Re-Engineering, Austempering, and Selective Laser Hardening of a 4340 Latch Body Used in the Cargo Hook of a CH-47 Military Helicopter

摘要

The latch body is a safety-critical 4340 steel part that is currently used in the cargo hook of a CH-47 military helicopter. Approximately 5×2×2 inches in dimension, this safety-critical part is nestled within the cargo hook assembly and facilitates the operation of the load beam (hook) during its payload cycles. This paper mainly focuses on the methodology and design advantages of converting a wrought two-piece latch-body into a single-piece machined component. The application of austempering heat treatment to improve mechanical properties and eliminate surface cracking vis-a-vis generic oil quenching and tempering treatment is discussed. The application of laser technology for surface hardening of the austempered latch body is reported. Mechanical testing of austempered 4340 steel, microstructural examination, characterization of the laser and induction-hardened layers, and preliminary testing to evaluate the integrity of the hardened layers is presented.