strathSEEA

Although stainless steel alloys and nickel based alloys are re-known for the effectiveness of their passive layer in avoiding corrosion degradation, the largest set back in their wider use has been their inability to deal with more extreme tribological applications; this being due to their relatively low hardness and tendency to wear.

 

High temperature (>500°C) thermochemical surface engineering using carbon or nitrogen gas has proved difficult as the passive layer does not allow the nitrogen or carbon atoms to pass through, meaning that diffusion beneath the passive layer could not take place.

 

The small increase in the hardness of the alloy that was achieved came at the expensive of the corrosion resistance of the passive layer as the C and N atoms react with the chromium to form carbides, reducing the effectiveness of the chromium in forming an oxide layer. Therefore high temperature surface engineering has been found to be an inappropriate method of strengthening the surface of austenitic alloys.

 

The solution was found via a low temperature carburising process.