What is hot-rolled steel?
Hot-rolled steel is steel that has been rolled into its final shape while red-hot, above its recrystallisation temperature. This is how the familiar structural sections are made: I-beams and H-sections (in Europe HEA, HEB and IPE, in the UK universal beams and columns), channels, angles, flats and heavy plate. After rolling, the surface carries a blue-grey oxide layer called mill scale.
Properties
- Large, heavy sections can only be made by hot rolling.
- Low residual stress: the steel deforms at high temperature without work hardening, making it tough and easy to weld.
- Tolerances: shrinkage on cooling makes dimensions less precise and corners slightly rounded compared with cold-formed steel.
- Surface: rough and covered in mill scale; blast clean before painting.
- Grades: in construction usually S235 or S355 to EN 10025, where the number is the minimum yield strength in N/mm².
Hot-rolled versus cold-formed
Cold-formed steel is bent or roll-formed from thin sheet at room temperature into C and Z purlins, hollow sections or light steel framing. It is lighter and more precise but thin-walled. Hot-rolled sections are used for long spans, lintels, beams for knocking through walls, and columns.
Practical tips
- Beam for an opening in a wall: always have a structural engineer size the section. Building control will normally ask for the calculation.
- Order it protected: blasted and primed, or hot-dip galvanised for outdoor use.
- Fire: unprotected steel loses strength quickly in a fire; boarding or intumescent paint may be required.
- Bearings: provide padstones or spreader plates as the engineer specifies.
- Weight: plan lifting gear and temporary props before delivery.
Related terms
- Mill scale
- Cold-formed steel
- Corrosion
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