Difference between Whiteheart Process and Blackheart Process

🔗Different types of malleable cast iron – Whiteheart, Blackheart and Pearlite

Both white heart process and blackheart process are a type of annealing process done on the white cast iron to produce malleable cast iron. Some distinguishing features of this process are listed below.

Whiteheart process	Blackheart process
Annealing of white cast iron in an oxidizing atmosphere	Annealing of white cast iron in the inert/ neutral atmosphere
White cast iron used for this process has high amount carbon and sulfur content.	White cast iron used for this process has lower amount carbon and sulphur content.
White cast iron packed with hematite ore then heated slowly to 950°C. Maintained at this temperature for five days.	White cast iron packed with neutral substance like sand then heated slowly to 900°C. Maintained at this temperature about two days.
Carbon at the surface oxidized and lose as carbon dioxide gas.	There is no oxidization of carbon.
Microstructure: For thin section consist almost entirely ferrite. For a thick section, the surface contains ferrite; core and intermediate zone contains pearlite, ferrite, and temper carbon.	Microstructure: Entirely ferrite and temper carbon.
Nonuniform mechanical properties, mechanical properties vary with thickness.	The mechanical properties are uniform throughout the section.
The fracture appears as steely-white. Hence it is called white-heart.	The fracture give the dark appearance, hence it called blackheart.