Research On Effects Of Heat Treatment On The Microstructure And Properties Of K65 Hot Induction Bend

Hot induction bends play a key role in the construction of long-distance pipelines, moreover, the bends often under harsher working conditions than straight pipes.This, in turn, necessitates the use of the heavy wall bends with higher stength. However, the research on bends is not taken seriously due to the demand of bends is less than the straight pipes. According to the current production experience of bends, the production of heavy wall bends with high stength is lack of experience to reference.Therefore, to carry out fundamental researchs for developing heavy wall K65 bends is very important,which have important significance for developing heavy wall K65 bends,and construction for the Sino-Russian pipeline.The experiments were carried out on a Gleeble-3500 thermal simulator to simulate the actual production process of three kinds of K65 hot induction bends. Then the tempering process is done in a boxing tempering furnace. By using microscope, scanning electron microscope, electron backscattered diffraction and transmission electron microscope, the relationship between microstructures and mechanical properties in K65 bends in different bending conditions are explored.The results showed that the PF microstructures decrease and the AF microstructures increase with the increase of the heating temperature. As the heating temperature further increases, the BF microstructures increase and the grains grow severely. The value of strength increases gradually with the increase of the heating temperature. The value of toughness decreases with the increase of the heating temperature. When the heating temperature is 1030 ?C, the toughness of three kinds of steels became very poor.Under the little cooling rate, the main microstructure of steel A and B is PF, a small amount of GB. With the large cooling rate, the main microstructure is GB. The grains are fine, which makes the toughness better. However, under large cooling rate, the microstructure of steel C is consist of GB and BF which has big size of effective grain, leading to deterioration in the toughness.Some fine particles appear after the three kinds of steels were tempered. The EDS analysis indicates that the particles are NbC. When the tempering temperature increased from 500 ?C to 550 ?C, the strength increased and the impact value changed slightly.