CONCEPT:Machinability:The EASE with which the machining of a given material can be carried out is called as machinability.Under similar conditions of machining, the workpiece on which the better surface finish is produced will indicate the better machinability.The workpiece on which the longer tool life is obtained will get better machinability.The workpiece on which the specific cutting ENERGY required is lower will indicate the better machinability workpiece.Machinability of any material can be specified by Machinability index which is defined as the ratio of cutting velocity of the workpiece to the cutting velocity of standard work material. White cast iron:These are produced by the fast cooling of liquid material.Due to the fast cooling rate cementite PHASE is form instead of graphite, and hence the white C.I is the hardest and strongest cast iron material.Therefore the machinability of white cast iron is not possible.Relative machinability of some commonly USED materials are:Magnesium and its alloys Excellent machinability Aluminium and its alloysZinc and its alloysCopperBrassGun MetalGoodBearing bronzeGrey cast iron, Malleable CIMuntz metalFree cutting steelWrought ironLow carbon steelStainless steelFairNickel steelHigh-speed steelPoorWhite cast iron Not machinableCarbides