Case-hardening is a surface heat treatment based on carbon diffusion. This method greatly improves wear and fatigue resistance on the surface, while maintaining good mechanical properties in the core. Traditionally performed in an atmosphere, low-pressure low-pressure carburizing is becoming increasingly popular, thanks to the many advantages of vacuum technology.
Benefits of case-hardening
Case-hardening is one of the most common heat treatments, involving the diffusion of carbon onto the surface of the parts. Hardening is then applied to reinforce hardness. This method gives steels greater resistance to wear and fatigue. While case-hardening mainly impacts the surface layer of parts, their natural core properties are enhanced by quenching, which is another advantage of this process. Treated components thus retain their mechanical strength and resilience, while benefiting from improved surface resistance.
Traditionally, case-hardening was carried out in an atmosphere, but over the last few decades, the development of vacuum technologies has seen this process evolve. It is now possible to choose low-pressure carburizing, which offers numerous advantages.
Advantages of low-pressure technology
Low-pressure carburizing is a vacuum technology, as opposed to atmospheric treatment. The first advantage of this method concerns oxidation: as the operation takes place in an air-free, oxygen-free environment, the risk of surface oxidation is virtually nil. Similarly, the absence of an oxidizing atmosphere prevents the formation of intergranular oxides. These elements form in the grain boundaries that make up the steel's structure, creating micro-cracks and weakening the part.
What's more, vacuum technology guarantees perfectly clean parts. Following low-pressure carburizing, there's no need for sandblasting or additional cleaning, which reduces the overall cost of the process. This method also considerably limits the risk of deformation: the homogeneity of temperature, gas or oil cooling, all under vacuum, prevent parts from being greatly deformed by excessive thermal shock during cooling, for example. As a result, low-pressure carburizing saves time and simplifies the part production process, as there is no longer any need for a large machining allowance on the parts to be treated. In some cases, parts can be processed directly and emerge finished, which is also a real money-saver for machinists.
More environmentally-friendly heat treatment
Vacuum treatment is one of the most environmentally-friendly technologies available, giving it an extra edge over traditional methods. The furnaces used to treat parts in this way run on electricity, not gas. As French electricity production remains carbon-neutral, this low-pressure technique produces no waste and emits no CO2.
Why low-pressure carburizing?
Low-pressure carburizing is increasingly used throughout the world, thanks to its many advantages. More ecological than other processes, it is the perfect answer to the environmental demands of decarbonizing industry. What's more, consuming less energy and delivering clean, virtually finished parts saves both time and money, which is what professionals are increasingly looking for.
An old technology that has come a long way
This technology is actually older than it seems. The Thermi Lyon group has been mastering it since 1994, and has seen the need for vacuum treatment increase over the years. Thirty years ago, this method remained fairly confidential, reserved for the world of aeronautics, as it was an excellent way of treating martensitic stainless steel, which is very common in this sector. However, vacuum furnaces were not suitable for large production runs, as in the automotive industry, for example. With the growing need to develop more environmentally-friendly processes, vacuum furnaces have undergone a number of evolutions, and now offer a particularly attractive productivity capacity.
Effectiveness similar to that of atmospheric treatments
Today's furnaces, for example, enable low-pressure carburizing at temperatures of 1,000 degrees Celsius, compared with only 920 degrees Celsius for a gas-heated atmospheric process. Similarly, today's treatment cycles are much shorter, which also helps to reduce final bills. In certain circumstances, a single part may require 10 hours of treatment under atmosphere and only 5 hours under vacuum (if the specifications allow high-temperature treatment).
While it still seems essential to offer atmospheric treatment to customers with very large production runs or very large parts, vacuum technologies are becoming increasingly popular and cost-effective, thanks to their democratization. To meet this growing demand, the Thermi Lyon group has decided to invest in a new fully-automated vacuum furnace for its TREMPELEC automotive site, and another for the THERMI-LYON site for the aerospace market.
Specific articles will be published for these two investments with our partner vacuum furnace manufacturer. In its perpetual concern to respect CSR and environmental protection, the group has been interested in vacuum technologies for decades, and has planned the installation this year of 5 vacuum furnaces and only one atmospheric model, to match the evolution of the market and needs.
