yvonne@nydcasting.com 
1. Chemical composition factors
Influence of carbon content: If the carbon content is too high, greater thermal stress and structural stress will be generated during the solidification process of the casting. Because high-carbon high-manganese steel will undergo eutectoid transformation during solidification, the volume changes, which can easily lead to cracks.
Influence of sulfur and phosphorus impurities: Sulfur will form sulfides with low melting points, and phosphorus will cause cold brittleness. They gather at the grain boundaries, reduce the strength of the grain boundaries, and make the castings prone to cracks at the grain boundaries due to thermal stress during the cooling process.
2. Casting process factors
Pouring temperature: If the pouring temperature is too high, the temperature gradient increases during cooling, creating greater thermal stress. High-temperature pouring also causes longer solidification time, resulting in coarse grains and lower strength. Toughness decreases, and the risk of cracks increases. If the pouring temperature is too low, fluidity becomes poor, leading to defects like insufficient pouring and cold shut. These parts are also prone to cracks during the subsequent cooling process.
Cooling rate: If the casting cools too fast, the temperature difference between the inside and outside of the casting is large, which will produce large thermal stress. Especially for castings with complex shapes and uneven wall thickness, this thermal stress is more likely to cause cracks. For example, the thin-walled part cools quickly and the thick-walled part cools slowly, and cracks are easily generated at the junction due to stress concentration.
3. Casting structure factors
Shape complexity: Castings with complex shapes, such as those with alternating thin-wall and thick-wall structures, and structures such as ribs and holes inside, shrink inconsistently during the cooling process, which will produce complex stress states and easily form cracks.
Wall thickness difference: When the wall thickness difference between different parts of the casting is too large, the thick-walled part cools slowly and the thin-walled part cools quickly. This uneven cooling will cause thermal stress concentration, thereby causing cracks.
What are the effects of different casting processes on crack defects in high manganese steel castings?
1. Sand casting
Advantages: The sand casting process has strong adaptability and can cast high manganese steel castings with complex shapes. The sand mold dissipates heat slowly, causing the casting to cool at a slow rate. If the casting design is unreasonable, like large wall thickness differences, different shrinkage times during cooling may cause thermal stress concentration, leading to cracks. Although sand molds have good yieldability and deform as the casting shrinks, if the mold is too compact and yieldability worsens, the risk of cracks will also increase.
Disadvantages: During sand casting, the interaction between high manganese steel liquid and sand mold may produce gas. If the exhaust is not smooth, the gas may form pores inside the casting, and stress concentration will occur around these pores, which may become the starting point of cracks during subsequent cooling or use.
2. Investment casting
Advantages: Investment casting can obtain high manganese steel castings with high dimensional accuracy and good surface quality. However, the mold shell of investment casting is generally thinner and dissipates heat quickly. For high manganese steel castings, too fast cooling speed will lead to a large temperature difference between the inside and outside of the casting, resulting in large thermal stress. Especially for large or uneven wall thickness castings, this thermal stress can easily cause cracks in the casting.
Disadvantages: In the pouring process of investment casting, the filling capacity of molten steel is very important. If the fluidity of molten steel is not good, defects such as insufficient pouring or cold shut may occur, and these defective parts are prone to cracks during the cooling process. In addition, the pouring system design of investment casting is complex. If the molten steel flows unsteadily during pouring, stress will be introduced, increasing the possibility of cracks in the casting.
3. Lost Foam Casting
Advantages: In lost foam casting, the pattern vaporizes during pouring, avoiding dimensional deviation and surface defects from demolding. However, when casting high manganese steel, if gases from foam vaporization are not discharged in time, pores may form inside the casting, or surface defects like wrinkles may appear. Stress concentration will occur around these defects, which are easy to cause cracks.
Disadvantages: In the process of lost foam casting, the pouring temperature and speed control of molten steel are required to be high. If the pouring temperature is too high and the foam pattern vaporizes too fast, it may cause the molten steel to boil and splash, resulting in defects such as inclusions and pores in the casting, thereby increasing the possibility of cracks. Improper pouring speed will also affect the filling and solidification of molten steel and cause cracks.