| Abstrakt: |
Stress corrosion cracking of HY-180M steel was studied at 22°C in an aqueous solution of 3.5 pct NaCl (pH = 6.5). The steel had a nominal weight percentage composition of 10Ni-14Co-2Cr-lMo-0.16C and was heat treated to yield a fracture toughness value of K ≃ 160 MPa . m. The SCC velocity ( v) was studied as a function of stress intensity ( K ) and electrochemical potential ( E) using precracked compact tension specimens, a Ag/AgCl reference electrode and a 1000 h exposure test. Also, the polarization behavior, microstructure, fractography and corrosion products were studied. The results showed that SCC was markedly dependent upon E, and did not occur when E =-0.52 V (-0.72 V), which corresponded closely to the thermodynamically reversible potential of iron. However, SCC occurred at a more noble potential of-0.28 V (-0.48 V ) and at a less noble potential of-0.80 V (-1.00 V). The stress intensity below which SCC was not observed was K ≃ 5.5 MPa . m at -0.28 V and K ≃ 60 MPa . m at -0.80 V . Also, Region I behavior ( v dependent upon K ) and Region II behavior ( v independent of K ) were observed. Cracking was considered to occur solely by hydrogen embrittlement at -0.80 Vshe, whereas anodic dissolution processes played a necessary role, either directly or indirectly, in SCC at -0.28 V . The indirect effects were discussed in relation to hydrolysis effects in the crack promoting hydrogen embrittlement and/or corrosion product wedging stresses. [ABSTRACT FROM AUTHOR] |
