Converter phosphorus-retaining smelting process

Abstract

The invention belongs to the technical field of converter steelmaking, and particularly relates to a converter phosphorus-retaining smelting process. According to the method, the binary alkalinity R of the slag is always controlled to be 2.0-2.5, and the oxygen flow is large and 22000 m < 3 > / h in the whole process; and the gun position is controlled to be 1200-1400 mm, and the early-stage gun position is 1200 mm, so that early-stage temperature rise is accelerated, a decarburization stage is quickly entered, dephosphorization is inhibited, the loss of molten steel is reduced, the steel tapping amount is increased, the consumption of steel and iron materials is reduced, and meanwhile, the smelting cost is reduced. The phosphorus retention rate in the molten iron reaches 33-55% under the condition that phosphorus-containing alloy is not added, the requirements of various phosphorus-containing steel types are met, and the method is suitable for large and medium-sized converter phosphorus-retaining smelting methods.

Description

Technical Field

[0001] The invention belongs to the technical field of converter steelmaking, in particular to a converter phosphorus-preserving smelting process. Background Art

[0002] One of the basic tasks in the steelmaking process is dephosphorization, which is one of the harmful elements in steel. Generally, phosphorus reduces the toughness of steel, and the most prominent harm of phosphorus is cold brittleness, so in the smelting process, phosphorus is generally controlled as low as possible. For weathering steel and free-cutting steel, phosphorus is a beneficial element. A certain phosphorus content in the finished product can improve the corrosion resistance, hardness, and impact resistance of the steel. In traditional smelting methods, it is impossible to ensure that phosphorus is at a high level under high alkalinity and large slag volume.

[0003] The mainstream steel mills in China that produce weathering steel and free-cutting steel use converter smelting, in which ferrophosphorus alloying is used to meet the chemical composition requirements. Converter smelting uses molten iron from blast furnaces and scrap steel as raw materials. The molten iron contains a high level of phosphorus, but it is removed during the oxygen decarburization process. Each furnace of weathering steel and free-cutting steel produced by blast furnace steel needs to add 60-100kg of ferrophosphorus, which is high in production cost. There are cutting-edge researches in the prior art. For example, a method for smelting high-phosphorus weathering steel with vanadium-extracting semi-steel is disclosed in application number CN201710432507.8. The steelmaking converter is loaded with vanadium-extracting semi-steel, scrap steel, nickel plate and copper plate; the amount of scrap steel added is controlled at 6-8%; Si+Ti+Mn≤0.10wt%, C 3.40-3.90wt% in the vanadium-extracting semi-steel, and the temperature is 1350-1400°C. This method is based on the fact that the silicon, titanium and manganese contents in the semi-steel are traces. The converter steelmaking reduces the scrap steel ratio, slag basicity and slag-making material addition amount during the blowing process, controls the gun position and oxygen flow rate during the blowing process, increases the final tapping temperature, and removes an appropriate amount of slag after tapping, so as to achieve the purpose of high phosphorus in the final molten steel of weathering steel smelted by semi-steel. However, this method depends on the adjustment of the components of the raw materials, and there are certain difficulties in its promotion, and it is not cost-effective. For another example, application number CN201110389717.6 is a converter steelmaking phosphorus-preserving smelting method, which divides the smelting time into three stages: the front, middle and back stages. By adjusting the amount of lime added, the binary basicity R of the slag is always controlled between 2.0 and 2.8; by adjusting the flow rate and gun position of the oxygen lance, the mass percentage of the oxygen blowing amount in the front, middle and back stages to the total oxygen blowing amount is controlled at 18-22%, 55-65% and 18-22% respectively, and the oxygen jet impact depth in the early and middle stages is controlled at 60-70% of the molten steel depth, and the oxygen jet impact depth in the later stage is controlled at 70-80% of the molten steel depth; the residual carbon content in the final molten steel is controlled at 0.05-0.1%, and the phosphorus retention rate in the molten iron can reach 30% to 70% without adding phosphorus-containing ore, thereby achieving the required phosphorus-preserving smelting, but the performance of the final formed product needs to be further improved. Therefore, how to optimize the converter smelting process, effectively utilize the phosphorus in molten iron, and eliminate the use of ferrophosphorus is a technical problem that the industry urgently needs to solve. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention proposes a converter phosphorus retention smelting process, which can achieve a phosphorus retention rate of 33-55% in molten iron without adding phosphorus-containing alloys, meet the requirements of various phosphorus-containing steel grades, and is suitable for large and medium-sized converter phosphorus retention smelting methods.

[0005] The converter phosphorus smelting method of the present invention controls the binary basicity R of the slag to be between 2.0 and 2.5 at all times, and the oxygen flow rate is a large flow rate of 22000m 3 / h; The gun position is controlled at 1200mm-1400mm, the early gun position is 1200mm, which speeds up the early temperature rise, quickly enters the decarburization period, and inhibits dephosphorization. The process gun position is 1200-1400mm to control the process metal splashing, and the later gun position is 1200mm; the terminal temperature is controlled at 1640-1680℃.

[0006] Research shows that binary basicity is an important factor in controlling phosphorus content. Higher binary basicity is conducive to dephosphorization, but not conducive to phosphorus retention. When the binary basicity is too low, the slag becomes acidic slag, corroding the furnace lining and not conducive to furnace protection. The binary basicity explored above can maintain the phosphorus content of molten iron without damaging the furnace lining. Therefore, without using any phosphorus-containing alloys, the phosphorus retention rate of molten iron is between 33-55%, achieving the phosphorus content requirements for smelting high-phosphorus steels such as weathering steel and free-cutting steel.

[0007] At the same time, after adopting the present invention, the basicity is controlled at 2.0-2.5, the usage of slag-making raw materials is reduced, the amount of slag is reduced, thereby reducing the loss of molten steel, increasing the output of steel, reducing the consumption of steel materials, and reducing the smelting cost.

[0008] In addition to the above phosphorus conservation measures, they also include: 1) Do not add lime to make slag, only use lightly burned dolomite to make slag, and control the magnesium oxide content of the slag to 10-15%. Under the condition that the basicity of the slag is controlled at 2.0-2.5, the magnesium oxide of the slag reaches saturation, and the magnesium oxide content of the slag usually reaches more than 15%, which increases the viscosity of the slag, reduces the erosion of the slag on the furnace lining and the role of phosphorus retention.

[0009] 2) While ensuring that there is no splashing during the process, appropriately increase the oxygen supply intensity to reduce the oxidizing nature of the slag.

[0010] 3) High temperature is conducive to phosphorus retention, so the converter final temperature is best controlled between 1640-1680℃; preferably 1670℃.

[0011] Beneficial effects of the present invention: The present invention enables the phosphorus retention rate in molten iron to reach 33-55% without adding phosphorus-containing alloys, meets the requirements of various phosphorus-containing steel grades, and is suitable for large and medium-sized converter phosphorus-retaining smelting methods. Binary basicity is an important factor in controlling phosphorus content. Higher binary basicity is conducive to dephosphorization, but not conducive to phosphorus retention. When the binary basicity is too low, the slag becomes acidic slag, corrodes the furnace lining, and is not conducive to furnace protection. The binary basicity explored above can retain the phosphorus content of molten iron without damaging the furnace lining. Therefore, without using any phosphorus-containing alloys, the phosphorus retention rate of molten iron is between 33-55%, achieving the phosphorus content requirements of smelting high-phosphorus steel grades such as weathering steel and free-cutting steel.

[0012] At the same time, after adopting the present invention, the basicity is controlled at 2.0-2.5, the usage of slag-making raw materials is reduced, the amount of slag is reduced, thereby reducing the loss of molten steel, increasing the output of steel, reducing the consumption of steel materials, and reducing the smelting cost, increasing the viscosity of the slag, and reducing the erosion of the slag on the furnace lining and the phosphorus retention effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a photo of the gun position during the converter process; Figure 2 This is a photo of the oxygen lance flow rate in the converter process. DETAILED DESCRIPTION

[0014] The technical solution of the present invention is further defined below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.

[0015] Example 1 A converter phosphorus-retaining smelting process: 1. Blast furnace molten iron conditions The rest is iron and inevitable impurities 2. Converter loading: 83.4t of hot metal + 10t of scrap steel, total loading 93.4t. Among them, the scrap steel is ordinary social scrap steel, and there is no special requirement for scrap steel.

[0016] 3. Converter smelting Early stage of converter: after normal ignition, add 1500kg, without lime, the total amount of slag-making light-burned dolomite is controlled at 20-25kg / ton steel, using 22000m 3 / h large flow rate for oxygen blowing smelting, the gun position is controlled at the lowest gun position of 1200mm, the temperature is raised quickly, the decarburization period is entered as early as possible, and the oxygen blowing time is 3.5 minutes.

[0017] In the middle stage of converter: as the temperature rises, the remaining light-burned dolomite is added in small batches, with a total amount of 3020kg. A large flow of oxygen is blown throughout the process, and the gun position is adjusted at 1200-1400mm. Cold material is used to control the process temperature to prevent metal splashing caused by too fast heating. The oxygen blowing time is 8 minutes.

[0018] Late stage of converter: maintain high flow rate oxygen blowing smelting throughout the whole process, the final pressure lance position is 1200mm, the final carbon content is 0.05%, the steel-out temperature is 1658℃, the steel-out phosphorus is 0.065%, no need to add ferrophosphorus, and the finished product phosphorus is 0.062%.

[0019] 4. Slag composition Example 2 A converter phosphorus-retaining smelting process: 1. Blast furnace molten iron conditions The rest is iron and inevitable impurities 2. Converter charge: 89t molten iron + 8t scrap steel, total charge 97t, of which the scrap steel is ordinary social scrap steel and there is no special requirement for scrap steel.

[0020] 3. Converter smelting Early stage of converter: after normal ignition, add 1300kg, without lime, the total amount of slag-making light-burned dolomite is controlled at 20-25kg / ton steel, using 22000m 3 / h large flow rate for oxygen blowing smelting, the gun position is controlled at the lowest gun position of 1200mm, the temperature is raised quickly, the decarburization period is entered as early as possible, and the oxygen blowing time is 3.5 minutes.

[0021] In the middle stage of converter: as the temperature rises, the remaining light-burned dolomite is added in small batches, with a total amount of 3500kg. A large flow of oxygen is blown throughout the process, and the gun position is adjusted at 1200-1400mm. Cold material is used to control the process temperature to prevent metal splashing caused by too fast heating. The oxygen blowing time is 8 minutes.

[0022] Late stage of converter: maintain high flow rate oxygen blowing smelting throughout the whole process, the final pressure lance position is 1200mm, the final carbon content is 0.04%, the steel tapping temperature is 1647℃, the steel tapping phosphorus is 0.073%, no need to add ferrophosphorus, and the finished product phosphorus is 0.074%.

[0023] 4. Slag composition Example 3 A converter phosphorus-retaining smelting process: 1. Composition of blast furnace molten iron The rest is iron and inevitable impurities 2. Converter charge: 85.5t molten iron + 9t scrap steel, total charge 94.5t, of which the scrap steel is ordinary social scrap steel and there is no special requirement for scrap steel.

[0024] 3. Converter smelting Early stage of converter: after normal ignition, add 1822kg, without lime, the total amount of slag-making light-burned dolomite is controlled at 20-25kg / ton steel, using 22000m 3 / h large flow rate for oxygen blowing smelting, the gun position is controlled at the lowest gun position of 1200mm, the temperature is raised quickly, the decarburization period is entered as early as possible, and the oxygen blowing time is 3.5 minutes.

[0025] In the middle stage of converter: as the temperature rises, the remaining light-burned dolomite is added in small batches, with a total amount of 3800kg. A large flow of oxygen is blown throughout the process, and the gun position is adjusted at 1200-1400mm. Cold material is used to control the process temperature to prevent metal splashing caused by too fast heating, and the oxygen blowing time is 8 minutes.

[0026] Late stage of converter: maintain high flow rate oxygen blowing smelting throughout the whole process, the final pressure lance position is 1200mm, the final carbon content is 0.047%, the steel tapping temperature is 1670℃, the steel tapping phosphorus is 0.093%, no need to add ferrophosphorus, and the finished product phosphorus is 0.096%.

[0027] 4. Slag composition

Claims

1. A converter phosphorus-retaining smelting process, characterized in that: The steps include: 1) Use light-burned dolomite to make slag and control the magnesium oxide content of the slag to 10-15%; 2) Under the condition that the slag basicity is controlled at 2.0-2.5 in advance, the magnesium oxide in the slag reaches saturation; Improve the oxygen supply intensity and reduce the oxidizability of the slag; the process gun position is controlled between 1200-1400mm; 3) Control the converter temperature to 1640-1680℃.

2. A converter phosphorus-retaining smelting process according to claim 1, characterized in that: In step 1), the total amount of dolomite is controlled at 20-25 kg / ton of steel.

3. A converter phosphorus-retaining smelting process according to claim 1, characterized in that: In step 2), the oxygen flow rate for increasing the oxygen supply intensity is 22000m 3 / h.

4. A converter phosphorus-retaining smelting process according to claim 1, characterized in that: In step 2), the specific operation of controlling the gun position at 1200mm-1400mm is as follows: the early gun position is 1200mm, accelerating the early temperature rise, quickly entering the decarburization period, inhibiting dephosphorization, the process gun position is 1200-1400mm, controlling the process metal splashing, and the late gun position is 1200mm.

5. A converter phosphorus-retaining smelting process according to claim 1, characterized in that: In step 3), the temperature of the converter is controlled as follows: the tapping temperature is 1640-1680°C, and the mid-term temperature is controlled at 1680°C.

6. A converter phosphorus-retaining smelting process according to claim 5, characterized in that: The steel tapping temperature is 1670°C.

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