The stress-strain curves and microstructure evolution o£ a microalloyed steel - 0.05C
1.57Mn
0.50Cu
0.05Nb
0.014Ti
0.001 2B between 800 and 1 100 X. have been tested and studied by Gleebe-1500 hot simulator using single pass reduction test method
and based on the experimental results the grain size model and the critical strain of dynamic recrystallization have been established. It is obtained the grain size of the microalloyed steel shall be fined with decreasing of deformation temperature and increasing of deformation rate.