DEVELOPMENT OF HEAT TREATMENT TECHNOLOGY OF CENTRIFUGALLY CAST ROLLS WITH WORKING LAYER OF CHROMIUM-NICKEL-MOLYBDENUM CAST IRON
The paper is dedicated to analysis of heat treatment of cast iron products. It is noted that heat treatment is performed for reduction of internal stresses, graphitization, decarurization, to change structure and properties. During the experiments technological parameters of heat treatment of centrifugally cast rolls with working layer of chromium-nickel-molybdenum cast iron have been determined. They are necessary to develop effective process in special car bottom gas furnaces. It is shown that such treatment contributes to reduction of residual stresses in the rolls after casting. The aim of this paper was to study the effect of heat treatment on the structure, hardness level and stress state of sheet-rolling rolls. Studies of as-cast rolls showed that various combinations of matrix with secondary carbide inclusions were observed depending of proportions of chemical components in the analyzed cast iron and cooling rate of the cast billet. Hardness level changed depending on their quantitative relations. Results of stressed state study of castings by means of coercive force measurement showed a non-uniform distribution of its values along the working surface of roll barrels. A regime of low-temperature (T = 673 K) annealing proposed in the work permitted to obtain a more uniform structure of the working layer of rolls. As a result, inhomogeneity of properties along working layer surface decreased two times compared to as-cast state.