ATS34 Heat Treat Info from Hitachi!

Oct 5, 1998
I posted this in the shoptalk forum, but since there are often questions about ATS34 on the General forum I thought it would be OK to add it here as well. I have posted a couple of documents about heat treating ATS34 on my website. These are documents Hitachi faxed to Brian Lyttle, and then he faxed them to me.

These documents contain Hitachi's recommendations for heat treating ATS34 in knifemaking applications, and compare ATS34 to D2 and 440C. I think many will find their conclusions interesting. I wish Hitachi would do a better job of distributing this info.

I hope this generates some useful discussion of ATS34 heat treating, and the suitability of ATS34 for high quality knives.

This fits with what Ernest Mayer of Black Cloud Knives has been saying for over a year. Ernest even had it independently tested and I think the numbers were 20% better corrosion resistance, toughness and edge holding.

Rick Shultz of Mission posted information on rec.knives to this effect 6 months to a year ago.

I am to understand that Pat Crawford is using the lower tempering cycle.

Hopefully people will stop listening to those who say... "If it ain't broke, don't fix it" and start looking for what is best.

Marion David Poff aka Eye, one can msg me at If I fail to check back with this thread and you want some info, email me.

Check out my review of the Kasper AFCK, thougths on the AFCK and interview of Bob Kasper.

Thanks for posting that Matt.

Interesting info, especially the confirmation of Ernie's findings regarding rust resistance and toughness.

I had suspected that the extra rust resistance in the lower-cycle version was because more chromium was tied up in carbides in the upper-cycle version. Hitachi basically confirmed that. Which means the lower-cycle version should lose so edge-holding ability for jobs where edge-toughness isn't the priority. Unfortunately, Hitachi didn't test this head-to-head.

Actually, Rick first made the Hitachi recommendations available over two years ago. All I had ever seen up to now though, was a text table of tempering temperatures and and one sentence recommending the lower range for improved toughness and corrosion resistance. No explanation of the mechanism, or quantitative comparison. These new documents fill in some of those holes.

I have used the lower range since I started using ATS34. I had to delay switching to ATS34 from 440C for almost a year until I found someone I could trust to heat treat it. This was because everyone available to me used the upper temperature. I had made my choice based on Rick and Ernie's work, but a lot of heat treaters and knifemakers were ignoring them. I would like to see other people avoid that frustration, and understand their choices.

I'm also a little concerned that knifemakers who have found that ATS34 has superior performance at lower tempering temps are being forced to switch to other alloys simply because of a perception in the marketplace that ATS has brittleness and corrosion problems.

Take BG42, as I understand it, it is being heat treated at two different temperatures - one the Latrobe recommendation, and another conciderably lower. To date I have not seen any comparison of performance at the two different temperatures. The question then becomes - what is the best way to heat treat BG42 in cutlery applications? Right now, it seems not to matter, if you say you are using BG42, you are right in the eyes of the market. BG42 may well be the next logical step in mid range cutlery stainless (since it's cheaper than the particle metallurgy choices) but I want to know what the best HT is before I switch to it.


In the table "Comparison of Properties" in the first document, Hitachi does rate edge holding as better than D2 at Rc 60-61. Like you say, too bad they did not compare ATS34 to ATS34. Since the complaints with ATS34 have been more in the way of brittleness and corrosion resistance, if the edgeholding is still better than (or even the same) as D2, which is still very popular among knife users, I think that ATS stacks up very well as a "package" of properties. Unfortunately, blade material selection is still an excercise in compromise.


[This message has been edited by Matt Harildstad (edited 26 August 1999).]
Well, well, well...isn't THIS interesting.

Unfortunately discussions of the subject have been characterized by what were percieved to be personal attacks. Paul Bos told me last year he wouldn't even try the lower-temp cycle because Ernie Mayer (maybe) pissed him off. Note the maybe - Paul told me it was "some knifemaker in Arizona slurring him". I've now got reason to believe it may have been another maker.

In any case, since I'm about to own a REKAT Sifu in ATS34 with a planned heat-treat by Paul Bos, I feel this question must finally be addressed. I'm sorry Paul's feelings were hurt and I regret having been a part of that BUT this is metallurgy dammit, not a friggin' soap opera.

I've seen written accounts of the performance of Ernie Mayer's ATS34 short swords. My Outsider is ATS34 with a Hitachi/Meyer-style heat-treat done by Harald Moeller and I've personally driven the "secondary tip" clean through a coconut and into the formica counter below on a straight smash - with no damage. I've rode up to four hours in the rain with the sheath fully open to the elements on a motorcycle, blade drenched, NO OIL of any type, zero rust. I don't mean I cleaned the rust off, I mean it didn't rust - all I did was dry it without oil once home and let the sheath dry without the knife in it. I've never oiled it...and I'll have it with me Saturday at the show and pizza party afterwards.

Ernie Mayer is now doing outside heat-treat/cryo contracts. I'll say flat out: I want HIM to do my Sifu versus Paul Bos. I'll accept a Bos-treated Sifu if there's no choice but we're starting to see overwhelming evidence that Paul is ignoring hard science from the steel's developer.

This isn't "vendetta" talking. Paul has been a MAJOR factor in the proliferation of the custom knife market, he was Engnath's heat-treater, he's done *wonderful* things for the industry and by all accounts his work is very reliable, with very few "bad batch" type the heat-treat biz, that's unusual and commendable. I have the highest respect for him.

But: I also want the best blade I can get. And the overwhelming evidence now is that Paul Bos isn't going to maximize that steel.

Jim March
Ya, some of what Hitachi claims sounds like marketing overcoming reality somewhat. They also claim that ATS-34 takes a great finish, which is contrary to the experience of knife makers I think. It is notorious for having an orange-peel look when mirror finished. This was also true of an Ernie Mayer ATS-34 blade I had with a mirror finish.

I wouldn't worry too much about the Sifu though Jim. The Pioneer blades are pretty tough. And as the late great Bob Engnath said, Paul Bos has heat treated thousands of his ATS-34 blades, and he had gotten only one or two back. I think Bos heat treated blades are pretty good, but unfortunately, not as good as they can be.

Steve, you'll be at the Pizza party, right?

Harald did part of The Outsider's finish in mirror. It's *flawless*. You don't have to take my word for it, you'll have it in hand Saturday.

Note that Harald "only" did a "home-brew cryo cycle" involving dry ice for 24 hours in an old opens-at-the-top freezer. And it still came out really, REALLY good. Ernie uses a true liquid nitrogen process.

I'd also value Bob's opinion here...seriously.

Jim March

Thank you, and I hope you don't think I was diminishing your contribution.

Because what you have given is a real contribution.


Marion David Poff aka Eye, one can msg me at If I fail to check back with this thread and you want some info, email me.

Check out my review of the Kasper AFCK, thougths on the AFCK and interview of Bob Kasper.

Steve, all, something else: Hitachi doesn't gain if people use one temperature cycle over another with their steel! I can't think of a single reason for them to falsify their data in this area and a whole lotta good reasons involving credibility not to.

Jim March
There is nothing surprising about the results of that data. If you read any basics materials book on steels that exact behavior is noted for exactly the reasons described. Both cycles have their uses, and it makes sense the high wear one is used often as ATS-34 was developed as a better wear resistant steel than 440C.

However, I don't think that wear resistance is the end all, be all in knives. Generally you need enough toughness to support the edge or it will microfracture causing wear much faster during normal use than a "high wear" steel.

While people often cite CPM's as being high wear resistant, I was never that excited by that. You could simply leave M2 at 68 RC and get very high wear resistance. It was the relatively high toughness that caught my attention.

I was using 154 CM about 12 to 13 years ago and used the low temp cycle on it as well as when I changed over to ATS-34. I tried the higher temp cycle on some cupons on the 154CM, and ATS. I have noticed bigger grain growth in the above steels when tempered on the high cycle. In my limited experiance, bigger grain growth means less corrosion resistance and lower toughness. I have been playing with the low temp temper on BG-42 with the same results, but havent made up any cupons to break and look at yet. What I am wondering is why it has taken Hitachi so long to come out with this when its been known by knifemakers for close to 15 years! As far as ATS-34 having the wear resistance as D-2? D-2 still smokes it if both are heat treated properly and are the same Rockwell hardness.


[This message has been edited by Rob Simonich (edited 03 September 1999).]
Very well said on the D2 comparison!!

[This message has been edited by Dr.Lathe (edited 04 September 1999).]