GRAIN-REFINEMENT BY DYNAMIC RECRYSTALLIZATION DURING THE SIMULATED WARM-ROLLING OF INTERSTITIAL FREE STEELS

Multipass torsion tests were used to investigate the warm-rolling behavior of three interstitial free (IF) steels containing Ti and/or Nb. All the tests were carried out at a strain rate of 2 s-1, and the samples were water-quenched immediately after particular passes. Whereas the finishing passes were always executed in the single-phase ferrite region, the roughing passes were applied either in the austenite phase (hot/warm-rolling) or in the ferrite region (warm/warm-rolling). In the former case, the temperature of the first roughing pass was 1260-degrees-C, while it was 850-degrees-C for the warm/warm method. It is shown that dynamic recrystallization occurs to a degree that depends on the composition of the steel and the finishing temperature. Although the finish-rolling loads for warm-rolling (in the ferrite region) are no higher than for conventional strip-rolling rolling in the austenite region, the ultrafine ferrite grain sizes of 1 to 2-mu-m that are produced by warm-rolling are an order of magnitude finer than those resulting from conventional processing.