Low-temperature impact-resistant alloy steel and preparation method thereof

Abstract

The invention relates to low-temperature impact-resistant alloy steel and a preparation method thereof, and belongs to the technical field of alloy steel preparation. Cr powder, V powder, Nb powder and other metal powder are mixed to regulate and control element components in a steel matrix, the element components act together, growth of austenite grains is hindered in the matrix machining process, the precipitation strengthening effect is achieved, and the low-temperature impact-resistant alloy steel is obtained. The strength and toughness of the steel are improved. In the casting process, the low-temperature impact performance of the cast steel can be effectively improved by controlling factors such as the casting temperature, the grouting rate and the forced cooling rate. The surface stress of the steel is relieved by matching with a treatment method of dipping in molten zinc liquid, so that the steel can be suitable for more processing methods, a zinc layer can be sacrificed, heat input and deformation of the steel can be relieved and part of stress can be absorbed and dispersed in the welding and wind cutting processes when the steel is subjected to operations such as welding and wind cutting, and the steel is prevented from being damaged. The prepared steel has the characteristics of good processability at low temperature and strong impact resistance at low temperature.

Description

Technical Field

[0001] The invention relates to the technical field of alloy steel preparation, in particular to a low-temperature impact-resistant alloy steel and a preparation method thereof. Background Art

[0002] Alloy steel is widely used in modern industry, especially in fields that require low-temperature impact resistance, such as oil and gas extraction, polar engineering, aerospace, etc. In its application process, the low-temperature brittleness of metals is a problem often encountered when selecting materials. Taking ordinary carbon steel as an example, the toughness-brittleness transition temperature of some ferritic steels is only -20℃, which is a common temperature in northern my country in winter. When this type of steel is used below this temperature, the toughness will drop significantly. Therefore, it is necessary to optimize the forging process of alloy steel. Usually, heat treatment processes and other methods are used to temper the steel, or the balance effect of the environment on the steel is improved by extending the placement time to achieve the purpose of improving the performance of the steel. However, it usually requires too high a heat treatment temperature or a long time of balance to maintain the working performance of the steel at low temperatures.

[0003] In addition, the stress of steel strengthened by heat treatment will be concentrated on the surface, and the high temperature generated in the process will change the metallographic structure of the steel, which may lead to the loss of heat treatment effect, affect its overall mechanical properties, and make the steel unable to be directly processed by welding and wind cutting. Therefore, a new preparation process is needed to cast steel so that it has good working performance at low temperature. Summary of the invention

[0004] The object of the present invention is to provide a low-temperature impact-resistant alloy steel and a preparation method thereof, so as to solve the problems raised in the background technology. Cr powder is mixed with metal powders such as V powder and Nb powder to regulate the element components in the steel matrix, so that they work together to hinder the growth of austenite grains during the matrix processing, exert precipitation strengthening effects, and improve the strength and toughness of the steel. In the casting process, controlling factors such as casting temperature, grouting rate, and forced cooling rate can effectively improve the low-temperature impact performance of cast steel. The treatment method of impregnating molten zinc liquid is matched to relieve the surface stress of the steel, so that the steel can be applied to more processing methods. When undergoing operations such as welding repair and wind cutting, the zinc layer can be sacrificed to relieve the heat input and deformation of the steel, and part of the stress can be absorbed and dispersed during welding repair and wind cutting. The obtained steel has the characteristics of good processing performance at low temperature and strong impact resistance at low temperature.

[0005] To achieve the above object, the present invention provides the following technical solutions: A method for preparing low-temperature impact-resistant alloy steel comprises the following steps: S1. Melting, refining and composition control: Select low-carbon steel without rust, oil or impurities, place it in a ladle furnace to smelt it into molten iron, then perform desulfurization and deoxidation treatment, take samples in the ladle, detect the impurity content in the molten iron sample, control the S content in the molten iron to be ≤0.015%, the P content to be ≤0.02%, and the C content to be ≤0.2%, then add the reinforcing alloy powder into the system and stir for 10-20 minutes; S2, melt casting and heat preservation: setting the terminal temperature of the ladle furnace to 1600°C-1700°C, and casting the molten iron obtained in step S1 using a mold after reaching the specified temperature to obtain a cast billet; placing the cast billet at 1000°C-1400°C for 0.5-2 hours and then rolling it, the final rolling temperature is 900-920°C, and cooling it to room temperature after molding to obtain an ingot; S3, ingot tempering treatment: ⅰ. The ingot obtained in step S2 is heated to 900-950-920°C at a heating rate of 5-10°C / min, kept for 3-4 hours, and then air-cooled to room temperature; ⅱ. Then heat up to 900-950℃ at a heating rate of 5-10℃ / min, keep warm for 3-4 hours, and then water cool to below 50℃; ⅲ. Then increase the treatment temperature to 620-680°C at a heating rate of 10-20°C / min, keep warm for 4-6 hours, and then air cool to below 50°C; ⅳ. Finally, the treatment temperature is increased to 580-650°C at a heating rate of 5-10°C / min, kept at this temperature for 4-6 hours, and then air-cooled to room temperature to obtain a quenched and tempered ingot; S4. Ingot processing: wash the tempered ingot with water, and then immerse it in an acid solution, raise the acid solution temperature to 80-90°C, and immerse it for 10-40 minutes. Then wash the steel surface with clean water, and then immerse it in a plating aid to ensure that all surfaces of the tempered ingot are completely immersed. After the tempered ingot is taken out and naturally solidified, a low-temperature impact-resistant alloy steel is obtained.

[0006] Furthermore, in step S1, the specific operation of the desulfurization and deoxygenation treatment is as follows: The molten iron obtained by melting low-carbon steel is placed in an inert atmosphere, and the first slag removal is carried out. Subsequently, a desulfurization and deoxidization agent is added to the molten iron system and stirred for 10-30 minutes, and then a second slag removal is carried out; wherein the desulfurization and deoxidization agent is obtained by mixing aluminum powder, calcium oxide and limestone in a mass ratio of (1-3): (1-2): (1-2), and the amount of the desulfurization and deoxidization agent used is 0.03wt%-0.07wt% of the total amount of low-carbon steel.

[0007] Furthermore, in step S1, the reinforced alloy powder is obtained by mixing Cr powder, Cu powder, Ni powder, V powder and Nb powder with a particle size range of 0-60 μm in a mass ratio of 5:(1-3):(1-3):(0.1-1):(0.1-1), and the amount of the reinforced alloy powder used is 1-3wt% of the low carbon steel.

[0008] Furthermore, in step S2, the casting temperature is 1565±5°C and the steel tapping temperature is 620±10°C.

[0009] Furthermore, in step S4, the plating aid is obtained by mixing 120-125 g / L zinc chloride solution and 220-225 g / L ammonium chloride solution.

[0010] Furthermore, in step S4, the temperature for immersing the substrate using the plating agent is 440° C.-460° C., and the immersing time for the plating agent is 2-5 minutes.

[0011] Compared with the prior art, the present invention has the following beneficial effects: In the technical solution of the present invention, metal powders are used to regulate the elemental components in the steel matrix. When Cr powder is used to strengthen the steel, it will improve the hardness and wear resistance of the steel, so that it can withstand greater impacts. However, during the tempering of the steel, its tough-to-brittle transition temperature will increase, increasing its brittleness. In the present invention, Cr powder is mixed with metal powders such as V powder and Nb powder. When they work together, the growth of austenite grains can be hindered during the matrix processing, and the precipitation strengthening effect can be exerted to improve the strength and toughness of the steel. When Ni powder and Cr powder are mixed with other metal powders, the tough-to-brittle transition temperature of the steel can be reduced. Cu powder can suppress the brittleness caused by tempering to reduce the problem of Cr powder causing the tough-to-brittle transition temperature of the material to increase.

[0012] In the technical solution of the present invention, controlling the casting process can improve the mechanical properties of steel during production, including low-temperature impact resistance. In the casting process, controlling factors such as casting temperature, grouting rate, and forced cooling rate can effectively improve the low-temperature impact resistance of cast steel. The treatment method of impregnating with molten zinc liquid can relieve the surface stress of the steel, so that the steel can be applied to more processing methods. When undergoing operations such as welding repair and wind cutting, the zinc layer can be sacrificed to relieve the heat input and deformation of the steel, and can absorb and disperse part of the stress during welding repair and wind cutting, which will not cause cracks in the steel or local stress concentration. It has a breaking force, so that the produced steel can operate normally in a low-temperature environment and reduce the possible cracking of the steel. In addition, the zinc layer also helps to delay the corrosion of the steel in a low-temperature environment, thereby indirectly improving its overall impact resistance. DETAILED DESCRIPTION

[0013] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0014] Example 1 A method for preparing low-temperature impact-resistant alloy steel comprises the following steps: S1. Melting, refining and composition control: 100,000 kg ± 5 kg of rust-free, oil-free and impurity-free low-carbon steel is selected and placed in a ladle furnace to smelt into molten iron. The molten iron is placed in a nitrogen atmosphere and the first slag removal is performed. Subsequently, a desulfurization and deoxidation agent is added to the molten iron system for stirring. The treatment time is 10 minutes. Subsequently, the second slag removal is performed, and samples are taken from the ladle to detect the impurity content in the molten iron sample. The S content in the molten iron is controlled to be ≤0.015%, the P content is ≤0.02%, and the C content is ≤0.2%. Subsequently, a reinforcing alloy powder is added to the system and stirred for 10 minutes. The deoxidation and desulfurization agent is obtained by mixing aluminum powder, calcium oxide and limestone in a mass ratio of 1:1:1, and the amount of the deoxidation and desulfurization agent used is 0.03wt% of the total amount of low-carbon steel; The reinforced alloy powder is obtained by mixing Cr powder, Cu powder, Ni powder, V powder and Nb powder with a particle size range of 0-60 μm in a mass ratio of 5:1:1:0.1:0.1, and the amount of the reinforced alloy powder used is 1wt% of the low carbon steel.

[0015] S2, melt casting and heat preservation: set the end temperature of the ladle furnace to 1600°C, and after reaching the specified temperature, cast the molten iron obtained in step S1 using a mold, the casting temperature is 1565±5°C, the tapping temperature is 620±10°C, and a cast billet is obtained; keep the cast billet at 1000°C for 0.5 hours, then roll it, the final rolling temperature is 900°C, prepare a cylindrical sample with a diameter of 10 cm, and then cool it to room temperature to obtain an ingot; S3, ingot tempering treatment: ⅰ. The ingot obtained in step S2 was heated to 900°C at a heating rate of 5°C / min, kept at this temperature for 3 hours, and then air-cooled to room temperature; ⅱ. Then heat up to 900°C at a heating rate of 5°C / min, keep warm for 3 hours, and then water cool to below 50°C; ⅲ. Then, the treatment temperature was increased to 620°C at a heating rate of 10°C / min, kept at this temperature for 4 hours, and then air-cooled to below 50°C; ⅳ. Finally, the treatment temperature was raised to 580°C at a heating rate of 5°C / min, kept at this temperature for 4 hours, and then air-cooled to room temperature to obtain a quenched and tempered ingot; S4, ingot processing: the quenched and tempered ingot is washed with water, and then immersed in a 10wt% sulfuric acid solution, the acid solution temperature is increased to 80°C, the immersion time is 10 minutes, and then the steel surface is washed with clean water, and then immersed in a plating agent, the immersion temperature of the plating agent is 440°C, and the immersion time of the plating agent is 2 minutes. After ensuring that all surfaces of the quenched and tempered ingot are completely immersed, the quenched and tempered ingot is taken out, taken out, and naturally solidified to obtain a low-temperature impact-resistant alloy steel; The plating aid is obtained by mixing equal volumes of 120 g / L zinc chloride solution and 220 g / L ammonium chloride solution.

[0016] Example 2 A method for preparing low-temperature impact-resistant alloy steel comprises the following steps: S1. Melting, refining and composition control: 100,000 kg ± 5 kg of rust-free, oil-free and impurity-free low-carbon steel is selected and placed in a ladle furnace to smelt into molten iron. The molten iron is placed in a nitrogen atmosphere and the first slag removal is performed. Subsequently, a desulfurization and deoxidation agent is added to the molten iron system for stirring. The treatment time is 20 minutes. Subsequently, the second slag removal is performed, and samples are taken from the ladle to detect the impurity content in the molten iron sample. The S content in the molten iron is controlled to be ≤0.015%, the P content is ≤0.02%, and the C content is ≤0.2%. Subsequently, a reinforcing alloy powder is added to the system and stirred for 15 minutes. The deoxidation and desulfurization agent is obtained by mixing aluminum powder, calcium oxide and limestone in a mass ratio of 2:1:2, and the amount of the deoxidation and desulfurization agent used is 0.05wt% of the total amount of low-carbon steel; The reinforced alloy powder is obtained by mixing Cr powder, Cu powder, Ni powder, V powder and Nb powder with a particle size range of 0-60 μm in a mass ratio of 5:2:2:0.5:0.5, and the amount of the reinforced alloy powder used is 2wt% of the low carbon steel.

[0017] S2, melt casting and heat preservation: set the end temperature of the ladle furnace to 1650°C, and after reaching the specified temperature, cast the molten iron obtained in step S1 using a mold, the casting temperature is 1565±5°C, the tapping temperature is 620±10°C, and a cast billet is obtained; keep the cast billet at 1200°C for 1 hour, and then roll it, the final rolling temperature is 910°C, prepare a cylindrical sample with a diameter of 10 cm, and then cool it to room temperature to obtain an ingot; S3, ingot tempering treatment: ⅰ. The ingot obtained in step S2 was heated to 920°C at a heating rate of 10°C / min, kept at this temperature for 3-4 hours, and then air-cooled to room temperature; ⅱ. Then heat to 920°C at a heating rate of 10°C / min, keep warm for 3.5 hours, and then water cool to below 50°C; ⅲ. Then, the treatment temperature was increased to 650°C at a heating rate of 20°C / min, kept at this temperature for 5 hours, and then air-cooled to below 50°C; ⅳ. Finally, the treatment temperature was raised to 600°C at a heating rate of 10°C / min, kept at this temperature for 6 hours, and then air-cooled to room temperature to obtain a quenched and tempered ingot; S4, ingot processing: the quenched and tempered ingot is washed with water, then immersed in a 10wt% sulfuric acid solution, the acid solution temperature is raised to 80°C, the immersion time is 25 minutes, then the steel surface is washed with clean water, then immersed in a plating agent, the immersion temperature of the plating agent is 450°C, the immersion time of the plating agent is 3 minutes, and after ensuring that all surfaces of the quenched and tempered ingot are completely immersed, the quenched and tempered ingot is taken out and naturally solidified to obtain a low-temperature impact-resistant alloy steel; The plating aid is obtained by mixing equal volumes of 120 g / L zinc chloride solution and 220 g / L ammonium chloride solution.

[0018] Example 3 A method for preparing low-temperature impact-resistant alloy steel comprises the following steps: S1. Melting, refining and composition control: 100,000 kg ± 5 kg of rust-free, oil-free and impurity-free low-carbon steel is selected and placed in a ladle furnace to smelt into molten iron. The molten iron is placed in a nitrogen atmosphere and the first slag removal is performed. Subsequently, a desulfurization and deoxidation agent is added to the molten iron system for stirring. The treatment time is 30 minutes. Subsequently, the second slag removal is performed, and samples are taken from the ladle to detect the impurity content in the molten iron sample. The S content in the molten iron is controlled to be ≤0.015%, the P content is ≤0.02%, and the C content is ≤0.2%. Subsequently, a reinforcing alloy powder is added to the system and stirred for 20 minutes. The deoxidation and desulfurization agent is obtained by mixing aluminum powder, calcium oxide and limestone in a mass ratio of 3:2:2, and the amount of the deoxidation and desulfurization agent used is 0.07wt% of the total amount of low-carbon steel; The reinforced alloy powder is obtained by mixing Cr powder, Cu powder, Ni powder, V powder and Nb powder with a particle size range of 0-60 μm in a mass ratio of 5:3:3:1:1, and the amount of the reinforced alloy powder used is 3wt% of the low carbon steel.

[0019] S2, melt casting and heat preservation: set the end temperature of the ladle furnace to 1700°C, and after reaching the specified temperature, cast the molten iron obtained in step S1 using a mold, the casting temperature is 1565±5°C, the tapping temperature is 620±10°C, and a cast billet is obtained; keep the cast billet at 1400°C for 2 hours, and then roll it, the final rolling temperature is 920°C, prepare a cylindrical sample with a diameter of 10 cm, and then cool it to room temperature to obtain an ingot; S3, ingot tempering treatment: ⅰ. The ingot obtained in step S2 was heated to 950°C at a heating rate of 10°C / min, kept at this temperature for 4 hours, and then air-cooled to room temperature; ⅱ. Then heat up to 950℃ at a heating rate of 10℃ / min, keep warm for 3-4 hours, and then water cool to below 50℃; ⅲ. Then, the treatment temperature was increased to 680°C at a heating rate of 20°C / min, kept at this temperature for 6 hours, and then air-cooled to below 50°C; ⅳ. Finally, the treatment temperature was raised to 650°C at a heating rate of 10°C / min, kept at this temperature for 6 hours, and then air-cooled to room temperature to obtain a quenched and tempered ingot; S4, ingot processing: the quenched and tempered ingot is washed with water, and then immersed in a 10wt% sulfuric acid solution, the acid solution temperature is increased to 90°C, the immersion time is 40 minutes, and then the steel surface is washed with clean water, and then immersed in a plating agent, the immersion temperature of the plating agent is 460°C, and the immersion time of the plating agent is 5 minutes, ensuring that all surfaces of the quenched and tempered ingot are completely immersed. After the quenched and tempered ingot is taken out and naturally solidified, a low-temperature impact-resistant alloy steel is obtained; The plating aid is obtained by mixing equal volumes of 125 g / L zinc chloride solution and 225 g / L ammonium chloride solution.

[0020] Comparative Example 1 A method for preparing low-temperature impact-resistant alloy steel comprises the following steps: S1. Melting, refining and composition control: 100,000 kg ± 5 kg of rust-free, oil-free and impurity-free low-carbon steel is selected and placed in a ladle furnace to smelt into molten iron. The molten iron is placed in a nitrogen atmosphere and the first slag removal is performed. Subsequently, a desulfurization and deoxidation agent is added to the molten iron system for stirring. The treatment time is 10 minutes. Subsequently, the second slag removal is performed, and samples are taken from the ladle to detect the impurity content in the molten iron sample. The S content in the molten iron is controlled to be ≤0.015%, the P content is ≤0.02%, and the C content is ≤0.2%. Subsequently, a reinforcing alloy powder is added to the system and stirred for 10 minutes. The deoxidation and desulfurization agent is obtained by mixing aluminum powder, calcium oxide and limestone in a mass ratio of 1:1:1, and the amount of the deoxidation and desulfurization agent used is 0.07wt% of the total amount of low-carbon steel; The reinforced alloy powder is obtained by mixing Cr powder, Cu powder, Ni powder, V powder and Nb powder with a particle size range of 0-60 μm in a mass ratio of 5:1:1:0.1:0.1, and the amount of the reinforced alloy powder used is 1wt% of the low carbon steel.

[0021] S2, melt casting and heat preservation: set the end temperature of the ladle furnace to 1600°C, and after reaching the specified temperature, cast the molten iron obtained in step S1 using a mold, the casting temperature is 1565±5°C, the tapping temperature is 620±10°C, and a cast billet is obtained; keep the cast billet at 1000°C for 0.5 hours, then roll it, the final rolling temperature is 900°C, prepare a cylindrical sample with a diameter of 10 cm, and then cool it to room temperature to obtain an ingot; S3, ingot tempering treatment: ⅰ. The ingot obtained in step S2 was heated to 900°C at a heating rate of 5°C / min, kept at this temperature for 6 hours, and then air-cooled to room temperature; ⅱ. The treatment temperature was then raised to 680°C at a heating rate of 5°C / min, kept at this temperature for 4 hours, then cooled to 580°C and kept at this temperature for 4 hours, and then air-cooled to room temperature to obtain a quenched and tempered ingot; S4, ingot processing: the quenched and tempered ingot is washed with water, then immersed in a 10wt% sulfuric acid solution, the acid solution temperature is raised to 80°C, the immersion time is 10 minutes, then the steel surface is washed with clean water, then immersed in a plating agent, the immersion temperature of the plating agent is 440°C, the immersion time of the plating agent is 2 minutes, and after ensuring that all surfaces of the quenched and tempered ingot are completely immersed, the quenched and tempered ingot is taken out and naturally solidified to obtain a low-temperature impact-resistant alloy steel; The plating aid is obtained by mixing equal volumes of 120 g / L zinc chloride solution and 220 g / L ammonium chloride solution.

[0022] Comparative Example 2 A method for preparing low-temperature impact-resistant alloy steel comprises the following steps: S1. Melting, refining and composition control: 100,000 kg ± 5 kg of rust-free, oil-free and impurity-free low-carbon steel is selected and placed in a ladle furnace to smelt into molten iron. The molten iron is placed in a nitrogen atmosphere and the first slag removal is performed. Subsequently, a desulfurization and deoxidation agent is added to the molten iron system for stirring. The treatment time is 10 minutes. Subsequently, the second slag removal is performed, and samples are taken from the ladle to detect the impurity content in the molten iron sample. The S content in the molten iron is controlled to be ≤0.015%, the P content is ≤0.02%, and the C content is ≤0.2%. Subsequently, a reinforcing alloy powder is added to the system and stirred for 10 minutes. The deoxidation and desulfurization agent is obtained by mixing aluminum powder, calcium oxide and limestone in a mass ratio of 1:1:1, and the amount of the deoxidation and desulfurization agent used is 0.07wt% of the total amount of low-carbon steel; The reinforcing alloy powder is Cr powder with a particle size range of 0-60 μm, and the usage amount is 1wt% of the low carbon steel.

[0023] S2, melt casting and heat preservation: set the end temperature of the ladle furnace to 1600°C, and after reaching the specified temperature, cast the molten iron obtained in step S1 using a mold, the casting temperature is 1565±5°C, the tapping temperature is 620±10°C, and a cast billet is obtained; keep the cast billet at 1000°C for 0.5 hours, then roll it, the final rolling temperature is 900°C, prepare a cylindrical sample with a diameter of 10 cm, and then cool it to room temperature to obtain an ingot; S3, ingot tempering treatment: ⅰ. The ingot obtained in step S2 was heated to 900°C at a heating rate of 5°C / min, kept at this temperature for 3 hours, and then air-cooled to room temperature; ⅱ. Then heat up to 900°C at a heating rate of 5°C / min, keep warm for 3 hours, and then water cool to below 50°C; ⅲ. Then, the treatment temperature was increased to 620°C at a heating rate of 10°C / min, kept at this temperature for 4 hours, and then air-cooled to below 50°C; ⅳ. Finally, the treatment temperature was raised to 580°C at a heating rate of 5°C / min, kept at this temperature for 4 hours, and then air-cooled to room temperature to obtain a quenched and tempered ingot; S4, ingot processing: the quenched and tempered ingot is washed with water, then immersed in a 10wt% sulfuric acid solution, the acid solution temperature is raised to 80°C, the immersion time is 10 minutes, then the steel surface is washed with clean water, then immersed in a plating agent, the immersion temperature of the plating agent is 440°C, the immersion time of the plating agent is 2 minutes, and after ensuring that all surfaces of the quenched and tempered ingot are completely immersed, the quenched and tempered ingot is taken out and naturally solidified to obtain a low-temperature impact-resistant alloy steel; The plating aid is obtained by mixing equal volumes of 120 g / L zinc chloride solution and 220 g / L ammonium chloride solution.

[0024] Comparative Example 3 A method for preparing low-temperature impact-resistant alloy steel comprises the following steps: S1. Melting, refining and composition control: 100,000 kg ± 5 kg of rust-free, oil-free and impurity-free low-carbon steel is selected and placed in a ladle furnace to smelt into molten iron. The molten iron is placed in a nitrogen atmosphere and the first slag removal is performed. Subsequently, a desulfurization and deoxidation agent is added to the molten iron system for stirring. The treatment time is 10 minutes. Subsequently, the second slag removal is performed, and samples are taken from the ladle to detect the impurity content in the molten iron sample. The S content in the molten iron is controlled to be ≤0.015%, the P content is ≤0.02%, and the C content is ≤0.2%. Subsequently, a reinforcing alloy powder is added to the system and stirred for 10 minutes. The deoxidation and desulfurization agent is obtained by mixing aluminum powder, calcium oxide and limestone in a mass ratio of 1:1:1, and the amount of the deoxidation and desulfurization agent used is 0.07wt% of the total amount of low-carbon steel; The reinforced alloy powder is obtained by mixing Cr powder, V powder and Nb powder with a particle size range of 0-60 μm in a mass ratio of 5:0.1:0.1, and the amount of the reinforced alloy powder used is 1wt% of the low carbon steel.

[0025] S2, melt casting and heat preservation: set the end temperature of the ladle furnace to 1600°C, and after reaching the specified temperature, cast the molten iron obtained in step S1 using a mold, the casting temperature is 1565±5°C, the tapping temperature is 620±10°C, and a cast billet is obtained; keep the cast billet at 1000°C for 0.5 hours, then roll it, the final rolling temperature is 900°C, prepare a cylindrical sample with a diameter of 10 cm, and then cool it to room temperature to obtain an ingot; S3, ingot tempering treatment: ⅰ. The ingot obtained in step S2 was heated to 900°C at a heating rate of 5°C / min, kept at this temperature for 3 hours, and then air-cooled to room temperature; ⅱ. Then heat up to 900°C at a heating rate of 5°C / min, keep warm for 3 hours, and then water cool to below 50°C; ⅲ. Then, the treatment temperature was increased to 620°C at a heating rate of 10°C / min, kept at this temperature for 4 hours, and then air-cooled to below 50°C; ⅳ. Finally, the treatment temperature was raised to 580°C at a heating rate of 5°C / min, kept at this temperature for 4 hours, and then air-cooled to room temperature to obtain a quenched and tempered ingot; S4, ingot processing: the quenched and tempered ingot is washed with water, then immersed in a 10wt% sulfuric acid solution, the acid solution temperature is raised to 80°C, the immersion time is 10 minutes, then the steel surface is washed with clean water, then immersed in a plating agent, the immersion temperature of the plating agent is 440°C, the immersion time of the plating agent is 2 minutes, and after ensuring that all surfaces of the quenched and tempered ingot are completely immersed, the quenched and tempered ingot is taken out and naturally solidified to obtain a low-temperature impact-resistant alloy steel; The plating aid is obtained by mixing equal volumes of 120 g / L zinc chloride solution and 220 g / L ammonium chloride solution.

[0026] Comparative Example 4 A method for preparing low-temperature impact-resistant alloy steel comprises the following steps: S1, smelting, refining and composition control: select 100000kg±5kg of rust-free, oil-free and impurity-free low-carbon steel, place it in a ladle furnace to smelt it into molten iron, place the molten iron in a nitrogen atmosphere, perform the first slag removal, then add a desulfurization and deoxidizer to the molten iron system for stirring, the treatment time is 10 minutes, then perform the second slag removal, take samples in the ladle, detect the impurity content in the molten iron sample, control the S content in the molten iron to be ≤0.015%, the P content to be ≤0.02%, and the C content to be ≤0.2%, then add the reinforcing alloy powder to the system and stir for 10 minutes; Among them, the deoxidation and desulfurization agent is aluminum powder, and the usage amount is 0.07wt% of the total amount of low carbon steel; The reinforced alloy powder is obtained by mixing Cr powder, Cu powder, Ni powder, V powder and Nb powder with a particle size range of 0-60 μm in a mass ratio of 5:1:1:0.1:0.1, and the amount of the reinforced alloy powder used is 1wt% of the low carbon steel.

[0027] S2, melt casting and heat preservation: set the end temperature of the ladle furnace to 1600°C, and after reaching the specified temperature, cast the molten iron obtained in step S1 using a mold, the casting temperature is 1565±5°C, the tapping temperature is 620±10°C, and a cast billet is obtained; keep the cast billet at 1000°C for 0.5 hours, then roll it, the final rolling temperature is 900°C, prepare a cylindrical sample with a diameter of 10 cm, and then cool it to room temperature to obtain an ingot; S3, ingot tempering treatment: ⅰ. The ingot obtained in step S2 was heated to 900°C at a heating rate of 5°C / min, kept at this temperature for 3 hours, and then air-cooled to room temperature; ⅱ. Then heat up to 900°C at a heating rate of 5°C / min, keep warm for 3 hours, and then water cool to below 50°C; ⅲ. Then, the treatment temperature was increased to 620°C at a heating rate of 10°C / min, kept at this temperature for 4 hours, and then air-cooled to below 50°C; ⅳ. Finally, the treatment temperature was raised to 580°C at a heating rate of 5°C / min, kept at this temperature for 4 hours, and then air-cooled to room temperature to obtain a quenched and tempered ingot; S4, ingot processing: the quenched and tempered ingot is washed with water, then immersed in a 10wt% sulfuric acid solution, the acid solution temperature is raised to 80°C, the immersion time is 10 minutes, then the steel surface is washed with clean water, then immersed in a plating agent, the immersion temperature of the plating agent is 440°C, the immersion time of the plating agent is 2 minutes, and after ensuring that all surfaces of the quenched and tempered ingot are completely immersed, the quenched and tempered ingot is taken out and naturally solidified to obtain a low-temperature impact-resistant alloy steel; The plating aid is obtained by mixing equal volumes of 120 g / L zinc chloride solution and 220 g / L ammonium chloride solution.

[0028] Comparative Example 5 A method for preparing low-temperature impact-resistant alloy steel comprises the following steps: S1. Melting, refining and composition control: 100,000 kg ± 5 kg of rust-free, oil-free and impurity-free low-carbon steel is selected and placed in a ladle furnace to smelt into molten iron. The molten iron is placed in a nitrogen atmosphere and the first slag removal is performed. Subsequently, a desulfurization and deoxidation agent is added to the molten iron system for stirring. The treatment time is 10 minutes. Subsequently, the second slag removal is performed, and samples are taken from the ladle to detect the impurity content in the molten iron sample. The S content in the molten iron is controlled to be ≤0.015%, the P content is ≤0.02%, and the C content is ≤0.2%. Subsequently, a reinforcing alloy powder is added to the system and stirred for 10 minutes. The deoxidation and desulfurization agent is obtained by mixing aluminum powder, calcium oxide and limestone in a mass ratio of 1:1:1, and the amount of the deoxidation and desulfurization agent used is 0.07wt% of the total amount of low-carbon steel; The reinforced alloy powder is obtained by mixing Cr powder, Cu powder, Ni powder, V powder and Nb powder with a particle size range of 0-60 μm in a mass ratio of 5:1:1:0.1:0.1, and the amount of the reinforced alloy powder used is 1wt% of the low carbon steel.

[0029] S2, melt casting and heat preservation: set the end temperature of the ladle furnace to 1600°C, and after reaching the specified temperature, cast the molten iron obtained in step S1 using a mold, the casting temperature is 1565±5°C, the tapping temperature is 620±10°C, and a cast billet is obtained; keep the cast billet at 1000°C for 0.5 hours, then roll it, the final rolling temperature is 900°C, prepare a cylindrical sample with a diameter of 10 cm, and then cool it to room temperature to obtain an ingot; S3, ingot tempering treatment: ⅰ. The ingot obtained in step S2 was heated to 900°C at a heating rate of 5°C / min, kept at this temperature for 3 hours, and then air-cooled to room temperature; ⅱ. Then heat up to 900°C at a heating rate of 5°C / min, keep warm for 3 hours, and then water cool to below 50°C; ⅲ. Then, the treatment temperature was increased to 620°C at a heating rate of 10°C / min, kept at this temperature for 4 hours, and then air-cooled to below 50°C; ⅳ. Finally, the treatment temperature was raised to 580°C at a heating rate of 5°C / min, kept at this temperature for 4 hours, and then air-cooled to room temperature to obtain a quenched and tempered ingot; S4. Ingot processing: The quenched and tempered ingot is washed with water, and then a low-temperature impact-resistant alloy steel is obtained.

[0030] The mechanical properties of the alloy steels prepared in Examples 1-3 and Comparative Examples 1-5 were tested. For the alloy steels prepared in different groups, samples of 75*Φ10 were taken out for testing of yield strength, tensile strength, elongation at break and -50°C impact energy. The tensile test of the samples was carried out at room temperature according to the method described in GB / T 228.1-2010. The impact energy was tested at -50°C according to the method described in GB / T 229-2007. Five readings were obtained for each sample and the average value was taken. The test results are shown in Table 1 below.

[0031] Table 1 Mechanical properties test of alloy steel prepared in Examples 1-3 and Comparative Examples 1-5

[0032] As can be seen from Table 1 above, the alloy steel sample prepared in Example 2 has the best strength and toughness, and has the best low-temperature impact resistance. As can be seen from the results in Comparative Example 1, treating the material according to multiple heat treatment steps during the forging process can significantly improve its mechanical properties including low-temperature impact resistance. As can be seen from the results in Comparative Examples 2 and 3, using multiple elements to strengthen the steel matrix can balance the overall mechanical properties of the steel. Compared with the single-component impurity removal of aluminum powder, the use of limestone, calcium oxide and other components together is also beneficial to improving the mechanical properties of the material.

[0033] Now the welding performance test is carried out on the steels prepared in Examples 1-3 and Comparative Examples 1-5. Two steels prepared in different groups are flat-butt welded at -50°C, and the number of welds is 20. Submerged arc welding is carried out using a welding wire with a diameter of 4 cm, a welding speed of 50 cm / min, and a welding current of 200 A. No additional annealing treatment is performed after welding to avoid hitting the joint after welding. The slag is removed after 30 minutes of uniform environment, and the welding quality is observed. Subsequently, the method described in GB / T 11345-2013 "Manual Ultrasonic Flaw Detection Method and Quality Grading Method for Steel Welds" is used to detect the probability that the steel meets the inspection level II or above. The test results are shown in Table 2 below.

[0034] Table 2 Welding performance test of the steels prepared in Examples 1-3 and Comparative Examples 1-5

[0035] From the results in Table 2, the steels prepared in Examples 1-3 have better low temperature welding performance. From the results in Comparative Example 5, it can be seen that galvanizing the steel can improve the welding performance of the steel in a low temperature environment such as -50°C.

[0036] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0037] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for preparing low-temperature impact-resistant alloy steel, characterized in that: The following steps are involved: S1. Melting, refining and composition control: Select low-carbon steel without rust, oil or impurities, place it in a ladle furnace to smelt it into molten iron, then perform desulfurization and deoxidation treatment, take samples in the ladle, detect the impurity content in the molten iron sample, control the S content in the molten iron to be ≤0.015%, the P content to be ≤0.02%, and the C content to be ≤0.2%, then add the reinforcing alloy powder into the system and stir for 10-20 minutes; S2, melt casting and heat preservation: setting the terminal temperature of the ladle furnace to 1600°C-1700°C, and casting the molten iron obtained in step S1 using a mold after reaching the specified temperature to obtain a cast billet; placing the cast billet at 1000°C-1400°C for 0.5-2 hours and then rolling it, the final rolling temperature is 900-920°C, and cooling it to room temperature after molding to obtain an ingot; S3, ingot tempering treatment: ⅰ. The ingot obtained in step S2 is heated to 900-950°C at a heating rate of 5-10°C / min, kept at this temperature for 3-4 hours, and then air-cooled to room temperature; ⅱ. Then heat up to 900-950℃ at a heating rate of 5-10℃ / min, keep warm for 3-4 hours, and then water cool to below 50℃; ⅲ. Then increase the treatment temperature to 620-680°C at a heating rate of 10-20°C / min, keep warm for 4-6 hours, and then air cool to below 50°C; ⅳ. Finally, the treatment temperature is increased to 580-650°C at a heating rate of 5-10°C / min, kept at this temperature for 4-6 hours, and then air-cooled to room temperature to obtain a quenched and tempered ingot; S4. Ingot processing: wash the tempered ingot with water, and then immerse it in an acid solution, raise the acid solution temperature to 80-90°C, and immerse it for 10-40 minutes. Then wash the steel surface with clean water, and then immerse it in a plating aid to ensure that all surfaces of the tempered ingot are completely immersed. After the tempered ingot is taken out and naturally solidified, a low-temperature impact-resistant alloy steel is obtained.

2. The method for preparing a low-temperature impact-resistant alloy steel according to claim 1, characterized in that: In step S1, the specific operation of desulfurization and deoxygenation treatment is as follows: The molten iron obtained by melting low-carbon steel is placed in an inert atmosphere, and the first slag removal is performed. Subsequently, a desulfurization and deoxidization agent is added to the molten iron system and stirred for 10-30 minutes, and then a second slag removal is performed; wherein the desulfurization and deoxidization agent is obtained by mixing aluminum powder, calcium oxide and limestone in a mass ratio of (1-3): (1-2): (1-2), and the amount of the desulfurization and deoxidization agent used is 0.03wt%-0.07wt% of the total amount of low-carbon steel.

3. The method for preparing a low-temperature impact-resistant alloy steel according to claim 1, characterized in that: In step S1, the reinforcing alloy powder is obtained by mixing Cr powder, Cu powder, Ni powder, V powder and Nb powder with a particle size range of 0-60 μm in a mass ratio of 5:(1-3):(1-3):(0.1-1):(0.1-1), and the amount of the reinforcing alloy powder used is 1-3wt% of the low carbon steel.

4. The method for preparing a low-temperature impact-resistant alloy steel according to claim 1, characterized in that: In step S2, the casting temperature is 1565±5°C and the tapping temperature is 620±10°C.

5. The method for preparing a low-temperature impact-resistant alloy steel according to claim 1, characterized in that: In step S4, the plating aid is obtained by mixing 120-125 g / L zinc chloride solution and 220-225 g / L ammonium chloride solution.

6. The method for preparing a low-temperature impact-resistant alloy steel according to claim 1, characterized in that: In step S4, the temperature for immersing the substrate using the plating agent is 440° C.-460° C., and the immersing time for the plating agent is 2-5 minutes.

7. An alloy steel obtained by the method for preparing low-temperature impact-resistant alloy steel as described in any one of claims 1 to 6.

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