At Sandvik Materials Technology, Argon gas is used as furnace atmosphere when heattreating hot rolled wire. Upon heating chromium steel wire, a rich oxidelayer forms on the wire surface. The abstract of this masters thesis is to enhance the understanding of the constitution of the oxidelayers and the influence of the furnace atmosphere. This will be achieved by performing a number of annealing experiments on laboratory level. Also, the aim is to understand the chemical reactions and physical mecanisms controlling the Pickling process.