STUDIES ON FRACTURE TOUGHNESS OF CARBON STEEL

Abstract

An attempt has been made to find the fracture toughness of hypo-eutectoid carbon steel by cylindrical tensile test specimen having circular notch at the middle of the specimen. Though this type of specimen has not been standardized by the ASTM. The carbon steel rod of 7 mm outer dia and inner dia is taken as 5.6 mm in the first case and 4.2 mm in the second case. Here.three different notch angles.have been taken. Attempts have been made to evaluate,the fracture toughness in different heat-treated specimen. In this work fracture toughness has been compared between as-received steel and annealed steel. The chemical composition of the material has been found as C %= 0.52, Si %=0.09, Mn %=1.03, P %=0.02, S %=0.01, For this present work TENSOMETER is used for the tensile testing. The tensile specimen has been cut from the as-received rod of 10 mm dia, and then heat-treatment (annealing) is given to some of the samples. Stress —strain curves obtained from the tensile test have been re-plotted into Force-Extension curves.. From this test final fracture load was taken for the evaluation of the fracture toughness. Fracture toughness of as-received and annealed samples were compared with different notch angles and notch depths. SEM on fractured surface of the tensile test specimen has been done to find out the extent mode of fracture.