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Research Papers: Materials and Fabrication

Investigation of Hydrogen Assisted Cracking in High and Low Strength Steels

[+] Author and Article Information
Samerjit Homrossukon

Faculty of Engineering, Thammasat University, 99 Moo 18 Phaholyothin Rd., Ampher Khlongluang, Pathumthani 12121, Thailand

Sheldon Mostovoy

Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, IL 60616

Judith A. Todd

Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, PA 16802

J. Pressure Vessel Technol 131(4), 041405 (Jul 01, 2009) (11 pages) doi:10.1115/1.3089498 History: Received February 09, 2007; Revised July 03, 2008; Published July 01, 2009

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 50mA/cm2 in 1N H2SO4+25mg/lAs2O3 and tested under three-point-bend decreasing load. The HAC growth rate for the 1022 steel (1.4×107cm/s) was found to be approximately two orders of magnitude slower than that of the 4140 steel (3.3×105cm/s), while the threshold stress intensity factor for the 1022 steel (37.0±1.0MPam1/2) was significantly higher than that of the 4140 steel (7.0±0.5MPam1/2). 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.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Three-point-bend specimen (LT orientation) with attached knife-edges

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Figure 2

Schematic showing loading fixture: A=bolts, B=loading arms, C=fixture columns, D=fixture beams added to maintain the stability of the loading arms, and E=strain gauges

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Figure 3

Hydrogen assisted cracking test cell (mode I decreasing load)

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Figure 4

Dog-bone specimen for hydrogen analysis under an applied stress

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Figure 5

(a) Modified fixture for dog-bone specimen; (b) T-block steel (loading accessory)

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Figure 6

Schematic showing tensile loading of dog-bone specimen in modified three-point-bend fixture used for hydrogen charging in the stressed condition

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Figure 7

Relationship between crack velocity (da/dt) and stress intensity factor (KI) for the 4140 steel, cathodically charged at −50 mA/cm2 in 1N H2SO4+25 mg/lAs2O3 and tested under three-point-bend decreasing load

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Figure 8

Relationship between crack velocity (da/dt) and stress intensity factor (KI) for the 1022 steel, cathodically charged at −50 mA/cm2 in 1N H2SO4+25 mg/lAs2O3 and tested under three-point-bend decreasing load

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Figure 9

Crack path in the 4140 steel, cathodically charged at −50 mA/cm2 in 1N H2SO4+25 mg/lAs2O3, and tested under three-point-bend decreasing load with Kinitial=14 MPa m1/2

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Figure 10

Optical micrograph showing uncharged 4140 steel specimen centerline. a=electric discharge machined (EDM) notch, b=fatigue precrack, and c=increasing load crack

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Figure 11

Crack path in the 1022 steel, cathodically charged at −50 mA/cm2 in 1N H2SO4+25 mg/lAs2O3, and tested under three-point-bend decreasing load with Kinitial=47 MPa m1/2

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Figure 12

Optical micrograph showing uncharged 1022 steel specimen centerline; a=EDM notch, b=fatigue crack, and c=increasing load crack

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Figure 13

Optical micrograph of the 1022 steel hydrogen charged specimen etched in 3% nital (the arrows indicate cracks in the banded pearlitic regions)

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Figure 14

Microcrack nucleated at inclusion in hydrogen charged 1022 steel

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Figure 15

Schematic showing equilibrium of the crack opening forces

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Figure 16

(a) Crack driving force (FG,H=G) and crack resistance (FR=R) versus hydrogen concentration (CH) for the 4140 steel with KI=7 MPa m1/2, and (b) magnified view of G and G+ΔGH

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Figure 17

Crack driving force (FG,H=G) and crack resistance (FR=R) versus hydrogen concentration (CH) for the 1022 steel with KI=7 MPa m1/2

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Figure 18

Hydrogen concentration (CH) required for crack initiation versus applied stress intensity factor (KI) for (a) 4140 and (b) 1022 steels, cathodically charged at −50 mA/cm2 in 1N H2SO4+25 mg/lAs2O3, and tested under three-point-bend decreasing load

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Figure 19

Hydrogen concentration (CHi) required for crack initiation versus applied stress intensity factor (KI) for steels with yield strengths ranging from 310 MPa to 2000 MPa, cathodically charged at 10–100 mA/cm2 in 3–7% H2SO4

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