According to the Automotive Overview of the Steel Industry Road Map, one of the steel enabling technologies is low-pressure vacuum carburizing (LPC) with (high-pressure) gas quenching (LPC + HPGQ). This technology is rapidly gaining popularity with original equipment manufacturers for cost, efficiency and environmental reasons, and several efficient LPC furnace designs have been constructed and successfully implemented throughout the world within the past decade. Cold wall design and low output gas emission allow LPC furnaces to be integrated into the manufacturing line instead of requiring a separate heat-treating facility.
From a product standpoint, LPC eliminates grain-boundary oxidation, decarburization, and heat treat scale producing higher quality parts in terms of cleanliness and fatigue performance. LPC case depth is more uniform and shows less variation within and between heat-treat loads than case depth produced from traditional gas carburizing. Gas quenching produces less distortion than oil and salt bath quenching due to more uniform heat extraction. Some LPC designs provide increased heat treat flexibility where several different parts with different surface areas and mass can be simultaneously carburized at different carburizing temperatures and to different case depths.
In this issue, several manufacturers of low-pressure vacuum carburizing equipment support the claims mentioned above and present a wide-ranging view of LPC technology capabilities. A wide variety of issues, capabilities, benefits, technology improvements and developments, and successes are presented by AFC-Holcroft and ALD Thermal Treatment, ECM Inc., Ipsen International, Seco/Warwick, Surface Combustion and Twin Disc Inc. (for a user's viewpoint).
The reader can learn a great deal about low-pressure vacuum carburizing from these pages including:
- The development stages of vacuum carburizing
- Reasons to vacuum carburize
- The flexibility and capabilities of vacuum carburizing systems
- How modular system construction and control software flexibility allow the use of such systems in a wide variety of plant configurations with the capability to adapt rapidly to changing production processes
- How computer-control system technology allows quick parameter selection without time-consuming experimenting, which is especially important in plants that are running variable short-series jobs
- The importance of precise carburizing atmosphere input into the furnace and getting the atmosphere uniformly around the workload
- What a manufacturer of heavy-duty power transmissions has learned about the benefits of LPC and what pitfalls to watch out for to ensure getting quality heat-treated parts.
Atmosphere carburizing isn't quite ready to throw up the white flag as can be seen in the article from Air Products on the improvement that can be realized by ever-tighter control/regulation of furnace carburizing atmosphere. Competing technologies will continue to encourage further advancements and improvements in all areas.