Hydrogen-assisted ductile fracture in spheroidized 1518 steel

Abstract

Hydrogen was introduced into smooth and notched tensile specimens of spheroidized 1518 steel by electrocharging under controlled galvanostatic conditions. The role of hydrogen during void nucleation and growth was investigated by identifying two different void nucleation modes. Hydrogen promoted void nucleation at average-sized carbide particles by reducing the critical interfacial strength, σ C, from 1200 to 1000 MPa (using a dislocation model). The stress-induced hydrogen segregation to the particle interfaces during deformation was estimated to explain the hydrogen-reduced σ C. Void growth in both longitudinal and lateral directions was enhanced by internal pressurization of hydrogen. In order to better quantify such hydrogen-enhanced void growth, the internal hydrogen pressure inside a void was calculated on the basis of thermodynamics. The final void coalescence stage was analyzed by assuming that the void nucleation rate follows a normal distribution.