High-manganese non-magnetic earthquake-resistant steel bars and their surface treatment methods

Abstract

This invention relates to the field of reinforcing steel and its surface treatment technology, and discloses a high-manganese non-magnetic earthquake-resistant reinforcing steel. Its chemical composition by weight percentage is: C: 0.27~0.33%, Si: 0.37~0.45%, Mn: 20.5~23.0%, P: ≤0.030%, S: ≤0.030%, Nb: 0.017~0.025%, V: 0.28~0.35%, Alt: 0.025~0.037%, N: 0.25~0.50%, with the remainder being Fe and trace residual elements. This invention also discloses a surface treatment method for the high-manganese non-magnetic earthquake-resistant reinforcing steel. This invention, by optimizing the chemical composition of the high-manganese non-magnetic earthquake-resistant reinforcing steel and combining it with a combined surface process of shot blasting, hot acid cleaning, and surface passivation, enables the product to maintain excellent mechanical properties while achieving extremely low remanence and relative permeability, and the non-magnetic surface properties remain stable even after natural aging.

Description

Technical Field

[0001] This invention relates to the field of reinforcing steel bars and their surface treatment technology, specifically to a high-manganese non-magnetic earthquake-resistant reinforcing steel bar and its surface treatment method. Background Technology

[0002] With the rapid development of modern construction and infrastructure engineering towards intelligence and precision, the market demand for specialized building materials is becoming increasingly urgent. Furthermore, the government has proposed and is actively promoting products capable of operating in strong magnetic environments to meet the needs of specialized fields such as high-precision laboratories, medical imaging centers, rail transportation, power facilities, and national defense projects. Non-magnetic steel bars, as a new type of building material with low magnetic permeability, high corrosion resistance, and excellent mechanical properties, can completely replace the disadvantages of traditional steel bars in special environments, demonstrating enormous market potential.

[0003] However, existing non-magnetic steel bar technology mainly focuses on smelting and rolling processes, with limited research on surface treatment technology after the finished steel bars are produced. This leads to the following problems with the existing technology: 1) Incomplete removal of oxide scale and rust from the surface of the reinforcing steel leads to high residual magnetism, which fails to meet the requirements for extremely low magnetic properties; 2) If the surface treatment is not effectively passivated, the steel bars are easily contaminated during storage and transportation, affecting the stability of the non-magnetic properties; 3) Existing surface treatment methods do not take into account the protection of the austenitic structure of high-manganese non-magnetic steel bars, and the treatment process may damage the non-magnetic properties of the material.

[0004] Chinese patent (publication date: December 9, 2022, publication number: CN115449598A) discloses a method for preparing non-magnetic steel bars, including: KR pre-desulfurization of molten iron, converter smelting, nitrogen blowing, LF refining, VD vacuum refining, continuous casting, shot blasting inspection, and steel rolling. The method involves obtaining low-sulfur molten iron through KR pre-desulfurization before smelting. Furthermore, in the nitrogen blowing step, calcium carbide, calcium aluminate, lime, and iron oxide scale are added to the molten steel. This unique top-slag process, with sufficient refining nitrogen blowing time, effectively deforms and floats inclusions in the molten steel, absorbing them into the top slag. The final finished steel bar typically has inclusions smaller than 20 μm. However, this invention does not address the surface treatment method for the finished steel bars, thus failing to guarantee the stability of the non-magnetic properties of the steel bars in the service environment.

[0005] Chinese Patent (Publication Date: February 3, 2024, Publication No.: CN117512308A) discloses a non-magnetic steel bar and its preparation method. The method includes heating a billet with a set chemical composition; rolling the heated billet and controlling the rolling process parameters to obtain hot-rolled steel; and cooling the hot-rolled steel and controlling the final cooling temperature to obtain a non-magnetic steel bar. The absolute magnetic permeability of this non-magnetic steel bar is 1.28 × 10⁻⁶. -6 -1.30×10 -6 The steel reinforcement has a strength of h / m, which meets the requirements for non-magnetic or extremely low magnetic properties of steel bars used in maglev railway tracks. However, this invention also does not address the surface treatment process of the finished steel bars, and therefore cannot solve the adverse effects of surface oxides on magnetic properties.

[0006] Chinese Patent (Publication Date: April 23, 2014, Publication No.: CN103741023A) discloses a method for smelting non-magnetic steel. The method involves tapping steel from an electric furnace, stirring the molten steel with argon gas at a flow rate ≥100 m³ / h for 2 minutes, and then refining it with electricity. Electricity is then supplied with an argon gas flow rate of 20-30 m³ / h. When the molten steel temperature reaches ≥1600℃, power is cut off, manganese is added, and the molten steel is stirred with argon gas at a flow rate ≥100 m³ / h for 2 minutes before refining with electricity. The process is repeated until the argon gas flow rate reaches 20-30 m³ / h. Under the condition of power supply at a flow rate of m³ / h, when the molten steel temperature is ≥1560℃, 300kg of aluminum briquettes and 100kg of aluminum powder are added for reduction; after reduction for 10 minutes and the molten steel temperature is ≥1650℃, samples are taken for chemical composition analysis, and aluminum wire is fed under an argon flow rate ≥80m³ / h; power is supplied under an argon flow rate ≥80m³ / h and 200kg of aluminum powder is added, and reduction is carried out for 10 minutes; when the power supply time is ≥20 minutes and the molten steel temperature is 1640-1650℃, refining is completed. The ingot qualification rate of this invention is 97.09%. Similarly, this invention does not show a method for surface treatment after the production of high-manganese non-magnetic earthquake-resistant steel bars, and cannot solve the adverse effects of surface oxides on magnetic properties.

[0007] In summary, none of the existing patents on non-magnetic steel bars clearly demonstrate the surface treatment method after the production of high-manganese non-magnetic earthquake-resistant steel bars. Therefore, it is essential to develop a high-manganese non-magnetic earthquake-resistant steel bar and its surface treatment method. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of the above-mentioned technologies by providing a high-manganese non-magnetic earthquake-resistant steel bar and its surface treatment method. By optimizing the chemical composition of the high-manganese non-magnetic earthquake-resistant steel bar and combining it with a combined surface process of shot blasting, hot acid cleaning and surface passivation, the product can achieve extremely low remanence and relative permeability while maintaining excellent mechanical properties, and the non-magnetic properties of the surface remain stable after natural aging.

[0009] To achieve the above objectives, the high-manganese non-magnetic seismic-resistant steel bar designed in this invention has the following chemical composition by weight percentage: C: 0.27~0.33%, Si: 0.37~0.45%, Mn: 20.5~23.0%, P: ≤0.030%, S: ≤0.030%, Nb: 0.017~0.025%, V: 0.28~0.35%, Alt: 0.025~0.037%, N: 0.25~0.50%, with the remainder being Fe and trace residual elements.

[0010] Preferably, its mechanical properties meet the following requirements: yield strength ≥ 400 MPa, tensile strength ≥ 750 MPa, and elongation ≥ 35.0%.

[0011] Preferably, its magnetic properties satisfy: remanence ≤ 0.7 nT, relative permeability ≤ 1.05.

[0012] Preferably, its microstructure is austenitic.

[0013] The roles and proportions of each element are as follows: C: Carbon can improve product strength through solid solution strengthening and promote the stability of austenitic structure. However, excessive carbon content will reduce the plasticity, toughness and weldability of the material. The carbon content is set at 0.27 to 0.33 wt%.

[0014] Si has a strong solid solution strengthening effect and exists in steel in solid solution form. In order to obtain higher strength, if the Si content is too high, the plasticity and toughness of the material will decrease significantly. The Si content is set at 0.37 to 0.45 wt%.

[0015] Mn: High manganese content can improve the transformation of austenite structure in steel, and at the same time, it can ensure the stability of austenite structure under severe processing. Therefore, the Mn content should be controlled between 20.5 and 23.0 wt%.

[0016] P and S: P and S elements are prone to segregation in steel and have a certain impact on the surface quality of steel and a significant impact on the toughness of steel. Considering the difficulty of removing P and S in the steelmaking process, the upper limit is set to 0.030 wt%.

[0017] Nb mainly plays a solid solution strengthening role, which can significantly improve the tensile strength of steel and also improve the weldability. The Nb content is set at 0.017~0.025wt%.

[0018] Vanadium (V) has significant precipitation strengthening and grain refinement strengthening effects. For high-strength steel, considering the strengthening effect of vanadium, its lower limit is guaranteed to be 0.28 wt%. However, as the vanadium content increases, it becomes more difficult to improve the toughness of the steel. Therefore, the V content is set to 0.28~0.35 wt%.

[0019] Alt: Alt elements can stabilize the austenite structure and refine the austenite grains. The Alt content is set to 0.025~0.037wt%.

[0020] N: Nitrogen is a strong austenite stabilizing element that will maximally inhibit the transformation of austenite into other structures. The N content is set at 0.25~0.50wt%.

[0021] A surface treatment method for high-manganese non-magnetic seismic-resistant steel bars includes the following steps: S1) Shot blasting: Stainless steel shot is used to blast the surface of the finished steel bars to remove the oxide scale and rust layer. At the same time, this process also causes a certain amount of plastic deformation on the surface of the steel bars and forms uniform, tiny and dense pits on the surface of the steel bars, which increases the surface area and roughness, and provides better surface adhesion for subsequent anti-corrosion and other processes. S2) Hot acid cleaning: This process follows GBT226-2015. Specifically, it uses hot acid corrosion method, using hydrochloric acid aqueous solution to perform hot acid corrosion cleaning on the shot-blasted steel bars to remove residual oxides on the surface. Then, it is rinsed with sodium carbonate aqueous solution and deionized water in sequence until there is no visible liquid residue on the surface. The steel bars are then taken out and dried. S3) Surface passivation treatment: The cleaned steel bars are immersed in sodium nitrite passivation solution for passivation treatment, then rinsed with deionized water until the surface is clean, and finally dried to obtain high manganese non-magnetic seismic steel bars with surface treatment.

[0022] Preferably, in step S1), the stainless steel shot is made of 430 material, which can avoid the introduction of magnetic impurities during the shot blasting process. The diameter is 0.8 mm, and the shot blasting time is 45~55 min. This can thoroughly remove the surface oxide scale while forming a suitable roughness on the surface of the steel bar, providing good surface conditions for subsequent pickling and passivation.

[0023] Preferably, in step S2), the concentration of the hydrochloric acid aqueous solution is 18%, the corrosion time is 55~65 min, and the corrosion temperature is 65~75℃. Within this parameter range, hot acid corrosion can effectively remove the dense oxides remaining on the surface of the steel bar after shot blasting, while avoiding excessive corrosion damage to the matrix, and ensuring that the mechanical and magnetic properties of the steel bar are not affected.

[0024] Preferably, in step S2), the volume ratio of the sodium carbonate aqueous solution is 3% to 5%. During neutralization and rinsing, the residual acidic substances on the surface of the steel bars can be effectively removed, preventing the acidic residue from adversely affecting the subsequent passivation effect.

[0025] Preferably, in step S3), the passivation time is 4 to 6 minutes. Within this time range, a complete and dense passivation film can be formed on the surface of the steel bar, effectively isolating oxygen and moisture in the air, preventing surface contamination and corrosion during storage and transportation, and ensuring the long-term stability of the non-magnetic properties.

[0026] Preferably, in steps S2) and S3), drying is performed using a drying oven. Compared with natural air drying, drying in a drying oven can quickly remove surface moisture, avoid surface contamination and rust risks caused by residual moisture, shorten the production cycle, and improve production efficiency.

[0027] Compared with the prior art, the present invention has the following advantages: 1. By optimizing the chemical composition of high-manganese non-magnetic seismic-resistant steel bars and rationally controlling the contents of C, Si, Mn, Nb, V, Alt, and N, while ensuring excellent mechanical properties such as yield strength, tensile strength, and elongation, extremely low remanence and relative permeability are achieved, and the microstructure is stable austenite; 2. A combined surface treatment process of shot blasting → hot acid cleaning → surface passivation is adopted. Through the synergistic effect of multiple steps, the oxide scale and rust layer and other magnetic residues on the surface of the steel bars are thoroughly removed, reducing the residual magnetism on the surface from the source. At the same time, the surface passivation treatment forms a complete passivation film on the surface of the steel bars, ensuring that the residual magnetism and relative permeability remain at an extremely low level after natural aging.

[0028] 3. 430 stainless steel shot is used for shot blasting, which avoids the magnetic contamination that may be introduced by traditional carbon steel shot. With a reasonable diameter and shot blasting time, the oxide scale can be removed while forming a surface roughness that is beneficial to subsequent processing. 4. The hot acid cleaning process uses an 18% hydrochloric acid aqueous solution to corrode the substrate at 65~75℃ for 55~65 minutes, and then uses a 3%~5% sodium carbonate aqueous solution to neutralize and rinse. This can effectively remove dense oxide residues while avoiding excessive corrosion that could damage the austenitic matrix. 5. Passivation treatment with sodium nitrite passivation solution for 4-6 minutes, followed by drying in a drying oven, forms a dense passivation protective film on the surface of the steel bars, effectively preventing secondary pollution and corrosion during storage and transportation, and improving the product yield and reliability. Attached Figure Description

[0029] Figure 1 This is a microstructure diagram of the high-manganese non-magnetic earthquake-resistant steel bar in Embodiment 1 of the present invention (×200). Figure 2 This is a microstructure diagram (×500) of the high-manganese non-magnetic earthquake-resistant steel bar in Embodiment 1 of the present invention. Detailed Implementation

[0030] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the invention.

[0031] A high-manganese non-magnetic seismic-resistant steel bar has the following chemical composition by weight percentage: C: 0.27~0.33%, Si: 0.37~0.45%, Mn: 20.5~23.0%, P: ≤0.030%, S: ≤0.030%, Nb: 0.017~0.025%, V: 0.28~0.35%, Alt: 0.025~0.037%, N: 0.25~0.50%, with the remainder being Fe and trace residual elements.

[0032] Among them, the mechanical properties are: yield strength ≥ 400 MPa, tensile strength ≥ 750 MPa, elongation ≥ 35.0%; the magnetic properties are: remanence ≤ 0.7 nT, relative permeability ≤ 1.05; the microstructure is austenite.

[0033] The production process of the above-mentioned high-manganese non-magnetic earthquake-resistant steel bars is as follows: batching → converter smelting → LF refining → continuous casting of small billets → heating → bar rolling → controlled cooling → finished steel bars.

[0034] The surface treatment method for finished high-manganese non-magnetic seismic-resistant steel bars includes the following steps: S1) Shot blasting: Stainless steel shot is used to blast the surface of the finished steel bars to remove the oxide scale and rust layer, and to form uniform, tiny and dense pits on the surface of the steel bars. The stainless steel shot is made of 430 material, with a diameter of 0.8mm, and the shot blasting time is 45~55min. S2) Hot acid cleaning: This process follows GBT226-2015, specifically employing a hot acid corrosion method. Hydrochloric acid solution is used to perform hot acid corrosion cleaning on the shot-blasted steel bars to remove residual oxides from the surface. Then, the surface is rinsed sequentially with sodium carbonate solution and deionized water until no visible liquid residue remains. The steel bars are then dried in a drying oven. The concentration of the hydrochloric acid solution is 18%, the corrosion time is 55-65 minutes, the corrosion temperature is 65-75℃, and the volume ratio of the sodium carbonate solution is 3%-5%. S3) Surface passivation treatment: The cleaned steel bars are immersed in sodium nitrite passivation solution for passivation treatment for 4 to 6 minutes. Then, they are rinsed with deionized water until the surface is clean. Finally, they are dried in a drying oven to obtain high manganese non-magnetic seismic steel bars with surface treatment.

[0035] Examples 1-4 and Comparative Examples 1-6 are set according to the weight percentage of chemical components. The specific component values ​​are shown in Table 1 below: Table 1 Chemical composition of each example and comparative example The surface treatment parameters for each embodiment and comparative example are shown in Table 2: Table 2 Surface treatment parameters for each embodiment and comparative example The mechanical and magnetic properties of each embodiment and comparative example are shown in Table 3: Table 3 Mechanical and magnetic properties of each embodiment and comparative example The microstructure of Example 1 is shown below. Figures 1-2 Examples 1-4 integrate all preferred technical features, and by optimizing the chemical composition ratio and strictly controlling the process parameters of each surface treatment process, high-manganese non-magnetic earthquake-resistant steel bars with optimal mechanical properties and non-magnetic properties were obtained.

[0036] In comparison, both methods have problems with proportions: The shot blasting time in Comparative Example 1 was too short to completely remove the oxides from the surface of the steel bars, resulting in a large amount of residual oxides and high residual magnetism, which could not meet the performance requirements of this invention.

[0037] The shot blasting time in Comparative Example 2 was longer than that in Comparative Example 1, but it still could not completely remove the oxides on the surface of the steel bars. A small amount of oxides remained on the surface of the steel bars, resulting in high residual magnetism, which could not meet the performance requirements of the present invention.

[0038] The corrosion temperature of Comparative Example 3 is room temperature, which cannot completely remove the dense oxides on the surface of the steel bars in a short time, and is also time-consuming, which does not meet the performance requirements of this invention.

[0039] The corrosion time of Comparative Example 4 is relatively short, and it cannot completely remove the dense oxides on the surface of the steel bars, thus failing to meet the performance requirements of this invention.

[0040] The passivation time of Comparative Example 5 is too short, and a complete passivation film cannot be formed on the surface of the steel bar, which affects subsequent storage and transportation and cannot meet the performance requirements of this invention.

[0041] Comparative Example 6 uses natural air drying after passivation, which cannot guarantee that the surface of the steel bar will not be contaminated, and it is also time-consuming, which cannot meet the performance requirements of this invention.

[0042] This invention relates to high-manganese non-magnetic seismic-resistant steel bars and their surface treatment method. By optimizing the chemical composition of the high-manganese non-magnetic seismic-resistant steel bars and rationally controlling the contents of C, Si, Mn, Nb, V, Alt, and N, excellent mechanical properties such as yield strength, tensile strength, and elongation are ensured while achieving extremely low remanence and relative permeability, with a stable austenitic microstructure. A combined surface treatment process of shot blasting → hot acid cleaning → surface passivation is employed. Through multi-step synergistic action, the oxide scale and rust layer and other magnetic residues on the steel bar surface are thoroughly removed, reducing surface remanence from the source. Simultaneously, the surface passivation treatment forms a complete passivation film on the steel bar surface, ensuring that the remanence and relative permeability remain extremely low even after natural aging. 430 material is selected. Shot blasting with stainless steel shot avoids the magnetic contamination that may be introduced by traditional carbon steel shot. With appropriate diameter and blasting time, it can remove oxide scale while forming a surface roughness that is beneficial to subsequent treatment. The hot acid cleaning process uses an 18% hydrochloric acid aqueous solution to corrode at 65~75℃ for 55~65 minutes, followed by neutralization and rinsing with a 3%~5% sodium carbonate aqueous solution. This effectively removes dense oxide residues while avoiding excessive corrosion that could damage the austenitic matrix. Passivation treatment with sodium nitrite passivation solution for 4~6 minutes, followed by drying in a drying oven, forms a dense passivation protective film on the surface of the steel bars. This effectively prevents secondary contamination and corrosion during storage and transportation, improving the product yield and reliability.

[0043] It should be noted that the above description of the technical solutions is exemplary, and this specification may be embodied in different forms and should not be construed as limiting it to the technical solutions set forth herein. Rather, providing these descriptions will ensure that the disclosure of this invention is thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Furthermore, the technical solutions of this invention are defined only by the scope of the claims.

[0044] The aspects disclosed in this specification and claims are merely examples, and therefore, this specification and claims are not limited to the details shown. In the foregoing description, detailed descriptions of relevant known functions or configurations have been omitted where it would unnecessarily obscure the focus of this specification and claims.

[0045] Finally, it should be noted that the above description is a further detailed explanation of the invention in conjunction with specific embodiments. It should not be considered that the specific implementation of the invention is limited to these descriptions. For those skilled in the art, any simple substitutions made without departing from the concept of the invention should be considered within the scope of protection of this invention. The above embodiments are merely representative examples of the invention. Obviously, the invention is not limited to the above embodiments and many variations are possible. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the invention should be considered within the scope of protection of this invention.

Claims

1. A high-manganese non-magnetic earthquake-resistant steel bar, characterized in that: Its chemical composition by weight percentage is as follows: C: 0.27~0.33%, Si: 0.37~0.45%, Mn: 20.5~23.0%, P: ≤0.030%, S: ≤0.030%, Nb: 0.017~0.025%, V: 0.28~0.35%, Alt: 0.025~0.037%, N: 0.25~0.50%, with the remainder being Fe and trace residual elements.

2. The high-manganese non-magnetic earthquake-resistant steel bar as described in claim 1, characterized in that: Its mechanical properties meet the following requirements: yield strength ≥ 400 MPa, tensile strength ≥ 750 MPa, and elongation ≥ 35.0%.

3. The high-manganese non-magnetic earthquake-resistant steel bar as described in claim 1, characterized in that: Its magnetic properties satisfy: remanence ≤ 0.7 nT, relative permeability ≤ 1.

05.

4. The high-manganese non-magnetic earthquake-resistant steel bar as described in claim 1, characterized in that: Its microstructure is austenite.

5. A surface treatment method for high-manganese non-magnetic earthquake-resistant steel bars as described in any one of claims 1 to 4, characterized in that: Includes the following steps: S1) Shot blasting: Stainless steel shot is used to blast the surface of the finished steel bars to remove the oxide scale and rust layer, and to form uniform, tiny and dense pits on the surface of the steel bars. S2) Hot acid cleaning: The steel bars after shot blasting are cleaned by hot acid corrosion using hydrochloric acid aqueous solution to remove residual oxides on the surface. Then, they are rinsed with sodium carbonate aqueous solution and deionized water in sequence until there is no visible liquid residue on the surface. They are then taken out and dried. S3) Surface passivation treatment: The cleaned steel bars are immersed in sodium nitrite passivation solution for passivation treatment, then rinsed with deionized water until the surface is clean, and finally dried to obtain high manganese non-magnetic seismic steel bars with surface treatment.

6. The surface treatment method for high-manganese non-magnetic earthquake-resistant steel bars as described in claim 5, characterized in that: In step S1), the stainless steel shot is made of 430 material, has a diameter of 0.8 mm, and the shot blasting time is 45~55 min.

7. The surface treatment method for high-manganese non-magnetic earthquake-resistant steel bars as described in claim 5, characterized in that: In step S2), the concentration of the hydrochloric acid aqueous solution is 18%, the corrosion time is 55-65 min, and the corrosion temperature is 65-75℃.

8. The surface treatment method for high-manganese non-magnetic earthquake-resistant steel bars as described in claim 5, characterized in that: In step S2), the volume ratio of the sodium carbonate aqueous solution is 3% to 5%.

9. The surface treatment method for high-manganese non-magnetic earthquake-resistant steel bars as described in claim 5, characterized in that: In step S3), the passivation time is 4~6 minutes.

10. The surface treatment method for high-manganese non-magnetic earthquake-resistant steel bars as described in claim 5, characterized in that: In steps S2) and S3), drying is performed using a drying oven.

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