A method for preparing zero-magnetic steel bars for special non-magnetic concrete structures

Abstract

This invention relates to the field of steel bar production, and more particularly to a method for preparing zero-magnetic steel bars for special non-magnetic concrete structures, comprising the following steps: S1, smelting: melting raw materials and adjusting the chemical composition; S2, rolling: changing the shape and size by rolling to produce steel bars; S3, non-magnetic steel post-treatment: removing surface magnetic materials through physical pretreatment, chemical pretreatment and powder spraying; the zero-magnetic steel bars for special non-magnetic concrete structures produced by these steps ensure that the remanence is ≤0.5nT (measured at zero distance of 2cm). The zero-magnetic steel bars produced in this way have multiple advantages such as zero magnetism, high strength, good ductility, and corrosion resistance, and are reasonably priced, making them suitable for industrial production and large-scale use.

Description

Technical Field

[0001] This invention relates to the field of steel bar production technology, and in particular to a method for preparing zero-magnetic steel bars for special non-magnetic concrete structures. Background Technology

[0002] Zero-magnetic steel bars (or zero-magnetic steel reinforcement) are building materials with extremely low magnetic properties, which are crucial for special engineering projects or environments requiring extremely low magnetic interference. Zero-magnetic steel is a type of steel with an austenitic structure (non-magnetic structure) at room temperature. With the development of superconducting technology, high magnetic field technology is required in superconducting coil power storage, superconducting power generation, magnetohydrodynamic power generation, magnetic levitation linear motors, nuclear fusion, and other fields. If easily magnetized materials are present in such high magnetic fields, the magnetic field distribution will be disrupted, and eddy currents will be generated in the materials. This will not only cause the materials to heat up and lose energy, but may also damage the entire component. Therefore, zero-magnetic steel bars have a broad application prospect. However, currently, traditional non-magnetic steel bars (such as 45Mn17Al3, 316L, 304L, etc.) have certain magnetic or remanent magnetization problems. In addition, other alternative materials, such as aluminum alloys and titanium alloys, have some limitations and problems in terms of mechanical properties and price. Therefore, it is particularly urgent to develop a zero-magnetic steel bar with extremely low magnetic properties and good mechanical properties. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] To address the shortcomings of existing technologies, this invention aims to provide a method for preparing zero-magnetic steel bars for special non-magnetic concrete structures. This method solves the problems existing in the prior art by adding a large amount of Mn, reducing the proportion of the ferrite phase, achieving an austenitization degree of over 99.9%, ensuring a remanence of ≤0.5nT (measured at a zero distance of 2cm), thus achieving a zero-magnetic level. Furthermore, by controlling process parameters such as heating temperature, rolling temperature, and rolling speed during the rolling process, the zero-magnetic steel bars possess excellent mechanical properties and are reasonably priced, making them suitable for industrial production and large-scale use.

[0005] (II) Technical Solution

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing zero-magnetic steel bars for special non-magnetic concrete structures. The zero-magnetic steel bars, expressed as a percentage by weight, have the following chemical composition: C (carbon): 0.14-0.22%, Si (silicon): ≤1.0%, Mn (manganese): 20.5-25.0%, P (phosphorus): ≤0.03%, S (sulfur): ≤0.03%, Al (aluminum): 1.5-2.5%, V (vanadium): 0.04-0.30%, N (nitrogen): 0.1-0.3%, with the remainder being Fe (iron). The preparation method includes the following steps:

[0007] S1. Smelting: Melting raw materials and adjusting their chemical composition;

[0008] S2. Rolling: The process of changing the shape and size of steel bars through rolling.

[0009] S3. Post-treatment of non-magnetic steel: Improve magnetic properties through heat treatment, cold rolling and magnetic testing.

[0010] Preferably, the process route for smelting in step S1 is electric furnace steelmaking + LF furnace refining + ingot casting.

[0011] Preferably, the tapping temperature during the electric furnace molten steelmaking process in step S1 is 1620-1680℃.

[0012] Preferably, in step S1, the baking temperature of the ingot mold during the smelting and casting process is >50°C before pouring; before pouring, the ingot mold is filled with argon gas, and argon gas is used to protect the pouring process, with the pouring temperature controlled within 1500-1510°C.

[0013] Preferably, the rolling process in step S2 includes: heating the steel ingot to 1150℃-1250℃, holding it in the furnace for ≥4 hours, and rolling it into a square billet after it is taken out of the furnace; heating it again to 1000℃-1200℃, holding it for ≥3 hours, using a controlled rolling and controlled cooling process, with the water cooling temperature controlled at 700℃-800℃, and then air cooling on a cooling bed.

[0014] Preferably, step S3, the post-treatment of non-magnetic steel, includes physical pretreatment, chemical pretreatment, and powder coating.

[0015] Preferably, the physical pretreatment includes: the steel bars are passed through 16 shot blasters, with 4 shot blasters forming a group, for a total of 4 groups. The first group of shot blasters is filled with G18 steel shot abrasive, the second group of shot blasters is filled with bearing steel grit and cutting shot abrasive in a 2:1 ratio, the third group of shot blasters is filled with quartz sand abrasive, and the fourth group of shot blasters is filled with glass sand abrasive. In addition, there are 2 passes of pneumatic cleaning device. The physical pretreatment speed is controlled at 1-2.2 m / min.

[0016] Preferably, the chemical pretreatment includes pickling the zero-magnetic steel bar with a 10%-35% hydrochloric acid solution for 30-60 minutes, followed by passivation in a sodium nitrite solution for 10-20 minutes after rinsing with water, and then rinsing with water and drying.

[0017] Preferably, the baking temperature of the non-magnetic steel bar in the powder coating is 200-230℃, and the powder coating is performed in two passes.

[0018] (III) Beneficial Effects

[0019] The zero-magnetic steel bars produced by this method meet the following physical properties: yield strength ≥500MPa, tensile strength ≥650MPa, elongation after fracture ≥25%, and magnetic properties ≤0.5nT (measured at a distance of 2cm). The austenite content of the produced zero-magnetic steel bars is ≥99.9%, and its purity index meets the requirement that the total of eight inclusions is ≤6.5. By adding a large amount of Mn, the proportion of ferrite phase is reduced, and the degree of austenitization of the microstructure reaches more than 99.9%, ensuring that the remanence is ≤0.5nT (measured at a distance of 2cm), thus achieving a zero-magnetic level. In addition, by adding an epoxy resin coating, the steel bars are protected against minor damage or structural vibration, improving their chemical corrosion resistance and preventing the steel bars from being contaminated with magnetic substances. The zero-magnetic steel bars produced in this way have multiple advantages such as zero magnetism, high strength, good ductility, corrosion resistance, and shock resistance. Moreover, they are reasonably priced and suitable for industrial production and large-scale use. Detailed Implementation

[0020] This invention provides a technical solution: a method for preparing zero-magnetic steel bars for special non-magnetic concrete structures, the method comprising the following steps:

[0021] S1. Smelting: The raw materials are melted, the chemical composition is adjusted and impurities are removed. The process route for this step is electric furnace steelmaking + LF furnace refining + ingot casting.

[0022] The electric arc furnace (EAF) steelmaking process includes: adding lime to the furnace bottom before charging, and starting oxygen blowing to aid melting after the molten pool is formed. The oxygen reacts with carbon and phosphorus in the molten pool to generate carbon monoxide and phosphorus oxide, thus controlling the carbon and phosphorus content. The carbon content is controlled to be <0.1%, and the dephosphorization target is <0.005%. Once the dephosphorization target is achieved, slag removal and slag extraction are performed to ensure the cleanliness of the oxide slag. Lime and fluorite are added to rebuild the slag, with a lime-to-fluorite ratio of 3:1, ensuring uniform slag distribution. Aluminum ingots, aluminum granules, and carbon powder are added for reduction to prepare white slag for at least 20 minutes. The furnace is then heated to [temperature missing]. The temperature T ≥ 1650℃, and composition analysis is performed to ensure that the aluminum content is > 0.1%. Based on the analysis results, electrolytic manganese is added in appropriate batches to adjust the manganese content to the upper-middle limit. Before tapping, aluminum is added to the ladle, and the tapping temperature is ensured to be within the range of 1620-1680℃. At this time, the chemical element content of the molten steel is: C: 0.15-0.17%, Si: 0.25-0.35%, Mn: 21-22%, P≤0.028%, S≤0.005%, Al: 1.6-1.8%, V: 0.04-0.3%, N: 0.1-0.3%.

[0023] The LF furnace refining process includes: Upon arrival at the LF furnace refining station, molten steel is immediately subjected to temperature measurement and sampling analysis. The temperature is then raised to 1650℃, and slag is added after slag formation. This process continues until the slag turns white and exhibits good fluidity. After slag adjustment, other alloys are added in appropriate amounts according to the steel composition, and a weak blowing process is performed for 5 minutes. This ensures that alloying elements are evenly distributed in the molten steel, reducing inhomogeneity and improving the quality of the steel, while ensuring that all components except aluminum reach the target range. Aluminum ingots are then added to achieve an aluminum content of 1.6-1.8%, along with appropriate amounts of lime and high-temperature fluorite for slag adjustment. The temperature is then raised to 1650℃. After ensuring that the composition and temperature meet the requirements, the molten steel is hoisted to the casting platform. The ladle is then preheated to ensure a smooth tapping process. Before tapping, argon gas is ensured to flow freely, and argon gas is blown 3 minutes in advance. This step aims to improve the quality and purity of the molten steel, remove impurities, and fine-tune the alloy composition to ensure that the prepared prestressed steel bars have the required performance and quality.

[0024] The casting process includes: First, cleaning the inner wall of the ingot mold to remove slag, rust, cold steel, and debris to ensure a smooth inner wall. The ingot mold is preheated to over 50°C before pouring to avoid problems caused by temperature differences. A large temperature difference between the ingot mold and the molten steel can lead to uneven cooling and solidification, which can cause porosity, cracks, or other defects. Preheating the ingot mold also helps reduce thermal stress on the material. Before pouring, the ingot mold is filled with argon gas for argon protection during pouring. This is to prevent the molten steel from contacting oxygen in the air and avoiding oxidation. Argon protection also reduces gas inclusions in the molten steel and reduces the formation of bubbles. The pouring temperature is controlled at 1500-1510°C. Once the mold is ready, preheated molten steel is poured from the ladle into the mold. In the mold, the molten steel cools and solidifies rapidly, forming an ingot. Once the billet has fully solidified, the mold can be opened to remove the ingot.

[0025] S2. Rolling: The process of changing the shape and size of steel bars through rolling.

[0026] The rolling process includes: grinding the steel ingot produced in step S1; heating the steel ingot to 1150℃-1250℃ to ensure sufficient plasticity during processing, making it easy to deform and process into the required shape; holding it in the furnace for ≥4 hours to ensure uniform internal temperature and sufficient time for temperature equalization; rolling it into a square billet after exiting the furnace; then reheating it to 1000℃-1200℃ and holding it for ≥3 hours to improve the temperature uniformity of the material and ensure the success of subsequent rolling; then hot rolling, where the square billet is rolled through a series of rollers and rolling tools to process it into the required shape and size of the reinforcing bar; then water cooling to control the temperature at 700℃-800℃, which is used to control the structure and hardness of the material. The temperature range of water cooling ensures reduced recrystallization and recovery as well as grain control; finally, air cooling on a cooling bed to solidify the structure of the material and ensure that it has the required mechanical properties.

[0027] S3. Post-treatment of non-magnetic steel: The post-treatment of non-magnetic steel includes physical pretreatment, chemical pretreatment and powder coating;

[0028] The physical pretreatment includes: the steel bars are passed through 16 shot blasting machines, with 4 machines forming a group, for a total of 4 groups. The first group of shot blasting machines is filled with G18 steel shot abrasive, the second group is filled with a 2:1 ratio of bearing steel grit and cutting shot abrasive, the third group is filled with quartz sand abrasive, and the fourth group is filled with glass sand abrasive. Two pneumatic cleaning devices are added in addition. The physical pretreatment speed is controlled at 1-2.2 m / min. The purpose of physical shot blasting pretreatment is to clean the surface of non-magnetic steel through the impact of abrasives, remove dirt and impurities, and provide a clean and rough surface for the next step of chemical pretreatment and powder coating, thereby improving the coating adhesion.

[0029] The chemical pretreatment includes: first, treating the surface of the non-magnetic steel with a 10%-35% hydrochloric acid solution for 30-60 minutes; after washing with water, the treated material is then passivated in a sodium nitrite solution for 10-20 minutes, followed by washing and drying again at a temperature controlled at 50-100℃. The chemical pretreatment is mainly an acid pickling process, used to remove magnetic iron oxide scale and residual impurities generated at high temperatures. At the same time, sodium nitrite passivation helps improve surface adhesion and prevent further corrosion.

[0030] The powder coating process includes: after chemical pretreatment, the non-magnetic steel undergoes surface coating processing within 6 hours. First, the non-magnetic steel is heated to 200-230℃ to improve coating adhesion. After heating, the non-magnetic steel bar is powder coated twice to complete the preparation of the epoxy resin coating. The coating thickness is controlled at 100-200μm. This coating can withstand minor damage or structural vibration, improve the steel bar's resistance to chemical corrosion, and prevent the steel bar from being contaminated with magnetic substances. Through the above steps, a non-magnetic steel bar product with superior performance can be finally formed.

[0031] The following will describe the technical solution of the present invention clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] Example 1: A zero-magnetic steel bar for special non-magnetic concrete structures, comprising the following chemical composition by weight: C (carbon): 0.14%, Si (silicon): 0.5%, Mn (manganese): 20.5%, P (phosphorus): 0.01%, S (sulfur): 0.01%, Al (aluminum): 1.5%, V (vanadium): 0.1%, N (nitrogen): 0.1%, with the remainder being Fe (iron).

[0033] The above-mentioned processing method for zero-magnetic steel bars includes the following steps:

[0034] 1. Smelting: Raw materials and auxiliary materials are added to the electric furnace, and the furnace is heated to 1650℃ to melt the steel. The steel is then tapped into the LF furnace. After the composition is slightly adjusted, argon gas is introduced into the ladle and the ladle is hoisted to the casting platform. The initial pouring temperature is 1500℃. The molten steel is poured from the ladle into the mold and cooled to form steel ingots.

[0035] 2. Rolling: The ground steel ingots are first heated to 1150℃ in the bar mill for 4 hours, then rolled into square billets. They are then heated again to 1000℃ in the long products mill for 3 hours, and then hot rolled into steel bars. A controlled rolling and cooling process is used, with the water cooling temperature controlled at 700℃, followed by air cooling on a cooling bed.

[0036] 3. Post-treatment of non-magnetic steel: including physical pretreatment, chemical pretreatment and powder coating;

[0037] Physical pretreatment: The steel bars are subjected to physical shot blasting. The steel bars pass through 16 shot blasters, with 4 shot blasters forming a group, for a total of 4 groups. The first group of shot blasters is filled with G18 steel shot abrasive. The second group of shot blasters is filled with bearing steel grit and cutting shot abrasive in a 2:1 ratio. The third group of shot blasters is filled with quartz sand abrasive. The fourth group of shot blasters is filled with glass sand abrasive. In addition, there are 2 passes of pneumatic cleaning device. The physical pretreatment speed is controlled at 1-2.2m / min.

[0038] Chemical pretreatment: The zero-magnetic steel bar is pickled with 10% hydrochloric acid solution for 60 minutes. After being washed with water, it is passivated with sodium nitrite solution for 10 minutes, then washed with water and dried. The drying temperature is controlled at 50℃.

[0039] Powder coating: The non-magnetic steel is heated to 200℃ and powder coated to form an epoxy resin coating. The powder coating is applied in two passes, and the final coating thickness is controlled at 100μm.

[0040] Example 2: A zero-magnetic steel bar for special non-magnetic concrete structures, comprising the following chemical composition by weight: C (carbon): 0.16%, Si (silicon): 0.5%, Mn (manganese): 22.5%, P (phosphorus): 0.01%, S (sulfur): 0.01%, Al (aluminum): 1.5%, V (vanadium): 0.15%, N (nitrogen): 0.15%, with the remainder being Fe (iron).

[0041] The above-mentioned processing method for zero-magnetic steel bars includes the following steps:

[0042] 1. Smelting: Raw materials and auxiliary materials are added to the electric furnace, and the furnace is heated to 1650℃ to melt the steel. The steel is then tapped into the LF furnace. After the composition is slightly adjusted, argon gas is introduced into the ladle and the ladle is hoisted to the casting platform. The initial pouring temperature is 1500℃. The molten steel is poured from the ladle into the mold and cooled to form steel ingots.

[0043] 2. Rolling: The ground steel ingots are first heated to 1200℃ in the bar mill and left in the furnace for 4 hours. After being taken out of the furnace, they are rolled into square billets and then heated again to 1100℃ in the long product mill for 3 hours. After that, they are hot rolled into steel bars using a controlled rolling and controlled cooling process. The water cooling temperature is controlled at 700℃, and then the bars are air cooled on a cooling bed.

[0044] 3. Post-treatment of non-magnetic steel: including physical pretreatment, chemical pretreatment and powder coating;

[0045] Physical pretreatment: The steel bars are subjected to physical shot blasting. The steel bars pass through 16 shot blasters, with 4 shot blasters forming a group, for a total of 4 groups. The first group of shot blasters is filled with G18 steel shot abrasive. The second group of shot blasters is filled with bearing steel grit and cutting shot abrasive in a 2:1 ratio. The third group of shot blasters is filled with quartz sand abrasive. The fourth group of shot blasters is filled with glass sand abrasive. In addition, there are 2 passes of pneumatic cleaning device. The physical pretreatment speed is controlled at 1-2.2m / min.

[0046] Chemical pretreatment: The zero-magnetic steel bar is pickled with 15% hydrochloric acid solution for 45 minutes. After being washed with water, it is passivated with sodium nitrite solution for 15 minutes, then washed with water and dried. The drying temperature is controlled at 75℃.

[0047] Powder coating: The non-magnetic steel is heated to 210℃ and powder coated to form an epoxy resin coating. The powder coating is applied in two passes, and the final coating thickness is controlled at 150μm.

[0048] Example 3: A zero-magnetic steel bar for special non-magnetic concrete structures, comprising the following chemical composition by weight: C (carbon): 0.20%, Si (silicon): 0.6%, Mn (manganese): 25%, P (phosphorus): 0.01%, S (sulfur): 0.01%, Al (aluminum): 2.0%, V (vanadium): 0.2%, N (nitrogen): 0.2%, with the remainder being Fe (iron).

[0049] The above-mentioned processing method for zero-magnetic steel bars includes the following steps:

[0050] 1. Smelting: Raw materials and auxiliary materials are added to the electric furnace, and the furnace is heated to 1650℃ to melt the steel. The steel is then tapped into the LF furnace. After the composition is slightly adjusted, argon gas is introduced into the ladle and the ladle is hoisted to the casting platform. The initial pouring temperature is 1500℃. The molten steel is poured from the ladle into the mold and cooled to form steel ingots.

[0051] 2. Rolling: The ground steel ingots are first heated to 1250℃ in the bar mill and left in the furnace for 4 hours. After being taken out of the furnace, they are rolled into square billets and then heated again to 1150℃ in the long product mill for 3 hours. After that, they are hot rolled into steel bars using a controlled rolling and controlled cooling process. The water cooling temperature is controlled at 700℃, and then the bars are air cooled on a cooling bed.

[0052] 3. Post-treatment of non-magnetic steel: including physical pretreatment, chemical pretreatment and powder coating;

[0053] Physical pretreatment: The steel bars are subjected to physical shot blasting. The steel bars pass through 16 shot blasters, with 4 shot blasters forming a group, for a total of 4 groups. The first group of shot blasters is filled with G18 steel shot abrasive. The second group of shot blasters is filled with bearing steel grit and cutting shot abrasive in a 2:1 ratio. The third group of shot blasters is filled with quartz sand abrasive. The fourth group of shot blasters is filled with glass sand abrasive. In addition, there are 2 passes of pneumatic cleaning device. The physical pretreatment speed is controlled at 1-2.2m / min.

[0054] Chemical pretreatment: The zero-magnetic steel bar is pickled with 25% hydrochloric acid solution for 40 minutes. After being washed with water, it is passivated with sodium nitrite solution for 15 minutes, then washed with water and dried. The drying temperature is controlled at 75℃.

[0055] Powder coating: The non-magnetic steel is heated to 220℃ and powder coated to form an epoxy resin coating. The powder coating is applied in two passes, and the final coating thickness is controlled at 150μm.

[0056] Example 4: A zero-magnetic steel bar for special non-magnetic concrete structures, comprising the following chemical composition by weight: C (carbon): 0.22%, Si (silicon): 0.8%, Mn (manganese): 27%, P (phosphorus): 0.01%, S (sulfur): 0.01%, Al (aluminum): 2.5%, V (vanadium): 0.3%, N (nitrogen): 0.3%, with the remainder being Fe (iron).

[0057] The above-mentioned processing method for zero-magnetic steel bars includes the following steps:

[0058] 1. Smelting: Raw materials and auxiliary materials are added to the electric furnace, and the furnace is heated to 1650℃ to melt the steel. The steel is then tapped into the LF furnace. After the composition is slightly adjusted, argon gas is introduced into the ladle and the ladle is hoisted to the casting platform. The initial pouring temperature is 1500℃. The molten steel is poured from the ladle into the mold and cooled to form steel ingots.

[0059] 2. Rolling: The ground steel ingots are first heated to 1250℃ in the bar mill and held in the furnace for 4 hours. After being taken out of the furnace, they are rolled into square billets and then heated again to 1200℃ in the long product mill for 3 hours. After that, they are hot rolled into steel bars using a controlled rolling and controlled cooling process. The water cooling temperature is controlled at 700℃, and then the bars are air cooled on a cooling bed.

[0060] 3. Post-treatment of non-magnetic steel: Post-treatment of non-magnetic steel includes physical pretreatment, chemical pretreatment and powder coating;

[0061] Physical pretreatment: The steel bars are subjected to physical shot blasting. The steel bars pass through 16 shot blasters, with 4 shot blasters forming a group, for a total of 4 groups. The first group of shot blasters is filled with G18 steel shot abrasive. The second group of shot blasters is filled with bearing steel grit and cutting shot abrasive in a 2:1 ratio. The third group of shot blasters is filled with quartz sand abrasive. The fourth group of shot blasters is filled with glass sand abrasive. In addition, there are 2 passes of pneumatic cleaning device. The physical pretreatment speed is controlled at 1-2.2m / min.

[0062] Chemical pretreatment: The zero-magnetic steel bar is pickled with 35% hydrochloric acid solution for 30 minutes. After being washed with water, it is passivated with sodium nitrite solution for 15 minutes, then washed with water and dried. The drying temperature is controlled at 100℃.

[0063] Powder coating: The non-magnetic steel is heated to 230℃ and powder coated to form an epoxy resin coating. The powder coating is applied in two passes, and the final coating thickness is controlled at 200μm.

[0064] Comparative Example 1: The rest is the same as Example 4, except that the weight ratio of Mn (manganese) in the chemical composition is 10%;

[0065] Comparative Example 2: The rest is the same as Example 4, except that the weight ratio of Mn (manganese) in the chemical composition is 0%;

[0066] Comparative Example 3: The rest is the same as Example 4, except that the weight ratio of Mn (manganese) in the chemical composition is 40%;

[0067] Comparative Example 4: Commercially available 304L non-magnetic steel bars;

[0068] Comparative Example 5: Commercially available non-magnetic aluminum alloy steel bars;

[0069] The zero-magnetic steel bars prepared in the above embodiments and comparative embodiments were subjected to the following tests, and the results are shown in Table 1.

[0070]

[0071]

[0072] Table 1

[0073] As can be seen from the data in Table 1, the zero-magnetic steel bar processed by the present invention has significant advantages in yield strength, tensile strength, elongation and magnetism compared with the zero-magnetic steel bar of the prior art. In particular, the advantages of the zero-magnetic steel bar processed in Example 4 are more obvious. Therefore, the chemical composition ratio and processing technology of the zero-magnetic steel bar in Example 4 are the preferred solutions.

[0074] Through numerous experiments, the applicant broke with convention and achieved an austenitization degree of over 99.9% in the microstructure by using a chemical composition of C (carbon): 0.14-0.22%, Si (silicon): ≤1.0%, Mn (manganese): 20.5-25.0%, P (phosphorus): ≤0.03%, S (sulfur): ≤0.03%, Al (aluminum): 1.5-2.5%, V (vanadium): 0.04-0.30%, N (nitrogen): 0.1-0.3%, with the remainder being Fe (iron). By adding a large amount of Mn, the proportion of ferrite phase was reduced, ensuring a remanence of ≤0.5nT (measured at zero distance of 2cm), thus achieving a zero magnetic level.

[0075] Through numerous experiments, the applicant has discovered that the zero-magnetic steel bars produced using these steps for special non-magnetic concrete structures exhibit the best performance. The physical properties of the steel bars produced using this invention are: yield strength ≥ 500 MPa, tensile strength ≥ 650 MPa, elongation after fracture ≥ 25%, and magnetic properties ≤ 0.5 nT (measured at a distance of 2 cm). The zero-magnetic steel bars for special non-magnetic concrete structures produced using this invention possess excellent resistance to chemical corrosion and superior physical properties. This is of great significance for special engineering projects or environments requiring extremely low magnetic interference, and can help ensure the accuracy and reliability of various scientific research, medical, defense, and industrial applications.

[0076] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing zero-magnetic steel bars for special non-magnetic concrete structures, characterized in that, The chemical composition of the zero-magnetic steel bar, expressed as a weight percentage, is as follows: C (carbon): 0.14-0.22%, Si (silicon): ≤1.0%, Mn (manganese): 20.5-25.0%, P (phosphorus): ≤0.03%, S (sulfur): ≤0.03%, Al (aluminum): 1.5-2.5%, V (vanadium): 0.04-0.30%, N (nitrogen): 0.1-0.3%, with the remainder being Fe (iron). The preparation process follows these steps: S1. Smelting: Melting raw materials and adjusting their chemical composition; S2. Rolling: The process of changing the shape and size of steel bars through rolling. S3. Post-treatment of non-magnetic steel: Steel bars are treated through physical pretreatment, chemical pretreatment and powder coating processes. The process route for smelting in step S1 is electric furnace steelmaking + LF furnace refining + ingot casting. The electric furnace steelmaking process includes: controlling the carbon and phosphorus content by blowing in oxygen to react with carbon and phosphorus in the molten pool to generate carbon monoxide and phosphorus oxide, with the carbon content endpoint being <0.1% and the dephosphorization target value being <0.005%; adding lime and fluorite to re-form slag, with the lime to fluorite ratio being 3:1; raising the temperature to ≥1650℃; adding aluminum ingots, aluminum granules and carbon powder to reduce and prepare white slag for a duration of not less than 20 minutes; adding electrolytic manganese to adjust the manganese content to 21-22%; and tapping the steel at a temperature of 1620-1680℃. The LF furnace refining process includes: heating to 1650℃, slag conditioning after slag formation, weak blowing for 5 minutes, adding aluminum ingots to meet the aluminum content of 1.6-1.8%, and adding lime and high-temperature fluorite for slag conditioning to ensure red-batch steel tapping; The rolling process in step S2 includes: heating the steel ingot to 1150℃-1250℃, holding it in the furnace for ≥4 hours, and rolling it into a square billet after it is taken out of the furnace; heating it again to 1000℃-1200℃, holding it for ≥3 hours, using a controlled rolling and controlled cooling process, with the water cooling temperature controlled at 700℃-800℃, and then air cooling on a cooling bed.

2. According to claim 1, in the method for preparing zero-magnetic steel bars for special non-magnetic concrete structures, the baking temperature of the steel ingot mold during the casting process in step S1 is >50°C before pouring; argon gas is filled into the steel ingot mold before pouring, and argon gas is used to protect the pouring, with the pouring temperature controlled within 1500-1510°C.

3. The method for preparing zero-magnetic steel bars for special non-magnetic concrete structures according to claim 1, characterized in that, The physical pretreatment includes: the steel bars are passed through 16 shot blasters, with 4 shot blasters forming a group, for a total of 4 groups. The first group of shot blasters is filled with G18 steel shot abrasive, the second group of shot blasters is filled with bearing steel grit and cutting shot abrasive in a 2:1 ratio, the third group of shot blasters is filled with quartz sand abrasive, and the fourth group of shot blasters is filled with glass sand abrasive. Two pneumatic cleaning devices are added. The physical pretreatment speed is controlled at 1-2.2 m / min.

4. The method for preparing zero-magnetic steel bars for special non-magnetic concrete structures according to claim 1, characterized in that, The chemical pretreatment includes pickling the zero-magnetic steel bars with a 10%-35% hydrochloric acid solution for 30-60 minutes, followed by passivation with sodium nitrite solution for 10-20 minutes after water washing, and then water washing and drying, with the drying temperature controlled at 50-100℃.

5. The method for preparing zero-magnetic steel bars for special non-magnetic concrete structures according to claim 1, characterized in that, The powder coating process includes heating a non-magnetic steel to 200-230°C and then applying powder coating to the non-magnetic steel to form an epoxy resin coating. The powder coating is applied in two passes, and the final coating thickness is controlled to be 100-200 μm.

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