Tensile behaviour of 42CrMo4 steel submitted to annealed, normalized, and quench and tempering heat treatments with in-situ hydrogen charging

Abstract

42CrMo4 steel was submitted to annealing, normalizing, and quench and tempering heat treatments to produce steel microstructures with different hardness levels. Afterwards, tensile tests using notched specimens were conducted in air and in two different hydrogenated conditions by means of in-situ electrochemical hydrogen charging tests. Two different electrolytes and density currents were employed to produce low and high hydrogenated conditions. The influence of microstructure and hardness on hydrogen embrittlement was determined and scanning electron microscopy (SEM) analysis was used to identify the respective operative failure micromechanisms. A significant loss in notched strength was observed when hydrogen was introduced during the tensile tests on all tested microstructures, giving rise to changes in the predominant operative failure micromechanism. Embrittlement indexes increase as the electrochemical conditions applied introduce higher hydrogen concentrations and as the steel hardness increases. The notched tensile strength measured with in-situ hydrogen charging in the normalized and annealed grades is lower than that of quenched and tempered steels for the same hardness.