Forwarded from Світове дерево (✙ Микола Єлісєєв ✙)
Let us talk about another aspect of metalwork, namely, heat treatment of steels.
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Forwarded from Світове дерево (✙ Микола Єлісєєв ✙)
Some time ago, I did cover the topics of blacksmithing tools and their use. But I did omit one very essential topic for any beginner, namely, heat treatment of various metals. So, let me try and explain the basics of this process today
Now you might ask, why do you even need to heat treat your work? Well, ferrous alloys, namely, steel with a high enough amount of carbon can be used for different applications. Your knifes must be hard enough to retain a cutting edge, but soft enough not to shatter from the slightest touch. The harder something is, the more brittle it is, as well. A tool like a drill bit or a tap could be extremely hard, to be able to cut through stell. In order to achieve the needed hardness, you need to heat treat your work.
Any heat treatment of carbon steel consists of two steps. First, you quench it. Then, you temper it. Quenching is the rapid cooling of steel, heated above the critical point beforehand, in oil, water, or other liquid media. Tempering is the slow cooling of steel, heated below the critical point, in open air, or in an environment with a controlled temperature drop, like an electrical oven.
This process works in the following way. In a heated piece of metal, the atoms bounce around (oscillate) with relatively high speeds. When we cool them rapidly, they are "frozen" in place, with no way to relax, forming large hard grains inside the piece. But when cooled slowly, they have time to relax, reducing their speed slowly, and storing less energy and inner stresses in them, forming smaller, softer, grains, and a much more strong piece.
For different types of steel, the points to which it must be heated for quenching or tempering are different. The critical point is usually around 800 degrees Celsius, and the tempering temperature is usually in the interval of 120-320 degrees. Before doing any heat treatment, one must relieve all inner stresses inside the workpiece. To do that, a process, called normalisation, is used. You need to heat the steel above its critical point, and let it cool down slowly, in open air, or sandwiched between pieces of foam concrete. This cycle must be repeated several times, before hardening.
In general, quenching in motor oil gives better results, because oil has a smaller heat conductivity, and formes less steam. Water could lead to warped, or even cracked, pieces, and steam explosions, if the piece is large, and the vessel one uses for quenching is small.
#metalwork #heattreatment
Now you might ask, why do you even need to heat treat your work? Well, ferrous alloys, namely, steel with a high enough amount of carbon can be used for different applications. Your knifes must be hard enough to retain a cutting edge, but soft enough not to shatter from the slightest touch. The harder something is, the more brittle it is, as well. A tool like a drill bit or a tap could be extremely hard, to be able to cut through stell. In order to achieve the needed hardness, you need to heat treat your work.
Any heat treatment of carbon steel consists of two steps. First, you quench it. Then, you temper it. Quenching is the rapid cooling of steel, heated above the critical point beforehand, in oil, water, or other liquid media. Tempering is the slow cooling of steel, heated below the critical point, in open air, or in an environment with a controlled temperature drop, like an electrical oven.
This process works in the following way. In a heated piece of metal, the atoms bounce around (oscillate) with relatively high speeds. When we cool them rapidly, they are "frozen" in place, with no way to relax, forming large hard grains inside the piece. But when cooled slowly, they have time to relax, reducing their speed slowly, and storing less energy and inner stresses in them, forming smaller, softer, grains, and a much more strong piece.
For different types of steel, the points to which it must be heated for quenching or tempering are different. The critical point is usually around 800 degrees Celsius, and the tempering temperature is usually in the interval of 120-320 degrees. Before doing any heat treatment, one must relieve all inner stresses inside the workpiece. To do that, a process, called normalisation, is used. You need to heat the steel above its critical point, and let it cool down slowly, in open air, or sandwiched between pieces of foam concrete. This cycle must be repeated several times, before hardening.
In general, quenching in motor oil gives better results, because oil has a smaller heat conductivity, and formes less steam. Water could lead to warped, or even cracked, pieces, and steam explosions, if the piece is large, and the vessel one uses for quenching is small.
#metalwork #heattreatment
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