This article summarizes the terminology for gas reactions, and discusses low-temperature nitriding and nitrocarburizing of stainless steels. It describes the various nitriding processes, namely, high- and low-pressure nitriding, oxynitriding, sulfonitriding, oxysulfonitriding, ferritic nitrocarburizing and austenitic nitrocarburizing. The article includes a discussion on the difficulties in specimen cleaning, importance of furnace purge, uses of pre and post oxidation, depassivation, or activation, and requirements for perfect nucleation in nitriding process. In nitriding, the successful atmosphere control depends on various potentials. The article summarizes the methods of measuring potentials in nitriding and nitrocarburizing, provides useful information on the furnaces used, and the safety precautions to be followed in the nitriding process. It also describes the sample preparation procedures and testing methods to ensure the quality of the sample.

This article provides a background of the complex relationship between titanium and its alloys with aqueous environments, which is dictated by the presence of a passivating oxide film. It describes the corrosion vulnerability of titanium and titanium oxides by the classification of oxide failure mechanisms. The mechanisms are spatially localized oxide film breakdown by the ingress of aggressive anions; spatially local or homogenous chemical dissolution of the oxide in a strong reducing-acid environment; and mechanical disruptions or depassivation such as scratching, abrading, or fretting. Titanium alloys can be classified into three primary groups such as titanium alloys with hexagonal close-packed crystallographic structure; beta titanium alloys with body-centered cubic crystallographic structures; and alpha + beta titanium alloys including near-alpha and near-beta titanium alloys. The article also illustrates the effects of alloying on active anodic corrosion of titanium and repassivation behavior of titanium and titanium-base alloys.

Stainless steels are essential for the modern industrial civilization because of their corrosion resistance, especially in the chemical, petrochemical, and food industries. This article discusses the classification of the various types of stainless steels, including martensitic, ferritic, austenitic, duplex (ferritic-austenitic), and precipitation-hardening stainless steels. It presents a checklist of characteristics to be considered in selecting the proper type of stainless steel for a specific application. The article also outlines the need to promote the formation of an effective protective passive layer in stainless steels. It discusses hardness, fatigue and fretting properties, tribological properties, wear resistance, and corrosion-wear process of the S-phase layer. The article describes two thermochemical nitriding techniques of stainless steels: plasma-assisted nitriding techniques and non-plasma assisted nitriding processes. It also describes the difficulties in stainless steel nitriding/carburizing.

This article discusses the environmental factors and kinetics of atmospheric corrosion, aqueous corrosion, and soil corrosion of carbon steels. It also provides information on corrosion in concrete and steel boilers.

Cathodic protection (CP) is an electrochemical means of corrosion control widely used in the marine environment. This article discusses two types of CP systems: impressed current systems and sacrificial anode (passive) systems. It describes the anode materials used in these systems and the CP criteria. The article examines the design considerations and procedures involved in the CP of marine pipelines, offshore structures, and ship hulls. An illustration of sacrificial anode calculation is also provided.

This article reviews the influence of local strains and corrosion fatigue on the initiation of fatigue cracks in duplex stainless steels. It provides useful information on fatigue crack growth, fatigue strength, and fracture toughness of duplex stainless steels. The article discusses the fatigue and fracture behavior of duplex stainless steels during stress-corrosion cracking. It details the elevated-temperature properties of duplex stainless steels, such as creep-fatigue behavior and thermal cycling properties.

Stainless steels are characterized as having relatively poor wear resistance and tribological properties, but they are often required for a particular application because of their corrosion resistance. This article describes the classification of stainless steels and wear. Stainless steels have been classified by microstructure and are categorized as austenitic, martensitic, ferritic, or duplex. The main categories of wear are related to abrasion, erosion, adhesive wear, and surface fatigue. The article presents a list that proposes the alloy family that could be the optimal selection for a particular wear mode. The corrosion modes include dry sliding, tribocorrosion, erosion, erosion-corrosion, cavitation, dry erosion, erosion-oxidation, galling and fretting.

Mixtures of acids or acids and salts are of great importance to the chemical process industry (CPI) for use in digestion of solids, as a promoter in reactions, as a scale remover, and as a complexant. This article emphasizes the assessment of the performance of Ni-Fe-Cr-Mo alloys in mixed acids and salts in an objective manner. It tabulates the nominal compositions of pertinent Ni-Fe-Cr-Mo corrosion-resistant alloys. The article describes the acid and acid-plus-salt mixtures classified into the following general categories: nonoxidizing acid mixtures (H 2 SO 4 +H 3 PO 4 ), nonoxidizing acids with halides (H 2 SO 4 +HCl), oxidizing acid mixtures without halides (H 2 SO 4 +HNO 3 ), and oxidizing acid mixtures with halides (HNO 3 +HF). It also illustrates the effect of alloying elements on the corrosion rate in the nonoxidizing mixtures and oxidizing acid mixtures.

This article illustrates the three techniques for producing glassy metals, namely, liquid phase quenching, atomic or molecular deposition, and external action technique. Devitrification of an amorphous alloy can proceed by several routes, including primary crystallization, eutectoid crystallization, and polymorphous crystallization. The article demonstrates a free-energy versus composition diagram that summarizes many of the devitrification routes. It provides a historical review of the corrosion behavior of fully amorphous and partially devitrified metallic glasses. The article describes the general corrosion behavior and localized corrosion behavior of transition metal-metal binary alloys, transition metal-metalloid alloys, and amorphous simple metal-transition metal-rare earth metal alloys. It concludes with a discussion on the environmentally induced fracture of glassy alloys, including hydrogen embrittlement and stress-corrosion cracking.

Crevice corrosion involves three fundamental types of processes such as electrochemical reactions, homogeneous chemical reactions, and mass transport. This article describes the critical factors of crevice corrosion, including crevice geometry, material, environment, crevice corrosion stifling, and pitting relationships. It explains the crevice corrosion of stainless steel, nickel alloys, aluminum alloys, and titanium alloys with examples. The article reviews the types of testing methods that have been developed for differentiating and ranking the resistance of alloys toward crevice corrosion. It also presents the strategies for the prevention of crevice corrosion or lessening its effects, such as design awareness, use of inhibitors, and electrochemical control methods.

The surface of irons and steels can be hardened by introducing nitrogen (nitriding), nitrogen and carbon (nitrocarburizing), or nitrogen and sulfur (sulfonitriding) into the surface. This article lists the principal reasons for nitriding and nitrocarburizing, and summarizes the typical characteristics of nitriding processes along with a general comparison of carburizing processes in a table. It describes the two most common nitriding methods: gas nitriding and ion (plasma) nitriding. The article discusses the wear behavior of nitrided layers and the wear resistance of selected steels. Rolling-contact fatigue (RCF) occurs in rolling contacts such as bearings, rolls, and gears. The article provides a discussion on rolling-contact fatigue of nitrided steels for aerospace bearing components.

Steel storage tanks are the primary means for storing large volumes of liquids and gaseous products. The stored fluid could be water, but it could also be volatile, corrosive, and flammable fluid requiring special precautions for storage as well. Corrosion is generally worst where the tank is in contact with the soil. This article describes the soil characteristics and addresses cathodic protection (CP) criteria for submerged metallic piping systems. It provides information on the data required for designing a CP system, alone or in conjunction with a protective coating system. These data are collected from predesign site assessments, tank electrical characteristics, and soil-resistivity measurements. The article addresses NACE Standard RP0169, which gives requirements and desired characteristics for coating in conjunction with CP. It also explains the methods of protecting aboveground storage tanks and underground storage tanks.

Passivation; pickling, that is, acid descaling; electropolishing; and mechanical cleaning are important surface treatments for the successful performance of stainless steel used for piping, pressure vessels, tanks, and machined parts in a wide variety of applications. This article provides an overview of the various types of stainless steels and describes the commonly used cleaning methods, namely, alkaline cleaning, emulsion cleaning, solvent cleaning, vapor degreasing, ultrasonic cleaning, and acid cleaning. Finishing operations of stainless steels, such as grinding, polishing, and buffing, are reviewed. The article also explains the procedures of electrocleaning, electropolishing, electroplating, painting, surface blackening, coloring, terne coatings, and thermal spraying. It includes useful information on the surface modification of stainless steels, namely, ion implantation and laser surface processing. Surface hardening techniques, namely, nitriding, carburizing, boriding, and flame hardening, performed to improve the resistance of stainless steel alloys are also reviewed.

Low-temperature carburization hardens the surface of austenitic stainless steels through the diffusion of interstitial carbon without the formation of carbides. This article provides an overview on austenitic stainless steels and low-temperature carburization. It reviews the competing technologies and commercial application of low-temperature carburization. The article discusses several processing parameters, including activation of the surface, proper surface preparation, selection and condition of the alloy to be carburized, treatment temperature, and carburizing atmosphere for successful low-temperature carburization of austenitic stainless steels and other chromium-containing alloys. It describes the performance properties of the low-temperature carburized layer: fatigue resistance, wear resistance, erosion resistance, and corrosion resistance.

Liquid metal induced embrittlement (LMIE) is the reduction of the fracture resistance of a solid material during exposure to a liquid metal. This article discusses the mechanisms and occurrence condition of LMIE and describes the effects of metallurgical factors, such as grain size, temperature and strain rate, stress, inert carriers, and fatigue, on LMIE. It provides a detailed discussion on LMIE in ferrous and nonferrous metals and their alloys. In addition, the article highlights the ways of preventing embrittlement in metals and alloys.

This article presents information regarding the use of protective coatings in municipal potable water systems, including raw water collection and transmission, water treatment plants, and treated water distribution. It provides useful guidance for the selection and use of protective coatings in these municipal water systems. The most commonplace corrosion-damage mechanisms are highlighted. The article describes the most common materials of construction found in municipal water systems, namely, cast iron, ductile iron, carbon steel, precast concrete cylinder pipe and reinforced concrete pipe, prestressed concrete tanks, and stainless steel. It provides information on the most common generic coating systems used for new steel tanks and water storage tanks. It concludes with a discussion of quality watch-outs when selecting or using protective coatings in municipal water systems.

This article is a compilation of color etchants that have been developed for a limited number of metals and alloys. It describes the optical methods for producing color, such as polarized light and differential interference contrast, with illustrations. The article discusses film formation and interference techniques such as anodizing, chemical etching, and tint etching. It provides a description of reagents that deposit sulfide films and molybdate films. The article concludes with a discussion on the thermal and vapor deposition methods to produce color.

Titanium alloys are often used in highly corrosive environments because they are better suited than most other materials. The excellent corrosion resistance is the result of naturally occurring surface oxide films that are stable, uniform, and adherent. This article offers explanations and insights on the most common forms of corrosion observed with titanium alloys, including general corrosion, crevice corrosion, anodic pitting, hydrogen damage, stress-corrosion cracking, galvanic corrosion, corrosion fatigue, and erosion-corrosion. It also provides practical strategies for expanding the useful application range for titanium and includes a comprehensive overview of available corrosion data.

This article provides information on the municipal wastewater system components such as piping, pump stations, headworks, clarifiers, aeration structures, digesters, biosolids dewatering equipment, and sludge stabilization. It explains the major corrosion damage mechanisms to which those component parts of the system are exposed. It presents useful guidelines for selecting and using protective coatings in municipal sewerage collection systems and water reclamation facilities in wastewater treatment plants. The article includes annotated flow diagrams of a wastewater collection system, wastewater treatment plants, and spreadsheets listing the most widely used generic coating systems by structure and substrate material. It concludes with a section on quality watchouts when selecting or using protective coatings in municipal wastewater systems.

This article tabulates the chemical composition of iron-base, titanium-base, and cobalt-base alloys and illustrates the microstructures of these materials. It discusses the surface morphology and chemistry of oxide-film-covered alloys and provides insights into the interaction. The article illustrates the interfacial structure of a biomaterial surface contacting with the biological environment. It describes the corrosion behavior of stainless steel, cobalt-base alloy, and titanium alloys. The electrochemical methods used for studying metallic biomaterials corrosion are also discussed. The article concludes with information on the biological consequences of in vivo corrosion and biocompatibility.