Effects of Si and Sn Contents and Heat-Treatment Temperature on the Corrosion Behavior of AISI 439 Ferrite Stainless Steel

This study was conducted to evaluate the corrosion resistance and optimize the heat-treatment process of AISI 439 ferrite stainless steel silicon and tin alloys with reduced chromium. The microstructure of the specimens and deposition under each condition were analyzed. The production of oxide films was compared based on the thickness of the film and the change in the contents of each element. In addition, electrochemical analyses of each heat-treatment condition was used to quantitatively compare corrosion resistance and passive film stability based on the relative chromium, silicon, and tin contents. It was found that the addition of silicon and tin compensated for the decrease in corrosion resistance induced by the chromium reduction. The addition of the two elements inhibited iron (Fe) oxide production in the surface oxide film, thereby improving the corrosion resistance of the material and improving the stability of the passive film. Moreover, the SiO2 and SnO2 layers inhibited the production of Fe oxide and contributed to the stability of the film along with Cr2O3, the main component of the passive film. However, when the heat treatment temperature increased above a specific temperature, the oxide inhibitory effect of the two elements was relatively offset. Nevertheless, further research to optimize the content of the three elements will help develop materials with superior mechanical properties and corrosion resistance.

Localized Corrosion Resistance on Additively Manufactured Ti Alloys by Means of Electrochemical Critical Localized Corrosion Potential in Biomedical Solution Environments

This study proposes a new method, electrochemical critical localized corrosion potential (E-CLCP), in order to evaluate localized corrosion resistance of biomedical additive manufacturing (AM) titanium (Ti) alloys. The procedures for determining E-CLCP are completely different from that of the electrochemical critically localized corrosion temperature (E-CLCT) method (ISO 22910:2020). However, its application should be limited to pH and temperature of the human body because of the temperature scan. E-CLCP displays the localized corrosion resistance of AM Ti alloys based on the human body’s repassivation kinetics, whereas E-CLCT displays the localized corrosion resistance of the alloys based on passive film breakdown in much harsher corrosive environments.

Kinetic Monte Carlo Modelling of Dissolution and Passive Film Formation in Fe-Cr Alloys

<p>Stainless steels differ from iron in that chromium content allows for the formation of a passive iron-chromium oxide film which is only nanometres in thickness, offering protection from the environment. While the composition of this oxide layer has been established, the mechanism of its formation is not well understood. In particular, the threshold level of chromium for oxide formation is significantly lower then the chromium content of the alloy itself. We present a Cahn Hilliard type analytical model that relates the onset of passivation to an instability which leads to a phase segregating current above 17% Cr in a bulk alloy. Proposing that this current could lead to Cr enrichment at a surface, we compare atomistic simulations with and without a surface driven Cr current. We implemented a kinetic Monte Carlo algorithm with extensions to allow for vacancy assisted nearest neighbour migration in a body centered cubic alloy, tracking a surface, dissolution and surface passivation. We compare the time evolution of Fe dissolution rates, Cr surface enrichment and the threshold for passive film formation and find that the Cr current has a significant impact on each of these properties.</p>