Does anyone have detailed instructions on heat treating 440C?

A couple of sites that I have found on the Net show different times to "soak" the blade:

This site says five minutes, which I find hard to believe.
www.admiralsteel.com/reference/sstltech.html (http://www.admiralsteel.com/reference/sstltech.html)

This one says " Soak times can generally be taken as one hour per inch of thickness. For example 15 minutes would be about right for a quarter inch thick blade."
www.knives.com/heatreat.html (http://www.knives.com/heatreat.html)

Most other sites say to hold for 30 minutes.

Kevin, 10-15 minutes is plenty for the transformation to occur when you are dealing with sections as thin as most knife blades.

Thanks Don, a couple more questions:

Do you place the blade in a cold oven and ramp the temperature up slowly, or do you place the cold blade into the oven at "temperature"?

Do you "presoak" the blade at a lower temperature, before raising it to the "critical" temp.?

Start with a cold oven. Crucible's data sheet for 440C says:

"Large sections or complex parts should be preheated to 1425 F, equalize, then raise to the autienizing temperature (1850-1900 F)"

I would just ramp right up from a cold oven to 1875 F, hold for 10 minutes, and air quench. Tempering, (2 hours each temper) should be:

for 59 RC- 212F
for 56 RC- 400F
for 54 RC- 600F

Be sure to use foil wrap (or some other decarb preventive measure).

Kevin
I have been heat treating 440C for about 20 years. All of the previous replies are correct. My rule of thumb is 1 hour per inch of thickness...+ or - a minute or two...best to go a little over than under on the time. Carpenter Steel recomends a double quench at 550 degrees...on hour each time.
I also Sub-0 (Zero) quench using liquid nitrogen. I live in a rural area, a farming community....large dariy farm where they do artificial breeding. The bull seamen is, of course, stored in these tanks. When I pick a day that I am going to heat treat I give the local ABS ( American Breaders Society) man a call and he drops of a tank ( with out the bull stuff). I Sub-0 quench the blade after tempering ( place in the tanks at room tempature)....I leave them there for about 24 hours.
Sub-0 quench will add about 1 or 2 point to the hardness and add alot of toughness.
If you choose the Sub-0 quench you might want to throw a drill bit or two into the quench.....makes them tough too.....The most important thing to remember is not to put the knives in the liquid nitrogen....HOT.....remember room tempature! I have a rockwell tester that I purchased some time back and it helps but I have found that if you do your heat treading and Sub-0 quench the same way every time the hardness of your blades will not vary much at all on the RC scale. My most recent purchase is a digital parameter to double check the parameter on my Paragon Oven.... I have found that the analog parameter will vary as much a 10 degrees at different times......I don't know why.....I just feel it is always good to have a back-up and a good double check. If you have any other question drop me an E-mail.
I hope we have helped.
Jim

Thanks for all the info guys, I really appreciate it.

Does anyone "sub-zero quench" with dry ice?