Process Optimization and Microstructure Analysis to Understand Laser Powder Bed Fusion of 316L Stainless Steel

Nathalia Diaz Vallejo,Cameron Lucas,Nicolas Ayers,Yongho Sohn,Holden Hyer,Kevin Graydon

doi:10.3390/met11050832

Abstract

The microstructural development of 316L stainless steel (SS) was investigated over a wide range of systematically varied laser powder bed fusion (LPBF) parameters, such as laser power, scan speed, hatch spacing and volumetric energy density. Relative density, melt pool width and depth, and the size of sub-grain cellular structure were quantified and related to the temperature field estimated by Rosenthal solution. Use of volumetric energy density between 46 and 127 J/mm3 produced nearly fully dense (≥99.8%) samples, and this included the best parameter set: power = 200 W; scan speed = 800 mm/s; hatch spacing = 0.12 mm; slice thickness = 0.03; energy density = 69 J/mm3). Cooling rate of 105 to 107 K/s was estimated base on the size of cellular structure within melt pools. Using the optimized LPBF parameters, the as-built 316L SS had, on average, yield strength of 563 MPa, Young’s modulus of 179 GPa, tensile strength of 710 MPa, and 48% strain at failure.

Highlights

Additive manufacturing (AM), commonly known as three-dimensional (3D) printing, is an emerging technology initially proposed for producing prototypes, but nowadays employed for building functional and structural components with complex geometry from a 3D model [1,2]
The aim of this study is to provide a comprehensive understanding of the effect of laser powder bed fusion (LPBF) processing parameters, namely the laser power, scan speed, hatch spacing, independently and systematically varied to extreme magnitudes, on densification, melt pool characteristics and microstructure development in 316L stainless steel (316L SS) based on the volumetric energy density approach
The results reported contribute to a better understanding of LPBF process for SS316 by providing quantified microstructural data, which would be valuable for simulations

Summary

Introduction

Additive manufacturing (AM), commonly known as three-dimensional (3D) printing, is an emerging technology initially proposed for producing prototypes, but nowadays employed for building functional and structural components with complex geometry from a 3D model [1,2]. The results from the studies of dissimilar metal welds and joints [4,5], could be useful to understand the melting and solidification phenomena that could help to locally tailor alloy composition and properties in additive manufacturing. Austenitic stainless steels commonly processed in LPBF systems are grade 304L [22,23] and 316L [14,15,24,25,26]. The austenitic 316L stainless steel (316L SS) with chromium-nickelmolybenum alloying additions, has a carbon content lower than 0.03 wt. Weldability, and corrosion resistance, 316L is of great interest to numerous applications including marine [29], biomedical equipment [30] and fuel cells [31]

Objectives

Methods

Results

Conclusion