25CrMo4.
The workhorse alloy of the modern steel frame. Higher chromium shrugs off the torch: fine carbides keep the grain from growing, so 25CrMo4 keeps its properties through brazing and welding — exactly where lesser steels lose theirs.
the numbers.
Figures from the Columbus 2024 steel catalogue. Test bars, not marketing bars.
| 900MPa | ultimate tensile strength — dependable, documented | UTS |
| 800MPa | yield strength — a high floor for hard use | YS |
| 12% | elongation at break, measured on Ap5 | AP5 |
built for the torch.
“Every frame is born in fire. The question is what the steel remembers afterwards.”
25CrMo4 carries more chromium than a garden-variety CrMo, so it resists overheating at the joint. Its carbides prevent grain enlargement under the flame — the tube keeps the mechanical properties it was drawn with, through brazing and welding alike.
That resilience is why it anchors Zona, and the 29r and FAT mountain families.
- Base
- 25CrMo4
- Grain
- carbide-pinned
- Butting
- triple & double
- Character
- all-purpose · hi-res
no drama.
“The first builder’s alloy: it forgives the second pass.”
TIG with OK TIGROD 13.12 (AWS 5.28 ER 80S-G), braze with Castolin Silver Alloy 38230. Because the grain stays fine under heat, 25CrMo4 is the alloy we recommend where workshop conditions vary and frames must simply last.
- TIG filler
- OK TIGROD 13.12
- AWS
- 5.28 ER 80S-G
- Braze
- CASTOLIN 38230
DRAWN INTO — the Zona tubeset →