The features of dynamic transformation for grain refinement of low carbon steels are presented and representative results of trial hot strip productions are reported. Laboratory experiments have established that dynamic transformation occurs in under-cooled austenite under suitable deformation conditions. Trial production results showed that utilizing the dynamic transformation concept, grain refinement of ferrite is feasible in commercial hot strip mills: a ferrite grain size of 2~3 μm can be obtained, along with various controlled second phases.