Duplex and Super Duplex Stainless Steels: A Critical Review of Anisotropy, Micromechanics, Processing, Welding, and Service Performance

Duplex and super duplex stainless steels (DSS and SDSS) are defined by an inherent two-phase ferritic-austenitic microstructure that produces direction-dependent mechanical, fracture, and environmental behavior across length scales. This anisotropy originates in the micromechanics of the two-phase system: deformation incompatibility, load partitioning, local constraint, and damage evolution are all governed by the interaction of ferrite, austenite, and their shared interfaces. Phase balance, phase morphology, crystallographic texture, and thermomechanical history collectively determine how these micromechanical effects propagate upward in scale, influencing crack path selection, toughness, fatigue resistance, environmental cracking susceptibility, mechanical performance, and structural reliability in service.

This review examines DSS and SDSS through the lens of anisotropy and multiscale micromechanics. It addresses the relationships among composition, processing, microstructural evolution, and mechanical and physical properties, with attention to phase orientation, metallurgy and in-service performance. A central emphasis is on how the two-phase structure governs local stress and strain redistribution, phase-boundary response, directional load transfer, and environmental susceptibility, and how these features are altered by heat treatment, thermal exposure, and welding thermal cycles.

Critical knowledge gaps remain. Multiscale constitutive frameworks capable of capturing directional two-phase response are lacking, and the micromechanical behavior of welded and additively manufactured DSS and SDSS components is not well understood. Progress requires moving beyond isotropic simplifications toward anisotropy-resolved property measurement, microstructure-informed constitutive modeling, and integrated processing-to-service studies conducted across relevant length scales.

This work will present a multi-length-scale materials selection in the design path forward. This microstructure-sensitive, structure-property framework treats anisotropy not as a complication, but as a governing feature to be characterized and modeled. Such a framework is essential for materials selection in component design and fitness-for-service assessment of DSS and SDSS.