Composition: 0,40-0,50 C; 0,50-0,80 Mn; 0,15-0,40 Si; <0,035 P; <0,035 S.

Processing: Casting.

Etching: 15-30s inmersion un 2% nital.

Micrographs show the typical microestructure of an as cast carbon steel without rolling or forging. The amounts of primary ferrite and pearlite differ from those predicted by the level rule due to the non-equilibrium conditions during cooling. In a 0.40% C steel, the amount of primary ferrite should be close to 50%, which is more than that observed in the micrographs. The fast cooling rate also results in a primary ferrite with a Widmanstatten-type structure with preferential nucleation at the grain boundaries.

This acicular morphology of ferrite decreases the steel toughness. Therefore, this steel should not be used for critical components. Annealing, normalizing or hot rolling can be used to get rid of this undesirable microstructure.

This type of steel is ideal for quenching and tempering (austenizing at 840-860ºC/oil quenching/tempering 550 - 660ºC). It can also be used for induction hardening when surface hardness values of the order of 55 HRC are needed. Examples of applications include shafts, tools, gears, etc. The relatively high carbon content compromises the weldability of this steel. 

Fe-Fe₃C diagram

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