Influence of hexagonal scanning strategy island size on microstructure, residual stress, and corrosion behavior of 17-4 PH SS made by L-PBF

Abstract

17-4 Precipitation-hardened steel has attracted worldwide attention due to its applications. In the manufacture of 17-4 PH SS using SLM, several parameters play an important role. In the present study, the hexagonal island sizes were varied as 1.25-2.5-3.75-5-6.75-7.5-8.75-10 mm to understand the microstructure, microhardness, residual stresses, and corrosion behavior of 17-4 precipitation hardened stainless steel fabricated by laser-powder bed fusion with a scan rotation angle of 90°. The results indicate that the average time per layer decreases as the island size increases. The quality of the surface increased with a decrease in hexagonal island size as scan length reduced. The hardness varied with island size and higher hardness was exhibited due to fine grain size. The medium island size microstructure consists of regular molten pools and lower heat accumulation. Large and small molten pools were observed on the front and side surface respectively for samples with different hexagonal island sizes. Austenite phase was detected in all samples with the highest intensity at hexagonal inside out sample with an island size of 2.5 mm at 43.500°. Both hexagonal samples with 2.5 mm island size and 10 mm samples almost exhibit ɣ-austenite phase in the finer grain size area, as per EBSD orientation maps. The residual stresses increased as the hexagonal island size increased because when a large island size is used, it produces a long scanning track with a weak pre-heating effect, resulting in a high-temperature gradient and high residual stress. Higher corrosion resistance was obtained for 2.5 mm hexagonal scan strategy island size because of finer grain size and lower defects.