Technological features of cast iron treatment

Abstract

The paper deals with the use of vibration technology, which is an effective means of reducing residual stresses in castings. Vibration can be used to achieve a stress relief sufficient to prevent further warping of castings due to the redistribution of residual stresses. In addition, it was shown that residual stresses in cast iron castings can be reduced without vibration by additional static loading with holding under load. The research resulted in obtaining the necessary data to assign vibration modes. It was established that the stress amplitude has a decisive influence on the magnitude of the reduction of residual stresses during vibration. The duration required for the complete stabilization of the stress relief process under vibratory action was determined. As a result of prolonged holding under load after vibration, processes may occur in the sample material that return it to the state before vibration. In other words, if the stress reduction process after vibration stops, it may be reactivated after a certain time. It has been established that for cast iron castings, in which residual stresses reach approximately 10 kg/mm², the stress amplitude during vibration should not exceed 3–4 kg/mm², otherwise there is a risk of cracks in the castings during vibration. The nature of the stress reduction during vibration is probably the same as during natural aging, only the speed of this process during vibration is much higher. After repeated vibration, observations of the samples continued for another four months. After this period, no changes in the magnitude of the stresses compared to the stresses remaining after vibration were detected. The results of this work give grounds to recommend conducting industrial tests of new methods of aging cast iron castings by vibration or static loading with the aim of their widespread introduction into industry.