When you consider the process of recrystallization and grain growth you see that grains can’t really grow until total solution is achieved. So with a steel having more than .8% carbon more of it than is necessary will be in solution before the grains start to grow, making retained austenite and other issues a problem even before the dreaded grain growth. For this reason 1084 can handle 1500F but 1095 really should be heated to more around 1475F.
Contrary to what hypersensitive would-be internet warriors may perceive, the actual problem with low tech methods is relaying exactly how to do something to another by typing on a screen, or expecting somebody with less experience to be able to nail something that took an old-timer years to develop the eye for. If you can simply soak for 10 minutes at 1475F before quenching into a fast oil, followed by a 425F temper... well it is fairly easy to pass on the information for success. Non-magnetic is actually rather ephemeral or vague since most would have a hard time bringing the entire blade to 1414F simultaneously without the tools that would themselves negate the need for a magnet. And when people are intent on getting things just right despite reservations about their skill level they tend to be very literal about directions; I have given the magnet advice to people with very limited heat sources only to have to revisit the concept when they heated the blade while suspended by a magnet over a quench, assuming when the blade dropped it was just right.
First off, relax, being tense causes us to do things that are not in the best interest of the steel at temp. Slowly heat the steel nice and evenly until it begins to glow (in a dimly lit room), start checking with the magnet, but still remain relaxed, you and the steel are just taking a calm stroll through the austenitizing range.
From the sound of your past experience with the surface blemishes, you had bad atmosphere control, not heat issues. Heat only exacerbates a atmosphere problem that would be a problem even without over heating. If using a torch, use a larger tip with less oxygen, you are just heating not welding. If you are using a forge, build a brick tunnel over the fire to contain the heat and back off the air draft. No forging operation, even welding, ever requires the air blast wide open, if you are moving solid fuel pieces with the air, you have too much. Once again it should be a calm and tranquil tone with the impression that you have all the time in the world to get this done, despite the reality that it will only take a few minutes.
Carbon has to be put into play if it is going to harden your blade so below non-magnetic is useless. When just enough carbon is in solution to get the job done, enough is enough. So 100F above the Currie point is detrimental overkill. You want the Goldilocks zone so once the magnet stops sticking, work on getting the whole blade an single even color for a few seconds, this is the critical part. The magnet will stop sticking at around 1414F but if your fire is calm and steadily heating you should push it up 50F to 60F more in the effort of equalizing. At this point quench the blade.
I am with Stacy, oversimplified, “foolproof” methods such as the magnet always seem to leave out the most critical ingredient- the 10 to 20 freaking years of experience the guy telling you it is a piece of cake has in order to make that statement. If it were that easy we would all have ABS ratings and would have moved onto something that actually challenges us long ago.
