Effect of quenching and tempering treatment on microstructure and properties of 1000 MPa grade hydropower steel
Effect of different quenching and tempering processes on microstructure and mechanical properties of 1000 MPa grade hydropower steel was studied using scanning electron microscopy,transmission electron microscopy,tensile and impact testing machines.The results show that the microstructure of the experimental steel after quenching is quasi-equiaxed,and the lath martensite is fine.In the quenching temperature range of 890-950 ℃,with the increase of quenching temperature,the size of martensite packet increases,and the microstructure is transformed into tempered sorbite after tempering at 620 ℃.The precipitation of carbides and their interaction with dislocation during tempering improve the strength of the experimental steel.As the quenching temperature increases,the yield strength and tensile strength of the experimental steel increase,while the elongation remains basically unchanged,the impact absorbed energy at-60 ℃ shows a trend of first slowly increasing and then sharply decreasing,and the impact fracture mode changes from ductile fracture to brittle cleavage fracture.After quenching at 920 ℃ for 30 min and tempering at 620 ℃ for 60 min,the comprehensive mechanical properties of the experimental steel reach the optimal level,with yield strength,tensile strength,elongation and-60 ℃ impact absorbed energy of 970 MPa,986 MPa,15％and 185 J,respectively,meeting the performance requirements of 1000 MPa grade hydropower steel.
hydropower steelquenching and tempering treatmentmicrostructure evolutionmechanical propertystreng-thening mechanism
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