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Future investment in carburizing equipment requires knowledge of the capabilities of current technologies. This article provides insights into atmosphere and vacuum carburizing methods and compares their advantages and disadvantages.
There is renewed interest in understanding the pros and cons of atmosphere and vacuum carburizing as companies consider which technology to invest in for the future. Today, this interest is being fueled by the desire to substitute high gas-pressure quenching technology for oil-quenching technology in a number of applications. Distortion issues and alternative manufacturing methods are driving this agenda. Now that vacuum carburizing is once again being viewed as a cost-effective alternative to atmosphere carburizing, the question arises, what benefits does each technology offer?
Competing technologies
Today, as shown in Fig. 1, atmosphere carburizing is the de facto industry standard. This method of carburizing represents a good compromise between cost and performance. Future growth, as indicated by Fig. 2, suggests that the greatest potential will come in vacuum carburizing. This method of carburizing offers proven metallurgical and environmental benefits.
It is unfortunate that the technologies are viewed as competitors instead of complementing one another. An existing "atmosphere versus vacuum" mentality has fostered an "us versus them" mentality, which has hurt both technologies. This resulted from the need in the 1960s for better control of the atmosphere carburizing process. One series of investigations into a solution to this problem led to the development of vacuum carburizing. It was immediately viewed as an alternative to atmosphere carburizing, promoting enhanced metallurgical properties and shorter cycle times. It was marketed as a panacea for all the problems of atmosphere carburizing, and, thus, initiated competition between the two technologies. Had vacuum carburizing proved to be a robust technology at that time, it is generally believed that a significant portion of today's installed equipment base would use this technology. Its failure to achieve commercial success can be directly related to reliability and cost. For example, creation of soot was the bane of vacuum carburizing. But perhaps a more accurate explanation lies in the fact that the equipment designs and process parameters were not optimized, and the technology's capabilities were oversold to the heat-treating community.
So which technology will succeed in the future? Not surprisingly, both. And both will be needed to...