I’m just an amateur guy who messed with metal on occasion
And straight up not following the logic
I know heating and quenching makes it harder, which is good for knives and such, but also makes it more brittle I guess? And likely to crack?
The descriptions on this subject are literally “over explaining the scientific molecular composition of metal” or “so anyway make hot then make un hot, dat good”
But I was trying to bend some metal today, heated it up a few times and got it near its shape, then cooled it by quenching so no one would grab it and burn their hands on it while I stepped away, came back and heated again and it just broke lol
In: Other
A few precise terms to unpack here.
First, lots of different metals behave in different ways. But the most common type of steel behaves this way, so I’ll explain that.
Second, “strong” and “less likely to break” are closer to opposites than synonyms. Almost anything you do to make metal stronger will also make it more brittle. A pencil is “stronger” than an eraser, but also easier to break.
In common steel, heating it up causes it to change phase (>!from ferrite to austenite, if you want to google more!<). If you cool it slowly, it returns to the original phase. If you cool it quickly by quenching, the phase basically freezes halfway between the 2 phases (>! We call this martensite!<).
This 3rd phase is very hard, but very stressed out. It usually has residual stress from the rapid cooling because the phases change volume (fun fact, this is why katanas are curved. The edge is quenched more rapidly than the rest, causing it to expand slightly).
Typically, you want to follow the quench with a lower heat–enough to relax the atoms enough to get rid of the residual stress, but not enough to change phases again).
In your specific case, I’d guess your initial quench was too fast and caused cracking. Rehearing expanded the metal and pulled the crack apart.
TLDR: tell your kid that they need an A to get a good job and they will be stressed, but motivated to study. Tell them if they don’t get an A then they’ll be homeless and unloved, and they will be so stressed they snap. And maybe your neighbor’s kid is made of aluminum instead of steel and needs a totally different motivation.
As other people have said, it really depends on the metal. And not just the metal, but also on the alloying elements added to the main one. The most common thing you would quench is steel. What happens there is there’s carbon present which is dissolved in the steel when it’s really hot. Then (depending on the alloy), if there’s enough carbon you can cool it quickly to harden, or quench it.
The thing is kinda the problem with the terms you’re using, what you’re seeing, and then like technical definitions. First is strength. There’s a few different definitions here, one of the more common ones is yield strength, or when the material starts to deform. Another is ultimate strength, or how much it takes for it to actually break. Materials that are ductile tend to start deforming and then can bend for a while before they finally break. Brittle materials take more to start deforming, but then break soon or immediately after this point.
So getting back to steel, when you quench it, you change it from ductile to hard and brittle. Applying heat can help make it less brittle, and enough over time will change it back to ductile. However, this is just steel. Other materials respond differently, for example aluminum is what you call hot short where if you hear it up and try to forge it with a hammer it is brittle and will crack.
Tldr there’s a lot of variables at play that makes it hard to explain simply without specifying more than “metal”. If there’s more specifics I might be able to help more
When talking about properties we need to be careful about phrasing (im not a native english speaker so hopefully i didnt mess up too) :). I’m not sure what you mean by stronger.
Quenching makes steel harder and brittle. Brittle is what makes something easy to break.
So in metal you have soft vs harder, or brittle vs tought.
Depending on usage of your material, you need to pick a combination of those.
Quenching will usually leave a very hard surface but it will be too brittle, so we usually heat it up again to 300-700°C to remove stress in material which builded up due to very fast cooling. This will lower hardness a little bit, but it wont be as brittle anymore.
There is a lot to it, had a whole year course on faculty on heat treatments of steel, so if you have more questions feel free to ask 🙂
Someone else explained a lot better for general metallurgy, but steel specifically is pretty interesting in this regard. Quenching steel freezes the carbon atoms added to the iron in the forging process into a structure with strong bonds. In this way, you can think of steel as being analogous to an alloy of iron and diamond.
The answer is it depends.
Metal atoms form crystal structures, and there are many different structures that the atoms can form depending on their properties and what other elements are alloyed in there.
You could spend an entire academic career learning about crystal structures and material science in general.
To keep it as brief as possible, [Steve Mould has a great video with a perfect visual analogy using metal balls.](https://www.youtube.com/watch?v=xuL2yT-B2TM).
Honestly, just watch that.
It’ll show how crystal structures form “grains”, how the size of those grains can change and how they’re affected by temperature, etc.
I worked in a copper alloy producing plant. Typically annealing was done at a higher temperature (~1450F) and water quenched to preserve the grain structure. The product was either then left in that condition or it would be cold drawn, cold drawn and heat treated (600F) or just heated treated and air cooled. These treatments would create the grain structures and physical properties required by the customer or specification. All metal heat treatments, either annealing or ageing (hardening) are performed at different temps specific to the material.
Latest Answers