Welcome to Tools and Process.
A new series of short videos in which I will talk about the tools I use and my process
for accomplishing certain goals.
Today, I will cover some aspects of heat treating.
Heat treating is the process of hardening carbon steel to a specific hardness.
It requires heat and controlled cooling of the steel.
My heat source for long swords is an Evenheat KF 45 electric kiln.
For smaller knives, I normally use the forge to bring the steel up to critical temperature.
As preparation I remove all vertical grinder marks from swords by draw filing.
Another important tip is that the sword needs to be on its edge instead of lying on the
floor.
Putting the sword on the floor of the kiln leads to uneven heating and warping of the
blade.
Since my high carbon steel is 1075, I program that Rampmaster to bring the temperature to
1500F (815C) and hold it there for 6 minutes.
To find the critical temperature of high-carbon steels, you need to refer to a table that
you can often find on the Internet.
Curiously when searching for 1075, you will find at least 4 different temperature and
3 of them are completely wrong.
The first step in my heat treating regime is to normalize the blade.
Since steel is in crystal form, the repeated heating in the forge causes the steel to form
larger and larger grains that make it brittle.
Slowly cooling it down from its critical temperature reduces the size of these grains.
This is also a good opportunity to check for warping which may occur when the bevels have
been ground unevenly.
I was also hoping to show you some recalecence which happens right when the carbon in the
iron matrix transitions from austenite to ferrite.
That transition releases visible heat.
You have to check my spear video where you can see that clearly.
Here, I unfortunately stepped into the video.
The next step after normalizing is hardening the blade.
Steel can only be hardened when it has enough carbon content.
Generally, the more carbon the harder you can make the steel.
As I had mentioned before, the steel has a crystal form and the position of the carbon
in the iron matrix determines the hardness of the steel.
There are three carbon arrangements you should be aware of: ferrite which is soft, martensite
which is hard and austenite which is the carbon arrangement when the steel is at critical
temperature.
When working with pattern-welded steel, the pattern becomes visible under heat due to
color differences in oxidization.
As you can see for the sword here.
Now, it's time to heat the blade back up to critical temperature and then quench it quickly
in a high speed quenching oil.
The oil will cool the blade down rapidly and cause the austenite to convert to the hard
marentsite.
When quenching in oil, I alward wear full face protection.
If the oil gets too hot, it can rapidly ignite and flames can spurt up into your face.
Before quenching the blade, I quickly check it with a magnet to verify that it is no longer
magnetic.
When I insert the blade I also move it up and down vertically to prevent a rapid transition
of hardness in the tang.
Coming back to the quenching oil, I am using Parks #50 which has a high flash point and
my quenching tank is also large enough so that the whole tank does not become too hot.
Other oils with lower flash points are much more dangerous to use.
So be careful.
After quenching the blade is brittle but the pattern so much more visible.
If the blade has been ground unevenly, heated unevenly or quenched unevenly, it may develop
a warp and as a result may no longer be straight.
However, I will show you a trick that you can use during tempering to straighten blades.
Before we go there, let's quickly check the hardness with a file.
On the hard part of the blade, the file will skid and on the unhardened parts it wil bite.