Type Certification of 18 Ni Maraging Steels for Landing Gears

Abstract

Maraging steels exhibit unique properties, such as high strength with excellent fracture toughness, ease of machining and above all distortion free thermal processing. These attractive properties and advantages of maraging steel do not outweigh the initial cost resulting from high alloy content and especially in certain structural components where in much of the forging is machined as swarf. However, with the constant drive to prove the technology when maximum strength and stiffness per unit volume becomes the major criteria, the choice of material may overwhelmingly become maraging steel. Above requirements necessiate a landing gear material for Indian fighter aircraft to have a combination of high strength, sufficient stiffness, excellent fatigue strength, utmost cleanliness, resistance to micro-structural degradation, freedom from surface anomalies, good corrosion & stress corrosion resistance and superior toughness to meet the current damage tolerant design criteria. M/s Midhani in consultation with airworthiness authorities took up the task to develop & manufacture this steel to the laid down type test schedule. The steel has satisfactorily met all the requirements and landing gear has been successfully forged, machined and fitted to the prototype. This paper describes the metallurgical aspects that are relevant for developing the maraging steel along with a brief note on the properties - chemical, microstructural and mechanical. An attempt is made in the presentation to show that the indigenously developed and produced maraging steel is indeed at par with aeronautical grade materials, including maraging steels of international sources.