Electrochemical study of UNS S32550 super duplex stainless steel corrosion in turbulent seawater using the rotating cylinder electrode

The cathodic and anodic characteristics of freshly polished and pre-reduced UNS S32550 (ASTM A479) super duplex stainless steel in a filtered and conductivity-adjusted seawater have been investigated under controlled flow conditions. A rotating cylinder electrode was used together with both steady and non-steady-state voltammetry and a potential step current transient technique to investigate the electrode reactions in the fully characterized electrolyte. Both oxygen reduction and hydrogen evolution were highly irreversible and the material exhibited excellent passivation and repassivation kinetics. Relative corrosion rates were derived and the corrosion mechanism of the alloy was found to be completely independent of the mass-transfer effects, which can contribute to flow-induced corrosion.

Effect of sample geometry on regression rate of the melting interface for carbon steel burned in oxygen

Promoted-ignition testing on carbon steel rods of varying cross-sectional area and shape was performed in high pressure oxygen to assess the effect of sample geometry on the regression rate of the melting interface. Cylindrical and rectangular geometries and three different cross sections were tested and the regression rates of the cylinders were compared to the regression rates of the rectangular samples at test pressures around 6.9 MPa. Tests were recorded and video analysis used to determine the regression rate of the melting interface by a new method based on a drop cycle which was found to provide a good basis for statistical analysis and provide excellent agreement to the standard averaging methods used. Both geometries tested showed the typical trend of decreasing regression rate of the melting interface with increasing cross-sectional area; however, it was shown that the effect of geometry is more significant as the sample's cross sections become larger. Discussion is provided regarding the use of 3.2-mm square rods rather than 3.2-mm cylindrical rods within the standard ASTM test and any effect this may have on the observed regression rate of the melting interface.

Sintering of freeformed maraging steel with boron additions

This paper describes the sintering of an 18Ni(350) maraging steel with additions of boron, with the aim of producing high hardness rapid tooling. Reaction of the boron with the alloying elements in the maraging steel resulted in the formation of a Mo- and Ti-rich borides. The former melted at similar to1220degreesC, providing a liquid phase for enhanced sintering. Although densification could occur regardless of the boron content, especially at high temperature, 0.4% B was required to produce a near full density component. The formation of the various borides depleted the matrix of critical age hardening elements. However, by altering the starting powder composition to compensate for this, hardness close to the wrought alloy has been achieved. This hardness was comparable to a common die casting tool steel. Examples of dies produced using selective laser sintering (SLS) are also shown. (C) 2003 Elsevier B.V. All rights reserved.

Semi-analytical solution for nonlinear vibration of laminated FGM plates with geometric imperfections

This paper investigates the nonlinear vibration of imperfect shear deformable laminated rectangular plates comprising a homogeneous substrate and two layers of functionally graded materials (FGMs). A theoretical formulation based on Reddy's higher-order shear deformation plate theory is presented in terms of deflection, mid-plane rotations, and the stress function. A semi-analytical method, which makes use of the one-dimensional differential quadrature method, the Galerkin technique, and an iteration process, is used to obtain the vibration frequencies for plates with various boundary conditions. Material properties are assumed to be temperature-dependent. Special attention is given to the effects of sine type imperfection, localized imperfection, and global imperfection on linear and nonlinear vibration behavior. Numerical results are presented in both dimensionless tabular and graphical forms for laminated plates with graded silicon nitride/stainless steel layers. It is shown that the vibration frequencies are very much dependent on the vibration amplitude and the imperfection mode and its magnitude. While most of the imperfect laminated plates show the well-known hard-spring vibration, those with free edges can display soft-spring vibration behavior at certain imperfection levels. The influences of material composition, temperature-dependence of material properties and side-to-thickness ratio are also discussed. (C) 2004 Elsevier Ltd. All rights reserved.

Transpassivation of Fe-Cr-Ni stainless steels

A transpassivation model was proposed for Fe–Cr–Ni stainless steels. In this model, the important steps and processes involved in transpassivation were illustrated. With some reasonable assumptions, transpassivation behaviours were predicted, such as the changes in film composition, film thickness, anodic current density and AC impedance spectrum in transpassive and secondary passive regions. It was demonstrated that these theoretical predictions were in good agreement with experimentally observed transpassivity of Fe–Cr–Ni stainless steels.