Graham - you explain the heat treat process and how to straighten a blade better than anyone I have EVER heard. Thank you so much for sharing your knowledge. I so appreciate you doing that.
Early in the series, when Jason Knight was a judge, he mentioned that if you take the knife out of the oil and it bursts into flames, then it is not sufficiently cooled. And one may notice while watching, how often a bladesmith takes a knife out of the oil, there is a giant and visibly appealing fire ball, and when tested the blade fails by chipping, breaking, or bending.
What a brilliant channel. I’ve been making knives for many years and much of my knowledge has been gleaned from scouring UA-cam. This channel told me in 5 minutes what I figured out over about 5 years from practice, reading and watching.Thank you and congratulations on a brilliant resource.
Hi Joel! Thanks for the lovely comment! Glad to hear the video was of some help! We have lots more really useful things to tackle and myths to debunk so stay tuned! You should check one of our other videos with Graham helping makers: The ONE and ONLY THING you need to get the best grain size ua-cam.com/video/Yv5Xz8rI6Fs/v-deo.html
Awe definitely want some more to this series Graham. I'm sure you can come up wioth some more jewels of information for us Thankyou very much for sharing.
Hi Talabavin! Well, let’s just say we have more about tempering coming next month and also, I am talking to Graham about showing us some of his pattern-welded (Damascus) billets he makes! Thanks again for your comment!
Thanks for explaining why you can straighten right out of quench. I wait until I stop feeling vibrations in my tongs. Will even use a hammer and anvil to straighten right out of quench sometimes. You got almost a minute good thirty seconds. However never tried clamping plate/angle iron right out of quench. Do that in temper but going to give it a try it after quench now.
No problem 👍 thanks for watching again! If you have some interest in watching 'stock removal' knife makers, it may be worth checking out Alfie (Cabin Knives in London) make his own unique 'Botttlenose Knife': ua-cam.com/play/PLFssspwgISv_9BLJOHY3xSk2SpJQxILyy.html
Love it!! Read about this years ago and started stumbling my way through it. learning it costed me a few blades by getting greedy after I got them a little too cold but definitely worth the effort and you get the added benefit of a little bit of self tempering or martempering. Never understood why professional makers don't do this.
@@GemAppleTom may not be the correct name for it but a quick Google search describes a process which is similar to what is happening the heat from the spine(from being thicker)bleeds to the rest of the knife causes it to develop tempered martinsite. Again im no expert so I may be getting some terms crossed up.
@@dmounce5513 Right, got you. Not heard the term but get the mechanism. Probably not a surprise I'd not heard since my background is industrial heat treatment. It sounds like something to avoid for control's sake. I'm not a blade maker (would like to take it up at some point) so can't say how important it is. Intuition tells me it isn't but I'd be quite happy to learn otherwise. Can you use self tempering to avoid needing to temper at all?
@@GemAppleTom Haven't done alot of testing without doing normal tampering cycles afterwards the one Profesional knife maker that I have heard talk about doing this stuff is kevin cashen. He talked about abuse testing one after marquenching and from what I recall was pretty durable if i remember correctly said they threw it at concrete stomped it but finally broke it hitting it with a hammer. I'll try to find my recording of it to make sure im quoting him accurately.
Just because you miss the pearlite start temp that doesn't mean you will be always be fast enough to get to your martensite start temp. If you allow it to cool slowly after missing the knee, you can still hit the bainite start temp and form a bad microstructure.
Only just getting into smithing, so watching a heap of stuff on the subject. Good sensible advice from you guys it seems, keep it coming! Quick question for you, if you had a blade that was hardened and bent but fully cooled, would it be possible to re-heat it up to a malleable enough state for straightening without damaging the martensite structure? Would that have the same effect as straightening while still in the cooling phase, as you describe in the video, or do other things come into play?
If it's cooled down to room temperature it should be fully martensite and straightening before tempering will be a quick and easy way to crack it. Temper first before doing anything. You might get enough ductility back after the temper to straighten. You'd be better asking someone with practical blade making experience, though. The material will remain martenstic until you heat it up enough to normalise or anneal it. But the higher the temperature you temper the more hardness you'll lose and more ductility you gain. (There are a few quirks with some steels but the above is a pretty good rule of thumb to go by)
Love the themes you are on these days! Can you do a episode amout tempering as well? Debunk some og the "bullshit" myths of 5 times 1 hour at different temperatures, and so on?
Multiple tempers can still be necessary for high alloy steels*. Not so much with plain carbon steels. *high alloy steels can contain a large about of retained austenite after quenching. A temper cycle can transform it into untemoered martensute which will require another tempering cycle.
get the data sheets for tempering (yes it's a graph again) and temper accordingly. if it says you need to get to 540°C for 3hrs to reach 57hrc and that's what you are after then you need to do that😂 (just a example)
I would be interested in how to calculate the time needed for tempering, normalising, hardening. The data of the knife steel is a given from the manufacturer (tempering, normalising, hardening temperature), but different size and thickness change the soak time somehow? Because math and science and things?... I don't know. This is the part that I struggle the most with. Would be great if some light could be shad upon this. :)
The rule of thumb for soak times used in industry is; 1/2 hour + 1/2 hour per inch of thickness. Yes, large sections do make things more complicated especially for high temperature cycles. E.g. getting the core to the right temp for the right duration while avoiding grain growth at the surface. Thin sections like blades are quite easy in that respect though have their own problems with distortion.
🤔i have been thinking of how to put this for the last 2 hours and No offence intended and i kinda shocked myself at all but there is a very very easy so obvious way to know when to take your steel out of the Quench media. pull the blade out when the media stops boiling. a lquide Boil's when it has hit the right temperature turn from liquid to gas. Most quench oils vaporize/flash at 176.666667C/350 F with Parks 50 its 135C/275 F and water its 100 C/212F your blade will be at that temperature when it stops boiling (it will still cause the oil. If i recall right Martinsite forms at the speed of sound and I believe its in an unstable configuration that acts like Austinite until it has cooled to Somewhere close to room temperature. so you dont need to count you need to watch and pull your blade out right when it stops boiling...however dont set in on something on one side as that will alter its cooling rate on that side causing a warp. Lock it virtually in a vise or clamp it between plates or boards and let it cool to room temprature.😅 This is so easy and Obvious i feel like i am Trolling you and i am not. IF i am wrong here please tell me and i will delete this as i do not want to contribute to the Myths about heat treating.
Thank you Sir... Good stuff... I recently got some nice aluminum quench plates and have been doing this on all my heat treats and love it although I've had a blade come out with a warp after all albeit slight... I'm assuming from the video that that's not a regular occurrence... Great tip on oil flashpoint too, tyvm for your time...
I use steel plates and clamps. But at the moment i am building something better. A wood working vise with wide jaws, with a steel plate welded to the inside of each jaw. So i can do the same thing that his hydraulic press is doing, but for about $50. I was also considering a hydraulic press, if money is no option, id go that route
If you clamp the knife after the first cooling in oil and then dump the whole clamped steel with the knife into an ice-bath does that almost secure a good hardening or will the ice-water cool it to fast?
Very helpful info and video! Does canola oil ignite at around 450c as well? That’s all I’ve got so if it works the same I’ll try making some sort of press.
Okay, so let me see if I understand this correctly: once you have quenched your blade to the martensite start temperature (quickly enough to “hit the knee” on the TTT chart), then you have some length of time to straighten your blade as needed while the temperature drops and the martensite continues to form. As the martensite forms, the blade gets stiffer and stiffer, and at a certain point*, there’s enough martensite locking the blade into shape that further post-quench straightening is not possible. Is that about right? *I’m guessing that this is somewhere between M50 and M70, depending on how much additional correction is needed.
You're doing the straighten while the material is still austenitic but diffusion has slowed down enough to prevent really rapid pearlite formation (the area below the knee/nose of the TTT curve).
@@jhcc289 You had the jist of it and if you'd done as you described you'd get the practice right but possibly not pass an exam question on it. Proper diagrams make all the difference.
Thank you, @@GemAppleTom. As a non-metallurgist, I’m working hard on understanding the science of what’s going on here, and I appreciate the additional information. However, in the interests of full accuracy, I am compelled to point out that the correct spelling is “gist”!
By cryogenic treatment do you mean cooling down to liquid nitrogen temperatures or lower and holding for 24 or so hours (deep cryogenic)? Or do you mean going to normal freezer temperatures or just a bit lower and holding for about an hour (cold treatment)?
@@GemAppleTom Thanks Tom, I watched a chanel that used liquid nitrogen after "it had cooled down".I would be interested in knowing what it does to the metal and the elements within that metal.
@@brendameech4492 Right... tempering in general first. Apologies if this is telling you what you already know but it might help people who are new. When quenching the idea is to completely transform the steel from austenite to martensite and do it quick enough to prevent any formation of ferrite or pearlite. After quenching you can still have pockets of austenite still present - retained austenite. This is less common with plain carbon steels like 1080 but is a lot more common with stainless and high alloy steels. In high alloy steels the martensite transformation may not even be complete at room temperature. The retained austenite is not very stable however and with a bit of energy can still transform to martensite later. Normal tempering with give back a lot of toughness to the martensite that was formed - just what tempering is meant to do. It can also allow the retained austenite to transform leaving you with a mix of tempered and untempered martensite. You'll need a second temper (and maybe a third if there's still some remaining austenite) to temper that new martensite but you'll also be re-tempering the original martensite. Having the mix of single and double tempered martensite is not always a problem and much better than doing only a single temper and leaving untempered martensite. It's not so much of an issue with low alloy steels - a single temper wI'll do the trick generally.
@@brendameech4492 The idea of cold treatment is drop the temperature low enough that all of the retained austenite will transform to martensite. Then when you temper you shouldn't have to worry about different regions having different properties. This can be done in a home freezer for some alloys. From memory, -20C for 1h was the common industrial spec The benefits of cold treatment are consistency with properties, less distortion - martensite and austenite have different expansions during heating and cooling, saved money on tempering since you can drop one of the steps. (There are some high alloy steels that will still need double tempers but for different reasons). Deep cryogenics is...controversial. You will certainly make absolutely certain that there is no retained austenite at liquid nitrogen temperatures. A bit overkill in my opinion but not wrong and you'll get the benefits of cold treatment. Holding high alloy steel (or any other material according to the websites that sell the treatment) at LN2 temperature for 24+h can have other benefits such as improved wear resistance. But... The industry at the start was plagued by snake oil sales men. Wild claims and explanations that invoked Einstein and such which doesn't bear close scrutiny. The whole idea got a bad reputation. There is sensible research into it now though. (My Dad did one of the earliest actually well put together papers on it and coincidentally a colleague in my first job was looking into it as well.) There are hints in some steels, some of the time that something might be going on but it's a small effect if it's there. Personally I think cold treatment is something that needs to be more widespread. Cryogenics, even if there are benefits, don't give enough of one to be worth it.
i would love to know what happens in greater detail what happens when you quench the steel 50+°C above it's maximum hardening temperature. (yeah, i asked that through Instagram before but maybe that's an interesting topic for other people too. A question to this video: is platequenching with thick aluminium plates and pressured air fast enough to harden carbon steels? maybe in a automatic setup where the air blows like in one of the air hockey tables the second the press closes.
No. Carbon steels require very fast quenching rates. In 1095 for example, to start the martensitic transformation you need to cool around 1000 F in 1 second. You can't do that in air.
Its not fast enough for high carbon, plenty of high-alloy tool steels will plate+air quench though if you're not wanting a full stainless blade. Anything like A2 to A8 series, pretty much all the D-series steels, some of the S-series shock resistant stuff all make for some really tremendous blades if you're looking for a lot of carbon and chromium. Plates are pretty quick, but they're not as quick as a fast-oil and for any of the W1, W2, 1095, 1084 variety of high carbon, low alloy steels you will also need a specific fast oil to attain full hardness out of them- don't go using vege or motor oils on them. The cheap knife straightener is just a woodwork vise with two bits of aluminum or steel plates stuck in them- get your knife quenched for a good 10sec in the oil and in between the plates, clamp down gently and give it a minute. Wont cost you more than 30bucks if you do a bit of shopping but save you ages of fiddling with jigs and so on trying to knock it out in the temper
@@ASJC27 Just to make life complicated, the cooling rate required to get martensite isn't constant. You're quite correct that something like a 1080 does need rapid quenching (aluminium plates are quite quick but not quick enough) *at the start* of quenching. The cooling rate required decreases as the temperature goes down so at lower temperatures the aluminium plates will do the job Here's a pretty good video on TTT curves that explains it better than I can in text. ua-cam.com/video/JJWKfAeak2M/v-deo.html
@@GemAppleTom just watched the video. thanks for recommending this, it's absolutely awesome for understanding this. (we only get to know the iron- carbon diagram in school) so my understanding is even with the air hockey air flow at full pressure and the aluminium simple carbon steels won't be hardened unless i quench them in oil like Graham explained in the video.
Finally some one who knows and isn't just blathering but actually knows what he is talking about. Liked, subbed.
Graham - you explain the heat treat process and how to straighten a blade better than anyone I have EVER heard. Thank you so much for sharing your knowledge. I so appreciate you doing that.
Hi Steve and thanks for the lovely feedback. I’m sure Graham will appreciate it!
Early in the series, when Jason Knight was a judge, he mentioned that if you take the knife out of the oil and it bursts into flames, then it is not sufficiently cooled. And one may notice while watching, how often a bladesmith takes a knife out of the oil, there is a giant and visibly appealing fire ball, and when tested the blade fails by chipping, breaking, or bending.
What a brilliant channel. I’ve been making knives for many years and much of my knowledge has been gleaned from scouring UA-cam. This channel told me in 5 minutes what I figured out over about 5 years from practice, reading and watching.Thank you and congratulations on a brilliant resource.
Hi Joel! Thanks for the lovely comment! Glad to hear the video was of some help! We have lots more really useful things to tackle and myths to debunk so stay tuned!
You should check one of our other videos with Graham helping makers: The ONE and ONLY THING you need to get the best grain size
ua-cam.com/video/Yv5Xz8rI6Fs/v-deo.html
This is the learning I need.
Awe definitely want some more to this series Graham. I'm sure you can come up wioth some more jewels of information for us
Thankyou very much for sharing.
Hi Talabavin! Well, let’s just say we have more about tempering coming next month and also, I am talking to Graham about showing us some of his pattern-welded (Damascus) billets he makes! Thanks again for your comment!
@@UKBladeshow fabulous i did wonder about the Damascus he makes so looking forward to that
Thank You for the education! You are my expert and again Thank You So Much 😊
Thanks for watching!
Thanks for explaining why you can straighten right out of quench. I wait until I stop feeling vibrations in my tongs. Will even use a hammer and anvil to straighten right out of quench sometimes. You got almost a minute good thirty seconds. However never tried clamping plate/angle iron right out of quench. Do that in temper but going to give it a try it after quench now.
Happy to hear you found the video helpful! Thanks for watching again Mike and see you in another one of our videos!
You just changed my entire game
British Steel! Sheffield!
🥳🥳🥳
You already know... lol. Great stuff. 🍻
Thanks again Jackson 🍻
Thanks for the good explanation
Hi Willem! Thanks for your comment! I hope you enjoyed Graham’s series!
Tried this and problem solved, thank you for your help.
Thanks Marcus! Happy to hear that our collaboration work with Graham gave you some help!
- Vinz
Thank you for the detailed information!
that was highly educational! Thanks so much for taking the time to teach us all
Hi 👋 thanks for the Comment!
Thank you
You're very welcome cabletie69! We hope you'll also enjoy the rest of the series HERE: ua-cam.com/play/PLFssspwgISv-q8YPgoAg1XNZYw9YbMkJT.html
Great info thanks for sharing
No problem 👍 thanks for watching again! If you have some interest in watching 'stock removal' knife makers, it may be worth checking out Alfie (Cabin Knives in London) make his own unique 'Botttlenose Knife': ua-cam.com/play/PLFssspwgISv_9BLJOHY3xSk2SpJQxILyy.html
Manny thanks sir. Now I have to build myself a nice press.. to make my life easier. 😅 keep up the great program! Greeting from Mcknife1, South Afrika
Great to see official confirmation for what I have been doing for a while now. Didn't know about the flash temp, I will use that from now on.
Glad we could be of some help! Cheers Bruce!
the best knifemaking tip i ever heard! Thank you for this video! :D
Glad it was helpful!
Fantastic knowledge. Thank you for explaining.
Cheers Jeffrey!
Lot of good info in that👍if it comes out of the quench oil and it warps.not much time to get it sorted 🙄 always have a back up😁all the best Lincoln 🤙👍
Cheers Lincoln!
Amazing resource Graham, thank you very much.
Graham is a fantastic source of knowledge for sure! Thanks for sharing your feedback!
- Vinz
Thank you for sharing your knowledge with us, given me a few good tips!!
Glad it was helpful!
Love it!! Read about this years ago and started stumbling my way through it. learning it costed me a few blades by getting greedy after I got them a little too cold but definitely worth the effort and you get the added benefit of a little bit of self tempering or martempering. Never understood why professional makers don't do this.
Thanks for the comment D!
Self tempering? I’m familiar with martempering (even though it’s a misnomer - marquenching is a better name for it) but not self tempering.
@@GemAppleTom may not be the correct name for it but a quick Google search describes a process which is similar to what is happening the heat from the spine(from being thicker)bleeds to the rest of the knife causes it to develop tempered martinsite. Again im no expert so I may be getting some terms crossed up.
@@dmounce5513 Right, got you. Not heard the term but get the mechanism. Probably not a surprise I'd not heard since my background is industrial heat treatment. It sounds like something to avoid for control's sake.
I'm not a blade maker (would like to take it up at some point) so can't say how important it is. Intuition tells me it isn't but I'd be quite happy to learn otherwise. Can you use self tempering to avoid needing to temper at all?
@@GemAppleTom Haven't done alot of testing without doing normal tampering cycles afterwards the one Profesional knife maker that I have heard talk about doing this stuff is kevin cashen. He talked about abuse testing one after marquenching and from what I recall was pretty durable if i remember correctly said they threw it at concrete stomped it but finally broke it hitting it with a hammer. I'll try to find my recording of it to make sure im quoting him accurately.
another amazing, video full of knowledge, keep it up vinz
Cheers man! Speak to you again soon dude!
Just because you miss the pearlite start temp that doesn't mean you will be always be fast enough to get to your martensite start temp. If you allow it to cool slowly after missing the knee, you can still hit the bainite start temp and form a bad microstructure.
A celebratory cup of tea after missing the pearlite nose is not best practice...
Only just getting into smithing, so watching a heap of stuff on the subject. Good sensible advice from you guys it seems, keep it coming! Quick question for you, if you had a blade that was hardened and bent but fully cooled, would it be possible to re-heat it up to a malleable enough state for straightening without damaging the martensite structure? Would that have the same effect as straightening while still in the cooling phase, as you describe in the video, or do other things come into play?
If it's cooled down to room temperature it should be fully martensite and straightening before tempering will be a quick and easy way to crack it.
Temper first before doing anything. You might get enough ductility back after the temper to straighten.
You'd be better asking someone with practical blade making experience, though.
The material will remain martenstic until you heat it up enough to normalise or anneal it. But the higher the temperature you temper the more hardness you'll lose and more ductility you gain.
(There are a few quirks with some steels but the above is a pretty good rule of thumb to go by)
Love the themes you are on these days! Can you do a episode amout tempering as well? Debunk some og the "bullshit" myths of 5 times 1 hour at different temperatures, and so on?
Multiple tempers can still be necessary for high alloy steels*. Not so much with plain carbon steels.
*high alloy steels can contain a large about of retained austenite after quenching. A temper cycle can transform it into untemoered martensute which will require another tempering cycle.
get the data sheets for tempering (yes it's a graph again) and temper accordingly.
if it says you need to get to 540°C for 3hrs to reach 57hrc and that's what you are after then you need to do that😂 (just a example)
Hi Heir thanks for the comment! As a matter of fact, we do have a short series on tempering in the next month or so. Stay tuned!
@@UKBladeshow awsome! Looking forward to it!
super resourceful! thanks a lot!
You're welcome!
I would be interested in how to calculate the time needed for tempering, normalising, hardening.
The data of the knife steel is a given from the manufacturer (tempering, normalising, hardening temperature), but different size and thickness change the soak time somehow? Because math and science and things?... I don't know. This is the part that I struggle the most with. Would be great if some light could be shad upon this. :)
The rule of thumb for soak times used in industry is;
1/2 hour + 1/2 hour per inch of thickness.
Yes, large sections do make things more complicated especially for high temperature cycles. E.g. getting the core to the right temp for the right duration while avoiding grain growth at the surface.
Thin sections like blades are quite easy in that respect though have their own problems with distortion.
Thank you sir
You’re welcome! Thanks for watching!
🤔i have been thinking of how to put this for the last 2 hours and No offence intended and i kinda shocked myself at all but there is a very very easy so obvious way to know when to take your steel out of the Quench media. pull the blade out when the media stops boiling. a lquide Boil's when it has hit the right temperature turn from liquid to gas. Most quench oils vaporize/flash at 176.666667C/350 F with Parks 50 its 135C/275 F and water its 100 C/212F your blade will be at that temperature when it stops boiling (it will still cause the oil. If i recall right Martinsite forms at the speed of sound and I believe its in an unstable configuration that acts like Austinite until it has cooled to Somewhere close to room temperature. so you dont need to count you need to watch and pull your blade out right when it stops boiling...however dont set in on something on one side as that will alter its cooling rate on that side causing a warp. Lock it virtually in a vise or clamp it between plates or boards and let it cool to room temprature.😅 This is so easy and Obvious i feel like i am Trolling you and i am not. IF i am wrong here please tell me and i will delete this as i do not want to contribute to the Myths about heat treating.
Thank you Sir... Good stuff... I recently got some nice aluminum quench plates and have been doing this on all my heat treats and love it although I've had a blade come out with a warp after all albeit slight... I'm assuming from the video that that's not a regular occurrence... Great tip on oil flashpoint too, tyvm for your time...
Probably a one-off Kevin but let us know if you continue to get it and I will nag Graham to see if we can help out hahaha thanks Kevin!
I use steel plates and clamps. But at the moment i am building something better. A wood working vise with wide jaws, with a steel plate welded to the inside of each jaw. So i can do the same thing that his hydraulic press is doing, but for about $50. I was also considering a hydraulic press, if money is no option, id go that route
What would happen if after oil quenching below 600, one cooled it faster (such as a water quench or cryo?
If you clamp the knife after the first cooling in oil and then dump the whole clamped steel with the knife into an ice-bath does that almost secure a good hardening or will the ice-water cool it to fast?
Great video. I have made a straightening plate, but would like to know what the temperatures you quoted are in C of F?
Hi Jim. Sorry if it was unclear but we only use Celsius in the UK. Thanks for the question!
@@UKBladeshow so 450°-250° C clamp zone?
Very helpful info and video! Does canola oil ignite at around 450c as well? That’s all I’ve got so if it works the same I’ll try making some sort of press.
Okay, so let me see if I understand this correctly: once you have quenched your blade to the martensite start temperature (quickly enough to “hit the knee” on the TTT chart), then you have some length of time to straighten your blade as needed while the temperature drops and the martensite continues to form. As the martensite forms, the blade gets stiffer and stiffer, and at a certain point*, there’s enough martensite locking the blade into shape that further post-quench straightening is not possible. Is that about right?
*I’m guessing that this is somewhere between M50 and M70, depending on how much additional correction is needed.
ua-cam.com/video/JJWKfAeak2M/v-deo.html
This might make it a bit easier to visualise.
You're doing the straighten while the material is still austenitic but diffusion has slowed down enough to prevent really rapid pearlite formation (the area below the knee/nose of the TTT curve).
@@GemAppleTom Hmm - in other words, No, I have misunderstood the situation. I guess I need to go back and study a bit more.
@@jhcc289 You had the jist of it and if you'd done as you described you'd get the practice right but possibly not pass an exam question on it. Proper diagrams make all the difference.
Thank you, @@GemAppleTom. As a non-metallurgist, I’m working hard on understanding the science of what’s going on here, and I appreciate the additional information.
However, in the interests of full accuracy, I am compelled to point out that the correct spelling is “gist”!
I would love to have your thoughts on cryogenic treatment
By cryogenic treatment do you mean cooling down to liquid nitrogen temperatures or lower and holding for 24 or so hours (deep cryogenic)? Or do you mean going to normal freezer temperatures or just a bit lower and holding for about an hour (cold treatment)?
@@GemAppleTom Thanks Tom, I watched a chanel that used liquid nitrogen after "it had cooled down".I would be interested in knowing what it does to the metal and the elements within that metal.
@@brendameech4492 Right... tempering in general first. Apologies if this is telling you what you already know but it might help people who are new.
When quenching the idea is to completely transform the steel from austenite to martensite and do it quick enough to prevent any formation of ferrite or pearlite.
After quenching you can still have pockets of austenite still present - retained austenite. This is less common with plain carbon steels like 1080 but is a lot more common with stainless and high alloy steels. In high alloy steels the martensite transformation may not even be complete at room temperature. The retained austenite is not very stable however and with a bit of energy can still transform to martensite later.
Normal tempering with give back a lot of toughness to the martensite that was formed - just what tempering is meant to do. It can also allow the retained austenite to transform leaving you with a mix of tempered and untempered martensite. You'll need a second temper (and maybe a third if there's still some remaining austenite) to temper that new martensite but you'll also be re-tempering the original martensite.
Having the mix of single and double tempered martensite is not always a problem and much better than doing only a single temper and leaving untempered martensite.
It's not so much of an issue with low alloy steels - a single temper wI'll do the trick generally.
@@brendameech4492
The idea of cold treatment is drop the temperature low enough that all of the retained austenite will transform to martensite. Then when you temper you shouldn't have to worry about different regions having different properties.
This can be done in a home freezer for some alloys. From memory, -20C for 1h was the common industrial spec
The benefits of cold treatment are consistency with properties, less distortion - martensite and austenite have different expansions during heating and cooling, saved money on tempering since you can drop one of the steps. (There are some high alloy steels that will still need double tempers but for different reasons).
Deep cryogenics is...controversial. You will certainly make absolutely certain that there is no retained austenite at liquid nitrogen temperatures. A bit overkill in my opinion but not wrong and you'll get the benefits of cold treatment.
Holding high alloy steel (or any other material according to the websites that sell the treatment) at LN2 temperature for 24+h can have other benefits such as improved wear resistance. But...
The industry at the start was plagued by snake oil sales men. Wild claims and explanations that invoked Einstein and such which doesn't bear close scrutiny. The whole idea got a bad reputation. There is sensible research into it now though. (My Dad did one of the earliest actually well put together papers on it and coincidentally a colleague in my first job was looking into it as well.) There are hints in some steels, some of the time that something might be going on but it's a small effect if it's there.
Personally I think cold treatment is something that needs to be more widespread. Cryogenics, even if there are benefits, don't give enough of one to be worth it.
@@brendameech4492 ua-cam.com/video/P9U0zXTqeSE/v-deo.html
This video goes into some more of the details.
Heck yeah, this is how I do it... not with that cool of a press though! lol
🥳 cheers dude! Enjoy the weekend buddy!
i would love to know what happens in greater detail what happens when you quench the steel 50+°C above it's maximum hardening temperature.
(yeah, i asked that through Instagram before but maybe that's an interesting topic for other people too.
A question to this video: is platequenching with thick aluminium plates and pressured air fast enough to harden carbon steels?
maybe in a automatic setup where the air blows like in one of the air hockey tables the second the press closes.
No. Carbon steels require very fast quenching rates. In 1095 for example, to start the martensitic transformation you need to cool around 1000 F in 1 second. You can't do that in air.
@@ASJC27 Aluminium plates + pressured air quench pretty fast
Its not fast enough for high carbon, plenty of high-alloy tool steels will plate+air quench though if you're not wanting a full stainless blade.
Anything like A2 to A8 series, pretty much all the D-series steels, some of the S-series shock resistant stuff all make for some really tremendous blades if you're looking for a lot of carbon and chromium.
Plates are pretty quick, but they're not as quick as a fast-oil and for any of the W1, W2, 1095, 1084 variety of high carbon, low alloy steels you will also need a specific fast oil to attain full hardness out of them- don't go using vege or motor oils on them.
The cheap knife straightener is just a woodwork vise with two bits of aluminum or steel plates stuck in them- get your knife quenched for a good 10sec in the oil and in between the plates, clamp down gently and give it a minute. Wont cost you more than 30bucks if you do a bit of shopping but save you ages of fiddling with jigs and so on trying to knock it out in the temper
@@ASJC27 Just to make life complicated, the cooling rate required to get martensite isn't constant.
You're quite correct that something like a 1080 does need rapid quenching (aluminium plates are quite quick but not quick enough) *at the start* of quenching. The cooling rate required decreases as the temperature goes down so at lower temperatures the aluminium plates will do the job
Here's a pretty good video on TTT curves that explains it better than I can in text.
ua-cam.com/video/JJWKfAeak2M/v-deo.html
@@GemAppleTom just watched the video.
thanks for recommending this, it's absolutely awesome for understanding this.
(we only get to know the iron- carbon diagram in school)
so my understanding is even with the air hockey air flow at full pressure and the aluminium simple carbon steels won't be hardened unless i quench them in oil like Graham explained in the video.
What do you do if you only edge quench your blades? Or use clay to get hamons?
Ive never had to do all that to make it hard.
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:D Thanks for taking time to comment! Hope to see you in our other vids!
That reggae out of nowhere was a bit of a shock to the system.
Haha that was the intention, hopefully the video was still valuable
Please adopt me lol
🤣🤣🤣
I feel stupid after listening to this guy......and confused..haha