Stress corrosion cracking of high strength HY-180M steel in 3.5 Pct NaCl

TLDR: In this article, the authors studied stress corrosion cracking of HY-180M steel at 22°C in an aqueous solution of 3.16C and was heat treated to yield a fracture toughness value ofK ∼ 160 MPa. m1/2.

Abstract: 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 ofK Ic ≃ 160 MPa . m1/2. The SCC velocity (v) was studied as a function of stress intensity (K I) 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 uponE, and did not occur whenE =-0.52 VSHE (-0.72 VAg/AgCl), which corresponded closely to the thermodynamically reversible potential of iron. However, SCC occurred at a more noble potential of-0.28 VSHE (-0.48 VAg/AgCl ) and at a less noble potential of-0.80 VSHE (-1.00 VAg/AgCl). The stress intensity below which SCC was not observed was KISCC ≃ 5.5 MPa . m1/2 at -0.28 VSHE and KISCC ≃ 60 MPa . m1/2 at -0.80 VSHE . Also, Region I behavior (v dependent uponK 1) and Region II behavior (v independent ofK 1) 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 VSHE . The indirect effects were discussed in relation to hydrolysis effects in the crack promoting hydrogen embrittlement and/or corrosion product wedging stresses.