Hot isostatic pressing of laser powder-bed-fused 304L stainless steel under different temperatures

Abstract

Hot isostatic pressing (HIP) is becoming a key strategic technology for post-processing metallic materials fabricated with laser powder bed fusion (LPBF), acting to eliminate the processing-induced pores and improve the mechanical properties. This paper comprehensively investigated material characteristics (porosity, residual stress, microstructures, phase composition, and inclusion), mechanical properties (microhardness, tensile properties, and fatigue properties), and deformation behaviors of LPBF 304L austenitic stainless steel (ASS) subjected to HIP process with different temperatures (965°C, 1165°C, and 1365°C). Experimental results indicated that the grain size, inclusion size, recrystallization fraction, and dimple size increased with increasing HIP temperature, which resulted in homogenized microstructure, reduced yield strength and microhardness, and significantly improved ductility. The fatigue life of HIP-treated samples after surface post-treatment was mainly influenced by porosity, inclusion, residual stress, and dislocation density. The HIP-1165°C samples with low porosity and small-sized inclusions had a higher fatigue life than HIP-965°C and HIP-1365°C samples. In addition, the evolution of crystallographic texture and inclusion composition associated with the HIP temperature were systematically revealed with the aid of orientation distribution function (ODFs) and elemental mappings. This study provides a profound understanding of the rational design of the hybrid process of LPBF and HIP.