Mechanical Engineering - Engineering Materials - Discussion

Actually Both 'A' and 'C' are correct because by adding Mg to white cast iron during annealing we get graphite in nodule form which is responsible for Malleability.

Through an annealing of white cast iron, the brittle structure is transformed into the malleable form.

Carbon agglomerates into small roughly spherical aggregates of graphite leaving a matrix of ferrite or pearlite according to the exact heat treatment used.

My view about this question is that option A is also right.

Malleable iron is cast as white iron, the structure being a metastable carbide in a pearlitic matrix. Through an annealing heat treatment, the brittle structure as first cast is transformed into the malleable form.

Carbon agglomerates into small roughly spherical aggregates of graphite leaving a matrix of ferrite or pearlite according to the exact heat treatment used. Three basic types of malleable iron are recognized within the casting industry: black heart malleable iron, white heart malleable iron and pearlitic malleable iron.

The white cast iron heated up to 920 degrees and cooled very slowly this process is called annealing.

White cast iron is heated above a Recrystallisation temperature of 910 degrees centigrade.

Holding at that temperature for 45 hrs and allowing them to slow cooling. In this process, graphite flakes are converted into nodules/spheroids. This process is known as Mallebelisation treatment.

@Digin.

Adding mg to produce ductile iron/SGI Spheroidal Graphite Iron/nodular iron.

The annealing process involves heating white cast iron for an extended period and then cooling it slowly.
This heat treatment process helps convert the brittle structure of white cast iron into a more ductile and malleable form by breaking down the cementite into graphite clusters.