Call for Charpy toughness samples

Thus my question about it effectively not being tempered. What would the expected as quenched hardness range of the 8670 be?
Never a break from tough questions around here.
Some hardness tests, like Vickers are basically linear with tensile strength:
Vickers-vs-tensile-strength.jpg

Rockwell C hardness, however, is not:
Rockwell-vs-tensile-strength.jpg

I don't have a tensile strength conversion above 60 Rc, so here is a plot up to 70 Rc comparing to Vickers which is similar to the plot above but to higher hardness:
Vickers-vs-Rockwell-C.jpg

However, even a curve is more or less a straight line if on a small enough scale. And in the 58-66 Rc range we are talking about, the trend is very linear:
Rockwell-vs-Vickers-zoom.jpg

Therefore I wouldn't be too concerned about there being greater increases in strength from 61 to 63 Rc than from 58 to 60 Rc, as the difference is pretty small.

As it turns out, toughness often starts to level off at high hardness, rather than an acceleration to zero. One example is the CruForgeV data I posted before. Or in this data on Vanadis 4 Extra:
vanadis-4-extra-toughness.jpg

Therefore I maintain that the low toughness value for 8670 at ~64 Rc was due to insufficient tempering and not due to an inherent hardness effect.
 
He means testing at every rockwell point. For example, 8670 scored 51.0 at rc 59.7 and only 6.1 at 63.9 rc, but we don't know how it would do at the hardnesses in between.

We will know in the next batch. I tempered in 50f increments from 250f to 450 or 500f. I’ll have to look at my sheet.
 
Do you have that Republic L6 in your next batch? Does sit have moly and vanadium?

My L6 was from Aldo. It’s in the batch that I sent to chuck for grinding. I’m not sure if it has the moly.
 
I think that the Aldo stuff was the non-moly Carpenter RDS type.
My L6 was from Aldo. It’s in the batch that I sent to chuck for grinding. I’m not sure if it has the moly.
 
I posted this to Patreon today, so I'm copying it here as well:

Since the 52100 article we have measured a few conditions of 52100 toughness with our standard procedure that we have used with several steels now. There was one condition (3 specimens averaged) from Warren Krywko and several from Devin Thomas.

Warren used the following procedure:

1650 10 min air cool to magnetic.
1550 10 min air cool to magnetic.
1450 10 min air cool to magnetic.
austentize at 1475 for 10min, quench in DT-48 oil.
Temper at 300f for 2hX2

Devin used the following procedure:

1700F 20 minutes, air cool

1460F 30 minutes, air cool

DET anneal - 1460F for 30 minutes, furnace cool to 1260°F, air cool

Austenitize for 15 minutes (1450, 1475, 1500, 1525, and 1550 were done on separate specimens)

Half of the samples were given a cryo treatment in liquid nitrogen for 30-60 minutes

Temper at 400F twice for 1h

Warren

Warren's specimens resulted in 61.9 Rc and toughness of 19.7 ft-lbs. He has also done some samples with other austenitizing and tempering temperatures and will update you when those have been tested.

Devin

Devin's specimens being across several heat treatment variables resulted in more information, of course, so I have some plots for showing the results. I have also compared the results with the journal article that I cited in the 52100 history and properties article. Using cryo resulted in a little bit higher hardness, as expected:

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The greatest difference in hardness was at the highest tested austenitizing temperature where we would expect the greatest amount of retained austenite to present in the non-cryo version. And that was confirmed with retained austenite measurements, which were very similar to the values in the journal article:

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The 7% or so with a 1550°F austenitize is still relatively low. Retained austenite usually improves toughness as you can read about in Cryo Part 2. And that was found in this study as well:

1


There was a significant drop in toughness with a 1550°F austenitize when in combination with cryo. Not sure exactly why. There was a peak in toughness around 1500°F both with or without cryo. The rule of thumb I usually recommend is a lower austenitizing temperature for enhanced toughness, so it is mildly surprising that a peak in toughness was found at 1500°F. I would probably blame it on more retained austenite, but the same trend was found with the cryo treatments where little or no retained austenite was measured. Perhaps some reduction in carbide volume by utilizing the higher temperatures led to improved toughness. Then when the temperature was too high there was either some grain growth or plate martensite formation. The recommended austenitizing range for 52100 is usually 1500-1550°F, and the selected temperature is based on the speak of quenching and thickness of the material. These were quenched in Parks 50 which is a relatively fast quench, often used as a less extreme replacement for water quench.

Cryo led to higher hardness, but when the toughness is plotted against hardness instead the non-cryo samples still show higher toughness:

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I also showed Warren's sample overlaid with the others, it looks like it is on the same trend as the cryo samples though Warren did not use cryo. Why Devin's samples showed superior toughness is difficult to guess. It could be that the material is cleaner, or the processing prior to austenitizing led to a better microstructure, or that the 300°F temper used by Warren led to slightly reduced toughness.

The hardness was in the same range as the journal article, though a bit higher at austenitizing temperatures lower than 1550°F:

1


This was a fun start to 52100 toughness testing. Hopefully this is helpful to people that are looking for help in their 52100 heat treating. The peak in toughness with 1500°F is particularly good information, and we know now that the prior processing used results in good final properties. That is why toughness testing is so useful, because there are usually minor surprises when running experiments, and it removes the guesswork for achieving optimal properties.

One final chart to show where 52100 fits with other non-stainless steels:

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And a table summary with other steels:

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Very cool. The graph shows that 52100 has among the best toughness relative to hardness at its typical hardness range, tied with zwear. You can draw an inverse line/curve (toughness vs hardness) among these better performing steels and this would be how all other steels are judged. Of course, there is also abrasion resistance so maybe a 3D graph is needed.

I'm surprised that 52100 is impacted by cryo treatment, though it does lose toughness. The limit without cryo appears to be ~61 rc, maybe can be pushed a little higher with lower tempering temperature, but if higher hardness is desired as in a kitchen knife, then cryo seems the way to go. From a more general perspective based on the tests done here on other steels, it seems cryo only has benefit if aiming for higher hardness and otherwise unbeneficial. For my own knives however, I do desire this extra hardness. A 2 point rc difference allows the thin 10 degrees per side for cutting through fish and meat like laser, while the edge retention is significantly improved by both the thinner bevel angle and then multipled again by the extra edge retention from the hardness itself.

Previously, it was thought that A2 steel was the limit for alloying where cryo became useful. Now it seems to be 52100. This also raises the question of the production process. I know finer electro-spray-form A2 is significantly tougher than ingot A2 based on datasheets I've seen, so perhaps 52100's toughness can also be improved with powder metallurgy or at least electro-spray-form.
 
My first sample was from steel bought from Aldo a few years back, which is a generic 52100 as far as I know. The newer samples I sent were from Chuck at AKS. I didn’t do any processing of the newer samples, as Chuck advertises his steel as ready to harden as is. I think someone mentioned Chuck’s 52100 is Bolhler? I’m not sure about that though.

On another note, I should be able to get into the shop next week, and also get the LN. We had a very cold couple weeks, and diesel trucks don’t like cold. My heating system can’t keep up once it gets colder than -20c. We went down to -37c. More samples will be coming soon.
 
Very cool. The graph shows that 52100 has among the best toughness relative to hardness at its typical hardness range, tied with zwear. You can draw an inverse line/curve (toughness vs hardness) among these better performing steels and this would be how all other steels are judged. Of course, there is also abrasion resistance so maybe a 3D graph is needed.

I'm surprised that 52100 is impacted by cryo treatment, though it does lose toughness. The limit without cryo appears to be ~61 rc, maybe can be pushed a little higher with lower tempering temperature, but if higher hardness is desired as in a kitchen knife, then cryo seems the way to go. From a more general perspective based on the tests done here on other steels, it seems cryo only has benefit if aiming for higher hardness and otherwise unbeneficial. For my own knives however, I do desire this extra hardness. A 2 point rc difference allows the thin 10 degrees per side for cutting through fish and meat like laser, while the edge retention is significantly improved by both the thinner bevel angle and then multipled again by the extra edge retention from the hardness itself.

I used the 300f temper to get Rc62, what I typically use in a kitchen knife with 52100. This heat treatment results in performance quite similar to aeb-l at the same hardness.
 
My first sample was from steel bought from Aldo a few years back, which is a generic 52100 as far as I know. The newer samples I sent were from Chuck at AKS. I didn’t do any processing of the newer samples, as Chuck advertises his steel as ready to harden as is. I think someone mentioned Chuck’s 52100 is Bolhler? I’m not sure about that though.

On another note, I should be able to get into the shop next week, and also get the LN. We had a very cold couple weeks, and diesel trucks don’t like cold. My heating system can’t keep up once it gets colder than -20c. We went down to -37c. More samples will be coming soon.

Maybe the colder temperatures you have in the shop are giving a cryo-like effect and therefore you are getting higher hardness with lower toughness.
 
The Bohler 52100 also has more carbon, 1.05% vs .94% which would make a difference to everything.
 
I see that we are going to be getting data regarding W2. Is it Aldo's W2 or Don Hanson's?
 
Very cool. The graph shows that 52100 has among the best toughness relative to hardness at its typical hardness range, tied with zwear. You can draw an inverse line/curve (toughness vs hardness) among these better performing steels and this would be how all other steels are judged. Of course, there is also abrasion resistance so maybe a 3D graph is needed.

I'm surprised that 52100 is impacted by cryo treatment, though it does lose toughness. The limit without cryo appears to be ~61 rc, maybe can be pushed a little higher with lower tempering temperature, but if higher hardness is desired as in a kitchen knife, then cryo seems the way to go. From a more general perspective based on the tests done here on other steels, it seems cryo only has benefit if aiming for higher hardness and otherwise unbeneficial. For my own knives however, I do desire this extra hardness. A 2 point rc difference allows the thin 10 degrees per side for cutting through fish and meat like laser, while the edge retention is significantly improved by both the thinner bevel angle and then multipled again by the extra edge retention from the hardness itself.

Previously, it was thought that A2 steel was the limit for alloying where cryo became useful. Now it seems to be 52100. This also raises the question of the production process. I know finer electro-spray-form A2 is significantly tougher than ingot A2 based on datasheets I've seen, so perhaps 52100's toughness can also be improved with powder metallurgy or at least electro-spray-form.

52100 is way cleaner in the cast wrought condition. In the stuff I did there is only .001%S and .006P. There is no need to go PM or spray form because all of the carbides disolve at ~1650-1700. PM and spray form are used to to deal with large primary carbides, 52100 only has secondary carbides.

A2 likewise has very few primary carbides and it can easily be homogenized at 2150f. Look for ESR A2 for a tougher material.

All knife steels have some retained austenite after quenching and the RA can be reduced or eliminated using some kind of cold treatment.

Hoss
 
I'm surprised that 52100 is impacted by cryo treatment, though it does lose toughness. The limit without cryo appears to be ~61 rc, maybe can be pushed a little higher with lower tempering temperature, but if higher hardness is desired as in a kitchen knife, then cryo seems the way to go. From a more general perspective based on the tests done here on other steels, it seems cryo only has benefit if aiming for higher hardness and otherwise unbeneficial. For my own knives however, I do desire this extra hardness. A 2 point rc difference allows the thin 10 degrees per side for cutting through fish and meat like laser, while the edge retention is significantly improved by both the thinner bevel angle and then multipled again by the extra edge retention from the hardness itself.

Previously, it was thought that A2 steel was the limit for alloying where cryo became useful. Now it seems to be 52100. This also raises the question of the production process. I know finer electro-spray-form A2 is significantly tougher than ingot A2 based on datasheets I've seen, so perhaps 52100's toughness can also be improved with powder metallurgy or at least electro-spray-form.
300-350°F temper is definitely worth looking into for higher hardness. Carbon is the best element for stabilizing austenite; it's definitely not alloy only that leads to retained austenite.
 
This is very useful. Is it possible to also add CATRA numbers as another sorted column?
CATRA can be estimated, but the purpose of the table is to present experimental values and I don't have them to compare with toughness.
 
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