Abstract
The changes in microscopic structures and mechanical properties occurring during the repetition of heating and cooling were investigated on cast iron. The repeating temperature ranges were as follows; (1) from 800°C to 600°C, (2) from 650°C to 350°C, (3) from 350°C to 150°C and (4) from 800°C, 650°C, 600°C, 350°C and 150°C to the room temperature, respectively.
In the case (1), the tensile strength and the brinell hardness decreased gradually with increasing number of repetition, and showed about 40% reduction from the initial values after 15 times of repetition. These values, however, did not changed on further repetition. The similar results were also obtained in the repeated annealing (800°C). In these studies, the dissolution of pearlite and the increase in the percentages of graphite and ferrite areas were detected. In the case (2) and in the repeated annealing (650°C), the mechanical properties remained unchanged, even though the repetition was continued up to 15 times. After 20 times of repetition, however, 20% reduction was detected in the tensile strength and brinell hardness. The repeating tests in the ranges of temperatures below 350°C showed no effect on the mechanical properties.
It was also revealed that the mass effect decreased with increasing number of repetition like the behaviors of strength or hardness. These results seemed to suggest that the changes in mechanical properties and mass effect were closely associated with the repetition of heating over the eutectoid temperature of this material (700°C).
