|About this Abstract
||2014 TMS Annual Meeting & Exhibition
||Multiscale Approaches to Hydrogen-assisted Degradation of Metals
||Hydrogen Environment Assisted Cracking (HEAC) of Modern Ultra-high Strength Stainless Steel
||Greger Pioszak, Richard Gangloff
|On-Site Speaker (Planned)
Two Ni<SUB>3</SUB>Ti-strengthened martensitic stainless steels, aged to high yield strength (1700-1860 MPa), exhibit markedly different HEAC in 3.5% NaCl solution. Both alloys resist cracking within a polarization window mildly cathodic to open circuit (-225 mV<SUB>SCE</SUB>) where threshold stress intensities approach K<SUB>IC</SUB> (75-100 MPa√m). Severe intergranular cracking occurs in Custom<SUP>®</SUP>465-H900 when cathodically polarized below -475 mV<SUB>SCE</SUB>, with thresholds of 10-14 MPa√m and Stage II crack growth rates of 1-3 μm/s. Ferrium<SUP>®</SUP>PH48S<SUP>™</SUP>-H900 is susceptible to HEAC, but only below -600 to -750 mV<SUB>SCE</SUB>; thresholds are similar at -975 mV<SUB>SCE</SUB>, but Stage II growth rates are consistently lower (0.1-0.2 μm/s) and cracking is transgranular likely through martensite interfaces. Reduced growth rates may be attributed to H trapping at dispersed TiC, which reduces H diffusivity in Ferrium<SUP>®</SUP>PH48S<SUP>™</SUP>. The transition from intergranular to transgranular HEAC may relate to a grain boundary phase, elemental segregation, or H localization. Experiments are in progress to test these hypotheses.
||Planned: Paper Selections