Heat treating 1084 Steel

By Kevin R. Cashen
"Steel 1084 Forged blade Computer Controlled oven Here is how I would do it if you took my salts away from me:

I would still prefer a coal forge for most of the operations, due to the ability to control the atmosphere, but I would like the oven for my anneal. I can always get a better heat treat out of a coal forge with an enclosed fire, than a gas forge due to the ability to localize and control the heat.

Specs sheets will give you a different temperature for each steel, but decalescence is what it is all about. Watch for the color the steel glows just as it is rebounding from the shadowy transformation range, this will be correct for what ever steel you are using since you are actually watching the transformation completing itself.

I would ALWAYS use a properly formulated quench oil,

1084 is so close to the eutectiod, that you need virtually no soak time at all at 1500F.. The magnet will tell you the Currie point of iron (around 1414F.) but will not tell you Acm (when complete austenite is achieved), and it will not be accurate at all on cooling, only on heating. Ar1 (transformation on cooling) is always much lower and is not where you want to quench from. Give it a try some time, heat a piece of steel to non-magnetic. As it cools see how long it takes for the magnet to stick. It will be almost black again before this happens.

I guess what I am saying is that you can make a fantastic knife with just a bit of practice and very simple tools like a forge, you just need to avoid the hocus pocus. Be aware that repeatable consistent results can be better had with more sophisticated equipment. The better your tools the more consistent the results. The single most powerful tool is KNOWLEDGE! Then the little things will add to your success. A proper quenchant design for your steel type will greatly increase your success without going as far as salt baths.

Keep the grain size small, keep the carbon in the steel, get things as hard as you can and then temper to the desired rockwell and you will do real well.

. Normalize
2.a Soak in Oven at 1550? 10? minutes"

This is an eutectoid steel, it will come completely into solution at the lowest temp of any steel. Get it to 1550F and go right to cooling as evenly as possible. the grains will be a little larger that you want to end up with but they will be equally even in size.

2.b Air Cool
2.c Soak in Oven at 1500? 10 minutes
2.d Air Cool
2.e Soak in Oven at 1475? 10 minutes
2.f Air Cool"

A couple of heats at 1250F to 1325F will give you a very soft steel without the step 3 with 10XX steels. In 10xx steels above .80% carbon you will get spheroidal shaped carbide clusters. This makes for a very soft material but be aware that you will need to soak a little longer to pull that carbon back into solution when you heat treat. I often get phone calls from makers wondering what they did wrong with a hypereutectoid steel that has extra carbide forming elements. They get an odd damascus like pattern all over the blade. I tell them to soak longer or raise the temperature before the quench to dissolve those extra carbides and alloy banding and the problem will go away.

3. Anneal
3.a Soak in oven at 1500? 10 minutes
3.b Oven Cool"

This will give you a traditional lamellar anneal (course pearlite) as opposed to the aforementioned spheroidal treatment. Be aware that this treatment will result in a courser grain, but it will be quite even and will recrystalize quite well on heating for the quench.

"4. Grind to final shape

5. re-Normalize
5.a Soak in Oven at 1500? 10 minutes
5.b air cool"
Quite honestly I would dispense with this normalizing step entirely. If you got things just how you want them before the grinding, don't mess with it any more. If you keep the thing cool while grinding you shouldn't have too many stress issues. There will be some strain energy from a course grinding belt but you can handle this, as well as getting things a little too warm with a stress relieving treatment (900F-1250F) without the radical treatment of another normalization.

"6. Harden
6.a Soak in Oven at 1500? 10 minutes
6.b Quench in commercial fast-quench quenching oil at 140? degrees"
I could not tell you how long to soak in an oven with the insulative affect of still air, but I can tell you that spheroidized 1084 requires only a 2 or 3 minute soak in salts to completely go into solution in blades type cross sections. O1 on the other hand requires at least 4 to 5 minutes to reach the mark in the same annealed state.

Make some small test samples and give them all the same anneal. Soak the first to 3 minutes and quench. Soak the next to four minutes and so on... out to perhaps 10 minutes. Do rockwell tests on each piece and you will notice a point of maximum hardness where longer soaks just don't matter. This will be your soak time in your oven. This would be a good place to use the anti scale compound if you are using and oven. It has been my experience that ovens and kilns are the most oxidizing of all methods of heating, with the exception of perhaps a torch.

The quench and its temperature sound good. Be sure to agitate! I drives me crazy to see smiths just hold the piece still in the oil and then complain that the oil isn't fast enough! In the words of Frederic Douglas "agitate, Agitate, AGITATE!" Don't swish the blade side to side in the oil, move it quickly tip to tang, to slice cleanly through the oil, if quenching horizontal; up and down or spine to edge, if vertical.

"7. Temper 3 times at 400 one hour each"

If you definitely know your results a single 2 hour temper will do the trick. I use 2 or 3 not because there is any magic associated with it, but this allows me to zero in on an exact HRC for each blade. After the first soak, I take a reading and then repeat with the temp bumped up a bit to increase the draw. I then take another reading and if it is where I want it, great! If it is not I go for a third. Industry also uses multiple tempers to cope with any retained austenite that may be present. The first tempering will convert it and make more martensite, so the second temper can zap the newly formed hard stuff.

The sooner you can get to the temper after the blade has reached Mf (THIS IS ROOM TEMP AT LEAST) the better off you will be. Not letting the blade completely cool to Mf will result in many problems, not the least of which would be the previously mentioned retained austenite.

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