Abstract
The influence of Si on the decarburization and carburization of heat-resisting austenitic alloys were investigated in the temperature range from 800 to 1 000°C in an impure helium atmosphere. This atmosphere simulates the primaly coolant of high temperature gas cooled reacter. The results were as follows. The alloys with 0.50.6 wt% Si were heavily carburized or decarburized above 900°C depending on the temperatures tested, while the carburization and decarburization of the alloy with 3.4 wt% Si were negligible small in the tested temperature range. In the alloy with high Si content, the carburization or decarburization was suppressed, because a thin SiO2 film, having a strong corrosion-resistant properties, might be formed beneath the surface-layer of (Mn, Cr) oxide. However, the films defoliate the surface oxide layers on cooling.
