This article discusses two general mechanisms of corrosion in molten salts. One is the metal dissolution caused by the solubility of the metal in the melt. The second and most common mechanism is the oxidation of the metal to ions. Specific examples of the types of corrosion expected for the different metal-fused salt systems are also provided. The metal-fused salt systems include molten fluorides, chloride salts, molten nitrates, molten sulfates, hydroxide melts, and carbonate melts. The article concludes with information on prevention of molten salt corrosion.

This article describes the dip brazing process and the principal types of furnaces used for molten-salt-bath dip-brazing applications. It provides information on equipment maintenance, which is divided into temperature control, control of the liquid, and maintenance of the vessel. The article presents the typical salts used for molten-salt dip brazing of carbon and low-alloy steels with selected filler metals in tabular form. It concludes with information on dip brazing of stainless steels, cast irons, and aluminum alloys and safety precautions of the process.

This article provides information on the salt baths used for a variety of heat treatments, including heating, quenching, interrupted quenching (austempering and martempering), case hardening, and tempering. It describes two general types of salt bath systems for steel hardening: the first type uses atmosphere austenitizing followed by salt quench and the second type employs austenitizing salt baths with rapid transfer to the quench salt. The article provides a detailed account on the construction, advantages and disadvantages, and limitations of isothermal quenching furnaces, submerged-electrode furnaces, immersed-electrode furnaces, and externally heated furnaces. It discusses the important applications of various furnace designs, including the austempering of ductile iron, the hardening of tool steels, and the isothermal annealing of high-alloy steels.

This article discusses corrosion resistance of titanium and titanium alloys to different types of corrosion, including galvanic corrosion, crevice corrosion, stress-corrosion cracking (SCC), erosion-corrosion, cavitation, hot salt corrosion, accelerated crack propagation, and solid and liquid metal embrittlement. A short section discusses the addition of alloys that can improve the corrosion resistance of titanium.

Soluble salts on a surface can affect a steel substrate or coating in two principal ways: corrosion acceleration and osmotic blistering. This article provides a detailed discussion on the mechanisms for each of these deleterious effects. It describes the most detrimental anions with regard to corrosion, namely, chlorides, sulfates, and nitrates, and provides information on recognition and testing of the presence of soluble salts. The salt-measurement techniques and commercially available equipment are also described. The article provides information on research regarding tolerable levels of salts beneath coatings. The information shows that there appears to be a threshold limit to the salt contamination that a given coating/coating system can tolerate in a given environment.

Molten salts, in contrast to aqueous solutions in which an electrolyte (acid, base, salt) is dissolved in a molecular solvent, are essentially completely ionic. This article begins with an overview of the thermodynamics of cells and classification of electrodes for molten salts: reference electrodes and indicator electrodes. It explains that corrosion in molten salts can be caused by the solubility of the metal in the salt, particularly if the metal dissolves in its own chloride. The article describes the factors that affect the corrosion of titanium, namely, the titanium chloride content of the magnesium chloride melt, magnesium or sodium content, and oxygen content of the product. It concludes with a discussion on the oxygen activity in the titanium metal product.

This article provides a detailed discussion on the corrosion of steel and stainless steel under insulation. Stress corrosion cracking mechanism, types of alloys susceptible to corrosion, factors influencing corrosion, and corrosion prevention methods, are also discussed.

The thermoreactive deposition and diffusion process is a heat-treatment-based method to form coatings with compacted layers of carbides, nitrides, or carbonitrides, onto some carbon/nitrogen-containing materials, including steels. The amount of active carbide forming elements/nitride forming elements, coating temperatures and time, and thickness of substrates influence the growth rate of coatings. This article lists carbide and nitride coatings that are formed on carbon/nitrogen-containing metallic materials, and describes the coating process and mechanism of coating reagents. It details the growth process and nucleation process of carbide and nitride coatings formed on the metal surface. The article discusses the advantages, disadvantages, and characteristics of the various coating processes, including high-temperature salt bath carbide coating, high-temperature fluidized-bed carbide coating, and low-temperature salt bath nitride coating.

High-temperature corrosion can occur in numerous environments and is affected by various parameters such as temperature, alloy and protective coating compositions, stress, time, and gas composition. This article discusses the primary mechanisms of high-temperature corrosion, namely oxidation, carburization, metal dusting, nitridation, carbonitridation, sulfidation, and chloridation. Several other potential degradation processes, namely hot corrosion, hydrogen interactions, molten salts, aging, molten sand, erosion-corrosion, and environmental cracking, are discussed under boiler tube failures, molten salts for energy storage, and degradation and failures in gas turbines. The article describes the effects of environment on aero gas turbine engines and provides an overview of aging, diffusion, and interdiffusion phenomena. It also discusses the processes involved in high-temperature coatings that improve performance of superalloy.

This article provides useful information on the occurrence of corrosion in crude oil refinery units, namely, crude unit, catalytic and thermal cracking units, hydroprocessing units, amine sweetening units, and sour water units. Types and applications of corrosion inhibitors, namely, neutralizers, filming inhibitors, scavengers, microbiocides, and anti-foulants and scale inhibitors, are reviewed. The article describes the direct and indirect corrosion monitoring methods used to reduce equipment damage due to corrosion events and to assess the reliability and useful service life of process equipment.

This article describes the uses of the liquid carburizing process carried out in low and high temperature cyanide-containing baths, and details the noncyanide liquid carburizing process which can be accomplished in a bath containing a special grade of carbon. It presents a simple formula for estimating total case depth, and illustrates the influence of carburizing temperature, duration of carburizing, quenching temperature, and quenching medium with the aid of typical hardness gradients. The article provides information on controlling of cyaniding time and temperature, bath composition, and case depth, and presents examples that relate dimensional change to several shapes that vary in complexity. It also provides information on the quenchant removal and salt removal processes, lists the applications of liquid carburizing in cyanide baths, and discusses the process and importance of cyanide waste disposal in detail.

High temperature corrosion may occur in numerous environments and is affected by factors such as temperature, alloy or protective coating composition, time, and gas composition. This article explains a number of potential degradation processes, namely, oxidation, carburization and metal dusting, sulfidation, hot corrosion, chloridation, hydrogen interactions, molten metals, molten salts, and aging reactions including sensitization, stress-corrosion cracking, and corrosion fatigue. It concludes with a discussion on various protective coatings, such as aluminide coatings, overlay coatings, thermal barrier coatings, and ceramic coatings.

This article reviews the corrosion behavior in various environments for seven important nickel alloy families: commercially pure nickel, Ni-Cu, Ni-Mo, Ni-Cr, Ni-Cr-Mo, Ni-Cr-Fe, and Ni-Fe-Cr. It examines the behavior of nickel alloys in corrosive media found in industrial settings. The corrosive media include: hydrochloric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, hydrobromic acid, nitric acid, organic acids, salts, seawater, and alkalis. The modes of high-temperature corrosion include oxidation, carburization, metal dusting, sulfidation, nitridation, corrosion by halogens, and corrosion by molten salts. Applications where the corrosion properties of nickel alloys are important factors in materials selection include the petroleum, chemical, and electrical power industries. Most nickel alloys are much more resistant than the stainless steels to reducing acids, such as hydrochloric, and some are extremely resistant to the chloride-induced phenomena of pitting, crevice attack, and stress-corrosion cracking (to which the stainless steels are susceptible). Nickel alloys are also among the few metallic materials able to cope with hot hydrofluoric acid. The conditions where nickel alloys suffer environmentally assisted cracking are highly specific and therefore avoidable by proper design of the industrial components.

Martempering and austempering processes may eliminate the need for conventional oil quenching and tempering. This article presents the suitability of steels for martempering and austempering. It discusses the compositions of oils suitable for marquenching and modified marquenching and also presents safety precautions recommended for the use of martempering oils. Finally, the article explains the effect of agitation and water in a molten salt bath.

This article describes the advantages of martempering and the use of oil and salt as quenchants in the martempering process. It also discusses safety precautions to be followed by an operator and reviews the steels that are suitable for martempering. The article provides information on the importance of controlling process variables in martempering, including austenitizing temperature, temperature of the martempering bath, time in the bath, salt contamination, water additions to salt, agitation, and the rate of cooling from the martempering bath. It also describes specific situations in which distortion problems have been encountered during martempering. The article contains tables that indicate typical applications of martempering in salt and oil by listing commonly treated steel parts and giving details of martempering procedures and hardness requirements. The article also lists equipment requirements for oil and salt martempering of steel.