AIR CIRCULATION FURNACES: Provide with a ventilator to guarantee a good heat transfer, also at lower temperatures. 
AGEING: Exposing hardened steel for a long time to a temperature below approx. 120 °C. Meanwhile cooling in cold water, to avoid as much as possible slow changes in the fine structure that in the long run may originate small size changes (e.g. diameters). A stronger effect is achieved with low-temperature cooling.
AUSTENITE: Structure of steel before it can be hardened. 

AUSTENITIZE: Bring at hardening temperature and maintain this temperature during a determined period.
BAINITIC HARDENING: After austenising, cool down in a warm medium of approx. 240 - 350 °C and keep the work pieces then for a long period at this temperature. Followed by cooling it further at room temperature with the aim to reach a maximum toughness. Afterwards tempering is no longer necessary.
BELL-TYPE FURNACES: Used to harden/anneal work pieces on a fixed floor, later placing the bell over them. 
Examples are the hard annealing of rolls of wire and strip.
BELT CONVEYOR FURNACE: Long furnaces where the work pieces are transported (mass production) by chains, rolls or pushing them on through the furnace. Generally a quench bath is integrated in the line, whereupon the work piece leaves the installation by means of a second transporter.

CARBON (C): Indispensable element necessary to harden steel. The soft carbon (graphite) is not present as such in steel, yet it has joined the present iron (ferrite) to become iron carbide.
CARBONITRIDING: Incorporation of both carbon and nitrogen in steel, where the incorporation of nitrogen dominates. Within a short period the layer thickness becomes approx. 0.2 mm.
CARBURIZING: (also known as to case-harden or cementing). On the outside of steel with low carbon contents, powder or salt C (carbon) atoms are comes atoms are diffused in the skin by means of a gas. After fast cooling a hard layer is originated with a thickness to approx. 3 mm.

CEMENTITE: Compound of iron and carbon. Examples are: chromium carbides, vanadium carbides, etc.
CHAMBER FURNACES: Gas or electrical heated. These types of furnaces are commonly used in tool and die shops, annealing companies and many other branches of the industry.
DECARBONIZING: Burning of the carbon from the steel surface in red-hot state, in order to originate, among other things, an ugly appearance and an insufficient hardness. For this reason the air present must be kept away, by heating under protection gas or vacuum, from the steel surface.
DEFORMATION: (warping) Changing the size or the form of a work piece through heat treatment.
DIFFUSION: Moving particles (atoms) of one material to the other and in the opposite way, so that during HT-soldering a gradual transfer arises in the material composition. This phenomenon also takes place at thermochemical processes.
FERRITE: Soft iron crystals.
FLAME HARDENING: The steel surface is quickly heated with a blowpipe to a depth varying from 2 to 10 mm and immediately.
GAS NITRIDING Incorporation of nitrogen to a depth of approx. 0.6 mm. The process lasts long and is only applicable to special nitrated steels.
HARDENING: Austenitizing and cooling at such speed that in a large part of the work piece a hardness increase occurs through formation of martensite.
HARDENING AND TEMPERING: After hardening high tempering at > 500 °C, so that a ‘tough hard’ fine refined structure is originated. The process is widely applied in machine and motor construction.
HARDNESS PENETRATION DEPTH: Depending on the alloy, the work piece dimension and cooling medium, steel can be hardened up to its core or to a certain depth. The achieved hardness penetration depth is determined by the Jominy test.
HD BRAZING®: A form of high temperature soldering as a result of which a very high-quality compound is originated which can be applied in a high vacuum environment. 

HT BRAZING: This concerns all soldering operations from a temperature of approx. 800 C.
INDUCTION HARDENING: By means of a current coil heat is developed through the changing magnetic field and the resistance of steel. This steel can be hardened to a certain depth under the surface (roughly speaking from 1 to 5 mm). This process is used at local hardening.
ISOTHERMAL HARDENING: After austenitizing cooling in a warm medium, leaving a short time at temperature and then cooling in air. Next, tempering is still necessary. The objective of this method is:  minimum distortion and avoiding crack risks.

ION NITRIDING: (also called ion nitriding) In this case the nitride gas becomes conductive and the work piece operates in a retort as a cathode. A plasma of nitrogen ions is originated that ‘bomb’ the surface. In this way it is also possible to carburizing (plasma carbonizing).
LEDEBURITE: A surplus to carbon that except the cementite, is present as so-called double or complex carbides. Ledeburite is difficult to dissolve and very hard.
MAGNETIC ANNEALING: Influencing the magnetic properties (mostly diminishing) of the magnetic properties, by means of an annealing process in steel. 
MARTENSITE: Structure of steel after being hardened.

NITRO-CARBONIZING: Incorporation of both carbon and nitrogen in steel, where the incorporation of nitrogen dominates. In this case a lot of variations are possible. 

NITROTEC®: Nitro-carbonizing of non- or low-alloyed material, followed by oxidation treatment. This originates a hard wear-resistant surface with corrosion-resistant properties. 
PATENTING: Heat treatment of wire and strip to perform a favorable structure before the cold drawing treatment.

PERLITE: Reference structure of steel in soft state, consisting of ferrite and iron/nitrogen carbides (the so-called cementite).
PIT FURNACES: Furnaces with cylindrical cross section that are often flush mounted into the floor. These are specifically suitable for heat treatment of long and bar-shaped work pieces.

POLYMERING: Synthetic cooling agent with adjustable cooling speed.

PRECIPITATION HARDENING: Precipitation hardening is applied to alloys with one or multiple elements that are hard to dissolve in the matrix. These are often stainless steel variants.
PROTECTED HARDENING: In furnaces provided with a retort, the work piece is hardened under protecting gaseous atmosphere, as a result of which the surface is not affected. Instead of inert gasses also so-called active gasses can be added, with which gas nitriding or carburizing is possible.
QUENCHING: Fast cooling down in water or oil.
REDUCING: Under the influence of a vacuum environment of gas (often hydrogen), the surface of a work piece becomes white.

RESIDUAL AUSTENITE: During the hardening not all austenite is transformed into hard martensite so that a certain percentage of residual austenite remains.
SOLUTION ANNEALING: Dissolve annealing is used to dissolve possible present secretions.
STRESS RELIEVING: Minimizing the internal stress by means of annealing. This stress is introduced during the steel production or machining.

STAINIHARD®: A nitro-carbonizing process for austenitic stainless steel.
SURFACE ANNEALING: Flattening (more) of a work piece by means of an annealing process. Therefore weights are installed on the work piece during the annealing process. 
SUB ZERO COOLING: Transfer steel immediately after hardening in, for example, liquid nitrogen in order to reach a transformation as complete as possible of austenite into martensite. To limit residual austenite with the aim of minimizing the increase of the work piece in time. 
TEMPERING: The tensions which are originated by hardening, are removed by again heating with a small loss of hardness.

THERMOCHEMICAL HARDENING PROCESSES: Collective name for processes where from the outside other elements are diffused in the steel surface, for example: gas nitriding, carburizing, chromium coating, etc.
VACUUM HARDENING: The work piece is heated in a furnace with a vacuum environment. In this way the surface remains completely white. After the work piece is austenitised under vacuum, it is high-pressure hardened by means of nitrogen. Cooling speeds are reached that may substitute oil cooling. 
VAPOR DEPOSITION: Also indicated as CVD (=Chemical Vapor Deposition) and consists of covering material with extraordinary wear-resistant coating of titanium carbide (TiC) or titanium nitride (TiN). A small film of 2 - 20 microns is vapor deposited in a reactor vessel at temperatures between 800 and 1050 °C. Different variations are possible such as chromium and tungsten carbides, nitrides and borides. Frequently the hardening can be combined with the CVD treatment, where in general air-hardening steel steel is applied. In the PVD method (= Physical Vapor Deposition), vapor deposition is performed at lower temperatures (between 80 and 150 °C). The layer thickness is 2 - 5 microns. This method is frequently applied for the coating of drills, mills and reamers, which are mostly hardened in advance.
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