Microstructure and Mechanical Properties of High Strength Hot-Rolled TRIP Steel Containing Vanadium

Laboratory hot rolling experiments on a low-carbon TRIP steel containing vanadium have been carried out to study the microstructure characteristics and mechanical properties. The results showed that the multiphase microstructure with ferrite, granular bainite and retained austenite could be obtained if the finish rolling initial temperature was properly decreased and the finishing temperature was controlled in the range of A(e3)similar to A(r3), and the tensile strength achieved 930 MPa or above. The average ferrite grain size was about 4.5 mu m in this experiment, the vanadium nitrides and vanadium carbides precipitated dispersedly within ferritic grains or at grain boundaries, and the higher dislocation density existed in ferrite matrix. EBSD analyses revealed that the high angle boundaries accounted for a large proportion and the misorientation angles were within the interval between 29 degrees and 60 degrees mostly. When the finishing temperature was 800 degrees C and the final air cooling temperature was 630 degrees C, the steel had excellent mechanical properties, which was characterized by combination of high strength(about 930MPa), high elongation(21.7%), low yield/strength ratio(0.49) and as well as high work-hardening exponent(0.23).