What cold forming does to steel

What happens during bending

When the roller line bends cold sheet, the material undergoes plastic deformation at the bend. This has two consequences:

• Work hardening: yield strength rises locally, the material becomes stronger.
• Reduced formability: the same material tolerates less further forming and behaves more brittlely.

The effect is strongest in the corners and negligible in the flat plate elements.

Why this matters in design

Because the corners are stronger, the average yield strength of the section is somewhat higher than that of the base material. EN 1993-1-3 allows this to be taken into account under limited conditions.

Its practical significance is moderate: a thin-walled section is usually limited by stability, not by material strength. Where the cross-section is stocky or the connection governs, it can help.

Why the bend radius matters

If the bend is too sharp for the grade and thickness, the edge can crack. A section with a cracked edge is not what the structural calculation assumed: the cross-section is damaged and its stability is worse.

So:

• the manufacturer matches the bend radius to the material,
• higher-strength steel gets a larger radius,
• the corner of the section is rounded in reality, and the design allows for it.

Why the edge is checked in production

Quality control on the finished profile includes flange and lip width, straightness and squareness. Sound edges and accurate geometry are not a cosmetic question: the effective cross-section — the part that actually carries load — depends on them. Quality control at the machine.

The same thing is certified from the product side by the CE marking: that the section was correctly produced from the coil. What CE marking certifies.

Residual stresses

Cold forming also leaves residual stresses in the section. These affect stability behaviour, and they are already built into the standard’s design expressions through the test results behind them. There is no need to calculate them separately in everyday design.

The point

Cold forming does not weaken the steel, it changes how it behaves. What matters is that the geometry is accurate — because that is the geometry the structure works with.