Oz said:
If I understand you correctly gold does not go through a phase similar to steel (martensite or austentite). From blacksmithing my understanding was that iron formed a martensite (high hardness) due to the rapid cooling that traps the carbon atoms instead of letting them diffuse.
That's not what happens. When carbon bearing material (steel) is heated to the critical point, its structure, which was body-centered cubic, is transformed to face centered-cubic. Rapid quenching prevents the face-centered cubic from returning to body centered. That is the mechanism by which steel (or iron, assuming it has enough carbon dissolved within) is hardened.
That is why low carbon iron could not be hardened by quenching.
Mild steel, or steel with less than roughly .3% carbon, can't be hardened because it lacks the required percentage of carbon that is transformed upon heating, although I recently read an article that claims that even mild steel can be hardened if it is quenched rapidly enough. Tends to go against the rules, but I am not a metallurgist, so I am unable to refute or support the idea.
I really did not want to belittle the point with technical descriptions that often do not work out in the real world. If based on your experience gold that is taken to a dull red heat is annealed regardless of the rate of cooling that is good enough for me.
It's not only my opinion, it's supported in fact.
Here's a little test you can perform so you will understand better. If you have access to rolls, roll a small piece of gold without annealing. You'll notice that each pass through the rolls will be harder than the previous pass. It's not attributed to increased surface area alone, it's because you are cold working the gold, which responds by work hardening. After you have taken your piece through the rolls maybe three times, you'll find it quite hard, springy, in fact. If it is quite long, it will support itself when held horizontally. Now, place it on a piece of fire brick and heat it to dull red. Do not quench. When it has cooled, hold it horizontally and tell me what it does. Next, run it through the rolls, making it thinner yet. Tell me how hard it was to send through the rolls after annealing, as compared to the last pass before annealing.
For the record, work hardening and the carbon cycle have nothing in common aside form each of them making the metal in question harder than it once was.
There is yet another process for hardening, and it encompasses both ferrous and non-ferrous alloys. It's called precipitation hardening, which is the method by which aluminum is heat treated (artificially aged, and then only certain alloys) and many other exotic alloys. Vascomax is one of them. Vascomax 350 can be heat treated to 350,000 psi, and it does not require anything but an air quench. Heat treat is accomplished in the furnace, at reasonably low temps, where hardness is created by crystal growth. 17-4 PH is such an material. There are also many air quenching tool steels.
Harold
