Mathematical models have been used for over five decades in industrial heat-treating operations. Most of these modeling efforts have emanated from academia or research institutes, with the primary approach of mathematically capturing heat-treating processes and validating quality predictions. In this article, a contrarian but more realistic scenario is considered, where two industrial problem descriptions become the starting point. The technical complexity of the industry problem has been elaborated for a deeper understanding of the issue along with elaboration of the approach and potential methods for determining a solution. Then, quantitative analyses of practical industrial problems are demonstrated. Finally, the potential shift in these approaches with the advent of Industry 4.0 is outlined.

This article reviews the factors influencing carburization to improve wear resistance of steel, such as operating temperature, cost, production volume, types of wear, and design criteria. It details the types of wear, namely abrasive wear and adhesive wear. The article discusses the characteristics of carburized steels that affect wear resistance, including hardness, microstructure, retained austenite, and carbides. It also describes the processing considerations for carburization of titanium.

This article commences with a brief introduction on the hardenability of carburized steels, and then reviews the factors used in the selection of carburizing steels and heat treatment methods. The factors include quench medium, stress considerations, case depth, and type of case. The article provides information on steels for carburized gears with emphasis on gear design requirements, selection process, selection of carbon content, case and core hardness, microstructure, and toughness and short-cycle fatigue.

The plasma carburizing process is basically a low-pressure carburizing process making use of a high-voltage electrical field applied between the load to be treated and the furnace wall producing activated and ionized gas species responsible for carbon transfer to the workpieces. This article begins with an overview of the theoretical background and the range and limitations of glow-discharge plasma. It describes the plasma carburizing process, which is carried out with methane or propane. Plasma carburizing processes of sinter metals and stainless steels, and the influence of current pulse length on carbon input of low-pressure carburizing process are also described. The article presents the basic requirements and process parameters to be considered in plasma carburizing equipment. It also exemplifies a still-working plasma process in industrial measure.

Carburization is the process of intentionally increasing the carbon content of a steel surface so that a hardened case can be produced by martensitic transformation during quenching. Like carburizing, carbonitriding involves heating above the upper critical temperature to austenitize the steel. This article introduces the fundamentals, types, advantages and limitations, and the complications of various forms of carburizing, namely, pack carburizing, liquid carburizing or salt bath carburizing, gas carburizing, and low-pressure (vacuum) carburizing. The related process of carbonitriding is also briefly described in the article.

Low-pressure carburizing (LPC) is one of the most popular case-hardening processes and is applied to increase the fatigue limit of dynamically loaded components. It takes place in a pressure range between 5 and 15 mbar (4 and 11 torr) and at temperature range between 870 and 1050 deg C. The LPC process runs in two different types of equipment: single-chamber furnaces and treatment chambers. This article reviews the use of simulation software for prediction of carbon profiles and typical quality control procedures. It describes the physical principles and typical applications of LPC.

This article describes the thermodynamics and kinetics of gas carburizing reactions, and details the mass transfer mechanism during gas carburizing. It discusses the various considerations involved in carburizing process planning, and reviews successful operation of the gas carburizing process based on the control of three principal variables: temperature, atmosphere composition or carbon potential, and time. The article also describes the selection criteria for alloy, carbon sources, atmosphere types, and carbon monoxide level for endothermic carburizing atmospheres. It provides information on carburizing modeling, case depth prediction, case depth measurement, and case depth evaluation as well as on carburizing equipment, and also covers the factors affecting distortion after carburizing.

This article describes the uses of the liquid carburizing process carried out in low and high temperature cyanide-containing baths, and details the noncyanide liquid carburizing process which can be accomplished in a bath containing a special grade of carbon. It presents a simple formula for estimating total case depth, and illustrates the influence of carburizing temperature, duration of carburizing, quenching temperature, and quenching medium with the aid of typical hardness gradients. The article provides information on controlling of cyaniding time and temperature, bath composition, and case depth, and presents examples that relate dimensional change to several shapes that vary in complexity. It also provides information on the quenchant removal and salt removal processes, lists the applications of liquid carburizing in cyanide baths, and discusses the process and importance of cyanide waste disposal in detail.

Pack carburizing is a process in which carbon monoxide derived from a solid compound decomposes at the metal surface into nascent carbon and carbon dioxide. In addition to discussing the pros and cons of pack carburizing, this article provides information on the carburizing medium, compounds, furnaces, and containers used in pack carburizing. The successful operation of the pack carburizing process depends on the control of principal variables such as carbon potential, temperature, time, case depth, and steel composition. The three types of furnaces most commonly used for pack carburizing are the box, car-bottom, and pit types. Carburizing containers are made of carbon steel, aluminum-coated carbon steel, or iron-nickel-chromium heat-resisting alloys. The article also provides information on the packing procedure of workpieces.