Double twist torsion testing to determine the non recrystallization temperature

John G Speer,Kip O Findley,Trevor J Ballard,Emmanuel De Moor

doi:10.1038/s41598-021-81139-1

Abstract

A double-twist torsion testing technique has been developed using a 316 stainless steel as an exemplar material to experimentally assess recrystallization behavior and determine the non-recrystallization temperature (Tnr). This new method was compared to the traditional methods of double-hit compression and multi-step hot torsion testing. The double-twist torsion test allows Tnr to be related to the extent of austenite recrystallization through measurements of fractional softening while accommodating multiple deformation and recrystallization steps with a single specimen. The double-twist torsion test resulted in average Tnr values similar to those determined with multi-step hot torsion, and a partially recrystallized microstructure was observed in the vicinity of the calculated Tnr for all three methods. The ability of the double-twist torsion test to relate the experimental Tnr to the evolution of austenite recrystallization via fractional softening measurements while incorporating effects of multiple deformation steps offers an advantage over traditional methods for quantifying changes in austenite recrystallization during thermomechanical processing.

Highlights

A double-twist torsion testing technique has been developed using a 316 stainless steel as an exemplar material to experimentally assess recrystallization behavior and determine the nonrecrystallization temperature (Tnr)
The recrystallization behavior is described by the non-recrystallization temperature (Tnr), typically defined as the temperature below which complete static recrystallization ceases to occur during the interpass time between rolling passes, though slightly varying definitions e xist[4,6,7]
The double-twist torsion test resulted in average Tnr values similar to those determined with multi-step hot torsion testing. Tnr from the fractional softening approach (1014 ± 9 °C) was near, though slightly lower than, T nr calculated from the first (1030 ± 23 °C) and second (1041 ± 13 °C) set of deformation passes, respectively using the mean flow stress versus inverse temperature approach

Summary

Introduction

A double-twist torsion testing technique has been developed using a 316 stainless steel as an exemplar material to experimentally assess recrystallization behavior and determine the nonrecrystallization temperature (Tnr). The ability of the double-twist torsion test to relate the experimental Tnr to the evolution of austenite recrystallization via fractional softening measurements while incorporating effects of multiple deformation steps offers an advantage over traditional methods for quantifying changes in austenite recrystallization during thermomechanical processing. Requires a reliable way to predict Tnr and changes in recrystallization behavior for a given alloy and process strategy Both double-hit compression and multi-step hot torsion testing have been used to simulate industrial hot rolling and determine T nr. These two methods result in slightly different definitions, T nr values, and corresponding microstructures depending on the method selected[7,10,11,12,13]. The effects of multiple deformation events and recrystallization steps are, not incorporated

Methods

Results

Conclusion