Yes, many people doing 1084 HT in a forge do it by eye. A 2BF is pretty primitive, but should work for 1084HT. As soon as you get the skills and funds, build a larger and proper forge.
The steel from Aldo and many other suppliers comes in the structure of spheroidite. This is a from of pearlite with the carbon balled up in balls and bundles of carbides. This leaves the matrix nearly pure iron, and thus is soft to machine and work with tools. The carbides are tightly bundles, and will need to be "un-bundles" to let the carbon free so it can make hard steel in the final quench during HT.
I will start with a mini-metallurgy class -
Steel at temperatures below 1400F is either pearlite, martensite or spheroidite. Where and how the carbon is placed in reference to the iron determines these structures. The cube has eight iron atoms sharing a single carbon atom in the center of the cube. The carbon is in the "center" of each cube.
When we heat the steel and cross the critical point ( Curie point for practical purposes), the carbon changes from body centered cubic to face centered cubic. This places four iron atoms sharing each carbon atom on the cube. The carbon is now on the "face" of each cube side. This places a ;lot more carbon where it will be available as the steel cools and changes back to martensite in the quench. We use the term "putting more carbon into solution" for this austenite heating part of HT.
Ok, enough science ( well not really enough, but enough for now).
A few tips for doing a forge HT are:
1) Your eyes are only so good in guessing the color of hot steel, and thus the heat of the blade. Use a magnet to determine the color of the steel when it becomes non-magnetic. Use this color as a base line for approximately 1400-1425F. Compare the base line color at 1400F to what you think is a redder or oranger color. It may not be exactl, but it will be close enough for the purposes you need.
2) Turn your forge down to as low as it will run with a stable flame. Few forges will run at 1500F without PID control, so it will still be hotter than you want.
3) Do the HT in subdued light. Bright sun or lighting can make your eyes think that the steel is much cooler than it actually is. Doing HT at night or on a cloudy day is good. If indoors, turn a 60 watt bulb on behind you and turn off the overhead lights.
4) Turn the blade constantly, moving it in and out of the hotter places in the forge.
5) A muffle pipe is a good thing when trying to get longer soaks without overheating the edge and tip.
The HT:
The first cycle is at around 1650F. This step is to make sure that the carbon locked up in the carbides gets dissolved and goes back into solution as austenite. It could be 1850F and it wouldn't really matter. What you want is the steel roughly 200 degrees hotter than the non-magnetic point. This is around the point where it starts changing from a red color to an orange color. Letting it cool to black lets the steel convert back to pearlite. The grain may be enlarged somewhat, but that is OK right now. Try and keep the blade at the red-orange color, paying the most attention to the tip and edge. While a 15 minute soak may be impossible, at least a few minutes isn't too difficult.
The second cycle is to get the grain reduced and to make sure the carbides are evenly distributed. It should be at or around the target temperature for the HT. 1450-1500 is good. This is just about a shade brighter red than non-magnetic. Basically, you want to hold the steel at just above non-magnetic for a good soak. Cooling to black locks in the new smaller grains.
The third cycle is sub-critical, and should be below the non-magnetic point. The blade should be light red and should still stick to the magnet. Cool to black or quench .. it doesn't matter, since the blade is not changing structure/phase. This step is to remove any stresses from the blade and make it soft. After this step, check the blade for straightness and adjust as needed.
Now the blade has all the carbon back into solution and evenly distributed. It has a reduced grain size, and is stress free. It is ready for the final heat where it will be austenitized at around 1475-1500F ( austenitization) and quenched to convert the austenite into martensite. In this step, the 1084 blade only needs to be held at the target temp for sufficient time to allow the blade to be evenly heated all the way through. Pay attention to color of the edge and tip mainly. These are the parts that you want to harden perfectly. It won't matter ( and may actually be better) if the spine is a bit less hard than the edge as long as the edge is perfect.
Now, back to the metallurgy for a moment:
What would happen if the tight spheroid balls of carbides didn't dissolve ...? The steel would have large places of carbon starvation. In effect it would be plain iron with little bits of harder steel in it. This would be a very soft blade, and the Rockwell hardness would test quite low after the quench. This is what the cycling gets rid of.
