Medium Carbon Steel

Medium carbon steels sit around 0.36–0.48% carbon. That is enough carbon to respond properly to hardening and tempering, which is the whole point of the family: you can set the final strength of the part by heat treatment rather than accepting whatever the mill supplied.

This makes them the standard choice for anything transmitting torque or carrying bending load — shafts, axles, spindles, couplings, studs, tie rods. Hardened and tempered EN8 delivers a good balance of strength and toughness across the whole section, not just at the surface.

Three variants exist for good reasons, and the difference matters. EN8 is the standard. EN8D is the same steel held to tighter chemistry and cleanliness limits, so its properties are more consistent batch to batch. EN8M adds sulphur to make it far easier to machine, at the cost of some ductility and weldability.