Elmax, tempering low or high

That is a very useful PDF! Thanks!

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Two possibilities for elmax... I think the higher austenitization temp is to get more carbon in solution, and have a higher hardness afterwards, but also more RA. The lower tempering range seems logical for a kitchen knife. My oven's thermocouple goes to 1100 degrees C max...
 
CocoMonGo said:
hi all, i was researching on Elmax myself and chanced upon this tread. Thought I share what I found - http://www.uddeholm.com/files/HPS_Steel_for_knives.pdf

If you look at their recommendation they are suggesting 200-250C yet are able to reach 62HRC.
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They recommend a higher austenizing temperature for this as well (2100 F). If you have the Verhoeven book for bladesmiths, he recommends a procedure for minimizing RA and how to tell if you've reached it. Now, he recommends it for much simpler steels than Elmax, so it may not work there. The basic procedure required access to a hardness tester. Basically, try a range of austenizing temperatures followed by cold treatments. Measure hardness as quenched and after the cold treatment. If the change is too great, you're austenizing temperature can be lowered to reduce the amount of RA. IIRC, he suggests a change greater than half a point HRc is too much and the austenizing temperature can be lowered. It's critical to remember he is talking about hardness measured on the same sample before and after cold/cryo, using the same hardness tester. You can't get your samples mixed up, and then compare readings on the shop tester to readings from a lab. I'll also repeat this because it bears repeating. This is suggested in his book for much simpler steels than Elmax, specifically 13c26, 12C27, and AEB-L class steels. It may not work the same for Elmax.
 
I have talked to a few people with knowledge about the question, but there wasn't really a satisfying answer, so I decided to make two similar test knives and do a high and a low temper. Here are my results. I did a kind of snap temper to knife 2 because I didn't had enough time left to do a real temper that evening, and I was afraid for cracking of the fresh formed martensite when leaving it alone for a day. The temperature was pretty low so I don't think it would make great changes to the hardness.

Overall the high temper seems better to me. I think it gives lower hardness on the martensite, but the carbides precipitate and that gives it a much higher hardness. At a low temper these carbides don't even precipitate so they don't give a real advantage...And why do we buy such an expensive high performance steel with all the alloying elements? To make use of them, so I figured this would be better. Also, ductility and wear resistance increase to my knowledge in the case of high tempering. The stain resistance decreases, but that is less important to me.

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Van Zanten said:
I have talked to a few people with knowledge about the question, but there wasn't really a satisfying answer, so I decided to make two similar test knives and do a high and a low temper. Here are my results. I did a kind of snap temper to knife 2 because I didn't had enough time left to do a real temper that evening, and I was afraid for cracking of the fresh formed martensite when leaving it alone for a day. The temperature was pretty low so I don't think it would make great changes to the hardness.

Overall the high temper seems better to me. I think it gives lower hardness on the martensite, but the carbides precipitate and that gives it a much higher hardness. At a low temper these carbides don't even precipitate so they don't give a real advantage...And why do we buy such an expensive high performance steel with all the alloying elements? To make use of them, so I figured this would be better. Also, ductility and wear resistance increase to my knowledge in the case of high tempering. The stain resistance decreases, but that is less important to me.
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Why do you think the high temper seems better? I do not ask this because I don't agree. You'll have to do some cutting and see if it's better or not. Not precipitating the carbides is the advantage in some cases. Alloying elements can be useful without precipitating in carbides. Chromium stays in the martensite and adds corrosion resistance for example.
 
Yes, Cr is indeed one example. But there is also Si, Mn, Mo, V.

I think the real sacrifices on a high temper are reduced toughness and reduced corrosion resistance. The real advantages are higher hardness (in my test case), increased wear resistance, less RA. According to Uddeholm Sweden, ductility also increases. I think for a kitchen knife a lot of toughness is not required, hardness and wear resistance are king.
 
BTW a temper should always be the last operation - untempered martensite is not so good.
That's a lot of discussion for a kitchen knife ! One or two hardness points can make a noticeble diffence in cutting and sharpening but other factors don't play much part.My kitchen cutting does not take place at high temperature !! LOL Remember that the shape of the edge is a major part also.
 
I would tend to agree that a lot of toughness isn't needed for kitchen use. I'm not sure I'd agree on the loss of corrosion resistance, but it still may be enough. My kitchen knives are rusting in the block, and are a 440A class stainless.
 
Van Zanten said:
I think for a kitchen knife a lot of toughness is not required, hardness and wear resistance are king.
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Edge retention is a complicated thing. Higher abrasion resistance and a more shallow diamond indention does not necessarily mean better edge retention. You're not cutting abrasive food or you wouldn't have any teeth left. Kitchen knives lose their edge because they clack against cutting boards and bone etc. You want fine edge stability in a kitchen knife and generally speaking this is found with a rapid quench to Mf without delay (no snap temper, no pause) and a low temper.

What is secondary hardness? Well, the retained austenite decomposes (a very good thing) and carbon leaks out of the martensite combining with various alloys forming secondary carbides (not a good thing). You have to consider what a hardness tester is actually measuring. It is the depth a diamond point can dent a sample and it does not tell the whole story. That secondary hardness hump is reduced RA (yay!) and additional carbides that resist the diamond penetrater. You have weaker, softer, carbon lean martensite and a larger carbide fraction that may work great in thick sections and cutlery designed for abrasive material, but it does not promote the fine edge stability you want in a kitchen knife.

For fine edge stability you need to prevent RA. Without resorting to the secondary temper this can generally be achieved with a rapid quench (this reduces carbon migration during the quench) and a continuous quench to martensite finish. Mf is frequently given as -100F but this is not completely accurate. Mf is an antiquated term (there is no such thing as zero RA) and the lower you go the more conversion you'll get. -100F represents the low hanging fruit but lower temperatures convert more, which may or may not be significant, it depends on many factors.

Any snap temper of any sort will cause RA to stabilize. It makes sense if you think about it. It would pointless to snap temper if it didn't do anything, but it does, and by reducing strain energy you're reducing the mechanism that makes RA convert. Also, any significant delay into cryo allows RA to stabilize.

The HT process is more than just the temperatures used and the hardness measured. It is the timing of the steps and the micro structures formed. And the process for a chopper is different than the process for a kitchen knife. I wouldn't be so fast to dismiss the low temperature temper until you've quenched the steel optimally and cut with it.
 
Thank you Nathan. This got me thinking.

Kitchen knives lose their edge because they clack against cutting boards and bone etc.
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I agree.

The abrasion resistance may be a pro when making a sawing motion on the cutting board, something chef's do a lot when cutting.

About the martensite, indeed this is best on a low temper with as much carbon in it as possible. I wonder what the alloying elements do in the steels matrix when they are not precipitated? Cr helps to prevent corrosion, but what do for example the Mo and V do in the matrix? Are they still very useful when they have not formed carbides? I know they may have been useful for other things like V helps prevent grain growth, but I really mean after all HT is done, do they make a better edge retention?
 
me2 said:
The more I think about this, the more I don't think I'd like Elmax in a knife.
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What's not to like? :confused: It's fairly easy to work with... grinds like CPM-154 (hard or soft) and seems easier to grind than CPM-3V soft, and is definitely easier to grind/finish than 3V when hardened. It takes a fine, keen edge. It's tough. It's stain-resistant. It finishes beautifully. It's not crazy-difficult to sharpen. The only drawback I see is that it's a little hard to find in certain sizes, and it's a bit on the pricy side. I charge my clients accordingly; they understand and are happy to pay for it.

me2 said:
I would tend to agree that a lot of toughness isn't needed for kitchen use.
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I strongly disagree. I realize that I'm flying directly in the face of conventional wisdom, but bear with me for a moment...

Van Zanten said:
The abrasion resistance may be a pro when making a sawing motion on the cutting board, something chef's do a lot when cutting.
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I'm no chef, but personally I haven't noticed a lot of dulling in my own kitchen knives and those I've sharpened for others (factory and handmade, cheap steels and super steels) due to sawing/slicing on (wooden) cutting boards, and certainly not from cutting meat or veggies... the number one cause of dulling I see on kitchen knives is due to nitwits scraping their edge under hard pressure, sideways/across the cutting board. That drives me crazy... either be gentle or use the spine! But like it or not, that happens all the time, even in the hands of professional chefs who really ought to know better. The second most-common cause of dulling is banging thin, hard edges against bone and stuff as Nathan said. Those are toughness issues, not strength/abrasion-resistance issues.

Van Zanten said:
I wonder what the alloying elements do in the steels matrix when they are not precipitated? Cr helps to prevent corrosion, but what do for example the Mo and V do in the matrix? Are they still very useful when they have not formed carbides? I know they may have been useful for other things like V helps prevent grain growth, but I really mean after all HT is done, do they make a better edge retention?
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I'm interested in this as well. Cr and Mo are instrumental in raising red-hardness among other things, but like you I'm curious if "free" alloying elements have a significant effect on edge retention, or if they serve us best when treated for maximum carbide development. I suspect the latter is true.

Slightly off-topic, but I can say with confidence that Elmax at 58Rc is very, very tough, even with a thin edge. Not just "tough for a stainless", but tough enough to go head-to-head with, and even out-perform classic high-toughness steels like 1095 and O1 at 58Rc when used for rough tasks like chopping and splitting knotty oak and "drilling" holes in it with the tip and scraping it to make tinder, while not losing its edge or showing wear/chipping. I do not know the exact times/temps protocol for getting Elmax to perform that well at 58Rc; you would have to ask Brad at Peters HT, since they have treated all my Elmax blades.
 
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Nathan the Machinist said:
Edge retention is a complicated thing. Higher abrasion resistance and a more shallow diamond indention does not necessarily mean better edge retention. You're not cutting abrasive food or you wouldn't have any teeth left. Kitchen knives lose their edge because they clack against cutting boards and bone etc. You want fine edge stability in a kitchen knife and generally speaking this is found with a rapid quench to Mf without delay (no snap temper, no pause) and a low temper.

What is secondary hardness? Well, the retained austenite decomposes (a very good thing) and carbon leaks out of the martensite combining with various alloys forming secondary carbides (not a good thing). You have to consider what a hardness tester is actually measuring. It is the depth a diamond point can dent a sample and it does not tell the whole story. That secondary hardness hump is reduced RA (yay!) and additional carbides that resist the diamond penetrater. You have weaker, softer, carbon lean martensite and a larger carbide fraction that may work great in thick sections and cutlery designed for abrasive material, but it does not promote the fine edge stability you want in a kitchen knife.

For fine edge stability you need to prevent RA. Without resorting to the secondary temper this can generally be achieved with a rapid quench (this reduces carbon migration during the quench) and a continuous quench to martensite finish. Mf is frequently given as -100F but this is not completely accurate. Mf is an antiquated term (there is no such thing as zero RA) and the lower you go the more conversion you'll get. -100F represents the low hanging fruit but lower temperatures convert more, which may or may not be significant, it depends on many factors.

Any snap temper of any sort will cause RA to stabilize. It makes sense if you think about it. It would pointless to snap temper if it didn't do anything, but it does, and by reducing strain energy you're reducing the mechanism that makes RA convert. Also, any significant delay into cryo allows RA to stabilize.

The HT process is more than just the temperatures used and the hardness measured. It is the timing of the steps and the micro structures formed. And the process for a chopper is different than the process for a kitchen knife. I wouldn't be so fast to dismiss the low temperature temper until you've quenched the steel optimally and cut with it.
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For whatever it's worth, I love reading your posts. It's so nice to read information based on experience backed with real science (not just data sheets made to sell the steel).
 
Cashmore said:
For whatever it's worth, I love reading your posts. It's so nice to read information based on experience backed with real science (not just data sheets made to sell the steel).
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Agreed! Nathan has spent a great deal of time on these fascinating topics, and it's always a pleasure and a learning experience to read his thoughts on them. He's taught me a great deal. Thanks, Nathan! :)
 
james terrio said:
What's not to like? :confused: It's fairly easy to work with... grinds like CPM-154 (hard or soft) and seems easier to grind than CPM-3V soft, and is definitely easier to grind/finish than 3V when hardened. It takes a fine, keen edge. It's tough. It's stain-resistant. It finishes beautifully. It's not crazy-difficult to sharpen. The only drawback I see is that it's a little hard to find in certain sizes, and it's a bit on the pricy side. I charge my clients accordingly; they understand and are happy to pay for it.


I strongly disagree. I realize that I'm flying directly in the face of conventional wisdom, but bear with me for a moment...


I'm no chef, but personally I haven't noticed a lot of dulling in my own kitchen knives and those I've sharpened for others (factory and handmade, cheap steels and super steels) due to sawing/slicing on (wooden) cutting boards, and certainly not from cutting meat or veggies... the number one cause of dulling I see on kitchen knives is due to nitwits scraping their edge under hard pressure, sideways/across the cutting board. That drives me crazy... either be gentle or use the spine! But like it or not, that happens all the time, even in the hands of professional chefs who really ought to know better. The second most-common cause of dulling is banging thin, hard edges against bone and stuff as Nathan said. Those are toughness issues, not strength/abrasion-resistance issues.


I'm interested in this as well. Cr and Mo are instrumental in raising red-hardness among other things, but like you I'm curious if "free" alloying elements have a significant effect on edge retention, or if they serve us best when treated for maximum carbide development. I suspect the latter is true.

Slightly off-topic, but I can say with confidence that Elmax at 58Rc is very, very tough, even with a thin edge. Not just "tough for a stainless", but tough enough to go head-to-head with, and even out-perform classic high-toughness steels like 1095 and O1 at 58Rc when used for rough tasks like chopping and splitting knotty oak and "drilling" holes in it with the tip and scraping it to make tinder, while not losing its edge or showing wear/chipping. I do not know the exact times/temps protocol for getting Elmax to perform that well at 58Rc; you would have to ask Brad at Peters HT, since they have treated all my Elmax blades.
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My view of "lots of toughness" may be hopelessly skewed. I used to do impact tests on steel plate coupons that would stop a 300 ft-lb Charpy hammer using a V notch sample. I meant that for applications short of bone chopping, toughness doesn't come into play that much. No steel I know is tough enough to handle the treatment cheap stainless steels get in the average home kitchen. The edges on those knives don't wear away, they get beaten into submission.

Different alloying elements are added in varying amounts for different reasons. Moly is known for it's hot hardness imparting ability in higher amounts. However, it also contributes to hardenability, and is a major component in air hardening steels. Manganese's primary use is to help control sulpher, though modern steel making makes this less important. Another primary use is to improve hardenability. These two don't add to hardenability if they're tied up in carbides. Mn doesn't really form carbides in the first place, but that's another issue. Nickel and Silicon don't form carbides either. They stay dissolved in the matrix. Both contribute to toughness, silicon by inhibiting carbide formation. I suspect Nickel works the same way, but have yet to find a source to confirm this. Vanadium is a very strong carbide former and very little is not in carbide form. Vanadium carbide takes high temperature to dissolve, so it's used to pin grain boundaries and control grain growth at high temperatures. In steels like W2, that is almost it's exclusive contribution. In Elmax, it does more. Precipitated tungsten carbides, in some forms, are harder than Vanadium carbide. However, you can't get those unless you put the tungsten in the matrix first, so it can precipitate later. They also tend to be extremely fine and well distributed, in precipitated form. It can get pretty complicated, especially once you move out of the limited scope of knife steels. Many free elements will contribute to edge retention in indirect ways, such as by maintaining finer grain size, improving toughness, or preventing unwanted phases, ie hardenability.

James, what do you consider a thin, acute edge?
 
Nice post me2, thank you!

me2 said:
James, what do you consider a thin, acute edge?
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The two Elmax kitchen knives I ground last week measure out with edges at .010" before sharpening with a bevel angle of approximately 5 degrees. I feel that a final edge of 20-degrees inclusive is acute enough when the edge is that thin. You could bring that down to 15 degrees but I don't know how much that would really help cutting/slicing performance.
 
That's definitely thinner than most. You tend to have your Elmax drawn back to 58? Is the 5 degree measure inclusive or per side?
 
me2 said:
That's definitely thinner than most. You tend to have your Elmax drawn back to 58? Is the 5 degree measure inclusive or per side?
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Thin is in and light is right, baby!

5 degrees inclusive. That's not completely accurate, I'm just using a simple little gauge to measure it, so it could be a degree or two wider.

To date I've been having almost everything tempered 58Rc. I like the way toughness seems to be at our near its peak there with so many steels, while still offering good strength and wear-resistance. These are the first kitchen blades I've made in Elmax, but I've had good success with CPM-154 with the same geometries and hardness, so I'm pretty confident it will be OK.

I'm considering running some at 60 or 62 and see if they get chippy, or if they're much harder to sharpen. Clients hate a knife that's difficult to touch up.
 
I want to thank everybody for the help, my idea of quenching in foil in oil in a straightening device was not good, it gave me lots and lots of trouble, I ruined two knives. The third was plate quenched, liquid nitrogen cryo, and has become 61HRc. Here it is:

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