THE PECULIARITIES OF THE FRACTURE OF HETEROPHASE INCLUSIONS OF THE TYPE "HIGH- MELTING PHASE SURROUNDED BY A LIGHT-MELTING SHELL" IN THE DEFORMATION OF STEELS

Abstract

Purpose. The aim of the work was to study of the peculiarities of crack initiation in heterophase inclusions of the "high-melting phase surrounded by a low-melting shell" type during deformation of steels. Methods. The destruction of heterophase inclusions of various types was investigated during deformation of specimens from steels 08T, 08Yu, 12GS, 08kp, 09G2S, NB-57, 08GSYuTF in the temperature range 20...1 200 °C [1; 5]. Samples of steels were subjected to tension, compression and bending in vacuum at temperatures of 20…1 200 °C on Instron-1195 and IMASH-5C with special grippers, the movement speed of which was 20 mm / min. Methods of investigation –petrography and optical microscopy (Neophot-21) were used. Results. It was found that in the process of deformation of the steels in different temperature regimes, microcracks originating near heterophase inclusions of the "high-melting phase surrounded by low-melting shell" type can be brittle and ductile. In this case, the role of the level of plasticity of the phases making up the inclusion, which depends on the deformation temperature, is important. The features of microcrack initiation are shown for different combinations of plastic and non-deformable phases of inclusions. The interaction of heterophase inclusions and a steel matrix during deformation is analyzed. It has been established that the nucleation and growth of microcracks within inclusions of the "high-melting phase surrounded by a low-melting shell" type occurs both in the phases and along the internal interphase boundaries. Scientific novelty. Specific features of the initiation of microcracks associated with heterophase inclusions of the " high-melting phase surrounded by a low-melting shell" type, which have a different combination of brittle and plastic phases during deformation of steels, have been established. It is shown that the critical degrees of deformation of the samples, upon reaching which noticeable microcracks appeared along the internal interphase boundaries, depend on the temperature and the nature of the phases of the inclusions. Practical significance. The use of the results obtained will make it possible to develop technologies for producing steels with regulated types of heterophase nonmetallic inclusions, which will significantly increase their technological and operational characteristics, as well as prevent the formation of various kinds of defects during the processing of steels by pressure and the operation of products.