Defects of the hardened layer at laser exposure

Abstract

Purpose. It is necessary to investigate the influence of non-metallic inclusions on the formation of defects during laser processing. The aim of the work was to study the defects of the hardened layer of steels under laser action, associated with the presence of non-metallic inclusions. Methods. The materials for investigation were commercial steels containing different non-metallic inclusions. The specimens of different steels with preliminary polished surface were exposed to laser beaming on the installations GOS-30M and GUANTUM-16. The research methods were applied - petrography, X-ray microscopy (MS-46 Cameca) and optical microscopy (Neophot-21) to study defects and identify of inclusions. Results. It has been established that various types of defects appear on the surface and in the surface layer of steel under laser action, which are not connected and are associated with non-metallic inclusions. It is shown that non-metallic inclusions are the reason for the appearance of various kinds of defects in the hardened layer of steel products during laser processing (cracks, cavities, violation of the geometry of the hardened layer). The reasons for the appearance of defects associated with the presence of inclusions of various types are discussed. Scientific novelty. A classification of defects in the hardened layer is presented. The nature and features of the formation of defects, associated with the appearance of high-speed thermal stresses, structural inhomogeneity, as well as melting, thermal destruction and evaporation of inclusions emerging to the surface and located within the hardened layer, have been established. It is noted that the detected defects are ready-made centers of destruction of a steel product or part under conditions of static and dynamic loads, as well as contact stresses. Practical significance.  It is shown that the unsatisfactory quality of the hardened layer associated with the presence of various kinds of defects near nonmetallic inclusions contributes to a decrease in the mechanical and operational characteristics of a steel product. The use of the obtained results will make it possible to develop technologies for laser processing of steels with regulated quality parameters of the hardened layer, which will prevent the formation of various kinds of defects.

Keywords: steel; laser treatment; defects; cracks; hardened layer; non-metallic inclusions