A method for efficient utilization of 0-3mm stainless steel slag

Abstract

This invention relates to the field of solid waste utilization in stainless steel smelting, and a method for the efficient utilization of 0-3mm stainless steel slag, comprising the following steps: Step 1: Briquetting small-particle stainless steel slag; Step 2: Baking the slag steel briquettes; Step 3: Using the slag steel briquettes; Step 4: molten steel from AOD smelting undergoes LF refining before being continuously cast in the continuous casting process. The beneficial effects of this invention are: 1. By baking the small-particle slag steel briquettes and using them in the AOD furnace, the loss of chromium and nickel elements caused by high-temperature burning and oxidation in the electric furnace is reduced. 2. Baking after briquetting using high-temperature steam inside the factory improves baking efficiency and reduces baking costs. 3. Adding small-particle slag steel briquettes to the AOD furnace can replace expensive nickel-iron alloys for fine-tuning the composition, reducing smelting costs, realizing the recycling of waste resources, and reducing environmental pollution.

Description

Technical Field

[0001] This invention relates to the field of utilization of solid waste from stainless steel smelting, and more particularly to a method for the efficient utilization of 0-3mm stainless steel slag. Background Technology

[0002] The stainless steel production process generates 15-25% slag. During slag removal, a large amount of molten stainless steel and metal particles are carried into the slag. To recover metal resources such as Cr, Ni, and Fe from the stainless steel slag, it undergoes hot quenching, crushing, magnetic separation, gravity separation, and water washing to separate stainless steel slag particles of different sizes. The smaller particles (0-3mm) have high moisture content, making moisture removal difficult.

[0003] Conventional processes involve adding stainless steel slag to the electric arc furnace. Patent 202310367909.X, "A Method for Smelting 300 Series Stainless Steel Using Electric Arc Furnace Slag Steel," describes a process where 300 series electric arc furnace slag steel is washed with water, magnetically separated to remove waste slag, and then dried until the moisture content is less than 1%. Small slag steel particles are then bagged and sent to the material yard for use in the electric arc furnace. However, our company, facing the issue of high moisture content in 0-3mm small-particle slag steel, also needs to dry and bake it before entering the electric arc furnace. This drying process is time-consuming, requires a large area, and is costly. To prevent spillage during charging and dust collection during the smelting process, the baked small slag steel must be bagged before being added to the electric arc furnace, making the process complex and costly.

[0004] Electric arc furnace smelting requires oxygen blowing for fluxing. However, the high-temperature burn-off from the electric arc and the oxygen blowing process result in significant oxidation losses in the small-particle slag steel, leading to low yield and high cost. Therefore, there is an urgent need to develop a method for directly using 0-3mm small-particle stainless slag steel in AOD steel production to achieve its efficient utilization.

[0005] The purpose of this invention is to develop a method for mixing 0-3mm stainless steel slag with a binder to form pellets, which allows the small-particle steel slag to be used in AOD (Alternating Dry Ore) processes, replacing expensive nickel-iron and other precious alloys. This avoids high-temperature burn-off and oxidation during electric furnace smelting, increases chromium and nickel yield, achieves efficient utilization of small-particle steel slag, reduces smelting costs, and minimizes environmental pollution. Summary of the Invention

[0006] The purpose of this invention is to address the above-mentioned problems by providing a method for the efficient utilization of 0-3mm stainless steel slag.

[0007] The objective of this invention is achieved as follows: a method for the efficient utilization of 0-3mm stainless steel slag, comprising the following steps: Step 1: Small-particle stainless steel slag briquetting: 0-3mm slag from 300 series stainless steel, after water washing and magnetic separation, is mixed evenly with a binder. The ratio of slag to binder by weight percentage is slag steel:binder = 88-90:10-12. The mixed slag is extruded into briquettes using a roller briquetting machine at a pressure of 15-20 MPa, yielding finished stainless steel slag briquettes with a diameter of Φ50-60mm. The composition of the finished stainless steel slag briquettes is: C≤0.5%, Si≤0.5%, Ni: 3.0-6.5%, C r: 6.0~10.0%, the remainder being iron and unavoidable impurities; Step 2: Baking of slag steel briquettes: The slag steel briquettes produced in Step 1 are placed in a tunnel kiln, and high-temperature steam of 300-500℃ is introduced into the tunnel kiln for baking. The baking time is 3-5 hours. When the moisture content is ≤1.0%, the baking is completed, and the baked briquettes are transported to the AOD high-level silo in the steelmaking plant; Step 3: Use of slag steel briquettes: In the middle and late stages of AOD smelting, slag steel briquettes are added from the high level, with an addition amount of 3-20 tons. After AOD decarburization is completed, ferrosilicon and lime are added for deoxidation, reduction, and desulfurization; Step 4: After LF refining, the molten steel from AOD smelting is continuously cast in the continuous casting process.

[0008] In step one, the binder is a mixture of starch, magnesium chloride and polyvinyl alcohol in a certain proportion, with the weight ratio of starch, magnesium chloride and polyvinyl alcohol being 48-52:38-42:8-12.

[0009] The beneficial effects of this invention are: 1. By baking small slag steel pellets and using them in an AOD furnace, the loss of chromium and nickel elements caused by high-temperature burning and oxidation in the electric furnace is reduced.

[0010] 2. After pelleting, the pellets are baked using high-temperature steam inside the factory, which improves baking efficiency and reduces baking costs.

[0011] 3. Adding small slag steel pellets to AOD can replace expensive nickel-iron alloys for fine-tuning the composition, reducing smelting costs, realizing the recycling of waste resources, and reducing environmental pollution. Attached Figure Description

[0012] The present invention will now be further described with reference to the accompanying drawings.

[0013] Figure 1 This is a flow chart of the smelting process of the present invention. Detailed Implementation

[0014] This invention relates to the field of solid waste. More specifically, it relates to the use of solid waste in steelmaking processes. This invention provides a method for the efficient utilization of 0-3mm stainless steel slag. The specific process is as follows: 0-3mm small slag steel particles, selected by wet processing from stainless steel slag, are mixed with a binder and then briquetteed. The briquetteed slag steel pellets are then baked with high-temperature gas to remove moisture and are sent to an AOD (Alternating Oxygen Demand) high-level silo. During the stainless steel blowing process, steel pellets are added to fine-tune the temperature and composition.

[0015] This method allows small-particle slag steel, which was originally used in electric furnaces, to be moved to the AOD process to replace precious nickel-iron alloys. This reduces the electric furnace smelting process and blowing losses, improves the recovery rate of chromium and nickel in small-particle slag steel, and lowers smelting costs.

[0016] This invention involves uniformly mixing small-particle slag steel with a binder at a weight ratio of 90:10. The binder consists of starch, magnesium chloride, and polyvinyl alcohol in a weight ratio of 5:4:1. The uniformly mixed slag steel particles are then extruded using a roller briquetting machine at a pressure of 15-20 MPa to obtain finished slag steel briquettes. These briquettes are then fed into the high-level silo of the AOD furnace. During the later stages of smelting, the slag steel briquettes are added to replace nickel-iron and pure nickel to adjust the composition and temperature. After the AOD smelting composition and temperature reach the required levels, the steel is reduced and tapped.

[0017] 1. Process route: Small slag steel briquettes — baking and drying — feeding into AOD high-level silo — added into the furnace from the high-level silo in the later stage of smelting — smelting end — LF refining — continuous casting.

[0018] 2. The efficient use steps in the small-particle slag steelmaking process are as follows: ① Briquetting of small-particle stainless steel slag: After slag removal by water washing and magnetic separation, 0-3mm slag steel of 300 series stainless steel is mixed evenly with a binder. The ratio of slag steel to binder is based on the weight percentage: slag steel: binder = (88-90): (10-12). The binder is a mixture of starch, magnesium chloride, and polyvinyl alcohol in a certain proportion. The weight ratio of starch, magnesium chloride, and polyvinyl alcohol is 50:40:10 (the binder ratio is relatively fixed, and its bonding effect is better). A double-roller briquetting machine (model 520) is used. Briquetting machine; double roller briquetting machine is mainly used to press powdery materials into briquettes. It extrudes the mixed slag steel into briquettes at a pressure of 15-20 MPa to obtain finished stainless slag steel briquettes. The finished briquettes are Φ50-60mm in size and have the following composition: C≤0.5%, Si≤0.5%, Ni: 3.0-6.5%, Cr: 6.0-10.0%, with the remainder being iron and unavoidable impurities. (Using this briquetting process, the briquette formation rate reaches 95%, and the average briquette strength reaches 2100N, which has high strength and is not easily pulverized during transportation and feeding.)

[0019] ② Baking of slag steel briquettes: Place the slag steel briquettes into a tunnel kiln, and introduce high-temperature steam at 300-500℃ into the kiln. Use the recovered steam from the plant for baking. Baking time is 3-5 hours. When the moisture content is ≤1.0%, baking is completed. Transport the baked briquettes to the AOD high-level silo in the steel plant. A tunnel kiln is a kiln used to fire materials such as ceramics, sponge iron, and lime, and can also be used to bake materials. Other baking equipment, such as annealing kilns or heating furnaces, can also be used to bake briquettes. The appropriate equipment can be selected based on the actual equipment available at the production site.

[0020] ③ Use of slag-steel briquettes: In the middle and late stages of AOD smelting, slag-steel briquettes are added from a high position, with an addition amount of 3 to 20 tons. After AOD decarburization, ferrosilicon and lime are added for deoxidation, reduction and desulfurization. The addition amount of ferrosilicon is 18 to 25 kg / t, and the addition amount of lime is 8 to 10 kg / t. The slag basicity is controlled at 1.8 to 2.2. After reduction, the composition of the molten steel meets the requirements of the steel grade, the sulfur content in the steel is S≤0.005%, and the temperature reaches 1630-1650℃ before tapping the steel.

[0021] 3. After being refined by LF, the molten steel produced by AOD smelting is continuously cast in the continuous casting process. Example 1

[0022] The 180-ton AOD furnace smelting of 304 uses small-particle slag steel briquettes: 304 nickel-based stainless steel is smelted using 180-ton AOD furnace, and the main chemical composition by mass percentage is: C≤0.03%, Si≤1.0%, Mn≤2.0%, P≤0.040%, S≤0.005%, Cr: 17.5~18.5%, Ni: 7.8~8.5%.

[0023] Process flow: Small slag steel briquettes — baking and drying — feeding into AOD high-level silo — added into the furnace from the high-level silo in the later stage of smelting — smelting end — LF refining — continuous casting.

[0024] (1) After washing and magnetic separation, 0-3mm slag steel from 300 series electric arc furnace slag steel is mixed evenly with a binder. The ratio of slag steel to binder is 90:10 by weight. The binder consists of starch, magnesium chloride, and polyvinyl alcohol in a weight ratio of 50:40:10. The mixed slag steel is extruded into briquettes using a roller press at a pressure of 15-20 MPa to obtain finished stainless slag steel briquettes. The composition is: C≤0.5%, Si≤0.5%, Ni:3.0-6.5%, Cr:6.0-10.0%.

[0025] (2) Place the slag steel briquettes into the tunnel kiln, and introduce high-temperature steam at 300-500℃ into the kiln. Use the recovered steam in the plant to bake the briquettes for 3-5 hours. When the moisture content is ≤1.0%, the baking is completed. Transport the baked briquettes to the AOD high-level silo of the steelmaking plant.

[0026] (3) Use an electric furnace or medium-frequency furnace to melt the pre-melted stainless steel and add it to the AOD furnace. The weight of the pre-melted liquid is 150 tons. In the middle and late stages of AOD smelting, add 10 tons of stainless steel slag pellets to adjust the temperature of the molten steel and reduce the cost, thereby reducing the amount of nickel iron (Ni: 25%) by 2 tons. After the AOD blowing decarburization is completed, use ferrosilicon and lime reduction desulfurization.

[0027] (4) After the AOD tapping, the molten steel is sent to the LF furnace for refining and temperature adjustment, and then hoisted to the continuous casting process for continuous casting.

[0028] By using small-particle slag steel briquettes instead of nickel-iron for temperature and composition adjustments, the nickel recovery rate reached 97.5%, and the cost per ton of steel was reduced by 70 yuan / ton. Example 2

[0029] 45-ton AOD furnace smelting 316L using small slag steel briquettes: 316L nickel-based stainless steel is smelted using a 45-ton AOD furnace, with the main chemical composition by mass percentage as follows: C≤0.03%, Si≤1.0%, Mn≤2.0%, P≤0.040%, S≤0.005%, Cr: 16.0~18.0%, Ni: 12.0~15.0%.

[0030] Process flow: Small slag steel briquettes — baking and drying — feeding into AOD high-level silo — added into the furnace from the high-level silo in the later stage of smelting — smelting end — LF refining — continuous casting.

[0031] (1) After washing and magnetic separation, 0-3mm slag steel from 300 series electric arc furnace slag steel is mixed evenly with a binder. The ratio of slag steel to binder is 90:10 by weight. The binder consists of starch, magnesium chloride, and polyvinyl alcohol in a weight ratio of 50:40:10. The mixed slag steel is extruded into briquettes using a roller press at a pressure of 15-20 MPa to obtain finished stainless slag steel briquettes. The composition is: C≤0.5%, Si≤0.5%, Ni:3.0-6.5%, Cr:6.0-10.0%.

[0032] (2) Place the slag steel briquettes into the tunnel kiln, and introduce high-temperature steam at 300-500℃ into the kiln. Use the recovered steam in the plant to bake the briquettes for 3-5 hours. When the moisture content is ≤1.0%, the baking is completed. Transport the baked briquettes to the AOD high-level silo of the steelmaking plant.

[0033] (3) Use an electric furnace or medium-frequency furnace to melt the pre-melted stainless steel and add it to the AOD furnace. The weight of the pre-melted liquid is 40 tons. In the middle and late stages of AOD smelting, add 3 tons of stainless steel slag pellets to adjust the temperature of the molten steel and reduce the cost, and reduce the amount of Ni25% nickel iron by 0.6 tons accordingly. After the AOD blowing decarburization is completed, use ferrosilicon and lime reduction desulfurization.

[0034] (4) After the AOD tapping, the molten steel is sent to the LF furnace for refining and temperature adjustment, and then hoisted to the continuous casting process for continuous casting.

[0035] By using small-particle slag steel briquettes instead of nickel-iron for temperature and composition adjustments, the nickel recovery rate reached 98%, and the cost per ton of steel was reduced by 80 yuan / ton.

[0036] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for the efficient utilization of 0-3mm stainless steel slag, characterized in that: Includes the following steps: Step 1: Small-particle stainless steel slag briquetting: 0-3mm slag steel from 300 series stainless steel, after water washing and magnetic separation, is mixed evenly with a binder. The ratio of slag steel to binder is 88-90:10-12 by weight percentage. The mixed slag steel is then extruded into briquettes using a roller briquetting machine at a pressure of 15-20 MPa to obtain finished stainless steel slag briquettes. The finished briquettes have a diameter of Φ50-60mm. The composition of the finished stainless steel slag briquettes is: C≤0.5%, Si≤0.5%, Ni: 3.0-6.5%, Cr: 6.0-10.0%, with the remainder being iron and unavoidable impurities. Step 2: Baking of slag steel briquettes: Place the slag steel briquettes produced in Step 1 into a tunnel kiln, and introduce high-temperature steam at 300-500℃ into the tunnel kiln for baking. Baking time is 3-5 hours. When the moisture content is ≤1.0%, baking is completed. Transport the baked briquettes to the AOD high-level silo in the steelmaking plant. Step 3: Use of slag steel briquettes: In the middle and late stages of AOD smelting, add slag steel briquettes from a high position, with an addition amount of 3 to 20 tons. After AOD decarburization is completed, add ferrosilicon and lime for deoxidation, reduction and desulfurization. Step 4: After AOD smelting and LF refining, the molten steel is continuously cast in the continuous casting process.

2. The method for efficient utilization of 0-3mm stainless steel slag according to claim 1, characterized in that: In step one, the binder is a mixture of starch, magnesium chloride and polyvinyl alcohol in a certain proportion, with the weight ratio of starch, magnesium chloride and polyvinyl alcohol being 48-52:38-42:8-12.

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