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The expansion curves of continuous cooling transformation at different cooling rates was determined for U75V rail steel by THERMECMASTOR- Z thermal simulator，and continuous cooling transformation curve was obtained.The influedce of cooling rate on microstructure and hardness was studied.On the other hand，the softening behavior of isothermal deforming at austenite area 850～1000℃ within interval of passes has been also studied by double-pass compression test.The results show that the product of austenite transformation was pearlite when the cooling rate was lower than 10℃.Troostite and martensite were gained at the cooling rate of 10℃•s-1. Only martensite was received when the cooling rate was in the range of 10～ 50℃•s-1.the hardness of steel increased with the increase of cooling rate.Results also indicated that 30% deformation and 3S-1 deforming rate，as deformation temperature ≥1000℃，relaxation time for performing recrystallization was≤100s，and as deformation temperature≤880 ℃，it was difficult even extending relaxation time to put forward recrystallization of steel.