Heat and surface treatments- Terms

AGING – The process of holding metals at room temperature or at a

predetermined temperature for the purpose of increasing their hardness

or strength by precipitation. Aging is also used to increase dimensional

stability in metals such as castings.

AGE HARDENING – Change in the physical properties, e.g., hardness and

strength, that occurs in certain light metals after heat treatment.

ALLOYING OF METAL – The addition of varying proportions of other

elements to a basic metal in order to produce an alloy having specific

properties.

ANODIC TREATMENT – Formation of a protective layer of oxide on

the surface of aluminium and its alloys by electrolytic action, in order

to resist corrosion.

ANNEALING – A heat treatment in which metals are heated and then cooled

very slowly for the purpose of decreasing hardness. Annealing is used to

improve machinability and to remove stresses from weldments, forgings

and castings. Also used to remove stresses resulting from cold working

and to refine and make uniform the microscopic internal structures of

metals.

ANODIZING – To subject a metal to electrolytic action, as takes place at

the anode of a cell, in order to coat it with a protective or decorative

film, used for nonferrous metals.

AUSTEMPERING – A heat treating process consisting of quenching a ferrous

alloy at a temperature above the transformation range in a medium

such as molten lead, the temperature of the quenching medium is maintained below that of pearlite and above that of martensite formation

to produce a tough, hard microstructure.

AUSTENITIZING – The process of forming austenite ( a solid solution of

iron and carbon and sometimes other elements ).

BLACK OXIDE COATING – Coating produced by converting the surface

of iron or steel to black iron oxide having a thickness of about 0.0025

mm.

CADMIUM PLATING – Electroplating process for the application of

cadmium to steel and iron parts to prevent rust.

CALORIZING – Rust proofing process for ferrous metals in which an

aluminium film is formed on the surface of the metal. Means of

protecting iron from oxidation at elevated temperatures.

CARBURIZING – A process that introduces carbon into a heated solid

ferrous alloy by having it in contact with a carbonaceous material.

The metal is held at a temperature above the transformation range for

a period of time. This is generally followed by quenching to produce

a hardened case.

CASE HARDENING – Heating a steel in the presence of a solid, liquid or

gas, rich in carbon, in order to enable the surface to be hardened,

while retaining a tough, ductile core.

CHROMIUM PLATING – Electrolytic deposition of chromium on a metal

surface, as a protection against corrosion, to provide improved wearing

properties, or to build up an undersize part.

CHROMIZING – Similar to carburizing. Low carbon steel parts are packed

with a mixture of alumina and chromium powder and heated in a

hydrogen atmosphere, forming a surface layer of chromized material

of 10 to 20% chromium, according to time and temperature of heating.

COLOURING METAL – Production of a coloured surface on a metal or

alloy by the use of heat or chemical action, or by a combination of the

two.

COSLETTIZING – Rust proofing process in which an iron phosphate skin

is formed on the surfaces of ferrous parts, the skin follows even the

microscopic irregularities, yet is remarkably tough and corrosion

resistant.

DECARBONIZATION – The loss of carbon from the surface of a ferrous

alloy as a result of heating it in the presence of a medium such as

oxygen that reacts with the carbon.

ELECTROLYTIC POLISHING – Method of polishing metals in which

the work forms the anode of an electrical circuit, and is suspended in

a suitable bath of acid.

ELECTROPLATING – Deposition of a metal on a surface by electrolytic

action.

FLAME HARDENING – Process of hardening by which steel or cast iron

is raised to a high temperature by a gas torch flame and then almost

immediately quenched.

GALVANIZING – Rust prevention treatment which consists of coating the

metal (iron or steel) with a fairly thick film of zinc.

HARDENING – Process of increasing the hardness of a ferrous alloy by

austenitizing and quenching, also the process of increasing the hardness

of some stainless steels and non-ferrous alloys by solution heat

treatment and precipitation.

HARD SURFACING – Arc welding a surface layer usually at strategic spots

on a part, using an electrode having a suitable alloy content for the

purpose. Also known as SURFACING and FACING.

HEAT TREATMENT – Operation or combination of operations, involving

the heating and cooling of a metal or alloy in its solid state with the

object of changing the characteristics of the material.

HOT ROLLING – Surface layers of noble metals are often hot rolled (or

inlayed) on less noble metals.

INDUCTION HARDENING – Heating the surface of cast iron or tool

steel by means of electromagnetic currents followed by a quench.

LACQUERING – A protective coat given to an article to prevent the polished

surface from tarnishing, to prevent oxidation or to improve the general

appearance and make the article more pleasing to the eye, and hence

more saleable.

MARTEMPERING – The process of quenching an austenitized ferrous alloy

to a temperature just above or near the M’s point and maintaining until

the temperature throughout the part is uniform. The alloy is then allowed

to cool slowly in air through the range of martensitic formation.

METALLIZING – Metal spraying process in which the coating metal is

melted (either in a gas flame or in a separate melting pot), then

atomized by an air blast and deposited in atomized form on the surface

to be coated.

NEGRADIZING – Rust proofing process in which a ferrosoferric oxide

surface is produced on steel or iron.

NICKEL PLATING – Deposition of nickel on a metal by electrolytic action

to provide a protective surface or to build up the surface of a worn or

undersize part.

NITRIDING – A process of case hardening in which a special ferrous alloy

is heated in an atmosphere of ammonia or is in contact with any other

nitrogenous material. By this, surface hardening is achieved by the

absorption of nitrogen without quenching.

NORMALIZING – Process applied to iron base alloys, such as steel, to

refine the grain structure and remove the effects of previous processing

for example hot rolling.

ORGANIC FINISHING – Coating a surface with a continuous film of an

organic material for protecting the surface from corrosive influences,

for enhancing the appearance or a combination of both.

PARKERIZING – A coslettizing process in which a patented mixture of

iron and manganese phosphates is used in solution to provide a rust

proof surface on iron and steel parts.

PHOSPHATE COATING – Coating produced by converting the surface

of iron or steel parts to insoluble phosphate, such as iron phosphate

or zinc iron phosphate.

PICKLING – Treatment of objects with an acid solution to remove all oxide,

scale or dirt. Usually done to clean and brighten the surface, although

sometimes used for etching.

POWDER COATING – Surface coating of almost any metal or alloy applied

to another by powder method.

PRECIPITATION HARDENING – A process of hardening an alloy by

heat treatment in which a constituent precipitates from a supersaturated solid solution while at room temperature or at some slightly elevated

temperature.

QUENCHING – Rapid cooling of a metal in a bath of fluid during heat

treatment after it has been heated to a given temperature, thus trapping

the molecules of the metal in the desired structure.

RECRYSTALLIZATION – A process in which the distorted grain structure

of metals that are subjected to mechanical deformation is replaced by

a new strain free grain structure during annealing.

RUST PROOFING – Treatment of iron and steel parts to render them

resistant to rust, implies a more permanent form of protection.

SHERADIZING – Heat treatment process in which zinc dust is used for

producing a rust proof surface on ferrous metals. It derives its title from

the name of the inventor SHERARD OSBORN COWPER COLES.

SILICONIZING – Process in which iron and steel parts are impregnated

with silicon for improving the surface resistance to corrosion, heat

and wear.

SOAKING – A prolonged heating of a metal at a predetermined temperature

to create a uniform temperature throughout its mass.

SOLUTION HEAT TREATMENT – A process in which an alloy is heated

to a predetermined temperature far a length of time that is suitable to

allow a certain constituent to enter into solid solution. The alloy is

then cooled quickly to hold the constituent in solution, causing the

metal to be in an unstable supersaturated condition. This condition is

often followed by age hardening.

STRAIN HARDENING – An increase in hardness and strength of a metal

that has been deformed by cold working or at temperatures lower

than the recrystallization range.

SUBZERO HEAT TREATMENT – Method of heat treatment of steel,

introducing a cooling period or periods at a temperature well below

freezing point, the object being to ensure complete transformation of

austenite to martensite.

TEMPERING STEEL – Heat treatment designed to relieve the stresses and

brittleness set up in carbon or alloy steel tools and other parts after

hardening and to restore the required degree of toughness and ductility

to hardened steel. 

TINNING – Application of a layer of tin to the surface of another metal,

either as a protection against corrosion or as a preliminary to soldering.

WORK HARDENING – Phenomena in which the grains become distorted

and elongated in the direction of working (rolling). This process, also

called STRAIN HARDENING, hardens and strengthens metals but

reduces their ductility.

ZINC PLATING – Electroplating process for the deposition of zinc on

metallic surfaces.