Jay Fisher's New Web Page on HT & Cryo

interesting stuff really, I do have a question about this part :
"Some elements are added to these steels (like vanadium) that help to create initialization nuclei for grains to grow, creating a finer grained steel. There is continuous, ongoing research in the microscopic grain precipitation field, with new alloys, new combinations, and new reactions over every horizon. What an exciting time to be alive!"

Is this to say that vanadium helps to create smaller grains and thus more grain boundaries, does this translate directly to wear resistance? What role does RC hardness and tempering have on Vanadium's effect on the alloy?
 
Hi, Tim.
It seems that carbide growth, precipitation of carbides from the carbon in the interstitial spaces, needs to start somewhere. This is mainly in tempering of martensite. Carbides have to grow, or be kicked off to form initialization areas. Vanadium, evidently, has the structure atomically and molecularly to encourage this. I'm guessing it has to do with the bonding arrangement of the atom and electrons, etc. Add to that that vanadium carbides are extremely hard and thus wear resistant, much more so than iron carbide, and chromium carbide, and vanadium definitely increases the wear resistance of steels. As far as grain size, this isn't something you have control of, apart from just correctly processing the steel per manufacturers white papers and data sheets. It is true that with more grain boundaries, microscopic crack propogation is discouraged, and with larger grain, crack propogation is increased. In a general way, in old school fracture examination after hardening, this is why at a break, the appearance of a clean, uniform, fine-grained structure means you're at least close to the mark, and a large, crystalline facets mean you're not. But don't confuse this for microscopic and submicroscopic grain structure, you'll need some serious apparatus and lapping and etcing procedure to see that. And some studies are sub-microscopic! A knifemaker only has to process these steels as recommended to get the best structure possible, and the recommendations come from the steel maker.
For the Rockwell hardness, it depends on what you, as a knifemaker, are shooting for. This is something that is gained through experience, making many knives and having them used in the field. Also, by using a variety of alloys, you'll discover just what are the limitations of each one, for there is no ultimate alloy. What a maker shoots for in tempering specifically depends on the steel type, the grind geometry, the overall structural geometry of the knife, and the intended use. As I've said on my site, I've had professional chefs request two identical boning knives, one at 55HRC for a springy feel, and one at 61, so it's stiff and more wear resistant. I've always believed that balance in each knife must be considered.
Thanks for the great question!
 
Sorry I missed this thread .
Ben we're discovering and inventing things in metallurgy all the time ! I'm still learning even as a retired metallurgist, still fascinated !
Jay, " sub-microscopic grain size " ? Electron microscopes work at around 1 million power ! Please explain .
timos, vanadium doesn't reduce grain size but rather inhibits grain growth.
 
I am just delving into this heat treat process in detail, so there are many many terms that I am having trouble finding a definition for. Initialization Nuclei ...that term alone sent me off reading about quantum computing for about an hour yesterday (I forgot just about everything I read already).
I get that Jay Fishers delivery of info is a bit polarizing but it certainly does get the brain going, Im asking waay better questions after having read all that. Maybe

Ok maybe i should start more at the beginning. here is a noob sort of question. In metallurgist speak "precipitate" means what?
 
Replying to METE: Sub-microscopic is the term I've read frequently, used in studies where a standard traditional optical microscope was used to examine crystalline microstructures. So, yes, an SEM is referred to in studies as being used to examine "sub-microscopic" structures. I suppose a more accurate term might be "sub-optical-microscopic," but all of the references I read use the term "sub-microscopic." From what I understand, there were developments only in the last decade or two that allowed a more frequent, economical way to study these structures, and it is from these fairly recent developments, we are able to understand more of what goes on in these materials and treatment. There are some references to this very development that changed the thinking about Trootsite and Sorbite, for instance.
It is truly an exciting time to be alive, when great developments can not only be experienced, but learned about by tradesmen, craftsmen, and artists, as well as the scientific community.
 
Timos: a great starting reference would be from the official organizations that sponsor and regulate activities and education in this field, and ASM (American Society for Metals, a professional organization for materials scientists and metallurgists). Type this into your search engine: "ASM Fundamentals of the Heat Treating of Steel" you'll see a basic PDF document on the subject.(sorry, I have no way to directly link it in this medium). By using the same term without the "ASM" you'll see plenty of official organizational documents and learning resources on the subject. It's really fascinating, because the neat thing is that you can use what you learn in your own creations.
 
timos , the common definition of "precipitate" is in the hardening process of 'precipitation hardening ' where a secondary compound is formed which strengthens the metal . One of the basic strengthening mechanisms .Secondary hardening of tool steels , cryo [ formation of the small eta carbides ], are two often spoke of these days. Importantto understand these things.

Jay, I graduated in 1965 when we were limited to optical microscopes at 1000 power.A couple of years later we have electron beam microscopes at 100,000 !! A HUGE change , rewrite the books , throw out incorrect theories !!! Now we have about 1,000,000 including videos of dislocations interacting with precipitates ! WOW
Please try to use up to date terms. Difficult at times but necessary ! Been there done that ,HA, HA !

Called back as I was leaving so I'll continue.....Precipitation starts on something like an existing precipitate, dislocations ,grain boundaries, impurities etc,. They grow from there .When first formed the particle [wedged into the lattice] strains the lattice. This is called " cohesion ".It's important as it strenghtens the metal . As the particle grows with time and temperature that cohesion is lost. This can be seen on the hardness/tempering temperature curve of secondary hardening.
When hardness starts to drop ,so does cohesion ! You are then left with just particle strengthening.
Some steels such as 17-4 PH , that PH tells you the primary strengthening mechanism.
So size and distribution of the particles is important .
 
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Jay and mete, thank you both for taking the time to asnwer my Qs...I will read up on that ASM material.

-tim
 
mete said:
timos , the common definition of "precipitate" is in the hardening process of 'precipitation hardening ' where a secondary compound is formed which strengthens the metal . One of the basic strengthening mechanisms .Secondary hardening of tool steels , cryo [ formation of the small eta carbides ], are two often spoke of these days. Importantto understand these things.

Jay, I graduated in 1965 when we were limited to optical microscopes at 1000 power.A couple of years later we have electron beam microscopes at 100,000 !! A HUGE change , rewrite the books , throw out incorrect theories !!! Now we have about 1,000,000 including videos of dislocations interacting with precipitates ! WOW
Please try to use up to date terms. Difficult at times but necessary ! Been there done that ,HA, HA !
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Hey, METE. Sorry, I was using the exact definition for sub-microscopic: "too small to be seen by an ordinary light microscope." I thought that was clear.
 
It's dreadfully unfortunate that you would repost another maker's deleted post, Mr. Fisher. Salem intentionally removed it, and obviously for a reason. Whatever smearing of your character you perceive in it was removed when he deleted it, and returned when you re-added it. Truly unfortunate.

I think too many get wrapped up in their perception of 'truth' in this field, although this field isn't any different in this respect than any other field - certainly not in my experience. It's important to remember that, regardless of how much we research something, we're all still limited by the field of our own vision. Humility is probably the best course of action, and likely the only way genuine dispersion of legitimate information can be achieved. After all, the same folks you're stating are liars can make many of the same claims of anecdote experience that you are! Dangerous grounds, for sure...

Hope everyone can take a step or two back from this and ponder a little.

Also, two identical knives will exhibit the same degree of 'flex' regardless of hardness, until they reach their point of deformation or fracture. An rc55 blade won't be any 'flexier' than an identical blade at rc60, unless you mean that it's been pushed to the point of deformation of breakage.
 
Jay, I just tried to find a phone number for you, but it appears as though you intentionally don't have it listed. If you're interested in speaking with me, please email me at. I'd love a chance to chat with you.
 
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JayFisher said:
Now, about your comment about flex, after making thousands of knives, I will clearly state that if you take two nearly identical (because absolutely identical is not possible) blades, and harden and temper one to 55HRC, and another to 60HRC, you'll see that the softer one flexes more than the harder one. So I don't know what you mean.
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Jay, I think it is a semantics or terminology issue, here. The elastic modulus for any given steel, regardless of heat treat, remains the same. Hardness dictates how the steel will perform once the elastic limit has been reached. As quenched, full hard steel will fracture and catastrophically fail... Tempered martensite will resist deformation but eventually break... While fully annealled/unhardened steel will readily deform past the elastic limit without much additional force. The scientific fact remains that they all have the same elastic limit. The only variable is the material's cross-section, as I understand it.

Most of us see it as increased "flexibility" when in reality it is bridled(tempered) "strength".
 
Rick Marchand said:
Jay, I think it is a semantics or terminology issue, here. The elastic modulus for any given steel, regardless of heat treat, remains the same. Hardness dictates how the steel will perform once the elastic limit has been reached. As quenched, full hard steel will fracture and catastrophically fail... Tempered martensite will resist deformation but eventually break... While fully annealled/unhardened steel will readily deform past the elastic limit without much additional force. The scientific fact remains that they all have the same elastic limit. The only variable is the material's cross-section, as I understand it.

Most of us see it as increased "flexibility" when in reality it is bridled(tempered) "strength".
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Hey Rick. Yep, correct.
What I was trying to illustrate is that if you temper the same geometry of blade at 55, it will have more apparent flexibility than if you left it at 60. That's why you really can't support a boning knife at 60-62, it will snap. I guess I wasn't clear enough.

After talking to several people, I realize that I had my say, and now I'll delete my posts. I don't want to get embroiled in endless argument, it will go nowhere and no opinions will be changed. Guys can read what they like, believe what they like, and do as they please, and all I ask is for the same respect I give others, by not calling people names and insulting personalities or personal traits.

To those of you who read this and think that something is to be learned or is of some value on my website, thank my clients, they are the real performers, and I will continue to maintain and offer my opinion and understanding on my site, one of the largest in the world of its type. If you think there is something to be learned there, you are welcome.

If you can't stand what you read there, or don't like what I make, please do seek out the knifemakers whose works you do like, and offer them your patronage. No matter who is hand-making knives, it's a lot harder than it looks to do it well, and that does deserve respect.

Happy New Year!
 
Hi Jay,happy new year to you and yours.I believe I read in your article that you sometimes do a cryo quench in between tempers.I read a while back on the hyper free blades website explaining benefits to basically all stainless steels. By the way I only do what you describe as a shallow cryo (dry ice).Curious if you have any thoughts on this?Any extra conversion? Thanks,Lu
 
Lu1967 said:
Hi Jay,happy new year to you and yours.I believe I read in your article that you sometimes do a cryo quench in between tempers.I read a while back on the hyper free blades website explaining benefits to basically all stainless steels. By the way I only do what you describe as a shallow cryo (dry ice).Curious if you have any thoughts on this?Any extra conversion? Thanks,Lu
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Happy New Year, Lu.
Yes, I do deep thermal cycling between tempers, but it depends on the steel alloy type. You'll need to do some background research on this and call your steel supplier or manufacturer for the exact recommendation. Since some steel suppliers aren't always open with this information, in a basic way, you can do your own studies and tests, to see if you notice any difference. I do in mine, but it depends on your setup and the economy of this. Keeping the cooling medium stored and/or cold while tempers are going on can be a problem, since all of this needs to take place without undue delays. However, deep cyrogenic cycling between tempers does contribute to cyclic conversion and thermal conditioning that I describe at this link in most high alloy hypereutectoid and stainless steels. And it makes sense to do it if you can.
If you are using dry ice, there is a large variability of temperatures of the bath, and this is based on the actual temperature of the dry ice, and how you can maintain that temp after sublimation. Time is a big factor, since cryogenic quenching needs a good long soak, since the carbide precipitation and transformations are sluggish. This also depends on the steel type. Most cryogenic processing companies will shoot for a balance of economy vs. cold time, but, of course, I'm not shorting because of the cost; I want the best possible result for my clients. Your method may differ. Other concerns with dry ice method are thermal shock to the blades during stabilization, uniform distribution of temperature in the bath, and safety and storage of the particular liquid medium used. I suppose that in the long run, mechanical SCT and DCT liquid nitrogen would cost less, once the setup is paid for, but again, that depends on your situation and amount and type of knife blades made and processed.
Thanks for the great question!
 
Hi Jay,thanks for the response.I always follow the manufacturer heat treat data sheet,but also uderstand that these aren't specifically for knives.Lots of good info lately here on bladeforums from you, Devon T. and others.It's a real treat when the real pros share hard earned info.Thanks again,Lu
 
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