Heat Treatment

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Kukri knife Heat Treatment (local hardening) by KHHI nepal

Our heat-treatment is done in a basic and traditional way but performed very carefully and skillfully. The partial water quenching (differential hardening) technique is adopted which is very effective for large knives like kukris that are made from high carbon steel like 5160 and 52100. The heat treating goes in a natural process from Forging to Finishing. The same method that has been in practice for generations and something that is synonymous to a kukri is undertaken by KHHI nepal. Here the objective is to respect and continue with the reputation, exceptional blade smith and legacy of our forefathers (Kamis). 

The 3 crucial steps of the heat treatment go naturally...

Normalization:
Maker picks up at least 4 kukris at a time which is made one at a time. First the 1st piece is forged and hammered and put to rest then 2nd one picked up and so forth. This method is intentionally done to naturally normalize each piece in the making process.

Quenching (hardening):
The kukri is evenly heated on all surfaces till it reaches the critical temperature (cherry red color) in a charcoal furnace. Then it is taken out of the fire and quickly the edge is gently scrubbed by a file to clean it. This also gives some time for air-cool for the heated blade and then room temperature water is poured all along the bevel from ricasso to tip until the maker is satisfied. He then flips over the knife and continues pouring the water. During the whole process he checks for any kind of warp that may occur due to high stress created in the blade. Finally the water is poured on the other surface of the blade as it starts to cool down further. Such partial quenching method gives optimum hardness to the edge, much less hardness to the panel and almost no hardness to the spine. This various hardness gives stiffness and softness (cushion) at the same time. This is something that has been in practice for centuries with phenomenal result. We as a maker do not even dare to change it or improve it or better it.

Tempering:
The natural process of preparing (finishing) the knife auto corrects the brittleness. The kukri goes through a series of machining steps in which enough heat is generated which in return naturally tempers the blade in each step. This eases the strain within the blade triggered by quenching and the blade becomes tough from brittle. The blade is never dipped in water, rather cooled in still air.

The above mentioned heat treatment process is deeply investigated and well tested by KHHI Nepal. Now and then we also forcefully snap off a blade or two to check and study the grain structure of the steel. The blade is thoroughly tested for edge strength, retention, deformation and flexibility. Edge is forcefully whacked in dry horn for edge strength and very hardly scrubbed against brass rod to check its springiness. Such heat treatment has never let us down and is one of the main reasons behind the success of the company. Its not only an excellent classic technique but also helps to conserve our rich blade smith that has been a major part of our history, culture and recognition. 

PS: Heat Treatment in Oil is possible on request. No extra charge is applied.