heat treat- a few questions

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skiracer218

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Jul 27, 2014
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So, I'm a new knife maker, and I just finished my first few respectable knife blades (all 01). Like the title says, I have a few questions.


First, I've read some stuff warning of the dangers of grinding the edge too thin before HT. I'm not trying to sharpen it or anything, but I want to leave as little grinding for after HT as possible. How thin is too thin? Second, I have most of the materials kicking around the shop already to make some sort of small forge and HT myself, and I'm curious what kind of results this would actually yield. Would the results be that much worse than if I sent it out to a professional? And If I do send it out to be done, who would you recommend? What should I expect price-wise for a professional HT? Third, I would also like a little advice on the hardness. I've seen a lot of stuff saying O1 should be run in the 58-60 range, is that about right? Lastly, I'm curious as to how hot the steel has to get before I lose the HT. I've heard a lot of really random anecdotal stuff, but never anything with real numbers attached.

Thanks in advance,

Jon
 
Totally on board with this question: I just made my first, full flat ground 1095 kitchen knife and it's ground to 1mm at its thinnest, 1.5mm at the heel. I'm totally in a similar situation and would love to hear some feedback from experienced guys (or gals.)

Thanks,
(also) John
 
skiracer218 said:
So, I'm a new knife maker, and I just finished my first few respectable knife blades (all 01). Like the title says, I have a few questions.


First, I've read some stuff warning of the dangers of grinding the edge too thin before HT. I'm not trying to sharpen it or anything, but I want to leave as little grinding for after HT as possible. How thin is too thin? Second, I have most of the materials kicking around the shop already to make some sort of small forge and HT myself, and I'm curious what kind of results this would actually yield. Would the results be that much worse than if I sent it out to a professional? And If I do send it out to be done, who would you recommend? What should I expect price-wise for a professional HT? Third, I would also like a little advice on the hardness. I've seen a lot of stuff saying O1 should be run in the 58-60 range, is that about right? Lastly, I'm curious as to how hot the steel has to get before I lose the HT. I've heard a lot of really random anecdotal stuff, but never anything with real numbers attached.

Thanks in advance,

Jon
Click to expand...

Lets see here:

1) Too thin is when you head treat your blade and it warps and you can't fix it by bending or grinding the warp out. It really does help to keep some meat on the edge. Depending on the knife and what I am doing I go down to .02" thick at the edge and heat treat. But it usually is .03 - .04" thick at the edge, thickness of a dime.

2) You can heat treat and get a hardened blade out of O-1 doing it a lot of different ways (some better than others). It really does help to have an oven to soak the blade for the 15 - 20 minutes, to get it right. You could do it in a forge but you would have to practice a lot to get it just right, lots of moving the blade and keeping it at the same temp.

2.5) If I was to send blades out it would be to Peter's Heat treating. They usually charge, if I remember right, $20-25 for the first 4 blades and then if you have a ton of blades you get a really good deal, but I don't send out, ever, so I don't know. ( I know a guy who sends like 20 blades out at a time and spends $150 maybe, I can't remember the actual number but after you send in more than 4 it helps to send a lot from what I hear).

3) I like my O-1 to hit 60RC.

4) You mess up the heat treat if you get your steel hotter than the tempering temp that you used to temper your blade. So say 400F. If you see colors when you grind, then you screwed up.


-Brian-
 
First off, welcome to Shop Talk, and this lovely addiction we call knife making. If you fill out your profile info/location we might be able to suggest some viable heat treaters in or around your area.

For thickness pre-HT, I typically try not to go any thinner than a US dime. That said, it really depends on the original geometry and thickness of the blade. If it's 3/32" or thinner, I usually won't even grind it until after HT, especially if it's a longer blade like a fillet knife, or long AND wide, like a chef's knife.

That said, if your grinds are even, your heat is even, and it's not that big of a blade, it might come out of the quench as straight as it went in. However, I do like to leave a little extra meat to grind off any scale and/or decarb.

As for the results of a home built forge, that all depends on what exactly you have for materials, and how good you are at building forges! :) On the other hand, O1 does benefit from a bit of a soak time, so I personally prefer to use a temperature controlled HT oven when heat treating O1. I have seen several makers successful with a forge, however. You just need to watch your temps.

Cost for heat treat? Somewhere around $5 or $6 per blade, up to even $10 or $15 per. It depends on where you send it and how many you send at once.

58-60 should be fine.

After heat treat, as long as you keep the blade temp lower than what you temper at, you'll be ok. As a general rule, if it starts turning colors, you're grinding too hot (AFTER heat treat). Before heat treat, you don't need to worry.
 
Welcome to Shop Talk. Filling out your profile would be a really helpful thing. It will tell us a bit about you as well as where you are. there might be an experiences maker nearby that could offer help with HT.

The normal answer you will get to "How thick should the edge be" is an old one - About as thick as a dime.
However, that is just plain wrong. It is "About half the thickness of a dime".
A dime is 1.35mm, or .053". The thickness of the edge for carbon steels at HT, getting an oil quench, should be about .025-.030", or.75-1mm. On stainless steel, the edge can be down to .010-.020".
Sand the blade to 400 grit and get every deep scratch out. These will be a lot harder to remove in hardened steel. If the edge is too thick after sanding the bevels, just file/sand it back a few strokes to thicken it.
 
These are all awesome replies! I at least have some hope that my blade will not turn into a donut and get sucked into another dimension during heat treat, now that I've heard your responses.
 
I would go Rc61/62 on O1. Its pretty tough, and it balances all its properties well at that hardness. This was suggested to me by a very well known expert on O1, as my 15N20 knives at Rc62 were performing as well as my Rc60 O1 knives. Rc58-60 is the range of most simple steels, the 10xx series steels. Steels with alloys that add toughness can go harder. I run O1, 52100, and 15N20, all at Rc 61/62 for general use without problem, and higher in the kitchen. I typically use edges around 0.010 and 20 degrees per side with these steels for general use.

My suggestion is to do a run of 5 identical klnives, and heat treat them at 59, 60, 61, 62, and 63 and see where your sweet spot is for your use. Then you know for sure what is YOUR best hardness. Just FYI, I have never had a knife returned for chipping since running these numbers. I did have one returned for edge rolling when heat treated at Rc58 though.

Edit: if you go too thin on the edge, you can just grind the edge back until its 0.020 to 0.030.
 
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