A low-cost, easy-to-machine steel for jacquard needle cylinder and a manufacturing method thereof

Abstract

This invention discloses a low-cost, easily machinable steel for jacquard machine syringes and its manufacturing method. The elemental composition of this steel, by mass percentage, is: C: 0.45–0.51%, Si: 0.40–0.50%, Mn: 0.50–0.80%, Cr: 0.10–0.15%, P≤0.045%, S: 0.055–0.070%, Cu: 0.10–0.20%, Al: 0.010–0.030%, N: 0.008–0.012%, Ti: 0.015–0.035%, with the balance being Fe and unavoidable impurities. The diameter specification is φ250–300 mm. The manufacturing method includes converter high-strength carbon smelting, LF refining, RH / VD vacuum degassing (using nitrogen as the lifting gas), continuous casting (low superheat 30-45℃, M+F-EMS combined electromagnetic stirring, segmented large reduction), and rolling (total reduction rate of rough rolling ≥60%, single-pass reduction rate ≥30%). Through synergistic design of chemical composition and optimization of the entire process, the surface hardness of the steel after quenching is ≥58HRC, cutting efficiency is improved by more than 30%, tool life is extended by 2 times, and the overall manufacturing cost is reduced by more than 30%, solving the problems of poor machinability and high cost of traditional syringe steel.

Description

Technical Field

[0001] This invention belongs to the field of iron-based metal technology, specifically relating to a special steel for jacquard machine cylinders in textile machinery and its manufacturing method, and in particular to a low-cost, easy-to-process steel and its production process that ensures high hardness and high wear resistance while possessing excellent machinability. Background Technology

[0002] The continuous development and technological upgrading of the global textile industry have driven steady growth in the market demand for circular knitting machines, significantly increasing the demand for steel used in the manufacture of their core component—the cylinder. As the core region of the global textile industry, the Asia-Pacific region, leveraging its industrial cluster effect and labor cost advantages, has become a major consumer market for this type of steel. In the manufacture of conventional circular knitting machine cylinders, traditional medium carbon steel has long dominated due to its lower material cost and is widely used in the production of ordinary knitted products. However, as circular knitting machines continue to evolve towards intelligence, high speed, and high precision, more stringent requirements are being placed on the comprehensive mechanical properties of the steel used in cylinder manufacturing (including wear resistance, fatigue strength, and dimensional stability).

[0003] Meanwhile, syringe manufacturing involves high-precision machining processes for complex geometries. In existing technologies, traditional steels used for syringe manufacturing (such as medium carbon steel 45) generally suffer from poor machinability. Specifically: 1) Low cutting efficiency: Limited tool feed rate leads to longer processing time per piece; 2) Severe tool wear: Tools wear out quickly and have a short lifespan, requiring frequent replacements, which increases tool costs; 3) Difficulty in controlling the surface quality and precision of the machining process: This affects the final performance of the syringe. High overall manufacturing costs: The combined costs of materials, processing time, and cutting tools significantly increase the manufacturing cost of syringes. This technological situation has prompted the industry to focus on developing new types of steel for syringe manufacturing. Research and development directions need to be balanced: 1) Excellent comprehensive mechanical properties: Meets the requirements of high-speed, high-precision circular knitting machines for cylinder wear resistance, fatigue life and dimensional stability; 2) Excellent machinability: Designed to significantly improve cutting efficiency (shorten machining time) and greatly reduce tool wear; 3) Reasonable material costs: While meeting performance and processing requirements, maintain competitive material costs.

[0004] Developing a new type of syringe manufacturing steel that simultaneously possesses high strength, high wear resistance, high dimensional stability (excellent comprehensive mechanical properties), excellent machinability (to achieve efficient and low-cost processing), and reasonable material cost has become an urgent technical issue to solve current technical bottlenecks and meet market demands. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a low-cost, easy-to-process steel for jacquard machine syringes and its manufacturing method, which addresses the above-mentioned prior art. Through the unique design of chemical composition, the steel has excellent homogeneity, significantly improved cutting performance, reduced milling time for parts, increased number of milled teeth, greatly improved processing efficiency and reduced tool costs.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows: a steel suitable for low-cost and easy-to-process jacquard machine syringes, wherein the elemental composition of the steel by mass percentage is C: 0.45-0.51%, Si: 0.40-0.50%, Mn: 0.50-0.80%, Cr: 0.10-0.15%, P: ≤0.045%, S: 0.055-0.070%, Cu: 0.10-0.20%, Al: 0.010-0.030%, N: 0.008-0.012%, Ti: 0.015-0.035%, with the balance being Fe and unavoidable impurity elements.

[0007] The diameter of the raw steel for the low-cost, easy-to-process jacquard machine syringe described in this invention is φ250-300mm.

[0008] The following section, combining principles of metallurgy and materials science, elaborates in detail the design basis and synergistic mechanism of each element in this invention: C content requirements Carbon is the most economical, effective, and fundamental strengthening element in steel, significantly improving its strength and hardness through solid solution strengthening and carbide formation. The selection of carbon content requires a comprehensive consideration of the balance between hardenability, wear resistance, and toughness.

[0009] In this invention, the lower limit of carbon content is set at 0.45% based on the following considerations: if the carbon content is lower than 0.45%, even after appropriate heat treatment, the surface hardness of the steel will be difficult to reach the high wear resistance standard of ≥58HRC required by the jacquard machine cylinder, and it will not meet the wear resistance requirements of the cylinder groove during high-speed knitting. The upper limit of carbon content is set at 0.51% based on the following considerations: if the carbon content is higher than 0.51%, the toughness of the steel will decrease significantly, and the cylinder will be prone to brittle fracture when subjected to cyclic stress during service. At the same time, excessively high carbon content will make it difficult to break the chips during steel cutting, which will affect the cutting performance.

[0010] To meet the high wear resistance requirement of a surface hardness ≥58HRC after quenching of the jacquard machine syringe, the present invention controls the carbon content to 0.45% to 0.51%, preferably 0.47% to 0.51%.

[0011] Si content requirements Silicon, as an effective deoxidizer and solid solution strengthening element, can significantly improve the strength and hardness of steel, while also improving its elastic limit and tempering stability. Silicon can dissolve in ferrite, hindering dislocation movement through lattice distortion, thereby increasing the strength of steel.

[0012] A silicon content of 0.40% is necessary to ensure sufficient deoxidation and solid solution strengthening. If the silicon content is below 0.40%, the deoxidation of the molten steel is insufficient, resulting in more residual oxide inclusions and reducing the purity of the steel; at the same time, the solid solution strengthening effect is insufficient, affecting the strength of the steel.

[0013] The upper limit of 0.50% for silicon content is based on the following considerations: Excessive silicon content easily reacts with oxygen to form high-hardness silicate inclusions. These hard inclusions accelerate tool wear and significantly shorten tool life during machining. Simultaneously, excessive silicon also promotes the strip-like distribution of sulfide inclusions (such as MnS), deteriorating machinability. Therefore, to balance strength and machining performance, this invention controls the Si content at 0.40%–0.50%.

[0014] Mn content requirements Manganese (Mn) plays multiple beneficial roles in steel: First, it can significantly improve the hardenability of steel and expand the austenite stability zone, thereby improving the uniformity of cross-sectional hardness after quenching and tempering, ensuring that steel for large-diameter (φ250-300mm) syringes can obtain a uniform hardened structure from the surface to the core; Second, manganese combines with sulfur (S) to form high-melting-point MnS, which can completely eliminate the grain boundary hot brittleness caused by FeS and provide lubrication elements for cutting. MnS inclusions can act as solid lubricants during cutting, reducing cutting resistance and tool wear; Third, Mn can refine the pearlite structure, synergistically improving strength and toughness; Fourth, high Mn content promotes bainite phase transformation, making the bainite formation rate in steel positively correlated with Mn content.

[0015] The lower limit of the Mn content in this invention is 0.50% to ensure sufficient MnS inclusions with S and adequate hardenability. The upper limit is 0.80% to avoid excessive segregation. Considering the high S content (0.055-0.070%) in the steel of this invention, if the Mn content is too low, the amount of free FeS may increase, leading to hot brittleness. Controlling the manganese content within the range of 0.50-0.80% achieves the optimal Mn / S ratio balance.

[0016] P content requirements Phosphorus exhibits a typical "double-edged sword" effect in steel: when added in small amounts (≤0.035%), it enhances the strength of the matrix through solid solution strengthening, improves chip breaking performance, and enhances resistance to atmospheric corrosion; while excessive amounts (>0.045%) significantly reduce plasticity and impact toughness, and induce cold brittleness caused by grain boundary segregation.

[0017] Phosphorus exhibits significant solid solution strengthening effects in ferrite, effectively increasing the strength of steel. Simultaneously, phosphorus reduces the toughness of steel, making chips easier to break, thus improving chip-breaking performance. However, excessive phosphorus content can cause severe grain boundary segregation, leading to brittle fracture of the steel at low temperatures, which is fatal for syringe components that need to withstand cyclic impact loads.

[0018] Based on the above considerations, the present invention controls the phosphorus content to ≤0.045%, preferably 0.025 to 0.035%.

[0019] S content requirements Sulfur (S) exhibits a significant dual effect in steel, and controlling its content is one of the core technical challenges of this invention.

[0020] When present in appropriate amounts, sulfur combines with manganese to form spindle-shaped MnS inclusions. During cutting, these inclusions act as a solid lubricant, reducing friction between the tool and chips, thereby reducing cutting forces and extending tool life. Simultaneously, MnS acts as a stress concentration source, improving chip breaking performance and preventing long chip entanglement. Compared to strip-shaped inclusions, spindle-shaped MnS inclusions have a smaller negative impact on the mechanical properties of steel while providing better lubrication.

[0021] However, when the sulfur content exceeds a certain threshold, free FeS will form a low-melting-point eutectic with iron, which will cause grain boundary melting during hot working and lead to hot cracks. In addition, excessive sulfur will also make the inclusions coarse and unevenly distributed, cut the matrix structure, and seriously affect the transverse mechanical properties and fatigue properties of steel.

[0022] This invention controls the sulfur content to be between 0.055% and 0.070%. This specific range was selected based on the following considerations: if the sulfur content is below 0.055%, the number of MnS inclusions is insufficient, resulting in limited lubrication and minimal improvement in cutting performance; if the sulfur content is above 0.070%, the risk of hot cracking during hot working increases significantly, and the transverse plasticity and toughness of the steel decrease significantly, affecting the overall reliability of the syringe. The range of 0.055-0.070% ensures sufficient machinability while avoiding the risk of hot brittleness, representing the preferred range after comprehensively considering cutting performance, mechanical properties, and hot working feasibility.

[0023] It should be noted that this sulfur content range is significantly lower than that of conventional sulfur-based free-cutting steels (such as 46S20, which has an S content of 0.15-0.25%). Therefore, while ensuring machinability, the negative impact on the mechanical properties of the steel is smaller, which fully demonstrates the innovation of this invention in balancing performance.

[0024] Cr content requirements Cr is a moderate carbide-forming element. Adding an appropriate amount of Cr to steel can improve the strength and hardness of the steel through solid solution strengthening and carbide precipitation. Chromium can form carbides such as (Cr,Fe)7C3, which precipitate after quenching and tempering, producing a secondary hardening effect and improving the wear resistance and tempering softening resistance of the steel.

[0025] The lower limit for chromium content is set at 0.10% to ensure sufficient hardenability and carbide formation. The upper limit is set at 0.15% to control costs, as chromium is a relatively expensive alloying element, and the hardness requirements are already met in this invention through a reasonable ratio of elements such as C and Mn, so chromium only needs to be used as an auxiliary strengthening element.

[0026] To ensure that the hardened layer depth of the jacquard machine syringe meets the process requirements, the present invention controls the Cr content to be between 0.10% and 0.15%.

[0027] Cu content requirements When Cu forms a solid solution in steel, it causes lattice distortion in the matrix, hindering dislocation movement and thus increasing the strength and hardness of the steel. Cu forms complex inclusions with Mn and S, which can reduce cutting resistance and extend tool life. Furthermore, copper can significantly improve the atmospheric corrosion resistance of steel, which is beneficial for the long-term use of syringes in humid workshop environments.

[0028] The lower limit of the copper content is set at 0.10% to ensure sufficient solid solution strengthening and corrosion resistance. The upper limit is set at 0.20% based on the following considerations: when the Cu content is too high, melting easily occurs at the grain boundaries during hot working (such as rolling and forging), leading to hot cracking (i.e., "copper embrittlement"). Therefore, this invention controls the copper content to be between 0.10% and 0.20%.

[0029] Ti content requirements Ti achieves multiple strengthening effects in steel by forming high-melting-point carbonitrides. Specifically: Grain refinement: Ti forms high-melting-point TiC, TiN or Ti(C,N) composite inclusions with C and N. These fine particles pin the grain boundaries at high temperatures, effectively preventing austenite grain coarsening and playing a grain refinement and strengthening role. Fixed interstitial atoms: Ti preferentially combines with N, reducing the adverse effects of free N on the steel properties; Precipitation enhancement: The dispersed precipitation of fine TiC particles during the tempering process can produce a significant precipitation enhancement effect.

[0030] Setting the lower limit of Ti content at 0.015% is the minimum threshold to ensure grain refinement. If the Ti content is lower than this value, the number of TiN / TiC particles formed will be insufficient, and the grain refinement strengthening effect will not be obvious.

[0031] The upper limit of Ti content is set at 0.035% based on the following considerations: If the Ti content is too high, the formed TiN particles will coarsen, transforming from a refining agent into harmful coarse inclusions, which will reduce the toughness and fatigue performance of the steel. At the same time, excessive Ti will increase the viscosity and the number of inclusions in the molten steel, deteriorating the purity of the molten steel.

[0032] The present invention precisely controls the Ti content to 0.015% to 0.035%, which can refine the grains while avoiding the coarsening of inclusions due to excessive Ti.

[0033] Al content requirements Al is added as a deoxidizing element in steel. In addition to reducing dissolved oxygen in molten steel, Al combines with N to form dispersed, fine AlN particles, which can refine the grain size. At high temperatures, AlN particles can pin grain boundaries, preventing austenite grain coarsening, thereby obtaining fine ferrite grains.

[0034] Setting the lower limit of aluminum content at 0.010% is necessary to ensure sufficient deoxidation and adequate AlN formation. If the Al content is lower than this value, deoxidation is insufficient, the dissolved oxygen content in the molten steel is high, and coarse oxide inclusions are easily formed; at the same time, the number of AlN particles is insufficient, and the fine grain strengthening effect is limited.

[0035] However, when the Al content is too high, brittle inclusions such as Al2O3 are easily formed during the steel smelting process, reducing the purity of the molten steel. These hard Al2O3 inclusions will aggravate tool wear during machining, which is detrimental to cutting performance. Therefore, the Al content in this invention is controlled at 0.010-0.030%.

[0036] N content requirements Nitrogen, as an interstitial atom, can form nitrides with Al and Ti, strengthening the steel matrix and improving toughness through the following mechanisms: on the one hand, nitrides are dispersed at high temperatures, effectively preventing austenite grain coarsening; on the other hand, as a non-uniform nucleation core, they promote the formation of fine ferrite grains. However, excessively high N content can significantly affect continuous casting production—easily inducing surface cracks in continuously cast billets, leading to surface quality deterioration. Based on the above characteristics, this invention precisely controls the N content within the range of 0.008% to 0.012%, a range that fully utilizes the grain-refining strengthening effect while avoiding quality risks in the continuous casting process.

[0037] Al, N, and Ti achieve an optimized balance of strength, toughness, corrosion resistance, and machinability in steel through a triple synergistic mechanism of "grain boundary pinning - interstitial fixation - inclusion control." The core of this composition design lies in utilizing the thermodynamic differences and size effects between the elements to exert a strengthening effect across different temperature ranges. In the high-temperature range (>1300℃): TiN precipitates first, playing a role in initial grain refinement; In the intermediate temperature range (1000-1300℃): AlN begins to precipitate and forms a composite pinning effect with TiN; In the low-temperature range (<1000℃): the precipitation of fine TiC provides the final dispersion enhancement effect.

[0038] The composition system of this invention is optimized within the overall framework of "medium carbon matrix + appropriate amount of sulfur for free cutting + Al-Ti-N microalloying grain refinement strengthening + trace amount of Cr / Cu auxiliary strengthening". Compared with traditional medium carbon free cutting steel, the significant feature of this invention is that, while maintaining a low alloy cost (without adding expensive alloying elements such as Nb, V, and Ni), it simultaneously achieves the technical goals of surface hardness ≥58HRC after quenching and significantly improved machinability through the dual effects of synergistic lubrication of S-Mn-Cu and microalloying grain refinement strengthening of Al-Ti-N.

[0039] This invention also provides a low-cost, easy-to-process steel manufacturing method for jacquard machine syringes, comprising the following process steps: converter smelting → LF ladle refining → vacuum degassing (VD or RH) → continuous casting → continuous rolling.

[0040] The following is a detailed explanation of each process step: I. Converter Smelting The converter employs a high-carbon extraction method to increase the final high-carbon extraction rate, controlling the carbon content of the tapped steel to ≥0.10% and the temperature to ≥1600℃, while simultaneously stabilizing the phosphorus content of the tapped steel between 0.010% and 0.030%. Practice shows that the higher the carbon content of the tapped steel, the lower the oxygen content in the crude steel, the less inclusions are formed, and the higher the purity.

[0041] In conventional converter smelting, a "low-carbon extraction" operation is typically used to reduce phosphorus content. However, low-carbon extraction leads to over-oxidation of the molten steel, increasing the dissolved oxygen content and thus the amount of inclusions produced during deoxidation. Higher carbon content in the tapped steel results in lower oxygen content in the crude steel, leading to fewer inclusions and higher steel purity. By employing a high-carbon extraction method, the dissolved oxygen content in the molten steel can be minimized while ensuring effective dephosphorization, reducing the formation of non-metallic inclusions at the source and laying the foundation for obtaining high-purity syringe steel.

[0042] II. LF Out-of-furnace Refining Process During the LF refining process, Ar gas is used as the stirring medium, and SiC powder and aluminum particles are added to the surface of the steel slag for slag surface diffusion deoxidation. At the same time, forced deoxidation of the molten steel is achieved by feeding Al wire, reducing the dissolved oxygen to ≤15ppm. To prevent the molten steel from absorbing gas and oxidizing at the end of the refining process, weak argon gas is blown from the bottom and covered with carbonized rice husks to maintain a reducing atmosphere in the furnace.

[0043] During the refining process, the amount of alloy added is precisely controlled to ensure that all elemental compositions fall within the designed content range. This invention pays particular attention to the white slag retention time—which should be no less than 10 minutes—to ensure sufficient deoxidation and desulfurization effects while avoiding excessively long refining times that could contaminate the molten steel.

[0044] White slag is a crucial control indicator in the LF refining process. The formation of white slag indicates that the (FeO+MnO) content in the slag has decreased to an extremely low level. At this point, the slag possesses strong reducing properties, enabling it to continuously deoxidize and desulfurize the molten steel. Maintaining the white slag state for more than 10 minutes ensures that inclusions are fully floated and removed, while simultaneously achieving deep deoxidation and desulfurization.

[0045] III. Vacuum Degassing Process Using VD or RH vacuum degassing process with nitrogen as the booster gas, the high vacuum time is controlled within 5 minutes and the low vacuum is maintained within 10 minutes to ensure that the hydrogen (H) content is ≤2ppm. Shortening the vacuum time can effectively reduce production costs and avoid furnace lining erosion caused by excessively long vacuum treatment.

[0046] The use of nitrogen as the booster gas is one of the differentiating features of this invention. Conventional processes often use argon as the booster gas, but argon is expensive. This invention creatively selects nitrogen as the booster gas, which, while meeting the requirements of vacuum degassing, also helps to precisely control the N content in the steel (0.008-0.012%), providing the necessary nitrogen source for the subsequent formation of AlN and TiN, thus achieving the integration of vacuum degassing and composition control.

[0047] IV. Continuous Casting Process Continuous casting is one of the most critical process steps in the manufacturing method of this invention, and its overall effect directly determines the internal quality and compositional uniformity of the steel.

[0048] A 390mm × 510mm billet shape was selected, and low-superheated molten steel was used for casting, controlling the superheat between 30 and 45℃. Low-superheated casting reduces the temperature gradient during solidification, inhibits the growth of columnar crystals, and promotes the formation of equiaxed crystals. If the superheat is below 30℃, the fluidity of the molten steel deteriorates, and nozzle blockage is likely to occur during casting; if it is above 45℃, columnar crystals develop, the proportion of the central equiaxed crystal region decreases, and segregation intensifies. A low casting speed of 0.40 m / min is used to induce a large number of equiaxed crystal nuclei and form an equiaxed crystal network, effectively inhibiting columnar crystal growth and thus expanding the central equiaxed crystal region.

[0049] A combined M+F-EMS electromagnetic stirring process (M-EMS: electromagnetic stirring in the crystallizer; F-EMS: electromagnetic stirring at the solidification end) is adopted, with M-EMS parameters of 4Hz / 300A and F-EMS parameters of 15Hz / 200A. M-EMS generates a rotating magnetic field within the crystallizer, promoting uniform growth of the primary billet shell and equiaxed crystal nucleation. F-EMS generates stirring in the solidification end region, breaking up coarse columnar crystals and further promoting equiaxed crystal formation. Simultaneously, it breaks up "bridging" structures, redistributing the solute-enriched residual molten steel and effectively reducing the central segregation of elements such as carbon and sulfur.

[0050] The secondary cooling section uses a weak cooling process to control the cooling intensity: if the secondary cooling intensity is too high, it will lead to an excessive temperature gradient in the billet cross section, which will intensify the growth of columnar crystals and reduce the proportion of equiaxed crystals. Therefore, the secondary cooling water volume is set to 0.10L / kg.

[0051] A segmented large reduction process of 15.5mm is implemented in sections 4 to 10. During the reduction process, mechanical force causes plastic deformation in the incompletely solidified core of the billet, squeezing the residual molten steel enriched with solute upstream and promoting composition homogenization. The advantage of segmented large reduction is that the reducing force is gradually released, avoiding internal cracks caused by excessive reduction in a single step, while uniformly improving the core quality along the entire length of the billet.

[0052] The obtained continuously cast billets are placed in a cooling pit at a temperature of ≥500℃ for ≥48 hours for slow cooling. Slow cooling in the pit can prevent thermal stress cracks caused by rapid cooling of the billet, and at the same time allow hydrogen atoms sufficient time to diffuse out of the steel, further reducing the hydrogen content.

[0053] By employing the aforementioned composite process of low superheat casting (30–45°C) + M+F-EMS electromagnetic stirring (M-EMS: 4Hz / 300A, F-EMS: 15Hz / 200A) + segmented large reduction (4–10 segments totaling 15.5mm), columnar crystal growth is suppressed and the central equiaxed crystal region is expanded to over 60%, reducing the segregation index of elements such as C and S from 1.2 in the traditional process to below 1.05, and increasing the core defect repair rate of the steel by 40%.

[0054] V. Continuous Rolling Process During conventional heating, the temperature is controlled between 1200 and 1250℃. Because the rolling ratio is <5, a large reduction process is used to improve the core quality of the rolled material. The initial rolling temperature is set at 1000~1150℃. The selection of the initial rolling temperature needs to take into account both the deformation capacity and the grain refinement effect: if the temperature is too high, the grain will coarsen, and if the temperature is too low, the deformation resistance will increase significantly, making it difficult to roll down.

[0055] The first stage is rough rolling, with the total reduction rate increased to 60% and the maximum single-pass reduction rate ≥30%. The specific significance of this process parameter is that when the rolling ratio is small, the shear strain experienced by the steel core during deformation is insufficient, making it difficult to break up the as-cast structure in the core and eliminate segregation. By increasing the total reduction rate in the rough rolling stage and setting a large single-pass reduction (≥30%), sufficient deformation of the core structure can be achieved with a smaller total deformation, forcing the coarse as-cast grains to break up and the loose pores to close, thereby fully compensating for core defects. The second stage is precision rolling, rolling to the finished thickness (φ250-300mm).

[0056] The initial rolling temperature of the finishing mill is controlled at 950~1050℃, and the final rolling temperature is controlled at 860~920℃. The total reduction rate of the finishing mill is 18%~25%, and 5~7 passes are used for rolling. The reduction rate of each pass is controlled at 8%~15%, and the reduction amount of each pass is evenly distributed. During the rolling process, only weak water cooling is applied to the rolls, and the rolled workpiece is not directly sprayed for cooling.

[0057] The initial rolling temperature of the finishing mill is within the austenitic stable range, ensuring good plasticity and continuous rolling stability of the rolled piece while preventing further grain coarsening. The final rolling temperature avoids the phase transformation range, ensuring uniform overall microstructure of the rolled piece. This stage no longer employs large reduction processes, relying instead on multi-pass small deformation rolling. This precisely corrects the shape of the rolled piece, improving the roundness and dimensional accuracy of the finished product to meet the subsequent precision machining requirements of the syringe. Furthermore, it further refines the surface grains and densifies the surface microstructure, enhancing the wear resistance of the steel surface. The uniformly distributed reduction per pass gradually releases rolling stress, and combined with a temperature control method that avoids direct cooling, it reduces the temperature difference between the surface and core of the steel, preventing microstructure delamination and uneven performance.

[0058] After rolling, the steel is rapidly cooled in a pit for ≥48 hours. Slow cooling after rolling allows the residual stress inside the steel to be fully released, preventing white spot defects (especially hydrogen-induced cracks) caused by rapid cooling, and also has a positive impact on the uniformity of the microstructure.

[0059] Through the above control, the overall microstructure of the rolled material is a uniform and fine pearlite + ferrite structure with uniform grain size, no obvious coarse grains, and excellent isotropic microstructure.

[0060] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention strengthens the matrix by precisely controlling basic elements such as C (0.45~0.51%) and Mn (0.50~0.80%), and improves cutting lubrication by combining S (0.055~0.070%) with Mn to form MnS inclusions. At the same time, it refines the grains by utilizing the triple synergy of Ti (0.015~0.035%), Al (0.010~0.030%), and N (0.008~0.012%). Without adding expensive alloying elements, the surface hardness of the steel after quenching is ≥58HRC, the cutting efficiency is improved by more than 30%, and the material cost is reduced by 15%~20% compared with traditional high-performance steel.

[0061] 2. This invention employs a composite process of "low superheat casting (30~45℃) + M+F-EMS electromagnetic stirring (M-EMS: 4Hz / 300A, F-EMS: 15Hz / 200A) + segmented large reduction (4~10 segments with a cumulative reduction of 15.5mm)" to suppress columnar crystal growth and expand the central equiaxed crystal region to over 60%, thereby reducing the segregation index of elements such as C and S from 1.2 to below 1.05 and increasing the core defect repair rate of the steel by 40%.

[0062] 3. The unique composition and process design of this invention endows the steel with both excellent machinability and comprehensive mechanical properties: the tool life is extended by 2 times during cutting, the milling time of a single piece is reduced by 40%, and the high-speed wear resistance requirements of the cylinder of the large circular knitting machine are met. It is also compatible with the high precision requirements of intelligent textile equipment for core components, and the overall manufacturing cost is reduced by more than 30%. Attached Figure Description

[0063] Figure 1 This is a morphology diagram of sulfides in the steel examples of the present invention.

[0064] Figure 2 The microstructure of traditional 45 steel is shown in the comparative diagram. The matrix is ​​mainly composed of coarse pearlite and ferrite, with uneven grain size and poor microstructure continuity.

[0065] Figure 3 The microstructure diagram of this invention shows that the matrix grains are fine and uniform in size, forming a dense pearlite + ferrite structure.

[0066] Figure 4 This is a diagram of a jacquard machine cylinder in an embodiment of the steel materials of the present invention. Detailed Implementation

[0067] The technical solution of the present invention will be described in more detail below with reference to preferred embodiments. However, these embodiments are merely descriptions of preferred implementations of the present invention and should not be construed as limiting the scope of the present invention in any way.

[0068] The steel specifications for Examples 1-2 are Φ250mm, with a rolling ratio of 4.5.

[0069] The converter has a charge capacity of 100 tons, including 85 tons of molten iron and 15 tons of scrap steel. During the converter smelting process, oxygen blowing and slag formation are carried out, and high carbon extraction is performed. The tapping temperature is 1610℃, with a final carbon content of 0.13% and a P content of 0.020%. Alloys and slag are added during tapping. The ladle is then hoisted to the LF furnace.

[0070] The LF furnace is powered on. After the slag is oxidized, aluminum powder, aluminum granules, and carbon powder are added in batches for diffusion deoxidation. Al wire is fed in for precipitation deoxidation. At the same time, the chemical composition is adjusted to meet the specifications. The white slag time is guaranteed to be 10 minutes, and the temperature at the LF furnace outlet is 1610℃.

[0071] High vacuum time (RH) is 3 minutes, low vacuum time is 7 minutes, and RH end temperature is 1560℃; soft argon blowing is 15 minutes.

[0072] The continuous casting process employs a protective pouring method to isolate the molten steel from the air. The tundish temperature is 1540℃, with a superheat of 32~38℃, and the casting speed is set at 0.40m / min. The resulting continuously cast billet is then slowly cooled in the pit at 500℃ for 48 hours.

[0073] The continuously cast billet is heated to 1240℃ and held for 4 hours. The initial rolling temperature is 1100℃ and the final rolling temperature is 950℃. After rolling, it is slowly cooled in a pit for 48 hours.

[0074] Examples 3-4 involve steel with a specification of Φ300mm and a rolling ratio of 2.81. The converter has a charge capacity of 100 tons, including 90 tons of molten iron and 10 tons of scrap steel. During the converter smelting process, oxygen is blown to form slag. The tapping temperature is 1600℃, and the final carbon content is 0.17%. The phosphorus content is 0.025%. Alloys and slag are added during tapping. The ladle is then hoisted to the LF furnace.

[0075] The LF furnace is powered on. Argon gas stirring is used during the refining process. The intensity of the argon gas stirring is adjusted to prevent the molten steel from being exposed. After the slag has solidified, aluminum powder, aluminum granules, and carbon powder are added in batches for diffusion deoxidation. An Al wire is then fed in for precipitation deoxidation. The white slag is maintained for 12 minutes. The temperature exiting the LF furnace is 1594℃. High vacuum time (RH) is 4 minutes, low vacuum time is 9 minutes, RH end temperature is 1565℃, and soft argon blowing is 12 minutes.

[0076] The continuous casting process was carried out under protective conditions to isolate the molten steel from the air. The tundish temperature was 1538℃, the superheat was 30~36℃, and the casting speed was set at 0.40m / min. The resulting continuously cast billet was placed in the pit at 530℃ for slow cooling for 48 hours.

[0077] The continuously cast billet is heated to 1220℃ and held for 4 hours. The initial rolling temperature is 1090℃ and the final rolling temperature is 950℃. After rolling, it is slowly cooled for 50 hours.

[0078] The chemical composition of the steel involved in the above embodiments is shown in Table 1. Table 1 Chemical composition (%)

[0079] The segregation index of the steel billets in the above embodiments and those in the traditional process is shown in Table 2.

[0080] Table 2

[0081] The segregation index of C and S in the billet produced by traditional process is about 1.2. The composite process of this invention can stably control the segregation index below 1.05, which greatly improves the uniformity of element distribution and avoids the problem of uneven local hardness and wear resistance caused by component segregation.

[0082] The comparison of the central equiaxed crystal region of the above embodiments with that of the traditional continuous casting process is shown in Table 3.

[0083] Table 3

[0084] The process of this invention increases the proportion of central equiaxed crystal regions from 32% to 65% (>60%), effectively suppressing columnar crystal growth and significantly optimizing the microstructure density, overall mechanical properties and dimensional stability.

[0085] The sulfide index of the above embodiments and traditional medium carbon free-cutting steel is shown in Table 4.

[0086] Table 4

[0087] This invention uses a precise ratio of S and Mn and a clean steel process throughout the entire process to control MnS inclusions into small spindle shapes, significantly reducing the inclusion level. It retains the solid lubrication and chip breaking function of MnS while avoiding the defects of long strip inclusions that cut the matrix and reduce toughness.

[0088] The inspection results of the jacquard machine syringes in the above embodiments are shown in Table 5 below.

[0089] Table 5. Inspection Results of Jacquard Machine Syringes

[0090] Traditional 45 steel has insufficient hardness after quenching, failing to meet the wear resistance requirement of ≥58HRC; it also suffers from high cutting resistance, poor chip breaking, low machining efficiency, and rapid tool wear. The steel of this invention, under the same working conditions, reduces machining time by 40%, increases tool life by 100%, and increases milling throughput by approximately 60%, demonstrating significant overall machining performance advantages.

[0091] In addition to the above embodiments, the present invention can also adjust parameters such as billet thickness and continuous casting process according to the production requirements of converters and electric furnaces of different tonnages. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A low-cost, easily processed steel for jacquard machine syringes, characterized in that, The elemental composition of the steel, by mass percentage, includes: C 0.45–0.51%, Si 0.40–0.50%, Mn 0.50–0.80%, Cr 0.10–0.15%, P≤0.045%, S 0.055–0.070%, Cu 0.10–0.20%, Al 0.010–0.030%, N 0.008–0.012%, Ti 0.015–0.035%, with the balance being Fe and unavoidable impurity elements.

2. The low-cost, easily processed steel for jacquard machine syringes according to claim 1, characterized in that, The mass percentage of C is 0.47 to 0.51%, and the mass percentage of P is 0.025 to 0.035%.

3. The low-cost, easily processed steel for jacquard machine syringes according to claim 1, characterized in that, The diameter of the steel is φ250~300mm.

4. The low-cost, easily processed steel for jacquard machine syringes according to claim 1, characterized in that, The surface hardness of the steel used for the syringe is ≥58HRC after quenching.

5. A method for manufacturing low-cost, easily machinable steel for jacquard machine syringes according to any one of claims 1-4, characterized in that, The process includes the following steps: Step 1, Converter smelting: The high-carbon drawing operation method is adopted, and the carbon content of the tapped steel is controlled at ≥0.10%, the temperature at ≥1600℃, and the phosphorus content of the tapped steel is 0.010%~0.030%; Step 2, Ladle refining: Stir with Ar gas in the LF furnace, add SiC powder and aluminum particles for slag surface diffusion deoxidation, feed Al wire for forced deoxidation, make dissolved oxygen ≤15ppm, and adjust the elemental composition to the design range; Step 3, Vacuum degassing: Use VD or RH process with nitrogen as the booster gas. High vacuum time ≤ 5 minutes, low vacuum time ≤ 10 minutes, and control hydrogen content ≤ 2 ppm. Step 4, Continuous casting: Select a 390mm×510mm billet shape, control the superheat of molten steel at 30~45℃, cast speed 0.40m / min, adopt M+F-EMS combined electromagnetic stirring, secondary cooling water flow 0.10L / kg, implement a segmented large reduction process with a cumulative 15.5mm in 4~10 sections to obtain the continuously cast billet; Step 5, Rolling: Heating temperature 1200~1250℃, initial rolling temperature 1000~1150℃, total roughing reduction rate ≥60%, single-pass reduction rate ≥30%, finish rolling to finished thickness, and slow cooling in the pit for ≥48 hours after rolling.

6. A method for manufacturing a low-cost, easily machinable steel for jacquard machine syringes according to claim 5, characterized in that, In step (2), the white slag refined in the LF furnace is held for ≥10 minutes.

7. A method for manufacturing a low-cost, easily machinable steel for jacquard machine syringes according to claim 5, characterized in that: In step (4), the M-EMS parameter is 4Hz / 300A and the F-EMS parameter is 15Hz / 200A.

8. A method for manufacturing a low-cost, easily machinable steel for jacquard machine syringes according to claim 5, characterized in that, After obtaining the continuous casting billet in step (4), it is placed in the pit for slow cooling at a temperature of ≥500℃ for ≥48 hours.

9. A method for manufacturing a low-cost, easily machinable steel for jacquard machine syringes according to claim 5, characterized in that, In step (5), the initial rolling temperature of the finishing mill is controlled at 950~1050℃, and the final rolling temperature is controlled at 860~920℃; the total reduction rate of the finishing mill is 18%~25%, and 5~7 passes are used for rolling, with the single pass reduction rate controlled at 8%~15%.

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