Materials database

Higher-carbon CrMo Q&T steel — 0.42-0.50% C vs 0.38-0.45% for 42CrMo4. Higher maximum hardness (HRC 52-56 surface after induction) and tensile strength (UTS 1000-1200 MPa QT) at the expense of slightly reduced toughness and weldability. Used where 42CrMo4 is not quite hard/strong enough: heavy-duty gear shafts, large bolts (12.9 class), crankshafts, and torsion bars.

Free-cutting variant of 50CrMo4 — S 0.020-0.040% for machinability. Higher C (0.46-0.54%) than 42CrMoS4 = higher hardness after Q&T (UTS 1100-1300 MPa). Used for high-strength shafts, torsion bars, and heavy-duty bolts produced on CNC automatics where maximum CrMo strength with machinability is needed.

Mid-carbon unalloyed Q&T steel — 0.27-0.34% C. Between C22E and C35E — good weldability with moderate strength after Q&T. Modern designation for Ck30. Used for lightly loaded shafts, levers, bolts, and machine parts.

Mid-carbon unalloyed Q&T steel — 0.32-0.39% C. Good balance between strength and toughness/weldability. Modern designation for Ck35. Used for moderately loaded shafts, axles, bolts, connecting rods, and machine parts where C45 would be too hard and C22E too soft. Also suitable for surface hardening (flame/induction) to HRC 50-55.

Mid-carbon unalloyed Q&T steel — 0.37-0.44% C. Slightly below C45E in carbon content but very similar properties. Modern designation for Ck40. Used for crankshafts, connecting rods, axles, bolts, and machine parts. Suitable for flame/induction hardening to HRC 52-56.

High-carbon unalloyed Q&T steel — 0.47-0.55% C. Higher strength than C45E at the expense of reduced weldability and toughness. Modern designation for Ck50. Suitable for induction hardening to HRC 55-60. Used for heavy-duty shafts, rail wheels, clutch plates, and springs where maximum unalloyed strength is needed. Also used for agricultural equipment and wear parts.

High-carbon unalloyed Q&T steel — 0.52-0.60% C. Modern designation for Ck55. Good strength after Q&T (UTS 800-950 MPa) and excellent surface hardness after induction hardening (HRC 56-60). Used for rail wheels, crankshafts, heavy-duty shafts, and wear parts.

Plain carbon quenched & tempered steel — 0.57-0.65% C. Highest practical C for Q&T without excessive brittleness. Good surface hardness (HRC 55-60) with adequate core toughness. Modern designation C60E (EN 10083-2), traditional Ck60 still widely used. Used for crankshafts, connecting rods, rail wheels, axles, and machine tool spindles where alloy cost is not justified.