Martensitic stainless steel parts used in carbonaceous atmosphere at high temperature are subject to corrosion which results in a large amount of lost energy and high repair and maintenance costs. This work therefore proposes a model for surface development and corrosion mechanism as a solution to reduce corrosion costs. The morphology, phase, and corrosion behavior of steel are investigated using GIXRD, XANES, and EIS. The results show formation of nanograin–boundary networks in the protective layer of martensitic stainless steel. This Cr2O3–Cr7C3 nanograin mixture on the FeCr2O4 layer causes ion transport which is the main reason for the corrosion reaction during carburizing of the steel. The results reveal the rate determining steps in the corrosion mechanism during carburizing of steel. These steps are the diffusion of uncharged active gases in the stagnant–gas layer over the steel surface followed by the conversion of C into C4− and O into O2− at the gas–oxide interface simultaneously with the migration of Cr3+ from the metal-oxide interface to the gas-oxide interface. It is proposed that previous research on Al2O3 coatings may be the solution to producing effective coatings that overcome the corrosion challenges discussed in this work.

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Tribological behavior of Ti-5Al-2.5Sn, Ti-10V-2Fe-3Al and Ti-38Al carburized via current heating technique with graphite powders was studied. In carburizing, the direct current was applied across the graphite powders and alloys with a fixed electric power from 120 to 180 W for 20 min in argon atmosphere. The alloys were characterized using XRD, SEM, and hardness tester. Tribological behavior of the alloys was examined by pin-on-disk tribological test. Formation of TiC, TiC with VC and Ti 2 AlC with TiC on Ti-5Al-2.5Sn, Ti-10V-2Fe-3Al and Ti-38Al, respectively, could improve surface hardness and reduce friction coefficient leading to improve wear resistance of the alloys. Coatings of TiC totally exhibited higher wear resistance than that of Ti 2 AlC. Improvement of wear resistance was influenced by quality of coatings which could be sorted in descending as TiC, TiC with VC and Ti 2 AlC with TiC in the carburized Ti-5Al-2.5Sn, Ti-10V-2Fe-3Al and Ti-38Al, respectively.

Fe-2.25Cr-1Mo a widely used material for headers and steam tubes of boilers. Welding of steam tube to header is required for production of boiler. Heat affected zone of the weld can have poor mechanical properties and poor corrosion behavior leading to weld failure. The cost of material used for steam tube and header of boiler should be controlled. This study propose a new materials design for boiler welding to improve the lifetime and cost control, using tungsten inert gas (TIG) welding of Fe-2.25Cr-1Mo tube to carbon steel pipe with chromium-containing filler. The cost of production could be reduced by the use of low cost material such as carbon steel pipe for boiler header. The effect of chromium content on corrosion behavior of the weld was greater than that of the microstructure. The lifetime of the welded boiler can be increased by improvement of mechanical properties and corrosion behavior of the heat affected zone.

AISI 4340 steel is widely used in automotive and aircraft industries as gear components. In such applications, surface hardening processes such as carburizing are required in order to improve the life time of the components. There are many studies showing the tribological behavior of the carburized steel, but the corrosion behavior has not yet been clarified. This paper reports on both tribological and corrosion behaviors of the carburized AISI 4340 steel. Factor associated with carburizing, such as the quantities of deposited carbon, dissolved carbon, and formed Cr23C6 and Fe3C, affect the tribological and corrosion behaviors of the steel by improving hardness, friction, lubrication, and wear resistance; but corrosion resistance is reduced. The dissolved carbon affects the formation of the oxide layer of the carburized steel, by obstructing the continuous oxide layer formation and by decreasing the chromium content of the steel, leading to the decrease in the corrosion resistance of the steel.