Numerical evaluation of hydrogen-induced cracking susceptibility in X70 steel welds using finite-element method

This research was carried out to numerically calculate the amount of hydrogen in pre-heated and post-heated X70 steel weldments with a specific geometry. The study included experimental and simulation components. In the simulation phase, a self-restraint cold cracking sensitivity test was modeled according to ISO17642-2 standard. The heat transfer problem during the welding process was solved and the residual stresses were calculated throughout the model. Hydrogen diffusion and its distribution in steel weldments were also simulated through finite-element method. In the experimental phase, the hydrogen content of cellulosic and low-hydrogen electrodes was measured using the mercury displacement method based on ISO3690 standard. The simulation results were validated. Thermal validation was conducted by comparing the real and simulated weld pool dimensions, while mechanical validation was achieved by matching simulated residual stresses with measurements obtained through X-ray diffraction. The plastic strain and local hydrogen concentration resulted from the mechanical and diffusion simulations, respectively. Comparing them with the experimental results, a relationship between plastic strain and hydrogen concentration was developed, expressing the amount of critical hydrogen concentration for a given plastic strain in X70 steel to determine the safe area without hydrogen-induced cracking. hydrogen-induced cracking will not occur if hydrogen concentration is less than this critical amount.