Microstructure properties of tempered D6ac steel

► We evaluated microstructure properties of tempered D6ac steel. ► The forming process has a high microhardness of martensite phase at surface layer. ► XRD spectra observed that the residual austenite and/or mixed structures of ferrite with the precipitation of carbides. ► Ferrite decreased and that of carbon and chromium elements increased upon increasing the tempering temperature.