Mn-cr non-magnetic reinforcing bar and production method

Abstract

This invention relates to the field of non-magnetic steel technology, and discloses a Mn-Cr non-magnetic steel bar and its production method. The Mn-Cr non-magnetic steel bar comprises the following components by mass percentage: C: 0.45%–0.55%, Si: 0.20%–0.40%, Mn: 18.0%–22.0%, V: 0.20%–0.30%; Nb: 0.02%–0.04%; Cr: 9.0%–10.0%, N: 0.10%–0.20%, P≤0.025%; S≤0.010%, with the remainder being Fe and other unavoidable impurities. This invention adopts an alloy design concept centered on high-nitrogen solid solution, strictly limiting aluminum content, reducing manganese, and increasing carbon. It also systematically integrates a complete set of suitable production processes, including precise nitrogen blowing throughout the process, weak cooling continuous casting, and slow heating.

Description

Technical Field

[0001] This invention relates to the field of non-magnetic steel technology, and in particular to a Mn-Cr non-magnetic steel bar and its production method. Background Technology

[0002] Non-magnetic steel, with its core characteristic of eliminating or reducing the influence of magnetic fields, has become an indispensable material in key fields such as power (e.g., generator retaining rings), high-end transportation (e.g., magnetic levitation components), national defense (e.g., minesweeper hulls) and precision equipment. Its low-cost and high-performance development is of great strategic significance for ensuring the implementation of major projects and national defense security.

[0003] For example, Chinese patent document CN117802392A discloses a method for preparing zero-magnetic steel bars for special non-magnetic concrete structures. The chemical composition of the zero-magnetic steel bars, 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 F. e(iron), in the preparation process, the following steps are followed: S1, smelting: melting the raw materials and adjusting the chemical composition; S2, rolling: changing the shape and size by rolling to make steel bars; S3, non-magnetic steel post-treatment: treating the steel bars by physical pretreatment, chemical pretreatment and powder spraying removal process; the process route of the smelting in step S1 is electric furnace steelmaking + LF furnace refining + ingot casting; however, the defects of this scheme are: (1) it contains a high degree of Al, and the high content of aluminum is very easy to react with oxygen and nitrogen in the steel to generate high melting point alumina or aluminum nitride clusters. These inclusions will deposit and block the molten steel pouring nozzle during continuous casting, leading to production interruption, seriously deteriorating the quality of the billet, and even causing steel leakage accidents; (2) the production process of this scheme is many and complex, and it requires the use of ingot casting process, resulting in low steel bar yield and high cost. After rolling, special post-treatment measures are also required, which is actually not suitable for large-scale industrial production. Summary of the Invention

[0004] To address the aforementioned problems, this invention aims to provide a Mn-Cr non-magnetic steel bar with similar performance but lower cost.

[0005] The technical solution of the present invention is as follows: This invention provides a Mn-Cr non-magnetic steel bar, which, by mass percentage, comprises the following components: C: 0.45%–0.55%, Si: 0.20%–0.40%, Mn: 18.0%–22.0%, V: 0.20%–0.30%; Nb: 0.02%–0.04%; Cr: 9.0–10.0%, N: 0.10%–0.20%, P≤0.025%; S≤0.010%, with the remainder being Fe and other unavoidable impurities.

[0006] According to one embodiment of the present invention, the composition of the Mn-Cr non-magnetic steel bar also satisfies: 26.5≤I=13C+Mn≤29.15; where C represents the mass percentage of C in the Mn-Cr non-magnetic steel bar, and Mn represents the mass percentage of Mn in the Mn-Cr non-magnetic steel bar.

[0007] According to one embodiment of the present invention, the room temperature microstructure of the Mn-Cr non-magnetic steel bar is austenite.

[0008] The present invention also provides a method for producing Mn-Cr non-magnetic steel bars according to the above embodiments, comprising the following steps: S1, smelting molten iron and scrap steel into crude steel liquid, and deoxidizing it during tapping; S2, transferring the deoxidized steel ladle to a refining furnace for refining; S3, transporting the refined steel ladle to a continuous casting platform and casting it into steel billets; S4, the steel billets entering a heating furnace until the billet microstructure is uniformly austenitized and carbonitrides are dissolved; S5, the austenitized steel billets are tapped, rolled, and then cooled to obtain the Mn-Cr non-magnetic steel bars.

[0009] According to one embodiment of the present invention, the specific process of step S1 is as follows: molten iron and scrap steel are added to an electric furnace or converter in a ratio of 6:4 to 8:2 to smelt crude steel. When the phosphorus content of the crude steel is not higher than 0.015% and the sulfur content is not higher than 0.005%, the steel is tapped at 1650 to 1700°C. During tapping, a deoxidizer is added to the ladle for deoxidation, wherein the deoxidizer accounts for 0.10% to 0.12% of the mass of the molten steel in the ladle.

[0010] According to one embodiment of the present invention, the deoxidizer is one or more of silicon-calcium-barium deoxidizer, rare earth deoxidizer, and magnesium deoxidizer.

[0011] According to one embodiment of the present invention, the specific process of step S2 is as follows: After deoxidation, the ladle is transferred to the refining furnace and heated to 1540-1550°C. 2.7-2.8 kg / t of lime and 3.4-3.5 kg / t of pre-melted refining slag are added to further remove P, S and inclusions. High-carbon ferromanganese is added in batches at a rate of 300-320 kg / t. The high-carbon ferromanganese is melted in batches by electric arc heating in the refining furnace using an LF furnace. Nitrogen blowing and stirring are carried out throughout the refining process, with a nitrogen flow rate of 250-350 ml / min. After refining, the ladle is allowed to stand and stirred with nitrogen for ≥10 minutes, with a nitrogen flow rate of 100-150 ml / min. 1.30-1.40 kg / t of solid nitrogen enhancer is added, and the N content of the solid nitrogen enhancer is 25%-33%.

[0012] According to one embodiment of the present invention, the specific process of step S3 is as follows: the refined steel ladle is transported to the continuous casting table and cast into steel billets. The initial casting temperature is 1400-1430℃, and a weak cooling process is adopted: the flow rate of cooling water in the crystallizer is 100-150 liters / minute, and the water flow rate in the fan-shaped section is 0.5-0.6 liters / kg.

[0013] According to one embodiment of the present invention, in step S4: the heating furnace is set with the following parameters: heating rate of 15-16°C / min, heating temperature of 1050-1120°C, and holding temperature for 30-40 minutes.

[0014] According to one embodiment of the present invention, in step S5: the tapping temperature is controlled at 1000-1070°C, and the cooling bed temperature is controlled at 800-870°C after rolling to obtain the Mn-Cr non-magnetic steel bar.

[0015] The role of alloying elements in this invention is as follows: C: During the heating process of the steel billet, C dissolves in the austenite and, during the cooling process after rolling, forms carbides with alloying elements such as V and Nb, which can significantly improve the strength of the steel. C is also an element that expands the austenite phase region, especially when combined with Mn, it can further expand the austenite phase region, ensuring the formation of a single austenite structure at room temperature and maintaining extremely weak magnetic properties. However, as the C content increases, the ductility and toughness of the steel reinforcement decrease.

[0016] Si plays a role in solid solution strengthening, improving the yield strength and tensile strength of steel bars. However, if the Si content is too high, it will cause the grains of high-Mn steel to be coarse, reducing its ductility and toughness.

[0017] Mn is a strong austenite-forming element that can expand and stabilize the austenite phase region. It is the most important element for obtaining austenitic structure and ensuring extremely weak magnetic properties at room temperature. It can also dissolve in austenite, playing a role in solid solution strengthening and improving the strength of steel bars. However, in high-Mn steel, as the Mn content increases, the size of deformation twins increases, which actually reduces the strength.

[0018] V: During the heating process of steel billet, it dissolves in austenite and, during the cooling process after rolling, it forms carbonitrides with C and N to precipitate diffusely, significantly increasing the strength of the steel. Excessive V weakens the precipitation strengthening effect and is expensive, increasing production costs.

[0019] Nb: Dissolves in austenite during the heating process of steel billet. During the cooling process after rolling, it forms carbonitrides with C and N, which hinder grain growth and play a role in grain refinement and strengthening. Excessive Nb content leads to high prices and increased production costs.

[0020] Cr: Its primary function is to enhance the rust resistance of steel bars by forming a Cr2O3-rich passivation film on the surface of the steel matrix. The magnetic properties of iron oxides are also significantly increased, ensuring the steel bars maintain extremely weak magnetic properties during long-term use. Additionally, it distorts the austenite lattice, producing a solid solution strengthening effect and increasing the material's strength. However, excessively high Cr levels can decrease elongation.

[0021] Ni (N) can replace austenite-forming elements such as Ni and Co, suppressing ferrite production in steel, making the austenite structure more stable, ensuring extremely weak magnetic properties, and forming nitrides with V and Nb, significantly improving the strength of steel. However, excessively high N content will increase the ductile-brittle transition temperature, increasing the brittleness of the steel.

[0022] P and S: These are harmful impurity elements, especially S, which has an adverse effect on the toughness, corrosion resistance, and extremely weak magnetic properties of steel bars. The lower the content in steel, the better.

[0023] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention aims to develop a non-magnetic steel alternative material with lower production costs while maintaining similar performance. To achieve high stability and low cost non-magnetic steel bars, this invention adopts an alloy design concept centered on high-nitrogen solid solution, strictly limiting aluminum content, reducing manganese and increasing carbon, and systematically integrates a complete set of adapted production processes, including precise nitrogen blowing throughout the process, weak cooling continuous casting, and slow heating. This effectively solves the feasibility problem in the industrial production of high-nitrogen steel while ensuring comprehensive performance.

[0024] First, it exhibits excellent elongation at room temperature. Given that non-magnetic steel is primarily used in room-temperature environments, room-temperature elongation at fracture is a key performance indicator. The preferred embodiment of this invention (Example 1) achieves an elongation at fracture of up to 62% at room temperature. This high elongation gives non-magnetic steel a core advantage in critical applications such as precision instrument rooms, medical MRI, and marine engineering: it not only provides a safety warning through significant plastic deformation, preventing brittle sudden structural failure, but also absorbs stress under complex construction conditions and long-term loads due to its good toughness, avoiding the generation and propagation of microcracks. This synergistically ensures the stability of its extremely weak magnetism and high corrosion resistance throughout its service life, fundamentally meeting the stringent requirements of special buildings for materials that are "strong, tough, non-magnetic, and reliable." The main reasons for achieving this high elongation are: 1. By setting an appropriate I value (because C can significantly expand the austenite phase region, resulting in a stable austenite structure at lower Mn contents; in addition, C is cheaper than Mn, so substituting Mn with C reduces costs while obtaining good weak magnetic properties. If the I value is below 23.85, some austenite will transform into martensite at room temperature, reducing weak magnetic properties and elongation), a single, stable austenite structure can still be obtained even with a different composition system than in the prior art, providing a foundation for high plasticity; 2. Nb carbonitrides can effectively pin grain boundaries during heating and rolling, inhibiting austenite grain growth. Fine-grained microstructure not only improves strength through the Hall-Page effect, but also significantly enhances the plasticity and toughness of the material. 3. In view of the poor thermal conductivity and high thermal stress of high alloy steel, a weak cold continuous casting and slow heating (15-16℃ / min) process was adopted, which effectively prevented macroscopic defects such as internal cracks and surface cracks from being generated in the billet during solidification and heating, and avoided these initial defects from becoming the origin of fracture in subsequent deformation, thereby ensuring high elongation.

[0025] Second, the stability of magnetic properties during long-term use. In contrast, the surface of the prior art tends to form a discontinuous and non-dense alumina (Al2O3) film after prolonged use, while the present invention forms a continuous, dense, and highly adhesive chromium oxide (Cr2O3) passivation film. Under conditions where the material cost and basic performance are similar between the present invention and the prior art, the Cr content in the present invention is significantly higher than the Al content in the prior art, resulting in a denser and more continuous chromium oxide film. The excellent adhesion and self-healing ability of the chromium oxide film effectively prevents oxygen and moisture penetration, while the discontinuous alumina film may lead to further oxidation of the steel reinforcement surface, generating iron oxides such as Fe3O4, Fe2O3, α-FeOOH, and γ-FeOOH. These iron oxides are strongly magnetic, significantly increasing the relative permeability of the material, thus failing to guarantee the stability of the extremely weak magnetic properties of the non-magnetic steel reinforcement during long-term service. Third, this application, through an aluminum-free composition design, avoids the problems of Al2O3 inclusions and the strong bonding between aluminum and nitrogen, which easily leads to AlN formation, caused by the addition of large amounts of aluminum. Therefore, it eliminates the need for deep purification and composition fine-tuning through RH vacuum refining. Simultaneously, it innovatively employs full-process nitrogen blowing technology in the LF furnace refining stage, achieving steel homogenization, temperature control, and efficient nitrogen alloying under atmospheric pressure. This "composition-process" synergistic optimization path ensures steel purity and high nitrogen solid solution effect while successfully omitting the expensive RH vacuum refining process, significantly reducing equipment investment and production costs, and simplifying the production process. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 The images are scanning electron microscope (SEM) images of the samples prepared in Examples 1 to 3 of the present invention. In the images, energy spectrum 19, energy spectrum 20, and energy spectrum 21 represent the samples of Example 3, Example 2, and Example 1, respectively. Figure 1 It can be seen that a dense chromium oxide film can be formed on the surface of the products in Examples 1 to 3. In addition, it can be seen that as the chromium content increases, the chromium oxide film becomes denser, more uniform, and has stronger coating properties. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0029] This invention provides a Mn-Cr non-magnetic steel bar, which, by mass percentage, comprises the following components: C: 0.45%–0.55%, Si: 0.20%–0.40%, Mn: 18.0%–22.0%, V: 0.20%–0.30%; Nb: 0.02%–0.04%; Cr: 9.0%–10.0%, N: 0.10%–0.20%, P≤0.025%; S≤0.010%, with the remainder being Fe and other unavoidable impurities.

[0030] According to one embodiment of the present invention, the composition of the Mn-Cr non-magnetic steel bar also satisfies: 26.5≤I=13C+Mn≤29.15; where C represents the mass percentage of C in the Mn-Cr non-magnetic steel bar, and Mn represents the mass percentage of Mn in the Mn-Cr non-magnetic steel bar.

[0031] According to one embodiment of the present invention, the room temperature microstructure of Mn-Cr non-magnetic steel bars is austenite.

[0032] The present invention also provides a method for producing Mn-Cr non-magnetic steel bars according to the above embodiments, comprising the following steps: S1, smelting molten iron and scrap steel into crude steel liquid, and deoxidizing it during tapping; S2, transferring the deoxidized steel ladle to a refining furnace for refining; S3, transporting the refined steel ladle to a continuous casting platform and casting it into steel billets; S4, the steel billets entering a heating furnace until the billet microstructure is uniformly austenitized and carbonitrides are dissolved; S5, the austenitized steel billets are tapped, rolled, and then cooled to obtain Mn-Cr non-magnetic steel bars.

[0033] According to one embodiment of the present invention, step S1 is specifically as follows: molten iron and scrap steel are added to an electric furnace or converter in a ratio of 6:4 to 8:2 to smelt crude steel. When the phosphorus content of the crude steel is not higher than 0.015% and the sulfur content is not higher than 0.005%, the steel is tapped at 1650 to 1700°C. During tapping, a deoxidizer is added to the ladle for deoxidation, wherein the deoxidizer accounts for 0.10% to 0.12% of the mass of the molten steel in the ladle.

[0034] According to one embodiment of the present invention, the deoxidizer is one or more of silicon-calcium-barium deoxidizer, rare earth deoxidizer, and magnesium deoxidizer.

[0035] According to one embodiment of the present invention, step S2 is specifically as follows: After deoxidation, the ladle is transferred to a refining furnace and heated to 1540-1550°C. 2.7-2.8 kg / t of lime and 3.4-3.5 kg / t of pre-melted refining slag are added to further remove P, S and inclusions. High-carbon ferromanganese is added in batches at a rate of 300-320 kg / t. The high-carbon ferromanganese is melted in batches by arc heating in the refining furnace using an LF furnace. Nitrogen blowing and stirring are carried out throughout the refining process, with a nitrogen flow rate of 250-350 ml / min. After refining, the ladle is allowed to stand and stirred with nitrogen for ≥10 minutes, with a nitrogen flow rate of 100-150 ml / min. 1.30-1.40 kg / t of solid nitrogen enhancer is added, with the N content of the solid nitrogen enhancer being 25%-33%.

[0036] According to one embodiment of the present invention, the specific process of step S3 is as follows: the refined steel ladle is transported to the continuous casting table and cast into steel billets. The initial casting temperature is 1400-1430℃, and a weak cooling process is adopted: the flow rate of cooling water in the crystallizer is 100-150 liters / minute, and the water volume in the fan-shaped section is 0.5-0.6 liters / kg.

[0037] According to one embodiment of the present invention, in step S4: the heating furnace is set with the following parameters: heating rate of 15-16°C / min, heating temperature of 1050-1120°C, and holding temperature for 30-40 minutes.

[0038] According to one embodiment of the present invention, in step S5: the tapping temperature is controlled at 1000-1070°C, and the cooling bed temperature is controlled at 800-870°C after rolling to obtain Mn-Cr non-magnetic steel bars.

[0039] Examples 1 to 3 and Comparative Examples 1 to 3 of this invention were all produced according to the aforementioned method. The specific parameter settings for each method are shown in Table 1. The obtained products were tested by photoelectric direct-reading spectroscopy, X-ray fluorescence spectroscopy, or chemical wet analysis, and their chemical composition and I value are shown in Table 2.

[0040] It should be noted that: Example 1 uses silicon-calcium-barium deoxidizer and rare earth-based deoxidizer; Example 3 uses magnesium-based deoxidizer; Comparative Examples 1 to 3 all use silicon-calcium-barium deoxidizer; Examples 1 to 3 and Comparative Examples 1 to 3 all use silicon-manganese nitride solid nitrogen-increasing agent with an N content of 28%, which may have slight errors during the manufacturer's production.

[0041] Table 1

[0042] Table 2

[0043] The mechanical properties, magnetic permeability, and chloride ion limits of the embodiments and comparative examples of this invention are shown in Table 3. According to GB / T1499.2-2018, the yield strength of HRB400 is ≥400MPa, and the tensile strength is ≥540MPa. In YB / T 6148-2023, "High-manganese non-magnetic steel plates for power transformers," magnetic permeability is the core indicator for defining "non-magnetic steel" and distinguishing grades. This standard defines "non-magnetic steel" as "steel with a relative magnetic permeability not greater than 1.05." The chloride ion limit, i.e., the critical chloride ion concentration, is typically >1.0% for stainless steel reinforcing bars (such as 304 and 316).

[0044] Among them: Although the rolling process of Comparative Example 1 met the requirements of steps S4 and S5, the composition did not meet the requirements, resulting in the elongation, relative permeability, and chloride ion limit of the steel bar not meeting the requirements of the aforementioned national and industry standards; The composition of Comparative Example 2 met the requirements, but the rolling process did not meet the requirements of steps S4 and S5, resulting in the elongation, relative permeability, and chloride ion limit not meeting the requirements of the aforementioned national and industry standards, but it was better than Comparative Example 1; The composition of Comparative Example 3 did not meet the requirements of claim 1, and the rolling process did not meet the requirements of steps S4 and S5, resulting in a further reduction in the elongation, relative permeability, and chloride ion limit.

[0045] Table 3

[0046] In Table 3: ReL is the yield strength; Rm is the tensile strength; A is the elongation after fracture at a gauge length of 5d (d is the nominal diameter of the steel bar).

[0047] This application defines an austenite stability index I (I=13C+Mn) and limits it to the range of 26.5 to 29.15. Its core lies in transforming the microstructure control of materials science into a quantifiable and controllable engineering parameter. In the Mn-Cr non-magnetic steel prepared in this application, carbon and manganese synergistically stabilize austenite, effectively suppressing martensitic phase transformation and ensuring the formation of a stable single-phase austenite microstructure at room temperature and during subsequent processing. This mechanism directly guarantees the product's fundamental properties of non-magnetism and high plasticity. Simultaneously, this formula provides a clear basis for composition adjustments during production, enhances process controllability, and forms effective patent protection through a concise mathematical relationship.

[0048] Based on the requirements of the YB / T 6148-2023 standard, the non-magnetic steel bar of this application does indeed meet the two core indicators of "relative magnetic permeability ≤ 1.05" and "elongation after fracture ≥ 40%" in the standard. Its performance has reached the same level as that of non-magnetic steel plates used in high-end transformers. This indicates that the non-magnetic steel bar has great potential for cross-industry application in specific high-end fields. Although the standard targets steel plate form, mainly used for magnetic shielding structures inside power transformers, the steel bar product of this application, due to its equivalent performance in non-magnetism and high plasticity, can target other fields that require similar material properties but are more suitable for wire or reinforcing bar structures. For example, in the construction of precision instrument laboratories, medical MRI rooms, particle accelerators, or high-precision navigation facilities, where completely non-magnetic reinforced concrete structural foundations or shielding cages are required, the non-magnetic steel bar of this application is an ideal reinforcing material. Furthermore, in specialized vessels (such as scientific research vessels), seabed observation networks, or national defense and security facilities sensitive to magnetic field interference, the concrete used for pouring critical components can achieve electromagnetic stealth or zero interference while ensuring structural strength. Its elongation rate of up to 40% also ensures the safety and reliability of components under complex stress conditions.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A type of Mn-Cr non-magnetic steel bar, characterized in that, The Mn-Cr non-magnetic steel bar comprises the following components by weight percentage: C: 0.45%~0.55%, Si: 0.20%~0.40%, Mn: 18.0%~22.0%, V: 0.20%~0.30%; Nb: 0.02%~0.04%; Cr: 9.0%~10.0%, N: 0.10%~0.20%, P≤0.025%; S≤0.010%, with the remainder being Fe and other unavoidable impurities.

2. The Mn-Cr non-magnetic steel bar according to claim 1, characterized in that, The composition of the Mn-Cr non-magnetic steel bar also satisfies: 26.5≤I=13C+Mn≤29.15; where C represents the mass percentage of C in the Mn-Cr non-magnetic steel bar, and Mn represents the mass percentage of Mn in the Mn-Cr non-magnetic steel bar.

3. The Mn-Cr non-magnetic steel bar according to claim 1 or 2, characterized in that, The room temperature microstructure of the Mn-Cr non-magnetic steel bar is austenite.

4. A method for producing Mn-Cr non-magnetic steel bars according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Smelting molten iron and scrap steel into crude steel, and deoxidizing it during tapping; S2. The deoxidized steel ladle is transferred to the refining furnace for refining. S3. The refined steel ladle is transported to the continuous casting table and cast into steel billets; S4. The steel billet enters the heating furnace until the billet microstructure is uniformly austeniticized and carbonitrides are dissolved. S5. After the austenitized steel billet is tapped, it is rolled and then cooled to obtain the Mn-Cr non-magnetic steel bar.

5. The production method according to claim 4, characterized in that, The specific process of step S1 is as follows: Molten iron and scrap steel are added in an electric furnace or converter at a ratio of 6:4 to 8:2 to smelt crude steel. When the phosphorus content of the crude steel is not higher than 0.015% and the sulfur content is not higher than 0.005%, the steel is tapped at 1650 to 1700°C. During tapping, a deoxidizer is added to the ladle for deoxidation, wherein the deoxidizer accounts for 0.10% to 0.12% of the mass of the molten steel in the ladle.

6. The production method according to claim 5, characterized in that, The deoxidizer is one or more of silicon-calcium-barium deoxidizer, rare earth deoxidizer, and magnesium deoxidizer.

7. The production method according to claim 5 or 6, characterized in that, The specific process of step S2 is as follows: After deoxidation, the ladle is transferred to the refining furnace and heated to 1540–1550℃. 2.7–2.8 kg / t of lime and 3.4–3.5 kg / t of pre-melted refining slag are added to further remove phosphorus, sulfur, and inclusions. High-carbon ferromanganese is added in batches at a rate of 300–320 kg / t. The refining furnace melts the high-carbon ferromanganese in batches using an electric arc heating system in an LF furnace. Nitrogen blowing and stirring are carried out throughout the refining process at a flow rate of 250–350 ml / min. After refining, the ladle is allowed to stand for at least 10 minutes with nitrogen blowing and stirring at a flow rate of 100–150 ml / min. Solid nitrogen enhancer at 1.30–1.40 kg / t is also added, with an N content of 25%–33%.

8. The production method according to claim 5 or 6, characterized in that, The specific process of step S3 is as follows: The refined steel ladle is transported to the continuous casting table and cast into steel billets. The initial casting temperature is 1400-1430℃, and a weak cooling process is adopted: the flow rate of cooling water in the crystallizer is 100-150 liters / minute, and the water flow rate in the fan-shaped section is 0.5-0.6 liters / kg.

9. The production method according to claim 5 or 6, characterized in that, In step S4: The heating furnace is set with the following parameters: heating rate 15-16℃ / min, heating temperature 1050-1120℃, and holding temperature for 30-40 minutes.

10. The production method according to claim 5 or 6, characterized in that, In step S5: The tapping temperature is controlled at 1000-1070℃, and after rolling, the cooling bed temperature is controlled at 800-870℃ for cooling to obtain the Mn-Cr non-magnetic steel bar.

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