MICROSTRUCTURAL ASPECTS ON THE CORROSION OF STEELS IN SIMULATED CHAR COMBUSTION ATMOSPHERES

摘要

Corrosion experiment were carried out on austenitic stainless steels and nickel alloys in simulated char combustion atmospheres. The samples were exposed at temperatures 625, 650 and 700 °C in an N_2-6% H_2O-15%CO_2-4%O_2-0.1 %SO_2 atmosphere covered with synthetic deposits of 2%Na_2SO_4-7%K_2SO_4-10%CaSO_4 for 500-10000h. The corrosion kinetics is recorded by measuring the scale thickness and metal loss in metallographic cross sections. Subsequent analysis of scale composition and reacted metal microstructure was carried out with Light Optical Microscopy (LOM) and Scanning Electron Microscopy (SEM). The results show the higher stability of high chromium alloys such as DMV 310N and DMV USC 141 compared to alloys with lower chromium content. In contrast, the precipitation state of the alloy is very important as significant attack was observed on sensitized grain boundaries by internal sulfidation. The paper will present results especially on this important point.