Micromechanics and microstructure evolution during in situ uniaxial tensile loading of TRIP-assisted duplex stainless steels

Abstract

Two transformation-induced plasticity (TRIP) assisted duplex stainless steels, with three different stabilities of the austenite phase, were investigated by synchrotron X-ray diffraction characterization during in situ uniaxial tensile loading. The micromechanics and the deformation-induced martensitic transformation (DIMT) in the bulk of the steels were investigated in situ. Furthermore, scanning electron microscopy supplemented the in situ analysis by providing information about the microstructure of annealed and deformed specimens. The dependence of deformation structure on austenite stability is similar to that of single-phase austenitic steels where shear bands and bcc-martensite (α') are generally observed, and blocky α' is only frequent when the austenite stability is low. These microstructural features, i.e. defect structure and deformation-induced martensite, are correlated with the micro-and macro-mechanics of the steels with elastoplastic load transfer from the weaker phases to the stronger α', in particular this occurs close to the point of maximum rate of α' formation. A clear strain-hardening effect from α' is seen in the most unstable austenite leading to a pronounced TRIP effect.

Promoting austenite formation in laser welding of duplex stainless steel—impact of shielding gas and laser reheating

“…The FDX 27 DSS is a relatively new alloy designed to improve the formability of DSS, where the influence of welding on microstructure and properties has been little studied. The specific characteristics of FDX 27 DSS such as high ductility and formability rely on the transformation-induced plasticity effect [28,29], requiring a sufficient austenite fraction. Hence, ensuring sufficient formation of austenite during laser welding is of great importance to expand the range of possible applications of this grade.…”

Macro and micro mechanical in-situ characterization using synchrotron diffraction of architectured micro-composite duplex stainless steels

“…The high strength/elongation and the deviation from the law of mixture were found to be the most important features of conventional DSS. These characteristics are usually attributed, in the literature, to several factors: i) differences in plastic behavior between the ferritic and austenitic phase [6] [7]; ii) residual stress and texture effects [8]- [11]; iii) Transformation Induced Plasticity (TRIP) [12], [13]; iv) other microstructural effects such as the formation of precipitations, phases' grain size or the morphology [14]- [16].…”

“…Indeed, the pearlite lamellae transfer the load more effectively to the cementite phase. In more recent works, the effect of volume fraction, morphology and phase distribution in dual-phase steel has been extensively reported in [18]- [21] Several authors used multi-scale modeling and in-situ and ex-situ experiments to analyze the different parameters cited above and in particular the load sharing and stress interaction between phases and consequently the micro stress-strain curves [22][23] [6], [12], [15]. However, this approach seems to be insufficient to explain the complex plastic interaction between the ferrite and the austenite in conventional DSS microstructures [2], [12].…”

“…To predict and understand the flow behavior of these composites, a comparison with a micromechanical model has been then carried out. Several studies demonstrated the performance of such models to predict the stress-partitioning of various multiphase alloys and composite such as Cu-Mo [26], Duplex stainless steel [12], [27]- [29], Ferrite-Cementite [30].…”

Experimental and Numerical Evaluation on Deformation and Fracture Mechanism of Cast Duplex Stainless Steel Tubular Specimen

“…The deformation behavior and fracture mechanism of CDSSs are of great significance for its service and improvement of the material production process, and the tensile test is the most basic test for studying the mechanical properties of materials. During the last years, some authors have studied the deformation mode and microstructure evolution of CDSSs under tensile loading by means of various methods [ 5 , 6 , 7 , 8 , 9 ]. Guo et al considered that the slip lines first appear in the austenite matrix, and slip lines in ferrite can be caused by deformation in austenite or the bulk deformation of the ferrite itself [ 5 ].…”