How to Thermal Cycle Knife Steel

Experiments and recommendations on how to process steel after forging. Hardness and toughness measurements along with images of the microstructure. Some controversial conclusions!
Article that goes with this video with more details and sources cited: knifesteelnerds.com/2021/08/2...
Knife Steel Nerds Patreon: / knifesteelnerds
Knife Engineering Book: knifesteelnerds.com/2020/07/2...

[@christiannasca3520]

What I normally do when watching KZbin videos is to speed up the playback speed to 1.25x in order to save time and not get bored. When watching your videos I sometimes have to do the opposite and slow down the playback speed to 0.75x, because otherwise I cannot keep up processing the incoming information and end up with information overload. And that is although I am a mechanical engineer and have studied the basics of metallurgy. Yet, watching your videos is like trying to drink from a fire hose. 😂 Nevertheless, thank you for your excellent work and sharing the results on KZbin. I still prefer information overload of scientific data providing real insight into details over insignificant or boring or even plain wrong information offen found in other sources online. 👍🏻🤓🙋🏻

[@OUTDOORS55]

Just bought your book and cant wait to get into it! Glad you are out there taking some of the mythology out of heat treating Science. 👍

[@thomasmarais5008]

A buddy of mine mentioned that I'm a bladesmith to a metallurgist he knows. The metallurgist said that bladesmiths often have an understanding of metallurgy that is similar to how a peasant would understand astronomy as a kind of magic. I've interacted with enough older smiths who are so tied to tradition and over-emphasise "experience" (really they've just entrenched a completely incorrect understanding of the mechanics of metallurgy) to know that this is harsh, but true. I'm happy you're out here providing a great resource to set the record straight

[@DapperDan42]

I can see that I will need to watch this video multiple times to really get some of the concepts, awesome information!

[@jprall44]

Love to see videos dumbed down slightly and show the specific process for each steel. i.e. just 1095 forged and material removal start to finish step by step. I believe that it would be super valuable as a go to resource for all knife makers and bladesmiths!

[@DS-sw6ol]

25x

[@highplains7777]

What, you're not a genius either!?!

[@highplains7777]

All joking aside, I appreciate being challenged. Keep trying and you will get it.

[@WildFerment]

Thanks for normalising our understanding of these issues. There’s a lot of misinformation thermal cycling it’s way through the forums. You’ve quenched the hard and brittle keyboard warriors with your balanced wisdom; they should be annealing before you… If you were a steel I reckon you’d cut 1000mm on the catra and still notch 50ft-lbs, all at 65RC ;)

[@fishdude666ify]

This is BY FAR the most appropriately named KZbin channel I've ever come across. You're welcome.🤓

[@zgi5950]

In the ocean of misinformation and internet hoaxes, your work stand out as a floating island of truth and knowledge. Thank you very much! As always!

[@Richard-nb4iv]

Just as I almost got through watching this video my wife heard a noise at the front door. Amazon just delivered a copy of the book Knife Engineering written by Dr. Larrin Thomas. Coincidence? I think not!

[@dmw_cutlery]

i love everything you do mr tomas .... i listen and religiously read everything you post .... thank you for your work

[@prenticegoodwin3522]

Thank you so much for taking the time to make these videos. With this channel as well as your book I really feel like I have a really good start to becoming a good knife maker one day. ( saving up for a good belt grinder now)

[@larsmils2994]

Awesome video, can't wait to get the book in the mail one of the days. Good to see someone apply science to the knife making world, instead of guessing this or that works best, and having sub par hard to repeat results.

[@ranger5281]

Bravo. Nice research, full of useful and ultimately time saving lessons for knife makers, especially those who forge. Patreon certainly is an inspired creation.

[@yojimbosecurityninja]

Love it. Keep the videos coming. I can't get enough!

[@RobanyBigjobz]

Complicated topic made easy to understand and underpinned with real data. Outstanding :)

[@mannsdan]

Super interesting and practical! Thanks Larrin!

[@KieranShort]

Whoa. This is an extraordinary bit of work. Thanks for sharing!

[@londiniumarmoury7037]

Thanks for this video Larrin.

[@StuartSmithHandForgedKNives]

this video needs more views. Very useful info.

[@anatineduo4289]

I need to listen to this again :)

[@nils-ph3zs]

Great video larrin :) I also really loved the myth-debunking podcast!

[@micgalovic]

Good video, plenty of great information. Great mustache too!

[@anthonyhinton583]

Awesome video man, you could change the name to Knife Steel Wizard!!! This is next level information.

[@davebrookbank4831]

Thank you I learned a few new things, great info.

[@Barryhatchet]

Thanks so much for the He Man shout outs! #NerdPride. Can you do some videos on how steel changes during hammer forging?

[@jensdavidsen4557]

Greetings Larrin, Can you share your thoughts on the relationship, (if there truly is one), between normalizing cycles and warpage and / or cracking? It was always my understanding that the goal of normalizing was to reduce one's chances of ending up with a warped or cracked blade after quench...alas...I forged and ground what I believed to be a gorgeous 1065 camp knife - spent quite a few hours on it, normalized it 4x by simply heating and leaving on my anvil then quenched in water and cracked the piss out of it (5 cracks on the spine and 3 on the edge and it was mildly warped). Really thought a plain jane 1065 blade could be water quenched. Fun part was that at least one of the cracks occurred when it was in my bare hand already cool enough to safely handle...I felt and heard the crack. The blade was forged from a section of a bit of mystery scrap steel - I forged and ground a section flat, took it to my lab (I'm an analytical chemist) and analyzed on our Spark OES and identified it as a textbook example of 1065. You have my sincere thanks for all you do, - Jens

[@Barryhatchet]

Can you do a video on hamon on blades?

[@alex_8-D]

Great video but I need to read more before I can fully understand it but that's a good thing

[@kenh8979]

Larrin, you do great with your research and I thank you very much. I so have a question, When you test "as received" and it seems that's as good for HT'ing as when the steel is normalized, wouldn't that depend on the condition the steel is when received? If it's heavy speriodized or as AKS says of all their steels, "read for HT"?

[@KnifeSteelNerds]

Almost all steel comes from the manufacturer in a spheroidized condition. There may be some variation in the exact microstructure but AKS isn’t getting steel in a special condition that other suppliers aren’t getting.

[@kenh8979]

@@KnifeSteelNerds Thank you for your response.

[@JiiJiitalo]

Great video again! Takes some time for all the information to dissolve to brain 😅

[@h2tym]

Another excellent video. What are your thoughts on “stress relief cycles” (for 1084) performed after machining and prior to quenching? Does this process actually prevent some warping during the quench as it is advertised?

[@KnifeSteelNerds]

I briefly covered stress relief cycles in the written article

[@h2tym]

@@KnifeSteelNerds thank you Sir! I have it in my inbox and will read it.

[@davidherald9895]

Great video - I have a question: at ~18:17 you have a slide on the screen - is this supposed to be for Annealing in a furnace? - I am confused by that slide because you have a heading on the top about thermal-cycling in a forge and then mention normalizing but cooling in vermiculite, and at the bottom of the slide you say "best condition for final austenitize in a furnace".... is this slide correct? Great video - I really appreciate the work and education!

[@KnifeSteelNerds]

Looks correct to me. It is a process for thermal cycling in a forge if you are going to do the final austenitize in a furnace.

[@captaincaed]

I guess I'm curious to know how larger/smaller grain sizes affect the ability to sharpen a knife edge at different grits. For example, if your desire was a very fine 6-8k razor edge, would grain refinement be desirable? If you favored an edge that's "toothy" for produce, does that microstructure have an impact? Love reading and watching!

[@KnifeSteelNerds]

No the grain size wouldn’t really affect the sharpening behavior unless the toughness is very bad. Carbide structure affects sharpening though.

[@captaincaed]

@@KnifeSteelNerds cheers! That helps put another detail from the video into context.

[@Regdiggs]

I have a question maybe you can answer it. Im currently making a knife out of a piece of flatstock i have had for years. Dont know where i got it or what it is but i discovered it hardens by accident. After forging the knife and running a couple test pieces through the thermocycling, hardening and tempering process even though the tempering process did soften the steel enough that it can be worked and wasnt so brittle the grain structure remained the same as it was right after the quench why is this?

[@miltoncarroll2385]

What happens when you do a partial hardening in oil, and then switch to water other than the possibility of explosion

[@Null_76]

Awesome video. So much great information. I have a question though. So often I see heat treat soak times given in ranges (e.g. 10 to 20 minutes). Is this dependent on thickness or the condition of the steel (or both)?

[@KnifeSteelNerds]

For 1/8” low alloy steels that are annealed (either by you or the manufacturer) 10 minutes is good to shoot for. Thicker stock needs more time. Steels with some alloy in them like 52100 might be better with 15 minutes. Generally using 15-20 minutes or even longer doesn’t hurt anything if it’s annealed.

[@Null_76]

Thanks for the quick reply. Would you recommend heat treating some samples of a chosen steel (for sake of argument 52100) and testing the hardness when working out such details? I know there are many variables and it may open a huge can of worms. Bottom line should a kingmaker shoot for the process that produces the highest hardness before tempering? Thanks.

[@KnifeSteelNerds]

@@Null_76 Measuring hardness is always a good idea. But no the maximum hardness isn’t necessarily a sign of optimal properties. Toughness for example is also an important property to balance with. I have an article on heat treating 52100 that you might find helpful.

[@Null_76]

I will check it out. Thanks so much.

[@Null_76]

@@KnifeSteelNerds I have spent a lot of time on your site and there is one topic I have not seen discussed. Perhaps I wasn't looking hard enough. Namely the topic is the cleanliness of the steel. I have heard you mention it on you tube, but not really in depth. Again, I think 52100 is a good steel to discuss here, because I have heard several times that the quality varies quite a bit. I have some 52100 stock from New Jersey Steel Baron which I have heard is good and I splurged on some Carpenter VAR stock. I would assume that the vacuum remelted stock would have more reliable and reproducible properties. Do you think it is really worth the investment (2X price) to by the cleanest steel? Or does it even matter that much for knives? Thanks.

[@michaelbrauer3351]

Dr. Thomas, May I check my understanding? For steels commonly used in bladesmithing (specifically 5160, 1095, W2) and using a forge and magnet, you suggest quenching from a normalized state correct? Does this mean that the DET anneal is performed before the normalization? I am just confused as to where the DET anneal should be in the process. Thank you so much in advance!!

[@KnifeSteelNerds]

If heat treating with a forge the DET anneal would not be performed.

[@michaelbrauer3351]

@@KnifeSteelNerds I feel like that kid in class who doesn’t shut up, ha! Could a DET anneal be performed, but not as part of the heat treating? Or do you mean no DET anneal all together? My understanding is that if the piece needs to be machined, drilled, etc. then annealing makes life easier. Normalizing would then produce a pearlitic structure that will readily austenitize during final heat treatment and use of a magnet. Am I off my rocker? 🤔 Thank you so much!

[@tobiasb154]

Is there such a thing as differential wear resistance? Like a katana has differential hardening, or how case hardening creates a carbon gradient that is differentially hard, is there a way to have one side of a steel wear faster than the other?

[@garethbaus5471]

It is probably easier to do that with a coating, titanium nitride might be a good choice for that. If you are doing it DIY it is fairly easy to coat one side of the steel with carbide, although you won't necessarily get a very clean edge.

[@michaelwhalen1907]

You broke my brain....😵‍💫

[@michaelwhalen1907]

honestly though its a fantastic video jammed with useful info for knife makers.

[@micktheweld]

If a steel held at the correct austenitizing temperature but for longer than the recommended hold time can this result in grain growth?

[@KnifeSteelNerds]

Yes though if it’s at the right temperature the grain growth is so slow it doesn’t really matter.

[@Barryhatchet]

What are your favorite “tough” steels? If you were going for extreme toughness in a blade, what would you use?

[@KnifeSteelNerds]

5160, 8670, Z-Tuff/CD1, AEB-L, etc.

[@Barryhatchet]

Thanks for the reply. I don’t see much in Z-Tough out there but I would love to try it. I have Z-Max thanks to Spyderco but that is on the other side of the spectrum but I hope Spyderco would make some more mules on the tougher side like Z-Tough.

[@MountainFisher]

@@Barryhatchet How hard do you want your knife to be? I used to make axes out of S5 an old oil/water quench shock steel that is much tougher at HRC 59 it is 158 foot lbs. on the Charpy Notch test Dr. Thomas uses. For axes I had to use water to quench because it is so thick, but the few knives I made I quenched in a fast oil and tempered them down to 60 hard, but above 59 hard toughness drops sharply, but it's still tougher than most steels at 80 ft. lbs. S7 isn't as hardenable as S5 btw. Problem with acquiring S5 is knife suppliers do not carry it, though some do carry S7 for throwing knives or tomahawks, but it can be hardened to 59. S5 only comes in 3/8ths or thicker from some steel suppliers, but it's inexpensive.

[@josephb3024]

Question, for simple carbon steels is it best to after forging normalize (at your recommended temps) is twice good? Then two? Grain refinement cycles, and then DET annealing once, or because you of the DET do I not need to do any grain refinement cycles? Thanks in advance!

[@josephb3024]

Also does multiple DET anneals have a benefit or is once enough?

[@KnifeSteelNerds]

One normalize, one anneal

[@josephb3024]

thank you so much for clarifying. Regards Joseph.

[@gjDOnBBQ]

When talking about "air cooling" for normalization, I'm sitting right now at about 20F. If I heat my oven to 1550F, and allow the blade to heat up then shut it down and open the door, will I negatively affect the normalizing due to the ambient air temp??

[@cubee2006]

Cooling in a furnace would be a “furnace cool” rather than an air cool. The 20F won’t affect things too much.

[@BenjaminHodgens]

I’m not a dumb man but I have a difficult time extracting actionable information from these highly dense videos. It’d be nice if you could make summarization statements for us midwits.

[@Noone-rt6pw]

I need some understanding before this, it's too fast. Is there a book?

[@KnifeSteelNerds]

knifesteelnerds.com/2020/07/22/new-book-knife-engineering-steel-heat-treating-and-geometry/

[@willcreasey8516]

Why do aluminum plates work for a plate quench? Why not copper plates, steel plates, etc? I’ve always wondered how this works, even though it may not be a question of steel it is still a technique and I wonder how it works.

[@KnifeSteelNerds]

it can be other plates but aluminum is common

[@ernestobarrameda6464]

How bout hardening the blades 3 times does it make better knives

[@timrodriguez1]

🤠👍

[@billmanning8806]

My grandpa was 'a Neil.' And my grandma always wanted to take him to the Texas state capital where I think she hoped to 'Austin-it-tize' him. Is this what you're talking about? 🙂

[@bdgackle]

More data is required on the laser thermometer: WERE you dying of hypothermia?

[@einundsiebenziger5488]

Shouldn't the thumbnail say "one cycle" instead of "once cycle"?

[@KnifeSteelNerds]

Only if you want it to be grammatically correct

[@einundsiebenziger5488]

@@KnifeSteelNerds Shouldn't grammar be treated with the same respect as the heat of steel😉?

[@thewalnutwoodworker6136]

You best spent 20 minutes of your life watching a nerd talk about graphs!

[@garysumlin8355]

To much for a dummy like me damn

[@rgrslim]

Dr's

[@ricksmit2239]

Dude i commend your knowledge. but all you are doing here is throwing around data and numbers which only SHELDON could pick up at the speed at which you go through all the data. i am half way in. and all you really gave was data. making people quit before or if any helpful advice arrives... I understand there might be a time issue for videos on youtube, i don't know i'm not a creator. but this would have been one of the best videos if you just took your time and did things. Could have been a college course video. But like i say i commend your knowledge.