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Subject on This Issue:
* Steels & Properties
* Heat Treatment


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Terminology For Materials, heat Treatment And Calibration

1. A to Z General Terminology

A

ABRASIVE BLASTING

A pressurised stream of hard metal or oxide grit material used to clean and/or roughen surfaces prior to coating.

ACCICULAR STRUCTURE

A microstructure characterized by needle shaped constituents

ACICULAR FERRITE

A highly substructured nonequiaxed ferrite that forms upon continuous cooling by a mixed diffusion and shear mode of transformation that begins at a temperature slightly higher than the temperature transformation range for upper bainite. It is distinguished from bainite in that it has a limited amount of carbon available; thus, there is only a small amount of carbide present.

AGE HARDENING

A process of precipitation that increases hardness and strength and ordinarily decreases ductility. See aging

AGE SOFTENING

Spontaneous decrease of strength and hardness that takes place at room temperature in certain strain hardened alloys, especially those of aluminum.

AGING

Aging is a structural change, usually by precipitation, that occurs in some alloys after a preliminary heat treatment or cold working operation. Aging may take place in some alloys at room temperature in moderate time (days) or in others may be done in shorter time at furnace temperatures. Over-aging may be done at a temperature above normal to produce some desirable modification.

AIR HARDENING STEEL

A teel containing sufficient carbon and other alloying elements to harden fully during cooling in air or other gaseous mediums from a temperature above its transformation range. The term should be restricted to steels that are capable of being hardened by cooling in air in fairly large sections, about 2 in. (50 mm) or more in diameter. Same as self-hardening steel.

ALLOY

A substance having metallic properties and composed of two or more chemical elements of which at least one is an elemental metal.

ALLOYING ELEMENTS

Chemical elements constituting an alloy; in steels, usually limited to the metallic elements added to modify the properties of the steel.

ALUMINIZING

Forming a corrosion and oxidation-resistant coating on a metal by coating with aluminum and usually diffusing to form an aluminum-rich alloy.

ANNEALING

A very general term describing the heating of metal to a suitable temperature, holding for a suitable time, and cooling at a suitable rate to accomplish the objective of the treatment. Annealing may be done to:
A. Relieve stresses
B. Induce softness
C. Improve physical, electrical or magnetic properties
D. Improve machinability
E. Refine the crystalline structure
F. Remove gases
G. Produce a specific microstructure

ANNEALING ATOMOSPHERE (PROTECTIVE)

In metallurgical practice, the gases surrounding the work in a furnace or otheer high temperature apparatus. The character of the atmosphere varies with the work being carried out and, in nature, may be oxidizing, reducing or neutral.

ANNEALING CARBON

Fine, apparently amorphous carbon particles formed in white cast iron and certain steels during prolonged annealing. Also called temper carbon.

ANNEALING TWIN

A twin form in a crystal during recrystallization.

ANNEAL TO TEMPER

A final partial anneal that softens a cold worked nonferrous alloy to a specified level of hardness or tensile strength.

ANODISING

The production of an oxide layer on aluminum alloys. The process is electrolytic, a typical electrolyte being sulphuric acid. Treatment at room temperature produces thin, decorative layers with some corrosion protection. Treatment at 0oC produces hard, thicker layers (up to 100µ) with wear resistance. They can be post sealed to give improved corrosion resistance.

ARTIFICIAL AGING

Aging above room temperature. See aging. Compare with natural aging.

ATMOSPHERE

The gaseous environment in which the metal being treated is heated for processing. Atmospheres are used to protect from chemical change or to alter the surface chemistry of steel through the addition or removal of carbon, nitrogen, hydrogen, and oxygen and to add certain metallic elements such as chromium, silicon, sulphur, etc.

AUSTEMPERING

A heat treatment process that consists of quenching a ferrous alloy from a temperature above the critical range in a medium having aa rate of heat extraction (usually molten salt) sufficiently high to prevent the formation of high-temperature transformation products; and in maintaining the alloy, until transformation is complete, at a temperature below that of pearlite and above that of martensite formation.

AUSTENITE

Austenite is the name given any solid solution in which gamma iron is the solvent. Austenite is a structure name and means nothing as to composition. Austenite is the structure from which all quenching heat treatments must start, which is characterized by a face-centered cubic structure.

AUSTENITIZING

The process of forming austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing).

AUSTENITIZING TEMPERATURE

The temperature at which a steel is substantially all austenite.

B

BAINITE

The product formed when austenite transforms between 450°F and 900°F. Bainite is an acicular aggregate of ferrite and carbide and varies in hardness between Rc 30 and Rc 55.

BAKING

(1)Heating to a low temperature to remove gases. (2)Curing or hardening surface coatings such as paints by exposure to heat. (3)Heating to drive off moisture, as in the baking of sand cores after molding.

BARK

An older term used to describe the decarburized skin that develops on steel bars heated in a non-protective atmosphere.

BLASTING

A pressurised stream of some materials (Glass, plastic, metal, etc) applied on a surface to clean and/or roughen. It can be, depending on the media, abrasive an non-abrasive.

BLUE ANNEALING

Heating hot rolled ferrous sheet in an open furnace to a temperature within the transformation range and then cooling in air, in order to soften the metal. The formation of bluish oxide on the surface is incidental.

BLUING

Subjecting the scale-free surface of a ferrous alloy to the action of air, steam, or other agents at suitable temperature, thus forming a thin blue film of oxide and improving the appearance and resistance to corrosion. Note: This term is ordinarily applied to sheet, strip, or finished parts. It is used also to denote the heating of springs after fabrication to improve their properties.

BOND STRENGTH

The strength of the adhesion between the coating and the substrate. A number of test methods are in use to measure the bond strength of coatings.

BORONISING

The diffusion of boron into the surface of a component (usually steel) by a high temperature (approx 900oC) gas or pack process. Produces hard phases within the surface (Typically 100µ deep).

BRIGHT ANNEALING

Annealing work in a protective atmosphere so that there is no discoloration as the result of heating. In some atmospheres, oxides may be reduced.

BRITISH THERMAL UNIT (BTU)

The quantity of heat required to raise the temperature of one pound of water 1ºF at or near its point of maximum density; aa unit of heat measurement

BRITTLE TEMPERING RANGE

Some hardened steels show an increase in brittleness when tempering in the range of about 450°F to 700°F even though some tempering causes some softening.

C

CARBIDE

A compound of carbon with one or more metallic elements

CARBONITRIDING

A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and, by diffusion, create a concentration gradient. The process is completed by cooling at a rate that produces the desired properties in the workpiece.

CARBON STEEL

Steel which is essentially iron plus carbon with no intentionally added alloy. Also known as ordinary steel, straight carbon steel, or plain carbon steel.

CARBURIZING

Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature usually above Ac3, in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing temperature or by cooling to room temperature, then reaustenitizing and quenching

CASE

The surface layer of a steel whose composition has been changed by the addition of carbon, nitrogen, chromium, or other material at high temperature.

CASE HARDENING

A generic term covering several processes applicable to steel that change the chemical composition of the surface layer by absorption of carbon nitrogen, or a mixture of the two and, by diffusion, create a concentration gradient. The processes commonly used are carburizing and quench hardening; cyaniding; nitriding and carbonitriding. The use of the applicable specific process name is preferred.

CEMENTITE

The common name for iron carbide, Fe3C, the chemical combination of iron and carbon.

CHEMICAL VAPOUR DEPOSITION (CVD)

The deposition of a coating by means of a chemical reaction in gases in a chamber producing components which deposit on and adhere to the substrate.

CHROMATING

Chromate conversion is a process which completely degreases and removes all traces of the oxide film, replacing it by immersion (a rinse) with chromate coating which can then be painted. It is used as a post-treatment for cadmium, zinc and aluminium coatings

CHROMISING

High temperature (approx 900oC) pack or gaseous diffusion of chromium into the surface of a component to enhance high temperature corrosion and oxidation resistance.

COATING

The application of a thin (generally less than 1mm) layer of material onto the surface of a substrate.

COLD WORKING

Plastic deformation of a metal at a temperature low enough so that recrystallization does not occur during cooling.

CONTROLLED COOLING

Cooling ffrom an elevated temperature process in a predetermined manner to achieve specific properties.

CONTROL THERMOCOUPLE

A thermocouple installed within the furnace volume which is used to control the heat input to the working zone.

CONTROLLED ATMOSPHERIC FURNACE

Heat Treatment Furnace used for heat treatment of tool steels where the atmosphere is generated outside the furnace, and introduced into the heating chamber in such a way as to allow positive control. One of the distinguishing features of this furnace is that the moisture content of the atmosphere is controllable. The presence of water vapor in the furnace will have a profound effect on both the tendency for decarburization and scaling. These atmospheres are almost always produced by endothermic generators.

CORE

The interior part of a steel whose composition has not been changed in a case hardening operation.

CORRECTION FACTOR

Correction factors are used to adjust the readings of thermocouples, which have some degree of error, to the actual temperature. The procedures must clearly state how to calculate and use correction factors. The Supplier is allowed to extrapolate correction factors but ONLY for type ‘S’, this exception is for NO other type T/C. The Supplier is NOT required to round correction factors of wire used for tests or load couples.

CORROSION

Chemical or electrochemical reaction between a metal and the local environment whether wet or dry which results in deterioration in the properties of the metal.

CREEP

The flow or plastic deformation of metal held for long periods of time at stresses lower than their normal yield strength.

CRITICAL COOLING RATE

The rate of continuous cooling required preventing undesirable transformation. For steel, it is the minimum rate at which austenite must be continuously cooled to suppress transformations above the Ms temperature.

CRITICAL POINT

A temperature point at which a structure change either starts, is completed, or both when a material is being heated or cooled.

CRITICAL RANGE

The temperature range between an upper and lower critical point for a given material.

CRITICAL TEMPERATURE

That temperature, during heating, at which a phase transformation takes place and austenite is formed. Same as critical point or transformation temperature.

D

DECARBURIZING

The process (usually unintentional) of removing carbon from the surface of a steel, usually at high temperature, when in contact with certain types of atmosphere.

DEFORMATION

Change in dimensions, as the result of an applied stress

DENSITY

The per unit volume of a substance, usually expressed in grams per cubic centimeter or in pounds per cubic foot.

DIAMOND-LIKE CARBON

A thin carbon-based coating applied by either PVD or PACVD. It has high hardness and low friction.

DIFFUSION

(1) Spreading of a constituent in a gas, liquid, or solid tending to make the composition of all parts uniform (2) The spontaneous movement of atoms or molecules to new site within a material.

DISSOCIATION

The chemical breakdown of a compound into simpler compounds or elements. One of the most common examples is the dissociation of ammonia (NH3) into nitrogen and hydrogen.

DRAW

The common term used interchangeably with Tempering.

E

ELECTROLESS NICKEL

The autocatalytic deposition of nickel/phosphorous and nickel/boron have many useful corrosion and tribo/corrosion applications. Unlike the electrolytic processes, they produce a deposit with completely uniform coverage. In the case of Ni P, deposits around 25 to 50 microns thick with a hardness of about 500Hv is obtained, but thermal ageing at temperatures around 400°C can develop hardness values in excess of 1000Hv.

ELECTROPLATING

The application of a layer of metal onto a substrate in a conducting solution of metal slats.

EMBRITTLEMENT

Reduction in the normal ductility of a metal due to a physical or chemical change. Examples include blue brittleness, hydrogen embrittlement, and temper brittleness.

EQUILIBRIUM DIAGRAM

A graphical representation of the temperature, pressure and composition limits of phase fields in an alloy system as they exist under conditions of complete equilibrium. In metal systems, pressure is usually considered constant.

EQUOTIP HARDNESS TESTER

A portable hardness tester which takes measurements on the surface of metals in "L-values" which read directly from the digital display unit. This tester reports "L-value" hardness by measuring a velocity change when a spring propelled tungsten carbide test tip impacts a metal surface and rebounds therefrom. Conversion curves have been developed for steel which permit the "L-value" to be displayed in the conventional Rockwell, Brinell, Vickers and Shore hardness scales.

EROSION

Removal of material from a surface caused by the flow of particles within a liquid or gas.

EUTECTOID

(1)An isothermal reversible reaction in which a solid solution is converted into two or more intimately mixed solids on cooling, the number of solids formed being the same as the number of components in the system. (2) An alloy having the composition indicated by the eutectoid point on an equilibrium diagram. (3) An alloy structure of intermixed solid constituents formed by a eutectoid reaction.

EXOTHERMIC REACTION OR MATERIAL

Certain materials undergo chemical reactions when heated in an arc or plasma and produce extra heating. This can be useful in improving adhesion of the coating to the substrate. There is also a potential explosive or fire hazard when handling powders which are exothermic.

F

FATIGUE

Failure by progressive fracture caused by repeated applications or reversals of stress.

FERRITE

Ferrite is the name given any solid solution in which alpha iron is the solvent. Ferrite is strictly a structure name and means nothing as to composition.

FERROUS

Metallic materials in which the principal component is iron.

FILE HARDNESS

Hardness as determined by the use of a file of standardized hardness on the assumption that a material that cannot be cut with the file is as hard as, or harder than, the file. Files covering a range of hardness may be employed.

FLAME HARDENING

(Surface hardening) a controlled process consisting of heating a desired area (localized) with an oxyfuel burner(s) to high temperature and then quenching to produce a desired hardness. Several types of flame hardening are available: spot/stationary hardening, progressive, progressive spinning, and drop quench.

FULL ANNEALING

An imprecise term that denotes an annealing cycle to produce minimum strength and hardness. For the term to be meaningful, the composition and starting condition of the material and the time-temperature cycle used must be stated.

G

GALLING

Damage to the surfaces of materials sliding in contact with each other, usually caused by the localised welding together of high spots. Common for materials like stainless steel, aluminium alloys and titanium.

GALVANISING

A hot dip process for deposition of zinc for galvanic corrosion protection of steel.

GRAIN

A particle of metal or alloy in which the space lattice pattern is continuous except for small irregularities.

GRAIN GROWTH

Growth of some grains at the expense of others, resulting in an overall increase in average grain size.

GRAIN SIZE

For metals, a measure of the areas or volumes of grains in a polycrystalline materials, usually expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, the grain size refers to that of the matrix unless otherwise specified. Grain sizes are reported in terms of number of grains per unit area or volume, average diameter, or as a grain-size number derived from area measurements.

GRAPHITE

One of the crystal forms of carbon; also thee uncombined carbon.

H

HARDENABILITY

The fundamental characteristic of a steel which determines the ease of preventing the transformation of austenite to anything else but martensite during the quench.

HARDNESS

The property of a substance determined by its ability to resist abrasion or indentation by another substance. For metals, hardness is usually defined in terms of the size of an impression made by a standard indenter. (Brinell, Rockwell, etc.)

HARD CHROME PLATING

The electrolytic deposition of chromium to form a very hard (1000Hv), tough coating with good wear resistance. The structure is micro-cracked.

HARDENING

Increasing hardness by suitable treatment, usually involving heating and cooling. When applicable, the following more specific terms should be used: age hardening, case hardening, flame hardening, induction hardening, precipitation hardening and quench hardening.

HARDNESS TEST

A test designed to assess the resistance to penetration from a load. The surface is indented under a defined load and the depth of penetration is observed.

HEAT SINK

A mass of material equivalent to the heat transfer characteristics of the limiting section thickness of the part being heat treated. A thermocouple surrounded by the heat sink is expected to represent the temperature of the limiting section thickness of the part.

HEAT SINK (DURING TUS)

Use of heat sinks MUST be covered specifically in procedures. The thickness of a heat sink should not exceed the thickness of the thinnest part of material that will be processed in the furnace.

HEAT TREATMENT

Heating and cooling a solid metal or alloy in such a way as to obtain desired conditions or properties. Heating for the sole purpose of hot working is excluded from the meaning of this definition.

HOMOGENIZING

An annealing treatment at fairly high temperature designed to eliminate or reduce chemical segregation.

HYDROGEN EMBRITTLEMENT

The brittleness induced in steel by the absorption of hydrogen, most commonly from a pickling or plating operation.

I

INCLUSIONS

Particles of impurities (usually oxides, sulphides, silicates and such) which separate from the liquid steel and are mechanically held during solidification. In some grades of steel, inclusions are made intentionally high to aid machinability.

INDUCTION HARDENING

A form of hardening in which the heating is done by induced electrical current. The localised surface heating of a medium carbon steel by an induction coil so that the temperature is raised above 900oC. The part is quenched (or self-quenches by virtue of the remaining cool bulk of the component) and tempered to produce a hard martensitic structure at the surface.

ION-IMPLANTATION

A process in which a beam of positive ions is projected towards and into the surface. It is carried out in partial vacuum and the ions diffuse into the surface layer of the substrate. Typically this is carried out with nitrogen giving a nitrided effect.

INTERMEDIATE TEMPERATURE

A temperature that the part must be cooled below or heated above prior to continuing the next sequence stage of the heat treat process.

INTERRUPTED QUENCH

Stopping the cooling cycle at a predetermined temperature and holding at this temperature for a specific time before cooling to room temperature. Usually done to minimize the likelihood of cracking, or to produce a particular structure in the part.

ISOTHERMAL ANNEALING

Austenitizing a ferrous alloy and then cooling to and holding at a temperature at which austenite transforms to a relatively soft ferrite carbide aggregate.

ISOTHERMAL TRANSFORMATION

A change in phase at any constant temperature.

ISOTHERMAL TREATMENT

A type of treatment in which a part is quenched rapidly down to a given temperature, then held at that temperature until all transformation is complete.

J

JOMINY TEST

See end-quench hardenability test

L

LASER ALLOYING

The application of a powder to a surface followed by fusing and alloying into the surface via the heat from an impinging laser.

LASER GLAZING

The melting and quenching of a surface to form a fine grained structure or 'glaze'.

LASER HARDENING

The localised surface heating of a medium carbon steel by an incident laser so that the temperature is raised above 900oC. The part is quenched (or self-quenches by virtue of the remaining cool bulk of the component) and tempered to produce a hard martensitic structure at the surface.

LASER WELDING

The application of a powder to a joint followed by melt fusing via the heat from an impinging laser

LEAK UP RATE (LEAK RATE)

A test in which the furnace chamber is evacuated, isolated from the evacuation source, and the leakage determined within the system by observing the pressure rise per unit of time. NOTE: Leak up rate expressed in microns/hours (1 micron= 10-3 torr).

LEMELLAAR STRUCTURE

A constituent microstructure composed of an intimate mixture of platelets of two phases, typically resulting from an eutectoid reaction. The structure of pearlite in the iron carbon system.

LONG JOB AUDIT

Multi step heat treat process which has been completed.

M

MAGNETRON SPUTTERING

See Sputtering. In this PVD process, the sputtering action is enhanced by intense magnetic fields.

MARTEMPERING OR MARQUENCHING

Martempering is a form of interrupted quenching in which the steel is quenched rapidly from its hardening temperature to about 450°F, held at 450°F until the temperature is uniform, then cooled in air to room temperature. Actual hardening does not occur until the air cooling starts and is accomplished with a minimum temperature differential. Martempering is indicated for low to medium alloy steels when distortion may be a problem.

MARTENSITE

The very hard transformation product which forms austenite when a steel is quenched and cooled below about 450°F. Technically, martensite can be considered to be a supersaturated solution of carbon in tetragonal (distorted cubic) iron. Under the microscope it appears as an acicular or needlelike structure. Hardness of martensite will very from Rc 30 to Rc 68 depending on the carbon content.

METAL TEMPERATURE

When called out in a spec or procedure, mandates the use of load thermocouples unless otherwise specified by the prime.

METALLOGRAPHY

Study or science of structures of metals and alloys, particularly visual examination by means of the microscope

MICRON

A linear distance of 0.001 mm

MICROGRAPH

A micrograph is produced when a section of the coating is taken, polished to show the particulate layers and then photographed through a microscope.

MICRO-HARDNESS

Hardness is measured on a microscopic scale using a microhardness tester.

MICCROHARDNESS TEST

That hardness test used to test small parts or micro constituents in metals.

MICROSTRUCTURE

The structure of a metal as reveled at high magnification, usually at 100x and higher.

MIL

One thousandth of an inch (0.001 inch).

N

NICKEL PLATING

The electrolytic deposition of nickel to forma corrosion barrier or to reclaim a worn part. Can also include hard ceramic particles to from a wear resistant composite coating.

NITRIDING

The process of adding nitrogen to the surface of a steel, usually from dissociated ammonia as the source. Nitriding develops a very hard case after a long time at comparatively low temperature, without quenching.

NITROCARBURIZING

Any of several processes in which both nitrogen and carbon are absorbed into the surface layers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create a concentration gradient. Nitrocarburizing is done mainly to provide an antiscuffing surface layer and to improve fatigue resistance. Compare with carbonitriding.

NORMALIZING

Heating a steel to a temperature about 100ºC F above the critical range (Ac3 or Acm) and cooling in still air. This process is used to eliminate all effects of prior processes and to render the part uniform in structure

O

OVERHEATING

Heating a metal or alloy to such a high temperature that its properties are impaired . When the original properties cannot be restored by further heat treating, by mechanical working, or by a combination of working and heat treating, the overheating is known as burning.

OVERTEMPERATURE CONTROL

A furnace system that reduces or halts heat input by the furnace in response to a detected overtemperature condition.

OVERTEMPERATURE THERMOCOUPLE

An independent thermocouple installed in the furnace volume that is used to monitor any Overtemperature occurrence and generate an alarm and/or cut back or shut down heat input.  The purpose for this control is to protect customer parts and the furnace from overheating.

OXIDATION

Chemical reaction between the surface elements and oxygen causing oxides of the elements to be formed.

OXIDISING

The production of a stable oxide layer on a steel component by heating in a controlled atmosphere. Provides corrosion protection and reduced friction.

P

PASSIVATING

The post treatment (usually by chromating) of nickel, cadmium or zinc coatings to reduce their corrosion rates.

PEARLITE

A metastable lamellar aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures above the bainite range.

PHASE
A physically homogeneous and distinct portion of a material system.

PHASE DIAGRAM

A graphical representation of the equilibrium temperature and composition limits of phase fields and phase reactions in an alloy system.

PHYSICAL VAPOUR DEPOSITION (PVD)

A term covering all the vapour deposition processes including Ion plating, It does not include CVD as this is chemical not physical.

PLASMA NITRIDING

Also called Ion nitriding. A vacuum glow discharge technique of nitriding. See Nitriding.

POROSITY

The presence of pores or voids in a coating whether connected or not. Porosity is not the same as pull-out.

PRECIPITATION HARDENING

Hardening caused by the precipitation of a constituent from a supersaturated solid solution. See also age hardening and aging.

PREHEATING

Heating before some further thermal or mechanical treatment. For tool steel, heating to an intermediate temperature immediately before final austenitizing. For some nonferrous alloys, heating to a high temperature for a long time, to homogenize the structure before working. In welding and related processes, heating to an intermediate temperature for a short time immediately before welding, brazing, soldering, cutting, or thermal spraying

PROCESS ANNEANING

Heating a ferrous alloy to a temperature close to, but below, the lower limit of the transformation range and then cooling, in order to soften the alloy for further cold working.

Q

QUALITY CONTROL

All aspects of the control of the heat treatment process including the surface preparation, heat treatment, process control, tests as specified.

QUENCHING

A process of rapid cooling from an elevated temperature by contact with liquids, gases, or solids.

R

RECARBURIZE

(1)To increase the carbon content of molten cast iron or steel by adding carbonaceous material, high carbon pig iron, or a high-carbon alloy. (2) To carburize a metal part to return surface carbon lost in processing also known as carbon restoration.

ROCKWELL HARDNESS TEST

An indentation hardness test based on the depth of penetration of a specified penetrator into the specimen under certain arbitrarily fixed conditions.

ROUND ROBIN

A statistical comparison of hardness test machine operator results on a given hardness test machine (including digital machines) and hardness test block.  Operators should be “blind” to the test block value being used.  Readings should not be rounded.  An individual’s mean shall be within +/-2 sigma of the group mean. If more than one machine is to be evaluated, have one “standard” hardness test machine operator check each machine and compare other hardness test machine operators against the “standard operator”.  Round Robins are also required for microhardness test impressions, IGA/IGO and diffusion coatings.

S

SCALE

The oxide formed on a metal by heating in air or other oxidizing atmosphere.

SECONDARY HARDNESS

The higher hardness developed by certain alloy steels when they are cooled form a tempering operation. This should always be followed by a second tempering operation.

SOAK

The holding time at temperature to assure that all parts aare at required temperature for sufficient time for the metallurgical reaction to occur

SOAK TIME

The time specified on the drawing or material specification is the amount of time the part's heaviest section or furnace temperature, depending on specification, is within the required temperature range. The specified time is a minimum time unless it is tolerance or a range is given.

SOLUTION TREATMENT

Heating an alloy to a suitable temperature, holding at that temperature long enough to cause one or more constituents to enter into solid solution, and then cooling rapidly enough to hold these constituents in solution.

SPHEROIDIZING

A heat treating process used to change all of the carbides in steel to rounded particles, or spheroids. A completely spheroidized structure is the softest and most workable structure for any composition.

SPUTTERING

This is a glow discharge process whereby bombardment of a cathode releases atoms from the surface which then deposit onto a nearby target surface to form a coating.

STABILIZING TREATMENT

(1)Before finishing to final dimensions, repeatedly heating a ferrous or nonferrous part to or slightly above its normal operating temperature and then cooling to room temperature to ensure dimensional stability in service (2)Transforming retained austenite in quenched hardenable steels, usually by cold treatment.(3) heating a solution-treated stabilized grade of austenitice stainless steel to 870 to 900 deg C (1600 to 1650 deg F) to precipitate all carbon as TiC, NbC, or TaC so that sensitization is avoided on subsequent exposure to elevated temperature.

STEEL

An alloy of iron and carbon which may contain other elements in which the carbon content does not exceed about 2.0% and which is malleable at some temperature in the solid state.

STOPPING OFF

(1)Applying a resist.(2) Depositing a metal (copper, for example) in localized areas to prevent carburization, decarburization, or nitriding in those areas.

STRAIN

A measure of the extent to which a body is deformed when it is subjected to a stress.

STRESS

The force per unit area on body that tends to cause it to deform. It is a measure of the internal forces in a body between particles of the material of which it consists as they resist separation, compression, or sliding.

STRESS-CORROSION CRACCKING

Failure by cracking under combined action of corrosion and stress, either external (applied) or internal (residual).

STRESS RELIEVING

A process of reducing residual stresses in a metal object by heating to a temperature below the lower critical and holding for a sufficient time. This temperature may be applied to relieve stresses induced by casting, quenching, normalizing, machining, cold working, or welding.

STRESS RISEERS

Factors, such as sharp change in contour or surface defects, which concentrate stresses locally.

STRESS RESIDUAL

Stress present in a body that is free of external forces or thermal gradients. Stresses may be ccaused by cold working, heat treating, or welding.

SUB-CCRITICCAL ANNEAL

Heat treating to a temperature below that which austenite is formed and above the temperature normally used for stress relieving of the material that is being treated.

SUBSTRATE

The parent or base material to which the coating is applied.

SUPERSATURATED

Metastable solution in which the dissolved material exceeddds the amount the solvent can hold in normal equilibrium at the temperature and under the other conditions that prevail.

SURFACE HARDENING

A generic term covering several processes applicable to a suitable ferrous alloy that produces, by quench hardening only, a surface layer that is harder or more wear resistant than the core. There is no significant alteration of the chemical composition of the surface layer. The processes commonly used are induction hardening, flame hardening, and shell hardening. Use of the applicable specific process name is preferred.

SYSTEM ACCURACY CHECK/TEST OR PROBE CHECK (SAC/SAT)

This is performed to assure the accuracy of the furnace control system in each control zone.  Also used to detect changes in the furnace control system over time.

T

TEMPER

(1)In heat treatment, reheating hardened steel or hardened cast iron to some temperature below the eutectoid temperature for the purpose of decreasing hardness and increasing toughness. The process also is sometimes applied to normalized steel.(2) In tool steels, temper is sometimes used, but inadvisably, to denote the carbon content. (3) In nonferrous alloys and in some ferrous alloys(steels that cannot be hardened by heat treatment), the hardness and strength produced by mechanical or thermal treatment or both, and characterized by a certain structure, mechanical properties, or reduction in area during cold working.

TEMPER BRITTLENESS

Brittleness that results when certain steels are held within, or are cooled slowly through, a certain range of temperature below the transformation range. The brittleness is manifested as an upward shift in ductile-to-brittle transition temperature, but only rarely produces a low value of reduction of area in a smooth-bar tension test of the embrittled material.

TEMPER COLOR

A thin, tightly adhering oxide skin (only a few molecules thick) that forms when steel is tempered at a low temperature, or for a short time, in air or a mildly oxidizing atmosphere. The color, which ranges from straw to blue depending on the thickness of the oxide skin, varies with both tempering time and temperature.

TEMPERATURE UNIFORMITY SURVEY (TUS)

Determination of temperature uniformity of a furnace as a measure of the temperature variation within the working zone.  The size of the working zone defines the number of thermocouples required (see AMS 2750 for guidelines).  Use the values of uniformity from AMS 2750 when not otherwise specified.

TEMPERED MARTENSITE EMBRITTLEMENT

Embrittlement of ultrahigh-strength steels caused by tempering in the temperature range of 205 to 400oC (400 to 750oF); also called 350oC or 500oF embrittlement. Tempered martensite embrittlement is thought to result from the combined effects of cementite precipitation on prior-austenite grain boundaries or interlath boundaries and the segregation of impurities at prior-austenite grain boundaries.

TEMPER EMBRITTLEMENT

Embrittlement of alloy steels caused by holding within or cooling slowly through a temperature range just below the transformation range. Embrittlement is the result of the segregation at grain boundaries of impurities such as arsenic. antimony, phosphorus, and tin; it is usually manifested as an upward shift in ductile-to-brittle transition temperature. Temper embrittlement can be reversed by retempering above the critical temperature range, then cooling rapidly.

TENSILE STRENGTH

A measure of the resistance that a material offers to tensile stress. It is defined as the stress, expressed as the force per unit cross sectional area, required to break it.

THERMAL EMBRITTLEMENT

Intergranular fracture of maraging steels with decreased toughness resulting from improper processing after hot working. Thermal embrittlement occurs upon heating above 1095oC (2000oF) and then slow cooling through the temperature range of 815 to 980oC (1500 to 1800oF), and has been attributed to precipitation of titanium carbides and titanium carbonitrides at austenite grain boundaries during cooling through the critical temperature range.

THERMAL EXPAANSION

The increase in linear dimensions of a material accompanying an increase in temperature.

THERMAL STRESSES

Stresses in metal resulting from non-uniform distribution of temperature.

THERMOCOUPLE

A device for measuring temperatures, consisting of lengths of two dissimilar metals or alloys that are electrically joined at one end and connected to a voltage-measuring instrument at the other end. When one junction is hotter than the other, a thermal electromotive force is produced that is roughly proportional to the difference in temperature between the hot and cold junctions.

TORSION

Strain created in a material by twisting action

TOUGHNESS

Property of absorbing considerable energy before fracture; usually represented by the area under a stress-strain curve, and therefore, involving both ductility and strength.

TRANSFORMATION RANGE OR TRANSFORMATION TEMPERATURE RANGE

The temperature interval within which austenite forms while ferrous alloy are being heated. Also, the temperature interval within which austenite disappears while ferrous alloy are being cooled. The two ranges are distinct sometimes overlapping but never coinciding. The limiting temperatures of the ranges depend on the composition of the alloy and on the rate of change of temperature, particularly during cooling.

V

VACUUM LEVEL

"Higher" or "better" vacuum means "lower" pressure.  Required levels will usually be specified by the drawing or material specification, and unless otherwise stated are maximum pressure levels. For conversion: 1 torr= 1mm Hg = 133 Pascal =1.0x103 microns. For examples, when 1 micron is specified, 0.1 micron is a higher Vacuum or lower pressure

W

VICKERS HARDNESS

An indentation hardness test employing a 136º F diamond pyramid indentor and variable loads enabling the use of one hardness scale ffrom very soft lead to tungsten carbide.

WORK HARDNESS

Hardness developed in metal resulting from cold working.

WORKING ZONE

The volume of the heated region of a furnace which meets the requirements of the furnace survey.  NOTE: All parts or material must be contained in this working zone. Note: Furnaces may have more than one zone.

WORKING INSTRUMENT

As per AMS 2750 one working instrument performs one or more of three functions: recording, controlling and indicating.  These 3 functions may be conducted by one device or by more than one device, but all 3 functions are not required to make up one working instrument.
 
WORKLOAD THERMOCOUPLE

Any thermocouple which is attached to the part or heat sink which is being heat treated.

2.            Critical Points for Fe-C Phase Diagram

Acm, A1, A3, A4.

Same as Aecm, Ae1, Ae3 and Ae4. The temperatures of phase changes at equilibrium.

Accm

In hypereutectoid steel, the temperature at which the solution of cementite in austenite is completed during heating.

Ac1

The temperature at which austenite begins to form during heating.

Ac3

The temperature at which transformation of ferrite to austenite is completed during heating.

Ac4.

The temperature at which austenite transforms to delta ferrite during heating.

Aecm, Ae1, Ae3, A4

Defined under transformation temperature.

Arcm

In hypereutectoid steel, the temperature at which precipitation of cementite starts during cooling

Ar1

The temperature at which transformation of austenite to ferrite or to ferrite plus cementite is completed during cooling.

Ar3

The temperature at which austenite begins to transform to ferrite during cooling.

Ar4

The temperature at which delta ferrite transforms to austenite during cooling.

Ar'

The temperature at which transformation of austenite to pearlite starts during cooling.

Mf

The temperature at which martensite formation on cooling is essentially finished. See transformation temperature for the definition applicable to ferrous alloys.

Ms

The temperature at which martensite starts to form on cooling. See transformation temperature for the definition applicable to ferrous alloys.

 
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