Fracture toughness determination of heat treated AISI D2 tool steel using AE technique

Abstract

In this study, acoustic emission behavior of a tool steel during fracture toughness tests was investigated. Selected steel (AISI D2 cold-work tool steel) was heat treated at 5 different conditions (austenitized at 1 010°C and tempered at 0, 300, 450, 525 and 575°C) and its properties were characterized using standard metallographic examinations, hardness and tensile tests. Compact specimen testing according to ASTM standard E 399 and acoustic emission technique were used to determine the fracture toughness value (KIC) and fracture process. Determination of fracture toughness using AE technique was carried out according to classical and two modified methods. Results showed that: (a) by increasing tempering temperature, plain strain fracture toughness (KIC) values and the fraction of ductile fibrous fracture increase except at 525°C when tempering process leads to secondary hardening, (b) fracture toughness values determined, using AE technique is lower than standard ASTM E399, (c) estimation of KIC values, using modified methods (AECR and AEER), is more accurate in comparison with the classical AE method and (d) the effect of tempering temperature on AE characteristics during fracture toughness test is similar to its effect on hardness. © 2011 ISIJ.