This paper aims to investigate the unique substructure and grain growth of 316L stainless steel processed by selective laser melting (SLM) and clarify the mechanism. Results showed that the grain orientation on the x-z plane parallel to the build direction was the same type as the y-z plane, which all grow along the heat flow direction to form elongated columnar grains passing through the multi-layer fusion line. The epitaxial growth direction of grains changed abruptly with the vary of temperature gradient direction. Moreover, to expound the substructure formation based on solidification theory, a finite element model was established to obtain the distribution map of cooling rate G × R and solidified morphology G/R.

Fused Filament Fabrication (FFF) technology is used to create metal parts in this paper. A binder formula is developed for 316L stainless steel powder, composed of polypropylene (PP), styrene ethylene butylene styrene (SEBS) and paraffin wax (PW). The binder is mixed with the 316L stainless steel powder to produce mixture which is then extruded into filament. The optimum binder formula, PP:SEBS:PW = 5:2:2, is obtained by orthogonal experiment. After optimization, mixture viscosity is reduced, filament tensile strength is guaranteed, rigidity is improved. The filament can be printed by a desktop FFF printer to obtain green parts. Binder within the green parts can be sufficiently removed by solvent and thermal debinding, and the shape of printed parts can be maintained well. After sintering, shrunken 316L stainless steel parts can be created, some pores distributed inside. With finer metal powder, the relative density of sintered part can be increased to 96%. The research ideas of this paper can provide effective methods for the development and optimization of binder.

The present work investigates the microstructures, mechanical properties and deformation behaviors of the 316L stainless steel fabricated by selective laser melting (SLM). The initial dislocation density of as-SLM and conventional samples is measured using x-ray diffraction (XRD). It is found that the high dislocation density is obtained by SLM, contributing to the enhancement of yield strength. Twinning has occurred at the early stage of SLM deformation, which undergoes obvious grain rotation and twinning development during the tensile tests. However, only a few transformed martensite is presented in the deformed samples, and no significant grain orientation changes are observed.

A three-dimensional numerical model is developed to investigate the influence of sulfur content on the transitions of thermo-capillarity and flow dynamics during laser powder bed fusion (LPBF) of 316L powders. The impacts of variations in sulfur contents on thermal behaviors involving heat transfer and solidification characteristics, thermo-capillarity transition, as well as the spatial and directional transitions in flow dynamics, are analyzed through mechanistic modeling techniques. It is observed that transient thermal behaviors, including melt pool profile, track morphology, and solidification processes, are significantly influenced by the contained sulfur concentration. High sulfur concentrations tend to result in finer microstructures and equiaxed grains. Through simulations, it is noted that the transition in the sign of temperature coefficient of surface tension (TCST) is more easily observable in low-sulfur level but disappears as the sulfur concentration is extremely low (0.0001%) With sulfur content increasing, a more homogenized velocity distribution is observed, accompanied with heightened flow complexity denoted by the emergence of additional branch flows and vortices. These findings offer valuable insights into the underlying physics of melt pool dynamics in the LPBF process and present a potential approach for process optimization.

Wire arc additive manufacture (WAAM) technology has a good development prospect, and can be used to manufacture large metal components with complex shapes in combination with traditional machining equipment. This paper adjusts the parameters from the perspective of heat input and arc control. It is found that the stacking quality of 316L stainless steel is the best when the arc voltage is 40V and the arc current is 360A. It is proposed to obtain the flat layers by pressure machining after every layer is stacked, which can create favorable conditions for manufacturing large-size components. And through the hot rolling experiment, it is proved that pressure machining can improve the density and uniformity of the microstructure, and thus enhance the comprehensive mechanical properties of components built by WAAM.