Nickel-base alloys used for low-temperature aqueous corrosion are commonly referred to as corrosion-resistant alloys (CRAs), and nickel alloys used for high-temperature applications are known as heat-resistant alloys, high-temperature alloys, or superalloys. The emphasis in this chapter is on the CRAs and in particular nickel-chromium-molybdenum alloys. The chapter provides a basic understanding of general welding considerations and describes the welding metallurgy of molybdenum-containing CRAs and of nickel-copper, nickel-chromium, and nickel-chromium-iron CRAs. It discusses the corrosion behavior of nickel-molybdenum alloys and nickel-chromium-molybdenum alloys. Information on the phase stability and corrosion behavior of nickel-base alloys is also included.

Corrosion failures of welds can occur even when the proper base metal and filler metal have been selected, industry codes and standards have been followed, and welds have been deposited that possess full weld penetration and have proper shape and contour. This chapter describes some of the general characteristics associated with the corrosion of weldments. The role of macro- and microcompositional variations, a feature common to weldments, is emphasized in this chapter to bring out differences that need to be realized in comparing the corrosion of weldments to that of wrought materials. The discussion covers the factors influencing corrosion of weldments, microstructural features of weld microstructures, various forms of weld corrosion, and welding practice to minimize corrosion.

This chapter discusses some of the metallurgical factors that affect corrosion of weldments and describes a few considerations for selected nonferrous alloy systems: aluminum, titanium, tantalum, and nickel.

This chapter introduces the basic ferrous physical metallurgy principles that need to be understood by the metallographer. The discussion focuses on the variations in microstructures that are generated as a result of the phase transformations that occur during both heat treatment (as in steels) and solidification (as in cast irons). The chapter describes how the development of the iron-carbon phase diagram, coupled with the understanding of the kinetics of phase transformations through the use of isothermal transformation diagram, were breakthroughs in the advancement of ferrous physical metallurgy. Several examples of the morphological features of microstructural constituents in steels are also presented.

This chapter discusses the effects of hot working on the structure and properties of steel. It explains how working steels at high temperatures promotes diffusion, which helps close cavities and pores, and how it changes the shape and distribution of segregates, offsetting their effect. It describes the effect of hot working on nonmetallic inclusions and the many properties influenced by them. It discusses the recrystallization mechanism by which hot working produces microstructural changes and explains how to control it by adjusting temperature, degree of reduction, and cooling rates. It describes special cases of segregation, including banding and why it occurs, and the application of closed die forging. The chapter also presents several examples of hot working defects, including forging laps, cracks, and overheated or burned steel.

This chapter serves as a study and guide on the main phase constituents of cast aluminum-silicon alloys, alpha-Al solid solution and Si crystals. The first section focuses on the structure of Al-Si castings in the as-cast state, covering the morphology of the alpha-Al solid solution grains and the process by which they form. It describes how cooling rates, temperature gradients, and local concentrations influence the topology of the crystallization front, and how they play a role in determining the morphology and dispersion degree of the grains observed in cross sections of cast parts. It also describes the mechanism behind dendritic grain crystallization and how factors such as surface tension, capillary length, and lattice symmetry affect dendritic arm size and spacing. The section that follows examines the morphology of the silicon crystals that form in aluminum-silicon castings and its effect on properties and processing characteristics. It discusses the faceted nature of primary Si crystals and the modification techniques used to optimize their shape. It also describes the morphology of the (alpha-Al + Si) eutectic, which can be lamellar or rodlike in shape, and explains how it can be modified through temperature control or alloy additions to improve properties such as tensile strength and plasticity and reduce shrinkage.

This chapter concentrates on the better-known and widely studied phenomenon of pitting corrosion of passive metals. The discussion focuses on different parameters that influence pitting corrosion, namely environment, metal composition, potential, temperature, surface condition, and inhibitors. It also provides information on various stages of pitting: passive film breakdown, metastable pitting, pit growth, and pit stifling or death.

This chapter discusses the complex polarization characteristics of active-passive metals and addresses related problems in interpreting their corrosion behavior. It begins by presenting several experimentally derived polarization curves for iron, comparing and contrasting them with the iron-water Pourbaix diagram. It then explains how anodic polarization is extremely sensitive to the environment and, as a result, a reasonably complete curve for a given metal-environment system usually can only be inferred. It goes on to describe how such curves are constructed, demonstrating the procedures for a wide range of alloys and environments. The examples also show how factors such as alloy concentration, crystal lattice orientation, temperature, and dissolved oxygen affect corrosion behavior.

This chapter discusses various factors that affect corrosion of stainless steel weldments. It begins by providing an overview of the metallurgical factors associated with welding. This is followed by a discussion on preferential attack associated with weld metal precipitates in austenitic stainless steels as well as several forms of corrosion associated with welding. The effects of gas-tungsten arc weld shielding gas composition and heat-tint oxides on corrosion resistance are then covered. Microbiological corrosion of butt welds in water tanks is also illustrated. In addition, the chapter provides information on corrosion of ferritic and duplex stainless steel weldments.

This chapter introduces many of the key concepts on which metallurgy is based. It begins with an overview of the atomic nature of matter and the forces that link atoms together in crystal lattice structures. It discusses the types of imperfections (or defects) that occur in the crystal structure of metals and their role in mechanical deformation, annealing, precipitation, and diffusion. It describes the concept of solid solutions and the effect of temperature on solubility and phase transformations. The chapter also discusses the formation of solidification structures, the use of equilibrium phase diagrams, the role of enthalpy and Gibb’s free energy in chemical reactions, and a method for determining phase compositions along the solidus and liquidus lines.

This chapter discusses the progress that has been made in the development of superalloy operating temperatures, properties, and performance. It also provides forward-looking projections based on advances in process modeling, alloying, and production techniques.

This chapter discusses the processes used in manufacturing to thermally alter the properties of metals and alloys. It begins with a review of the iron-carbon system, the factors that affect hardenability, and the use of continuous cooling transformation diagrams. It then explains how various steels respond to heat treatments, such as annealing, normalizing, spheroidizing, tempering, and direct and interrupted quenching, and surface-hardening processes, such as flame and induction hardening, carburizing, nitriding, and carbonitriding. It also addresses the issue of temper embrittlement and discusses the effect of precipitation hardening on aluminum and other alloys.

Many of the structural characteristics of steel products are a result of changes that occur during solidification, particularly volume contractions and solute redistribution. This chapter discusses the solidification process and how it affects the quality and behaviors of steel. It explains how steel shrinks as it solidifies, causing issues such as pipe and voids, and how differences in the solubility of solid and liquid steel lead to compositional heterogeneities or segregation. It describes the dendritic nature of solidification, peritectic and eutectic reactions, microporosity, macro- and microsegregation, and hot cracking, as well as the effects of solidification and remelting on castings, ingots, and continuous cast products. It explains how to determine where defects originate in continuous casters and how to control alumina, sulfide, and nitride inclusions.

During fusion welding, the thermal cycles produced by the moving heat source causes physical state changes, metallurgical phase transformations, and transient thermal stresses and metal movement. This chapter begins by discussing weld metal solidification behavior and the solid-state transformations of the main classes of metals and alloys during fusion welding. The main classes include work- or strain-hardened metals and alloys, precipitation-hardened alloys, transformation-hardened steels and cast irons, stainless steels, and solid-solution and dispersion-hardened alloys. The following section provides information on the residual stresses and distortion that remain after welding. The focus then shifts to distortion control of weldments. Inclusions and cracking are discussed in detail. The chapter also discusses the causes for reduced fatigue strength of a component by a weld: stress concentration due to weld shape and joint geometry; stress concentration due to weld imperfections; and residual welding stresses. Inspection and characterization of welds are described in the final section of this chapter.

Structurally differentiated intermetallic phases are important constituents in the microstructure of aluminum alloys, with the potential to influence properties, behaviors, and processing characteristics. These phases can form in aluminum-silicon alloys with transition metals (Fe, Mn, Ni, Cr, V, Ti) and with metals such as Mg and Cu. This chapter is a compilation of phase diagrams, microstructure images, and tables, providing information on more than 30 binary, ternary, and quaternary alloy systems associated with intermetallic phases in aluminum-silicon castings. Each section includes tabular information and data on the intermetallic phases in the aluminum corner of the equilibrium phase diagram, the characteristics of the crystal lattice of intermetallic phases, the chemical composition of the alloy intermetallic phases, and equilibrium reactions in the alloy system.

Titanium is a lightweight metal used in a growing number of applications for its strength, toughness, stiffness, corrosion resistance, biocompatibility, and high-temperature operating characteristics. This chapter discusses the applications, metallurgy, properties, compositions, and grades of commercially pure titanium and alpha and near-alpha, alpha-beta, and beta titanium alloys. It describes primary and secondary fabrication processes, including melting, forging, forming, heat treating, casting, machining, and joining as well as powder metallurgy and direct metal deposition. It also compares and contrasts the properties of wrought, cast, and powder metal titanium products and discusses corrosion behaviors.

This chapter is a detailed study of the localized corrosion behavior of steel, copper, and aluminum alloys. It applies the basic principles of electrochemistry, as well as materials science and solid and fluid mechanics, to explain the causes and effects of pitting, crevice corrosion, stress corrosion cracking, and corrosion fatigue. It describes the underlying mechanisms associated with each process and how they relate to the microstructure of the metal or alloy, the physical condition of the surface, and other factors such as the coupling of the metal to a dissimilar metal or surface film.

Induction heating, in most applications, is used to selectively heat only a portion of the workpiece that requires treatment. This chapter covers the basic principles, features, and metallurgical aspects of induction heating. The discussion includes the conditions required for induction heating and quenching, the use of magnetic flux concentrators to improve the efficiency of surface heating, and the quenching systems used for induction hardening. The discussion also provides information on time-temperature dependence in induction heating, workpiece distortion in induction surface hardening, residual stresses after induction surface hardening and finish grinding, and input and output control of steel for induction surface hardening of gears.