Method for controlling TFe content of tundish slag in IF steel continuous casting process

Abstract

The invention belongs to the field of metallurgy, and particularly relates to a method for controlling the TFe content of tundish slag in the IF steel continuous casting process, which comprises the following steps of: a) recording the adding weight W1 of a tundish covering agent in an impact area when tundish IF steel is cast; b) in the middle stage of large ladle casting of each furnace, taking a slag sample in a tundish impact area; c) detecting the mass percentage content Ci of TFe in the slag sample; d) if Ci is greater than or equal to 3wt%, adding a modifier into the impact area of the middle ladle when the large ladle of the (i + 1) th furnace of the middle ladle is cast; the modifier comprises limestone and aluminum particles, and the mass ratio of the limestone to the aluminum particles is K: 1; the modifier is bagged, and the net weight of each bag is recorded as W0; the adding bag number of the modifier is recorded as Ni = 0.32 * W1 * Ci * (K + 1) / W0. The method provided by the invention can effectively reduce the TFe content of the tundish slag and reduce the secondary oxidation pollution of the molten steel on the premise of not influencing the stability of the tundish steel casting process.

Description

Technical Field

[0001] The invention belongs to the field of metallurgy, and in particular relates to a method for controlling TFe content in tundish slag during continuous casting of IF steel. Background Art

[0002] The slag in the middle ladle (formed by the slag of the middle ladle covering agent) in the continuous casting process plays an important metallurgical function, such as heat preservation, adsorption of inclusions, purification of molten steel, and prevention of secondary oxidation of molten steel in contact with air. However, in the continuous casting process of IF steel, due to the high total iron (TFe) content in the top slag of the ladle, the corresponding top slag has strong oxidizing properties. At the end of the ladle casting, a part of the top slag containing high TFe enters the middle ladle (lower slag) with the molten steel, resulting in the continuous accumulation of TFe in the slag of the middle ladle.

[0003] When the TFe content in the tundish slag accumulates to a high level, the highly oxidizing tundish slag contacts the molten steel, causing secondary oxidation of the molten steel, thus affecting the cleanliness of the molten steel. In particular, in the tundish impact zone, the ladle top slag with high TFe content flowing in at the end of the ladle casting is blocked by the retaining walls on both sides and cannot flow into the casting areas on both sides of the tundish. The TFe content of the tundish slag in the tundish impact zone accumulates rapidly, and the contact process with the molten steel causes relatively serious secondary oxidation pollution of the molten steel. In addition, the molten steel flowing in at high speed through the long water nozzle forms a violent impact and agitation on the tundish impact zone, further aggravating the secondary oxidation pollution of the molten steel by the ladle slag in this area.

[0004] Therefore, in order to inhibit the secondary oxidation contamination of molten steel by the tundish slag in the tundish impact zone, it is necessary to develop corresponding tundish slag modification technology under the premise of maintaining the stability of the tundish working conditions and effectively control the TFe content of the tundish slag. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for controlling the TFe content of the tundish slag during the continuous casting of IF steel, which can effectively reduce the TFe content of the tundish slag and reduce the secondary oxidation pollution of molten steel without affecting the stability of the tundish casting process.

[0006] The present invention provides a method for controlling TFe content in tundish slag during continuous casting of IF steel, comprising the following steps:

[0007] a) When pouring the IF steel in the tundish, record the weight of the tundish covering agent added in the impact zone, recorded as W1;

[0008] b) In the middle of each ladle casting, take slag samples in the impact zone of the tundish;

[0009] c) Detect the TFe mass percentage of the slag sample, denoted as C i , i refers to the i-th furnace of the middle package;

[0010] d) If Ci ≥3wt%, then add the modifier into the impact zone of the tundish when the i+1th furnace ladle is poured;

[0011] The modifier is composed of limestone and aluminum particles, the mass ratio of the limestone to the aluminum particles is K:1, K=4-6; the modifier is packed in bags, and the net weight of each bag is recorded as W0;

[0012] The number of bags of the modifier added is recorded as N i , the calculation method is: N i =0.32×W1×C i ×(K+1) / W0. When the calculation result is not an integer, the calculated value is rounded up as the final result.

[0013] Preferably, the particle size of the limestone is 3 to 7 mm; the particle size of the aluminum particles is 2 to 4 mm.

[0014] Preferably, W0≤10kg.

[0015] Preferably, the modifier is prepared according to the following steps: limestone and aluminum particles are mixed and bagged to obtain the modifier.

[0016] Preferably, the mixing is carried out in a mixer; the ratio of the nominal volume of the mixer to the total volume of the limestone and aluminum particles is ≥5:1; the mixing speed of the mixing is 60 to 90 r / min; and the mixing time of the mixing is ≥20 min.

[0017] Preferably, the sampling amount of the slag sample is ≥100g.

[0018] Preferably, the slag sample is cooled and ground before being tested to obtain a slag sample powder.

[0019] Preferably, the particle size of the slag-like powder is ≤200 mesh.

[0020] Preferably, the device used for the detection is a handheld spectrometer.

[0021] Preferably, the modifier is added around the long shroud in the impact zone of the tundish.

[0022] Compared with the prior art, the present invention provides a method for controlling the TFe content of tundish slag during the continuous casting of IF steel, comprising the following steps: a) recording the added weight of the tundish covering agent in the impact zone when the IF steel in the tundish is poured, which is recorded as W1; b) taking a slag sample in the impact zone of the tundish in the middle of each ladle casting; c) detecting the mass percentage of TFe in the slag sample, which is recorded as C i , i refers to the i-th furnace of the package; d) if C i≥3wt%, then add a modifier into the impact zone of the tundish when the i+1th furnace ladle is poured; the modifier is composed of limestone and aluminum particles, the mass ratio of the limestone to the aluminum particles is K:1, K=4-6; the modifier is packed in bags, and the net weight of each bag is recorded as W0; the number of bags of the modifier added is recorded as N i , the calculation method is: N i =0.32×W1×C i ×(K+1) / W0, when the calculated result is a non-integer, the calculated value is rounded up as the final result. Based on the composition of IF steel and the characteristics of the production process, the present invention designs a special modifier for modifying and reducing TFe in the intermediate ladle slag, which can not only ensure the slagging performance but also avoid the erosion of the intermediate ladle refractory material; on this basis, based on the production process data such as the TFe content of the slag during the steel pouring process, a method for controlling the TFe content of the intermediate ladle slag including a method for calculating the theoretical amount of the modifier is proposed. The method provided by the present invention can effectively reduce the TFe content of the intermediate ladle slag and reduce the secondary oxidation pollution of molten steel without affecting the stability of the intermediate ladle steel pouring process; in addition, the modified intermediate ladle slag has a strong Al2O3 inclusion adsorption performance, which helps to further improve the ability of the intermediate ladle slag to purify molten steel. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The present invention provides a method for controlling TFe content in tundish slag during continuous casting of IF steel, comprising the following steps:

[0025] a) When pouring the IF steel in the tundish, record the weight of the tundish covering agent added in the impact zone, recorded as W1;

[0026] b) In the middle of each ladle casting, take slag samples in the impact zone of the tundish;

[0027] c) Detect the TFe mass percentage of the slag sample, denoted as C i , i refers to the i-th furnace of the middle package;

[0028] d) If C i ≥3wt%, then add the modifier into the impact zone of the tundish when the i+1th furnace ladle is poured;

[0029] The modifier is composed of limestone and aluminum particles, the mass ratio of the limestone to the aluminum particles is K:1, K=4-6; the modifier is packed in bags, and the net weight of each bag is recorded as W0;

[0030] The number of bags of the modifier added is recorded as N i , the calculation method is: N i =0.32×W1×C i ×(K+1) / W0. When the calculation result is not an integer, the calculated value is rounded up as the final result.

[0031] In the method provided by the present invention, the components of the middle package covering agent preferably include Al2O3, CaO, MgO and SiO2; wherein the content of Al2O3 is preferably 30-40wt%, specifically 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt% or 40wt%; the content of CaO is preferably 40-50wt%, specifically 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt%, 46wt%, 47wt%, 48wt%, 49wt%, 50wt%, 51wt%, 52wt%, 53wt%, 54wt%, 55wt%, 56wt%, 57wt%, 58wt%, 59wt%, 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, 69wt%, 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, 89wt%, 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, 98wt%, 99wt%, 100wt%, 101wt%, 102wt%, 103wt%, 104wt%, 105wt%, 106wt%, 107wt%, 108wt%, 109wt%, 110 %, 5wt%, 46wt%, 47wt%, 48wt%, 49wt% or 50wt%; the content of MgO is preferably 10-20wt%, specifically 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%; the content of SiO2 is preferably 2-10wt%, specifically 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%.

[0032] In the method provided by the present invention, the addition amount of the middle bag covering agent is preferably 200-800kg, specifically 200kg, 250kg, 300kg, 350kg, 400kg, 450kg, 500kg, 550kg, 600kg, 650kg, 700kg, 750kg or 800kg.

[0033] In the method provided by the present invention, the sampling amount of the slag sample is preferably ≥100g, more preferably 100-300g, specifically 100g, 120g, 150g, 170g, 200g, 230g, 250g, 270g or 300g.

[0034] In the method provided by the present invention, the slag sample is preferably cooled and ground before being tested to obtain a slag sample powder; the particle size of the slag sample powder is preferably ≤200 mesh.

[0035] In the method provided by the present invention, the device used for the detection is preferably a handheld spectrometer.

[0036] In the method provided by the present invention, if C i≥3wt%, indicating that the TFe content in the slag from the ladle and the impact zone of the middle ladle is relatively high and has strong oxidizing property, which can easily lead to secondary oxidation pollution in the molten steel. It is necessary to reduce the TFe content by adding a modifier.

[0037] In the method provided by the present invention, the CaO content of the limestone in the modifier is preferably ≥50wt%, more preferably 50-55wt%, specifically 50wt%, 51wt%, 52wt%, 53wt%, 54wt% or 55wt%; the SiO2 content of the limestone is preferably ≤5wt%, more preferably 0.5-5wt%, specifically 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%; the particle size of the limestone is preferably 3-7mm.

[0038] In the method provided by the present invention, the Al content of the aluminum particles in the modifier is preferably ≥95wt%, more preferably 95-99wt%, specifically 95wt%, 96wt%, 97wt%, 98wt% or 99wt%; the particle size of the aluminum particles is preferably 2-4mm.

[0039] In the method provided by the present invention, the mass ratio of limestone to aluminum particles in the modifier is (4-6):1, specifically 4:1, 4.2:1, 4.5:1, 4.7:1, 5:1, 5.2:1, 5.5:1, 5.7:1 or 6:1.

[0040] In the method provided by the present invention, the net weight W0 of each bag of the modifier is preferably ≤10kg, more preferably 0.5-10kg, specifically 0.5kg, 1kg, 2kg, 3kg, 4kg, 5kg, 6kg, 7kg, 8kg, 9kg or 10kg.

[0041] In the method provided by the present invention, the modifier is preferably prepared according to the following steps: limestone and aluminum particles are mixed and bagged to obtain the modifier. Wherein, the mixing is preferably carried out in a mixer; the ratio of the nominal volume of the mixer to the total volume of the limestone and aluminum particles is preferably ≥5:1, more preferably (5-15):1, specifically 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1 or 15:1; the stirring speed of the mixing is preferably 60-90r / min, specifically 60r / min, 65r / min, 70r / min, 75r / min, 80r / min, 85r / min or 90r / min; the stirring time of the mixing is preferably ≥20min, more preferably 20-90min, specifically 20min, 30min, 40min, 50min, 60min, 65min, 70min, 80min or 90min.

[0042] In the method provided by the present invention, the modifier is preferably added around the long shroud of the impact zone of the tundish to avoid stacking of the added modifier, which affects the modification effect and slagging in the impact zone.

[0043] The technical solution provided by the present invention is based on the composition of IF steel and the characteristics of the production process, and a special modifier for reducing TFe in the tundish slag is designed, which can not only ensure the slagging performance but also avoid the erosion of the tundish refractory material; on this basis, based on the production process data such as the TFe content of the tundish slag during the steel casting process, a method for controlling the TFe content of the tundish slag including a method for calculating the theoretical amount of the modifier is proposed. The technical solution provided by the present invention can effectively reduce the TFe content of the tundish slag and reduce the secondary oxidation pollution of molten steel without affecting the stability of the tundish steel casting process; in addition, the modified tundish slag has a strong Al2O3 inclusion adsorption performance, which helps to further improve the ability of the tundish slag to purify molten steel.

[0044] For the purpose of greater clarity, the invention is described in detail through the following examples.

[0045] Example 1

[0046] Under the process flow of converter LD→vacuum RH→continuous casting CC, the slag in the tundish of slab single tundish is modified for continuous casting of 10 furnaces of IF steel:

[0047] (I) Preparation of modifier:

[0048] (1) The raw materials for preparing the modifier are limestone and aluminum particles. The weight ratio of limestone to aluminum particles is K:1, K=5. The properties of the two raw materials are shown in Table 1:

[0049] Table 1 Raw material composition properties

[0050]

[0051] (2) Add the above raw materials into a blender in proportion and mix them evenly. The nominal volume of the blender and the volume of the raw materials are in a ratio of 12:1. The blending time is 25 min and the blender speed is 65 r / min. Fluorite, sodium salt and other solvents are prohibited during the process.

[0052] (3) The mixed modifier is packaged into small bags, with each bag weighing W0 = 5 kg.

[0053] (II) Modifier addition process:

[0054] (1) When the IF steel of the tundish is poured, the weight of the tundish covering agent added in the impact zone is recorded as W1=400kg; the composition of the tundish covering agent used is shown in Table 2:

[0055] Table 2: Composition of the coating agent (unit: wt%)

[0056] <![CDATA[Al2O3]]> High MgO <![CDATA[SiO2]]> 34.1 44.4 15.2 6.3

[0057] (2) In the middle of each ladle casting, take about 150g of slag sample from the impact zone of the middle ladle, and grind it into powder quickly using an automatic grinder after cooling. The powder particle size is ≤200 mesh;

[0058] (3) Using a handheld spectrometer to detect and determine the TFe content of the tundish slag sampled in step (2); the results showed that the contents of the tundish slag in the third, sixth and ninth furnaces were all higher than 3%, reaching C3 = 3.7%, C6 = 3.1%, and C9 = 4.2%, respectively;

[0059] (4) Since C3, C6, and C9 all exceed 3%, it is necessary to add a modifier for modification. The amount of modifier added is as follows:

[0060] N3 = 0.32 × W1 × C3 × (K + 1) / W0 = 0.32 × 400 × 3.7% × (5 + 1) / 5 = 6 bags;

[0061] N6 = 0.32 × W1 × C3 × (K + 1) / W0 = 0.32 × 400 × 3.1% × (5 + 1) / 5 = 5 bags;

[0062] N9 = 0.32 × W1 × C3 × (K + 1) / W0 = 0.32 × 400 × 4.2% × (5 + 1) / 5 = 7 bags;

[0063] In the above formula, when the calculation result is not an integer, the calculated value is rounded up as the final result;

[0064] (5) Based on the result of step (4), it can be determined that in order to reduce the TFe of the slag in the impact zone of the tundish, 6 bags, 5 bags, and 7 bags of modifier should be taken respectively when the 4th, 7th, and 10th tundishes are poured, and they should be quickly added into the impact zone of the tundish at one time. When adding, the modifier should be evenly distributed around the long nozzle to avoid stacking of the added modifier, which would affect the modification effect and slagging in the impact zone.

[0065] After applying the technology of this embodiment, the erosion resistance of the material in the impact zone of the tundish slag modification process is normal, the slag-forming performance of the tundish is good, no crusting occurs, the TFe in the slag in the impact zone of the tundish is stably controlled within 3%, and the average [Al]s (acid-soluble aluminum, indicating the content of aluminum in molten steel) burn-out from RH outlet to the continuous casting tundish is reduced from 73ppm before application to 57ppm.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for controlling the TFe content of tundish slag during continuous casting of IF steel, characterized in that: The following steps are involved: a) When pouring the IF steel in the tundish, record the weight of the tundish covering agent added in the impact zone, recorded as W1; b) In the middle of each ladle casting, take slag samples in the impact zone of the tundish; c) Detect the TFe mass percentage of the slag sample, denoted as C i , i refers to the i-th furnace of the middle package; d) If C i ≥3wt%, then add the modifier into the impact zone of the tundish when the i+1th furnace ladle is poured; The modifier is composed of limestone and aluminum particles, the mass ratio of the limestone to the aluminum particles is K:1, K=4-6; the modifier is packed in bags, and the net weight of each bag is recorded as W0; The number of bags of the modifier added is recorded as N i , the calculation method is: N i =0.32×W1×C i ×(K+1) / W0. When the calculation result is not an integer, the calculated value is rounded up as the final result.

2. The method according to claim 1, characterized in that The particle size of the limestone is 3-7 mm; the particle size of the aluminum particles is 2-4 mm.

3. The method according to claim 1, characterized in that The W0≤10kg.

4. The method according to claim 1, characterized in that: The modifier is prepared according to the following steps: The limestone and aluminum particles are mixed and bagged to obtain a modifier.

5. The method according to claim 4, characterized in that The mixing is carried out in a mixer; the ratio of the nominal volume of the mixer to the total volume of the limestone and aluminum particles is ≥5:1; the mixing speed of the mixing is 60-90r / min; and the mixing time of the mixing is ≥20min.

6. The method according to claim 1, characterized in that The sampling amount of the slag sample is ≥100g.

7. The method according to claim 1, characterized in that Before testing, the slag sample is cooled and ground to obtain slag sample powder.

8. The method according to claim 7, characterized in that The particle size of the slag-like powder is ≤200 mesh.

9. The method according to claim 1, characterized in that: The device used for the detection is a handheld spectrometer.

10. The method according to claim 1, characterized in that The modifier is added around the long shroud in the impact zone of the tundish.

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