Glossary

Aging

A process that utilizes an soak of several hours at an elevated temperature to speed precipitation of a component from the supersatured solid solution.  Typically done to aluminum alloys and stainless steel alloys such as 17-4 or 15-5. 

Annealing

A treatment consisting of heating uniformly to a temperature, within or above the critical range, and cooling at a controlled rate to a temperature under the critical range.  This treatment is used to produce a definite microstructure, usually one designed for best machinability, remove stresses, induce softness, and alter ductility, toughness or other mechanical properties.

Austempering

A hardening process performed on both Steels and Irons to achieve a bainitic microstructure that typically results in mechanical properties that have higher ductility, resistance to shock, and uniform hardness than the same properties found had the material been quench and tempered to the same hardness with a resulting martensitic microstructure.  

Blasting (Abrasive)

Typically an operation done by machines utilizing centrifugal force to propel some abrasive against an object.  The amount of force and type of abrasive should be monitored dependant upon the hardness and finish of the object in question.  Typically this process is meant for the removal of scale and other surface contaminants when used subsequent to any heat-treating. 

Case Hardening

A treatment that hardens the a ferrous alloy product in a way that makes its outer portion markedly harder thant its inner portion or core.

Carburizing

A process resulting from the exposure of a material (typically steel) above it's critical temperature to an atmosphere containing more carbon than the material has been manufactured with.  This process then results in the formation of metal carbides  which imparts a high surface hardness and wear resistance to the material.  The depth of carburization can be controlled by time and temperature.  The surface hardness can be controlled by subsequent tempering temperatures. 

Carbonitriding

A process very similar to Carburizing except that this process is typically run for plain carbon & low alloy steels such as 1018 which require an addition of Nitrogen to increase wear resistance and surface hardness due to the lack of hardenability in the base material.

Carbon Restoration

A process that replenishes the surface layer of a material that has lost carbon due to exposure of the material to an elevated temperature in an oxidizing enviroment.  Typically this process is done subsequent to the hardening of investment castings. 

Charpy Impact Test

A test to determine the behavior of materials when subjected to high rates of loading, usally in bending, tension or torsion.  The quantity measured is the energy absorbed in breaking the specimen by a single blow.

Core

The inner portion of a metal or metal alloy product which is softer than its "Case" or outer portion.

Cryogenic Treatment/Cryo-Treating/Deep Freezing

typically performed to insure there is no retained austenite left in the microstructure after quenching.  Retained austenite is very brittle and left unaddressed can cause dimensional instability and cracking and can manifest itself by causing the material to be low in hardness and strength.  The treatment is typically done between -100F to -300F which should transform the austenite into martensite.  A post-cryo temper is then suggested to address the un-tempered martensite issues. 

DI (Ideal diameter)

The diameter of a round steel bar that will harden at the center to a given percent of martensite when subjected to an ideal quench. 

Elongation

In tensile testing, the increase in gage length, measured after the fracture of a specimen within the gage length, usually expressed as a percentage of the original gage length. 

Full Annealing

Full annealing of a ferrous alloy product is achieved by austenitizing and then allowing it to cool slowly through the transformation range.

Flame Hardening

A process that utililizes direct impingement of an oxy-gas flame onto a defined surface area followed by a quench operation which is designed to increase the surface hardness and mechanical properties of the part in a selective area. 

Gas Nitriding

A thermal process that diffuses Nitrogen into the surface of steel where it forms Nitrides with such elements as Aluminum, Chromium, Molybdenum, and Vanadium.  A low temperature process that takes 10 to 40 hours depending on the case depth required.  

Hardness

Resistance of a metal to plastic deformation, usually by indentation.  

Hardenability

The property of a ferrous alloy that dictates the distribution and depth of hardness that is induced when the alloy is quenched.

Homogenization

A heat-treat process typically applied to castings where the casting process has resulted in chemical segregation and unwanted microstructures.  Usually a process run at an elevated temperature that requires many hours and slow cooling to allow for diffusion of the alloying elements and formation of grains that are beneficial to the subsquent use of the casting. 

IsoThermal Annealing

To IsoThermal Anneal a ferrous alloy product it must be austenitized then cooled and held at a temperature at which austenitite will transform into a softer, ferric carbide aggregate.

Jig Tempering

A straightening process done by clamping the object between two thicker plates and then processing the fixture at an elevated temperature so the object will remain in a straighter configuration at room temperature when un-fixtured. 

Killed Steel

Steel treated with a strong deoxidizer to reduce oxygen to a level where no reaction occurs between carbon and oxygen during solidification. 

Lap

A surface imperfection which appears as a seam.  It is caused by the folding over of hot metal, fins, or sharp corners and then rolling or forging them into the surface but not welding them.  Laps on tubes can form from seams on pierced mill billets.

Machinability

This is a generic term for describing the ability of a material to be machined.  To be meaningful, machinability must be qualified in terms of tool wear, tool life, chip control, and/or surface finish and integrity. 

Marquench Hardening

Typically a process employed using an elevating quench media, ie: molten salt, where the temperature of the media exceeds the Martensite Start(Ms) temperature of the material being quenched.  The time period that the material is kept in the quenchant should be long enough to insure temperature uniformity, but, not long enough to start forming bainite.  Used for minimizing distortion on sensitive parts and for minimizing the risk of cracking on higher alloy materials.  

Maraging

A hardening treatment applied to a particular group of iron base alloys in order to precipitate one or several intermetallic 
compounds in a matrix of what amounts to carbon-free martensite.

Mechanical Testing

Mechanical testing reveals the elastic and inelastic behavior of a material when a force is applied to it and the results are then used to confirm if the material is suitable for it's intended mechanical application.  Tests typically done after heat-treating include: Tensile, Yield, Elongation, Reduction of Area, Hardness, and Charpy Impact testing.

Normalizing

A treatment consisting of heating uniformly to temperature at least 100F above the critical range and cooling in still air at room temperature.  The treatment produces a recrystallization and refinement of the grain structure and gives uniformity in hardness and structure to the product. 

Oil Quench Hardening

Typically the slowest liquid quench media employed by a commercial heat-treater.  Used for tool steel material such as O-1 and medium alloy steels such as 4140, 4340 and 4150.  The oil is usually employed in range above room temperature to slow the transformation from Austenite to Martensite to minimize distortion and subsquently cracking.  

Pickling

An operation by which surface oxide (Scale) is removed by chemical action.  Sulfuric acid is typically used for carbon and low-alloy steels.  After the acid bath, the steel is rinsed in water.

Polymer Quench Hardening

Typically a media that will produce a cooling rate between water and oil.   However, several varieties and subsequent percentages of Polymer additions to a quench are available so that several different cooling rates can be approximated.  Typically used for quenching low to medium alloy steels or larger section sizes of higher alloy materials. 

Quenching

A treatment consisting of heating uniformly to a predetermined temperature and cooling rapidly in air or liquid medium to produce a desired crystalline structure.

Recrystallization

Recrystallization is the transition from one crystal structure to another as a metal is heated or cooled through a critical temperature.

Reduction of Area

The difference, expressed as a percentage of original area, between the original cross-sectional area of a tensile test specimen and the minimum cross-sectional area measured aftercomplete separation.

Seam

A defect on the surface of a metal which appears as a crack.  Experience indicates that most seams are created during the cooling or reheating of cast structures.

Solution Anneal

A process performed on Steels and Aluminum.  The process consists of heating the material up to a temperature above the critical temperature of the material long enough for its various alloying elements such as carbon to go into solution.  After this, the material is quickly cooled to prevent these alloying elements to come out of solution.  

Spheroidize Anneal

A special type of annealing that requires an extremely long cycle.  This treatment is used to produce globular carbides and maximum softness for best machinability in some analyses, or to improve cold formability.

Straightening

Straightening can be done via mechanial means at room temperature, thermally by heating of a localized area on the object, or by applying mechnaical pressures at an elevated temperature.  

Stress Relieve

A thermal treatment to restore elastic properties and to minimize distortion on subsequent machining or hardening operations.  This treatment is usally applied to material that has been heat treated (quench and tempered).  Normal practice would be to heat to a temperature 100F lower than the tempering temperatures used to establish mechanical properties and hardness.  

Sub-Critical Annealing

An annealing process that runs in a temperature range between stress relieving and full-annealing.  It is typically defined as a process run below the critical temperature of the iron-carbon equilibrium diagram which for steel and heat-treaters includes a range of 1250F to 1400F.   Typically used to soften materials that have been cold worked and are too hard or brittle for subsequent cold work operations. 

Tempering

A treatment consisting of heating uniformly to some predetermined temperature under the critical range, holding at that temperature a designated period of time and cooling in air or liquid.  This treatment is used to produce one or more of the following end results: A) to soften material for subsequent machining or cold working, B) to improve ductility and relieve stresses resulting from prior treatment or cold working, and C) to pruduce the desired mechanical properties or structure in the second step of a double treatment. 

Tensile Strength

In tensile testing, ratio of maximum load to original cross-sectional area.

Water Quench Hardening

Typically the most severe quench used by commercial heat-treat companies.  Used for low DI materials such as low alloy tool steels like W-Series and plain carbon steels such as 1045.  Usually accomplished by using artifically cooled water and high aggitation which can then be manifested in high risks of cracking and distortion.

Yield Point

The first stress in a material, usually less than the maximum attainable stress, at which an increase in strain occurs without an increase in stress.  If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points. 

Yield Strength

The stress at which a material exhibits a specified devation from the proportionality of stress and strain.  An offset of 0.2% is commonly used.

Vacuum Carburizing -LPC (Low Pressure Carburizing)

Back in the 1970's when Vacuum carburizing was first commercially introduced it was run using classically carburzing atmospheres and pressures just below atmospheric pressures.  In order to force the carburized gas throughout the load a strong fan had to be utilized on the loads and the resultant problems manifested themselves in loss of carbon control, case-depth uniformity issues, and sooting.  In the late 1980's a new development called Low Pressure Carburizing (LPC) came on the market.  The premise was that running low pressures in the vacuum furnace during the carburization cycle would reduce sooting and improve carbon penetration throught the load without the need for vigourous agitation of the atmosphere.  Subsequent improvements have resulted in an efficient process that can finely control the case depth layers via improved engineered atmospheres that have increased amounts of carbon in them along with faster cycle times due to higher temperature operating ranges.