Environment-friendly low young modulus super free-cutting ferritic stainless steel, preparation method and application thereof

Abstract

This invention provides an environmentally friendly low Young's modulus super-free-machining ferritic stainless steel, its preparation method, and its applications. The composition, by mass percentage, is as follows: C: 0.008–0.012%, Si: ≤0.2%, Mn: 1.3–1.6%, P: 0.004–0.008%, S: 0.28–0.32%, Cr: 13.4–13.9%, Al: 6.5–6.9%, Mo: 0.6–0.8%, Nb: 0.02–0.04%, Sn: 0.04–0.06%, Se: 0.008–0.012%, Te: 0.016–0.023%, Bi: 0.07–0.09%, Mg: 0.0002–0.0018%, N: ≤0.008%, O: ≤0.006%, and the balance being Fe and unavoidable impurities. This invention employs the EAF-AOD-LF-(forging)-(grinding)-hot rolling-drawing and peeling-annealing 1-(cold drawing 1-annealing 2)-cold drawing 2 process to finally produce wire with a material texture of strong {110} and weak {012} filaments, and a Young's modulus of 141 GPa in the cold-deformed form. This technical solution, when applied to ballpoint pen tip materials, is expected to replace nickel-copper alloys as the tip material for gel pens; when applied to gel pen tip materials, it offers advantages such as low cost and low writing resistance.

Description

Technical Field

[0001] This invention relates to a metallic material, and more particularly to an environmentally friendly low Young's modulus, highly machinable ferritic stainless steel, its preparation method, and its applications. Background Technology

[0002] In the pen manufacturing industry, the ballpoint pen tip, as a key component, has extremely stringent requirements for the machinability, wear resistance, and corrosion resistance of the materials used. Currently, commonly used materials for ballpoint pen tips include leaded brass, nickel-copper alloys, and free-machining ferritic stainless steel. Leaded brass and nickel-copper alloys are both copper-based materials, offering superior machinability compared to free-machining ferritic stainless steel, but their wear resistance and corrosion resistance are weaker. Nickel-copper alloys have better corrosion resistance and wear resistance than leaded brass, but are more expensive; currently, leaded brass has been largely replaced by nickel-copper alloys.

[0003] Although free-machining ferritic stainless steel has advantages over nickel-copper alloys, such as lower cost, better corrosion resistance, and better wear resistance, the fundamental reason it has not yet replaced nickel-copper alloys is that the Young's modulus of free-machining ferritic stainless steel is higher than that of nickel-copper alloys, resulting in a harder writing feel and stronger damping. The pen tip material is usually matched with the ink material. Currently, for ballpoint pens where smooth writing is not a primary concern but high corrosion resistance is required, free-machining ferritic stainless steel is used for the pen tip; for oil-based pens where smooth writing is more important, nickel-copper alloys are used for the organic solvent ink. Because oil-based pens offer a smoother writing experience than ballpoint pens, their market prospects are broader.

[0004] In the field of ultra-free-machining ferritic stainless steel, typical materials include SF20T from Shimomura Special Steel Co., Ltd. and DSR6F from Daido Steel Co., Ltd., which are based on the composition of free-machining ferritic stainless steel with the addition of elements such as Pb and Te. Since Pb is a toxic element, the production, service, and recycling of these materials pose risks of environmental pollution and harm to human health. Replacing Pb with Bi is currently the development trend in the field of ultra-free-machining stainless steel. Related enterprises and universities in my country have also applied for relevant patents, including publication numbers CN 109898025A, CN 10892999B, CN 11354392A, CN 111334712B, CN108315643B, and CN 109865804B.

[0005] The Young's modulus of traditional Fe-Cr ferritic stainless steel in its cold-transformed form is around 200 GPa, while that of nickel-copper alloy (CuNi12Mn5Pb2) in its cold-transformed form is around 115 GPa, a difference of 73.9%. If the Young's modulus of ultra-free-machining ferritic stainless steel can be significantly reduced, it is hoped that ultra-free-machining ferritic stainless steel can be used to replace nickel-copper alloy in the field of ballpoint pen tip materials to a certain extent, thereby reducing the writing resistance of ballpoint pens to a certain extent. Summary of the Invention

[0006] To address the problems mentioned in the background section, this invention provides an environmentally friendly, low Young's modulus, highly free-machining ferritic stainless steel, its preparation method, and its applications. Its machinability and corrosion resistance are comparable to existing highly free-machining ferritic stainless steel materials, while significantly reducing cost and elastic modulus. This material can be used in ballpoint pen tip materials, potentially replacing nickel-copper alloys as a material for gel pen tips; its application in gel pen tips offers advantages such as low cost and low writing resistance. This material is Pb-free, environmentally friendly, copper-free, low-cost, and easy to manufacture and use.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An environmentally friendly, low Young's modulus, ultra-free-machining ferritic stainless steel, with the following composition by mass percentage: C: 0.008–0.012%, Si: ≤0.2%, Mn: 1.3–1.6%, P: 0.004–0.008%, S: 0.28–0.32%, Cr: 13.4–13.9%, Al: 6.5–6.9%, Mo: 0.6–0.8%, Nb: 0.02–0.0 4%, Sn: 0.04-0.06%, Se: 0.008-0.012%, Te: 0.016-0.023%, Bi: 0.07-0.09%, Mg: 0.0002-0.0018%, N: ≤0.008%, O: ≤0.006%, and the balance Fe and unavoidable impurities, wherein the ferritic stainless steel material has a strong {110}, weak {012} wire texture.

[0009] Preferably, the environmentally friendly low Young's modulus super-free-machining ferritic stainless steel of the present invention has the following composition by mass percentage: C: 0.009-0.012%, Si: ≤0.04%, Mn: 1.5-1.6%, P: 0.004-0.008%, S: 0.29-0.32%, Cr: 13.5-13.9%, Al: 6.7-6.9%, Mo: 0.6-0.8%, Nb: 0.03-0.04%, Sn: 0.052-0.06%, Se: 0.009-0.012%, Te: 0.018-0.023%, Bi: 0.082-0.09%, Mg: 0.0006-0.0018%, N: ≤0.003%, O: ≤0.0012%, and the balance being Fe and unavoidable impurities.

[0010] Preferably, the environmentally friendly low Young's modulus super-free-machining ferritic stainless steel of the present invention is characterized in that its composition satisfies a Te / Se mass ratio of 1.9 to 2.1.

[0011] Preferably, the raw materials are sequentially processed through EAF-AOD-LF-molding-forging-grinding-hot rolling to obtain environmentally friendly low Young's modulus super free-machining ferritic stainless steel wire; during the rolling process, the Young's modulus in the annealed state is not higher than 156 GPa, and the Young's modulus in the cold-transformed state is not higher than 142 GPa.

[0012] The specific components of this invention are:

[0013] C: Carbon is an austenite-forming element. To ensure no austenite phase formation and avoid a decrease in thermoplasticity due to the precipitation of a small amount of austenite, the carbon content should be as low as possible. Furthermore, to ensure that the precipitation temperature of M23C6 type carbides is lower than the hot rolling temperature, the carbon content should also be as low as possible; however, excessively low carbon content increases smelting costs. In this invention, the manganese content is controlled between 0.008 and 0.012 wt.%.

[0014] Si: Silicon can reduce the activity of carbon in steel to a certain extent, thereby reducing the Young's modulus and plasticity of the material, similar to the effects of aluminum. However, silicon's effect on reducing the Young's modulus is less significant than that of aluminum, while its effect on reducing plasticity is more significant. Since the super-free-machining ferritic stainless steel of this invention contains a large amount of aluminum, silicon can actually be replaced entirely with aluminum. However, since impurities of Si are unavoidable in molten steel, scrap steel, and alloy raw materials, from the perspective of material plasticity, when the aluminum content reaches 6.5 wt.%, the maximum silicon content that can be added is 0.2 wt.%. This invention only needs to control the silicon content below 0.2 wt.%.

[0015] Mn: Manganese is a fundamental element for the formation of free-machining phase sulfides and a key element for inhibiting the precipitation of the hot-brittle phase FeS; therefore, the manganese content should be as high as possible. However, manganese is also an austenite-forming element, so to avoid austenite phase formation, the manganese content should be as low as possible. In this invention, the manganese content is controlled at 1.3–1.6 wt.%.

[0016] P: Phosphorus, as a traditional grain boundary segregating element, is beneficial for reducing grain boundary bonding, decreasing material plasticity, and improving chip breaking performance during cutting. Phosphorus can promote the segregation of tin on sulfide surfaces, improving the material's resistance to pitting corrosion. However, phosphorus also promotes the segregation of tin and bismuth at ferrite grain boundaries, significantly reducing the material's thermoplasticity. In this invention, the phosphorus content is controlled at 0.004–0.008 wt.%.

[0017] S: Sulfur is one of the main free-machining elements, mainly existing in the form of sulfides; the machinability of materials increases with increasing sulfur content in steel; sulfides can act as precipitates for elemental Bi, and increasing sulfur content is beneficial for the uniform distribution of elemental Bi in steel; however, increasing sulfur content reduces the thermoplasticity of the material. In this invention, the sulfur content is controlled at 0.28–0.32 wt.%.

[0018] Cr: Chromium is a ferrite-forming element and also plays a passivating role in stainless steel. For traditional clean ferritic stainless steel, a chromium content of 16 wt.% is usually sufficient to meet corrosion resistance requirements. However, for free-machining steel, the free-machining phase reduces the material's pitting corrosion resistance, usually requiring an increased chromium content to meet the material's long-term service requirements in inks. The chromium content of traditional ultra-free-machining ferritic stainless steel is typically around 20 wt.%. This invention, due to the large addition of corrosion-resistant element aluminum, can reduce the chromium content and save alloy costs. In addition, chromium is an element that increases the Young's modulus of ferrite; from the perspective of reducing Young's modulus, the lower the chromium content, the better. This invention controls the chromium content at 13.4–13.9 wt.%.

[0019] Aluminum (Al) is a strong deoxidizing element in steelmaking; its role in steel is similar to that of chromium and silicon; it is a ferrite-forming element, reducing the activity of carbon in steel; aluminum dissolved in steel increases the lattice constant, thereby reducing the Young's modulus, while simultaneously increasing the material's strength (solid solution strengthening) and decreasing its plasticity; aluminum reduces the stacking fault energy of ferrite, affecting the material's dynamic recrystallization and dynamic recovery behavior, as well as its cold deformation texture strength; aluminum is also a corrosion-resistant element, acting as a passivating agent. Furthermore, aluminum deoxidation products, such as alumina inclusions, are another form of aluminum in steel. Large, hard alumina inclusions are detrimental to machinability and require inclusion modification treatment. From the perspective of aluminum reducing the Young's modulus, a higher aluminum content is better; however, excessively high aluminum content reduces material plasticity, requiring additional cold drawing passes, increasing cold rolling costs and failure losses. This invention controls the aluminum content at 6.5–6.9 wt.%.

[0020] Mo: In traditional free-machining ferritic stainless steel, molybdenum plays two main roles: first, it inhibits the precipitation of austenite phase, preventing hot brittleness caused by multiphase structure; second, it improves the material's resistance to pitting corrosion. In this invention, due to the addition of a large amount of aluminum to the ferritic stainless steel, the possibility of austenite phase precipitation can be completely suppressed; only molybdenum needs to be added from the perspective of pitting corrosion resistance. The molybdenum content in this invention is controlled at 0.6–0.8 wt.%.

[0021] Niobium (Nb) is a MC-type carbide-forming element that can lower the precipitation temperature of M23C6, preventing the precipitation of coarse M23C6 carbides during hot rolling. Excessive niobium content leads to excessively high precipitation temperatures and large precipitate sizes, which is detrimental to grain homogenization control during hot rolling. The target for niobium content control in this invention is to ensure that MC-type carbide precipitation mainly occurs during the hot rolling finishing process. The niobium content in this invention is controlled at 0.02–0.04 wt.%.

[0022] Sn: Tin segregates at grain boundaries, reducing grain boundary bonding and improving machinability; tin also increases the pitting potential of stainless steel; tin segregates between the free-machining phase and the steel matrix, improving corrosion resistance; excessive tin content significantly reduces the thermoplasticity of the material; tin has a certain inhibitory effect on the grain boundary segregation of bismuth, and the addition of a small amount of tin to the steel in this invention improves high-temperature thermoplasticity to some extent. The tin content in this invention is controlled at 0.04–0.06 wt.%.

[0023] Se and Te: Both selenium and tellurium are elements that improve the sulfide morphology during hot deformation. Traditional super-cutting ferritic stainless steel uses active oxygen and tellurium in the molten steel to regulate sulfide morphology. Because the material of this invention has a high aluminum content, the active oxygen in the molten steel is below 10 ppm. Therefore, this invention appropriately adds selenium to improve sulfide morphology. However, excessive selenium and tellurium will lower the melting point of the composite inclusions (Mn,Cr,Fe)(S,Se,Te), increasing the tendency to crack during hot deformation. The composite inclusions (Mn,Cr,Fe)(S,Se,Te) will decompose during post-rolling cooling, and Te will precipitate from the composite inclusions. In this invention, the selenium content is controlled at 0.008–0.012 wt.%; the tellurium content is controlled at 0.016–0.023 wt.%; and the preferred Te / Se mass ratio is 1.9–2.1.

[0024] Bi: Similar to lead, bismuth exists in steel in elemental form. Bismuth has a better effect on improving the machinability of stainless steel than lead, and the higher the bismuth content, the better the machinability. However, bismuth significantly reduces the thermoplasticity of the material, and the thermoplasticity decreases with increasing bismuth content. In this invention, the bismuth content is controlled at 0.07 to 0.09 wt.%.

[0025] Mg: In the material of this invention, Mg mainly exists in the form of magnesium aluminum spinel. Magnesium treatment is performed before bismuth, tellurium, and selenium alloying to refine and dissociate alumina inclusions in the molten steel, transforming them into nano-sized magnesium aluminum spinel inclusions. These inclusions are less prone to agglomeration and growth, and can serve as nucleation sites for second phases such as aluminum nitride and sulfides during solidification, promoting the uniform distribution of the free-machining phase in the steel. The magnesium content in this invention is controlled at 0.0002–0.0018 wt.%.

[0026] Nitrogen (N) combines with aluminum to form aluminum nitride inclusions, which significantly inhibit solidification grain growth; however, excessively large aluminum nitride inclusions are detrimental to machinability. This invention controls the nitrogen content to <0.008 wt.%.

[0027] O: Since aluminum and magnesium are strong deoxidizing elements, oxygen in steel mainly exists in the form of magnesium aluminum spinel. The oxygen content in this invention is controlled to be <0.006 wt.%.

[0028] A method for preparing environmentally friendly low Young's modulus super free-machining ferritic stainless steel according to the present invention, wherein the raw material is sequentially subjected to EAF-AOD-LF-in-mold casting-forging-grinding-hot rolling to obtain wire rod, and the method steps are as follows:

[0029] (1) EAF process: using 400 series stainless steel scrap as raw material, the carbon content is adjusted to below 0.01wt.% during the oxidation period; during the reduction period, the alloy composition of the molten steel is roughly adjusted according to the order of adding low carbon ferrochrome-ferromolybdenum-ferroaluminum, and the smelting endpoint temperature is 1620~1630℃.

[0030] (2) AOD process: Then, molybdenum blocks, chromium blocks, low-carbon ferromanganese, ferroniobium, aluminum ingots, tin ingots, and ferrosulfite are added to the molten steel in sequence, and the molybdenum, chromium, manganese, niobium, aluminum, tin and sulfur content of the molten steel is adjusted according to the target range; the smelting endpoint temperature is 1540~1560℃.

[0031] (3) LF process: The LF refining time is at least 30 minutes; after refining, under the condition of bottom blowing argon soft stirring, 0.0004 times the mass of the molten steel is fed into the molten steel with magnesium-aluminum cored wire; the magnesium-aluminum cored wire is composed of 5% magnesium powder, 15% aluminum powder and 85% iron powder by mass percentage; after feeding the wire, the molten steel is stirred by soft blowing argon for at least 5 minutes; then bismuth particles, tellurium particles, selenium particles and iron powder are added to the iron bucket in a mass ratio of 12:2:1:10, and the total amount of bismuth particles, tellurium particles, selenium particles and iron powder added is 0.0032 times the mass of the molten steel. The iron bucket is inserted into the bottom of the ladle through a steel rod; after stirring the molten steel by soft blowing argon for at least 5 minutes, the steel is tapped.

[0032] (4) Ingot casting process: The metal is solidified by ingot casting, and the pouring temperature of the steel is controlled at 1525~1535℃ to obtain ingot casting.

[0033] (5) Forging process: The die-cast ingot is cut into a round billet with a diameter not greater than 160mm; the pre-forging heating temperature is ≥1150℃ and the soaking time is at least 120min; during the forging process, the forging temperature is ≥900℃ and the billet temperature is ≥forging temperature; if the billet temperature is lower than the forging temperature during the forging process, the billet needs to be reheated in the furnace, and the reheating time is at least 30min; the deformation amount per pass during the forging process is not greater than 15%; after forging, the billet is air-cooled to not higher than 600℃ and then slowly cooled in the pit to obtain the billet;

[0034] (6) Grinding process: The billet is ground before hot rolling to ensure that the surface is bright and free of cracks and pore defects;

[0035] (7) Hot rolling process: The heating furnace adopts a reducing atmosphere. The heating rate below 600℃ shall not exceed 10℃ / min. Then, it is heated to 900-1000℃ at a rate of 12-15℃ / min, and finally heated to 1160℃ at a rate of 4-8℃ / min, and held for 40-75min. Hot rolling is divided into three stages: discontinuous dynamic recrystallization rolling, continuous dynamic recrystallization zone rolling, and continuous dynamic recrystallization and non-recrystallization mixed crystal rolling.

[0036] The first stage of hot rolling is discontinuous dynamic recrystallization rolling: it adopts roughing mill and intermediate mill, the initial rolling temperature is not lower than 1100℃, the elongation coefficient of the first and second passes is controlled not higher than 1.1, the elongation coefficient of subsequent single passes is controlled in the range of 1.25 to 1.42, and the elongation coefficient of single passes increases with the number of passes. The final rolling temperature is not lower than 1050℃, and after rolling, it is air-cooled for at least 5 seconds and then water-cooled.

[0037] The second stage of hot rolling is continuous dynamic recrystallization rolling: pre-finishing mill is used for rolling, the initial rolling temperature is 970-980℃, the single-pass elongation coefficient is controlled within the range of 1.24-1.32, and the single-pass elongation coefficient decreases with the increase of the number of passes. The final rolling temperature is not lower than 940℃, and water cooling is not allowed after rolling.

[0038] The third stage of hot rolling is continuous dynamic recrystallization and non-recrystallization mixed crystal rolling: rolling is carried out using a finishing mill and a reducing sizing mill. The rolling temperature should be increased as much as possible, the mill should be cooled with water, the elongation coefficient per pass should be controlled to be no higher than 1.24, the final rolling temperature should be no lower than 920℃, the wire drawing temperature should be no lower than 880℃, and then the temperature is cooled to 620-650℃ by air cooling, and then air cooled to room temperature to obtain ferritic stainless steel wire.

[0039] Preferably, in step (4), the die casting ingot is shaped into an octagonal ingot or a round ingot to reduce the probability of corner cracking during forging and heating; the cross-sectional dimensions should be minimized as much as possible to reduce the hot working compression ratio or elongation coefficient.

[0040] Preferably, in step (7), the total elongation coefficient of the hot-rolled wire is controlled to be not less than 20 in the first stage of hot rolling and not less than 4 in the third stage of hot rolling.

[0041] Preferably, in step (7), the total elongation coefficient of the second stage rolling can be inferred from the total elongation coefficient of the hot rolling, the total elongation coefficient of the first stage rolling, and the total elongation coefficient of the third stage rolling. The total elongation coefficient of the second stage rolling = the total elongation coefficient of the hot rolling / the total elongation coefficient of the first stage rolling / the total elongation coefficient of the third stage rolling.

[0042] Preferably, in step (7), the method for preparing environmentally friendly low Young's modulus super free-cutting ferritic stainless steel wire of the present invention sets the cooling water volume of each rolling mill and whether to use a heat insulation cover to meet the rolling temperature and cooling control requirements.

[0043] Preferably, in step (7), the hot-rolled wire rod is rolled at a speed controlled within the range of [(0.06~0.07)×total elongation coefficient] m / s. This value is mainly influenced by the thermoplasticity of the material during the third stage of rolling and is lower than the rolling speed of traditional free-cutting ferritic stainless steel 430F.

[0044] An application of the environmentally friendly low Young's modulus ultra-free-machining ferritic stainless steel described in this invention involves sequentially processing ferritic stainless steel wire through a process of drawing and peeling, annealing 1, (cold drawing 1, annealing 2), and cold drawing 2, ultimately producing ferritic stainless steel bright wire material for use in ultra-high-speed machining of high-precision parts.

[0045] Preferably, the preparation method of the ferritic stainless steel bright wire includes the following steps:

[0046] a. Drawing and peeling process: The ferritic stainless steel wire is continuously drawn, with the drawing speed controlled at 9-10 m / min, the peeling amount controlled at 0.1-0.3 mm, and the drawing elongation coefficient at 1.05-1.21, so that the wire reaches the required annealed wire diameter.

[0047] b. Annealing Process 1: The drawn and peeled filaments are subjected to continuous online annealing under a protective atmosphere. The annealing temperature is not lower than 960℃, and the holding time is at least 5 minutes.

[0048] c. Cold drawing 1-annealing 2 process: The annealed wire is cold drawn. Cold drawing 1 process: can be single-pass or multi-pass drawing. The elongation coefficient of a single pass drawing is controlled below 1.26, and the cumulative elongation coefficient of drawing before continuous annealing is controlled below 1.52. Annealing 2 process: the annealing temperature is not lower than 920℃, and the holding time is 1-2 minutes. The diameter of the annealed wire is determined by the final diameter of the wire and the elongation coefficient of drawing 2 process.

[0049] d. Cold drawing 2: The annealed wire is finely drawn to the final diameter in a single pass, and the drawing elongation coefficient is controlled at 1.15~1.22 to obtain ferritic stainless steel silver bright wire. The material texture is a strong {110} and weak {012} wire texture. The Young's modulus of the cold-drawn ferritic stainless steel silver bright wire is not higher than 142 GPa.

[0050] Compared with the prior art, the present invention has the following outstanding substantive features and significant advantages:

[0051] 1. The low Young's modulus, ultra-free-machining ferritic stainless steel of this invention, compared with foreign SF20T or existing domestic technologies (CN109898025A, CN 108929999B, CN... The cost of alloy 113584392A is reduced by approximately 9,000 yuan / ton, while the costs of smelting, hot rolling, and annealing processes increase by approximately 1,000 yuan / ton. The yield is comparable to existing technologies, resulting in a total production cost reduction of approximately 8,000 yuan / ton compared to existing technologies. The low Young's modulus super-free-cutting ferritic stainless steel of this invention has a Young's modulus of 156 GPa in the annealed state and 142 GPa in the cold-drawn state (finished wire), representing a 29.0% reduction compared to the 200 GPa of existing super-free-cutting ferritic stainless steel. The corrosion resistance and wear resistance of the low Young's modulus super-free-cutting ferritic stainless steel of this invention are comparable to existing super-free-cutting ferritic stainless steel. In summary, the ferritic stainless steel of this invention, when used in ballpoint pen tip materials, offers advantages such as low cost and low writing resistance.

[0052] 2. The production cost of the low Young's modulus super-free-machining ferritic stainless steel of this invention is only one-third that of nickel-copper alloy; its Young's modulus is 23.5% higher than that of nickel-copper alloy (115 GPa), which is already quite similar; its corrosion resistance and wear resistance are superior to those of nickel-copper alloy; this technical solution can replace nickel-copper alloy as the material for the tip of an oil-filled pen. Attached Figure Description

[0053] Figure 1 Metallographic photograph (polished) of one-quarter section of the longitudinal cross-section of a wire.

[0054] Figure 2 Metallographic photograph of a quarter section of the longitudinal section of a wire (etched by ferric chloride + hydrochloric acid solution).

[0055] Figure 3 Example: EBSD analysis of the cross-section of a wire yielded surface distribution map of the axial (z) inverse pole figure and the large-angle grain boundary map (>15°).

[0056] Figure 4 Example: EBSD analysis of axial (z) inverse pole plot of a wire cross section.

[0057] Figure 5An example of a ballpoint pen tip processed from a single thread. Detailed Implementation

[0058] The technical solutions of the present invention will be described in detail below through embodiments. The following embodiments are merely exemplary and used to explain and illustrate the technical solutions of the present invention, and should not be construed as limiting the technical solutions of the present invention.

[0059] Example 1:

[0060] In this embodiment, an environmentally friendly low Young's modulus super-free-machining ferritic stainless steel has the following composition by mass percentage: C: 0.009%, Si: 0.04%, Mn: 1.5%, P: 0.004%, S: 0.29%, Cr: 13.5%, Al: 6.7%, Mo: 0.6%, Nb: 0.03%, Sn: 0.052%, Se: 0.009%, Te: 0.018%, Bi: 0.082%, Mg: 0.0006%, N: 0.003%, O: 0.0012%, and the balance being Fe and unavoidable impurities; the ferritic stainless steel material has a strong {110}, weak {012} wire texture.

[0061] The method for preparing environmentally friendly low Young's modulus super-free-machining ferritic stainless steel in this embodiment involves sequentially processing the raw material through EAF-AOD-LF-in-mold casting-forging-grinding-hot rolling to obtain wire rod. The method steps are as follows:

[0062] (1) EAF process: 20-ton electric arc furnace is used for smelting. After adding 400 series stainless steel scrap, pig iron and lime, the electric furnace is turned on for smelting. After the oxidation period, the carbon content is 0.0052wt.%. During the reduction period, the alloy composition of the molten steel is roughly adjusted according to the order of adding low carbon ferrochrome-ferromolybdenum-ferroaluminum. The final smelting temperature is 1620℃.

[0063] (2) AOD process: Then, molybdenum blocks, chromium blocks, low-carbon ferromanganese, ferroniobium, aluminum ingots, tin ingots, and ferrosulfite are added to the molten steel in sequence, and the molybdenum, chromium, manganese, niobium, aluminum, tin, and sulfur content of the molten steel is adjusted according to the target range; the smelting endpoint temperature is 1550℃.

[0064] (3) LF process: The ladle is hoisted to the LF station, the temperature is measured, and the power is turned on; after the slag is completely melted, Ca-Si powder is added in batches for reduction, and the refining time is 30 minutes; after refining, under the condition of bottom blowing argon soft stirring, 8 kg of magnesium-aluminum cored wire is fed into the molten steel; the magnesium-aluminum cored wire is composed of 5% magnesium powder, 15% aluminum powder, and 85% iron powder by mass percentage; after the wire feeding is completed, soft blowing argon continues for 5 minutes; a closed iron bucket containing 30.72 kg of bismuth particles, 5.12 kg of tellurium particles, 2.56 kg of selenium particles, and 25.6 kg of iron powder is inserted into the bottom of the ladle through a steel rod; after soft blowing argon stirring for 5 minutes, the steel is tapped.

[0065] (4) Molding process: The metal is solidified by molding. The pouring temperature of the steel is controlled at 1530℃. The molded ingot is a round ingot with a head diameter of 290mm and a tail diameter of 230mm. After the steel billet is demolded and cooled, the riser is cut off to obtain the molded ingot.

[0066] (5) Forging process: The die-cast ingot is cut into a round billet with a diameter of 150mm; the forging heating temperature is 1150℃ and the soaking time is 120min; the initial forging temperature is 1120℃, the deformation per pass during the forging process is less than 15%, the final forging temperature is 920℃, and a round billet with a diameter of 200mm is forged; the billet is held in the furnace for 30min, the initial forging temperature is 1110℃, the deformation per pass during the forging process is less than 15%, the final forging temperature is 960℃, and a round billet with a diameter of 150mm is forged; after forging, the billet is air-cooled to 580℃ and then slowly cooled in a pit to obtain the billet;

[0067] (6) Grinding process: The billet is ground before hot rolling to ensure that the surface is bright and free of cracks and pore defects;

[0068] (7) Hot rolling process: The heating furnace adopts a reducing atmosphere, and the temperature is raised to 400℃ at 8℃ / min, raised to 600℃ at 9℃ / min, heated to 950℃ at 13℃ / min, and heated to 1160℃ at 6℃ / min, and held for 60min; hot rolling is divided into three stages: discontinuous dynamic recrystallization rolling, continuous dynamic recrystallization zone rolling, and continuous dynamic recrystallization and non-recrystallization mixed crystal rolling;

[0069] The first stage of hot rolling is discontinuous dynamic recrystallization rolling: the roughing mill and the intermediate mill are used for rolling, the initial rolling temperature is 1120℃, the final rolling temperature is 1060℃, the diameter after rolling is 31mm, the guide rail is transported for 6 seconds, and then weak water cooling is performed.

[0070] The second stage of hot rolling is continuous dynamic recrystallization rolling: it is rolled using a pre-finishing mill with an initial rolling temperature of 975℃ and a final rolling temperature of 950℃, resulting in a diameter of 15.5mm after rolling; water cooling is not allowed after rolling.

[0071] The third stage of hot rolling is continuous dynamic recrystallization and non-recrystallization mixed crystal rolling: a finishing mill and a reducing mill are used for rolling. The initial rolling temperature is 940℃, and the final rolling temperature is 925℃. The rolling speed is controlled at 40m / s. The wire drawing temperature is 890℃, followed by air cooling to 630℃, and then air cooling to room temperature. The finished ferritic stainless steel wire has a diameter of 6mm. The specific elongation coefficients for each pass are shown in Table 1.

[0072] Table 1. Elongation coefficient of hot rolling process in Example 1

[0073]

[0074] An application of the environmentally friendly low Young's modulus ultra-free-machining ferritic stainless steel described in this embodiment involves sequentially processing ferritic stainless steel wire through a process of drawing and peeling, annealing 1, (cold drawing 1, annealing 2), and cold drawing 2, ultimately producing ferritic stainless steel silver-bright wire material for use in ultra-high-speed machining of high-precision parts.

[0075] In this embodiment, the preparation method of the ferritic stainless steel bright wire includes the following steps:

[0076] a. Drawing and peeling process: Ferritic stainless steel wire is continuously drawn at a speed of 9m / min, with a peeling amount of 0.2mm and a drawing elongation coefficient of 1.15, so that the wire reaches the required annealed wire diameter. The wire size after drawing and peeling is 5.4mm.

[0077] b. Annealing process 1: The drawn and peeled wire is continuously annealed online under a protective atmosphere. The annealing temperature is 960℃ and the holding time is 5min.

[0078] c. Cold drawing 1-annealing 2 process: Diameter 5.4mm; drawing to diameter 4.9mm; drawing to diameter 4.4mm; continuous annealing, annealing temperature 920℃, holding time 2min; drawing to diameter 4.0mm; drawing to diameter 3.6mm; continuous annealing, annealing temperature 920℃, holding time 1.5min; drawing to 3.3mm; drawing to 3.0mm; continuous annealing, annealing temperature 920℃, holding time 1.5min; drawing to 2.8mm; drawing to 2.5mm; continuous annealing, annealing temperature 920℃, holding time 1.0min;

[0079] d. Cold drawing 2: The annealed wire is finely drawn in a single pass to the final diameter, and then finely drawn to 2.3mm to obtain ferritic stainless steel silver bright wire.

[0080] Experimental test analysis:

[0081] The ferritic stainless steel silver-bright wire prepared in Example 1 was cut into shorter pieces and used as samples for experimental testing and analysis. Microscopic observations were conducted on the longitudinal and cross-sectional sections of the wire. Figure 1 Metallographic photograph (polished) of one-quarter section of the longitudinal cross-section of a wire. Figure 2 Metallographic photograph of a quarter section of the longitudinal section of a wire (etched by ferric chloride + hydrochloric acid solution). Figure 3 Example: EBSD analysis of the cross-section of a wire yielded surface distribution map of the axial (z) inverse pole figure and the large-angle grain boundary map (>15°). Figure 4 Example 1: EBSD analysis of the cross-section of a wire material, axial (z) inverse pole figure. The figure shows a uniform microstructure with fine inclusions, and the free-machining phase is evenly distributed within the steel. The material texture in Example 1 is a strong {110}, weak {012} filament texture.

[0082] Example 2:

[0083] This embodiment is basically the same as Embodiment 1, except that:

[0084] In this embodiment, an environmentally friendly low Young's modulus super-free-machining ferritic stainless steel has the following composition by mass percentage: C: 0.012%, Si: 0.04%, Mn: 1.6%, P: 0.008%, S: 0.32%, Cr: 13.9%, Al: 6.9%, Mo: 0.8%, Nb: 0.04%, Sn: 0.06%, Se: 0.012%, Te: 0.023%, Bi: 0.09%, Mg: 0.0018%, N: 0.0028%, O: 0.0011%, and the balance being Fe and unavoidable impurities; the ferritic stainless steel material has a strong {110}, weak {012} wire texture.

[0085] The method for preparing environmentally friendly low Young's modulus super-free-machining ferritic stainless steel in this embodiment involves sequentially processing the raw material through EAF-AOD-LF-in-mold casting-forging-grinding-hot rolling to obtain wire rod. The method steps are as follows:

[0086] (1) EAF process: 20-ton electric arc furnace is used for smelting. After adding 400 series stainless steel scrap, pig iron and lime, the electric furnace is turned on for smelting. After the oxidation period, the carbon content is 0.0052wt.%. During the reduction period, the alloy composition of the molten steel is roughly adjusted according to the order of adding low carbon ferrochrome-ferromolybdenum-ferroaluminum. The final smelting temperature is 1630℃.

[0087] (2) AOD process: Then, molybdenum blocks, chromium blocks, low-carbon ferromanganese, ferroniobium, aluminum ingots, tin ingots, and ferrosulfite are added to the molten steel in sequence, and the molybdenum, chromium, manganese, niobium, aluminum, tin, and sulfur content of the molten steel is adjusted according to the target range; the smelting endpoint temperature is 1560℃.

[0088] (3) LF process: The ladle is hoisted to the LF station, the temperature is measured, and the power is turned on; after the slag is completely melted, Ca-Si powder is added in batches for reduction, and the refining time is 30 minutes; after refining, under the condition of bottom blowing argon soft stirring, 8 kg of magnesium-aluminum cored wire is fed into the molten steel; the magnesium-aluminum cored wire is composed of 5% magnesium powder, 15% aluminum powder, and 85% iron powder by mass percentage; after the wire feeding is completed, soft blowing argon continues for 5 minutes; a closed iron bucket containing 30.72 kg of bismuth particles, 5.12 kg of tellurium particles, 2.56 kg of selenium particles, and 25.6 kg of iron powder is inserted into the bottom of the ladle through a steel rod; after soft blowing argon stirring for 5 minutes, the steel is tapped.

[0089] (4) Ingot casting process: The metal is solidified by ingot casting. The pouring temperature of the steel is controlled at 1535℃. The ingot casting uses round ingots with a head diameter of 290mm and a tail diameter of 230mm. After the steel billet is demolded and cooled, the riser is cut off to obtain the ingot casting.

[0090] (5) Forging process: The die-cast ingot is cut into a round billet with a diameter of 160mm; the forging heating temperature is 1150℃ and the soaking time is 120min; the initial forging temperature is 1120℃, the deformation per pass during the forging process is less than 15%, the final forging temperature is 920℃, and a round billet with a diameter of 200mm is forged; the billet is held in the furnace for 30min, the initial forging temperature is 1110℃, the deformation per pass during the forging process is less than 15%, the final forging temperature is 960℃, and a round billet with a diameter of 160mm is forged; after forging, the billet is air-cooled to 600℃ and then slowly cooled in a pit to obtain the billet;

[0091] (6) Grinding process: The billet is ground before hot rolling to ensure that the surface is bright and free of cracks and pore defects;

[0092] (7) Hot rolling process: The heating furnace adopts a reducing atmosphere, and the temperature is raised to 400℃ at 8℃ / min, raised to 600℃ at 9℃ / min, heated to 950℃ at 13℃ / min, and heated to 1160℃ at 6℃ / min, and held for 75 min; hot rolling is divided into three stages: discontinuous dynamic recrystallization rolling, continuous dynamic recrystallization zone rolling, and continuous dynamic recrystallization and non-recrystallization mixed crystal rolling;

[0093] The first stage of hot rolling is discontinuous dynamic recrystallization rolling: the roughing mill and the intermediate mill are used for rolling, the initial rolling temperature is 1120℃, the final rolling temperature is 1060℃, the diameter after rolling is 31mm, the guide rail is transported for 6 seconds, and then weak water cooling is performed.

[0094] The second stage of hot rolling is continuous dynamic recrystallization rolling: it is rolled using a pre-finishing mill with an initial rolling temperature of 980℃ and a final rolling temperature of 950℃, resulting in a diameter of 15.5mm after rolling; water cooling is not allowed after rolling.

[0095] The third stage of hot rolling is continuous dynamic recrystallization and non-recrystallization mixed crystal rolling: a finishing mill and a reducing mill are used for rolling. The initial rolling temperature is 940℃, and the final rolling temperature is 925℃. The rolling speed is controlled at 45m / s. The wire drawing temperature is 890℃, followed by air cooling to 650℃, and then air cooling to room temperature. The finished ferritic stainless steel wire has a diameter of 6mm. Specifically, the elongation coefficients for each pass in this embodiment are the same as in Embodiment 1, as shown in Table 1.

[0096] An application of the environmentally friendly low Young's modulus ultra-free-machining ferritic stainless steel described in this embodiment involves sequentially processing ferritic stainless steel wire through a process of drawing and peeling, annealing 1, (cold drawing 1, annealing 2), and cold drawing 2, ultimately producing ferritic stainless steel silver-bright wire material for use in ultra-high-speed machining of high-precision parts.

[0097] In this embodiment, the preparation method of the ferritic stainless steel bright wire includes the following steps:

[0098] a. Drawing and peeling process: Ferritic stainless steel wire is continuously drawn at a speed of 10m / min, with a peeling amount of 0.3mm and a drawing elongation coefficient of 1.21, so that the wire reaches the required annealed wire diameter. The wire size after drawing and peeling is 5.4mm.

[0099] b. Annealing process 1: The drawn and peeled wire is continuously annealed online under a protective atmosphere. The annealing temperature is 960℃ and the holding time is 5min.

[0100] c. Cold drawing 1-annealing 2 process: Diameter 5.4mm; drawing to diameter 4.9mm; drawing to diameter 4.4mm; continuous annealing, annealing temperature 920℃, holding time 2min; drawing to diameter 4.0mm; drawing to diameter 3.6mm; continuous annealing, annealing temperature 920℃, holding time 1.5min; drawing to 3.3mm; drawing to 3.0mm; continuous annealing, annealing temperature 920℃, holding time 1.5min; drawing to 2.8mm; drawing to 2.5mm; continuous annealing, annealing temperature 920℃, holding time 2.0min;

[0101] d. Cold drawing 2: The annealed wire is finely drawn in a single pass to the final diameter, and then finely drawn to 2.3mm to obtain ferritic stainless steel silver bright wire.

[0102] Example 3:

[0103] This embodiment is basically the same as the above embodiments, except that:

[0104] In this embodiment, an environmentally friendly low Young's modulus super-free-machining ferritic stainless steel has the following composition by mass percentage: C: 0.009%, Si: 0.2%, Mn: 1.3%, P: 0.004%, S: 0.28%, Cr: 13.4%, Al: 6.5%, Mo: 0.6%, Nb: 0.02%, Sn: 0.04%, Se: 0.008%, Te: 0.016%, Bi: 0.07%, Mg: 0.0002%, N: 0.003%, O: 0.006%, and the balance being Fe and unavoidable impurities; the ferritic stainless steel material has a strong {110}, weak {012} wire texture.

[0105] The method for preparing environmentally friendly low Young's modulus super-free-machining ferritic stainless steel in this embodiment involves sequentially processing the raw material through EAF-AOD-LF-in-mold casting-forging-grinding-hot rolling to obtain wire rod. The method steps are as follows:

[0106] (1) EAF process: 20-ton electric arc furnace is used for smelting. After adding 400 series stainless steel scrap, pig iron and lime, the electric furnace is turned on for smelting. After the oxidation period, the carbon content is 0.0052wt.%. During the reduction period, the alloy composition of the molten steel is roughly adjusted according to the order of adding low carbon ferrochrome-ferromolybdenum-ferroaluminum. The final smelting temperature is 1620℃.

[0107] (2) AOD process: Then, molybdenum blocks, chromium blocks, low-carbon ferromanganese, ferroniobium, aluminum ingots, tin ingots, and ferrosulfite are added to the molten steel in sequence, and the molybdenum, chromium, manganese, niobium, aluminum, tin, and sulfur content of the molten steel is adjusted according to the target range; the smelting endpoint temperature is 1550℃.

[0108] (3) LF process: The ladle is hoisted to the LF station, the temperature is measured, and the power is turned on; after the slag is completely melted, Ca-Si powder is added in batches for reduction, and the refining time is 30 minutes; after refining, under the condition of bottom blowing argon soft stirring, 8 kg of magnesium-aluminum cored wire is fed into the molten steel; the magnesium-aluminum cored wire is composed of 5% magnesium powder, 15% aluminum powder, and 85% iron powder by mass percentage; after the wire feeding is completed, soft blowing argon continues for 5 minutes; a closed iron bucket containing 30.72 kg of bismuth particles, 5.12 kg of tellurium particles, 2.56 kg of selenium particles, and 25.6 kg of iron powder is inserted into the bottom of the ladle through a steel rod; after soft blowing argon stirring for 5 minutes, the steel is tapped.

[0109] (4) Molding process: The metal is solidified by molding. The pouring temperature of the steel is controlled at 1530℃. The molded ingot is a round ingot with a head diameter of 290mm and a tail diameter of 230mm. After the steel billet is demolded and cooled, the riser is cut off to obtain the molded ingot.

[0110] (5) Forging process: The die-cast ingot is cut into a round billet with a diameter of 150mm; the forging heating temperature is 1150℃ and the soaking time is 120min; the initial forging temperature is 1120℃, the deformation per pass during the forging process is less than 15%, the final forging temperature is 920℃, and a round billet with a diameter of 200mm is forged; the billet is held in the furnace for 30min, the initial forging temperature is 1110℃, the deformation per pass during the forging process is less than 15%, the final forging temperature is 960℃, and a round billet with a diameter of 150mm is forged; after forging, the billet is air-cooled to 580℃ and then slowly cooled in a pit to obtain the billet;

[0111] (6) Grinding process: The billet is ground before hot rolling to ensure that the surface is bright and free of cracks and pore defects;

[0112] (7) Hot rolling process: The heating furnace adopts a reducing atmosphere, and the temperature is raised to 400℃ at 8℃ / min, raised to 600℃ at 9℃ / min, heated to 950℃ at 13℃ / min, and heated to 1160℃ at 6℃ / min, and held for 60min; hot rolling is divided into three stages: discontinuous dynamic recrystallization rolling, continuous dynamic recrystallization zone rolling, and continuous dynamic recrystallization and non-recrystallization mixed crystal rolling;

[0113] The first stage of hot rolling is discontinuous dynamic recrystallization rolling: the roughing mill and the intermediate mill are used for rolling, the initial rolling temperature is 1120℃, the final rolling temperature is 1060℃, the diameter after rolling is 31mm, the guide rail is transported for 6 seconds, and then weak water cooling is performed.

[0114] The second stage of hot rolling is continuous dynamic recrystallization rolling: it is rolled using a pre-finishing mill with an initial rolling temperature of 975℃ and a final rolling temperature of 950℃, resulting in a diameter of 15.5mm after rolling; water cooling is not allowed after rolling.

[0115] The third stage of hot rolling is continuous dynamic recrystallization and non-recrystallization mixed crystal rolling: a finishing mill and a reducing mill are used for rolling. The initial rolling temperature is 940℃, and the final rolling temperature is 925℃. The rolling speed is controlled at 40m / s. The wire drawing temperature is 890℃, followed by air cooling to 630℃, and then air cooling to room temperature. The finished ferritic stainless steel wire has a diameter of 6mm. Specifically, the elongation coefficients for each pass in this embodiment are the same as in Embodiment 1, as shown in Table 1.

[0116] An application of the environmentally friendly low Young's modulus ultra-free-machining ferritic stainless steel described in this embodiment involves sequentially processing ferritic stainless steel wire through a process of drawing and peeling, annealing 1, (cold drawing 1, annealing 2), and cold drawing 2, ultimately producing ferritic stainless steel silver-bright wire material for use in ultra-high-speed machining of high-precision parts.

[0117] In this embodiment, the preparation method of the ferritic stainless steel bright wire includes the following steps:

[0118] a. Drawing and peeling process: Ferritic stainless steel wire is continuously drawn at a speed of 9m / min, with a peeling amount of 0.2mm and a drawing elongation coefficient of 1.15, so that the wire reaches the required annealed wire diameter. The wire size after drawing and peeling is 5.4mm.

[0119] b. Annealing process 1: The drawn and peeled wire is continuously annealed online under a protective atmosphere. The annealing temperature is 960℃ and the holding time is 5min.

[0120] c. Cold drawing 1-annealing 2 process: Diameter 5.4mm; drawing to diameter 4.9mm; drawing to diameter 4.4mm; continuous annealing, annealing temperature 920℃, holding time 2min; drawing to diameter 4.0mm; drawing to diameter 3.6mm; continuous annealing, annealing temperature 920℃, holding time 1.5min; drawing to 3.3mm; drawing to 3.0mm; continuous annealing, annealing temperature 920℃, holding time 1.5min; drawing to 2.8mm; drawing to 2.5mm; continuous annealing, annealing temperature 920℃, holding time 1.0min;

[0121] d. Cold drawing 2: The annealed wire is finely drawn in a single pass to the final diameter, and then finely drawn to 2.3mm to obtain ferritic stainless steel silver bright wire.

[0122] Comparative Example 1:

[0123] Comparative Example 1 is a 2.3mm diameter Pb-Te-S series super free-machining ferritic stainless steel material produced by a domestic wire manufacturer.

[0124] Comparative Example 2:

[0125] Comparative Example 2 is a nickel-copper alloy material with a diameter of 2.3mm produced by a domestic copper alloy manufacturer.

[0126] Table 2. Composition ratios (wt.%) of preferred embodiments and comparative examples of the present invention

[0127] Element C Si Mn P S Cr Al Mo Nb Sn Example 1 0.009 0.04 1.5 0.004 0.29 13.5 6.7 0.6 0.03 0.052 Example 2 0.012 0.04 1.6 0.008 0.32 13.9 6.9 0.8 0.04 0.060 Example 3 0.009 0.02 1.3 0.004 0.28 13.4 6.5 0.6 0.02 0.040 Comparative Example 1 0.01 0.45 1.19 0.036 0.27 19.86 - 1.76 - - Comparative Example 2 - - 5.8 - - - - - - - Element Se Te Bi Mg N O Pb Cu Ni margin Example 1 0.009 0.018 0.082 0.0006 0.0030 0.0012 - - - Fe Example 2 0.012 0.023 0.090 0.0018 0.0028 0.0011 - - - Fe Example 3 0.008 0.016 0.070 0.0002 0.0030 0.0012 - - - Fe Comparative Example 1 - 0.02 - - - - 0.17 - - Fe Comparative Example 2 - - - - - - 1.5 43.1 12.3 Zn

[0128] Table 3. Comparison of the effects of preferred embodiments and comparative examples of the present invention

[0129]

[0130] As shown in Tables 1-3 above, compared with the comparative examples, the silicon, chromium, and molybdenum content of the present invention are significantly lower than those of the comparative examples, and it does not contain lead, copper, or nickel, resulting in lower material costs. The present invention is a tertiary stainless steel material. The comparative examples do not contain aluminum, niobium, tin, selenium, bismuth, or magnesium. Aluminum is a strong deoxidizing element in the steelmaking process; aluminum's role in steel is similar to that of chromium and silicon; aluminum is a ferrite-forming element, reducing the activity of carbon in steel; aluminum dissolved in steel increases the lattice constant of the steel, thereby reducing the Young's modulus of the material, while simultaneously increasing the material strength (solid solution strengthening) and reducing the material's plasticity; aluminum reduces the stacking fault energy of ferrite, affecting the dynamic recrystallization and dynamic recovery behavior of the material, as well as the cold deformation texture strength; aluminum is also a corrosion-resistant element, playing a passivating role. In addition, aluminum deoxidation products, alumina inclusions, are another form of aluminum in steel. Large-sized hard alumina inclusions are detrimental to machinability and require inclusion modification treatment. From the perspective of reducing Young's modulus, higher aluminum content is better; however, excessive aluminum content reduces material plasticity, requiring more cold drawing passes and increasing cold rolling costs and failure losses. This invention controls the aluminum content at 6.5–6.9 wt.%. Comparative Example 1 is a Pb-Te-S series free-machining ferritic stainless steel without added aluminum, with a Young's modulus of 200 GPa, unsuitable for use as a pen tip material in ballpoint pens, as it has high writing resistance. Comparative Example 2 is a nickel-copper alloy without added aluminum or iron. Bismuth, similar to lead, exists in elemental form in steel. Bismuth has a better effect on improving the machinability of stainless steel than lead, with higher bismuth content resulting in better machinability; however, bismuth significantly reduces the material's thermoplasticity, and thermoplasticity decreases with increasing bismuth content. This invention controls the bismuth content at 0.07–0.09 wt.%. This invention uses bismuth instead of lead to achieve the manufacture and use of environmentally friendly free-machining ferritic stainless steel. Tin can increase the pitting potential of stainless steel; tin segregates between the free-machining phase and the steel matrix, improving the material's corrosion resistance; tin has a certain inhibitory effect on the grain boundary segregation of bismuth. This invention regulates the material's properties through the interaction between tin and bismuth. Adding a small amount of tin to the steel in this invention improves its high-temperature thermoplasticity to some extent. The tin content in this invention is controlled at 0.04–0.06 wt.%. Selenium is an element that improves the morphology of sulfides in thermal deformation. Due to the high aluminum content of the material in this invention, the active oxygen in the molten steel is below 10 ppm. Appropriate addition of selenium in this invention improves the sulfide morphology. The selenium content in this invention is controlled at 0.008–0.012 wt.%. The comparative example does not contain selenium, so the sulfide morphology cannot be optimized by controlling the selenium content. In the material of this invention, Mg mainly exists in the form of magnesium aluminum spinel. Before alloying with bismuth, tellurium, and selenium, magnesium treatment is performed to refine and dissociate alumina inclusions in the molten steel, transforming them into nano-sized magnesium aluminum spinel inclusions. Magnesium aluminum spinel inclusions are not easy to aggregate and grow, and can serve as nucleation sites for second phases such as aluminum nitride and sulfides during solidification, promoting the uniform distribution of the free-machining phase in the steel.The magnesium content of this invention is controlled at 0.0002–0.0018 wt.%. The comparative example does not contain aluminum, therefore no magnesium was added. The material of this invention has a strong {110}, weak {012} filament texture, and its cold-shifted Young's modulus is 141 GPa. This technical solution, when applied to ballpoint pen tip materials, is expected to replace nickel-copper alloys as the tip material for gel pens; when applied to gel pen tip materials, it has the advantages of low cost and low writing resistance, for example... Figure 5 As shown. While the tensile strength of the environmentally friendly low Young's modulus super-free-machining ferritic stainless steel wire of this invention is significantly higher than that of the comparative example two nickel-copper alloy, it is comparable to that of the comparative example one Pb-Te-S system super-free-machining ferritic stainless steel. The average tool life for manufacturing ballpoint pen tips of the same specifications using the wire of this invention, and the average corrosion amount after 6 hours of immersion in 5% H2SO4 at room temperature, are comparable to those of the comparative example one Pb-Te-S system super-free-machining ferritic stainless steel. The corrosion resistance of the wire of this invention is significantly better than that of the comparative example two. In summary, the cutting performance and corrosion resistance of the wire of this invention are comparable to existing super-free-machining ferritic stainless steel materials, while significantly reducing cost and elastic modulus. This material can be applied to ballpoint pen tip materials and is expected to replace nickel-copper alloy materials as the tip material for ballpoint pens; when applied to gel pen tip materials, it has the advantages of low cost and low writing damping. The material of this invention is Pb-free, environmentally friendly, copper-free, low-cost, and easy to manufacture and use.

[0131] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent substitutions. As long as they meet the purpose of the invention and do not deviate from the technical principle and inventive concept of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. An environmentally friendly, low Young's modulus, ultra-free-machining ferritic stainless steel, characterized in that: Its composition, by mass percentage, is as follows: C: 0.008~0.012%, Si: ≤0.2%, Mn: 1.3~1.6%, P: 0.004~0.008%, S: 0.28~0.32%, Cr: 13.4~13.9%, Al: 6.5~6.9%, Mo: 0.6~0.8%, Nb: 0.02~0.04%, Sn: 0.04~0.06%, Se: 0.008~0.012%, Te: 0.016~0.023%. Bi: 0.07~0.09%, Mg: 0.0002~0.0018%, N: ≤0.008%, O: ≤0.006%, and the balance Fe and unavoidable impurities; the ferritic stainless steel material has a strong {110}, weak {012} wire texture; the environmentally friendly low Young's modulus ultra-free-machining ferritic stainless steel is prepared by the following method: the raw material is sequentially subjected to EAF-AOD-LF-in-mold casting-forging-grinding-hot rolling to obtain wire rod; the preparation method steps are as follows: (1) EAF process: using 400 series stainless steel scrap as raw material, the carbon content is adjusted to below 0.01 wt.% during the oxidation period; during the reduction period, the alloy composition of the molten steel is roughly adjusted according to the order of adding low carbon ferrochrome-ferromolybdenum-ferroaluminum, and the smelting endpoint temperature is 1620~1630℃. (2) AOD process: Then, molybdenum blocks, chromium blocks, low-carbon ferromanganese, ferroniobium, aluminum ingots, tin ingots, and ferrosulfite are added to the molten steel in sequence, and the molybdenum, chromium, manganese, niobium, aluminum, tin and sulfur content of the molten steel is adjusted according to the target range; the smelting endpoint temperature is 1540~1560℃. (3) LF process: The LF refining time is at least 30 min; after the refining is completed, under the condition of bottom blowing argon soft stirring, 0.0004 times the mass of the molten steel is fed into the molten steel with magnesium-aluminum cored wire; the magnesium-aluminum cored wire is composed of 5% magnesium powder, 15% aluminum powder and 85% iron powder by mass percentage; after the wire feeding is completed, the molten steel is stirred by soft blowing argon for at least 5 min; then bismuth particles, tellurium particles, selenium particles and iron powder are added to the iron bucket in a mass ratio of 12:2:1:10, the total amount of bismuth particles, tellurium particles, selenium particles and iron powder added is 0.0032 times the mass of the molten steel, and the iron bucket is inserted into the bottom of the ladle by steel rod; after stirring the molten steel by soft blowing argon for at least 5 min, the steel is tapped. (4) Ingot casting process: The metal is solidified by ingot casting, and the pouring temperature of the steel is controlled at 1525~1535℃ to obtain ingot casting. (5) Forging process: The die casting ingot is cut into a round billet with a diameter not greater than 160 mm; the pre-forging heating temperature is ≥1150℃ and the soaking time is at least 120 min; during the forging process, the forging temperature is ≥900℃ and the billet temperature is ≥forging temperature. If the billet temperature is lower than the forging temperature during the forging process, the billet needs to be reheated in the furnace, and the reheating time should be at least 30 minutes; the deformation amount in a single pass during the forging process should not exceed 15%; after forging, air cool to no higher than 600℃, and then put into the pit for slow cooling to obtain the billet; (6) Grinding process: The billet is ground before hot rolling to ensure that the surface is bright and free of cracks and pores. (7) Hot rolling process: The heating furnace adopts a reducing atmosphere. The heating rate below 600℃ shall not exceed 10℃ / min. Then, it is heated to 900~1000℃ at a rate of 12~15℃ / min, and finally heated to 1160℃ at a rate of 4~8℃ / min, and held for 40~75min. Hot rolling is divided into three stages: discontinuous dynamic recrystallization rolling, continuous dynamic recrystallization zone rolling, and continuous dynamic recrystallization and non-recrystallization mixed crystal rolling. The first stage of hot rolling is discontinuous dynamic recrystallization rolling: it adopts roughing mill and intermediate mill, the initial rolling temperature is not lower than 1100℃, the elongation coefficient of the first and second passes is controlled not higher than 1.1, the elongation coefficient of subsequent single passes is controlled in the range of 1.25~1.42, and the elongation coefficient of single passes increases with the number of passes. The final rolling temperature is not lower than 1050℃, and after rolling, it is air-cooled for at least 5 seconds and then water-cooled. The second stage of hot rolling is continuous dynamic recrystallization rolling: pre-finishing mill is used for rolling, the initial rolling temperature is 970~980℃, the single-pass elongation coefficient is controlled within the range of 1.24~1.32, and the single-pass elongation coefficient decreases with the increase of the number of passes. The final rolling temperature is not lower than 940℃, and water cooling is not allowed after rolling. The third stage of hot rolling is continuous dynamic recrystallization and non-recrystallization mixed crystal rolling: rolling is carried out using a finishing mill and a reducing sizing mill. The rolling temperature should be increased as much as possible, the mill should be cooled with water, the elongation coefficient per pass should be controlled to be no higher than 1.24, the final rolling temperature should be no lower than 920℃, the wire drawing temperature should be no lower than 880℃, and then the temperature is cooled to 620~650℃ by air cooling, and then air cooled to room temperature to obtain ferritic stainless steel wire.

2. The environmentally friendly low Young's modulus super-free-machining ferritic stainless steel according to claim 1, characterized in that: The composition, by mass percentage, is as follows: C: 0.009~0.012%, Si: ≤0.04%, Mn: 1.5~1.6%, P: 0.004~0.008%, S: 0.29~0.32%, Cr: 13.5~13.9%, Al: 6.7~6.9%, Mo: 0.6~0.8%, Nb: 0.03~0.04%, Sn: 0.052~0.06%, Se: 0.009~0.012%, Te: 0.018~0.023%, Bi: 0.082~0.09%, Mg: 0.0006~0.0018%, N: ≤0.003%, O: ≤0.0012%, and the balance being Fe and unavoidable impurities.

3. The environmentally friendly low Young's modulus super-free-machining ferritic stainless steel according to claim 1 or 2, characterized in that: Its composition satisfies the Te / Se mass ratio of 1.9 to 2.

1.

4. The environmentally friendly low Young's modulus super-free-machining ferritic stainless steel according to claim 1, characterized in that: The raw materials are sequentially processed through EAF-AOD-LF-molding-forging-grinding-hot rolling to obtain environmentally friendly low Young's modulus ultra-free-machining ferritic stainless steel wire; during the rolling process, the Young's modulus in the annealed state is not higher than 156 GPa.

5. A method for preparing the environmentally friendly low Young's modulus super-free-machining ferritic stainless steel according to claim 1, characterized in that: The raw materials are sequentially processed through EAF-AOD-LF-in-mold casting-forging-grinding-hot rolling to obtain wire rods. The method steps are as follows: (1) EAF process: using 400 series stainless steel scrap as raw material, the carbon content is adjusted to below 0.01 wt.% during the oxidation period; during the reduction period, the alloy composition of the molten steel is roughly adjusted according to the order of adding low carbon ferrochrome-ferromolybdenum-ferroaluminum, and the smelting endpoint temperature is 1620~1630℃. (2) AOD process: Then, molybdenum blocks, chromium blocks, low-carbon ferromanganese, ferroniobium, aluminum ingots, tin ingots, and ferrosulfite are added to the molten steel in sequence, and the molybdenum, chromium, manganese, niobium, aluminum, tin and sulfur content of the molten steel is adjusted according to the target range; the smelting endpoint temperature is 1540~1560℃. (3) LF process: The LF refining time is at least 30 min; after the refining is completed, under the condition of bottom blowing argon soft stirring, 0.0004 times the mass of the molten steel is fed into the molten steel with magnesium-aluminum cored wire; the magnesium-aluminum cored wire is composed of 5% magnesium powder, 15% aluminum powder and 85% iron powder by mass percentage; after the wire feeding is completed, the molten steel is stirred by soft blowing argon for at least 5 min; then bismuth particles, tellurium particles, selenium particles and iron powder are added to the iron bucket in a mass ratio of 12:2:1:10, the total amount of bismuth particles, tellurium particles, selenium particles and iron powder added is 0.0032 times the mass of the molten steel, and the iron bucket is inserted into the bottom of the ladle by steel rod; after stirring the molten steel by soft blowing argon for at least 5 min, the steel is tapped. (4) Ingot casting process: The metal is solidified by ingot casting, and the pouring temperature of the steel is controlled at 1525~1535℃ to obtain ingot casting. (5) Forging process: The die casting ingot is cut into a round billet with a diameter not greater than 160 mm; the pre-forging heating temperature is ≥1150℃ and the soaking time is at least 120 min; during the forging process, the forging temperature is ≥900℃ and the billet temperature is ≥forging temperature. If the billet temperature is lower than the forging temperature during the forging process, the billet needs to be reheated in the furnace, and the reheating time should be at least 30 minutes; the deformation amount in a single pass during the forging process should not exceed 15%; after forging, air cool to no higher than 600℃, and then put into the pit for slow cooling to obtain the billet; (6) Grinding process: The billet is ground before hot rolling to ensure that the surface is bright and free of cracks and pores. (7) Hot rolling process: The heating furnace adopts a reducing atmosphere. The heating rate below 600℃ shall not exceed 10℃ / min. Then, it is heated to 900~1000℃ at a rate of 12~15℃ / min, and finally heated to 1160℃ at a rate of 4~8℃ / min, and held for 40~75min. Hot rolling is divided into three stages: discontinuous dynamic recrystallization rolling, continuous dynamic recrystallization zone rolling, and continuous dynamic recrystallization and non-recrystallization mixed crystal rolling. The first stage of hot rolling is discontinuous dynamic recrystallization rolling: it adopts roughing mill and intermediate mill, the initial rolling temperature is not lower than 1100℃, the elongation coefficient of the first and second passes is controlled not higher than 1.1, the elongation coefficient of subsequent single passes is controlled in the range of 1.25~1.42, and the elongation coefficient of single passes increases with the number of passes. The final rolling temperature is not lower than 1050℃, and after rolling, it is air-cooled for at least 5 seconds and then water-cooled. The second stage of hot rolling is continuous dynamic recrystallization rolling: pre-finishing mill is used for rolling, the initial rolling temperature is 970~980℃, the single-pass elongation coefficient is controlled within the range of 1.24~1.32, and the single-pass elongation coefficient decreases with the increase of the number of passes. The final rolling temperature is not lower than 940℃, and water cooling is not allowed after rolling. The third stage of hot rolling is continuous dynamic recrystallization and non-recrystallization mixed crystal rolling: rolling is carried out using a finishing mill and a reducing sizing mill. The rolling temperature should be increased as much as possible, the mill should be cooled with water, the elongation coefficient per pass should be controlled to be no higher than 1.24, the final rolling temperature should be no lower than 920℃, the wire drawing temperature should be no lower than 880℃, and then the temperature is cooled to 620~650℃ by air cooling, and then air cooled to room temperature to obtain ferritic stainless steel wire.

6. The method for preparing environmentally friendly low Young's modulus super-free-machining ferritic stainless steel according to claim 5, characterized in that: In step (4), the die casting ingot is shaped into an octagonal ingot or a round ingot to reduce the probability of corner cracking during forging and heating; the cross-sectional dimensions should be minimized as much as possible to reduce the hot working compression ratio or elongation coefficient.

7. The method for preparing environmentally friendly low Young's modulus super-free-machining ferritic stainless steel according to claim 5, characterized in that: In step (7), the total elongation coefficient of hot-rolled wire is controlled to be no less than 20 in the first stage of hot rolling and no less than 4 in the third stage of hot rolling.

8. The method for preparing environmentally friendly low Young's modulus super-free-machining ferritic stainless steel according to claim 5, characterized in that: In step (7), the hot-rolled wire rod is rolled at a speed controlled within the range of [(0.06~0.07) × total elongation coefficient] m / s.

9. The application of the environmentally friendly low Young's modulus super-free-machining ferritic stainless steel as described in claim 1, characterized in that: Ferritic stainless steel wire is subjected to a series of processes including drawing and peeling, annealing 1, cold drawing 1, annealing 2, and cold drawing 2 to finally obtain ferritic stainless steel silver bright wire, which is used for high-precision parts machining in ultra-high speed cutting.

10. The application of the environmentally friendly low Young's modulus super-free-machining ferritic stainless steel according to claim 9, characterized in that: The preparation method of the ferritic stainless steel bright wire includes the following steps: a. Drawing and peeling process: The ferritic stainless steel wire is continuously drawn with a drawing speed of 9~10 m / min, a peeling amount of 0.1~0.3 mm, and a drawing elongation coefficient of 1.05~1.21, so that the wire reaches the required annealed wire diameter. b. Annealing process 1: The wire after drawing and peeling is continuously annealed online under a protective atmosphere. The annealing temperature is not lower than 960℃ and the holding time is at least 5 minutes. c. Cold drawing 1-annealing 2 process: The annealed wire is cold drawn, and the cold drawing 1 process is carried out: it can be single-pass or multi-pass drawing, the single-pass drawing elongation coefficient is controlled below 1.26, and the cumulative drawing elongation coefficient before continuous annealing is controlled below 1.52; the annealing 2 process is carried out, the annealing temperature is not lower than 920℃, and the holding time is 1~2 min; the diameter of the annealed wire is determined by the final diameter of the wire and the drawing elongation coefficient of the cold drawing 2 process; d. Cold drawing 2: The annealed wire is finely drawn to the final diameter in a single pass, and the drawing elongation coefficient is controlled at 1.15~1.22 to obtain ferritic stainless steel bright wire; the Young's modulus of the cold-drawn ferritic stainless steel bright wire is not higher than 142 GPa.

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