Metallurgical investigation on failure of plain carbon steel piston rod used in hydraulic jack: Role of inclusions and surface roughness

Abstract

Piston rod fabricated out of plain carbon steel in annealed condition used in 50 kN hydraulic jack failed during the structural qualification of ogive payload fairing of launch vehicle. A detailed metallurgical analysis was carried out on failed piston rod using thorough characterisation and testing. Fractography observation revealed brittle cleavage features indicative of brittle failure. Extensive roughness at the thread surface was also observed. Higher content of sulphide and alumina inclusions with slightly higher content of sulphur and phosphorus beyond the acceptable limit were observed in the material. Fractography of tensile tested specimens revealed ductile failure whereas impact tested specimens showed brittle failure. The failure analysis observations have also shown brittle failure of component under dynamic loading conditions. Hence, presence of higher inclusions and impurities in the material coupled with roughness at the thread surface are the reasons for the brittle failure of piston rod.