International Hydrogen Conference (IHC 2012): Hydrogen-Materials Interactions
3 Measurement and Modeling of Temperature Dependent Internal Hydrogen Assisted Cracking in Cr-Mo Steel
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The intrinsic temperature dependence of internal hydrogen assisted cracking (IHAC) of 2¼Cr-1Mo steel base plate and weld metal is measured with several fracture mechanics approaches, including a new-slotted specimen. Slow-rising displacement threshold stress intensity (KIH) increases as IHAC is eliminated with rising temperature from -50 to 125°C. Hydrogen concentration proximate to the crack tip (CTσ), stress enhanced and microstructure trapped, provides a similitude parameter; equal KIH is produced for equal CTσ. The CTσ from FEA diffusion analysis decreases with decreasing-bulk H concentration and decreasing-exponential of the H-binding energy to temperature ratio for trap sites along the bainite interface crack path. IHAC is eliminated below a critical CTσ, and thus above a critical temperature due to H detrapping. The relationship between KIH and CTσ is predicted from a decohesion-based micromechanics model. Similitude provides the basis to predict a minimum pressurization temperature for pressure vessel operation without IHAC.