Columnar fine grained structure and chemical composition features of austenitic stainless steels 316L and 321 produced by the laser beam powder bed fusion

Abstract

One of the promising ways of producing metal parts with the required properties and geometry is the technology of fusing powder layers by the using of laser beam. In the present work, the specific structure of samples obtained by the laser powder layer bed fusion is investigated. A comparative analysis of the structure of austenitic steels 316L and 321 with slightly different chemical composition are carried out. The epitaxial mechanism of the formation of elongated grains whose dimensions in the building direction is often several times higher than the powder layer thickness is considered. The reason for the formation of the droplet-shaped boundaries between the fusion layers is explained. The formation of ultrafine columnar grain substructure (the characteristic dimensions of the elements are less than 1 mcm) for both of this steels is explained.