LF (Ladle Furnace) desulfurization method for high-sulfur molten iron

Abstract

The invention belongs to the technical field of steelmaking processes, and particularly relates to an LF furnace desulfurization method for high-sulfur molten iron. Comprising the following steps that (1) passivated lime and passivated magnesium powder are injected for desulfurization, the injection treatment time is 400-700 seconds, and when the S content is 0.050-0.060%, a converter working procedure is carried out; (2) active lime, high-magnesium lime and a slag former are added, the alloy is added when one third of tapping is carried out, and the active lime is added into a steel ladle when converter molten steel leaves a station; and (3) when the molten steel enters an LF (ladle furnace), firstly carrying out oxygen determination and aluminum wire feeding, controlling Als in the molten steel to a steel judgment middle limit, then carrying out arc starting and slagging, adding aluminum particles, lime and a fluoride-free slagging agent in two batches after 2 minutes, carrying out bottom blowing of argon, carrying out secondary temperature measurement and oxygen determination after slagging is completed, carrying out submerged arc after alloy addition is completed, and adding a high-aluminum slag modifier. The method has the effect of improving the castability of the molten steel, a slag system better meets the cleanliness requirement, and harmful inclusions in the molten steel are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking technology, and in particular to a LF furnace desulfurization method for high-sulfur molten iron. Background Art

[0002] Except for special steels such as cutting steel, the S element is a harmful element in steel. The S element exists in the form of iron sulfide in steel. It has a low melting point and is easily melted at high temperatures, causing the steel to crack during hot working. This phenomenon is called hot brittleness. The specific effects of the S element on the performance of steel include: reducing the ductility and toughness of the steel and increasing the risk of fracture. During hot working, the workpiece cracks due to the premature melting of iron sulfide. In addition, the S element also affects welding performance and reduces corrosion resistance. Therefore, it is necessary to reduce the S content in molten steel during the steelmaking process.

[0003] At present, the common low-sulfur steel smelting process is: hot metal pretreatment - converter smelting - LF refining - RH vacuum refining - continuous casting. The desulfurization process in hot metal pretreatment generally requires sulfur to be removed to less than 0.005%. The converter adds scrap steel, auxiliary materials, etc. containing sulfur elements or slag surface sulfur. Generally, LF is the last desulfurization process. In recent years, the hot metal conditions of major domestic steel mills have gradually deteriorated, especially the hot metal S conditions are generally high, and the S content ranges from 0.100-0.200%. Therefore, it is a difficult problem for major companies to study the method of LF furnace to undertake desulfurization tasks and implement it efficiently and economically. Summary of the invention

[0004] The purpose of the present invention is to propose a LF furnace desulfurization method for high-S molten iron, which does not require the use of pre-melted slag and only requires changing the timing, amount and sequence of adding raw materials to overcome the shortcomings of the prior art.

[0005] To achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows:

[0006] A method for desulfurizing a high-sulfur hot metal in an LF furnace, comprising the following steps:

[0007] (1) Desulfurization process

[0008] Spray passivated lime and passivated magnesium powder for desulfurization, the spraying time is 600-700 seconds, and the converter process is entered when the S content is 0.050-0.060%;

[0009] (2) Converter process

[0010] Active lime, high-magnesium lime and slag-making agent are added. The alloy is added when 1 / 3 of the steel is tapped. Active lime is added to the ladle when the converter molten steel is discharged.

[0011] (3) LF process

[0012] When the molten steel enters the LF, first determine the oxygen and feed aluminum wire to control the Als in the molten steel to the middle limit of steel judgment. Then, start the arc to make slag. After 2 minutes, add aluminum particles, white lime, and fluoride-free slag-making agent in two batches. Bottom-blow argon at 2.00 MPa with a flow intensity of 30 - 50 m 3 / h. After slag-making, measure the temperature and determine the oxygen for the second time. If Als < 0.01%, conduct secondary slag-making. Then, add white lime, fluoride-free slag-making agent, and high-aluminum slag-adjusting agent for alloying. After the alloy addition is completed, carry out submerged arc. Finally, adjust the argon flow intensity to 10 - 20 m 3 / h and soft blow for 8 minutes.

[0013] In the above technical solution, further, in the desulfurization process, the addition amount of passivated lime is 1.0 - 5.0 kg / ton of steel, and the addition amount of passivated magnesium powder is 0.4 - 1.5 kg / ton of steel.

[0014] In the above technical solution, further, in the converter process, the addition amount of active lime is 17 - 21 kg / ton of steel, the addition amount of high-magnesium lime is 9 - 16 kg / ton of steel, the addition amount of slag-making agent is 0 - 5 kg / ton of steel, and the addition amount of active lime in the ladle during tapping is 0 - 5 kg / ton of steel.

[0015] In the above technical solution, further, in the LF process, the addition amount of the first batch of aluminum particles is 80 ± 20 kg, the addition amount of white lime is 200 kg, the addition amount of fluoride-free slag-making agent is 180 kg, the addition amount of the second batch of aluminum particles is 50 ± 20 kg, the addition amount of white lime is 300 kg, the addition amount of fluoride-free slag-making agent is 120 kg. If the incoming S > 0.050%, on the basis of 0.050%, for every 0.010% increase, 15 kg more of the second batch of aluminum particles is added.

[0016] In the above technical solution, further, in the LF process, the addition amount of white lime is 0 - 200 kg, the addition amount of fluoride-free slag-making agent is 50 kg, and the addition amount of high-aluminum slag-adjusting agent is 150 kg.

[0017] In the above technical solution, further, in the LF process, according to the LF slag-making sample, feed aluminum wire according to Als lower limit + 0.025%. When Als < Als steel judgment lower limit + 0.025% after slag-making, the amount of aluminum wire fed (unit: meter) = (Als steel judgment lower limit + 0.025% - incoming sample Als) * 10000 * 80. When Als ≥ Als steel judgment lower limit + 0.025% after slag-making, do not feed aluminum wire.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. The method of the present invention saves the cost and time of hot metal pretreatment, and the cost and time of the remaining processes increase little, achieving the purpose of low-cost and high-efficiency desulfurization.

[0020] 2. The present invention does not require the use of refined pre-melted slag, and has no essential path change compared with the original technology. The purpose can be achieved by simply adjusting the raw material ratio and the timing of addition.

[0021] 3. The present invention has the effect of improving the castability of molten steel. By adopting the LF furnace desulfurization method of the present invention, the slag system is made to better meet the cleanliness requirements and reduce harmful inclusions in the molten steel. DETAILED DESCRIPTION

[0022] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0023] Example 1

[0024] The test was conducted using Q235B (improved) steel, with a ladle of 220t, and included the following steps:

[0025] (1) molten iron inlet [S] = 0.139%, desulfurization process spraying time 420 seconds, passivation magnesium powder consumption 100 kg, passivation lime consumption 373 kg, after desulfurization treatment [S] = 0.051%;

[0026] (2) In the converter process, 4000 kg of lime, 2600 kg of high-magnesium lime and 70 kg of slag-making agent were added. All materials were added in batches during the smelting process. The alloy was added when 1 / 3 of the steel was discharged. 900 kg of active lime was added to the ladle when the steel was discharged. The end point [S] = 0.081%. The full analysis sample [S] = 0.074% and [Als] = 0.0170% were taken later.

[0027] (3) When the molten steel enters the LF station, the temperature and oxygen are measured at 1566°C, [O] = 2.894 ppm, and the slag is heated for 12 minutes. After 2 minutes of arc slag formation, the first batch of materials is added in sequence: 80 kg of aluminum particles, 200 kg of lime, and 180 kg of fluoride-free slag agent. Three minutes after the first batch of materials is added, the second batch of materials is added in sequence: 80 kg of aluminum particles, 300 kg of lime, and 120 kg of fluoride-free slag agent. The bottom blowing of argon gas is 2.00 MPa, and the flow intensity is 30-50 m 3 / h; The furnace steel has no Als requirement, and is controlled according to the general upper limit of 0.045%. Therefore, the furnace does not need to feed aluminum wire. After slag making, take the LF inlet sample composition, [Als] = 0.0302%, and then make alloying fine adjustments, add 100kg of white ash, 50kg of non-fluorinated slag agent, and 100kg of high-aluminum slag adjusting agent. This process lasts for 10 minutes, and finally blows argon at an intensity of 10-20m 3 / h for 8 minutes, and take LF off-station samples, [S] = 0.014%, which is in line with the regulations.

[0028] Example 2

[0029] The test was conducted using Q355B (thin) steel with a ladle of 220t, including the following steps:

[0030] (1) molten iron input [S] = 0.131%, desulfurization process spraying time 480 seconds, passivation magnesium consumption 103 kg, passivation lime consumption 430 kg, after desulfurization treatment [S] = 0.050%;

[0031] (2) In the converter process, 4000 kg of lime, 2400 kg of high-magnesium lime and 70 kg of slag-making agent were added. All materials were added in batches during the smelting process. The alloy was added when 1 / 3 of the steel was discharged. 900 kg of active lime was added to the ladle when the steel was discharged. The end point [S] = 0.064%. The subsequent full analysis sample [S] = 0.078%, [Als] = 0.0204%;

[0032] (3) When the molten steel enters the LF station, the temperature and oxygen are measured at 1565°C, [O] = 5.787 ppm, and the slag is heated for 12 minutes. After 2 minutes of arcing and slag making, the first batch of materials is added in sequence: 80 kg of aluminum particles, 200 kg of lime, and 180 kg of fluoride-free slag agent; 3 minutes after the first batch of materials is added, the second batch of materials is added in sequence: 80 kg of aluminum particles, 300 kg of lime, and 120 kg of fluoride-free slag agent; the bottom blowing of argon gas is 2.00 MPa, and the flow intensity is 30-50 m 3 / h; the Als of the steel in this furnace is required to be controlled within the range of 0.010%-0.050%. The midway sampling [Als] = 0.047%, which is on the upper limit. Therefore, the furnace does not need to feed aluminum wire. Then, alloying fine-tuning is performed by adding 100kg of white ash, 50kg of non-fluorinated slag agent, and 100kg of high-aluminum slag adjusting agent. This process lasts for 10 minutes. After the alloy is added, the arc is buried. Finally, the argon blowing intensity is 10-20m 3 / h for 8 minutes, and take LF off-station samples, [S] = 0.008%, [Als] = 0.030%, which is in line with the regulations.

[0033] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the implementation methods. The protection scope of the present invention shall be subject to the scope defined in the claims. Other different forms of changes or modifications may be made based on the above description. Obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for desulfurizing high-sulfur hot metal in an LF furnace, characterized in that: It includes the following steps: (1) Desulfurization process Inject passivated lime and passivated magnesium powder for desulfurization. The injection treatment time is 400 - 700 seconds. When the S content is 0.050 - 0.060%, it enters the converter process; (2) Converter process Add active lime, high - magnesium lime and slag - forming agent. The alloy is added when 1 / 3 of the steel is tapped. When the converter molten steel leaves the station, active lime is added to the ladle; (3) LF process When the molten steel enters the LF, the aluminum wire is first fed with oxygen to control the Als in the molten steel to the steel judgment limit, then the arc is started to make slag, and aluminum particles, lime and non-fluorinated slag agent are added in two batches after 2 minutes, and argon gas is blown at 2.00MPa at the bottom, with a flow intensity of 30-50m 3 / h, after slagging, the temperature and oxygen are measured again. If Als < 0.01%, secondary slagging is carried out, and then lime, non-fluorinated slag agent, and high-aluminum slag agent are added for alloying. After the alloy is added, the arc is buried. Finally, the argon flow intensity is adjusted to 10-20m 3 / h, soft blowing for 8min.

2. The smelting method for desulfurization of high-sulfur molten iron according to claim 1, characterized in that: In the desulfurization process, the addition amount of passivated lime is 1.0 - 5.0 kg / ton of steel, and the addition amount of passivated magnesium powder is 0.4 - 1.5 kg / ton of steel.

3. The smelting method for desulfurization of high-sulfur molten iron according to claim 1, characterized in that: In the converter process, the addition amount of active lime is 17 - 21 kg / ton of steel, the addition amount of high - magnesium lime is 9 - 16 kg / ton of steel, the addition amount of slag - forming agent is 0 - 5 kg / ton of steel, and the addition amount of active lime in the ladle during tapping is 0 - 5 kg / ton of steel.

4. The smelting method for desulfurization of high-sulfur molten iron according to claim 1, characterized in that: In the LF process, the addition amount of the first batch of aluminum pellets is 80 ± 20 kg, the addition amount of white lime is 200 kg, the addition amount of non - fluorinated slag agent is 180 kg, the addition amount of the second batch of aluminum pellets is 50 ± 20 kg, the addition amount of white lime is 300 kg, the addition amount of non - fluorinated slag agent is 120 kg. If the incoming - station S > 0.050%, on the basis of 0.050%, for every 0.010% increase, 15 kg more of the second - batch aluminum pellets are added.

5. The smelting method for desulfurization of high-sulfur molten iron according to claim 1, characterized in that: In the LF process, the addition amount of white lime is 0 - 200 kg, the addition amount of non - fluorinated slag agent is 50 kg, and the addition amount of high - aluminum slag - adjusting agent is 150 kg.

6. The smelting method for desulfurization of high-sulfur molten iron according to claim 1, characterized in that: In the LF process, according to the LF slag - making sample, feed aluminum wire at Als lower limit + 0.025%. When Als < Als steel - judging lower limit + 0.025% after slag - making is completed, the amount of aluminum wire fed (unit: meter) = (Als steel - judging lower limit + 0.025% - incoming - station sample Als) * 10000 * 80. When Als ≥ Als steel - judging lower limit + 0.025% after slag - making is completed, no aluminum wire is fed.