Study of the microstructural evolution during austenitization of an ASTM A335 P91 steel.

MX particles provide the key to control the size and size distribution of austenite grains, which is significantly important in designing materials with specific mechanical properties. In previous works it was reported that samples of a T91 steel austenized at 1050ºCfor times between 0 and 40 minutes following heating at a rate of 50 ºC/s exhibit a heterogeneous austenitic grain size distribution after austenite holding for 20 to 30 minutes from the austenite plateaus tart.

Besides, it was observed that all the second phase particles coming from the as-received state are present at the beginning of the austenite holding and that the dissolution of the MM23C6 carbides and a change of the chemical identity of MX precipitates occur within the first 5 minutes of holding. In the present work the detailed evolution of second phase precipitates over the 5 first minutes of austenite holding, obtained by means of a high speed, high resolution dilatometer is studied and followed by scanning and transmission electron microscopy.