treatment is omitted.

[0057] Performance results: The steel strip has a hardness of only 210HV0.5 and a tensile strength of 520MPa, which cannot meet the high strength requirements of the rack. Furthermore, the steel strip thickness tolerance is ±0.028mm, and the residual stress is high. After a period of time, the tooth profile changes slightly, resulting in an increase in the tooth pitch deviation to ±0.045mm.

[0058] Comparative Example 4: No surface phosphating treatment This comparative example uses the same chemical composition and smelting and rolling process as Example 2. After completing all metallurgical and heat treatment processes, the surface zinc-manganese phosphating solution treatment step is omitted, and conventional zinc-based phosphating solution treatment is used.

[0059] Performance results: The coefficient of friction of the steel strip reached as high as 0.38. The wire skipping rate increased sharply to 6.5%.

[0060] In summary, this invention establishes a comprehensive quality control system through chemical composition micro-alloying, a converter-LF-RH triple smelting process, high-precision rolling, and surface phosphating treatment. This significantly improves the purity, dimensional accuracy, and performance uniformity of No. 50 cold-rolled steel strip, effectively solving core problems such as wire skipping, breakage, and insufficient precision in traditional processes. Verification through examples shows that all indicators of the steel strip of this invention meet the precision manufacturing requirements of high-end measuring tape racks, and the production cost is reduced by 25% compared to traditional processes, demonstrating significant industrial application value and market competitiveness.

[0061] The above description is merely a preferred embodiment of this application and is not intended to limit the application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications made within the spirit and principles of this application are not permitted. Equivalent substitutions and improvements should all be included within the scope of protection of this application.

Claims

1. A method for preparing a high-uniformity anti-slip wire measuring tape toothed rack using titanium-containing 50# cold-rolled steel strip, characterized in that, Includes the following steps: (1) Set the Si / Mn ratio in the molten steel to Si=0.35%-0.45% and Mn=0.8%-0.9%, and introduce the microalloying element Ti, controlling its content at 0.015%-0.025%; (2) The smelting process is carried out by a converter-LF refining-RH vacuum degassing triple process; during the RH vacuum degassing process, the vacuum degree is controlled to be ≤67 Pa and the degassing time is ≥25 min; and calcium treatment is carried out to obtain steel billets; (3) The obtained steel billet is hot rolled, and the final rolling temperature is controlled at 830-870℃ and the coiling temperature is 620-670℃; (4) The obtained hot-rolled steel strip is subjected to six-roll cold rolling with a cold rolling rate of 60%-65%. The thickness tolerance of the cold-rolled steel strip is controlled within ±0.01mm, and the thickness of the cold-rolled steel strip is 0.77-0.80mm. (5) The cold-rolled steel strip is subjected to quenching and tempering treatment using dual-furnace temperature control technology; (6) The steel strip after step (4) is subjected to zinc-manganese phosphate treatment, and the free acidity of the phosphate solution is controlled to be 10-15 points and the total acidity is 80-100 points, so as to form a phosphate film with a thickness of 2-3 μm on the surface of the steel strip.

2. The preparation method according to claim 1, characterized in that, In step (1), the chemical composition of the molten steel used in the smelting is as follows by mass percentage: C: 0.50-0.51%, Si: 0.35-0.45%, Mn: 0.8-0.9%, Ti: 0.015-0.025%, Al: 0.025-0.030%, P≤0.015%, S≤0.010%, with the balance being Fe.

3. The preparation method according to claim 1 or 2, characterized in that, In step (2), the amount of calcium treatment agent added in the calcium treatment is 0.8-1.0 kg / t steel.

4. The preparation method according to claim 1, characterized in that, The dual-furnace temperature control technology is as follows: the temperature control accuracy is ±5℃; first, austenitize at 860±5℃ for 30-35 min, then temper at 480±5℃ for 55-60 min; then perform low-temperature annealing at 550±10℃ for 2-2.5 h.

5. The preparation method according to claim 1, characterized in that, In step (6), the phosphating treatment is carried out at a temperature of 50-60°C for 12-15 minutes. The chemical composition of the zinc-manganese phosphating solution used, by mass percentage, is as follows: ZnO 2-3%, Mn(H2PO4)2 8-10%, H3PO4 5-7%, NaNO2 0.3-0.5%, citric acid 0.2-0.4%, with the remainder being deionized water.

6. A titanium-containing 50# cold-rolled steel strip for a high-uniformity anti-slip wire measuring tape toothed rack prepared by the method described in any one of claims 1-5, characterized in that, The cold-rolled steel strip simultaneously meets the following performance indicators: a) Thickness is 0.77-0.80 mm, with a thickness tolerance of ±0.01 mm; b) Non-metallic inclusions are rated ≤1.0, with oxygen content ≤0.0025% and nitrogen content ≤0.008%; c) The surface is covered with a zinc-manganese phosphate film with a thickness of 2-3 μm, and the tooth surface friction coefficient based on this phosphate film is 0.20-0.25; d) Its metallographic structure is uniform tempered sorbite with a hardness of 290-330 HV0.5 and a hardness fluctuation of ≤5 HB; e) The tensile strength is 770-800 MPa, and the tensile strength fluctuation is ≤10 MPa; f) Surface defect control requirements: pitting depth < 0.01 mm, scratch incidence rate < 0.5 scratches / meter.

7. The application of the high uniformity anti-slip wire measuring tape rack of claim 6 in the manufacture of high precision measuring tape racks using titanium-containing 50# cold-rolled steel strip.

8. The application according to claim 7, characterized in that, The tooth pitch deviation of the high-precision measuring tape rack is ≤ ±0.02 mm.

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