Effect of Microalloying on Hot-Deformation Resistance during Rolling

The influence of microalloying elements on mean flow stresses (MFS) developed during plate rolling was investigated in steel grades with tensile strengths from 490 to 580 MPa (API X60 to X70). The present work discusses current results from an on-going project to study the hot deformation resistance during plate rolling. The experiments were carried out in laboratory-scale facilities. Six steels were tested, ranging from plain C-Mn to Nb-Mo-V-microalloyed (Ti added) chemistries. The analysis of MFS was done based on the Sims formula, and it was demonstrated that the most influential factor in MFS was the rolling temperature. The effects of the various alloying elements on the MFS were observed, however, the incremental increase in MFS caused by a single microalloying element like Nb, or V was shown to be comparatively small. On the other hand, multiple microalloying additions such as Nb-V, Nb-Mo, Nb-V-Mo cause remarkable increase in MFS during processing. All specimens exhibited a ferrite plus pearlite microstructure, and the microalloyed grades produced excellent mechanical properties. Steels containing niobium developed fine grains and superior toughness.