Using high resolution numerical simulations -- addressing the dynamics, the star formation, and the chemical evolution -- we follow the formation of disc galaxies during wet major mergers in which each protogalaxy is embedded in a hot gaseous halo. We witness the destruction of the discs of the protogalaxies and the inside-out formation of a new disc, which is both massive and extended. We also witness the formation of a classical bulge component whose mass relative to the disc varies from one run to another, taking values that cover all the range from lenticulars to spiral galaxies. The rotation curves of our model galaxies are found to be flat. In all our simulations the disc has substructures, such as bars, lenses, spirals and rings, with realistic morphology, including ansae and boxy/peanut bulges. We will briefly discuss some dynamics of these substructures, as well as the formation and properties of the thin and thick disc components. Last but not least, we will present results on metallicity and make comparisons with observations in the bar/bulge regions of our Galaxy.