heat treat questions

scott.livesey

Dealer - Purveyor
kevin's answers about 52100 kept coming back to keeping your heat under tight control. Is +/- 25 degrees F tight enough temperature control? that is about the best i can hope for in my manual lab furnace with analog temperature gauge. the steel is for small (3 to 4 inch) paring/utility knives. How long a soak time at 1650F when normalizing? i dont have access to liquid nitrogen, would dry ice and acetone bath be worthwhile?
does anyone have any heat treat info on Aldo's current batch of 15N20? if not, would it heat treat similar to L6?
thank you again for your help.
scott
 
I think that that temperature range will be fine but I don't know if 52100 is complex enough to benefit from cryo treatment. For normalizing, I think if you hold it long enough for it to heat evenly all the way through it should be finem, that might take a few minutes though. It will depend a bit on your furnace. You are only looking for phase change here. Austinizing would be a different matter; I'd say 5-10 minutes on it from the time it comes up to temperature. If you want the heat treating info for the 15N20 that Aldo has I'd drop him a line and ask. I don't know how close the L6 would be as it tends to have a bit higher carbon.

Doug
 
thanks doug,
aldo's site has nothing listed about the 15n20. cryo for 52100 is recommended by carpenter, crucible, and latrobe. can i get the blades cold enough in dry ice/acetone bath?
 
thanks doug,
aldo's site has nothing listed about the 15n20. cryo for 52100 is recommended by carpenter, crucible, and latrobe. can i get the blades cold enough in dry ice/acetone bath?

Carpenter, Crucible and certainly Latrobe make the steel for bearing manufacturers, all of the heat treating specs are geared towards making bearings. Retained austenite in a perfect sphere, designed to handle compressive loads, will produce a different set of variables, and even opportunities, in dealing with it. Almost all the specs for 52100 for its intended use as bearings show an austenitizing temp of around 1550F., this will result in a spike in retained austenite that when later converted, in a sphere, can create an outward force which could be handy in compressive strength, in a knife blade it is just a problem that needs to be fixed. I'm not saying that RA is desirable in a bearing either, I am just saying when and how it is dealt with can be.

If you want to pursue the other claims of lattice improvement or special precipitates that are claimed by cryo folks, or if you are dealing with steels having Cr above 12% or significant amounts of nickel then, freezing is the way to go. Folks really into cryo have a lot of curious ideas about it, but if you are seeing any significant increase in HRC hardness from freezing a blade made from a simple alloy or carbon steel, something is not right in your initial heat treatment; and simply correcting your temperatures is far easier than setting up an unnecessary cryo system.

Following the bearing making specs, I found that starting at 1500F you could expect as much as a full point Rockwell drop in as-quenched hardness for every 25 degrees due to the pro-eutectoid carbon brought into play. If these samples were subjected to liquid nitrogen with no other treatments that lost Rockwell hardness was regained; only two phases account for that- austenite making up its mind about being martensite. The same steel heated from 1425F to 1500F in 25 degree increments saw a climb in HRC with a possible 67 HRC in the middle of that range, until it leveled off at 1500F.

Scott, if you have a 25+/- window to work in I would set your heat for 1475F and not sweat it too much, it should work out in that sweet spot. The 15n20 will respond well to heating to around 1500F with an oil quench.
 
You are right about Aldo not posting the heat treating specs on his web site. That's why I recommended that you call him or contact him by email. He could also give you the specific assay for the lot of steel that he's selling.

You have to keep in mind what Kevin said about the heat treating data that you get from the manufacturers for all steels, not just 52100. That data is for industrial users for sizes greater than knife blades, something like 1" or more thickness. I do have to admit that I discovered that I was overlooking the obvious when Kevin said that, at least in the case of 52100, that they were also written with the intended use of the steel in mind. Of course that data was for making bearings and bearing races. Of course we will have to modify that for making knives.(sound of hand slapping forehead-again)

One thing to watch when someone claims that they increased the HRc of a piece of steel by a certain process. The precision level of most devices use to measure hardness is ± 2 HRc. Taking multiple reading and averaging them will dilute this a little but basically any measurements with in that range are statistically the same. That does not mean that there was no increase or decrease with that range of error but it could put it in a gray area, depending on the number of samples that were being taken. It also makes a huge difference if these results were found on one knife or a hundred knives. You just have to know how the testing was done.

Doug
 
thank you both for the help. will try 1475 for first batch using 52100. i also understand about almost all manufacturers data sheets are not talking about cutlery applications. am glad i can skip cryo for the immediate future. i have also seen some of the hype about cryo, even "CRYO YOUR CARBREATOR AND SAVE 50 MPG".
thanks again,
scott
 
And I'm certain that they'd be happy to sell you the product to cryo treat your carburetor not for $40.95, not even $30.95, but for only $19.95 AND, if you order in the next 10 minutes, they will double your order! Just pay separate shipping and handling.

There's a lot of pure hype out there for a lot of things involved with knife making. Some of it is snake oil and some of it is at least reasonably good. Don't forget that Super Glue started out being marketed as above. Just be a little skeptical and think about the claims. Personally, I think that 52100 does have it's applications as a knife steel. As Kevin said, you can do some weird things with the heat treating to change the performance characteristics of the steel and I have had some pretty good luck with the steel. However, I think that I need to go back to a steel that doesn't need that element of luck to get the heat treatment right with a gas forge. I'm still going to send out that blade that I did the two stage isothermal quench on to see if I got the mixture of martensite and bainite that I was aiming for.

Doug
 
There are always pitfalls in approaching things in an oversimplified way. Some folks say you simply need to follow the industrial spec sheets exactly and you will do “just fine”, but not even industry does that. Other say that the industrial spec sheets should be ignored because knives are “different” :31:, I have yet to figure out how the shape the steel is in changes its chemistry or properties?? If things were as simple as so many want us to believe then why do we spend lifetimes trying to master this craft, indeed why is it even worth pushing ourselves if it is just that simple?

That being said, logic and knowledge can get us through even the toughest spots. Which steels need to follow the industrial heat treating specifications and which parts of the specs are critical can be worked out by some basic deductions. Which steels where made for very specific applications? What are those applications, and how close do they resemble knife type functions?

Example:

52100- made specifically for bearings so the heat treatment suggested by industry is going to be for the properties that 90% of the world wants from this steel, and it ain’t cutting stuff.

1084, 1095, W2- made as general purpose steel for a wide variety of applications of high hardness and wear resistance, the suggested heat treatment will be much less exclusive to knifemaking.

O-1, L6- as tools steels they are very specific in their intended applications, however, those applications parallel knife functions quite well, so you can almost take the industry specs to the bank.

I think it all starts with a much more systematic approach to steel selection than what knifemakers seem to use. Find applications in industry that resemble what you want your tool to do and then find the steels that industry developed to perform that task. This should get you both a material with the greatest desired properties as well as heat treating specs that are in line with your goals. It just seems to make a lot more sense than using whatever steel is free, cheapest or suggested (or hyped) by other makers, and then jumping through all kinds of heat treating hoops in order to pound a square peg into a round hole.

P.S. the carburetor thing is a new one to me, but it is not surprising, or even as whacky as most of the claims I have seen. I think it is tragic that the cryo folks have so overreached in the marketing with nonsense that there could be really useful things in an area of study that one often has to throw the baby out with the bath water because the bath water is so muddied you can no longer find the baby. It is like NASA being turned exclusively over to UFO conspiracy theorist, and the heavens remained unexplored while they sell Roswell saucer debris on the Home Shopping Network.
 
Kevin, point well taken about the chemistry but cross section can make a difference in response to heat treating, even though the difference may be rather small. It might be just matter of the data sheet recommending a water quench as a secondary, or even primary, method of hardening in parts 1" or greater with a regular cross section, when it's not the greatest thing for something like a knife blade. That's without getting into the weird stuff like film heat-transfer control or austempering.

Doug
 
Kevin, point well taken about the chemistry but cross section can make a difference in response to heat treating, even though the difference may be rather small. It might be just matter of the data sheet recommending a water quench as a secondary, or even primary, method of hardening in parts 1" or greater with a regular cross section, when it's not the greatest thing for something like a knife blade. That's without getting into the weird stuff like film heat-transfer control or austempering.

Doug

The quench is indeed one of those areas where the shape and size effects the approach to heat treating, it doesn’t change the chemistry but it can affect the properties if you don’t consider this. But when I think of “industrial specs” the ASM Heat Treater’s Guide immediately comes to mind, and it is very good about specifying that oil can be used for any of the simple carbon steels under 1/4 to 3/16 thickness. So at least there the industrial specs are spot on, but you need to use some of your own initiative regarding the quench recommendations for the W series tool steels.

But it is in the heating, not the cooling, that too many folks erroneously dismiss the industrial specs due to size and shape. Soak time should be counted at temperature, so the time it takes to bring thicker or thinner shapes to temperature should be irrelevant. You still need time for proper solution once the austenitizing temperature is reached. Clear evidence of this is how many makers also dismiss the industrial specs because the tempering numbers don’t match up to what they get in their knives, which is, in turn, evidence that the soak time was insufficient.
 
Scott, if you have a 25+/- window to work in I would set your heat for 1475F and not sweat it too much, it should work out in that sweet spot. The 15n20 will respond well to heating to around 1500F with an oil quench.
hi,
i have not worked with the 52100 yet. have made and heat treated 4 small knives of 15N20. heated blades to 1500F, soak for 10 minutes, oil quench, temper at 350F for 2 hours. two of the knives tested Rc57. I am not sure if this is due to the heat treat or way the knife fit in the testing machine.
to improve the process, I am bypassing the furnaces manual control and adding a digital temperature display, a pid controller, and some kiln furniture so the item being heat treated is closer to the thermocouple.
scott
 
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