To me, metallurgy is the most interesting part of making a knife. I became fascinated with it when I read _Steel Metallurgy for the Non-metallurgist_ which I've now read three times.
Walter Interesting stuff, more details than i need, but still good. Question: do you have a blade that "bent" out of shape in an experiment like you describe, it would be interesting to actually see how does it look to better understand what you just spoke about, I'm sure many audiences will agree with me: "a picture worth a thousand words". Thanks.
My problem is he skips the middle ground to me...he goes from basics the shot I know straight into gobbledygook and I'm like dude the page before was elementary school this page is doctorate level..
Walter I'm a total novice on steels but find the subject fascinating. I thought you did a great job of describing not just the bainite but the tempering process in general. I have a great understanding of this world now. And like everyone else who has ever watched Kill Bill I & II, would love to own an invincible blade. LOL Thanks, you communicate well.
Note that bainite has a huge temperature/time range that will create it. If you use one temp/time combination, you change to bainite at a high temperature and a different combination means that you change to bainite at a low temperature. However, one time/temp combination also changes other properties of the steel (size of the individual grains, what happens to the grains that do not form bainite (you never get 100% of any crystal due to local changes in components (carbon. iron. other elements) in the mixture), etc. When things like shock resistance are important, these small variations can have severe effects on the final product. For example, in low-carbon chromium-nickel steel used to make high-strength armor plate, it was found that if the hardening/tempering technique caused any bainite to from at the higher temperature portion of the process ("upper bainite"), the steel became excessively brittle, but the same amount of bainite formed at a low temperature ("lower bainite") did not cause any significant loss of toughness against a high-speed impacting projectile. So, bainite is much more complex in its properties than most other crystal forms in steel, in that its formation history is more important, not just what is in the final product.
Thanks for the video. You have been a great inspiration. Just brainstorming an idea: I have not tried that yet, but I have been wondering for some time whether a visible hamon on spring-steel blade could be achieved by carbonitriding the edge. Carbonitriding is comparatively easily done (although it costs some time and a lot of heat), the steel thus made is very hard and has different colour than carbon steel and it loses hardness less due to tempering. Maybe such edge would be harder than martensitic edge, therefore it would be much more prone to chipping, but maybe not.
4 years late, but a big question: What steels can you easily create Bainite with (as you refer to a minimal range). I'm thinking of a skeleton spine Damascus (ribs and all) to keep things in order with a spine cut and wrap. Yes, you are at best you are looking at a 3-7% increase in strength and non-malleability, but the combinations are literally unimaginable.. I'm going to try it.
Wait. Did I just watch a 20 minute video of Walter Sorrels talking about steel metallurgy? Hell, I did, and didn't even notice until it was over :D Really interesting.
Now THIS is the kind of video many of us subscribed for in the first place! Well done. Thank you. My one point of contention is that you barely scratched the surface. I would've absolutely loved a longer video where you really delved in and nerded out. I'm sure many others would've also. Giving the quick layman's explanation first followed by lots more technical theory and practical experience/anecdotes shouldn't be so hard to follow considering the type of audience you attract. We all want to learn from your greater experience after all. Food for thought.
Interesting but just not enough nerd out haha... there is also the approach of a partial bainite for virtually no loss of HRC but 10% (approx~) extra toughness for water jet etc blanks throughout the stock in general rather than pre forged or pre ground blades with the goal of differentially hardening with the bevel/spine of differing thickness,, so rather than holding for a full bainite for a long hold time the heat cycle at the appropriate temperature is shorter to achieve/encourage a hint of the bainite properties without loss of the initially desired HRC to the detriment of the blade.
Hey, Walt! I gotta say the thumbnail for this video was misleading. It showed you at the anvil with a hot piece of steel beating it to fit and form. Then I clicked the video, and there was a surprising lack of ringing steel and roaring forge. Then I watched the whole video... This friggin' rocked. While I was mildly disappointed to not see the afore mentioned hammering and forging, I learned something about metallurgy, phase diagrams, and the structure of steel that I didn't know. It was honestly fascinating, and until now, I didn't even know what bainite was. Like my Pop used to say, "any day you learn something new, that day wasn't wasted." Thanks for vid, Walt. You rock!
Have you made any larger blades or swords out of 3V? On paper, it seems like a great choice if you wanted a more usable blade with edge hardness over 55 hr (and semi stainless, abrasion resistance, etc.) Should be able to run it at what, 58+ hrc assuming the geometry is correct? My understanding is that 3V is very tough when it comes to the Charpy impact test.
Awesome video. I *am* one of those guys that enjoys nerding out over these types of topics. And while I do not expect to do any heat treating myself, I very much enjoy understanding the process. I appreciate how you presented it. In this case "the weeds" were critical to understanding the challenges of getting to a bainite micro structure in the steel (versus martensic steels and perlite structures). Thanks so much for your videos.
Nerd Alert, like music to my ears. Listening to fellow knife and tool makers talk about metallurgy is always refreshing and informative, no matter how much I think I know about it.
I'm not a blade smith, but I find the art of heat treating , fascinating. ( i'm a nerd ) . You never explained the properties and qualities of Bainite, All in all very informative , thank you
bainite is a bit weird, and how easily it can be explained really depends on your knowledge of metallurgy. I can't remember the exact properties of bainite but it should be tougher than pearlite with almost the same hardness/strength.
Bainite is harder than austenite/pearlite (course and fine) but not as hard as martensite. When you clay a blade you are putting a very hard edge on and a softer more ductile pearlite backing. Bainite will be more ductile than martensite, but less than pearlite. Swords being long and taking heavy shock, the bainite would allow more give or allowance before crack, fracture, or failure.
What alloys lend themselves to this type of heat treatment? They'd have to allow you to 1) miss the pearlite nose with a high temperature quench, and 2) reach the bainite phase in a reasonable amount of time.
I don't know too many people with the equipment to properly control the heat long enough to create bainite in their home workshop, but yes certain steels would function better than others depending on the alloying elements. However basically all steels can do this as long as they are held at the proper temperature for the proper time.
This was a great video. You should do more of these. Also don't buy a blade from a small village in America either if you don't know the guy has all the equipment, right!
To make a long story short, went to a 2 yr. college for welding in 1970-71. Metallurgy was part of our curiccullum and now I So wish I would have paid more attention then. :(. Enjoyed the video!!
Would a Bainite body for a hatchet or Ax be good? Thinking of having the tough side for camp hammering and such but good hard edge to retain the sharpness. Not really clear on what a Bainite process would be good for I guess.
Sorry but I don’t have all the equipment to make a knife laying around in my garage. I just want to know what kind of steel I want in the knife I’m looking to buy.
That was really interesting Walter. Your "buyer beware" bit regarding q. controls and overall knowledge is good to know. I imagine there are plenty of cowboys out there in this field.
So if I understand it correctly, there are a *number* of ways of making a soft spine with a hard edge. You can clay it up and make a hamon, you can go through a longer process to produce bainite, or you can forge with more than one metal (the "taco shell" comes to mind) and just use a softer metal for the spine. Am I getting the proper gist?
Wouldn’t choosing a bainite over pearlite spine increase how ridged the spine is and therefore increase the stress on the martensite edge during impact? From what I understand the bainite won’t deaden as much force/resonance as the pearlite. The resonance could compromise the martensite edge essentially causing cracking or chipping. The use of differential hardened steel is usually to keep a sharp edge while allowing the softer metal core to absorb the impact, reducing the chance of breaking.
Given the number of times Howard Clark was mentioned, and the dismissal of the utility of bainite swords, I wonder how many of Howard Clark's swords were included in the evaluation?
Why wouldnt one just make a full martensitic blade and differentially temper it? For example put the cutting edge in water and heat the spine with a blowtorch until it has a spring temper (blue color), then get it out and let the temper rise to the edge until it is straw color. Or invent some process to do the same thing more precisely with expensive tooling. For real where are the drawbacks with this? With my rather minimal knowledge I cant find any...
The procedure you describe can be done and afaik is done, even on double edged swords - you can heat the center to blue and the edge to straw, thus retaining sharp and hard edge and springy blade. But there is a snag - you cannot thus make a visible hamon. W S. describes here a process how to make a blade that has springy spine, hard edge and a hamon.
I personally for most steel go with a martensite / pearlite differentially heated blade as you suggest. However the bainite can only be achieved with long controlled heating time. Not something you can do with a blow torch. The idea behind bainite is you are getting a combination in a sense of the martensite / pearlite. The overall blade with be less forgiving than than the pearlite, however it will be harder and stronger, if you can keep some martensite in for edge, then you would have a sharp, and potentially depending on the steel characteristics stronger blade. You would only want this for swords however, smaller knives you would want them fully martensitic and tempered.
Minor point. Just for completeness (not a criticism). Pearlite is a structure of ferrite and cementite. Specifically, it is a eutectoid structure if you really want to go nerd out.
Also, you probably don't want to dip a sword into liquid lead. Liquid metal embrittlement can cause a lot of problems. The lead can essentially wick inbetween the grains and cause the serious mechanical problems. Really neat if you want to go down a nerd rabbit hole.
Heh, not just the guys, but us gals enjoy this sort of thing, too! You did an excellent job explaining the different types of crystallization, thank you for that!
I took an introductory class in materials science, specifically metals, as part of my mechanical engineering curriculum, and I have to say it was super interesting. It seems like it can get really really complex trying to predict rates of diffusion through some kind of "distance" and at some temperature, which is what drives all of these relationships between the different phases. Also it seems like you gets really complex when you start talking about crystallographic planes and whatnot. It was definitely an interesting class.
Some misinformation in here for time and temperature. Bainite (founded by baine in the 40’s) bottom formation temperature for hyper eutectoid steel .7 10 series is 531 f. This is for lower bainite. Upper bainite has a bottom line of 575 f. As far as time 30 seconds ferrite plates form, after that carbide enrichment begins to occur. Beyond 30 minutes nothing occurs. When the introduction of chromium occurs in ratio above 13% the windows change dramatically.
Love the metallurgy talk, I have many books on the subject that target blade making, and I found this video very interesting and easy to follow topic! New to bladesmithing but it's taking over my life!!!
Gave away to a friend a Japanese katana I owned because it would bend occasionally from cutting thru pine slats or larger branches. Just assumed, apparently mistakenly so, the blade was improperly made.
Now I'm wondering, what exactly goes down on the microscopic level when a knife dulls? and what would it take theoretically for a knife to never dull / be unbreakable? This science is needed.
It’s a matter of iron and carbon atoms being gradually removed from the edge of the knife, rendering it less effective. As for making a knife unbreakable/never having to sharpen..you’d have to make the edge super hard and extremely tough; unfortunately to make the edge harder, you sacrifice the toughness of the material. That’s why blades are tempered, to extend their durability and make the edge less prone to chipping, cracking, and breaking. Even adding extra metals into the alloy can make the metal more brittle, depending on the concentration of aforementioned metals..but the change in the alloy also depends on that concentration, so you’d have to balance out what you want when selecting your alloy.
i remember in year 12 engineering studies we learned that nasa and others have been trying to grow a single "grain" or crystal of steel large enough to be useful, and that it would be extraordinarily tough. i dont remember the specifics but it was supposed to be an extremely good material. though i think they've given up so maybe it turned out to not be all that great, or it was just impossible
Walter Soros, hopefully you'll read this. I bought an L6 round stock to make a war club years ago. I didn't know what I was getting, and it was on sale so there you go. Could you cover this topic on all steel war clubs? I was planning on shipping it out to get professionally heat traated anyway. Thanks.
Thanks for the video. Much respect for your knowledge, but just didn't get your explanation with that steel ruler jumping all around the image. I see 4 color-coded time vs. temperature plots. It would be good if you would walk through each of the four plots. It looks like bringing the temperature down from 700+ along plot 1 gives you a martensite/austenite mixture, along plot 2 gives you martensite, along plot 3 gives a bainite/martensite mixture, and along plot 4 gives you a fine pearlite steel. Is that the correct idea? Also, you didn't really explain the "highway" in the middle of the diagram. Lot of info packed into that diagram!
I'm conjecturing the swords made by the Gill family in Birmingham in the 17 and 1800's may have had a high proportion of bainite- not sure, molten lead quench and temper? Still, these had an incredible reputation for toughness.
Walter, could you heat your oil to 225 degrees then place the blade directly into a sandbox that was heater and held at 450 degrees. You could leave it in there for days if you wanted. Might give you the hardened blade you're looking for. I've never seen a heated sandbox but it couldn't be hard to make. Use electric coils under the metal box and measure the temperature. Just saying...
Wow. In the weeds was the most accurate statement in the video. You know Howard does a class called "understanding the ites" that you probably should take.
How about super clean L2 CrV Low carbon Mod 0.51% Carbon? I'm buying this Hot rolled Steel designed for making drop forged Tools, From a local Supplier, And it makes Nice Tomahawks and Hammers.
Excellent information. it sounds like a lot of effort is taken to give carbon steel the bend resistance of spring steel. If thats the case, why not just use a mono-tempered 5160 instead? it seems like a much more reliable and less labor intensive way to achieve the same "truck spring" results. (the only loss is the hamon) Granted, i'll accept that bainite is certainly a valid demonstration of the versatile capabilities of simple carbon steel. But otherwise it seems like the same results can be had easier.
Its a valid point but us metal people like to try the new steels as there have been some major new offerings in the past decade or so, price is important as well. 5160 makes a good sword, as does 52100 - sorta 5160's beefed up brother, but deep hardening and with the alloying elements, yes you would lose the traditional hamon. Howard Clark and Walter are both Japanese sword aficionados' and the hamon is very important for the traditional sense. Also some steels are no longer easy to get like L7, 1084, many of the tool steels have come and gone in various versions. Some steels are hard to get in some countries or area's, some smiths have more practice with certain steels and a comfort level. But yes aside from the passion to experiment with metals - your mono steel 5160 is a valid point.
Man, I love your videos even if you are a Clemson fan, but watching this one was "fraught with difficulties". That graph reminded me of something from my Advanced Macro Economics class many years ago. Hahaha!
If I air Quinch S7 Tool steel From 1700f to 450f "Surface temperature 🌡️" And immediately Temper it at 450f for 5Hrs in a preheated Kiln. Wouldn't that make S7 bainite? I have some amazing S7 punchs, Drifts and hot cuts I heat treated in my Kiln.
can you make a new katana build using a Orikaeshi Sanmai assembly of the sword?? It can really put a test on your forging skill... and it will be very interesting since in youtube has not much video showing them forge this way traditionally...
I'd like to see a video of how you film your videos, I am only twelve years old and I started making knives about a month ago, I though about making a knife making Chanel for beginners and I dint really know how to get good videos. I really like your videos and want to get some ideas in how to film videos. I'd like if you wrote back to me or something to know if you could. Thanks for the great videos. Also do you think 80CRV2 is good for a fighting knife? Thanks!
Could you make a sword perfect by forge welding three steels, really high carbon for the edge, spring steel center, and mild steel back? Maybe 01, 5160, then mild steel.
Those first ten minutes were AWESOME, and spurred some questions - so, (of course sticking to that chart as a reference), the colder you get, the more martinsite you get. Now, I've never forged metal in my life. I just watch you and Forged In Fire. One thing that always seems to kill contestants on that show is dunking the hot blade in water. It turns the structure to sugar and makes the metal super brittle. So, obviously quenching too cold too fast is also bad. Would you be willing to explain that a little further?
quenching too fast puts an enourmous amount of stress on the steel and causes it to set up microscopic cracks absolutely everywhere. i dont know who said it turns to sugar, thats dumb. but there are some steels that get good results by putting it in liquid nitrogen immediately after the initial quench
From my metallurgical past studies - The concept behind the sugar comment, is that the grains would be so large you could see them with the naked eye like sugar. The smaller the grain boundary when the atomic structures realign after heat treating will be far strong than large grain boundaries. This is a temperature vs time calculation. Also the carbon content does play a role as more carbon less temperature needed, etc.... Once the steel is heated over (I believe its 727 degrees) then you are into the austenite phase. If it is not hot enough, then you still have just your iron and carbon atoms in their solid form that hasn't converted to austenite yet. So you cannot begin to form pearlite, martensite, bainite, etc... by quenching as the solution will not be converted fully to Austenite. If you heat and hold the temperature too long, then the grains boundaries (segments of atoms of carbon, iron, and alloys interstatial and there is another one I forget substituation? Vacancies occur and atoms switch around) will grow, when the atoms convert to pearlite / ferrite/ martensite/retained austenite. This growth allows for fracture much easier as it removes the distance force has to move as its like a clear highway instead of road block, rerouting around the smaller grains. Hope that helps, also the liquid nitrogen or dry ice and acetone - get under 112 deg pretty much is what is needed, is often used more with the heavily alloyed steels like stainless sometimes air hardening carbon steels as well. When you oil quench, or more often forced air plate quench, you often cannot hit the full 100% Martensite curve. Martensite will continue to nucleate and form after quench if it is brought well below a certain temperature. So the dry ice or liquid nitrogen treatment is to remove some of the retained austenite and transform it to martensite, making the blade harder (strong but more brittle which is why a temper is still required afterwards) and in essence a better cutter! Geez didn't mean to write a book but I hope that helps some with these questions.
what would be the result if you took a long narrow piece of steel and forged it into a single edges blade that you bend in the center to an acute angle such as [^] then once the blade is edge up the one side and down the other side of the tight bend, set the temper and then bend/tension the folded blade until the two halves cross each other and pin them with a bracket () i asked this to a blacksmith and he said i might have something that messed with harmonics, possible improving the cutting potential against softer materials....?
I wonder what exactly would happen if one were to produce a double edged blade, but applying a hamon to the edge while keeping the center "spine" open to heat, then soaking it around 250-300 degrees over a 20 hour or so period, then reversing the process to treat the edge.
I think you'd be doing a lot of work for nothing. I assume your intention is to produce a bainite core to the blade, and then try and preserve the bainite when heat treating the edge? When you did the HT on the edges, the rest of the blade would come back up to austenitic temperatures as well, which would mean the bainite structure was lost. This is all assuming I understood your intention correctly of course... Ernest Sheffield, there shouldn't be any grain growth. Grain growth happens at much higher temperatures, simply soaking for a long time at a lower temperature would not have a similar effect.
Why not just use tempered Martensite for your edge and blue the spine? Honestly, if you wish to cut something hard like metal using a conventional Japanese sword, better use an angle grinder. 😂 Tools really have their respective builds, venturing to a new usage invites innovative modifications not only with the heat and cold treatment, but as well as with the steel formulation and tool geometry.
That was a great and very interesting subject. I tend to nerd out on everything to do with mathematics and the sciences and admittedly archeology and history.... so overtly nerd away buddy!
NERD ALERT!!! Well said. I can't make a knife if I wanted because of my high sensitivity to light (I'm legally blind) but I love these videos. It is awesome to hear a metal master try to bring such a complex theme to us the mortal kind. I did find a reference that may help other non-nerds get a grip on what it means. These guys say that BAINITE is pound per pound lighter and stronger than Titanium.... this is their actual posting "Flash® Bainite is a patented process for heattreating steel that yields the Strongest, Most Ductile, Lean Alloyed, Readily Weldable, Least Costly Maximum Strength METAL known to man. A50 tensile ranges from 1100 to 2080MPa (160-302ksi) while total elongation up to 10-11% is not uncommon. Flash 500 at 1900MPa and 10% elongation exceeds titanium-6Al-4V's strength to weight ratio making it pound per pound stronger at only 56% the volume. Flash 500 is 10% the cost of Ti-64." This was found at www.flashbainite.com
I recently just got my hands on some, I haven't tried forging yet not even sure it can be forged well, need to study more was going to do a blade with stock removal first / try to nail the heat treat and see what happens.
These are rather new steels. process has been around, but not cost effective. Still rather expensive, but they have developed a way to force more nitrogen in than the steel would by nature hold .
To me, metallurgy is the most interesting part of making a knife. I became fascinated with it when I read _Steel Metallurgy for the Non-metallurgist_ which I've now read three times.
by j.d verhoeven??
That's the one.
Walter
Interesting stuff, more details than i need, but still good.
Question: do you have a blade that "bent" out of shape in an experiment like you describe, it would be interesting to actually see how does it look to better understand what you just spoke about, I'm sure many audiences will agree with me: "a picture worth a thousand words".
Thanks.
Sam Harper sounds like my next book.. Cheers!
My problem is he skips the middle ground to me...he goes from basics the shot I know straight into gobbledygook and I'm like dude the page before was elementary school this page is doctorate level..
One of the best, simplistic overviews of metallurgy and application to knifemaking i’ve seen. Great job on this Walter....fascinating.
Great video as always.
A minor nitpick:
Ferrite has carbon in it, it is around 0.01w% or less depending on temperature history. But it is there.
This was a hell of a good explanation. Lots of easy to follow extra tidbits added in.
Always love these vids Walter. Awesome info.
Walter I'm a total novice on steels but find the subject fascinating. I thought you did a great job of describing not just the bainite but the tempering process in general. I have a great understanding of this world now. And like everyone else who has ever watched Kill Bill I & II, would love to own an invincible blade. LOL Thanks, you communicate well.
Note that bainite has a huge temperature/time range that will create it. If you use one temp/time combination, you change to bainite at a high temperature and a different combination means that you change to bainite at a low temperature. However, one time/temp combination also changes other properties of the steel (size of the individual grains, what happens to the grains that do not form bainite (you never get 100% of any crystal due to local changes in components (carbon. iron. other elements) in the mixture), etc. When things like shock resistance are important, these small variations can have severe effects on the final product. For example, in low-carbon chromium-nickel steel used to make high-strength armor plate, it was found that if the hardening/tempering technique caused any bainite to from at the higher temperature portion of the process ("upper bainite"), the steel became excessively brittle, but the same amount of bainite formed at a low temperature ("lower bainite") did not cause any significant loss of toughness against a high-speed impacting projectile. So, bainite is much more complex in its properties than most other crystal forms in steel, in that its formation history is more important, not just what is in the final product.
Friday 5 x 4.56. During my early days in metallurgy, those time/temperature/conversion charts were the Bain of my existence. ; )
"bain" lol
nerd out, f*** yeah!
Walter, I love that you go into the metallurgy. Wish you did it more often. Also, love watching you beat on some steel.
Thanks for the video. You have been a great inspiration.
Just brainstorming an idea:
I have not tried that yet, but I have been wondering for some time whether a visible hamon on spring-steel blade could be achieved by carbonitriding the edge. Carbonitriding is comparatively easily done (although it costs some time and a lot of heat), the steel thus made is very hard and has different colour than carbon steel and it loses hardness less due to tempering. Maybe such edge would be harder than martensitic edge, therefore it would be much more prone to chipping, but maybe not.
4 years late, but a big question: What steels can you easily create Bainite with (as you refer to a minimal range). I'm thinking of a skeleton spine Damascus (ribs and all) to keep things in order with a spine cut and wrap. Yes, you are at best you are looking at a 3-7% increase in strength and non-malleability, but the combinations are literally unimaginable.. I'm going to try it.
great video! over my head a bit but i was on the edge of my seat the whole time! thanks so much Walter.
Nerding out about steel is awesome.
Wait. Did I just watch a 20 minute video of Walter Sorrels talking about steel metallurgy?
Hell, I did, and didn't even notice until it was over :D
Really interesting.
Good info...... really shows the depth of your knowledge
Well done, on a tough subject! Placement of Nerd Alert was EPIC!
Now THIS is the kind of video many of us subscribed for in the first place! Well done. Thank you. My one point of contention is that you barely scratched the surface. I would've absolutely loved a longer video where you really delved in and nerded out. I'm sure many others would've also. Giving the quick layman's explanation first followed by lots more technical theory and practical experience/anecdotes shouldn't be so hard to follow considering the type of audience you attract. We all want to learn from your greater experience after all. Food for thought.
Thanks for the view point. Always like to hear your take on things sir.
Interesting but just not enough nerd out haha... there is also the approach of a partial bainite for virtually no loss of HRC but 10% (approx~) extra toughness for water jet etc blanks throughout the stock in general rather than pre forged or pre ground blades with the goal of differentially hardening with the bevel/spine of differing thickness,, so rather than holding for a full bainite for a long hold time the heat cycle at the appropriate temperature is shorter to achieve/encourage a hint of the bainite properties without loss of the initially desired HRC to the detriment of the blade.
Could you possibly do a video about h-13 steel for tooling? Thank you and awesome video!
Hey, Walt! I gotta say the thumbnail for this video was misleading. It showed you at the anvil with a hot piece of steel beating it to fit and form. Then I clicked the video, and there was a surprising lack of ringing steel and roaring forge. Then I watched the whole video...
This friggin' rocked. While I was mildly disappointed to not see the afore mentioned hammering and forging, I learned something about metallurgy, phase diagrams, and the structure of steel that I didn't know. It was honestly fascinating, and until now, I didn't even know what bainite was.
Like my Pop used to say, "any day you learn something new, that day wasn't wasted."
Thanks for vid, Walt. You rock!
Have you made any larger blades or swords out of 3V? On paper, it seems like a great choice if you wanted a more usable blade with edge hardness over 55 hr (and semi stainless, abrasion resistance, etc.) Should be able to run it at what, 58+ hrc assuming the geometry is correct? My understanding is that 3V is very tough when it comes to the Charpy impact test.
Awesome video. I *am* one of those guys that enjoys nerding out over these types of topics. And while I do not expect to do any heat treating myself, I very much enjoy understanding the process. I appreciate how you presented it. In this case "the weeds" were critical to understanding the challenges of getting to a bainite micro structure in the steel (versus martensic steels and perlite structures). Thanks so much for your videos.
Absolutely interesting the whole way through, thanks Walter. Feel free to do a deep dive into metallurgy sometime, I'll be there.
Nerd Alert, like music to my ears. Listening to fellow knife and tool makers talk about metallurgy is always refreshing and informative, no matter how much I think I know about it.
I'm not a blade smith, but I find the art of heat treating , fascinating. ( i'm a nerd ) . You never explained the properties and qualities of Bainite, All in all very informative , thank you
bainite is a bit weird, and how easily it can be explained really depends on your knowledge of metallurgy. I can't remember the exact properties of bainite but it should be tougher than pearlite with almost the same hardness/strength.
Bainite is harder than austenite/pearlite (course and fine) but not as hard as martensite. When you clay a blade you are putting a very hard edge on and a softer more ductile pearlite backing. Bainite will be more ductile than martensite, but less than pearlite. Swords being long and taking heavy shock, the bainite would allow more give or allowance before crack, fracture, or failure.
What alloys lend themselves to this type of heat treatment? They'd have to allow you to 1) miss the pearlite nose with a high temperature quench, and 2) reach the bainite phase in a reasonable amount of time.
I don't know too many people with the equipment to properly control the heat long enough to create bainite in their home workshop, but yes certain steels would function better than others depending on the alloying elements. However basically all steels can do this as long as they are held at the proper temperature for the proper time.
easiest steel to form bainite is 4340. Look at its t-t-t graph and it will make sense.
How can I be sure that an L6 blade
I bought is really bainite tempered?
No need to apologize for not dumbing things down. There are some people interested in this who don't need to see non-stop sword to ice-block action.
A great explanation of what happens during a successful quench - I can see me showing this to a lot of people. Thanks, Walter.
I'm certainly not a nerd but this video had great info that enabled me to understand blade metallurgy much better. Much appreciated.
Nice to know, and excellent way of explaining things.
Fascinating. Want to learn more about Damascus blades.
Thanks you! Answered alot of the questions I had...
Pls explain carbides formation and distribution in lower bainite phase in austempering.
This was a great video. You should do more of these. Also don't buy a blade from a small village in America either if you don't know the guy has all the equipment, right!
Very enlightening. You are very articulate, thanks so much.
Mr. Sorrells is one of the best sword makers and a real class act. Thanks for the video sir very educational.
To make a long story short, went to a 2 yr. college for welding in 1970-71. Metallurgy was part of our curiccullum and now I So wish I would have paid more attention then. :(. Enjoyed the video!!
Would a Bainite body for a hatchet or Ax be good? Thinking of having the tough side for camp hammering and such but good hard edge to retain the sharpness. Not really clear on what a Bainite process would be good for I guess.
Sorry but I don’t have all the equipment to make a knife laying around in my garage. I just want to know what kind of steel I want in the knife I’m looking to buy.
That was really interesting Walter. Your "buyer beware" bit regarding q. controls and overall knowledge is good to know. I imagine there are plenty of cowboys out there in this field.
So if I understand it correctly, there are a *number* of ways of making a soft spine with a hard edge. You can clay it up and make a hamon, you can go through a longer process to produce bainite, or you can forge with more than one metal (the "taco shell" comes to mind) and just use a softer metal for the spine.
Am I getting the proper gist?
Great Job. Your content never disappoints. Thanks Walter
Wouldn’t choosing a bainite over pearlite spine increase how ridged the spine is and therefore increase the stress on the martensite edge during impact? From what I understand the bainite won’t deaden as much force/resonance as the pearlite. The resonance could compromise the martensite edge essentially causing cracking or chipping. The use of differential hardened steel is usually to keep a sharp edge while allowing the softer metal core to absorb the impact, reducing the chance of breaking.
While it would reduce chance of bending, wouldn’t it increase stress on the cutting edge?
Might as well nerd out. Everyone else is selling $30 T-shirts. I'd rather have the knowledge than the T-shirt!
Eric Snyder but what about SWOOOORRRDSSS?
I really enjoyed this video. Thanks!!!
Good sir your Japanese swords are already magical. No fairy dust required.
Given the number of times Howard Clark was mentioned, and the dismissal of the utility of bainite swords, I wonder how many of Howard Clark's swords were included in the evaluation?
Am I detecting some Clark Envy from Mr. Sorrels?
@@oldekline in my opinion HC blades are better ..
Why wouldnt one just make a full martensitic blade and differentially temper it? For example put the cutting edge in water and heat the spine with a blowtorch until it has a spring temper (blue color), then get it out and let the temper rise to the edge until it is straw color. Or invent some process to do the same thing more precisely with expensive tooling. For real where are the drawbacks with this? With my rather minimal knowledge I cant find any...
The procedure you describe can be done and afaik is done, even on double edged swords - you can heat the center to blue and the edge to straw, thus retaining sharp and hard edge and springy blade. But there is a snag - you cannot thus make a visible hamon. W S. describes here a process how to make a blade that has springy spine, hard edge and a hamon.
chstoney ah well makes sense! Thank you
I personally for most steel go with a martensite / pearlite differentially heated blade as you suggest. However the bainite can only be achieved with long controlled heating time. Not something you can do with a blow torch. The idea behind bainite is you are getting a combination in a sense of the martensite / pearlite. The overall blade with be less forgiving than than the pearlite, however it will be harder and stronger, if you can keep some martensite in for edge, then you would have a sharp, and potentially depending on the steel characteristics stronger blade. You would only want this for swords however, smaller knives you would want them fully martensitic and tempered.
Minor point. Just for completeness (not a criticism). Pearlite is a structure of ferrite and cementite. Specifically, it is a eutectoid structure if you really want to go nerd out.
Also, you probably don't want to dip a sword into liquid lead. Liquid metal embrittlement can cause a lot of problems. The lead can essentially wick inbetween the grains and cause the serious mechanical problems. Really neat if you want to go down a nerd rabbit hole.
Heh, not just the guys, but us gals enjoy this sort of thing, too! You did an excellent job explaining the different types of crystallization, thank you for that!
I took an introductory class in materials science, specifically metals, as part of my mechanical engineering curriculum, and I have to say it was super interesting. It seems like it can get really really complex trying to predict rates of diffusion through some kind of "distance" and at some temperature, which is what drives all of these relationships between the different phases. Also it seems like you gets really complex when you start talking about crystallographic planes and whatnot. It was definitely an interesting class.
TLDL version: The good quality knife you already have is good quality.
what does TLDL stand for?
Some misinformation in here for time and temperature. Bainite (founded by baine in the 40’s) bottom formation temperature for hyper eutectoid steel .7 10 series is 531 f. This is for lower bainite. Upper bainite has a bottom line of 575 f. As far as time 30 seconds ferrite plates form, after that carbide enrichment begins to occur. Beyond 30 minutes nothing occurs. When the introduction of chromium occurs in ratio above 13% the windows change dramatically.
Love the metallurgy talk, I have many books on the subject that target blade making, and I found this video very interesting and easy to follow topic! New to bladesmithing but it's taking over my life!!!
proof is in the pudding, we want to see destructive tests with Bainite swords.
Gave away to a friend a Japanese katana I owned because it would bend occasionally from cutting thru pine slats or larger branches. Just assumed, apparently mistakenly so, the blade was improperly made.
That's why I like a shorter blade. In my mind a ko katana should be harder to bend from a wild cut gone wrong.
Now I'm wondering, what exactly goes down on the microscopic level when a knife dulls? and what would it take theoretically for a knife to never dull / be unbreakable? This science is needed.
It’s a matter of iron and carbon atoms being gradually removed from the edge of the knife, rendering it less effective.
As for making a knife unbreakable/never having to sharpen..you’d have to make the edge super hard and extremely tough; unfortunately to make the edge harder, you sacrifice the toughness of the material. That’s why blades are tempered, to extend their durability and make the edge less prone to chipping, cracking, and breaking. Even adding extra metals into the alloy can make the metal more brittle, depending on the concentration of aforementioned metals..but the change in the alloy also depends on that concentration, so you’d have to balance out what you want when selecting your alloy.
Imagine a saw blade with the teeth bent out away from the spine.
HamTheBacon Make a Power Wrought Blade.
The blade/material you are looking for is called "Unobtanium", it is found on the planet in the movie " Avatar" !! Lololol
i remember in year 12 engineering studies we learned that nasa and others have been trying to grow a single "grain" or crystal of steel large enough to be useful, and that it would be extraordinarily tough. i dont remember the specifics but it was supposed to be an extremely good material. though i think they've given up so maybe it turned out to not be all that great, or it was just impossible
is it possible to differentially temper a sword thats already been monotempered?
I can't see why it wouldn't be.
Interesting question though.
Walter Soros, hopefully you'll read this. I bought an L6 round stock to make a war club years ago. I didn't know what I was getting, and it was on sale so there you go. Could you cover this topic on all steel war clubs? I was planning on shipping it out to get professionally heat traated anyway. Thanks.
Nerdy, yes, but so, so informative. Thanks, Walter!
Thanks for the video. Much respect for your knowledge, but just didn't get your explanation with that steel ruler jumping all around the image. I see 4 color-coded time vs. temperature plots. It would be good if you would walk through each of the four plots. It looks like bringing the temperature down from 700+ along plot 1 gives you a martensite/austenite mixture, along plot 2 gives you martensite, along plot 3 gives a bainite/martensite mixture, and along plot 4 gives you a fine pearlite steel. Is that the correct idea? Also, you didn't really explain the "highway" in the middle of the diagram. Lot of info packed into that diagram!
I'm conjecturing the swords made by the Gill family in Birmingham in the 17 and 1800's may have had a high proportion of bainite- not sure, molten lead quench and temper? Still, these had an incredible reputation for toughness.
Walter, could you heat your oil to 225 degrees then place the blade directly into a sandbox that was heater and held at 450 degrees. You could leave it in there for days if you wanted. Might give you the hardened blade you're looking for. I've never seen a heated sandbox but it couldn't be hard to make. Use electric coils under the metal box and measure the temperature. Just saying...
Wow.
In the weeds was the most accurate statement in the video.
You know Howard does a class called "understanding the ites" that you probably should take.
Great video. The metallurgy is important to understand.
This is a awesome video. Thank you sir for posting it.
Great video, this answered a lot of questions for me
Like to see presentation on how bainite is formed . development during transformation.
Awesome video! Love the information.
the riddle of steel
Could you possibly make a large blade Bowie knife and show it?
Seems that cold chisels get bainite more easily than swords.
Narrow benefits can sometimes be the difference between life or death,
5160, 1075, and 80CRV2 for swords all day 👌
How about super clean L2 CrV Low carbon Mod 0.51% Carbon? I'm buying this Hot rolled Steel designed for making drop forged Tools, From a local Supplier, And it makes Nice Tomahawks and Hammers.
Great information. I watched this twice. Thanks
Excellent information. it sounds like a lot of effort is taken to give carbon steel the bend resistance of spring steel. If thats the case, why not just use a mono-tempered 5160 instead? it seems like a much more reliable and less labor intensive way to achieve the same "truck spring" results. (the only loss is the hamon)
Granted, i'll accept that bainite is certainly a valid demonstration of the versatile capabilities of simple carbon steel. But otherwise it seems like the same results can be had easier.
Its a valid point but us metal people like to try the new steels as there have been some major new offerings in the past decade or so, price is important as well. 5160 makes a good sword, as does 52100 - sorta 5160's beefed up brother, but deep hardening and with the alloying elements, yes you would lose the traditional hamon. Howard Clark and Walter are both Japanese sword aficionados' and the hamon is very important for the traditional sense. Also some steels are no longer easy to get like L7, 1084, many of the tool steels have come and gone in various versions. Some steels are hard to get in some countries or area's, some smiths have more practice with certain steels and a comfort level. But yes aside from the passion to experiment with metals - your mono steel 5160 is a valid point.
Man, I love your videos even if you are a Clemson fan, but watching this one was "fraught with difficulties". That graph reminded me of something from my Advanced Macro Economics class many years ago. Hahaha!
Great video! Thanks for this. Awesome topic!
If I air Quinch S7 Tool steel From 1700f to 450f "Surface temperature 🌡️" And immediately Temper it at 450f for 5Hrs in a preheated Kiln. Wouldn't that make S7 bainite? I have some amazing S7 punchs, Drifts and hot cuts I heat treated in my Kiln.
can you make a new katana build using a Orikaeshi Sanmai assembly of the sword?? It can really put a test on your forging skill... and it will be very interesting since in youtube has not much video showing them forge this way traditionally...
Thank you.
Would bainite be good to use for the core of pattern welded, Frankish styled swords?
What about authentic wootz steal?
I'd like to see a video of how you film your videos, I am only twelve years old and I started making knives about a month ago, I though about making a knife making Chanel for beginners and I dint really know how to get good videos. I really like your videos and want to get some ideas in how to film videos. I'd like if you wrote back to me or something to know if you could. Thanks for the great videos. Also do you think 80CRV2 is good for a fighting knife? Thanks!
Damn that was interesting. Thank you
Could you make a sword perfect by forge welding three steels, really high carbon for the edge, spring steel center, and mild steel back? Maybe 01, 5160, then mild steel.
not really
Awesome explanation!!!
Those first ten minutes were AWESOME, and spurred some questions - so, (of course sticking to that chart as a reference), the colder you get, the more martinsite you get.
Now, I've never forged metal in my life. I just watch you and Forged In Fire. One thing that always seems to kill contestants on that show is dunking the hot blade in water. It turns the structure to sugar and makes the metal super brittle. So, obviously quenching too cold too fast is also bad.
Would you be willing to explain that a little further?
quenching too fast puts an enourmous amount of stress on the steel and causes it to set up microscopic cracks absolutely everywhere. i dont know who said it turns to sugar, thats dumb. but there are some steels that get good results by putting it in liquid nitrogen immediately after the initial quench
From my metallurgical past studies - The concept behind the sugar comment, is that the grains would be so large you could see them with the naked eye like sugar. The smaller the grain boundary when the atomic structures realign after heat treating will be far strong than large grain boundaries. This is a temperature vs time calculation. Also the carbon content does play a role as more carbon less temperature needed, etc.... Once the steel is heated over (I believe its 727 degrees) then you are into the austenite phase. If it is not hot enough, then you still have just your iron and carbon atoms in their solid form that hasn't converted to austenite yet. So you cannot begin to form pearlite, martensite, bainite, etc... by quenching as the solution will not be converted fully to Austenite. If you heat and hold the temperature too long, then the grains boundaries (segments of atoms of carbon, iron, and alloys interstatial and there is another one I forget substituation? Vacancies occur and atoms switch around) will grow, when the atoms convert to pearlite / ferrite/ martensite/retained austenite. This growth allows for fracture much easier as it removes the distance force has to move as its like a clear highway instead of road block, rerouting around the smaller grains. Hope that helps, also the liquid nitrogen or dry ice and acetone - get under 112 deg pretty much is what is needed, is often used more with the heavily alloyed steels like stainless sometimes air hardening carbon steels as well. When you oil quench, or more often forced air plate quench, you often cannot hit the full 100% Martensite curve. Martensite will continue to nucleate and form after quench if it is brought well below a certain temperature. So the dry ice or liquid nitrogen treatment is to remove some of the retained austenite and transform it to martensite, making the blade harder (strong but more brittle which is why a temper is still required afterwards) and in essence a better cutter! Geez didn't mean to write a book but I hope that helps some with these questions.
Why is your wedding band on the right hand?? Inquiring minds wanna know.. Love the vids!
what would be the result if you took a long narrow piece of steel and forged it into a single edges blade that you bend in the center to an acute angle such as [^] then once the blade is edge up the one side and down the other side of the tight bend, set the temper and then bend/tension the folded blade until the two halves cross each other and pin them with a bracket ()
i asked this to a blacksmith and he said i might have something that messed with harmonics, possible improving the cutting potential against softer materials....?
so in reality you have a wide sword with a hole in the middle? it would be pointless
I wonder what exactly would happen if one were to produce a double edged blade, but applying a hamon to the edge while keeping the center "spine" open to heat, then soaking it around 250-300 degrees over a 20 hour or so period, then reversing the process to treat the edge.
what degrees? degress potato? :D
BL0P0, are you dyslexic?
Elric the Impaler of course you're not ?
If I'm understanding you right, then you would have some major grain growth. But I could be misunderstanding greatly.
I think you'd be doing a lot of work for nothing. I assume your intention is to produce a bainite core to the blade, and then try and preserve the bainite when heat treating the edge? When you did the HT on the edges, the rest of the blade would come back up to austenitic temperatures as well, which would mean the bainite structure was lost.
This is all assuming I understood your intention correctly of course...
Ernest Sheffield, there shouldn't be any grain growth. Grain growth happens at much higher temperatures, simply soaking for a long time at a lower temperature would not have a similar effect.
Why not just use tempered Martensite for your edge and blue the spine? Honestly, if you wish to cut something hard like metal using a conventional Japanese sword, better use an angle grinder. 😂
Tools really have their respective builds, venturing to a new usage invites innovative modifications not only with the heat and cold treatment, but as well as with the steel formulation and tool geometry.
That was a great and very interesting subject. I tend to nerd out on everything to do with mathematics and the sciences and admittedly archeology and history.... so overtly nerd away buddy!
NERD ALERT!!! Well said. I can't make a knife if I wanted because of my high sensitivity to light (I'm legally blind) but I love these videos. It is awesome to hear a metal master try to bring such a complex theme to us the mortal kind. I did find a reference that may help other non-nerds get a grip on what it means. These guys say that BAINITE is pound per pound lighter and stronger than Titanium.... this is their actual posting "Flash® Bainite is a patented process for heattreating steel that yields the Strongest, Most Ductile, Lean Alloyed, Readily Weldable, Least Costly Maximum Strength METAL known to man. A50 tensile ranges from 1100 to 2080MPa (160-302ksi) while total elongation up to 10-11% is not uncommon. Flash 500 at 1900MPa and 10% elongation exceeds titanium-6Al-4V's strength to weight ratio making it pound per pound stronger at only 56% the volume. Flash 500 is 10% the cost of Ti-64." This was found at www.flashbainite.com
very nice! cheers from Brazil!
Awesome video!
There are steels that have almost no carbon in them(0.1%) and use nitrogen instead. Have you used any of them before Walter?
I recently just got my hands on some, I haven't tried forging yet not even sure it can be forged well, need to study more was going to do a blade with stock removal first / try to nail the heat treat and see what happens.
These are rather new steels. process has been around, but not cost effective. Still rather expensive, but they have developed a way to force more nitrogen in than the steel would by nature hold .