Why does ductility decrease with increasing hardness

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[692]Extensibility (Ductility). All rigid bodies undergo changes in shape as a result of tension and compression, depending on their degree of hardness. The changes in shape are either permanent or vanish with the forces acting on them. In the former case the bodies are called plastic (malleable, kneadable), in the latter caseelastic. A sufficient degree of is associated with plasticity toughness, of the resistance of the particles to separation, these are the names of the bodiesductile or stretchy.

The property of greater or lesser ductility is very different from substance to substance and also in the various states of the same substance. At first the ductility appears as a certain function of the atomic weight, which shows the periodic system of the elements of Lothar Meyer and Mendelejeff; then it depends on the temperature, usually in such a way that it increases with increasing temperature (iron and other metals, glass); furthermore, it changes through processing, in that the ductility tends to decrease and the elasticity to increase through hammering, rolling, and drawing; rapid cooling decreases ductility and increases brittleness; with slow cooling, the ductility is also maintained in the cold. - Small impurities and admixtures of other substances, such as carbon, sulfur, silicon, phosphorus, iron and copper, often have a very great influence. The same body appears to be ductile to a different extent depending on its use of tension or pressure (pulling or rolling) or depending on the speed of the action (hammering), so that a scale of ductility cannot be given with certainty, as can a certain measure for this property of the Body is missing. The following metals are ductile: gold (gold leaf can be produced up to a thickness of less than 0.01 mm), silver, platinum (less when hammering and rolling than when drawing), copper, lead, tin, aluminum, zinc, iron, etc., while antimony, Bismuth, chromium, manganese, tungsten and others are brittle metals. The zinc shows a very special behavior, which when poured is brittle at normal temperature, at 205 ° it is so brittle that it can be powdered in a mortar. In contrast, it can be rolled at 100–150 ° and, when rolled, retains its ductility and flexibility even after cooling. Similarly, lead and tin are brittle near their melting point. Copper is easier to forge cold than warm, and bell metal is the opposite of that. Steel, it is quickly cooled, red-hot, malleable, slowly cooled, hard and brittle. For more information on ductility, see the individual bodies, especially metals and alloys.

Aug. Schmidt.