Guide for Stress Relieving of Cast Iron

Stress relieving is a heat treatment process used to reduce internal stresses in materials, including cast iron. Cast iron is a strong and brittle material that can develop residual stresses during the casting process or due to machining operations. Stress relieving can help improve the dimensional stability and mechanical properties of cast iron components.

Note that:

  1. Most grey iron castings, especially those with uneven sections, often contain internal stress caused by uneven cooling during casting. This residual stress can lead to dimensional changes and even the formation of cracks.
  2. To prevent these issues, a stress relieving treatment is necessary. However, for critical and highly alloyed castings, the stress relieving cycle should be agreed upon by both the manufacturer and the purchaser.

Stress Relieving of Cast Iron

To perform stress relieving on cast iron, the following steps are typically followed:

  • a) Load the furnace while maintaining a temperature below 100°C.
  • b) Heat the furnace to a temperature range of 510-650°C over a period of approximately 3 hours. The specific stress relieving temperature should be determined based on the composition of the grey iron or as mutually agreed upon by the manufacturer and purchaser.
  • c) Hold the furnace at the stress relieving temperature for 1 hour.
  • d) Cool the furnace gradually to a temperature range of 200°C-300°C.
  • e) Finally, allow the casting to air cool.
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It’s important to note that stress relieving is typically performed after any machining or welding operations on the cast iron component. This helps to minimize the risk of distortion or cracking during the stress relieving process.

Stress relieving can be carried out in a controlled atmosphere furnace or using other methods such as induction heating or flame heating. The specific parameters and procedures may vary depending on the type of cast iron and the desired outcome.

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