Hardfacing refers to the deposition of a specially selected material onto a component in order to reduce wear in service as a preventative measure or return a worn component to its original dimensions as a repair procedure. This article provides information on various hardfacing materials, namely, iron-base overlays, chromium carbide-based overlays, nickel- and cobalt-base alloys, and tungsten carbide-based metal-matrix composite overlays. It discusses the types of hardfacing processes, such as arc welding processes, and laser cladded, oxyacetylene brazing and vacuum brazing processes. The arc welding processes include shielding metal arc welding, gas metal arc welding/flux cored arc welding, gas tungsten arc welding, submerged arc welding, and plasma transferred arc welding. The article also reviews various factors influencing the selection of the appropriate hardfacing for specific applications.

This article describes some examples of the different welding processes for gray, ductile, and malleable irons. These processes include fusion welding, repair welding, shielded metal arc welding, gas metal arc welding, flux cored arc welding, gas tungsten arc welding, submerged arc welding, oxyfuel welding, and braze welding. The article discusses various special techniques, such as groove-face grooving, studding, joint design modifications, and peening, for improving the strength of a weld or its fitness for service. The article describes other fusion welding methods such as electrical resistance welding and thermite welding. It reviews thermal spraying processes, such as flame spraying, arc spraying, and plasma spraying, of a cast iron.

Plasma arc welding (PAW) can be defined as a gas-shielded arc welding process where the coalescence of metals is achieved via the heat transferred by an arc that is created between a tungsten electrode and a workpiece. This article focuses on the operating principles and procedures, current and operating modes, advantages, disadvantages, and applications of PAW. It discusses the personnel and equipment requirements, as well as the joints used in the process. The power source, plasma control console, water cooler, welding torch, and gas supply system for the plasma and shielding gases are also reviewed.

The shielding gas used in an arc welding process has a significant influence on the overall performance of the welding system. These gases are argon, helium, oxygen, hydrogen, nitrogen, and carbon dioxide. This article discusses the shielding gas selection criteria for plasma arc welding, gas metal arc welding, and flux cored arc welding. It describes the basic properties of shielding gases, namely, dissociation, recombination, reactivity potential, oxidation potential, and gas purity. The article also provides information on the influence of the shielding gas on weld mechanical properties and self-shielded flux cored arc welding.

This article describes the process, advantages, limitations, applications, and equipment used for shielded metal arc welding (SMAW). It provides information on the types of electrodes, weld schedules, and welding procedures. The article explains the electrodes used in the SMAW process that have different compositions of core wire and a variety of flux-covering types and weights. It includes information on gravity and firecracker welding and discusses dry and wet types of underwater welding. Finally, the article reviews the safety considerations to be followed during SMAW.

Fluxes are added to the welding environment to improve arc stability, provide a slag, add alloying elements, and refine the weld pool. This article discusses the effect of oxygen, which is an important chemical reagent to control the weld metal composition, microstructure, and properties. It provides information on the inclusions that form as a result of reactions between metallic alloy elements and nonmetallic tramp elements, or by mechanical entrapment of nonmetallic slag or refractory particles. The article reviews the considerations of flux formulation during shielded metal arc welding and flux cored arc welding (FCAW). It describes the types of fluxes used for submerged arc welding and FCAW as well as five essential groups of flux ingredients and their interactions.

Fluxes are added to the welding environment to improve arc stability, to provide a slag, to add alloying elements, and to refine the weld pool. This article describes the effect of oxygen that directly reacts with alloying elements to alter their effective role by reducing hardenability, promoting porosity, and producing inclusions. It proposes basicity index for welding as a measure of expected weld metal cleanliness and mechanical properties. The article discusses alloy modification in terms of slipping and binding agents, slag formation, and slag detachability. It reviews the types of fluxes for different arc welding processes, such as shielded metal arc welding (SMAW), flux-cored arc welding (FCAW), and submerged arc welding (SAW).

Cast iron can be described as an alloy of predominantly iron, carbon, and silicon. This article discusses the classification of cast irons, such as gray cast iron, white cast iron, malleable cast iron, ductile cast iron, and compacted graphite iron. It reviews the various special techniques, such as groove face grooving, studding, joint design modifications, and peening, for improving the strength of a weld or its fitness for service. The article discusses the need for postweld heat treatment that depends on the condition of the casting, possible distortion during subsequent machining, the desired finish of the machined surfaces, and prior heat treatment. It describes various welding process for welding cast irons, including oxyfuel welding, braze welding, shielded metal arc welding, gas metal arc welding, and gas-tungsten arc welding.

This article addresses consumable selection and procedure development for the welding of stainless steels. The WRC-1992 diagram and the Schaeffier diagram, are used to illustrate the rationale behind many filler-metal choices. The article discusses the basic metallurgy and base metals of five major families of stainless steels: martensitic stainless steels, ferritic stainless steels, austenitic stainless steels, precipitation-hardening (PH) stainless steels, and duplex ferritic-austenitic stainless steels. Stainless steels of all types are weldable by virtually all welding processes. The article describes the common arc welding processes with regard to procedure and technique errors that can lead to loss of ferrite control with the common austenitic stainless steel weld metals that are designed to contain a small amount of ferrite for protection from hot cracking. The arc welding processes include shielded-metal arc welding, gas-tungsten arc welding, and gas-metal arc welding.

This article describes the classification of ferritic stainless steels. It reviews the metallurgical characteristics of various ferritic grades as well as the factors that influence their weldability. The article provides a discussion on various arc welding processes. These processes include gas-tungsten arc welding (GTAW), gas-metal arc welding (GMAW), flux-cored arc welding (FCAW), shielded metal arc welding (SMAW), and plasma arc welding (PAW). The selection criteria for welding consumables are discussed. The article also explains the welding procedures associated with the ferritic stainless steels. It concludes with information on weld properties.

Aluminum and its alloys can be joined by as many or more methods than any other metal. This article discusses the properties of aluminum, namely hydrogen solubility, electrical conductivity, and thermal characteristics. It analyses the primary factors commonly considered when selecting a welding filler alloy. These include ease of welding or freedom from cracking, tensile or shear strength of the weld, weld ductility, service temperature, corrosion resistance, and color match between the weld and base alloy after anodizing. The article provides a detailed description of gas-shielded arc welding processes for welding of aluminum alloys and also reviews other welding processes such as oxyfuel gas welding and laser-beam welding.

Nickel alloys can be joined reliably by all types of welding processes or methods, with the exception of forge welding and oxyacetylene welding. This article discusses the heat treatment of nickel alloys and tabulates nominal compositions of selected weldable wrought nickel and nickel alloys. It provides information on gas-tungsten arc welding, gas-metal arc welding, plasma arc welding, shielded metal arc welding, and submerged arc welding for welding nickel alloys. The article reviews the defects encountered in the arc welding of nickel alloys, including porosity, cracking, and stress-corrosion cracking. It provides information on the factors that influence the choice of filler metal and welding process of nickel alloys.

Copper and copper alloys offer a unique combination of material properties that makes them advantageous for many manufacturing environments. This article begins with a discussion on common metals that are alloyed with copper to produce the various copper alloys. It then reviews the factors that affect the weldability of copper alloys, including thermal conductivity of the alloy being welded, shielding gas, type of current used during welding, joint design, welding position, and surface condition. The article provides information on arc welding processes such as gas-metal arc welding, shielded metal arc welding, submerged arc welding, plasma arc welding, and gas-tungsten arc welding. It concludes with a discussion on safe welding practices.

Shielded metal arc welding (SMAW), commonly called stick or covered electrode welding, is a manual welding process whereby an arc is generated between a flux-covered consumable electrode and a workpiece. This article discusses the advantages and limitations and applications of the SMAW process and describes the equipment used. It provides information on various coated electrodes used in the SMAW process, including mild and low-alloy steel-covered electrodes, stainless steel covered electrodes, and nickel and copper alloys covered electrodes. It reviews weld schedules and procedures, as well as the variations of the SMAW process. The article concludes with information on the special applications of the SMAW process and safety considerations.

This article discusses the susceptibility of carbon steels to hydrogen-induced cracking, solidification cracking, lamellar tearing, weld metal porosity, and heat-affected zone (HAZ) mechanical property variations. The composition and mechanical properties of selected carbon steels used in arc welding applications are listed in a table. The article presents process selection guidelines for arc welding carbon steels. It provides information on the shielded metal arc welding, gas-metal arc welding, and flux-cored arc welding, gas-tungsten arc and plasma arc welding, submerged arc welding, electrogas welding, electroslag welding, and stud arc welding.