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u/W7ENK 3d ago
That's called quenching.
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u/darkbluefav 3d ago
Why not just leave it to cool off gradually?
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u/Seanmeado 3d ago
Grain structure ends up very different. If you give it lots of time at higher temps, you end up with a coarse (generally softer and weaker) grain structure. If you quench like this, you make the grain structure much more fine and it's both harder and stronger.
When heat treating metals, there's a gazillion variables you need to control for, the rate at which you cool it being one of the most important.
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u/Thwarting8139 3d ago
Note also that it's a big tradeoff, and you very rarely want steel that's just been quenched. Freezing the grain structure in place with a quench makes the steel very brittle and lowers toughness, so there is almost always a post-quenching step like annealing or tempering which allows the steel to regain some toughness.
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u/darkbluefav 3d ago
This gal steels
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u/Unhottui 3d ago
How can she know all of this? How can she know!?
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u/darkbluefav 3d ago
Did some extensive research and found some clues. Even their fingernails are metallic!
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u/xrelaht 3d ago
Materials scientist here co-signing this excellent comment. Iâll add that you can end up with structure thatâs too fine and thus material which is harder than you want, which can often be corrected through annealing (holding at a moderate temperature for a long time). The cooling rate you mention is also related to why the liquid in one of the clips here catches on fire: itâs being oil quenched so that the quench temperature isnât limited by the boiling point of water.
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u/Metengineer 2d ago
Metallurgist here. In steel the hardness is not as much a function of grain fineness as the microstructure produced. We typically want to refine the grain structure to add toughness at a given hardness.
We would temper a steel after quench to reduce the internal stresses and hardness. Annealing is more of a reset where we heat the steel above the transformation temperature and allow it to slow cool. Typically an anneal is done during processing to remove the hardness imparted during deformation such as forging or rolling to reset the steel and allow for further deformation.
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u/DeepSpaceNebulae 3d ago
Some high pressure turbines use blades that are âgrownâ as one single crystal. This avoids grain boundary weakness and makes them extremely resistant to heat and stress
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u/Low_Requirement_5680 3d ago
Why do the big structures go up in flames?
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u/T3rraque 3d ago
Because they were quenched in oil instead of water
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u/Ok-Pomegranate858 3d ago
Ohhh I was wondering. Steam explosions aren't fun.
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u/taintosaurus_rex 3d ago
It has less to do with the steam explosion and more to do with the resulting metal qualities. As the comment above stated, the rate in which the steel cool affects it's properties. Cooling faster makes it stronger, but also makes it more brittle. If you need stronger steel that retains some amount of elasticity, then you can quench it in a variety of liquids, typically different oils. Because oils have a higher boiling point than water, the oil contacting the steel will be warmed to a higher temperature before being dissipated, and therefore cooling the part slower.
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u/entoaggie 3d ago
Another factor is that with water, the hot metal flash boils any water that physically contacts it, creating an insulating layer of steam. Iâm not sure if itâs called the Liedenfrost effect in this context, but it is the same thing happening. Just like drops of water bouncing around on the surface of a hot skillet.
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u/xrelaht 3d ago
Yeah, but these are industrial sites: theyâd just add extra safeties if that were the only consideration. Oil is sometimes used because certain steel alloys will become brittle if quenched to 100°C (the boiling point of water). Oil can be brought to much higher temperatures. Downside is itâs flammable.
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u/gu_doc 3d ago
What stops the oil from just burning until itâs all gone?
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u/Anton_Pannekoek 3d ago
Because the oil is not hot enough to ignite, let's say 200 degrees C, and even if there are flames, the deep oil acts like a heat reservoir and takes that heat away. So small amounts burn but not all of it.
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u/IlexPauciflora 3d ago edited 3d ago
This. Also the medium you quench in affects said cooling time. Some steel is water quenchable, while others may require oils or brine. There's also gas quenching which uses gases like nitrogen or argon for cooling, but I'm not at all familiar with them.
There is a tradeoff. Harder metal is more brittle and likely to break. After quenching, there's often annealing to soften the metal enough to be flexible. This keeps the edge of your new knife from chipping off or snapping the first time you use it to pry something, not that you should do that.
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u/Ok-Pomegranate858 3d ago
Whats the liquid used? I'd have expected water to react more violently...
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u/JohnnyWix 3d ago
I believe it is water for the first ones, and oil for the last few that burst into flames. I donât know about all industries but in mine there has been a shift away from oil for environmental reasons. But water is a bit more picky as it isnât just plain water, but typically a ârecipeâ containing other additives. I am not an expert, just tangentially involved with a supplier.
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u/wordscollector 3d ago
Interesting. So the exact opposite of glass?
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u/Seanmeado 3d ago
Good question!! Actually no, it's quite similar. Tempered glass is created when you heat glass up, then rapidly cool it just like this! They usually do a forced air quench instead of a liquid quench, if I remember right.
Prince Ruperts Drops are an extreme example of this. You heat the glass up until it's properly molten, then quench it in water.
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u/PineapplePizzaIta 3d ago
Because based on how fast you cool it off, you obtain a different metal microstructure
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u/Few_Candidate_8036 3d ago
It rapidly locks the iron and carbon molecules together and forms a very hard latice structure. Cooling slowly would end up with the same soft metal you started with
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u/Shaggy_One 2d ago
For a more technical explanation while also being easy to understand, Alec Steele made a long video on a lab that creates specific alloys of steel. I've linked to the timestamp of him explaining the reason cooling speed and time is important for steel at 7:40. It's a very cool video if you're at all interested in metallurgy. https://youtu.be/p6qsshPF-oA?&t=460
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u/DaanOnlineGaming 3d ago
Cooling fast will give you a martensite structure, it is about as hard as steel gets, but also brittle. Cooling slowly gives the precipitates time to move and cluster making a softer metal. Martensitic steel is often heat treated again to make it less brittle.
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u/Sheldonopolus 3d ago
Quenching. Itâs a process to harden the metal/alloys.
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u/OldFaithlessness5008 3d ago
It's the quenchiest
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u/leavethegherkinsin 3d ago
What is the liquid?
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u/Cliffinati 3d ago
The ones with no fireball water, if there's a fireball it's oil
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u/leavethegherkinsin 3d ago
Wow, I'd think the water would produce a lot more steam.
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u/AshlynnCashlynn 3d ago
ok why tf did some of them burst into flames???
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u/harper_honey 3d ago
In several of the videos, they are using oil rather than water. The material properties after quenching are affected by the rate at which the metal cools. Quenching in oil cools the metal slower than quenching in water and that can be advantageous for some parts.
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u/Lonely_Avocado_2109 3d ago
You can also quench using polymer. You get similar results and it's safer. Depends on what the material specification demands.
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u/billypancakes 3d ago
To add: It depends on the alloy too. Most treatable steels have an O or W leading their alloy designation to indicate whether they are meant to be quenched in oil or water. You want to quench for maximum hardness possible, then temper it back to where you want in a much more controllable process.
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u/CanAlwaysBeBetter 2d ago
That explains why they're quenching which plenty of other comments also explained
The question was why touching oil seems to cause other parts of the metal to spontaneously combust.
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u/ConsistentPersimmon 2d ago
I could be wrong, but I believe they also quench in oil and other non water liquids. I did a bit of knife making and was always taught to quench in cooking oil or motor oil. Less chance of cracking the steel etc.
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u/-A113- 3d ago
This editing sucks. Just show the clips and donât cut away. Donât add annoying music
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u/edjumication 2d ago
I live with other people so I never browse reddit with audio so that part doesnt bother me.
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u/Erizial 3d ago
Unsatisfying as fuck, every single one of those clips was cut way too short.
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u/Far_Ad3346 3d ago
Isnt there a sub for gifs that end too soon? Every one of these clips belongs in that sub.
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u/PGSylphir 3d ago
My parents used to work in the biggest metallurgical company in the country, I loved to go on the annual visits where I could go inside the furnace floors and see all this metal being worked on, fucking enormous beams, the heat was insane but it's so fucking cool to see in person.
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u/showtimebabies 3d ago
That still doesn't mean you can take your hot frying pan from the stove straight into water
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u/DaSecretSlovene 2d ago
The quenching pool is full of oil/polymer, not water. It would literally explode as steam if theyâd directly drop the 800C hot steel as on the video
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u/Cosmic_Quasar 3d ago
I'm no expert with this stuff. My experience with quenching goes as far as Forged in Fire knowledge lol.
The last thing looked like it had gears that were meant to turn. Is it like forged as one piece? I just wouldn't have guessed that you would assemble an item while still red hot and then quench it as a single item. I know some things require hot/cold expansion/shrink to fit parts securely together, but this looked like more than just that.
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u/_DoubleDutchess_ 3d ago
I got a job in a forge, but I wasnât allowed to do this.
So I threw a temper tantrum.
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u/envybelmont 3d ago
Sounds like you got a little hot under the collar. Hope they didnât cast you aside from that. Probably didnât want the new guy to forge-t any safety measures.
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u/Firm_Music5317 3d ago
What would the temp of the water after it goes in?
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u/DaSecretSlovene 2d ago
Not water, but oil or polymer. Depends on what you use. Either way you preheat the pool upto 200C to remove any condensation which might cause a steam explosion. The temperature difference between the ingot and the quenching oil is about 600C but these oils are engineered in such a way to conduct heat very quickly (weâre talking about 150 C/s) so the overall heat shock isnt that big at all
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u/Horror_Ad9899 3d ago
does water make metal catch fire because of oxygen or what?
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u/faxyou 3d ago
Iâm upvoting this because of the music used
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u/rfleming944 2d ago
Do you know what the songs called? It feels like âsharks keep swimmingâ, but I know itâs not them.
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u/fkenned1 2d ago
What in the world are they dipping that in that doesn't violently boil the moment red hot steel (especially in that quantity) touches it?
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u/Mr_Uso_714 2d ago
The first groupâŚ. Thereâs only one person not wearing a mask. Same person is smoking a cigarette đ¤Łâ
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u/ElFarfadosh 3d ago
Why is there something looking like a cloth placed on top of the red thing in the second-to-last clip?
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u/nullvoid26 3d ago
The last two are oilâŚ. Used for hardening. Waterâs ability to absorb heat is phenomenal.
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u/envybelmont 3d ago
The explosion from the second one shows just how rapidly the water absorbed the heat. So much so that it reached its limit and literally exploded.
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u/ghost_zuero 3d ago
That first slab of metal (if high carbon steel) would be a lifetime supply of material for a blacksmith, his son and probably grandson
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u/Gildagert 3d ago
Can't be that hot, the water didn't even burn.
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u/envybelmont 3d ago
Did you watch the last two?
Also, most quenching is done in oil to avoid explosive super heated water bursts like the one in clip 2.
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u/MonkeyCartridge 3d ago
I like how oil quenching is slower but so much more dramatic like it has something to prove.
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3d ago
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u/No-Deer379 3d ago
I donât think they all are the ones that go up in flames are but the ones that donât I think they are just plain water
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u/pushdose 3d ago
I did this in my garage last night. Hot knife blank into oil. I can tell you, itâs incredibly satisfying. Every single time.
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u/Screwbles 2d ago
It's insane how much mass some of these parts contain, and the entire thing is cherry hot.
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u/Aaaaaabar 2d ago
I want to just put these things in the most coldest water ever like -50 degree water in like antartica or something and just watch it
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u/SnooWalruses380 2d ago
Quenching freeze the steelâs phase and thus keep its properties going forward.
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u/strydar1 2d ago
why does it spontaneously flame. my guess is that it's hot enough to break molecular bonds so splits water I to hydrogen and oxygen? But that seems improbable to međ¤ˇ
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u/phallus-enjoyer 2d ago
the music reminds me of being sick with a headache and not being able to sleep, just rolling in circles in your mind for ages going crazy, same feeling and oppressive feeling on the psyche
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u/Dye-ah-ree-uh 1d ago
Cold tempering will make it less ductile, these must all be load-bearing components
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u/TryDry9944 1d ago
"And then it's off to a nice cooling dip in th-OH MY GOD- OH JESUS. Wh-what the fuck just happened?"
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u/TheJackalsDoom 1d ago
Metalwork is always so cool to me. How humans figured this kinda stuff out is wild.
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u/Relative_Initial_601 16h ago
When the material is getting dipped what is causing the flames?
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u/FreeHat9001 3d ago
https://giphy.com/gifs/7TtvTUMm9mp20