strathSEEA

It is suggested that any future works be split into the following sub-headings:

 

• Atomic spacing - hardness relationship investigations

• Surface hardness investigations

• Stainless Steel 353 carbide formation analysis

• Nickel based samples composition investigations

 

Atomic Spacing - Hardness Investigations

 

One finding of particular interest was that materials whose microstructure contained larger atomic spacing were able to be more effectively case hardened via carburisation. An investigation as to why this is the case, whether it be due to the larger interstitial spacing or a different reason would allow for a greater understanding of material selection for subjection to carburisation and also allow for a greater control over the carburisation process.

 

Surface Hardness Investigations

 

It was clear that in the case of the iron samples, in the absence of carbides, the surface hardness of the polished side was always greater than the hardness of the non-polished side. It was suspected this was due to stress relaxation at the surface which is associated with a rougher finish. However the relationship between the two factors was not further investigated. This could in part be achieved via carbon depth profiling which would reveal the precise distribution of the carbon throughout the modified layer. Comparison between this and the hardness depth profile would be useful in determining if the main hardening method was by solid solution hardening or via any other hardening methods.

 

Stainless Steel 353 Carbide Formation Analysis

 

Throughout the investigations, the one material which proved troublesome was Stainless Steel 353. Although not appearing to react well to the carburisation process, it was the 2nd hardest of all the alloys post treatment. It was discovered this was due to formation of carbides acting to encourage precipitation hardening. Due to machine availability, the identification of these carbides was not possible. Therefore further research into the composition of these carbides is recommended. If the formation of these carbides can be controlled, then this alloy and others similar could have a use where a hard material with an extremely smooth surface finish is required.

 

Nickel Based Sample Composition Investigations

 

Unfortunately due to the extremely poor ability of the Nikrothal samples to form a carburised layer, it was difficult to draw conclusions regarding the nickel based samples. Although still poor relative to the iron based samples (which was to be expected), an increase in hardness of up to 76.6% was witnesses in the K22 treated Inconel 617 sample, meaning that the carburisation of nickel based alloys can still have potential.

 

There were many differences in the composition between the two nickel based samples, in particular with relation to the nickel, molybdenum, cobalt and also the silicon content. It was thought the largest factor regarding the materials ability to absorb carbon was the nickel weight percentage. However a more detailed investigation into the effect which each of these three elements has on a materials ability to be case hardened is recommended.

Only when an understanding of this is achieved using a single carburisation treatment, is it then seen to be worth investigating the effectiveness of alternative carburisation time temperature regimes.