O-1 or A-2 ?

J

JH225

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Feb 7, 1999
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I am looking for opinions on which would be a better steel to use on small fixed blades ( about 5-7" OAL).A-2 or O-1?
In regards to edgeholding ability, grinding difficulty, corrosion resistance, general performance capabilities, and anything else that you can think of.

Thanks
 
Both are excellent. A2 is a higher quality steel, is air quenched and has a higher chromium content than 01 (5% vs. .5%). Therefore A2 is little better in the corrosion resistance department. However, O1 is easier to heat treat.

If I could have the same knife with either steel, I would probably take the A2- assuming that it was treated properly. It is just a better steel overall. However, if someone is just getting started in knifemaking, and is trying to decide on which steel to use, I would recommend starting with O1. It is cheaper, easier to work with, and makes a fine blade (just ask Bill Moran).
 
Speaking of A2, I can't remember where I heard this but someone said that A2 can be heattreated without leaving the edge fairly thick to avoid warping. And that you don't need to make a secondary edge bevel like most blade steels need. does any one know why?
 
I don't know the scientific reason, but A2 is very stable during the heat treat. That's why Chris Reeve makes his knives out of it, if they were made from less stable alloys they'd warp more and that'd drive prices up.
 
A2 is an airhardening steel.... When you quench steel in oil or brine it cools the surface faster than the core, and naturally it shrinks as it cools, so fast it can cause warping and even cracking (though knife blades are relatively thin so they're more likely to warp than crack). That's less of a problem with airhardening steels, one reason they were invented.

-Cougar Allen :{)
 
Air-hardening steels are essential for making really big chunky things because quenching a thing like that causes the outside to cool and shrink faster than the inside and cracks are inevitable, but the effect of quenching on something thin like a knife blade is different -- warping can be a nuisance but it's not that serious.

You can do a differential temper with oil (or water) hardening steels. I wrote a post on another forum recently explaining why that's impossible with most of the high-alloy steels ... it's just as easy to paste that in here as it would be to make a link to it:

The kind of heat treatments that most of the high-alloy steels
require aren't practical to do any way except to the whole blade.
You have to bring it to a temperature and hold it there for long
periods, sometimes hours, heat and cool at controlled rates,
stopping for a timed heat soak at certain temperatures ... you
can't do that kind of thing to part of a blade without affecting the
rest of it.

You can't do that kind of thing with a torch or forge and a bucket
of oil, either. Few of the knifemakers who work with such steels
do their own heat-treating; they send their blades out to shops
that specialize in that and have the equipment.

-Cougar Allen :{)
 
Or were you asking for a comparison of oil-hardening to water-hardening steels? I might as well answer that question whether that was what you were asking or not ... somebody's likely to be interested....
smile.gif


Basic steel -- just iron and carbon -- is water-hardening. It has to be cooled fast or it won't harden fully. Oil-hardening steels were developed next -- an oil quench doesn't cool the steel as fast so you can make bigger things out of it. Then air-hardening steels were developed to make even bigger things.

In practice when you're working with something as thin as a knife blade you can probably get away with interchanging water and oil quenches with either type of steel. With something thicker if you tried that you'd run into trouble; if you quenched an oil-hardening steel in water it would crack or if you quenched a water-hardening steel in oil the core wouldn't cool fast enough to get fully hard all the way through, but thin things like blades are more forgiving.

If you're working with scrap steel like old files and springs quench it in oil. Used motor oil is fine or just about any kind of oil you happen to have around. One kind of oil might cool it at a little different rate than another, but not enough to make any real difference. Of course your blades might sell better if you can say you quench them in pure extra virgin olive oil hand-pressed from olives grown on a south-facing mountainside in Sicily and harvested on a waxing moon....

-Cougar Allen :{)
 
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