For deeper hardnening steels, you need to change your strategy for forming hamon. Traditional hamon are very complex with various microstructures occuring at different places up the blade. It uses the clay in several ways to form these structures. Simple edge quenched blades will not have the residual proeuetectoid features intermingled with the makeup on the body of the blade since they will be heated the same as the edge and thus dissolved and allowed to form pure pearlite. The clay will result in a thin zone of differential temperature transfer at the interface with the ashi lines. This zone will result in a concentration of extra ferrite or cementite in a thin line accent at the top of the hamon. This will be accentuated by the increasing contamination of the pure martensite by very fine pearlite as one approaches this line giving it a brighter contrast.
I think you are getting an idea of how traditional hamon are not just simple martensite and pearlite
.
The traditional methods use the clay to control both heating and cooling of parts of the blade in order to produce this complex situation, since it was used on very shallow hardening steel, the majority of the effects were due to controlling the cooling.
If you want to use deeper hardening steels for hamon type applications, you will be tinkling in the wind trying to control the cooling since the steel is designed to defeat your efforts. Instead change you focus to the heating. Apply your clay in a way (thicker) that will interfere with the spine reaching proper austenization temperature but still allow the edge to get there.
Many say that you cannot get hamon on deeper hardening steel, while others argue that they have done it, the truth is in the middle. You can produce a visible division between different phases in the steel but you will not have it look just like traditional hamon due to the different approach required.
Yes, I have done a few blades out of 5160 that had a very visable hardening line, I used thicker clay and planned how I would direct the heating with it and let the oil just do its thing on the edge.
