Structure and Mechanical Properties of HTP Pipeline Steel X80

The structure and mechanical properties of pipeline steel X80 produced in laboratory by means of D450mm mill through controlled rolling and controlled cooling were tested.The results show that the yield strength of tested steel has reached above 600 MPa,and the ratio of tensile strength to yield strength is 0.87,and ductile-brittle transition temperature is lower than -60 ℃,and good strength and toughness are obtained.Low content of P,S,high content of Mn and fine microstructure have good effect on reducing the ductile-brittle transition temperature.Two different precipitations are observed in pipeline steel X80,and the large ones are mainly Nb,Ti(CN)with size range of 50 nm to 0.2 μm,and the small ones are mainly NbC with size lower than 30 nm.Remarkable strengthening and grain refinement can be caused by these nano-precipitations.