During the Oxy flame cutting process, metal is heated in a quick, but controlled manner, causing oxidation in specific areas of the steel plate. When removed, these areas become cavities and as the reaction increases, creates mergers for connected cuts. While oxygen and heat alone cannot cut through material, using a constantly heated torch and a steady stream of oxygen combined, thick steel can lose protective inherent properties, yet still remain solid, allowing for a smooth cut.
For most mild steels, heating to 700-900° C brings the material to its ignition point, without causing melting (kindling temperature). A pure oxygen stream is then aimed at the heated area and an exothermic reaction is created between the oxygen and the material. This creates iron oxide which is removed by the constant stream of oxygen, eventually creating a pierce point, cutting through the metal surface.