X-Ray and Neutron Scattering Studies of the 9Ni Cryogenic Steel and its Weld Joint

To guarantee the reliability and safe operation of large-scale metallic structures exposed to cryogenic temperatures for extended periods, it is important to evaluate structural properties of the base metal as well as the welded zone in order to prevent damages that could occur. Spatially-resolved high-energy synchrotron diffraction, pulsed neutron diffraction and small-angle neutron scattering have been used to study short, intermediate and mesoscopic range order in cryogenic 9Ni steel as well as the structural changes induced by the welding. Pristine 9Ni steel appears to be a metastable Fe-Ni alloy with main bcc martensitic phase and a minority fcc austenitic phase. Welding of 9Ni steel using SMAW technique has revealed a fast intergranular nickel diffusion at high temperatures during welding originated from high nickel content in the SMAW welding alloy.