High Temperature Corrosive Environment in a Sintering Plant for Pig Iron Production and Its Effect on Different Steel Grades
The harsh environment in a sintering plant for pig iron production leads to high temperature corrosion of the sinter grates. In the present study, a detailed analysis of the corrosives in such applications is given to understand materials failure. Various steels are tested, revealing effects of various alloying concepts, the resulting phases and their corrosive behavior in this complex corrosive environment at ≈900 °C. In order to understand the underlying corrosion mechanisms, detailed analyses are performed. Results indicate mainly chlorine, sulfur, and oxidation based corrosive decay at elevated temperature and a high relevance of protecting alloying elements within the steels.
Formation of Si diffusion layer on stainless steels and their high temperature corrosion resistance in molten salt
Abstract The surface alloying of Si into SUS430 and SUS304 stainless steels was achieved by a pack-cementation method. A high-temperature corrosion test was undertaken under a corrosive ash in a high-temperature gas, which simulated the environment of a waste incinerator. The effect of the surface alloying of Si on the high temperature corrosion resistance of these stainless steels was examined. The result of the corrosion test showed that the corrosion mass loss of the siliconized stainless steel was lower than that of non-treated stainless steel. It was thought that the high temperature corrosion resistance in the corrosive ash containing large amounts of molten salt was improved by the surface alloying of Si. The change in corrosion loss with test time in the corrosive ash was also examined. The corrosion loss of the non-treated stainless steels rapidly increased. On the other hand, the corrosion rate of the siliconized stainless steels was small. It was found from the observation and EPMA analysis of a cross-section of the specimen after the corrosion test that, for the non-treated stainless steels, the metallic elements were dissolved into the molten salt. On the other hand, for the siliconized stainless steels, a scale consisting of silicon oxide was formed on the steels. As a result, the dissolved metallic elements were small. The electrochemical studies indicated that there was an effect of the surface alloying of Si on the hot corrosion resistance of the stainless steels. Hence, the corrosion potentials of the siliconized steels were higher than those of the non-treated steels. The increase in the anodic current densities for the siliconized steels was smaller than that for the non-treated steels. It was thought that the electrochemical corrosion reaction was difficult to occur due to the surface alloying of Si into the stainless steels.
Hot corrosion of some superalloys and role of high-velocity oxy-fuel spray coatings : a review
Abstract Hot corrosion is a serious problem in power generation equipment, gas turbines, internal combustion engines, fluidized bed combustion, industrial waste incinerators and paper and pulp industries. No alloy is immune to hot corrosion attack indefinitely although there are some alloy compositions that require a long initiation time at which the hot corrosion process moves from the initiation stage to the propagation stage. Superalloys have been developed for high-temperature applications. However, these alloys are not always able to meet both the high-temperature strength and high-temperature corrosion resistance simultaneously, so the need to be protected from corrosion. The high-temperature protecting system must meet several criteria, provide adequate environment resistance, be chemically and mechanically compatible with the substrate, be practically applicable, reliable and economically viable. This paper briefly reviews the hot corrosion of some Ni- and Fe-base superalloys to understand the phenomenon. Comprehensive reviews of the corrosion of coatings have appeared regularly since early 1970; the purpose of this paper is not to repeat the published materials but rather to focus on research trends and to point out some research prospects. High-velocity oxy-fuel (HVOF) spraying is a new and rapidly developing technology in combating high-temperature corrosion and is now challenging the vacuum plasma spraying technique (VPS), which is very expensive (capital costs approximately 2 million US$). HVOF coatings have very low porosity, high hardness, high abrasive resistance, good wear resistance with a strong ability to resist high-temperature corrosion resistance. The purpose here is to summarize the performance of such coatings on various substrates. The effect of coatings thickness, residual stresses induced in the substrates, pre and postheat treatment of the HVOF coatings have been reviewed with the aims of summarizing their high-temperature corrosion resistance properties.