EFFECT OF HYDROGEN ON FRACTURE OF U-NOTCHED BEND SPECIMENS OF QUENCHED AND TEMPERED ALSL4340 STEEL

U-notched bend specimens of quenched and tempered AISI 4340 steel were deformed in the uncharged condition and after either precharging or dynamically charging with hydrogen. In the uncharged condition fracture initiated at the notch surface and progressed in mode II along a characteristic slip trace. For precharged specimens, strain to fracture was markedly reduced, cracks nucleated internally in a mode I manner and the crack progressed to the surface in mode II. Dynamic charging reduced plastic strain to essentially zero at crack nucleation, which occurred when the notch root stress reached the yield stress, and the crack grew by mode I. The results are compared to those on lower strength steels and are discussed in view of theories for hydrogen degradation of mechanical properties. © 1979 American Society For Metals And The Metallurgical Society of AIME.