Calculations concerning precipitate growth during impact extrusion

An analysis of carbide particle growth during impact extrusion of 440A stainless steel was made and it was concluded that diffusion enhancements of the order of 8000 or more would be needed to produce particles with 25 A radii under such conditions. Deformation-induced excess vacancy enhanced diffusion was examined for the conditions of impact extrusion and it was learned that significant diffusion enhancement would not occur by this mechanism. Finally, dislocation ''pipe'' diffusion as a possible diffusion enhancement mechanism was evaluated. Although it would appear that ''pipe'' diffusion is capable of providing large enhancements, the experimental results were contradictory to the behavior predicted by the ''pipe'' diffusion model. The overall conclusion is that carbide particles cannot grow to physically meaningful sizes during impact extrusion