Hot Corrosion of Mechanical Alloy MA 754 Induced by Na₂SO₄-NaCl Mixtures

Abstract

In order to study the behavior of hot corrosion of mechanical alloy MA 754 induced by Na₂SO₄-NaCl mixtures in comparison with that of conventional wrought alloy having similar chemical composition, modified coating tests were conducted in still air in the temperature range from 900 to 1 100°C. The extent of corrosion was estimated by corrosion loss and total depth of penetration. The mixing rate of NaCl was varied from 0 to 100wt%. Results obtained were as follows :
1) Corrosion loss of MA 754 increased abruptly at 25% NaCl, then increased gradually with an increase in NaCl content.
2) Total depth of penetration of MA 754 increased with increasing NaCl content and had a maximum value at about 75% NaCl.
3) For the corrosion of MA 754, internal penetration in the longitudinal direction was more significant than that in the transverse direction. This tendency was recognized markedly at 900 and 1 000°C, but at 1 100°C there was no difference between two directions because of little internal penetration.
4) The corrosion loss and the total depth of penetration for MA 754 were larger than those of wrought alloys especially in mixed salt. The poor corrosion resistance of MA 754 was due to grain coarsening treatment.