The work of steel in structures significantly depends on the structure of steel and on the variability of its properties.
Soft steel, as you know, consists mainly at a normal temperature of two components – ferrite and cementite; Ferrite-mail pure iron, which has a dissolved carbon and other elements in small, in small,; Ferrite has the correct crystalline structure of a centered cubic lattice and forms individual grains (crystallites) oriented in various directions in steel; The second component of steel Cementite, iron carbide (FE3C) – forms a mixture with ferritis – perlite that fills individual sections and layers between ferrite grains (dark spots on slices).
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Ferritten flesh and plastic, perlite is solid, elastic and quite durable. The work of steel depends on the ratio of these two components. The smaller the grain, the more evenly distributed by the volume of steel and the more evenly on average the orientation of the grains relative to each other is distributed on average.
In accordance with this, steel is more homogeneous, durable, plastic and isotropic; The fluidity site rises and becomes more length; The length (according to deformations) of the regional relief area, as well as relative lengthening when rupture, also increases. At the same time, the viscosity of steel increases, the ability to absorb external energy when hit. Therefore, small grain is the first sign of high -quality steel. The uniformity of grains is of great importance.
A mixture of large and small grains makes steel unequal due to the significant difference in resistance to plastic deformations of large and small grains. This may take place in thermal processing of steel after sticking (phenomenon of secondary recrystallization). In the plastic stage, with heterogeneous grain (uneven in size), sharply different speeds and the magnitude of plastic deformations are obtained, which can lead to a violation of the continuity and microscopic cracks. With a predominant crystallographic orientation of grains, which occurs after sticking or at low temperatures during the rolling process, when the so -called “slow structure” forms, steel becomes anisotropic with an increase in mechanical properties in the direction of the pre -emptive crystallographic orientation.
