Method for reducing cracking of refractory material
By adding steel fibers to the matrix clay of the container material for high-temperature alloy casting and preparing an alumina coating on its surface, a specific drying and calcining process is adopted to solve the problems of poor thermal shock and cracking of the container material, and efficient high-temperature alloy casting and high density and low cost of the material are achieved.
Patent Information
- Application Number
- CN202411989596.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-31
- Publication Date
- 2025-05-13
AI Technical Summary
At this stage, the thermal shock properties of the container materials for casting high-temperature alloys are poor, which leads to prone to cracking during the casting process, which in turn affects the purity and casting efficiency of the high-temperature alloy.
By adding steel fibers to the matrix clay and preparing an alumina coating on its surface, the ratio of the body thickness of the flow tank matrix clay to the thickness of the alumina coating is reasonably designed to reduce the cracking phenomenon of the coating.
It effectively reduces the cracking phenomenon of refractory materials, improves the density and adhesion of the flow channel, ensures the purity and casting efficiency of high-temperature alloys, and reduces costs.
Smart Images
Figure CN119977519A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of refractory material processing, in particular to a method for reducing cracking of refractory materials. Background Art
[0002] High-temperature alloys, mainly including nickel-based, iron-based and cobalt-based alloys, are widely used in aerospace, energy, automobile and medical fields due to their excellent mechanical properties, thermal creep resistance, corrosion resistance and surface stability at high temperatures. The preparation of high-temperature alloys mainly relies on technologies such as vacuum induction melting (VIM), vacuum arc melting (VAR), electroslag remelting (ESR) and electron beam remelting (EBR), or a combination of these technologies. As a key container for high-temperature alloy casting, the launder greatly affects the quality of the metal and the efficiency of the casting process. The launder container material for casting high-temperature alloys is mainly manufactured by casting and molding processes of corundum materials and mullite materials. However, during the casting process, the casting speed is relatively fast, generally 8-12 kg / s, and the casting time is 15-20 minutes. During the casting process, the molten steel flowing through the launder will produce slight local shrinkage, aggravating the internal stress of the launder. After use, the launder will crack and have to be repaired to introduce exogenous impurities, which will seriously affect the purity of the high-temperature alloy.
[0003] It is difficult to find a container material that has both good thermal shock resistance and good chemical stability for casting high-temperature alloys. Among traditional ceramic refractory oxides, the better the thermal shock resistance of the material, the lower its chemical stability, and the better the chemical stability of the material, the worse its thermal shock resistance. For example, although the cheaper Al2O3 is not as thermodynamically stable as ZrO2 and 3Al2O3·2SiO2, Al2O3 exhibits higher thermal shock resistance, so coating technology materials are gradually favored by researchers. Introducing surface coatings on the substrate surface can not only improve thermal shock resistance, but also reduce costs. However, most of the research on coating technology materials focuses on improving the chemical stability of the coating itself to prevent melt contamination, rather than improving its already poor thermal shock resistance and the degree of fit between the coating and the body. At the same time, the application of coatings also faces a series of challenges such as short shelf life of slurry, poor sintering performance, and low adhesion to various substrates.
[0004] Therefore, in view of the problems that the current container materials for high-temperature alloy casting have poor thermal shock resistance and low adhesion to the substrate, a method for reducing the cracking of refractory materials is needed. Summary of the invention
[0005] The object of the present invention is to provide a method for reducing cracking of refractory materials to solve the problems raised in the above background technology.
[0006] To achieve the above object, the present invention provides the following technical solution: A method for reducing cracking of refractory materials comprises the following steps:
[0007] Step 1: adding steel fiber to matrix clay: the coarse particle size range of the matrix clay is 10-3 mm; the fine particle size range is 3-0.15 mm; the coarse and fine particle strength ratio is 7:3; the mass ratio of matrix clay to 310 end hook steel fiber is 15:1, and the mixture is evenly mixed and cast to obtain a clay matrix green body.
[0008] Step 2: Determine the expansion coefficient of the coating: the ratio of the expansion coefficient of the alumina coating (α1) to the expansion coefficient of the flow channel matrix clay body (α2) is 0.5≤α1 / α2≤1.5;
[0009] Step 3: Determine and design coating thickness: The ratio of the trough matrix clay body thickness (D) to the alumina coating thickness (d) is required to be 11.5≤D / d≤16.5.
[0010] Step 4: Prepare alumina coating-clay flow trough by sol-gel impregnation and pulling method: stir the alumina sol evenly, then put the clay matrix green body in step 1 into the alumina sol, fully immerse it for 60-120 minutes, and then pull the clay matrix out of the solution at a certain pulling speed. During this pulling process, the excess alumina sol solution is returned to the liquid tank under the action of gravity. At the same time, the solution film entrained on the surface of the clay matrix forms a solute solid film as the solvent evaporates, which prompts the colloid particles to gradually form a uniform and dense stacking, reducing the number of pores.
[0011] Step 5, vacuum step-by-step drying: use vacuum drying tunnel kiln for step-by-step drying, place in vacuum drying tunnel kiln and dry at 100-150°C for 60-90min, then dry at 60-100°C for 120-180min, finally dry at 30-60°C for 60-90min, and cool naturally to room temperature. In this process, vacuum low-temperature baking and drying are performed, and stress is released, which is conducive to the full discharge of gas, reducing the degree of cracking of alumina gel, and is conducive to the formation of a complete and tightly bonded coating.
[0012] Step 6, high-temperature calcination: the sample dried in step 5 is heated in a tunnel kiln from room temperature to 450°C at a heating rate of 3°C / min, and kept warm for 60 min; then the temperature is increased to 750°C, 950°C, 1100°C, and 1200°C at a heating rate of 5°C / min, and kept warm for 60 min for calcination.
[0013] Step 7, insulation and slow cooling: The surface of the sample after high-temperature calcination in step 6 is protected by a thermal insulation cotton cover, and then kept warm at 900°C, 700°C, 500°C, and 300°C for 60 minutes respectively, and finally slowly cooled to below 200°C.
[0014] Preferably, in the step 1, the coarse particle size range of the matrix clay is 7-3 mm; the fine particle size range is 3-0.3 mm; the coarse and fine particle strength ratio is 7:3; the mass ratio of the matrix clay to the 310 end hook steel fiber is 15:1, and they are evenly mixed.
[0015] Preferably, in step 2, the ratio of the expansion coefficient of the alumina coating (α1) to the expansion coefficient of the launder matrix clay body (α2) is 0.8≤α1 / α2≤1.
[0016] Preferably, the thickness of the alumina coating in step 3 is determined and designed so that the ratio of the thickness of the trough matrix clay body (D) to the thickness of the alumina coating (d) is required to be 13.5≤D / d≤15.5.
[0017] Preferably, the immersion in step 4 is for 60-90 minutes.
[0018] Preferably, the vacuum drying process in step five is: vacuum degree ≤50Pa, drying at 120°C for 60 min, then drying at 80°C for 120 min, and finally drying at 50°C for 60 min.
[0019] Compared with the prior art, the beneficial effects of the present invention are: reasonably designing the ratio of the thickness of the flow channel matrix clay body (D) to the thickness of the alumina coating (d), adopting a vacuum drying tunnel kiln for step-by-step drying, and slowly cooling with insulation, which is conducive to the full discharge of gas, reduces the degree of cracking of the alumina coating, and is conducive to the formation of a complete and tightly bonded coating. The final flow channel has high density, few cracks, no pollution, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 This is a macroscopic photo of the material surface prepared according to Example 1 of the present invention.
[0021] Figure 2 This is a macroscopic photo of the material surface prepared according to Comparative Example 1 of the present invention.
[0022] Figure 3 This is a macroscopic photograph of the surface of the material prepared according to Comparative Example 2 of the present invention. DETAILED DESCRIPTION
[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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] See also Figure 1-Figure 3 The present invention provides a technical solution: a method for reducing cracking of refractory materials, including adding steel fiber to matrix clay, determining the expansion coefficient of the coating, determining and designing the coating thickness, preparing alumina coating-clay launder by sol-gel impregnation and pulling method, vacuum step-by-step drying, high-temperature calcination, and heat preservation and slow cooling, and the specific steps include:
[0025] Step 1: adding steel fiber to matrix clay: the coarse particle size range of the matrix clay is 10-3 mm; the fine particle size range is 3-0.15 mm; the coarse and fine particle strength ratio is 7:3; the mass ratio of matrix clay to 310 steel fiber end hook steel fiber is 15:1, and the mixture is evenly mixed and cast to obtain a clay matrix green body.
[0026] Step 2: Determine the expansion coefficient of the coating: the ratio of the expansion coefficient of the alumina coating (α1) to the expansion coefficient of the flow channel matrix clay body (α2) is 0.8≤α1 / α2≤1;
[0027] Step 3: Determine and design coating thickness: The ratio of the trough matrix clay body thickness (D) to the alumina coating thickness (d) is required to be 13.5≤D / d≤15.5.
[0028] Step 4: Prepare alumina coating-clay flow trough by sol-gel impregnation and pulling method: stir the alumina sol evenly, then put the clay matrix green body in step 1 into the alumina sol, fully immerse it for 60-120 minutes, and then pull the clay matrix out of the solution at a certain pulling speed. During this pulling process, the excess alumina sol solution is returned to the liquid tank under the action of gravity. At the same time, the solution film entrained on the surface of the clay matrix forms a solute solid film as the solvent evaporates, which prompts the colloid particles to gradually form a uniform and dense stacking, reducing the number of pores.
[0029] Step 5, vacuum step-drying: use vacuum drying tunnel kiln for step-drying, place in vacuum drying tunnel kiln and dry at 100-150°C for 60-90min, then dry at 60-100°C for 120-180min, finally dry at 30-60°C for 60-90min, and cool naturally to room temperature. In this process, vacuum low-temperature baking and drying are carried out to release stress, which is conducive to the full discharge of gas, reduce the cracking degree of alumina gel, and facilitate the formation of a complete and tightly bonded coating.
[0030] Step 6, high-temperature calcination: the dried sample is heated from room temperature to 450°C at a heating rate of 3°C / min in a tunnel kiln and kept at that temperature for 60 min; then the temperature is increased to 750°C, 950°C, 1100°C and 1200°C at a heating rate of 5°C / min, and kept at that temperature for 60 min for calcination.
[0031] Step 7: Insulation and slow cooling: The surface of the sample after high-temperature calcination is protected by a thermal insulation cotton cover, and then kept warm at 900°C, 700°C, 500°C, and 300°C for 60 minutes respectively, and finally slowly cooled to below 200°C.
[0032] Example 1
[0033] This embodiment is applied to a pouring trough for a vacuum induction furnace with a volume of 2.5 ton.
[0034] Adding steel fiber to matrix clay: premix the matrix clay in an Erich high-power mixer for 5 minutes according to the ratio of 7:3 for coarse particles of 7-3 mm and fine particles of 3-0.15 mm. Turn off the high-speed rotor, keep the mixing disk rotating, slowly add the end hook steel fiber (the mass ratio of matrix clay to 310 end hook steel fiber is 15:1), mix at a low speed for 5 minutes, complete the homogenization process, and cast to obtain the clay matrix green body.
[0035] Determination of the expansion coefficient of the coating: the ratio of the expansion coefficient of the alumina coating (α1) to the expansion coefficient of the trough matrix clay body (α2) is 0.8≤α1 / α2≤1;
[0036] Coating thickness determination and design: The ratio of the trough matrix clay body thickness (D) to the alumina coating thickness (d) is required to be 13.5≤D / d≤15.5.
[0037] Preparation of alumina coating-clay flow trough by sol-gel impregnation and pulling method: stir the alumina sol evenly, then put the clay matrix green body in step 1 into the alumina sol, allow it to be fully immersed for 60-90 minutes, and then pull the clay matrix out of the solution at a certain pulling speed.
[0038] Vacuum step-by-step drying: vacuum drying tunnel kiln is used for step-by-step drying. The vacuum drying process is: vacuum degree ≤50Pa, drying at 120℃ for 60min, then drying at 80℃ for 120min, and finally drying at 50℃ for 60min.
[0039] High-temperature calcination: The dried sample was heated from room temperature to 450°C at a heating rate of 3°C / min in a tunnel kiln and kept at that temperature for 60 min; then the temperature was increased to 750°C, 950°C, 1100°C, and 1200°C at a heating rate of 5°C / min and kept at that temperature for 60 min for calcination.
[0040] Insulation and slow cooling: After high-temperature calcination, the surface of the sample is protected by a thermal insulation cotton cover and then slowly cooled to below 200°C.
[0041] The launder finally prepared by the present invention has a moderate coating thickness of 1.7 mm to 1.8 mm, and the vacuum step-by-step drying and cooling processes are reasonable. During the launder vacuum drying process, the stress is released, the gas is fully discharged, and the cracking degree of the aluminum oxide coating is reduced, which is conducive to forming a complete and tightly bonded coating.
[0042] Comparative Example 1
[0043] A method for reducing cracking of refractory materials is carried out according to the method in Example 1, except that the ratio of the thickness of the launder matrix clay body (D) to the thickness of the alumina coating (d) is 17.5≤D / d≤20.5, the size effect is large, and the thickness of the alumina coating (d) is small, which is 1.2 mm to 1.4 mm.
[0044] The launder prepared by this method had a thin alumina coating, which peeled off after sintering and could not be perfectly bonded to the clay matrix.
[0045] Comparative Example 2
[0046] A method for reducing cracking of refractory materials is carried out according to the method in Example 1, except that the vacuum drying process is: vacuum degree ≤50Pa, drying at 120°C for 240 minutes, and then the surface of the sample is not protected by an insulation cotton cover plate and is directly taken out of the furnace for cooling.
[0047] The flow trough prepared by this method adopts a one-step drying method for vacuum drying instead of step-by-step drying, and no slow cooling is performed, which results in the coating being graded and cracked on the surface of the flow trough after sintering.
[0048] The attached figure and table show the surface quality of the launder after sintering. Figure 1 The crack condition of the flow channel after use is shown in Table 1, and the statistics of the flow channel life results are shown in Table 2.
[0049] Table 1 Cracks of the flow channel after use
[0050] Sample No. Number of cracks Example 1 0 Comparative Example 1 6 Comparative Example 2 2
[0051] Table 2 Life of the flow channel after use
[0052] Sample No. Lifespan (number of pouring times) Example 1 5 Comparative Example 1 3 Comparative Example 2 3
[0053] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.
Claims
1. A method for reducing cracking of refractory materials, characterized in that: The following steps are involved: Step 1: Add steel fiber to matrix clay: evenly mix matrix clay and 310 end hook steel fiber, and cast to obtain a clay matrix green body; Step 2: Determine the expansion coefficient of the coating: the ratio of the expansion coefficient of the alumina coating (α1) to the expansion coefficient of the launder matrix clay body (α2) is 0.5≤α1 / α2≤1.5, preferably 0.8≤α1 / α2≤1; Step 3: Determine and design coating thickness: The ratio of the thickness of the trough matrix clay body (D) to the thickness of the alumina coating (d) is required to be 11.5≤D / d≤16.5, preferably 13.5≤D / d≤15.5; Step 4: Prepare the alumina coating-clay launder by sol-gel impregnation and pulling method: stir the alumina sol evenly, then put the clay matrix green body in step 1 into the alumina sol, fully immerse it for 60-120 minutes, and then pull the clay matrix from the solution at a certain pulling speed; Step 5, vacuum step drying: vacuum step drying, placed in a vacuum drying tunnel kiln at 100-150°C for 60-90min, then dried at 60-100°C for 120-180min, finally dried at 30-60°C for 60-90min, and naturally cooled to room temperature; Step 6, high temperature calcination: the sample after vacuum step-drying was heated from room temperature to 450°C in a tunnel kiln at a heating rate of 3°C / min, and kept at that temperature for 60min; then the temperature was respectively increased to 750°C, 950°C, 1100°C, and 1200°C at a heating rate of 5°C / min, and kept at that temperature for 60min for calcination; Step 7: Insulation and slow cooling: The surface of the calcined sample is protected by a thermal insulation cotton cover, and then kept warm at 900°C, 700°C, 500°C, and 300°C for 60 minutes respectively, and finally slowly cooled to below 200°C.
2. A method for reducing refractory cracking according to claim 1, characterized in that: In the step three, the coating thickness is reasonably determined and designed to relieve internal stress, effectively prevent cracks from occurring, and solve the problem of thermal expansion mismatch between the coating and the substrate.
3. A method for reducing cracking of refractory materials according to claim 1, characterized in that: The step 5 uses vacuum step drying, which is conducive to the full discharge of gas, ensuring the formation of a complete and tightly bonded coating that can perfectly fit the substrate without cracking or falling off of the coating.
4. A method for reducing cracking of refractory materials according to claim 1, characterized in that: In step seven, a heat-insulating cotton cover plate is required for heat preservation and slow cooling, and the temperature is kept at 900°C, 700°C, 500°C, and 300°C for 60 minutes respectively. There is a gradient difference, which is conducive to crack elimination.