Influence of Silicon Content on Fracture Toughness of Ferritic Spheroidal Graphite Cast Iron

Abstract

  The influence of Si content on fracture toughness, such as K_IC, J_IC and R_SC, of ferritic spheroidal graphite cast iron were investigated in the Si content range between 2.34% and 3.47%. The fracture toughness tests were carried out by using 15mm thick CT test pieces at the temperatures of 20°C and −100°C. At 20°C, the specimens with Si contents up to about 3.2% showed ductile fracture. When Si content is about 2.6%, the J_IC and K_IC values are highest, 3.06kg/mm and 223kg/mm^3/2 respectively. As Si content increases up to 3.2%, J_IC and K_IC decrease gradually. But when Si content is about 3.5% the specimen is in the fracture-toughness-transition region, where the mode of fracture becomes brittle and the fracture toughness decreases greatly, and the J_IC and K_IC values decrease to 0.97kg/mm and 125kg/mm^3/2. At −100°C, the fracture conditions of all specimens are brittle. There is a large drop in the J_IC and K_IC values of each specimen compared to those at 20°C. The value of Si content in the fracture-toughness-transition region is about 1% less than that of 20°C.