Tkach T. Formation of the structure and properties of thick sheets of low carbon steel after heating and deformation in the intercritical temperature range

Object of research: processes of structural and phase transformations with different temperature-deformation treatments of low-carbon steels. The purpose of the dissertation work is to increase the mechanical properties of sheet steel rolled products from low carbon steels on the basis of the establishment of regularities in the formation of grain structure, depending on heating regimes, deformations in the intercritical temperature range and subsequent cooling. Methods of research: light quantitative and qualitative microscopy; diffraction electron microscopy; standard methods of mechanical stretching tests, impact strength, hardness determination according to Rockwell; determination of the grain size of the ferrite by the program Metal 1.0. Theoretical and practical results: the controlled mode of steel rolling 10Г2ФБ and 09Г2С; developed the mode of heating and cooling from the temperatures of the intercritical interval for grinding the grain structure and increasing the impact strength of rolled products from the constructional steels type 10G2FB and 09G2S; the practical application of the developed metallographic method for detecting the grain boundaries of the former austenite allows us to determine the real quantification of the phases and to find out the former provisions of the interphase boundaries when heating low carbon steels to the temperatures of the intercritical interval. Scientific novelty: for the first time, for the steels 10G2FB and 09G2C, the bimodal character of the distribution of the size of ferrite grains is determined, depending on the heating temperatures in the intercritical interval; for the first time scientific positions have been obtained on the basis of which the method of the metallographic detection of the interphase boundaries of ferrite-austenite with the heating of low carbon steel 10G2FB, 09G2S and 20 to the temperatures of the intercritical interval is developed; for the first time, the dependence of the strength and impact strength properties on the temperatures of the end of the deformation in the intercritical interval and the rye of further cooling were determined; got further development of the establishment of the quantitative ratio of phases of ferrite-austenite with the heating of low carbon steel 10G2FB, 09G2S and 20 to the temperatures of the two-phase region by theoretical and experimental methods. The degree of implementation: the proposed improved mode of controlled rolling was tested in industrial conditions at PJSC MMK IIlyich. Scope: production of sheet metal rolled products made of low-carbon steels for oil and gas pipelines.