Evolution and Prospects of Aerospace Carburizing Gear Steels

This study classifies progression of aerospace carburizing gear steels into three distinct generations, segmented by operational temperature ranges. It further provides a systematic comparison of evolving composition, strengthening mechanisms, fatigue and wear properties. First ‐generation carburizing gear steels primarily feature low‐carbon, low ‐alloy compositions with ultimate tensile strengths (UTS) of 1200–1570 MPa, yield strengths (YS) of 1000–1365 MPa, elongation (EL) of 11–16%, surface hardness of 58–62 HRC, with typical service temperatures below 200 °C. Relatively, second‐generation carburizing gear steel increased proportion of secondary‐hardening elements, achieving modest gains in strength and ductility. By leveraging Fe 3 C strengthening and partially suppressing high‐temperature softening through secondary precipitation phases, the upper service temperature limit was extended to 350 °C. Third‐generation steels incorporate higher Cr, Ni, and Co, fully leveraging secondary‐hardening effects. UTS reaches 1620–1764 MPa, YS rises to 1200–1551 MPa, EL increases to 16–21%, surface hardness ranges from 61 HRC to 70 HRC. Simultaneously, breakthroughs in red hardness and stability at 500 °C were realized. However, rapid strength degradation exceeding 500 °C remains unavoidable. High‐temperature oxidation resistance, lightweighting, ultra‐high strength define the future of aerospace carburizing gear steels. This study systematically analyzes core challenges to provide a theoretical basis for innovation and sustainable development.