Surface Engineering by Expanded Austenite
Alloys
Stainless Steels
All steels are an alloy of which the primary element is iron (Fe), with the alloying elements commonly being carbon (C), chromium (Cr), nickel (Ni), manganese (Mn) and molybdenum (Mo). The definition of a stainless steel is one which has a minimum mass percentage of chromium of 10.5%.
The main advantage of this high chromium content is that the chromium reacts when exposed to oxygen to form a passive layer on the surface of the material, approximately 2nm – 3nm thick. This coating results in the materials exhibiting corrosive resistant properties over a lengthy period of time, due to the way in which the oxide layer can repair itself by continually reacting with the surrounding environment.
These corrosive resistant features along with its good manufacturability make stainless steels a favourable material to be used in many everyday applications, with common uses ranging from household items to the automotive and airspace industries.
The disadvantages of stainless steels over the more common carbon steels is the reduction in hardness due to the decrease in the carbon weight percentage (wt%) and also the fact that it can suffers from an increased wear rate known as galling which has limited its potential tribological and tribochemical applications. However the mechanical properties of the alloyed material can be further altered with the introduction of additional alloys, the effect of which can be found here.
