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.

Austenite reversion kinetics and stability during tempering of an additively manufactured maraging 300 steel

“…Maraging steels are highly alloyed steels with a low carbon content which exhibit excellent mechanical resistance, combined with good toughness and ductility [1][2][3][4][5][6]. The austenite-to-martensite transformation in maraging steels contrasts sharply with that of conventional steels, since its low carbon content results in a tough and ductile martensite [1,2,[4][5][6].…”

“…Maraging steels are highly alloyed steels with a low carbon content which exhibit excellent mechanical resistance, combined with good toughness and ductility [1][2][3][4][5][6]. The austenite-to-martensite transformation in maraging steels contrasts sharply with that of conventional steels, since its low carbon content results in a tough and ductile martensite [1,2,[4][5][6]. The main strengthening mechanism of maraging steels occurs during appropriate aging heat treatments, causing precipitation of intermetallic phases such as Fe2Mo, Fe7Mo6, Ni3Ti and NiAl , providing a tensile strength above 1500 MPa [1][2][3][4][5][6].…”

Embrittlement Fracture Behavior and Mechanical Properties in Heat-Affected Zone of Welded Maraging Steel

“…Steel materials can be categorized based on room temperature (RT) tensile strength, σ B , into two types: (1) high-strength steel (HSS) [1] and advanced high-strength steel (AHSS) [2,3], used for plates and pipes in civil, building, ship, vessel, and vehicle construction [4][5][6] within general industrial structure sectors, and (2) ultra-high strength steel (UHSS) [1], employed in the manufacture of aircraft, space-rockets, dies, deep-sea submersibles, and centrifugal separators for uranium enrichment [7][8][9][10][11], pertinent to advanced technology sectors. The development of HSSs aims to enhance economic efficiency by minimizing material and construction costs.…”

Influence of reverted austenite on fatigue life of 18 % nickel maraging steel

“…Fatigue is the major failure mechanism in several applications. Fatigue, for example, has been cited as a key cause of landing gear failures [1]. Maraging steels have considerable inherent strength and toughness, but they have relatively poor fatigue strength [2][3][4][5].…”