XPS investigation of surface films on high Cr-Ni ferritic and austenitic stainless steels

The surface films of high Cr-Ni ferritic and austenitic stainless steels, which have 21–39 wt.% chromium and 5–28 wt.% nickel, after grinding with SiC paper down to grit 1200, ultrasonic cleaning in acetone and 24 h exposure in a dessicator, were investigated by the XPS technique. The surface films were composed of chromium hydroxide at the top surface and chromium oxide at the bottom surface. The chromium oxide layer was considered to be divided into two sublayers, which are the layer of chromium oxide and iron oxide containing iron and nickel (depending on the nickel content; “Layer A”) and the layer of chromium oxide containing chromium, iron and nickel (Layer “B”). When the contents of chromium and nickel in the alloy increase, the thickness of the chromium oxide layer decreases. However, the thickness of Layer A increases. The thickness of Layer A in relation to chromium and nickel contents shows a S-shaped curve similar to the plot between pitting potentials and the contents of chromium and nickel. The influences of the thickness and nickel content of Layer A on the pitting corrosion resistance of the tested alloys are discussed. If nickel content in alloys is high, it may be found in Layer A and may increase the pitting corrosion resistance of the tested alloys.