Cooling media for blade hardening

Regarding cooling media, the recipe is as follows: all carbon steels are calmed in water, and alloyed ones - in oil.

Water rapidly removes heat, so the cooling rate in it is high. The oil is softer and more gradual. In principle, high-carbon steel can be quenched in oil, and low-alloy steel in water, but the result will be average. Most often, such attempts lead to under-firing of the first and cracking of the second.

It is also possible to regulate the cooling rate by means of various additives. Vinegar and table salt increase it, while soap solutions and other emulsions decrease it. Accordingly, liquid transformer oil or machine oil cools the workpiece more intensively than thicker grades.

It should be borne in mind that only liquid creates conditions for uniform and forced cooling of the blade. Attempts to shove a red-hot piece of iron, for example, into a snowdrift, are doomed to failure - the instantly formed steam cushion reliably insulates the metal, and it will cool down rather slowly without having been hardened. At the same time, certain grades of high-alloy steels are successfully calmed by cooling the parts in a stream of air, but preheating to 1050-1100 C.

The way of diving is very important. blade into the quenching medium. Straight double-edged blades are lowered into the liquid strictly vertically, vertically, and knife-like (regardless of curvature and length) - obliquely, with a point down and forward, with a blade down. In this case, the first blade that comes into contact with the liquid instantly cools and acquires high hardness, and the blade body itself (especially the back) remains more plastic.

It is extremely important to maintain the verticality of the plane of the blade, since the slightest blockage to the side will lead to inevitable curvature.
The immersion movement itself should be decisive, fast and smooth, without timidity and convulsions.

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