Abstract: Effect of ion milling on the content and stability of retained austenite in TRIP780 steel was investigated. Firstly, TRIP780 steel specimens were prepared by electropolishing to remove the stress layer on their surface, then ion milled and the retained austenite in the specimens was examined by field emission scanning electron microscope. The retained austenite content in the TRIP780 steel before and after ion milling was further analyzed qualitatively and quantitatively by electron backscatter diffraction (EBSD).The results show that, compared with electropolishing, the ion milling can also remove the stress layer on the specimen surface, however, the retained austenite content in the TRIP780 steel specimen after ion milling is greatly reduced from the original 10.1% to 0.02%, and the Kikuchi pattern of the retained austenite after ion milling is obviously worse or even blurred. The retained austenite content in the ion-milled TRIP780 steel decreases significantly, and the phase structure changes from the original face-centered cubic to the body-centered cubic (fcc→bcc), thus indicating the retained austenite is extremely unstable after ion bombardment and is prone to phase transformation, which is also verified in the quasi-in-situ experiment of retained austenite. The ion milling induces lattice distortion, resulting in a significant decrease in the clarity and resolution of the Kikuchi pattern.

Key words: ion milling, TRIP780 steel, retained austenite, EBSD, Kikuchi pattern