Hydrogen embrittlement ofAdvanced High-Strength Steels for sheet metal cold forming

Hydrogen embrittlement is one of the most impacting issues for the use of the Advanced High-Strength Steels in structural applications. For these steels, the reduction of the strength and ductility can occur even for low dissolved concentrations, andcan entail sheet metal failures during both manufacturing and service. Therefore, the threshold of the hydrogen concentration, above which the loss in strength and ductility is hazardous for the engineering application, is a crucial design parameter. Typically, this critical hydrogen concentration is estimated once the correlations between the above properties and hydrogen concentration are known.This research focuses on the assessment of the critical hydrogen concentration for sheet metal cold forming steels. Uniaxial slow strain rate tests on un-notched and notched samples, and small punch tests on sheet metal discs were performed for two different advanced high-strength steels as a function of the hydrogen concentration. The above tests were simulated using a material model, including a hydrogen migration and damage model coupled with a fracture criterion. The model parameters were identified by a trial-and-error procedure that reproduces the sample's response under the tested conditions.Based on the results of the simulations, correlations between the fracture strength and strain at fracture and hydrogen concentration were derived, and the critical hydrogen concentrations were estimated for thestudied materials.