Correcting for the Effects of Static and Metadynamic Recrystallization during the Laboratory Simulation of Rod Rolling.

Abstract

Torsion testing was performed to assess the effect of applying a strain rate correction to the pass strains and interpass times when simulating high strain rate mill processing using relatively low strain rate laboratory tests. The experiments were carried out on a low carbon steel grade, and the temperatures, strains, and interpass times selected were representative of those employed in the pre-finishing stands of rod rolling. In the first part of the study, the metadynamic softening kinetics of the steel were established over a range of strain rates, using a new technique whereby comparatively few specimens are needed. Multiple pass deformations were then performed at a series of strain rates using corrected and uncorrrected pass strains and interpass times, and the softening behaviours were compared. It was found that the strain rate corrections appropriate for laboratory tests must take into account the different softening kinetics that apply prior to and after the peak strain of dynamic recrystallization. Otherwise, erroneous conclusions are likely to be drawn about the extent of strain accumulation, which will then lead to errors when laboratory findings are applied to mill practice. A properly corrected simulation of an actual rod mill finishing schedule indicates that static recrystallization is absent in the finishing stands, leading to cycles of strain accumulation and dynamic recrystallization, followed by metadynamic recrystallization and nearly complete softening.