Effect of hot isostatic pressing on microstructural and micromechanical properties of additively manufactured 17–4PH steel

Abstract

Microstructural and mechanical characterization techniques were utilized to establish the effect of the combined hot isostatic pressing (HIP) and standard H1025 heat treatment schedule on the properties of 17–4PH steel manufactured by means of laser powder bed fusion (LPBF). The as-printed (AP) sample initially consists of a dual-phase microstructure, with 78% martensite and 22% retained austenite. Then, the combined HIP and H1025 applied to the AP sample resulted in lower retained austenite of 7%. The microstructural analysis indicates that the post-processing after printing alleviated the process-induced defects reducing the overall defect content from 0.37% to 0.01%. Moreover, it is observed that the characteristic melt pools are dissolved, resulting in a homogeneous microstructure with reduced grain sizes. A room-temperature compression testing was then applied to the sample before and after post-processing treatment. It has been identified that, in both samples, the retained austenite transforms into martensite, a characteristic of the transformation-induced plasticity effect. The critical stress to initiate the dynamic transformation was then determined to be lower in the HIP sample than that of the AP sample. Based on the results, it can be concluded that the combined HIP+H1025 processing employed in this work effectively increased the mechanical properties of LPBF-fabricated 17–4PH steel. • 17–4Ph steel was fabricated via laser powder bed fusion. • Characterization of the samples was done by the means of EBSD analysis. • Using double differential method, the critical stresses for initiation of dynamic transformation of HIP sample was higher.