Search Results for cryogenic cooling

This article examines residual stresses in quenched and surface-hardened steels by focusing on its theoretical background, formation mechanisms of residual stress, effects of tempering and cryogenic cooling on residual stress, effects of residual stress on the service performance of components, and measurement, computation, and relaxation of residual stress.

Cold treating of steel can be used to enhance the transformation of austenite to martensite and improve the stress relief of castings and machined parts. Cryogenic treatment of steel is a distinct process that uses extreme cold to modify the performance of materials. This article explains the practices employed and equipment used in the cold treatment of steel. It also presents the results of using cryogenic treatment to enhance steel properties.

This article provides a discussion on the mechanical properties of metals, ceramics, and polymers and fiber-reinforced polymer composites at low temperatures. It reviews the factors to be considered in tensile and compression testing of these materials. The article details the equipment used for low-temperature tensile and compression tests with illustrations. It concludes with a discussion on the various test methods and their ASTM standard for compression and tension testing.

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.

Thermal inspection comprises all methods in which heat-sensing devices or substances are used to detect irregular temperatures. Inspection of workpieces can be used to detect flaws and undesirable distribution of heat during service. Though there are several methods of thermal inspection and many types of temperature-measuring devices and substances, this article focuses only on thermography, which is the mapping of isotherms, or contours of equal temperature, over a test surface, and on thermometry, which is the measurement of temperature. Thermography techniques can be classified as contact thermographic methods using cholesteric liquid crystals, thermally quenched phosphors, and heat-sensitive paints, and noncontact techniques using hand-held infrared scanners, high-resolution infrared imaging systems, and thermal wave interferometer systems. Contact thermometric inspection devices include bolometers, thermocouples, thermopiles, and meltable substances, whereas radiometers and pyrometers come under the noncontact category.

This article is an atlas of fractographs that helps in understanding the causes and mechanisms of fracture of miscellaneous metals and alloys and in identifying and interpreting the morphology of fracture surfaces. The metals and alloys covered include tungsten, iridium, magnesium-base, iron-base, molybdenum-base, and tantalum-base materials. The fractographs illustrate fatigue striations, slow-bending fracture, quasi-cleavage fracture, corrosion-fatigue fracture, fatigue crack, intergranular cleavage, microvoid coalescence, tension-overload fracture, crack propagation, impact fracture, and high-cycle fatigue failure.

Cryogenic temperatures cause many structural alloys to become brittle, which is an unacceptable condition in most structural applications and is rectified by optimizing the weld composition. Although nonmatching weld compositions are most appropriate, differences between the welds and parent material in terms of thermal contraction, corrosion, and other factors must be considered. This article discusses these differences and describes the effect of these factors on the choice of the weld filler metal. It also provides a detailed discussion on the effects of cryogenic services on mechanical properties of the parent metal.