Optimization method for inhibiting large-size steel ingot core cracking based on finite element model

Abstract

The invention discloses an optimization method for inhibiting large-size steel ingot core cracking based on a finite element model, which comprises the following steps: building a finite element simulation model according to an original casting process; optimizing casting parameters according to the finite element simulation model; formulating an optimization mode according to the optimized parameters; and preparing a mold according to the optimization mode, and carrying out experimental verification. Through finite element simulation analysis and experimental verification, the process for inhibiting the cracking of the core part of the large-size steel ingot is effectively optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of metal casting, and particularly to an optimization method for suppressing core cracking of large-sized steel ingots based on a finite element model. Background Art

[0002] In the experiment of vacuum melting 200 kg-level steel ingots, it was found that there were large-scale cracks in the core of the steel ingots, which seriously affected the subsequent forging process and led to product scrapping. If traditional experimental trial and error were used, not only would a large amount of manpower and material resources be wasted, but also the experimental cycle would be very long, making it difficult to meet production requirements. Casting simulation software can perform numerical simulation calculations and visual analysis on the filling and solidification simulation of this process, guiding designers to optimize and improve the process. After the numerical calculation reaches a certain optimization level, experiments can be supplemented for verification, and finally an optimized casting process method without cracks can be determined.

[0003] The influence of process parameters on hot cracking covers a very wide range. By controlling the design of the casting mold and the pouring process, the flow and solidification process of the molten metal are affected, thereby affecting various properties of the casting in the hot cracking sensitive area and ultimately affecting the formation of final hot cracks. When the composition is determined, the controllable parameters that have a greater impact on hot cracking include pouring temperature, mold temperature, and casting equipment, etc., and simulation can well conduct comparative simulations on the above situations and give prediction results.

[0004] Currently, some technologies for preparing metal castings to suppress crack generation have emerged. Among them, some technologies have proposed a method for eliminating cracks in casting iron molds, mainly solving the casting crack defects of iron molds for coated sand casting of iron molds with a length of 1500 mm, a width of 1000 mm, and a thickness of 200 mm, increasing the service life of the iron mold to 100,000 times; this optimization process is simple, but lacks scalability. Some technologies have proposed a method for determining the thermal physical properties of steel for casting, giving a method for determining the thermal physical properties of steel ingots, but no subsequent applications are provided. Some technologies have proposed an optimization method for improving the surface cracking of large steel ingots based on a finite element model, which can reduce the surface tension of the edges of the steel ingot at the end of solidification and reduce the longitudinal cracks on the surface of the edges of the steel ingot, but only stay at the simulation level, without experimental verification, and only focus on the easily achievable surface cracks.

[0005] Therefore, those skilled in the art are committed to providing an optimization method for suppressing core cracking of large-sized steel ingots based on a finite element model, providing a casting method that can suppress casting cracks of large-sized steel ingots, and giving an experimentally feasible process optimization plan. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is how to provide a process optimization method that can suppress casting cracks of large-sized steel ingots.

[0007] To achieve the above object, the present invention provides an optimization method for suppressing core cracking of large-sized steel ingots based on a finite element model, comprising the following steps:

[0008] S1. Build a finite element simulation model according to the original casting process;

[0009] S2. Optimize the casting parameters according to the finite element simulation model;

[0010] S3. Develop an optimization method according to the optimized parameters;

[0011] S4. Prepare a mold according to the optimization method and conduct experimental verification.

[0012] Preferably, in step S1, the original casting process is obtained from the equipment drawing of the steel ingot.

[0013] Further, step S1 includes:

[0014] S11. Obtain thermal physical properties parameters and stress data according to the chemical composition of the steel ingot material;

[0015] S12. Establish a three-dimensional casting model of the steel ingot, perform mesh division and parameter setting on the three-dimensional casting model;

[0016] S13. Perform simulation calculations on the temperature field and stress field during the casting process of the three-dimensional casting model.

[0017] Preferably, in step S12, the three-dimensional casting model includes a metal steel ingot mold, a base, a riser, and a gate.

[0018] Preferably, in step S12, the parameter setting includes setting the heat transfer coefficient of the temperature field and the boundary conditions of the temperature field.

[0019] Further, in step S13, according to the simulation calculation results, analyze the factors inducing cracking.

[0020] Preferably, in step S2, the optimized casting parameters include: mold preheating temperature, pouring temperature, bottom heat transfer condition, and lateral cooling condition.

[0021] Further, in step S2, according to the optimized casting parameters, repeat steps S11 - S13 to obtain the degree of suppression of casting cracks by the casting parameters.

[0022] Preferably, in step S3, the optimization methods include: improving the gate form, wrapping with heat insulation felt, reducing the mold thickness, increasing the riser volume, and increasing the bottom cooling rate.

[0023] Further, in step S3, according to the selected optimization method, steps S11 - S13 are repeated to obtain an optimization result.

[0024] The present invention has at least the following beneficial technical effects:

[0025] The present invention conducts simulation and emulation on multiple casting parameters, finds out the influence of each process parameter on the casting process, and further determines the optimization method for suppressing crack generation. The finite element simulation model can well simulate and emulate according to the actual process production conditions, with a fast calculation cycle, saving manpower and material resources; conducts comparative simulation and emulation on multiple casting parameters, and the parameter analysis is complete; combined with experimental verification, the method has high reliability.

[0026] The following will further illustrate the concept, specific structure and technical effects generated by the present invention with reference to the accompanying drawings, so as to fully understand the purpose, features and effects of the present invention. Description of the Drawings

[0027] Figure 1 is the flowchart of the method for suppressing core cracking of large - sized steel ingots based on a finite element model in an embodiment of the present invention;

[0028] Figure 2 is the flowchart of step S1 in an embodiment of the present invention;

[0029] Figure 3 is the schematic diagram of a steel ingot mold and a casting mold;

[0030] Figure 4 is the schematic diagram of the solidification time simulation result. Among them, figure a) shows the solidification time when the two - phase region exists, and figure b) shows the total solidification time;

[0031] Figure 5 is the schematic diagram of the strain - induced hot - cracking tendency;

[0032] Figure 6 is the optimized design drawing of the pouring cup and gate;

[0033] Figure 7 is the schematic diagram of the temperature field optimization comparison. Among them, figure a) shows the temperature field of the original process plan, and figure b) shows the temperature field of the optimized plan. Detailed Embodiments

[0034] The following introduces the preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0035] In the drawings, components with the same structure are denoted by the same reference numerals, and components with similar structures or functions are denoted by similar reference numerals throughout. The dimensions and thicknesses of each component shown in the drawings are arbitrarily shown, and the present invention does not limit the dimensions and thicknesses of each component. To make the drawings clearer, the thicknesses of some components are appropriately exaggerated in the drawings.

[0036] The present invention provides a method for suppressing cracking of large-sized steel ingots based on a finite element model. According to the original process plan that generates casting cracks, finite element modeling and simulation are carried out, and the temperature field and stress field during the casting process of the original process method are simulated and calculated to obtain the temperature field and stress field distribution during the solidification process of the large-sized steel ingot, and analyze the possible or feasible casting parameters for suppressing cracks. Then, through controlling the mold preheating temperature, pouring temperature, changing the bottom and lateral cooling conditions, modifying the gate design, regulating the hot top structure, etc., comparative simulation is carried out, and a process optimization method for suppressing casting cracks is proposed; according to the feasible process optimization method, a vacuum melting device that can suppress casting cracks is designed and prepared, and the feasibility of the optimization method is verified through experiments.

[0037] As Figure 1 shown, the method for suppressing cracking of the core of a large-sized steel ingot based on a finite element model in this embodiment includes the following steps:

[0038] Step S1. Build a finite element simulation model according to the original casting process.

[0039] In this step, the original casting process can be obtained from the equipment drawings of the steel ingot. Based on the equipment drawings, a three-dimensional casting model of the steel ingot is established, the thermophysical properties and stress data of the steel ingot are input, the boundary conditions are set, and simulation calculations are carried out. According to the simulation calculation results, the factors inducing cracking of the steel ingot are analyzed.

[0040] Specifically, as Figure 2 shown, this step includes the following processes:

[0041] Step S11. Obtain the thermophysical properties and stress data according to the chemical composition of the steel ingot material. Among them, the steel ingot material composition comes from the equipment drawings.

[0042] Step S12. Establish a three-dimensional casting model of the steel ingot, and perform mesh division and parameter setting on the three-dimensional casting model. Among them, the three-dimensional casting model comes from the equipment drawings and includes four parts of the solid, namely the metal section steel ingot mold, the base, the riser, and the gate; the parameter setting includes the setting of the heat transfer coefficient of the temperature field and the boundary conditions of the temperature field.

[0043] Step S13. Perform simulation calculations on the temperature field and stress field during the casting process of the three-dimensional casting model. Further, according to the simulation calculation results, analyze the factors inducing cracking.

[0044] Step S2: Optimize the casting parameters based on the finite element simulation model.

[0045] In this step, the optimized casting parameters include: mold preheating temperature, pouring temperature, bottom heat transfer condition, and lateral cooling condition. According to the optimized casting parameters, repeat steps S11 - S13 to obtain the degree of inhibition of casting cracks by the casting parameters.

[0046] Step S3: Determine the optimization method according to the optimized parameters.

[0047] In this step, the optimization methods include: improving the gate form, wrapping with heat insulation felt, reducing the mold thickness, increasing the riser volume, and increasing the bottom cooling rate. According to the selected optimization method, repeat steps S11 - S13 to obtain the optimization result.

[0048] Step S4: Prepare the mold according to the optimization method and conduct experimental verification.

[0049] In this step, prepare the mold according to the optimization method, start the induction melting equipment, and conduct experimental verification. Through the experiment, verify the reliability of the optimization method.

[0050] This application takes a 200 - kg special steel ingot as an example to establish a method for suppressing the core cracking of large - size steel ingots based on a finite element model, as follows.

[0051] According to the chemical composition of the steel ingot material, obtain the thermal physical properties parameters and stress data of the steel ingot material for simulation calculation.

[0052] Establish a three - dimensional casting model of the steel ingot, conduct mesh generation and parameter setting for the three - dimensional casting model. Process the heat transfer coefficient and boundary conditions of the temperature field. Reasonable heat transfer values include: heat transfer between the metal mold and the sand mold, 50 W / (m·K); heat transfer between the molten metal and the sand mold, 80 W / (m·K); heat transfer between the molten metal and the metal mold, 300 W / (m·K).

[0053] As Figure 3 shown, the geometric model of the 200 - kg special steel ingot and the pouring mold system established according to the equipment drawings includes four solid parts: the metal - type steel ingot mold, the base, the riser, and the gate; divide the finite - element mesh to obtain a three - dimensional finite - element mesh containing 85249 nodes and 508050 elements, and the average mesh size is 10 mm.

[0054] Conduct simulation calculations on the temperature field and stress field during the casting process of the three - dimensional casting model. The simulation calculation results are as Figure 4 and Figure 5 shown. Analyze the factors inducing cracking. Figure 4 The results show that the solidification time at the center of the ingot, especially in the fuzzy zone state, is significantly shorter than other positions, less than 50 s, which is prone to cause insufficient feeding.Figure 5 The shown strain-dominated hot cracking index also indicates a certain tendency of hot cracking.

[0055] On the established model, optimize the parameters of the three-dimensional casting model of the ingot. The process parameters include mold preheating temperature, pouring temperature, bottom heat transfer condition, and lateral cooling condition. According to the optimized process parameters, repeat the foregoing steps to obtain an evaluation of the degree of inhibition of casting cracks by the process parameters, and give the process optimization method.

[0056] In the process optimization method, such as Figure 6 the "shower type" gate shown can make the molten metal pour into the mold "gently" evenly from the circumference, which can effectively reduce the impact effect of the molten metal on the center of the ingot, improve the temperature uniformity, avoid the appearance of "low local solidification time area" in the core of the ingot, and thus reduce the tendency of solidification heat cracks. Other optimization methods include: wrapping with heat insulation felts, reducing the mold thickness, increasing the riser volume, and increasing the bottom cooling rate. By increasing the riser volume, not only the riser volume is enlarged, but also the dispersion of the gate is increased to a certain extent, weakening the impact of the molten metal on the edge; increasing the bottom cooling rate can adopt the method of forced water cooling.

[0057] According to the process optimization method, formulate an optimization plan, repeat the finite element simulation process, and conduct a preliminary evaluation. As Figure 7 shown in Figure b) in, the evaluation results show that these process plans are reasonable: 1) the minimum value of the metal mold shell thickness is reduced from the original 70 mm to 30 mm; 2) wrap heat insulation felts with a thickness of 60 mm outside the metal mold and the riser, and among them, the heat insulation felt of the metal mold only covers half close to the riser; 3) use high-temperature asbestos glue for the sand mold materials (including the pouring cup and the riser); 4) further enlarge the top diameter of the riser from the original 70 mm to 100 mm; 5) add heat storage materials (ductile iron base) with a height of 100 mm at the bottom of the metal mold; 6) add a shower type gate cup as Figure 6 shown.

[0058] Finally, according to the optimized process, prepare the mold, turn on the induction melting equipment, and conduct experimental verification. This embodiment has been verified three times continuously to verify the reliability of the optimization method.

[0059] The optimization method for suppressing the cracking of the core of large-sized steel ingots based on the finite element model of the present invention conducts simulation analysis on the influence of process parameters such as mold preheating temperature, pouring temperature, bottom and lateral cooling conditions, gate design, and hot top structure, etc., which are easy to control, has a fast calculation cycle, saves manpower and material resources; conducts comparative simulation for a variety of casting parameters, and the parameter analysis is complete; combined with experimental verification, the method has high reliability.

[0060] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field according to the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall fall within the protection scope determined by the claims.

Claims

1. An optimization method for suppressing core cracking of large-sized steel ingots based on a finite element model, characterized in that It includes the following steps: S1. Build a finite element simulation model according to the original casting process; S2. Optimize the casting parameters according to the finite element simulation model; S3. Develop an optimization method according to the optimized parameters; S4. Prepare a mold according to the optimization method and conduct experimental verification.

2. The optimization method for suppressing core cracking of large-sized steel ingots based on a finite element model according to claim 1, characterized in that In step S1, the original casting process is obtained from the equipment drawing of the ingot.

3. The optimization method for suppressing core cracking of large-sized steel ingots based on a finite element model according to claim 2, characterized in that, Step S1 includes: S11. Obtain the thermal physical properties parameters and stress data according to the chemical composition of the ingot material; S12. Establish a three-dimensional casting model of the ingot, and conduct mesh division and parameter setting on the three-dimensional casting model; S13. Conduct simulation calculations on the temperature field and stress field during the casting process of the three-dimensional casting model.

4. The optimization method for suppressing core cracking of large-sized steel ingots based on a finite element model according to claim 3, wherein, In step S12, the three-dimensional casting model includes a metal ingot mold, a base, a riser, and a gate.

5. The optimization method for suppressing core cracking of large-sized ingots based on a finite element model according to claim 3, characterized in that, In step S12, the parameter setting includes the setting of the heat transfer coefficient of the temperature field and the boundary conditions of the temperature field.

6. The optimization method for suppressing core cracking of large-sized steel ingots based on a finite element model according to claim 5, characterized in that, In step S13, analyze the factors inducing cracking according to the simulation calculation results.

7. The optimization method for suppressing core cracking of large-sized steel ingots based on a finite element model according to claim 6, wherein In step S2, the optimized casting parameters include: mold preheating temperature, pouring temperature, bottom heat transfer condition, and lateral cooling condition.

8. The optimization method for suppressing the core cracking of large-sized steel ingots based on a finite element model according to claim 7, characterized in that In step S2, according to the optimized casting parameters, repeat steps S11 - S13 to obtain the degree of inhibition of casting cracks by the casting parameters.

9. The optimization method for suppressing core cracking of large-sized ingots based on a finite element model according to claim 8, characterized in that, In step S3, the optimization methods include: improving the gate form, wrapping with heat insulation felt, reducing the mold thickness, increasing the riser volume, and increasing the bottom cooling rate.

10. The optimization method for suppressing core cracking of large-sized steel ingots based on a finite element model according to claim 9, characterized in that, In step S3, according to the selected optimization method, repeat steps S11 - S13 to obtain the optimization result.

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