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| MECHANISM OF HYDROGEN INDUCED CRACKING IN STEELS |
| Chu Wuyang; Xiao Jimei and Li Shiqiong (Beijing University of Iron and Steel Technology) |
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Cite this article:
Chu Wuyang; Xiao Jimei and Li Shiqiong (Beijing University of Iron and Steel Technology). MECHANISM OF HYDROGEN INDUCED CRACKING IN STEELS. Acta Metall Sin, 1981, 17(1): 10-119.
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Abstract The nucleation aria propagation of hydrogen induced cracking in various environments capable of supplying hydrogen such as H_2 gas, H_2S gas, distilled water, H_2S solution, 0.1N K_2Cr_2O_7 solution, acetone, alcohol and hydrogen introduced by charging have been traced by metallographic shadowing technique in four low-alloy steels with a wide range of tensile strength (900 to 1800 MPa). The variation of K_(ISCC)(Or K_(ⅠH)) with strength of the steels in these environments has also been investigated. It is shown that if K_Ⅰ of the crack tip exceeds K_(ISCC) (or K_(IH)), a hydrogen induced delayed plasticity will occur in all the environments experimented, followed by a nucleation and propagation of hydrogen induced cracking, i.e., with the entry of the hydrogen atoms, the size of the plastic zone and the plastic deformation in front of the crack tip are enlarged continuously with time. In ultrahigh strength steels, the hydrogen induced cracking is nucleated at the tip of the closure of the two paths of delayed plastic zones. These discontinuous cracks will grow and join one another with the progress of the delayed plasticity. In lower strength steels, the initial pre-crack propagates continuously along the path near to the border of the delayed plastic-elastic region with the enlargement of hydrogen induced delayed plastic zone. Thus, it is concluded that hydrogen induced delayed plasticity might be necessary and sufficient condition for hydrogen induced delayed cracking for Mode Ⅰ crack.In all the environments used, the K_(ISCC) (or K_(IH))is increased, and the da/dt decreased with the decrease of the strength of the steel. With identical strength level, anodic polarization in water or addition of the inhibitor (0.1N K_2Cr_2O_7) may bring about an increase in K_(ISCC) and a fall in da/dt, however, cathodic polarization in water affects inversely. Lower K_(ISCC) and higher da/dt are obtained for stress corrosion in saturated aqueous solution of H_2S or electrolytic charging during loading. It was also observed that another mechanism of hydrogen induced cracking, i.e. hydrogen pressure mechanism is operative during severe electrolytical charging without external stress.
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Received: 18 January 1981
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