A method of vacuum chamber calcium treatment

Abstract

The application discloses a method for calcium treatment in a vacuum chamber, which mainly comprises the following steps: adding calcium-containing alloy and other alloy into molten high-silicon steel in a vacuum state, and simultaneously performing calcium treatment and alloying, so as to improve the calcium yield in the vacuum state, reduce calcium treatment spatter, relieve the spatter of steel slag in the vacuum chamber during the calcium treatment process, and simultaneously reduce the calcium treatment cost. The calcium treatment process of the application replaces the traditional calcium treatment mode of a wire feeder, and solves the difficulty of wire feeding in the vacuum state. The application fully utilizes the trace calcium in ordinary ferrosilicon to perform calcium treatment on molten steel, replaces calcium-silicon alloy, mixes and feeds high-purity ferrosilicon and ordinary ferrosilicon after RH decarburization, determines the proportion according to the silicon content and carbon content of the two kinds of ferrosilicon, and simultaneously performs calcium treatment and alloying.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, and specifically relates to a method for calcium treatment in a vacuum chamber. Background Technology

[0002] Currently, the steel grades used in CSP continuous casting machines are mainly aluminum-killed steel grades. Under high casting speeds, the tundish does not have the ability to remove inclusions, and the requirements for the purity and fluidity of the molten steel are very stringent. In order to ensure the castability of the molten steel, all aluminum-containing steel grades produced by CSP casting machines must undergo calcium treatment to generate low-melting-point inclusions.

[0003] Normally, calcium treatment of aluminum-containing molten steel is mainly carried out by feeding calcium wire through a wire feeder. After steel refining, calcium treatment is carried out by feeding calcium wires such as aluminum-calcium wire, silicon-calcium wire, and pure calcium wire to form low-melting-point inclusions and improve the pourability of molten steel.

[0004] There are two methods for calcium treatment in RH furnaces. One method is to break the vacuum after steel refining and use a wire feeder to treat the molten steel with calcium. The other method is to add a calcium-containing alloy to the molten steel in a vacuum chamber after refining. This method has the problem of low calcium recovery rate under vacuum conditions. Under negative pressure, the calcium alloy evaporates at the temperature of the molten steel and is drawn away. At the same time, the violent reaction in the vacuum chamber causes severe molten steel splashing, and a large amount of molten steel splashes into the hot bending tube, resulting in severe steel adhesion inside the hot bending tube.

[0005] Ordinary ferrosilicon contains less than 0.03% carbon and up to 1.5% calcium. The trace amounts of calcium in ferrosilicon can be fully utilized for calcium treatment of molten steel, achieving both alloying and calcium treatment. However, considering the relatively high carbon content of ordinary ferrosilicon, it cannot be used exclusively for both alloying and calcium treatment. This invention, based on the steel composition control requirements, first uses ultra-low carbon ferrosilicon for alloying, and then adds ordinary ferrosilicon calcium treatment according to the acceptable carbon content, achieving an optimal control ratio that satisfies composition control requirements while simultaneously performing calcium treatment. Summary of the Invention

[0006] This invention provides a method for calcium treatment using trace amounts of calcium in ferrosilicon under vacuum conditions. This method performs calcium treatment simultaneously with alloying, which solves the problem of calcium sputtering during calcium treatment and reduces production costs.

[0007] Therefore, the present invention adopts the following technical solution: A method for treating calcium in a vacuum chamber includes the following steps: Step 1: Converter boiling tapping. During the tapping process, add 200-500 kg of lime, 120 kg of fluorite, and 100 kg of steel slag modifier. Immediately after tapping, shut off the bottom blowing argon to ensure the total oxygen content in the molten steel.

[0008] Step 2: After tapping from the converter, the molten steel is quickly hoisted to the RH furnace. During the pre-vacuuming process, oxygen is sampled and determined. Decarburization is carried out based on the carbon content entering the station and the free oxygen in the molten steel. After decarburization, the free oxygen is controlled at 0.025%-0.035%. Before alloying, the carbon content is controlled below 0.0012%.

[0009] Step 3: After the RH furnace molten steel is decarburized, oxygen determination is carried out. Based on the oxygen determination results, aluminum alloy with an aluminum content of 99.9% is added for deoxidation. 20 kg of aluminum alloy is added for every 100 ppm of oxygen content.

[0010] Step 4: After deoxidation, take samples to test the carbon content, and calculate the amount of high-purity ferrosilicon and ordinary ferrosilicon to be added based on the carbon content value; Ordinary ferrosilicon has a carbon content between 0.1% and 0.3%, a calcium content between 0.75% and 1.5%, and a silicon content greater than 72%; high-purity ferrosilicon has a carbon content less than 0.03%, a calcium content less than 0.01%, and a silicon content greater than 75%.

[0011] Step 5: The carbon content of high-silicon, high-aluminum steel should be within 0.0040%, and the silicon content should be between 0.95% and 1.15%. When using two types of ferrosilicon to add silicon, the carbon increase of the two alloys should be considered comprehensively. First, use high-purity ferrosilicon to control the silicon content at 0.75%-0.95%, and then use ordinary ferrosilicon to add silicon to 0.95%-1.15%.

[0012] Step Six: Considering the silicon recovery rate of 95% and the carbon recovery rate of ferrosilicon is 99%, high-purity ferrosilicon and ordinary ferrosilicon can be mixed together and added to molten steel simultaneously. Before alloying, control the carbon content of the molten steel at 0.0010%-0.0015%. First, use high-purity ferrosilicon to control the silicon content at 0.75%-0.95%, adding 1280kg-1630kg, increasing the carbon content by 0.0003%-0.0004%. Then, use ordinary ferrosilicon to adjust the silicon content to 0.95%-1.15%, adding 355kg-535kg, increasing the carbon content by 0.0009%-0.0013%. After alloying, the theoretical carbon content is 0.0022%-0.0032%, meeting the requirement of a carbon content within 0.0040%.

[0013] Step 7: After adding ordinary ferrosilicon, the net circulation time of the molten steel is controlled at 6-8 minutes. If the control time is less than 6 minutes, the calcium content will fluctuate greatly. If the control time is greater than 8 minutes, the calcium content will be low. After calcium treatment, the net circulation time of the molten steel is controlled at 6-8 minutes, the calcium content in the molten steel is in the range of 0.0010%-0.0020%, and the calcium recovery rate is 25-30%.

[0014] Step 8: After the molten steel circulation is completed, let the molten steel stand still for 15-20 minutes before hoisting it to the continuous casting machine for pouring.

[0015] The beneficial effects of this invention are as follows: This invention fully utilizes trace amounts of calcium from ordinary ferrosilicon to perform calcium treatment on molten steel, replacing silicon-calcium alloys. After RH decarburization, high-purity ferrosilicon and ordinary ferrosilicon are mixed and proportioned, with the ratio determined based on the silicon and carbon content of the two types of ferrosilicon. Calcium treatment is performed simultaneously with alloying. This invention uses trace amounts of calcium from ordinary ferrosilicon to perform calcium treatment on molten steel, reducing vacuum chamber splashing during the calcium treatment process. Detailed Implementation

[0016] The present invention will be further described below with reference to specific embodiments: Example 1 Step 1: Before production, the composition of the molten steel is planned. In the example, the high-silicon, high-aluminum steel grade requires a carbon content of ≤0.0040%, a silicon content of 0.95%-1.15%, and a calcium content controlled between 0.0007%-0.0030%. Before production, the carbon, silicon, and calcium content of each batch of ferrosilicon is tested. In the example, the high-purity ferrosilicon has a carbon content of 0.027%, a silicon content of 75.5%, and a calcium content of 0.01%; the ordinary ferrosilicon has a carbon content of 0.18%, a silicon content of 73.4%, and a calcium content of 1.37%. The converter uses boiling tapping. During the tapping process, 305 kg of lime, 108 kg of fluorite, and 104 kg of steel slag modifier are added. The bottom blowing argon is immediately shut off after tapping to ensure the total oxygen content in the molten steel. The tapping volume is 122 tons.

[0017] Step Two: After tapping from the converter, the molten steel is promptly hoisted to the RH furnace. During the pre-vacuuming process, oxygen samples are taken for determination. The free oxygen content in the incoming molten steel is 0.054%, and the carbon content is 0.036%. Based on the carbon content and free oxygen content in the incoming molten steel, decarburization is performed, with oxygen blowing for 40m³. 3 Forced decarbonization is carried out.

[0018] Step 3: After the RH furnace steel is decarburized, oxygen determination is carried out. After deoxidation, the free oxygen content is 0.0335%. Based on the oxygen determination result, 67 kg of aluminum shot with an aluminum content of 99.9% is added for deoxidation.

[0019] Step 4: After deoxidation, take samples to test the carbon content (0.0011%), silicon content (0.001%), and calcium content (0.0001%). Calculate the amount of high-purity ferrosilicon and ordinary ferrosilicon to be added based on the carbon and silicon content test values.

[0020] Step 5: Use high-purity ferrosilicon to add silicon to 0.85%, and then use ordinary ferrosilicon to add silicon to 1.05%.

[0021] Step Six: Based on the proportions of ultra-low carbon ferrosilicon and ordinary ferrosilicon and the ferrosilicon yield of 95%, weigh the two types of ferrosilicon. The actual amount of high-purity ferrosilicon added is 1448 kg, and the amount of ordinary ferrosilicon is 353 kg. The high-purity ferrosilicon and ordinary ferrosilicon are mixed in the same hopper.

[0022] Step 7: Six minutes after the deoxidation cycle ends, the two alloys are added to the molten steel all at once. The molten steel splashing in the vacuum chamber is observed through a high-temperature camera. There is no violent splashing during the process.

[0023] Six minutes after the alloy was added, the void was broken. After the void was broken, a sample was taken to test the composition. The carbon content was 0.0022%, the silicon content was 1.04%, and the calcium content was 0.0009%.

[0024] According to alloy theory calculations, the carbon content is 0.020%, the silicon content is 1.07%, and the calcium content is 0.0010%, which matches the actual values.

[0025] Step 8: After the molten steel completes its clean circulation, the molten steel is allowed to stand still for 15-20 minutes before being hoisted to the continuous casting machine for pouring. The stopper rod remains stable during the pouring process.

[0026] Example 2 Step 1: Before production, the composition of the molten steel is planned. In the example, the high-silicon, high-aluminum steel grade requires a carbon content of ≤0.0040%, a silicon content of 0.95%-1.15%, and a calcium content controlled between 0.0007%-0.0030%. Before production, the carbon, silicon, and calcium content of each batch of ferrosilicon is tested. In the example, the high-purity ferrosilicon has a carbon content of 0.022%, a silicon content of 76%, and a calcium content of 0.01%, while the ordinary ferrosilicon has a carbon content of 0.15%, a silicon content of 72.8%, and a calcium content of 1.42%. The converter uses boiling tapping. During the tapping process, 336 kg of lime, 103 kg of fluorite, and 98 kg of steel slag modifier are added. The bottom blowing argon is immediately shut off after tapping to ensure the total oxygen content in the molten steel. The tapping volume is 120 tons.

[0027] Step Two: After tapping from the converter, the molten steel is promptly hoisted to the RH furnace. During the pre-vacuuming process, oxygen samples are taken for determination. The free oxygen content in the incoming molten steel is 0.048%, and the carbon content is 0.042%. Based on the carbon content and free oxygen content in the incoming molten steel, decarburization is performed, followed by oxygen blowing for 30m³. 3 Forced decarbonization is carried out.

[0028] Step 3: After the RH furnace steel is decarburized, oxygen determination is carried out. After deoxidation, the free oxygen content is 0.0376%. Based on the oxygen determination result, 58 kg of aluminum shot with an aluminum content of 99.9% is added for deoxidation.

[0029] Step 4: After deoxidation, take samples to test the carbon content (0.0010%), silicon content (0.001%), and calcium content (0.0001%). Calculate the amount of high-purity ferrosilicon and ordinary ferrosilicon to be added based on the carbon and silicon content test values.

[0030] Step 5: Use high-purity ferrosilicon to add silicon to 0.85%, and then use ordinary ferrosilicon to add silicon to 1.05%.

[0031] Step Six: Based on the proportions of ultra-low carbon ferrosilicon and ordinary ferrosilicon and the ferrosilicon yield of 95%, weigh the two types of ferrosilicon. The actual amount of high-purity ferrosilicon added is 1410 kg, and the amount of ordinary ferrosilicon is 350 kg. The high-purity ferrosilicon and ordinary ferrosilicon are mixed in the same hopper.

[0032] Step 7: Six minutes after the deoxidation cycle ends, the two alloys are added to the molten steel all at once. The molten steel splashing in the vacuum chamber is observed through a high-temperature camera. There is no violent splashing during the process.

[0033] Six minutes after the alloy was added, the void was broken. After the void was broken, a sample was taken to test the composition. The carbon content was 0.0020%, the silicon content was 1.03%, and the calcium content was 0.0011%.

[0034] According to alloy theory calculations, the carbon content is 0.0017%, the silicon content is 1.07%, and the calcium content is 0.0010%, which matches the actual values.

[0035] Step 8: After the molten steel completes its clean circulation, the molten steel is allowed to stand still for 15-20 minutes before being hoisted to the continuous casting machine for pouring. The stopper rod remains stable during the pouring process.

[0036] This invention uses trace amounts of calcium from ordinary ferrosilicon to calcium-treat molten steel, replacing silicon-calcium alloys. This significantly reduces costs. A comparison table of alloy costs in Example 1 of this invention and the original scheme using silicon-calcium alloys is shown below: Based on the above calculations, the cost of producing high-silicon, high-aluminum alloys using this invention is reduced by approximately 40 yuan per ton of steel compared to the original solution, representing a 21% reduction, which is a very significant cost reduction.

Claims

1. A method for calcium treatment in a vacuum chamber, characterized in that, After deoxidation of the steel in the converter boiling tapping process, it is transferred to the RH furnace. During the pre-vacuuming process, oxygen is determined by sampling. Decarburization is carried out based on the carbon content of the incoming steel and the free oxygen in the molten steel. After the decarburization of the molten steel in the RH furnace is completed, oxygen determination is carried out. After deoxidation, samples are taken to test the carbon content. The amount of high-purity ferrosilicon and ordinary ferrosilicon added is calculated based on the carbon content value to ensure that the carbon increase after adding the alloy meets the requirements. First, high-purity ferrosilicon is used to control the silicon content at 0.75%-0.95%, and then ordinary ferrosilicon is used to add silicon to 0.95%-1.15%. High-purity ferrosilicon and ordinary ferrosilicon are mixed together and added to the molten steel at the same time.

2. The method for vacuum chamber calcium treatment according to claim 1, characterized in that, Specifically, the following steps are included: Step 1: Converter boiling tapping. During the tapping process, lime, fluorite and steel slag modifier are added in proportion. After tapping, the bottom blowing argon is immediately turned off to ensure the total oxygen content of the molten steel. Step 2: After the steel is tapped from the converter, the molten steel is promptly hoisted to the RH furnace. During the pre-vacuuming process, samples are taken to determine the oxygen content. Based on the carbon content entering the station and the free oxygen in the molten steel, decarburization is carried out. After decarburization, the free oxygen content is controlled at 0.025%-0.035%. Before alloying, the carbon content is controlled below 0.0012%. Step 3: After the RH furnace steel is decarburized, oxygen determination is carried out, and aluminum alloy is added for deoxidation based on the oxygen determination results; Step 4: After deoxidation, take samples to test the carbon content, and calculate the amount of high-purity ferrosilicon and ordinary ferrosilicon to be added based on the carbon content value; Ordinary ferrosilicon has a carbon content between 0.1% and 0.3%, a calcium content between 0.75% and 1.5%, and a silicon content greater than 72%; high-purity ferrosilicon has a carbon content less than 0.03%, a calcium content less than 0.01%, and a silicon content greater than 75%. Step 5: The carbon content of high-silicon, high-aluminum steel should be below 0.0040%, and the silicon content should be between 0.95% and 1.15%. When using two types of ferrosilicon to add silicon, control the carbon increase. First, use high-purity ferrosilicon to control the silicon content at 0.75%-0.95%, and then use ordinary ferrosilicon to add silicon to 0.95%-1.15%. Step Six: Considering the silicon recovery rate of 95% and the carbon recovery rate of ferrosilicon is 99%, high-purity ferrosilicon and ordinary ferrosilicon are mixed together and added to molten steel simultaneously. Before alloying, the carbon content in the molten steel is controlled at 0.0010%-0.0015%. First, high-purity ferrosilicon is used to control the silicon content at 0.75%-0.95%, with an addition amount of 1280kg-1630kg, resulting in a carbon increase of 0.0003%-0.0004%. Then, ordinary ferrosilicon is used to adjust the silicon content to 0.95%-1.15%, with an addition amount of 355kg-535kg, resulting in a carbon increase of 0.0009%-0.0013%. After alloying, the theoretical carbon content is 0.0022%-0.0032%, meeting the requirement of a carbon content within 0.0040%. Step 7: After adding ordinary ferrosilicon, the net circulation time of the molten steel is controlled at 6-8 minutes, the calcium content in the molten steel is in the range of 0.0010%-0.0020%, and the calcium recovery rate is 25-30%. Step 8: After the molten steel circulation is completed, let the molten steel stand still for 15-20 minutes before hoisting it to the continuous casting machine for pouring.

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