Microstructure and mechanical properties of the austenitic stainless steel 316L fabricated by gas metal arc additive manufacturing

Abstract

The austenitic stainless steel 316L was fabricated by gas metal arc additive manufacturing (GMA-AM) and its microstructure and room temperature tensile properties were investigated. Results show that in the GMA-AM 316L plate, a large number of well-aligned austenitic dendrites vertically orient, forming large columnar grains in the middle and some dendrites bent toward the plate surfaces, forming small columnar grains near the edges. The microstructure of GMA-AM 316L consists of δ, γ and σ phases. After one layer was deposited, the δ phase exhibited reticular morphology within austenitic dendrites. The δ phase redissolved in austenite with the intermetallic σ phases forming at γ/δ interfaces under the thermal cycles influence of subsequent three deposition layers. And under the thermal influence after the fourth layers, both δ and σ phases turned into fine vermicular morphologies within austenitic dendrites. The tensile properties of GMA-AM 316L steel are comparable to wrought 316L and exceed the industry requirements for 316L. Its fracture type is ductile fracture due to the obvious fracture surface dimples. The microcracks initiate at the interior of σ phases and grow into large cracks leading to materials failure.