Thread: O-1, 1084, 1095, or what?

Not everyone who can harden a knife blade correctly, can be counted on to do the same with a razor. The use of A-2, air hardened, is so attractive for avoiding distortion that it begs the question "Why aren't they all doing it?" I think Mike Blue is correct in saying it becomes adequately hard, but this is something I would advise checking from specifications before tying up time and trouble in one.

The best air-hardening comes from cold, moving air. It is sometimes hardened in oil, and a possibility worth trying on a quickly made test piece is dipping the thin edge in oil while holding the spine out of it. I don't believe this could cause a frowning curve of the spine, but it will put the edge under tension, and reduce any tendency for it to become wavy.. The only thing I can imagine going wrong is the edge cracking with a sharp spink.

Japanese swords have a hamon pattern because they need the edge to be hard, but the body of the blade to be tough and resilient, and resist chopping, parrying and waving around. I can't see any functional reason for it in a razor.

Originally Posted by Caledonian

Not everyone who can harden a knife blade correctly, can be counted on to do the same with a razor. The use of A-2, air hardened, is so attractive for avoiding distortion that it begs the question "Why aren't they all doing it?" ...

The best air-hardening comes from cold, moving air. It is sometimes hardened in oil...

... is the edge cracking with a sharp spink.

Japanese swords have a hamon pattern because they need the edge to be hard, but the body of the blade to be tough and resilient, and resist chopping, parrying and waving around. I can't see any functional reason for it in a razor.

In reverse order: there is a functional reason for swords, none for razors. But, it does look very cool because it's hard to get right in a small blade. At least to my eye.

Now, having just attended a Razor Meet. There were plenty of blades being waved about. Much shorter than katana, much sharper too. A lot of hair died to prove their mettle. (Sorry bad bad pun).

At the recent mid-mo, several keen observers during the heat treatment demo witnessed the "dreaded ping," from a healthy distance away I might add, although I might start using "sharp spink" now. It's a great way to refer to what happens.

A2 will also harden in salt baths. Moving air is still the simplest and least expensive safest way to get it done.

The first is the best. I started out using A2 and abandoned it. I didn't have the right tools (that I know about now) and didn't like contending with the natural brittleness of A2 when hardened. The right tool I needed then was a good heat treatment oven. Then I could have dialed in the tempering temperature correctly and simplified my life. I wish I knew then, what I know now. It's a good, underrated steel for all that.

Keep in mind that many commercial heat treating facilities will only work with air-hardening steels. The equipment used to get the most out of air-hardening steels is sophisticated and specialized; they can't just take a blade out of the oven and quench it in oil for you.

Be sure that your heat treating company is experienced with the alloy you are using. Talk to the person doing the treating about your specific needs. I thought I was familiar with CPM154 after reading the Crucible data-sheets, but I learned so much more just talking to Paul Farmer (my heat treater) for an hour. He speaks the language of time and temperature fluently.

Phillip

I have a small electric furnace which was quite inexpensive on eBay, and large enough for a razor, folding knife blade, etc. But I bought it hoping to enamel and print dials for antique pocket watches. In most respects it was excellent value, and might have carried on forever in applications such as enamelling, fusing glass, etc. But on my first attempt to run it up to its full temperature, which would have been needed for A-2 steel, it blew its element.

I found the wire, which was easily accessible and changeable, soft and malleable. Wikipedia told me that this means it is nichrome, which shouldn't have stood the temperature. Kanthal, which does, is soft as supplied, but brittle after it has been up to temperature. Another eBay supplier produced kanthal wire, and supplied the calculation on the length needed to make a 750w element, like the original.

We have to remember a cardinal rule of the advertising industry. If something is high sugar, it is probably describable as low fat, and vice versa. Abrasion resistance sounds mightly like what will make a blade hold a sharp edge, and it is undoubtedly a big part of it. In a knife which is too stout to bend much, it is probably the main one, but for something like a cavalry sword, it has to be sacrificed for some of the qualities of a spring. But the edge of a razor is so extremely thin and finely angled, that the ability to be laid over or straightened out by the strop is important too. A blade with which nothing seems to be wrong, but which lacks the necessary malleability and toughness, may be good long enoughj to impress and win prizes, and yet require too much rehoning to be wholesome, in a few years of life.

As Caledonian mentioned, you want a balance of optional characteristics. This is determined both by heat treat and alloy composition. When heat treating, you must balance hardness and toughness. The better your treatment is, the higher each value will be, (the opposite is true for a poor heat treat), but it is ultimately a tradeoff. There are other factors to consider as well. I learned that there are two different tempering methods to bring CPM154 to 60-61; one produces a much cleaner blade than the other, requiring less finishing time.

There are also characteristics determined more by the alloy. These include abrasion resistance and corrosion resistance. This is why, even in an annealed state, 440a won't rust and A11 will trash your grinding belts.

Originally Posted by PDobson

...When heat treating, you must balance hardness and toughness. ...

Well, it depends. There are phase structures that provide a hard tough state. I doubt they can be achieved with typical stainless chemistries though. The steels that are amenable to this process are not air hardening, nor exceptionally complex alloys, but they are not low alloy steels either.

All the professional heat treatment companies have enough business to dictate to the customer just what they will, or won't heat treat. Some of them undoubtedly specialize in some form of HT process. Smaller shops will be more likely to be more generalized and capable of salt, air, oil or water quenching and the varieties thereof. I would hardly claim that the industry is dominated by air hardening steels.

It's good to know that Paul Bos has trained an effective replacement. Paul is the best at heat treating stainless materials. He didn't heat treat carbon steels, but I'm certain he understood it.

The best answer is to look around. Find a couple different shops that will do small jobs. They might be willing to add a couple blades into another batch here and there. Or they might tell you they won't do less than X number of blades to make it worth warming up the equipment. If they are good shops, they will tell you what they work best with. If they are really good, they will tell you who to go to, who will do what you want.

It's good to be flexible.

When I come to think of it, nothing in common use for tooling resists abrasion better than tungsten carbide, and although brittle, it is not undesirably so in many applications. Razor enthusiasts are not unenterprising, and we now have synthetic stones which will hone it. But I haven't heard of anyone making a razor out of it, or inserting a carbide edge in a steel spine. Clearly hardness and abrasion resistance aren't everything.

I've heard of a few WC/steel composite knives in the custom world. My understanding is that for knives the edges of the carbide blades get chippy at lower angles. As a result, the knives had to be relatively obtuse. The optional application was for roughly cutting highly abrasive materials: even if it did chip it would keep cutting forever.

Just looked it up: the knife I was thinking about is by Warren Thomas. There's actually some pretty brilliant engineering involved, but I sure wouldn't want to shave with it.

Phillip

Lots of people, things and tax money go wrong, every day, with brilliant engineering. Not long ago I saw someone using microscopy of razor edges to "prove" what I thought a somewhat dubious case. I know a lot less about razors than I do about metals and processes, at the uneasy meeting of amateur and professional. But I found that at least under a 60x illuminated magnifier, I could produce splendid-looking edges in phosphor bronze and broken picture-frame glass. "Briiliant" might be pitching it a bit immodestly, but truth is also a virtue. It doesn't mean they would have worked, though.