EVALUATION OF THE SUITABILITY OF WARM WATER FOR INTERRUPTED QUENCHING OF DUCTILE CAST IRONS

Abstract

The Evaluation of the suitability of warm water for interrupted quenching of ductile cast irons was carried out. The interrupted quenching process was carried out by austenitizing at 850°C for 30minutes, quenching in warm water at 80°C temperature for 40seconds and then quickly transferred to another furnace maintained at different predetermined temperatures and holding periods. The selected furnace temperatures were between 175°C, and 450°C, while the holding times varied from 30 to 180 minutes. Final cooling was carried out in air. After heat treatment, the Rockwell hardness (Rc) value of each specimen was measured and microstructural examination carried out. Statistical Package for Social Science (SPSS) was used to develop a computer model and computer software from the hardness values obtained. Results showed that the maximum and minimum hardness values of 53HRc and 19HRc were obtained respectively. Metallographic analysis showed that untempered martensite was obtained at holding temperature below 250°C, tempered martensite at 250-c to 325°C, tempered martensite at holding temperature of 375-c for short holding times, over-temping occurred beyond the holding temperature of 400°C for all holding times. For the model developed, the correlation coefficient was found to be between 0.9925 and 0.9595 while the standard error was between 2.162 and 2.823. This new heat treatment process route for ductile iron has provided a cheap, easy and efficient means of producing tempered ductile iron without using the conventional method which is relatively expensive to procure, not readily available and energy consuming.