Hot-rolled steel sheet

S stands for structural steel, 235 is the minimum yield strength in MPa for thicknesses up to 16 mm, and JR indicates an impact energy of 27 J tested at +20°C. Grades S275JR and S355JR have correspondingly higher strength with similar weldability, which is why S355JR often allows the thickness of a component and the weight of a structure to be reduced.

Black (unpickled) sheet has mill scale on the surface which forms during hot rolling. Pickled sheet has this layer removed chemically and is protected with oil, so it has a clean surface ready for painting, laser cutting, bending and pressing. Black sheet works well in structures where mill scale is not a problem or is removed by shot blasting.

Grades with the letters MC are thermomechanically rolled steels intended for cold forming. They combine a high yield strength, from 355 to 700 MPa, with good bendability and weldability, which is why they are used in frames, vehicle bodies, machinery and structures where lower weight matters. S355JR is the classic structural steel for welded structures and thicker components.

DD11 to DD14 are low-carbon hot-rolled steels intended for cold forming. DD11 is suitable for bending and simple pressing, while the following grades, DD12, DD13 and DD14, offer increasing drawability, up to deep drawing. They are chosen for pressings, machine components and parts which are further formed after blanking.

For structures and parts that are cut, welded and bent: trailer frames and chassis, steel and support structures, industrial fencing, machinery and equipment, building and agricultural components. Black or pickled sheet, without a mill certificate or second-grade, is chosen by manufacturers who do not need a mill certificate.

Hot-rolled sheet is produced by rolling at high temperature, so it has wider dimensional tolerances, mill scale on the surface (in the black version) and is available in large thicknesses, at Hen-Stol from 1.20 to 100 mm. It is cheaper and is chosen for welded structures, frames, brackets and parts cut by plasma or laser. Cold-rolled sheet has a smooth surface, tighter dimensions and smaller thicknesses, which is why it goes into housings, metal furniture and pressing.

Both are structural steels with good weldability. S235JR has a guaranteed minimum yield strength of 235 MPa, S355JR of 355 MPa, i.e. half as much again. Under the same loads S355JR allows a thinner sheet, hence a lighter structure and less material, which often offsets the higher price per tonne. S235JR remains the choice where price and ease of bending matter and strength is not critical. Both grades are in the Hen-Stol range, also as overrolled steel and overproduction without a mill certificate.