In order to study the effect of cementite morphology on the structure and properties of sub-structure of pearlite in SWRS82B steel,related heat treatment process was established:The sample was cooled to 300 ℃ at the cooling rate of 70,100,200 ℃/s and isothermal to 3~15 s after austenitized at 880 ℃ for 15 min.Then heated to isothermal at 550 ℃ for 1 min,the last was the rapid cooling to room temperature. The results of SEM and TEM observation and MTS tensile testing machine show that,when the supercooling time was 3 s,the cementite was fragmented by different degree from the whole lamellar with the increase of cooling rates. When the cooling rate was 200 ℃/s,the cementite was broken down in large area,and nanoscale cementite was found.The tensile strength decreased firstly and then increased,but the elongation increased continuously.When the cooling rate was 70 ℃/s,the tensile strength and elongation decreased with the increase of the supercooling time. The nanoscale cementite decrease with the extension of the supercooling time;while reached to 15 s,the low bainite began to appear.