Duplex stainless steels (DSSs), which often exhibit excellent mechanical properties, have been applied in many fields. However, the introduction of Ni elements can significantly increase their manufacturing cost. Additionally, their strength-ductility synergy should be enhanced for fabricating various lightweight parts. In this study, Ni-free high-N DSSs that could be relatively inexpensive and possess excellent strength-ductility synergy were designed and fabricated via laser powder bed fusion (LPBF) and post-heat treatment. The introduction of high-content N elements (0.42 wt%) could increase the stability of the austenite phase, produce the solid solution strengthening, and combine with Cr to form numerous CrN nanoprecipitates within the ferrite phase (∼90 vol%) of as-built samples. During the post-heat treatment process, these nanoprecipitates were utilized as nucleation sites to promote the formation of austenite phase, refining grains and increasing austenite content. Additionally, higher content of O elements (0.098 wt%) promoted the in-situ formation of silicate nanoparticles in as-built samples, and retained in as-quenched samples (ferrite: ∼40 vol%), facilitating strength-ductility synergy. Compared to as-built samples, the ultimate tensile strength of as-quenched samples was slightly decreased from 1197.1 MPa to 926.3 MPa, while their uniform elongation was substantially increased from 4.2 % to 25.6 %. After post-heat treatment, as-quenched DSSs possessed excellent strength-ductility synergy compared to other reported heat-treated LPBF-fabricated DSSs, attributed to grain refinement strengthening, nanoparticles, solid solution strengthening, and back stress strengthening. This innovative alloy provides an opportunity for the use in various applications, in particular where low-cost, yet high strength-ductility are required.
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Dec 7, 2024
E Ajay + 3
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Open Access