400mpa grade seawater corrosion resistant high manganese non-magnetic steel bar and production method

Abstract

The application provides a 400MPa-grade seawater corrosion-resistant high-manganese non-magnetic steel bar steel and a production method, and the composition is as follows: C 0.20-0.35%, Si 0.25-0.40%, Mn 15-25%, Cr 3-5%, P≤0.025%, S≤0.020%, V 0.05-0.10%, Al 2.0-3.5%, N 0.015-0.020%, 4.2≤L=1.5×[C]+0.20×[Mn]+0.20×[Cr]+10.0×[N]≤5.8, and the rest is Fe and inevitable impurity elements. Compared with the prior art, high Mn is adopted, C, N and Al are matched to ensure the low magnetic permeability of the steel bar; Cr and V are added, and the production method is matched to ensure the mechanical properties and corrosion resistance of the product.

Description

Technical Field

[0001] This invention belongs to the technical field of hot-rolled steel bars for reinforced concrete and their production process, and particularly relates to a 400MPa grade high-manganese non-magnetic steel bar resistant to seawater corrosion and its production method. Background Technology

[0002] Non-magnetic steel, as a functional steel material, requires a stable austenitic microstructure at room temperature. Austenite with a face-centered cubic structure is paramagnetic, and its relative permeability μ is slightly greater than 1. Its magnetization in a magnetic field is close to a "non-magnetic" phenomenon, hence the name "non-magnetic steel." In the construction industry, non-magnetic steel is used in magnetic shielding structures to protect against magnetic fields and safeguard building structures.

[0003] Patent CN 115478219 A, published on December 16, 2022, discloses a low-magnetic rebar for construction and its preparation method. The composition is: C 0.08-0.60%; Si 0.10-1.00%; Mn 15.00-28.00%; Al 0.02-4.50%; P≤0.045%; S≤0.045%; Nb 0.01-0.30%; Ti 0.01-0.20%; V 0.01-0.20%, with the balance being iron and unavoidable impurities. The production method involves: steel smelting, continuous casting or ingot casting, homogenization of steel billet in a heating furnace, continuous rolling, water cooling, pickling, high-pressure water cleaning, and hot water and rust inhibitor treatment to obtain the low-magnetic rebar product.

[0004] However, the yield strength Rp of the products produced by the aforementioned existing technology is... 0.2 The mechanical properties are ≥335MPa, which does not meet the 400MPa level requirement. In addition, to ensure low magnetic properties, additional processes such as pickling and rust inhibitor treatment are required, which greatly increases the production cost.

[0005] Therefore, it is essential to provide a product with simple manufacturing process and better mechanical properties. Summary of the Invention

[0006] The purpose of this invention is to provide a 400MPa grade seawater corrosion resistant high-manganese non-magnetic steel bar and its production method. By adding Mn, Cr, and Al, and combining this with steelmaking and rolling processes, an austenitic structure is formed at room temperature, meeting the requirement of magnetic permeability ≤1.05. By adding V, its precipitation strengthening effect is utilized to improve the mechanical properties of the steel bar, achieving R... eL ≥400MPa, R mIt has a strength of ≥600MPa and an alumina (A) of ≥30%. It also exhibits excellent resistance to seawater corrosion. The corrosion resistance was evaluated using a perimeter immersion corrosion test, and it is at least twice that of ordinary HRB400E steel reinforcement. This meets the technical requirements for the mechanical properties of non-magnetic steel reinforcement in key coastal projects. Furthermore, the production process of this invention is not complex, making it suitable for large-scale industrial production and widespread application.

[0007] The specific technical solution of this invention is as follows:

[0008] A 400MPa grade high-manganese non-magnetic steel for seawater corrosion resistance comprises the following components by mass percentage:

[0009] C 0.20-0.35%, Si 0.25-0.40%, Mn 15-25%, Cr 3-5%, P≤0.025%, S≤0.020%, V 0.05-0.10%, Al 2.0-3.5%, N 0.015-0.020%, with the remainder being Fe and unavoidable impurity elements.

[0010] The chemical composition of the 400MPa grade seawater corrosion resistant high-manganese non-magnetic steel bar meets the following requirements: 4.2≤L=1.5×[C]+0.20×[Mn]+0.20×[Cr]+10.0×[N]≤5.8. This is to obtain high strength and non-magnetic properties.

[0011] In the formula, each symbol represents the content of its corresponding chemical component × 100%.

[0012] The microstructure of the 400MPa grade seawater corrosion resistant high manganese non-magnetic steel is austenitic.

[0013] The R of the 400MPa grade seawater corrosion resistant high manganese non-magnetic steel bar eL ≥400MPa, R m ≥600MPa, A≥30%. It also exhibits good resistance to seawater corrosion, with an average corrosion rate of 2.20~2.62g / (m²). 2 •h); The corrosion resistance was evaluated by immersion corrosion test, and the corrosion resistance was 2 times or more than that of ordinary HRB400E steel bars.

[0014] Preferred, R eL ≥430MPa, R m ≥630MPa, A≥45%.

[0015] This invention provides a method for producing 400MPa grade seawater corrosion resistant high-manganese non-magnetic steel bars, comprising the following process flow:

[0016] Smelting → LF furnace refining → RH vacuum treatment → continuous casting → rolling.

[0017] The smelting process employs an electric furnace or converter, specifically as follows: first, scrap steel and ferromanganese alloy are added, followed by molten iron, with the molten iron comprising 30-50% and the scrap steel and ferromanganese alloy comprising 70-50%. Electrodes are turned on, and the oxygen lance is started to heat the steel. The endpoint requirements are: P ≤ 0.010%, S ≤ 0.010%, and temperature 1560-1610℃. Slag is blocked during tapping. When approximately 1 / 4 of the molten steel has been tapped, aluminum ferroalloy and slag are added. When approximately 3 / 4 of the molten steel has been tapped, aluminum cakes are added. After tapping, an appropriate amount of aluminum granules is evenly sprinkled onto the slag surface based on the amount of slag discharged.

[0018] The LF furnace refining process involves bottom-blowing argon gas throughout the ladle process, with the argon flow rate controlled to prevent molten steel from splashing out of the ladle. Pre-melted refining slag (0.83-1.65 kg / t) and lime (6.67-8.33 kg / t) are added, with TFe+MnO in the slag ≤ 1.0%. Based on the composition analysis before entering the LF furnace, alloys are added before, during, and after the refining process to adjust the content of Si, Mn, Cr, V, and Al. Al is added via aluminum wire feeding, while other alloys are added in block form through the charging system. The temperature exiting the LF furnace is 1565-1585℃.

[0019] The RH vacuum degassing process involves the following steps: The temperature of the molten steel entering the RH vacuum furnace is 1525-1545℃; during the initial vacuum phase, the vacuum holding time is ≥12 minutes; based on the composition analysis results from the initial vacuum phase, composition adjustments are made during the middle vacuum phase, ensuring a vacuum holding time of ≥8 minutes after adjustment. The temperature exiting the RH vacuum furnace is 1485-1505℃.

[0020] The continuous casting refers to the continuous casting of 150 small square billets, which adopts full-process protective casting, with an initial casting temperature of 1445-1470℃, a crystallizer cooling water flow rate of 3000 liters / minute, and a secondary cooling water ratio of 0.8-1.2 liters / kg to ensure the surface quality of the square billets.

[0021] The rolling process is carried out using a continuous bar mill, with the heating temperature controlled at 1150-1250℃ and the tapping temperature controlled at 980-1080℃. After finishing rolling, a three-stage water cooling process is adopted, with the temperature dropping by 150-250℃, and the temperature of the upper cooling bed controlled at 800-900℃.

[0022] The design concept of this invention is as follows:

[0023] Carbon (C): This element is beneficial for forming single-phase austenite and has good solid solution strengthening properties, effectively improving the strength of steel. However, with increasing C content, although a single austenite structure can be obtained under water quenching or air cooling, excessively high C content will reduce the plasticity of the steel and increase the tendency for austenite grain growth, thereby leading to increased magnetic permeability. In this invention, the C content is controlled at 0.20-0.35%.

[0024] Si (Si) primarily functions as a deoxidizer in steel. Due to its much smaller atomic radius compared to austenite, Si exhibits significant solid solution strengthening. However, as a non-carbide-forming element, Si reduces the solubility of carbon (C) in austenite, leading to carbide precipitation and negatively impacting the stability of the austenitic structure. In this invention, the Si content is controlled at 0.25-0.40%.

[0025] Mn is a strong austenite-forming element that expands the austenite region and stabilizes the austenite structure. Most of the Mn in steel can dissolve in austenite to form a substitutional solid solution. Furthermore, as the Mn content increases, the temperature of the austenite-to-martensite transformation further decreases, increasing the stability of austenite. In this invention, the Mn content is controlled at 15-25%.

[0026] Cr: It is an important element for the formation and stabilization of austenite. The addition of Cr can improve the corrosion resistance of steel, but its content in high-manganese steel is generally no more than 5% to avoid the formation of high-temperature ferrite. In this invention, the Cr content is controlled at 3.0-5.0%.

[0027] V: A strong carbonitride-forming element, the fine, dispersed VC, VN, and V(CN) precipitates it forms inhibit austenite grain growth. Simultaneously, these fine, dispersed VC, VN, and V(CN) precipitates promote austenite nucleation and improve steel strength through coherent distortion and dispersion strengthening. In this invention, the V content is controlled at 0.05-0.10%.

[0028] Al (Al) increases the stacking fault energy of austenite and strongly inhibits martensitic transformation, stabilizing the austenitic microstructure. It is one of the key elements in austenitic steel. However, the upper limit of Al content depends on whether high-temperature δ-ferrite appears, while the lower limit depends on whether the transformation from low-temperature austenite to martensite can be avoided. In this invention, the Al content is controlled at 2.0-3.5%.

[0029] Nitrogen (N) is a strong austenite-forming element and also an interstitial solid solution element. It forms VN and V(CN) compounds with V, significantly increasing the strength of steel. In this invention, the N content is controlled at 0.015-0.020%.

[0030] P and S are harmful impurity elements that are detrimental to ensuring the strength, ductility, and low magnetic properties of steel. In this invention, P ≤ 0.025% and S ≤ 0.020%.

[0031] Based on my country's actual situation of being lacking Ni but rich in Mn, a high Mn composition design is adopted, with the addition of a certain amount of C, N, and Al to cooperate with Mn, expand and stabilize the austenite phase region, and form a single austenite structure at room temperature, thereby ensuring the low magnetic permeability of the steel reinforcement. A certain amount of Cr is added to give it good resistance to seawater corrosion. A certain amount of V is added to utilize its precipitation strengthening effect and improve the mechanical properties of the steel reinforcement. The billet is heated at a higher temperature to promote the solid solution of the above elements. (5) After rolling, three-stage water cooling is adopted, and the temperature drops by 150-250℃ to avoid the formation of martensite and other structures, and to ensure the magnetic permeability of the steel reinforcement at room temperature.

[0032] Compared with existing technologies, this invention, produced according to the above-mentioned composition, using electric furnace or converter smelting, LF furnace refining, RH vacuum degassing, 150 square billet continuous casting, and bar rolling, can produce high-manganese chromium-containing non-magnetic steel bars with excellent performance. Its mechanical properties reach: yield strength R... eL ≥400MPa, tensile strength R m With a strength ≥600MPa and an elongation at break (A) ≥30%, the mechanical properties meet the requirements for HRB400E steel reinforcement in GB 1499.2. The relative permeability is ≤1.05, evaluated using the measurement method for weak magnetic materials in GJB 937-90. Corrosion resistance is evaluated using a peripheral immersion corrosion test, showing resistance twice or more than that of ordinary HRB400E steel reinforcement. It can meet the needs of non-magnetic construction in key coastal projects. Furthermore, the steel reinforcement of this invention has low production costs and a feasible production process, possessing good market prospects. Attached Figure Description

[0033] Figure 1 This is a typical room temperature microstructure of a 400MPa grade seawater corrosion resistant high-manganese non-magnetic steel bar (magnification 100). Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. 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 present invention.

[0035] Example 1-Example 2

[0036] A 400MPa grade high-manganese non-magnetic steel for seawater corrosion resistance comprises the following composition by mass percentage as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurity elements.

[0037] Comparative Example

[0038] A high-manganese non-magnetic steel for reinforcing bars comprises the following composition by mass percentage as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurity elements.

[0039] Table 1. Smelting chemical composition (%) of the examples and comparative examples

[0040] Case C Si Mn P S V Cr Al N L value Example 1 0.32 0.35 16.6 0.013 0.008 0.08 4.6 2.6 0.018 4.90 Example 2 0.30 0.32 17.1 0.011 0.007 0.09 4.8 2.5 0.019 5.02 Comparative Example 0.20 0.35 15.2 0.015 0.007 0.07 3.2 2.3 0.015 4.13

[0041] The production method of the 400MPa grade seawater corrosion resistant high-manganese non-magnetic steel bar described in Example 1 includes the following steps:

[0042] (1) Electric furnace smelting (120 tons): First add scrap steel + ferromanganese alloy, then add molten iron. The proportion of molten iron is 42%, and the proportion of scrap steel + ferromanganese alloy is 58%. Turn on the electrodes and start the oxygen lance to heat up. The endpoint is 0.010% P, 0.008% S, and the temperature is 1585℃. Tap the steel while blocking the slag. When about 1 / 4 of the molten steel has been tapped, add aluminum iron and slag. When about 3 / 4 of the molten steel has been tapped, add aluminum cake. After tapping, according to the amount of slag, evenly sprinkle an appropriate amount of aluminum particles onto the steel slag surface.

[0043] (2) LF furnace refining: Argon gas is blown from the bottom of the ladle throughout the process, with the argon flow rate determined by preventing molten steel from splashing out of the ladle; 150 kg of pre-melted refining slag and 900 kg of lime are added, with the slag containing 1.0% TFe + MnO. Based on the composition analysis results before entering the LF furnace, alloys are added before, during, and after the LF furnace refining process to adjust the content of Si, Mn, Cr, V, and Al elements. Al is added by feeding aluminum wire, while other alloys are added in block form through the charging system. The temperature exiting the LF furnace is 1575℃.

[0044] (3) RH vacuum degassing: The temperature of the molten steel entering the RH vacuum furnace is 1535℃. The vacuum holding time in the early stage is 12 minutes. The vacuum holding time in the middle stage after composition adjustment is 8 minutes. The temperature of the steel exiting the RH vacuum furnace is 1490℃.

[0045] (4) Billet continuous casting: initial casting temperature 1470℃, crystallizer cooling water flow rate 3000 liters / minute, secondary cooling water ratio 1.0 liters / kg.

[0046] (5) Bar rolling mill: heating temperature, tapping temperature control and upper cooling bed temperature are shown in Table 2.

[0047] The production method of the 400MPa grade seawater corrosion resistant high-manganese non-magnetic steel bar described in Example 2 includes the following steps:

[0048] (1) Electric furnace smelting (120 tons): First add scrap steel + ferromanganese alloy, then add molten iron, with molten iron accounting for 35% and scrap steel + ferromanganese alloy accounting for 65%. Turn on the electrodes and start the oxygen lance to heat up. The endpoint is 0.010% P, 0.007% S, and the temperature is 1565℃. Tap the steel while blocking the slag. When about 1 / 4 of the molten steel has been tapped, add aluminum iron and slag. When about 3 / 4 of the molten steel has been tapped, add aluminum cake. After tapping, according to the amount of slag, evenly sprinkle an appropriate amount of aluminum particles onto the steel slag surface.

[0049] (2) LF furnace refining: Argon gas is blown from the bottom of the ladle throughout the process, with the argon flow rate determined by preventing molten steel from splashing out of the ladle; 100 kg of pre-melted refining slag and 800 kg of lime are added, with the slag containing 0.8% TFe + MnO. Based on the composition analysis results before entering the LF furnace, alloys are added before, during, and after the LF furnace refining process to adjust the content of Si, Mn, Cr, V, and Al elements. Al is added via aluminum wire feeding, while other alloys are added in block form through the charging system. The temperature exiting the LF furnace is 1565℃.

[0050] (3) RH vacuum degassing: The temperature of the molten steel entering the RH vacuum furnace is 1525℃; the vacuum holding time in the early stage is 14 minutes. Based on the composition analysis results in the early stage of vacuum, the vacuum holding time is adjusted in the middle stage of vacuum and then 11 minutes. The temperature of the steel exiting the RH vacuum furnace is 1500℃.

[0051] (4) 150 square billet continuous casting: full-process protective casting is adopted, the initial casting temperature is 1445℃, the flow rate of cooling water in the crystallizer is 3000 liters / minute, and the secondary cooling water ratio is 0.9 liters / kg.

[0052] (5) Bar rolling mill: heating temperature, tapping temperature control and upper cooling bed temperature are shown in Table 2.

[0053] The production method of the high-manganese non-magnetic steel bar described in the comparative example includes the following steps:

[0054] (1) Electric furnace smelting: First add scrap steel + ferromanganese alloy, then add molten iron, with molten iron accounting for 50% and scrap steel + ferromanganese alloy accounting for 50%. Start the electrodes and start the oxygen lance to heat up. Endpoint requirements: 0.014％P 0.007% S, temperature 1610℃. Slag blocking and tapping: When about 1 / 4 of the molten steel has been tapped, aluminum iron and slag are added; when about 3 / 4 of the molten steel has been tapped, aluminum cakes are added; after tapping, according to the amount of slag discharged, an appropriate amount of aluminum granules are evenly sprinkled onto the steel-slag surface.

[0055] (2) LF furnace refining: Argon is blown into the ladle throughout the process, with the argon flow rate determined by preventing molten steel from splashing out of the ladle; 200 kg of pre-melted refining slag and 1000 kg of lime are added, with the slag containing 0.7% TFe + MnO. Based on the composition analysis results before entering the LF furnace, alloys are added before, during, and after the LF furnace refining process to adjust the content of Si, Mn, Cr, V, and Al elements. Al is added via aluminum wire feeding, while other alloys are added in block form through the charging system. The temperature exiting the LF furnace is 1585℃.

[0056] (3) RH vacuum degassing: The temperature of the molten steel entering the RH vacuum furnace is 1545℃; the vacuum holding time in the early stage is 14 minutes. Based on the composition analysis results in the early stage of vacuum, the composition in the middle stage of vacuum is adjusted to ensure a vacuum holding time of 13 minutes, and the temperature of the steel exiting the RH vacuum furnace is 1505℃.

[0057] (4) Continuous casting of billets: the initial casting temperature is 1470℃, the flow rate of cooling water in the crystallizer is 3000 liters / minute, and the secondary cooling water ratio is 1.1 liters / kg to ensure the surface quality of the billets.

[0058] Table 2 Rolling parameters for each embodiment and comparative example

[0059] Case Heating temperature (°C) Steel tapping temperature (°C) Temperature of the upper cooling bed (°C) Example 1 1230 1060 840 Example 2 1160 1020 835 Comparative Example 1170 1040 915

[0060] The mechanical properties, metallographic structure, and magnetic permeability of the embodiments and comparative examples of this invention are shown in Table 3. Wherein: R eL R is the yield strength. m A 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).

[0061] Table 3 Mechanical properties, metallographic structure and relative magnetic permeability of the examples and comparative examples

[0062] Case <![CDATA[R eL (MPa)]]> <![CDATA[R m (MPa)]]> A(％) Metallographic structure relative permeability Example 1 435 635 49 austenite 1.003 Example 2 440 640 52 austenite 1.002 Comparative Example 395 620 47 austenite 1.003

[0063] The test solution for the immersion corrosion test was a 3.5% NaCl solution; the solution temperature was 35±2℃, the drying temperature was 45±2℃, and the humidity was 30±2℃. Each cycle lasted 60±5 minutes, including 12±2℃ immersion and 48±2℃ exposure. The test cycles were 2, 3, 6, 9, and 12 days; three sets of parallel samples were taken within each cycle.

[0064] The average corrosion rate of corrosion-resistant steel bars is between 2.20 and 2.62 g / (m). 2 The relative corrosion rate of HRB400E ordinary steel bars is 45.01–48.78%.

[0065] Relative corrosion rate = Corrosion rate of corrosion-resistant steel bar / Corrosion rate of comparative steel bar (HRB400E) × 100%.

[0066] Table 4 shows the average corrosion rate and relative corrosion rate of the immersion corrosion tests in each embodiment and comparative example.

[0067]

[0068] The data underlined above do not meet the requirements of this invention.

[0069] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A 400MPa grade seawater corrosion resistant high-manganese non-magnetic steel for reinforcing bars, characterized in that, The 400MPa grade seawater corrosion resistant high-manganese non-magnetic steel for steel bars comprises the following components by mass percentage: C 0.20-0.35%, Si 0.25-0.40%, Mn 15-25%, Cr 3-5%, P≤0.025%, S≤0.020%, V 0.05-0.10%, Al 2.0-3.5%, N 0.015-0.020%, with the remainder being Fe and unavoidable impurity elements; The chemical composition of the 400MPa grade seawater corrosion resistant high manganese non-magnetic steel bar meets the following requirements: 4.2≤L=1.5×[C]+0.20×[Mn]+0.20×[Cr]+10.0×[N] ≤5.8; The R of the 400MPa grade seawater corrosion resistant high manganese non-magnetic steel bar eL ≥400MPa, R m For steel reinforcement with a strength ≥600MPa and an alumina ≥30%, the average corrosion rate is 2.20-2.62 g / (m²). 2 ·h).

2. The 400MPa grade seawater corrosion resistant high-manganese non-magnetic steel for reinforcing bars according to claim 1, characterized in that, The microstructure of the 400MPa grade seawater corrosion resistant high manganese non-magnetic steel is austenitic.

3. A method for producing 400MPa grade seawater corrosion resistant high-manganese non-magnetic steel bars as described in claim 1 or 2, characterized in that, The production method includes the following process flow: Smelting → LF furnace refining → RH vacuum treatment → continuous casting → rolling.

4. The production method according to claim 3, characterized in that, The smelting process involves first adding scrap steel and ferromanganese alloy, then adding molten iron, with the molten iron accounting for 30-50% and the scrap steel and ferromanganese alloy accounting for 70-50%. The final requirements are: P≤0.010%, S≤0.010%, and temperature 1560-1610℃.

5. The production method according to claim 3, characterized in that, The LF furnace refining process is carried out at a temperature of 1565-1585℃.

6. The production method according to claim 3, characterized in that, The RH vacuum degassing process involves the following steps: the temperature of the molten steel entering the RH vacuum furnace is 1525-1545℃; in the early stage of vacuum, the vacuum holding time is ≥12 minutes; in the middle stage of vacuum, the composition is adjusted, and after adjustment, a vacuum holding time of ≥8 minutes is guaranteed; the temperature exiting the RH vacuum furnace is 1485-1505℃.

7. The production method according to claim 3, characterized in that, The continuous casting process has an initial casting temperature of 1445-1470℃, a crystallizer cooling water flow rate of 3000 liters / minute, and a secondary cooling water ratio of 0.8-1.2 liters / kg.

8. The production method according to claim 3, characterized in that, The rolling process is carried out using a continuous bar mill, with the heating temperature controlled at 1150-1250℃ and the tapping temperature controlled at 980-1080℃. After finishing rolling, a three-stage water cooling process is adopted, with the temperature dropping by 150-250℃, and the temperature of the upper cooling bed controlled at 800-900℃.

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