Influence of Silicon, Boron and Rare-Earth Metals on Corrosion Resistance of Austenitic Chromium-Nickel Steel

The effect of silicon (in range 0.14–0.78 wt %), boron, and rare-earth metals (REM) on the corrosion resistance of low-carbon austenitic chromium-nickel steel of 03Kh18N11 (AISI 304L) grade was studied. It is shown that all steels in the quenched state when tested in boiling 56 and 65% HNO₃ solutions have comparable corrosion rates, which do not exceed the critical norm (0.5 mm/year) in accordance with GOST 6032–2017 (State Standard). Testing samples in boiling 27% HNO₃ + 4 g/L Cr⁺⁶ solution are susceptible to intergranular corrosion (IGC). The corrosion rate and the penetration depth of IGC increase with additional silicon concentration from 0.14 to 0.78 wt %. The study focused on the effect of nitric acid concentration and test temperature has shown that steel with 0.78 wt % Si has significant corrosion losses exceeding the critical ones when testing in 56 and 65% HNO₃ solutions with temperature of 120 and 130°С. But steel with high silicon content (0.78 wt %) and low carbon concentration (0.020–0.022%) after quenching in a range of 1080–1150°C and tempering at 650°C does not exceed the critical norm on average corrosion rate. Only 0.01 wt % increase in carbon concentration leads to a significant (more than 30 times) increase in corrosion rate of sensitized steel. It is shown that microalloying with REM does not impair corrosion resistance of sensitized steel. In contrast to REM, alloying chromium-nickel steel with even a small addition of boron (0.0015%) reduces steel corrosion resistance by an order of magnitude. Corrosion rate inverse dependence on quenching temperature is observed when, with increasing temperature, corrosion rate of 02Kh18N11GS0.38R steel increases.