Unexpected hamon

AddictChris

AddictChris

Joined
May 18, 2019
Messages
43
just hardened and tempered my first attempt at a proper 8” chef knife.

I used W1 drill rod from Grainger. Grainger gets it from a company named Precision Marshall, and I got the chemical breakdown directly from Precision Marshall. Key points are what I was looking for, 0.95-1.05% carbon, bout 0.35 manganese, etc.

I wanted it because it should be good for differential hardening, and making katanas. I’m not able to find any supply of W2 in the size I would need for this, so this is a good alternative. I can get all I want, and no shipping charge because I can pick it up

I’ve made a couple smaller kitchen knives and it’s been good to me. Hardens easily.

Anyhoo, after grinding off the surface crap caused by my heat treatment, and getting to 120 grit, I notice there’s a hamon. It’s definitely a hamon. Its on both sides, and the sides match fairly closely (not identical, but very similar)

I did not intentionally differentially harden this blade. No clay, no cement, I fully immersed it in the quench.

There was some scale that formed during normalization cycles. On previous blades I did normalization wrapped in stainless foil. This time I did not and there was definitely some scale.

Can scale cause a differential hardening?

The hamon is actually in a really good place all along the edge, And I’m content to leave it, but for future reference I’d like to learn how it happened :)
 
Last edited:
based on the location of the hamon, all along the edge down the full length of the blade, I don’t see how that could have been a factor, but to answer the question it went in tip first.
 
You could get a hamon from quenching edge first. I don't think I would be able to help you, but others will if you post pics.
 
tkroenlein said:
Temp, soak time, quenchant.
Click to expand...

1475 F, 10 min soak, room temperature parks 50.

Kiln is one step from quench tank, and i rehearse the quench before I do it so probably no more than 2 seconds from kiln to quench.

Blade came up to temp with the kiln (evenheat kf18), and the blade is thin (0.14” at the spine) so it was definitely evenly hot throughout.

Used this same process on several previous knives with the same steel. All fully hardened.

The only difference this time is scale on the blade
 
Yes, surface condition can affect the speed of the quench.

A non polished, scale free surface is best. Take finish to clean ~120 grit for fastest quenching. Scale or a polished finish will slow the quench.

This is why they make anti scale compounds for heat treating, also the Japanese use a very thin coating of clay that blows off during the quench.

Commercial heat treaters avoid scale when heat treating simple and low alloy steels.

Hoss
 
This is one of the things that I yell at the TV while watching FiF, they keep cycling the blade in the forge over and over with out removing the scale and building up more scale and then wonder why it won’t harden properly.

Hoss
 
DevinT said:
This is one of the things that I yell at the TV while watching FiF, they keep cycling the blade in the forge over and over with out removing the scale and building up more scale and then wonder why it won’t harden properly.

Hoss
Click to expand...

Normally I have the blade in a SS foil wrap for normalizing. This time I had a new touchmark I wanted to try out but neglected to use it earlier when I should have, so I left the wrap off in order to stamp it. I didn’t grind it clean before quench because I had already ground it as thin as I would risk before hardening so I was kind of stuck with the scale till after.

Good lesson though for next time and it’ll actually look cool (probably)
 
What happens to make an auto-hamon with fast steels like 1095, W-1, W-2 is they have a very shallow pearlite nose. The thicker spine does not quite pass the nose at 1000°F. This makes the thinner edge ( with less heat to loose) cool faster than the spine. Depending on the time in the quenchant (or interrupted quenching), and the quenchant speed, the hotter spine may also auto-temper the edge, making a temper line.

The factors are - method of heating the blade, surface condition of blade, austenitization temperature, quenchant type, quenchant temperatures, quench time.
 
I call these "natural hamons".

It's simply due to the geometry; thick spine and thin edge and how it reacts during the quench.
 
You must log in or register to reply here.
Back
Top