Antibacterial Property and Precipitation Behavior of Ag-Added 304 Austenitic Stainless Steel

A 304 stainless steel with the addition of 0.27 wt% Ag was found to exhibit excellent antibacterial properties. Based on Thermo-Calc calculation, a special heat treatment was introduced to obtain Ag precipitate in this steel. Antibacterial experiments show that the alloy can kill the adhering Escherichia coli effectively. Since the Ag element plays a key role in killing the adhered bacteria, microstructures of Ag and Ag-rich compounds were characterized by scanning electron microscopy and transmission electron microscopy. Ag-rich compounds with the size of a few microns were found to be embedded within the matrix and along grain boundaries, Moreover, pure Ag particles with a lattice parameter of 0.422 nm were found within the austenite matrix. The orientation relationship between the matrix and Ag particles was identified. Nano-sized Ag particles were precipitated during heat treatment, and the interfacial energy between Ag precipitates and matrix was determined by Becker’s model calculation.