^ this is the secondary hardening hump. While the hardness (and strength) of the matrix is going down some with the higher tempers, the measured hardness is offset by the precipitation of secondary carbides. And, in the standard heat treat that has a lot of retained austenite (due to the slow quench and relatively high final quench temperature) the decomposition of retained austenite. It's a good heat treat for tool and die that needs minimize risk of cracking and distortion and benefits from some stabilized RA and carbon lean martensite because there is minimal part growth. <--- this is very important in tool and die. But it lacks fine edge stability because the weak areas of over tempered martensite and RA are like the perforations in a postage stamp, allowing a narrow feature like a knife edge to chip off or fold over. It doesn't work well in a thin knife edge. You need a more homogeneous micro structure and the harder and higher strength matrix of a lower temper range. But this approach requires addressing the tendency of 3V to want to stabilize retained austenite with a faster quench and deeper quench than would be advised in tool and die type work. This is the trick to any of the low temper tweaks. We're acknowledging that we're not working with huge monolithic chunks of (very expensive) high precision steel parts with hugely varying sections, but are working on relatively thin and comparatively uniform knife blades that are just fine even if they grow a little. And they do. The industry standard heat treat isn't optimized for knives.
Lots of manufacturers use the industry standard heat treat and it is very durable. And it has a crumbly mushy edge that sort of defeats the purpose of an abrasion resistant steel in a rough use application because it would just go dull from impacts. Our delta heat treat protocol addresses this issue and it is the purpose of the protocol.
