Structure of a non-quenched and tempered steel-(%)0.37~0.38C

0.82~0.92Si

1.78～1.81Mn

0.06Ti

0.015Nb with three different V-N content-(%)0.130V-0.0215N

0.130V-0.0304N and 0.001V-0.0207N was studied by optical microscope and transmission electron microscope

strain-stress curves of the steel were measured by Gleeble 1500 thermal simulation machine and continuous cooling transformation curves of the steel and each phase content in  steel at 900 ℃ and 600 ℃ in equilibrium state were calculated by JMatPro 4.1 software.Results showed that the structure of the steel was pearlite + proeutectoid ferrite; with increasing N content

the amount of pearlite increased with boundary ferrite coarsening; and with decreasing V content

the amount of pearlite increased with bainite and ferite coarsening; the size of precipitates in proeutectoid ferrite and in eutectoid ferrite was ≤3 nm;and the stress during train for steel with higher V and / or N content was larger.