Analysis on Microstructure and Strengthening Mechanisms of V-Ti Micro-alloyed HRB600 High Strength Steel Rebar

Continues cooling phase transformation behavior and strengthening mechanisms of the V-Ti containing rebarsteel were systematically studied by thermal simulation testing machine,HR-TEM and OM.The result showed that the microstructure of used rebar was composed of ferrite and pearlite at 0.5～1.5 ℃/s cooling rate; the bainite transformation occurred and the ratio of bainite increased at 1.5～5 ℃/s cooling rate; the martensite structure appeared and gradually become the main structure at 5～25 ℃/s cooling rate.The strengthening mechanisms of V-Ti containing test steel were mainly precipitation strengthening and fine-grain strengthening,and V（C,N）+TiN mainly precipitated as rounded rectangle fine particles dispersing and its size was 10～60 nm.The V-Ti containing rebar was pilot-manufactured by using cooling rate of 1.0～1.5 ℃/s,which shows yield strength above 630 MPa,tensile strength above 820 MPa,elongation of 20%,maximum gross elongation of 11%,and the ratio of tensile strength and yield strength of 1.25.