Carbon steel (mild steel)

Mild steel is the most corrosive and therefore the least expensive of the three most commonly perforated metals.
 
It is manufactured in either sheet or coil form by roller flattening it to the desired thickness either initially whilst the steel is still hot or again after it has cooled, each of the mild steel types listed below are referred to as either Hot Rolled or Cold Rolled.
Differences in the processes result in products that differ in terms of cost, quality, and mechanical properties. 
Hot Rolled is typically less expensive and produced in thicker gauges of 1.5 mm and upwards, whereas Cold Rolled provides tighter tolerances, better surface finishes, and while it can be produced in practically any gauge, it is most readily available in thinner gauges 1.5 mm – 0.4 mm.
 
Due to mild steel being susceptible to corrosion, it is often used in either unexposed applications or with a protective coating. Coatings such as paint and powder are applied after perforating and completely protect the material. Zinc and aluminised based coated metals (i.e. aluminised pre-galvanised, galvannealed, etc.) are produced and supplied from the mill and may not completely protect the material where the mild steel substrate is exposed during the perforating process.
 
Commercial Steel (HR, CR, GALVANISED, ALUMINISED )
Low cost steel that has good drawing, forming, and welding qualities, moderate strength, but is subject to strains, fluting, and fracture due to ageing. To reduce the affects caused by aging, Drawing Steel is recommended.

Drawing Steel (HR, CR)
Steel with a greater degree of ductility and uniformity of properties than seen in commercial steel providing improved performance during manufacturing.

Forming Steel (GALV)
A steel with lower strength and higher elongation than commercial steel. Recommended when stresses from forming either crack or weaken commercial steel.