Ok,
Soft Iron contains a low amount of carbon this leads to a grain structure of mainy ferrite grains with the occasional pearlite grain with perlite made up of sheets of ferrite and cementite.
Cementite is a very hard material making it brittle and unmalleable.
Normal iron has more carbon and hence more pearlite and therefore it is harder.
If the carbon content goes above .08% (weight), then it will form cast iron which has an cementite precipitate and becomes even harder.