Generally, if you're doing forge work, you'll have a general purpose forge. Some people have a seperate welding forge that may be a bit more robust to resist flux and can obtain somewhat higher temps. You general work forge should be able to obtain temps upwards of 2200F. As for control, the ability to know and control temperature in your forge is a great advantage. Many makers use a well controlled forge to heat treat. This requires the ability to know the actual temp and be able to hold it to within 10 degrees or so. This usually involves a PID controller which controls the fan speed on a blown forge. Atmospheric forges can also be very accurate if set up right, and you can tell the temp using a pyrometer. It's also necessary to be able to adjust the "atmosphere" of a forge to produce a reducing or oxidizing atmosphere.
Most makers who do heat treating with a variety of steels use a seperate heat treating oven for that purpose. These ovens can reach temps of 2200 as well, but will be able to accurately hold that temp for an indefinite period of time in a very narrow range of fluctuation. This allows heat treating of a variety of simple and complex steels inlcuding stainless and high alloy steels. As for tempering, this is done after hardening (hardening consists of reaching critical temperature, holding it for a specified period of time for you steel, and quenching in appropriate medium...fast oil, brine, medium oil, or air/plate quench). Tempering is often done in a household oven that has been fully heat saturated (been on for a while to stabilize temps) or in a well controlled toaster oven with something like a brick placed in it to increase its thermal mass. Tempering happens at a much lower temp than hardening with usual tempering ranges from 350 to 500F.
As for quench tanks, people use a variety of tanks shapes. Some use a 5 gallon surplus ammo can; others use vertical steel tubes with a stand welded on. I've even used a very large stainless pot. It's a good idea to have a lid that fits to not only prevent contamination of the quenching medium, but also to put out any flare ups that may occur.
You'll also find that a drill press is indespensible as well as a good set of files (needle and regular). I personally find a hundred uses for razor blades and buy them in bulk. A good set of dial calipers will serve you well, and a height guage is also very handy as well as a truly flat surface (granite plate).
And if you're forging, you need some type of anvil. Avoid the cheap-o harbor freight cast anvils. Find a good used anvil without too much sway and with a few areas of clean, crisp edges. My anvil is well over 80 years old and still going strong.
For stock removal or forging, you'll find a good belt grinder is extremely useful. 2x72" is the common size for our industry, but they can be a bit pricey.
I'm sure there's more, but this is just off the top of my head.
--nathan
