Arc welding applies to a large and diversified group of welding processes that use an electric arc as the source of heat to melt and join metals. This chapter provides a detailed overview of specific arc welding methods: shielded metal arc welding, flux cored arc welding, submerged arc welding, gas metal arc welding, gas tungsten arc welding, plasma arc welding, plasma-GMAW welding, electroslag welding, and electrogas welding. The basic characteristics of gases used for shielding during arc welding are briefly discussed.

Resistance welding is a group of processes in which the heat for welding is generated by the resistance to the flow of an electrical current through the parts being joined. This chapter discusses the processes, advantages, and limitations of specific resistance welding processes, namely resistance spot welding, resistance seam welding, projection welding, flash welding, and upset welding.

This chapter discusses the fusion welding processes, namely oxyfuel gas welding, oxyacetylene braze welding, stud welding (stud arc welding and capacitor discharge stud welding), high-frequency welding, electron beam welding, laser beam welding, hybrid laser arc welding, and thermit welding.

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.

Beryllium has been successfully joined by fusion welding, brazing, solid-state bonding, and soldering. This chapter describes these processes in detail along with their advantages and disadvantages. It also addresses application considerations such as surface preparation, joint design, and testing.

This chapter provides a basis for understanding the influence of stainless steel alloy composition and metallurgy on the welding process, which involves complex dynamics associated with melting, refining, and thermal processing. It begins with an overview of the welding characteristics of the categories of stainless steels, namely austenitic, duplex, ferritic, martensitic, and precipitation-hardening stainless steels. This is followed by a discussion of the selection criteria for materials to be welded. Various welding processes used with stainless steel are then described. The chapter ends with a section on some of the practices to ensure safety and weld quality.

This chapter examines the effects of welding on the structure of metal, particularly the changes induced in the isothermal regions adjacent to the weld. It presents more than 150 images identifying structures and features associated with fusion and solid-state welding processes, including electroslag, TIG, gas, electron-beam, and arc welding as well as vacuum diffusion, forge, friction, electrical-resistance, and explosive welding. It also discusses the effect of welding temperature, pressure, and composition on the transformations that occur in and around the weld, and it includes a short section on brazing and braze welding.

The formation of defects in materials that have been fusion welded is a major concern in the design of welded assemblies. This article describes four types of defects that, in particular, have been the focus of much attention because of the magnitude of their impact on product quality. Colloquially, these four defect types are known as hot cracks, heat-affected zone microfissures, cold cracks, and lamellar tearing.

This article describes the repair of weld defects and failed structures. It provides information on three factors that must first be considered before attempting a repair, namely material weldability, nature of the failure that prompted the repair, and involvement of any code requirements. The article discusses the processes involved in welding process selection and the methods of preparing base metal for repair welding. It presents the guidelines for weld repairs of various ferrous (carbon steels, cast irons, and stainless steels) and nonferrous (for example, titanium) base metals.

This chapter covers the basics of weldability of cast steels such as carbon and low alloy steels, corrosion-resistant high alloy steels, nickel-base alloys, heat-resistant high alloy steels, and wear-resistant high austenitic manganese steels. It provides an overview of weld overlay and hard facing; cast-weld construction; and plasma arc cutting and plasma arc welding. The chapter discusses different types of welding processes. These include shielded metal-arc welding, air carbon arc cutting process, gas tungsten-arc welding, gas metal-arc welding process, flux-cored arc welding, submerged arc welding, and electroslag and electro-gas welding.

Solid-state welding processes are those that produce coalescence of the faying surfaces at temperatures below the melting point of the base metals being joined without the addition of brazing or solder filler metal. This chapter discusses solid-state welding processes such as diffusion welding, forge welding, roll welding, coextrusion welding, cold welding, friction welding, friction stir welding, explosion welding, and ultrasonic welding.

It is well established that solidification behavior in the fusion zone controls the size and shape of grains, the extent of segregation, and the distribution of inclusions and defects such as porosity and hot cracks. Since the properties and integrity of the weld metal depend on the solidification behavior and the resulting microstructural characteristics, understanding weld pool solidification behavior is essential. This article provides a general introduction of key welding variables including solidification of the weld metal or fusion zone and microstructure of the weld and heat-affected zone. It discusses the effects of welding on microstructure and the causes and remedies of common welding flaws.

This article reviews nondestructive and destructive test methods used to characterize welds. The first process of characterization discussed involves information that may be obtained by direct visual inspection and measurement of the weld. An overview of nondestructive evaluation is included that encompasses techniques used to characterize the locations and structure of internal and surface defects, including radiography, ultrasonic testing, and liquid penetrant inspection. The next group of characterization procedures discussed is destructive tests, requiring the removal of specimens from the weld. The third component of weld characterization is the measurement of mechanical and corrosion properties. Following the discussion on the characterization procedures, the second part of this article provides examples of how two particular welds were characterized according to these procedures.