In this paper, we discuss the optimization of chemical composition, processing (forging and rolling) and heat treatment parameters to obtain the best combination of mechanical properties in case of a Fe-15Cr-5Ni-4Cu precipitation hardenable stainless steel. The ε-copper precipitates that form during aging are spherical in shape and coherent with the matrix and principally provide strengthening in this alloy. The orientation relationship is found to be Kurdjumov-Sachs (K-S), which is common in fcc-bcc systems. Results obtained from metallurgical evaluation (mechanical property and metallography) on 15-5 PH alloy during type certification on 3 different melts were used for the optimization, attempted in this study. The mechanical properties following strain deformation has been carried out using optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). In the aged conditions, the 15-5 PH alloy exhibited brittle failure with extensive cleavage and/or quasicleavage fracture. This paper reports all results and also factually shows that indigenously developed and produced 15-5 PH stainless steel matches in its properties with the equivalent aeronautical grade precipitation hardening stainless steels globally produced by internationally renowned manufactures.

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.

Softcomag 49AA alloy consisting of 49 wt per cent Fe, 49 wt. per cent Co and 2 wt per cent V is a soft magnetic alloy with a combination of very high saturation magnetisation and high magnetostriction and used for several aeronautical applications such as generators (stators and rotors), fixed iron moving armature units etc. Though this alloy is brittle in nature, it can be formed into hot rolled bars and cold rolled sheets by adopting suitable thermo mechanical treatments. In order to indigenise and subsequent type certification for aeronautical applications, the alloy was produced using 100 per cent virgin raw materials in a vacuum induction melting (VIM) furnace which not only ensures substantial reduction of inclusions, but also the production of homogeneous alloy as a result of induction stirring. The chemical composition was examined and hot working parameters of the alloy were so optimised that they would result in the best combination of magnetic, physical and mechanical properties for the end use, which forms the central theme behind the developmental activity that was simultaneously covered by a comprehensive certification process. The material thus produced is subjected to stringent quality control checks in accordance with stipulated airworthiness norms. The paper discusses in detail the indigenisation efforts and airworthiness certification of the alloy Softcomag 49AA and its comparison with equivalent grades, namely PERMENDUR 49 and VACOFLUX 50.