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Duplex and super duplex stainless steels have high corrosion resistance, excellent mechanical properties, and high impact strength. Such characteristics make these steels able to operate in various segments of the industry, especially in aggressive environments. These alloys have higher strength than austenitic and ferritic stainless steels and their operation is generally restricted to temperatures lower than 300 °C. Most steels and alloys only exhibit elasto-viscoplastic behavior at temperatures higher than 1/3 of the absolute melting temperature. The objective of this work was to make an experimental study showing that the duplex and superduplex steels present a rate-dependent behavior even at room temperature (around 25 °C). Two different alloys: duplex stainless steel UNS 31803F51 and super duplex UNS S32760GRF55 were used in the study. Simple models were proposed to describe how the rate-dependent portion of the stress (called at this paper "the viscous term") depends on the strain rate. A simple procedure to identify experimentally all material constants that appear in the theory is presented. The experimental results are in very good agreement with the model predictions.

The addition of certain pozzolanic materials to Portland cement significantly changes the properties of the hardened matrix. If it has too high content of blast furnace slag, as the case of blast furnace Portland cements (BFPC), the early and late compressive strengths can be severely delayed or reduced. The objective this work was to investigate the potential of alkali-activation of BFPC and metakaolin (MK) blends by different types and contents of alkali-activators. The results clearly showed the influence of the MK pozzolanic activity and the type and content of activator used, in the development of compressive strengths of BFPC-MK blends. Microstructural analysis by SEM/EDS, DSC and XRD shown that the consumption of portlandite and the extra formation of C-S-(A)-H phases are the main positive effects registered. However, MK also promotes the formation of ettringite and unstable hydrated calcium aluminate phases, which, with the course of hydration, undergo a change in structure and volume loss, contributing to the reduction of final strengths. Content of 25% MK and 7.5% Na2SiO3 provided the best mechanical strength. The microstructures formed showed greater formation of ettringite, however there was also a reduction in portlandite and massive formation of C-S-H and C-S-(A)-H products.

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