A special continuous casting mould functional protection material for automobile hot forming steel

Abstract

The application provides a special continuous casting crystallizer functional protection material for automobile hot forming steel, and belongs to the technical field of metallurgical auxiliary materials, which comprises raw materials in the following mass percentages: pre-melted material 60.0-66.0%, lithium carbonate 1.8-3.2%, light-burned white alkali 4.5-8.5%, bentonite 1.0-3.0%, high fluorite powder 4.4-6.4%, high bauxite 1.0-3.0%, cryolite 3.0-5.0%, sodium fluoride 2.5-4.5%, sodium feldspar 1.0-3.0%, binder 2.0-4.0%, Japanese imported carbon black 2.0-4.0%, and graphite carbon 2.1-4.1%. The application uses the CaO-SiO2-A12O3-Na2O-CaF2 system protection slag, and the appropriate amount of lithium carbonate is added, so that the viscosity of liquid slag can be reduced, the adverse effects of Cr2O3 and A12O3 are eliminated, and the good performance of the protection slag is maintained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgical auxiliary materials, in particular to a special continuous casting crystallizer functional protection material for automobile hot forming steel. BACKGROUND

[0002] With the deepening of China's industrialization process, the automobile industry has a huge driving role in strengthening the national economy and improving people's living standards. Safety is the main performance index that people buying cars value. Sales will tell you how many airbags this car has, whether it has active brakes, pre-collision warning, etc. Some sales may also tell you how much hot forming steel this car uses. The tensile strength of general high-strength steel plates is about 400-450 MPa, and the tensile strength of hot forming steel can be increased to 1300-1600 MPa after a series of treatments, which is 3-4 times that of ordinary steel. Hot forming steel is applied to key parts of the vehicle body frame, such as A, B, C pillars, front and rear bumpers, door impact beams, door inner panels, and side walls, etc. In recent years, under the background of increasingly strict requirements for automobile fuel consumption and emissions, hot forming steel plates can enable more civilian vehicles to achieve lightweighting while ensuring safety. Hot forming steel can reduce the weight of the vehicle body or as little as possible while improving vehicle safety. Under the requirements of various safety crash test institutions (IIHS, ENCAP, CNCAP, etc.), vehicles using hot forming steel technology are lighter than vehicles using the same amount of hot forming steel to achieve the same safety crash star level.

[0003] The design and invention of the special crystallizer functional protection material for hot forming steel should meet the composition characteristics of the steel grade, ensure stable and smooth continuous casting in the steel plant, and realize the true metallurgical properties of the crystallizer functional protection material. The design difficulties are: there are many alloying elements such as B, Mn, Ti, Al, and Cr in the steel composition, which can easily denature and deteriorate the composition of the crystallizer functional protection material, change the original physical and chemical properties, and affect the subsequent continuous casting; secondly, the carbon content in the steel grade is high, and the high-carbon steel has poor hot strength, which is easy to stick and cause continuous casting interruption. SUMMARY

[0004] Therefore, in order to overcome the above design difficulties, the present application provides a special continuous casting crystallizer functional protection material for automobile hot forming steel, which uses a CaO-SiO2-A12O3-Na2O-CaF2 system of protection slag, and adds an appropriate amount of lithium carbonate, which can reduce the viscosity of the liquid slag, eliminate the adverse effects of Cr2O3, A12O3, etc., and maintain the good performance of the protection slag.

[0005] To solve the above technical problems, the present application provides a special continuous casting crystallizer functional protection material for automobile hot forming steel, which comprises raw materials in the following mass percentages:

[0006] Pre-melt 60.0-66.0%, lithium carbonate 1.8-3.2%, light-burnt white alkali 4.5-8.5%, bentonite 1.0-3.0%, high fluorite powder 4.4-6.4%, high alumina soil 1.0-3.0%, ice crystal stone 3.0-5.0%, sodium fluoride 2.5-4.5%, sodium feldspar 1.0-3.0%, binder 2.0-4.0%, Japanese imported carbon black 2.0-4.0%, graphite carbon 2.1-4.1%.

[0007] Further, the binary basicity CaO / SiO2 in the protective slag of the protective material is 1.1-1.3.

[0008] Further, the protective slag comprises the following chemical components in mass percentage:

[0009] SiO2 20.3-36.6%, CaO 22.4-42.0%, Li2O ≤2.0, Al2O3 2.5-9%, K2O+Na2O 4.0-12.5%, F- 3.0-9.5, MgO ≤6.5%, Fe2O3 ≤2.5%.

[0010] Further, the pre-melt comprises the following chemical components in mass percentage:

[0011] SiO2 22.0-38.0%, CaO 25.0-40.0%, Li2O ≤2.0, Al2O3 2.0-9%, R2O 4.0-15.0%, F- 2.0-8.0, MgO 2.0-8.0%, Fe2O3 ≤2.5%.

[0012] Further, the R element in the R2O is Na element and K element.

[0013] In summary, the present application has at least one of the following beneficial technical effects compared with the prior art:

[0014] 1. The automobile hot forming steel special continuous casting crystallizer functional protective material realizes two functions and five metallurgical effects:

[0015] The two functions are to ensure the stable and smooth operation of the continuous casting process and to improve the surface and subsurface quality of the casting blank. The five effects are as follows:

[0016] a. Heat insulation, reducing the heat loss of the molten steel, inhibiting the occurrence of bridging and crust (cold steel) in the crystallizer, improving the meniscus temperature, and maintaining the smooth passage of the slag channel;

[0017] b. Air isolation, preventing secondary oxidation of the molten steel;

[0018] c. Lubricating the casting blank to reduce the adhesion of the casting blank;

[0019] d Improve the heat transfer of crystallizer, and further reduce the surface defects of the casting blank;

[0020] e Absorb non-metallic inclusions, and the molten slag can assimilate the inclusions floating on the interface of the steel slag, ensure the uniformity and stability (chemical stability and thermal stability) of the molten slag, and reduce the degeneration of the functional protective material.

[0021] 2、The added lithium carbonate can form lithium oxide, and the lithium carbonate is decomposed into lithium oxide under high temperature conditions, Li2CO3=CO2+Li2O, Li + is the ion with the smallest radius in the melt, and has low steric hindrance, and has the tendency to replace other metal cations in the network structure of the molten slag. The atomic mass of Li+ is relatively small, and when the mass fraction of Li2O and Na2O is the same, Li2O can more easily provide more network-breaking O2-, and the network-breaking effect of the free oxygen ion O2- makes the protective slag cause the depolymerization of the molten slag structure.

[0022] 3、The present application can also reduce the viscosity and softening temperature of the molten slag, and improve the flow performance of the slag film, can reduce the viscosity of the liquid slag, and can make the condensed slag restore the glass state, control the crystallization temperature, research shows that, with the increase of 1% of Li2O, the melting temperature of the slag is reduced by 60℃, and the viscosity is reduced by 0.032Pa.s, the melting temperature and viscosity are reduced, and the fluidity of the liquid slag is enhanced.

[0023] 4、The present application eliminates the adverse effects of Cr2O3, Al2O3 and the like, and maintains the good performance of the protective slag, the molten steel contains Al450ppm, aluminum reacts with oxygen in the crystallizer protective slag to generate a large amount of Al2O3 inclusions, in addition, SiO2 in the protective slag is reduced by Al, which causes great changes in the composition and performance of the protective slag, and the added lithium oxide can react with Al2O3 to form 2LiAlO, inhibit the reduction of SiO2, and play a role in stabilizing the heat flow;

[0024] Cr in the molten steel is a active element, which is easy to react with O to generate (Cr-Al)2O3 and other complex inclusions, resulting in the degeneration of the protective slag and the deterioration of the use effect of the protective slag.

[0025] 5、In addition, the binary basicity of the functional protection material is designed to be slightly high, 1.1-1.3, so that high-melting-point crystals such as cuspidite (3CaO.2SiO2.CaF2) and calcium aluminum melilite (2CaO.Al2O3.SiO2) are easily precipitated in the liquid slag, thereby changing the thermal resistance of heat transfer of the slag film and slowing down heat transfer. Meanwhile, the precipitation and growth of the crystals, the solid-state slag film formed between the liquid protection slag melted into the crystallizer and the billet shell, and the liquid slag layer, when the crystallization temperature is high, the liquid slag is easy to precipitate high-melting-point crystals such as melilite and cuspidite, thereby affecting the lubricating performance of the protection slag. At the same time, a large amount of crystals are precipitated in the solid-state slag film, which changes the thermal resistance of heat transfer of the slag film;

[0026] The basicity has a significant effect on the crystallization rate, and as the basicity increases, the crystallization rate of the protection slag also increases significantly. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the described embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art belong to the scope of protection of the present application.

[0028] The main composition of the molten steel and the process parameters of the hot forming steel are as follows:

[0029] The continuous casting section is (230-250) x (900-1880), the drawing speed is 1.2-1.6 m / min, and the liquidus temperature is 1511℃,

[0030] Table 1

[0031]

[0032] In view of the design process of the functional protection material special for the hot forming steel of the automobile, the following research and invention are carried out:

[0033] 1. Hot-formed steel contains many alloying elements and belongs to high-alloy steel. Among them, easily oxidized elements such as Al and Cr readily form Cr2O3, Al2O3, etc., which are high-melting-point oxides, making the molten steel sticky. During continuous casting, Ti in the molten steel forms TiN, TiO2, and calcium titanium, etc. When the functional protective material absorbs and dissolves these inclusions to a certain extent, high-melting-point crystals such as wollastonite and calcium chromate will precipitate, destroying the glassy state of the molten slag. This leads to a significant increase in the melting point of the functional protective material, and the molten slag becomes thicker and forms a crust, affecting the surface quality of the cast billet. This invention employs a protective slag based on the CaO-SiO2-Al2O3-Na2O-CaF2 system, with the addition of an appropriate amount of lithium carbonate. Lithium carbonate is a strong co-solvent, and the resulting lithium oxide, as an alkali metal network oxide, has a small ionic radius, weak electron repulsion around the atomic nucleus, and very low steric hindrance to ion displacement. This facilitates ion recombination during crystallization. The addition of lithium carbonate increases the crystallization rate of the slag film. Furthermore, it can reduce the viscosity and softening temperature of the molten slag, improve the flow properties of the slag film, reduce the viscosity of the liquid slag, restore the condensed slag to a glassy state, control the crystallization temperature, eliminate the adverse effects of Cr2O3, Al2O3, etc., and maintain the good performance of the protective slag.

[0034] 2. Hot-formed steel grades have high carbon content. High-carbon steel is characterized by poor thermal strength, low casting temperature, and a tendency to stick and leak steel, causing continuous casting interruptions. The functional protective material has low viscosity and solidification temperature, a high tendency for glassy slag film, and good lubrication performance. In addition, the binary basicity of the functional protective material is designed to be slightly higher, at 1.1~1.3, which makes it easy for high-melting-point crystals to precipitate in the liquid slag. This changes the thermal resistance of heat transfer in the slag film, thereby slowing down heat transfer. At the same time, the precipitation and growth of crystals create pores in the solid slag film, reducing heat transfer, inhibiting lateral heat flow, increasing thermal resistance, slowing down the transfer of heat from the solidified billet shell to the crystallizer, and controlling the formation of cracks.

[0035] 3. The transition temperature of the functional protective material is set at 1090℃ (as shown in Table 2 below). The relatively low melting temperature can effectively maintain the movement of slag along the billet shell in the crystallizer without solidification, which is beneficial to improving the lubrication of the billet in the crystallizer. The viscosity of the functional protective material at 1300℃ is 0.078 Pa•s, which is suitable and can avoid the stickiness of molten steel caused by the formation of high-melting-point oxides in the protective slag in the later stage of steel casting. It has good lubrication performance, and the billet is free of defects. The low transition temperature and viscosity can also reduce the deformation of the functional protective material and maintain its chemical and thermal stability during the melting process.

[0036] Table 2

[0037]

[0038] 4. The flux is composed of light-burnt white alkali, high fluorite powder, high alumina soil, ice crystal, sodium fluoride, and sodium feldspar, which can effectively adjust the solidification temperature of the protective slag; the carbonaceous material is Japanese imported carbon black with finer mesh, which has better dispersibility in the continuous casting production grinding and plays a better wrapping role, and plays a role of heat insulation and melting speed control in use. The binder can reduce the density difference between the carbonaceous material and the base material, maintain the uniformity of the composition performance of the slurry, and have good formability in the spray granulation process, and the functional protective material produced has a bulk density of 0.6-0.8 g / cm3 and a particle size of 0.15-0.22 mm, which is suitable for the bulk density and particle size, which can ensure the heat preservation performance of the protective slag and prevent the secondary oxidation of the molten steel, and at the same time, the protective slag has excellent spreading property and air permeability.

[0039] The present application adopts the following seven embodiments for testing:

[0040]

[0041] The experimental scheme is as follows:

[0042] A steel plant casts hot formed steel, and the process flow is: hot metal pretreatment - converter - LF furnace - RH (VD) furnace - continuous casting - stack cooling - slab inspection - heating - rolling - steel plate surface inspection - normalizing + tempering - steel plate inspection, wherein the continuous casting adopts a straight arc type continuous casting machine of Aosteel, the arc radius is 12 meters, the effective length of the crystallizer copper plate is 900 mm, the pouring section is: 230 / 250×(900-1880) mm, and the pouring pulling speed is: 1.2-1.6 m / min.

[0043] After adopting the seven embodiments in the table, the field experiment shows that the functional protective material of the present application melts uniformly in the crystallizer, has few slag rings, the liquid slag thickness is 8-12 mm at normal pulling speed, the consumption per ton of steel is 0.3-0.5 kg, and the user's demand can be met.

[0044] The above is the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled persons in the technical field, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A functional protective material for continuous casting crystallizers specifically designed for automotive hot-forming steel, characterized in that, Includes raw materials in the following weight percentages: Premelted material 60.0-66.0%, lithium carbonate 1.8-3.2%, light calcined white soda ash 4.5-8.5%, bentonite 1.0-3.0%, high fluorite powder 4.4-6.4%, high alumina 1.0-3.0%, cryolite 3.0-5.0%, sodium fluoride 2.5-4.5%, albite 1.0-3.0%, binder 2.0-4.0%, imported Japanese carbon black 2.0-4.0%, graphite carbon 2.1-4.1%; The binary basicity (CaO / SiO2) in the protective slag of the protective material is 1.1-1.

3. The transition temperature of the functional protective material is 1090℃; the viscosity of the functional protective material at 1300℃ is 0.078 Pa·s.

2. The functional protective material for continuous casting crystallizers of automotive hot-forming steel as described in claim 1, characterized in that, The protective slag comprises the following chemical components by mass percentage: SiO2 20.3–36.6%, CaO 22.4–42.0%, Li2O ≤ 2.0%, Al2O3 2.5–9%, K2O + Na2O 4.0–12.5%, F - 3.0~9.5, MgO ≤ 6.5%, Fe2O3≤2.5%.

3. The functional protective material for continuous casting crystallizers of automotive hot-forming steel as described in claim 1, characterized in that, The premelted material comprises the following chemical components by mass percentage: SiO2 22.0~38.0%、CaO 25.0~40.0%、Li2 O ≤2.0、Al2 O3 2.0~9%、R2 O 4.0~15.0%、F - 2 .0~8 .0、MgO 2 .0~8 .0%、Fe2 O3≤2 .5%.

4. The functional protective material for continuous casting crystallizers of automotive hot-forming steel as described in claim 3, characterized in that, In the R2O, R is composed of Na and K elements.

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