Análise da taxa de corrosão dos aços Hardox® 450 e Hardox® 500 em diferentes meios com temperaturas variadas

Abstract

The objective of this work was to determine the corrosion rates of Hardox® 450 and Hardox® 500 steels in 0.1 mol/L HNO3, NaOH, Na2SO4, and 3.5% NaCl (by weight) aerated solutions at temperatures of 16,24, 35 and 45°C. Corrosion parameters were determined by electrochemical method according to ASTM G 59-97. For the determinations, a potentiostat / galvanostat AUTOLAB, model PGSTAT30 was used. It was observed that the Hardox® 450 and 500 steels are active in the solutions of sodium sulfate, nitric acid and sodium chloride. In NaOH solution, these steels are passivated at all temperatures tested. The passivation film on steels in the sodium hydroxide is responsible for the low corrosion rates, around 0.023 mm/year for Hardox® 450 and 0.032 mm/year for Hardox® 500 at 24°C. The corrosion rates of the steels in the sodium sulphate were considered severe with values of 0.706 mm/year and 0.590 mm/year for Hardox® 450 and 500 steels, respectively. The corrosive behavior of Hardox® 450 and 500 steels in 0.1 mol/L nitric acid at 24°C means that these materials are not recommended in this medium without a surface protection treatment, since they presented rates of corrosion of 41.30 mm/year for Hardox® 450 and a lower corrosion rate of 28.00 mm/year for Hardox® 500. In 3.5% sodium chloride medium Hardox® 450 and 500 steels presented corrosion rates of 0.46 mm/year and 0.52 mm/year, at 24°C, respectively. For a better analysis of the corrosion rates of the Hardox® steels studied, the same electrochemical tests were carried out with SAE 1020 and AISI 316L steel samples. SAE 1020 steel presented the highest corrosion rates, while AISI 316L stainless steel exhibited the best performance against corrosive processes in the media and conditions studied.