Effect of threshold stress intensity on fracture mode transitions for hydrogen-assisted cracking in AISI 4340 steel |
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Authors: | Su-Il Pyun Hyo-Keun Lee |
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Affiliation: | (1) Department of Materials Science and Engineering, Korea, Advanced Institute of Science and Technology (KAIST), Chongyangni, Seoul, Korea |
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Abstract: | Fracture mode transition in hydrogen-assisted cracking (HAC) of AISI 4340 steel has been studied from an equilibrium aspect
at room temperature with 8.6-mm-thick double cantilever beam (DCB) specimens. The threshold stress intensity,K
th
, necessary for the occurrence of HAC and the corresponding fracture surface morphology have been determined as a function
of hydrogen pressure and yield strength. The K
th
increases with decrease in hydrogen pressure at a given yield strength and also with decrease in yield strength at a given
hydrogen pressure. AsK
th
increases, the corresponding HAC fracture mode changes from the intergranular (IG) and quasi-cleavage (QC) modes to the microvoid
coalescence (MVC) mode. The experimental results indicate that the critical hydrogen concentration for crack extension in
the IG mode is higher than that for crack extension in the MVC mode. The fracture mode transition with varying hydrogen pressure
and yield strength is discussed by simultaneously considering the micromechanisms for HAC and the hydrogen pressure and yield
strength dependencies ofK
th
. |
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Keywords: | |
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