TENSILE PROPERTIES AND MIICROHARDNESS EVOLUTION IN MEDIUM CARBON SHEETS SUBJECTED TO CONTINUOUS SPD PROCESS

Development of technologies to produce the very fine structure is currently very intensively accelerated. Even in scientific research, it is recognized that precisely controlled forming processes, including special processes, enabling control of technological parameters with regard to the structure refinement, and tied with the strengthening of materials, currently had the highest gradient of utilization efficiency of the scientific research findings in practice. Severe plastic deformation (SPD) processes have been extensively investigated in the last decade to facilitate the production processes on nano-structured or ultrafine-grained (UFG) materials with unique utility properties. This work deals with analysis of utilization the forming equipment that uses a method of metal forming - DRECE (Dual Rolling Equal Channel Extrusion), which was designed to produce a material with ultra-fine grain structure. Increasing the mechanical properties of the formed sheet metal strip is primary. It has demonstrated that the forming method leads to an increase of strength characteristics (Yield strength and Ultimate tensile strength) of the investigated medium carbon steel Ck55, while a slight decrease in plasticity of the formed steel. DRECE forming method has a positive effect on the microhardness distribution. With the increasing number of passes was observed that a HV0.1 difference between lower and upper sheet surface decreases to the minimum value, which depends on the processing of the initial state of the investigated sheet. The increasing dislocation density of cold severely deformed medium carbon steel resulted in an increase of the tensile properties and hardness.