Influence of silicon and microalloying elements on the corrosion resistance of austenitic steel

The effect of silicon concentration (in the range of 0.14-0.78 wt. %) and microalloying of boron and rare-earth metals (REM) on the corrosion resistance of low-carbon austenitic nickel-chromium steel type CH18N11 (AISI 304L) was studied. Increasing the concentration of silicon in the steel with 0.14 to 0.78 wt. % increases the rate of intergranular corrosion in a highly oxidizing environment (nitric acid): in the quenched state only when tested in a solution of 27 % HNO3 + 4 g/l Cr+6 and in a sensitized state. At the same time, an increase the quenching temperature to 1150 °С can significantly reduce the corrosion rate of steel with 0.78 wt. % Si, little effect on the corrosion rate became in steel with 0.14 wt. % Si. Showed a different nature of etching samples during testing. When tested in nitric acid, low-silicon steel corrodes mainly along the boundaries of twins and high-silicon steel mainly along the boundaries of austenitic grains. The combined effect of increasing the concentration of nitric acid (from 20 to 65 %) and the test temperature (from 100 to 130 °C) was investigated. From the surface of high-silicon steel samples, significant grains loss occurs under test conditions of 56 and 65 % HNO3 at 120 and 130 °C, which increases the corrosion loss of samples of this steel. At the same time, grains loss from steel with a low silicon concentration wasn’t observed. At lower temperatures and the nitric acid concentrations of corrosive loss steels closer. It is shown, that microalloying with rare-earth elements does not impair the corrosion resistance of sensitized steel. Unlike REM, alloying of chromium-nickel steel even with a small addition of boron (0.0015 %) reduces the corrosion resistance of steel by an order of magnitude. Increasing the quenching temperature of boron steel has led to an increase in corrosion rate.