Search

Abstract: The effect of grain size on plasticity was investigated based on the theories of dislocation pile-up and Frank–Read (FR) source activation in ultrafine grained materials. The possible reason of the experimental phenomena of decrease in plasticity as grain size refined in ultrafine grained materials was theoretically analyzed and the critical grain size for plasticity decrease was proposed. The results predicted that there was a critical grain size of about 4–5μm with the present parameters of X80 microalloyed steel where the plasticity would shift from increase to decrease as grain refined, which well agreed with the experimental data described in the references in ultrafine grained materials. The mechanism of decreasing in plasticity as grain size refined was dominantly due to the decrease of probability of activation of FR source. The modeling for predicting the critical grain size has been built up which would be very helpful to optimize microstructure for obtaining excellent combination of strength and plasticity. [Copyright &y& Elsevier]

Abstract: The current study systematically investigated the anisotropy of fracture behavior in commercial API X100 pipeline steel. The experimental results showed that the temperature for transition from ductile to brittle fracture was significantly different in samples with different orientations, defined as anisotropy of fracture behavior in this paper. The inhomogeneity distribution of microstructure (grain size) and the crystallographic texture were systematically analyzed. The difference in grain size of the samples with different orientations can be reasonably ignored in this study. Therefore, the anisotropy of fracture behavior is attributed to the crystallographic textures in which the deformation and transformation texture components were included. The effect of crystallographic texture on the anisotropy of ductile to brittle fracture transition temperature was theoretically interpreted based on the relationship among yield strength, fracture strength, and their average orientation factor. [Copyright &y& Elsevier]

Abstract: Refinement of grain size is the most effective approach to obtain high toughness especially at low temperature with high strength level. Ultra-fine grain size can be achieved by dynamic recrystallization at large Z condition, by imparting large deformation at low temperature. Large Z condition is associated with a large critical strain for dynamic recrystallization. Large strain can be accumulated pass by pass in industrial multi-pass rolling processing to overcome large critical strain for dynamic recrystallization through optimization of composition and rolling schedule. The static recrystallization during passes should be suppressed completely in order to eliminate mixed grain size. [Copyright &y& Elsevier]