Bizarre blade clouding after HT?

[DWidling]

Hey everyone,
I recently started heat-treating W2 and have had the same issue on two separate blades: a sort of ghosting on the blade that looks like small clouds. The best way I can describe it is that it looks a bit like the way a hamon looks after you've just sanded the scale and decarb off the blade. That sort of very faint cloud where the difference between the two hardnesses is.

Problem is that I'm not doing a hamon on these blades. I'm using a Paragon at 1460, and straight into Parks 50, tip first and edge down (into the oil at about a 45 degree angle). I'm doing 8.5" chef's knives, 1/8" blanks with no grinding done to them, and quenching right into the can that Parks provides.

I'm noticing the ghosting mostly around the spine and nearest to the tang, where the blade is closest to the surface of the oil when it's being quenched. Wondering if maybe some parts of that area aren't hardening fully, and that's what's causing the ghosting? I thought it might be decarb that I hadn't ground through at first but I took off quite a bit and the ghosting didn't disappear.

Additional remarks: the patterns are different on both sides, and don't seem to correspond to each other in any meaningful way.

Any insights are appreciated. If nothing else I think I'll switch to a vertical tube for quenching, and see how that works.

 

[Willie71]

It’s an accidental Hamon.

 

[DWidling]

It’s an accidental Hamon.

Thanks for the insight. Do you have any idea how it's caused? How it might be avoided in the future?

 

[David Schott]

Ricasso area thicker, quench in some way did not get that thicker top area down below the hardening point fast enough so you see a transition line between the hard steel nearer to the blade/edge and the softer perlite above those little lines and to the rear of them.

If you want NO harmon (lots actually love them accentuated by etching in ferric chloride) you need to quench faster and deeper into the spine/ricasso/front handle area to ensure you get full hardening back past whatever part of the blade you want visible without those lines. On a thin long blade that softer spine could be a bit of an advantage giving you some more flex.

 

[DWidling]

Ricasso area thicker, quench in some way did not get that thicker top area down below the hardening point fast enough so you see a transition line between the hard steel nearer to the blade/edge and the softer perlite above those little lines and to the rear of them.

If you want NO harmon (lots actually love them accentuated by etching in ferric chloride) you need to quench faster and deeper into the spine/ricasso/front handle area to ensure you get full hardening back past whatever part of the blade you want visible without those lines. On a thin long blade that softer spine could be a bit of an advantage giving you some more flex.

Thanks for your insight David. I love the hamon as well, when it's done on purpose. This blade is for a client who has custom ordered a clean blade, and I don't want to deliver it with bizarre splotches along the spine.

 

[David Schott]

Thanks for your insight David. I love the hamon as well, when it's done on purpose. This blade is for a client who has custom ordered a clean blade, and I don't want to deliver it with bizarre splotches along the spine.

Problem with hamons is they dont just show when etched. They sand at slightly different rates as well and the higher the finish, come out on their own to some degree.

Maybe tell him thats not the "blade" but the extended upper ricasso and based on the design blade you wanted to keep it softer steel

 

[DWidling]

Problem with hamons is they dont just show when etched. They sand at slightly different rates as well and the higher the finish, come out on their own to some degree.

Yup I found that out on the first iteration of this blade!

Maybe tell him thats not the "blade" but the extended upper ricasso and based on the design blade you wanted to keep it softer steel

haha no tricks here! The spottiness is pretty obviously not intentional, even to the untrained eye.

 

[Willie71]

To prevent this, a faster quench, or use steel that is deeper hardening, such as 52100.