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View Full Version : What makes a certain makers heat treat better than anothers?



greasedbullet
07-07-2013, 05:31 PM
I don't know where to post this, but this seems the right place. I have heard several people say "_____'s heat treat on AEB-L is the best there is." and "____'s heat treat has gotten a lot better since he first started." So I am wondering what makes certain heat treatments better than others. I guess what I am asking is if I hand you two pieces of 52100 that have been heat treated to 61hrc by 2 different makers and another that has been heat treated to 61hrc by a professional heat treatment company what are the differences and why is one better than the other even though they are the same hrc?

Zwiefel
07-07-2013, 07:14 PM
I will expose whatever combination of knowledge and ignorance I have on this topic to hope I dispell some erroneous ideas I have...


I think that for a given HRC, the differences are about toughness vs chippiness. VG10 seems to be a good example of this....in the wrong hands (Shun seems to be blamed for this a lot) it's very chippy, but in good hands, it can be a great steel.

Also, I think limiting the discussion to a given HRC might be useful for discussion purposes, but different makers will choose different HRC's as part of the overall balance they are trying to achieve.

tk59
07-07-2013, 07:22 PM
To me, burr removal is a big piece, especially for stainless.

Marko Tsourkan
07-07-2013, 07:31 PM
Custom heat treatment offers some advantages over commercial.

There is a window of time when transformation from austenite to martensite happens (hardening), and that window is quite short (2-3 minutes). In other words, if one works with small batches, one can get blanks quicker from one step of HT to another and that can result in more transformation from austenites to martesites (hardness, more uniform grain structure, etc). Resilient burr, wire edge, often are the symptoms of retained austenites (those that didn't convert to martensites).

How you evaluate a good HT?
- Toughness & sharpness
- Wear resistance
- Hardness

If one optimizes steps in HT process, picks the right temperatures from which to quench and at which to temper, one should get a well rounded knife that would sharpen easily, take a keen edge and hold it without rolling or chipping, and retain sharpness for a long time. In case of 52100, if you manage to refine grain, quench at the right temperature, temper at a right temperature, cryo treatment, of course, you get a very fine structure of the steel that feature all of the above qualities and responds very well to stropping on diamond. This will prolong time between sharpening sessions for months - a good thing for pro users, I was told.

greasedbullet
07-07-2013, 08:44 PM
Also, I think limiting the discussion to a given HRC might be useful for discussion purposes, but different makers will choose different HRC's as part of the overall balance they are trying to achieve. I was limiting the discussion. I guess I was asking about the differences between this sample of 52100 at 61hrc and another sample at the same hardness made by a different maker.


Custom heat treatment offers some advantages over commercial.

There is a window of time when transformation from austenite to martensite happens (hardening), and that window is quite short (2-3 minutes). In other words, if one works with small batches, one can get blanks quicker from one step of HT to another and that can result in more transformation from austenites to martesites (hardness, more uniform grain structure, etc). Resilient burr, wire edge, often are the symptoms of retained austenites (those that didn't convert to martensites).

How you evaluate a good HT?
- Toughness & sharpness
- Wear resistance
- Hardness

If one optimizes steps in HT process, picks the right temperatures from which to quench and at which to temper, one should get a well rounded knife that would sharpen easily, take a keen edge and hold it without rolling or chipping, and retain sharpness for a long time. In case of 52100, if you manage to refine grain, quench at the right temperature, temper at a right temperature, cryo treatment, of course, you get a very fine structure of the steel that feature all of the above qualities and responds very well to stropping on diamond. This will prolong time between sharpening sessions for months - a good thing for pro users, I was told.

That was exactly what I was looking for. So basically two identical pieces of steel that are heat treated to the same hrc will still have different performance based on the amount of time they spend in the "oven"....?.

Also if there is a 2-3min. window where there are both austenites and martensites and austenites are bad why not wait 4 minutes so you only get martensites?

JBroida
07-07-2013, 08:59 PM
and what temp they take it to, how long it stays there, how they quench, what they use to quench, how they temper, and so on

greasedbullet
07-07-2013, 09:14 PM
Hmm, does anyone know of a good place to read about this? I have seen a few videos that touched on this, but nothing really this detailed or involved.

Marko Tsourkan
07-07-2013, 10:23 PM
I was limiting the discussion. I guess I was asking about the differences between this sample of 52100 at 61hrc and another sample at the same hardness made by a different maker.



That was exactly what I was looking for. So basically two identical pieces of steel that are heat treated to the same hrc will still have different performance based on the amount of time they spend in the "oven"....?.

Also if there is a 2-3min. window where there are both austenites and martensites and austenites are bad why not wait 4 minutes so you only get martensites?

There is a number of factors. For every steel there is a range of temperatures it could be heat treated (austenitizing and tempering), and the outcome will depend on those temperatures, time soaked at that temperature, speed of cooling, cryo treatment and other steps.

I am just going to run a two hypothetical cases scenario. To simplify things, I will take cryo out of the equation and in both cases steel is soaked during austenitising and tempering same amount of time.

Scenario #1
If you heat treat at close to the lower temperature in the range, you get smaller grain size (more toughness, easier to sharpen) but wear resistance will suffer, as at the lower temp you get less of the components dissolved into a steel matrix. Nonetheless, say you get 64RC as quenched. You temper at a certain temperature, 2 sessions 1 hour each, and the end result is 61RC. Totally doable.

Scenario #2
If you heat treat at close to the upper temperature in the range, you get a larger grain size (less toughness, more wear resistance). Say, as quenched you get 66RC. You raise your tempering temperature, and do 2 sessions of tempering and the end result is 61RC.

First one will perform very differently than the second one - it will be easier to sharpen, and will have very stable edge. Second will have more wear resistance, but might be prone to chipping.

What I described is the window after the quench, while the transformation is still occurring. Certain steps in custom heat treatment allow to reduce retained austenites to the minimum (if not zero). You will know that by increased hardness of your heat treated blanks and ease of sharpening - burr will raise very evenly and will be easy to remove. There is a reason why commercial HT blades are in the 60-61RC range, as when you heat treat a large batch there is a time lag between processes, and that short window of opportunity is missed. For instance, cryo treatment the next day makes no difference on the steel whatsoever.

Hope this makes sense.

A good place to read about this stuff is Devin's subforum and website.
M

Lefty
07-07-2013, 10:53 PM
Marko, I've read a fair bit about this topic, and discussed it with multiple makers. What you wrote is the most straightforward, and accurate (in my mind) explanation I've come across.

greasedbullet
07-07-2013, 11:04 PM
Interesting. Thank you very much. I am just now learning enough to know what I don't know.

JBroida
07-07-2013, 11:48 PM
There is a reason why commercial HT blades are in the 60-61RC range, as when you heat treat a large batch there is a time lag between processes, and that short window of opportunity is missed. For instance, cryo treatment the next day makes no difference on the steel whatsoever.

Hope this makes sense.

A good place to read about this stuff is Devin's subforum and website.
M

Yes and no... i've seen a lot of heat treatments done from many people... both in large quantity and in smaller. This is not always the case. I think you would be surprised to see the attention to detail and lack of time-lag that can occur in places doing more than just a knife or two at a time. I know i was surprised when i first saw some of the more talented people do larger quantity heat treatments with the same kind of attention to detail that people doing one or two at a time can do.

Also, the 60-61 range you see from Japan often is not necessarily a function of this... i would wager (based on what i have seen and the people i have talked to here), that this rockwell hardness is more about what they think will be best for the knife than a function of their ability to do more complex heat treatments (which many of them actually do, even though we dont see or talk about it here).

At the same time, there are also large factories that do things more in the way you might be thinking, but even then, they can still use very complex processes. I know the first time i went to seki (where factory production is more common), i was shocked to see that they can incorporate cryo treatments in a very quick time with no trouble. Some companies even use machines that do the entire process of annealing, heat treating, cryo, and quenching.

Marko Tsourkan
07-08-2013, 12:25 AM
Yes and no... i've seen a lot of heat treatments done from many people... both in large quantity and in smaller. This is not always the case. I think you would be surprised to see the attention to detail and lack of time-lag that can occur in places doing more than just a knife or two at a time. I know i was surprised when i first saw some of the more talented people do larger quantity heat treatments with the same kind of attention to detail that people doing one or two at a time can do.

Also, the 60-61 range you see from Japan often is not necessarily a function of this... i would wager (based on what i have seen and the people i have talked to here), that this rockwell hardness is more about what they think will be best for the knife than a function of their ability to do more complex heat treatments (which many of them actually do, even though we dont see or talk about it here).

At the same time, there are also large factories that do things more in the way you might be thinking, but even then, they can still use very complex processes. I know the first time i went to seki (where factory production is more common), i was shocked to see that they can incorporate cryo treatments in a very quick time with no trouble. Some companies even use machines that do the entire process of annealing, heat treating, cryo, and quenching.

I didn't have any particular commercial heat treatment operation in mind. I doubt that US commercial HT for knives is much different than anywhere else, but I might be mistaken.

I am sure automating processes is possible as well as additional steps like cryo, or molted salts furnaces, but it costs money and there has to be a market for knives, in which price you can factor a cost of production and still make profit if you are maker and do HT in house. If you are a commercial HT operation, then it has to get enough volume, and pay per service, to justify investment into expensive HT equipment. This kind of stuff is more likely to see at placed that do HT for Boeing.

If you could recommend knives from Seki brands that have HT automated, to test for performance, it would be an interesting study.

M

PierreRodrigue
07-08-2013, 02:01 AM
This is all are correct in parts... Rockwell hardness is only part of the equation, the method to get to a desired hardness is equally, or more important than the final number a tester spits out. Oven vs salts, higher vs lower temps both in the initial HT, and temper draws, cryo or no cryo all effect the toughness, hardness, edge holding of a given steel, and its up to the individual maker to make the determination of what his goal is. It will not make every end user happy, nor will it be the same method used by every maker for a given steel. This is a great line of discussion. Its interesting to read others thoughts on theory, and how they feel the final product is improved or potentially stalled. Is there a "perfect" method? Maybe... That's what makes this all so much fun. Every maker has their opinion of what makes the best HT for a given steel. Others think they can improve upon it, and they likely can. Some can not. It doesn't make the process wrong, its just simply that makers method. At the end of the day, 90% of end users will say WOW!! Thats one heck of a knife! The anal few out there may be able to detect differences, but may not be able to tell exactly what that difference is. Its these few that push the makers to squeeze that extra bit from their process, and will rave that Mr. "A" is better than Mr. "B" Awesome! Mr. "C" will come along, and emulate one or the other, and as I said, it makes for a great read. It will never be agreed upon to everyone's satisfaction. Buy a knife, use it. If you like it great! If you don't, sell it buy another.

The automation on the HT process is more than possible, and is done on a very regular basis in the US as well as other parts of the world. Google Paul Bos and read a while. Its been his business for 50+ years. Working for Buck knives, "bulk" was a necessity. Also the shear number of custom makers using his services is a testament to the process. But again, its a process. Is it perfect? A lot will say yes, some will say no.

JBroida
07-08-2013, 04:16 AM
pierre... a very well put statement. I agree wholeheartedly.

Marko, there are a few out there... however, the vast majority that make it to america are on the softer side and probably wouldnt be to your liking. For example, glestain uses cryo, but i would wager that you dont care much for their steel or HT. Anyways, the point is many things are possible, and making general blanket statements without sufficient knowledge, will get this conversation nowhere.

DevinT
07-08-2013, 10:52 AM
You guys are funny, you have to quench in the urine of a red headed holy man to obtain the best results.

Hoss

JBroida
07-08-2013, 10:55 AM
clearly, but their population has declined in recent years and the results from genetically modified red-headed holy men urine are not the same :P

*thanks Devin for brightening up the conversation :)

maxim
07-08-2013, 11:05 AM
I just think you guys enjoying the smell when you do it :groucho: :)

Marko Tsourkan
07-08-2013, 11:11 AM
Actually, urine was used for quenching in the ancient times (and brine is used today), so yes, whoever discovered that method, thought it discovered a holy grail, except it was long before Christianity took hold.

Anything can be automated at a cost. I am pretty sure German makers have state of art HT facilities, but their choice of steel and hardness results in a product that can't stand up to some custom heat treated products.

Even though I agree in principle that it is possible for commercial HT to do better than custom, if I were to bet on say DT AEB-L (heat treated in a small workshop) vs commercial HT of AEB-L heat treated in modern, automated facility in US or outside, I would not hesitate to bet on DT, and am not a betting man. DT HT is likely to result in a harder blade but there would be other notable differences that stem directly from the custom HT. Face it, if he can jack up the wear resistance in a steel that only has .6% of the carbon, he got to do something that a commercial HT doesn't.

Commercial HT makes sense when one is an upcoming maker and doesn't have the room/facility/means/knowledge to do HT himself or when one does a production and outsourcing some steps is just a part of the model.

If one is anal, a control freak of sorts, outsourcing HT is out of question. This is the most important part of the process if you ask me, and you want to have 100% control over the outcome. It's like outsourcing a preparation of the most important component of a dish to a third party. How many chefs do that?

M

Chuckles
07-08-2013, 12:14 PM
Many of the very best Chefs rarely make the food in their restaurants. Thomas Keller comes to mind. At certain point the need for the growth of the business necessitates a shift in responsibilities from production to training and quality control. It definitely requires taking a leap of faith. 'You are only as good as the people that work for you' is an adage that applies just as well to Chefs as knife makers. How many people work for you depends on how many you want to serve. Wolfgang Puck vs. Jiro dreams of sushi.

Marko Tsourkan
07-08-2013, 12:41 PM
I guess my small-maker mentality prevents me from giving up control over certain things, but there are limits on my output that are related to this decision, so in that sense, outsourcing is a part of business growth if growth is in plans.

Lefty
07-08-2013, 02:42 PM
This thread is a must read.

Pierre, you've taught me boat loads about HT, and your post really rounded out Marko's initial one. Combined (with Jon's comments, of course), we have a very good summary of how intricate and individual ht can be. Basically, what it seems to boil down to is: there are fantastic "mixes" or "cocktails" that are used. If you want more wear resistance, or sharpness, or whathaveyou, it's a good idea to use a knife or maker that/who is known for the qualities you desire.

JMJones
07-08-2013, 04:58 PM
One thing to note to someone just starting to learn about this stuff


As Devin's post alluded to, there is a ton of bad info out there regarding heat treat. The process and results have been hyped, romanticized, theorized, BS'ed, and lied about probably since its discovery. There is of course a ton of great info out there as well, it is important but often difficult to try to differentiate the two. There is no one foolproof or perfect approach but the more you learn and understand, the more you will be able to define your process and how you get your knives to perform to your standards. Good luck!

DevinT
07-08-2013, 07:04 PM
Great post JMJ.

For those who are interested in doing their own heat treating I recommend the following; get yourself a furnace or salt pot, a Rockwell tester, a liquid nitrogen dewar, quenching oil and maybe some quench plates. Read some books on the subject and then go out there and cut some test pieces from the same batch of steel and vary the temperature 25' at a time, test the hardness, put the heat treated samples in a vice and break them and look at them under magnification, see what you can see and then make a knife and cut with it. You will see some grain coarsening with too high a temperature and breaking them will show how tough they are. Sometimes it's not very scientific but you can learn a lot.

And last but not least, don't do anything dumb and call it the greatest heat treatment known to man. There are several things that happen to steels when you heat them up, most of them are bad.

Hoss

greasedbullet
07-08-2013, 07:13 PM
What would be some good books? I know there is a lot of ambiguous or incorrect info out there.

JBroida
07-08-2013, 07:14 PM
yup... a microscope is key (as is polishing the steel before looking at it and breaking it to look at that too). And ask questions. Some people have figured out interesting ways to achieve results. In reality, there is no one right way, but having a good logically sound method is very important.

DevinT
07-08-2013, 07:22 PM
What would be some good books? I know there is a lot of ambiguous or incorrect info out there.

Steel Metallurgy for the Non-Metallurgist by John D. Verhoeven is a very good one to start with.

Hoss

greasedbullet
07-08-2013, 07:40 PM
Thanks, that is now in my "read pretty darn soon" list.

maxim
07-09-2013, 04:42 AM
Ok now i have question for your quenching gurus :D

I am not expert in it in any way, i just know what i like and thats about it.

But what is over hardened blade for you ??
My understanding is when i have seen some over hardened knives edge just crumbled. Chips is not uniform or rounded, Difficult to explain but it is like some kind of car glass.

On the other hand, one costumer ones came to me with not one of my knives and said my knife is over hardened should i return it ?? It chips all the time etc.
After i expected it it was clear to me that it was not the case at all ! it was just very thinly grownd and user may be used it wrong too. After i sharpened it and put bit higher angle on it all was gone and he was super happy.

Now for some people it is very hard to see what is over hardened blade and what is just super hard. Personally i love them to be as hard as possible. But still without that crumpling thing.
Chips i don't care much about.

I know some may not like knives that way but it is what it is :D

hehe hope you understand what i mean with my crappy English

So my question i guess is What is for you over hardened blade ? And how can we decide what is right heat-thread or wrong ?

greasedbullet
07-10-2013, 12:31 PM
I just wanted to thank everyone that participated in this discussion. It helped a lot and is a very good read for anyone that is interested in heat treating.

3200+++
07-10-2013, 08:38 PM
me too. i had no clue about the subject and it is very interesting.

Benuser
07-10-2013, 08:55 PM
Very helpful indeed.

keithsaltydog
07-21-2013, 06:40 PM
Good thread,I found out about AEB-L reading Devins page on the web.