Fracture Toughness Testing of Nickel Alloyed Permanent Moulded Austempered Ductile Iron Using Single Edge Notch Bending Specimens

Laboratory Fracture Toughness test have been reported on Permanent moulded Austempered Ductile Iron (PMADI) with Nickel as alloying element utilizing conventional austempering process. The Nickel additions were made at different levels from 0.5 wt % to 2 wt % in steps of 0.5 %. Single edge notch bending specimens (SENB) austempered at 3200C for 120 Min were subjected to three pointbending test to evaluate the plane strain fracture toughness (KIC). From the experimental results, it was found that the samples containing 1.5% Nickel exhibit superior fracture toughness characteristics in comparison with 0.5 %, 1 % and 2 % Nickel content. The effect of crack length to width (a/w) ratio on fracture toughness is also discussed. The fracture toughness of 1.5% bearing Nickel sample showed an increase of about 17 % more in comparison with unalloyed PMADI sample austempered under similar conditions. Finite element analysis using ANSYS were carried out and the stress distribution was found to be maximum around the region of crack. The results were construed based on the analysis of retained austenite content, distribution of Bainite and the matrix microstructure of nickel alloyed PMADI samples.