Crystec Technology Trading GmbH

During annealing the workpiece is heated to a certain temperature and then cooled slowly. Different objectives can be pursued with this:
With coarse-grain annealing the goal is to increase the size of individual crystallites. This reduces strength and increases ductility, which is desired for certain machining operations.
Stress-relief annealing is carried out at relatively low temperatures between 480°C and 680°C and serves to remove residual stresses induced by mechanical deformation or machining. Otherwise the steel properties should remain largely unchanged.
Diffusion annealing can last up to 2 days, is performed at relatively high temperatures between 1050°C and 1300°C and aims to achieve an even distribution of foreign atoms in the metal lattice. The cooling rate determines the phase development and thus the steel properties.
Recrystallization annealing restores the crystallite structure present before cold deformation. For this the workpiece is heated to temperatures just above the recrystallization temperature, typically between 550°C and 700°C. The recrystallization temperature depends on the material and the degree of deformation.
The normalizing of steels is one of the most important heat treatment processes. It aims to form a fine-grained microstructure of crystallites evenly distributed through the part. For higher-carbon steels the annealing temperature is just below 800°C; for low-carbon steels the temperature for normalizing rises up to 950°C.
In soft annealing existing precipitates of cementite or pearlite are reduced to lower hardness and strength to facilitate forming. Typical temperatures for this are 680°C - 780°C.
JTEKT supplies both continuous and batch furnaces for all annealing processes, for operation in atmospheric conditions as well as vacuum furnaces.

When hardening unalloyed steel in quenching furnaces, the workpiece is first heated to a temperature between 800°C and 900°C so that, in the case of low-carbon steel, austenite is fully present. For alloyed steels the required temperature can differ significantly.
To prevent corrosion, exothermic gas can be used in the furnace. Exothermic gas is produced in a suitable gas generator from hydrocarbons and, besides CO, H₂ and N₂, also contains CO₂ and H₂O.

After quenching the steel is cooled so quickly that carbon atoms cannot move to more favorable lattice sites because the diffusion rate of carbon at low temperatures is too low to permit such rearrangement.
However, as the temperature drops the iron lattice still changes structure and martensite forms. Due to lattice defects and stresses, martensite is very hard and strong but also poorly ductile and brittle.
Thick parts require correspondingly high cooling rates to be fully hardened throughout. In practice the parts are immersed in an oil bath or water bath. Water gives the most effective quench because of its high heat transfer, but when the part is immersed a vapor film initially forms at the surface (Leidenfrost effect) which reduces heat transfer. Care must be taken to immerse the part in such a way that uniform liquid contact over the entire piece is ensured. Alternatively, aqueous polymer solutions can be used in the quench bath.
Heating of the parts can be done in a chain conveyor or mesh-belt furnace, at the end of which the parts drop or slide into the quench bath, or in a hood furnace that is loaded from below and from which large parts can be rapidly extracted.

Vacuum furnaces are also used for quenching processes and hardening. The reduced pressure prevents oxidation or discoloration of the part surfaces.

After quenching or hardening in oil or emulsions, the workpieces must be washed before they can be further treated in the tempering oven. JTEKT offers dedicated washing machines for this purpose; however, washing steps can also be integrated into a hardening line. The steps of heating, quenching, washing and tempering can then be carried out in a single system.

Unlike classical through-hardening by quenching and tempering, modern heat treatment also allows targeted surface hardening. This produces an extremely wear-resistant, hard surface layer combined with a tough, elastic core. It is ideal for components that must withstand high surface loads without losing dimensional stability. Several precisely controllable hardening processes are available for these requirements.

Carburizing / Case hardening

Carburizing is particularly suitable for low-carbon steels. During the process the workpiece is tempered at high temperature in a carbon-rich, endothermic process gas. This gas is generated from methane, ethane or propane in a gas reactor and consists mainly of carbon monoxide (CO), hydrogen and nitrogen.

The steel is heated in a carburizing or case-hardening furnace to temperatures between 900°C and 1000°C. In this environment carbon diffuses from the process gas into the steel surface and enriches it to a depth of about 1 mm, close to the solubility limit of austenite. This creates a layer optimally prepared for subsequent quenching and tempering.

JTEKT furnaces of the KCF type are used, known for their high temperature constancy, energy efficiency and process reliability. Carburizing can be performed in continuous lines or in batch systems depending on production volume and part geometry.

Versatile furnace technologies for every requirement

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  Continuous push-through furnace with ceramic roll transport
  Especially suitable for sensitive or precision-critical parts. Ceramic rolls provide dimensionally stable, clean and heat-resistant support.
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  Continuous chain conveyor carburizing furnace
  Ideal for high throughput and consistent quality. Continuous material flow enables reproducible results with minimal downtime.
• ●
  Continuous rotary drum furnace for carburizing
  Particularly suitable for bulk goods or small parts. The rotating furnace ensures even treatment of all pieces and can be extended with quench, wash and temper modules if required.

Carbonitriding is a highly precise thermochemical process for creating wear-resistant surface layers. Unlike pure carburizing, nitrogen is supplied to the workpiece in the gas phase during heating in addition to carbon. Nitrogen is typically supplied in the form of ammonia (NH₃), which leads to the targeted formation of nitrides in the near-surface region.

At lower process temperatures in the range of 650 - 770°C nitrogen diffuses efficiently into the steel. After quenching a thin but extremely hard layer of nitrides and carbides forms above the nitrogen-containing martensite zone. If carbonitriding is carried out at higher temperatures (770–930°C), this particular surface layer does not form because carbon diffuses significantly faster in this temperature window. Nitrogen also stabilizes the austenite phase and thus allows a gentler quench while still achieving significantly increased surface hardness.

Compared to case hardening, the hardened layer produced by carbonitriding is thinner but offers a very economical solution for parts that require high wear resistance at lower case depths. As with carburizing, quenching and tempering follow the gas-phase step to achieve optimal hardness, microstructure and dimensional stability.

Precise furnace technology for carbonitriding processes

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  Carbonitriding furnace
  Ideal for standard processes in the 650°C to 930°C range. Well suited for near-series production with defined case depths and short cycle times.
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  Flameless carbonitriding furnace with vacuum quench bath
  The premium solution for the most demanding requirements. Flameless operation produces an extremely clean, homogeneous process atmosphere ideal for precision-critical parts. The integrated vacuum quench bath provides particularly controlled, oxidation-free quenching and excellent part quality.

Nitriding is one of the most effective surface-hardening methods when high dimensional stability, low distortion and extreme surface hardness are required. In a nitriding furnace nitrogen diffuses into the steel surface at relatively low temperatures of 500 to 550°C. Ammonia (NH₃) is used as the nitrogen source; its decomposition releases active nitrogen, which enters the interstitial sites of the steel and creates lattice strain that is the basis for the characteristic hardness increase without quenching or martensite formation. Partial nitride precipitation occurs during controlled cooling.

In nitrocarburizing, carbon is introduced in addition to nitrogen, typically in the form of carbon monoxide or hydrocarbons. Because carbon solubility in the already nitrogen-enriched steel is low, carbon remains primarily in the immediate surface region. During cooling, hard carbonitrides form there. Nitrocarburizing processes are also significantly shorter than classical nitriding, which provides an economic advantage in series production.

Nitrided and nitrocarburized steels feature a very hard, low-friction and corrosion-resistant surface layer. The layer is thin and offers excellent sliding properties and improved polishability. Although it is less wear-resistant and comparatively brittle, it provides an optimal balance of performance, cost and process reliability for many applications, for example in machinery, automotive engineering or precision tools.

Modern furnace technology for nitriding and nitrocarburizing processes

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  Nitriding furnace / hood furnace
  The classic solution for uniform nitrogen uptake and excellent temperature stability. Particularly suitable for precisely controlled nitriding and nitrocarburizing processes.
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  Two-stage nitriding furnace
  Ideal for demanding part geometries and optimized process cycles. Two-stage atmosphere and temperature control achieves especially uniform case zones, reduced cycle times and high-quality surface results.