I’ve heard that saying countless times and no amount of googling gave me a satisfactory answer.
In: 8838
Lots of answers here keep saying that it’s hard, and therefore brittle. I’m going to try to ELI5 but with a little more depth:
TL;DR
* Steel can be hardened or softened
* “Hardening” involves heating, followed by rapid cooling.
* “Annealing” and “tempering” are ways of softening steel
* Soft (annealed) steel deforms easily without cracking (like Play-Doh)
* Hardened steel tends to crack when deformed (like glass)
* You can hit Play-Doh with a chunk of glass. You could hit a chunk of glass with Play-Doh. But if you hit a chunk of glass with another chunk of glass, things are going to start cracking
* If you hit a piece of hardened steel with another piece of hardened steel, you’ll tend to crack one of them
Long version
Steel is an amazing material. Its strength and hardness can vary tremendously depending on what other materials are mixed into it (alloyed with it) and how it has been processed. Many types of steel can have their strength and hardness adjusted simply by heating and cooling them in the right order and at the right speed. This is great because you can make the steel soft, which makes it easier to cut it, file it, grind it, etc. When you’re done working with it, you can give it a heat treatment that makes it as hard as it needs to be for the finished product.
At this point you might be wondering – how exactly do we define hardness, and why does it matter? Hardness is literally how difficult it is to put a scratch or a notch into the steel. Think of wood — easy to dent, therefore it’s not very hard. Aluminum (like the lid of a Macbook) is also rather soft, and therefore easy to scratch or dent. Steel is rather hard, and some steels can be VERY hard.
But hardness isn’t the only trait we care about with materials. Otherwise we’d just make all the steel as hard as possible, all the time. Another important strength is toughness. You can think of toughness sort of like opposite of brittleness. A material that’s very tough can take abuse without cracking or shattering. A very tough material can absorbe a lot of energy, say from an impact. It might bend, dent, or deform in some way, but still not crack.
Generally, with steel, toughness and hardness work against each other. If you harden a piece of steel, it’s toughness drops. That means it’s really hard to dent it or scratch a piece of hardened steel, but if you push it past the limits of its strength, it is MUCH more likely to crack. Very hard steels (like the kinds used for cutting other steels) can be so brittle that they will shatter or at least crack if you drop them on the wrong surface. On the other hand, if you anneal the steel (soften it), it becomes much tougher, and will tend not to crack even when highly deformed. Imagine bending up a wire coat hanger. It’s not going to crack.
Hammers have to be rather hard; otherwise the hammer’s head would eventually mushroom out and become useless. They also need to be rather tough, to avoid shattering. So, there’s a bit of a compromise. They try to make the hammer hard enough that it’s going to be harder than whatever you’re likely to hit with it, but not too far beyond that. That way, when the hammer hits a nail, the nail is more likely to deform and the hammer is unlikely to be dented, scratched or nicked by the relatively soft steel of the nail. And hopefully its toughness is high enough that it can still take some abuse without shattering.
When you take two hammers and smack them together, you’re hitting two pieces of relatively hard, relatively brittle steel against one another. Inevitably, one of them is slightly harder than the other, so if you hit them hard enough, you’re going to start deforming the softer hammer. But it may not be able to tolerate that deformation without cracking. If it does crack, the pieces will tend to fly off with lots of energy (both because you hit it so far and strained the metal, like a spring, and also because of any internal stresses that may exist in the metal from the heat treating process). So there’s a decent chance that you’re going to send shards of steel flying.
That’s the general reason why hitting hammers with hammers is a bad idea.
**EDIT:** Thanks everyone for all the upvotes and the awards! I had no idea anyone would find this response so interesting. I’m thrilled to have provided an answer that was helpful to so many people! Thank you for taking the time to read, and for letting me know you enjoyed it!
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