ALKALI SULFATE DEPOSITS INDUCED HOT CORROSION OF IRON BASED ALLOYS AT INTERMEDIATE TEMPERATURES
碱金属硫酸盐沉积引起的铁基合金在中温下的热腐蚀

Hot corrosion behavior of commercial iron, Fe-Cr and Fe-Al alloys in the presence of either a Na_2SO_4 or Na_2SO_4-K_2SO_4 deposit on their surfaces in oxygen-rich atmospheres containing SO_3at intermediate temperatures was studied. The results showed that the hot corrosion of iron based alloys occurring in the experimental conditions was caused by liquid sulfate eutectics of Na_2SO_4-Fe_2(SO_4)_3 or Na_2SO_4-K_2SO_4-Fe_2(SO_4)_3. The corrosion behavior of the materials was dependent upon temperature, gas composition, alloying element content and deposit component. The examinations of corrosion morphology indicated that the proceeding of hot corrosion was accompanied by the increase in thickness of a porous Fe_2O_3oxide layer and the rapid growth of a comparetively compact oxide layer right on the metal surface. In addition, sulfides were observed at the metal / oxide interface as well as in the compact oxide layer. On the basis of experimental results, an electrochemical mechanism is proposed to illustrate hot corrosion processes of iron based alloys at intermediate temperatures. The effects of temperature, gas composition, alloying element content and deposit component on corrosion behavior are also discussed.