Darrel, some interesting observations there!
I have to say I'm starting to come around to the notion of carburizing for knives. My fear was that the case depth would be too shallow. I believe this is remedied by doing a diffusion heat treatment after the carburizing (what is referred to the the QuesTek .pdf as "a typical boost and diffuse cycle").
Their .pdf files are here, hopefully I can get the hyperlink to work this time...
http://www.questek.com/questekalloys.html
This spreads out the carbon over a deeper zone and prevents the surface from getting too much and thus remaining too brittle after the subsequent tempering. It becomes a matter of proper heat treatment design for the alloy at hand: carburize for the right time to inject the right amount, then diffusion anneal for the right temperature and time to get the desired concentration profile, then temper properly. Classical ferrous metallurgy!
What's said here goes as well for nitriding and carbo-nitriding. Nitriding would have the additional bonus of being less detremental to the corrosion resistance of a stainless steel. The over-hard case surface Darrel mentions on nitrided gears can be softened by a suitable post-nitriding diffusion treatment as mentioned above.
What are the broader rammifications of this? Namely it opens up one's choice of materials. Rather than worry about the hardenability of a particular steel, you can choose one that is tougher and/or easier to work with and then tailor the hardness/impact resistance balance at the edge through the case hardening and heat treating design. There are steel alloys out there like Ferrium C69 that are strong and tough and would take well to this processing. Essentially look at gears being made for aerospace and high-end automotive use and you'll find examples. Yes, work on lightweight heavy-duty gears is what prompted QuesTek to develop a material like Ferrium C69 (note: the same composition is sold by them under the name GearMet C69!).
For you traditionalists out there, a carburized knife profile is similar to the Japanese lamination technique called 'makuri'.
http://japanesesword.homestead.com/files/nihonto.htm
The downside to this is that good carburizing/carbonitriding/nitriding is really something best left to pros with the capital... and you'll be giving up having your eyes and hands involved with every step.
Any thoughts?
[This message has been edited by GrantP (edited 01-24-2001).]
[This message has been edited by GrantP (edited 01-25-2001).]
[This message has been edited by GrantP (edited 01-25-2001).]
