AN FIM/AP STUDY OF THE MO CONCENTRATION WITHIN FERRITE AUSTENITE INTERFACES IN AN FE-0.88 AT-PERCENT C-1.06 AT-PERCENT MO ALLOY

The field ion microscope/atom probe method was employed to measure the Mo concentration in alpha / gamma and alpha / alpha boundaries in an alloy isothermally reacted at 585 degree C for 30 s. An evidently non-equilibrium enrichment ratio of ca. 2 was found at both types of boundary. The alpha / alpha boundaries are suggested to result mainly from sympathetic nucleation of ferrite at alpha / gamma boundaries. It is also likely that the alpha / alpha boundaries inherit the Mo concentration of the predecessor alpha / gamma boundaries. The results are consistent with previous proposals of Mo segregation to alpha / gamma boundaries acquired during the operation of a solute drag-like effect upon growth. Both alpha / gamma and alpha / alpha types of boundary showed significant C enrichment. The extent of this enrichment is uncertain due to the possibility of changes in C adsorption during quenching. The bulk ferrite contained 0. 20 plus or minus 0. 05 at percent C, a concentration somewhat greater than the predicted paraequilibrium value of 0. 14 at percent C. The difference between the two concentrations can be explained by C segregation to dislocations in ferrite. 37 Refs.