Titanium-containing boron-containing low-nitrogen cold heading steel and method for manufacturing the same

Abstract

The application discloses a titanium-containing boron-containing low-nitrogen cold upsetting steel and a preparation method thereof. The preparation method of the titanium-containing boron-containing low-nitrogen cold upsetting steel comprises the following steps: selecting low-nitrogen raw materials, denitrogenation pretreatment, converter smelting, LF furnace refining and continuous casting. The nitrogen content in the steel is effectively reduced to below 60 ppm by adopting the low-nitrogen raw materials and a series of denitrogenation treatment processes.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steelmaking, in particular to a low-nitrogen cold heading steel containing titanium and boron and a preparation method thereof. BACKGROUND

[0002] With the development of steelmaking industry technology, the control of steel quality is becoming more and more demanding, especially the control of gas content in steel. Cold heading steel is widely used in bolts, nuts and other types of standard parts, and its processing process has large deformation and fast forming speed, so the processing performance requirement is relatively harsh. When the nitrogen content in steel increases, the strength, hardness and brittleness of the steel increase, and the plasticity and toughness decrease significantly.

[0003] For medium and low carbon steel, nitrogen can cause aging and blue brittleness. Steel with high nitrogen content will become brittle after a long time, that is, the "aging" or "aging" phenomenon occurs. High nitrogen content in steel increases the aging of the steel. Nitride diffusion and precipitation speed is very slow, but gradually changes the performance of the steel. The precipitation of nitrides will cause the metal lattice to twist and produce a lot of internal stress, thereby deteriorating the plasticity and impact toughness of the steel, making the steel brittle; nitrogen makes the brittleness of low-carbon steel similar to the damage of phosphorus, but more serious than phosphorus; phosphorus causes cold brittleness of steel, does not produce aging, and high phosphorus content in steel will exacerbate the damage of nitrogen. When the nitrogen content in steel is high, the surface of the steel will turn blue when heated to a temperature of 250-450℃, the strength of the steel will increase, and the impact toughness will decrease, which is called "blue brittleness". At the same time, the increase of nitrogen content in steel will also deteriorate the welding performance of the steel. SUMMARY

[0004] Therefore, it is necessary to propose a low-nitrogen cold heading steel containing titanium and boron and a preparation method thereof in view of the above technical problems.

[0005] In one aspect of the present application, a preparation method of a low-nitrogen cold heading steel containing titanium and boron is provided, which comprises the following steps:

[0006] Selecting low-nitrogen raw materials with nitrogen content less than 350ppm;

[0007] Denitrification pretreatment of low-nitrogen raw materials;

[0008] The low-nitrogen raw material after denitrification pretreatment is subjected to converter smelting, in the early stage of converter smelting, CO gas generated by C-O reaction is used to realize the early denitrification of the converter, in the middle stage of converter smelting, a denitrification agent is added, the denitrification agent can react with nitrogen to generate nitride, thereby reducing the nitrogen content in the steel, in the late stage of converter smelting, the denitrification agent is added again to further reduce the nitrogen content in the steel, at the same time, oxygen is blown by an oxygen lance, the lance position is controlled at 150 cm to 190 cm, the time is 0.5 min to 1 min, the end point temperature is controlled at 1600 ℃ to 1640 ℃, the C content is 0.06% to 0.10%, and the nitrogen content in the molten steel is controlled at 20 ppm to 30 ppm;

[0009] The molten steel obtained after converter smelting is placed in an LF furnace for refining, argon is opened, the molten steel is measured after the slag shell is broken, the temperature of the molten steel is controlled to be higher than the theoretical liquidus temperature of the molten steel by 40 ℃ or more, the denitrification agent is added again, the argon flow rate is controlled at 150 Nl / min to 160 Nl / min in the early stage of refining, the argon flow rate is controlled at 180 Nl / min to 160 Nl / min in the middle stage of refining, and the argon flow rate is controlled at 120 Nl / min to 160 Nl / min in the late stage of refining, so as to avoid nitrogen absorption in the refining process and finally control the nitrogen increase in the LF furnace refining process to be less than 15 ppm;

[0010] The molten steel after LF furnace refining is subjected to continuous casting, whole-type tundish casting is adopted, the argon sealing flow rate of the ladle long nozzle is controlled at 60 Nl / min to 100 Nl / min to ensure the sealing performance and reduce the intake of air in the casting process, and the final nitrogen content of the steel is controlled to be less than 60 ppm.

[0011] In some embodiments, the low-nitrogen raw material is any one or more of low-nitrogen iron ore, scrap steel, scrap iron and low-nitrogen slag.

[0012] In some embodiments, the denitrification pretreatment of the low-nitrogen raw material comprises:

[0013] The low-nitrogen raw material is placed in a heat treatment furnace and heated to 1500 ℃ to 1600 ℃ for 5 min to 10 min.

[0014] In some embodiments, in the converter smelting, a high-lifting and supplementary blowing blowing process is adopted to reduce the late-stage supplementary blowing time and reduce the nitrogen increase in the blowing process.

[0015] In some embodiments, the denitrification agent is any one or more of aluminum, vanadium, titanium, niobium, manganese and magnesium.

[0016] In some embodiments, the denitrification agent is titanium and manganese.

[0017] In some embodiments, before the converter tapping, the ladle bottom argon blowing is opened, and the flow is controlled at 600N l / min-1200Nl / min, and the argon is used to replace the air in the ladle;

[0018] The converter tapping hole is maintained well to ensure that the steel flow during the tapping process is in a "cylindrical" shape, avoiding the increase of the contact surface between the molten steel and the atmosphere during the tapping process, causing the molten steel to absorb nitrogen, and controlling the tapping time between 250s-350s.

[0019] In some embodiments, during the tapping process, aluminum blocks are added to the steel, with an addition amount of 1-1.5kg / ton of steel, and the aluminum content is controlled according to the target of 0.015%-0.035%;

[0020] In the late stage of tapping, the argon flow is adjusted (80N l / min-150N l / min), and a weak blowing mode is adopted until the molten steel is lifted away from the argon blowing station.

[0021] In some embodiments, during the LF furnace refining process, with the power supply process, diffusion deoxidizing agents are added to the slag surface: calcium carbide particles 0.4-0.6kg / ton of steel, a small amount of aluminum beans and composite silicon carbide for diffusion deoxidizing operation, and "white slag" is quickly created.

[0022] In the second aspect of the present application, a titanium-containing and boron-containing low-nitrogen cold upsetting steel is also proposed, which is prepared by any one of the above preparation methods.

[0023] Compared with the prior art, the beneficial effects of the present application are:

[0024] Reducing nitrogen content: by using low-nitrogen raw materials and a series of denitrification treatment processes, the nitrogen content in the steel is effectively reduced to below 60ppm. This is very important for cold upsetting steel, because high nitrogen content will cause the strength and hardness of the steel to increase, while reducing its plasticity and toughness.

[0025] Controlling impurities such as sulfur and phosphorus: although the technical solution mainly focuses on the control of nitrogen, it also affects the content of other impurity elements such as sulfur and phosphorus. Through the converter smelting and LF furnace refining process, the content of these impurity elements can be effectively controlled, thereby improving the purity of the steel.

[0026] Optimizing the smelting process: a series of smelting processes are adopted in the technical solution, including converter smelting and LF furnace refining, by controlling parameters such as temperature and gas flow, precise control of the composition of the molten steel is achieved, thereby ensuring the quality of the steel.

[0027] Using denitrification agents: by adding denitrification agents, nitrides can be generated by reacting with nitrogen, thereby further reducing the nitrogen content in the steel.

[0028] Improving the processing performance of steel: By reducing the nitrogen content, the aging and blue brittleness phenomenon during the processing of cold heading steel can be effectively avoided, thereby improving the processing performance of the steel and making it more suitable for the manufacture of standard parts such as bolts, nuts, etc.

[0029] Ensuring the welding performance of steel: The reduction of nitrogen content in the steel in the technical solution is also beneficial to improving the welding performance of the steel, thereby expanding the application range of the steel.

[0030] Controlling cost: By precisely controlling the smelting process, unnecessary impurities and nitrogen loss are avoided, thereby improving the utilization rate of raw materials and reducing production cost.

[0031] In summary, the technical solution effectively reduces the nitrogen content in the steel through a series of precise process control means, improves the quality and processing performance of the steel, and at the same time ensures the welding performance, which has significant economic and technical benefits. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The preparation flow chart of the titanium-containing and boron-containing low-nitrogen cold heading steel in the exemplary embodiments of the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0034] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer", "front end", "rear end", "two ends", "one end", "the other end" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore cannot be understood as a limitation on the present application. In addition, the terms "first" and "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0035] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "provided with", "connection" and the like should be understood in a broad sense, for example, "connection" can be fixed connection, can also be detachable connection, or integrally connected; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0036] As described in the background, for medium and low carbon steel, nitrogen can cause aging and blue brittleness. The performance of steel with high nitrogen content will become brittle after a long time, that is, "aging" or "aging" phenomenon. High nitrogen content in steel increases the aging of steel. The diffusion and precipitation rate of nitrides in steel is very slow, but gradually changes the performance of the steel. The precipitation of nitrides also causes the distortion of the metal lattice and generates a lot of internal stress, thereby deteriorating the plasticity and impact toughness of the steel, making the steel brittle; nitrogen causes brittleness of low carbon steel similar to the damage of phosphorus, but more serious than phosphorus; phosphorus causes cold brittleness of steel, does not produce aging, and if the phosphorus content in the steel is high, it will aggravate the damage of nitrogen. When the nitrogen content in the steel is high, the surface of the steel is blue at a temperature of 250-450°C, the strength of the steel increases, and the impact toughness decreases, which is called "blue brittleness". At the same time, the increase of nitrogen content in the steel will also deteriorate the welding performance of the steel.

[0037] To improve the above problems, in the first aspect of the present application, a preparation method of a titanium-containing and boron-containing low-nitrogen cold heading steel is provided, which mainly includes the following steps: selecting low-nitrogen raw materials, denitrification pretreatment, converter smelting, LF furnace refining and continuous casting. By using low-nitrogen raw materials and a series of denitrification treatment processes, the nitrogen content in the steel is effectively reduced and can be controlled below 60 ppm.

[0038] Specifically, in some embodiments, a preparation method of a titanium-containing and boron-containing low-nitrogen cold heading steel includes the following steps:

[0039] Selecting low-nitrogen raw materials with nitrogen content less than 350 ppm, the low-nitrogen raw materials being any one or more of low-nitrogen iron ore, scrap steel, scrap iron and low-nitrogen slag;

[0040] Denitrification pretreatment of the low-nitrogen raw materials: heating the low-nitrogen raw materials to 1500-1600°C in a heat treatment furnace for 5-10 min;

[0041] The low-nitrogen raw material after denitrification pretreatment is subjected to converter smelting, in which a high-ladle-replenishing blowing process is adopted to reduce the late-stage replenishing blowing time and the nitrogen increase in the blowing process. In the early stage of the converter smelting, CO gas generated by the C-O reaction is used to realize the early-stage denitrification of the converter, in the middle stage of the converter smelting, a denitrification agent is added, the denitrification agent being any one or more of aluminum, vanadium, titanium, niobium, manganese and magnesium, the denitrification agent being capable of reacting with nitrogen to generate nitride, thereby reducing the nitrogen content in the steel, in the late stage of the converter smelting, the denitrification agent is added again to further reduce the nitrogen content in the steel, at the same time, oxygen is blown by the oxygen lance, the lance position is controlled at 150 cm to 190 cm, the time is 0.5 min to 1 min, the end-point temperature is controlled at 1600 ℃ to 1640 ℃, the C content is 0.06% to 0.10%, the nitrogen content in the molten steel is controlled at 20 ppm to 30 ppm, before the converter tapping, the bottom argon blowing of the ladle is opened, the flow rate is controlled at 600 N l / min to 1200 N l / min, the argon is used to replace the air in the ladle, the converter tapping hole is maintained well to ensure that the molten steel flow in the tapping process is in a "cylinder" shape, the increased contact surface between the molten steel and the air in the tapping process is avoided to prevent the molten steel from absorbing nitrogen, and the tapping time is controlled at 250 s to 350 s, along with the tapping process, aluminum blocks are added to the molten steel, the addition amount is 1 to 1.5 kg per ton of steel, and the aluminum content is controlled according to the target of 0.015% to 0.035%; in the late stage of the tapping, the argon flow rate is adjusted (80 N l / min to 150 N l / min) to adopt a weak blowing mode until the molten steel is lifted away from the argon blowing station.

[0042] The molten steel obtained after the converter smelting is placed in an LF furnace for refining, argon is opened, the molten steel is measured in temperature after the slag crust is broken, the molten steel temperature is controlled to reach the theoretical liquidus temperature of the molten steel plus 40 ℃ or above, the denitrification agent is added again, the argon flow rate is controlled at 150 N l / min to 180 N l / min in the early stage of the refining, the argon flow rate is controlled at 180 N l / min to 220 N l / min in the middle stage of the refining, and the argon flow rate is controlled at 120 N l / min to 160 N l / min in the late stage of the refining to avoid the nitrogen absorption in the refining process and finally control the nitrogen increase in the LF furnace refining process to be below 15 ppm, along with the power supply process of the LF furnace, the diffusion deoxidation agent, i.e., calcium carbide particles 0.4 to 0.6 kg per ton of steel, a small amount of aluminum beans and composite silicon carbide, is added to the slag surface for diffusion deoxidation operation to quickly generate "white slag".

[0043] The molten steel after the LF furnace refining is subjected to continuous casting, the whole-type tundish casting is adopted, the argon sealing flow rate of the ladle long nozzle is controlled at 60 N l / min to 100 N l / min to ensure the sealing performance and reduce the air absorption in the casting process, and the final nitrogen content of the steel is controlled to be below 60 ppm.

[0044] Example 1

[0045] The application relates to a preparation method of a low-nitrogen cold upsetting steel containing titanium and boron.

[0046] The mixture of scrap steel, scrap iron and low-nitrogen scrap residue with a nitrogen content lower than 350 ppm is selected as the low-nitrogen raw material. The low-nitrogen raw material is subjected to denitrogenation pretreatment: the low-nitrogen raw material is placed in a heat treatment furnace and heated to 1500 DEG C for 5 min.

[0047] The low-nitrogen raw material subjected to the denitrogenation pretreatment is subjected to converter smelting. In the converter smelting, a high-ladle-blown blowing process is adopted to reduce the late blowing time and the nitrogen increase in the blowing process. In the early converter smelting, CO gas generated by the C-O reaction is utilized to realize the early denitrogenation of the converter. In the middle converter smelting, a denitrogenation agent is added, the denitrogenation agent is titanium and manganese, the denitrogenation agent can react with nitrogen to generate nitride, thereby reducing the nitrogen content in the steel, and the denitrogenation agent is added again in the late converter smelting, so as to further reduce the nitrogen content in the steel. Meanwhile, the oxygen lance blows oxygen, the lance position is controlled at 150 cm, the time is 0.5 min, the terminal temperature is controlled at 1600 DEG C, the C content is 0.06%, the nitrogen content in the molten steel is controlled at 20-30 ppm, before the converter is tapped, the ladle bottom argon blowing is opened, the flow is controlled at 600 N l / min, the argon is used to replace the air in the ladle, the converter tapping hole is maintained, the steel flow in the tapping process is in a "cylinder" shape, the increased contact surface between the molten steel and the air in the tapping process is avoided, the molten steel is prevented from absorbing nitrogen, and the tapping time is controlled at 250 s. Along with the tapping process, aluminum blocks are added into the steel, the adding amount is 1 kg / ton of steel, and the aluminum content is controlled according to the 0.015% target.

[0048] The molten steel obtained after the converter smelting is placed in an LF furnace for refining. The argon is opened, the molten steel is measured after the slag crust is broken, the temperature of the molten steel is controlled to be higher than the theoretical liquidus temperature of the molten steel by 40 DEG C or above, the denitrogenation agent is added again, the argon flow is controlled at 150 N l / min in the early refining, the argon flow is controlled at 180 N l / min in the middle refining, the argon flow is controlled at 120 N l / min in the late refining, the nitrogen absorption in the refining process is avoided, and the nitrogen increase in the LF furnace refining process is finally controlled to be below 15 ppm. Along with the power supply process of the LF furnace, the diffusion deoxidation agent, i.e. calcium carbide particles 0.4 kg / ton of steel, a small amount of aluminum beans and composite silicon carbide, is added to the slag surface to perform the diffusion deoxidation operation, and the "white slag" is rapidly formed.

[0049] The molten steel after the LF furnace refining is subjected to continuous casting. The whole-type tundish casting is adopted, the argon sealing flow of the ladle long nozzle is controlled at 60 N l / min, the sealing performance is ensured, and the air absorption in the casting process is reduced.

[0050] The cold heading steel obtained according to the preparation method of Example 1 is detected, and the nitrogen content is 0.0035%.

[0051] Example 2

[0052] A preparation method of a low-nitrogen cold heading steel containing titanium and boron comprises the following steps:

[0053] A mixture of scrap steel, scrap iron and low-nitrogen scrap residue with a nitrogen content lower than 350 ppm is selected as a low-nitrogen raw material.

[0054] The low-nitrogen raw material is subjected to denitrogenation pretreatment: the low-nitrogen raw material is placed in a heat treatment furnace and heated to 1600 ℃ for 10 min;

[0055] The low-nitrogen raw material subjected to the denitrogenation pretreatment is subjected to converter smelting, in which a high-ladle-slag-blowing blowing process is adopted to reduce the late blowing time and the nitrogen content in the blowing process. In the early stage of the converter smelting, CO gas generated by the C-O reaction is used to realize the denitrogenation of the converter, in the middle stage of the converter smelting, a denitrogenation agent is added, the denitrogenation agent is titanium and manganese, the denitrogenation agent can react with nitrogen to generate nitride, thereby reducing the nitrogen content in the steel, in the late stage of the converter smelting, the denitrogenation agent is added again to further reduce the nitrogen content in the steel, and at the same time, the oxygen lance blows oxygen, the lance position is controlled at 190 cm, the time is 1 min, the end point temperature is controlled at 1640 ℃, the C content is 0.10%, the nitrogen content in the molten steel is controlled at 30 ppm, before the converter is tapped, the ladle bottom argon blowing is opened, the flow rate is controlled at 1200 Nl / min, the argon is used to replace the air in the ladle, the converter tapping hole is maintained well to ensure that the steel flow in the tapping process is in a "cylinder" shape, the increased contact surface between the molten steel and the air caused by the scattered flow in the tapping process is avoided, the molten steel is prevented from absorbing nitrogen, and the tapping time is controlled between 350 s, along with the tapping process, aluminum blocks are added to the steel, the addition amount is 1.5 kg / ton of steel, and the aluminum content is controlled according to the target of 0.035%; in the late tapping stage, the argon flow rate is adjusted (150 Nl / min), a weak blowing mode is adopted, and the molten steel is lifted away from the argon blowing station.

[0056] The molten steel obtained after the converter smelting is placed in an LF furnace for refining, argon is opened, the molten steel is measured after the slag crust is broken, the temperature of the molten steel is controlled to be higher than the theoretical liquidus temperature of the molten steel by 40 ℃, the denitrogenation agent is added again, the argon flow rate is controlled at 180 Nl / min in the early stage of the refining, the argon flow rate is controlled at 220 Nl / min in the middle stage of the refining, the argon flow rate is controlled at 160 Nl / min in the late stage of the refining, the nitrogen absorption in the refining process is avoided, and finally the nitrogen content in the LF furnace refining process is controlled to be less than 15 ppm, along with the power supply process of the LF furnace, the diffusion deoxidation agent: calcium carbide particles 0.6 kg / ton of steel, a small amount of aluminum beans and composite silicon carbide are added to the slag surface to perform the diffusion deoxidation operation, and "white slag" is quickly formed.

[0057] The LF-refined molten steel is continuously cast, and the whole type tundish casting is adopted, the argon sealing flow rate of the long nozzle of the ladle is controlled at 100 Nl / min, the sealing performance is ensured, and the air suction during the casting process is reduced.

[0058] The cold heading steel obtained according to the preparation method of Embodiment 2 is detected, and the nitrogen content is 0.0035%.

[0059] In the second aspect of the present application, a low-nitrogen cold heading steel containing titanium and boron is also provided, which is prepared by any one of the above preparation methods.

[0060] Finally, it should be noted that: the above is only the preferred embodiment of the present application, and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced equivalently. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing titanium- and boron-containing low-nitrogen cold heading steel, characterized in that... This includes the following steps: Low-nitrogen raw materials with a nitrogen content of less than 350 ppm are selected; The low-nitrogen raw material is subjected to denitrification pretreatment; Low-nitrogen raw materials that have undergone denitrification pretreatment are smelted in a converter. In the early stage of converter smelting, CO gas generated by the CO reaction is used to achieve early denitrification in the converter. In the middle stage of converter smelting, a denitrifying agent is added. The denitrifying agent can react with nitrogen to form nitrides, thereby reducing the nitrogen content in the steel. In the later stage of converter smelting, the denitrifying agent is added again to further reduce the nitrogen content in the steel. At the same time, oxygen is blown in an oxygen lance, with the lance position controlled at 150cm~190cm, the time 0.5min~1min, the final temperature controlled at 1600℃~1640℃, and the C content 0.06%~0.10%, so that the nitrogen content in the molten steel is controlled at 20ppm-30ppm. The molten steel obtained after converter smelting is placed in an LF furnace for refining. Argon gas is turned on, and the slag shell is blown out. The temperature of the molten steel is measured and controlled to reach above the theoretical liquidus temperature of molten steel +40°C. The denitrifying agent is added again. In the early stage of refining, the argon gas flow rate is controlled at 150NL / min-180NL / min. In the middle stage of refining, the argon gas flow rate is controlled at 180NL / min-220NL / min. In the later stage of refining, the argon gas flow rate is controlled at 120NL / min-160NL / min to avoid nitrogen absorption during the refining process. Finally, the nitrogen increase during the LF furnace refining process is controlled to be below 15ppm. The molten steel refined in the LF furnace is continuously cast using an integral tundish. The argon seal flow rate of the long nozzle of the ladle is controlled at 60NL / min-100NL / min to ensure sealing performance, reduce air intake during the casting process, and control the final nitrogen content of the steel to below 60ppm.

2. The method for preparing titanium-containing, boron-containing, low-nitrogen cold heading steel according to claim 1, characterized in that... The low-nitrogen raw material is any one or more of low-nitrogen iron ore, scrap steel, scrap iron, and low-nitrogen waste residue.

3. The method for preparing titanium-containing, boron-containing, low-nitrogen cold heading steel according to claim 1, characterized in that... The denitrification pretreatment of the low-nitrogen raw material includes: The low-nitrogen raw material is placed in a heat treatment furnace and heated to 1500℃-1600℃ for 5min-10min.

4. The method for preparing titanium-containing, boron-containing, low-nitrogen cold heading steel according to claim 1, characterized in that... In converter smelting, a high-pulling and supplementary blowing process is adopted to reduce the supplementary blowing time in the later stage and reduce the amount of nitrogen added during the blowing process.

5. The method for preparing titanium-containing, boron-containing, low-nitrogen cold heading steel according to claim 1, characterized in that... The denitrifying agent is any one or more of aluminum, vanadium, titanium, niobium, manganese, and magnesium.

6. The method for preparing titanium-containing, boron-containing, low-nitrogen cold heading steel according to claim 5, characterized in that... The denitrifying agent is titanium and manganese.

7. The method for preparing titanium-containing, boron-containing, low-nitrogen cold heading steel according to claim 1, characterized in that... Before tapping steel from the converter, the bottom blowing argon gas in the ladle is turned on, and the flow rate is controlled at 600NL / min-1200NL / min. The air in the ladle is replaced by argon gas. Maintain the converter tapping port properly to ensure that the steel flow during the tapping process is cylindrical, avoid the steel from spreading during the tapping process, which would increase the contact area between the molten steel and the atmosphere and cause the molten steel to absorb nitrogen, and control the tapping time between 250s and 350s.

8. The method for preparing titanium-containing, boron-containing, low-nitrogen cold heading steel according to claim 7, characterized in that... During the steelmaking process, aluminum blocks are added to the steel at a rate of 1-1.5 kg / ton, with the aluminum content controlled at a target of 0.015%-0.035%. In the later stages of steel tapping, the argon flow rate is adjusted to 80NL / min-150NL / min, and a weak blowing method is used until the molten steel is lifted away from the argon blowing station.

9. The method for preparing titanium-containing, boron-containing, low-nitrogen cold heading steel according to claim 1, characterized in that... During the refining process in the LF furnace, along with the power supply process, a diffusion deoxidizer is added to the slag surface: 0.4-0.6 kg of calcium carbide particles per ton of steel, a small amount of aluminum granules, and composite silicon carbide to carry out diffusion deoxidation and quickly create "white slag".

10. A titanium- and boron-containing low-nitrogen cold heading steel, characterized in that... It is prepared by the method of any one of claims 1-9.

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