Glossary
Heat Treating Glossary
Age Hardening
The hardening of a material via precipitation from solid solution of coherent transitional phases which produce a strain in the atomic lattice.
Alloy
A substance of metallic properties composed of two or more elements, at least one of which is a metal.
Annealing
A heat treatment process that softens the metal and produces desired changes in its microstructure. Annealing is used to improve machinability, dimensional stability, relieve stresses and define the crystalline grain structure of the material.
Bright AnnealingAnnealing in a protective atmosphere to prevent discoloration of a bright surface.
Carbide Coating
TiC and SiC coating is a vacuum deposition process where titanium or silicon carbide compound is formed on graphite components.
Carbonitriding
A case hardening process in which introduces carbon and nitrogen into the surface of a ferrous or PM alloy by heating the alloy in contact with a gaseous carbonaceous material and ammonia. The heat treating process is completed by quenching at a set rate to produce the desired properties of the workpiece.
Carburizing
A surface hardening process that introduces carbon into the surface of a solid ferrous alloy by heating the alloy in contact with a carbonaceous material to a temperature above the transformation range and holding at that temperature until a desired level of carbon is absorbed and diffused inward from the surface. This is generally followed by quenching to produce a hardened case.
Ceramic
An inorganic, nonmetallic, thermally-stable material, usually a crystalline structure. Ceramic consists of one or more metals in combination with a non-metal, usually oxygen, but can include nitrides, borides, carbides, silicides, and sulfides. They are characterized by a high temperature strength, good electro-thermal insulation, and high chemical stability.
Degassing
A heat treatment process that removes gas from the metal; vacuum processing is used to degas titanium, copper, and tantalum.
Diffusion Bonding
A joining process that involves atomic movement from one metal part to another, typically in the same alloy family, to form a strong metallurgical bond. This occurs at high temperature (but below the melting point) and pressure. The process is particularly facilitated in a vacuum because of the elimination of oxygen, allowing for a high integrity bond.
Emissivity
A measure of thermal emittance; measured by the ratio of the radiation emitted by a surface to the radiation emitted by a blackbody (a surface that emits all the heat energy that it absorbs) under the same conditions.
Eutectic Alloy
An alloy of two or more elements that exhibits isothermal freezing with the simultaneous precipitation of alternate phases at a lower temperature than any of the pure elements in the alloy. In the liquid form, a eutectic usually exhibits high fluidity.
Gas Carburizing
Carburizing in the presence of hydrocarbon gases which react on the surface of the steel to release nascent carbon which diffuses into the surface of the steel to improved wear and fatigue resistance.
Gas Nitriding
A process of case hardening in which a ferrous alloy, usually of special composition, is heated in an atmosphere of ammonia to produce surface hardening by the absorption of nitrogen without quenching.
Glass
A super-cooled liquid ceramic material, commonly composed of silicates and oxides, that forms by cooling the viscous materials without sufficient time for a crystalline lattice structure to form.
Hardening and Tempering
A common heating and cooling treatment used to harden and strengthen the metal. One way to measure is by using various hardness scales including Brinell and Rockwell. Hardened metal is reheated in order to temper it; hardness is lowered but the ductility is increased. Vacuum process will result in bright finishes. Temperature of the temper operation determines the final strength, hardness, and ductility.
Homogenizing
A heat treatment process that holds the metal at a high temperature to eliminate or decrease chemical segregation by diffusion.
Hydriding / Dehydriding
Hydriding is the addition of hydrogen to metal to embrittle it for pulverizing. After pulverizing, hydrogen is removed through dehydriding so the material becomes ductile.
Hydrogen Annealing
Annealing under a controlled atmosphere of hydrogen to prevent oxidation or discoloration of parts.
Ion Nitriding
A high-voltage glow discharge is used to bombard low and medium alloy steels, tool steels, and stainless steel surfaces with nitrogen ions. The nitrogen ions form nitrides with the alloy elements and diffuse into the part resulting in clean, surface hardening.
Magnetic Annealing
Hydrogen annealing is used to improve the magnetic properties of carbon steel by decarburizing the steel.
Melting Point
The temperature upon which a chemically pure substance changes from a solid state to a liquid state.
Metal Oxide
A compound of oxygen with a metal. Most metals react with oxygen under appropriate temperature and pressure conditions, and oxidation can occur slowly at room temperature to form a thin oxide coat that can serve to protect the metal.
Nitriding
A chemical process which diffuses nascent nitrogen into the surface layers of low carbon steels in order to improve surface hardness and wear resistance.
Normalizing
The process of heating a ferrous alloy to a temperature above the transformation range to create a phase change in the metal's microstructure, then cooling in air, or as in vacuum heat treating, at a rate equivalent to air cooling. The benefit of normalizing is the refinement of the grain structure.
Precipitation Hardening
A process of hardening by precipitating an element from a supersaturated solid solution to form coherent transitional precipitates, which produces a strain in the atomic lattice.
Refractory Metal
A metal that has a melting point well above the common alloying bases (i.e. iron, cobalt, nickel). They include niobium (columbium), tantalum, molybdenum, tungsten, and rhenium. These metals maintain high strength and hardness at elevated temperatures.
Sintering
A heating process that bonds adjacent particles in a powder mass to increase strength and density. High temperature vacuum sintering is performed at elevated temperatures below the melting point of the metal, up to 2650°F, and higher for refractory metals.
Soldering
A joining process by heating the metals to a suitable temperature below the solidus of the base metals and applying a filler metal having a liquidus not exceeding 840°F. The filler metal is distributed between the closely-fitted surfaces of the joint by capillary action.
Solid Solution
A constituent of alloys is formed when atoms of one metal are incorporated into the crystals of another metal.
Solution Treating
A process of heating an alloy and holding it at a suitable temperature until one or more of the constituents enters a solid solution, at which point the solution is cooled rapidly to hold the alloy in a supersaturated condition.
Stress Relieving
A uniform heating process followed by slow, uniform cooling; the process reduces stresses in fabricated or machined parts, and results in dimensional stability.
Thermocouple
A device for measuring temperatures made of two dissimilar metal or alloy wires joined at one end and connected to a voltage-measuring instrument at the other end. Common types include J, K, N, R, S, and W (also known as C).
Vacuum Brazing
A thermal vacuum process that joins metals when a braze alloy creates a metallurgical bond between the metal components; finished parts are bright and clean. Vacuum Brazing is usually performed at temperatures above 1000°F, but always below the solidus of the base metals.
Vacuum Heat Treating
The process of heating alloys in a vacuum chamber at pressures down to 10-6 Torr. Cooling is performed with inert gas at pressures ranging from sub-atmospheric to as high as 10 atmospheres (10 bar). The controlled environment produces bright, clean, high-integrity parts, which eliminates the need for many finishing operations.
Vapor Pressure
The gas pressure exerted when a substance is in equilibrium with its own vapor. The vapor pressure is a function of the substance and the temperature.