C40R
1.1189Unalloyed special steel with controlled sulfur (R grade, S 0.020–0.040%) and 0.40% carbon for improved machinability. Same base composition as C40E but with intentional sulfur for better chip formation in automated machining. Used for shafts, bolts, gears, and general machine parts requiring good strength with high production rates.
Mechanical properties
Related materials
C45E
1.1191Unalloyed 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.
C25E
1.1158Unalloyed special steel with controlled chemistry (E grade) and ~0.25% carbon. Tighter P and S limits (max 0.025%) than standard C25 for improved consistency. Suitable for quenching and tempering to moderate strength levels. Good machinability and weldability. Used for shafts, bolts, transmission parts, crankshafts, and machine components of moderate stress.
C30
1.0528Medium-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.
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