Comparison
C45 vs 42CrMo4
C45 is the inexpensive carbon steel for shafts in small diameters. 42CrMo4 is the alloy quenched and tempered steel Danish machine building uses when the core has to perform too. Same kind of part – shaft, pin, gear – different hardenability.
Hardenability, not “quality”
C45 hardens in the case. In Ø30 that may be enough. In Ø120 the core is soft, whatever the furnace says. Chromium and molybdenum in 42CrMo4 move that limit. You pay for hardenability, not for a finer name.
- C45 · 1.0503 – non-alloy, EN 10083-2, small cross-sections
- C45E · 1.1191 – same family, tighter P/S
- 42CrMo4 · 1.7225 – Cr-Mo, EN 10083-3, moderate diameters
When C45 wins
Modest diameter, moderate strength requirements, and a price that has to be defensible on a production run. C45N when the drawing requires +N. Welding is not the argument – then it is S355J2.
When to switch to 42CrMo4
When the diameter grows, when +QT and a core value are on the drawing, or when C45 has given a soft core before. The next step after 42CrMo4 is 34CrNiMo6 – not more C45.
Frequently asked questions
- Can 42CrMo4 always replace C45?
- Technically often yes in small diameters, economically rarely. C45 is the right steel when cross-section and requirement fit. Switch when the core falls off.
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