Microstructural aspects upon hydrogen environment embrittlement of various bcc steels

Several commercial bcc steels with various combinations of ferritic, pearlitic, bainitic and martensitic microstructures were tensile tested in gaseous hydrogen (10 MPa) at room temperature. Fractography of all bcc/bct steels tested in gaseous hydrogen showed clear indications of hydrogen assisted fracture morphology. Comparing these results with those of austenitic stainless steels, it can be assumed that hydrogen enhanced localized plasticity (HELP) is also the primary failure mechanism in all bcc microstructures (ferritic, ferritic/pearlitic, bainitic, martensitic) investigated here. Neither strength nor final grain size nor prior austenite grain size were identified as sole primary factors influencing hydrogen embrittlement. The only steel with a negligible loss in macroscopic ductility was a precipitation hardenable grade indicating that incorporating irreversible traps might be a successful way to reduce the susceptibility of bcc steels to hydrogen embrittlement. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.