Production method of low-magnetism corrosion-resisting steel bar

Abstract

The invention relates to a production method of a reinforcing steel bar, in particular to a production method of a low-magnetism corrosion-resisting reinforcing steel bar. Belongs to the technical field of reinforcements. The production method of the low-magnetism corrosion-resisting steel bar comprises the working procedures of chemical component setting, steelmaking, pouring, blank making, coping, rough rolling, intermediate rolling, finish rolling and the like. By increasing the manganese content, properly adding nickel elements, optimizing alloying elements, emphatically adjusting the chromium content and combining the technical means of hot rolling parameter optimization, shot blasting, acid pickling and the like, the mechanical property and excellent corrosion resistance are guaranteed, the yield strength is larger than or equal to 400 MPa, and the ductility is larger than or equal to 40%; the production cost of the steel bar is reduced, and excellent performance is reserved.

Description

Technical Field

[0001] The invention relates to a production method of steel bars, in particular to a production method of low-magnetic corrosion-resistant steel bars, and belongs to the technical field of steel bars. Background Art

[0002] As a functional steel material, low-magnetic steel has been widely used in special magnetic shielding building structures, rail transportation, zero-magnetic medicine, high-tech, nuclear power, military industry and other fields in recent years.

[0003] Currently, nearly all low-magnetic steels on the market have some issues, ranging from poor corrosion resistance to high production costs to poor mechanical properties and high remanence. For example, traditional non-magnetic steel 45Mn17Al3 has poor corrosion resistance, while 316L and 304L have high remanence, relatively high production costs, and relatively low mechanical properties. Other materials, such as aluminum alloys and titanium alloys, also present challenges in terms of mechanical properties and pricing.

[0004] Patent document CN117512308A discloses a non-magnetic steel bar and its preparation method. This solution heats, rolls and cools a cast billet with a set chemical composition, controls the process parameters, and produces a non-magnetic steel bar with an absolute magnetic permeability of (1.28~1.30)×10^-6 h / m. Specifically, the set chemical composition includes the following components by mass fraction: C 0.55~0.65%, Cr 3.0~3.5%, Mn 18.0~18.5%, Si 0.45~0.55%, N 0.014~0.015%, V 1.70~1.73%, P ≤0.010%, S ≤0.010%, O ≤0.0010%. This solution uses ultra-high manganese content to replace nickel to maintain a fully austenitic structure, thereby achieving the effects of low magnetism, low cost, and high mechanical properties. However, this material has the disadvantage of being corrosion-resistant. Therefore, it is very necessary to develop a low-magnetic steel bar with good economy, low relative magnetic permeability and high corrosion resistance. Summary of the Invention

[0005] The present invention aims to address the aforementioned issues and thus provides a method for producing low-magnetic, corrosion-resistant steel bars. This method utilizes the economical "manganese-replacing-nickel" approach. By optimizing the composition of alloying elements, focusing on adjusting the chromium content, and combining hot-rolling parameter optimization with other technical measures, it reduces the production cost of the steel bars while retaining their excellent corrosion resistance, mechanical properties, and low magnetic properties.

[0006] The technical solutions of the present invention for solving the above problems are as follows: A method for producing low-magnetic corrosion-resistant steel bars comprises the following steps: S1. Prepare a steel ingot with a set chemical composition; S2, heating the steel ingot to 1200°C~1300°C, S3, rolling the steel ingot through at least 10 passes to form a billet; S4. Grind after cooling. Grind requires that the surface has no obvious defects. S5, heating the billet to 1000° C. to 1200° C.; S6, the billet is subjected to 5-10 passes of rough rolling to produce round steel of φ70-100 mm, and then the billet is subjected to intermediate rolling and finishing rolling, and is air-cooled and cut to length to produce steel bars; The set chemical composition includes the following components by mass fraction: C 0.08~0.16%, Cr 9.0~12.0%, Ni 0.8~3.8%, Mn 18.0~23.5%, N 0.15~0.4%, Si ≤1.0%, Cu ≤0.5%, P ≤0.01%, S ≤0.01%, O ≤0.001%; the balance is iron.

[0007] Existing technology shows that to reduce the relative magnetic permeability of steel bars, there are several methods, including but not limited to the following: 1. Ingredient design Adding non-ferromagnetic elements can reduce the magnetic permeability of the material. For example, adding 1% to 3% silicon can increase the resistivity, reduce eddy current loss, and reduce the magnetic permeability. For example, silicon steel is often used in transformers, and its magnetic permeability is lower than that of ordinary carbon steel. Aluminum as a deoxidizer can refine the grain size, increase the resistivity, and indirectly reduce the magnetic permeability. Adding sufficient nickel can achieve full austenitization and significantly reduce the magnetic permeability. 2. Heat treatment process By high temperature annealing, ferrite is transformed into austenite, reducing the magnetic permeability of the material; When hot rolling is used, fine-grained ferrite structure is formed and magnetic permeability is reduced by controlling the final rolling temperature and cooling rate; 3. Cold working control Reduce plastic deformation such as cold drawing and cold rolling to avoid the magnetic domain pinning effect caused by excessive dislocation density; 4. Grain refinement Refining the grains through modifiers or controlled rolling processes reduces the resistance to domain wall movement, thereby reducing the magnetic permeability; 5. Surface treatment Such as zinc, nickel or copper plating, spraying epoxy resin, polyurethane and other non-magnetic coatings, etc.

[0008] However, not all of the above methods are applicable to the present invention in solving this problem. After comprehensively considering various issues, the inventors have established a technical direction based on ultra-high manganese austenitic stainless steel steel bars to further solve the corrosion resistance problem.

[0009] High-manganese austenitic stainless steels, such as Series 2 stainless steels, are characterized by a combination of high manganese (typically 5% to 10% Mn) and nitrogen, along with low or no nickel. By partially replacing nickel with manganese and nitrogen, these stainless steels can reduce material costs while maintaining the stability of the austenitic structure, which is essential for maintaining low magnetic permeability.

[0010] On the one hand, the increase in manganese content brings significant effects, such as increased tensile strength and yield strength; on the other hand, it also brings significant problems, such as decreased corrosion resistance: high manganese easily forms manganese sulfide inclusions, which become the starting point of chloride ion corrosion and reduce pitting corrosion resistance.

[0011] In the present invention, the manganese content is further increased from 5% to 10% in the prior art to 18.0 to 23.5%, which will further lead to a decrease in pitting corrosion resistance. In order to solve this problem, the present invention increases the chromium content from 3.0 to 3.5% to 9.0 to 12.0%. Chromium is the most core alloying element in stainless steel, which gives the material corrosion resistance and works with other elements to stabilize the microstructure. After chromium is oxidized, a dense chromium oxide layer (thickness of about 2 to 10 nm) is generated, which covers the metal surface and prevents oxygen, water, acid, alkali, etc. from further corroding the matrix; after the passivation film is destroyed, it will also regenerate rapidly in an oxygen-containing environment to maintain corrosion resistance. In addition, chromium and carbon easily form chromium carbide (Cr 23 C6), resulting in local chromium depletion (sensitization phenomenon), which is prone to cracking in high temperature or corrosive environment. Therefore, the present invention also controls the C content to 0.08-0.16%.

[0012] As a preferred embodiment of the above technical solution, the method further includes steps S7 and S8. S7, shot blasting the steel bars obtained in S6 to remove the surface oxide layer; S8. After the surface oxide layer is removed, the steel bar is pickled and passivated, then the surface is rinsed clean with high-pressure water and finally dried.

[0013] The inventors have also found that corroded steel bars can also lead to an increase in magnetic permeability. Therefore, the present invention further performs pickling and passivation on the prepared steel bars, and performs shot blasting before passivation.

[0014] As a preferred embodiment of the above technical solution, in step S3, the initial rolling temperature is 1200°C to 1300°C, the final rolling temperature is not lower than 800°C, and the reduction in each pass does not exceed 10%.

[0015] As a preferred embodiment of the above technical solution, in step S6, the initial rolling temperature during rough rolling is 1000°C to 1200°C, the final rolling temperature is not lower than 8000°C, and the reduction in each pass does not exceed 10%.

[0016] High-temperature aging promotes the formation of σ phase, resulting in a decrease in toughness. Therefore, in the above-mentioned technical solutions of the present invention, the final rolling temperature is always no less than 800°C. High-manganese steel has low plasticity and requires multiple passes of small-deformation rolling (e.g., staged control of the total reduction ratio) to prevent cracking and improve surface finish.

[0017] As a preferred embodiment of the above technical solution, in step S6, the rolling speed during the rolling process of the intermediate rolling and finishing rolling mills is controlled at 0.2 m / s to 0.3 m / s.

[0018] As a preferred embodiment of the above technical solution, in step S6, the workpiece is isothermally heated to 950°C before entering the intermediate rolling and finishing rolling mills.

[0019] Due to composition and production equipment reasons, a two-stage rolling process is adopted to ensure product surface quality. First, the ground ingots are rolled into billets of appropriate sizes, and then further ground to remove surface defects. Secondly, the ground billets are rolled a second time. During the rolling process, to ensure that their mechanical properties can reach HRB400 level, the temperature of all specifications of steel bars entering the intermediate rolling unit is controlled according to the production site conditions before entering the intermediate rolling unit, and the rolling speed of the finished product rolling mill is controlled. For example, before entering the intermediate and finishing rolling units, the intermediate billet of 20 threaded steel (φ20 rebar) is first isothermally heated to 950℃ before entering the rolling mill. The finished product speed is controlled at 3.2m / s to ensure its stable mechanical properties.

[0020] As a preferred embodiment of the above technical solution, the shot blasting treatment includes four treatment groups in sequence. The first treatment group adds G18 steel shot abrasive inside the shot blasting wheel, the second treatment group adds bearing steel sand and cut shot abrasive in a ratio of 2:1 inside the shot blasting wheel, the third treatment group adds quartz sand abrasive inside the shot blasting wheel, and the fourth treatment group adds glass sand abrasive inside the shot blasting wheel.

[0021] Existing shot blasting techniques for steel bars typically use a single abrasive, such as cast iron shot or cut wire shot with an HRC of 40-50. However, in the above-mentioned technical solution, the G18 steel shot abrasive, made from crushed alloy steel shot, has an HRC of approximately 53-60. It offers high hardness, toughness, and impact resistance, making it widely used for cleaning and strengthening metal surfaces. Bearing steel grit, with an HRC of approximately 56-65, is a high-hardness steel grit suitable for high-precision bearing manufacturing and shot blasting operations requiring angular retention. Cutting shot abrasive, with an HRC of approximately 40-50, offers lower hardness but greater toughness, making it suitable for removing oxide scale from steel surfaces. Quartz sand abrasive has an HRC of approximately 7, and glass sand abrasive has an HRC of approximately 6-7.

[0022] The present invention employs multiple treatment groups and a variety of abrasives during shot blasting. The first treatment group removes the majority of the scale (e.g., 80%), achieving uniform removal with dispersed residual points. The remaining small portion (e.g., 20%) consists not only of intact scale residue but also of scale residue that has been reduced in size (e.g., from flakes to dots) and dispersed across the steel bar surface. This is because, while G18 steel shot has a high hardness, it lacks relatively good toughness, potentially causing it to break during the shot blasting process and fail to be completely removed. Using it to completely remove scale through parameter adjustment can lead to over-blasting. The present invention innovatively proposes a 2:1 ratio of bearing steel grit to cutting shot abrasive for the second treatment group. The bearing steel grit has a higher hardness and can remove the remaining 20% of scale residue due to the insufficient hardness of the G18 steel shot abrasive. The cutting shot abrasive, while having a relatively low HRC, has good toughness and can also remove the remaining 20% of scale residue due to the insufficient toughness of the G18 steel shot abrasive.

[0023] Therefore, in the above technical solution of the present invention, the first two treatment groups are aimed at removing oxide scale. This is because the steel grade of the present invention has significantly improved hardness compared to the low-magnetic steel bars used in the prior art. Therefore, it is no longer possible to use only cast iron shot or cut wire shot with HRC 40-50 as in the prior art.

[0024] The abrasive in the third treatment group is quartz sand. This treatment group is not aimed at the oxide scale, but at the substrate after the oxide scale is ground off. It repairs the damage by grinding. Its mechanism is similar to grinding to repair surface defects, but the shot blasting effect is significantly better. The abrasive in the fourth treatment group is glass sand. Glass contains about 75% silica. It is equivalent to a compound of quartz sand and other sands, but the effect of directly using glass sand is better. Its function is to perform a secondary repair on the surface repaired by quartz sand, thereby further repairing the defects on the surface of the steel bar substrate, reducing the specific surface area of the steel bar substrate, and reducing the surface roughness; thus preparing for the subsequent pickling and passivation.

[0025] As a preferred embodiment of the above technical solution, the processing speed of the shot blasting is controlled at 1~2.2m / min.

[0026] As a preferred embodiment of the above technical solution, the pickling and passivation treatment is specifically carried out by using a 15wt% sulfuric acid solution for pickling and passivation for 30 to 60 minutes.

[0027] In the prior art, pickling and passivation are generally performed using HNO3 or HF+HNO3. However, in the present invention, due to the pre-treatment of four shot blasting treatments, and the steel grades of the present invention differ from those of the prior art, pickling with HNO3 or HF+HNO3 would produce a more violent reaction, which would easily lead to surface reconstruction due to rust, thereby increasing surface roughness, causing surface pitting, and even corroding the substrate. In other words, moderate pickling can effectively reduce surface roughness and smoothen the surface. For example, the Ra of unpickled cold-rolled steel sheet is approximately 1.0-2.0 μm, while the Ra after pickling is approximately 0.5-1.0 μm. Excessive pickling, however, is detrimental. For example, pickling 304 stainless steel in 20% HCl (60°C) for 5 minutes increases its Ra from 0.8 μm to 1.5 μm; if the pickling time is extended to 10 minutes, the Ra reaches 2.5 μm. Excessive pickling can be understood from two perspectives: the intensity of the reaction and the duration of the pickling treatment. Therefore, after discovering the above problem, the inventors changed the pickling solution to a 15wt% sulfuric acid solution. Normally, a 15wt% sulfuric acid solution is not suitable for use as a pickling solution. However, in the present invention, due to the steel type and the specific shot blasting process, the intensity of the reaction can be better controlled. Combined with the control of the treatment time, the Ra after pickling can be reduced to within 0.2μm.

[0028] As a further optimization of the above technical solution, after the pickling is completed, the surface of each steel bar needs to be rinsed clean with a high-pressure water gun, and after rinsing, the steel bar needs to be soaked in alkaline hot water for 30 minutes to remove the residual acid attached to the surface of the steel bar to prevent the residual acid from adhering to the surface of the steel bar and causing rust, and finally the steel bar is completely dried.

[0029] As a preferred embodiment of the above technical solution, step S1 configures a steel ingot with a set chemical composition, which specifically includes the following processes: adding 10a kg of lime to the furnace bottom before charging the electric furnace, and starting to blow oxygen to assist fluxing after the molten pool is formed; the end point carbon is less than 0.05%, the target value for P removal is less than 0.005%, and after the P removal reaches the target, the slag is flowed and pulled, and the oxidized slag is pulled clean; adding 3-5a kg of lime and an appropriate amount of fluorite to re-slag, and after the slag is uniform, adding aluminum ingots, aluminum particles, and carbon powder to reduce and make white slag, and the white slag time is not less than 20 minutes; turning on the power and heating to T≥1650℃ for sampling and analysis, Al>0.1%, and then adding electrolytic manganese in batches according to the analysis results to match Mn to the upper and middle limits, adding aluminum to the ladle before tapping, and the tapping temperature of the electric furnace is 1620-1680℃; after the molten steel reaches the LF furnace refining station, immediately measuring the temperature and sampling for analysis; turning on the power and heating, and starting slag adjustment after slag melting; adjusting the slag while turning on the power until the slag color turns white and the slag flows Good performance; adjust the argon flow rate after slag adjustment and maintain a weak blowing state; add other alloys in appropriate amounts according to the composition of molten steel, and take samples for analysis after 3 to 7 minutes of weak blowing; other components reach the target range, the ladle slag is clean, add a small amount of lime and high-temperature fluorite to adjust the slag, turn on the power to increase the temperature, and after the composition and temperature meet the requirements, hang the ladle on the casting platform; bake the ladle in advance to ensure that the red envelope can be tapped; ensure that the argon is unobstructed before tapping, and blow argon at least 2 minutes in advance; the cap, protective slag, carbonized rice husk, flow steel bricks and other auxiliary materials must be well baked to ensure the principle of first bake first use; clean the slag, rust and cold steel on the inner wall of the ingot mold to ensure that the inner wall is smooth, and the baking temperature of the ingot mold is >50℃ before pouring; fill the ingot mold with argon before pouring, and the pouring temperature is controlled at 1490~1520℃.

[0030] In the above technical solution of the present invention, a is a specific value used to match the amount of raw materials in the furnace.

[0031] The quality of the steel ingot is not only related to the set chemical composition, but also to the smelting technology. The implementation of the above technical solution of the present invention can make the steel ingot have the advantages of uniform composition distribution and good quality stability.

[0032] As a preferred embodiment of the above technical solution, the steel ingot obtained by casting is first cooled and then ground, and then connected to the heating described in step S2. The grinding requires that the surface has no obvious defects.

[0033] In summary, the present invention has the following beneficial effects: 1. Compared with the existing technology, the present invention reduces the production cost of steel bars while retaining excellent corrosion resistance, mechanical properties and low magnetic properties by increasing the manganese content, appropriately adding nickel, optimizing alloying elements, focusing on adjusting the chromium content, and combining hot rolling parameter optimization, shot blasting, pickling and other technical means. Among them, nickel and manganese are used to maintain austenitization, so that the degree of austenitization of the structure reaches more than 99.9%; the increase in chromium mainly improves the corrosion resistance of the steel grade; the optimization of other alloying parameters, such as the control of carbon, silicon and nitrogen, can stabilize the steel grade's structure and optimize the mechanical properties and corrosion resistance of the steel grade; 2. The steel grade of the present invention ensures mechanical properties and excellent corrosion resistance by increasing the number of passes during hot rolling, limiting the reduction in each pass, optimizing the initial rolling temperature, and strictly controlling the final rolling temperature. The yield strength is ≥400 MPa and the elongation is ≥40%; 3. The present invention adopts a specific shot blasting process for steel bars with specific chemical compositions. The first treatment group uses a high-hardness abrasive to remove most of the oxide scale, making the residual oxide scale dispersed. The second treatment group uses a combination of a higher hardness and a lower hardness but more ductile abrasive to remove the remaining point-like oxide scale, making the oxide scale basically removed. The third and fourth treatment groups repair and re-repair the substrate surface, significantly reducing the substrate surface roughness and reducing the specific surface area. 4. The present invention adopts sulfuric acid pickling and passivation for steel bars of specific composition that have undergone specific shot blasting treatment, and thoroughly removes the residual oxide scale by chemical means to initially form a passivation film (which then slowly reacts with oxygen in the room temperature air environment to form a passivation film). Compared with the existing technology, the passivation effect is significantly improved, thereby improving the corrosion resistance of the steel bars of the present invention, ensuring that the remanence is ≤50nT and the relative magnetic permeability is <1.005. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the metallographic diagram of the steel bar in Example 1; Figure 2 This is the metallographic diagram of the steel bar of comparative example 2. DETAILED DESCRIPTION

[0035] The present invention is further explained below with reference to the accompanying drawings.

[0036] This specific implementation method is an explanation of the present invention, not a limitation of the present invention. Any changes made by those skilled in the art after reading the description of the present invention will be protected by patent law as long as they are within the scope of the claims.

[0037] Example 1 In terms of smelting, the process route of electric furnace + LF refining furnace + die casting is adopted. 1 ton of lime is added to the bottom of the furnace before charging the electric furnace, and oxygen blowing to assist fluxing is started after the molten pool is formed; the end carbon is less than 0.05%, and the target value of P removal is less than 0.005%. After the P removal target is achieved, the slag is flowed and pulled, and the oxidized slag is pulled clean; 500kg of lime and an appropriate amount of fluorite are added to re-slag. After the slag is uniform, aluminum ingots, aluminum particles, and carbon powder are added to reduce and make white slag, and the white slag time is not less than 20 minutes; the power is turned on and the temperature is raised to T≥1650℃ for sampling and analysis. Al>0.1%, and then electrolytic manganese is added in batches according to the analysis results to match Mn to the upper and middle limits. 4 aluminum strips are added to the ladle before tapping, and the tapping temperature of the electric furnace is 1650℃. After the molten steel reaches the LF furnace refining station, the temperature is measured and samples are taken for analysis immediately; the power is turned on to increase the temperature, and slag adjustment is started after the slag is melted; the slag is adjusted while the power is turned on until the slag turns white and the slag has good fluidity; after slag adjustment, the argon flow rate is adjusted to maintain a weak blowing state; other alloys are added in appropriate amounts according to the composition of the molten steel, and samples are taken for analysis after 5 minutes of weak blowing; when other components reach the target range and the ladle slag is clean, a small amount of lime and high-temperature fluorite are added to adjust the slag, the power is turned on to increase the temperature, and after the composition and temperature meet the requirements, the ladle is placed on the casting platform. The ladle is baked in advance to ensure that the red envelope can produce steel; before producing steel, ensure that the argon gas is unobstructed and blow argon gas 3 minutes in advance; the cap, protective slag, carbonized rice husk, flow steel bricks and other auxiliary materials must be baked well to ensure the principle of first bake first use; clean the slag spots, rust, cold steel and garbage on the inner wall of the ingot mold to ensure that the inner wall is smooth, and the baking temperature of the ingot mold is greater than 50℃ before pouring; before pouring, the ingot mold is filled with argon gas, and argon gas protects pouring. The pouring temperature is controlled at about 1500℃, and after cooling, it is transferred to the grinding workshop for grinding. Grinding requires that there are no obvious defects on the surface (such as pores, cracks, etc.).

[0038] The rolling process consists of two steps. First, the ground steel ingot is heated to 1200℃ in the bar mill, kept in the furnace for 4 hours, and in the soaking stage for 2.5 hours. After being taken out of the furnace, it is rolled into 147mm by 13 passes of 750 rolling mill. 2 Square billet; after cooling, it is transferred to the grinding workshop for grinding. Grinding requires that there are no obvious defects on the surface (such as linear cracks, warping, triangular cracks, etc.); after grinding, it is transferred to the long product plant for secondary heating to 1000℃, with 3h in the furnace and 1.5h in the soaking section. After the billet is taken out of the furnace, it adopts the controlled rolling and controlled cooling process. It first undergoes 6 passes of rough rolling into 90mm round steel, and then enters the intermediate rolling and finishing rolling units for rolling. During the rolling process, the rolling speed is controlled at 0.2m / s, and the finished product speed is controlled at 3.2m / s. The finished product is air-cooled on the cooling bed and then cut to length, packaged and labeled.

[0039] Post-processing process: mainly divided into two steps. The first step is physical shot blasting. The physical shot blasting mainly passes through 16 shot blasting machines, each 4 shot blasting machines are a group, a total of 4 groups. The first group of shot blasting machines adds G18 steel shot abrasives, the second group of shot blasting machines adds bearing steel sand and cutting shot abrasives with a ratio of 2:1, the third group of shot blasting machines adds quartz sand abrasives, the fourth group of shot blasting machines adds glass sand abrasives, plus 2 passes of pneumatic sweeping devices, the physical shot blasting speed is controlled at 1.5m / min; the second step is chemical treatment, using 15% sulfuric acid solution for pickling and passivation for 30min, then rinse the surface with high-pressure water, and after rinsing, soak the steel bars in alkaline hot water for 30min to remove the residual acid attached to the surface of the steel bars to avoid rust caused by residual acid adhering to the surface of the steel bars, and finally dry the steel bars completely.

[0040] The steel bar prepared in this embodiment is a φ6mm threaded steel bar, and the design formula of the threaded steel bar is as follows: C 0.16%, Cr 10.0%, Ni 1.2%, Mn 18.0%, 0.22%≤N≤0.4%, Si ≤1.0%, Cu ≤0.5%, P ≤0.01%, S ≤0.01%, O ≤0.001%; the balance is iron.

[0041] Figure 1 The metallographic diagram of this embodiment is shown in FIG. Figure 1 It can be seen that the metallographic structure is fully austenitic.

[0042] The room temperature tensile properties are tested according to GB / T 228.1, the non-metallic inclusion grade is assessed according to GB / T 10561, and the magnetic properties are tested according to GB13012-2008-T.

[0043] After testing, the yield strength is ≥400MPa, the tensile strength is ≥560MPa, the elongation after fracture is ≥40%, the remanence is ≤50nT, the relative magnetic permeability is <1.005, the sum of eight inclusions is ≤6.5, and PREN is ≥13.5; PREN = Cr% + 16×N%).

[0044] Example 2 The only difference from Example 1 is that the steel bar prepared in this embodiment is a φ10 mm threaded steel bar, and the design formula of the threaded steel bar is as follows: C 0.12%, Cr 12.0%, Ni 2.0%, Mn 23.0%, N ≤0.4%, Si ≤1.0%, Cu ≤0.5%, P ≤0.01%, S ≤0.01%, O ≤0.001%; the balance is iron.

[0045] Example 3 The only difference from Example 1 is that the steel bar prepared in this embodiment is a φ10 mm threaded steel bar, and the design formula of the threaded steel bar is as follows: C 0.08%, Cr 12.0%, Ni 3.8%, Mn 23.0%, N ≤0.4%, Si ≤1.0%, Cu ≤0.5%, P ≤0.01%, S ≤0.01%, O ≤0.001%; the balance is iron.

[0046] Comparative Example 1 The only difference from Example 1 is that: The post-processing process is divided into two steps. The first step is physical shot blasting, which uses cut shot abrasive with HRC of about 40~50; the second step is pickling and passivation, using 15wt% HNO3, and the treatment time is 30min.

[0047] Room-temperature tensile properties were tested according to GB / T 228.1, non-metallic inclusion grade was assessed according to GB / T 10561, and magnetic properties were tested according to GB13012-2008-T. Testing revealed that the φ6mm rebar from Comparative Example 1 exhibited yield strength ≥400 MPa, tensile strength ≥560 MPa, elongation ≥40%, remanence ≥50 nT, relative permeability >1.01, the sum of eight inclusions ≤6.5, and a PREN ≥13.5 (PREN = Cr% + 16 × N%).

[0048] Comparative Example 2 The only difference from Example 1 is that the design formula of the threaded steel is as follows: C 0.55~0.65%, Cr 3.0~3.5%, Mn 18.0~18.5%, Si 0.45~0.55%, N 0.014~0.015%, V1.70~1.73%, P ≤0.010%, S ≤0.010%, O ≤0.0010%.

[0049] Figure 2 The metallographic diagram of this comparative example is Figure 2 It can be seen that there is obvious ferrite in the metallographic structure, accounting for about 2% of the whole; it can be reasonably inferred that the remanence and relative magnetic permeability cannot meet the requirements, the yield strength will also decrease, and the PREN value will not meet the requirements.

Claims

1. A method for producing low-magnetic corrosion-resistant steel bars, comprising the following steps: S1. Prepare a steel ingot with a set chemical composition; S2, heating the steel ingot to 1200° C. to 1300° C.; S3, rolling the steel ingot through at least 10 passes to form a billet; S4. Grind after cooling. Grind requires that the surface has no obvious defects. S5, heating the billet to 1000° C. to 1200° C.; S6, the billet is subjected to 5-10 passes of rough rolling to produce round steel of φ70-100 mm, and then the billet is subjected to intermediate rolling and finishing rolling, and is air-cooled and cut to length to produce steel bars; The set chemical composition includes the following components by mass fraction: C 0.08~0.16%, Cr 9.0~12.0%, Ni 0.8~3.8%, Mn 18.0~23.5%, N 0.15~0.4%, Si ≤1.0%, Cu ≤0.5%, P ≤0.01%, S ≤0.01%, O ≤0.001%; the balance is iron.

2. The method for producing a low-magnetic corrosion-resistant steel bar according to claim 1, wherein: Also includes steps S7 and S8, S7, shot blasting the steel bars obtained in S6 to remove the surface oxide layer; S8. After the surface oxide layer is removed, the steel bar is pickled and passivated, then the surface is rinsed clean with high-pressure water and finally dried.

3. The method for producing low-magnetic corrosion-resistant steel bars according to claim 1, wherein: In step S3, the initial rolling temperature is 1200°C to 1300°C, the final rolling temperature is not lower than 800°C, and the reduction in each pass does not exceed 10%.

4. The method for producing low-magnetic corrosion-resistant steel bars according to claim 1, wherein: In step S6, the initial rolling temperature during rough rolling is 1000°C to 1200°C, the final rolling temperature is not lower than 800°C, and the reduction in each pass does not exceed 10%.

5. The method for producing low-magnetic corrosion-resistant steel bars according to claim 1, wherein: In step S6, the rolling speed during the rolling process of the intermediate rolling and finishing rolling mills is controlled at 0.2 m / s to 0.3 m / s.

6. The method for producing low-magnetic corrosion-resistant steel bars according to claim 2, wherein: The shot blasting treatment includes four treatment groups in sequence. The first treatment group adds G18 steel shot abrasive inside the shot blasting wheel, the second treatment group adds bearing steel sand and cut shot abrasive in a ratio of 2:1 inside the shot blasting wheel, the third treatment group adds quartz sand abrasive inside the shot blasting wheel, and the fourth treatment group adds glass sand abrasive inside the shot blasting wheel.

7. The method for producing low-magnetic corrosion-resistant steel bars according to claim 6, wherein: The processing speed of the shot blasting is controlled at 1-2.2 m / min.

8. The method for producing low-magnetic corrosion-resistant steel bars according to claim 2, wherein: The pickling and passivation treatment is specifically carried out by using a 15wt% sulfuric acid solution for pickling and passivation for 30 to 60 minutes.

9. The method for producing low-magnetic corrosion-resistant steel bars according to claim 1, wherein: Step S1 configures a steel ingot with a set chemical composition, specifically including the following process: adding 10a kg of lime to the furnace bottom before charging the electric furnace, and starting oxygen blowing to assist fluxing after the molten pool is formed; The final carbon value is less than 0.05%, the target value of P removal is less than 0.005%. After the P removal reaches the target, the slag is flowed and pulled, and the oxidized slag is pulled cleanly; 3~5a kg of lime and an appropriate amount of fluorite are added to re-slag, and after the slag is uniform, aluminum ingots, aluminum particles, and carbon powder are added to reduce and make white slag, and the white slag time is not less than 20 minutes; power on and heat to T≥1650℃ for sampling and analysis, Al>0.1%, and then add electrolytic manganese in batches according to the analysis results to adjust Mn to the upper and middle limits, add aluminum to the ladle before tapping, and the tapping temperature of the electric furnace is 1620~1680℃; after the molten steel reaches the LF furnace refining station, immediately measure the temperature and take samples for analysis; power on and heat, and start slag adjustment after slag melting; adjust the slag while powering on until the slag color turns white and the slag fluidity is good; adjust the argon after slag adjustment Control the air flow rate and maintain a weak blowing state; add other alloys in appropriate amounts according to the composition of the molten steel, and take samples for analysis after 3 to 7 minutes of weak blowing; when other components reach the target range, the ladle is clean, add a small amount of lime and high-temperature fluorite to adjust the slag, turn on the power to increase the temperature, and after the composition and temperature meet the requirements, hang the ladle on the casting platform; bake the ladle in advance to ensure that the red envelope can tap steel; ensure that the argon gas is unobstructed before tapping, and blow argon gas at least 2 minutes in advance; the cap, protective slag, carbonized rice husks, flow steel bricks and other auxiliary materials must be well baked to ensure the principle of first bake first use; clean the slag, rust and cold steel on the inner wall of the ingot mold to ensure that the inner wall is smooth, and the baking temperature of the ingot mold is >50℃ before pouring; fill the ingot mold with argon before pouring, and control the pouring temperature at 1490~1520℃.

10. The method for producing low-magnetic corrosion-resistant steel bars according to claim 9, characterized in that: The cast steel ingot is first cooled and then ground, and then connected to the heating described in step S2. The grinding requires that the surface has no obvious defects.

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