Kinetics of secondary carbide precipitation in boron-modified cobalt alloys of MAR-M509 type

The effect of B addition, introduced in different amounts (0.01, 1.48%) in heat-resistant cobalt-casting alloys of the MAR-M509 type, on the kinetics of precipitation of secondary carbides Cr sub 23 C sub 6 is investigated during annealing at 975 deg C for 21 h. Structure analysis of Co alloys tested in the as-cast condition and after annealing is also presented. It has been found the B significantly shortens the icubation time for forming nuclei carbides of Cr sub 23 C sub 6 . Boron at 0.09% causes size reduction of primary phases, whereas higher B additions create additional boride phases of the MB type of high tungsten content. Dilatometer curves for the precipitation of secondary carbides Cr sub 23 C sub 6 in Co alloys of the MAR-M509 type have been described using Wert's empirical equation, W sub t = kt exp n . Graphs, Photomicrographs. 12 ref.--AA