Thread: Through hardening vs shallow hardening

I've been reading up on the different types of steel, mainly to try and determine the few steels that I want to work with. One of the things that I've read is that if you want to end up with a hamon, you need a shallow hardening steel like 1095 and not a through hardening steel like O1.

I used to think that any time you'd use differential hardening, you'd end up with a hamon, but that does not seem to be true. What is exactly the difference between the through / shallow hardening, and why does differential hardening (such as is done with e.g. 52100) not always lead to a hamon?

My understanding is that it's something to do with quench speeds to get under the pearlite nose.
W serires and 10 series type steels you have very little time to do this to get any hardness at all. For 1095 don't quote me but I think it's about 1/2 a second. The more time you have to cool the steel during quench, 01 for instance the greater chance of achieveing hardness, I'm not sure which chemical constituent causes this slower through hardening to occur.
For the purposes of a hamon I understand the best conditions are just a marginaly hot enough forge temperature and a shallow hardening steel to get that all and nothing effect. I believe it should be possible under the right conditions to get an impressive hamon even without the use of clay. Clay thould only be put of as a thin wash anyway to nudge things in the right direction.
I'm no expert and it's just my understanding, but hope this helps.

I was told that shallow hardening is achieved in steel types with no to very low content of mangane. I guess that the mangane helps the martensite to build up more homogenously (I don't know if that is a word ) And that is what companies want. A product that is easy to harden and is as hard in the entire piece. For blade freaks like us, trying to achieve a temper line, we need a more simple product. I think a knifemaker got a steel company to start manufacturing D2 and that's how it started.

@Bruno I can see that your location is Belgium. Where do you buy steel? I can recommend Nordell in sweden. They sell UHB 20C and it will make a nice hamon. I accidently made a hamon on my first razor, by not dipping the entire blade in oil

have a nice day
-kristian

Yes, I believe it is manganese

Deckard's correct, the main effect on hardenability is the addition of manganese to the alloy mix, up to about 2.0% if I remember correctly. The hardening line forms best with the lowest possible amount of manganese and most steel mills won't guarantee any amount less than 0.3% and usually it's described as a range between 0.3-0.5%

It is still possible to differentially harden steels that contain chromium or other alloys that bind carbon, but some of them, like O-1 or 52100 have enough that the hardening line does not show very well, if at all.