By Fire and Sword - Exploration of metallic materials


By Fire and Sword - Exploration of metallic materials


Our modern lives are full of many metal products, from the Volkswagen streetcar to the Shenzhou spacecraft that travels among the stars, to the giant ship of 10,000 tons to the micron electrode. Our human society has been mechanically transformed since its inception. "There is more iron than meat." What do we know about the iron bumps that have been with us since the beginning of civilization?

Let's get acquainted with these silent, familiar friends.

1. Star Trash

Metal is the afterglow from frozen stars.

We all know that nuclear fusion is the driving force behind stars glowing and heating up, without overcoming their enormous gravity. It can also produce tremendous amounts of energy. Hydrogen fusion is the most common and widely used form of nuclear fusion. It takes place on the Sun. Four hydrogen atoms can be forcibly "fused", resulting in one helium-atom under the harsh conditions of a star. According to the mass-energy equation, the mass that is lost during this process will be transformed into an incredible release of energy. One tiny fraction of the infinite energy from fusion is sufficient to provide food for hundreds of millions of people on Earth.

It is impossible to control nuclear fusion and can only be used for creating hydrogen bombs that cause chaos and destruction. The Sun, however, is a large hydrogen bomb because it is a main sequence star.

Our curiosity takes us further. Is the nuclear fusion chain complete? Or is there a black point in the periodic table where they can see a giant light that appears divine enough to cause eternal death?

Consider our Sun as an illustration: When most of the hydrogen elements are converted into helium elements, the initial stable burning sun will become a red giant. The threshold for helium-fusion will be reached when the temperatures and pressures of the planet's core continue to rise. The already dimming giant star will then glow with a brilliant backlight called a "helium flash" and finally become a super-dense, diamond-like star - a white dwarf, which will always be accompanied by darkness and cold.

Things get even more complicated for massive stars, which are much larger than the Sun. The greater the volume, the more chances of rebirth. Each "heavier" element acts as an emperor, transmitting the flames of fusion and delaying the end of time. However, the conditions for synthesis are becoming more difficult and the released energy is decreasing in strength.

This long-lasting system finally collapsed when the Iron was given the fusion torch. This is the number of elements. 26 has a high specific binding energy and a stable nucleus. However, the fusion reaction releases energy that cannot be met. When a huge star forms a superhigh pressure gaseous iron core it will be destroyed. The basic frenzy-prone environment that allows the iron element to continue to mix the drunken poison to quench the thirst will end at the last moment. Many heavy elements will then be born that rank lower on the periodic table. The star-studded supernova blast will eventually end the star's brief but brilliant life. These heavy elements either become trapped by a massive gravitational force or are crushed into neutron stars, black holes or with the help an explosive force, escape from a gravitational trap to become magnificent nebulae scattered across the Universe.

It is responsible for almost all of the heavy elements in our universe. The big man Tianzi took out a large, golden-steel knife with an annular shoulder and pulled it from his waist. He would not have known that he needed at least one star to collect the heavy elements.

Second, Bronze Age

However, it was not "Starkiller" iron that first opened the door to civilization for people, but "heavier" copper.

In fact, in terms of reserves in the earth's crust, copper is not as good as iron. However, most of the iron on the earth's surface was oxidized during the "Great Oxidation", which may be associated with early life over 2 billion years ago, so mining and smelting iron ore is much more difficult than copper ore.

Modern archaeological evidence shows that humans have been using copper for a long time. Even 6000-7000 years ago there was evidence of the large-scale use of copper products in the Mesopotamia of Western Asia, where early civilizations were just emerging. This new material, more useful than stone tools, soon sparked a technological revolution in ancient times. After much deliberate or unintentional research, an alloy with a low melting point, easy workability and good hardness has been discovered - bronze.

The Bronze Age begins.

In a modern context, many copper alloys are commonly referred to as bronze. However, thousands of years ago bronze, used in large quantities by our ancestors, was mainly a copper-tin alloy mixed with copper, tin and lead. After this mixing, bronze has a lower melting point and better fluidity, making it an ideal casting material. National treasures such as the square lotus crane pot, the cloud pattern copper bath, the Hou (Xi) Muwu tripod, the Xiyang square statue, and the Sanxingdui statues are all cast in bronze.

Contrary to the impression that most modern people take for granted based on excavated cultural relics, bronze that has not been oxidized and eroded is not "green"; The Dukes of Spring and Autumn, galloping across the battlefield on four chariot horses, are all clad in dazzling golden yellow bronze armor.

Bronze is also much harder than soft brass and can be forged into sharp weapons. However, bronze weapons are still somewhat fragile in the eyes of warriors, and can easily be smashed to pieces or even "smashed into sand" on the battlefield in a wild fight. Therefore, weapons made of bronze are often heavy battle axes, broad spearheads, and short and sharp one-handed swords. Some overly thin bronze swords are often used for ceremonial rituals rather than actual combat weapons.

Why is bronze apparently hard but not strong enough? This starts with the basic definition of hardness.

In engineering, hardness refers to the ability of a material surface to resist the penetration of a harder object. Whether steel balls (Brinell hardness) or diamonds (Rockwell hardness) are used, the measurement of hardness cannot be directly related to the "hardness" that we understand in our daily lives. In practical applications, the hardness index is mainly used to describe the wear resistance of objects.

For example, what we call "brittle" glass is actually so hard that it requires a special glass knife with diamonds to cut it. However, when the glass is subjected to an external force, it is easy to break. This "more flex than bend" characteristic is brittleness. It corresponds to "plasticity", which is deformed under the action of an external force, but does not break. As for the property that is actually used to describe the "viscosity" of an object and the resistance to deformation and destruction under external loads, it has its own independent name "strength". However, bronze weapons are only slightly lacking in durability.

But when a barreled gunpowder-powered firearm fired a deadly volley, the bronze returned to the fray. Bronze, carefully selected in proportion, has excellent properties in castings. In the modern period, before the advent of modern industrial steel, bronze has always been the main material for casting giant artillery pieces. The key weapon of the Ottoman Empire for the destruction of Constantinople in 1453 was the "City Cannon", cast in bronze. I believe that all sci-fi lovers who have read Three Bodies III: Immortal Death still remember the terrifying power of this gigantic war beast.

As history entered the industrial age, many of the physical and chemical properties of copper began to play a role in modern life. Copper is a good conductor of electricity and heat, making it an important material for wires and heatsinks. From modern electrical appliancesore that we have on hand, we can find a lot of copper components when we disassemble any of them. The good ductility of copper is very suitable for mass production of stampings such as bullet cases. The property that copper is not easily magnetized is also good news for mechanical parts such as the spirals of mechanical watches, which require precision work. In addition, bronze, "remelted" by modern metallurgical technologies, is even stronger and plays a key role in various machines.

However, if we take a look around, we can see that the most common metal is probably iron, which ends up with stars.

Third, Iron Roar

"How is steel hardened?"

I'm afraid that many people who come into contact with steel every day will not be able to answer this question. Due to the "Great Oxidation" event, a large amount of iron ore on the surface of the earth was completely tasteless to the ancestors of the classical period. The earliest steel used by humans was a meteorite from space. These finished pieces of iron floating in the universe are naturally of high purity and after etching, they reveal extremely beautiful unique crystallization patterns, that is, meteorites can only be formed when the temperature of meteorites slowly cools down in the units of millions of years. in space special structure.

The Hittites were the first to turn iron ore into steel. As early as 4,000 years ago, this military nation living in the Anatolian Peninsula took the lead in overcoming the technical difficulties of iron and steel smelting and immediately began to expand overseas. Although the Hittite Empire had always considered steelmaking a national secret, the technology spread like wildfire across the three continents of Asia, Europe, and Africa. Since then, mankind has opened the "Steel Age", which continues to this day.

No matter how amazing changes have taken place in smelting technology over the centuries, the basic principles remain exactly the same. When smelting, iron ore, coke and limestone (flux) must be introduced into the blast furnace in a certain proportion. After continuous heating, the iron oxide is reduced, and in our general context, "pig iron" is obtained.

It is interesting that although the word "iron" is in the name of cast iron, in fact it is not pure iron, but contains a lot of carbon and other impurities. In addition, the mechanical properties of cast iron are not good enough, especially since cast iron, which is now rarely used, is hard and brittle - friends who use old-fashioned cast iron ladles at home may get the impression that such a large black pan often breaks when dropped. , Even if the food is cooked too hard, a hole may form. Because of this, even in modern times, large metal parts such as cannons, which are best cast in one piece, still often have to be made from copper.

In the currentIn a “hate iron but not steel” situation, we need to recycle cast iron by throwing it back into a high-oxygen, high-temperature converter or even an electric decarburization furnace and simultaneously remove sulfur and phosphorus, as well as other harmful elements that do not affect the characteristics of steel. After such "steelmaking" steps, the familiar steel products officially leave the plant.

Depending on the different carbon content, the properties of steel also have obvious changes. Low carbon steel has good toughness, but is not strong enough, medium carbon steel has the most average performance characteristics and is widely used in production and everyday life. carbon content 0.45%. Carbon steel is mainly used as cutting tools and molds.

Of course, when steel was invented, it was first used in war. The earliest iron work is currently the Hittite short knife.

Although the term "sword casting" is often used in rhetoric to describe the making of swords, after the advent of the Iron Age, this term, which has been in use since the Bronze Age, is no longer accurate. Compared to casting, forging technology can improve the mechanical properties of steel products better. Repeated folding and forging can make the grains in the metal fine and uniform, and at the same time remove the impurities and pores introduced during smelting. The carbon content of steel produced in ancient times is often uneven, and it must be bent and forged for decarburization to stabilize the carbon content, so there is a saying that "steel can be made after hundreds of improvements." And these good steels, which are repeatedly bent and forged like kneaded dough, often form graceful and delicate patterns on the surface, which are often called "镔铁" in various romance novels.

Now that the qualified steel ingots are prepared, the next step is to "use good steel at the forefront". Since the Bronze Age, there has been a controversy in the choice of materials for the sword: the cutting edge must be of high hardness so that the blade does not crumble as much as possible, but the body of the sword must be stronger so that it does not crumble. break when used aggressively. Obviously, with the ancient technology of melting one steel, it is difficult to satisfy both requirements at the same time. Thus, "hard clad soft" or "hard clad soft clamp" clad steel technologies have been adopted all over the world. By combining steel materials with different properties, both the hardness of the cutting edge and the strength of the body of the sword are achieved. to your account.

After forging, a freshly baked steel rod needs further heat treatment, the most important of which is water or oil quenching. This rapid cooling process can greatly increase the sword's hardness. Besides,swords formed after repeated forging sometimes require "quenching"—that is, reheating and softening—to remove the intense stresses built up within the material.

To further enhance the effectiveness of the sword, the ancients even heat-treated their brains. For example, the Japanese sword, famous for its excellent sharpness, has a unique technique of "cauterizing the blade with earth". Simply put, this technique consists in winding the soil around the formed blade, leaving only the edge section outside. Thus, during the hardening and cooling process, the ground coated blade body cools more slowly and has better toughness, while the exposed cutting edge cools faster and the hardness increases significantly. Modern test results show that the hardness of a quality Japanese knife increases dramatically in the blade area, reaching even several times the hardness of the back of the knife, which is indeed a precious knife. The iconic "wavy pattern" on the Japanese sword is the dividing line of the overlying ground - the pattern of the blade.

However, even if it is a magical weapon that has been hardened for thousands of years, rust caused by slight oxidation of the steel is still inevitable. For this annoying problem, the ancients really have no better remedy than diligently rubbing and oiling. If you want to solve this problem once and for all, you will have to rely on modern materials science, which has advanced by leaps and bounds over the past two hundred years.

The stainless steel we know is actually an alloy steel with a relatively high chromium content. As soon as stainless steel comes into contact with air, the chromium alloyed in it forms a passivating film 1-2 nanometers thick on the surface, thus isolating further oxidation of the steel by air; oxide film. Therefore, it is not surprising that stainless steel is widely used in engineering, medicine and everyday life.

In addition to stainless steel, there are many alloy steels in our lives. For example, manganese steel has achieved all-round development in hardness, strength and toughness. Except for a small defect, inconvenient for secondary processing after a single casting, it almost satisfies all the fantasies of the ancients about steel, comparable to the legendary "Mysterious Iron". Manganese steel can be seen in tank armor, caterpillars, excavator buckets and other parts that require long "hard work". High hardness tungsten steel can be used as high-quality high-speed steel, even under high-temperature high-speed friction, tungsten steel can remain hard and sharp, and can even be used to make armor. sub-caliber bullets capable of destroying tanks with one hit.

With the further development of science and technology. People's research has also penetrated to the level of microscopic criss.steel structure, and smelting technology has also made great progress. "Powder steel" has appeared, which pulverizes molten steel into powder and then recombines it with high temperature and high pressure. The internal structure of this expensive steel is very uniform, and its amazing mechanical properties surpass the imagination of the ancients.

However, no matter how "superevolutionary" steel is, it still cannot get rid of the problem of its own excessive density. For emerging high-speed vehicles, aircraft and even spacecraft, strong steel is clearly too heavy.

Fourth, Mithril

In Tolkien's masterpiece The Lord of the Rings, the master of fantasy literature created an extremely rare magical metal, mithril, in Middle-earth. Chain mail woven from it, invulnerable to guns, water and fire, but light as a feather, is an invaluable national treasure of the kingdom of the dwarves.

Is there really such a metal that takes into account weight, strength and physico-chemical stability?

This is a titanium alloy.

Titanium is quite a magical metal. Although its chemical properties are quite active, a passivating film similar to stainless steel can form on the surface, showing excellent stability. The titanium commonly used today is basically a titanium alloy containing other metals such as aluminium. Interestingly, two light metals, titanium and aluminum, were more expensive than gold because they were difficult to obtain when they were first discovered by humans. In modern European courts, aluminum cookware was once the ultimate feature, surpassing gold and silver, which makes us laugh and cry in our time.

Today, with the development of science, titanium alloys are produced enough for large-scale applications. Titanium alloy is light, cold and heat resistant, and strong enough to make it an ideal material for aerospace vehicles, and even some high-end racing cars will be made from it. In addition, this silver white metal also has excellent compatibility with our body tissues. Titanium alloy medical components implanted in the body can safely stay in the body for decades, in addition, titanium is not magnetic, and there are titanium alloy implants in the body. alloy. Patients who have lost food can safely enter the MRI machine for imaging studies without injury.

Just like a group of black tech mercenaries called "Mithril" in the sci-fi cartoon Steel Frenzy. If we want mithril from fantasy to become reality, we can only rely on our own hands and brains. Those superheavy elements that cannot even “suppress” supernovae and practically do not exist in the Universe are now being born one after another in human colliders. With jointWith the development of science and technology, future metal materials will continue to accompany us to create new wonders one after another.