Influence of heat treatment on the microstructure, ultrasonic attenuation and hardness of SAF 2205 duplex stainless steel

Microstructural changes in duplex stainless steel due to changes in annealing temperature are characterized by ultrasonic pulse-echo technique and optical microscopy. SAF 2205 duplex stainless steel are heat treated at 1100, 1200, 1300 or 1350 °C for 30 min, and water quenched. The heat treatment at 1350 °C resulted in coarse grained ferrite, which favored formation of Widmanstatten austenite with fast cooling. Ultrasonic velocities and attenuation co-efficient of ultrasonic waves produced with 5 MHz transducers were evaluated for these heat-treated samples by pulse-echo method. The micro structural changes with annealing temperature are correlated to the ultrasonic characteristics of the alloy. The surface hardness characteristics of the samples are largely found to be dictated by the phases that are present. Results also showed that the both ferrite content and grain size have a combined effect on the velocity and hardness, while the attenuation is purely decided by the grain size alone.