Seawater-corrosion-resistant high-manganese light steel and production method thereof

Abstract

The invention discloses seawater corrosion resistant high-manganese light steel and a production method thereof. The high-manganese light steel comprises the following chemical components in percentage by weight: 0.20 to 0.80 percent of C, 0.05 to 0.15 percent of Si, 22.0 to 26.0 percent of Mn, 10.0 to 12.0 percent of Al, 0.20 to 0.80 percent of Cr, 0.05 to 0.22 percent of Ni, 0.10 to 0.50 percent of Cu, less than or equal to 0.015 percent of P, less than or equal to 0.020 percent of S and the balance of Fe and inevitable impurity elements. The production method comprises the steps of billet heating, forging, heating, rolling, water toughening and annealing heat treatment. The high-manganese light steel provided by the invention is uniform in steel plate structure and excellent in seawater corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation, and in particular relates to a high-manganese lightweight steel resistant to seawater corrosion and a production method thereof. Background Art

[0002] The vast deep sea is a huge treasure trove of resources, rich in mineral resources, oil resources, deep-sea biological resources, etc. The seawater pressure is huge, it is dark and has complex terrain. If you want to conduct deep-sea exploration, you must develop corresponding equipment. Therefore, high-end marine equipment and steel for offshore drilling platforms have become research hotspots.

[0003] High manganese light steel has the characteristics of high strength, high toughness and light weight, and is gradually widely used in ships, navigation and marine engineering. For example, the ultra-high strength and thickness steel plates produced by high manganese steel are used as key supporting components of marine drilling platforms. The design of using manganese instead of nickel can not only greatly reduce costs, but also meet the future deep-sea and polar marine platforms' demand for ultra-high strength steel safety performance. These high manganese light steel equipment serving in the marine environment will inevitably be in contact with seawater for a long time, and then be corroded by seawater, resulting in rust, pitting, fracture and other phenomena; and marine engineering is far away from land, and it is not as easy to repair and maintain regularly as ships. Once an accident occurs, it will not only cause huge economic losses, but also seriously harm the marine ecology, making it a key issue that must be solved in the development of the marine economy. In recent years, scholars' research on high manganese steel has mainly focused on mechanical properties, plastic deformation mechanisms, friction and wear properties, etc., while research on the corrosion resistance of high manganese steel materials has rarely been reported.

[0004] In view of the severe marine service environment of high manganese lightweight steel, in order to fully ensure production stability and the safety of personnel and ecology, high manganese lightweight steel is required to have excellent seawater corrosion resistance. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a high manganese lightweight steel resistant to seawater corrosion. The structure of the steel plate obtained after water toughening + annealing heat treatment is a uniform austenite structure, which has excellent resistance to seawater corrosion.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: A seawater corrosion-resistant high-manganese lightweight steel, the chemical composition and its weight percentage are: C: 0.20-0.80%, Si: 0.05-0.15%, Mn: 22.0-26.0%, Al: 10.0-12.0%, Cr: 0.20-0.80%, Ni: 0.05-0.22%, Cu: 0.10-0.50%, P≤0.015%, S≤0.020%, the balance is Fe and unavoidable impurity elements.

[0007] The functions of the chemical elements in the seawater corrosion-resistant high manganese lightweight steel of the present invention are as follows: C, Mn, Si: Carbon and manganese are both austenite-forming and stabilizing elements, expanding the austenite phase; carbon, manganese and silicon are all dissolved in the matrix to play a role in solid solution strengthening; excessive carbon and silicon elements are likely to form large-sized hard carbides during subsequent heat treatment, thereby reducing toughness; manganese is an important element for increasing the stacking fault energy of steel, thereby changing the deformation strengthening mechanism of steel and increasing the strength and toughness of steel.

[0008] Al: Aluminum is dissolved in the austenite matrix to produce lattice distortion. It is an extremely effective element for reducing the density of steel and increasing the stacking fault energy. Studies have shown that a 1% increase in aluminum content can reduce the weight of steel by 1.3%. Adding aluminum to high manganese steel can promote the formation of a large number of fine K carbides. Aluminum can improve the corrosion resistance of steel.

[0009] Cu, Cr, Ni: After copper is added to the steel, the steel contacts the Cu precipitated on the surface, which promotes the anodic passivation of the steel and forms a protective rust layer on the steel surface, which blocks the Cl in seawater. -1 Continue to contact the corroded matrix; and copper is enriched on the steel surface in the form of CuO, especially in the inner rust layer, blocking the holes or gaps in the rust layer, improving the density of the inner rust layer, and thus preventing further corrosion by seawater; chromium can promote the amorphous transformation of corrosion products to form a denser and more stable clustered rust layer, and promote the rust layer to have cationic selectivity, hindering the Cl in seawater -1 Through, thus improving the seawater corrosion resistance; nickel elements in the rust layer to form spinel-type stable NiFe 2 O 4 phase, and transform to a fine and dense structure, improving the density and stability of the rust layer, NiFe 2 O 4 Refining the rust layer while preventing Cl in seawater -1 It diffuses further inward, thereby improving the ability to resist seawater corrosion.

[0010] Furthermore, the microstructure of the high manganese lightweight steel after water toughening + annealing heat treatment is uniform austenite accompanied by fine K carbides.

[0011] Furthermore, the high manganese lightweight steel of the present invention has an average annual corrosion rate CR ≤ 0.20 mm / y after being fully immersed in a neutral salt solution (3.5% NaCl deionized water solution) for 168 hours, and has excellent seawater corrosion resistance.

[0012] Furthermore, the present invention adopts a seawater corrosion simulation test to detect the seawater corrosion resistance of the steel plate. The heat-treated steel plate is processed into a sample of 15mm×10mm×4mm. In order to reduce the test error, the average value of three parallel samples is used; the seawater simulation solution adopts a neutral 3.5% salt solution, the pH of the 3.5% NaCl deionized water solution is 7.0, and the test temperature is 25°C; the sample is suspended and immersed in a large beaker of the simulated solution. In order to prevent the evaporation of water in the solution, the beaker mouth is sealed with plastic wrap, and the corrosion test is carried out in a constant temperature and humidity chamber. The corrosion time of the present invention is 168h; the corrosion rate of the steel is calculated according to the weight loss method in the ASTM G1-03 (2011) standard, and the calculation formula is CR=(87600*∆m) / (t*ρ*S), where CR is the average annual corrosion rate (mm / y), ∆m is the mass loss of the sample before and after corrosion (g), and S is the total area of ​​the sample (cm 2 ), ρ is the sample density (g / cm 3 ), t is the corrosion time (h).

[0013] The present invention also provides a method for producing high-manganese lightweight steel resistant to seawater corrosion, comprising steel billet heating + forging, heating + rolling, water toughening + annealing heat treatment.

[0014] Furthermore, in the steel billet heating + forging of the present invention, the steel billet heating temperature is 1200-1250°C, and the steel billet insulation time is 120-150min; the steel billet heating can dissolve the chemical elements of the steel and make the steel composition and structure uniform; the heated steel billet is forged into a slab with a thickness of 50-60mm, and the final forging temperature is ≥850°C. During the forging process, large-sized grains or inclusions can be broken, the grains can be refined, and the orientation of the structure can be reduced.

[0015] Furthermore, the steel billet heating + rolling of the present invention reheats the forged slab to 1200-1230° C., keeps the temperature for 90-120 minutes, and rolls the slab to a thickness of 30-35 mm in a single pass, with a final rolling temperature of ≥870° C. The single-pass rolling method can further refine the grains and improve the strength and toughness of the steel.

[0016] Furthermore, in the water toughening treatment in the water toughening + annealing heat treatment of the present invention, the hot-rolled steel plate is heated to 920-960°C, kept warm for 120-160 minutes, and quickly water-cooled to room temperature; the coarse carbides in the grains and on the grain boundaries of the steel billet can be fully dissolved during the water toughening heat treatment process, thereby improving the strength and toughness of the steel; in order to avoid stress cracking, before the steel billet is heated to 700-730°C, the temperature is slowly increased at a low heating rate of 15-20°C / min, and it is kept at 700-730°C for 20-30 minutes, and then the heating rate is appropriately increased to continue heating to 920-960°C, and the heating rate is 25-30°C / min; in the reverse phase change annealing process, the water-quenched steel plate is heated to 550-620°C, kept warm for 60-100 minutes, and forced air-cooled to room temperature. Studies have shown that increasing the cooling rate after annealing is beneficial to the formation of fine nano-scale K carbides, thereby improving the strength and toughness of the steel; after water toughening + annealing heat treatment, an austenite structure with fine dispersed K carbides is obtained.

[0017] The high manganese light steel produced by the invention has uniform structure, excellent seawater corrosion resistance and can increase the service life of the steel.

[0018] The beneficial effects of adopting the above technical solution are: 1. The high manganese light steel provided by the present invention mainly has C, Mn and Al as main chemical components, and has excellent seawater corrosion resistance by adding trace alloy elements; hot rolling forming has low requirements on hot rolling equipment and simple production process.

[0019] 2. The high manganese light steel provided by the present invention obtains an austenite structure after water toughening + annealing heat treatment. The structure is uniform, accompanied by fine K carbides, and has excellent seawater corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a microstructure photo of the high manganese lightweight steel of Example 1. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Example 1

[0022] A high-manganese lightweight steel resistant to seawater corrosion is smelted in an electric furnace and cast into a 50kg steel ingot. Its chemical composition and weight percentage determined by direct reading spectrometer are: C: 0.20%, Si: 0.05%, Mn: 22.0%, Al: 10.0%, Cr: 0.20%, Ni: 0.05%, Cu: 0.10%, P: 0.009%, S: 0.017%, and the balance is Fe and unavoidable impurities; its production process includes billet heating + forging, billet heating + rolling, water toughening + annealing heat treatment, as follows: (1) Billet heating + forging: Heat the billet to 1200℃, keep it warm for 120min, forge it into a 50mm thick slab, and the final forging temperature is 850℃.

[0023] (2) Billet heating + rolling: The forged slab with a thickness of 50 mm is reheated to 1200 °C, kept at this temperature for 90 min, and rolled into a 30 mm thick steel plate in a single pass. The final rolling temperature is 870 °C, and then air-cooled to room temperature.

[0024] (3) Water toughening + annealing: The hot-rolled steel plate is heated to 700°C at a heating rate of 15°C / min, kept at this temperature for 20 min, then heated to 920°C at a heating rate of 25°C / min, kept at this temperature for 120 min, and quickly cooled to room temperature with water; the water-hardened steel plate is heated to 550°C, kept at this temperature for 60 min, and forced air-cooled to room temperature.

[0025] The high manganese light steel prepared in this embodiment is a uniform austenite structure with fine κ carbide precipitation, such as Figure 1 The structures of the high manganese light steel in the other embodiments are the same as that in embodiment 1 and are not provided in sequence.

[0026] According to ASTM G1-03 (2011) standard, the average annual corrosion rate CR of steel after immersion in 3.5% neutral salt solution for 168 hours is 0.18mm / y. Example 2

[0027] A high-manganese lightweight steel resistant to seawater corrosion is smelted in an electric furnace and cast into a 50kg steel ingot. Its chemical composition and weight percentage determined by direct reading spectrometer are: C: 0.30%, Si: 0.08%, Mn: 23.0%, Al: 10.5%, Cr: 0.30%, Ni: 0.10%, Cu: 0.15%, P: 0.007%, S: 0.013%, and the balance is Fe and unavoidable impurities; its production process includes billet heating + forging, billet heating + rolling, water toughening + annealing heat treatment, as follows: (1) Billet heating + forging: Heat the billet to 1210°C, keep it warm for 130 min, forge it into a 52 mm thick slab, and the final forging temperature is 857°C.

[0028] (2) Billet heating + rolling: The forged slab with a thickness of 52 mm is reheated to 1205 °C, kept at this temperature for 95 min, and rolled into a 32 mm thick steel plate in a single pass. The final rolling temperature is 875 °C, and then air-cooled to room temperature.

[0029] (3) Water toughening + annealing: The hot-rolled steel plate is heated to 710°C at a heating rate of 20°C / min and kept at this temperature for 22 min. Then, it is further heated to 930°C at a heating rate of 30°C / min, kept at this temperature for 130 min, and quickly cooled to room temperature with water. The water toughened steel plate is heated to 570°C, kept at this temperature for 70 min, and forced air cooled to room temperature.

[0030] The high manganese light steel prepared in this embodiment is a uniform austenite structure with fine κ carbide precipitation. According to ASTM G1-03 (2011) standard, the average annual corrosion rate CR of the steel after immersion in a 3.5% neutral salt solution for 168 hours is 0.15 mm / y. Example 3

[0031] A high-manganese lightweight steel resistant to seawater corrosion is smelted in an electric furnace and cast into a 50kg steel ingot. Its chemical composition and weight percentage determined by direct reading spectrometer are: C: 0.35%, Si: 0.10%, Mn: 23.6%, Al: 11.0%, Cr: 0.32%, Ni: 0.15%, Cu: 0.22%, P: 0.010%, S: 0.010%, and the balance is Fe and unavoidable impurities; its production process includes billet heating + forging, billet heating + rolling, water toughening + annealing heat treatment processes, as follows: (1) Billet heating + forging: Heat the billet to 1220°C, keep warm for 135 min, forge into a 55 mm thick slab, and the final forging temperature is 855°C.

[0032] (2) Billet heating + rolling: The forged slab with a thickness of 55 mm is reheated to 1210 °C, kept warm for 100 min, and rolled into a 31.5 mm thick steel plate in a single pass. The final rolling temperature is 872 °C and air-cooled to room temperature.

[0033] (3) Water toughening + annealing: The hot-rolled steel plate is heated to 715°C at a heating rate of 17°C / min and kept at this temperature for 25 min. It is then heated to 935°C at a heating rate of 26°C / min, kept at this temperature for 140 min, and quickly cooled to room temperature with water. The water toughened steel plate is heated to 590°C, kept at this temperature for 80 min, and forced air cooled to room temperature.

[0034] The high manganese light steel prepared in this example is a uniform austenite structure with fine κ carbide precipitation. According to ASTM G1-03 (2011) standard, the average annual corrosion rate CR of the steel after immersion in a 3.5% neutral salt solution for 168 hours is 0.10 mm / y. Example 4

[0035] A high-manganese lightweight steel resistant to seawater corrosion is smelted in an electric furnace and cast into a 50kg steel ingot. Its chemical composition and weight percentage determined by direct reading spectrometer are: C: 0.50%, Si: 0.12%, Mn: 24.5%, Al: 11.2%, Cr: 0.45%, Ni: 0.20%, Cu: 0.35%, P: 0.013%, S: 0.008%, and the balance is Fe and unavoidable impurities; its production process includes billet heating + forging, billet heating + rolling, water toughening + annealing heat treatment processes, as follows: (1) Billet heating + forging: Heat the billet to 1225°C, keep it warm for 140 min, forge it into a 57 mm thick slab, and the final forging temperature is 862°C.

[0036] (2) Billet heating + rolling: The forged slab with a thickness of 57 mm was reheated to 1220 °C, kept at this temperature for 110 min, and rolled into a 33 mm thick steel plate in a single pass. The final rolling temperature was 877 °C, and then air-cooled to room temperature.

[0037] (3) Water toughening + annealing: The hot-rolled steel plate is heated to 720°C at a heating rate of 16°C / min and kept at this temperature for 27 min. It is then heated to 940°C at a heating rate of 28°C / min, kept at this temperature for 150 min, and quickly cooled to room temperature with water. The water toughened steel plate is heated to 600°C, kept at this temperature for 85 min, and forced air cooled to room temperature.

[0038] The high manganese light steel prepared in this example is a uniform austenite structure with fine κ carbide precipitation. According to ASTM G1-03 (2011) standard, the average annual corrosion rate CR of the steel after immersion in a 3.5% neutral salt solution for 168 hours is 0.11 mm / y. Example 5

[0039] A high-manganese lightweight steel resistant to seawater corrosion is smelted in an electric furnace and cast into a 50kg steel ingot. Its chemical composition and weight percentage determined by direct reading spectrometer are: C: 0.62%, Si: 0.13%, Mn: 25.0%, Al: 11.5%, Cr: 0.70%, Ni: 0.21%, Cu: 0.45%, P: 0.012%, S: 0.012%, and the remainder is Fe and unavoidable impurities; its production process includes billet heating + forging, billet heating + rolling, water toughening + annealing heat treatment processes, as follows: (1) Billet heating + forging: Heat the billet to 1240°C, keep warm for 145 min, forge into a 58 mm thick slab, and the final forging temperature is 860°C.

[0040] (2) Billet heating + rolling: The forged slab with a thickness of 58 mm was reheated to 1225 °C, kept at this temperature for 115 min, and rolled into a 34.1 mm thick steel plate in a single pass. The final rolling temperature was 876 °C, and then air-cooled to room temperature.

[0041] (3) Water toughening + annealing: The hot-rolled steel plate is heated to 725°C at a heating rate of 18°C / min and kept at this temperature for 29 min. It is then heated to 950°C at a heating rate of 29°C / min, kept at this temperature for 155 min, and quickly cooled to room temperature with water. The water toughened steel plate is heated to 610°C, kept at this temperature for 90 min, and forced air cooled to room temperature.

[0042] The high manganese light steel prepared in this example is a uniform austenite structure with fine κ carbide precipitation. According to ASTM G1-03 (2011) standard, the average annual corrosion rate CR of the steel after immersion in a 3.5% neutral salt solution for 168 hours is 0.14 mm / y. Example 6

[0043] A high-manganese lightweight steel resistant to seawater corrosion is smelted in an electric furnace and cast into a 50kg steel ingot. Its chemical composition and weight percentage determined by direct reading spectrometer are: C: 0.80%, Si: 0.15%, Mn: 26.0%, Al: 12.0%, Cr: 0.80%, Ni: 0.22%, Cu: 0.50%, P: 0.015%, S: 0.020%, and the balance is Fe and unavoidable impurities; its production process includes billet heating + forging, billet heating + rolling, water toughening + annealing heat treatment processes, as follows: (1) Billet heating + forging: Heat the billet to 1250°C, keep it warm for 150 min, forge it into a 60 mm thick slab, and the final forging temperature is 858°C.

[0044] (2) Billet heating + rolling: The forged slab with a thickness of 60 mm is reheated to 1230 °C, kept at this temperature for 120 min, and rolled into a 35 mm thick steel plate in a single pass. The final rolling temperature is 878 °C, and then air-cooled to room temperature.

[0045] (3) Water toughening + annealing: The hot-rolled steel plate is heated to 730°C at a heating rate of 19°C / min and kept at this temperature for 30 min. Then, it is further heated to 960°C at a heating rate of 27°C / min, kept at this temperature for 160 min, and quickly cooled to room temperature with water. The water toughened steel plate is heated to 620°C, kept at this temperature for 100 min, and forced air cooled to room temperature.

[0046] The high manganese light steel prepared in this example is a uniform austenite structure with fine κ carbide precipitation. According to ASTM G1-03 (2011) standard, the average annual corrosion rate CR of the steel after immersion in a 3.5% neutral salt solution for 168 hours is 0.16 mm / y.

Claims

1. A high manganese lightweight steel resistant to seawater corrosion, characterized in that: The chemical composition and weight percentage of the high manganese lightweight steel are: C: 0.20-0.80%, Si: 0.05-0.15%, Mn: 22.0-26.0%, Al: 10.0-12.0%, Cr: 0.20-0.80%, Ni: 0.05-0.22%, Cu: 0.10-0.50%, P≤0.015%, S≤0.020%, and the balance is Fe and unavoidable impurity elements.

2. The high manganese lightweight steel resistant to seawater corrosion according to claim 1, characterized in that: The microstructure of the high manganese light steel after water toughening + annealing heat treatment is a uniform austenite structure accompanied by fine K carbides.

3. The high manganese lightweight steel resistant to seawater corrosion according to claim 1, characterized in that: After the high manganese light steel is subjected to water toughening + reverse phase transformation annealing heat treatment and fully immersed in a neutral salt solution for 168 hours, the average annual corrosion rate CR is ≤0.20 mm / y.

4. A method for producing a high manganese lightweight steel resistant to seawater corrosion according to any one of claims 1 to 3, characterized in that: It includes billet heating + forging, heating + rolling, water toughening + annealing heat treatment.

5. The method for producing a high manganese lightweight steel resistant to seawater corrosion according to claim 4, characterized in that: The billet is heated and forged, the billet heating temperature is 1200-1250°C, the billet insulation time is 120-150min, the heated billet is forged into a slab with a thickness of 50-60mm, and the final forging temperature is ≥850°C.

6. The method for producing a high manganese lightweight steel resistant to seawater corrosion according to claim 4, characterized in that: The steel billet is heated and rolled, and the forged slab is reheated to 1200-1230°C, kept warm for 90-120 minutes, and rolled into a slab with a thickness of 30-35 mm in a single pass, with a final rolling temperature of ≥870°C.

7. The method for producing a high manganese lightweight steel resistant to seawater corrosion according to claim 4, characterized in that: The water toughening + annealing heat treatment is to heat the hot-rolled steel plate to 700-730°C at a heating rate of 15-20°C / min, keep it at temperature for 20-30 minutes, then continue to heat it to 920-960°C at a heating rate of 25-30°C / min, keep it at temperature for 120-160 minutes, and quickly water cool it to room temperature; heat the water toughened steel plate to 550-620°C, keep it at temperature for 60-100 minutes, and force air cool it to room temperature.

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