Low temperature impact tests in austempered ductile iron and other spheroidal graphite cast iron structures

Abstract

Impact tests at low temperatures were carried out aimed at comparing the response of five spheroidal graphite (SG) cast iron with different microstructures and to analyze the influence of the solidification structure size. "Y" blocks with two different thicknesses (13 and 75 mm) were cast using the same industrial melt. The following matrix microstructures were obtained by applying different heat treatments: pearliticferritic (as-cast condition), fully ferritic (sub-critical annealing), fully pearlitic (normalizing) and two ausferritic matrices (ADI grades 2 and 4). Charpy impact tests were performed on unnotched specimens at temperatures ranging from -100°C to +200°C. The results showed a little variation of the upper and lower shelf energy values with the solidification structure size for each matrix type. However, there was a strong displacement in the transition temperature towards increasing temperatures as the solidification structure size enlarged. This effect is also related to the matrix microstructure. The highest impact energy values were obtained on ADI grade 2 samples, and the lowest ones on the samples with pearlitic matrix.