Small lexicon

Technical Chinese

Foreword

Different and unclear concepts of heat treatment terms often lead to misunderstandings, uncertainties and sometimes even to unwanted component properties. For example, what is meant by the term case hardening depth (CHD) after a case hardening process?

A clear definition of CHD can be found in DIN EN 10052, which defines the terms used in the heat treatment of ferrous materials. Our small lexicon "The common language" describes terms based on this standard. It is intended to help avoid misunderstandings and errors. The selection of terms is based on our practical experience. We will be happy to add more at your suggestion.

Lexicon from A - Z

Cooling down

The temperature of a workpiece is lowered, which can be done in one or more steps. The means of cooling should be specified, e.g. oven, air, gas, oil, water.

Quenching

Process in which cooling takes place faster than in still air. The conditions under which quenching takes place should be specified precisely, e.g. quenching in gas (gas quenching), quenching in oil (oil quenching), quenching in water (water quenching).

Quenching temperature

Temperature at which quenching begins.

Tempering

Process that usually takes place after hardening or other heat treatment in order to achieve the required property values. Heating once or several times to a specified temperature, which is usually <700°C, holding at this temperature and subsequent appropriate cooling are part of this process. Tempering generally leads to a decrease in hardness, but in some cases to an increase in hardness.

Carburizing

Enrichment of the surface layer of a workpiece with carbon by thermochemical treatment in the austenitic state. The means by which carburizing is carried out should be specified, e.g. carburizing in gas (gas carburizing), carburizing in plasma (plasma carburizing).

Austenite

γ solid solution - Solid solution (solid solution) of one or more elements in γ-iron, which is in a stable state between 911 and 1392°C in pure iron. Its crystal structure is face-centered cubic.

Austenitizing

Heat treatment step in which the material is brought to an appropriate temperature to achieve austenite.

Austenization temperature

Temperature at which the component is held during austenization.

Bainite

A structural component that forms between the temperature ranges of pearlite and martensite formation. In this component, ferrite is supersaturated with carbon, whereby the carbon is partially precipitated as carbides.

Bainitize

Isothermal transformation in the bainite stage. This process consists of austenitizing and then quenching to a temperature above the martensite start temperature (Ms) at such a rate as to avoid any formation of ferrite and pearlite, and holding at this temperature to transform the austenite or completely into bainite. Subsequent cooling to room temperature is not subject to any special regulations.

Carbonitriding

Enrichment of the surface layer of a workpiece with carbon and nitrogen by a thermochemical treatment above 723°C. It should indicate the medium in which carbonitriding is carried out, e.g. carbonitriding in gas (gas carbonitriding), carbonitriding in a salt bath (salt bath carbonitriding).

Diffusion annealing

is a special annealing process to reduce inhomogeneities in the material. It is also known as solution or homogenization annealing.

Direct hardening

Hardening is carried out by direct quenching from the carburizing or carbonitriding temperature. If necessary, cooling to the most suitable temperature for hardening is carried out first.

Double hardening

Direct hardening is followed by a second hardening at a lower temperature.

Through hardening

Hardening in which martensite is formed up to the core of the component.

Warm through

Second stage of heating a component in which the required temperature is reached across the entire cross-section.

Single hardening

Hardening takes place after cooling from the carburizing or carbonitriding temperature to room temperature.

Case hardening

Process consisting of carburizing or carbonitriding followed by hardening.

Case hardening depth (CHD)

The CHD - Case Hardening Depth is the vertical distance between the surface and the layer whose Vickers hardness is HV1 = 550. Other test forces and limit values may be applied by agreement.

Heating

Process by which a workpiece is heated (temperature at the edge is reached) and through-heated (temperature in the core is also reached) to the specified temperature across the entire cross-section.

Ferrite

Solid solution (solid solution) of one or more elements in α-iron, which is in a stable state at pure iron below 911°C. Its crystal structure is body-centered cubic.

Annealing

Describes a process in which the material is heated to a certain temperature, held at this temperature and then cooled.

Hardening

Process consisting of austenitizing and quenching, in which the transformation of austenite into martensite and possibly into bainite results in an increase in hardness.

Hold

Section of a temperature-time sequence in which a constant temperature is present. It must be specified which temperature is meant, e.g. that of the oven, the workpiece surface or the entire cross-section.

Induction hardening

Partial heating of the workpiece by means of electromagnetic induction using a medium or high-frequency electric field with subsequent quenching. Induction hardening is preferably used for heat-treatable steels.

Martensite

It is formed by a diffusionless transformation of austenite. As with ferrite, the crystal structure is body-centered cubic. However, in contrast to ferrite, it is supersaturated with carbon. This results, among other things, in the well-known increase in hardness.

Martinsitstart temperature (Ms)

Temperature at which martensite formation begins (starting with cooling).

Low pressure carburizing (LPC)

Carburizing in a vacuum furnace at a pressure below atmospheric pressure.

Nitriding

Enrichment of the surface layer of a component with nitrogen through thermochemical treatment. If significant amounts of oxygen are added to the agent, this is referred to as oxynitriding. The medium in which nitriding is carried out should be specified, e.g. nitriding in gas (gas nitriding), nitriding in plasma (plasma nitriding).

Nitriding hardness depth (NHD)

The NHD - Nitriding Hardness Depth is the vertical distance from the surface of a nitrided or nitrocarburized workpiece to the point at which the hardness corresponds to a specified hardness limit (GH). The hardness limit (GH) is usually defined as Vickers hardness HV 0.5. GH = (actual core hardness + 50) x HV 0.5 (rounded to 10 HV in each case).

Nitrocarburizing

Enrichment of the surface layer of a workpiece with nitrogen and carbon to form a compound layer by thermochemical treatment. The means in which nitrocarburizing is carried out should be specified, e.g. nitrocarburizing in gas (gas nitrocarburizing), nitrocarburizing in plasma (plasma nitrocarburizing).

Normal annealing

This process consists of austenitizing and subsequent cooling in still air. Other media with an appropriate cooling rate can be used.

Perlite

A structural component consisting of ferrite and carbide lamellae that is formed during the transformation of austenite with a eutectoid composition. The formation temperature is above the range of bainite formation.

Stress-relief annealing

Internal stresses are largely relieved without significantly changing the microstructure. The process consists of heating and holding at a sufficiently high temperature, followed by appropriate cooling.

Thermochemical treatment

Heat treatment to achieve a change in the chemical composition of the base material through mass transfer with a suitable agent, e.g. carburizing.

Connection layer

It is formed during thermochemical treatment directly on the surface and consists of one or more chemical compound(s). These are formed from the diffusing element(s) and certain elements of the base material, e.g. a nitride layer after nitriding.

Remuneration

Process of hardening and tempering at elevated temperatures to achieve the required combination of mechanical properties, in particular high toughness and ductility.

Heat treatment

Process in the course of which a workpiece is fully or partially exposed to time-temperature sequences in order to change its properties and/or microstructure. If necessary, the chemical composition of the material is changed during the process (thermochemical treatment).

Soft annealing

Process for reducing the hardness of a material to a specified value.

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