| Popis: |
In applications where a combination of good strength and corrosion resistance is required, 17 − 4 precipitation hardenable (PH) stainless steel is a common material choice. This alloy is traditionally processed through a combination of casting, rolling, and machining. A variety of heat treatments are used to anneal and harden the material via precipitation strengthening. While additive manufacturing (AM) removes many geometric design constraints from these traditional forming processes, until recently, structures fabricated via laser powder bed fusion (L-PBF) were porous and contained undesirable columnar grain structures that contributed to unpredictable and anisotropic mechanical properties. However, recent advances in L-PBF processing technology including improved gas flow, powder atomization, and print parameter optimization enable printing of high-quality AM 17 − 4 PH with properties that are comparable to traditionally processed material. With the ultimate goal of establishing mechanical property baselines involving numerous L-PBF processes, six vendors (including this work) fabricated tensile and fatigue samples of 17 − 4 using a variety of machines. Ultimately, after standard solution annealing and heat treating, the microstructure and mechanical properties across vendors converged with very few, easily explainable exceptions. In particular, powder atomized in nitrogen promoted formation of retained austenite that lead to a yield point phenomenon in as-built conditions and high surface roughness from as-built surfaces reduced the fatigue strength. However, with conventional post-processing heat treatments and surface polishing, AM 17 − 4 PH behaved comparably and consistently to conventionally processed material. |
