EFFECTS OF RAPID HEATING CONTINUOUS ANNEALING ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ULTRA HIGH-STRENGTH TRIP-AIDED STEEL

The effects of rapid heating continuous annealing on microstructure and mechanical properties of ultra-high strength and low silicon TRIP steel containing phosphorus and vanadium were investigated. The results show that the yield and tensile strengths are increased with increasing intercritical annealing temperature during rapid continuous annealing. However, the intercritical annealing temperature can not increase blindly to ensure its excellent combined mechanical properties. When the heating rate is 80 degrees C /s and intercritical annealing temperature is 880 degrees C the retained austenite not only contains fine blocky structure, but also a large amount of interlath retained austenite films A great amount of V(C, N) precipitates exists within ferritic matrix, and the sizes of most of the precipates are in the range from 4 to 9 nm. The tested steel has excellent mechanical properties: R-m= 1010 MPa, R-P0.2=690 MPa, delta=23.6%, n=0.27, r=1.17, the product of strength and ductility (R-m x delta) is 23836 MPa.%. If the intercritical annealing temperature is too high or too low, the comprehensive mechanical properties will be deteriorated since the volume fraction of retained austenite reduces, morphology changes and its size increase.