Free cutting steel and applications of free cutting steel

 Free cutting steel

The important features of free
cutting steels are their high machinability and high
quality surface finish after finishing. 


These properties are due to higher sulphur and phosphorus. Sulphur exists in the form of
manganese sulphide (MnS) which forms inclusions in
steel. 


These inclusions promote the formation of discontinuous
chips and also reduce friction on
the surface
being
machined so produces good
surface finish
easily. 


Phosphorus is
dissolved in
the ferrite and
increases hardness and brittleness. Lead up to 0.35% can be added to improve
the machinability of steel. 


These have high sulphur content
present in form of manganese sulphide inclusions causing the chips to break short on
machining. Mn and P make steel hardened
and brittle. 


Lead (0.2% to 0.35%) is sometimes added to steel improving machinability
properties of steel. This consists of three Bessemer grades B1111, B1112, B1113
which differ in sulphur content
and the sulphurised steels from C1108 to C1151. 


The tool life achieved in machining free cutting steels is from 2 to 2.5 times
higher than when carbon steels of the same carbon content. However, it must be
noted that free cutting steels have lower dynamic strength characteristics and
are more susceptible to corrosion.


 Free cutting steels are frequently supplied
in the cold drawn or work hardened form. These cold drawn steels have a high
tensile strength and hardness but less ductile when compared to other kind of
steels.

Applications of free cutting steel

These steels are used for
manufacturing axles, bolts, screws, nuts, special duty shafts, connecting rods,
small and medium forgings, cold upset wires and rods, solid turbine rotors,
rotor and gear shaft, armature, key stock, forks and anchor bolts screw stock,
spring clips, tubing, pipes, light weight rails, concrete reinforcing etc.

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