Abstract
This work aims to find suitable 42CrMo4 steel grades for working in energetic applications dealing with high pressure hydrogen gas. Consequently, the influence of the tempering time on the hydrogen embrittlement (HE) sensitivity of 42CrMo4 steel quenched and tempered at 600 °C is studied. Compact tension (CT) specimens were pre-charged with gaseous hydrogen in a pressurized reactor at 19.5 MPa and 450 °C for 21 h and tested for fracture toughness afterwards in air. The hydrogen concentration introduced in the steels was determined using thermal desorption analysis (TDA). The fracture micromechanisms were subsequently identified by means of scanning electron microscopy (SEM). Electrochemical hydrogen permeation (EHP) tests were also performed to gain better insight into the interaction between hydrogen atoms and the microstructure of these steel grades, and consequently to justify the results. The fracture toughness of hydrogenated 42CrMo4 steel increases considerably with the tempering time, being this behaviour correlated with the density of hydrogen traps in the steel. Brittle fracture micromechanisms, associated with the hydrogen-enhanced decohesion mechanism HEDE (martensitic lath decohesion and intergranular fracture) were present to a lesser or greater degree in all the tempering times.
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