Interstitial-free steel means that almost all of the carbon has been removed: usually 0.020 % maximum (by mass). The 1001 designation uses the same system for carbon steels as SAE J403, with the 1xxx meaning plain carbon (no alloying) elements, and the last two digits indicating the nominal carbon composition, in this case, 0.010 % by mass. The annealing treatment would depend on exactly how the steel producer hot-rolled and cold-rolled the steel coil. There is no post-forming heat treatment used for this grade-- this grade is used in the automotive industry for body applications that require extremely good formability. Since there is essentially no carbon, it will not respond to any type of hardening treatment, only the softening treatments (stress relieving, annealing, etc.).
