Malleable cast iron is produced 1. By quick cooling of cast iron. 2. By adding magnesium to molten cast iron. 3. from white cost iron by annealing. Which of the above statements is/are correct?

Malleable cast iron is produced 1. By quick cooling of cast iron. 2. By adding magnesium to molten cast iron. 3. from white cost iron by annealing. Which of the above statements is/are correct? Correct Answer 3 only

Explanation:

Types of Cast Iron –

• Malleable Cast Iron: Malleable cast iron is produced from white cast iron by annealing. During annealing treatment graphite nucleates and grows from the Fe₃C to form nodules, 900-950°C for many days / cooling slowly. It is heat-treated iron-carbon alloy, which solidifies in the as-cast condition with a graphite-free structure, i.e., the total carbon content is presence in the cementite form (Fe₃C).

Malleable Cast Iron: Carbon : 2.3 – 2.7 wt%, Si: 1.0 – 1.75 wt%, Reasonable strength and improved ductility (Malleable).

• White Cast Iron – Fe₃C + Pearlite, hard and brittle. Show a ‘white’ crystalline fractured surface. High compressive stress.
• Grey Cast Iron – Microstructure: Graphite flakes in a ferrite or pearlite matrix weak and brittle in tension. Strong in compression.

Excellent wear resistance casting shrinkage is low.

• Nodular or Ductile Iron – Addition of mg and / or cerium to grey iron converts the graphite flakes to nodules.