Application & Process List

Click on the process to expand the section.

Low Pressure Carburizing: The Process

Carburizing is a thermochemical treatment which consists in enriching a layer of material in carbon at the part's periphery, and to then make an abrupt cooling or quenching. It is called low pressure or under vacuum in order to highlight the absence of air and therefore of oxygen during the process.

  • Hardness on the surface
  • Wear resistance
  • Strain resistance
  • Absence of intergranular oxidation
Low Pressure Carbonitriding

Low pressure carbonitriding (CNBP) is a thermochemical surface treatment in which nitrogen - obtained from ammonia NH3 dissociation - interacts with carbon during these phases:

  • Superficial surface fixing by chemical reaction of the carburizing element
  • Inward diffusion
  • Superficial hardening of the parts using martensitic quenching
  • Increased compressive residual stresses

In low pressure, the efficiency of introducing nitrogen in the materials is proved when ammonia is introduced into the combustion chamber during certain stages of intermediate and final diffusion.

The NH3 partial pressure is the same when carburizing. The number and length of carbonitriding steps depend on the depth and the concentration of nitrogen desired under the surface. The process temperature can reach 960°C and is much higher than atmosphericarbonitriding. This allows deep diffusion of nitrogen - up to 1 mm - and nitrogen levels on the surface of up to 0.6%, with much shorter time cycles.

The gases produced by cracking are burned downstream of the pumping unit in order to meet environmental standards. CNBP offers undeniable resistance gains to gearing strain.

It has been demonstrated that, in the case of transmission pinions, the combination of CNBP and staged gas quenching during the martensitic phase 180°C-200°C-STOP-QUENCH- produced strain resistance gains of about 30%, as shown by the Woelher curves regarding low pressure carburizing followed by direct gas quenching.

This method is very promising for future development of high torque transmissions.

Double Flow Gas Quenching

A gas quenching cell is a mechanism under pressure, which allows a load to be cooled at different speeds and pressures (up to 20 bar absolute). This cell was designed to quench either witnitrogen or helium with remarkable cooling efficiency and uniformity. Gas cooling is performed with two water/gas heat exchangers located on each side of the load. The water flow and temperature determine the exchanger cooling power and thus thload's’s cooling rate. The gas flo, usually nitrogen, is performed by two mixed-flow turbines, located on either side of the load. The large diametedesign of these turbines is crucial toptimizese the gas velocity and the power of the engines. The power of each engine is 250KW for nitrogen and 130KW for helium.

Gas direction is variable - either from top to bottom or bottom to top - thanks to an ingeniousystem of f lateral shells moving with a set of 2 cylinders in 1 second. The advantage of this alternating flow is to offer the possibility to reduce the thermal gradients between the top and bottom of the load, and therefore, improving the hardness tolerance and distortion. The programming of this alternating flow is specific to each recipe.

Single Flow Gas Quenching

The gas quenching cell is an enclosed area under pressure, which allows a load to be cooled at different rates and at different pressures (up to 20 bar absolute).

The load is cooled from top to bottom. It is carried out by using two water/gas heat exchangers located on each side of the load. The water and temperature flow process the cooling power of exchangers and thus the cooling rate of the load.

The nitrogen gas flow is performed by two 130 KWatts axial turbines, located above the load, in the upper part of the cell. The turbine concept is crucial to optimize the gas velocity and the power of the engines.

The quenching speed during quenching can be modulated and adjusted by changing the turbine speed quench pressure.

Over time, improvements were made in chamber design to even cell cooling: turbine blades, grid flow distribution, supply and exchanger surfaces etc.

Gas Quenching

Gas quenching is a cooling process focused on quality. More than 80% of ECM Technologies's™ European and North American clients have adopted gas quenching. ECM Technologies devotes great efforts in R&D to optimize this technology. Gas quenching is a cleaner process and therefore easy to integrate. The gas quenching parameters can be precisely adjusted to provide a substantial improvement in quality.

Integrated and Ecological

ECM Technologie's™ vacuum furnaces are an economic and ecological alternative. With ICBP® furnaces, gas quenching takes place in a specific cell in which the loaded parts are quickly transferred from their heating cell after low pressure carburizing.

The parts are then cooled by a high pressure gas injection, up to 20 bar, stirred by two turbines. Unlike with oil quenching, it is no longer necessary to wash, recycle or treat the effluent when upon exit. Gas quenching is a cleaner and cheaper process which respects the environment. It is a uniform, predictable and reproducible process because it eliminates the calefaction phenomena generated by oil quenching.

Gas quenching produces significant quality gains which can easily lead to savings, such as a decreasing percentage of waste or a reduction in post machining operations. With gas quenching, parts are closer to their final dimensions, with a high level of reproducibility. Companies like Delphi, which now use oil and gas quenching, increase the proportion of gas quenched parts for diesel pumps parts while keeping the oil quenching for more massive components.

Oil Quenching

The oil quenching cell allows the quenching of up to 750 kg loads, for a useful size of L1000 x L610 x H750mm

Two Versions Exists:
  • Cold oil version: area of work: 60 to 100°C
  • Hot oil version: area of work: 110 to 180°C

This cell works under vacuum or under partial nitrogen pressure, thus ensuring the absence of oxidation on the surface of the low pressure carburized parts.

It has an internal lift and two level positioning: Quenching and dewatering / loading unloading.
The e oil, vigorously stirred by two immersed hydraulic brewers, can handle large loads thus limiting calefaction phenomena. The layout of these brewers is different depending on the tray version.

The oil speed can vary and can reach 1,3m/sec

The oil cooling is ensured by a continuous water/oil or air/oil exchanger group depending on the operating temperature. Installation of the quench tank requires the construction of a waterproof and airtight tank.

Optional, if the parts are to undergo intermediate machining before the oil quenching, accelerated load cooling with 1 bar nitrogen can be achieved with a turbine located in the upper part of the quenching tank. The nitrogen is cooled using an internal water/gas heat exchanger.

Metallurgical Results

With ECM's™ Low Pressure Carburizing solutions, oxidation is eliminated, thermal treatment being carried out in a vacuum or partial pressure of gas-free oxygen. Carburized layer interface with the base material is a lot more regular. Carbon profile never shows decarburization on the surface: no bell-shaped profile!

The carburizing depth can also be precisely controlled; results have shown a very high degree of uniformity in batches of parts and even on one part only. Moreover, the difference in enrichment depth between the side and the bottom tooth is greater than 30% after conventional carburizing and oil quenching. After low pressure carburizing and gas quenching it is less than 15%. This reduces the specification carburizing depth and thus the cycle time. It also helps reduce stress and toothing distortion after quenching.

Mechanical Properties

There is an excellent hold to the pitting resulting from the absence of intergranular oxidation (IGO).
The ECM process makes a difference when strain or shock resistance is of importance, e.g. to increase torque in new generation gearboxes.

With perfect control of the carbon and nitrogen (if carbonitriding) enrichment, low pressure carburizing contributes to increase the surface compressive stresses which favor strain resistance. On our systems, low-pressure carbonitriding® and well controlled gas quenching lead to improved mechanical properties (shock and strain)

Controlling Distortion

The heat treatment does not necessarily imply that the parts will not meet the dimensional tolerances. ECM's™ processes, especially gas quenching, allow a better distortion control of the parts because the cooling rate after carburizing can be easily adjusted for each part shape according to specific procedures. The momentary interruption of the quenching- STEP QUENCH - is an additional tool which reduces heat stress in the material during quenching and improves distortion.

The results are very uniform, between parts and loads. Distortion is generally predictable, and its amplitude and direction more homogeneous. Therefore in some situations, they can be anticipated during processing before treatment.

• At best, the expensive final treatment is unnecessary.
• In general, the amount of material to be removed and the number of treatments are reduced.

Environmental Benefits
  • No open flames or curtains needed
  • No added heat from furnace in heat treat
  • Cleaner facility
  • Safe operation (no hot doors or hot moving parts)
  • Reduction of process gas use
  • Reduction of emissions
  • When using gas quenching system: No environmental issues with oil present in facility; No post-heat treat wash necessary