Research On The Effects Of Controlled Rolling And Controlled Cooling On The Microstructure Regulation And Mechanical Properties Of High-strength Earthquake-resistant Steel Bars

Rebar is a very important material in major engineering structures,and its fine-grained structure determines the strength and seismic resistance of rebar.The combination of microalloying elements and controlled rolling and controlled cooling has an important influence on the microstructure transformation of high-strength anti-seismic rebars.The Gleeble-3800 thermal simulator was used to measure the phase transformation law and thermal expansion curve under the conditions of different cooling rates,and obtained the continuous cooling transformation(CCT)curve of high-strength anti-seismic rebars.The results showed that when the cooling rate were 0.3 ?/s?3 ?/s,the experimental steel with 0.017% Nb and 0.023% Nb occurred ferrite transformation and pearlite transformation.The microhardness of two experimental steels increased slowly with the increase of cooling rate.When the cooling rate was 0.5 ?/s,the main precipitates of 0.017% Nb and 0.023% Nb experimental steels were(Nb,V,Ti)C,which were circular in shape,and the average particle size ranges were 10?20 nm and 10 nm,respectively.The rolling process conditions also have an important influence on the microstructure and mechanical properties of high-strength anti-seismic rebars.Four experimental steels with different compositions were designed,and the Gleeble-3800 thermal simulator was used to simulate thermal deformation and final cooling temperature control.The results showed that the microstructure of 1#?4#experimental steels were mainly composed of ferrite and pearlite.As the final cooling temperature decreased,the tensile strength and yield strength of 1#,2#,3#,and 4#experimental steels increased.The tensile strength and yield strength of 4#experimental steel reached the maximum at the final cooling temperature of 650?under the conditions of process I and process II,which were 712.94 MPa,562.7 MPa and 655.62 MPa,522.76 MPa,respectively.The fractures of 1#,2#,3#,and 4#experimental steels belonged to the ductile fractures,and the depth of equiaxed dimples first increased and then decreased.The main precipitated phases in the 3#experimental steel were(V,Nb,Ti)C and(Nb,V,Ti)C,which were round and square,and the average particle size ranges were 2-5 nm and 20-30 nm,respectively.The main precipitation phases in the 4# experimental steel were(Nb,Ti,V)C,(Ti,Nb,V)C and(V,Nb,Ti)C,which were round and long,and the average particle size ranges were 10-20 nm,30-50 nm and 2-5 nm,respectively.