Development of structure o£ microalloying medium-carbon steel (% : 0.32 -0.38C

0.001-0.010B

≤0.05Als) controlling rolling and cooling with deformation at 760-820 ℃. and initial cooling at 750-840 °C has been studied by hot compression test by Gleeble-1500 thermal simulation machine. Results show that the average ferrite grain size decreases with decreasing deformation temperature and increases with increasing initial cooling temperature

and with decreasing deformation temperature the percentage of ferrite increases and the spheroidizing trend of pearlite is more obvious ； the optimum process parameters are deformation temperature-790 ℃ and initial cooling temperature-840 ℃. to get maximum ferrite volume percentage- 64.5% that is far more than that 54% in general medium-carbon steel. The definite BN particles at grain boundary are available to improve the plastic deformation of B steel.