Metal. Steel

Steel is a ductile (deformable), an alloy of iron with carbon (within 2%) and some other elements. Iron-base steel. The structure of the steels in the equilibrium state the percentage of carbon formed depends on the final form of the microstructure of steels and alloys. It can determine the structural diagram of Fe - Fe3C in accordance with the processes that occur in the composition of the alloy. The properties of steels and alloys affect the carbon and constant impurity (process). They are the necessary components, so they are difficult to remove in the smelting of (S, P), from the charge - scrap metal doped (Cr, Ni, etc.), in the process of reduction (Mn, Si). Constant impurity (manganese, silicon, carbon, sulfur, phosphorus, nitrogen, oxygen, hydrogen) are present in solid or gaseous form. At the same time, they do not affect significantly the position of critical points of the diagram Fe - Fe3C. Dependence lies in the possibility of forming separate phases with iron (the main component) and the place of occurrence of these phases. If carbon is to increase the carbon content (up to 1,2%), then increase the hardness, strength, yield strength, the electric resistance, brittleness threshold (0.1% contributes to the temperature threshold of brittleness at 20 ? C), the coercive force. At the same time, plasticity, viscosity, density, thermal conductivity, the magnitude of the residual induction, the elongation and narrowing down. Since the physical properties change, then this leads to a number of negative processes and, specifically, weldability, deformation at stamping, etc. Low-carbon steel, characterized by good weldability. But High-carbon and medium-steel, require the application of heat during welding, which prevents the formation of cracks, so kakzamedlyaetsya cooling and other manufacturing operations. Marganetssluzhit processing aid began to increase their degree of reduction, to eliminate the harmful effect of sulfur. The content of manganese as an impurity should not exceed 0,8%. He resides in alloys and steels in the form of a solid solution-Fe, as well as how to apply technology that has no significant effect on the properties of steel. Enter for deoxidation in the steel and also silicon. His soderzhaniene above 0.37% in steels for welded structures - in the range: 0,12 - 0,25%. Silicon is present in the solid state and-Fe, no significant effect on the properties of steel and alloys. Sulfur, as a process impurity, the content of 0.035 ... 0.045%, insoluble in austenite. It is present in the form of brittle sulphide Fe S, Mn S, which are part of the eutectic melting temperature 985 ? C. Eutectic, most often crystallizes at the grain boundaries. If the sulfur content increases, the decrease properties of steels (mechanical, physical and chemical). A, namely, plasticity, toughness, corrosion resistance, abrasion resistance, reduces weldability izdeliy.K redact leads a high content of sulfur in hot deformation, ie We see tears on inclusions Fe S. In the solid solution and-Fe in steels and alloys, the presence of phosphorus. Its share as a mixture of technology is in the range 0,025 - 0,045%. Phosphorus is a harmful impurity in steels and alloys, as well as sulfur. If the increase of its contents for a bit of a percent, then the strength increases, but decreases ductility, toughness, increased fragility, fluidity, the threshold of cold brittleness. Justified by the fact that phosphorus causes intracrystalline liquation, pretty strong, promotes the growth of grains in the metal. Under elevated carbon content, strongly adverse influence phosphorus to the metal. Adversely affect the properties of the metal oxygen and nitrogen. They are present in small amounts, as a result, steel contaminated by nonmetallic inclusions (oxides, nitrides, gas phase). Therefore called the anisotropy of mechanical properties, while the fragility increases, the threshold of cold brittleness, and strength and endurance decreases. Aging steel case with an oxygen content of more than 0,03% and the hot brittleness - more than 0,1%. Nitrogen reduces the ductility of steel, but also increases the hardness iprochnost. At the same time, if the nitrogen content increased, the strain aging occurs. It develops slowly at room temperature and quickly heated to 250 ? C. In the solid state and nahoditsyav-Fe metal hydrogen. He mozhetskaplivatsya in the pores and dislocations. If its content increases in the metal, the increased fragility. Occur in the rolled products hairline cracks that develop hydrogen, which is released in the pores. Flocs lead to destruction metal, so metal that contains them, do not admit to the industry. There is a steel alloy. It contains in addition to conventional wheels - special, which are introduced in certain combinations. By alloying elements are: Cr, Ni, Mn, Si, Mo, Wo, V, Al, B, Ti and others of their content is more than 1%. It is a complex doping provides the best technological properties. Ie increasing impact strength, yield strength, relative narrowing and hardenability, lowers the threshold of cold brittleness, the rate of hardening, the deformation of products, the formation of cracks. Improved mechanical properties of alloy steels in the products, which have a large cross section (diameter greater than 15 -20 mm), compared to carbon steel. 3 groups of elements that are used in steel alloys: 1. Mn, Si, Cr, B; 2. Ni, Mo; 3. V, Ti, Nb, W, Zr various elements used for doping, not only because of the physical properties, but also for economic reasons. Classification of alloying elements on the mechanism of their effects on metals: 1. impact on the polymorphic transformation (a-Fe -> g-Fe); 2. formation of carbides with the carbon (Cr, Fe) 7 C3; (Cr, Pe) 23 C6; Mo2 C, etc. 3. formation of intermetallic compounds with iron (Fe7 Mo6; Fe3 Nb), etc.