A method for increasing nitrogen content of threaded steel based on two-step method using aluminum ash

Abstract

The application provides a method for increasing nitrogen content of screw steel by using aluminum ash based on a two-step method, which comprises grinding and screening the primary aluminum ash block twice, and using undersize to make products to replace silicon nitride, ferrovanadium nitride and the like to increase nitrogen and deoxidize, so that the aluminum ash is harmlessly treated. The primary undersize product is mainly aluminum oxide, which can effectively reduce the viscosity of slag in the converter smelting process and promote the converter slag to increase nitrogen; the secondary undersize product is mainly aluminum nitride, and the aluminum nitride is decomposed under the heating of molten steel, and the nitrogen exists in the form of N ‑ The decomposed aluminum has deoxidizing capacity, the oxygen content in the molten steel is greatly reduced, the yield of vanadium-nitrogen, silicon-manganese and other alloys is effectively improved, and good economic benefits are obtained. The application can utilize the aluminum ash by grading treatment, realizes the maximization of the value of the aluminum ash under the premise of harmless utilization, and reduces the waste of production materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal smelting and relates to a method for increasing the nitrogen content of threaded steel based on a two-step method using aluminum ash. BACKGROUND

[0002] Threaded steel is the main product of the company's building materials, and its cost control directly affects the profitability of the product. Vanadium-nitrogen alloy is used for micro-alloying during the production of threaded steel, and the absorption of aluminum in steel is directly related to the nitrogen content of the molten steel.

[0003] To solve the problem of increasing nitrogen in molten steel, the industry has tried high-flow bottom blowing of nitrogen for threaded steel, but the nitrogen-increasing effect is not obvious, so most enterprises still use silicon nitride, vanadium iron nitride, etc. to increase nitrogen, resulting in high micro-alloying cost. How to increase the initial nitrogen content of threaded steel through other low-cost methods has become a technical problem in the industry.

[0004] Chinese invention patent 202111384145.2 discloses a production method for increasing the nitrogen content of vanadium micro-alloyed threaded steel, including: 1) controlling the converter endpoint C: 0.06-0.12%, adding silicon iron, silicon manganese and aluminum manganese iron for deoxidation during converter tapping, maintaining the oxygen content in the steel less than 40ppm, and controlling the converter slag amount below 60mm; 2) after the molten steel enters the station, add the first batch of slag material, 1-5kg / t of nitrogen-increasing refining slag, 1-5kg / t of lime, and at the same time, open the nitrogen gas bottom blowing to flatten the slag material, control the nitrogen gas bottom blowing flow rate at 30-40m 3 / h; 3) lower electrode heating and slagging, while adjusting the nitrogen gas bottom blowing flow rate to 20-30m 3 / h, according to the slagging condition, supplement the nitrogen-increasing refining slag and lime, the nitrogen-increasing refining slag is 1-5kg / t, and the lime is 1-5kg / t; stop the nitrogen gas bottom blowing after heating for 5-10min, measure the temperature and take samples; 4) according to the composition of the molten steel, adjust the composition of the molten steel and add the slag material, the nitrogen-increasing refining slag is 1-5kg / t, the lime is 1-5kg / t, and the nitrogen gas bottom blowing flow rate is controlled at 10-20m 3 / h; 5) after the composition and temperature adjustment of the molten steel is completed, use nitrogen gas for soft blowing treatment of the molten steel, the nitrogen gas flow rate for soft blowing of the molten steel is 1-5m 3 / h, and the soft blowing time is >5min.

[0005] The Chinese invention patent 202111409574.0 discloses a nitrogen-increasing refining slag for producing vanadium micro-alloyed threaded steel, which is mainly composed of aluminum ash containing aluminum nitride, and is mixed with auxiliary materials such as limestone and adhesive, and then is uniformly mixed with water, pressed and formed by a mold, and dried to obtain the nitrogen-increasing refining slag. The mass percentage of each component is as follows: aluminum ash 50-90%, limestone 10-30%, and adhesive 5-25%. In the refining process, the nitrogen-increasing refining slag is added into the ladle refining furnace in batches, the AlN in the nitrogen-increasing refining slag is decomposed by high-temperature electric arc, the pH value of the slag is adjusted to maintain the nitrogen content in the slag of the refining furnace at a certain level, the nitrogen content in the steel is increased through diffusion between the steel and the slag, the nitrogen yield in the molten steel is stabilized, the vanadium micro-alloying effect is improved, the mechanical properties of the steel are improved, and the production process cost is saved.

[0006] Aluminum ash is a product generated in the production of electrolytic aluminum, aluminum processing or aluminum casting. It is mainly derived from non-melting inclusions, oxides, additives floating on the surface of aluminum melt during the production process of melting aluminum and aluminum alloy, and reaction products produced by physical and chemical reactions with additives, etc. It is generated in all production processes where aluminum is melted. Aluminum ash contains aluminum and various valuable elements, mainly composed of metallic aluminum (5-70%), aluminum nitride (10-50%), aluminum oxide (20-40%), other metal oxides (2-10%), and salt flux (2-30%). According to the different content of metallic aluminum, aluminum ash can be divided into primary aluminum ash and secondary aluminum ash. The aluminum content of primary aluminum ash ranges from 15 to 70%, and the secondary aluminum ash is black in color, with an aluminum content of 5-15%.

[0007] The content of metallic aluminum and aluminum oxide in aluminum ash is high, which is a valuable renewable resource. The deliquescence of aluminum nitride in aluminum ash will release ammonia gas, which is a malodorous gas and has flammable and explosive properties. The salt flux in aluminum ash is mainly chlorides and fluorides, and the content of soluble fluorides is very high. Therefore, if aluminum ash is not properly treated, it will cause serious pollution to the ecological environment of land, water body and air.

[0008] The harmfulness of aluminum ash is mainly the ammonia gas produced by the hydrolysis of soluble fluorides and aluminum nitride. In the steelmaking molten steel, aluminum nitride decomposes into aluminum and ionic nitrogen, but the soluble fluorides are easy to volatilize due to their low melting point, so they must be treated before use to avoid pollution to the environment. Therefore, although the above two patents can increase nitrogen, the soluble fluorides will cause environmental pollution, so the use of aluminum ash to increase the nitrogen content of threaded steel needs to be combined with the composition characteristics of aluminum ash under the premise of meeting environmental protection, so as to ensure the legalization of the use of aluminum ash. SUMMARY

[0009] The present application aims at the problems existing in the prior art, and provides a method for increasing nitrogen content of threaded steel based on a two-step method by using aluminum ash, so as to solve the problem that the micro-alloy VN added due to low nitrogen content of threaded steel cannot maximize the strengthening effect.

[0010] To this end, the present application adopts the following technical solutions:

[0011] A method for increasing nitrogen content of threaded steel based on a two-step method by using aluminum ash, comprising the following steps:

[0012] Step a. Coarse grinding of primary aluminum ash blocks by using a rod mill, and screening by using a roller screen, and the screen plate is selected to be 36 meshes, and the aluminum oxide, aluminum nitride, aluminum fluoride and sodium fluoride peeled from the surface of the primary aluminum ash blocks become the primary undersize, and the primary oversize enters a ball mill for fine grinding; in this step, the primary aluminum ash blocks are preferentially screened by using a 36-mesh roller screen, so that the aluminum content in the primary undersize can be controlled to be less than 5%, and the elemental aluminum content in the ball material processed by using the primary undersize is reduced, and the waste of metallic aluminum is effectively avoided;

[0013] Step b. After the primary oversize enters the ball mill for fine grinding, the primary oversize enters the roller screen for screening, and the screen plate is selected to be 36 meshes, and a small part of the peeled aluminum oxide, aluminum nitride and ground aluminum powder become the secondary undersize, and the secondary oversize is aluminum pieces with an aluminum content of more than 90%, and the aluminum pieces are reused for melting and ingot casting;

[0014] Step c. The primary undersize obtained in step a is mixed with 15-20% active calcium oxide, and is pressed into balls by using a high-strength ball press, and is added in the converter smelting process of threaded steel production, so as to realize slagging and nitrogen increasing; in this step, 3-5% sodium fluoride and 8-5% aluminum fluoride in the aluminum ash can effectively reduce the viscosity of the slag, and at the same time, together with 45-53% aluminum oxide, can effectively reduce the melting point of the slag, so as to realize rapid slagging;

[0015] Step d. The secondary undersize obtained in step b is mixed with 15-20% active calcium oxide, and after being uniformly mixed, is treated by using a nitriding rotary furnace, and after the treatment, 10-15% limestone is added as an aggregate, and the material is pressed into balls by using a high-strength ball press, and is added in the converter tapping process of threaded steel smelting, so as to realize deoxidization and nitrogen increasing; the calcium oxide content of the limestone is greater than 53%.

[0016] Further, in step a, the rod milling time of the primary aluminum ash blocks is controlled to be 8-12 min, and only by rod milling, 80-90% of the aluminum oxide, aluminum nitride, aluminum fluoride and sodium fluoride on the surface of the primary aluminum ash blocks can be peeled.

[0017] Further, the step b, the ball milling time of the first sieve residue is controlled in 12-18 min, more than 90% of the aluminum oxide and aluminum nitride on the surface of the first sieve residue can be stripped by ball milling for 1-5 min, and the first sieve residue is ground to 36 mesh or more by ball milling for 11-13 min, so as to increase the aluminum content in the second sieve residue; the step can strip the aluminum oxide and aluminum nitride on the surface of the first sieve residue by ball milling, the aluminum content in the second sieve residue is increased to 90-95%, the product quality is ensured when the sieve residue is reused for melting and ingot casting, and the aluminum content in the second sieve residue is increased by grinding 30-35% of the total amount of pure aluminum to 36 mesh or more.

[0018] Further, in the step c, 16-18% of active calcium oxide is added to the first sieve residue, and any aqueous binder is strictly prohibited, the first sieve residue and the active calcium oxide are uniformly mixed at a ratio of 0.25-0.33, and then the mixture is pressed into a ball by a high-strength pressure ball machine; during the converter smelting process, the ball is added in batches at a usage amount of 5-6 kg / t;

[0019] The aluminum nitride in the ball reacts under high-temperature conditions in the molten steel as follows:

[0020]

[0021] The decomposed nitrogen is dissolved in the molten steel, the nitrogen content before tapping is increased by 5-8 ppm, and the subsequent nitrogen-increasing cost is reduced;

[0022] Further, in the step d, 15-20% of active calcium oxide is added to the second sieve residue after being uniformly mixed, and then the mixture is treated by a nitriding rotary furnace; during the nitriding process, nitrogen gas is continuously introduced, the gas flow is controlled at 1-2.5 L / min, the pressure in the furnace is controlled at 0.3-0.5 Kpa, and the temperature in the furnace is maintained above 950℃, and the nitriding treatment time is more than 30 min; in this step, the second sieve residue is uniformly mixed and heated with 15-20% of active calcium oxide, the active calcium oxide can effectively absorb F- generated by the thermal decomposition of sodium fluoride and aluminum fluoride, realize the solidification and absorption of fluorine, and through the high-temperature and high-pressure conditions in the nitriding process, 70-80% of the elemental aluminum with a particle size of 36 mesh or more in the second sieve residue is converted into aluminum nitride, and the nitrogen content in the second sieve residue is increased to 14-17%, which creates conditions for subsequent manufacturing of nitrogen-increasing materials.

[0023] Further, in the step d, 10-15% of limestone with calcium oxide content greater than 53% is added to the material after nitriding as an aggregate to press into a ball, and the ball is added into a ladle during the steel tapping process; the addition of 10-15% of limestone with calcium oxide content greater than 53% as an aggregate can improve the strength of the pressed ball, and the high-quality limestone expands in volume after being heated, the material is crushed to increase the specific surface area, which is beneficial to the rapid progress of the deoxidization and nitrogen-increasing reaction;

[0024] The aluminum nitride and aluminum in the material of this step produce the following reaction in the steel liquid:

[0025]

[0026] The aluminum is used for steel liquid deoxidization, and the aluminum nitride is used for steel liquid nitrogen-increasing deoxidization.

[0027] The beneficial effects of the present application are:

[0028] 1. The present application divides the primary aluminum ash block into low-aluminum primary undersize and high-aluminum secondary undersize by twice screening, mixes the low-aluminum primary undersize with active calcium oxide in proportion, and directly compresses the mixture into balls, mixes the high-aluminum secondary undersize with active calcium oxide in proportion, and then performs nitriding treatment, which avoids the waste of directly adding aluminum into the converter, solves the cost increase of full nitriding treatment, and finally reduces the addition amount of aluminum ash products in the steel liquid, ensuring smooth continuous casting. The products made by the graded treatment of aluminum ash replace silicon nitride, vanadium iron nitride, etc. for nitrogen-increasing deoxidization, realize the harmlessness of aluminum ash, and the primary undersize products are mainly aluminum oxide, which can effectively reduce the slag viscosity and promote the converter smelting when added into the converter. The secondary undersize products are mainly aluminum nitride, which is decomposed in the steel liquid under heat, and the nitrogen exists in the form of N - which is beneficial to the generation and precipitation of V(C,N), and the decomposed aluminum has deoxidization capacity, greatly reduces the oxygen content in the steel liquid, effectively improves the yield of vanadium-nitrogen, silicon-manganese, etc., and has good economic benefits. The present application ingeniously utilizes the graded treatment of aluminum ash, realizes the maximization of the value of aluminum ash under the premise of harmless utilization, and reduces the waste of production materials.

[0029] 2. According to the technical measures of the present application, the nitrogen content at the end of the threaded steel smelting is increased from 40-55 ppm to 60-75 ppm, and the nitrogen content in the steel is increased to 80-95 ppm by the nitrogen-increasing effect of the vanadium-nitrogen alloy itself, which changes the vanadium in the solid solution state into the precipitated state, and reduces the use amount of vanadium-nitrogen alloy under the condition of constant steel strength. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The present application is a step flowchart. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be described in detail below in combination with the drawings and implementation methods.

[0032] The primary aluminum ash block processing system of this invention includes a rod mill, a primary drum screen, a ball mill, a secondary drum screen, a nitriding rotary furnace, a mixer, and a high-strength briquetting machine. The rod mill is used for coarse grinding of the primary aluminum ash blocks, removing alumina and aluminum nitride from the blocks. The primary drum screen separates the coarsely ground aluminum ash, separating most of the alumina, aluminum nitride, and the primary oversize material. The ball mill primarily removes residual alumina and aluminum nitride from the primary oversize material, while also grinding some of it to below 36 mesh to improve subsequent nitriding. The secondary drum screen separates the remaining alumina, aluminum nitride, and the primary oversize material below 36 mesh from the larger primary oversize material. The nitriding rotary furnace nitrids the undersize material after secondary nitriding, converting as much aluminum as possible into aluminum nitride. The mixer is mainly used for mixing the material before briquetting. The main function of the high-strength briquetting machine is to press the material into products meeting strength requirements without adding water-based binders.

[0033] Example 1

[0034] like Figure 1 As shown, a two-step method for increasing the nitrogen content of rebar using aluminum ash includes the following steps:

[0035] The aluminum ash blocks are first screened by a rod mill, the oversize material is then screened by a second ball mill, and the undersize material is mixed with active lime and pressed into converter slag nitrogen-enhancing material by a high-strength dry briquetting method. The mass percentages of each component are as follows: alumina 61.2%, calcium oxide 15%, aluminum nitride 14%, sodium fluoride 5%, aluminum fluoride 2.8%, and metallic aluminum 2%. During the converter smelting process, the material is added in batches of 5 kg / t. The smelting process is stable, and splashing is effectively controlled. The nitrogen content at the end of the converter smelting process is 45 ppm, which is 10 ppm higher than the conventional process of 35 ppm.

[0036] The material oversizes from the primary sieve enters a secondary ball mill for further screening. The oversize is reused for melting and ingot casting. The undersize is mixed with active lime and nitrided, then pressed with limestone to produce a deoxidizing and nitrogen-enhancing agent for steelmaking. The mass percentages of each component are as follows: aluminum nitride 62%, alumina 20%, calcium oxide 15%, and metallic aluminum 3%. After converter smelting, the steel is tapped after slag removal. The converter output is 128t. 80kg of the deoxidizing and nitrogen-enhancing agent is added first, followed by silicon manganese and ferrosilicon. The recovery rates of alloying elements silicon and manganese are increased by 2.1% and 1.3% respectively compared to the original process. The nitrogen content of the converter sample is 75ppm. In the refining furnace, 0.35kg / t of VN16 alloy is added as usual to complete the micro-alloying of the molten steel. The finished steel has a V content of 0.026% and a N content of 0.0098%, and the steel performance is improved by approximately 15MPa compared to the conventional process.

[0037] It can be seen that the aluminum ash is processed step by step according to the technical scheme, and is added during smelting of the threaded steel, so that the threaded steel can be efficiently increased in nitrogen, and the steel performance is stably improved under the condition of adding the same VN16 alloy.

[0038] Example 2

[0039] The primary aluminum ash block is ground and sieved, the sieve residue is sieved by secondary ball milling, and the undersize is mixed with active lime, and is pressed into converter slag conversion nitrogen material by high-strength dry ball pressing, and the mass percentage of each component is as follows: 58% of aluminum oxide, 20% of calcium oxide, 13% of aluminum nitride, 5% of sodium fluoride, 2.6% of aluminum fluoride, and 1.4% of metal aluminum. The total amount is 4 kg / t during the converter smelting process, and is added in batches, the smelting process is stable, the spatter is effectively controlled, the nitrogen content at the end of the converter smelting is 43 ppm, which is increased by 8 ppm compared with 35 ppm of the conventional process.

[0040] The primary sieve residue is sieved by secondary ball milling, the sieve residue is reused for melting and ingot casting, the undersize is mixed with active lime and is pressed into a deoxidizing nitrogen-increasing agent for steel tapping by nitriding treatment, and the mass percentage of each component is as follows: 62% of aluminum nitride, 20% of aluminum oxide, 15% of calcium oxide, and 3% of metal aluminum. After the converter smelting is completed, the slag is blocked and tapped, the converter tapping amount is 128 t, the deoxidizing nitrogen-increasing agent 65 kg is first added, and then silicon manganese and silicon iron are added, the alloy element silicon and manganese yield is increased by 1.8% and 1.1% respectively compared with the original process, and the nitrogen content of the converter outstation sample is 60 ppm. VN16 alloy 0.35 kg / t is added in the refining furnace according to the conventional use, and the molten steel is micro-alloyed, the V content in the steel product is 0.026%, the N content is 0.0080%, and the steel performance is increased by about 12 Mpa compared with the conventional process.

[0041] It can be seen that the aluminum ash is processed step by step according to the technical scheme, and is added during smelting of the threaded steel, so that the threaded steel can be efficiently increased in nitrogen, and the steel performance is stably improved under the condition of adding the same VN16 alloy.

Claims

1. A two-step method for increasing the nitrogen content of rebar using aluminum ash, characterized in that, Includes the following steps: Step a. The primary aluminum ash blocks are coarsely ground using a rod mill and then sieved using a drum screen with a mesh size of 36. The aluminum oxide, aluminum nitride, aluminum fluoride, and sodium fluoride that peel off from the surface of the primary aluminum ash blocks become the primary undersize material, while the primary oversize material is fed into a ball mill for fine grinding. Step b. After the material from the first sieve is finely ground in a ball mill, it is sieved in a drum screen with a mesh size of 36. A small portion of the alumina, aluminum nitride, and ground aluminum powder that are peeled off become the material under the second sieve. The material over the second sieve is aluminum sheet with an aluminum content of more than 90%. The aluminum sheet is reused for melting and casting ingots. Step c. Add 15-20% active calcium oxide to the primary undersize material obtained from step a, and press it into balls using a high-strength briquetting machine. Add the balls during the converter smelting process when producing rebar in steelmaking to reduce slag and increase nitrogen content. Step d. The secondary undersize material obtained from step b is mixed with 15-20% active calcium oxide and then processed in a nitriding rotary kiln. The processed material is then mixed with 10-15% limestone as aggregate and pressed into balls using a high-strength briquetting machine. These balls are added during the tapping process of the converter for rebar smelting to deoxidize and increase nitrogen content. The calcium oxide content of the limestone is greater than 53%.

2. The method for increasing the nitrogen content of rebar using aluminum ash in a two-step process according to claim 1, characterized in that, In step a, when grinding the aluminum ash block once, the grinding time is controlled at 8 to 12 minutes. It is only necessary to remove 80% to 90% of the aluminum oxide, aluminum nitride, aluminum fluoride and sodium fluoride from the surface of the aluminum ash block once by grinding.

3. The method for increasing the nitrogen content of rebar using aluminum ash in a two-step process according to claim 1, characterized in that, In step b, the ball milling time is controlled between 12 and 18 minutes. By ball milling for 1 to 5 minutes, more than 90% of the alumina and aluminum nitride on the surface of the primary sieve material can be peeled off. By extending the ball milling time to 11 to 13 minutes, the primary sieve material can be ground to a fineness of 36 mesh or higher, thereby increasing the aluminum content in the secondary sieve material.

4. The method for increasing the nitrogen content of rebar using aluminum ash in a two-step process according to claim 1, characterized in that, In step c, 16-18% of active calcium oxide is added to the primary sieve material. No water-based binder is allowed to be added. After the primary sieve material and active calcium oxide are mixed evenly, they are pressed into balls by a high-strength briquetting machine. When producing rebar in steelmaking, the mixture is added in batches at a rate of 5-6 kg / t during the converter smelting process.

5. The method for increasing the nitrogen content of rebar using aluminum ash in a two-step process according to claim 1, characterized in that, In step d, the material underwent secondary screening is mixed with 15-20% active calcium oxide and then processed in a nitriding rotary furnace. Nitrogen gas is continuously introduced during the nitriding process, with the gas flow rate controlled at 1-2.5 L / min, the furnace pressure controlled at 0.3-0.5 kPa, and the furnace temperature maintained above 950°C. The nitriding treatment time exceeds 30 min.

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