A2 vs 1095 Toughness

I think 1095 peak toughness is when tempered to achieve 55-57 hrc, so between 57-62hrc A2 should be tougher. At this hrc range 1095 has an embrittlement zone and it will have a toughness peak again at 65-66hrc (me2, please correct me if I'm wrong, you're one of my steel gurus).;)
 
Charpy testing a piece of notched piece of steel — not a specifically heat treated knife edge with no notch — by slamming a steel weight into it does give an indication of the impact toughness of that particular steel alloy.


But my sense is that the test is not very good for predicting the toughness of a particular knife. Hitting a pre-notched chuck of steel is different from chopping with a knife that has no notch in it and is heat treated to achieve some particular property or set of properties.


Even if the steel tested is controlled for Rockwell C hardness, the microstructure of the steel can be quite different and have a large affect on the performance of a knife blade.


In addition, toughness is not just impact toughness, but also toughness under stress. Those are two different conditions.


I had a CPM M4 knife blade re-heat treated to 64 Rc, and, for reasons I don’t know, was so brittle I could and did break it with just hand pressure. I have another blade in CPM M4 that I could never break — and I have tested it at pressure much higher than the first knife. So what is the toughness of CPM M4 at 64 Rc? The answer is that it depends on the heat treat, which changes — for better or worse — the microstructure of the steel.


But it’s easy to check for hardness, not as easy or cheap to check for the microstructure of the steel being tested at that hardness. Good heat treating can make the grain size as fine and uniform as possible for that steel — or not.




Here are some quotes from Crucible that I cherry picked from the link below:


Toughness testing is not as standardized as hardness testing. It may be difficult to correlate the results of different test methods. Common toughness tests include various impact tests and bend fracture tests.

…

Toughness data is useful to predict which steels may be more or less prone to chipping or breakage than other steels, but toughness data cannot alone predict the performance life of a knife.

…

Knife steels are usually supplied in the annealed condition to facilitate manufacture. These steels must be heat treated to develop their characteristic properties. The heat treating process alters the alloy distribution and transforms the soft matrix into a hard matrix capable of withstanding the pressure, abrasion and impacts inherent in knife use. Each step of the heat treating cycle is designed to perform a specific function, and, like links in a chain, the final product is only as good as its weakest component.

https://www.crucible.com/pdfs/SelectorKnifePocketRotatedCrucibleLLC.pdf
 
Thanks, I think. . The place I've seen the peak toughness for 1095 was on a graph from a book on tool steels. The peak is centered on a tempering temperature about 325 F. It doesn't recover to an equal toughness until it's tempered over 800 F.

If one uses torsional toughness, which I prefer for various reasons, 1095 has a higher toughness. However, that means using a heat treatment virtually no one uses for 1095, tempering it between about 315 and 330 F. In that light, unless one is ordering customs, with input on the HT procedure, A2 is tougher. A2s peak toughness is about 725 to 750 F, though hardness is lower. Interestingly, O1 is slightly tougher than both at it's peak.

Some numbers: A2 105 ft-lbs with hardness in the upper 50s HRc: 1095 115 ft-lbs with hardness in the mid 60s: O1 125 ft-lbs with hardness in the lower mid 60's.

These differences are fairly small in terms of toughness, but show how some steels might excel in certain applications.
 
hugofeynman said:
I think 1095 peak toughness is when tempered to achieve 55-57 hrc, so between 57-62hrc A2 should be tougher. At this hrc range 1095 has an embrittlement zone and it will have a toughness peak again at 65-66hrc (me2, please correct me if I'm wrong, you're one of my steel gurus).;)
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Sorry, meant to address this above. The hardness range of 55-57 for 1095 is not a peak, but it is the point where the toughness is sufficient that it will take full power accidental strikes into rocks and only dent instead of chip or crack. Steels like 1095 will only have one peak in the range of hardness for knives. Then there's a valley, and following that toughness starts to increase until the hardness is too low for knives. These higher tempering temperature ranges have the possibility of embrittlement, but for the most part it's avoided fairly easily. A2 HAS a higher alloy content and actually has 2 peaks in useful hardness for knives. One is near 400 F and the other is a bit higher and near 750 F.
One interesting thing regarding A2 vs 1095 is the range of temperatures which hit the peak toughness. 1095 might have a higher potential toughness, but the temperature range is very narrow to hit it. The graph has a very sharp peak and a range of maybe 25 degrees. Then range for A2 is nearly 100 degrees, and on the graph it's a broad easy hill.

Basically, 1095 makes an excellent thin cutter at very high hardness, if one has the temperature control to take advantage of it. A2 is considerably more forgiving, but good temperature control is always a good thing.
 
If you are talking about un-notched Charpy, then L6 is over 210 lb ft. at its peak hardness for toughness of 58Rc IIRC. The second toughness peak, which is slightly lower, is at 61Rc. ;) Of course, the downside of L6 is that it can cost a LOT more than say 1095 and it does not respond well to ham fisted HT methods.
I was told a few years back by a very knowledgeable maker that you can experiment with certain steels, as we have discovered in recent years with ones like CPM 3V, 52100, 15N20 AEB-L and D2. The same guy told me that with certain other steels, you "take what the chemistry gives you." IIRC, he used A2 as an example. As such, I would be inclined to use A2 at 60Rc and happy.
me2 said:
Thanks, I think. . The place I've seen the peak toughness for 1095 was on a graph from a book on tool steels. The peak is centered on a tempering temperature about 325 F. It doesn't recover to an equal toughness until it's tempered over 800 F.

If one uses torsional toughness, which I prefer for various reasons, 1095 has a higher toughness. However, that means using a heat treatment virtually no one uses for 1095, tempering it between about 315 and 330 F. In that light, unless one is ordering customs, with input on the HT procedure, A2 is tougher. A2s peak toughness is about 725 to 750 F, though hardness is lower. Interestingly, O1 is slightly tougher than both at it's peak.

Some numbers: A2 105 ft-lbs with hardness in the upper 50s HRc: 1095 115 ft-lbs with hardness in the mid 60s: O1 125 ft-lbs with hardness in the lower mid 60's.

These differences are fairly small in terms of toughness, but show how some steels might excel in certain applications.
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That's what i was referring to in terms of making sure what data really is. The values above are for torsional toughness. I havent seen them for L6.
 
Kevin Cashen said that he gave up trying with the un-notched Charpy test on Champalloy L6 at 200.
me2 said:
That's what i was referring to in terms of making sure what data really is. The values above are for torsional toughness. I havent seen them for L6.
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So between these two seems that properly heat treated A2 is the way to go.

A2 steel never attracted me, because is not "the best" in something, just and average (or above average, when well heat treated) steel. There are far tougher steels (my obsession is toughness) and more wear resistant steels. There are even steels that are better than A2 in both wear and toughness, like Cpm3v and Vanadis 4 extra (Vanadis probably only at high hardness, in 58-60 hrc A2 will probably win by a very small difference). I'm sure a knife made in A2 by Scott Gossman or Adam Kornalski will survive almost anything and will cut like hell! Heat treatment is the key, even more important than the steel itself.

1095 steel is "old school" steel, but not for the average heat treater, otherwise blade will fail and everybody will blame the steel! From what I've read ESEE makes a great job with their 1095 heat treatment and never heard of a broken ESEE 5. Maybe I didn't searched well...;)
 
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hugofeynman said:
So between these two seems that properly heat treated A2 is the way to go.
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are you talking as a buyer or maker? as a maker, Roman Landes thoughts stick with me. for highest potential, A2 requires a heat treat as involved and precise as stainless steels and CPM steels, but you end up with a blade that rusts, chips, cracks, and doesn't excel at anything.
 
scott.livesey said:
are you talking as a buyer or maker? as a maker, Roman Landes thoughts stick with me. for highest potential, A2 requires a heat treat as involved and precise as stainless steels and CPM steels, but you end up with a blade that rusts, chips, cracks, and doesn't excel at anything.
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Just my initial thoughts, Scott! But the OP is limited to these two steels. 1095 also needs precise temperature control and know how to make a proper knife.

Me, I wouldn't buy any! I would go Vanadis 4 extra for all around steel, small to medium knives and S1/S7/k600 for big ones. For "simple"/ more forgiving steels I would choose 80crv2, because depending on tempering temperature you can have a more wear resistant or a tougher blade or 5160, that excels on toughness!

Personally, I don't like "good enough" steels at everything. I like the top of the class for the task I'm willing to do!;)

Roman is a guy that I respect A LOT and my god of metallurgy! He and Haakonsen, hence the Vanadis 4 extra for small to medium knives, that's what Fredrik uses for more than ten years and low alloy for big choppers (Fredrik recommends A8mod, S7 steel and Landes recommends S series).

Still in defense of 1095, it can be differentially hardened and used even for swords! Never heard of an A2 steel sword (what doesn't mean there isn't one;)).

Great conversation about steels! Love this thread!;)
 
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I like A2 for my fixed blades a lot. I can maintain them in the field, and with a little care, I never see any rust. I like 1095HC also, but just have more Bark Rivers than Beckers, so end up using those more. Both work well. I do want to try 3V, but I am concerned about field sharpening.
 
People should stop quoting Mike Stewart really... That guy has no clue seriously. He several times said D2 is the same as 440C ... that is pretty ridiculous for any maker who really working with both steel.

Back on A2 vs 1095, A2 is tougher steel if both are fully hardened at their sweet spot HRC. But since 1095 can be effectively differential hardening like clay or even drawing back the spine while A2 doesn't and in reality there are plenty of makers doing that so I will say 1095 is overall tougher when it come to custom knife.
 
hugofeynman said:
Still in defense of 1095, it can be differentially hardened and used even for swords! Never heard of an A2 steel sword (what doesn't mean there isn't one;)).

Great conversation about steels! Love this thread!;)
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A2 swords: Phil Hartsfield, Rob Criswell, some others made a lot of A2 swords. They're very tough. Haven't heard of any breaking. A2 swords or knives ain't that common for multiple reasons, including cost.

I've heard of 1095 in swords here or there, but it's pretty uncommon. Why would a maker choose 1095 for a sword when he can go with the much tougher lower carbon 10xx, like 1055? I can see 1095 in a large knife, but don't really see the logic for using it in a sword.
 
GrReaper said:
A2 swords: Phil Hartsfield, Rob Criswell, some others made a lot of A2 swords. They're very tough. Haven't heard of any breaking. A2 swords or knives ain't that common for multiple reasons, including cost.

I've heard of 1095 in swords here or there, but it's pretty uncommon. Why would a maker choose 1095 for a sword when he can go with the much tougher lower carbon 10xx, like 1055? I can see 1095 in a large knife, but don't really see the logic for using it in a sword.
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Because 1095 is shallower hardening steel and will get you better hamon for Japanese kind of sword or katana.

Most of the time sword will get clay hardening which will leave the super tough pearlite structure at the spine. The higher carbon content of 1095 will give you harder edge while remaining tough due to the differential structure.

Actually Any 10XX with over 0.6C or W series will make a good sword when properly done. Aesthetic of harden line become the major concern depending on the expertise of the maker.
 
GrReaper said:
A2 swords: Phil Hartsfield, Rob Criswell, some others made a lot of A2 swords. They're very tough. Haven't heard of any breaking. A2 swords or knives ain't that common for multiple reasons, including cost.

I've heard of 1095 in swords here or there, but it's pretty uncommon. Why would a maker choose 1095 for a sword when he can go with the much tougher lower carbon 10xx, like 1055? I can see 1095 in a large knife, but don't really see the logic for using it in a sword.
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i would prefer a bit more carbon. A few years back, one of fellow forumites had Bailey Bradshaw make him a fully hardened katana from W2. Other well known word makers use clayed up 1086M and 1075. One reason that you wold use those steels is that you could have an edge hardness of say 60Rc.
 
You're right:

http://www.swordforum.com/forums/showthread.php?14543-Suitability-of-A2-Steel

I search better and sure you're right, there are swords made out of A2, but as you can see in that forum discussion (can't remember if we can publish other forums conversations. If not, moderators please accept my apologies), not the best choice. A2 may be tough compared with ridiculous choices like a D2 sword, but near an L6 (not even bainite) sword, A2 seems not the best choice. For a knife may be tough enough, when made right, but for a chopper 1095 steel differentially heat treated may be a bit better (tougher). Aren't Japanese katana made of something similar to 1095 or W1 differentially heat treated?
 
Twindog said:
I had a CPM M4 knife blade re-heat treated to 64 Rc, and, for reasons I don’t know, was so brittle I could and did break it with just hand pressure. I have another blade in CPM M4 that I could never break — and I have tested it at pressure much higher than the first knife. So what is the toughness of CPM M4 at 64 Rc? The answer is that it depends on the heat treat, which changes — for better or worse — the microstructure of the steel.
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You are totally right. The micro-structure of the steel is much more important than the specified HRC. People can have similar steel at exactly similar hardness but heaven and hell different in performance due to the dissimilar heat treat process.

In your case of M4 at 64 being so brittle might be the result from re-hardening without proper annealing in high speed steel. This kind of steel is tricky to re-HT and require very long and wasteful annealing process to get the carbon back to proper structure readily for hardening again.
 
hugofeynman said:
A2 may be tough compared with ridiculous choices like a D2 sword, but near an L6 (not even bainite) sword, A2 seems not the best choice.
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Certainly, like I said before, there are tougher steels than A2, and L6 is one of them. The S series shock steels, and some of the powdered Crucible steels also. So if flat out toughness is what you're looking for, then those would be what you should choose. Be prepared to pay a lot more for L6 though.
 
Problem is L6 is not what we are looking for on a small knife the edge may not chip but it will blunt and roll way faster in use. Just doesn't have the strength A2 has to offer.

Not sure what knives the OP was looking at or what tasks he had in mind. That is more important then trying to apply steel names to performance.
 
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