The 1200F step is a pre-heat to equalize the blade before the transition to austenite. It only needs to be long enough for the blade to fully come to 1200F. Most folks use 5 minutes when programming a HT oven, but a minute in a gas forge will be fine.
Here is how I HT O-1 in a forge:
1) Bring the forge up to its lowest stable temperature (for a PID controlled forge, bring to 1500F). Let run for 5-10 minutes to get the chamber fully soaked. In a regular forge, the chamber will likely be somewhere in the 1600-1800F range.
2) Put the blade in the forge and move in and out while turning so it heats up evenly. As needed, put it out completely and put back in to keep from getting too hot. You want the blade to come up to just barely red. NOT a bright red. It should still stick to a magnet. Keep the temperature at dull red for one minute, without crossing non-magnetic.
3) Allow to rise to 1500F. If the forge is PID controlled, that will be no problem ... since it is already at that temperature. If it is not, bring up to non-magnetic and then two shades red brighter. This is about 100F hotter than when the magnet stopped sticking. In a HT oven, you would soak for 10 minutes. In a PID controlled forge, hold for 5 minutes. In an uncontrolled forge, try to hold as long as possible ( one or two minutes) without overheating the edge or tip. Pul in and out while turning to keep the heating even.
4) Quench in medium sped oil warmed to 120-130F.
5) Temper twice at 400-425F.
Note - A blade coating to hold down decarb and scale is a good idea. Brownell's makes a good one. A light coat of satanite works, too.
