Abstract
Ash deposits, especially alkali and alkaline earth sulfates, have been said to be an important source of the hot corrosion of valves and pre-combustion chambers in automobile diesel engines.
In the present work, to clarify the corrosion behavior, crusible-type corrosion tests by CaSO4-C mixtures have been carried out on pure nickel, iron and their Cr-containing alloys in the temperature range from 650°to 1 100°C for 4 h in air.
The results obtained from gravimetric measurements and metallographic examination are summarized as follows :
1) The CaSO4 alone is not corrosive for above metals and alloys, however the addition of C causes very severe attack, especially on Ni-20% Cr alloy.
2) On Ni and Ni-20% Cr alloy the temperature dependence of the corrosion caused by CaSO4-20% C mixture is different from that of well-known SO2 gas corrosion; nickel shows a monotonic increase in weight loss with temperature and Ni-20% Cr alloy shows a maximum at about 875°C.
3) In the corrosion scale, the sulfides and the oxides of each element in alloys are recognized; this scale morphology is characteristic of the sulfidation-accelerated oxidation.
