Effect of thermally grown oxides on colour development of stainless steel

Stainless steels are used in an array of applications where their ability to take on colour is of aesthetic value. Although thermal colouring (heat tinting) is known, particularly in terms of its effect on welds, the surface development of thermally coloured stainless steel has not been considered in detail. This paper demonstrates the colour development of a bright annealed 304 stainless steel with time at temperature. The colour development has been quantified using colour spectrophotoscopy and the colour related to the growth of surface oxide features by scanning electron microscopy and the chemical profiles by X-ray photoelectron spectroscopy (XPS). There is a clear development of both the oxide thickness and chemistry, with increasing time with small nodules being the main features seen across the surface of the samples with time. The oxides have been shown to comprise of an outer iron rich oxide and an inner chromium/iron spinel layer.