4. METALS AND METAL PRODUCTS

General information about metals and alloys

The science of industrial methods for producing metals from ore is called metallurgy . The science of the structure, properties and technology of metal production - metallography .

Metals today are the main structural material, firstly, due to high operational and technological properties, and secondly, metal products and structures are easily connected to each other with bolts, rivets and welding.

In technology, not pure metals are usually used, but alloys. Alloys are systems consisting of several metals or metals and non-metals. All metals and alloys are conventionally divided into ferrous (ferrous) and non-ferrous (non-ferrous). The most widely used ferrous metals (iron-carbon alloys), which, depending on the carbon content, are divided into two groups - cast iron (carbon content more than 2.14%, usually from 2.5 to 4.5%) and steel (carbon content less than 2.14%, as a rule, rarely exceeds 1.5%). In addition to carbon, ferrous metals may contain small amounts of silicon, manganese, phosphorus, sulfur and other chemical elements.

Steel produce carbon and alloyed. Depending on the carbon content, carbonaceous are divided into low (up to 0.25% carbon), medium (0.25 ... 0.6%) and high carbon (> 0.6%). With increasing carbon content decreases ductility and increases the hardness of the steel; its strength also increases, but with a carbon content of more than 1%, it decreases again. Carbon steel for the purpose of subdivided into general purpose steel and tool.

Alloy steels in addition to the components included in carbon steel, contain alloying elements, each of which has its effect on the steel. Manganese (G) increases the strength, wear resistance of steel and resistance to shock loads without reducing its ductility. Silicon (C) improves elastic properties. Nickel (H) and chromium (X) improve mechanical properties, increase heat resistance and corrosion resistance. Molybdenum improves the mechanical properties of steel. By appointment, alloyed steels are divided into structural (0.02 ... 0.85% carbon), tool (0.65 ... 1.4%) and special (alloyed).

For the manufacture of building structures and fittings used structural steel, which have good ductility and low brittleness.

Non-ferrous metals include all metals and alloys based on aluminum, copper, zinc, and titanium. Copper and tin alloys (bronze) and copper and zinc (brass), etc. are used in construction.

Metals and alloys are polycrystalline bodies consisting of an infinite number of crystalline formations, grouped as separate tightly interconnected grains. The crystals have a cubic face-centered or body-centered lattice formed by metallic bonds. In addition to the chemical composition, the properties of ferrous metals also depend on the type and size of crystals.

Since the solid metal formed from the melt, its porosity is zero, that is, the average density coincides with the true one. Therefore, metal products are waterproof and airtight.

Metals have high strength, ductility, high electrical and thermal conductivity, malleability, weldability, the ability to reflect well electromagnetic waves and other specific properties. Metals are very technological: from them you can get products of various shapes and sizes and connect them with each other by welding, riveting, etc.

Disadvantages - high thermal conductivity (the device requires thermal insulation of metal structures of buildings). Metal structures of buildings must be specifically protected from the action of fire, because they lose stability and are deformed: aluminum is already at 100

С loses its bearing capacity, steel - at 500 С. Great damage to the economy causes corrosion of metals.

Metal technology

The main method for the production of ferrous metals is to produce pig iron and then process it into steel.

The raw materials for smelting iron are iron ores, solid fuels (coke) and fluxes.

Ore consists of minerals containing metal and waste rock (sandstone and clay).

In minerals, metals are in the form of chemical compounds (oxides, silicates, etc.). Industrial ore is a rock with a certain metal content. For example, for iron it is at least 30-50%, for copper 3-5%, for molybdenum 0.005-0.02%. In addition to the chemical composition, the ore for the blast furnace process must have a certain size of pieces.

The fuel in the blast furnaces serves not only as a source of heat, but also as a reagent that ensures the reduction of iron from ore and the formation of cast iron (by carburizing iron). The main type of fuel in blast furnaces is coke. Additionally, use natural gas. Coke is produced in coke ovens by dry distillation at a temperature of 1000 ° C (without air access) of coking coal.

Flux is required to remove residues of waste rock (consisting mainly of SiO2 and Al2O3) and ash from fuel combustion. These components, fusing with each other, form a blast furnace slag, which is a mixture of silicates and calcium aluminates and in the liquid state is removed from the furnace.

Preparation of ore includes crushing, enrichment and sintering.

The main method of producing iron from iron ore is high-temperature (up to 2000 ° C) treatment of the charge in blast furnaces, at which iron is reduced by reaction with carbon dioxide. At 1147 ° C in the blast furnace, the formation of molten iron begins and the melting of gangue and fluxes with the formation of slags as a result of the melting of CaO lime and the empty SiO2 and Al2O3 steam. Molten iron flows down the furnace, and the slag melt, as lighter, is on top of the iron. Cast iron and slag are periodically released through tap holes in the ladle. For each ton of iron, from 0.4 to 0.65 tons of fire-liquid slag is obtained, which is called blast furnace. In addition to iron and slag, blast furnace products are blast furnace gas and blast furnace dust. Cast iron goes to the casting machines for casting into "pigs" for processing into steel or products, and slags from the furnace are sent to granulation or to the dump. Depending on the composition, pig iron (white), foundry (gray) and ferroalloy are produced.

Blast furnace slags are a valuable raw material for the production of building materials (Portland cement, Portland slag cement, mixed cementless binders, aggregates for concrete, slag wool, slag and steel, etc.). They include up to 30 different chemical elements, mainly in the form of oxides. The main oxides are SiO2, Al2O3, CaO, MgO. FeO, MnO, P2O5, TiO2, V2O5, etc. are present in smaller quantities.

Steel is produced from pig iron and steel scrap (scrap) in converters (40%), martens (40%) and electric furnaces (20%). The essence of the metallurgical process of redistribution of iron into steel is to reduce the carbon content and impurities by oxidizing them and converting them to slag and gases during the smelting process. To do this, iron is first oxidized, and then reduced by the oxidation of silicon, silicon, manganese, Mn, aluminum, and carbon C. Ferromanganese, ferrosilicon, aluminum, etc. are used as deoxidizing agents.

In the production of steel, slags similar to blast furnaces, but having their own characteristics, are also formed. Melted steel is poured into ingots or processed into billets by the method of continuous casting.

Metal products manufacturing

Steel ingots - a semi-finished product from which necessary products are obtained. Generally used steel pressure treatment: the metal under the action of the applied force is deformed, keeping the acquired shape. To facilitate processing, steel is often preheated. There are the following types of metal forming: rolling, pressing, drawing, forging, stamping.

Construction metal products and structures

Of cast iron in the construction used mainly gray (cast) cast iron. From it, the elements of building structures that work in compression are obtained by casting: columns, support pads, arches, arches, metro pipes, floor slabs for industrial buildings, etc .; They also produce sanitary (radiators, baths, sinks, valves, manhole covers, pipes for sanitary cabins, sewer networks, industrial water drainage, etc.) and architectural and artistic products. Gray cast iron is used for casting pipes of furnace devices (furnace doors, latches, grate bars).

Construction metal products can be divided into building structures and steel reinforcement for reinforced concrete. They are made, as a rule, from structural carbon steels. Structural alloyed steels are used only for particularly important metal structures and reinforcement for prestressed reinforced concrete.

Metal building structures are divided into bearing, enclosing and combining the functions of bearing and enclosing. The supporting structures include arches, beams, trusses, columns, frames, ties, racks, pipes, structural structures of the coating, half-timbered beams, racks, stairs, etc. Bearing structures are made of rolling elements of various profiles (I-beams, channels, angles of equal and unequal legs), square and rectangular pipes, strip and sheet steel.

One-and multi-layer wall panels, frameworks and partitions panels can be attributed to the enclosing structures. In multilayer panels, one or two outer layers are made of profiled sheet metal - galvanized steel or aluminum, and the inner layer - heat insulating - is made of foam, polyurethane foam, etc.

Metal structures are used mainly in industrial construction, for the construction of bridges, as decorative elements of urban improvement - fences, lattices, bins, benches, public transport stops, etc.

In construction, metals have limited application, as they are required for other industries (mainly mechanical engineering), are expensive, require thermal insulation, protection against corrosion and high temperatures.