Effect of High Ti Contents on Austenite Microstructural Evolution During Hot Deformation in Low Carbon Nb Microalloyed Steels

Abstract

This work has focused on the study of hot working behavior of Ti-Nb microalloyed steels with high Ti contents (> 0.05%). The role of Nb during the hot deformation of low carbon steels is well known: it mainly retards austenite recrystallization, leading to pancaked austenite microstructures before phase transformation and to refined room temperature microstructures. However, to design rolling schedules that result in properly conditioned austenite microstructures, it is necessary to develop models that take into account the effect of high Ti concentrations on the microstructural evolution of austenite. To that end, in this work torsion tests were performed to investigate the microstructural evolution during hot deformation of steels microalloyed with 0.03% Nb and different high Ti concentrations (0.05%, 0.1%, 0.15%). It was observed that the 0.1% and 0.15% Ti additions resulted in retarded softening kinetics at all the temperatures. This retardation can be mainly attributed to the solute drag effect exerted by Ti in solid solution. The precipitation state of the steels after reheating and after deformation was characterized and the applicability of existing microstructural evolution models was also evaluated. Determined recrystallization kinetics and recrystallized grain sizes reasonably agree with those predicted by equations previously developed for Nb-Ti microalloyed steels with lower Ti concentrations (<0.05%).

Thermomechanical Processing of Steels

“…The present Special Issue on Thermomechanical Processing of Steels includes eleven research papers [1][2][3][4][5][6][7][8][9][10][11]. A wide range of steel grades are covered in these papers.…”

“…A wide range of steel grades are covered in these papers. Although most of the papers deal with low carbon microalloyed grades [1,3,6,9,10], several papers study ferritic stainless steels [2,5,7] and others focus on grades such as Fe-Al-Cr alloys [4], medium-Mn Nb microalloyed steels [8], and medium carbon V microalloyed grades [11].…”

“…While some papers cover specific performance problems and optimization alternatives for industrial processing conditions [3,7,8], most of the papers deal with more fundamental analyses of physical metallurgy mechanisms and microstructural evolution [1][2][3][4][5][6][7][9][10][11].…”

“…García-Sesma et al [6] focused their paper on the study of hot working behavior of Ti-Nb microalloyed steels with high Ti contents (>0.05%). After analyzing the torsion tests, it was observed that the 0.1% and 0.15% Ti additions resulted in retarded softening kinetics at all temperatures.…”

Rapid Visualization of Microstructural Evolution during Hot Strip Rolling Using Phenomenological Models and the Laguerre–Voronoi Diagram

“…Unfortunately, the basic assumption that microstructure after deformation should be homogeneous and fully composed of equiaxed recrystallized grains regardless of recrystallization occurring or not inconsistent with the actual mixed microstructure consisting of both equiaxed recrystallized and elongated nonrecrystallized grains, [ 11–14 ] indicating that the austenite microstructural heterogeneity caused by partial recrystallization is not taken into consideration in the conventional methods. Furthermore, the macroscale microstructural states revealed in Sellars's work cannot provide a direct view of their evolutions due to lack of details; [ 15–18 ] therefore, other microscale microstructural features, such as the sizes and their distributions of both equiaxial and elongated grains, and the mixed fraction of microstructure must be employed to describe the microstructural state more precisely.…”