Effect of Multiple Tempering on Mechanical Properties and Microstructure of Ledeburitic Tool Steel AISI D3

Abstract

The effects of multiple tempering on the mechanical properties and microstructure of ledeburitic tool steel AISI D3 were investigated. Austenized samples at: 940 °C and 970 °C were used The subsequent tempering was carried out in three stages with the same temperatures: 250-350-450-550 ° C; for 1 hr. The microstructure was revealed at optical (OM) and electronic (SEM) levels and then X-ray diffraction analysis (DRX) was made along with an X-ray scatter spectrometry (EDS) test. It was found that the yield stress (σf), the maximum tensile strength (σr) and ductility (ɛ) decrease with the number of temperings. The microstructures, in the three stages, show primary, massive and small carbides of type M7C3 , and Cr7C3 , accompanied by precipitated fine carbides of the same type, with the presence of the phases: Fe3C, Cr0.03 Fe0.97 and residual austenite (γr ), the latter phase is minimized with the third temper. These precipitates occur at each stage of tempering simultaneously or as the temperature increases. The variation of these properties is closely related to the microstructure obtained.