Treatment method of converter end point peroxidation molten steel

Abstract

The invention discloses a treatment method of converter end point peroxidation molten steel, and belongs to the technical field of ferrous metallurgy. According to the method, the oxygen content [O] in molten steel is detected after converter blowing is finished, when the oxygen content [O] in the molten steel is larger than 450 ppm, it is judged that the molten steel is in a peroxidation state, calculated granular iron with the corresponding weight is added into a converter, nitrogen purging and standing homogenization are conducted, and finally tapping is conducted. According to the invention, the basic problem that the oxygen content of the molten steel body is high is directly and efficiently solved by changing the situation that the viscosity of the slag is improved by adjusting the components of the slag in the prior art. According to the method, in-furnace pre-deoxidation can be rapidly and accurately conducted on the peroxide molten steel before tapping, the oxygen content of the molten steel can be effectively reduced, the content of iron oxide in final slag can be synchronously reduced, and therefore the purposes of stabilizing the alloy yield, reducing the production cost, protecting a furnace lining and improving the quality of the molten steel are achieved.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a method for treating molten steel with peroxide at the end of a converter. Background Technology

[0002] Converter steelmaking is a major process in modern steel production. The endpoint of converter blowing has a significant impact on steel quality, production costs, and furnace maintenance. Stable endpoint control is beneficial to various economic indicators. However, due to low calorific value of molten iron or fluctuations in process control, excessively high oxygen content at the endpoint of blowing can easily occur, a phenomenon known as "over-oxidation." Over-oxidation of molten steel leads to a series of problems: firstly, a decline in steel quality; secondly, low alloy yield; and thirdly, an accelerated rate of furnace lining erosion. Chinese patent application CN201510786906.5 discloses "a method for thickening converter endpoint slag," which adjusts the slag composition and increases slag viscosity by adding raw dolomite or lime particles in the later stages of converter blowing. While this method focuses on increasing slag viscosity by adjusting slag composition, it does not directly and efficiently solve the fundamental problem of high oxygen content in the molten steel itself. Summary of the Invention

[0003] In view of the above-mentioned prior art, the purpose of this invention is to provide a method for treating the over-oxidized molten steel at the end of a converter. This method can quickly and accurately pre-deoxidize the over-oxidized molten steel in the furnace before tapping, which can not only effectively reduce the oxygen content of the molten steel, but also simultaneously reduce the iron oxide content in the final slag, thereby achieving the goals of stabilizing alloy yield, reducing production costs, protecting the furnace lining, and improving the quality of molten steel.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for treating molten steel that has been peroxidized at the end of a converter. After the converter blowing process, the oxygen content [O] in the molten steel is detected. When the oxygen content [O] in the molten steel is greater than 450 ppm, the molten steel is determined to be in a peroxidized state. The calculated weight of granulated iron is added into the converter, and the steel is purged with nitrogen and allowed to stand for homogenization before finally being tapped. The amount of granulated iron added, M, is determined by the following formula: M = ([O] - 450) / (1000 × k) × w Where M is in kg; w is the weight of molten steel in t; [O] is the oxygen content of the molten steel at the end of the converter in ppm; and the constant k ranges from 0.065 to 0.080.

[0005] Furthermore, the granular iron is added quickly and in one go through the feeding system at the top of the converter.

[0006] Furthermore, the particle size of the granulated iron is 3mm~50mm; the chemical composition of the granulated iron, by mass percentage, is as follows: C: 4.0~6.0%, Si: 0.20~0.70%, Mn: 0.20~0.45%, P: <0.130%, S: <0.035%, with the remainder being Fe and unavoidable impurities.

[0007] Furthermore, during nitrogen purging, lower the oxygen lance to a height of 2-3m, switch to nitrogen mode, and purge for 10-20 seconds at a pressure of 1.2-1.5 MPa.

[0008] Furthermore, after nitrogen purging, the mixture is allowed to stand for 1-2 minutes to homogenize, while the bottom-blown gas is stirred at a flow rate of 700-740 Nm³ / h.

[0009] Furthermore, the bottom-blown gas is nitrogen or argon with a purity of ≥99.99%.

[0010] A second aspect of the invention provides the application of the aforementioned treatment method in reducing the oxygen content of molten steel.

[0011] The beneficial effects of this invention are: (1) This invention uses the data from the sub-gun to judge and quantify in real time, and uses the carbon-oxygen reaction to perform gas phase deoxidation. It is highly efficient and leaves no residual inclusions, which fundamentally improves the quality of molten steel.

[0012] (2) This invention solves the two core problems of "over-oxidation of molten steel" and "high FeO in slag". It creates ideal conditions for subsequent alloying, stabilizes and improves alloy yield, and significantly reduces the erosion of the furnace lining by the final slag, thereby reducing the furnace maintenance cost.

[0013] (3) The present invention has significant economic benefits. By increasing the alloy yield, reducing steel material consumption and furnace lining maintenance costs, the overall production cost is effectively reduced. At the same time, granulated iron is widely available and inexpensive, realizing "waste treatment".

[0014] (4) The process of this invention is simple. This method makes full use of existing converter equipment, requires no major modifications, has a simple operation process, short processing time, and is fully compatible with the existing fast-paced production mode without affecting production efficiency.

[0015] (5) This invention promotes the production of clean steel. The nitrogen purging and settling process promotes the flotation and removal of deoxidation products and inclusions, further purifying the molten steel and laying the foundation for the production of high-quality steel.

[0016] (6) The method described in this invention can flexibly control the amount of granulated iron added by adjusting the coefficient k according to the degree of peroxidation in actual production. It has wide adaptability and stable and reliable effect. Detailed Implementation

[0017] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0018] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0019] The core principle of this invention is the utilization of the carbon-oxygen reaction. The granular iron, rich in carbon (4.0~6.0%), rapidly reacts with excess dissolved oxygen in the molten steel after being added at high temperatures: [C] + [O] = CO. The generated CO gas escapes in the form of bubbles, effectively reducing the oxygen content in the molten steel without leaving solid inclusions. Furthermore, some carbon reacts with FeO in the slag: (FeO) + [C] = [Fe] + CO, thereby reducing the FeO content in the slag, protecting the furnace lining, reducing iron back to the molten steel, and improving metal recovery. The specific method is as follows: 1. Prepare granulated iron with a particle size of 3mm~50mm and transport it to the high-level silo of the converter for later use; the chemical composition of the granulated iron by mass percentage is: C: 4.0~6.0%, Si: 0.20~0.70%, Mn: 0.20~0.45%, P: <0.130%, S: <0.035%, with the remainder being Fe and unavoidable impurities.

[0020] 2. Endpoint determination. After the converter blowing is completed, the oxygen content [O] in the molten steel is detected by the auxiliary lance. When the oxygen content [O] in the molten steel is greater than 450 ppm, the molten steel is determined to be in an over-oxidized state, and this treatment method is activated.

[0021] 3. Determine the amount of granulated iron to be added based on the degree of peroxidation (actual value of [O]). The amount of granulated iron to be added, M (kg), is determined by the following formula: M=([O]-450) / (1000×k)×w Where w is the weight of molten steel (t), [O] is the oxygen content (ppm) measured at the end of the converter's auxiliary lance, and k is a value ranging from 0.065 to 0.080.

[0022] 4. Adding granulated iron. The granulated iron calculated in step 3 is added to the converter in one go through the feeding system at the top of the converter.

[0023] 5. Nitrogen purging. After the granulated iron is added, lower the oxygen lance to a height of 2-3m and switch to nitrogen mode. Purge for 10-20 seconds at a pressure of 1.2-1.5 MPa to strongly stir the molten pool, promote the melting and dissolution of the granulated iron, and facilitate its full reaction with the molten steel and slag.

[0024] 6. Settling and homogenization. After nitrogen purging, let stand for 1-2 minutes while maintaining bottom blowing gas (nitrogen or argon, purity ≥99.99%) stirring, with the flow rate controlled at 720 Nm³ / h, to allow deoxidation products to float, steel slag to react fully, and to achieve homogenization of steel composition and temperature.

[0025] 7. Steel tapping: After completing the above steps, proceed with the normal steel tapping operation, and carry out alloying and deoxidation operations according to conventional processes.

[0026] The test materials used in the embodiments of this invention, unless otherwise specified, are all conventional test materials in the art and can be purchased through commercial channels. The experiments of this invention were conducted in a 120t converter, which can hold a maximum of 144t of metal material.

[0027] Example 1 The molten Q235B carbon steel was smelted using a 120-ton converter. After the smelting was completed, the oxygen content [O] of the molten steel was measured at 628 ppm by the auxiliary lance, which was determined to be over-oxidized.

[0028] Step 1: Take granulated iron that meets the chemical composition requirements for later use.

[0029] Step 2: The weight of the molten steel is w = 130t.

[0030] Step 3: Calculate the range of granulated iron addition based on the maximum and minimum values ​​of coefficient k: 289~356kg; Step 4: Weigh 320kg of granulated iron from the silo. Since it is within the calculation range, add it to the converter in one go through the feeding system.

[0031] Step 5: Lower the gun to a position of 2.50m and purge with nitrogen gas at a pressure of 1.3Mpa for 15 seconds.

[0032] Step 6: Let stand for 1.6 minutes, while maintaining the bottom blowing gas flow rate at 720 Nm³ / h.

[0033] Step 7: After the settling period, tap the steel.

[0034] Tests showed that the FeO content in the final slag was 13.28%; calculations showed that the yields of silicon manganese and ferromanganese were both consistently above 90% during the alloying process of this furnace.

[0035] Example 2 The molten Q355B carbon steel was smelted using a 120-ton converter. After the smelting was completed, the oxygen content [O] of the molten steel was measured at 1022 ppm by the auxiliary lance, which was determined to be over-oxidized.

[0036] Step 1: Take granulated iron that meets the chemical composition requirements for later use.

[0037] Step 2: The weight of the molten steel is w = 130t.

[0038] Step 3: Calculate the range of granulated iron addition based on the maximum and minimum values ​​of coefficient k: 925~1138kg; Step 4: Weigh 1028 kg of granular iron from the silo. Since it is within the calculation range, add it to the converter in one go through the feeding system.

[0039] Step 5: Lower the gun to the 2.80m position and purge with nitrogen gas at a pressure of 1.36 MPa for 18 seconds.

[0040] Step 6: Let stand for 1.2 minutes, while maintaining the bottom blowing gas flow rate at 720 Nm³ / h.

[0041] Step 7: After the settling period, tap the steel.

[0042] Tests showed that the FeO content in the final slag was 13.58%; calculations showed that the yields of silicon manganese and ferromanganese were both consistently above 90% during the alloying process of this furnace.

[0043] Example 3 The molten Q355C carbon steel was smelted using a 120-ton converter. After the smelting was completed, the oxygen content [O] of the molten steel was measured at 829 ppm by the auxiliary lance, which was determined to be over-oxidized.

[0044] Step 1: Take granulated iron that meets the chemical composition requirements for later use.

[0045] Step 2: The weight of the molten steel is w = 130t.

[0046] Step 3: Calculate the range of granulated iron addition based on the maximum and minimum values ​​of coefficient k: 613~754kg; Step 4: The hopper weighs 656 kg of granular iron, which is within the calculation range, and adds it to the converter in one go through the feeding system.

[0047] Step 5: Lower the gun to a position of 2.20m and purge with nitrogen gas at a pressure of 1.40Mpa for 12 seconds.

[0048] Step 6: Let stand for 1.5 minutes, while maintaining the bottom blowing gas flow rate at 720 Nm³ / h.

[0049] Step 7: After the settling period, tap the steel.

[0050] Tests showed that the FeO content in the final slag was 13.85%; calculations showed that the yields of silicon manganese and ferromanganese were both consistently above 90% during the alloying process of this furnace.

[0051] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for treating peroxide-treated molten steel at the end of a converter, characterized in that, After the converter blowing is completed, the oxygen content [O] in the molten steel is tested. When the oxygen content [O] in the molten steel is greater than 450 ppm, it is determined that the molten steel is in an over-oxidized state. The calculated weight of granulated iron is added into the converter, and after nitrogen purging and static homogenization, the steel is finally tapped. The amount of granulated iron added, M, is determined by the following formula: M = ([O] - 450) / (1000 × k) × w Where M is in kg; w is the weight of molten steel in t; [O] is the oxygen content of the molten steel at the end of the converter in ppm; and the constant k ranges from 0.065 to 0.

080.

2. The method for treating the peroxide-treated molten steel at the converter endpoint according to claim 1, characterized in that, When adding granular iron, it is added quickly and all at once through the feeding system at the top of the converter.

3. The method for treating the peroxide-treated molten steel at the converter endpoint according to claim 1, characterized in that, The particle size of the granulated iron is 3mm~50mm; the chemical composition of the granulated iron by mass percentage is as follows: C: 4.0~6.0%, Si: 0.20~0.70%, Mn: 0.20~0.45%, P: <0.130%, S: <0.035%, with the remainder being Fe and unavoidable impurities.

4. The method for treating the peroxide-treated molten steel at the converter endpoint according to claim 1, characterized in that, When purging with nitrogen, lower the oxygen lance to a height of 2-3m, switch to nitrogen mode, and purge for 10-20 seconds at a pressure of 1.2-1.5 MPa.

5. The method for treating the peroxide-treated molten steel at the converter endpoint according to claim 1, characterized in that, After nitrogen purging, allow the mixture to stand for 1-2 minutes to homogenize, while maintaining bottom-blown gas stirring at a flow rate of 700-740 Nm³ / h.

6. The method for treating the peroxide-treated molten steel at the converter endpoint according to claim 5, characterized in that, The bottom-blown gas is nitrogen or argon with a purity of ≥99.99%.

7. The application of the treatment method according to any one of claims 1-6 in reducing the oxygen content of molten steel.