What's the difference and why?

[Doc Hollywood]

I am going to begin to grind my first blade and then send it out for heat treating.

I understand that you must grind out the blank and drill the holes prior to heat treating.

What is hardening and how and why is it done?

I am going to be using ATS34.

Thanks for all your help.

[AcridSaint]

Hardening is just what it sounds like, making the steel hard. Actually, hardening is only part of your heat treat process. After the steel is hardened it must be made a little softer to make a decent knife, this is tempering. You want the steel easy to grind and shape before it's a knife and you want it to be tough, take an edge and hold it once you've made the blade. Annealed (softened) steel is not very good at taking an edge and fully hardened steel is about as brittle as glass, so you need to find a balance, that's where tempering comes in.

ATS-34 is an air hardening steel and the simplest HT you can do on it is to simply heat it up to critical temp and let it cool in room temp air. Many folks use quench plates to speed up the process, even out the heat and most importantly keep the blade. There are other things that can be done, such as ramping, cryo, etc. It can be as simple or complex as you desire. HT is different for each steel, but is arguably one of the most important parts of the knife making process.

Check out www.engnath.com for more info on heat treating as well as other knifemaking info. If you want to search here for more info, try searching Heat Treat(ing) and temper(ing) instead of hardening. Hope that helps.

[Ed Caffrey]

simply put, Hardening is taking a material (in this case steel) to it's hardest possible state. The operation is performed to create a suitable hardness, for a specific application...in this case it will make the steel hard enough to not deform when pressure is applied to the thin cutting edge. Hardening is ONLY A PART of the "heat treating" process. Once the steel has been taken to it's hardest possible state, it is also brittle, which is something you DO NOT want in a knife blade. In order to achieve this, once the blade has been hardened, it is then tempered.
Tempering is a controlled softening of the steel. This is accomplished by reheating the steel to a temperature below that used in hardening, to achieve a blade that is hard enough to hold an edge, yet soft enough so as not to be brittle. In other words, you seek to achieve a balance between hardness and toughness, which can sometimes be a tightrope. These temps vary from steel to steel, and even from grind to grind.

Why is it done? If left in a non-hardening (annealed) state, the steel would be too soft to acquire and hold any type of sharp edge. The hardening also increase the difficulty of working, grinding, drilling that matieral. After hardening/tempering, it may be necessary to use a solid carbide bit to drill the material. Grinding, sanding, and finishing difficulty is also increase dramatically. This is why the majority of work on a knife is done in the annealed (soft state) before hardening and tempering.

[fitzo]

Doc, as a chiropractor you might have taken some chemistry and science courses, so hopefully this will add to what's been said:

Steel can exist in several different crystal structures. Hardening and tempering is the manipulation of crystal form and morphology through the selective application of heat and cooling to optimize the microstructure to select a desired set of wear resistance (edge retention) and toughness (strength) characteristics.

If that sounds like gibberish, then you have my apologies for wasting your time...

[Doc Hollywood]

Thank you all for the explanations. I understood all of that. As a newbie I want to fill my head with as much knowledge so I can hopefully make a wise decision on my plan of action. I know my first knives may be a flop so if I can reduce the learning curve it will hopefully be less expensive. I do not need to recreate the wheel it has already been invented. I just want to duplicte it and put my my own brand on it.

[AwP]

On detail that wasn't mentioned is that on air hardening steels, it's usually the entire knife, tang and all, that is hardened (with water and oil hardening it's much easier to only harden the blade). That is why you want to make your holes in the tang before HT as well, it's very difficult and requires special bits to drill hardened steel.