Abstract
Phase transformations in maraging steels grade 250, 300 and 350 aged at various temperatures have been studied using ultrasonic velocity measurements. It was found that the temperatures corresponding to various transformations can be easily monitored by observing the changes in ultrasonic longitudinal velocity. In the case of 350 maraging steel, for example, the precipitation starts at approx360 deg C and the austenite begins to form approx560 deg C. Maximum amount of austenite is observed in samples aged at 670 deg C. At aging temperatures > 770 deg C, the velocity approaches values coresponding to the annealed samples signifying that the process of precipitate dissolution has been completed. These results are consistent with the results obtained by resistivity measurements and x-ray diffraction studies.