Physicochemical effects of an interaction between stainless steels and N2O4 under 7 thermocycling conditions

The results of an investigation of an interaction between the dissociating N2O4 and the Kh18N10T and Kh16N15M3B stainless austenitic steels by X-ray electron probe analysis are given. The analysis has been performed at the MS-46 DLS ''CAMECA'' facility. The permetion of nitrogen and oxygen into steel has been studied and the chemical composition of oxide films, has been determined. Samples of very thin-walled tubes 6.2x0.4 mm of the above mentioned steels have been investigated. The thermocycling condition are the following: heating during 2.5-3 hrs at temperatures from 20 to 700 deg C, holding period from 10 to 12 hrs at 700 deg C, cooling to 20 deg C during 8-10 hrs. Total number of cycles is 200. The environmental pressure during tests is 5 MN/m2. It has been found that the sample surface is covered by a thin oxide film. Its composition is homogeneous, the main components are ferrum, chromium, oxygen and manganese. The suboxide layer of metal is depleted in chromium and manganese and correspondingly enriched in nickel. The experimental data also show that there is no nitration of austenite stainless steel surface layer interacting with N2O4 under the thermocycling conditions