The magnetic properties of grey cast iron differ broadly from low permeability and high coercive force to high permeability and low coercive force Whatever these changes may be, they primarily rest on the grey cast iron’s microstructure. The addition of alloying elements to achieve the needed magnetic properties is done by a change of the structure of grey cast iron. The various magnetic properties include carbide carbon, remanence, coercive force, magnetic field strength, max. magnetic permeability, hysteresis loss, magnetic field strength and resistivity.

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Ferrite comprises high magnetic permeability and low hysteresis loss; pearlite is considered as its opposite with extremely high hysteresis loss and low magnetic permeability. Pearlite is made into ferrite by a process of heat treatment called “annealing”. By this process, the magnetic permeability is increased four times. If the ferrite grains are enlarged, it can minimize hysteresis loss. The availability of cementite will minimize the remanence, permeability and magnetic flux density, whilst increasing the hysteresis loss and permeability. The availability of coarse graphite will minimize the remanence.

The transition from A-type graphite (a flake-shaped graphite whose distribution is uniform without any direction) to a D-type graphite (a nicely curled graphite with distribution non-directional between dendrites) can considerably increase the coercive force and magnetic induction.

Before the non-magnetic critical temperature is achieved, there is a significant increase in the temperature level which increases the grey cast iron’s magnetic permeability. The pure iron’s Curie point is the α-γ transition temperature of 770°C.  Now when the silicon’s mass percentage is 5 per cent, the Curie point will hit 730°C. You will find that the Curie point temperature of cementite minus silicon is 205-220°C. The matrix structure of grey cast iron’s common grades is majorly pearlite. The maximum permeability of grey cast iron lies in the range of 309-400 μH/m.

VR Foundries, based out of Coimbatore, is one of the most established Foundries in India dealing with Grey Iron and SG Iron Castings. Simply give us a shout for all your grey iron and SG iron castings’ needs.