Nesterenko S. Austenitic welds corrosion resistance increase with use of REM micro-alloying

The thesis is dedicated to investigation of welds corrosion resistance of austenitic chrome-nickel (18-8) and chrome- nickel- molybdenum (18-8-2) stainless steel samples. The welds were micro-alloyed with rare-earth metals (REM) and their compounds. Investigation has shown that the metal anodic solution was hindered and metal passivation occured more readily when welds were micro-alloyed by Y and/or its compounds and by complex mixture of Y and Ce. It was established that auto solution currents after full passivation REM-containing Cr – Ni – Mo metal are smaller than it has been observed for initial variant. Yttrium optimal content was 0.0025-0.0032 mass. %.. Our investigation established the optimal composition of the REM addition to welding covering which ensure the increase of austenitic welds corrosion resistance in H2SO4 solution. It has been demonstrated that after micro-alloying by optimal REM amount the structural components size in the welds have reduced, the grain bounds became clean, the melted metal structure was stabilized. This fact results in the rise of inter-grain corrosion resistance. A structural change leads to the micro-chemical heterogeneity decrease (especially for samples with Ni and Cr) and ensures continuous formation of passive protective films enriched with REM. This remarkable fact leads to more uniform electrode potential distribution on metal surface of the welding compound and hinders local corrosion development. New electrodes with REM were introduced for welding and equipment repair in the coke plant.