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Heat treatment

The most of my products are made in the "stock removal" method. That means the blades are cut out of the material, brought into form and then get their tempering. I purchase all my steel variants from a great steelwork with high quality standards.

To forge the blade from the same base material, but with a more coarse crosssection is pointless. Not even concerning grain refinement, because all steel base materials have got an outstanding microstructure and are annealed in my forge. If you are interested in more information about "why forging is better than cutting" you can read my article "prejudices" under "Swords".

Miscellaneous swordblades are, conditioned by the final form of the blade forged, and of course als damascus steel products, axes, pole arms etc. are forged. I almost forge these products on final dimension, but a bit material have to be over final dimensions, because the oxyde of the scaling have to be grinded off.

As mentioned above the blades get tempered after they got their form. Although I use a rather modern method for the forming of the blade, I am traditional in the field of tempering. I believe in the soul of a weapon and it is important to me to create this soul in a close process between smith and sword. As the masters from Japan all my products are tempered in a traditional coal-hearth without any measuring instruments, except my eyes and experience. Many sword- and knifemakers rely on electrical ovens or salt bath hardening to recreate exact results over and over again, but this is what I don't want. In today's measuring and checking craze they don't believe that a method that simple could bring success. However, like in the fisherman's business: "Who catches is right." My aim is highest quality and performance possible, but on an individial way. in the fire I fell the small peculiarities of every single blade. There are blades which are joinable other are not and I want to see and feel this. As a human, a blade could bring maximum perfomance, but at the same time be a unicum, which not was born out of retort. My products are regularly and randomly tested in Kiel and the results show that experience and practice on a coal-hearth nearly beat the cold digital way. You see, I catch!

The procedure of my tempering looks as following:

-The hardening furnace (a long fire of about 120cm length) gets ignited with wood. A picture of a furnace like that can be found in the article "Quality" under "Swords".

-The coal gets stacked as soon as the wood burns right.

-If the furnace has got the right temperature, the blade is inserted and without any air supply warmed up.

-After the shaping of the blade it gets normalised. The most steel variants from steelworks don't need that procedure, but prevention is better than cure. Normalization is a technique to remove irregularities in the microstructure of the steel and as a final aim to achieve a fine, consistent microstructure.
The finer the microstructure of the steel, the harder and tougher the material gets. Dependent what carbon-content the steel has got, I warm it up three times over the transformation point. After that the blades cools down in the air. You can also find a picture of this procedure in the article "Quality".

-To be able to work with the material before the hardening process it is neccessary to anneal the blade after it was normalised. For this purpose the blade is tempered to about 723°C (transformation border) and hold at this level for some time. After that the blade is tender and good to sand.

-The following step is the stress relief annealing of the blade. This procedure is very important, even with the "stock removal" method, because most of the rolled steel has got a lot of tension in it. To get rid of those tension I warm up the steel up to 600°C and hold the temperature at this level for about an hour. Every described step happens in my coal-hearth. It is a very elaborate and not that ordinary matter to treat a blade for such long time. It needs a lot of experience and knack. A sword with an average length of 72cm at 650°C is like a wet sponge. I have to move the blade everytime or turn it, the air supply have to be right and as the top of the mountain the coal have to be smoothed so that the sword is only just in the furnace.

-After those preparatory steps the blade is hardened and gets its soul. Therefore the blade is warmed up swift but gently to its hardening temperature. This hardening temperature is dependent on the carbon-content of the steel. As coarse guideline you could say, the higher the carbon-content the lower the hardening temperature. The hardening temperature always is above 723°C, because above this temperature the former cubic face centred microstructure of the steel changes to a body-centered cubic. In this new microstructure the carbon-atoms have got the possibility to dissolve and get part of the austenitic microstructure.
To hold the carbon-atoms in the austenitic part of the steel, I chill the blade down and the carbon-atoms are clamped where they are. With this process a new very hard structure is made, Martensit. I thought it would be better to describe it in a more easy way, because not everyone of you is a metallurgist.

-As the final step, the blade must be tempered. Through the clamped carbon atoms tensions arise, which I want to get rid of. This should happen within one hour after the hardening process, because it could happen that the tension get to big.

But back to topic. The tempering, the repeated supply of heat, eliminates the extreme hardness of the blade and slackens it. The brittleness and hardness decreases, but the flexibility increases a lot. When using a silicone-poor steel I use a temperature range about 160 to 200°. Some steel variants for the use with extreme strain can be tempered at 400 to 550°, but the area of 200 to 400° should be avoided, because steel variants with little or no silicone-content, blue-brittleness arises. This blue brittleness makes the blade brittle and prone to shock, like a blow with the sword.
Silicone moves the area of blue brittleness to a higher range. Out of this knowledge it is important to choose your steel, that it has got the wished hardness and flexibility at a tempering-temperature without blue brittleness.