Frittage des melanges pulverulents ternaires fer — chrome — manganese. Role exerce par l'atmosphere de traitement

The sintering behaviour of powder mixtures Fe20 CrxMn (0 ⩽ x ⩽ 25 w %) was considered. In the case of the basic mixture Fe20 Cr (heated under hydrogen) chromium diffuses partially into α-iron, then mainly into austenite, once the surface oxyde is reduced; on the other hand under argon, chromium diffusion is more limited, and operates only at high temperature into γ-iron. Whatever the treatment atmosphere, an addition of manganese leads to a noticeable diffusion of this element, first into iron (T < 730°C), then into chromium and iron (T > 730°C). Due to the greater mobility of manganese, disturbing KIRKENDALL effects are observed during sintering, especially in the case of the higher manganese contents. However, homogeneous and dense alloys can be obtained by sintering at high temperature; according to the manganese content, the structure consists of a single-phase α when x < 6.5 wt % Mn, or of two or three phases when x > 7 wt % Mn.