Austenitic stainless steel (ASS) is one of the best materials for applications in which corrosion resistance plays a key role in service performance. This distinct characteristic, combined with other outstanding properties, such as mechanical strength, toughness, conformability, and weldability, has promoted the wide use of this material in several industrial areas, such as medical and food processing. The increasing concern with health, safety and sanitation requirements has resulted in a demand for materials with antibacterial properties. In particular, Cu-bearing antibacterial stainless steels have attracted wide attention in recent years due to their high strength, superior creep and corrosion resistance. Outstanding antibacterial properties are accomplished with an appropriate amount of Cu addition and effective heat treatment. When precipitated on the ASS passive film, Cu forms ions that extract electrons from bacteria, resulting in their killing [1-3].

In this investigation, AISI 304 ASS with 3.5% Cu and AISI 316L ASS with 2.0% Cu were submitted to a solution heat treatment followed by an ageing treatment at 750 °C for three different ageing times: 0.5, 1 and 2 hours. The antibacterial activity of specimens without ageing treatment was also evaluated. For the bacterial tests, S. aureus ATCC 49230 was selected and, before each experiment, microorganisms were cultured in TSB for 24 h at 37 °C and 150 rpm. The initial suspensions at 1×105 Colony-Forming Units (CFU) mL-1 were prepared in fresh TSB. Analyses of the planktonic bacteria growth after 1, 3, 6 and 24 hours of incubation and of the bacterial adhesion and proliferation (sessile populations) after 6 and 24 hours were performed.

The results showed that the ageing treatment performed on the 304 ASS and 316L ASS alloyed with Cu led to an improvement in the antibacterial resistance for both materials, which is explained by Cu precipitation. For 0.5 hours of ageing (Figure 1) and an incubation time of 6 hours, an antibacterial rate of 99.67% and 99.99% for 304 ASS and 316L ASS, respectively, was achieved. Concerning an incubation time of 24 hours, an antibiofilm activity rate of 85.76% and 67.39% for 304 ASS and 316L ASS, respectively, was reached.