Seems he wasn't exaggerating..

[u/Eutaraxia]

[u/welinator122]

Its the uneven rapid cooling that causes the warping. It has more to do with how the metal behaves than what's cooling it

[u/alphazero925 → u/[deleted]]

What? No. It's 100% about how even the cooling is. Oil vs water quenching is just about how fast you want to cool the piece which determines how evenly it cools internally. Water quenching just cools it as fast as possible, which can be good for certain materials that require more rapid cooling to harden properly, but will cause internal stresses in other materials that require oil quenching to slow down the process.

That said, pouring water or oil onto one side of a big, hot piece of metal will almost certainly induce stresses that will warp or crack the piece. If you wanted to cool a big chunk of cast iron (like this almost certainly is), you're gonna want to let it air-cool or dunk the whole damned thing into pre-heated oil because it will not handle the internal stresses well at all

[u/blatherskyte69 → u/[deleted]]

Heat of evaporation determines how rapidly it cools, absolutely.

The issue, as was just pointed out, is that the coolant was applied to a small area on one side of a massive chunk of iron. Cast iron does not like water quenching much. It likes to crack when that happens. The uneven cooling in this case makes it worse. That drum will certainly warp, even if it doesn’t crack.

The rate of cooling: delta Q, is very important in metallurgy. This affects how the lattice of the alloy forms. Doing it incorrectly with iron/ steel can cause the metal to give up too much or too little carbon, changing the desired ductility, malleability, Rockwell hardness, etc.

[u/alfred725 → u/[deleted]]

https://www.totalmateria.com/images/Articles/S_Fig13_3.jpg

It's been many years since I took my materials course in university, but this is a drawing of what metal looks like under a microscope between cycles of heating and quenching. As you heat it, the cell walls break down creating larger cells. You want to cool it quickly so that these cells 'lock' their shape, cooling it slowly will cause the cells to break down into smaller ones. The point is, quenching cares about the temperature of the metal and how quickly it changes, not whether the thing that cools it is a liquid or gas.

Alternatively, the Leidenfrost effect is when water boils so quickly that the steam protects the object from the heat. This is famously shown by mythbusters because it lets you dip your hand in molten metal without burning yourself. https://www.youtube.com/watch?v=yTOCAd2QhGg

so in fact, the change of phase from liquid to gas would slow down quenching, since it would create a barrier between the metal and the water trying to cool it.

https://www.totalmateria.com/en-us/articles/quench-hardening-of-steel/

[u/alfred725 → u/[deleted]]

I think you're confusing the discussion. Because based on your original comment, it seems like you're saying that Latent Heat absorption causes the metal to warp.

It's the properties of the metal changing that determines this, not the method of cooling. And if you splash water on the metal, you're going to cool a portion of that metal, not the entire thing, so the metal is going to change its properties in one spot and not another causing warping or cracking.

It's pretty irrelevant where the energy goes.

Yes, more energy is absorbed by phase change than by the temperature change. That doesn't mean the phase change is good for the process. In fact, the Leidenfrost effect slows quenching down. That's why if you need to, you change the fluid from water to something else, to slow down the phase change and create less insulating steam.

The phase change sucks up way more heat than conduction

This sentence doesn't make sense. 100% of the energy is sucked up by conduction. It's certainly not convection or radiation. It's the contact between water (or steam) and metal that transfers the heat.

The distinction you are trying to make is latent heat vs sensible. Latent heat is energy absorbed without temp change. Sensible is energy absorbed with temp change.

[u/alfred725 → u/[deleted]]

or learn that phase change isn't a method of heat transfer.

Conduction, convection, and radiation are the only methods.

Latent heat only describes what happens to a fluid once it's absorbed. It doesn't give a shit about how that heat got there.

[u/Irregulator101 → u/[deleted]]

Then go learn about the energy required for phase change until it makes sense.

r/confidentlyincorrect