Superplasticity of fine-grained Fe-C alloys prepared by ingot and powder-processing routes

Tensile elongation behavior of fine-grained Fe-C alloys has been investigat ed as a function of cementite volume fraction, degree of microstructural re finement, and the Zener-Hollomon parameter. The strain rate-stress relation ships and creep strengths of Fe-C alloys with carbon contents from 1.3 to 5 .25 wt. % C are found to be similar when grain size is similar. Superplasti c ductility of ingot-processed alloys initially increases with carbon conte nt but starts to decrease after 2.1% C. The increase of tensile ductility w ith carbon content below 2.1% C is attributed to a reduction in the case of dynamic grain growth associated with an increase in the number of fine cem entite particles, whereas the decrease of tensile ductility above 2.1% C is due to an increase in the number of coarse cementite particles and an incr ease in the area of cementite/cementite grain boundaries. Superplastic duct ility of Fe-C alloys with carbon contents higher than 2.1% C can be signifi cantly enhanced when powder-processing routes are utilized instead of ingot -processing routes. Tensile elongation behavior of cementite-based alloys i s revealed to be different from that of iron-based alloys when compared as a function of the Zener-Hollomon parameter. (C) 1998 Kluwer Academic Publis hers.