Refining method for improving hit rate of nitrogen component of high-nitrogen steel

Abstract

The invention discloses a refining method for improving the hit rate of nitrogen components of high-nitrogen steel, and belongs to the field of ferrous metallurgy, the refining method specifically comprises the following processes of converter, LF furnace refining, RH furnace refining and continuous casting machine, (1) when the LF furnace is refined, bottom argon blowing is carried out on the LF furnace in the whole process, deoxidation slagging is carried out, the components of outbound molten steel are accurately controlled, and the outbound slag condition is adjusted to ensure the fluidity of steel slag; (2) refining an RH furnace: (1) adding carbonized rice husks into an RH station, taking a gas sample, and sending the gas sample to a test station to analyze the initial nitrogen content; (2) opening steel ladle bottom blowing argon in advance in the RH vacuum last stage; (3) adjusting and setting RH vacuum breaking, silicon nitride linear feeding speed and argon flow; (4) calcium treatment opportunity: adding carbonized rice husks, and statically stirring to set flow; (5) taking a gas sample to confirm the nitrogen content; according to the smelting method for improving and stabilizing the hit rate of the nitrogen components of the high-nitrogen steel, the quality requirement of the subsequent process on the high-nitrogen steel is guaranteed.

Description

Technical Field

[0001] The invention relates to a refining method, in particular to a refining method for improving the nitrogen component hit rate of high-nitrogen steel, and belongs to the field of steel metallurgy. Background Art

[0002] High nitrogen steel is a type of alloy steel with a high nitrogen content. High nitrogen steel has some unique performance characteristics: 1. High strength: The addition of nitrogen can significantly improve the strength of steel, and to a certain extent can replace some high-strength traditional alloy steels to achieve lightweight design of materials; 2. Good toughness: It usually has good toughness and performs better in harsh environments such as low temperature; 3. Corrosion resistance: Some high nitrogen steels have good corrosion resistance in specific media and can play a role in some special working conditions; 4. Good machinability: It has good machinability under certain conditions, such as cutting and welding. Due to its unique performance advantages, such as high strength, high toughness, good wear resistance and corrosion resistance, high nitrogen steel has broad application prospects in aerospace, automobile manufacturing, energy equipment and other fields. In order to give full play to the performance potential of high nitrogen steel, it is necessary to improve the hit rate of nitrogen composition in the refining process to ensure that the desired high nitrogen content is obtained in the steel liquid to meet the requirements of material performance design; However, the nitrogen composition of high nitrogen steel in the current production process is unstable, and it is difficult to control on site, and it is easy to have unqualified composition. How to accurately target the nitrogen content and prevent quality accidents caused by unqualified nitrogen content is of great significance.

[0003] Traditional steelmaking processes have certain difficulties in effectively adding nitrogen to molten steel and ensuring a high component hit rate. The solubility of nitrogen in molten steel is limited, and it is easily disturbed by various factors during the smelting process, resulting in nitrogen loss and uneven distribution. It is difficult to accurately control the nitrogen content and uniformity of high-nitrogen steel, which limits the full performance of high-nitrogen steel and the expansion of its application range.

[0004] Patent CN110157851A discloses a method for improving the nitrogen recovery rate of nitrogen-containing steel. This production method adds a small amount of FeS before vacuum degassing of molten steel. Under high vacuum degassing conditions, the S element, which is more active than the N element, is first removed. Under the same high vacuum time, the nitrogen recovery rate obtained by bottom blowing nitrogen when using LF+VD to produce nitrogen-containing steel is greatly improved. The nitrogen recovery rate can be increased by 50%, and the nitrogen element after vacuum can meet the requirements for steel grade determination. Patent CN111961790A discloses a method for controlling the nitrogen content of nitrogen-containing non-sulfur-containing steel. The present invention ensures that a relatively high sulfur content is maintained in the steel by feeding the sulfur line at the end of LF smelting, thereby improving the nitrogen fixation effect of nitrogen-containing non-sulfur-containing steel and reducing the denitrification rate of the vacuum process, so that the nitrogen content in the steel reaches 120-200ppm, and the nitrogen content is stably controlled, laying the foundation for the preparation of subsequent products. The present invention adopts nitrogen in both the converter smelting and RH refining stages, thereby improving the nitrogen addition efficiency of the steel and reducing the use of nitrogen alloys, thereby improving production efficiency and reducing manufacturing costs.

[0005] The above methods all obtain nitrogen components by adding sulfur, but the overall process time is long, the rhythm is tight, the nitrogen components are not stirred evenly, and the waiting time for gas sample analysis is long, which also leads to the inability to stably control the nitrogen content.

[0006] Therefore, developing a refining method that can overcome the above defects and improve the nitrogen component hit rate of high nitrogen steel has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0007] The technical problem to be solved by the present invention is to propose a refining method for improving the nitrogen component hit rate of high nitrogen steel in view of the shortcomings of the above-mentioned prior art. The method improves and stabilizes the smelting method of high nitrogen steel and the nitrogen component hit rate, thereby ensuring the quality requirements of high nitrogen steel in subsequent processes.

[0008] The technical solution of the present invention to solve the above technical problems is: A refining method for improving the nitrogen content hit rate of high nitrogen steel, specifically comprising the following process, converter → refining LF furnace → refining RH furnace → continuous casting machine, wherein: (1) During the refining of the LF furnace, argon is blown from the bottom of the LF furnace throughout the whole process to deoxidize and slag. The composition of the molten steel out of the station is accurately controlled, and the slag condition out of the station is adjusted to ensure the fluidity of the slag; (2) When refining RH furnace: ① Add carbonized rice husk into the RH station, take gas samples and send them to the testing station to analyze the initial nitrogen content; When RH molten steel arrives at the station, carbonized rice husk is added to the steel slag to flatten the slag surface so that the steel slag does not form a crust; ② Open the bottom of the ladle to blow argon in advance at the end of RH vacuum; 3 minutes before the end of vacuum, the argon flow rate of the ladle bottom blowing is adjusted to 30NL / min; ③RH breaks the air, feeds silicon nitride linear speed, and adjusts and sets the argon flow rate; After breaking the air, set the bottom blowing argon gas to 200 / 200 NL / min to ensure that the bottom blowing argon gas is good, and set the feeding line speed of silicon nitride to 100-130m / min; ④ Calcium treatment timing, adding carbonized rice husks, static stirring to set the flow rate; After the silicon nitride wire is fed in, it is stirred for 2-4 minutes to make the nitrogen content uniform, and then the calcium wire is fed in for calcium treatment. After the calcium treatment is completed, carbonized rice husks are added to the slag surface for covering. The static stirring flow rate is set at 50-80NL / min to ensure the static stirring effect.

[0009] ⑤ Take gas samples to confirm nitrogen content; After calcium treatment, stir quietly for 3-4 minutes, take gas samples to analyze nitrogen content, and take gas samples again after 8-10 minutes to analyze the change in nitrogen content. If it is insufficient, feed in time until the requirements are met.

[0010] The present invention further defines that in the aforementioned refining method for improving the nitrogen content hit rate of high nitrogen steel, when blowing argon in step (1), the bottom blowing flow rate is 150-200NL / min.

[0011] Technical effect: The present invention controls the argon flow rate. If the speed is too fast or too slow, the argon flow rate is too large or too small, the nitrogen yield rate is unstable. If the argon flow rate is large, the nitrogen yield rate is high, but it will cause serious temperature loss in the process; if the argon flow rate is small, the nitrogen yield rate is low, and the production rhythm does not allow it. The present invention improves the nitrogen yield on the basis of ensuring the production rhythm and production efficiency.

[0012] Technical effect: The present invention controls the flow rate of bottom-blown argon gas, and increases the heating level and bottom-blowing flow rate after the submerged arc is stable, which is beneficial to rapid slag formation, shortening the process time and improving efficiency.

[0013] In the above-mentioned refining method for improving the nitrogen content hit rate of high nitrogen steel, aluminum wire is added after the slag is melted in step (1), and the aluminum content of the process is controlled to be 0.020-0.030%.

[0014] Technical effect: The steel type of the present invention requires a lower aluminum content, and the aluminum is strictly controlled during the process. Exceeding the requirement will cause the finished product composition to be unqualified. The aluminum is controlled to ensure the quality of the final product.

[0015] In the above-mentioned refining method for improving the nitrogen content hit rate of high nitrogen steel, alloying is carried out after complete deoxidation in step (1), and the silicon content of the outgoing molten steel is controlled by the lower limit (the lower limit required by the finished product composition regulations) + 0.01%, leaving room for increasing silicon content in the RH feeding silicon nitride line.

[0016] Technical effect: The present invention strictly controls the silicon component, increases nitrogen in the silicon nitride line, controls according to the lower limit, prevents unqualified finished product components, and ensures the final quality.

[0017] In the aforementioned refining method for improving the nitrogen content hit rate of high nitrogen steel, when the slag condition at the outlet is adjusted in step (1), the slag condition is observed at the outlet. When the slag fluidity is poor, fluorite ≤ 50 kg is added, including the slag added during steelmaking from the converter, and the total slag amount is controlled to 7-10 kg / t (ratio of slag amount to molten steel weight).

[0018] Technical effect: The present invention checks the slag condition and adds fluorite to make adjustments. When the fluidity is poor, fluorite is added to ensure that the LF slag has good fluidity when it leaves the station. The added fluorite is ≤50KG, and the proportion is controlled, which is beneficial to controlling the total slag amount. Controlling the total slag amount can effectively prevent serious slag overflow due to the large amount of slag in the later stage.

[0019] In the above-mentioned refining method for improving the nitrogen content hit rate of high nitrogen steel, the iron oxide content of the steel slag leaving the station is ≤0.5% and the aluminum oxide content is 0.25-0.30% by mass percentage.

[0020] Technical effect: The present invention controls the contents of iron oxide and aluminum oxide in steel slag to effectively ensure the deoxidation effect and slag fluidity.

[0021] The beneficial effects of the present invention are: At present, the general process flow for producing high nitrogen steel in steel mills is converter → refining LF furnace → refining RH furnace (feeding silicon nitride line after vacuum) → continuous casting machine. In order to improve production efficiency and ensure continuous pouring of molten steel, high nitrogen steel is cast continuously with other steel grades, which leads to limited processing time of high nitrogen steel in the refining process. Nangang produces high nitrogen steel, which requires deep desulfurization (S≦0.005%), and the aluminum content in molten steel cannot be high (Alt≦0.030%). The composition of other precious alloys is narrow. Generally, the LF processing time of a furnace of steel is 40-50min, and the RH furnace processing time is 50-60min. The high silicon nitride line feeds a large amount, the rhythm is tight, the nitrogen component is not evenly stirred, and the waiting time for gas sample analysis is long, which also leads to the inability to stably control the nitrogen content.

[0022] The technical solution of the present invention is that LF adopts argon blowing throughout the bottom, deoxidation and slag making are carried out in the process, and the outgoing composition is accurately controlled; the LF outgoing slag condition is adjusted to maintain good fluidity; carbonized rice husk is added to soften the slag shell at the RH inlet, and gas samples are taken to send to the inspection station to inspect the initial nitrogen content; RH bottom blowing argon is turned on in the later stage of vacuum to keep the air-permeable bricks unobstructed; the silicon nitride line is fed and the argon flow rate is adjusted; after the calcium treatment is completed, the gas sample is taken at the timing, and the process of each step is strictly controlled, and the various processes cooperate with each other to save time and improve efficiency.

[0023] In the present invention, the argon flow rate of the silicon nitride wire fed after the RH is broken in the RH furnace is set to 200 / 200 NL / min, so as to ensure the argon stirring effect and make the nitrogen component evenly distributed in the molten steel.

[0024] The LF furnace of the present invention performs deoxidation and slag making by blowing argon at the bottom throughout the whole process, accurately controls the outgoing composition, and adjusts the outgoing slag condition, thereby providing qualified molten steel for the next process.

[0025] The present invention provides good conditions for increasing the hit rate of nitrogen content in molten steel by adding carbonized rice husk into the RH station, opening the bottom of the ladle in advance to blow argon at the end of vacuum, setting the line speed of silicon nitride feeding and the argon flow rate, the timing of calcium treatment, setting the flow rate of static stirring, and taking gas samples to confirm the timing of nitrogen content. If the speed is too fast or too slow, the argon flow rate is too large or too small, and the nitrogen recovery rate is unstable, if the argon flow rate is large and the nitrogen recovery rate is high, it will cause serious temperature loss in the process; if the argon flow rate is small, the nitrogen recovery rate is low, and the production rhythm is not allowed. DETAILED DESCRIPTION Example

[0026] This embodiment adopts a refining method of the present invention for improving the nitrogen component hit rate of high nitrogen steel. SA612 steel is selected in this embodiment. The steel is smelted in a 150-ton converter, a 150-ton LF furnace, and a 150-ton RH furnace. The main chemical components of SA612 steel are shown in Table 1 by mass percentage, the remainder is Fe, and the sum of each component is 100%; Table 1 Main chemical components of SA612 (%) The whole smelting process is controlled as follows: (1) Converter blowing. The control of the composition of the finished product at the end of blowing is shown in Table 2.

[0027] Table 2 Components at converter end point (%) (2) LF refining furnace ① Before production, timely understand the situation of converter slag and deoxidizer addition, observe the color and melting of slag on the surface of molten steel, and preliminarily judge the oxidizability and consistency of slag; ②After the molten steel enters the station, use a 10-6 grade lower electrode and a bottom blowing flow rate of 150-200NL / min; after the submerged arc is stable, increase the heating grade and bottom blowing flow rate to quickly slag; adjust the slag fluidity in time according to the slag conditions at the station; add fluorite ≤50KG per batch; add lime ≤200KG per batch, and control the total slag volume to 7-10kg / t (including the slag added during converter steelmaking); ③After the slag is melted, add aluminum wire in batches, 20-30kg per batch, and control the aluminum content in the process to 0.020~0.030%; ④ After complete deoxidation, alloying is carried out, and the silicon content of the outgoing molten steel is controlled at the lower limit (the lower limit required by the finished product composition regulations) + 0.01%, and space for increasing silicon in the RH feeding silicon nitride line is reserved; ⑤ If the amount of aluminum wire used is greater than 4 batches, observe the slag condition before leaving the station. If the slag has poor fluidity, add a small amount of fluorite ≤50KG to adjust the final slag. Ensure that the LF slag has good fluidity when leaving the station, and white slag leaves the station. Control the iron oxide content in the slag to be ≤0.5% and the aluminum oxide content to be 0.25-0.30% by mass percentage; LF uses argon blowing at the bottom throughout the whole process, slag melting → slag forming and submerged arc → heating and alloying → continuous slag deoxidation → desulfurization → adjustment of the outgoing slag condition. The outgoing composition control is shown in Table 3, and the remainder is Fe; Table 3 Main components of molten steel at the end of LF furnace (%) (3) Refining RH furnace ① When RH molten steel arrives at the station, add 10-25 kg of carbonized rice husk according to the slag conditions, spread the slag surface flat to prevent the steel slag from crusting, take gas samples, and send them to the testing station to analyze the initial nitrogen content; ② Open the bottom of the ladle to blow argon in advance at the end of RH vacuum; The vacuum degree is 0.3mbar, and the holding time is 15 minutes. To ensure that the air-permeable bricks are not blocked when the vacuum ends, the argon flow rate of the ladle bottom is adjusted to 30NL / min 3 minutes before the vacuum ends; When RH is degassed, ③RH breaks the air, feeds silicon nitride linear speed, and adjusts and sets the argon flow rate; After breaking the air, the bottom blowing argon is set to 200 / 200 NL / min to ensure good bottom blowing of argon. The feeding line speed of silicon nitride is set to 100-130m / min. The feeding line of silicon nitride is 450 meters. The argon flow rate of the silicon nitride feeding line is set to 200 / 200 NL / min to ensure the argon stirring effect and make the nitrogen component evenly distributed in the molten steel. ④ Calcium treatment timing, adding carbonized rice husks, static stirring to set the flow rate; After the silicon nitride line is fed, it is stirred for 2-4 minutes to make the nitrogen content uniform before it can be fed into the calcium line for calcium treatment. After the calcium treatment is completed, 10-25kg of carbonized rice husk is added to the slag surface for covering. The static stirring flow rate is set to 50-80NL / min to ensure the static stirring effect. The static stirring time is 15 minutes. The main components of the outgoing station are controlled in Table 4. The remainder is Fe, and the sum of each component is 100%.

[0028] Table 4 Main components of molten steel at the end of RH furnace (%) ⑤ Take gas samples to confirm nitrogen content; After calcium treatment, stir quietly for 3-4 minutes, take gas samples to analyze nitrogen content, and take gas samples again after 8-10 minutes to analyze the change in nitrogen content. If it is insufficient, feed in time until the requirements are met.

[0029] Through the whole process of LF bottom blowing argon, the process is well done for deoxidation and slag making, the outgoing composition is accurately controlled, the outgoing slag condition is adjusted → carbonized rice husk is added into the RH station, and the gas sample is taken for analysis of the initial nitrogen content at the testing station → at the end of RH vacuum, the ladle bottom is opened in advance to blow argon → RH breaks the air, the linear speed and argon flow rate of silicon nitride are set → the timing of calcium treatment, carbonized rice husk is added, the static stirring flow rate is set → the timing of taking gas samples to confirm the nitrogen content, the process can be used to control the N content of molten steel within: [N] 0.010-0.011%, achieving the purpose of stabilizing the nitrogen content hit rate of molten steel, and meeting the requirements of large-scale production on site.

[0030] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A refining method for improving the nitrogen component hit rate of high nitrogen steel, characterized in that: The specific process includes the following: converter → refining LF furnace → refining RH furnace → continuous casting machine, among which: (1) During the refining of the LF furnace, argon is blown from the bottom of the LF furnace throughout the whole process to deoxidize and slag. The composition of the molten steel out of the station is accurately controlled, and the slag condition out of the station is adjusted to ensure the fluidity of the slag; (2) When refining RH furnace: ① Add carbonized rice husk into the RH station, take gas samples and send them to the testing station to analyze the initial nitrogen content; When RH molten steel arrives at the station, carbonized rice husk is added to the steel slag to flatten the slag surface so that the steel slag does not form a crust; ② Open the bottom of the ladle to blow argon in advance at the end of RH vacuum; 3 minutes before the end of vacuum, the argon flow rate of the ladle bottom blowing is adjusted to 30NL / min; ③RH breaks the air, feeds silicon nitride linear speed, and adjusts and sets the argon flow rate; After breaking the air, the bottom blowing argon is set to 200 / 200 NL / min, and the feeding speed of silicon nitride is set to 100-130m / min. ④ Calcium treatment timing, adding carbonized rice husks, static stirring to set the flow rate; After the silicon nitride wire is fed in, stir for 2-4 minutes to make the nitrogen content uniform, then feed the calcium wire for calcium treatment. After the calcium treatment is completed, add carbonized rice husks to cover the slag surface, and set the static stirring flow rate to 50-80NL / min; ⑤ Take gas samples to confirm nitrogen content; After calcium treatment, stir quietly for 3-4 minutes, take gas samples to analyze nitrogen content, and take gas samples again after 8-10 minutes to analyze the change in nitrogen content. If it is insufficient, feed in time until the requirements are met.

2. The refining method for improving the nitrogen component hit rate of high nitrogen steel according to claim 1, characterized in that: When blowing argon in step (1), the bottom blowing flow rate is 150-200 NL / min.

3. The refining method for improving the nitrogen component hit rate of high nitrogen steel according to claim 1, characterized in that: In step (1), aluminum wire is added after the slag is melted, and the aluminum content in the process is controlled to be 0.020-0.030%.

4. The refining method for improving the nitrogen component hit rate of high nitrogen steel according to claim 1, characterized in that: Step (1) After complete deoxidation, alloying is carried out, and the silicon content of the outgoing molten steel is controlled at the lower limit + 0.01%, leaving space for RH feeding to the silicon nitride line to increase silicon.

5. The refining method for improving the nitrogen component hit rate of high nitrogen steel according to claim 1, characterized in that: When adjusting the slag condition at the exit in step (1), observe the slag condition at the exit. When the slag fluidity is poor, add fluorite ≤ 50 kg, including the slag added during converter steelmaking, and control the total slag amount to 7-10 kg / t.

6. The refining method for improving the nitrogen component hit rate of high nitrogen steel according to claim 1, characterized in that: The iron oxide content of the steel slag leaving the station is ≤0.5% by mass, and the aluminum oxide content is 0.25-0.30%.