Microstructure-Hardness-Corrosion Performance of 17-4 Precipitation Hardening Stainless Steels Processed by Selective Laser Melting in Comparison with Commercial Alloy

The 17-4 Precipitation Hardening Stainless Steel (PH SS) manufactured by Selective Laser Melting (SLM) has wide application perspectives, but they are limited due to defects and anisotropy. The selection of the appropriate process variables plays a fundamental part in the microstructure and in the determination of the final mechanical and corrosion properties. The main purpose of this study is to analyze the corrosion behavior, hardness and microstructure of 17-4 PH SS manufactured by SLM in comparison to the commercial counterparts. The anisotropic behavior was investigated by analyzing the microstructure-hardness and corrosion interrelationship, both in the surface of the construction platform and in the growth direction of the element. The corrosion behavior of the SLM 17-4PH SS in its natural state was investigated in relation to that of the 17-4 PH SS heat treated in a 0.1 M NaCl + 0.5 M H2SO4 solution, using three electrochemical techniques. The results confirmed that the corrosion resistance of SLM 17-4 PH SS was considerably better than that of the forging, even after 60 days of immersion in the test solution. This was attributed to the absence of important manufacturing defects, to the fine microstructure with an important amount of austenite produced by SLM, and to a small amount of non-metallic inclusions precipitated as a result of the fast cooling and the high speed of solidification associated with the SLM process.