Heat Treatment Tutorial.

My heat treatment usually consists of triple normalizing, triple hardening, and triple tempering.



Step 1: Normalizing.


Why normalize?

The main two reasons are these: 1) Normalizing refines the grains of the steel. 2) It reduces warping of the blade.

Most knifemakers will say something like: if you use stock removal methods then you don't need to normalize. They will say that only people that forge need to normalize.

In all honesty, both should normalize regardless. I mean, why wouldn't you want to refine the grain of your steel and reduce the chance of it warping?

You might be wondering why they say only makers that forge need to normalize. Well when you are hammering the metal you put a lot of stress on the metal and the grain of your metal is tighter in some areas than in others. Unless you are able to hit every part of the blade with the same amount of force with the same amount of heat, then chances are the grain structure will be different through out the blade. This creates stress in your knife.

Normalizing reduces the stress. Also after a certain point the grain will stop reducing in size through this process, which means the larger grains will catch up to the size of the smaller ones and etc.

So! How do we Normalize?

By getting the metal near critical temperature which is basically non-magnetic temp, then allowing it to air cool at normal speed to room temperature. The easiest way to do it is to heat up the blade and then lay it aside to cool down.

Normalizing isn't Annealing.

Annealing is softening the grain structure of metal. For carbon blade metal, is getting the metal to non-magnetic and cooling the steel down as slowly as possible. Which can take from a few hours to days to cool off. This makes it softer and easier to work. This is for carbon and ferrous metals.

The Annealing process for non-ferrous metals, like copper and brass, is the exact opposite. It's getting the metal hot and getting it cold as quickly as possible. Which is what hardening/quenching is for ferrous metals.

My process:

If I had my forge, I would simply put the knife in the forge and once it started getting red, I would check it until it started getting close to non-magnetic temperature. Once it's there I pull the knife out and set it aside to allow it to cool off.

Since I'm using a torch for this tutorial, I'll leave the knife in the vise to heat and cool it off. I like to normalize the whole knife. So once the blade is cooled off, I put the blade in the vise and do the same thing to the handle.

For the first run I always get close to, if not right at non-magnetic temperature then allow it to cool. From the pictures you can see when doing the blade I always start with heating the spine of the blade first. I then work may way to the edge, because you want an even heat through the knife. If you heat the edge first, then there is a chance you could actually warp the blade by getting one part too hot. So always start heating the thickest part of the blade first.

The second time, I will go just under non-magnetic temperature and allow it to cool off.

The third and finally time, I will go a few degrees under that and allow it to cool off. I usually go 20-ish degrees under the previous temperature each time.

How do you know exactly what temperature? Well you need to know your metal. There are many charts on the internet for popular metals used and a lot of times when you order metal from a company it comes with labels that tell what welding, hardening, etc temperatures are. I usually stop at hardening temperature then allow to cool, depending on the metal.

The way to tell exactly your heat of the knife by forge or torch is a temperature gun. There are ones out there that will go up to critical temperature for most of the metals. Which means all you have to do is point the laser sight at the metal and it will tell you the exact temperature. Once you've done it enough you'll be able to tell the temperature of the metal just by looking. Well for non-magnetic you should be able to after some time.

The last and most expensive way is to get a heat treating oven with a digital dial. Now that...would be awesome.

Anyway. After the third time of normalizing, we move on to hardening.

If you want to check your process and make sure everything is going according to plan, you could always get a microscope and check the grain structure of your metal after each normalizing step. It's pretty fun.




Next Step: [link]




I heard that the military didn't have enough funds to buy targets for firearms training...

Oooooh pick me! Pick me! I wanna be a target!

Logan Pearce
www.pearceknives.com