Due to environmental issues the interest for Bio fuels has increased in recent years. Fast pyrolysis is the process of converting biomass to biofuel by rapid heating at elevated temperatures (about 400°C) in absence of oxygen. However, high water content, low pH, and the presence of metal ions and chlorides make the Pyrolysis oil highly corrosive. In addition, the Pyrolysis oil can be highly abrasive due to residues from the pyrolysis process. Hence, materials currently used in the fuel system in ordinary combustion engines cannot withstand the harsh environment connected to the use of pyrolysis oil. In this study four different tool steel grades have been tested in the pyrolysis oil; Vanax 35, Vanax 75, Elmax and AISI O1, of which Vanax 35 and 75, newly developed at Uddeholms AB, are high nitrogen alloyed grades. After austenitizing the tool steels have been tempered at different temperatures in order to try to optimize the corrosion properties and the wear resistance. Samples of the steels have then been exposed in autoclaves at 4 different temperatures, 20°C, 70°C, 95°C and 13o°C to mimic the temperature at different parts of the fuel system. The measurements show that the corrosion rate is considerable lower for the two Vanax steels compared to the Elmax and the AISI 01 steels, who suffered a high rate of general corrosion. Of the Vanax materials the steels tempered at lower temperatures (200°C, 400°C and 450°C) show the best corrosion resistance whereas higher tempering temperatures, like 500°C, show a h igher mass loss. Thermodynamic calculations suggest that the improved corrosion resistance for the Vanax materials is due to formation of primary vanadium rich nitrides instead of primary chromium rich carbides at the austenitizing temperature. Consequently, for the Vanax group, higher amounts of chromium are dissolved in solid solution after quench which will help facilitating repassivation. The poorer corrosion properties at higher tempering ranges is probably due to the precipitation of chromium rich secondary phases during tempering, which reduces the chromium content of the martensitic matrix.
2011. 982-994 p.
European Corrosion Congress 2011, EUROCORR 2011; Stockholm; Sweden; 4 September 2011 through 8 September 2011