High manganese steel for ultra-low temperature and manufacturing method and application of high manganese steel plate for ultra-low temperature

Abstract

This invention discloses a high-manganese steel for ultra-low temperatures and a method for manufacturing high-manganese steel plates for ultra-low temperatures. The high-manganese steel for ultra-low temperatures comprises, by weight percentage: C: 0.35-0.55%, Si: 0.01-0.10%, Mn: 20.00-30.00%, Al: 0.01-0.10%, P≤0.005%, S≤0.003%, Cr: 3.0-5.0%, Cu: 0.3-1.0%, Ni: 0.2-1.20%, N≤0.008%, O≤0.002%, H≤0.0002%, with the balance being Fe and unavoidable impurity elements. The method for manufacturing the high-manganese steel plates for ultra-low temperatures includes steps such as hot metal pretreatment, K-OBM-S converter smelting, LF refining, continuous casting, annealing and grinding, hot rolling, and online solution treatment. This invention can ensure high steel purity, low phosphorus and sulfur content, small segregation in billets and steel plates, good low-magnification microstructure in billets, no cracks on the surface and inside of billets, and finished steel plates with low yield strength ratio, high tensile strength, high ultra-low temperature toughness, small coefficient of thermal expansion, and good fatigue resistance. By implementing this invention, the manufacturing cost of steel for liquefied natural gas storage tanks can be reduced to 1 / 3 of that of existing 9% Ni steel.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically relating to a method for manufacturing and applying high-manganese steel for ultra-low temperatures and high-manganese steel plates for ultra-low temperatures. Background Technology

[0002] Currently, the key metal materials used in large liquefied natural gas storage tanks are all 9% Ni steel. However, since this steel contains 9% precious nickel, and my country's nickel resources mainly rely on imports, with the total demand for steel for liquefied natural gas storage tanks in my country increasing significantly, there is an urgent need to develop low-cost, high-performance nickel-free new steel.

[0003] Compared to 9% Ni steel, high manganese steel is cheaper, has a smaller coefficient of thermal expansion, and better fatigue resistance. However, due to the high purity requirements, difficulty in alloying, and susceptibility to cracking in continuously cast billets, industrialized smelting and continuous casting production of high manganese steel for liquefied natural gas storage tanks is not yet feasible in my country, leaving the industrialization of high manganese steel for liquefied natural gas storage tanks in a state of flux.

[0004] Therefore, developing a manufacturing method for high-manganese steel and high-manganese steel plates for cryogenic applications is of great significance for meeting the demand for low-cost, high-performance steel for liquefied natural gas storage tanks. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a method for manufacturing high manganese steel for ultra-low temperature applications and a high manganese steel plate for ultra-low temperature applications.

[0006] The high-manganese steel for ultra-low temperature applications provided by this invention comprises, by weight percentage: C: 0.35–0.55%, Si: 0.01–0.10%, Mn: 20.00–30.00%, Al: 0.01–0.10%, P≤0.005%, S≤0.003%, Cr: 3.0–5.0%, Cu: 0.3–1.0%, Ni: 0.2–1.20%, N≤0.008%, O≤0.002%, H≤0.0002%, with the balance being Fe and unavoidable impurity elements.

[0007] The manufacturing method of high-manganese steel plate for ultra-low temperature applications provided by this invention includes the following steps:

[0008] (1) Iron pretreatment to reduce the P content in the iron to P≤0.007%;

[0009] (2) K-OBM-S converter smelting: molten iron is added to the K-OBM-S converter for smelting. After decarburization in the K-OBM-S converter to C≤0.13%, electrolytic manganese is added to the K-OBM-S converter in three batches. Aluminum shot is added for deoxidation when electrolytic manganese is added for the first and second batches. Nickel plate and copper are added when electrolytic manganese is added for the third batch. Ferrosilicon is added after the second and third batches of electrolytic manganese and oxygen is blown to raise the temperature.

[0010] (3) LF refining: The molten steel obtained from K-OBM-S converter smelting is fed into the LF furnace, heated by electricity, and the slag is adjusted. During the later stage of reduction, the composition is adjusted to: C: 0.35~0.55%, Si: 0.01~0.10%, Mn: 20.00~30.00%, Al: 0.01~0.10%, P≤0.005%, S≤0.003%, Cr: 3.0~5.0%, Cu: 0.3~1.0%, Ni: 0.2~1.20%, N≤0.008%, O≤0.002%, H≤0.0002%, with the balance being Fe and unavoidable impurity elements;

[0011] (4) Continuous casting, the crystallizer taper is designed at 1.2%, the nozzle type is small hole nozzle, the nozzle insertion depth is 110~125mm, the secondary cooling uses peritectic steel, electromagnetic stirring is added during the continuous casting process, the tundish temperature is controlled at 1420±10℃, and the casting speed is controlled at 0.6~0.8m / min.

[0012] (5) Annealing and grinding: The annealing temperature of the billet is controlled at 750-770℃. After annealing, the surface of the billet is ground, and the grinding amount is controlled at 2-3%.

[0013] (6) Hot rolling: The billet is heated to 1200-1230℃ in a heating furnace for homogenization, and then rolled by widening longitudinal rolling. The initial rolling temperature is controlled at 1040-1060℃ and the final rolling temperature is controlled at 910-940℃.

[0014] (7) Online solution treatment: The hot-rolled steel plate adopts online laminar flow cooling to achieve online solution treatment, and the steel plate reddening temperature is ≤300℃.

[0015] Furthermore, in the above-mentioned manufacturing method of high-manganese steel plates for ultra-low temperatures, in the K-OBM-S converter smelting step, the total amount of electrolytic manganese added is (30%~35%) × the tons of molten iron. The first addition of electrolytic manganese is 35%~40% of the total amount of electrolytic manganese added, the second addition is 30%~40% of the total amount of electrolytic manganese added, and the third addition is 20%~30% of the total amount of electrolytic manganese added. The amount of aluminum shot added during the first addition of electrolytic manganese is (0.3%~0.5%). × tons of molten iron, the amount of aluminum shot added during the second addition of electrolytic manganese is (0.2%~0.3%) × tons of molten iron, the amount of ferrosilicon added after the second addition of electrolytic manganese is (0.3%~0.4%) × tons of molten iron, the amount of ferrosilicon added after the third addition of electrolytic manganese is (0.6%~0.7%) × tons of molten iron, the amount of nickel plate added during the third addition of electrolytic manganese is (0.15%~0.25%) × tons of molten iron, and the amount of copper added during the third addition of electrolytic manganese is (0.5%~0.7%) × tons of molten iron.

[0016] Furthermore, in the above-mentioned method for manufacturing high-manganese steel plates for ultra-low temperatures, a special protective slag is used in the continuous casting step. The composition of the special protective slag is as follows: SiO2: 37-43%, CaO: 16-22%, Al2O3: 2-5%, MgO≤2.5%, Li2O: 5-7%, Na2O: 8-12%, C-total: 5-6%, F: 5-9%, and the CaO / SiO2 ratio is 0.4-0.6. The special protective slag has a melting point of 840-900℃ and a viscosity of 0.18-0.28 PaS at 1300℃.

[0017] Furthermore, in the above-mentioned method for manufacturing high-manganese steel plates for ultra-low temperatures, the yield strength R of the high-manganese steel plate for ultra-low temperatures... P0.2 ≥440MPa, tensile strength R m ≥830MPa, elongation A≥40%, transverse impact energy KV2≥120J at -196℃.

[0018] Furthermore, the present invention also provides the application of the above-mentioned high-manganese steel for cryogenic use or the high-manganese steel plate for cryogenic use manufactured using the above-mentioned manufacturing method for high-manganese steel plate for cryogenic use in liquefied natural gas storage tanks.

[0019] The manufacturing method of high-manganese steel and high-manganese steel plate for ultra-low temperature applications of the present invention can ensure high steel purity, low phosphorus and sulfur content, small segregation in the billet and steel plate, good low-magnification microstructure of the billet, no cracks on the surface and inside of the billet, and finished steel plate with low yield strength ratio, high tensile strength, high ultra-low temperature toughness, small coefficient of thermal expansion, and good fatigue resistance. Moreover, through the implementation of the present invention, the manufacturing cost of steel for liquefied natural gas storage tanks can be reduced to 1 / 3 of that of existing 9% Ni steel, which is of great significance for meeting the demand for low-cost, high-performance steel for liquefied natural gas storage tanks. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0021] The ultra-low temperature high-manganese steel of the present invention comprises, by weight percentage: C: 0.35-0.55%, Si: 0.01-0.10%, Mn: 20.00-30.00%, Al: 0.01-0.10%, P≤0.005%, S≤0.003%, Cr: 3.0-5.0%, Cu: 0.3-1.0%, Ni: 0.2-1.20%, N≤0.008%, O≤0.002%, H≤0.0002%, with the balance being Fe and unavoidable impurity elements.

[0022] The manufacturing method of the high-manganese steel plate for ultra-low temperature applications of the present invention includes the following steps:

[0023] (1) Iron pretreatment to reduce the P content in the iron to P≤0.007%.

[0024] (2) K-OBM-S converter smelting: Molten iron is added to the K-OBM-S converter for smelting. After decarburization in the K-OBM-S converter to C≤0.13%, electrolytic manganese is added to the K-OBM-S converter in three stages. The total amount of electrolytic manganese added is (30%~35%) × tons of molten iron. The first addition of electrolytic manganese is 35%~40% of the total amount of electrolytic manganese added, the second addition is 30%~40% of the total amount of electrolytic manganese added, and the third addition is 20%~30% of the total amount of electrolytic manganese added. Aluminum shot is added during the first and second additions of electrolytic manganese for deoxidation, and nickel plate and copper are added during the third addition of electrolytic manganese. After the second and third additions of electrolytic manganese, ferrosilicon was added and oxygen was blown to raise the temperature. Specifically, the amount of aluminum shot added during the first addition of electrolytic manganese was (0.3%–0.5%) × the number of tons of molten iron; the amount of aluminum shot added during the second addition of electrolytic manganese was (0.2%–0.3%) × the number of tons of molten iron; the amount of ferrosilicon added after the second addition of electrolytic manganese was (0.3%–0.4%) × the number of tons of molten iron; the amount of ferrosilicon added after the third addition of electrolytic manganese was (0.6%–0.7%) × the number of tons of molten iron; the amount of nickel plate added during the third addition of electrolytic manganese was (0.15%–0.25%) × the number of tons of molten iron; and the amount of copper added during the third addition of electrolytic manganese was (0.5%–0.7%) × the number of tons of molten iron.

[0025] (3) LF refining: The molten steel obtained from K-OBM-S converter smelting is sent to the LF furnace, heated by power supply, and slag is adjusted. During the later stage of reduction, the composition is adjusted to: C: 0.35~0.55%, Si: 0.01~0.10%, Mn: 20.00~30.00%, Al: 0.01~0.10%, P≤0.005%, S≤0.003%, Cr: 3.0~5.0%, Cu: 0.3~1.0%, Ni: 0.2~1.20%, N≤0.008%, O≤0.002%, H≤0.0002%, with the balance being Fe and unavoidable impurity elements.

[0026] (4) Continuous casting: The crystallizer taper is designed to be 1.2%, the nozzle type is a small-hole nozzle, the nozzle insertion depth is 110-125mm, the secondary cooling is peritectic steel, electromagnetic stirring is used in the continuous casting process, the tundish temperature is controlled at 1420±10℃, the casting speed is controlled at 0.6-0.8m / min, and a special protective slag is used in the continuous casting process. The composition of the special protective slag is: SiO2: 37-43%, CaO: 16-22%, Al2O3: 2-5%, MgO≤2.5%, Li2O: 5-7%, Na2O: 8-12%, C-total: 5-6%, F: 5-9%, and CaO / SiO2 is 0.4-0.6. The melting point of the special protective slag is 840-900℃, and the viscosity at 1300℃ is 0.18-0.28PaS.

[0027] (5) Annealing and grinding: The annealing temperature of the billet is controlled at 750-770℃. After annealing, the surface of the billet is ground, and the grinding amount is controlled at 2-3%.

[0028] (6) Hot rolling: The billet is heated to 1200-1230℃ in a heating furnace for homogenization, and then rolled by widening longitudinal rolling. The initial rolling temperature is controlled at 1040-1060℃ and the final rolling temperature is controlled at 910-940℃.

[0029] (7) Online solution treatment: The hot-rolled steel plate adopts online laminar flow cooling to achieve online solution treatment, and the steel plate reddening temperature is ≤300℃.

[0030] The following describes in detail the manufacturing method of high-manganese steel plate for ultra-low temperature applications according to the present invention with reference to the embodiments. The implementation methods in the following embodiments without specific conditions are carried out according to conventional methods and conditions, and the present invention does not make specific limitations in this regard.

[0031] Example 1

[0032] The manufacturing method of the high-manganese steel plate for ultra-low temperature applications in Example 1 specifically includes the following steps:

[0033] (1) Iron pretreatment to reduce the P content in the iron to 0.0061%.

[0034] (2) K-OBM-S converter smelting: A K-OBM-S converter with a nominal capacity of 80 tons is used for smelting. The amount of molten iron added to the K-OBM-S converter is 60 tons. After decarburization in the K-OBM-S converter to a C content of 0.13%, a total of 21 tons of electrolytic manganese is added to the K-OBM-S converter in three batches using feed troughs. 8 tons, 7 tons, and 6 tons of electrolytic manganese are added to the first, second, and third feed troughs, respectively. After each addition of electrolytic manganese, stirring is performed. At the same time, 0.25 tons and 0.15 tons of aluminum shot are added to the first and second feed troughs, respectively, for deoxidation, thereby improving the manganese yield. 0.14 tons of nickel plate and 0.35 tons of copper are added to the third feed trough. After the addition and stirring in the second feed trough, 0.2 tons of ferrosilicon are added and oxygen is blown at 210 Nm. 3 After heating is completed in the third feeding tank, 0.4 tons of ferrosilicon are added and oxygen is blown in at 230 Nm³. 3 The temperature is increased to ensure the required process temperature.

[0035] (3) LF refining: The LF arrival temperature is 1472℃. Slag samples are taken at the station. 500kg lime, 100kg fluorite, and 2 bags of aluminum powder are added for slag conditioning. A total of 7 bags of carbon powder, 350kg electrolytic manganese, 67kg Ni plate, and 600kg low-carbon ferrochrome are added during the LF process for alloying. The LF end temperature is 1473℃. The chemical composition is adjusted to: C: 0.35%, Si: 0.05%, Mn: 29.5%, Al: 0.03%, P: 0.004%, S: 0.001%, Cu: 0.35%, Cr: 4.5%, Ni: 0.80%, N: 0.008%, O: 0.0015%, H: 0.0001%, with the balance being Fe and unavoidable impurities. After soft stirring for 10 minutes, the steel is tapped.

[0036] (4) Continuous casting: The crystallizer taper is designed at 1.2%. The nozzle type is a special small-hole nozzle with a nozzle insertion depth of 120±5mm. The secondary cooling uses peritectic steel. Electromagnetic stirring is used in the continuous casting process. The electromagnetic stirring process parameters are 400A-5HZ-15s reversal, liquidus temperature 1390℃, tundish temperature 1412℃, casting speed 0.75m / min, and the aforementioned special protective slag is used.

[0037] (5) Annealing and grinding: The annealing temperature of the billet is 750℃. After annealing, the surface of the billet is ground with a grinding amount of 3%. The billet is tested at low magnification. The results are: general porosity grade 0.5, central porosity grade 0, general slab deviation grade 0, ingot shape deviation grade 0, and no cracks are found.

[0038] (6) Hot rolling: The billet is cold-charged into the furnace, the heating temperature is 1200℃, the heating time is 160 minutes, the billet enters the 4-roll 3300mm medium plate rolling mill for rolling, the iron scale is removed by high pressure water, the widening longitudinal rolling is adopted, the hot rolling specification is 6mm×2000mm×10000mm, the initial rolling temperature is 1050℃, the final rolling temperature is 910℃, the finished product is straightened after rolling to ensure the plate shape, and the steel plate is sheared online at the head and tail.

[0039] (7) Online solution treatment, the steel plate reddening temperature is 150℃.

[0040] (8) Straightening and trimming: The steel plate is cold straightened to ensure the plate shape requirements, and the edges are trimmed as required to ensure the finished product specifications of 6mm×1950mm×9000mm. Then the steel plate is marked and packaged.

[0041] Performance testing revealed the following mechanical properties of the ultra-low temperature high-manganese steel plate prepared using Example 1: Yield strength R P0.2 The tensile strength is 480 MPa, and the tensile strength R is... m With a strength of 840 MPa and an elongation of A of 42%, the average transverse impact energy KV2 at -196℃, measured using a 5*10*55mm half-sample, is 72 J.

[0042] Therefore, by implementing the manufacturing method of the ultra-low temperature high manganese steel plate in Example 1, the ultra-low temperature high manganese steel and ultra-low temperature high manganese steel plate prepared can be applied to the construction of liquefied natural gas storage tanks.

[0043] Example 2

[0044] The manufacturing method of the high-manganese steel plate for ultra-low temperature applications in Example 2 specifically includes the following steps:

[0045] (1) Iron pretreatment to reduce the P content in the iron to 0.0059%.

[0046] (2) K-OBM-S converter smelting: A K-OBM-S converter with a nominal capacity of 80 tons is used for smelting. The amount of molten iron added to the K-OBM-S converter is 60 tons. After decarburization in the K-OBM-S converter to a C content of 0.12%, a total of 18 tons of electrolytic manganese is added to the K-OBM-S converter in three batches using feed troughs. 7 tons, 7 tons, and 4 tons of electrolytic manganese are added to the first, second, and third feed troughs, respectively. After each addition of electrolytic manganese, stirring is performed. At the same time, 0.2 tons and 0.15 tons of aluminum shot are added to the first and second feed troughs, respectively, for deoxidation, thereby improving the manganese yield. 0.1 tons of nickel plate and 0.4 tons of copper are added to the third feed trough. After the addition and stirring in the second feed trough, 0.2 tons of ferrosilicon are added and oxygen is blown at 220 Nm. 3 After heating is completed in the third feeding tank, 0.4 tons of ferrosilicon are added and oxygen is blown in at 240 Nm³. 3 The temperature is increased to ensure the required process temperature.

[0047] (3) LF refining: The LF arrival temperature is 1475℃. Slag samples are taken at the station. 500kg lime, 100kg fluorite, and 2 bags of aluminum powder are added for slag conditioning. A total of 9 bags of carbon powder, 400kg electrolytic manganese, 35kg Ni plate, and 550kg low-carbon ferrochrome are added during the LF process for alloying. The LF end temperature is 1475℃. The chemical composition is adjusted to: C: 0.55%, Si: 0.05%, Mn: 22.5%, Al: 0.03%, P: 0.005%, S: 0.001%, Cu: 0.65%, Cr: 3.5%, Ni: 0.20%, N: 0.006%, O: 0.0015%, H: 0.0001%, with the balance being Fe and unavoidable impurities. After soft stirring for 10 minutes, the steel is tapped.

[0048] (4) Continuous casting: The crystallizer taper is designed at 1.2%. The nozzle type is a special small-hole nozzle with a nozzle insertion depth of 120±5mm. The secondary cooling uses peritectic steel. Electromagnetic stirring is used in the continuous casting process. The electromagnetic stirring process parameters are 400A-5HZ-15s reversal, liquidus temperature 1390℃, tundish temperature 1430℃, casting speed 0.65m / min, and the aforementioned special protective slag is used.

[0049] (5) Annealing and grinding: The annealing temperature of the billet is 770℃. After annealing, the surface of the billet is ground with a grinding amount of 2%. The billet is tested at low magnification. The results are: general porosity grade 0.5, central porosity grade 0, general slab deviation grade 0, ingot shape deviation grade 0, and no cracks are found.

[0050] (6) Hot rolling: The billet is cold-charged into the furnace, the heating temperature is 1200℃, the heating time is 160 minutes, the billet enters the 4-roll 3300mm medium plate rolling mill for rolling, the iron scale is removed by high pressure water, the widening longitudinal rolling is adopted, the hot rolling specification is 50mm×2000mm×10000mm, the initial rolling temperature is 1055℃, the final rolling temperature is 940℃, the finished product is straightened after rolling to ensure the plate shape, and the steel plate is sheared online at the head and tail.

[0051] (7) Online solution treatment, the steel plate reddening temperature is 290℃.

[0052] (8) Straightening and trimming: The steel plate is cold straightened to ensure the plate shape requirements, and the edges are trimmed as required to ensure the finished product specifications of 50mm×1950mm×9000mm. Then the steel plate is marked and packaged.

[0053] After performance testing, the mechanical properties of the high-manganese steel plate for ultra-low temperature applications prepared using Example 2 are as follows: Yield strength R P0.2 The tensile strength is 440 MPa, and the tensile strength R is... m The strength is 835 MPa, the elongation A is 50%, and the average transverse impact energy KV2 at -196℃ is 138 J.

[0054] Therefore, by implementing the manufacturing method of the ultra-low temperature high manganese steel plate in Example 2, the ultra-low temperature high manganese steel and ultra-low temperature high manganese steel plate prepared can be applied to the construction of liquefied natural gas storage tanks.

[0055] Example 3

[0056] The manufacturing method of the high-manganese steel plate for ultra-low temperature applications in Example 3 specifically includes the following steps:

[0057] (1) Iron pretreatment to reduce the P content in the iron to 0.0055%.

[0058] (2) K-OBM-S converter smelting: A K-OBM-S converter with a nominal capacity of 80 tons is used for smelting. The amount of molten iron added to the K-OBM-S converter is 60 tons. After decarburization in the K-OBM-S converter to a C content of 0.12%, a total of 19 tons of electrolytic manganese is added to the K-OBM-S converter in three batches using feed troughs. 7 tons, 7 tons, and 5 tons of electrolytic manganese are added to the first, second, and third feed troughs, respectively. After each addition of electrolytic manganese, stirring is performed. At the same time, 0.2 tons and 0.15 tons of aluminum shot are added to the first and second feed troughs, respectively, for deoxidation, thereby improving the manganese yield. 0.15 tons of nickel plate and 0.4 tons of copper are added to the third feed trough. After the addition and stirring in the second feed trough, 0.2 tons of ferrosilicon are added and oxygen is blown at 210 Nm. 3 After heating is completed in the third feeding tank, 0.4 tons of ferrosilicon are added and oxygen is blown in at 230 Nm³. 3 The temperature is increased to ensure the required process temperature.

[0059] (3) LF refining: The LF arrival temperature is 1465℃. Slag samples are taken at the station. 500kg of lime, 100kg of fluorite, and 2 bags of aluminum powder are added for slag conditioning. A total of 7 bags of carbon powder, 420kg of electrolytic manganese, 50kg of Ni plate, and 550kg of low-carbon ferrochrome are added during the LF process for alloying. The LF end temperature is 1472℃. The chemical composition is adjusted to: C: 0.45%, Si: 0.05%, Mn: 24.5%, Al: 0.03%, P: 0.003%, S: 0.001%, Cu: 0.45%, Cr: 4.0%, Ni: 0.50%, N: 0.007%, O: 0.0014%, H: 0.0001%, with the balance being Fe and unavoidable impurities. After soft stirring for 10 minutes, the steel is tapped.

[0060] (4) Continuous casting: The crystallizer taper is designed at 1.2%. The nozzle type is a special small-hole nozzle with a nozzle insertion depth of 115±5mm. The secondary cooling uses peritectic steel. Electromagnetic stirring is used in the continuous casting process. The electromagnetic stirring process parameters are 400A-5HZ-15s reversal, liquidus temperature 1390℃, tundish temperature 1420℃, casting speed 0.7m / min, and the aforementioned special protective slag is used.

[0061] (5) Annealing and grinding: The annealing temperature of the billet is 770℃. After annealing, the surface of the billet is ground with a grinding amount of 2%. The billet is tested at low magnification. The results are: general porosity grade 0.5, central porosity grade 0, general slab deviation grade 0, ingot shape deviation grade 0, and no cracks are found.

[0062] (6) Hot rolling: The billet is cold-charged into the furnace, the heating temperature is 1200℃, the heating time is 160 minutes, the billet enters the 4-roll 3300mm medium plate mill for rolling, the iron scale is removed by high pressure water, the widening longitudinal rolling is adopted, the hot rolling specification is 20mm×2800mm×10000mm, the initial rolling temperature is 1050℃, the final rolling temperature is 930℃, the finished product is straightened after rolling to ensure the plate shape, and the steel plate is sheared online at the head and tail.

[0063] (7) Online solution treatment, the steel plate reddening temperature is 270℃.

[0064] (8) Straightening and trimming: The steel plate is cold straightened to ensure the plate shape requirements, and the edges are trimmed as required to ensure the finished product specifications of 20mm×2700mm×9000mm. Then the steel plate is marked and packaged.

[0065] Performance testing revealed the following mechanical properties of the high-manganese steel plate for cryogenic applications prepared using Example 3: Yield strength R P0.2 The tensile strength is 450 MPa, and the tensile strength R is... m It has a strength of 842 MPa, an elongation of A of 48%, and an average transverse impact energy of KV2 at -196℃ of 138 J.

[0066] Therefore, by implementing the manufacturing method of the ultra-low temperature high manganese steel plate in Example 3, the ultra-low temperature high manganese steel and ultra-low temperature high manganese steel plate prepared can be applied to the construction of liquefied natural gas storage tanks.

[0067] In summary, the manufacturing method of the high-manganese steel and high-manganese steel plate for cryogenic applications of the present invention can ensure high steel purity, low phosphorus and sulfur content, minimal segregation in the billet and steel plate, good low-magnification microstructure of the billet, and absence of surface and internal cracks in the billet. The finished steel plate has characteristics such as low yield strength ratio, high tensile strength, high cryogenic toughness, low coefficient of thermal expansion, and good fatigue resistance. Moreover, through the implementation of the present invention, the manufacturing cost of steel for liquefied natural gas storage tanks can be reduced to one-third of that of existing 9% Ni steel, which is of great significance for meeting the demand for low-cost, high-performance steel for liquefied natural gas storage tanks. Specifically, compared with the prior art, the manufacturing method of the high-manganese steel and high-manganese steel plate for cryogenic applications of the present invention has the following advantages and beneficial effects:

[0068] (1) The first domestic company to develop K-OBM-S converter steel alloying technology for high manganese steel, which shortens the smelting time by more than 50 minutes compared with the existing converter + LF alloying, and significantly improves production efficiency.

[0069] (2) The billet has good low magnification structure, with general porosity of 0.5 grade, central porosity of 0 grade, general off-center plate of 0 grade, ingot off-center plate of 0 grade, and no cracks.

[0070] (4) The finished steel plate has excellent mechanical properties and a yield strength RP0.2 ≥440MPa, tensile strength R m ≥830MPa, elongation A≥40%, lateral impact energy KV2≥120J at -196℃, fully meeting the construction and use requirements of liquefied natural gas storage tanks or cryogenic containers;

[0071] (5) A special mold protective slag was developed, which delayed the reaction time between aluminum in steel and SiO2 in the protective slag, reduced surface and internal cracks caused by uneven heating and cooling, and made the surface and internal cracks of the billet zero.

[0072] It should be noted that, except for those explicitly described herein, the process methods of the present invention can be implemented using conventional methods or apparatus in the art. Unless otherwise specified, the terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, when a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Moreover, when multiple range descriptive features are provided, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0073] It should also be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device.

[0074] Furthermore, 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 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 present invention.

Claims

1. A method of manufacturing a high manganese steel plate for ultra-low temperature, characterized by, Includes the following steps: (1) Iron pretreatment to reduce the P content in the molten iron to P≤0.007%; (2) K-OBM-S converter smelting: molten iron is added to the K-OBM-S converter for smelting. After decarburization in the K-OBM-S converter to C≤0.13%, electrolytic manganese is added to the K-OBM-S converter in three batches. Aluminum shot is added for deoxidation when electrolytic manganese is added for the first and second batches. Nickel plate and copper are added when electrolytic manganese is added for the third batch. Ferrosilicon is added after the second and third batches of electrolytic manganese and oxygen is blown to raise the temperature. (3) LF refining: The molten steel obtained from K-OBM-S converter smelting is sent to the LF furnace, heated by power supply, and slag is adjusted. The composition is adjusted in the later stage of reduction to: C: 0.35~0.55%, Si: 0.01~0.10%, Mn: 20.00~30.00%, Al: 0.01~0.10%, P≤0.005%, S≤0.003%, Cr: 3.0~5.0%, Cu: 0.3~1.0%, Ni: 0.2~1.20%, N≤0.008%, O≤0.002%, H≤0.0002%, with the balance being Fe and unavoidable impurity elements; (4) Continuous casting, the crystallizer taper is designed at 1.2%, the nozzle type is small hole nozzle, the nozzle insertion depth is 110~125mm, the secondary cooling is peritectic steel, electromagnetic stirring is added during the continuous casting process, the tundish temperature is controlled at 1420±10℃, and the casting speed is controlled at 0.6~0.8m / min; (5) Annealing and grinding: The annealing temperature of the billet is controlled at 750~770℃. After annealing, the surface of the billet is ground, and the grinding amount is controlled at 2~3%. (6) Hot rolling: The steel billet is heated to 1200~1230℃ in a heating furnace for homogenization, and then rolled by widening longitudinal rolling. The initial rolling temperature is controlled at 1040~1060℃ and the final rolling temperature is controlled at 910~940℃. (7) Online solution treatment: Online solution treatment is achieved by online laminar flow cooling of hot-rolled steel plates, and the reddening temperature of the steel plates is ≤300℃; In the continuous casting step, a special protective slag is used. The composition of the special protective slag is: SiO2: 37~43%, CaO: 16~22%, Al2O3: 2~5%, MgO≤2.5%, Li2O: 5~7%, Na2O: 8~12%, C-total: 5~6%, F: 5~9%, and the CaO / SiO2 ratio is 0.4~0.

6. The special protective slag has a melting point of 840~900℃ and a viscosity of 0.18~0.28 PaS at 1300℃. The resulting billet has a good low-magnification microstructure, with general porosity at grade 0.5, central porosity at grade 0, general off-center plate at grade 0, and ingot shape off-center plate at grade 0. There are no cracks on the surface or inside the billet.

2. The manufacturing method of the high manganese steel plate for ultra low temperature according to claim 1, characterized by, In the K-OBM-S converter smelting process, the total amount of electrolytic manganese added is (30%~35%) × tons of molten iron. The first addition of electrolytic manganese is 35%~40% of the total amount, the second addition is 30%~40%, and the third addition is 20%~30%. When adding electrolytic manganese for the first time, the amount of aluminum shot added is (0.3%~0.5%) × tons of molten iron. When adding electrolytic manganese for the second time... When electrolytic manganese is added, the amount of aluminum shot is (0.2%~0.3%) × the number of tons of molten iron. After the second addition of electrolytic manganese, the amount of ferrosilicon is (0.3%~0.4%) × the number of tons of molten iron. After the third addition of electrolytic manganese, the amount of ferrosilicon is (0.6%~0.7%) × the number of tons of molten iron. When electrolytic manganese is added for the third time, the amount of nickel plate is (0.15%~0.25%) × the number of tons of molten iron. When electrolytic manganese is added for the third time, the amount of copper is (0.5%~0.7%) × the number of tons of molten iron.

3. The manufacturing method of the high manganese steel plate for ultra low temperature according to claim 1, characterized by, The high manganese steel plate for ultra-low temperature has a yield strength R P0.2 ≥ 440 MPa, a tensile strength R m ≥ 830 MPa, an elongation A ≥ 40%, and a transverse impact energy KV2 at -196 °C ≥ 120 J.

4. The application of the high-manganese steel plate for cryogenic use manufactured using the manufacturing method of the high-manganese steel plate for cryogenic use described in claim 1 in liquefied natural gas storage tanks.