Controlling the strain hardening behaviour of ductile cast iron by austempering process

Abstract

In this study experimental work was carried out to obtain and to control the strain hardening behaviour of ductile cast iron by austempering process. Tensile test, hardness test and micrography examinations were carried out for samples being subjected to 250-400 degrees C temperature and for time period 30 to 90 minutes austempering conditions. This was done to obtain the variation of strain hardening factor (n) and strength factor (K), hardness and micrography with austempering temperature and time period. The stress-strain curves were obtained. Using Holloman's relationship, the strain hardening factors were calculated. The results showed the improvement in n-value with austempering process. Furthermore, the n and K values decreased then increased with an increase in austempering temperature. The minimum values for n and K are at 300 to 350 degrees C austempering temperature. Finally, the results were compared with the results obtained by using a two-step austempering process. The results showed that the minimum values for n and K are also at 300 to 350 degrees C austempering temperature which is in a good correlation with the results obtained by two step method. Finally, it is concluded that the use of austempering process resulted in design flexibility and low cost in tooling machinery.