Development of an elevated-temperature tensile testing instrument for investigating dynamic grain growth in an interstitial-free steel

Exposure to elevated temperatures during plastic deformation, termed dynamic conditions, produces microstructures distinct from static annealing for a titanium interstitial-free (Ti-IF) steel sheet material. For similar annealing times, dynamic conditions produce larger grains than static annealing and a crystallographic texture that is unique. These differences are attributed to dynamic grain growth (DGG), which occurs by mechanisms different from those of static conditions. The mechanisms of DGG are not yet well understood. The objective of this work is to design and construct a testing instrument suitable for investigations that probe the mechanisms of DGG in Ti-IF steels. This instrument is required to deform a specimen in tension at elevated temperatures in a reducing atmosphere and then rapidly quench that specimen to preserve the microstructure developed during deformation. The instrument was constructed using a servohydraulic tensile test frame, a split tube furnace, and an original elevated-temperature testing enclosure with reducing gas and air quenching systems. It enabled elevated-temperature tensile tests of Ti-IF steel specimens without significant specimen oxidation. The mechanical data obtained from these tests are in agreement with existing data for the same material. Scanning electron microscopy revealed the presence of preserved subgrain structures in the microstructures of tested specimens. These experimental results confirm that the new instrument satisfies the stated design requirements and is suitable to advance the study of DGG phenomena in Ti-IF steel.