M250 grade maraging steel is used widely in satellite launch vehicle structures due to its excellent combination of strength and toughness. One of the maraging steel bolts used in interstage structures was found broken during the visual inspection of the hardware. The failed bolt was in assembled condition for several months. The bolt has failed at the stepped region before the start of threads. Crack initiated at the corrosion pits located at the stepped region and propagated inward in an intergranular mode. Fractography revealed brittle intergranular features and corrosion products were noticed on the outer periphery of the fracture surface. EDS analysis of the corrosion products near the fracture edge indicated the presence of chlorine. However, at the center of the bolt, the fractographic features correspond to transgranular mode of failure. Based on detailed metallurgical analysis, the failure of the bolt was attributed to ‘stress corrosion cracking.’

Stress Corrosion Cracking of a Maraging Steel Shear Bolt Used in the Interstage Structure of a Satellite Launch Vehicle

Failure analysis of M250 maraging steel stud used in Flex Nozzle Control actuator bracket of solid propulsion system

The present work deals with the ultra-high strength maraging steels, which are exotic materials used for high tech applications in aerospace and nuclear fields. Masking of a fabrication defect in a critical component by filling it with cheap mildsteel weldment to avoid rejection on visual inspection may lead to catastrophic failure when put into service. This paper is aimed to simulate formation of such a defect in a maraging steel rod and to analyse the probable metallurgical reasons leading to its premature failure using optical and scanning electron microscopy and energy dispersive spectroscopy.

Simulation of Metallurgical Failure of a Maraging Steel Tension Rod

Metallurgical Analysis of Failed M250 Maraging Steel Piston Rod of Tension Reduction Device Used in Aerospace System

An ultrahigh strength maraging steel bolt, used to fasten maraging steel bands in an aerospace separation system failed prematurely under a sustained stress of about 42 % of its tensile strength during its qualification tests prior to acceptance for flight. The metallographic investigation of this failed bolt revealed that certain defects on its surface were filled up by multipass welding causing an inhomogeneous microstructure as well as the accumulation of hydrogen at its sharp thread roots. This caused the delayed failure of the bolt at a lower stress level

A. Natarajan

Papers

Hydrogen Embrittlement of Maraging Steel Tension Bolt / Wasserstoffversprödung eines Spannbolzens aus Maraging-Stahl