Advanced steels have been studied aiming at realizing higher strength with high toughness by microstructural control, minimizing the use of alloying elements. Grain refinement is known to achieve high strength without scarifying toughness and Thermo-Mechanically Controlled Process (TMCP) has been studied to obtain ultrafine grained structure. During TMCP, work hardening, recovery, recrysatllization, phase transformation and precipitation take place competitively. Hence the control of these phenomena is a key issue of advanced TMCP. We have recently found that ausforming is quite effective to accelerate bainite transformation at very low temperatures (nano-bainite). The continuous deformation during cooling is effective to enhance ferrite transformation resulting in fine grains. These processes will be in situ studied by neutron diffraction.