Microstructural investigation of the effect of hot-isostatic-pressing treatment on a laser powder bed fused type 316L stainless steel

Microstructure variation before and after hot isostatic pressing (HIPing) treatments of a laser powder bed fused (LPBFed) 316L stainless steel has been investigated via complementary material characterizations. The results showed that HIPing closed most of the pores in the LPBFed 316L. In addition, most of the cellular structures that formed during printing were eliminated as a result of recrystallization and grain growth. The extent of recrystallization in the LPBFed 316L increased from 68% to 96% when the HIPing temperature was increased from 1150 °C to 1180 °C (4 h for both). Cellular structures with interrupted dislocation walls were observed within the un-recrystallized grains, whilst nano-sized oxide particles existed within both the un-recrystallized and recrystallized grains. However, chemistry of the nano-sized oxides changed from Mn and Si riched to Mn and Cr riched during the HIPing process. Microstructure evolution, and especially the abnormal recrystallization behavior of the material, was discussed based on the experimental observations. •Orientation variation besides the cell walls was usually less than 0.3° in the as built LPBFed 316 L.•Complete recrystallization was not achieved in LPBFed 316 L after HIPing at 1180 °C for 4 h.•The mechanisms for the abnormal recrystallization behavior of LPBFed 316 L were identified.