Vacuum carburizing of gears has typically been limited to parts with relatively small cross-sections. Most alloys currently in use require oil quenching to achieve adequate surface hardness and core properties in large gear applications. Pit or large batch IQ furnaces with endothermic atmospheres are often used to process this type of gear. The majority of vacuum carburizing equipment is designed for processing smaller parts with a high pressure gas quench. Recent equipment and process developments allow vacuum carburizing and oil quenching of very large gears and pinions - up to 70" diameter and 7,000 lbs. Fixture design and careful process control help minimize distortion, while providing the case uniformity and surface integrity that is unique to vacuum carburizing. This paper will discuss specific case studies involving large gears and pinions. Distortion, case hardness profiles and microstructures from conventional gas carburizing and vacuum carburizing will be examined and compared.
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