A TEM study of the crystallography of austenite precipitates in a duplex stainless steel

The ferrite → austenite transformation in a duplex stainless steel serves as a good model alloy for studying body-centered cubic (bcc) → face-centered cubic (fcc) transformations in metals and alloys. However, the morphology and crystallography of austenite precipitates have not been well understood. A detailed TEM study was made on the crystallography of austenite precipitates to improve the understanding of this transformation. The orientation relationship (OR) was reassessed by an OR matrix to characterize the three-dimensional crystallography between austenite and ferrite. Meanwhile, interfacial dislocation structures were investigated for all of the three prominent facets by using the Δg method and the dislocation contrast extinction method. Each facet was found to contain a set of dislocations parallel to the long axis of precipitates. Their Burgers vectors have been characterized; one of them, the Burgers vector [0 0 1]f∣[0 0 1]b, is reported for the first time in an fcc/bcc system. The O-line model was applied to explain the observations, and produced consistent results. However, some features cannot be explained by the O-line model. These will be further rationalized in the next paper.