Nonlinear ultrasonic assessment of precipitation hardening in ASTM A710 steel
- PDF / 140,754 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 23 Downloads / 244 Views
We investigated several specimens of ASTM A710 steel containing copper-rich precipitates with variations in the final aging treatment. X-ray diffraction line-broadening and small-angle neutron-scattering experiments revealed the existence of the precipitates and associated coherency strain. We determined the nonlinear ultrasonic parameter  for each specimen by harmonic-generation experiments and measured the ultrasonic longitudinal velocity L and attenuation ␣L. Although L and ␣L showed no consistent trends,  increased with increasing strain. This correlation is compared to a microstructural model for harmonic generation that includes a contribution from precipitate-pinned dislocations.
I. INTRODUCTION
In this paper, we describe experiments to measure the linear and nonlinear ultrasonic properties of steel specimens containing copper-rich precipitates. This work was part of a feasibility study1 to determine the potential of various nondestructive methods for sensing embrittlement in steel. Hardening by copper-rich precipitates can be a source of embrittlement in commercial steel alloys. In particular, reactor containment vessels for the nuclear power industry are subject to such embrittlement, due to radiation-enhanced diffusion and precipitate formation.2 At present, reactor vessels are qualified for operation by periodic testing of in situ surveillance specimens. The specimens’ fracture toughness is determined in destructive impact tests and then used to infer critical vessel properties such as embrittlement.2 Nondestructive methods to monitor vessel properties directly could improve on this conservative approach and extend vessel operation lifetime.3 Our feasibility study represents a first step toward achieving this goal. II. SPECIMEN PREPARATION
The experiments reported here used a surrogate material instead of actual reactor steels. That is, we chose a steel that could be embrittled through thermal treatment to produce microstructures similar to those created through irradiation. The surrogate material was a higha)
Also at the Department of Physics, University of Colorado, Boulder, CO 80309. b) Present address: Portsmouth Naval Shipyards, Portsmouth, NH 03801. 2036
http://journals.cambridge.org
strength, low-alloy steel with 1.13 mass% copper (ASTM A710). As in the reactor steel, embrittlement in this material occurs by formation of ultrafine (nanometersized) copper-rich precipitates. The precipitates restrict the motion of dislocations and thus increase the material’s hardness and yield stress.2 Two sets of specimens were produced. In the first set (series I), three bar specimens (approximately 2.5 × 5.0 × 25.0 cm) were heated to 900 °C for 1 h and then air cooled to room temperature. This solution treatment left the copper in the austenitic matrix while maintaining a small (∼10 m) grain size. One specimen was measured without additional aging. The two remaining specimens in series I were subjected to further aging treatments in which the temperature was varied. One specimen was held at 700 °C for
Data Loading...
