Thread: Looking for the best heat treatment for O1

Originally Posted by 10Pups

On the honing side you may be making deep scratches when starting the bevel that remain to the end of your progression. In other words if your using something like a DMT 325 to shape your bevel and then don't spend enough time at the 1k level the first stria may be causing problems later. The best way to eliminate that is changing the direction between stones and make sure you get all the previous marks out. A loupe is necessary of course.

I dont use DMT. I hone wiht japanese synthetics and naturals. I use loupe as well. Rather my fault is the "overhoning".

Originally Posted by 10Pups

Too hard will not hold an edge very well either.

I see, thanks.

Originally Posted by shooter74743

...Do you have one of the razors in hand that does not meet your expectations? If so, would you consider breaking it and taking some good pictures of the particle grain? Even if you can't get pictures, it will show more than your guessing...besides, it's not performing to what you expect.

Only other thing I can think of is your quenchant temperature. I have found that cold oils don't quench seem (to me) as well as warmer oil.

I agree Shooter but let's allow gregg71 to get his feet under him first. If you're going to photograph the broken blade, take a picture of the cross section not the profile, we want to see the end grain where it's broken. If it's not good grain it will look like beach sand and that means the steel was overheated sometime in the past. If it looks gray and the grains are difficult to see without a magnifying glass, your heat treatment and the steel are probably good.

Warming oil can increase the quench speed (I did mention that O-1 requires no delay removing from heat to oil?) and produce a harder blade than cool oil, but there's a balance point. The cool oil will quench the very edge easily and might make it too hard and the spine might be slightly softer. The warm oil will give the whole blade a more even hardness but at too warm, will produce lower hardness overall. This will take experimentation and good notes in gregg71's shop and he will then have a good graph to predict hardness for himself given his tools.

Gregg71: if you are willing to break an unsatisfactory blade...you are welcome into a club of daring individuals (mostly insane with occasional moments of brilliance). A lot of people will not risk all that hard work grinding something beautiful only to destroy it in the search for knowledge. On the other hand, it's only steel and that's cheap. And what is time when you're having fun being creative?

Thanks for the comment!

Originally Posted by shooter74743

Do you have one of the razors in hand that does not meet your expectations? If so, would you consider breaking it and taking some good pictures of the particle grain? Even if you can't get pictures, it will show more than your guessing...besides, it's not performing to what you expect.

Yes, I have. I have broked one but more will follow. I grinded couple of razors just for tests.

Originally Posted by shooter74743

Only other thing I can think of is your quenchant temperature. I have found that cold oils don't quench seem (to me) as well as warmer oil.

Then it should be no problem.

Originally Posted by Mike Blue

I agree Shooter but let's allow gregg71 to get his feet under him first. If you're going to photograph the broken blade, take a picture of the cross section not the profile, we want to see the end grain where it's broken. If it's not good grain it will look like beach sand and that means the steel was overheated sometime in the past. If it looks gray and the grains are difficult to see without a magnifying glass, your heat treatment and the steel are probably good.

I broked some and I will take some pictures and post them.

One more question: How many times can I re-HT a steel without significant loss?

And thank you very much for all these useful comments!

Just for another new maker's perspective, I have had a hard time honing O1 as well. When shaping/bevel setting with my DMT 220, I think it was fracturing the steel between grains, and one way or another, my edges were failing. On diamond film, however, (15 micron, 5 micron, 1 micron and 0.5 micron) it seemed to work.

My process is less controlled than yours (fire forged, then heat treated from fire to canola oil, and then 2 hrs at 400*F in the oven (I over-tempered a bit and the thin parts went to blue, so I ground them down by 1/4").

So maybe diamond film could work for you as well? My next step is to try a Naniwa SS 12k rather than Jnat (will have to buy that stone).

Hey Gregg I feel your pain I'm sure several of us have been in your shoes.

There are so many variables when making razors and sometimes a second opinion is a good idea. Why not send one of your finished blades to someone else to hone and maybe they will be able to help you work out whether it's honing or HT causing these issues?

I'd be happy to help but there may well be more experienced razor makers willing to have a look.

It's not that easy snapping a short 1/4" thick piece of hardened steel! Here is a 2.5mm thick knife from O1 I dropped on the way to the tempering oven once and it broke like glass....



I'm not sure of it's a good example of fine grain or not as the picture's not great and it was a couple of years ago now. I'd be interested to see your pictures

Originally Posted by gregg71

... How many times can I re-HT a steel without significant loss?...

I am going to define your concern as "how many times before I ruin the steel?" Any time steel is heated, the possibility that carbon could be lost from the surface to the environment occurs (decarburization). Repeat this enough under uncontrolled conditions and you will turn a fine steel into a medium steel. It will still require multiple attempts. Theoretically if you could control all the conditions, you could add carbon to the steel, or add enough to compensate for any you might lose. Then steel can be HT'd indefinitely.

It depends on several conditions. Time and temperature both have an effect. The type of heat atmosphere has an effect. The severity of the quench can end a HT attempt before you can save the blade.

If temperature is higher more carbon circulates to the surface of the steel. Where carbon can interact with oxygen, and the attraction to oxygen becomes stronger when the temperature is higher and the bond between carbon and iron is weaker, you will lose carbon to carbon dioxide and a decarburized scale will form on the surface. There are equations that specify how much carbon can be lost over a given time. 1/16 of an inch per hour comes to mind.

The quench puts a significant stress into the steel and the piece can break if the quench is too violent. Water versus oil is a good example. You'd like a quench that isn't so stressful.

I've never done a blade repeatedly just to find out the upper limit. But over the years, given my teacher's advice and my own experience, about three times is enough for a blade that is giving me trouble. If I can't get it to "settle into place" either to stop warping or get the right hardness, by then, it becomes a shop blade. Not good enough to sell or give away but good enough to use when I need a tool. Most blades will settle down by the second time if I prepare the material correctly (normalizing or thermal cycling).

That's a simple answer to a complicated question. It covers the common concerns.

Mikew: that's a good example of fine grain. The oxidized bit at the top? Is that a plunge cut from grinding exposed to the forge or a crack?

Originally Posted by Mike Blue

Mikew: that's a good example of fine grain. The oxidized bit at the top? Is that a plunge cut from grinding exposed to the forge or a crack?

It was a gyuto style kitchen knife and it basically broke at the tang. The black area at the top is where your index finger would sit when chopping. I suppose the under side of the choil?

I learned more in two days than I ever thought I would. Thank you very much for all!