Compositionally flexible austenitic stainless steel from recycling stainless scraps: effect of multiple impurity sources

The use of flexible compositional ranges is emerging as a recycling-oriented alloy design strategy that accommodates mixed-scrap variability while maintaining targeted performance. Here, we experimentally validate a compositionally flexible, scrap-tolerant austenitic stainless steel design using controlled laboratory remelting of realistic stainless-steel scrap mixtures, where mixed scraps introduce both principal element scatter (Cr, Ni, Mn) and coupled impurity inputs. Using direct remelting of standard (316L, 201) scraps and non-standard scraps enriched in C, N, and Nb, we quantify how impurity-driven compositional variability controls phase constitution, strength stability, and pitting corrosion within a defined flexible composition space. Alloys produced from mixed 316L and 201 scraps remained fully austenitic and mechanically stable despite up to 4 wt.% variation in principal elements, achieving a yield strength of 220 ± 20 MPa. Their pitting resistance increased with scrap-inherited Mo, giving pitting potentials of 220–320 mV (vs. SCE). Mass balance analysis further shows that C is largely retained during laboratory remelting, whereas N retention is strongly dependent on the scrap route: standard-scrap alloys show substantial N loss, while miscellaneous-scrap-containing alloys exhibit higher apparent N retention associated with Nb, W and V-bearing inputs. After considering N partitioning into Nb-rich M(C, N)-type precipitates, the strengthening analysis indicates that solid-solution strengthening remains the dominant strengthening contribution. These results demonstrate that compositionally flexible alloy design should be extended from a nominal Cr-Ni-Mn window to a scrap-aware framework that couples principal-element tolerance with secondary-element retention, matrix/precipitate partitioning and impurity consistency.