how to make a knife? comp process

how to make a knife? comp process

The steel.

Steel is simply the alloy of Iron with a small proportion of carbon that provides great hardness and elasticity. Steel alloys contain different components that provide different qualities depending on the proportions.
Carbon steels are made up of iron and carbon between 0.2 and 2%
. Stainless steels add to carbon steel percentages of chromium between 12 and 17%, Molybdenum up to 1% or vanadium up to 2% .

These materials provide distinct specific properties.

Carbon ensures hardness. While   Chrome provides the quality of stainless steel. The latter is softer, so other metals must be added to harden and prevent the knives from dulling.
On the other hand, Molybdenum and Vanadium act against corrosion and harden the steel.
Not all knives contain these components in their alloys. The fewer components, the less quality and they are cheaper . The brands that produce quality knives usually indicate the quality of the steel on the blade or on the packaging, using the letters Cr for Chromium, Mo for Molybdenum, V for Vanadium and N for Nitrogen, if it is reinforced with this material.

different qualities

The X50CrMoV15 quality widely used by German manufacturers indicates the use of a steel that contains 55% Carbon, 15% Chromium, 0.8% Molybdenum and 0.20% Vanadium. It may also contain less Chromium and the name changes to X45CrMoV15.
The 4116N quality is a variety of the previous one to which Nitrogen is added and improves the initial cutting properties, cutting duration, and corrosion resistance by 25%.

These steel alloys are produced in ingots. These, once rolled, are converted into bars to make the true forgings or sheet metal to make the cut sheets.

Heat treatment in the production of knives.

The blade is heated to a temperature of between approximately 850 and 1200 degrees Celsius . This operation called tempering. It is carried out under a controlled atmosphere with the addition of a specific gas to prevent the accumulation of scale . These sheets are then cooled very quickly and sharply by immersing them in cold water or oil. The thermal contrast of going from high temperature to low temperature generates fragility in the sheet and the risk of it breaking is very high. To solve this brittleness it is necessary to reheat  the sheets at a temperature between 200 and 400° C. This is called “tempering”, and the temperature will depend on the type of steel and the desired hardness. With tempering, the desired character and hardness are obtained, which vary according to each product.

Assessment of the hardness of a knife

This hardness is valued by means of a measurement index called the Rockwell HRC (Hardness Rockwell Scale).
For daily use knives, harnesses between 52 and 56 HRC are expected, for premium knives , harnesses between 56 and 65 HRC are expected.

The tempering operation is very delicate and requires rigorous control of the heating and cooling times, depending on the composition of the steel to be treated. The final hardness is not the only criterion, nor is it sufficient to confirm that a good quality blade has been obtained. For example, if the heat treatment has been too rapid, the steel structure is altered so that the blade will dull quickly with use, even if it is very hard. A rapid heat treatment implies hardness on the surface, but brittleness in the heart of the steel and therefore a soft or brittle blade, moreover, sensitive to corrosion.

Damascus steel.

A few years ago knives with Damascus blades became fashionable. This is a very old technique of forging that came from the Persia area and of which knowledge had been lost. It started with an alloy called wootz , very special and with a much higher amount of carbon than the current standard , and some impurities that gave it its characteristic appearance. The heat treatment varied in the quenching time and in the tempering time. This true Damascus technique is not the one used now.

Currently, production is based on steel sheets that can be folded on itself, forming different layers.  Thus, and after the forging process, when cleaning and chamfering, the damask pattern appears on the blades.

The beveled and sharp.

Once we have the body of the knife finished, tempered and tempered, we must lower the blade to prepare it for sharpening. This operation is called chamfering.

The blade is rectified by lowering the part that will be the cutting area . This process prepares the blade for subsequent sharpening and makes it more resistant. The bevel can be done in different ways: flat or curved, on one side or on both sides of the sheet . The type of bevel is made depending on each type of knife and its use.

Depending on the chosen method, the cut, after sharpening, will be more or less qualitative.

Types of Bevels

A. Flat symmetric bevel . Easy to perform and the subsequent sharpening provides a good quality cut.
B. Convex symmetric bevel . Easy to make and strong, back sharpening provides less efficient cutting ability than concave beveling.
C. Concave bevel . More difficult to perform, but sharpening will provide excellent cutting ability. Its negative part is that, when sharpening frequently, it ends up losing the area of ​​​​the cutting zone.
D. Flat asymmetric bevel . The easiest to do.
E. Concave asymmetric bevel . More difficult than the flat asymmetrical, but with better cutting results when sharpening.

After the beveling, sharpening is carried out. The expertise and experience of the operator will end up giving us a perfect cut. It can be sharpened using sharpening stones, grinders, by hand or mechanically. To check that the edge of the knife is perfect, a sheet of paper is held vertically and the cut is made on the side of the sheet. If the cut is clean, the sharpening is perfect.

The sharpening can be in the form of serrations or serrations , also called beading . It is produced for those knives that must cut or slice foods whose exterior is harder than the interior or has a crust. This sharpening is very common in bread knives, frozen slicing knives, steak knives, and tomato knives .
To finish the blade, polish it using bands of very fine-grain emery paper, each time lowering the grain until a uniform polish is achieved without streaks or mirrors.

The alveoli in the blades of the knives.

Some knives have alveoli in the blade . They are like small oval-shaped holes. The knives that frequently have these alveoli are the oriental Santoku. We will talk about them in a future chapter, salmon knives and more recently some chef’s knives. The reason for these gaps is to reduce friction between the blade and the food . In this way it slides better and cutting is easier.

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