Technical information

To compare different methods of measuring hardness, Dominial has a hardness comparison table available for you.
We can send these to you at your request.

If you are interested, call / mail us or visit us and we are happy to help.


or call: 0104345588

When nitrating the treatment does not so much determine the hardness, but more the type of material.

For example, the final hardnesses differ with the same nitrating treatment.

To gain insight into which material gets which hardness during nitration, we have a table available for this.

If you are interested, call / mail us or feel free to drop by and we are happy to help.


Telephone number: 0104345588

Nitrate Carbonate
lower treatment temperature
high treatment temperature (900-950°C)
lower layer thickness
larger layer thickness (0,5-4mm)
hardly any distortion Deformation (finishing or milling required)
hardness depending on the chosen material

e.g. 1.8505 becomes 1050 Hv (70 hrc) & 1.7225 becomes 700Hv

maximum hardness 63hrc
no after treatment extra heat treatment required (tempering)
low application speed (0.01 mm per hour) high application speed (0.1-0.2 mm per hour)
low pressure load with relatively high speeds high pressure load with low speeds

Hardening technical terms

Alphabetical overview of technical terms and process names from the hardening world.

Various technical terms and concepts as used in the heat treatment of tool steel. Some are not directly related to this, but are included because the tool maker may deal with it sideways.

Deter – cool at high speed in water or oil.

AUSTENITE – structure of steel at curing temperature, so just before startle (exception is stainless steel).

AUSTENITIZE – bring to a curing temperature and keep this temperature for a certain time.
BAINITE HARDEN – after austenitizing, cool in a warm medium of approx. 240 – 350 ºC and then keep the workpieces at this temperature for a long time (60 – 180 minutes). Then cool further in the air to room temperature, with the aim of achieving maximum toughness. Tempering is no longer necessary after this.
PROTECTED HARDENING – In ovens equipped with a retort, the workpiece is hardened under a protective gas atmosphere, so that the surface is not affected. Instead of inert gases, so-called active gases can also be supplied with which, for example, it can be nitrated or carbonated.
CARBONING – (also called setting-hardening or cementation), low-carbon steel is diffused into the skin at approx. 900 ºC carbon (through a gas, powder or salt). After rapid cooling, a hard layer with a thickness of up to approx. 3 mm is formed.
CARBONITRATION – absorption of both carbon and nitrogen in the steel, where carbon absorption dominates. The working temperature is approx. 870ºC and a layer thickness of approx. 0.2 mm is quickly obtained

CEmENTITE – connection between iron and carbon. Many elements can bond with carbon, however a limited number form so-called carbides, the name of which is reserved for compounds of carbon with metals (eg chromium carbides, vanadium carbides, etc.).

DEEP COOLING – transfer steel immediately after hardening into, for example, liquid nitrogen to achieve the most complete transformation of austenite into martensite.

FERRIET – soft iron crystals

FERRITRATION – Nitrocarburizing in a whirlpool bath oven

GAS NITRATION – only nitrogen uptake to a depth of approx. 0.5 mm, the process takes a long time and can only be used with special nitriding samples.

STEPPED CURING – After austenitizing, cool in a warm medium of approx. 180-200 ° C, let it warm for a short time (approx. 5-15 minutes) and then allow to cool in air. After this still has to be tempered. The aim of this method is: minimal deformation and avoidance of crack risks.

HARDENING – austenitizing and cooling at such a speed that hardness increases in a large part of the workpiece due to martensite formation.

CURING DEPTH – depending on the alloy, workpiece size and cooling medium, steel hardens to the core or to a certain depth. The curing depth is determined using the Jominy test.

INDUCTION HARDENING – via a current coil, due to the changing magnetic field and the resistance of the steel, heat is generated and the steel can be hardened to a certain depth below the surface (roughly from 1 to 5 mm). This process is suitable for relatively low curing depths.

CHAMBER OVENS – gas or electrically heated. These oven types are widely used in tool shops, annealing companies and many other industries. CARBON – indispensable element required to harden steel. The soft carbon (graphite) is not present as such in the steel, but has combined with the iron (ferrite) present to form iron carbide.

AIR CIRCULATION OVENS – equipped with a fan to ensure good heat transfer even at lower temperatures. Temperature range approx. 50 – 650 ºC.

LEDEBURITE – a surplus of carbon that is present outside the cementite as so-called double or complex carbides. Ledeburite is difficult to dissolve and very hard.

MARTENSITE – structure of steel after it has hardened.

NITROCARBONING – incorporation of both nitrogen and carbon into the steel, with nitrogen uptake dominating. Many variants are possible here. These processes are referred to as salt bath nitriding, soft nitriding, powder nitriding, nikotrating, tenifering, cyanating, ferriding, etc.

NITRATE – allow nitrogen to diffuse into the surface of steel, during a annealing process (approx. 500-550 ºC) from a nitrogen-emitting medium, creating a thin (in micron range), particularly wear-resistant layer.

CARBON – burning the carbon from the steel surface in a red-hot state, resulting in, among other things, an unsightly appearance (flaking) and a hardness that is too low. Therefore, the air present must be kept as far away from the steel surface as possible, for example by heating under shielding gas or under vacuum.

CLEARED – the stresses created by curing are relieved by heating for another half to two hours at about 200-300 ºC with little loss of hardness.

CARBING – see under Carbonation.

HEATING – heating until the desired temperature in the outer layer is reached.

PERLITE – starting structure of mild steel, consisting of Ferrite and iron / carbon carbides (the so-called Cementite).

POLYMERS – synthetic deterrents with adjustable cooling speed.

RESTAUSTENITE – During curing, not all austenite is converted to hard martensite (depending on alloy and chosen curing temperature), leaving a certain percentage of residual austenite.

SHAFT OVENS – Cylindrical section ovens that are often recessed into the floor. Specifically suitable for heat treating long and rod-shaped workpieces.

THERMOCHEMIC HARDENING PROCESSES – collective term for processes in which other elements diffuse from the outside into the steel surface e.g. nitriding, carburizing, inchromer etc.

VACUUM HARDEN – The workpiece is heated in an oven with vacuum retort. Since the air is pumped out of the retort, the surface remains completely blank. This environmentally friendly curing method is increasingly used and after the workpiece has been austenitized under vacuum, it is quenched by means of nitrogen under high pressure. This achieves speeds with which oil cooling can be replaced. Active gases can also be added for carbonation or nitration.

FINISHING – Highly tempered after curing (at approx. 500 – 630 ºC), resulting in a “tough-hard” fine breeding structure. The process finds a huge area of ​​application in machine and engine construction. AGING – expose hardened steel to temperatures up to approx. 120 ºC. Cool down in cold water in the meantime to avoid as much as possible slow changes in the fine structure, which could lead to small dimensional changes in the long term (eg calibers). A more powerful effect is achieved with deep cooling.

FLAME HARDENING – where the steel surface to a depth ranging from 2 to 10 mm is quickly heated with a burner and immediately quenched with water sprinklers. The process is usually used in machine building with lower alloy steels such as C45 or 1.7033. Edge knives and malleable or nodular cast iron can also be flame- or induction-hardened.

SHAPE CHANGE (warping) – change in the size or shape of a workpiece by heat treatment.

SWIRL DEVICES – comparable in heat transfer to salt baths. Instead of liquid salt, aluminum oxide powder is used, which is flushed with compressed air after it has been heated. The powder starts to move (starts to swirl) and then behaves like a liquid. It is an environmentally friendly process and it is also possible to supply active gases with which it is possible to carbonate or nitrocarbonate.

SALT BATH OVENS – where the steel is preheated in a hot air oven at approx. 500 ºC in a crucible with a special liquid salt, after which it is brought to a curing temperature. Particularly intensive and accurate heat transfer is achieved due to the direct contact with the salt and no decarburization can take place, even during quenching. A protective salt film always remains on the workpiece. The medium can be well regulated and provide both an inert and a carburizing atmosphere.

SILVER STEEL – has nothing to do with silver, but is on high-gloss ground rod material from approx. 1 to 30 mm round, which is used for the production of special drills, shafts and small parts in instrument and equipment construction. Usually available in two grades: unalloyed with approx. 1% C (eg 1.1545) and alloyed as 1.2210