Multiple quench

[Andrew Colglazier]

Very, very good! I've been forging indoors so I could see the color.

Yes, from what you say I have been getting the metal too hot. Thanks very much, everybody!

Andy

Kevin's research and info is very valuable to us makers out here, but it's hard to fully use for the charcoal using, shade tree maker

Are you forging in a low light area or outside in bright light? The temp of your hot steel will be greatly different from one to the other.

Most new makers overheat their blades when heating to be quenched. Bright orange to yellow is way too hot. Get the blade up to red in low light, as it slowly continues to come up in temp, it will brighten suddenly, hold it there for a bit, if you can and quench. A magnet will help find this temp (1400f to 1500f) but remember, a magnet will not stick to a overheated blade. So once you pass this temp, the magnet is no good.

For normalizing, heat to a little over non-magnetic once and twice at non-magnetic.

This should help the 'shade-tree-charcoal-smith' but listen to Kevin and work towards higher goals.

 

[Kevin R. Cashen]

Very, very good! I've been forging indoors so I could see the color.

Yes, from what you say I have been getting the metal too hot. Thanks very much, everybody!

Andy

Indoors is good, also try to maintain a consistent level of light from day to day. Most of the steel I have seen that looked like your image was forged or heated outside or with sunlight shining directly on the work place. This is why I detest it when books or sources use colors to describe temperature... "cherry red?" In whose shop??

That being said lets try. One should practice heating a bar of steel from one end in the dimly lit room you will work in and observe the color shift Don referred to. As the piece reaches critical it will begin an endothermic transformation (meaning it will get very hungry for heat and light energy), this will be very evident in a shadow or dimmer area in the steel. The steel will grow no brighter until the transformation is complete. Find that area on the heated side where the steel first gets brighter- that is critical temperature for that steel!:thumbup: learn it, live it! Contrary to the bilge we have all heard, the magnet will lie to us, that color cannot lie to us about the transformation since it is the transformation. When you learn this color you will be surprised at how much cooler it is for many alloys that what you thought it was.

In subdued lighting Yellow is only good for the very initial heavy forging operations and most hammering can be done in orange. Segregation is an every increasing issue that I am seeing in steel straight form the mill theses days, and this is one situation where forging does have the possibility of improving the steel, but only if you get it hot enough to move that stuff around, this obsession that bladesmiths have with low temperature forging only increases segregation. At the beginning get it hot and move that stuff around (both outside and inside) then drop down to normal austenitizing temperatures (around 1500F) for the lighter shaping. The last couple of heats can be sub-critical so that you can straighten and smooth out the piece without dinging it up badly, but be aware that the more you mess around in the 1300-1350F range, the more segregation will occur.

"grain size", "grain size", "grain size" (ad nauseum)...:jerkit: Bladesmiths have a morbid unhealthy obsession with grain size, yes smaller is good, but grain size is one of the quickest and easiest fixes a smith can do. In just a couple of heats (if done right) any grain size can be corrected, not so with carbide segregation, and if the carbides pool in the wrong spots they will make changing the grain size problematic. The problem is that fractured grain size is the only thing that 98% of all smiths can see so they focus on it; carbides have much more power to make or break a knife but "out of site, out of mind."

The same for normalizing get it hot the first heat and "normalize" things. Get everything evenly distributed and the grains equal in size, forget about what size it is for now as long as it is the same. On the next heats go for bright red where the magnet just stops sticking. Do it a couple of times allowing the piece to cool to at least around 700F (depending upon the alloy) before reheating. After the second or third heat you can throw a quench in there if you like, the added strain of martensite will eliminate around two cycles of air cooling in reducing grain size, just be certain you have reduced the grain to a reasonable level with gentler cools first since quenching large grain could result in cracking.

For annealing, the old stuff-it-in-the-forge thing may be alright for steel with less than .8% carbon, as long as you let the forge drop to "cherry red first” but it may be better to heat the blade to slightly non-magnetic and stuff it into wood ashes or vermiculite. For steel with over .8% carbon I am becoming much less supportive of those annealing methods as I look firsthand at the results. I would do my "multiple quenching" now and then cycle the hardened blade a few more times to dull red, never allowing the blade to go non-magnetic. Actually, no I wouldn't, I would simply put it in my kiln and run my standard spheroidizing program and go have dinner .

Forget the differing alloys; I think anyone could see why it is critical to know what steel you have since just changing the carbon levels a fraction will seriously impact how you will have to treat it. Get good steel! Take your lawnmower blades, old springs, railroad spikes; saw blades, tuna can lids, to the scrap yard so that they can turn them into good steel! Most scrap yards will even pay you for it! With enough poundage you could make enough to buy a brand new bar of steel!

 

[Fiddleback]

What is spheroidizing?

 

[mete]

Forming carbides into spheres !!! If we take a 1080 steel heat above critical and air cool we will get pearlite -alternating layers of carbide and ferrite. If we 'speroidize' the carbides will form spheres in a matrix of ferrite. This structure is much easier to machine and grind.

 

[Kevin R. Cashen]

What is spheroidizing?

Spheroidizing is the standard method of annealing in industry. Most smiths use lamellar anneals, they are called this because they form various forms of pearlite which is lamellar in nature. Heating you steel above critical and allowing to slow cool will cause pearlite to form at around 1000F. The slower you cool the coarser will be the pearlite, the coarser the pearlite is the softer will be the steel. But with steel that has lots of extra carbon the slow cool will allow any carbon in excess of .8% to collect in the grain boundaries.

Spheroidizing does not form pearlite but segregates the carbon out into many very fine spheroidal globs. Spheroidizing works best if the carbon is very evenly distributed throughout the matrix, so trying to spheroidize pearlite can be painfully slow and will result in rather irregular and coarse spheres. Hardened, bainitic, or very fine pearlitic steel will spheroidize the best. Spheroidized steel is much, much softer than pearlitic steel and is the easiest to cut and machine and in some alloys it is the only way to go since pearlite will have enough carbide sheets to just burn up and tear tools apart. I work mostly with L6 and O-1 with some occasional 1095, so you can see why I like this anneal. Just let L6 air cool n normalizing and it is all ready for spheroidizing.

Speroidal carbides can take a littler longer to go into solution so you need to add few more minutes to soak time before the quench. Spheroidizing is done at "sub-critical" temperatures so there is no effect on grain size. If one has done a good job at grain refinement in normalizing they could undo it with a lamellar anneal, but not with spheroidizing. The two common methods are to either harden the steel and then cycle it around 1335F (do not let it go nonmagnetic) , or heat it to above Ac1 and hold for around an hour and then cool at a rate of about 50 degrees per hour until below 1000F. The later will form the most complete spheroidal structure that is almost guaranteed to never squeak a drill bit or chatter a mill.

 

[Any Cal.]

I find this all very interesting, so thanks for the time and trouble you put into your posts. Thank you Kevin for the time you spend in your explanation. My question regarding all of this is as follows.

"How much difference does it make in real world performance on a knife if it has a heat treat sequence that involves normalizing rather than spheroidizing
or proper grain minimization rather than methods that can not acheive this?"

Would a knife outperform a similiar one of a supposedly better steel because of a perfect heat treat rather than simply a good one?

I ask because I am starting to form the opinion that only .1 percent or less of knife users will be able to tell the difference of steels that are not hugely different, i.e., 420 vs ATS34. If this was the case, how many are going to be able to tell the difference, if not told, between a knife w/ a perfect heat treat or a marginal one? Given this scenario, how much time/effort/expense should be put into perfect HT?

I absolutely love the thought of getting max performance out of a blade, esp. if it comes w/out additional compromise, but have to wonder if we are talking about a .5% difference in performance or a 5% difference.

Have a nice day all, and I am interested in any comments/opinions or actual facts to show that I am full of crap.

 

[mete]

I suppose that if you are satisfied with marginal performance then just buy cheap Chinese junk ! Those who look for a custom knife expect something more than marginal. It depends on the steel also.5160 is more forgiving while a high tech S30V is not. You could look through the forum to see problems of production knives of S30V obviously caused by improper HT.

 

[Fiddleback]

Thank you Kevin and Mete. I am a total neophite IMO, and your guidance is incredibly valuable to me. Sounds like in order to get into spheroidizing I've got to get a GOOD heat treat oven. I'll start saving my pennies.

 

[Kevin R. Cashen]

"How much difference does it make in real world performance on a knife if it has a heat treat sequence that involves normalizing rather than spheroidizing
or proper grain minimization rather than methods that can not achieve this?"...

Normalizing and spheroidizing are not interchangeable but instead complimentary. They are two entirely different operations for different purposes. One is normalizing and one is annealing. Whether the blade will be lamellar annealed or spheroidized, it should go through a good normalizing before either.

Would a knife outperform a similiar one of a supposedly better steel because of a perfect heat treat rather than simply a good one?...

Perfection is, and should be, unobtainable. One can hope to optimize the desired properties through heat treatment, but whether it is "good" or not is very subjective.

I ask because I am starting to form the opinion that only .1 percent or less of knife users will be able to tell the difference of steels that are not hugely different, i.e., 420 vs ATS34. If this was the case, how many are going to be able to tell the difference, if not told, between a knife w/ a perfect heat treat or a marginal one? Given this scenario, how much time/effort/expense should be put into perfect HT?...

I am not exactly sure about the percentages but I wholeheartedly agree with your opinion that the vast majority of knife buyers never push the blades to a level or direction that would show them a difference between a proper heat treatment and Hail Mary maneuvers. If it really did matter for most knife use, the old scrap steel, incredibly low carbon contents, or absolutely laughable heat treat practices that are so prevalent in bladesmithing would have been exposed for the problems that they are long ago.

But that being said, many bladesmiths are better at shaping the mind of the consumer than they are at shaping metal, since I have seen many knife failures that would have settled the question if the public hadn't been sold a numerous lines about a million other things a knife should do before actually cutting things!

If one is shooting blind temperatures with mystery steel and old motor oil, the differences will be much greater that a few percentage points, but nobody really looks to where it will be quite evident. The sad fact is that the only person that will really decide how good your heat treatment needs to be is you the maker. If you can live with marginal or "good enough" then don't broadcast your decision to settle (because who wants to save their $$$$ for they guy who settles) or start up the P.R. machine and sell your shortcomings as superior qualities that only you offer (don't laugh, this option seems to be more effective that all the heat treating in the world! )

But if one has to have the best they personally can do, then they can do it with a minimum of expense. Get a way to accurately judge temperature, a good quenchant matched to your steel (which you spent the price of a cheap meal on to know what the hell is in it), and a couple of good* books. Why not use these tools and rest at night knowing you did you absolute best that day to give a guy a great knife. Yes it will not be as good as the one you make tomorrow, but tomorrow is another day.

One does not need to spend a lot of money to do this, I have WAY more equipment than anybody would ever need to make a good knife and even I never went into debt building any part of my knife making operation, I just realized when it would cost much less to spend some money.

Most of what is in my lab does little to make the knives, and no knifemaker needs a lab. The reason I started the whole mad scientist gig was because I got tired of folks whizzing on my head and telling me it was raining. The market certainly wasn't capable of weeding out the B.S. so I decided to let the steel speak for itself. My operation is more like a CSI lab than a heat treating facility, but some of the facts gathered are invaluable for making my knives.

* Metallurgical or heat treating texts; every time I think I have found a decent book by a knifemaker they always have to include at least one page that effectively counteracts any of the good ones .

 

[Kevin R. Cashen]

Thank you Kevin and Mete. I am a total neophite IMO, and your guidance is incredibly valuable to me. Sounds like in order to get into spheroidizing I've got to get a GOOD heat treat oven. I'll start saving my pennies.

If you are stock removing you don't need anything for spheroidizing since msot steels will come from that mill that way. Forging is different, as soon as you heat it up the first time all the was done at the mill is gone. The best use for the oven is austenitizing at a known temperature, but if you really want to do isothermal type operations or spheroidizing you will want a oven capable of "rampable programing" .

 

[Matthew Gregory]

* Metallurgical or heat treating texts; every time I think I have found a decent book by a knifemaker they always have to include at least one page that effectively counteracts any of the good ones .

Which, of course, brings us full-circle and once again places the onus on you, my friend!

These forums are an invaluable tool. If you can dedicate the time to examine the posts, determine which individuals should be lent credibility, re-examine the posts, divine the pertinent information, start to reconsider who you were lending credibility, refer back to the previous posts, reevaluate the pertinent information, find that you've got the whole thing wrong, start over with the fundamentals, reread all the old books you have, conclude that they're based on conjecture and witchcraft, return to the forums, reread the posts on spheroidizing annealing, forget what you read, relearn it, confuse Ac1 for Ac3, spin in circles and spew vomit all over the drapes in the office...

...well, then, you can understand why someone really needs to write the next generation of reference material - so that it can be accessed in a timely fashion, and discussion can bloom from the one set of facts, rather than anyone and everyone's opinions!

I once again humbly offer my services (in any capacity with which they can be used)to anyone willing to reach for that chalice, although the choice for my champion was made quite a while ago!

 

[hardheart]

Mr. Cashen, perhaps best for another thread, but what are your opinions on individual knifemaker heat treats versus production facilities? Is batch treating better or worse than home grown work, on the average (the range & std deviation would probably be pretty large for custom work). A default position for many is that custom knives are all around better because of attention to detail, but your post does bring into question a critical component of the process of making a knife perform.

I see many posts here by makers who do seem to invest in equipment and education for appropriate processes, but is that the rule or the exception if one were to go down the list of exhibitors at a show?

 

[Kevin R. Cashen]

Which, of course, brings us full-circle and once again places the onus on you, my friend!...

Matt, you will be happy to know that I am in the process of putting things into motion and setting a course for myself that will make the eventua completion of a book almost inevitable. In order for me to complete something I often need to manuever it so that I have little to not choice.

 

[Matthew Gregory]

None of us differ from that trait, Kevin. It's only through repeated bludgeoning that I really finish anything. When we spoke last, one of the first things you mentioned was the possible commencement of such a text... or, at least, you insinuated as much at Harley's, and I kind of knew it... but you also know that subtlety is NOT one of my strong suits!

I better be in on the proofreading - I may not grasp what you're talking about, but I sure as hell know what the sentence structure ought to be!

Hope all is well with you, my friend... can't wait for Ashokan!

 

[Kevin R. Cashen]

Mr. Cashen, perhaps best for another thread, but what are your opinions on individual knifemaker heat treats versus production facilities? Is batch treating better or worse than home grown work, on the average (the range & std deviation would probably be pretty large for custom work). A default position for many is that custom knives are all around better because of attention to detail, but your post does bring into question a critical component of the process of making a knife perform.

I see many posts here by makers who do seem to invest in equipment and education for appropriate processes, but is that the rule or the exception if one were to go down the list of exhibitors at a show?

Hardheart, many have been at this longer than I but I have been in this business for over a quarter of a century now, and I am convinced now more than ever that the overblown reputation of the custom made knife is based solely on our preconceived notions of anything labeled "custom". While on the other hand, anything labeled "mass produced" immediately brings the words "lesser quality" to mind. Each manufacturer, whether production or custom, needs to be judged on an individual basis.

For some reason the single custom maker gets away with playing by different rules than the factories. If a factory advertised that they made their blades out of any scrap they could find and heat treated them by quickly heating them "hot enough" to toss into the vat of liquid that they proudly proclaimed they got for free after McDonalds was done with it... well we would all see $2 Taiwanese or Pakistani blades as a step up from such junk. Yet if some joker is doing the same by himself in the back of his garage, the results are works of art assumed to have functional qualities beyond all others ! (fun or hobby knives are just fine by me, but we are comparing with products from commercial firms here)

The custom maker doing them one at a time does have the advantage of more attention to details, but what good is it if they have no idea what those details are or no ability to control them. I am not sure if it is a good thing to be able to say "I personally heat treat every blade, one at a time, so that I can assure every one is as half-@$$ed as it can possibly be."

Most of the factory blades that have disappointed me were victims of bad design or poor steel selection, not heat treating. Many would have taken and held an excellent edge if the mass production process hadn't necessitated an atrocious edge geometry with lunky secondary bevels quickly ground on at the end of the assembly line. But I would take their heat treatment over 75% of the nonsense custom makers practice.

Many of the excellent heat treatments of factory knives are also now seen as inferior to the miserable internal conditions in custom knives since the P.R. machine has established soft, sub-par heat treatments as the way to achieve top performance in a plethora of abuses that require ductility instead of, heaven forbid, strength or actually taking and holding an edge while cutting something .

As for your question about the number of those who even care whether they nail a heat treatment or not, just look at any forum on the internet and see the number of people who say they don't need any fancy steel or tools, their motor oil and lard "works just fine", they don't have a need to know what the steel is since they have been happy with old files, lawnmower blades or any other scrap they can shape into a knife for many years, they look at heat treating spec sheets, written by the people who made the steel, like it is an unnecessary burden that the establishment is scamming us with. And these determinations are based upon the fact that sharpened metal skated a file and cut a soft material, or dead soft steel actually deformed when bent! Imagine that!

If anybody who has actually learned what "martensite" is and how it is made were to go back and re-read the standard reading for bladesmiths they would be a little less impressed and would quickly realize how small of a percentage of folks manage to make it out of the woods, considering it is the established wisdom in the field.


*I apologize if the tone of this post comes off as a little acerbic, but I read many, many things written on a half a dozen forums on the net and only decide to bother posting in around 10% of them, but eventually I get a belly full of stuff that even a whole bottle of Tums can’t handle and I tend to unload in one post. Forgive me if my pressure relieving gives anybody else some heartburn in the process.

 

[Matthew Gregory]

I am not sure if it is a good thing to be able to say "I personally heat treat every blade, one at a time, so that I can assure every one is as half-@$$ed as it can possibly be."

I thought about asking to use this for my signature line, but instead I think I'll just get it tattooed on my butt.


I think that a better way to title this thread would be "Why quench during thermal cycles?" rather than 'triple' anything... for whatever reason, the knifemaking world seems obsessed with doing things three times. Frankly, I'd rather learn how to do it once - and right - the first time!

I'll admit, though, that metallurgy seems to get more intimidating as I learn more of it, as if the learning curve is an increasingly steeper slope. It's threads like this that keep the stuff fresh in my mind. I know that you and many others may get tired of repeating this stuff to use neophytes, but you're not allowed to stop... at least until we need to replace your stomach lining!

Back to the topic! At what point does the law of diminishing returns become significant in grain size reduction? I'm aware that it will vary from steel to steel, application, etc., but is there a way to generalize something like this without digging a hole? Am I going to get a pounding for even asking such a feeble question?

 

[fitzo]

Ah, I think, in this age of manufactured words, "acerbicizing" is periodically both apropos and necessary!

Great post, Kevin. It provided me both wisdom and humor for the day. Thanks. :thumbup:

 

[mete]

Mr.Purple, three times normalizing is the practical limit. Hardenability drops [need faster quench].And of course just the time and fuel used to do it more .The properties you would get with smaller grains wouldn't be improved much either.

 

[Any Cal.]

So the problem is this.

If Maker A is using equipment that gives him an adequate heat treat, and Maker B is using equipment and knowledge that let him come close to dead on for the HT, who will ever know?

If Maker C is advertising a super steel that outcuts what A and B are using, and has an adequate heat treat routine, how many will bother buying from A or B?

My questions are only so you understand what I am trying to say. Even if a HT is nearly perfect, if there is no public awareness of the difference, it might as well not even exist. As Kevin mentioned, PR takes precedence. Just because someone expects more from a custom, does not mean that they will get it. Just because they expect more does not mean that they will ever know if they received it.

I am not trying to take anything away from the importance of the discussion, but am trying to see, from a business standpoint, as if I was the business owner, what difference it would make. Not the difference between used motor oil or Parks, but the difference between a common routine and one with the right control equipment and data.

 

[Matthew Gregory]

I am not trying to take anything away from the importance of the discussion, but am trying to see, from a business standpoint, as if I was the business owner, what difference it would make. Not the difference between used motor oil or Parks, but the difference between a common routine and one with the right control equipment and data.

From my own personal perspective, the difference only needs to be that I know the blade I have just made is made up to the best of my ability, and also that I know why it is. It's a question of ethics for me, and also one of personal interest in what I'm doing. I'll admit, the concepts are intriguing, so it's certainly less boring than for most.

If the ethics aren't of concern, and the performance changes are not recognized or acknowledged by the business owner, caveat emptor
. Perception is reality, though, right?

The industry I'm in is quite similar in this regard (as I suspect all are), in that the better portion of consumers have no interest in truth, they prefer their own views fed back to them to reinforce their belief. That market is generally predatory rather than mutually coexistent with their respective consumers... however, there exists a very small market for 'discerning' customers that might be looking for, well, better. Even that market is preyed on, as Arthur C. Clarke's law of technology holds true here, as well ("Any sufficiently advanced technology will be perceived as magic."), nevertheless the percentages of BS fall rapidly at this level, and the "super x" has less effect on the audience.

I guess it might be as simple as "The Matrix", and which pill one chooses to swallow, red or blue?


This reply is not meant as an indictment of you in any way, by the way, Any Cal. I get why you're asking the question, and I think it's a pertinent question. I just thought I'd offer my measly input.


Holy cow, was this post coherent to anyone, or was I just going a little 'stream of consciousness'?