Optimizing Your Atmosphere Furnace for Carburizing and Quenching

Heat treatment is necessary during the manufacturing process as it helps improve the quality of products being developed. In fact, without repeatable and reliable heat treatment, it is not possible to realize the overall quality of manufactured parts.

The cost involved in manufacturing is usually around 5% – just a small part of the overall production costs. However, this percentage can increase to 15% for each component when additional post-treatment processes associated with heat treatment are carried out.

One way to reduce these manufacturing costs is by minimizing part distortion. This can be achieved by optimizing the influencing parameters and natural factors of heat treatment, such as forming of the parts, steel melting, uniformity of microstructure, uniformity of heating, carburizing and heat extraction methods.

These last three processes can be effectively used to manufacture quality components in batch atmosphere furnaces. This article provides some useful tips on how to optimize both the atmosphere furnace and the manufacturing process.

Optimizing the Carburizing Process

At present, two industrial carburizing processes are being used; namely, low pressure carburizing in vacuum furnaces and gas carburizing in atmosphere furnaces. Atmosphere carburizing includes the following process steps:

  • Gas reactions
  • Convective gassing
  • Dissociation and adsorption
  • Diffusion

A better understanding of these steps is essential for achieving uniform carburizing. With respect to the process steps given above, perfect carburizing conditions occur when factors such as gassing and temperature uniformity, fast reaction kinetics, and flow over the components occur uniformly within the treatment chamber. Suitable conditions in these areas can positively affect the quality of components developed.

Temperature Uniformity

One of the basic parameters required for obtaining parts with ideal carburizing depth is uniform temperature.

Ipsen’s ATLAS® is a highly efficient batch atmosphere furnace in which temperature uniformity of ±130F can be achieved in the heat chamber. After completing the heating phases, all parts in the austenitic phase are at the same temperature.

In addition, Ipsen’s Recon® Burners can help improve the heating of batch furnaces. These efficient burners are single-ended recuperative tubes (SERT) equipped with unique ceramic inner tubes. They have the ability to increase thermal efficiency up to 75% and are characterized by high durability, low noise levels and low maintenance. These burners provide perfect heating conditions and optimize gas consumption.

Gassing Uniformity

Positive convective properties promote superior temperature uniformity inside the load area, as well as allow for excellent heat transfer to the load and a uniform process atmosphere.

Figure 1 shows how minimum temperature deviation in the load area combined with uniform process atmosphere leads to minimal case depth deviations across the load.

Representation of the fluid flow lines in a treatment chamber.

Figure 1. Representation of the fluid flow lines in a treatment chamber.

Constant introduction of the carrier gas and controlled additions of the enriching gas promote a furnace atmosphere able to create carburized components with the desired percentage of surface carbon and to a preferred case depth, all with highly repeatable results (Figure 2).

A furnace atmosphere during gas carburizing.

Figure 2. A furnace atmosphere during gas carburizing.

In addition, Ipsen’s Carb-o-Prof® system, an intuitive control system, helps in maintaining balance by monitoring, documenting and archiving the carburizing procedures in atmosphere furnaces. This uniformity of the carburizing effect results in homogeneous carburizing of the surface layer, as illustrated in Figure 3.

Uniform surface carburizing of a gear wheel.

Figure 3. Uniform surface carburizing of a gear wheel.

Ceramic Muffles

A number of unique features are found in batch atmosphere furnaces that aid in achieving ideal gassing and temperature uniformity during a range of processes. Ceramic muffles are one such part; they are made of carbide and silicon and are capable of improving the performance of heat-treating processes.

Ipsen’s ATLAS atmosphere furnaces offer optional ceramic muffles to protect the load from direct heat and to allow homogeneous distribution of temperature across the material being hardened. Uniform temperature is vital in case hardening as it not only maintains the depth of penetration, but it also controls carbon concentration.

Optimizing the Quenching Process

Conventional quench systems within batch atmosphere furnaces used to provide minimum flexibility when it came to changing the quench intensity. However, there is a huge potential for optimizing and creating a uniform quench in oil. Adoption of these techniques has resulted in a more homogeneous hardening of parts – in particular, gear components.

Oil Quench

Ipsen offers oil-quenching systems, such as SuperQuench®, that come with a complete agitation system. As a result, the system produces a homogeneous oil flow throughout the load section and uses a modifiable oil flow speed. As shown in Figure 4, by using the timing control of the agitators, the cooling curve for SuperQuench can achieve results that are very similar to the ideal cooling curve.

This aspect not only improves the flexibility and efficiency of oil quench systems, but also makes it possible to harden thicker cross-sections and low-alloyed materials. Moreover, by using a suitable control software, complex quench cycles can be easily carried out.

Representation of an ideal cooling curve with a high cooling rate to start and a cooling rate reduction when entering the martensitic phase.

Figure 4. Representation of an ideal cooling curve with a high cooling rate to start and a cooling rate reduction when entering the martensitic phase.

Ideal Quench Speed and Heat Extraction

In order to obtain a homogeneous heat extraction across the entire component, it is important to achieve an equal flow of oil around the whole part. This can be realized by using an efficient quench system. In addition, based on the hardenability of the respective steel and the thickness of the part, the effect of a higher flow velocity can further improve the quality of part.

Reducing Distortion

The objectives for a distortion-optimized quenching can be described as follows:

  • Homogeneous heat extraction on each part within a single load
  • Homogeneous heat extraction across the entire surface of the part
  • Part- and material-adapted timing to maintain the quench intensity

The above goals are met during the quenching cycle. Figure 5 shows how the new generation of systems helps produce quality parts and achieve excellent performance in contrast to a traditional oil bath.

Comparison of SuperQuench’s working principle (left) to that of a conventional oil bath (right).

Figure 5. Comparison of SuperQuench’s working principle (left) to that of a conventional oil bath (right).

Conclusion

During the carburizing and quenching of components in a batch atmosphere furnace, it is important that the flow across components is optimized and uniformity of gassing and temperature is achieved.

High-performance systems help in achieving ideal heat extraction and quench speeds, thus enabling industries to develop high-quality and distortion-free parts while also realizing low production costs throughout the heat treatment process.

With the help of Ipsen’s SuperQuench systems, Carb-o-Prof software, Recon Burners and ceramic muffles, it is possible to obtain optimal end results during the quenching and carburizing processes.

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This information has been sourced, reviewed and adapted from materials provided by Ipsen.

For more information on this source, please visit Ipsen.

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