It has been a while since the last update. But here it is, Forge Diaries: Episode 5.
If you have ever looked at an old blade, you may have marveled at the beautiful steel structure.
In this episode, I show how to make the steel for a knife like this. The first part is going
to be on refining wrought iron followed by making shear steel.
Wrought iron has lots of impurities and grain that is usually stretched significantly in
one direction. The wrought iron I am using here comes from the Wisconsin globe elevators
from 1887.
To refine the grain structure, I forged the wrought iron into a rectangular bar and am
cutting it into square pieces.
These square pieces are then stacked on top of each other so that each layer has its grain
running perpendicular to the layer above and below it.
I used a felt pen to indicate the grain direction so that I don't get confused when assembling
them.
As you may have seen in my other videos, forge welding is the process that turns the individual
layers back into a solid piece of iron.
It is a challenge to keep the mating surfaces clean. In the forge, the iron tends to develop
scale which gets in the way of the welding process. A flux such as the anhdyrous borax
I am using here, dissolves the scale by forming a liquid barrier that leaves the iron clean.
The iron is forged back into a long bar which is then cut and stacked again. This process
is repeated until the desired number of layers have been created. The more layers there are
in the iron the more refined the end product.
Here is an example of iron pieces with an increasing number of layers. Very hard to
see in the video but the grain has become much finer and the individual inclusions look
smaller.
The previous example showed individual squared stacked on top of each other. This is probably
not the most efficient process and limits the amount if iron that can be processed in
a single go. The next example shows a more efficient way of stacking the pieces that
also seems to work well.
First, I need to forge the round bar into a thinner rectangular bar. The power hammer
is a big help here and definitely speeds up the process. All of this could of course also
be done by hand. Ideally, with several helpers wielding large sledge hammers.
Here is an intermediate result. All the work I am showing you here is purely experimental
and that's why these videos are called Forge Diaries. Eventually, you will see all of these
processes being used to complete more interesting projects.
Given the cleaned bar, I cut the iron into recangular pieces that I re-assembled two
by two while switching grain direction.
Given the arrangement, the interesting question is if the iron will weld completely in the
forge. The gap that is side by side cannnot be worked directly by the power hammer. However,
the iron is very squishy and the hope is the flattening under the hammer will force the
gaps to close.
Now, we are back to the where we were in the previous experiment. The iron needs to be
forged into long strips that can be cut and welded again.
However, I will not show you that part. Here, you can see the iron after it has been cleaned
with a sand blaster.
So, let's review. We refine the iron by forge welding it and switching up grain directions
between layers. As frequently, Jim Austin from Alchemy Metalworks suggested I take a
look at that. Check out his classes if you live in the Bay Area.
Now, we look at creating steel from iron. The difference between iron and steel is literally
its carbon content.
At around .2% carbon we start calling iron steel. However, to be able to harden it and
use it for blades, we want at least .6% or even go as high as 1% carbon.
What you are seeing here, are several thin strips of iron that are being placed into
a closed container with a pack carburizing mixture.
The carburizing mixture contains mostly charcoal plus an energizer. I am using 20% calcium
carbonate but potassium carbonate is an option, too. Most industrial mixtures end up using
barium carbonate which is unfortunately toxic.
To force the carbon into the iron, we place the container into high heat. Inside of the
container, the mixture will create carbon monoxide and the gas will diffuse into the
iron. The carbon will not penetrate very deeply but enough for our purposes.
I am using my gas forge as a heat source and need to dial the temperature down enough to
not quickly destroy the container because it needs to stay inside of the forge for several
hours.
As you may have guessed, this experiment was a failure and resulted in a containment breach.
Visually it is quite intriguing though.
What I was expecting was a surface with a lot of visible blisters. There are some but
not nearly enough to indicate that the process was successful. However, I am going through
the motions of stacking the pieces up and forge welding them. At the very least, I can
still use the material for other projects.
After forge welding, I am removing the scale and will then attempt a spark test to get
an indication of carbon content.
Look at the sparks from the 1085 I am using as reference and compare them to the iron.
Nothing. So, let's prepare for another attempt.
This time I am placing the container into a temperature controlled oven and heat it
as 1900 Fahrenheit (approximately 1050 Celsius) for 4 hours.
I am hoping for more success this time. So, let's take a look inside.
As you can see the temperature is not very gentle to the container and I am losing a
lot of it every time I use it.
Still not a lot of blisters. Let's check out the spark test.
This looks a little bit better but there is clearly not a lot of carbon in there.
So, what's going on? To answer that question, I sent some of the iron to a lab to get tested.
The results were somewhat surprising. The iron has an incredibly high phosphorous content
and phosphorous inhibits carbon migration.
So, for the next experiment, I used old wagon tires that were known of has less phosphourous
in them.
The surface looks more blistered and the spark test is looking more promising, too. I call
this a qualified success and consider the material blister steel.
To turn it into shear steel, we need to stack it and forge welded into a much cleaner material.
This is what I am doing here.
This is a time consuming process - as everything you do by hand - but the visuals are pleasing
so bear with me.
Eventually, I ended up with three bars. Two that were refined wrought iron and one that
was shear steel. It's time to turn this into a pretty knife blade.
I am using a san mai construction in which the steel is being sandwhiched on both sides
by the pieces of refined iron.