INFLUENCE OF THE annealing TEMPERATURE ON THE HARDNESS of the built-up edge of medium carbon steel

Abstract

In metal forming processes, in some cases, galling occurs, which results in the formation of built-up edges on the surface of the tool. They usually damage the outer layer of the workpiece. The aim of the work is to broaden the knowledge about the structure and mechanisms of the formation of the build-ups structure. In this case, it concerns the build-up produced on the NC6 steel tool in the process of drawing the steel 30 strip at an elevated temperature. At a special stand enabling the process temperature change, the temperature of the greatest tendency to galling in dry friction conditions was determined at 620 °C. As a result of the research, the annealing temperature of the built-up material was determined at 500 °C. It was noted that the build-up formed at 620 °C has a hardness more than twice as high as the same build-up annealed for 1h at approximately similar temperature, 600 °C. The difference is due to the differences in the dynamics of the processes. The process of the build-up leads to the formation of a highly deformed supercooled structure which reaches the state of equilibrium during quasi-static annealing. The energy stored in the supercooled structure of the buildup during annealing at a relatively low temperature of 400 °C activates the recovery process, reducing the hardness by 30 %. Structural investigations have shown that the resulting build-up has a streak structure, probably created in the process of shearing successive layers of material. In build-up edge, the more strengthened layers alternate between layers with a lower degree of deformation.