The buckling curves, which enable the prediction of buckling resistance of steel structural elements, are physically connected with their type of cross-section, initial out-of-straightness, and the magnitude of residual stresses due to the different manufacturing technologies. It is known that hot-dip galvanisation changes and relives residual stresses, but so far the current design provisions do not take directly into account the impact of hot-dip galvanising on the reduction of residual stresses, and thus the reduction the generalised imperfection in the Ayrton-Perry model. The paper presents the difference between the relative buckling resistance of steel angles with residual stresses resulting from hot rolling and the same elements in which the magnitude of residual stresses was decreased by the hot-dip galvanising process. Carried out tests and geometrically and materially non-linear analyses with imperfections (GMNIA) have shown that angles with residual stresses reduced by heat treatment caused by hot-dip galvanising have higher buckling resistance compared to those with residual stresses after hot rolling. This increase ranges from 2 to 7%. The analyses carried out confirmed that the predicted reduction factors  exhibit values closer to the buckling curve ‘a’, but these values do not reach the ‘a0’ curve recommended by the EN 50341-1 standard.