Issue with a 52100 blade

Hi guys

I made up 3 little EDC skinner knives for me and two buddies of mine for a recent hunting trip. The knives worked well on the one buck we killed but after we have been back i just dont feel like these 3 knives hold a edge as long as they should.

HT info is as follows

Normalized by heating to 1675deg and air cool, then 1550 deg and air cool, then 1475deg and air cool.

Triple quench by heating to 1490deg and holding for 4 min then edge quenching in canola oil heated to 150deg. I did this process 3 times in a row with the blades cooling in the oil, i did not let them rest over night, all three heat treats were done back to back.

I tempered them twice at 350deg.

I tried to do a edge flex test over a brass rod and after having to push VERY hard i think the blade has flexed just a little but not gone back to straight, there seem to be just the smallest bend to the cutting edge.

A previous knife i had done a triple quench with while letting it rest overnight in my freezer in between each heat treat seems to hold a sharp edge for ever. and a single quench blade i did holds a great edge, i chopped down about 15 cedar limbs and it would still pull hair afterwards.

These knives just dont seem to hold the same edge as the previous blades. all of these knives are 52100 steel from ALdo. On these 3 knives i ground them down a little thinner than i normally have before heat treat, could this be carbon loss on the cutting edge ??

any ideas ??

thanks
steve

Something doesn't add up here. I am assuming that you are working with a regulated kiln or a molten salt bath here being that you are sighting the temperatures that you are using so you evidently have the equipment necessary to handle a more complex alloy like 52100. Your normalization routine looks right. Even though you didn't say how long you soaked it, you really don't have to hold it any longer than it take to heat it throughout.

You austinizing temperature, if anything, is just about 15° too high. Not enough to quibble about. Your tempering temperature is so low that all it could be doing is stress relief. I would be expecting your blade to be chipping out it should be so hard at that temperature. BTW, my brass rod test is to try to drive the edge though the rod with a mallet and see if it chips or indents.

I think that you are not giving the steel enough time to soak to dissolve the carbides and get the carbon into solution, even with the multiple austinizations. Another suggestion that I read on another post is to let you kiln come up to temper for 30-60 mimutes before you insert the blade to make sure it's well heated and time the austinization time from when the pyrometer returns to temperature then soak for 10 minutes. I also don't like the triple quench but I'm not getting into that discussion here. If you increase the soak time I would raise the tempering temperature to 450°, then test the blade and see how that works for you.

Doug

I soaked the blades at 1490deg for 4 min each time. I am using a even heat kiln. My only guess was that I ground the edges down to fine before the heat treat and burned out the carbon in the cutting edge.

I very seriously doubt it. I still doubt that you ever got enough carbon into solution if you are still leaving a bit of a bend in the edge doing a flex test after only tempering at 350° then you are not getting enough carbon into solution to form martensite. Carbon burn out is way over rated an you are not going to run into any appreciable amount at only 1490° Did you test your blade with a file before you tempered it? I bet if you do you will find that the file will bite into the steel. I've worked with 52100. I cut my soak back to 5 minutes because I use a gas forge to austinize and don't have the heat control that I need. I do a single quench in 525° peanut oil for about 10-15 seconds and then air quench (marquench) then tempered at 450° for 3 two hour cycles. When I use up the 52100 that I have I'm going to stop because I don't have the heat control that is necessary to heat treat it reliably and there's no outward sign that I've created excess retained austinite in a blade. I have also done isothermal tempering, or modified austempering, and have made a blade that would have probably passed the ABS performance test if I hadn't caused a stress riser by stamping the blade. The blade broke right through the stamp at just about 90° The blade that I marquenched I had to beat on with a 4 lb hammer, the tang was so soft that it just bent over, to get it to break after it had chopped through a 2X4 and still shaved hair. If I didn't burn out the carbon in the edges of my blades in my forge you didn't burn it out in your kiln.

Doug

I just don't get why this recipe worked so well for the last few knives and didn't work so well on these. I may not be doing the rod flex test correctly, I have only read about it never seen it.

Lerch, I'm not trying to put you down here. The big red flag was the super low tempering temperature that you are using. It's not just what I've done with with 52100, it's what others have done. If you go to Alpha Knife Supply, click on their blade material, then click on product information, I think you should be able to select 52100 and it will pull up heat treating information. It lists 450° to produce an HRc of about 58. My take on what's happening is that you are barely austinizing the steel with the short soak times and hardly dissolving any of the carbides to release carbon into solution and you're forming very little martensite. Therefore you need a very low tempering temperature to have any sort of cutting edge. If you are able to have one of those other knives tested somewhere I'm quite certain you will find that their hardness is on the low side. From what others who use 52100 have said about it, you austinizing temperature is good, AKS lists it a little higher even, you just are not giving it enough time to heat up.

Doug

I guess what i am confused by is the soak times your talking about. in your first response you said that you really dont have to hold the steel at temp any longer than it takes to heat it throughout, but then your saying that im barely allowing the carbon to go into solution with my short soak times. so im am a little confused there. from what i had thought i had read it seemed like my 4-5 minute soak times at 1490deg were pretty on the money

on the tempering temperature again i thought i was pretty close for a differentially heat treated blade

For normalization you don't have to hold the steel longer than it takes to heat the steel throughout because all you are interested in is phase change. For austinization for hardening you have to do more change the iron crystals from body centered to face centered you also have to give the carbon time to dissolve into the austinite. Something like 52100 adds another problem and that's a higher level of chromium carbides which need more time or higher temperature to break down and release their carbon. As a matter of fact, the only way to dissolve all of it's carbides is to melt the steel, at least according to Verhoeven and the atlas of IT diagrams I have. The higher temperature will cause a problem with grain growth so you have to give it more time. Also don't assume that just because you've closed the door on you kiln and the pyrometer has come back up to temperature that the steel has come back up to temperature you might have to add a few minutes to let it catch up. That's why I recommended a soak of 10 minutes prior to the quench. I know that all this stuff is enough to make your head spin. I still have to go back to the books occasionally and proof read my replies to make sure I have all my phases and heat conditions in agreement.

Doug

Okay, thanks

Ya when i am doing multiple blades i start the first blade from a relatively cool kiln and let it come to temp. my Evenheat is a digital so i program the temp and the soak time and let it run. i feel confident that the first blade, which starts from a relatively cool kiln, gets a good consistant heat treat so if the recipe calls for a 5 min soak then i let it run for that. if i do another blade after that then i place that blade in the kiln, which will be around 1000deg by that point and let it run for about a 7 min soak when it gets to temp to correct for the knife being cool and the oven being hot to start with.

i thought when i had been asking for heat treat info on 52100 that people were telling me to keep my soak time down to around 5 min to avoid grain growth.

THese blades are around .105 " thick , you think a 10min soak time would be better for multiple quench then what i am currently doing ?

thanks for the info

steve

I would really go for a 10 minute soak just to make sure that you are getting carbon into solution. I would also drop the triple quenches and rely on the triple normalizations for grain control, but that's up to you. Whatever, I really feel that you are not getting carbon into the mix . A real good person to as would be Kevin Cashen. He actually has the means to do microscopic testing on his test blades and he has worked with 52100. In another post he suggests that you try to contact him through his email address as it's more reliable but you might have luck with linking up with him through the board message center. I feeling that this is the kind of thing that he avoids addressing openly on the board.

Take care
Doug

The benefit of multiple quench is that we do not need to soak a little above critical. When hardening a blade it is above critical for less than 30 seconds. Soak times above critical can increase grain size, I have found that smaller grain size greatly enhances blade performance.

When Rex and Kevin did photomicrograps of multiple quench blades we forged down from 5 1/2 inch round bars of 52100 steel at low temperature (1625 f. maximum forging temp) temp), they found the grain size to be 15 and smaller and there was no measurable amount of retained austenite in the hardened portions of the blade.

The only way you will know the difference is to thoroughly test your blades, some to destruction and compare them to another blade from the same steel with a different heat treat.

Ok, Ed, I do understand your position that you are progressively adding more carbon into solution to form adequate martensite to harden the blade. My concern is that with each subsequent quench you are also stressing the steel and forming more microscopic cracks with the plate martensite, which is 100% with the carbon content found in 52100. My feeling is that it is better to shorten the soak time, do it once, and stress the steel once with a single quench. Of course this would take a scanning electron microscope to test completely.

Doug

Doug: we have never experienced any microscopic cracks through our methods,(using our 52100 steel) our last test blade did 14 - 180 degree flexes requiring over 70 foot pounds of torque before the hardened portion tore along the grain boundaries (instead of breaking through the grains). The same blade did 800 cuts before we quit testing for edge retention, and 10 edge flexes without a chip. It could have done more cuts but I figured 800 was enough. After the hardened portion tore we could have straightened the blade and still used it as a knife. The "secrets" are low temp forging, a high rate of reduction at low temp, post forging quenches, 3 sub critical anneals at 988f. Three hardening 24 hour cycles in a slow quench oil, (we use Texaco type A fluid an 18 second quench and per-heat it heat it to 165 f. )

We can discus theory and we can get as technical as you wish, but it will serve no purpose.

Our greatest contribution to the knife community is to encourage those who wish to make high endurance performance knives is to encourage makers to try various methods and thoroughly test the performance qualities of their knives doing what they are made to do and make their own decision based on performance not esoteric theory that may or may not pertain to knives.

In our experience three cycles seems to be the most efficient number, more make higher performance blades, but the time and expense in developing a blade is most efficient at 3 cycles, I have tried up to seven cycles, they improved with each cycle, but not economically feasible.

I have been working on a blade since Sept., pushing it to the limit. The blade will be tested to destruction and just maybe we will know some of the limits and some ideas of what to try next.

I do encourage discussion along these lines, no hard feelings or animosity (I hope).

Ed Fowler said:

...We can discus theory and we can get as technical as you wish, but it will serve no purpose...

Click to expand...

I believe it will serve the purposes of this subforum quite well though. I strongly encourage all to discuss proven metallurgical principles, for staying technical, or at least as it applies to precise and accurate information, serves many very important purposes.

Ed, I am certain by your own admission that you heat treat quite differently than the vast majority of metalworking industries and even most knifemakers. You are normally quite good at qualifying your advice with the point that you only speak for your experience with your methods and your steel. Sometimes however you slip, and such is the case with your statement:

“Soak times above critical can increase grain size”

My fear is that folks visiting this forum looking for sound information will read this and be misled by an opinion that is not shared by the vast majority of the heat treating, metallurgical and industrial world. Proper soaking is a well-established standard procedure, successfully used every day for its benefits. Overheating that exceeds the grain coarsening temperature for the steel will indeed result in grain growth, but proper soaking within the austenitizing range of the given steel will not. Basic principles of heat treatment bear this out as well as my personal experience and that of countless other knifemakers. If you wish to maintain that it is unique to your methods and experiences, I would accept that as a legitimate point, but the general statement above is not, and folks deserve to know that.

As for Doug’s reply, plate martensite forms in austenite containing .6%, or greater, carbon, with increasing levels until around 1% is reached where it will be the dominant structure. The determining factor is actually the temperature at which the martensite forms, and that is what the carbon content affects. Limiting the amount of carbon in solution is the best way to control Ms temperature, so a well-controlled austenitizing temperature can be key to this, regardless of how many times it is done.

Another point of accuracy that I have always been concerned about, as we have discussed in the past Ed, is the interchangeable use of the words “flex” and “bend”. From everything I have seen your tests involve bending (the blade takes a permanent set) to 90 degrees in one direction from true and then it is re-bent 90 degrees in the opposite direction from true. As I understand it, your goal is not to have the blade return to perfectly straight as soon as the load is removed, so this would not be a “flex”. Nor is it truly 180 degrees, which would bring the tip parallel to the tang in a “U” configuration on the first bend. Here I find myself much more comfortable with technical accuracy so that folks once again do not get the wrong idea from the chosen terminology.

In addition, something which we have also discussed, the torque measurements are only a reflection of the cross sectional thickness of the blade (as per the non-negotiable principles of area moment of inertia and Young’s modulus), and, without much more accurate tensile testing equipment, will tell you little about anything beyond the proportional limit (flexing). Once the yield point is reached (bending) a torque wrench won’t generate very useable numbers. So one can see how it can be very important to separate “flexing” from “bending”.

It is the “esoteric”, in your words, that I hope to avoid by insisting on accurate terms and descriptions. One man’s chosen terms may only mean anything to him or his close circle. The accurate terms, concepts and principles used by material science and industry were developed so that all could have a common understanding of the facts. It takes but a second to look up a word we are not familiar with, but once we do it is ours forever with which to better our accurate communication. Fortunately it is the steel alone that determines which laws of physics pertain to knives, so that we don’t have to try to find the man capable of doing the job of the one who created those laws.

Hard feelings and animosity are invariably the result of miscommunication or misunderstanding; I would very much like to avoid that here.

Kevin....Ask John Gault. Smile

I honestly never would have taken you for an Ayn Rand fan Ed. :001_smile: I just finished “Anthem” which is a much more concise and pointed statement of her views of the individual. But none of this helps Lerch with his heat treating issues, which I hope he has resolved.

She is my heroin. I read "Fountain Head" first, when "Atlas Shrugged" came out I bought a copy in as soon as I could find a copy, about 1957, I was in high school. I have read them both several times since that time and learned from each reading. I agree "Anthem" is another classic. I have read much of what she has written, but feel these are the cream of the crop. Hank Reardon is one of my heroes from Atlas Shrugged.

The lessons from her work for me are that some are destined to stand alone, to seek something better than borrowed knowledge from the past.

Our discussions may not help men like Lerch, other than to provide him and others with the knowledge that choices are available. I to not see any problems when it comes to heat treating, only opportunities. My next book, should I decide to finish it will contain many questions that still remain unanswered in my mind in the hope that others may chose to travel where others do not tread or maybe simply are reluctant to speak out.

I feel that it is a good thing that we have found one arena where we agree.

Ed Fowler said:

...I feel that it is a good thing that we have found one arena where we agree.

Click to expand...

Perhaps, but common interests do not always equal agreement. Perhaps we could find a book review forum or Ayn Rand fan site to explore that without creating further thread drift here.

Thank you guys for your info. i am still experimenting with the blades to see what is going to work best for me

Ed my buddy Brent Peck who visited you at your shop finally made it out to me with the stuff he got from you, Thank You very much!!! He told me all the info you shared with him about the knife of mine he showed you. THanks for all the info, i love the positive criticism and took all ya said to heart. Im still learning my way into what my personal style is and hearing info from you has been a great help.

thanks again

steve

Interesting stuff Ed. Thanks for posting.

However, (aside from testing),… I don’t see how we can talk about heat treating 52100 knife blades without some “esoteric theory” sneaking in.

I enjoyed "The Fountainhead".