Deformation of steel powder compacts during sintering: Correlation between macroscopic measurement and in situ microtomography analysis

Powder compacts obtained by warm pressing of steel powder containing lubricant were found to swell during a typical delubrication cycle and shrink during sintering. The final dimensional changes of the denser compact were strongly anisotropic. Dilatometry measurements showed that final deformation resulted from microstructure induced by prior die pressing and from various phenomena arising at different stages of the cycle, each of them leading to a specific anisotropic effect. To corroborate this assumption the microstructure evolution of the denser material throughout sintering has been observed using in situ synchrotron X-ray computed microtomography. In addition to visual examination, quantitative analysis of 3D images consisted in searching for a relationship between the morphology and the orientation of pores in 2D sections and measuring local strain with an image correlation technique. From this information a schematic description of the main phenomena responsible for the deformation of steel powder compacts during sintering is proposed.