Mamonova A. Regularity of formation of fine crystalline structure and optimization of processes of powder steel hot forming.

The object of investigation is the fine structure in powder steels of structural application. The aim is to establish the regularities of formation of a substructure in different regions of specimens from powder structural steels depending on technological manufacturing parameters and use qualitative characteristics of the fine structure for predicting and controlling the strength properties of powder structural steels. The used methods are - chemical, metallographic, scratch hardness, X-ray phase, X-ray diffraction, and electron probe X-ray analysis. Novelty of work - During powder steel hot formation several opposite processes have been disclosed, namely: fine structure elements integration and their disintegration, strengthening and softening, a strain hardening and self-annealing, healing of defects. It is shown, that during hot formation the essentially gradient fine crystalline structure is shaped on the profile of a blank. For the first time by use of the modern information handling of a X-radiography, - a method of harmonic analysis of an X-ray line profile and an approximation method with application of a package of computer programs, - the fine structure quantitative adjectives in various parts of press form are received in conformity with their chemical composition and process factors of their production. For the first time, with taking intragranular structures into consideration, heating temperatures are defined at which the structure of observable hot forming powder steel blanks are closed to isotropic. The practical significance of results - lies in the fact that, based on the regularities of formation of the fine structure of the iron matrix during interaction with Cr3C2, the choice of optimal technological parameters of the manufacturing process of a KKhZh-type structural wear-resistant material was substantiated. On the base of powders that were subjected to vibratory ball milling for 15-20 h and had a polygonized structure after reducing annealing, high-strength carbon steels withan inherited fine-crystalline structure were obtained.