Surface Hardening Treatment of Austenitic Stainless Steel

In the recent Nickel Development magazine, there was an interesting article on surface carburization treatment of austenitic stainless steel to increase hardness for wear resistance. Apparently, this company performs the surface treatment using plasma carburization at temperatures below 500 deg C to avoid sensitization;

http://www.nickelinstitute.org//index.cfm/ci_id/12760.htm

 

[mcguire]

Perhaps this can be done because at this low a temperature both iron and chromium carbides are thermodynamically favorable and form in proportion to their weight percent in the alloy, rather than forming predominantly chromium carbides and depleting the matrix of the chromium it needs for corrosion resistance.
At this temperature diffusion is slow, so it must be a very thin skin of harder alloy.

 

[metengr]

I thought that it seemed interesting because every once in a while, a question is asked in this forum regarding surface hardening of austenitic ss.

 

[unclesyd]

Even more interesting is their process for surface modification of Ti.

http://www.sdc-tanaka.co.jp/en/secound/second.html

 

[kenvlach]

Bodycote has had a similar, Kolsterising® plasma carburization process for some time, although Tanaka has perhaps lowered the temperature by 25-50°C; see
How to increase 304 SS hardness
thread330-49696
and
Bodycote’s site:
“Kolsterising® is a case-hardening process primarily for austenitic stainless steels. Wear resistance and resistance to galling is improved, while corrosion resistance remains unchanged.
The process involves diffusion of carbon into the work piece surface without the formation of chromium carbides. Post treatment surface hardness is equivalent to between 70 and 74 HRc. Standard case depths offered are 22 or 33 microns.”

http://htna.bodycote.com

[Note: look under Heat Treating]

At the relatively low temperatures and short process times, carbides do not form (except perhaps on a very minute scale) because of kinetic factors. Solution hardening results from cramming the lattice with interstitial carbon atoms.