Melting and casting
The raw materials are first melted together in the intense heat of an electric furnace – usually for between eight and 12 hours. The excess carbon is then removed and other alloying elements, such as nickel and molybdenum, are added, before the metal is cast into semi-finished forms.
In this stage, the steel is heated and passed through huge rolls, before blooms and billets are formed into bar and wire, while slabs are formed into plate, strip, and sheet.
Also called annealing, this is a process that heats and cools the steel under controlled conditions to relieve internal stresses and soften the metal.
Annealing causes build-up, or scale, to form on the steel. The can be removed using one of several methods, the most common of which are:
- Pickling – uses a nitric-hydrofluoric acid bath.
- Electrocleaning – an electric current is applied to the surface using a cathode and phosphoric acid.
This ensures the desired blank shape is achieved, and can also be used to trim the part to its final size. Mechanical cutting can be carried out in several ways – straight shearing, circle shearing, vertically positioned sawing, blanking, flame cutting, plasma jet cutting or nibbling.
Surface finish is an important specification for stainless steel products, especially in applications where appearance is important. Certain finishes also make stainless steel easier to clean, which is a key consideration for applications in the medical and catering industries. Several finishes can be achieved:
- A dull finish – produced by hot rolling, annealing, and descaling.
- A bright finish – produced by hot rolling and then cold rolling on polished rolls.
- A highly reflective finish – produced by cold rolling and annealing, by grinding with abrasives, or by buffing a finely ground surface.
- A mirror finish – achieved by polishing with progressively finer abrasives, followed by extensive buffing.
Steelmor has been stocking and manufacturing quality stainless steel products in South Africa for over 40 years. Visit www.steelmor.co.za to see our full range of products and services.