Episode 36 - Double Twist Torsion Testing to Determine TNR and Assess Partial Recrystallization

Gleeble Webinar Series - Episode 36
Double-Twist Torsion Testing to Determine the Non-Recrystallization Temperature (TNR) and Assess Partial Recrystallization
Presenter: Trevor Ballard, Colorado School of Mines
Abstract: Effective processing of microalloyed steels via controlled rolling requires an understanding of the recrystallization behavior of the material being rolled. Typically, this behavior is described by the non-recrystallization temperature (Tnr). Various techniques have been used to simulate thermomechanical processing and determine Tnr, but a rigorous analysis of the relationship between the calculated Tnr, the extent of austenite recrystallization, and the corresponding precipitation state has not been conducted.
The present study will describe the development of a novel double-twist torsion test to determine Tnr and predict changes in austenite recrystallization during thermomechanical processing. The double-twist torsion test has the advantage of relating the mechanical data generated during testing to the extent of austenite recrystallization via measurements of fractional softening while incorporating multiple deformation and recrystallization cycles on a single specimen. Initial development of the test using Gleeble processing on an austenitic 316 stainless steel and subsequent application of the test to a low carbon microalloyed steel will be described. Analysis of strain accumulation in the 316 stainless steel revealed a partially recrystallized microstructure in the vicinity of Tnr. Application of the double twist torsion test to a microalloyed steel predicted partial recrystallization over a wide temperature range with Tnr determined by traditional methods situated within the partial recrystallization regime.