Razorback - Knives said:
There is no secret. HTing info is only a mouse click away.
Scott
you mean like this:
Quite true, but I think the secret to HT is knowing what your doing. It is not so simple as you make it sound. Any knifemaker that tells me that HT'ng is easy and simple, will just make me walk away. It is far from simple.
I think what separates the great knifemakers from the so-so knifemakers is their HT and attention to detail. ATS34 can be great, mediocre, and junk depending on who does it. I had a Gerber ATS34 blade that was junk. Yet my Microtech 154CM (same thing) could hold an edge three times longer than my gerber. Microtech obviously has their steel HT'd by someone who knows what they are doing.
If you deal with only one type of steel and use that alone and have learned that heat treat and call it simple because of that, then fine. However, if you use many steels and do in house HT and call it simple, I'll be skippin along.
Here is the heat treat for O-1 that I took from Navachrome:
--------------------------------------------------------------------------------
When does the clock start ticking? The clock starts when steel temperature falls below 1333F. There's no need to quench at or near the Peak temperature. So when to quench? Between the Peak and 1333F, it's your call. There's no reason to subject the blade to any more thermal shock than necessary, so quench at the lowest temperature you can and still be above 1333F.
Place the blade into the muffle and when it gets hot enough, watch/check for Critical, using a magnet. Now the question is how much higher to heat the steel? Time and temperature are both at play here. A slower temperature climb over a longer soak period is about the same as a faster climb and shorter soak. Use both the 1400F and 1500F Tempilstiks, 1400F is right at Critical. Let the temperature rise and if you hit 1500F then withdraw the steel. You'll have the temperature bounded, lower and upper, with Tempilstiks. Shoot for 50-100 degrees above Critical and a soak of 1-3 minutes.
Withdraw the blade from the muffle and as it cools, watch the color change. Know what Critical looks like and quench right as you pass Critical going down. If you start seeing 'shadows' move across the steel you've hit the recalescence point and the steel's too cool to quench. Put it back into the muffle, go back up to peak, soak a bit and try again. This routine can be practiced with 1018 and although it won't harden you can get the procedure down.
One important point to understand: When the steel has reached Critical during the initial heating phase, the magnet test will work. However, the magnet doesn't work coming off Peak during the cooling phase. Further, the magnet won't work until the steel has cooled below Ar1 and is heated again. Steel needs to be 'reset', as it were.
Once the quench begins, it's off to the races, the clock has started. We need to get past the nose and down to maybe 900F in a second or so. That's pretty easy, cool until the color disappears from the steel. When the color is gone the steel is cooler than about 900F. At this point we have time, 15 minutes, to drop the temperature to 130F. In particular, we want things to happen slowly during the Martinsite transformation, about 450F to 130F, that's when the blade is getting hard. It doesn't happen during the quench, although that's where the drama is, it happens during the transformation.
Quench for less than a second--plunge and withdraw. If there is any color, immediately plunge and withdraw again. Be sure and get to 900F or cooler in under two seconds. The time period for plunging will depend to a large extent on knife size and thickness. What you want, when you withdraw from the initial plunge, is the color gone out of the steel, but that it's still hot enough to quickly evaporate water from the surface. These are the two temperature tests to bracket the blade's heat--no color and almost instant sizzle.
Now you have plenty of time. Take you time. You'll need something like a wad of wet burlap that you can touch with the back of the blade to cool it. Slowly, draw the heat out of the blade. Touch and sizzle, touch and sizzle. The sizzle should get longer and less violent until at around a minute or two there not a whole lot of sizzle left. The blade should be somewhere around 450F. You can test this temperature by watching tempering colors, you'll want straw yellow. Get to 450F within two minutes. In many cases, you can just let the blade air cool to 450F.
Rest now and let the blade air cool in air. You want to make it to about 130F within 15 minutes. Keep an eye on things, it wouldn't hurt to have an egg timer running at this point. Make the 130F/15 minute-mark and you've brought the blade in for a smooth thermal landing, perfect! When you can hold the blade in your bare hand--warm, but not hot to the point of discomfort, then begin the temper/draw phase of heat treatment. Discomfort is wondering when you can set the blade down, when you feel you could hold it indefinitely the temperature is about right. Don't let the blade drop below 125F. With thin sections, the step from 450F to 130F will often happen in less than 15 minutes so it doesn't hurt to insulate the blade and check it every few minutes. Extending the time for Martensite transformation to a full 15 minutes will be repaid many times over. The whole transformational magic happens during this period and it happens best when it happens slowly.
Immediately place the blade into a kitchen oven preheated to 450F (see tempering chart below). Using an oven thermometer wouldn't hurt. Close the oven door and wait two hours. Retrieve and let cool in air to room temperature. The resultant hardness of O1 steel should be around HRC 60. That's it, that's the heat treatment.
First, we hardened by bringing the temperature down from 1475F to 130F in a controlled manner, then we softened a little by tempering in the kitchen oven. See the tempering graph below.
It should be noted that 130F water and 130F steel are two very different things. Putting your hand in water that hot will create discomfort if not injury.
Make any adjustments to this procedure as you see fit and/or as results warrant.
___________________________________________________________________________
simple carbon steel, yet the HT can be tedious and complicated for such a simple steel. What happens when you use a more complex alloy steel. Don't things change a lot. My guess would be yes. Paul Bos has taken this into account because they have the means.
I understand why knifemakers like Carson/Lightfoot and others still like 440C and ATS34. If treated right these steels can do wonders. It's to bad that junk mfg and HT'ing has given these steels such a bad name.
