The evolution of dislocations in an austenitic region has a close relationship with the processing of precipitation during the alloy steel deformation. To verify the relevance of the refining structure of bainite and the pining dislocation networks of nano-size precipitation for Fe-40Ni alloy, the thermo-simulation test, metallographic analysis, quantitative measurement and Transmission Electron Microscope (TEM) technique were used to study the precipitation of deformated low carbon microalloyed steel in a relaxation processing at 850 ℃ and its influence on bainite formed during subsequent cooling. The experimental results demonstrate that the microstructures (mixed ultra-fine bainite and martensite) of the tested steel have been refined effectively during relaxation processing and it shows that the optimum refinement can be obtained by 60-200 s relaxation after being deformed. Meanwhile, the dislocations can be pinned by the strain-induced precipitation whose sizes are less than 10 nm. The experimental results obtained from the tested steel are in a good agreement with that of the Fe-40Ni alloy simulations.