Shot Peening Prior to Carburizing

[scnh]

Anyone have any data indicating the impact of trying to carburize the surface of a 9310 material which has been shot peened PRIOR to carburizing? i.e does shot peened surface act as a mask? Is diffusion process impacted by high residual compressive stresses?

Any input would be welcomed. Thanks!

 

[israelkk]

I am not a metallurgist but as I recall at the high temperature of carburising all internal stresses will be relieved.

 

[arunmrao]

Shot peening is the final operation on a component to have residual compressive stresses on the skin. Now subjecting a shot peened component to any kind of heat treatment releases the internal stresses. Hence there is no point in having shot peening midway in the process.

 

[rmw]

By mentioning shot peening prior to carburizing you aren't meaning shot blasting or grit blasting for cleaning purposes are you? Other wise shot peening as an intermediary step makes absolutely no sense as explained above.

rmw

 

[scnh]

Thank you all who have replied to this question. Your answers make a lot of sense. As each of you have mentioned, glass beading prior to carburizing has no real benefit. some aerospace specifications specifically mention there shall be no glass bead/shot peen prior to carburizing. I was trying to figure out where they were coming from. Perhaps concerns with surface finish and it's potential impact on carburizing? One aerospace customer has mentioned a phenomenon where a shot peened surface would act as some sort of stop-off and you might get uneven case depth. I'm just trying to reason the cause (if this is true).

 

[swall]

Scnh--this is anecdotal, but at my former employer, some reported research (before I worked there) into a carburizing problem showed that certain surface finishes can inhibit the uptake of carbon, resulting in uneven case, bare spots, etc.

 

[Steve898]

Shot peening prior to carburizing changes the texture of the surface, since the material is soft. On aerospace 9310, the carburizing depth can be specified with little tolerance, say +-.0025". The texture takes up some of that tolerance.
If you are asking about reprocess, then the "dimpling" has little effect, since the shot peen was on a very hard surface, and there is very little textural change.
There is concern, although I have seen no studies, that shot peening can "mask". I do not see a reason to suspect this, as previous posters state, the sp stress is removed upon heating.
My 2 cents.