A method for optimizing a casting process of a heat-resistant steel and a casting method

Abstract

The present application relates to the technical field of heat-resistant steel casting, in particular to a heat-resistant steel casting process optimization method and a casting process, which simulates the casting process through multi-physical field coupling simulation, judges whether there is a hot spot area or shrinkage phenomenon in the lower box of the sand mold, and improves the initially determined sand mold design scheme according to the simulation results, including adding a barbed riser, adjusting the size of the barbed riser, and setting a surrounding measure in the barbed riser. Through the above optimization measures, a casting process capable of effectively solving the shrinkage and shrinkage problems of the thick part of the lower box of the heat-resistant steel casting is obtained, which significantly improves the casting quality and production efficiency, the process yield is significantly improved, the hot spot volume is completely eliminated, and the shrinkage defect occurrence rate is significantly reduced. At the same time, the casting process is simulated through multi-physical field simulation technology, the number of tests is reduced, the raw materials are saved, and a reliable technical support is provided for the precision casting of high-temperature parts.

Description

Technical Field

[0001] This invention relates to the field of heat-resistant steel casting technology, specifically to a method for optimizing the heat-resistant steel casting process and a casting method. Background Technology

[0002] The structure of heat-resistant steel components such as turbine housings often contains multiple isolated thick sections. When manufacturing casting molds, it is inevitable that some of these thick sections will be located within the lower mold. Because risers in traditional casting methods are mostly located in the upper mold or on the side, the thick sections in the lower mold are far from the risers. Since heat-resistant steel has a wide solidification temperature range, heat spots form in the thick sections of the lower mold during solidification. This makes it impossible for traditional riser placement methods to effectively compensate for the shrinkage of these thick sections within the lower mold, resulting in defects such as shrinkage porosity and shrinkage cavities in the casting.

[0003] Some existing technologies use a combination of chills and insulation blocks to control the cooling sequence of heat-resistant steel. By attaching chills to the thick parts, the thick parts cool first, and insulation blocks are set in the feeding channels to keep the feeding channels unobstructed, thereby improving the temperature field of the casting. This allows the molten metal to replenish the thick parts through the feeding channels when they solidify.

[0004] However, in practical applications, this method is not ideal. While chills increase the cooling rate, they affect the final microstructure of the heat-resistant steel, and the rapid cooling of chills increases the risk of hot cracking. Heat-resistant steel has a wide solidification temperature range, and the fluidity of the molten metal decreases rapidly during solidification. When thick sections are not connected to the feeding channels, the riser feeding pressure is difficult to transmit to the center of the hot spot, resulting in ineffective replenishment of molten metal and defects such as shrinkage porosity and shrinkage cavities. Summary of the Invention

[0005] To address the technical problems of shrinkage porosity and shrinkage cavities in the thicker sections of the lower mold during the casting of heat-resistant steel, this application provides an optimized casting process method and a casting method for heat-resistant steel. The optimized casting process method includes the following steps:

[0006] S11. Based on the shape of the casting, determine the placement scheme of the casting, the structure of the upper and lower molds, set the distribution and size of the risers and the casting channels connecting each riser, establish the geometric model of the sand mold, and determine the sand mold design scheme in accordance with the principle of sequential solidification.

[0007] S12. Based on the sand mold design scheme, the multi-physics field coupling simulation method is used to simulate the casting process to determine whether there is a hot spot area in the lower box of the sand mold. If so, a barbed riser is set at the lower box position corresponding to the hot spot area, and the barbed riser is connected to the casting channel or the casting cavity.

[0008] S13, re-simulating the casting process according to the improved sand mold design scheme, judging whether the hot spot region exists the shrinkage phenomenon according to the simulation result, if yes, adjusting the size of the barbed riser, if no, outputting the improved sand mold design scheme;

[0009] S14, re-simulating the casting process according to the twice-improved sand mold design scheme, judging whether the hot spot region exists the shrinkage phenomenon according to the simulation result, if yes, setting the heat preservation measure at the communication between the barbed riser and the casting cavity, outputting the sand mold design scheme, if no, outputting the twice-improved sand mold design scheme.

[0010] Specifically, whether the hot spot region exists is judged by the following steps:

[0011] S121, calculating the overall average temperature of all units in the casting cavity;

[0012] S122, selecting one unit one by one, obtaining the simulation temperature of the unit, calculating the absolute difference between the simulation temperature and the average temperature of the unit, if the absolute difference is greater than the first threshold value and the simulation temperature of the unit is greater than the average temperature, marking the unit as a hot spot unit;

[0013] S123, repeatedly executing step S122 until all units participate in the calculation;

[0014] S124, when the number of hot spot units is greater than the second threshold value, and at least one hot spot unit has a common node with other hot spot units, it is determined that the hot spot region exists in the lower box;

[0015] Wherein, the unit is a unit in the finite element model of the sand mold.

[0016] Specifically, the size of the barbed riser is adjusted by the following steps:

[0017] S131, judging whether the size of the barbed riser exceeds the allowable value, if yes, setting the heat preservation measure at the communication between the barbed riser and the casting cavity, outputting the sand mold design scheme, if no, obtaining the volume of the hot spot region, calculating the volume ratio of the hot spot region to the thick part;

[0018] S132, according to the volume ratio of the hot spot region to the thick part, the size of the barbed riser is enlarged.

[0019] Specifically, the volume of the hot spot region is obtained by the following steps: calculating the total volume of all hot spot units, which is the volume of the hot spot region.

[0020] The application also provides a heat-resistant steel casting method, which is obtained by optimizing the above method, comprising the following steps:

[0021] S21, according to the sand mold design scheme, a sand mold is made, the lower box of the sand mold is provided with a barbed riser, the barbed riser is communicated with a casting cavity and a pouring runner, and heat preservation measures are arranged at the communication part of the barbed riser and the casting cavity;

[0022] S22, a sand core is made, and an anti-sand sticking coating is coated on the outer surface of the sand core;

[0023] S23, the cavity of the sand mold is cleaned, the sand core is placed in the lower box, and the upper box and the lower box are combined and sealed;

[0024] S24, the casting is poured, and after the casting is cooled, it is taken out and cleaned.

[0025] The technical effects and advantages of the present application: through multi-physical field coupling simulation, whether there is a hot spot area or a shrinkage phenomenon in the lower box of the sand mold is judged, and the initially determined sand mold design scheme is improved according to the simulation results, including adding a barbed riser, adjusting the size of the barbed riser, and setting a surrounding measure in the barbed riser. Through the above optimization measures, a casting method capable of effectively solving the shrinkage and shrinkage problem of the thick part of the lower box of the heat-resistant steel casting is obtained, which significantly improves the casting quality and production efficiency, the process yield is significantly improved, the hot spot volume is completely eliminated, and the shrinkage defect occurrence rate is significantly reduced. At the same time, the casting method is simulated through multi-physical field simulation technology, the number of tests is reduced, the raw materials are saved, and a reliable technical support is provided for the precision casting of high-temperature parts. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The flowchart of the casting process optimization method provided by the present application.

[0027] Figure 2 The sand box structure diagram in the casting method provided by the present application.

[0028] Figure 3 The flaw detection result of the part produced by the conventional casting method in the first embodiment of the present application.

[0029] Figure 4 The simulation result porosity probability graph of the conventional casting method in the first embodiment of the present application.

[0030] Figure 5 The simulation result porosity probability graph of the improved casting method in the first embodiment of the present application.

[0031] Figure 6 The flaw detection result of the part produced by the improved casting method in the first embodiment of the present application.

[0032] Figure 7 The crack flaw detection result of the part cast by the conventional casting method in the second embodiment of the present application.

[0033] Figure 8 This is a temperature cloud map showing the simulation results of the conventional casting method in Embodiment 2 of the present invention.

[0034] Figure 9 The temperature cloud map is a simulation result of the improved casting method in Embodiment 2 of the present invention.

[0035] The attached diagram is labeled as follows: 1. Casting cavity; 2. Casting runner; 3. Top riser; 4. Barbed riser; 41. Riser insulation sleeve. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The solidification characteristics and shrinkage behavior of heat-resistant steel differ significantly from those of ordinary steel. As a high-alloy steel, heat-resistant steel has a wider solidification temperature range and a broader solid-liquid coexistence region during solidification. This wide solidification range hinders the effective flow of liquid metal for compensating shrinkage, easily leading to shrinkage porosity and shrinkage cavities. Therefore, the application of sequential solidification principles is more crucial. Furthermore, within this broad solid-liquid region, the grain skeleton forms early but has low strength, and the liquid film persists for a long time, making it prone to cracking under shrinkage stress.

[0038] This invention provides a method for casting heat-resistant steel, which can solve the problems of shrinkage porosity and shrinkage cavities in the thicker parts of the lower mold during the casting of heat-resistant steel parts. The method includes the following steps:

[0039] S21. The sand mold is made according to the sand mold design scheme. The lower box of the sand mold is equipped with a barbed riser. The barbed riser is connected to the casting cavity and / or the casting flow channel. The inlet where the barbed riser is connected to the casting cavity is equipped with heat preservation measures.

[0040] S22. Prepare sand cores and apply anti-adhesion sand coating to the outer surface of the sand cores;

[0041] S23. Clean the cavity of the sand mold, place the sand core in the lower box, and seal the upper and lower boxes together.

[0042] S24. Cast the casting, and remove and clean it after it cools.

[0043] The casting method provided by this invention involves setting a barbed riser near the hot spot region and connecting the barbed riser to the branch structure of the casting runner. On the one hand, the turbulent molten metal can overflow from the barbed riser, improving the airflow in the molten metal and effectively reducing porosity defects. On the other hand, considering the limited volume of the lower box, the size of the barbed riser cannot be set too large, making it difficult to ensure that the barbed riser solidifies last. Therefore, an insulating sleeve or heating sleeve can be set at the position of the barbed riser, allowing the casting runner to heat the barbed riser. By heating the barbed riser, the thermal modulus of the barbed riser is increased, the solidification time of the barbed riser is delayed, and the hot spot region is fed back, thereby improving the shrinkage porosity defects in the thick part of the bottom of the lower box and increasing the yield.

[0044] Furthermore, sand cores are divided into reference cores and auxiliary cores. Reference cores are used for positioning the casting to ensure casting accuracy. For example, the flow channel core of a turbine housing can serve as a reference core, with its axis used to determine the accuracy of the entire assembly. Auxiliary cores are used to fill in the gaps in complex features, such as the main oil passage, cooling water jacket, and exhaust passage. Auxiliary cores can also be combined with other measures to improve process defects. For example, a chromite sand chilling core can be built in to increase the cooling rate and prevent thermal cracking, or a zircon powder coating can be sprayed on the surface of the auxiliary core to solve the problem of sand adhesion and improve surface roughness. Water-soluble core material can also be placed inside the auxiliary core to facilitate sand removal during demolding.

[0045] Considering that different parts have different structures, the casting method and sand box design scheme need to be adjusted according to the geometric characteristics and technical requirements of the parts. If the casting method and sand box design scheme are determined solely by manual experience, a large number of casting experiments are required, which is time-consuming and labor-intensive.

[0046] refer to Figure 1 This invention provides a method for optimizing the casting process of heat-resistant steel, comprising the following steps:

[0047] S11. Based on the shape of the casting, determine the placement scheme of the casting, the structure of the upper and lower molds, set the distribution and size of the risers and the casting channels connecting each riser, establish the geometric model of the sand mold, and determine the sand mold design scheme in accordance with the principle of sequential solidification.

[0048] S12. Based on the sand mold design scheme, use the multi-physics field coupling simulation method to simulate the casting process and determine whether there is a hot spot area in the lower box of the sand mold. If so, set a barbed riser at the lower box position corresponding to the hot spot area and connect the barbed riser to the casting channel or casting cavity.

[0049] S13. Re-simulate the casting process based on the improved sand mold design scheme. Determine whether there is shrinkage porosity in the hot spot area based on the simulation results. If so, adjust the size of the barb riser. If not, output the improved sand mold design scheme.

[0050] S14. Re-simulate the casting process based on the improved sand mold design. Determine whether there is shrinkage porosity in the hot spot area based on the simulation results. If so, set up heat preservation measures at the connection between the barbed riser and the casting cavity, and output this sand mold design. If not, output the improved sand mold design.

[0051] This optimization method uses finite element analysis to simulate the casting process, determining the rationality of the mold structure. Through the aforementioned optimization measures, this invention successfully solves the problems of shrinkage cavities and porosity in the thicker parts of the lower mold of heat-resistant steel castings, significantly improving casting quality and production efficiency, significantly increasing the process yield, completely eliminating hot spots, and significantly reducing the incidence of shrinkage defects. Simultaneously, by using multiphysics simulation technology to simulate the casting process, the number of experiments is reduced, raw materials are saved, and a reliable technical guarantee is provided for the precision casting of high-temperature components.

[0052] Specifically, riser dimensions are generally calculated using the modulus method. The modulus is the ratio of the volume of the solidified solid to the surface area for heat dissipation, denoted by the symbol M. The modulus is an important parameter for calculating risers, and it is usually slightly larger than the modulus of the solidified solid, typically taken as 1.1-1.2 times.

[0053] Multiphysics coupled simulation (MPS) simulates the flow pattern, temperature change, and shrinkage process of molten metal by coupling the flow field, temperature field, and stress field. Based on the finite element method (FEM), it simplifies the calculation process by dividing the complex geometric model into multiple simple-shaped elements. It establishes the equation of state for the molten metal using fundamental theories of thermodynamics and fluid mechanics, and iteratively solves the casting process using numerical analysis. This method is now widely used in casting simulation. Existing MPS casting simulation software includes ProCAST, COMSOL, MAGMASOFT, SuperCAST, and ANSYS Workbench. These simulation software programs integrate modules such as finite element mesh generation, thermal analysis, fluid analysis, stress analysis, and microstructure analysis. They can simulate the flow conditions during metal casting and analyze phenomena such as incomplete filling, cold shuts, gas entrapment, shrinkage porosity, and shrinkage cavities. The calculation results not only provide data such as the temperature and flow rate of the molten metal at each moment during the casting process, but also the probability of shrinkage porosity or shrinkage cavities in the casting (e.g., ...). Figure 4 and Figure 5 As shown in the figure, this provides a reliable basis for evaluating the casting process.

[0054] Generally, based on experience, for most projects, areas with a porosity greater than 92% in the calculation results will produce shrinkage cavities that do not meet quality requirements during actual casting. In some projects with high requirements for casting quality, the porosity requirement is much lower; in some projects, areas with a porosity greater than 80% in the simulation results will produce shrinkage cavities that fail to meet quality requirements during actual casting. Therefore, in steps S13 and S14, the criterion for determining whether shrinkage porosity has occurred can be whether the porosity of the hot spot area is greater than 92%. If so, shrinkage porosity exists.

[0055] Based on the simulation results of multiphysics coupled casting, it is possible to determine whether a hot spot region exists in the lower box, as well as the location and volume of the hot spot region. Specifically, the following steps are included:

[0056] S121. Calculate the overall average temperature of the unit inside the casting cavity;

[0057] S122. Select one unit at a time, obtain the simulated temperature of the unit, calculate the absolute difference between the simulated temperature and the average temperature of the unit, and if the absolute difference is greater than the first threshold and the simulated temperature of the unit is greater than the average temperature, then mark the unit as a hot spot unit.

[0058] S123. Repeat step S122 until all units participate in the calculation;

[0059] S124. When the number of hot spot units is greater than the second threshold, and at least one hot spot unit has a common node with other hot spot units, it is determined that there is a hot spot in the lower box.

[0060] The element referred to here is the element in the finite element model generated after the geometric model of the sand mold is meshed.

[0061] When identifying hot spot regions, the cooling rate of these regions is significantly slower compared to other regions. Therefore, while the temperature of other regions has already dropped below the solidus temperature, the temperature of the hot spot region remains much higher. Thus, determining the location of hot spot regions through temperature comparison can balance computational speed and accuracy. Simultaneously, the accuracy of mesh generation significantly impacts the results for each element, and abrupt changes in geometry can lead to large deviations between the results and the actual values ​​at the abrupt locations. Therefore, when identifying hot spot regions, it's crucial to determine if there are multiple hot spot elements. If only one or two elements exhibit unusually high temperatures, it indicates an anomaly caused by the mesh generation accuracy. The value of the second threshold depends not only on the mesh generation accuracy but also on the shape of the hot spot region. When the mesh size is small, the hot spot region should contain more elements. Conversely, when the mesh size is large, the number of elements in the hot spot region may decrease.

[0062] When determining hot spot units, the first threshold value can generally be set as the absolute difference between the solidus temperature of the heat-resistant steel and the overall average temperature. The hot spot region identification step can be performed after most areas of the casting have completed solidification. Specifically, the hot spot determination procedure can be triggered when the number of units with temperatures lower than the solidus temperature accounts for 90% of the total number of units. Since the solidification principle of heat-resistant steel is sequential solidification, risers are usually the last to solidify in order to ensure the feeding effect of the riser on the casting. Therefore, when the interior of the casting has completed solidification, some molten metal may still be present at the riser location.

[0063] After determining from the simulation results that a hot spot region exists inside the lower box, the size of the barbed riser needs to be adjusted, specifically including the following steps:

[0064] S131. Determine whether the size of the barbed riser exceeds the allowable value. If so, set up insulation measures at the connection between the barbed riser and the cavity, and output the sand mold design scheme. If not, obtain the volume of the hot spot area and calculate the volume ratio of the hot spot area to the thick part.

[0065] S132. The size of the barbed riser is enlarged according to the volume ratio of the hot spot area to the thick part.

[0066] For example, when the volume of the hot spot region accounts for 20% of the thick part, the size of the barbed riser can be increased by 1.2 times.

[0067] Specifically, the volume of the hot spot region can be calculated based on the total volume of all hot spot units in step S125.

[0068] The size of the barbed riser is generally limited by the size of the sand box. In addition, the size of the barbed riser is generally calculated according to the modular method and is at least 1.1-1.2 times the size of the solidified solid. Therefore, the allowable value of the barbed riser size needs to be determined according to the shape of the casting and the size of the sand box.

[0069] The modulus of solidified solids with complex shapes is often difficult to calculate accurately, which poses a challenge to determining the size of the barbed riser. Furthermore, the feeding effect of the barbed riser on the hot spot region is generally related to the fluidity of the molten metal in the feeding channel; the better the fluidity of the molten metal, the better the feeding effect on the hot spot region. Therefore, appropriately increasing the size of the barbed riser can delay the cooling of the molten metal within the riser and improve its feeding effect on the hot spot region. Example 1

[0070] The turbine housing casting method for a certain project uses a wet sand casting production line with 8 cavities per mold. The casting forms a thick section on the bolt platform inside the lower box. Conventional casting methods would result in porosity and shrinkage in this area. Figure 3 (As shown in the red box in the image), the maximum length of a single hole in the cut part was 1.41 mm, the maximum crack length was 2.66 mm, and the scrap rate was 45%.

[0071] The casting method is optimized through the following steps:

[0072] Initial process modeling: Based on the three-dimensional model of the turbine housing, the mold is initially designed, the initial riser size is calculated according to the modular method, and the chill system is arranged. Chromite chills are attached around the thick parts of the lower box.

[0073] The material parameters were set as follows: heat-resistant steel: ZG40Cr25Ni20, liquidus temperature 1480℃, solidus temperature 1360℃. Thermodynamic analysis was performed using multiphysics coupling simulation software to simulate the casting process. Two hot spots were detected, and a temperature gradient cloud map was generated to mark high-risk areas.

[0074] A barbed riser is installed at the hot spot at the bottom of the lower box, and the barbed riser is connected to the vertically installed feeding channel to facilitate fire intake. (Refer to...) Figure 2 .

[0075] The second simulation showed that the thermal blockage in the thick part at the bottom of the lower box disappeared.

[0076] To make a wet sand mold, the sand mold hardness is 85-90, and the casting temperature is controlled at 1530±10℃. The bottom barbed riser is set with an insulating riser to keep the feeding channel unobstructed.

[0077] After the casting had completely cooled, the sample was cut and subjected to fluorescent flaw detection. No obvious cracks or shrinkage cavities were found.

[0078] Figure 4 The simulation results of casting using traditional methods are shown. The red circle in the figure indicates a hot spot region that leads to shrinkage porosity. This hot spot region is located inside the lower mold, and the conventional top riser is too far from this location to effectively compensate for shrinkage. This application sets up a barbed riser near this region and connects it to the branch structure of the casting runner. On one hand, the turbulent molten metal can overflow from the barbed riser, improving the airflow in the molten metal and effectively reducing porosity defects. On the other hand, an insulation or heating jacket can be set at the barbed riser location, allowing the casting runner to heat the barbed riser. Considering the limited volume of the lower mold, the size of the barbed riser cannot be set too large, making it difficult to ensure that the barbed riser solidifies last. By heating the barbed riser, the thermal modulus of the barbed riser is increased, delaying the solidification time and compensating for shrinkage at the hot spot location.

[0079] Simulations were performed on the modified sand mold and casting method, such as... Figure 5 As shown, the original hot spot area disappeared, and the shrinkage porosity defect was improved. This was demonstrated through actual casting samples, such as... Figure 6 As shown, the sample has no shrinkage porosity or shrinkage cavity defects, and the scrap rate of parts cast by this method is reduced to 0.14%. Example 2

[0080] The heat-resistant steel shell casting process for a certain project uses a two-cavity mold, with the lower ferrule located at the bottom of the lower mold. Conventional casting methods resulted in severe shrinkage cavities. The largest single hole in the casting had a length of 1.41 mm, and the largest crack length was 2.66 mm. Figure 7 As shown, the scrap rate for conventional casting methods is 35%.

[0081] The casting method is optimized using the method provided by this invention, and the specific steps are as follows:

[0082] In NX, risers and gating systems are arranged according to the casting CAD model, and riser dimensions are set using the modular method;

[0083] Solidification simulation was performed using casting simulation software based on the material parameters of the heat-resistant steel, revealing an 8.7cm solidification layer at the bottom of the lower mold. 3 The hot spot area is located close to the shrinkage cavity and crack location (reference). Figure 8 ).

[0084] Modify the position and size of the riser, and set up a fire-inlet mechanism at the barbed riser position, then re-simulate;

[0085] After three iterations of simulation, the hot spot volume was reduced to 0.08 cm³. 3 (refer to Figure 9 ), determine the location and size of the riser and the fire-starting measures.

[0086] The pouring temperature is controlled at 1580±10℃, and the molding sand is preheated to 180℃ before pouring.

[0087] After pouring, the pressure was maintained for 12 minutes, and a uniform depression appeared at the necking of the riser. The casting was removed, cut, and inspected, and no obvious defects were found.

[0088] After the above-mentioned improvements to the casting method, the scrap rate of the part was reduced to almost zero.

[0089] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for optimizing the casting process of heat-resistant steel, characterized in that, Includes the following steps: S11. Based on the shape of the casting, determine the placement scheme of the casting, the structure of the upper and lower molds, set the distribution and size of the risers and the casting channels connecting each riser, establish the geometric model of the sand mold, and determine the sand mold design scheme in accordance with the principle of sequential solidification. S12. Based on the sand mold design scheme, the multi-physics field coupling simulation method is used to simulate the casting process to determine whether there is a hot spot area in the lower box of the sand mold. If so, a barbed riser is set at the lower box position corresponding to the hot spot area, and the barbed riser is connected to the casting channel or the casting cavity. S13. Re-simulate the casting process according to the improved sand mold design scheme. Determine whether there is shrinkage porosity in the hot spot area based on the simulation results. If so, adjust the size of the barb riser. If not, output the improved sand mold design scheme. S14. Re-simulate the casting process based on the improved sand mold design. Determine whether there is shrinkage porosity in the hot spot area based on the simulation results. If so, set up heat preservation measures at the connection between the barbed riser and the casting cavity, and output this sand mold design. If not, output the improved sand mold design.

2. The method according to claim 1, characterized in that, Determine if a hot spot region exists by following these steps: S121. Calculate the overall average temperature of all units within the casting cavity; S122. Select one unit at a time, obtain the simulated temperature of the unit, calculate the absolute difference between the simulated temperature and the average temperature of the unit, and if the absolute difference is greater than the first threshold and the simulated temperature of the unit is greater than the average temperature, then mark the unit as a hot spot unit. S123. Repeat step S122 until all units participate in the calculation; S124. When the number of hot spot units is greater than the second threshold, and at least one hot spot unit has a common node with other hot spot units, it is determined that there is a hot spot region in the lower box. The unit referred to here is a unit in the finite element model of a sand mold.

3. The method according to claim 2, characterized in that, The first threshold is the absolute difference between the overall average temperature and the solid phase temperature of the heat-resistant steel.

4. The method according to claim 1, characterized in that, The insulation measure is an insulating riser or a heating riser.

5. The method according to claim 2, characterized in that, In step S13, the size of the barbed riser is adjusted through the following steps: S131. Determine whether the size of the barbed riser exceeds the allowable value. If yes, set up heat preservation measures at the connection between the barbed riser and the casting cavity, and output this sand mold design scheme. If no, obtain the volume of the hot spot area and calculate the volume ratio of the hot spot area to the thick part. S132. The size of the barbed riser is enlarged according to the volume ratio of the hot spot area to the thick part.

6. The method according to claim 5, characterized in that, The volume of the hot spot region is obtained by the following steps: calculate the total volume of all the hot spot units, which is the volume of the hot spot region.

7. A method for casting heat-resistant steel, characterized in that, The casting method is obtained by the method described in any one of claims 1-6, and the casting method includes the following steps: S21. A sand mold is made according to the sand mold design scheme. The lower box of the sand mold is equipped with a barbed riser. The barbed riser is connected to the casting cavity and the casting flow channel. Insulation measures are provided at the connection between the barbed riser and the casting cavity. S22. Prepare a sand core and apply an anti-adhesion sand coating to the outer surface of the sand core; S23. Clean the cavity of the sand mold, place the sand core in the lower box, and seal the upper and lower boxes together. S24. Cast the casting, and remove and clean it after it cools.

8. The casting method according to claim 7, characterized in that, The sand core is divided into a reference core and an auxiliary core. The reference core is used for positioning the casting, and the auxiliary core is used for filling in complex features.

9. The casting method according to claim 8, characterized in that, The outer surface of the auxiliary core is coated with zircon powder.

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