Metallurgical Investigation and Life Cycle Assessment of a Piston Rod of Thin Slab Caster

This work focusses on failure analysis of piston rod of a pendulum shear machine in a thin slab caster. Failure of the piston rod led to plant breakdown and huge production loss. In-depth analysis using macro- and micro-fractography, chemical analysis, microstructural analysis using optical and scanning electron microscope coupled with energy-dispersive x-ray spectroscopy and tensile testing was carried out. Macroscopic features like smooth fracture surface with multiple ratchet marks and microscopic features like striations confirmed fatigue mode of failure. Fatigue cracks initiated from the sharp step that acted as stress concentration site. The presence of deep machine or tool marks near the step further aggravated the situation. A number of manufacturing issues like inferior grade of material, undesired heat treatment and the presence of manganese sulfide inclusions were observed. All these factors led to much reduced service life of 5 months as against an expected service life of 5 years. A methodology for calculation of stress intensity factor at different stages of fatigue crack propagation and calculation of number of fatigue cycle for crack propagation has been presented based on quantitative fractography using scanning electron microscope. Based on the study, counter-measures to prevent similar failures in future have been recommended.