Springer Online Journal Archives 1860-2000
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Abstract Solidification and microsegregation studies were performed on alloy CF-8M weld metal which solidified via the primary austenite/eutectic ferrite mode. All of the major alloying elements (chromium, nickel, molybdenum) were observed to segregate to interdendritic areas upon solidification. Electron microprobe analysis revealed a substantial chromium and molybdenum enrichment of the eutectic ferrite relative to the austenite dendrites even in structures water-quenched from the solidus temperature. Scanning transmission electron microscopy/energy dispersive spectrometry (STEM/EDS) profiles taken within the eutectic ferrite phase revealed a similar pattern of major element distribution as has been observed by other investigators in residual primary delta ferrite dendrites. Within the eutectic ferrite, the highest chromium and molybdenum content and the lowest nickel content was found at the eutectic ferrite/austenite boundary. STEM/EDS analyses of in situ water-quenched weld microstructures revealed that compositional modification of the eutectic ferrite had occurred upon cooling from the solidus. In particular, the chromium concentration of the eutectic-ferrite was observed to increase by approximately 3 wt% in the temperature range ∼ 1300 to ∼ 750°C. In the same temperature range, the nickel content of the eutectic-ferrite decreased by approximately 4 wt % and the molybdenum content increased within the same phase by approximately 1 wt%. The transformation of eutectic ferrite to austenite as the weld metal cools to room temperature is consistent with a volume diffusion-control mechanism.
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