This article describes the weldability tests that are used to evaluate the effects of welding on such properties and characteristics as base-metal and weld-metal cracking; base-metal and weld-metal ductility; weld penetration; and weld pool shape and fluid flow. It also describes several weldability tests for evaluating cracking susceptibility, classified as self-restraint or externally loaded tests. The article discusses the processes, advantages, and disadvantages of the weld pool shape tests, the weld penetration tests, and the Gleeble test.

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.

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.

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.

Weldment failures may be divided into two classes: those identified during inspection and mechanical testing and those discovered in service. Failures in service arise from fracture, wear, corrosion, or deformation. In this article, major attention is directed toward the analysis of service failures. The discussion covers various factors that may lead to the failure of arc welds, electroslag welds, electrogas welds, resistance welds, flash welds, upset butt welds, friction welds, electron beam welds, and laser beam welds.

This chapter discusses the melting and conversion of superalloys and the solidification challenges they present. Superalloys have high solute content which can lead to untreatable defects if they solidify too slowly. These defects, called freckles, are highly detrimental to fatigue life. The chapter explains how and why freckles form as well as how they can be prevented. It describes the criteria for selecting the proper melting method for specific alloys based on melt segregation and chemistry requirements. It compares standard processes, including electric arc furnace/argon oxygen decarburization melting, vacuum induction melting, vacuum arc remelting, and electroslag remelting. It also addresses related issues such as consumable remelt quality, control anomalies, melt pool characteristics, and melt-related defects, and includes a section that discusses the processes involved in converting cast ingots into mill products.

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.

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.

This article discusses the steps in the primary processing of stainless steels: melting, refining, remelting, casting, and hot rolling. It provides information of the major categories of defects in hot rolled stainless steels, namely hot mill defects, inclusion-related defects, and hot ductility-related defects.

Discontinuities are interruptions in the desirable physical structure of a weld. This article describes the types of weld discontinuities that are characteristic of the principal welding processes. Discontinuities covered are metallurgical discontinuities, discontinuities associated with specialized welding processes, and base metal discontinuities. In addition, information on the common inspection methods used to detect these discontinuities is provided.