Quenching refers to the rapid cooling of metal from the solution treating temperature, typically between 465 and 565 deg C (870 and 1050 deg F) for aluminum alloys. This article provides an overview on the appropriate quenching process and factors used to determine suitable cooling rate. It describes the quench sensitivity and severity of alloys, quench mechanisms and the different types of quenchants used in immersion, spray, and fog quenching. The article provides a detailed description of the quench-factor analysis that mainly includes residual stress and distortion, which can be controlled by proper racking. It concludes with information on agitation and the quench tank system used in the quenching of aluminum alloys.

The use of gases or molten salts as the quenchant for steel parts is commonly limited to the quenching of high-alloy steel or the carbonizing quenching of low-alloy steel. This article reviews the quenching process of steels with molten metals (quenchant) such as molten lead, molten bismuth, and molten sodium. It also contains tables that list the physical properties of lead, bismuth, sodium, and molten sodium.

Quenching is a widely used technique to strengthen titanium alloys. This article presents the metallurgical and structural background underlying the specific techniques applied in the quenching of various titanium alloys, and the ways to control and reduce residual stresses induced from quenching or other thermal or mechanical processes. It discusses the types and microstructures of titanium alloys, namely, alpha, alpha-beta, and beta alloys, and describes the general effects of the various heat treatments. The article provides information on quenching media, quenching rate, section size, and martensitic transformation in quenched titanium alloys. It shows how residual stresses in titanium alloys are evaluated and controlled. Finally, the article describes the stress-relief treatments used to reduce residual stresses.

This article provides information on the salt baths used for a variety of heat treatments, including heating, quenching, interrupted quenching (austempering and martempering), case hardening, and tempering. It describes two general types of salt bath systems for steel hardening: the first type uses atmosphere austenitizing followed by salt quench and the second type employs austenitizing salt baths with rapid transfer to the quench salt. The article provides a detailed account on the construction, advantages and disadvantages, and limitations of isothermal quenching furnaces, submerged-electrode furnaces, immersed-electrode furnaces, and externally heated furnaces. It discusses the important applications of various furnace designs, including the austempering of ductile iron, the hardening of tool steels, and the isothermal annealing of high-alloy steels.

Successful hardening depends on the hardenability of steel composition, the geometry of parts, the quenching system, and on the heat treating process used. This article provides a brief overview of the computation and use of quench factor analysis (QFA) to quantify as-quenched hardness for carbon and low-alloy steels. As a single-value parameter alternative to Grossmann H-values, QFA is a potential method to qualify a quenching medium or process or to effectively monitor variation of quench severity due to either the quenchant or the system. The article describes the procedures for experimentally determining the quench factors by using a type 304 austenitic stainless steel probe. Typical examples of the utilization of QFA for quenchant characterization are provided. The article also describes the methods for experimentally generating time-temperature-property curves.

This article describes various quenchants, namely, water and inorganic salt solutions, polymers (polyvinyl alcohol, polyalkylene glycol, polyethyl oxazoline, polyvinyl pyrrolidone and sodium polyacrylates), quench oils, and molten salts, which are used for heat treatment of ferrous alloys. It also provides information on the steps for controlling quenching performance for polymer quenchants and oils with an emphasis on measuring quenchant performance, safety measures, and oxidation.

This article focuses on the heat removal stages involved in quenching, and on the experimental setup used for measuring temperature and detecting sound signals with the help of illustrations and curves. The quenching process generates acoustic signals, which are the consequences of the phase transformation of steel and of the boiling process at the interface during the cooling process. The sound-pressure signal is captured by the hydrophone through sound-emission measurements that occur during steel quenching in different quenching media. The analysis of the results offers an interesting approach to evaluation and, more importantly, to monitoring, controlling, and optimizing the entire quenching process.

The presence of macroscopic residual stresses in heat treatable aluminum alloys can give rise to machining distortion, dimensional instability, and increased susceptibility to in-service fatigue and stress-corrosion cracking. This article details the residual-stress magnitudes and distributions introduced into aluminum alloys by thermal operations associated with heat treatment. The available technologies by which residual stresses in aluminum alloys can be relieved are also described. The article shows why thermal stress relief is not a feasible stress-reduction technology for precipitation-hardened alloys. It examines the consequences of aging treatments on the residual stress, namely, annealing, precipitation heat treatment, and cryogenic treatment. The article provides information on uphill quenching, which attempts to reverse thermal gradients encountered during quenching. It examines how quench-induced residual stresses in heat treatable aluminum alloys are reduced when sufficient load is applied to cause plastic deformation. The article also shows how plastic deformation reduces residual stress.

Quenchant agitation can be obtained by circulating quenchant in a quench tank through pumps and impellers. The selection of the agitation method depends on the tank design, type and volume of the quenchant, part design, and the severity of quench required. This article describes flow measurement methods, temperature control, materials handling, and filtration processes during the agitation process. The maintenance of quenching installations is also discussed.

Batch furnaces and continuous furnaces are commonly used in heat treating. This article provides a detailed account of various heat treating equipment and its furnace types, including salt bath equipment (externally heated, immersed-electrode and submerged-electrode furnaces), and fluidized-bed equipment (external-resistance-heated fluidized beds). It describes various auxiliary equipment used in cold-wall furnaces, namely, heating elements and pumping systems. Five types of heat-resistant alloys are used for furnace parts, trays, and fixtures: Fe-Cr alloys, Fe-Cr-Ni alloys, Fe-Ni-Cr alloys, nickel-base alloys and cobalt-base alloys. The article lists the recommended applications for alloys for parts and fixtures for various types of heat treating furnaces.

Emulsion cleaning is an industrial cleaning process that uses an organic solvent as the main active agent. This article provides information on the applications, concerns and limitations, and process parameters of emulsion cleaning. It describes the processing variables and equipment for three main stages of emulsion cleaning: immersion cleaning, secondary cleaning, and spray cleaning. In addition, the classifications, composition, and selection criteria are also discussed.

The selection of surface treatments for copper and copper alloys is generally based on application requirements for appearance and corrosion resistance. This article describes cleaning, finishing, and coating processes for copper and copper alloys. These processes include pickling and bright dipping, abrasive blast cleaning, chemical and electrochemical cleaning, mass finishing, polishing and buffing, electroless plating, immersion plating, electroplating, passivation, coloring, and organic coatings.

Ultrasonic cleaning involves the use of high-frequency sound waves that is above the upper range of human heating, or about 18 kHz, to remove a variety of contaminants from parts immersed in aqueous media. This article describes the process, design considerations and the equipment in ultrasonic cleaning. The components used in the generation of ultrasonic wave include piezoelectric and magnetostrictive transducers that are used in ultrasonic generators and tanks. The effects of solution type and its temperature on the effectiveness of ultrasonic cleaning are also discussed.

Aluminum or aluminum alloy products have various types of finishes applied to their surfaces to enhance appearance or improve functional properties. This article discusses the procedures, considerations, and applications of various methods employed in the cleaning, finishing, and coating of aluminum. These include abrasive blast cleaning, barrel finishing, polishing, buffing, satin finishing, chemical cleaning, chemical brightening, electrolytic brightening, chemical etching, alkaline etching, acid etching, chemical conversion coating, electroplating, immersion plating, electroless plating, porcelain enameling, and shot peening.

Nanofluids offer a completely different behavior of wetting kinetics and heat-removal characteristics, which are exploited in industrial heat treatment for quenching. This article provides information on the important thermophysical properties of nanofluids, namely, thermal conductivity, viscosity, specific heat, density, and surface tension. It reviews wetting and boiling heat-transfer characteristics of nanofluids as quenchants and highlights the importance of using nanofluids as effective quench media for the hardening process during heat treatment. The article describes the effect of nanoparticle addition on the microstructure, mechanical properties of components, wetting kinetics, and kinematics.

Heat treatment simulation helps to predict heat treatment results such as component microstructures, properties, residual stresses, and distortion, and thereby assists in reducing experimental effort in defining heat treatment parameters. This article discusses the modeling and simulation of age hardening as being the most important heat treatment to strengthen aluminum alloys. It provides information on the heat treatment simulation model, the yield strength model based on the responsible strengthening mechanisms, and the flow curve model based on mechanical tests. The article also discusses simulation of the quenching process, and provides examples for aluminum quenching simulation.

This article discusses different heat treating techniques, including quenching, homogenizing, annealing, stress relieving, stress equalizing, quench hardening, strain hardening, tempering, solution heat treating, and precipitation heat treating (age hardening) for different grades of aluminum alloys, copper alloys, magnesium alloys, nickel and nickel alloys, and titanium and titanium alloys and its product forms.

This article describes the general categories and metallurgy of heat treatable aluminum alloys. It briefly reviews the key impurities and each of the principal alloying elements in aluminum alloys, namely, copper, magnesium, manganese, silicon, zinc, iron, lithium, titanium, boron, zirconium, chromium, vanadium, scandium, nickel, tin, and bismuth. The article discusses the secondary phases in aluminum alloys, namely, nonmetallic inclusions, porosity, primary particles, constituent particles, dispersoids, precipitates, grain and dislocation structure, and crystallographic texture. It also discusses the mechanisms used for strengthening aluminum alloys, including solid-solution hardening, grain-size strengthening, work or strain hardening, and precipitation hardening. The process of precipitation hardening involves solution heat treatment, quenching, and subsequent aging of the as-quenched supersaturated solid solution. The article briefly discusses these processes of precipitation hardening. It also reviews precipitation in various alloy systems, including 2xxx, 6xxx, 7xxx, aluminum-lithium, and Al-Mg-Li systems.

This article reviews general corrosion of uranium and its alloys under atmospheric and aqueous exposure as well as with gaseous environments. It describes the dependence of uranium and uranium alloy corrosion on microstructure, alloying, solution chemistry, and temperature as well as galvanic interactions between uranium, its alloys, and other metals. The article provides information on the atmospheric corrosion of uranium based on oxidation in dry air or oxygen, water vapor, and oxygen-water vapor mixtures depending upon particular storage conditions. The mechanism and morphology of hydride corrosion of uranium are discussed. The article provides information on environmentally assisted cracking, protective coatings, and surface modification of uranium and its alloys. It also summarizes the environmental, safety, and health considerations for their use.

This article describes the heat treating (stress relieving, normalizing, annealing, quenching, tempering, martempering, austempering, and age hardening) of different types of steels, including ultrahigh-strength steels, maraging steels, and powder metallurgy steels. Tabulating the recommended temperatures for normalizing and austenitizing, it provides information on mechanism, cooling media, principal variables, process procedures, and applications of heat treating. In addition, the article gives a short note on the cold and cryogenic treatment of steel.