THE PECULIARITIES OF BRITTLE-PLASTIC TRANSITION IN THE FERROUS POWDERED MATERIALS

The issue of the study of the porous bodies’ deformation and the plasticity of their materials is important as it is related to the production of complex parts using the wide opportunities of drop stamping (DS). In this case, the increased requirements are imposed on the porous material plasticity as the emergent defects may be not removed at the final DS stages what impairs the strength properties. The information about the plasticity properties of a porous material in the heated state allows properly developing the technology of complex parts’ DS.

The paper investigates such structural defect of powdered materials as the porosity. The authors studied its influence on the mechanical properties of materials and analyzed the regularities of these properties’ changes in the interval of brittleplastic transition temperatures. The mechanical tests of the powdered specimens were carried out with the identification of the main dependencies of mechanical properties on the porosity in the interval of brittle-plastic transition temperatures. The authors selected the main deformation modes when the crack resistance is studied, identified the main factors influencing the peculiarities of brittle-plastic transition in the powdered materials, described the phenomena where the crack formation takes place, as well as defined the details of this process.

The study identified the nature of change of the strength coldbrittleness temperature (T_CL) and the plasticity coldbrittleness temperature (T_CH): if T_CL increases with the increase in porosity, T_CH decreases under the same condition. Thus, at the specimen porosity of 3–5 %, its value, depending on the powder type, is 100–150 K, and at the porosity of 10– 15 %, it is lower than 77 K for all powders.