Duplex stainless steel is made through a multi-stage steelmaking and forming route: raw materials are melted, refined in an AOD converter, cast into ingots or blooms, then forged or rolled into bar and solution annealed.
Steelmaking
Scrap steel and alloying additions are first melted in an electric arc furnace (EAF). The molten steel is then transferred to an AOD converter (argon oxygen decarburisation), where the main metallurgical work is done: dissolved gases are removed and the final composition fixed by additions of key alloying elements.
The steel then moves to a ladle furnace, where inclusions are modified, before being cast as individual ingots or as continuously cast blooms.
Forming into bar
The solid ingots or blooms are reheated, then forged or rolled to the required diameter. Solution annealing makes the internal structure of the bar consistent, after which the bar is quenched. Bars are finally mechanically peeled to remove the as-produced surface and give a consistent finish.