A production method for 200-250mm thick corrosion-resistant, high-strength, and hydrogen-resistant steel 12Cr2Mo1R

Abstract

This invention provides a production method for 200-250mm thick corrosion-resistant, high-strength, and tough hydrogen-resistant steel 12Cr2Mo1R, including converter dephosphorization, refined dephosphorization with low slag smelting, and staged high-pressure quenching. This method achieves good dephosphorization results, controlling the phosphorus content at 0.001%-0.002%, while reducing the number of slag removal operations and lowering costs by more than 15 yuan / t. By rationally controlling the water flow rate, water-to-water ratio, and quenching roller speed in the high and low pressure zones of the quenching machine, the cooling rate of the steel plate at each stage is ensured, improving the thickness effect of extra-thick plates. The overall plate unevenness can reach 3mm / m, ensuring bainitic structure throughout the entire thickness of the steel plate. Its yield strength is ≥450MPa, tensile strength is ≥580MPa, high-temperature tensile yield strength at 450℃ is ≥360MPa, impact toughness at -30℃ is ≥150J, yield strength after maximum simulated post-weld heat treatment temperature of 705℃*30h is ≥350MPa, and vTr54 ≤0℃ after minimum simulated post-weld heat treatment + step cooling test. Its plate shape, high-temperature tensile properties and excellent impact toughness fully meet the requirements for hydrogen-containing steel.

Description

Technical Field

[0001] This invention belongs to the field of extra-thick plate production, specifically relating to a production method of 200-250mm corrosion-resistant, high-strength and tough hydrogen-resistant steel 12Cr2Mo1R. Background Technology

[0002] Hydrogen energy is the most promising energy carrier for the future. Hydrogen refueling reactors that carry hydrogen energy need to operate for extended periods in environments with high temperatures of 400-500℃ and high pressures of 15-25MPa. The extremely low diameter and density of hydrogen atoms make them highly susceptible to hydrogen damage in the steel containers used for storage and transportation, causing a sharp decline in the material's mechanical properties. With the increasing production capacity of petrochemical equipment, higher quality requirements have been placed on the specifications, corrosion resistance, temper embrittlement resistance, and hydrogen stripping resistance of high-pressure reactor steel plates.

[0003] Chinese patent 2021115899142 discloses a method for producing 12Cr2Mo1R steel plates resistant to hydrogen-induced cracking. This method employs C+Al composite deoxidation to purify the molten steel, reducing inclusions and producing steel plates 100-200mm thick. However, besides the limited plate thickness, the high phosphorus content in the molten steel negatively impacts the steel plate's resistance to tempering under high-temperature conditions.

[0004] Chinese Patent 200710046655.2 discloses a 12Cr2Mo1R thick steel plate for hydrogen production equipment and its manufacturing method. The main method involves using a converter for smelting to reduce the content of Sb, Sn, and As, thereby lowering the J and X coefficients. Simultaneously, the high-pressure section is closed to prevent the large volume of water from rapidly quenching the steel plate surface into martensite, allowing it to directly enter the low-pressure section for cooling. A smaller water flow rate is selected in the low-pressure section to cool the steel plate to a certain temperature (surface temperature greater than 100℃) at a specific cooling rate (core greater than 0.5℃ / s). Considering the limited length of the pressure quenching machine, the steel plate is oscillated and cooled in the low-pressure section. The reasonable distribution of water flow on the upper and lower surfaces results in a good plate shape. However, this method is only suitable for steel plates less than 100mm thick; for steel plates thicker than 150mm, the performance at half the thickness cannot be guaranteed. Summary of the Invention

[0005] To meet the above technical requirements, the purpose of this invention is to provide a production method for 200-250mm thick corrosion-resistant, high-strength and tough hydrogen-resistant steel 12Cr2Mo1R, which not only obtains steel plates with a thickness of more than 150mm, but also ensures the performance at half the thickness.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a production method for 200-250mm thick corrosion-resistant, high-strength, and tough hydrogen-resistant steel 12Cr2Mo1R, wherein the steel adopts the following chemical composition by mass percentage (unit: wt%): C: 0.11~0.14, Si: 0.2~0.3, Mn: 0.3~0.6, P≤0.002, S≤0.003, Cr: 2.0~2.4, Mo: 0.9~1.1, Nb: 0.01~0.02, V: 0.01~0.03, and the others are Fe and residual elements;

[0007] The steel has a yield strength ≥450MPa, tensile strength ≥580MPa, high temperature tensile yield strength at 450℃ ≥360MPa, impact toughness at -30℃ ≥150J, yield strength after maximum simulated post-weld heat treatment temperature of 705℃*30h ≥350MPa, and vTr54≤0℃ after minimum simulated post-weld heat treatment + step cooling test.

[0008] The steel production method includes low-phosphorus steel smelting, VD refining, casting 950-1025mm thick water-cooled mold steel ingots, rolling, and heat treatment. The low-phosphorus steel smelting includes converter dephosphorization and LF refining dephosphorization. The heat treatment process employs staged high-pressure quenching and tempering, as detailed below:

[0009] 1) Converter dephosphorization: 1-2 tons of the final slag from the previous furnace with a basicity greater than 2 and a temperature of 1000-1200℃ are retained in the converter. Then, the molten iron after KR desulfurization is mixed with high-quality scrap steel in a 7:2 ratio in the converter for stirring and oxygen blowing dephosphorization. During this process, 800-1000 kg of lightly calcined dolomite and 2800-3500 kg of limestone are added in batches to form slag. The dephosphorization temperature is controlled at 1380-1430℃. When the brown flame at the converter mouth turns into a white flame and the molten steel temperature exceeds 1560℃, the steel is tapped with a phosphorus content ≤0.007%.

[0010] 2) LF refining and dephosphorization: The temperature of the molten steel reaching the LF refining furnace is 1530-1580℃. Limestone 800-1000kg, fluorite 300-600kg, and iron oxide scale 700-1200kg are added in batches for dephosphorization. After strong blowing and stirring, samples are taken. The argon blowing pressure is 0.5-0.8MPa, and the P content is controlled at 0.001%-0.002%. Then, slag is poured out at a small flow rate until steel sparks splash. Alloying elements are added, and slag is poured out when the slag color is white.

[0011] 3) Staged high-pressure quenching: The rolled steel plate is heated in a roller hearth quenching mill to a temperature of 900℃~930℃, and then sequentially enters the high-pressure zone and the low-pressure zone for quenching. The nozzle water pressure in the high-pressure zone is controlled at 0.6~0.9MPa, the nozzle water pressure in the low-pressure zone is controlled at 0.3~0.5MPa, and the quenching water temperature is controlled at 12~18℃. The high-pressure zone is divided into three sections, and the specific control parameters are as follows:

[0012] a. High-pressure zone section: Control the water flow rate to 300-380 m³ / h, maintain the roller speed at 1.8-2.4 m / min, and the water-to-water ratio at 1.4-1.8. Ensure that the cooling rate at 15-25 mm from the surface is 8-10 °C / s, so that the surface is cooled first and a small amount of martensite and bainite structures are generated. The surface reddening temperature is controlled at 480-560 °C.

[0013] b. High-pressure zone, second stage: control the water flow rate to 180-250 m³ / h, maintain the roller speed at 1.3-1.5 m / min, and the ratio of water flow from bottom to top at 1.2-1.5 to ensure the cooling rate of the steel plate is 4-7℃ / s, uniformly control the temperature of the upper and lower surfaces, and retain 100% bainite structure in the upper and lower 1 / 4 positions, while ensuring the tolerance of the thick plate shape.

[0014] c. High-pressure zone, three sections: control the water flow rate to 450-500 m³ / h, maintain the roller speed at 0.8-1.2 m / min, and the water-to-water ratio at 1.1-1.3 to ensure that the cooling rate at 1 / 3 of the steel plate is 1.5-3.0℃ / s. Rapid cooling with a large water flow rate allows the cooling rate to be transferred to 1 / 2 of the steel plate as much as possible. This rapid cooling better solves the heat transfer limitations of thick plates, ensures the temperature consistency between 1 / 3 of the steel plate and the surface layer, and prevents the formation of ferrite structure at 1 / 3 of the steel plate.

[0015] d. Low-pressure zone: Control the water flow rate to 300-350 m³ / h, maintain the roller speed at 0.6-0.8 m / min, and the water-to-water ratio to the water-to-water ratio to be 1.3-1.5. Ensure that the cooling rate at the 1 / 2 section is 0.80-1.2℃ / s. The high flow rate and low roller speed in the low-pressure zone serve two purposes: First, to ensure a high cooling rate at the 1 / 2 section, avoiding heat conduction from the steel core to the surface and preventing residual heat tempering. The appropriate roller speed will also minimize the risk of warping of the steel plate. Second, at a higher cooling rate, it ensures that there is more than 95% bainite structure at the 1 / 2 section, maximizing the cooling rate from the surface to the core of the steel plate. At the same time, the degree of supercooling will also increase, appropriately delaying the growth of ferrite grains into the untransformed matrix and refining the ferrite grain size in the microstructure.

[0016] 4) Tempering: Tempering temperature 700℃~730℃, holding time 4.0~4.5min / mm, followed by air cooling to room temperature.

[0017] The beneficial effects of this invention are as follows: During phosphorus removal in the converter, slag retention smelting is adopted. The high-temperature, high-basicity slag is conducive to the formation of initial slag, effectively improving the efficiency of P and S removal in the early stage, protecting the furnace lining, and reducing the amount of limestone used. The phosphorus content after the converter is controlled to ≤0.007%, which also helps to reduce the burden of dephosphorization in refining. After entering the refining stage, by rationally controlling the oxygen content and iron oxide, and through high-flow-rate argon blowing, a better dephosphorization effect can be achieved, keeping the P content controlled at 0.001% to 0.002%. The lower phosphorus content in the molten steel will improve the strength of the steel plate at high temperatures and its resistance to temper brittleness. Furthermore, using a single-slag converter and refining dephosphorization will increase the amount of gas recovered, reduce the number of slag dumping operations, improve the yield of molten steel, and reduce costs by more than 15 yuan / t.

[0018] This invention utilizes the water flow rate, water-to-water ratio, and quenching roller speed in the high and low pressure zones of the quenching machine to ensure the cooling rate of the steel plate at each stage, improving the thickness effect of extra-thick plates. A slightly higher roller speed in the first stage ensures less martensite formation on the surface, which, after high-temperature tempering, forms oriented sorbite, exhibiting good high strength and toughness. Subsequently, the cooling water flow rate is increased, and the quenching roller speed is appropriately reduced to ensure a certain amount of bainite structure is obtained at each stage. The addition of Cr expands the austenite region, causing the bainite transformation to shift towards lower temperatures. In the low-pressure zone, rapid cooling is still performed with a high flow rate and low roller speed, resulting in a higher core temperature. However, the cooling rate gradually decreases after penetrating to the halfway point. Mo appropriately inhibits the precipitation of proeutectoid ferrite, increasing the hardenability of the steel plate. Therefore, a small amount of ferrite structure is generated at the halfway point, ensuring that more than 95% bainite structure remains.

[0019] This invention combines low-slag smelting with refining and dephosphorization to reduce phosphorus content, ensuring the purity of molten steel, improving production efficiency, and reducing production costs. Staged high-pressure quenching and rapid cooling ensure a certain amount of bainite structure throughout the entire thickness of the steel plate, giving it high strength, good high-temperature resistance, low-temperature impact resistance, and resistance to temper brittleness. The flatness of the steel plate produced by this process is also significantly improved, with an unevenness of up to 3 mm / m.

[0020] The 200-250mm corrosion-resistant, high-strength and tough hydrogen-resistant steel 12Cr2Mo1R obtained by this invention has a yield strength ≥450MPa, tensile strength ≥580MPa, high-temperature tensile yield strength at 450℃ ≥360MPa, impact toughness at -30℃ ≥150J, yield strength after maximum simulated post-weld heat treatment temperature of 705℃*30h ≥350MPa, and vTr54≤0℃ after minimum simulated post-weld heat treatment + step cooling test. Its plate shape, high-temperature tensile properties and excellent impact toughness fully meet the requirements for hydrogen-resistant steel. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the metallographic structure of the steel plate obtained in an embodiment of the present invention at 500%. Detailed Implementation

[0022] The technical features of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] An embodiment of the present invention prepares to produce 220mm thick corrosion-resistant, high-strength and tough hydrogen-resistant steel 12Cr2Mo1R, using the following chemical composition by mass percentage (unit: wt%): C: 0.13, Si: 0.25, Mn: 0.46, P≤0.002, S≤0.003, Cr: 2.2, Mo: 0.98, Nb: 0.015, V: 0.026, the others being Fe and residual elements;

[0024] The steel is produced using the following process:

[0025] 1) Converter dephosphorization: 1-2 tons of final slag from the previous furnace with a basicity greater than 2 and a temperature of 1000-1200℃ are retained in the converter. Then, the KR desulfurized molten iron and high-quality scrap steel are stirred and oxygen-blown in the converter at a ratio of 7:2 for dephosphorization. The oxygen supply intensity is 130NL / (min·t), and the pressure is 1.1MPa. During this process, 800-1000 kg of lightly calcined dolomite and 2800-3500 kg of limestone are added in batches for slag formation. The dephosphorization temperature is controlled at 1380-1430℃. When the brown flame at the converter mouth turns into a white flame and the molten steel temperature exceeds 1560℃, the steel is tapped. The P content at tapping is 0.006%.

[0026] 2) Refining and dephosphorization: The temperature of the molten steel reaching the LF refining furnace is 1570℃. Limestone 800-1000kg, fluorite 300-600kg, and iron oxide scale 700-1200kg are added in batches for dephosphorization. After strong blowing and stirring, samples are taken. The argon blowing pressure is set to 0.6-0.8MPa, and the P content is controlled at 0.001%-0.002%. Then, slag is poured out at a small flow rate until steel sparks splash. Alloying elements are added, and slag is poured out when the slag color is white.

[0027] 3) VD refining: The VD holding time is controlled at ≥18min. It is required that the molten steel tumbling effect is good during the holding process under a vacuum of 67Pa, and the H content is required to be ≤1.2PPm.

[0028] 4) Water-cooled mold casting: 1025mm thick water-cooled mold casting is used.

[0029] 5) Heating: The steel ingot is heated in a regenerative heating furnace at a temperature of 1260℃ and held for 33 hours.

[0030] 6) Rolling: After the heat preservation is completed, rolling begins. The initial rolling temperature is 1020℃, the reduction per pass is 30-40mm, and the final rolling temperature is 950℃. The steel plate is then sent to the slow cooling pit for stacking cooling.

[0031] 7) Quenching: The steel plate is heated in a roller hearth quenching machine to a temperature of 910℃, and then sequentially enters the high-pressure zone and the low-pressure zone for quenching. The nozzle water pressure in the high-pressure zone is controlled at 0.8MPa, the nozzle water pressure in the low-pressure zone is controlled at 0.4MPa, and the quenching water temperature is controlled at 14~17℃. The high-pressure zone is divided into three sections, and the specific control parameters are as follows:

[0032] The entire quenching section is divided into a high-pressure zone and a low-pressure zone. The high-pressure zone is 5m long and divided into three sections: High-Pressure Zone Section 1, High-Pressure Zone Section 2, and High-Pressure Zone Section 3. Specifically, High-Pressure Zone Section 1 is 1.2m long, High-Pressure Zone Section 2 is 1.8m long, and High-Pressure Zone Section 3 is 2m long. The low-pressure zone is 17145mm long and is also divided into three sections: Low-Pressure Zone Section 1, Low-Pressure Zone Section 2, and Low-Pressure Zone Section 3. Each section is equipped with 15 sets of symmetrically arranged nozzles, with an interval of 381mm between adjacent sets of nozzles.

[0033] High-pressure zone section: control the water flow rate to 380 m3 / h, maintain the roller speed at 2 m / min, and the water-to-water ratio to the water-to-water ratio to be 1.6, so that it passes through at a relatively fast speed, ensuring that the cooling rate at 15-25 mm from the surface is 8-10℃ / s, so that the surface is cooled first and a small amount of martensite and bainite structure is generated. The surface reddening temperature is controlled at 540℃.

[0034] High-pressure zone, section two: control the water flow rate to 250 m3 / h, maintain the roller speed at 1.4 m / min, and the ratio of water flow from bottom to top to 1.2 to 1.5 to ensure the cooling rate of the steel plate is 4 to 7℃ / s, uniformly control the temperature of the upper and lower surfaces, and retain 100% bainite structure in the upper and lower 1 / 4 positions, while ensuring the tolerance of the thick plate shape.

[0035] High-pressure zone, three sections: control the water flow rate to 500 m³ / h, maintain the roller speed at 0.8 m / min, and the water-to-water ratio to the steel plate is 1.1. Ensure that the cooling rate at 1 / 3 of the steel plate is between 1.5 and 3.0 °C / s. Use a large water flow rate for rapid cooling so that the cooling rate can be transferred to 1 / 2 of the steel plate as much as possible. This rapid cooling better solves the heat transfer limitations of thick plates, ensures the consistency of the temperature between 1 / 3 of the steel plate and the surface layer, and prevents the formation of ferrite structure at 1 / 3 of the steel plate.

[0036] Low-pressure zone: Control the water flow rate to 350 m³ / h, maintain the roller speed at 0.8 m / min, and the water-to-water ratio to the water-to-water ratio to 1.3. Ensure that the cooling rate at the 1 / 2 section is 0.8–1.2 °C / s. The high flow rate and low roller speed in the low-pressure zone serve two purposes: First, to ensure a high cooling rate at the 1 / 2 section, avoiding heat conduction from the steel plate core to the surface and preventing residual heat tempering. The appropriate roller speed also helps to prevent the steel plate from warping. Second, at a higher cooling rate, it ensures that there is more than 95% bainite structure at the 1 / 2 section, maximizing the cooling rate from the surface to the core of the steel plate. At the same time, the supercooling will also increase, appropriately delaying the growth of ferrite grains into the untransformed matrix and refining the ferrite grain size in the microstructure.

[0037] 8) Tempering: Temper the steel plate in a normalizing furnace at a temperature of 725℃ and a holding time of 4.3 min / mm, then air cool to room temperature.

[0038] Performance tests were conducted on a 220mm thick corrosion-resistant, high-strength and tough hydrogen-resistant steel 12Cr2Mo1R obtained in the example. The tests included room temperature yield strength, tensile strength, high-temperature tensile strength at 450℃, and impact toughness at -30℃. The steel underwent a step-cooling experiment with a maximum simulated post-weld heat treatment temperature of 705℃ for 30 hours and a minimum simulated post-weld heat treatment temperature of 705℃ for 8 hours. Specific test performance data are shown in Table 1.

[0039] Table 1 Performance Data

[0040]

[0041] External inspection and flaw detection: The external inspection pass rate of the developed steel plate is 100%, and the final flaw detection of the steel plate meets the Class I flaw detection requirements of GB / T 2970 "Inspection Method for Thick Steel Plates".

[0042] The above description is only a preferred embodiment of the present invention. The above specific embodiments are not intended to limit the present invention. Any modifications, alterations or equivalent substitutions made by those skilled in the art based on the above description shall fall within the protection scope of the present invention.

Claims

1. A method for producing 200-250mm thick corrosion-resistant, high-strength, and tough hydrogen-resistant steel 12Cr2Mo1R, characterized in that: The steel has the following chemical composition by mass percentage: C: 0.11-0.14, Si: 0.2-0.3, Mn: 0.3-0.6, P≤0.002, S≤0.003, Cr: 2.0-2.4, Mo: 0.9-1.1, Nb: 0.01-0.02, V: 0.01-0.03, with the remainder being Fe and residual elements; The steel has a yield strength ≥450MPa, tensile strength ≥580MPa, high-temperature tensile yield strength at 450℃ ≥360MPa, impact toughness at -30℃ ≥150J, yield strength after maximum simulated post-weld heat treatment temperature of 705℃*30h ≥350MPa, and vTr54≤0℃ after minimum simulated post-weld heat treatment of 705℃*8h + step cooling test. The steel production method includes low-phosphorus steel smelting, VD refining, casting 950-1025mm thick water-cooled mold steel ingots, rolling, and heat treatment. The low-phosphorus steel smelting process includes converter dephosphorization and LF refining dephosphorization. The heat treatment process employs staged high-pressure quenching and tempering, as detailed below: 1) Converter dephosphorization: 1-2 tons of the final slag from the previous heat (basicity greater than 2, temperature 1000-1200℃) are retained in the converter. Then, the KR desulfurized molten iron and high-quality scrap steel are stirred and oxygen-blown in the converter for dephosphorization at a ratio of 7:

2. During this process, 800-1000 kg of lightly calcined dolomite and 2800-3500 kg of limestone are added in batches to form slag. The dephosphorization temperature is controlled at 1380-1430℃. When the brown flame at the converter mouth turns into a white flame and the molten steel temperature exceeds 1560℃, the steel is tapped with a phosphorus content ≤0.007%. 2) LF Refining Dephosphorization: The temperature of the molten steel reaching the LF refining furnace is 1530-1580℃. Limestone 800-1000kg, fluorite 300-600kg, and iron oxide scale 700-1200kg are added in batches for dephosphorization. After strong blowing and stirring, samples are taken. The argon blowing pressure is 0.5-0.8 MPa, and the P content is controlled at 0.001%-0.002%. Then, slag is poured out at a small flow rate until steel sparks splash. Alloying elements are added, and slag is poured out when the slag color is white. 3) Staged high-pressure quenching: The rolled steel plate is heated in a roller hearth quenching mill to a temperature of 900℃~930℃, and then sequentially enters the high-pressure zone and the low-pressure zone for quenching. The nozzle water pressure in the high-pressure zone is controlled at 0.6~0.9MPa, the nozzle water pressure in the low-pressure zone is controlled at 0.3~0.5MPa, and the quenching water temperature is controlled at 12~18℃. The high-pressure zone is divided into three sections, and the specific control parameters are as follows: a. High-pressure zone section: Control the water flow rate to 300-380 m³ / h, maintain the roller speed at 1.8-2.4 m / min, and the water-to-water ratio at 1.4-1.

8. Ensure that the cooling rate at 15-25 mm from the surface is 8-10 °C / s, so that the surface is cooled first and a small amount of martensite and bainite structures are formed. The surface reddening temperature is controlled at 480-560 °C. b. High-pressure zone two: control the water flow rate to 180-250 m3 / h, maintain the roller speed at 1.3-1.5 m / min, and the ratio of water flow to water flow to the top water at 1.2-1.5 to ensure the cooling rate of the steel plate is 4-7℃ / s, uniformly control the temperature of the upper and lower surfaces, and retain 100% bainite structure in the upper and lower 1 / 4 positions, while ensuring the tolerance of the thick plate shape; c. High-pressure zone, three sections: control the water flow rate to 450-500 m³ / h, maintain the roller speed at 0.8-1.2 m / min, and the ratio of water to water flow rate to the top water at 1.1-1.

3. Ensure that the cooling rate at 1 / 3 of the steel plate is 1.5-3.0℃ / s. Use a large water flow rate for rapid cooling so that the cooling rate can be transferred to 1 / 2 of the steel plate as much as possible. This rapid cooling better solves the limitation of heat transfer in thick plates, ensures the consistency of temperature between 1 / 3 of the steel plate and the surface layer, and prevents the formation of ferrite structure at 1 / 3 of the steel plate. d. Low-pressure zone: Control the water flow rate to 300-350 m³ / h, maintain the roller speed at 0.6-0.8 m / min, and the water-to-water ratio to the water-to-water ratio to be 1.3-1.

5. Ensure that the cooling rate at the 1 / 2 section is 0.80-1.2℃ / s. The high flow rate and low roller speed in the low-pressure zone serve two purposes: First, to ensure a high cooling rate at the 1 / 2 section, avoiding heat conduction from the steel core to the surface and preventing residual heat tempering. The appropriate roller speed will also minimize the risk of warping in the steel plate. Second, at a higher cooling rate, it ensures that there is more than 95% bainite structure at the 1 / 2 section, maximizing the cooling rate from the surface to the core of the steel plate. At the same time, the degree of supercooling will also increase, appropriately delaying the growth of ferrite grains into the untransformed matrix and refining the ferrite grain size in the microstructure. 4) Tempering: Tempering temperature 700℃~730℃, holding time 4.0~4.5min / mm, followed by air cooling to room temperature.

Images