C25E

Unalloyed special steel with controlled chemistry (E grade) and 0.42–0.50% carbon. Tighter P and S limits than standard C45 for improved consistency. The most widely used medium-carbon steel for quenching and tempering. Good balance of strength (620–850 MPa QT) and toughness. Through-hardening up to ø60mm. Surface hardening by induction to HRC 58. Used for shafts, gears, bolts, connecting rods, crankshafts, and general machine parts.

Medium-carbon unalloyed steel with approximately 0.30% carbon. Intermediate strength between C25 and C35. Good machinability and moderate weldability (preheating recommended for thicker sections). Used for moderately stressed structural parts, shafts, bolts, levers, and connecting rods in general mechanical engineering.

Medium-carbon unalloyed quality steel with 0.22–0.29% carbon. Good machinability and moderate strength in normalized condition. Standard P and S limits (less pure than C25E). Used for bolts, nuts, levers, shafts, and general machine parts not requiring high strength. Can be surface-hardened by induction or flame hardening.