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Do you know steel, what metallurgy, steel, heat treatment, casting-1

Author:YiShengbai    Date:2020-05-24 22:46:16

In the Stone Age, metal was very rare and therefore highly cherished. Copper and gold were the only sources of metals at the time, because only these two metals existed naturally in the earth's crust (others had to be extracted from ore), but the amount was not large. There is also iron in the earth's crust, but most of it comes from meteorites in the sky.


       Regarding the metal that fell from the sky, no one feels more deeply than Radivoke Lajic, who lives in northern Bosnia

     From 2007 to 2008, his family was hit by meteorite at least 5 times. Statistically speaking, the probability of such a thing happening is very small. Raic said that the aliens locked his home, which sounds reasonable. He expressed this opinion in 2008 and as a result his home was hit by a meteorite again. Scientists confirmed that the meteorite was correct, and began to study the magnetic field near his house, hoping to find out the reason behind this unusually high frequency.


        Rajic shows five meteorites that have hit his home since 2007

        Without gold, copper, and meteorite iron, our ancestors of the Stone Age could only make tools from flint, wood, and animal bones. Anyone who has used these materials knows that the tools made from them have very limited uses. When the wood is knocked, it is either broken, cracked, or broken into two pieces. Stones and animal bones are no exception. Metals are fundamentally different from these materials. Metals can be forged-they will flow and become plastic when heated. Not only that, the metal is getting stronger and stronger, and the blade can be hardened by iron alone, and as long as the metal is heated in the fire, the whole process can be reversed and the metal becomes soft.


        The human who first discovered this 10,000 years ago, finally found a material that is as hard as rock and plastic, can be shaped at will, and can be reused indefinitely. In other words, they found the most suitable material for making tools, especially for cutting tools like axe, chisel and blade.


        Our ancestors must have felt that the metal's ability to be soft and hard is amazing. I soon discovered that Brian felt the same way. He said that he had no knowledge of physics and chemistry. He made the invention by repeated trial and error, but in the end he succeeded. He hopes that I can help him measure the difference between the sharpness of the blade after the operation of his machine. Because of this evidence, he has the capital to discuss business with the razor company.


       Schematic diagram of metal crystals. The crystals in the razor are similar. The rows of small dots represent atoms

       The idea is that metals are composed of crystals. Because of the crystal, we usually think of transparent polyhedral ores, such as diamonds or jade. The crystal characteristics of metals are not visible from the surface, because metals are not transparent, and the crystal structure is usually so small that it must be seen with a microscope. Observing metal crystals with an electron microscope, it feels like seeing unruly floor tiles, and the crystals are distorted lines called "dislocations". A dislocation is a flaw inside a metal crystal, which means that the atom deviates from its original perfect structure and is an atom that should not be broken. Dislocations sound terrible, but they are actually very useful. The reason why metal can be a good material for making tools, cutters and blades is because of dislocations, because it can change the shape of metal.

 

        In this sketch, I have only drawn a few dislocations, which is convenient for readers to imagine. The number of dislocations in general metals is staggering, and they overlap and stagger

        You don't need a hammer to feel the power of dislocations. When you lift a paper clip, you bend the metal crystal. If the crystal is not bent, the paper clip will break like a wooden stick. The plasticity of the metal comes from the movement of dislocations within the crystal. Dislocation movement will carry a trace of this substance, moving from one side of the crystal to the other at supersonic speed. In other words, when you bend the paper clip, there are nearly 100,000,000,000,000 dislocations moving at a speed of several kilometers per second. Although each dislocation only moves a small piece of crystal (equivalent to an atomic face), it is enough to make the crystal a superplastic material rather than a fragile rock.


        The melting point of the metal represents the strength of the metal bond in the crystal, and also the dislocation tolerance is not easy to move. The melting point of lead is not high, so dislocations move easily, making lead very soft. Copper has a higher melting point and is therefore harder. Heating causes dislocations to move and rearrange and combine. One of the results is to make the metal softer.


        For prehistoric humans, the discovery of metal was an epoch-making moment, but the basic problem of not having a large number of metals has not been solved. One solution is to wait for more meteorites to fall from the sky, but this requires patience. About a few kilograms of meteorites fall into the earth every year, but most of them fall into the sea. Later, someone discovered something. This discovery not only ended the Stone Age, but also opened a door for humans to obtain a material that seems to be never depleted: they found a green stone, which was put in a hot flame and repeated With fiery ashes, it will become shiny metal. We now know that this green stone is malachite, and the shiny metal is of course copper. For our ancestors, this is definitely the most amazing discovery. The surrounding is no longer lifeless rocks, but the mysterious substance with inner life.

   Our ancestors can only cast this kind of magic on a few types of rocks, such as malachite, because to effectively transform a stone into a metal, not only must we recognize the correct rock, but we must carefully control its chemical state. But even if some stones are still stubborn, no matter how high the temperature is, there is no change at all. Our ancestors must still feel that these stones have hidden mysteries. They guessed right. The heating method is suitable for refining many minerals, but it is only a few thousand years later. After humans understand the chemical principles and how to control the chemical reactions of rocks and gases in flames, the melting method really has a new breakthrough.


         Without metallic copper, there would be no pyramid

         Since about 5000 BC, our ancestors have continued to make mistakes and refined copper smelting technology. Copper appliances not only contributed to the rapid advancement of human technology, but also gave birth to other technologies, as well as the emergence of cities and the first wave of human civilization. The Egyptian pyramids are the result of the massive application of copper utensils. The rocks used to build the pyramids were dug out of the mine and then cut into pieces of fixed size with copper chisels. It is estimated that the ancient Egyptians excavated about 10,000 tons of copper ore and produced 300,000 copper chisels. This is an unprecedented achievement.


         Without metal tools, even the slaves would not be able to build a pyramid. In particular, copper chisels are not suitable for cutting rocks because they are not hard enough. When used to beat limestone, they will quickly become dull, which makes this achievement even more remarkable. Experts estimate that every time a copper chisel is struck, it must be re-sharpened to continue using it. The same is true when copper is not suitable for razors.


         Gold is also a metal with low hardness, so the ring is rarely made of pure gold, otherwise it will be scratched soon. But as long as a few percent of other metals (such as silver or copper) are added to form an alloy, it will change the color of gold: silver will make gold white, and copper will make gold red. Not only that, but the alloy formed will Pure gold is hard, and much harder. As long as the metal is mixed with a small amount of other substances, its properties will change. This is the fun of studying metals.


         Taking gold-silver alloys as an example, you may be wondering where the silver atoms are. The answer is that silver atoms are embedded in the lattice of gold nuggets, occupying the position of one gold atom. It is because of the replacement of silver atoms that gold hardens.


         Atomic structure diagram of gold-silver alloy. Silver atoms replace some gold atoms in the crystal


         Alloys are usually harder than pure metals for a simple reason: the size and chemical properties of foreign atoms are different from the original metal atoms. Therefore, the embedding will disturb the physical and electronic structure of the original metal crystal, with a key consequence-making the dislocation more difficult to move. Dislocations are more difficult to move, crystal shapes are more difficult to change, and metals are harder. Therefore, the manufacture of alloys has become a technique for preventing the movement of dislocations.


         In nature, atomic substitution also occurs in other crystals. Pure alumina crystals are transparent, but as long as they contain iron atoms, they will turn blue and become commonly known as sapphire. Similarly, pure alumina crystals containing chromium atoms will also change color and become rubies.


         From the brass age, the bronze age to the iron age, in the continuous development of civilization, alloys are becoming harder and harder. Brass is very soft, it is a natural mineral, and it is easy to melt. Bronze is much harder than brass, is an alloy of copper, contains a small amount of tin, and occasionally includes arsenic. Therefore, if you have brass and know the method, you can make weapons and razors that are ten times stronger and harder than brass with just a little effort. The only trouble is that tin and arsenic are very rare. The people of the Bronze Age developed many carefully identified trade routes, and transported tin mines from Cornwall and Afghanistan to the centers of civilizations in the Middle East for this purpose.




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