Marcelo Camargo Severo de Macêdo

Influence of Deleterious Phases Precipitation in the Corrosion Resistance Measured by Double Loop Electrochemical Polarization Reactivation Test in Superduplex Stainless Steel

This work investigates the influence of deleterious phases precipitation on the corrosion resistance of two wrought superduplex stainless steels UNS S32750 with similar composition, but different grain sizes. Isothermal treatments were carried out to introduce different amounts of deleterious phases, such as chi (χ), sigma (σ) and secondary austenite (γ2). The specimens were tested by double loop electrochemical potentiodynamic reactivation test (DL-EPR). The kinetics of precipitation in the two steels was different due to the difference of the grain sizes. The results show a correlation between the sensitization degrees, measured by DL-EPR, with the amount of deleterious phases precipitated.

A statistical approach to estimate state variables in flow-accelerated corrosion problems

Abstract Sequential Monte Carlo or Particle Filter Methods have been widely used to deal with sequential Bayesian inference problems in several fields of knowledge. This technique involves approximation of probability sequences distributions of interest, by means of a large set of random samples, i.e. particles that are propagated along time with a simple Sampling Importance distribution, SI. A re-sampling technique is also used to improve the predictive probability. In this study, a methodology is proposed: apply the Bayesian filters to a state estimation problem involving the corrosion amount-time in a contraction–expansion geometry with the aid of Computational Fluid Dynamics to improve the accuracy of the results. The following filters were applied and compared: Sampling Importance Re-sampling filter (SIR filter) and Auxiliary Sampling Importance Re-sampling filter (ASIR filter). The corrosion model adopted is based on a double resistance due to the oxygen diffusion towards the wall through the hydrodynamic boundary layer and the oxide layer. Mass loss data over time are obtained from the literature to compare corrosion rates. Also, the influence of the corrosion products in rates of corrosion is discussed . Best results in corrosion damage estimation were obtained using the ASIR filter.

Influence of Cold Plastic Deformation in the Hardness and Corrosion Resistance of Superduplex Stainless Steels Aged at 475 °C

Superduplex stainless steels (SDSS) combine elevated mechanical properties with a high corrosion resistance in severe environments. This class of materials is employed in pipes, pressure vessels, heat exchangers, pumps and other components in industries that operate with highly corrosive fluids. However, in continuous service conditions, such as in reactors and heat exchangers, high temperatures can be achieved. Thus, the purpose of this work is the determination of the influence of prior cold plastic deformation, with true strain of 1.39, in hardness and corrosion resistance of SDSS UNS S32750 and UNS S32760 obtained after thermal aging at 475 °C. The motivation of this study is due to the fact that certain components of process equipment may be deformed at low or high temperatures, in hi h the delete ious α’ phase p e ipitatio ki eti s is o e i te se. The esults sho that old plastic deformation accelerates the precipitation kinetics of this phase in SDSS UNS S32750 and UNS S32760.