In my research, I focused on improving the casting process for bucket teeth made from high manganese steel, a material known for its excellent wear resistance and toughness in demanding applications like mining. The high manganese steel casting process often faces challenges such as shrinkage porosity and defects, which can lead to premature failure and increased costs. To address this, I employed numerical simulation using ProCAST software to analyze and optimize the filling and solidification stages. The goal was to enhance the quality of high manganese steel casting by reducing internal defects and improving mechanical properties.
The bucket tooth component, with a mass of 385 kg and maximum dimensions of 1340 mm × 425 mm × 255 mm, represents a large-scale casting that requires precise control to avoid issues like shrinkage and porosity. High manganese steel casting involves complex solidification dynamics due to the material’s high manganese content, which affects fluidity and thermal behavior. Initially, I designed a bottom-gating system with one mold containing two castings, incorporating risers for feeding and vents for gas escape. This setup was intended to facilitate smooth metal flow and minimize turbulence during the high manganese steel casting process.
To begin the simulation, I created a 3D model of the bucket tooth and gating system using UG software, which was then imported into ProCAST in x-t format. I performed mesh generation with Visual-Mesh, setting a grid size of 15 to balance accuracy and computational efficiency. This resulted in 224,490 surface elements and 3,405,826 volume elements. For the high manganese steel casting material, I defined its properties based on standard high manganese steel composition, with a liquidus temperature of 1388.7°C and solidus temperature of 1256.8°C. The mold material was resin sand, and I applied boundary conditions including gravity in the negative z-direction, natural air cooling, and an interfacial heat transfer coefficient of 500 W/(m²·K). The initial process parameters were a pouring temperature of 1600°C, mold preheat temperature of 400°C, and filling time of 85 seconds, with a total of 50,000 simulation steps.
The simulation of the initial high manganese steel casting process revealed several issues. During filling, the metal flow was smooth but slow, taking 85 seconds to complete, which led to elevated temperatures in certain regions. The temperature distribution during filling showed that the metal remained above the liquidus line, ensuring good fluidity, but this also contributed to prolonged solidification times. I analyzed the solidification process using the solid fraction results, which indicated that solidification started in the vents and gating system, progressing gradually to the casting body. By 1.1 × 10⁴ seconds, the gating system was nearly solid, while the bucket tooth center showed slower solidification, potentially causing shrinkage defects. The Total Shrinkage Porosity criterion in ProCAST predicted significant shrinkage porosity in the central part of the bucket tooth, as well as in the risers and gating system, which could compromise the integrity of the high manganese steel casting.
To quantify the defects, I used the shrinkage porosity rate θ, defined as the volume fraction of defective areas relative to the total casting volume. For the initial process, θ was high, indicating poor quality. The root causes were identified as slow filling speed, high pouring temperature, and low mold preheat temperature, all of which are critical in high manganese steel casting. To address this, I designed an optimization study focusing on three key parameters: pouring temperature (A), pouring speed (B), and mold preheat temperature (C). I set three levels for each factor, as shown in Table 1, and conducted nine simulation trials using an L9 orthogonal array to efficiently explore the parameter space.
| Level | Pouring Temperature A (°C) | Pouring Speed B (kg/s) | Mold Preheat Temperature C (°C) |
|---|---|---|---|
| 1 | 1550 | 16 | 600 |
| 2 | 1500 | 15 | 400 |
| 3 | 1450 | 14 | 200 |
The simulation results for each trial are summarized in Table 2, where the shrinkage porosity rate θ was calculated to assess the effectiveness of each parameter combination. A lower θ indicates better quality in the high manganese steel casting process.
| Trial | Pouring Temperature A (°C) | Pouring Speed B (kg/s) | Mold Preheat Temperature C (°C) | Shrinkage Porosity Rate θ (%) |
|---|---|---|---|---|
| L1 | 1550 | 16 | 600 | 33.45 |
| L2 | 1550 | 15 | 400 | 34.86 |
| L3 | 1550 | 14 | 200 | 35.47 |
| L4 | 1500 | 16 | 400 | 33.23 |
| L5 | 1500 | 15 | 200 | 33.12 |
| L6 | 1500 | 14 | 600 | 32.85 |
| L7 | 1450 | 16 | 600 | 32.08 |
| L8 | 1450 | 15 | 600 | 32.28 |
| L9 | 1450 | 14 | 400 | 32.75 |
From Table 2, trial L7 (A=1450°C, B=16 kg/s, C=600°C) yielded the lowest θ of 32.08%, indicating the optimal parameter set for high manganese steel casting. However, to prevent potential issues like mold erosion due to increased pouring speed, I also modified the gating system. I increased the sprue diameter to accelerate filling, added two additional ingates extending from the runner to improve flow distribution, and incorporated pouring basins at the base of each ingate for better slag trapping and cushioning. This redesigned gating system promotes more uniform filling and reduces turbulence in the high manganese steel casting process.
After implementing the optimized parameters and gating design, I reran the ProCAST simulation. The results showed a significant improvement in the high manganese steel casting quality. The filling time was reduced, and the temperature distribution became more uniform. The solidification analysis demonstrated faster cooling rates in the bucket tooth center, which enhanced feeding from the risers and minimized shrinkage. The solidification time t for a casting can be estimated using Chvorinov’s rule: $$ t = B \left( \frac{V}{A} \right)^2 $$ where B is a mold constant, V is the volume, and A is the surface area. For the optimized high manganese steel casting, the modified gating increased the A/V ratio, leading to quicker solidification. The thermal behavior during solidification can be described by the heat transfer equation: $$ \frac{\partial T}{\partial t} = \alpha \nabla^2 T $$ where T is temperature, t is time, and α is thermal diffusivity. In the optimized process, higher mold preheat temperature and lower pouring temperature reduced thermal gradients, facilitating directional solidification.
Comparing the solidification curves before and after optimization, I observed that the optimized high manganese steel casting solidified more rapidly in critical regions, reducing the risk of defects. The Total Shrinkage Porosity prediction confirmed that shrinkage was largely confined to the risers and gating system, with no significant defects in the bucket tooth itself. This aligns with the goal of producing high-integrity high manganese steel casting components. To validate the simulation, I conducted actual production trials. The pre-optimized casting exhibited visible shrinkage porosity in the riser zone, whereas the optimized high manganese steel casting showed excellent surface quality and no internal defects. Additionally, hardness measurements increased from 205 HV to 218 HV, and wear resistance improved, with wear mass decreasing from 185 mg to 160 mg under 1 J impact energy, demonstrating the enhanced performance of the optimized high manganese steel casting.
In conclusion, my study successfully optimized the high manganese steel casting process for bucket teeth through numerical simulation and parameter adjustment. The optimal parameters—pouring temperature of 1450°C, pouring speed of 16 kg/s, and mold preheat temperature of 600°C—combined with an improved gating system, resulted in faster solidification, reduced defects, and better mechanical properties. This approach highlights the importance of simulation in advancing high manganese steel casting technology, ensuring higher quality and efficiency in industrial applications. The repeated focus on high manganese steel casting throughout this research underscores its significance in achieving durable and reliable components for heavy-duty use.