Shirogami (White) No.1 & No.2 Questions...

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According to legend, Ganjiang and Moye quenched their swords using their own blood, wonder how would that work with Honyaki
I hear unicorn blood is the best, but only during full moon and only if facing magnetic north. The only caviat is if you demagnetize the blade, then direction doesn't matter as much, but you have to ride a colt full gallop while waving the blade in the air.
I feel like i remember larrin saying the microfracture thing wasnt true. Cant remember where.

Found it

"One of the concerns is that the faster oil leads to microcracks and therefore reduced toughness. Microcracks are real but they occur due to plate martensite formation not from overly-fast quenching. Plate martensite comes from very high carbon austenite so this is controlled by austenitizing (how much carbon is in solution) not from quenching."

Which Quenching Oil is Best for Knives? - Knife Steel Nerds
I meant to jump in earlier but here are a few thoughts on the subject:

1. On the topic of microcracks, I think people in different circles use the term differently. Metallurgical microcracks have a fairly specific definition, cracks that are on the scale of a few microns or smaller, these are all too small to see without magnification. I have heard knife makers use the term microcracks to just refer to cracks that are small and hard to see before polishing the knife. These would indeed be more common in a water quench.

2. I haven't heard Martensite Start (Ms) temperatures brought up yet and that could play a role here. Carbon has a strong strengthening effect on austenite making it harder for the shear required to form martensite to occur. Thus requiring the steel to be cooled to a lower temperature to increase the driving force of the austenite to martensite formation. There is a lot of information out there on calculating Ms temperatures and a lot of research has been done on the effects of different alloying elements but in this case, we have a relatively simple system so a simple equation should suffice. Using the linear K. W. Andrews equation to calculate the Ms of White 2 and White 3 we find:

White 2: Ms (˚C) = 539 - 423(0.95%C) - 30.4(0.25%Mn) = 129.6 ˚C ( 265.3 ˚F)
White 3: Ms (˚C) = 539 - 423(0.85%C) - 30.4(0.25%Mn) = 172.0 ˚C ( 341.6 ˚F)

Now these are unlikely to be the exact Ms temps (they look a bit low to me) but I think it gets the point across. Even small differences in carbon in solution have a very large impact on the Ms temp. The rate and uniformity of heat extraction in a water quench varies quite a bit based on temperature so maybe White 3 starts forming martensite while the quench is less uniform leading to more cracks.

3. Additional carbon above the roughly the eutectoid composition of steel leads to a decrease in hardenability. So we would expect White 3 to have greater hardenability than White 2. So it is possible that Smiths are either, using the slow quench medium because it is just as capable of hardening in the oil and leads to lower scrap rates, or because the slower medium is necessary in order for the steel to get the Hamon they want.

To be clear I'm not saying that 2 and 3 are the reason for this practice, just two possibilities that came to mind while I was thinking about this.