Two kinds of oil tank steels were fabricated by added B(B-steel) and Cu(Cu-steel) , and their microstructures, tensile and Charpy impact properties, undercooled austenite transformation were investigated. In this work,0.0016%B can improve hardenability distinctly. The B-steel was mainly composed of bainite at the cooling rate of 3°Cs-1, but the Cu-steel completely consisted of bainite when the cooling rate exceed 20°Cs-1. The steels manufactured by thermo-mechanical controlled process , test results indicated that the B-steel had the higher yield and tensile strength than the Cu-steel ,because their volume fractions and morphologies of bainite. The Cu-steel had the higher impact energy than the B-steel because of their higher effective grain size. Majority of the precipitation particles which were compounded of Nb and Ti existed as（Nbx,Ti(1-x)) (CyN(1-y)).