Reduction of Anisotropy in Cold-Rolled Duplex Stainless Steel Sheets by Using Sigma Phase Transformation

Abstract

The mechanical properties of rolled duplex stainless steel (DSS) products manufactured by the current industrial process exhibit a strong anisotropy. This fact is evidently due to the two-phase nature of DSSs. During industrial rolling, not only the morphology of the microstructure changes from coarse-grained isotropic in the cast slab to fine-grained anisotropic in the coil, with both phases elongated in the rolling direction (RD), but also clear and intense crystallographic rolling textures develop, especially in the ferritic phase. The objective of the present work was to modify the industrial processing route and parameters in such a way that the strong anisotropy of DSS coils and sheets is decreased and the amount of potential applications made from DSSs by deep drawing or roll forming operations is increased. To achieve this goal, after the industrial cold rolling, a heat treatment is proposed with the aim of modifying the morphology and crystallographic texture of the ferritic grains by the assistance of an enforced transformation to sigma phase. The final product obtained by this modified route showed a microstructure with grains of austenite and ferrite randomly distributed and a significant decrease of the texture intensities due to the retransformation of sigma into ferrite. As a result, DSS EN 1.4462 displayed an almost isotropic mechanical behavior and an improved aptitude to deep drawing operations.

Controlled cold rolling effect on microstructure and mechanical properties of Ce-modified SAF 2507 super duplex stainless steel

“…In order to further improve the surface processing quality and precision of SDSS workpieces, cold rolling process has been widely used in industrial practice because of its high dimensional precision, good surface quality, high strength and hardness [21]. Most of the reports are focused on the microstructure and mechanical properties of SDSS after cold rolling of SAF 2205 SDSS [22][23][24] except a few reports on SAF 2507 SDSS.…”

Strength Enhancement of Superduplex Stainless Steel Using Thermomechanical Processing

“…In the case of ultrafine microstructure, the EBSD observations presented in Figure 7 reveal a structure of subgrains in ferrite formed by recovery. As for austenite, which has a low SFE [12,13], grains have been recrystallized. It is interesting to note that, despite the cold-rolling reduction in the ultrafine microstructure (90%) being larger than that of the industrial microstructure (72%), the ferrite of the former was recovered, while that of the latter was recrystallized during the final annealing treatment, which was carried out under the same conditions in both cases.…”

“…The textures of the different phases obtained after the thermomechanical processing can be mainly described by a rolling texture that is characteristic of cubic structures [6,[11][12][13]. On one hand, ferrite texture is described by α-fiber orientations and especially by the {100}<011> orientation.…”

Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels

“…Cold-rolled duplex stainless steels exhibit a strong anisotropy due to their two-phase microstructure. During the industrial rolling process, both phases become elongated in the rolling direction, and also clear and intense crystallographic rolling textures develop, especially in the ferrite phase [ 16 , 17 ]. As a result of this anisotropy, the mechanical properties of rolled duplex stainless steels are strongly dependent on direction.…”