Preventing Heat Treat Blade Warp - O1 and primitive tools?

J

Jgjgjg

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Apr 13, 2020
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Gents, I'm glad to have found this forum. I've made 2 knives and assorted tools from O1 and a couple of leaf spring knives and tools. This has all been grinder, charcoal, and used motor oil action. It's worked out well enough.

My youngest daughter, the young chef in training, wants a knife and I want to make it a special lifetime gift. So I'm making her an O1 Left Handed chisel ground hollow back blade. By 'hollow back', I mean a hollow grind similar to that on the backs of Japanese chisels, and for the same reason.

Japanese chisels teach you two things right quick. First, have the hollow back is a heavenly thing when sharpening very hard steel. Second--ANY warping out of flat makes heaven into hell right fast.

So my question is this, when heat treating this knife, what's the best want to prevent warping? The picture below shows the blank. It's been filed flat and you can see the beginning of the hollow and the homejob scraper I'm using. Any help appreciated!

Meg-knife-1.jpg
 
Warp happens. The common advice of grind both sides evenly doesn't really apply to a chisel grind, so learning to correct the warp will help.
The safest way is after the first temper cycle, clamp the knife to a steel bar using washers as shims to reverse the warp. You may need to almost double the amount of warp. Temper again and see where you're at. After the second temper if you still need to work on it, drop the temperature by about 30 degrees and continue to shim, bend and bake till its straight.
And I'm gonna go ahead and say it. Do yourself a favor and get a couple gallons of canola oil!
 
Yep....for any sort of asymmetric grind, you'll want to grind in the bevels and "ura" after heat treatment. If you do it prior to HT, it's about a 100% guarantee to warp. There is going to be some amount of distortion after the quench anyways, even if you grind post heat treat, so it's a good idea to become familiar with dealing with warps regardless. You can search "3 point clamp method during tempering", but there is also the method I like to use when possible....as you quench the blade, there is a period of time where the steel is still in the austenite phase and hasn't yet begun to transform to martensite, which starts at around 400°F and finishes around 200°F or room temp. (technically the martensite finish temp is below zero, but for steels like O1 and for the purpose of straightening a blade above martensite start temp, we will say that the finish temp is room temp. But above 400°F, the steel is easily flexed, wear thick gloves or use a jig (I do it by hand with gloves). So in practice, place the blade in the quench, and agitate vertically or spine to edge (not side to side) for a good 5 count, then take the blade out of the quench and straighten it before it gets to ~400°F. You don't have long, and sometimes the blade reaches martensite start temp faster than you think, especially thin blades, at which point you need to straighten using the 3 point clamp method. Then there is a method where a ball peen hammer is used to straighten a blade by tapping on one side or the other (I don't recall which....search that as well). And also.....when working with O1, do yourself a favor and ditch the motor oil. Canola oil warmed to 130°F works very well for deep hardening steels like O1.
 
samuraistuart said:
Then there is a method where a ball peen hammer is used to straighten a blade by tapping on one side or the other
Click to expand...

Ha...There's a video of a really good Brazilian smith, Eduardo I think his name was, doing this. I'll see if I can find the link.
I tried this method once to straighten a tang on a hidden tang blade, and snapped the blade, not the tang, even though the tang is all I was hitting.
 
I would experiment on scrap blade with that video technique
I've done nothing only snap blades with it
 
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