The effect of heat treatment on environment assisted cracking susceptibility of 9% Ni steel

Abstract

The influence of temper temperature on the environment assisted cracking of seamless 9% Ni steel tubes were investigated using scanning electron microscope (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), slow strain rate tensile (SSRT) tests, hydrogen permeation tests and electrochemical measurements. Mechanical and electrochemical tests were conducted in sodium thiosulphate (Na 2 S 2 O 3 10 −3 mol L −1 ) solution at open circuit potential (OCP) and at cathodic potential. Results showed that 9% Ni steel had a higher ductility loss at OCP when compared with the results obtained under cathodic potential. The lower ductility loss at cathodic potential was attributed to the inhibition of the anodic dissolution. After the tests, the specimens were examined using scanning electron microscopy to characterise the fracture morphology. The fracture surface exhibited mixed morphology, with a ductile morphology in the centre and a brittle morphology near the edges.