Mechanical and Microstructural Anisotropy of Laser Powder Bed Fusion 316L Stainless Steel

Abstract

This paper aims at an in-depth and comprehensive analysis of mechanical and microstructural properties of AISI 316L austenitic stainless steel (W. Nr. 1.4404, CL20ES) produced by laser powder bed fusion (LPBF) additive manufacturing (AM) technology. The experiment in its first part includes an extensive study of the anisotropy of mechanical and microstructural properties in relation to the built orientation and the direction of loading, which showed significant differences in tensile properties among samples. The second part of the experiment is devoted to the influence of the process parameter focus level (FL) on mechanical properties, where a 48% increase in notched toughness was recorded when the level of laser focus was identical to the level of melting. The FL parameter is not normally considered a process parameter; however, it can be intentionally changed in the service settings of the machine or by incorrect machine repair and maintenance. Evaluation of mechanical and microstructural properties was performed using the tensile test, Charpy impact test, Brinell hardness measurement, microhardness matrix measurement, porosity analysis, scanning electron microscopy (SEM), and optical microscopy. Across the whole spectrum of samples, performed analysis confirmed the high quality of LPBF additive manufactured material, which can be compared with conventionally produced material. A very low level of porosity in the range of 0.036 to 0.103% was found. Microstructural investigation of solution annealed (1070 °C) tensile test samples showed an outstanding tendency to recrystallization, grain polygonization, annealing twins formation, and even distribution of carbides in solid solution.

Microstructure effect on sliding wear of 316L stainless steel selectively laser melted

“…These values are similar to those reported in the literature 26,36,37 and are generally consistent with the microstructure-property relationship reported for anisotropic 316L. 38 In the specific case of grain size, yield strength, and hardness are directly linked following the well-known Hall–Petch relationship.…”

Tensile anisotropy of powder bed fusion steel 316L: A practical study on the effect of build orientation

“…Overall, an increasing trend with build angle is present. The elongation at fracture (ef) data are consistent with the results previously reported by Tolosa, Garciandía [13], Pitrmuc, Simota [14] and particularly Charmi, Falkenberg [1], the vertical specimens experienced the highest ductility (ef) yet the lowest yield strength (σy). Typically, the ef mechanical property is more susceptible to L-PBF material variations (such as porosity), which in turn can increase/decrease ductility.…”

Zinc Ferrite Nanoparticle Coatings on Austenitic Alloy Steel

“…In this study, we further investigate the possibilities of enhancing the properties of CL20ES austenitic alloy steel powder with a zinc ferrite (ZnFe 2 O 4 ) surface layer towards higher hardness and higher chemical stability. CL20ES is the austenitic alloy steel powder of choice for selective laser 3D printing technology, which provides printed parts with good mechanical properties [33]. However, this type of steel is prone to surface oxidation during the 3D printing process.…”