Process-microstructure-corrosion of additively manufactured steels: a review

Among the alloy systems for the fabrication of metallic components using additive manufacturing (AM), steels as a broad family of alloys attract significant attention owing to their established mechanical and corrosion properties under various loading and environmental conditions. In an erosive/corrosive environment, the possible failure mechanisms necessitate consideration in materials selection and design. Although functional alloying elements are deliberately added to steels to improve corrosion resistance, the crucial role of initial microstructure and post-process heat treatments are equally critical and cannot be neglected. Specifically, the proper selection and optimization of AM process parameters are essential steps in minimizing microstructural defects. This comprehensive review provides a consolidated treatise of powder atomization techniques, AM process parameter control, rapid solidification principles, their roles on the as-built microstructure. The role of different phases and microstructures formed during post-process heat treatments, and corrosion behavior of various grades of AM steels are also presented. The review presents the interplay between process-microstructure-corrosion properties of the AM steels through the entire fabrication process - from powder feedstock to final AM product exposed to harsh environments. In the first section of this review paper, the authors comprehensively explain the important factors, which affect the processability and quality of AM steel components. In the second section, the authors focus on the microstructure of both as-printed and heat-treated AM steel products, the parameters which determine variations of the microstructure, the effect of microstructural features such as the grain size and the dendrite arm spacing on the mechanical properties, and the detrimental effect of inclusions embedded into the matrix. Finally, the third part of the paper is a comprehensive review of the corrosion of different types of stainless steels (316 L austenitic stainless steel, 420 martensitic stainless steel, martensitic precipitation-hardened stainless steels of 15-5 PH, 17-4 PH, and Corrax) fabricated by AM techniques.