An in situ high-temperature X-ray diffraction study of phase transformations in maraging 300 steel

Abstract

The phase transitions in the maraging 300 steel were studied using high temperature X-ray diffractometry. Maraging are ultra-high resistant steels with Ni-Co-Mo-Ti presenting a broad range of application in key areas such as nuclear and aerospace industries [1]. Prolonged high temperature exposure would lead to the formation of equilibrium austenite and ferrite phases [2]. Solution annealed maraging 300 steel was continuously heated at a 10 ºC/min rate from ambient temperature until 900 ºC and X-Ray measurements were done at 25, 400, 500, 600, 650, 700, 800 and 900 ºC. Dilatometric curve at the same heating rate and temperature range were performed and the results were compared with high temperature X-Ray diffraction. The martensite to austenite transformation and vice-versa could be detected by both techniques, although the precipitation could be detected only by dilatometry, associated to low volume of precipitates to be detected by X-Ray diffraction. The effect of austenite reversion at 600ºC was also studied after at 1, 2, 3 and 4 hour of exposure, showing that the amount of reverted austenite is proportional of time exposure at high temperature.