Pure bending of single-walled carbon nanotubes between (5,5) and (50,50) is studied using molecular dynamics based on the reactive bond order potential. Unlike smaller nanotubes, bending of (15,15) and larger ones exhibits an intermediate deformation in the transition between the buckled and fully kinked configurations. This transient bending regime is characterized by a gradual and controllable flattening of the nanotube cross section at the buckling site. Unbending of a kinked nanotube bypasses the transient bending regime, exhibiting a hysteresis due to van der Waals attraction between the tube walls at the kinked site.