The Effect of Molybdenum on Niobium Diffusivity in Austenite
EMSL Project ID
47658
Abstract
To capitalize on the increased processing temperature capability and reduction in processing times associated with high-temperature vacuum carburizing of steels, existing commercial carburizing alloys must be modified for high temperature grain stability due to the deleterious effects of abnormal grain growth on fatigue performance. Grain refinement may be achieved by pinning mobile grain boundaries with a distribution of microalloy precipitates, e.g. (Nb, Ti)(C,N), present at elevated temperature. Current literature lacks a unified explanation of the specific contribution of molybdenum (Mo) to microalloy precipitate stability at austenitic temperatures, and several studies allude to both an effect of Mo on niobium (Nb) diffusivity in austenite and preferential segregation of Mo to precipitate/matrix interfaces. Mo could possibly slow the diffusion of Nb at elevated temperature, thereby slowing the rate of Nb-containing microalloy precipitate dissolution and subsequent abnormal grain coarsening. The proposed study aims to investigate the effects of Mo on bulk Nb diffusion in iron (Fe) upon reheat to austenitic temperatures. A total of 12 diffusion couples will be prepared to investigate the effect of Mo on bulk diffusion of Nb in Fe and a binary Fe - Mo alloy. Diffusion profiles will be analyzed by time-of-flight secondary-ion mass spectroscopy (ToF-SIMS), and a diffusion coefficient of Nb in each Fe-based layer will be determined for each diffusion temperature.
Project Details
Project type
Limited Scope
Start Date
2012-09-10
End Date
2012-11-10
Status
Closed
Released Data Link
Team
Principal Investigator