Special continuous casting crystallizer function protection material for M2 high-speed steel

Abstract

The invention provides a continuous casting crystallizer function protection material special for M2 high-speed steel, and belongs to the technical field. The invention relates to a function protection material for a special continuous casting crystallizer for M2 high-speed steel, which comprises the following raw materials in percentage by mass: 35-45% of low-alkalinity sodium-containing pre-melting material, 3.5-7.5% of light-burned white alkali, 12-18% of high-grade fluorite powder, 2.5-7.5% of sodium fluoride, 0.5-5% of borax, 4-8% of cement clinker, 5.0-10.0% of wollastonite, 0.5-3.5% of bauxite, 4-8% of magnesia, 5.5-15% of carbonaceous material and 0.1-3.2% of binder, and the sum of the mass percentages of the raw materials is 100%. The invention discloses a special continuous casting crystallizer function protection material for M2 high-speed steel, which overcomes the defects of surface and subsurface cracks and the like in continuous casting of the M2 high-speed steel, improves the quality of a casting blank and ensures smooth operation of a process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgical auxiliary materials, and particularly relates to a special continuous casting crystallizer functional protection material for M2 high-speed steel. BACKGROUND

[0002] M2 (W6Mo5Cr4V2) high-speed steel is widely used in key fields such as cutting tools and molds, and important industries such as automobile manufacturing, aerospace and numerical control machining.

[0003] Continuous casting has the advantages of energy saving, cost reduction and productivity improvement. However, the application of continuous casting in high-speed steel production is very slow. The high-carbon and high-alloy composition leads to the formation of coarse carbides during solidification, and the surface of the billet is prone to cracks, subsurface porosity and other defects.

[0004] At present, the production methods of high-speed steel mainly include traditional casting method, powder metallurgy method, spray forming method and electroslag remelting method, and the traditional casting method process is still mainly used in actual industrial production. The casting process of high-speed steel has the problems of slow solidification speed, coarse grains, and a large amount of alloy carbides precipitating and growing along the grain boundaries during solidification, which leads to the formation of coarse carbides and intergranular carbide network, causing serious grain boundary embrittlement and reduced toughness. At the same time, repeated forging or rolling at high temperature is easy to cause cracking and low material yield. Due to its inherent shortcomings, this process has the problems of low production efficiency, high production cost and many surface defects, which does not meet the development trend of low-cost high-speed steel.

[0005] With the continuous improvement of continuous casting process, some advanced high-speed steel production enterprises have begun to use continuous casting technology to produce high-speed steel. The continuous casting of high-speed steel has the problems of difficult pouring, surface cracks, subsurface porosity and other defects, which seriously restricts the progress of the metallurgical continuous casting technology revolution.

[0006] The continuous casting crystallizer functional protection material (hereinafter referred to as the protection slag) has five functions in the crystallizer: heat insulation, prevention of secondary oxidation of molten steel, inclusion absorption, heat transfer control and lubrication, which can stabilize the continuous casting process, ensure process smoothness and improve the surface and subsurface quality of the billet. Therefore, it is of great significance to study the special continuous casting crystallizer functional protection material for M2 high-speed steel. At present, it is urgent to design a special protection slag for M2 high-speed steel to fill the market gap, promote product quality and production process stability, and create higher value for customers. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a special continuous casting crystallizer functional protection material for M2 high-speed steel to improve the surface and subsurface cracks and other defects of M2 high-speed steel continuous casting, improve the quality of the billet and ensure the smoothness of the process.

[0008] To solve the above technical problems, the technical scheme adopted by the present application is: a special continuous casting crystallizer functional protection material for M2 high-speed steel, comprising the following raw materials in mass percentage: low-alkalinity sodium-containing pre-melted material: 35-45%, light-burned white alkali: 3.5-7.5%, high-grade fluorite powder: 12-18%, sodium fluoride: 2.5-7.5%, borax: 0.5-5%, cement clinker: 4-8%, wollastonite: 5.0-10.0%, bauxite: 0.5-3.5%, magnesia: 4-8%, carbonaceous material: 5.5-15%, binder: 0.1%-3.2%, and the sum of the mass percentages of the raw materials is 100%.

[0009] Optionally, the chemical composition of the low-alkalinity sodium-containing pre-melted material includes, in mass percentage: SiO2 65-78%, CaO 4.5-12.5%, Al2O3 1-5%, R2O 5-15%, MgO 0.5-4.5%, and the balance is inevitable impurities, wherein R2O = K2O + Na2O, and the loss on ignition of the low-alkalinity sodium-containing pre-melted material is ≤1.5%.

[0010] Optionally, the mass percentage content of CaF2 in the high-grade fluorite powder is ≥97%, the mass percentage content of NaF in the sodium fluoride is ≥98.5%, the mass percentage content of Na2CO3 in the light-burned white alkali is ≥98%, and the mass percentage content of Al2O3 in the bauxite is ≥80%.

[0011] Optionally, the carbonaceous material is carbon black and graphite carbon, and the mass ratio of the carbon black to the graphite carbon is (0.5-5):(5-10).

[0012] Optionally, the binder is calcium lignosulfonate.

[0013] Optionally, the binary alkalinity of the special continuous casting crystallizer functional protection material for M2 high-speed steel is 0.50-0.80, the hemispherical point is 900-1020℃, and the viscosity at 1300℃ is 0.210-0.350 Pa·s.

[0014] Optionally, the chemical composition and mass percentage of the special continuous casting crystallizer functional protection material for M2 high-speed steel are: SiO2 27-37%, CaO 15.5-25.5%, Al2O3 1-5%, Fe2O3 ≤1.5%, MgO 2-6%, F - 6-12%, K2O + Na2O 11-17%, B2O3 0.5-5%, free carbon 8-12%, and the balance is inevitable impurities.

[0015] The main chemical components of W6Mo5Cr4V2 steel (in mass percent) include: carbon 0.85%~1.05%, tungsten 5.50%~6.75%, molybdenum 4.50%~5.50%, chromium 3.75%~4.50%, vanadium 1.75%~2.20%, which belongs to high-carbon high-alloy steel. On the one hand, during the solidification process of W6Mo5Cr4V2 steel, a large amount of alloying elements will promote the precipitation of coarse and brittle eutectic carbides at the grain boundaries, which will cut the cast blank matrix and even cause crack defects. On the other hand, the high content of alloying elements leads to high viscosity of the liquid steel, wide solidification temperature range, and large friction force between the primary shell and the mold wall. At the same time, the high-temperature strength of the shell is high, and the uneven solidification shrinkage is more prone to surface and corner cracks. In order to inhibit the coarsening of carbides, the ideal state is rapid cooling of the cast blank, but too fast cooling will intensify the uneven heat transfer between the shell and the mold, leading to thermal stress concentration and inducing cracks. Therefore, the heat transfer of the protective slag must be uniform and moderate to balance the needs of rapid cooling and uniform slow cooling.

[0016] In the prior art, a Chinese patent application with publication number CN106735023A discloses a high-oxygen enamel steel special continuous casting mold functional protective material, which is made of raw materials with the following mass percentages: pre-melted material 55.0~62.5%, lithium carbonate 4~6%, light-burnt white alkali 4~6%, borax 1~3%, high-grade fluorite powder 8~10%, high-alumina soil 1~4%, ice crystal stone 4~6%, sodium fluoride 3~5%, sodium feldspar 2~4%, fine glass powder 2~4%, imported carbon black 0~2%, and graphite 0~2%, and the sum of the contents of the raw materials is 100%. In the case of casting M2 high-speed steel using the protective material, the melting is unstable, the three-layer structure is not clear, the slag film inflow is not uniform enough, cracks appear on the surface and under the skin of the cast blank, and the crack rate is higher than 5%, which is not suitable for M2 high-speed steel continuous casting. For example, a Chinese invention patent with publication number CN103381474B discloses a bearing steel special continuous casting mold protective material, which has the following chemical components and mass percentages: SiO2 9.0~35.0%, CaO 22.0~28.0%, Al2O3 1.0~4.0%, Fe2O3 ≤2.0%, NaO 10.0~13.0%, F 6.0~9.0%, MgO 5.0~9.0%, fixed carbon 10~16%, volatile matter 5~11%, and binary basicity (CaO / SiO) 0.67~0.87. The protective material is used for M2 high-speed steel continuous casting, the liquid slag layer is thin, the slag film inflow is not uniform, and the problems of slag inclusion and steel leakage occur, which is not suitable for M2 high-speed steel continuous casting. The above-mentioned special protective slag is not suitable for M2 high-speed steel. Therefore, it is urgent to develop a special protective slag for M2 high-speed steel to meet the current continuous casting needs.

[0017] Compared with the prior art, the present application has the following advantages: The present application aims at the problems of M2 steel continuous casting process, such as the severe reaction of protective slag and liquid steel interface, insufficient slag film lubrication, and frequent surface cracks of the casting blank, caused by the characteristics of high carbon (0.85%~1.05%) and high alloy (Cr 3.75%~4.50%, Mo 4.50%~5.50%), and develops a functional protective slag with low viscosity, high glassization tendency and stable heat transfer characteristics, to realize the industrial application breakthrough of M2 high speed steel continuous casting process.

[0018] In the present application, a high proportion of low-alkalinity sodium-containing pre-melted material is added to the protective slag, the binary alkalinity R is 0.07~0.16, the melting uniformity is improved, the adiabatic insulation effect and environmental protection performance are optimized, the melting performance, fluidity and spreading property in the crystallizer are all superior to the application of conventional raw material base, and the ignition loss and volatilization are lower.

[0019] In the present application, a high proportion of magnesia (MgO) is added to the protective slag, aiming at the case that the high alloying elements of M2 high speed steel and the enrichment of high melting point substances easily cause the degeneration of the protective slag, the magnesia can improve the melting characteristics of the protective slag, the MgO as an alkaline oxide can destroy the silicate network structure, such as breaking the Si-O tetrahedral chain, thereby reducing the high temperature viscosity of the protective slag and improving the fluidity. The magnesia can also improve the controlled crystallization behavior of the protective slag, inhibit the precipitation of high melting point crystals, and stabilize the crystallization performance, which is specifically shown as follows: the MgO forms low melting point compounds (such as melilite and magnesio-roselith) with Al2O3 and SiO2, etc., inhibits the precipitation of harmful crystals such as cuspidite (Ca4Si2O7F2), prolongs the crystal incubation time, reduces the formation of slag ring, and based on the chemical stability, can also stabilize the initial performance of the protective slag after adsorbing inclusions. At the same time, the magnesia can also optimize the heat transfer and lubrication, the MgO can reduce the thickness of the solid slag film, reduce the crystallization rate, and at the same time improve the heat transfer characteristic time and heat flux density, which is helpful to uniform heat control and reduces the casting blank crack. By reducing the viscosity and transition temperature, the MgO promotes the formation of liquid slag film, improves the lubrication between the casting blank and the crystallizer, reduces the friction and the risk of leakage, solves the problems of large pouring difficulty and high production cost of M2 high speed steel casting. Moreover, the MgO has a large surface tension, which can improve the situation that the low melting point and low viscosity protective slag is easy to roll slag, and better control the surface quality and subsurface quality of the casting blank.

[0020] The application adds borax (B2O3) into the protective slag, aiming at the complex situation that the M2 high-speed steel has high alloying elements, many high-melting-point substances, low liquidus, low surface temperature of the molten steel, and the protective slag is difficult to melt and dissolve high-melting-point inclusions. The use of borax can reduce the melting point and viscosity of the protective slag. The melting point of B2O3 is low (about 450 DEG C), and it is easy to form a eutectic with other components (such as CaO.B2O3, MgO.B2O3), which can significantly reduce the melting temperature of the protective slag; in the high-temperature melting stage, B2O3 exists in the form of BO3 triangle, and this planar structure is more loose than SiO4 tetrahedron, which can destroy the continuity of the silicon-oxygen network, thereby significantly reducing the viscosity of the glass liquid. The viscosity-reducing property of B2O3 can partially replace fluorides, reduce the amount of CaF2, and promote green and environmentally-friendly production.

[0021] The application adds an appropriate proportion of carbonaceous material and binder into the protective slag base material, wherein: the binder is calcium lignosulfonate, the carbonaceous material is carbon black and graphite carbon, the calcium lignosulfonate is combusted before the carbonaceous material and releases gas, thereby reducing the consumption of the carbonaceous material, and the residue after combustion of the calcium lignosulfonate and the carbonaceous material together prevent the base material from forming sintered blocks and producing slag strips, so that the melting speed of the protective slag can be controlled, the carbon pick-up of the cast blank can be inhibited, the thickness of the molten slag layer can be kept stable, and the quality of the cast blank can be improved.

[0022] The application forms a composite silicate structure among the chemical components of the protective slag, the Si-O tetrahedron of the composite silicate structure forms a long chain by sharing two corners, and when MgO, CaO, Na2O, F - When the divalent or monovalent alkali metal oxide and fluoride are added into the silicate melt, the Si-O tetrahedral network structure is destroyed, the deformation resistance of the chain is reduced due to the increase of the fracture, thereby reducing the crystallization temperature of the protective slag and increasing the surface tension. The viscosity-temperature curve is gently inclined during the temperature reduction process at 1300 DEG C, the crystallization and solidification of the slag film are slow, the friction is reduced during the lubrication process of the slag film, so that the scratch of the blank shell caused by the large friction is reduced, and the phenomenon of leakage during the casting process is also reduced. The high surface tension of the protective slag can well stabilize the liquid surface of the crystallizer, and can separate the distance between the meniscus of the molten steel and the carbon-rich layer and the semi-molten layer, thereby significantly reducing the probability of slag inclusion and carbon pick-up of the cast blank. The obtained protective slag can not only meet the lubrication of the crystallizer during low-temperature casting, but also can ensure the stability of the molten slag, improve the quality of the cast blank, reduce the leakage rate, and meet the user's demand. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0024] Figure 1 Figure 1 is a diagram showing the surface quality of M2 high-speed steel billets. DETAILED DESCRIPTION

[0025] For a better understanding of the present application, reference will be made to the following examples which further illustrate the application. The application, however, is not to be limited to the following examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. It will be apparent, however, to one skilled in the art, that the present application can be practiced without one or more of these specific details.

[0026] Unless otherwise indicated, all starting materials are commercially available and, unless otherwise indicated, contain no other components than those explicitly named.

[0027] In the following description, the content of CaF2 in high-grade fluorite powder is ≥97% by mass.

[0028] The content of NaF in sodium fluoride is ≥98.5% by mass.

[0029] The content of Na2CO3 in light-burned white alkali is ≥98% by mass.

[0030] The content of Al2O3 in bauxite is ≥80% by mass.

[0031] The particle size of each starting material is passed through a 300-mesh sieve.

[0032] The following details the raw materials, chemical composition and performance parameters of the M2 high-speed steel special continuous casting mold functional protection material of the present application through five examples. Among them: The various raw materials and their mass percentages of the M2 high-speed steel special continuous casting mold functional protection material provided in Examples 1-5 are shown in Table 1.

[0033] The chemical composition and mass percentages of the low-alkalinity sodium-containing pre-melted material of the M2 high-speed steel special continuous casting mold functional protection material provided in Examples 1-5 are shown in Table 2.

[0034] The chemical composition and mass percentages of the M2 high-speed steel special continuous casting mold functional protection material provided in Examples 1-5 are shown in Table 3.

[0035] The physicochemical properties of the M2 high-speed steel special continuous casting mold functional protection material provided in Examples 1-5 are shown in Table 4.

[0036] Table 1 Weight percentages (wt%) of various raw materials of the functional protection material provided in Examples 1-5 Table 2 Mass percentage (wt%) of chemical composition of low basicity sodium-containing pre-melted material of Examples 1-5 Table 3 Mass percentage (wt%) of chemical composition of functional protection material provided by Examples 1-5 Table 4 Performance parameters of functional protection material of Examples 1-5 The following are comparative examples.

[0037] Comparative Example 1: A functional protection material for continuous casting crystallizer special for M2 high-speed steel, which is different from Example 2 in that the mass percentage of SiO2 in the sodium-containing pre-melted material used is 50%, and the mass percentage of CaO is 20%.

[0038] Comparative Example 2: A functional protection material for continuous casting crystallizer special for M2 high-speed steel, which is different from Example 2 in that the magnesia is omitted.

[0039] Comparative Example 3: A functional protection material for continuous casting crystallizer special for M2 high-speed steel, which is different from Example 2 in that the borax is omitted.

[0040] Comparative Example 4: A functional protection material for continuous casting crystallizer special for M2 high-speed steel, which is different from Example 2 in that the mass percentages of carbon black, graphite carbon, and calcium lignosulfonate are 2.0%, 2.0%, and 5.0%, respectively.

[0041] Comparative Example 5: A functional protection material for continuous casting crystallizer special for M2 high-speed steel, which is different from Example 2 in that the bauxite is replaced by high-alumina soil, and the mass percentage of Al2O3 in the high-alumina soil is ≥60%.

[0042] The preparation methods of the functional protection materials for continuous casting crystallizer special for M2 high-speed steel of Examples 1-5 and Comparative Examples 1-5 above are all obtained by uniformly mixing the raw materials.

[0043] The following is an effect evaluation.

[0044] A steel plant casts M2 high-speed steel, and the process flow is: hot metal pretreatment → combined blown converter → VD → bloom continuous casting, wherein the bloom continuous casting adopts a vertical continuous casting machine, the metallurgical length is 3500 mm, the crystallizer length is 750 mm, the effective length is 650 mm, the pouring section is 140 mm x 140 mm, and the pouring speed is 0.5-0.8 m / min.

[0045] The chemical composition of the molten steel of the above M2 high-speed steel is shown in Table 5 below.

[0046] Table 5 Molten steel composition of M2 high-speed steel The functional protection materials prepared in Examples 1-3 and Comparative Examples 1-5 of the present application were respectively used for continuous casting of M2 high-speed steel shown in Table 5, and the continuous casting process and conditions were the same, and each material was made in parallel for 5 times, the test conditions of each functional protection material were recorded, and the surface and subsurface cracks of the obtained casting blank were observed. The results are shown in Table 6.

[0047] Table 6 Test results of functional protection materials The results in Table 6 show that the functional protection material of the present application used for continuous casting of M2 high-speed steel has moderate flame in the crystallizer, uniform melting, good spreading, liquid slag thickness of 5-8 mm, consumption of 0.20-0.24 kg per ton of steel, good surface quality of the casting blank, crack rate less than 0.5%, no slag ring, and can better meet the needs of users.

[0048] Comparative Examples 1-5 and Example 2, only one parameter is changed, and the obtained functional protection material is also used for continuous casting of M2 high-speed steel, but the observation results show that some key indicators of the functional protection material of Comparative Examples 1-5 are obviously deteriorated. Overall, it is shown that the scheme of Example 2 is more beneficial to uniform melting and spreading of the protection slag, controlling appropriate liquid slag layer thickness and slag consumption, significantly reducing the crack rate of M2 high-speed steel continuous casting, improving the slag ring phenomenon, thereby improving the quality of the casting blank and ensuring the smooth process.

[0049] The surface quality of M2 high-speed steel blank prepared by using the continuous casting crystallizer protection material of Example 2 of the present application and without using the protection material is compared as shown in Table 7. Figure 1 After using the continuous casting crystallizer protection material of Example 2 of the present application, the surface of the steel blank has no cracks, and the surface quality meets the requirements.

[0050] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the specific embodiments of the present application can be modified or some technical features can be replaced by equivalent; without departing from the spirit of the technical solutions of the present application, they should be covered in the technical solution range of the present application claimed.

Claims

1. A functional protective material for continuous casting crystallizers of M2 high-speed steel, characterized in that: The raw materials include the following percentages by weight: low-alkalinity sodium-containing pre-melted material: 35-45%, light-burned white alkali: 3.5-7.5%, high-grade fluorite powder: 12-18%, sodium fluoride: 2.5-7.5%, borax: 0.5-5%, cement clinker: 4-8%, wollastonite: 5.0-10.0%, bauxite: 0.5-3.5%, magnesia: 4-8%, carbonaceous materials: 5.5-15%, and binder: 0.1%-3.2%, with the sum of the percentages of each raw material being 100%.

2. The functional protective material for M2 high-speed steel continuous casting crystallizer as described in claim 1, characterized in that: The chemical composition of the low-alkalinity sodium-containing premelted material, by mass percentage, includes: SiO2 65-78%, CaO 4.5-12.5%, Al2O3 1-5%, R2O 5-15%, MgO 0.5-4.5%, with the balance being unavoidable impurities. R2O = K2O + Na2O. The loss on ignition of the low-alkalinity sodium-containing premelted material is ≤1.5%.

3. The functional protective material for M2 high-speed steel continuous casting crystallizer as described in claim 2, characterized in that: The high-grade fluorite powder contains ≥97% CaF2 by mass.

4. The functional protective material for M2 high-speed steel continuous casting crystallizer as described in claim 3, characterized in that: The sodium fluoride contains ≥98.5% NaF by mass.

5. The functional protective material for M2 high-speed steel continuous casting crystallizer as described in claim 4, characterized in that: The mass percentage content of Na2CO3 in the light calcined white alkali is ≥98%.

6. The functional protective material for a continuous casting crystallizer of M2 high-speed steel as described in claim 5, characterized in that: The bauxite contains ≥80% Al2O3 by mass.

7. The functional protective material for a continuous casting crystallizer of M2 high-speed steel as described in claim 6, characterized in that: The carbonaceous material is carbon black and graphite carbon, and the mass ratio of carbon black to graphite carbon is (0.5-5):(5-10).

8. The functional protective material for a continuous casting crystallizer of M2 high-speed steel as described in claim 7, characterized in that: The binder is calcium lignosulfonate.

9. The functional protective material for a continuous casting crystallizer of M2 high-speed steel as described in claim 8, characterized in that: Its binary basicity is 0.50-0.80, hemispherical point is 900-1020℃, and viscosity at 1300℃ is 0.210-0.350 Pa•s.

10. A functional protective material for continuous casting crystallizers of M2 high-speed steel as described in any one of claims 1-8, characterized in that: Its chemical composition and mass percentage are as follows: SiO2 27-37%, CaO 15.5-25.5%, Al2O3 1-5%, Fe2O3 ≤1.5%, MgO 2-6%, F - 6-12%, K2O+Na2O 11-17%, B2O 30.5-5%, free carbon 8-12%, balance being unavoidable impurities.

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