Search Results for distortion control

The design of a tool-steel part directly affects the susceptibility to shape distortion on heating and cooling. This article provides information on the selection of chemical composition and the effect of composition on size distortion. It explains the various factors considered to control distortion in tools steels, namely, design, initial condition, machining procedure, and heat treatment. Distortion can occur both during and after heat treatment. The article discusses the chief ways to precisely control the extent of distortion by heat treating and auxiliary mechanical methods. Stabilizing treatments, namely, stabilizing by tempering and stabilizing by cold treatment are used to minimize dimensional changes that occur following heat treatment.

This article provides an overview of the effects of various material- and process-related parameters on residual stress, distortion control, cracking, and microstructure/property relationships as they relate to various types of failure. It discusses phase transformations that occur during heat treating and describes the metallurgical sources of stress and distortion during heating and cooling. The article summarizes the effect of materials and the quench-process design on distortion and cracking and details the effect of cooling characteristics on residual stress and distortion. It also provides information on the methods of minimizing distortion and tempering. The article concludes with a discussion on the effect of heat treatment processes on microstructure/property-related failures.

Quenching is one of the most important heat treating processes, because it is so closely related to dimensional control requirements and control of residual stresses. This article provides an overview of the fundamental material- and process-related parameters of quenching on residual stress, distortion control, and cracking. This overview is followed by various selected case histories of failures attributed to the quenching process.

Agitation is one of the most critical areas of quench system design. This article provides an overview of the impact of agitation on quench uniformity, followed by a general discussion of the selection and use of various types of agitators, including recirculation pumps, jet mixers, forced air (sparging), and impellers. A brief overview of heat-exchanger types and their selection criteria is also provided, along with simplified calculations for approximating heat-exchange requirements. The methods of selecting a quenchant are provided. Recommendations for system maintenance are also described. Much effort is placed on the proper design of the furnace for temperature and atmosphere uniformity, proper temperature control, and exact carbon potential. However, the design of the quench tank can have a drastic effect on the overall system performance, with proper design ensuring proper mechanical properties (hardness, strength, and fracture toughness) as well as distortion control.

The gas quenching process is usually performed at elevated pressures, and is therefore, mostly referred to as high-pressure gas quenching (HPGQ). This article describes the physical principles of HPGQ; the two main types of equipment used, namely, single-chamber furnaces and cold chambers; and the three gases used, namely, nitrogen, helium, and argon. It also discusses two different groups of fixture materials used, namely, high-nickel-content alloys and carbon-fiber-reinforced carbon materials. The article exemplifies the process of dynamic gas quenching and how core hardness values can be predicted in industrial practices. It also discusses the improvements in distortion control with the application of gas-flow reversing and dynamic gas quenching.

Press quenching is a specialized quenching technique that can be utilized during heat treatment to minimize distortion of complex geometrical components by using specialized tooling for generating concentrated forces that constrain the movement of the component in a carefully controlled manner. This article provides a detailed account of the fundamental components of quenching machines, including the upright machine section, control panel, lower die table, tooling, and the base. In addition, it summarizes the critical factors affecting component distortion during press-quenching.

Gas quenching is one of the standard quenching technologies used in fabricating metallic components. The gas quenching process is usually performed at elevated pressures and is therefore mostly referred to as high-pressure gas quenching (HPGQ). This article presents the physical principles of HPGQ and also presents the equipment for gas quenching. The article describes the three types of gas that are mainly used for HPGQ: nitrogen, helium, and argon. It provides the mathematical model for heat fluxes and temperatures during HPGQ. The article also presents typical industrial applications for HPGQ in addition to equipment process and safety.

This article presents an overview of the techniques used in the design for heat treatment and discusses the primary criteria for design: minimization of distortion and undesirable residual stresses. It provides theoretical and empirical guidelines to understand the sources of common heat treat defects. A simple example is presented to demonstrate how thermal and phase-transformation-induced strains cause dimensional changes and residual stresses. The article concludes with a discussion on the heat treatment process modeling technology.

This article presents an overview of common heat treating problems arising due to poor part design, material incapabilities, difficult engineering requirements, incorrect heat treatment practice, and nonuniform quenching with emphasis on distortion and cracking of quenched and tempered steels. It provides useful information on selection of steels for heat treatment, and discusses the causes of residual stresses, distortion (size and shape), and size changes due to hardening and tempering. The article elucidates the control techniques for such distortions. It describes the importance of decarburizing, and discusses the problems caused by heating, cracking, quenching, typical steel grades, and design.

Fusion welding induces residual stresses and distortion, which may result in loss of dimensional control, costly rework, and production delays. In thermal analysis, conductive heat transfer is considered through the use of thermal transport, heat-input, and material models that provide values for the applied welding heat input. This article describes how the solid-phase transformations that occur during the thermal cycle produced by welding lead to irreversible plastic deformation known as transformation plasticity. Residual stress and welding distortion are also discussed.

The fundamental objective of quenching is to preserve, as nearly as possible, a metastable solid solution formed at the solution heat treating temperature, by rapidly cooling to some lower temperature, usually near room temperature. This article provides an overview of the factors used to determine a suitable cooling rate and the appropriate quenching process to develop a suitable cooling rate. It discusses the three distinct stages of quenching: vapor stage, boiling stage, and convection stage. The article reviews the factors that affect the rate of cooling in production operations. It discusses the quenchants that are used in quenching aluminum alloys, namely, hot or cold water and polyalkylene glycol. The article also describes the racking practices for controlling distortion and the level of residual stresses induced during the quench.

This article provides an overview of steel gear heat treating processes and brings out the nuances of the various important heat treating considerations for steel gear applications. The heat treatment processes covered are annealing, carburizing, hardening, low-pressure carburizing, induction hardening, through hardening, and nitriding. In view of the emerging use of mathematical modeling and optimization, a brief overview of its application for process and design optimization is also provided.

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.

This article presents an outline of the physical metallurgical principles that are associated with heat treating of steels. It describes the iron-carbon phase diagram and various types of transformation diagrams, including isothermal transformation diagrams, continuous heating transformation diagrams, and continuous cooling transformation diagrams. The primary design criteria for heat treating of steels this article covers are the minimization of distortion and undesirable residual stresses. The article presents the theoretical and empirical guidelines to understand sources of common heat-treating defects and how they can be controlled. It also presents an example to demonstrate how thermal and transformation-induced strains cause dimensional changes and residual stresses.

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 advantages of martempering and the use of oil and salt as quenchants in the martempering process. It also discusses safety precautions to be followed by an operator and reviews the steels that are suitable for martempering. The article provides information on the importance of controlling process variables in martempering, including austenitizing temperature, temperature of the martempering bath, time in the bath, salt contamination, water additions to salt, agitation, and the rate of cooling from the martempering bath. It also describes specific situations in which distortion problems have been encountered during martempering. The article contains tables that indicate typical applications of martempering in salt and oil by listing commonly treated steel parts and giving details of martempering procedures and hardness requirements. The article also lists equipment requirements for oil and salt martempering of steel.

Of the various thermal processing methods for steel, heat treating has the greatest overall impact on control of residual stress and on dimensional control. This article provides an overview of the effects of material- and process-related parameters on the various types of failures observed during and after heat treating of quenched and tempered steels. It describes phase transformations of steels during heating, cooling of steel with and without metallurgical transformation, and the formation of high-temperature transformation products on the surface of a carburized part. The article illustrates the use of carbon restoration on decarburized spring steels. Different geometric models for carbide formation are shown schematically. The article also describes the different microstructural features such as grain size, microcracks, microsegregation, and banding.

Dimensional and shape changes caused by heat treatment have been the subject of scientific and industrial research for a very long time. This article provides an overview of the complexity of distortion and stress generation during heat treatment of steels. It discusses the measurement and evaluation of dimensional and shape changes with examples. The article describes the mechanisms at work during the generation of stresses and distortion during heat treatment. A hypothetical experiment with increasing application to real life is used to develop a systematization of unavoidable size and shape changes. The article also provides information on the carriers of distortion potential that cause measureable size and shape changes.