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The Bladesmith and the Knifemaker

The question that is asked is “What is the difference?”
The question is valid, as most people believe that there is no difference.
Often the reply is a Bladesmith creates a knife from a piece of steel, and a Knifemaker just makes a piece of steel look like a knife.
The confusion is a lack of understanding of the different methods of producing a knife.
The two basic methods of producing a knife from a piece of steel are:

1. Stock Removal.

This is the Knifemakers method.
Starting with a piece of steel and transferring a pattern onto the piece of steel, the steel is coated with layout fluid or similar coating, having seen marking pens, nail polish, and shoe polish being used, a template is then placed on the steel and an outline is scribed onto the steel from the template. The blade outline is then cut on a band saw or ground out, grinding to the layout lines refines the cut blade, and this process of making an outline shape is called Profiling. When the profile is complete, the bevels are ground, and this is how the Knifemaker removes stock from the steel and is therefore called using the Stock Removal method.

2.Forging.

This is the Bladesmiths method.
By heating a piece of steel in a forge until it reaches the “Plastic” state, it is then placed on an anvil and beaten into shape, great for relieving frustrations, the steel is shaped on the anvil to be 90% complete. In this, the blade is profiled, bevelled and shaped so that only a small amount of grinding needs to be done to finish the blade. The old age saying of a little time at the anvil saves a lot of time at the grinder. Therefore, the Bladesmith or Smith uses their skills to create the blade. A person who forges blades will be referred to as a Bladesmith or just a Smith, understandably these people are not called forgers.
The description above is very much an over simplification of the process of making knives, and is intended to convey the idea of how knives are made and is not intended as a course on Bladesmithing or Knifemaking.
Another explanation read somewhere that describes the process very simply.
A Bladesmith heats apiece of steel and taps it with a hammer until it looks like a knife,
a Stock Remover takes a piece of steel and grinds off everything that does not look like a knife.

The Purpose of Forging to Shape.

This is not a tutorial on how to forge a blade to shape, so sorry to disappoint those looking for a tutorial, this is a “Why” rather than a “How” article.
Forging to shape does not have the same meaning to all Bladesmiths, this is rather an explanation of why forge to shape and why attempt to achieve it.

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What Does All This Mean?

In forging the blade to shape, the Ricasso shoulders on both the blade and the guard area, Distal Taper on both the Blade and the Tang, the bevels and the choil have been shaped on the anvil.
This shows that the basic outline, Profile, of the blade has been established on the anvil.
To some Bladesmiths this is not the case, if only the blade is established the Profile is considered complete.
Why Be Concerned With Forging to Shape?
There are some obvious reasons; one is to show the Bladesmiths skill at the anvil in shaping a piece of steel to close to the final shape and size.
If nobody sees this process, why should the skill be shown?
What is the purpose of using this skill?
The next reason is that it is a time and money saver.
The old age saying of a little time at the anvil saves a lot of time at the grinder.
So how does this save time and money?
Well the less time at the grinder the less grinding belts used, the less grinding belts used the less money spent, so more money for other uses, makes sense?

Heat Treating – An Overview.

This overview is not intended as an instruction course in heat-treating; it is a brief overview of the processes with a brief explanation of each method.
The use of the term Transition temperature is used rather then the term Critical temperature is used in this article, to explain; this is the point when steel reaches a transition in that the steel becomes nonmagnetic.

Differential Hardening.

This is the process when transition is performed at the hardening phase and includes edge quenching, torch method and clay coating. Edge Quenching – In this process bring the whole blade to transition temperature,
at which point only the cutting edge is placed horizontally in the quench bath,
and carefully rocked upwards to the tip of the blade.
This process cools the cutting edge faster than the area exposed above the quench medium and therefore
the steel exposed above the quench line cools slower and is less hard.

Torch Method – The cutting edge only is rapidly brought to transition temperature using a torch,
and is then placed in the quench bath in the same manner as edge quenching,
this method is difficult to use on large blades as to hold an even temperature on a large blade
is almost impossible, so use this method on small knives only.

Clay Coating – Coat the back of the blade with clay or refractory cement,
bring the whole blade to transition temperature then place the blade in the quench bath,
the coated area on the back of the blade will cool slower then the uncoated edge and
the edge is therefore harder then the back of the blade.

Differential Tempering.

This is the process when transition is performed at the tempering phase.
In this process, the blade is hardened, tempered and the back spine is drawn back to springy with a torch.
The blade is placed in a tray of water, cutting edge down, to a depth of ⅓ to ½ of the width of the blade,
using a torch, carefully draw back the spine using a painting motion back and forth across the spine.
This is just two methods used, but whatever method is used the end result remains the same,
to achieve a blade that has been heat-treated to have a hard cutting edge and a springy spine.

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The Benefits Are?

On a blade that has been properly heat-treated, the spine has strength and is flexible while the cutting edge has good edge holding properties.
So the blade will be able to withstand lots of use and abuse, especially for larger blades that will be used to do some things they are not designed for, like chopping wood, opening cans, clearing a path through the woods, etc. It is beneficial for thinner knives to be flexible.
Looking at the requirements for passing the Journeyman or Master Smith examination, the blade is required to be clamped in a vice
and bent to 90º without breaking. So all that is required is a blade that is tempered to spring temper?
Wrong, before the bend test, the blade also has to cut through a 25mm free hanging rope, approximately 150mm from the end,
in one movement, the next test is to chop wood, 50x100mm, in half, twice, with no edge damage, and still
shave hair from the arm, this is what can be achieved by Differential Heat Treatment.

In Closing.

This was not intended as a tutorial in heat-treating, and is only intended to give an insight into the processes, how it is applied and why it is applied.
So this shows that there is more then one way to heat treat a blade, mostly to state that the blade has been Differentially Heat Treated covers the whole process, to be more specific, the use of the terms above can be applied to the specific method used.

Definitions:

Annealing– The process of getting steel soft enough to work with by heating it to hardening temperature and letting the steel cool down slowly. To cool the steel slowly, bury it in an insulating compound, something like Lime or Vermiculite, these are obtainable from your local Flower Nursery, let the steel cool to room temperature.

Hardening– The process of heating steel to hardening temperature and cooling it down rapidly in an oil bath, the oil can be of almost any type, the use of ⅓ by volume motorcar engine oil mixed with ⅔ by volume gearbox oil works quite well. i.e. 1 litre of engine oil to 2 litres of gearbox oil.

Tempering– The process of heating steel again to the tempering temperature to relieve the stresses induced during the hardening process, this will remove some of the hardness and give the steel toughness. Hardened steel is as brittle as a piece of glass; it can break if you drop it. Tempering removes this brittleness.

Transition– This is the point when steel changes, when heated the steel goes through strange states or phases, where it becomes nonmagnetic, this point is a transition point, also called Critical temperature.

What happens to steel during Heat Treatment?
Don’t go away yet.

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Here this gets very technical, and the use of words that needed a dictionary are used, so if you do not understand it do not feel lonely, it took awhile to get this in some sort of order. Carbon and Iron are formed together in different Phases; this depends on the percentage of Carbon and the temperature.
See Figure 1, Phase Diagram.

Photomicrographs courtesy of University of Manchester Internet Microscope
When steel is fully annealed it consists of a mixture of Iron and Iron Carbide, there are impurities and other alloys as well.
The Iron is in the crystalline form called Ferrite; the Iron Carbide is in the crystalline form called Cementite.
This structure consists of bands of the two and makes up the Pearlite.
This is the state that steel is soft and easier to work with.

Hope you are still here so far?

When steel is heated to the transition temperature (about 725ºC), it goes through a phase change,
at this point re-crystallising as Austenite, heating further to the hardening temperature (785-815 ºC) makes sure
that the steel completes its conversion to Austenite, at this transition point the steel becomes nonmagnetic and is Bright Red.
Now, cooling Austenite steel slowly, in other words, the steel will go back to its Pearlite state.
Ah Ha, now you know what Annealing is.

However, cooling Austenite steel rapidly in an oil bath, Quenching, a completely new state is created, this crystalline structure is called Martensite.
Martensite has a different structure that is more angular and needle like; this structure is also very hard. Ah Ha, now you know what Hardening is.

In this state, the steel is very brittle, can, and will break if it is bumped or dropped.
Remember that all those internal stresses are still in the steel, from the sudden quenching, and that is why it is so brittle and can break
OK, so what now? This stuff is hard and it will break.
This is no good for a knife.
Well the last step is to heat it again.
What? Yes, heat it again to the temperature where the Martensite partially decomposes and forms into Ferrite and Cementite.
The tempered steel is not as hard as in a pure Martensite state, but this is its tough state and that’s what you want, hard tough steel.
This is Tempering.

Figure 1: Phase Diagram.

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Let us look at some of the basics.
What is Steel?

Steel is a combination of iron and carbon, in its “Plastic” or soft state, it is a matrix consisting of Iron molecules (Ferrite), and suspended therein are molecules of Iron Carbide (Cementite).
Heating steel to set temperatures and then cooling at a set rate causes steel to undergo internal physical changes, these form other microstructures like Pearlite, Austenite and Martensite. The microstructures change the mechanical properties of steel and this is what makes steel so versatile.

Different Alloy elements are added to steel to make changes in the properties of steel.
This section is to try to show how these Alloys change the properties of steel.

Carbon Content.

Without Carbon it is not steel, simple, without Carbon the formation of Cementite does not happen, this includes the formation of Pearlite and Martensite. The hardest of these microstructures is Martensite. This is what Knifemakers are looking for in steel. The hardenability of steel increases with the increase in Carbon, (Limited to about 1.5%, amounts greater than 1.5% just make the steel brittle), so Carbon of about 0.65% is for hardenability, above this and up to 1.5%, wear resistance increases. Steel in the range of 0.5 to 1.5% Carbon is the steel that Knifemakers look for.
Low Carbon Steel: Contains less than 0.4%
Medium Carbon: 0.4 to 0.6%
High Carbon: 0.7 to 1.5%
Remember that Carbon is the important Alloying element of steel.

Chromium Content.

Chrome Content will increase hardness; this is an interesting element and has the effect of increasing the toughness of steel and the wear resistance. The most common use of Chrome is to increase the resistance to staining. “Stainless Steel” In reality is not “Stainless” This needs to be clarified; the steel is really “Stain Less” lets look at this. When Chrome is added to steel it becomes resistant to staining, it will rust, but not as quickly or in a way, that is not as noticeable. Tool steel made from Stainless steel will darken over time and rust. Steel with Chromium also has a higher transition temperature during heat treatment.

Manganese Content.

Manganese Content causes a small increase in the strength of Ferrite, also the hardness of the steel increases. Steel with a Chromium and Manganese content are mostly Oil quench, as the percentages change the steel can change from Oil to Air hardening. Manganese changes the quenching time. Steel with Manganese Content can be quenched in Oil, this making it less likely to crack, because there is less temperature shock in Oil quench. Manganese is found in most of the commercially available steels.

Vanadium Content.

Vanadium Content is the stuff that restricts Grain growth during heat treatment; this increases the toughness and strength of the steel.

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Nickel Content.

Nickel Content increases the strength of the Ferrite this increases the steels strength. In Low Carbon steel, it also increases toughness and hardenability. This also reduces distortion and cracking during the quenching part of heat treatment.

Silicon Content.

Silicon Content is added during the manufacturing process because it is used as a deoxifier during manufacture, it also increases the strength of Ferrite slightly.

Molybdenum Content.

Molybdenum Content has the effect of increasing the hardness penetration of the steel and slows down the quenching speed. High temperature tensile strength is also increased.

Tungsten Content.

Tungsten Content when used in small quantities combines with the free Carbides during heat treatment, this results in high wear resistance and little if any loss of toughness. Tungsten also gives steel a property known as RED hardness. The steel is made so as not to lose its working hardness at temperature, for example high speed tools generate high temperature due to friction, so Tungsten Content will enable the tool to retain its hardness.
The rest of the trace elements that have some effect on the steel are as follows:

Boron Content.

Boron Content increases the hardenability of steel quite a lot without causing ductility loss. The effectiveness of Boron is more noticeable in the Low Carbon steels. Boron Content is found in very small quantities in the range of 0.003% to 0.0005%.

Titanium Content.

Titanium Content used with Boron increases the effectiveness of Boron in the hardenability of the steel.

Copper Content.

Copper Content improves resistance to atmospheric corrosion; Copper Content is found in quantities in the range of 0.5% to 0.2%. In knife steel Copper Content affects the surface quality, also the grain boundaries due to migration when being hot-worked.

Niobium Content.

Niobium Content lowers the transition temperature in Low Carbon steel and helps create a fine grain structure. A reduction in Tempering and hardenability due to the formation of stable Carbides. The amount of Carbon dissolved into the Austenite during heat treatment.

Well that's all for now, will try to add more as time and circumstance allow.

If this information has been of any assistance to the novice Blademaker, please feel free to pass it on.
All that I will state is that this has been my own inspiration and specifically disclaim any responsibility or
liability for any damages or injuries incurred by the use or result of any information contained and listed and published, etc, etc, etc, herein.

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