Transformation toughening in dispersed-phase systems

Quantitative analysis of the dynamic evolution of multilevel structure during martensitic transformations has provided the foundation for kinetics-based constitutive relations for transformation plasticity during both the stress-assisted and strain-induced modes of mechanically induced transformation. Application in numerical modeling of ductile fracture by microvoid-softening-induced shear localization, in conjunction with metallographic observation of crack-tip transformation and localization processes, reveals transformation toughening processes operating on three structural length scales, generally associated with the flow stabilizing influence of pressure-sensitive strain hardening provided by strain-induced transformation. Application of the phenomena via dispersed-phase transformation plasticity in ultrahigh-strength martensitic steels has demonstrated record toughness levels in both commercial and experimental alloy steels.