In the list of the most important metals for human civilization, iron holds the first place. The reason lies in the fact that iron has a whole complex of remarkable properties, primarily high strength and hardness. If we want to praise a person for some of its quality, we often compare it with iron: "iron nerves", "iron character", "iron man". In all these lively expressions, a tribute to high respect for the most modest and indispensable metal of our life is involuntarily given.
It is difficult to enumerate the enormous number of things that surround us in the everyday life of things, devices, devices, machines and structures that a person has created from iron. Much easier, probably, to name those things in which there is no iron.
However, I want to make a reservation: neither I, nor any of you reading this book, have ever seen truly iron, that is, made of pure iron, products. Because iron in the proper sense of the word on Earth is only a few hundred grams, and even those are only in some large laboratories of scientific institutions. Pure iron fabulously expensive and does not have, moreover, special strength. All that we in life do not exactly call "iron", "iron", in fact it is made of simple, ordinary steel.
"Simple, ordinary steel ..." The engineer immediately winced, having read such a phrase. Because it is wrong. Uncover any technical reference book - you will see in it tens, hundreds of different names of steel.
Engineers refer steel to so-called ferrous metals (or "black" metals (not musicai style!)). The name "black" these metals - steel and cast-iron - got because at the time of their birth from iron ore, they can not do without coal. The furnace that generates ferrous metals is most often a blast furnace, a huge furnace with a height of 10-15-storey house. The furnace is loaded with ore mixed with coal (coke), and set on fire. Carbon of coke, burning up, emits a lot of heat, the temperature in the giant furnace blast furnace rises to 1600-1900 ° C, and in black smoke and flame, the ore melts, secreting iron. (In fact, everything, of course, is a bit more complicated.)
(How does a blast furnace work? You can look at YouTube in enough quantity, for example this one: )
Liquid, molten iron can dissolve many foreign substances in it, as hot water dissolves sugar. Being in the blast furnace, iron can dissolve even its walls, laid out of a special brick - if it does not interfere, of course. And we must "interfere" with him: adding more and more portions of ore and coke to the blast furnace, and the melted iron now and then is blown out (blown out) into special buckets.
However, part of the carbon of coke has time to dissolve in the gland. When the metal released from the blast furnace solidifies in the ladle, it will be dark in color. This is the first of the "black" metals, derived from iron-cast iron.
Both iron and steel are alloys of carbon with iron. Only in carbon steel is less than in cast iron. To produce steel, cast iron is blown with oxygen, while carbon "burns out", and steel is formed from cast iron.
In pure iron, no residue can dissolve no more than 2% of carbon. Alloys containing up to 2% carbon are called steels; alloys, in which more than 2% of carbon (usually from 2 to 5-6%), - cast iron.
Carbon in cast iron is contained in excess, so when the metal solidifies in the ladle, it is released in the form of tiny flakes, flakes or balls, settling more or less evenly between the grains of steel crystals.
This leads to a significant (in comparison with steel) reduction in the strength of the metal: cast iron its fragility is due only to excess carbon, creating in the body of metal microscopic pores and cracks.
In steel, carbon is dissolved without a residue, but even here its effect on the properties of the metal is very strong. It primarily affects the hardness of steel: the more carbon steel, the stronger it is in comparison with iron (stronger). But, in addition to carbon, in addition to phosphorus, sulfur, silicon, manganese, chromium, or some other chemical element, even several elements can fall into the steel at the moment of melting. All these impurities, even in the smallest amounts, seriously affect the properties of the metal. Sulfur and phosphorus so deteriorate the steel, which directly disrupt it. Therefore, metallurgists strive to reduce the content of sulfur and phosphorus in steel to the smallest.
All other impurities - and especially the admixtures of metals - are combined with steel and have a beneficial effect on its properties. Therefore, metallurgists often deliberately "clog up" steel with additives of small doses of chromium, nickel, molybdenum, tungsten, titanium and other metals.
Depending on the chemical composition of the steel, that is, whether it has a doping additive or not, all steel is classified as either a carbon family or a family of alloyed steels.
Carbon steels almost all of their properties are "dictated" by carbon; In doped, along with carbon, the presence of additives (alloying additives) is of great importance.
Carbon content of steel is attributed to: low-carbon (up to 0.25% carbon), medium-carbon (from 0.25 to 0.60% carbon) and high-carbon (from 0.60 to 2% carbon).
The same is true for alloyed steel: it is low-alloyed (no more than 2.5% admixture additives), medium-alloyed (2.5 to 10% additives) and high-alloyed (more than 10% additives).
Both carbon and alloying elements affect mainly the mechanical properties of steel, that is, its hardness, strength, etc. When creating certain machines or mechanisms, the engineer takes into account first of all the mechanical properties of steel; it is quite clear to him that the stronger the metal, the more efficient, reliable and durable it is. However, the effect of alloying additives on steel is much more pronounced. With an equal strength of two parts made of one of carbon steel and the other of alloyed, the second (alloyed) part will have a number of remarkable properties: it can have, for example, higher chemical resistance, impact resistance, electrical conductivity, hardenability and etc. But almost always alloy steel is more expensive than carbon steel. So it is uneconomical and undesirable to use it wherever carbon steel can be handled.
The next theme will be "Types of steels and examples of their application."
