Determination of Non-Recrystallization Temperature for Niobium Microalloyed Steel

In the present investigation, the non-recrystallization temperature (T-NR) of niobium-microalloyed steel is determined to plan rolling schedules for obtaining the desired properties of steel. The value of T-NR is based on both alloying elements and deformation parameters. In the literature, T-NR equations have been developed and utilized. However, each equation has certain limitations which constrain its applicability. This study was completed using laboratory-grade low-carbon Nb-microalloyed steels designed to meet the API X-70 specification. Nb- microalloyed steel is processed by the melting and casting process, and the composition is found by optical emission spectroscopy (OES). Multiple-hit deformation tests were carried out on a Gleeble(R) 3500 system in the standard pocket-jaw configuration to determine T-NR. Cuboidal specimens (10 (L) x 20 (W) x 20 (T) mm(3)) were taken for compression test (multiple-hit deformation tests) in gleeble. Microstructure evolutions were carried out by using OM (optical microscopy) and SEM (scanning electron microscopy). The value of T-NR determined for 0.1 wt.% niobium bearing microalloyed steel is similar to 951 degrees C. Nb- microalloyed steel rolled at T-NR produce partially recrystallized grain with ferrite nucleation. Hence, to verify the TNR value, a rolling process is applied with the finishing rolling temperature near TNR (similar to 951 degrees C). The microstructure is also revealed in the pancake shape, which confirms T-NR.

Automated summary

The study identified the non-recrystallization temperature (T-NR) of niobium-microalloyed steel to plan rolling schedules, showing that T-NR is influenced by alloying elements and deformation parameters, determined through multiple-hit deformation tests.