Research Of Tempering Behavior Of Retained Austenite In High C-high Cr Tool Steel

The tempering behavior of martensite and retained austenitean was mainly studiedin this article. As-quenched high Cr-high C tool steel is consisting of lath martensite,retained austenite and carbide. Two groups contained air-cooled samples andoil-quenched samples were compared under the same tempering conditions. Themicrostructures were observed by OM、SEM\ENSD and TEM, and the changes in thetotal austenite volume fraction and carbon concentration were monitored duringtempering neutron diffraction and X-ray diffraction. The main content and results is asfollows:(1)The volume fraction of blocky austenite grains increases by absorbing carbonatoms from martensite by tempering at573K, although film austenite decomposes toferrite and cementite, which indicate the different tempering behaviors between blockyaustenite and film austenite;(2)The total austenite volume fraction hardly changes or slightly increases by573-773K tempering but its stability is not so high. The critical tempering temperature ofmartensite transformation from blocky austenite upon cooling to RT is about773K;(3)Metastable austenite transforms to martensite more easily in a thin foil, then thesurface layer of a bulk specimen and finally the inner part due to the constrictive effectfor transformation shape and size change. The results obtained by TEM, SEM/EBSD,X-ray diffraction and neutron diffraction reflect such characteristic features.