Distortion Minimization using DCGQ Process for Reduced Cost and Improved Quality

Quenching is a thermal process that hardens steels, and increases component mechanical properties, by way of phase transformation. A high quenching rate, where a part is rapidly cooled, is typically desired for optimal mechanical properties. For high alloy aerospace steels (e.g. Ferrium C64) with high hardenability and high thermal resistance properties, though, the effect of cooling rate during martensitic transformation on the obtained hardness and mechanical properties is expected to be insignificant. One challenge with quenching for all steels is shape and size distortion. Distortion control for complex aerospace parts with complex geometric features, such as rotorcraft gears with thin-wall sections, can be very challenging and costly. A patented DANTE Controlled Gas Quench (DCGQ) process was developed for high precision distortion control during quench hardening. The DCGQ process follows a recipe of quenching time and the ambient gas temperature designed by computer modeling, with a specified maximum allowed temperature difference in the part section during the martensitic transformation. A prototype DCGQ chamber was fabricated and demonstrated under contracts funded by the U.S. Army’s Combat Capabilities Development Command (DEVCOM) Aviation and Missile Center (AvMC). The experimental results from coupon samples have validated its effectiveness on obtaining hardness, mechanical properties, and fatigue properties equivalent to those from a standard high pressure gas quench (HPGQ) process for various high alloy aerospace steels. For aerospace gears with challenging thin-wall sections, the DCGQ process can quench the part fast enough in the high temperature zone above the martensite start temperature to avoid potential diffusive phase and carbide formation issues. The DCGQ process also makes it possible to successfully heat treat aerospace gears with reduced distortion compared to traditional press quenching or high-pressure gas quenching (HPGQ). (Distribution Statement A. Approved for public release: distribution is unlimited)