Iron and Steel Institute of Z. I. Nekrasov NAS of Ukraine (Dnipro, Ukraine):
S. I. Gubenko, Dr. Eng., Prof., e-mail: sigubenko@gmail.com
E. V. Parusov, Cand. Eng., Senior Researcher, Head of Dept.
O. V. Parusov, Cand. Eng., Senior Researcher

The features of the fracture of the interphase inclusion-matrix boundaries under various thermal-deformation and aggressive actions are investigated. The reasons and conditions for the formation of cracks as a result of decohesion of the inclusion-matrix boundaries associated with the concentration of interfacial thermal and deformation stresses are discussed. It was found that the character of decohesion of the inclusion-matrix boundaries (rupture of interatomic bonds of a nonmetallic inclusion and a steel matrix) caused by interphase thermal stresses is due to the conditions of heating and cooling, depending on the type of processing (conventional heating, laser or electromagnetic treatment), which determines the possibility of passing relaxation processes associated with the redistribution of interfacial defects within the specified boundaries. The mechanisms and features of decohesion of the interphase inclusion-matrix boundaries at different methods and temperatures of deformation are discussed. It is shown that the decomposition of the inclusion-matrix boundaries upon deformation occurs in cases of certain types of nonmetallic inclusions (oxides, spinels, some sulfides). For different types of inclusions and steels, parameters have been determined that characterize the cohesive strength of the inclusion-matrix interface depending on the loading conditions. It is shown that decohesion (fracture) of the inclusion-matrix boundary into two free surfaces can be considered as the transformation of interphase misfit dislocations into surface steps as a result of loss of conjugation. The role of inclusion-matrix boundaries in the formation of cracks of fatigue and fatigue-corrosion origin is considered. It is shown that under the influence of aggressive media and cyclic stresses, the structure of the inclusion-matrix interphase boundaries degrades, which is associated not only with the accumulation of interfacial stresses, but also with the facilitation of the penetration of surfactant atoms from the environment along these boundaries. As a result, fatigue-corrosion destruction of the inclusion-matrix boundaries occurs, and the effect of an adsorptive decrease in their strength is manifested.

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