I Would like to make two scandi type knife one for myself and one for my daughter. I would be heat treating in a charcoal type fire and tempering probably in the stove. (I know I'll catch hell for the smell in the oven)
I would like to know what type of steel you would recommend O-1, 1095, and what size stock to order 1/16x1x18 or 1/16X1 1/2x18 or 1/8x1x18 or finally 1/8x1 1 1/2x18
Thank you.
I like scandi knives a LOT and own a lot of them, and do my ht on a coal forge.
Here some advice:
Stay away from hyperetectoid steels like 1095.
Go for 1075, which is best for such a project. It will harden nicely and you'll have a hard, flexible blade if you ht it properly.
Blade thickness depends on the style of blade you want to obtain. There are thin, supple blades and thick, stocky ones.
The first are good for fillet knives, or light working knives, or fishing knives.
The second make excellent hard working knives. Usually a short, thick blade on a large, comfortable handle is best.
So, thickness is something you should value by yourself, depending on knife destination.
Work the blade, then get your fire nice and uniform.
Extra-hot is unnecessary, and uniformity is much more relevant than actual heat, insofar as you get enough heat to go to critical.
Use finely broken charcoal. With the soft blast needed for HT it won't cost you too much charcoal anyway, and will help you get a more uniform heat.
Heat unformly the blade till non-mag, soak it for a minute, cranking down a little the blast, so to keep temp without going any higher, and let cool in still air to room temp.
This first normalizing is to ease stress in the blade.
It's VERY important, especially in the longer, thinner blades.
Look for warping and correct it when the blade is still dull red.
Heat again to non mag, uniformly, by moving the blade in the fire, spine up and spine down, let soak a little (time varies with thick or thin blades) then quench in oil.
This to refine grain.
Now, for the hardening.
Heat the blade as uniformly as possible, edge up, moving it in the low fire, till it's a deep, dull cherry red. Turn it around, edge down. Blast up a little the heat and heat the edge and tip till non-magnetic. Let soak a little, but it's really unnecessary to get the whole blade to non mag. Actually, it's best to avoid it and bring to non-mag just the edge and tip.
Quench in oil, plunging the blade vertically moving it gently around for the first 10 seconds or so, and then keeping it still.
Do not remove the blade till the oil has become still, so it will be cool enough to handle.
With thin blades, be VERY careful to plunge it verticall, as fast as possible (do not hit the bottom of the tank!
) and moving it along to and fro edgewise to avoid vapour pockets or other irregularities in cooling that would warp it.
For tempering, clean the blade from all oil using acetone, and grind away scale. VERY GENTLY.
Heat on a gentle fire till the blade goes to deep straw. Let the heat soak through the blade. Coloring is surface only, and the blade won't be really tempered if you stop it as soon as the color appears. Use gentle heat, or you'll shoot past the color and ruin the blade.
Keep the blade at this heat for at least 20 minutes for a thick blade.
Quench in oil again.
At this point, you may use a firebrick to keep the edge and tip away from direct heat, and let the spine go to blue on a hotter fire, or immerse the blade in water and torch the spine to deep blue. This will give a blade with a good cutting edge and flexible, tough blade.
The base of the blade, where it becomes the tang, and the tang itself should be tempered well into blue (at least) to be as resilient as possible.
Heat treat in the oven is an alternative, to 200 °C for 70-90 minutes for 1075, but will give a uniform temper, while you want a hard edge and flexible spine. The good part of working with carbon steel is that you can play as you want with temper
With thick blades you can also immerse in oil just the tip and edge, diagonally, and moving the blade to and fro,
When the spine is dull red, remove the blade and immediately clean the scale from the edge and tip . Let the heat soak from spine to edge and tip till they are straw colored, and quench fully.
You'll have a differentially heat treated blade, with soft, resilient spine and hard, tempered edge all in one step. Tricky, but time-saving.
It's a method I use in making screwdrivers, but never used on knives myself, even if there's people around who do it this way.
Cleaning away the scale quickly enough to see the color soaking through is the key.
