ISSN: 0090-3973
Page Count: 8

Evaluation of Intergranular Fracture Initiation in Transition Region of Retired Steam Turbine Rotor Steel Using Small Specimens and the Acoustic Emission Technique
Shimomura, K
Research Associate, Tohoku University,

Shoji, T
Associate Professor and Professor, Research Institute for Strength and Fracture of Materials, Faculty of Engineering, Tohoku University,

Takahashi, H

Abstract

Fracture toughness tests were performed at 150°C in the transition region for a Cr-Mo-V steel using four different sizes of compact tension specimens and with the use of the acoustic emission (AE) technique. Two fracture toughness parameters were obtained to evaluate the intergranular mode fracture toughness: one is the critical fracture toughness of K^JC calculated from J^c, the other is a fracture toughness of K^JAE characterized by the onset of microscopic pop-in cracking determined by AE. The values of K^JC and K^JAE of the smaller specimens show a great deal of scatter. Combining the fractographic studies, the source of toughness scatter is discussed in terms of the loss of plastic constraint. The results show that the lower bound values of K^JAE in the smaller specimen sizes are coincident with a valid fracture toughness, K^IC(AE), of the large specimen. An accurate evaluation of the intergranular mode fracture toughness is also discussed.

Keywords:
brittle fracture, elastic-plastic fracture, fracture toughness, J-integral, ductile-brittle transition, size effect, cleavage fracture, intergranular fracture, ductile tearing fracture, acoustic emission

Paper ID: JTE11019J
DOI: 10.1520/JTE11019J
ASTM International is a member of CrossRef.