Cold-formed steel is steel shaped at ambient temperature, without being heated first. The starting material is usually hot-rolled steel that is then worked cold. The designation CF (cold formed) refers to this.
The two main processes
- Cold rolling — the steel passes between rolls with a progressively smaller gap until the required thickness is reached. This is how very thin gauges are produced, well below a millimetre.
- Cold drawing — the material is pulled through a die and mechanically stretched to shape. It is used for tubes and bars with tight dimensional tolerances.
Alongside these there is roll forming: sheet is bent cold into sections, which is the standard way thin-walled building sections are made.
Properties compared with hot-rolled steel
| Cold-formed | Hot-rolled | |
|---|---|---|
| Surface | Smooth and bright, no mill scale | Rougher, with mill scale |
| Dimensional tolerance | Tight | Wider |
| Strength and hardness | Higher, through work hardening | Lower |
| Ductility | Lower | Higher |
| Corners | Sharper achievable | More rounded |
The key effect is work hardening: plastic deformation raises the strength but reduces the ductility. That has a structurally relevant downside — cold-formed steel gives less warning before failure. Where hot-rolled steel visibly deflects first, cold-formed material can fail far more abruptly. Bending already cold-drawn material is therefore discouraged; most of the ductility has been used up.
Uses in building
- Metal stud sections for non-loadbearing internal walls and ceilings
- C and Z purlins and side rails in light steel framing and portal frame buildings
- Profiled sheeting, cassette panels and composite panels
- Cable tray and support systems
- Thin-walled tube and hollow sections where dimensional accuracy matters
Points to watch
- Respect the bend radii. Every section manufacturer states a minimum bend radius. Bend it tighter and the material cracks on the outside of the bend.
- Corrosion protection. Thin-walled steel has little material to spare. Pre-galvanised coating or an equivalent finish is standard for practically every building application; check that the chosen class suits the exposure.
- The connections govern. At low wall thicknesses it is not the section that fails but the connection: bearing at bolt holes, pull-out of self-drilling screws. Check these separately.
- Welding is awkward. The thin wall and the existing coating make welding impractical; screwed and riveted connections are the norm.
Related terms
- Steel
- Structural metal
- Rolled beam
- Modulus of elasticity
- Elongation at fracture
- Corrosion
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