STRETCH ZONE, DUCTILITY AND TOUGHNESS STUDIES IN THE TRANSITION REGION OF 1045 STEEL

The variation of fracture toughness expressed by the J-integral, tensile and bulge ductility of 1045 steel which exhibits a transition from linear elastic behavior to elastic-plastic behavior, with temperature was investigated. The toughness study also included measurements of the stretch zone width from fractured surfaces to determine the process of crack blunting before the onset of crack growth. Three—point bending specimens were used for determination of the J-integral while square coupons of the material were tested for evaluation of the bulge ductility. Stretch zone width studies were carried out using scanning electron microscopy. The results show that the variation of JIC with temperature can be analyzed in terms of two distinctive regions with a transition temperature occuring where the material behavior changes from linear elastic to elastic-plastic at the crack tip. There is also a linear correlation between bulge ductility and stable crack growth. The transition from linear elastic to elastic-plastic behavior at the crack tip was confirmed from the stretch zone measurements.