Firstly, as Aspidistra indicates, you’re mixing up the steel raw material (wootz) with the finished blades (Damascus)
Secondly, yes, India did have slavery.
Of course, it’s all bunk, anyway. Although testing finished blades on bodiesdid happen. I think the two get confused.
I bet someone, somewhere, quenched steel in blood. Probably a bucket of cow blood (or blood from some other large food animal). But the idea of doing that is too sword-killing-like for it not to have been tried.
Actually, there are three stages.
For those who don’t want to click to the pdf, Stage A, or vapor stage, is where the temperature of the workpiece is high enough above the boiling point of the liquid that it is surrounded by a vapor blanket that insulates the workpiece from the quenchant.
Stage B, or the nucleate boiling stage, where the temperature of the surface of the workpiece is still above the boiling point of the quenchant, but not so high as to be able to support a vapor blanket. The most rapid heat transfer occurs in this stage.
Stage C, or the convection stage. The temperature of the surface of the workpiece is below the boiling poing (although the center of the workpiece may still be well above the boiling point). Here, the heat transfer is considerably slower than in Stage B, but usually much faster than Stage A.
The purpose if the quench is to cool the steel quickly enough to prevent changes in crystal structure to occur during cooling. For steels, this makes them very hard, but very brittle, and can result in high internal residual stressed. By reheating at a lower temperature (tempering), the hardness is reduced some, but the “toughness” (the opposite of brittleness) in increased.
What I find is so fascinating about this whole business is how man figured out the mechanics of hardening steel long before the science behind it was known. It is easy to understand the process once you know how the carbon content (as well as other alloying elements) interacts with the time and temperatures, and cooling rates. I just am amazed that man was able to figure it out without knowing the science behind it. Kind of like being able to build an atomic bomb before the concepts of atomic physics were known or understood.
Quenching in various liquids was probably tried. I have seen suggestions that quenching in urine would have been beneficial - as the nitrogen would have provided additional surface hardening - but later analysis shows that the time and concentration was not enough to actually provide any meaningful change to the metallurgy.
I think Damascus steel has has a long history of legend, as the art of making it was lost from view for a long time. As were a great many of the actual swords. Modern “Damascus” patterned kitchen and other knives are not real Damascus steel. Just a layering of two different steels beaten together to make twisty patterns.
I too am a fan of the show, and I have found these answers fascinating.
I know the “experts” on the show always get squeamish when they go for the water because that sometimes causes cracks (especially if it is too hot at that point).
It is amazing what they can turn out in just a few hours.
Some of the early blades were almost primitive by comparison to the later season blades.
One guy did such a great job that he even had time to put his stamp (logo whatever) on his finished blade.
Actually, I’ve heard that the methods [edit: for Damascus steel] were never lost-- People just thought they were, because the old methods stopped working right. This was apparently because the raw materials changed, and the new ores didn’t have the same trace elements present (specifically vanadium) that were essential for the process.
And quench-hardening also has something to do with the formation of certain types of crystalline defects in the metal. Note that “defect” is a technical term here meaning that the pattern of atoms in the crystal isn’t perfectly regular: It does not mean that the item with defects is inferior.
This. Here is a phase diagram for carbon steel, showing the equilibrium crystal structure one would expect for steel with a given carbon concentration (horizontal axis) held at a given temperature (vertical axis) long enough to reach that equilibrium.
And that’s the key, i.e. “long enough.” You heat up your steel to some target temperature and hold it there - an hour, several hours, whatever - and the crystalline structure gradually changes over to the one indicated in that part of the phase diagram. For our purposes, that’s typically something that’s good and hard at room temperature. The challenge now is to freeze it with that crystalline structure intact. If you cool it slowly, it spends too much time in some other undesirable equilibrium-crystalline-structure zone on that chart while it’s still hot enough for the crystalline structure to rearrange itself quickly into that new (undesirable) structure. So you cool it down fast, locking in that nice hard crystalline structure before it has a chance to rearrange itself. At room temperature, the equilibrium structure is something too soft to make good strong knife edges, but if you can get it down to room temp with the hard structure intact, the crystals can’t rearrange themselves with any alacrity; they are frozen in a shape they’d rather not be in, and it will take them a very, very long time to change over to the softer structure.
Quench diagrams show how fast you need to cool steel in order to obtain/preserve certain crystalline structures at certain depths below the surface of the metal. Different quench fluids - oil, brine, water, etc. - quench at different rates, and you can even dial in other rates if you agitate the quench fluid instead of keeping it quiescent. Different combinations of fluid/agitation produce different combinations of hardness and case depth on the finished piece.
