Search Results for controlled-atmosphere furnaces

Furnaces for heat treatment of tool steels include ceramic-lined salt bath furnaces, vacuum furnaces, controlled-atmosphere furnaces, and fluidized-bed furnaces. This chapter describes the classification, operating principles, application, advantages, and disadvantages of each type of furnace.

The temperature and atmosphere conditions must be precisely controlled in order to achieve the desired metallurgical results during heat treating operations. In order to ensure the repeatability of operation, a heat treating system must have the necessary sensors, timers, and variable (temperature, atmosphere, etc.) controllers to hold the process within prescribed or specified limits. This chapter discusses temperature and atmosphere sensors used in a heat treating system. The temperature sensors covered are contact and noncontact types. The atmosphere sensors covered are oxygen probe, dew point, and infrared. The chapter concludes with an overview of the development of integrated control systems.

Critical process variables must be controlled to ensure uniform and repeatable heat-treating results. This chapter covers the subject of controlling the heat-treating process. All heat-treating equipment utilizes various sensors, timers, and other components to monitor and control the process utilizing various control methods. The chapter focuses on temperature control and measurement, including a discussion about thermocouples and devices for measuring thermal and electrical conductivity.

This chapter discusses furnace atmospheres. It describes how furnace atmospheres protect metals, transfer heat, and supply alloying elements (carbon and nitrogen). The chapter focuses on the different types of atmospheres that are available to the heat treater: combustion products, air, exothermic, salt, nitrogen, endothermic, ammonia, hydrogen, inert gas, and vacuum.

Carbonitriding introduces and diffuses atomic nitrogen into the surface steel during carburization. This chapter focuses on case composition of a carbonitrided case, case depth, case hardenability, hardness gradients, void formation, and applications of carbonitriding. The chapter discusses furnaces suitable for carbonitriding, atmosphere constituents, batch furnace atmospheres, continuous furnace atmospheres, safety, temperature selection, quenching, tempering, and hardness testing of a carbonitrided case.

To ensure consistency, quality of results, and documentation compliance, audits are required when heat treating. This chapter introduces basic parts of the ISO certification program.

This chapter, a detailed account of furnaces and related equipment for heat treating, begins by describing three basic modes of heat transmission, namely conduction, convection, and radiation, followed by a discussion on the working principle, applications, advantages, and disadvantages of furnaces classified based on the heat transfer medium employed. The types of furnaces covered are batch-type, continuous-type, liquid bath, fluidized bed, and vacuum. The subsequent sections provide information on furnace parts, fixtures, quenching mediums, and quenching systems. The final section of the chapter describes the types of atmospheres available, emphasizing their applications and limitations.

This chapter focuses on gas carburizing. It includes a history of carburizing and explains the objectives of the carburizing process. The chapter discusses atmospheres, sources of carbon, reactions in the gas carburizing process, and effects of process variables such as temperature and time. Furnaces for gas carburizing are described and potential microstructure problems are introduced.

This chapter details the types of heat treating furnaces. It discusses energy sources and modes of heat transmission. The chapter’s focus is on the different types of batch furnaces and continuous furnaces, including box furnaces, integral-quench batch furnaces, pit furnaces, furnaces for heat treating with fluidized beds, and straight chamber continuous furnaces.

This chapter describes the general characteristics of major types of steel annealing, including the process of normalization, which is a process that refines or normalizes the microstructure of steel. The first part of the chapter begins with an overview of the three-stage process of recovery, recrystallization, and grain growth. This is followed by discussions on annealing processes, namely subcritical annealing, critical-range annealing, full annealing, isothermal annealing, annealing for microstructure, and solution or quench annealing. Next, the chapter describes two undesirable reactions that occur during annealing: decarburization and scaling. Information on the gases and gas mixtures used for controlled atmospheres is then provided. The second part of the chapter focuses on the processes involved in normalizing, along with information on furnace equipment for normalizing. In addition, the chapter includes information on processes involved in induction heating of steel.

This chapter discusses vacuum furnace processes and their design. The chapter focuses on the pressure levels, heating elements, pumping systems, temperature control systems, and quenching systems in vacuum furnaces. It then details specific applications of vacuum heat treating.

This chapter discusses equipment used for ferritic nitrocarburizing, including salt bath furnaces, atmosphere furnaces, and plasma furnaces. It also describes the processes involved in ferritic oxynitrocarburizing.

This chapter provides a discussion of nitriding furnace equipment and control systems. The discussion covers the essential design criteria of the furnace, types of nitriding furnaces, insulation for the reduction of furnace heat losses, and factors influencing furnace configuration and design. It also covers the processes involved in the construction and maintenance of retorts, methods for sealing a retort to prevent ammonia leaks, and safety precautions to be taken while using ammonia. Further, the chapter provides information on the factors for choosing a heating medium and discusses the processes involved in controlling temperature, gas dissociation, oxygen probes, and nitriding sensors.

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.

A fluidized-bed furnace system can be used for the gas nitriding process. This chapter focuses on fluidized-bed nitriding. It discusses the methods of heating a fluidized bed. The heating system can be electrical or gas, and internal or external. The chapter describes nitriding and oxynitriding processes in the fluidized-bed furnace. It also explains how to operate the fluid bed for nitriding. The chapter provides a discussion on the measurement of the gas dissociation.

Gaseous ferritic nitrocarburizing, like salt bath nitrocarburizing, involves the introduction of carbon and nitrogen into steel in order to produce a thin layer of iron carbonitride and nitrides, the "white layer" or compound layer, with an underlying diffusion zone containing dissolved nitrogen and iron (or alloy) nitrides. This chapter first presents the development and principles of the process. It then discusses the properties of gaseous ferritic nitrocarburized components. The chapter also presents the applications for the ferritic nitrocarburizing process. It provides an overview of the safety considerations.

This chapter discusses hardening processes that involve changes in surface composition. These case hardening treatments are broadly classified into four groups: carburizing, carbonitriding, nitriding, and nitrocarburizing. Key parameters and operating considerations for each treatment are discussed.

This chapter explains how decarburization can occur during carburizing processes and how to limit the severity of its effects. It describes the reactions and conditions that result in a loss of carbon atoms and how they vary with changes in the physical metallurgy of the affected material and the processing environment. It examines the characteristic features of decarburized microstructures and assesses their influence on hardness, residual stresses, and fatigue and fracture behaviors. It also discusses corrective measures and practical considerations regarding their use.

Steel heated in contact with air at temperatures in the tempering range takes on various temper colors due to the formation of a thin oxide film. This appendix provides information on the cause and source of oxidation of steel and time-temperature effect on SAE 1035 steel. In addition, figures that show temper colors after heating 1035 steel in circulating air are presented.