Probability of void coalescence in spheroidized pressure vessel steel

Abstract This paper presents a statistical model of the coalescence of voids nucleated by the effects of plastic deformation ahead of a crack tip on carbide particles. Statistical analysis of the microstructure has been used to define the nature of the dependence of the coalescence probability upon the distance from the crack tip. Application of this model to a spheroidized steel microalloyed with 0·043 wt% Nb has confirmed that the coalescence probability declines as the distance from the crack tip increases. As the coalescence of voids ahead of a crack tip governs the onset of stable propagation of the main crack, this model is particularly suitable for statistical prediction of the upper shelf of fracture toughness in the steels utilized for the fabrication of pressure vessels and pipings.