Directed laser deposition of super duplex stainless steel: Microstructure, texture evolution, and mechanical properties

Abstract

Microstructure and texture evolution of directed-laser deposited super-duplex stainless-steel, in the as-received block, were characterized using light and electron microscopies and electron backscattered diffraction. Mechanical properties in different directions were studied. Local FCC-depleted and FCC-rich zones and extensive precipitation of oxides were detected at the matrix wherein the different types of reformed austenite were surrounded by the elongated coarse ferrite. A vertical gradient of austenite content, caused by overall change in cooling rate, generated a waning hardness distribution along the building direction. The texture of austenite across the different deposition layers was not as intense as that of the ferrite. A dominant ⟨001⟩ ⫽ND fibre, embedding strong Cube {001}⟨100⟩, was calculated for ferrite on the layer away from the bottom while the Goss {011}⟨100⟩ appeared in the layer near the building substrate due to the considerable epitaxially developed grains. The less intensified multi-component texture of austenite at the layer near the substrate changed to ⟨011⟩ ⫽ND fibre adorned by Rotated-Goss and Goss components at the upper layers where an incomplete fibre {001}⟨uvw⟩ with a major Rotated-Cube was also partially inherited from the parent phase. The inter-phase boundaries obeying Kurdjumov-Sachs orientation relationship were predominantly formed at all layers. A slight increase of Σ3 coincidence site lattice interfaces was observed in austenite across the build direction. The possible mechanical anisotropy was depressed due to complex and multi-component transformation texture of the austenite. The material showed brittleness corresponding to significantly high tensile strength and low impact toughness.

Keywords

• Directed laser deposition
• Super-duplex stainless steels
• Microstructure
• Texture
• Mechanical properties