Continuous casting submersed nozzle for improving castability of rare earth steel

Abstract

The invention discloses a continuous casting submersed nozzle for improving castability of rare earth steel, the continuous casting submersed nozzle comprises a nozzle body, a slag line and an inner hole body, the inner hole body is a ZrO2-CaO-C material, the raw material of the inner hole body is calcium zirconate and graphite, and the inner hole body material comprises the following components in percentage by weight: 45-59% of ZrO2, 18-22% of CaO, 20-32% of C and the balance of inevitable impurities. According to the method, the problems of nodulation and blockage of the submersed nozzle in the continuous casting production process of the rare earth steel and reaming caused by poor corrosion resistance in use can be effectively relieved, the castability of the rare earth steel under multi-furnace continuous casting can be ensured, and the method is beneficial to improving the quality of a casting blank and realizing efficient and stable production of continuous casting.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of steelmaking, and particularly relates to a continuous casting submerged nozzle for improving the castability of rare earth steel. BACKGROUND

[0002] In continuous casting production, the submerged nozzle often gets clogged when casting rare earth steel, causing the liquid level in the crystallizer to fluctuate and unable to be normally cast, or causing abnormal final casting and other major losses. The problem of continuous casting submerged nozzle clogging is encountered by all steel plants, and the severity varies depending on the steel grade. Currently, rare earth steelmaking technology is increasingly widely used, and rare earth is usually added to molten steel as an alloying element to change the morphology of inclusions, purify molten steel, and improve the performance of steel. The commonly used rare earth elements in rare earth steelmaking are cerium (Ce) and lanthanum (La) (commonly represented by RE).

[0003] The rare earth element (RE) has a low melting point and is easily oxidized, so the castability of rare earth steel becomes a prominent problem. The rare earth element (RE) is oxidized in the molten steel to form high-melting-point rare earth oxides (RE2O3) and oxysulfides (RE2O2S), and the rare earth oxides and the Al2O3-C refractory of the continuous casting submerged nozzle react to form rare earth aluminates (REAlO3), rare earth silicates (RESiO4), and high-viscosity aluminum-rich glass phases, etc. These reactions cause the surface of the inner hole of the nozzle to be uneven and inclusions to gather. The rare earth inclusions in the steel and the particles of the reaction products of the molten steel and the refractory will adhere and gather on the inner lining of the nozzle, causing clogging. The nozzle clogging also brings many quality problems, such as the nozzle clogging causing flow deviation and crystallizer level fluctuation, the flaked clogging material floating and staying in the molten steel, etc., all of which cause surface and internal defects of the cast slab. The problem of continuous casting submerged nozzle clogging has not been completely solved, and has become one of the limiting links for improving the efficiency of continuous casting production. In addition, if the erosion and scouring resistance of the submerged nozzle is not good, the nozzle will be severely expanded, which will also affect the liquid level fluctuation and operation of continuous casting, and also cannot be normally cast. Therefore, to ensure the castability of the increasing amount of rare earth steel, the submerged nozzle must be resistant to clogging and clogging, and must be resistant to erosion, scouring, and expansion, to ensure long service life and precise implementation of the continuous casting process.

[0004] The research of improving the castability of rare earth steel by using plasma spraying technology to spray yttrium-stabilized zirconia (YSZ) on the submerged entry nozzle inner lining to form a zirconia anti-clogging coating was studied by Dalarna University in Sweden in October 2016, P-6. The principle is that the coating material YSZ prevents the reaction of Al2O3 and C in the molten steel and refractory, inhibits the decarburization oxidation of refractory, and slows down the reaction of Al2O3 in refractory with rare earth elements in the molten steel. Compared with the nozzle without YSZ coating on the inner lining, the nozzle with YSZ coating has the largest amount of molten steel per unit time, which indicates that the ZrO2 coating can slow down the formation of rare earth clogging, especially helpful for the castability of the nozzle. However, this method is high in cost, requires special plasma spraying equipment, and has low production efficiency during spraying; yttrium-stabilized zirconia (YSZ) itself is particularly expensive, which greatly increases the cost of each nozzle.

[0005] Patents related to anti-clogging nozzles include:

[0006] Chinese patent CN95110968.5 discloses an anti-clogging submerged entry nozzle, which mainly consists of 10-35% graphite, 50-85% stable zirconia or zirconia mullite, and 1-20% fluoride. The submerged entry composite nozzle for continuous casting is lined with this refractory material. It can effectively prevent the clogging of the nozzle caused by the adhesion of aluminum in the molten steel containing high aluminum content. The material contains low-melting-point fluoride in the inner lining material that contacts the molten steel. The principle is that the fluoride reacts with the Al2O3 inclusions in the molten steel to form a low-melting-point substance that is continuously washed away during continuous casting, thus not clogging. However, this nozzle is severely eroded due to the presence of CaF2 during multi-heat continuous casting, has a low service life, and has a fast water hole expansion and unstable castability.

[0007] Chinese patent CN200410060355.6 discloses a special steel continuous casting anti-clogging submerged entry nozzle, which has a body (1) made of Al2O3-C material and a slag line (2) made of ZrO2-C material; and a carbon-free anti-clogging inner lining (3) made of a carbon-free oxide and non-oxide composite material, with the oxide being corundum and spinel, and the non-oxide being nitride, such as silicon nitride, aluminum nitride, and boron nitride. The amount of oxide is 75-95 wt%, and the amount of non-oxide is 5-25 wt%. The inner lining material of the nozzle does not contain C, and takes advantage of the non-wetting property of non-oxides to molten steel. However, non-oxides are easily oxidized, which deteriorates their performance and affects the service life. Therefore, although it has anti-clogging effect, the number of continuous casting heats is not high.

[0008] The conventional continuous casting submerged nozzle generally has a body of Al2O3-C material with C content ≥25%, a slag line of ZrO2-C material with C content 12-18%, and an inner hole body of Al2O3-SiO2 material with Al2O3 content 65-80% and SiO2 content 15-30% without adding carbon-containing raw materials and thus almost without C. The inner hole body with such material has good thermal shock resistance, but has serious problems of clogging and blocking, and general chemical corrosion resistance. Therefore, the conventional submerged nozzle used by the steel plant can only have a general castability of less than 6 heats for casting rare earth steel, which cannot meet the requirements of high-efficiency and high-quality continuous casting production of variety steel.

[0009] In summary, the improvement of the prior art on the submerged nozzle is focused on changing the inner hole body or the inner lining material to improve the anti-blocking property of the continuous casting production, but is not good in terms of the anti-corrosion, anti-erosion, nozzle aperture and performance stability, which finally causes the liquid surface fluctuation and the casting blank quality problem during the continuous casting, and affects the castability under the high continuous casting heat number. SUMMARY

[0010] The present application aims to provide a continuous casting submerged nozzle for improving the castability of rare earth steel, which can effectively reduce the clogging and blocking of the submerged nozzle during the continuous casting production of rare earth steel, and the problem of poor anti-corrosion performance causing the reaming during use, can ensure the castability of rare earth steel under the multi-heat continuous casting, and is beneficial to improving the casting blank quality and realizing the high-efficiency and stable production of continuous casting.

[0011] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0012] A continuous casting submerged nozzle for improving the castability of rare earth steel, comprising a nozzle body, a slag line and an inner hole body, wherein the inner hole body is a ZrO2-CaO-C material prepared from calcium zirconate and graphite.

[0013] Preferably, the inner hole body material comprises, in terms of weight percentage, ZrO2: 45-59%, CaO: 18-22%, C: 20-32%, and the rest is inevitable impurities.

[0014] Preferably, the graphite is flake graphite or / and electrode graphite.

[0015] Preferably, the thickness of the inner hole body is 6-8 mm.

[0016] Preferably, the material of the nozzle body is Al2O3-C.

[0017] Preferably, the material of the slag line is ZrO2-C.

[0018] The chemical reactions between the rare earth oxides in the molten steel and the existing aluminum-carbon refractory material of the inner hole body of the submerged nozzle are as listed in the formula (1)-(7):

[0019] RE2O3 + Al2O3 = 2REAlO3 (1)

[0020] 2RE2O3 + Al2O3 = RE4Al2O9 (2)

[0021] 3RE2O3 + 5Al2O3 = 2RE3Al5O 12 (3)

[0022] 2[RE] + 2SiO2 = RE2O3 + 2[Si] + [O] (4)

[0023] RE2O3 + SiO2 = 2RE2SiO5 (5)

[0024] 2RE2O3 + 3SiO2 = RE4Si3O 12 (6)

[0025] RE2O3 + 2SiO2 = RE2Si2O7 (7)

[0026] Therefore, the rare earth oxide is most likely to combine with Al2O3 and SiO2 in the molten steel and the inner hole body of the nozzle to generate a complex oxide nodule. The melting point of the rare earth aluminate oxide is very high, and such a nodule is most likely to block the nozzle. Therefore, the inner lining material of the rare earth steel nozzle with good castability should be designed in the technical direction of not containing Al2O3 and a small amount of SiO2. However, Al2O3 and SiO2 in the molten steel cannot be avoided during use. If there is an oxide that can combine with Al2O3 and REAlO3 into a low-melting-point material phase at high temperature, the nodule blocking problem can be solved. In addition, the reaction can also densify and inhibit the erosion and hole expansion in the later use, so that the long service life and castability of the nozzle are ensured.

[0027] Therefore, the inner hole body material of the continuous casting submerged nozzle for improving the castability of the rare earth steel is designed as a ZrO2-CaO-C material system. The composition of the inner hole body material includes, in terms of weight percentage: ZrO2: 45-59%, CaO: 18-22%, C: 20-32%, and the rest is unavoidable impurities, wherein the impurities include SiO2, Fe2O3, etc., the inner hole body material does not contain Al2O3, and may contain a small amount of SiO2. Under the continuous casting conditions of the rare earth steel and the aluminum killed steel, no blocking material is generated, and a dense layer rich in zirconium components is generated on the working surface of the nozzle, so as to achieve high service life and excellent castability under high continuous casting furnace.

[0028] However, when preparing the nozzle inner hole body of the ZrO2-CaO-C material of the present application, it is found that CaO is directly added to the material for mixing and proportioning. CaO itself is very easy to hydrate, and cannot be made into a refractory material product, so it cannot be normally used in the continuous casting process.

[0029] This invention introduces CaO by adding calcium zirconate (CaZrO3). CaZrO3 has excellent resistance to hydration, avoiding the defects of easy hydration and pulverization when directly adding calcium-containing materials, thus enabling the manufacture of qualified refractory materials. At the same time, CaZrO3 has a high melting point of 2340℃, and strong resistance to slag erosion and molten steel erosion.

[0030] The submersible nozzle inner bore of this invention uses a ZrO2-CaO-C material to achieve anti-clogging: Under the high temperature of continuously cast molten steel, CaO decomposed from CaZrO3 combines with Al2O3 and REA1O3 in the molten steel to form a low-melting-point liquid phase of CaO-Al2O3 (REA1O3) (melting point 1413~1530℃). This low-melting-point liquid phase at high temperature is washed away by the flowing molten steel and does not adhere to the inner wall of the nozzle, thus eliminating the deposition and adhesion of nodules on the inner wall of the nozzle. In addition, the inner bore material or the molten steel and slag may contain SiO2. SiO2 promotes the decomposition of CaZrO3 at high temperature, decomposing it into CaO and m-ZrO2 phases. CaO easily forms a liquid low-melting-point substance with REA1O3 and RE2Si2O7, which is washed away by the molten steel, making the inner bore surface smooth and free of nodules. The following reactions also occur:

[0031] SiO2(s)+CaZrO3(s) = CaO.SiO2(s)+ZrO2(s) (8)

[0032] CaO.SiO2 has a melting point of 1500℃. The increased ZrO2 content in the final nozzle reaction layer leads to the formation of a dense, zirconium-rich layer. This dense layer prevents the further diffusion of REO3 and Al2O3 from the molten steel into the nozzle material. The zirconium-rich dense layer slows down the formation of rare earth nodules, particularly contributing to the castability of the nozzle. ZrO2 itself has excellent corrosion resistance and, in combination with REO... x And RE does not react or wet. Therefore, the internal porous material does not form nodules or undergo further reaction and erosion, and can maintain excellent and stable castability in multi-furnace continuous casting; at the same time, because the internal porous material designed in this invention is rich in C, the following chemical reactions also occur during use:

[0033] ZrO2 + 2C = CO2 + ZrC (9)

[0034] In this way, the internal material is reduced to form zirconium carbide (ZrC). Zirconium carbide is a high-melting-point material with high hardness and excellent high-temperature refractory properties, with a melting point as high as 3540℃. It is a high-performance material that combines wear resistance, high-temperature resistance, and corrosion resistance. In the later stages of application of the submersible nozzle described in this invention, the internal material, being rich in ZrO... 2、ZrC, C phase, further ensure that in rare earth steel high continuous casting furnace number under the both prevent blockage and resistance to erosion, resistance to erosion, such as comprehensive, excellent pourability.

[0035] The inner hole body material of the water gap designed in the application contains a large amount of C, C itself does not infiltrate molten steel and liquid slag, so that the inner hole body material has excellent resistance to erosion and does not adhere to nodules; and the addition of a large amount of C material reduces the thermal expansion of the inner hole body of the water gap, and the water gap obtained has excellent resistance to thermal shock. The C content in the inner hole body material of the water gap is 20-32%, which is mainly introduced by adding graphite material. If the C content is too high, the strength of the material is not enough, it cannot resist the high-temperature molten steel erosion, and it will also cause the water gap to have abnormal hole expansion during use, and the pourability is not good. If the C content is too low, the graphite carbon cannot form a continuous distribution in the matrix of the inner hole body material, the resistance to thermal shock and the resistance to molten steel infiltration of the new material are reduced, and the anti-blocking effect is affected; it is also necessary to have a C source and ZrO2 to generate ZrC in situ during use to ensure excellent application effect. The graphite used in the application can be flake graphite or / and electrode graphite, and the C content is 95-99wt%.

[0036] Compared with the prior art, the application has the following beneficial effects:

[0037] The inner hole body material of the application adopts ZrO2-CaO-C material, and by controlling the chemical composition ratio of the inner hole body, the inner hole body material generates an appropriate amount of high-melting-point glass phase (liquid phase) at the casting temperature, forming a smooth surface, and the rare earth oxide inclusions in the molten steel are not easy to adhere to the inner wall of the water gap, achieving the purpose of preventing the water gap from being blocked and nodules, improving the pourability, and the continuous casting furnace number of rare earth steel reaching more than 9; on the other hand, the reaction thickens to form a dense ZrO2 protective layer, so that the rare earth oxides and inclusions in the molten steel are not easy to have subsequent chemical erosion reaction with the inner hole body material, the water gap has good resistance to erosion and erosion, the inner diameter of the water gap does not change, the steel flow and the liquid level remain stable. The commonly used inner hole body material often contains a lot of Al2O3 and SiO2 components, and also has a reaction of being reduced by C and reacting with O and Al in the molten steel to generate Al2O3, which not only reduces the service life of the refractory material, but also causes the water gap to be blocked, and the continuous casting furnace number of rare earth steel is less than 6.

[0038] The inner hole body material of the present application is prepared by using calcium zirconate and graphite, CaO is introduced by adding calcium zirconate (CaZrO3), which avoids the defects of easy hydration and pulverization of calcium-containing materials when directly added, so that qualified refractory products can be manufactured, the water gap obtained can effectively slow down the generation of rare earth aluminates and rare earth silicates, and reduce the water gap nodulation; in use, an appropriate amount of high-melting-point liquid phase can be generated, forming a smooth surface, and the rare earth inclusions in the molten steel are not easy to adhere to the inner wall of the water gap, and the anti-blocking performance is good; meanwhile, the inner hole body material has good corrosion resistance and does not expand the hole. Therefore, the submerged water gap prepared by the present application can stabilize the liquid level of the crystallizer, improve the continuous casting furnace number of the tundish, has good continuous casting castability, and has high service life of the submerged water gap. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The present application is a schematic diagram of the submerged water gap.

[0040] Figure 2 The present application is a schematic diagram of the submerged water gap.

[0041] Figure 3 The present application is a schematic diagram of the submerged water gap.

[0042] Figure 4 The present application is a schematic diagram of the submerged water gap. DETAILED DESCRIPTION

[0043] The present application is further described below in conjunction with examples and drawings.

[0044] The manufacturing method of the submerged water gap of the present application is the same as the general manufacturing method of the water gap containing the inner hole body. The inner hole body material is prepared according to the chemical composition and raw materials in Table 1 and Table 2, antioxidant and binder are added, and then is uniformly mixed and isostatic pressing formed; then is combined with Al2O3-C body material and ZrO2-C slag line material to prepare a whole by isostatic pressing process.

[0045] The water gap obtained by the examples and comparative examples of the present application is used in the hot rolling ultra-high strength steel grade when rare earth is added in RH refining, and is used in continuous casting production after refining treatment is completed.

[0046] Figure 1 The present application is a schematic diagram of the submerged water gap, the submerged water gap comprises a water gap body 1, a slag line 2 and an inner hole body 3.

[0047] The element composition of the inner hole body material of the water gap of the examples and comparative examples of the present application is shown in Table 1, and the raw materials are shown in Table 2. The performance of the water gap obtained by the examples and comparative examples of the present application and the comparative examples currently used in the field is shown in Table 3.

[0048] Figure 2 and Figure 3 respectively are SEM photos of the inner hole body material of the water gap according to the embodiment 1 of the present application. And energy spectrum analysis is carried out, the XRD analysis spectrum of the inner hole body material is shown in Figure 4 , and the energy spectrum decomposition result is shown in Table 4.

[0049] From the photos, the morphology and material composition of the inner hole body material of the water gap after use of the present application are observed by SEM. The SEM morphology shows that a relatively dense layer (see spectrum Figure 1 portion) is formed on the surface of the inner hole body material. Combined with and according to the composition of the energy spectrum analysis (see Table 4), it is judged that the dense layer material is mainly zirconium carbide and zirconium oxide. It is shown that the original calcium zirconate is decomposed in use, and the zirconium oxide therein reacts with impurities in the molten steel to generate low-melting-point calcium aluminate and calcium silicate, which is washed away by the molten steel, so the anti-blocking effect is good.

[0050] From Figure 3 the photos, it can be clearly observed that the surface grows skeleton material (spectrum Figure 3 point) under 100 times magnification. The energy spectrum analysis is mainly zirconium carbide, which remains on the surface of the inner hole body of the water gap because of its resistance to erosion and washing; the internal dark area recess (spectrum Figure 2 point) contains calcium aluminate, zirconium oxide or a small amount of zirconium carbide.

[0051] Figure 4 The XRD analysis spectrum of the inner hole body material of the water gap after use of the present application verifies that, in addition to the original main phase of calcium zirconate and graphite, a large amount of zirconium carbide is generated in the inner hole body material of the water gap after use of the present application, and the residual amount of low-melting-point material containing calcium and aluminum is extremely small, which shows that the water gap generates low-melting-point material containing calcium in the early stage of use, which is taken away by the molten steel to prevent blocking; and a dense layer rich in zirconium carbide (ZrC) is generated in the later stage, which resists erosion and washing and does not expand the hole. In this way, the liquid level is stable and the castability is good under a high number of continuous casting furnaces.

[0052] From the above examples and comparative examples, it can be seen that the water gap obtained by the present application has good chemical erosion resistance and excellent washing resistance, does not expand the diameter in use, has good castability, and the number of continuous casting furnaces of rare earth steel reaches more than 9.

[0053] The problems of the water gap in the comparative examples are mainly caused by blocking, which makes the inner diameter of the inner hole body small and unable to cast; at the same time, the liquid phase formed on the surface of the water gap in the comparative examples is small, and the surface is not smooth; and because SiO2 is much in the comparative examples, the erosion resistance is not good in use, and the number of continuous casting furnaces of rare earth steel is less than 6.

[0054]

[0055]

[0056]

Claims

1. A continuous casting submerged nozzle for improving the castability of rare earth steel, comprising a nozzle body, a slag line, and an inner hole body, characterized in that, The inner hole body is made of ZrO2-CaO-C material prepared from calcium zirconate and graphite.

2. The continuous casting submerged nozzle for improving the castability of rare earth steel according to claim 1, characterized by, The inner hole body material composition includes, in percentage by weight: ZrO2: 45-59%, CaO: 18-22%, C: 20-32%, and the rest is inevitable impurities.

3. The continuous casting submerged nozzle for improving the castability of rare earth steel according to claim 1, wherein The graphite is flake graphite or / and electrode graphite.

4. The continuous casting submerged nozzle for improving the castability of rare earth steel according to claim 1, wherein The inner hole body thickness is 6-8 mm.

5. The continuous casting submerged nozzle for improving the castability of rare earth steel according to claim 1, wherein The water gap body material is Al2O3-C.

6. The continuous casting submerged nozzle for improving the castability of rare earth steel according to claim 1, wherein The slag line material is ZrO2-C.

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