Refinement of Coarse-Grained Austenite in a Nb-V-Ti Microalloyed Steel Processed by Medium-Thin Slab Casting and Direct Rolling Route

Abstract

Refinement of coarse-grained austenite in a Nb-V-Ti microalloyed steel during roughing rolling of medium-thin slab casting and direct rolling or Angang Strip Production (ASP) process was investigated with austenite grain size distribution instead of mean grain size. The evolution of grain size distribution was modeled by taking into account the following mechanism: dynamic, static and metadynamic recrystallization, strain-induced precipitation and retained strain. The results indicate that the refinement of coarse-grained austenite is mainly retarded by the coarse grain size and Nb in solution as strain induced precipitation may not occur during roughing rolling. The final austenite grain size distributions became narrower with increasing the entry temperature and total reduction. A processing map for roughing rolling was drawn and optimum processing conditions were defined. The results also reveal that the microstructural homogeneity of microalloyed steels produced by ASP process is better than that produced by thin slab casting and direct rolling process (TSDR) after roughing rolling.