Multiscale thermodynamic analysis on hydrogen-induced intergranular cracking in an alloy steel with segregated solutes

2015 ◽  
Vol 33 (6) ◽  
pp. 547-557 ◽  
Author(s):  
Masatake Yamaguchi ◽  
Ken-ichi Ebihara ◽  
Mitsuhiro Itakura
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Slow Crack Growth ◽  
High Strength Steels ◽  
High Strength ◽  
Intergranular Cracking ◽  
Fracture Surfaces ◽  
Mobile Hydrogen ◽  
Threshold Stress Intensity Factor

AbstractA multiscale analysis has been conducted on hydrogen-induced intergranular cracking at ambient temperature in medium strength (840 MPa) Ni-Cr steel with antimony, tin, and phosphorous segregation. Combining first-principles calculations and fracture mechanics experiments, a multiscale relationship between threshold stress intensity factor (Kth) and cohesive energy of grain boundary (the ideal work of interfacial separation, 2γint) was revealed. The Kth was found to decrease rapidly under a certain threshold of 2γint, where the 2γint decreases mainly by mobile hydrogen segregation on fracture surfaces. This segregation is considered to arise during formation of the fracture surfaces under thermodynamic equilibrium in slow crack growth. The resulting strong decohesion probably makes it difficult to emit dislocations at the microcrack tip region, leading to a large reduction in stress intensity factor. Our analysis based on this mobile hydrogen decohesion demonstrates that the Kth decreases dramatically within a low and narrow range of hydrogen content in iron lattice in high-strength steels.

Investigation of Hydrogen Assisted Cracking in Pressure Vessels

2006 ◽  
Author(s):  
Samerjit Homrossukon ◽  
Sheldon Mostovoy ◽  
Judith A. Todd
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
High Strength ◽  
Pressure Vessels ◽  
Crack Driving Force ◽  
Pressure Vessel Steels ◽  
Hydrogen Assisted Cracking ◽  
Threshold Stress Intensity Factor ◽  
Point Bend

Hydrogen assisted cracking (HAC) has been investigated in high strength 4140 and low strength Z17D pressure vessel steels, charged at −50 mA/cm2 in 1N H2SO4 + 25 mg/1 As2O3 and tested under three-point bend decreasing load. The HAC growth rate for Z17D steel (1.4×10−7 cm/s) was found to be approximately two orders of magnitude slower than that of 4140 steel (3.3×10−5 cm/s), while the threshold stress intensity factor for Z17D steel (∼37 MPa√m) was significantly higher than that of 4140 steel (∼7 MPa√m). This research will show that a single analytical model, based on the hypothesis that hydrogen both reduces crack resistance (R) and increases crack driving force (G), can explain HAC in 4140 and Z17D steels. The model predicts the hydrogen concentration required to initiate HAC as a function of the stress intensity factor and yield strength of the steel. Hydrogen-induced reduction of R was found to dominate HAC in 4140 steel, while hydrogen-induced reduction of R was combined with an increase in G for HAC cracking of Z17D steel.

Investigation of Hydrogen Assisted Cracking in High and Low Strength Steels

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Samerjit Homrossukon ◽  
Sheldon Mostovoy ◽  
Judith A. Todd
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Driving Force ◽  
High Strength ◽  
Crack Driving Force ◽  
Hydrogen Assisted Cracking ◽  
Threshold Stress Intensity Factor ◽  
Low Strength ◽  
Point Bend

Hydrogen assisted cracking (HAC) has been investigated in a high strength 4140 steel and a low strength AISI-SAE grade 1022 steel (supplied by Amoco, Naperville, IL—now BP), charged at −50 mA/cm2 in 1N H2SO4+25 mg/lAs2O3 and tested under three-point-bend decreasing load. The HAC growth rate for the 1022 steel (1.4×10−7 cm/s) was found to be approximately two orders of magnitude slower than that of the 4140 steel (3.3×10−5 cm/s), while the threshold stress intensity factor for the 1022 steel (37.0±1.0 MPa m1/2) was significantly higher than that of the 4140 steel (7.0±0.5 MPa m1/2). This research develops an analytical model, based on the hypothesis that hydrogen both reduces crack resistance (R) and increases crack driving force (G), to explain HAC in 4140 and 1022 steels. The model predicts the hydrogen concentration required to initiate HAC as a function of the applied stress intensity factor and yield strength of the steel. Hydrogen-induced reduction in R was found to dominate HAC in the 4140 steel, while hydrogen-induced reduction in R was combined with an increase in G for HAC cracking of the 1022 steel.

Slow Crack Growth in Glasses and Ceramics Under Residual and Applied Stresses

1989 ◽  
Vol 111 (1) ◽  
pp. 61-67 ◽  
Author(s):  
F. Erdogan
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Threshold Value ◽  
Crack Arrest ◽  
Growing Crack ◽  
Applied Stresses

The problem of slow crack growth under residual stresses and externally applied loads in plates is considered. Even though the technique developed to treat the problem is quite general, in the solution given it is assumed that the plate contains a surface crack and the residual stresses are compressive near and at the surfaces and tensile in the interior. The crack would start growing subcritically when the stress intensity factor exceeds a threshold value. Initially the crack faces near the plate surface would remain closed. A crack-contact problem would, therefore, have to be solved to calculate the stress intensity factor. Depending on the relative magnitudes of the residual and applied stresses and the threshold and critical stress intensity factors, the subcritically growing crack would either be arrested or become unstable. The problem is solved and examples showing the time to crack arrest or failure are discussed.

Engineering Relation for Dependence of Threshold Stress Intensity Factor for Delayed Hydride Cracking on Crack Orientation

2008 ◽  
Author(s):  
Douglas A. Scarth ◽  
Gordon K. Shek ◽  
Steven X. Xu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Threshold Stress ◽  
Pressure Tube ◽  
Threshold Stress Intensity ◽  
Tube Material ◽  
Fuel Bundle ◽  
Threshold Stress Intensity Factor ◽  
Cold Worked

Delayed Hydride Cracking (DHC) in cold-worked Zr-2.5 Nb pressure tubes is of interest to the CANDU industry in the context of the potential to initiate DHC at an in-service flaw. Examples of in-service flaws are fuel bundle scratches, crevice corrosion marks, fuel bundle bearing pad fretting flaws and debris fretting flaws. To date, experience with fretting flaws has been favourable, and crack growth from an in-service fretting flaw has not been detected. However, postulated DHC growth from these flaws can result in severe restrictions on the allowable number of reactor Heatup/Cooldown cycles prior to re-inspection of the flaw, and it is important to reduce any unnecessary conservatism in the evaluation of DHC from the flaw. One method to reduce conservatism is to take credit for the increase in the isothermal threshold stress intensity factor for DHC initiation at a crack, KIH, as the flaw orientation changes from an axial flaw to a circumferential flaw in the pressure tube. This increase in KIH is due to the texture of the pressure tube material. An engineering relation that provides the value of KIH as a function of the orientation of the flaw relative to the axial direction in the pressure tube has been developed as described in this paper. The engineering relation for KIH has been validated against results from DHC initiation experiments on unirradiated cold-worked Zr-2.5 Nb pressure tube material.

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