Stefano Chiovelli

Effects of Hydrogen on Pitting Susceptibility of Type 310 Stainless Steel

Abstract Type 310 (UNS S31000) stainless steel (SS) membranes were precharged with hydrogen at various current densities. Effects of hydrogen on pitting susceptibility were investigated by carrying...

Characterization and corrosion behavior of high-chromium white cast irons

Erosion-resistant high-chromium white cast irons (CWIs) are widely used in hydrotransport components, particularly in oil-sand operations. Due to the acceptance that corrosion processes can accentuate material degradation by erosion processes andvice versa, it is important to understand the corrosion resistance of these materials in the environments in which they are used. Three CWI alloys with different chemical compositions—chromium (26 to 40 wt pct) and carbon (2.5 to 4.3 wt pct)—were investigated in this study. Electrochemical DC potentiodynamic polarization and potentiostatic tests were carried out in a solution of 1000 ppm Cl− at a pH of 8.5 (obtained by adding NaOH) that simulates a recycle cooling water. A detailed characterization of the microstructures was also performed. There are significant effects of microstructural features and alloy composition on the corrosion behavior of CWIs. Two key factors have been shown to determine the corrosion behavior: the primary carbide area fraction and the amount of chromium as well as other elements in the matrix. The corrosion resistance of the CWI alloys strongly depends on the ratio of chromium content in the M7C3 carbide to that in the matrix (CrM7C3/Crmatrix).

Critical hydrogen charging conditions for martensite transformation and surface cracking in type 304 stainless steel

It is well known that the presence of hydrogen in 304 stainless steel can induce martensite transformation and surface cracking in austenitic stainless steels. The change in microstructure would affect the corrosion behavior. Martensite could be preferentially dissolved, which results in an increase in anodic dissolution and facilitates the formation of active paths for stress corrosion cracking. Hydrogen-induced martensite has some effects on pitting corrosion and is also found to be related to hydrogen embrittlement. In previous reports, almost all the results were obtained by charging the specimens at very high cathodic current densities ({ge}50mA/cm{sup 2}). The objective of this work is to investigate the critical charging conditions for hydrogen-induced martensitic transformation and surface cracking of 304 stainless steel.

Assessing Metal Matrix Composites for Corrosion and Erosion-Corrosion Applications in the Oil Sands Industry

Abstract Erosion-corrosion that arises when materials are transporting aqueous slurries can be a significant problem in the oil sands industry. Interactions between erosion and corrosion are complex and, as such, it is difficult to determine the rate of material loss with sufficient accuracy for the reliable prediction of equipment lifetime. A combination of electrochemical and gravimetric techniques were used in this study to assess erosion-corrosion rates under liquid-solid impingement in a simulated recycle cooling water environment containing 5 wt% solids at 25°C and 65°C. One material that has been successfully used on critical production equipment is tungsten carbide (WC) metal matrix composite (MMC) applied to the surface as a weld overlay. Four WC-based hardfacing overlays with different particle size distributions were investigated in this study. These overlays comprised 65 wt% WC hard phase with a metal matrix binder consisting of mainly Ni, Cr, Si, B, and Fe. The MMC overlays were applied using...

Pitting of carbon steel with banded microstructures in chloride solutions

Abstract The pitting corrosion behaviour of carbon steels with different banded microstructures has been investigated in chloride solutions using the in situ scanning reference electrode technique (SRET). The specimen surfaces were inspected with an optical microscope after SRET measurements and the variation of potential over the test surface was compared with the corrosion morphology. The regions of potential drop on the SRET maps are consistent with the sites and sizes of the observed pitting. Pitting susceptibility was found to vary with microstructure of the steel. The surface morphology showed that pits were predominantly initiated on the ferrite bands for specimens with martensite–ferrite microstructures, but preferentially on martensite for specimens with martensite–pearlite structures.

Effects of erosion on corrosion of type 430 and 316 stainless steels in aqueous environments

Abstract The effects of erosion on the corrosion of two types of stainless steel in aqueous 0·5M NaCl and 1M NaCl environments at ambient temperature have been studied using a modified rotating cylinder electrode system. Erosion by silica particles greatly increased the passive current density for both ferritic type 430 and austenitic type 316 stainless steels. It is suggested that two factors were largely responsible for the observed effects. The impact of the eroding silica particles on the specimen surface destroyed the passive film and removed corrosion products from the specimen surface; and impact with the fast moving silica particles generated numerous microplastic deformation sites on the metal surface which were activated owing to the presence of residual stress, dislocations and defects, etc., and the emission of low energy electrons.