Effect of boron and cross-section thickness on microstructure and mechanical properties of ductile iron

Abstract

Effect of boron contamination on the microstructure and mechanical properties of ductile iron, GJS-500-7 grade was studied. Three cast batches with the boron content of 10, 49 and 131 ppm were cast in a casting geometry containing plates with thicknesses of 7, 15, 30, 50 and 75 mm. Microstructure analysis, tensile test, and hardness test were performed on the samples which were machined from the cast plates. Addition of 49 ppm boron decreased pearlite fraction by an average of 34±6% in all the cast plates. However, minor changes were observed in the pearlite fraction by increasing boron from 49 to 131 ppm. Variation in the plate thickness did not affect the pearlite fraction. The 0.2% offset yield and ultimate tensile strength was decreased by an average of 11±1% and 18±2%, respectively. Addition of 49 ppm boron decreased Brinell hardness by 16±1%, while 11±2% reduction was obtained by addition of 131ppm boron.