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Microstructural characterization of precipitation hardening stainless steels processed by additive manufacturing

Abstract

Additive Manufacturing is a materials processing technique that has been developing rapidly and gaining industrial relevance. Precipitation-hardening (PH) stainless steels combine high mechanical strength with good corrosion resistance and therefore find specific applications in several industrial segments. Due to the high relative cost of these materials and the need to produce components with complex geometry in small batches, PH stainless steels are excellent candidates to be processed by Additive Manufacturing techniques such as selective laser melting (SLM). However, a better understanding of the microstructure and the resulting properties of this technique is still necessary. The objective of this research project is to characterize the microstructure of 15-5PH and 17-7PH steels processed by SLM in their as-built condition and after post-processing heat treatments. Several complementary characterization techniques will be employed: scanning electron microscopy, EBSD, X-ray diffraction, residual stress, macrotexture, potentiometry, dilatometry, hardness tests, transmission electron microscopy and atom probe tomography. Computational thermodynamic calculations, using the CALPHAD approach, will be employed to determine the optimal heat treatment conditions and to aid the study of the phase transformations during the processing and post-processing. The obtained results will have great potential for publication and may serve as parameters to assist the commercial manufacturing of structural components of PH stainless steel by means of Additive Manufacturing. (AU)