Chilling is another name of iron Cementite network commonly known as Carbides.
Carbides may occur in all iron-carbon alloys as a defect during solidification, depending on the chemical composition and wall thickness (cooling rate), regardless of the molding and the casting process. Carbide inclusions are characterized by poor machinability of the material and causes embrittlement
Carbide is present in the form of cementite in cast iron. As we know that cementite is of very hard and brittle in nature. When it is combined with the alloying elements of cast iron like vanadium, chromium and molybdenum it forms carbides. Due to this carbides hardness and wear resistance increases.
Causes
- Low Carbon Equivalent
- High pouring Temperature
- Under or poor inoculation
- Poor casting design
- High cooling rate
- High sulphur in the melt not neutralize by Mn.
- Use of damp sand or moisture containing sand
- High amount of carbide stabilizer elements
- Low silicon content in the melt
- Lack of directional solidification
- High amount of steel scrap in the charge
Remedies
- Improvement in carbon equivalent
- Avoid high pouring temperature
- Better inoculation techniques
- Improve casting design
- Avoid high cooling rates
- sulphur in the melt is neutralized by Mn.
- Eliminate the risk of moisture in sand & scrap as well
- Reduce the carbide stabilizing elements
- Improve silicon content in the melt
- Placement of chills for directional solidification
- Cut down the percentages of steel scrap
