Comparison
S355J2 vs C45
S355J2 and C45 both appear on Danish drawings as “ordinary steel”. They are not interchangeable. S355J2 is weldable structural steel with impact toughness at −20 °C. C45 is non-alloy carbon steel that can be hardened in small diameters. You choose by the process – not by the price alone.
What they are
S355J2 to EN 10025-2 is intended for welded structures. J2 is the certificate of toughness at −20 °C. C45 to EN 10083-2 is intended for machine parts that must be hardenable. The carbon that makes C45 hardenable is precisely what makes it a poor welding steel.
- S355J2 · 1.0577 – welded, not hardened
- C45 · 1.0503 – hardened in small cross-sections, welded only with reservations
- C45N is the same chemistry in +N – still not S355
Which to choose when
S355J2 for beams, plate, welded frames and parts that have to document impact toughness. C45 for shafts, bolts and turned parts where hardening or simple carbon strength is enough, and the diameter is modest. If the part has to be both welded and hardened, it is neither S355 nor C45 – then we are talking 25CrMo4 or another alloy with a procedure.
What the drawing often mixes up
A purchaser may write “St52” and mean S355J2, or “C45” on a part that is to be welded in place. We supply what the certificate can carry. We do not rewrite S355 as C45, and we do not promise a weld in C45 that you have no procedure for.
Frequently asked questions
- Can I weld C45 like S355J2?
- No, not as standard. C45 has more carbon and is a hardening/machine steel. S355J2 is the weldable structural steel.
- Can I harden S355J2 like C45?
- S355J2 is not a quenched and tempered steel. For hardened shafts it is C45 in small diameters or 42CrMo4 as the cross-section grows.
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