Improving pore morphology of PM 316L stainless steels by prealloyed powder prepassivation in 20% nitric acid

Abstract

The effect of prepassivation of prealloyed powder of 316L stainless steels on pore morphology and powder particle shape was investigated. Image analysis technique was used to study the effect of prepassivation, compaction and sintering temperature on the pore morphology of powder metallurgy 316L stainless steels. Porosity, dimension and morphology of the pores were characterised by means of four basic parameters: fraction of surface porosity, equivalent circle diameter, shape factor and elongation factor. In addition, SEM macrographs of powder particles were also investigated by applying the image analysis technique. The Feret’s average diameter and elongation factor were employed to describe the size and roundness of powder particles respectively. Annealing treatment reduced the equivalent circle diameter of pores and simultaneously improved fshape and felong towards higher values. It was proposed that the prepassivation treatment reduced irregularity of powder particles through elimination of sharp corners of powder particles by exposure to acid environment.