HYDROGEN EMBRITTLEMENT OF DUAL-PHASE STEELS

A study of HE in two dual-phase steels with tensile strengths of about 690 MPa (100 ksi) has shown that these steels are susceptible to the presence of hydrogen. HE results in a reduction in fracture strength, although no preyield failures are observed, and a change in fracture mode from ductile dimpling to transgranular cleavage. The greater the prestrain, the higher the fracture stress. The presence of 15 to 20 pct high carbon (0. 6 pct C) high strength martensite is responsible for HE. Delayed failure tests on notched specimens showed that for the as-received condition, the run-out stress (stress for no failures in 50 to 100 H) is above the macroscopic flow stress.