A supersaturated super stainless high-entropy steel with extraordinary comprehensive performances for marine application

Abstract

Super austenitic stainless steels (SASS) with ultra-high corrosion resistance are urgently needed in extreme corrosion environments. However, the solubility limit of the Cr and Mo contents in the SASS has hindered the development of corrosion resistance for a long time. Here, by combining the high-entropy alloy concept and additive manufacturing technology, we break through the limitation of alloying elements in existing SASS and introduce a bulk Fe-30Cr-30Ni-8Mo super stainless high-entropy steel (SSHS) with high Cr and Mo contents. It exhibits higher corrosion potentials and lower current density than 316L in the 3.5 wt.% NaCl solution. The high entropy effect and rapid solidification rate promote the formation of a single-phase solid solution structure with high Cr and Mo contents instead of harmful intermetallic, which effectively guarantees the formation of dense passive layers under corrosive conditions. The three-dimensional interfacial networks composed of coarse grain boundaries and ultra-fine cellular substructure boundaries in the Fe-30Cr-30Ni-8Mo SSHS can also provide effective diffusion paths for Cr and Mo atoms, promoting the formation of thick passive layers. In addition, the Fe-30Cr-30Ni-8Mo SSHS also shows excellent room-/cryogenic-temperature mechanical properties (yield strength of 785 MPa and ductility of 24% at 298 K; yield strength of 1103 MPa and ductility of 16.5% at 77 K). This work provides meaningful guidance for future compositional design and preparation techniques of stainless alloys.