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

Abstract

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 inter- critical 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°C/s and intercritical annealing temperature is 880°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:Rm = 1010 MPa,-Rp0.2=690 MPa,(5=23.6%,n=0.27,r=1.17,the product of strength and ductility(Rm xS) 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.