This article provides a detailed discussion on the types of furnace atmospheres required for heat treating. These include generated exothermic-based atmospheres, generated endothermic-based atmospheres, generated exothermic-endothermic-based atmospheres, generated dissociated-ammonia-based atmospheres, industrial gas nitrogen-base atmospheres, argon atmospheres, and hydrogen atmospheres. Atmospheres for backfilling, partial pressure operation, and quenching in vacuum are also discussed. Furnace atmospheres constitute four major groups of safety hazards in heat treating: fire, explosion, toxicity, and asphyxiation. The article reviews the fundamentals of principal gases and vapors. It describes how the evaluation of the atmospheric requirements of heat treating furnaces is influenced by factors such as cost of operation and capital investment.

This article presents a simple cost/pricing system that is reasonably accurate and could easily be recalculated if the yearly cost of any of the basic cost components change. Using the example of a commercial heat treating facility, the operational details are categorized as atmosphere processes, induction processes, aluminum processes, high-heat processes, and secondary processes. For the purpose of calculating the heat treatment processing cost per hour and the selling price for a piece of equipment, the costs are separated into direct costs, allocated costs, capitalized cost, and general and administrative costs. The article discusses the techniques involved in allocating costs to the group of equipment, and presents a description on the cost analysis of endothermic gas.

The atmosphere within a furnace chamber is a basic factor in achieving the desired chemical reactions with metals during heat treating. This article presents the fundamentals of heat treating atmospheres, and describes two groups of atmosphere control, namely, furnace atmosphere control and supply atmosphere control. The two basic types of atmospheric supply systems are generated atmospheres and nitrogen-base atmospheres. The article provides a brief overview of the gas reactions associated with oxidation and carbon control to ensure either carburization, or to prevent decarburization. It demonstrates how the carbon potential control is achieved by controlling water vapor concentration, carbon dioxide concentration, or oxygen partial pressure. The article also describes the various devices and analyzers used to monitor sampled gas from furnace atmospheres, namely, chromatographs, oxygen probes, Orsat analyzers, infrared analyzers, dewpoint analyzers, and hot-wire analyzers. Finally, it discusses the advantages, disadvantages, and limitations of these analyzers.

Cast nickel-base alloys are used extensively in corrosive-media and high-temperature applications. This article briefly reviews the common types of heat treatments of nickel alloy castings: homogenization, stress relieving, in-process annealing, full annealing, solution annealing, quenching, coating diffusion, and precipitation. It describes the three general strengthening mechanisms, namely, solid-solution hardening, age hardening, and carbide precipitation. The article summarizes the typical heat treatment of the general families of nickel-base castings used in industrial applications. It focuses on the solution treatment and age hardening of cast nickel-base superalloys and the heat treatment of cast solid-solution alloys for corrosion-resisting applications. The article also discusses the typical types of atmospheres used in annealing or solution treating: exothermic, endothermic, dry hydrogen, dry argon, and vacuum.

Controlled atmosphere chambers are used to control the surface chemistry of the metals that are being processed. This article focuses on the various types of controlled atmospheres used in induction heat treating and brazing, namely, inert gas atmospheres based on argon and helium; prepared and commercial nitrogen-base atmospheres; and brazing atmospheres. It provides detailed information on two types of controlled atmosphere chambers: atmosphere and vacuum. The article also describes the selection factors, advantages, and disadvantages of these chambers.

Control of temperature and furnace atmospheres has become increasingly critical to successful heat treating. Temperature instrumentation and control systems used in heat treating include temperature sensors, controllers, final control elements, measurement instruments, and set-point programmers. This article describes these items and discusses the classifications and control of furnace atmospheres. The article also describes the surface carbon control devices available for the wide variety of furnace atmospheres and evaluation of carbon control. Finally, the article provides a set of guidelines for safety procedures that are common to all industrial heat treating furnace installations.

This article describes the effects of furnace atmospheric elements on steels. These elements are air, water vapor, molecular nitrogen, carbon dioxide, and carbon monoxide. The article provides useful information on six groups of commercially important prepared atmospheres classified by the American Gas Association on the basis of method of preparation or on the original constituents employed. These groups are designated and defined as follows: Class 100, exothermic base; Class 200, prepared nitrogen base; Class 300, endothermic base; Class 400, charcoal base; Class 500, exothermic-endothermic base; and Class 600, ammonia base. These are subclassified and numerically designated to indicate variations in the method by which they are prepared. The article also contains a table that lists significant furnace atmospheres and their typical applications.