Material iterative development of aero carburizing gear steels

Abstract

In this paper, the intergenerational development, component characteristics, and strengthening mechanism of carburized gear materials for aerospace power transmission systems are reviewed. The first-generation carburized gear steel is low-carbon medium/low-alloy steel, and the surface hardening of the carburized layer structure is realized by Fe3C carbides. Due to the low content of alloying elements, the tempering resistance of the first-generation carburized gear steel is poor, and the general service temperature range is within 200 ℃. Among the first-generation carburized gear steels, the content of carbide-formation elements of 16Cr3NiWMoVNbE material is relatively high. This material can be developed for the second-generation carburized gear steel with a wide-range service temperature through the critical saturation carburization process. The second-generation carburized gear steel is a low-carbon medium/high-alloy steel. Some M2C strengthening phases with high tempering resistance can be precipitated during the tempering process by further improving the alloying degree and appropriately increasing the content of Mo element with strong tempering resistance. The overall service temperature range is raised to 350 ℃. The third-generation carburized gear steel is low-carbon ultra-high alloy steel, and the “secondary hardening” effect works thoroughly via computational methods. Therefore, the material can be used in a temperature range below 500 ℃ for a long time. The existing alloy structural steel system can not avoid the problem of rapid strength decay after long-term service at high temperatures above 500 ℃. Therefore, the next-generation carburized gear materials will be developed based on iron-based alloys with excellent oxidation resistance.

Keywords

• gear steel
• carburization
• secondary hardening
• precipitation hardening