The mutual interactions of dislocation lines containing collinear superjogs are investigated in face-centered cubic crystals by dislocation dynamics simulations in single slip and for various loading axes. The examination of the dislocation microstructures, dislocation densities and stress–strain curves allows the origin of work hardening during stage I to be clarified and explains the unusual hardening that is observed experimentally in [0 0 1] crystals at low stresses.