Additively Manufactured Full-Density Stainless Steel 316L With Binder Jet Printing

Binder jet printing (BJP), one of the early metal 3D printing technologies, has distinct advantages over the other 3D printing processes that employ locally melting or welding to build 3D parts. Some of the advantages of BJP include printed parts free of residual stresses, build plate not being required, and less powder usage. However, the BJP technology has been adopted only in limited applications such as prototyping and sand molding because of its difficulty in achieving full-density parts. Based on our previous work on stainless steel (SS) 420, the same BJP protocol was used to attain full-density parts made of SS 316L. The effect of the particle size, mixture ratio, and sintering additives on the densities of printed and sintered parts is investigated for SS 316L powder. Three distinct sizes of SS 316L powders are mixed to improve the packing density. A systematic study of the binder burn-out procedure is conducted using thermogravimetric analysis, leading to a complete removal of binder phase without oxidizing SS 316L powder. The optimal sintering condition for some powder mixtures is determined to obtain the maximum density with the addition of small amounts of boron compounds as sintering additives. The quality of the fully-sintered SS 316L parts is evaluated using the various measurements including density, microstructure, hardness, and surface roughness. As we did with SS 420, the relative density of 99.6% is obtained for SS 316L without structural distortion. This is the first demonstration of such density for SS 316L using the BJP technology without any infiltration.