An investigation on the weldability of a quenched and tempered 9% Ni-steel, using weld simulation and artificial aging to estimate the heat affected zone (HAZ) ductility at cryogenic temperatures is reported in the first part of this paper.A series of large scale tensile tests have also been carried out on 9% Ni butt welds, the results of which are presented in the second part.Charpy-V bars were subjected to various weld simulation cycles and subsequent heat treatments and after notching broken at a range of cryogenic temperatures.The simulated welding heat in general, even where varied between wide limits, causes a decrease in impact properties of the steel, although they are still acceptable even at the very lowest test temperatures (-196 C). Severe embrittlement can result from artificial aging, such as a plastic deformation followed by heating in the 200-400 C temperature range.This suggests that care must be taken when cold deformation is used or distortions are corrected in structures made of 9% Ni-steel.