I was hoping Tim or one of the other forgers would answer this, but they don't seem to be around. I work almost totally with stainless steels, but have done some tempering(not heat treating) of carbon steels. To answer your question in two parts:
1. For a great discussion on heat treating carbon steel, I recommend you go to
http://www.ckdforums.com.
Click on enter, then on the "how to's". There is a great article on heat treating(it's the first areticle under forging) by Max Burnett that is designed to be read by the newbie, and not by a metallurgist. He explains the process quite fully. No need to do the whole tutorial here and start talking about austenite, martensite, normalizing etc, when it's already available at CKD's excellant site.
2. Tempering. In Max's article he disdains using water(brine) as a quenching medium; however 1095 is listed as a "water quenching" steel under admiral steel's heat treat section. I've used both when quenching old file blades< which are mostly W-2 or maybe 1095>and found I like the water(brine) quench for those particular steels. You can also oil quench, irregardless of what the specs say, but you get a better steel if you follow the experts' advice: I think, anyway. To make a Brine quenching solution, I use Canning(not table) salt, and dissolve enough into my can of hot(not boiling) water so an egg taken out of the refrigerator floats. Never have quite figured out what to do with the egg after that. The water should be at a temp of around 170 degrees when you go to quench your blade. Also, I checked Admiral Steel's heat treat section, and they say that for 1095, 400 degrees F will give you an Rc of around 62, which is a bit brittle if you leave the whole knife in that state. First of all, you heat the blade, which should be at least clean(kind of polished a little helps) until you reach a "straw" colour, not for any specific amount of time; it will vary quite a bit depending on how accurate your oven is, the blade size, thickness etc.
Second...you can raise the oven temperature up to 450 degrees, and that will give you an Rc of around 56-57. Or.. you can heat at 400 degrees to 62, and then "soften" the back of the blade to blue colour, which is around Rc 45, while keeping the edge at 62 by (a) being very quick with a blow torch or (b) keeping the edge immersed in water while heating the back to blue. I use (b). That's known as differential heat treating or differential tempering, take your choice. I usually temper my blades 3 times, sticking them in the freezer for 3 days between the first 2 tempering cycles to do what is a sort of poor man's cryogenic treatment. Good way to get into an argument in some circles is to mention that method(the freezer). I"ve tempered both ways, with and without the freeze) and found the blade to have greater lateral strength ("flex") and hold an edge at least as well, if not better, than just a plain triple temper. Any carbon steel guys who read this, please inject your two cents(or more) in, since ya'll probably have more exprience. However, what I've describe is a sort of basic treatment which should work. Have fun.
