The inhibition of corrosion and hydrogen embrittlement in sae 4340 steel with the rare earth compound lanthanum 4 hydroxy cinnamate

A preliminary study has shown that the inhibitor lanthanum 4 hydroxy cinnamate ((La4OHcin) 3 ) at a concentration of 400 ppm in 0.01M NaCl (i) reduced the corrosion rate, and (ii) prevented the hydrogen embrittlement (HE) of SAE 4340 steel tensile specimens when tested under slow strain rate conditions. In the presence of the inhibitor, a complex film formed on the surface of specimens during the slow strain rate test, and no corrosion pits developed. This film was not observed when the inhibitor was not present, but the surface was covered in corrosion pits. Electrochemical tests indicated that the La(4OHcin) 3 acted as an anodic inhibitor in the NaCl solution. The prevention of HE by La(4OHcin) 3 is thought to be due to the ability of the inhibiting film to suppress the formation of corrosion pits and the accompanying evolution of hydrogen within the pits.