CHARACTERIZATION OF MICROSTRUCTURE AND DETERMINATION OF ELASTIC PROPERTIES IN SAF 2205 DUPLEX STAINLESS STEEL USING ULTRASONIC MEASUREMENTS

Microstructural changes in duplex stainless steel due to changes in annealing temperature are characterized by ultrasonic pulse-echo technique and optical microscopy. Duplex stainless steel was subjected to a series of heat treatments from 1100°C to 1350°C, followed by water quenching. The microstructure after heat treatment at 1350°C resulted in coarse grained ferrite, which favored formation of Widmanstatan austenite with fast cooling. Micro hardness and optical microscopy results are correlated with ultrasonic longitudinal and shear wave velocities, attenuation and ferrite count (%) in the specimens. Ultrasonic velocities and micro hardness decrease with annealing temperature in the 1100°C - 1200°C range, while they increase slightly beyond 1200 up to 1350°C. Ultrasonic attenuation exhibits an opposite behavior to velocity and hardness. Fast Fourier Transform exhibit a decrease of the spectral amplitude in specimens with high heat treatment temperature. The results show that the use of Ultrasonic measurements to correlate the ultrasonic parameters with the microstructures and hardness is very fast and reliable.