Atlas of Casting Defects
Negative
1/8” or less
1/8” or less
Dispersed throughout the casting but may be more severe in areas that are last to freeze
Metallurgical gas
Pinhole defects are typically smaller with a higher frequency than gas, slag or incomplete burnout. This defect is more common in plain carbon and low alloy steels than in higher alloy steels.
Metal penetrates into the primary Gases are absorbed in metal during melting. If the gas level in the melt exceeds the solid state solubility limit, bubbles are formed during solidification. The gases most responsible for this defect are hydrogen and nitrogen.
Alternate Mechanism
Chemically combined water in the mold is released by the increase in mold temperature during casting.
| Area | Possible Cause | Potential Correction |
|---|---|---|
| Shell | Chemically combined water in the mold released during casting |
Dry the molds completely after autoclave dewaxing. Increase the mold preheat temperature. |
| Foundry | High nitrogen, oxygen or hydrogen level in the melt |
Use more virgin metal or purchase metal with lower gas content |
| Foundry | Dirty, wet or rusty metal |
Metal should be clean, dry and free from rust and oils |
| Foundry | Wet ladles or pouring spouts |
Insure complete heating and dry out of furnace pour spouts and ladles |
| Foundry | Incomplete degassing |
Confirm degassing additions are correct |
| Foundry | High nitrogen, oxygen or hydrogen level absorption in the melt |
Reduce the casting temperature or time the metal is molten. Use a protective or inert atmosphere around melt |