The impact energy samples of non-quenched-tempered steel JGF45V hot-rolled state by finishing rolling at 1 000℃ and normalized state by normalizing at 860℃ are analyzed by metallography and scanning electron microscope. It is obtained that grain size is an important parameter affecting room temperature impact energy of non-quenched-tempered JGF45V steel. Through process test of decreasing the finishing rolling temperature from 1 000℃ to 900 ~930 % with the cooling rate being 0. 3 ℃/s

the grain size rating of steel increases from 5 to 7

and the room U-shaped impact energy increases from 32 J to ≥55 J.