Pouring is a critical step in the casting production process, and pouring temperature serves as a vital parameter. Variations in pouring temperature exert substantial influences on the internal microstructure, mechanical properties and surface quality of castings.
1. Defects Caused by Low Pouring Temperature
Pouring temperature is a key parameter in casting. Both excessively low and high temperatures can markedly impair casting quality.
（1）Cold Shuts and Misruns
Low pouring temperature first reduces the fluidity of molten metal, which prevents the molten metal from filling the mold cavity completely, resulting in defects such as cold shuts and misruns.
（2）Porosity
Porosity is one of the most common casting defects, originating from entrapped gas that fails to escape during casting. At low pouring temperatures, gas cannot be discharged smoothly as molten metal solidifies, thereby forming porosity and severely degrading the performance and quality of castings.
（3）Inclusions
Inclusions refer to impurities, non-metallic inclusions and other foreign substances trapped in the metal. Low pouring temperature deteriorates the fluidity of molten metal and extends its solidification time. Consequently, inclusions cannot float up and be removed readily; they tend to settle inside the casting and form internal slag inclusions, surface cold spots or wrinkles, which seriously compromise the mechanical properties and machinability of castings.
（4）Shrinkage Cavities
Shrinkage cavities are common casting defects formed by volume contraction of metal during solidification. Low pouring temperature slows down the solidification rate of molten metal and promotes the formation of more internal shrinkage cavities, impairing the mechanical and processing properties of castings.
2. Effects of Excessively High Pouring Temperature on Casting Quality
（1）Blowholes and Slag Inclusions
Excessively high pouring temperature increases the fluidity of molten metal, shortens filling time and accelerates metal flow. This may induce blowholes and slag inclusions during mold filling.
（2）Sprue Porosity and Internal Inclusions
An overly high pouring temperature leads to excessive pressure loss during casting cooling, triggering sprue porosity and internal inclusions.
（3）In addition, excessive pouring temperature causes surface sintering and oxidation of castings, worsening surface roughness and dimensional accuracy, and may even result in hot tearing on casting surfaces.