Abstract: Effect of tempering temperature after normalizing on the microstructure and properties of carbide-free bainitic steel seamless pipe was studied. The results show that when normalized at 930 ℃ and then tempered at below 600 ℃, the tensile strength of the tested material tends to decrease with the increase of tempering temperature and changes within the range of 973 MPa to 1012 MPa. When tempered at 300 ℃, the impact absorbed energy of the tested material is the maximum, as 72 J. When tempered at 400 ℃, the impact absorbed energy is the lowest, and the tempering brittleness of carbide-free bainitic steel appears. When tempered at above 400 ℃, the impact absorbed energy of the tested material increases. The elongation and the reduction of area reach the maximum when tempered at 300-350 ℃. When the tempering temperature is below 400 ℃, the microstructure of the tested material consists of carbide-free bainite, bulk ferrite and austenite. When the tempering temperature is over 400 ℃, the microstructure becomes granular bainite and bulk ferrite. Carbide-free bainitic steel seamless pipe has the better comprehensive mechanical properties when normalized at 930 ℃ and then tempered at 300 ℃.

Key words: carbide-free bainite steel, seamless steel pipe, tempering temperature, microstructure, properties