Microstructural Analysis of the Recrystallization Behavior of Low Alloyed Steels

Abstract

The recrystallization behavior of five low alloyed steels is investigated using double hit deformation tests. It is shown, that Niobium has the biggest influence in retarding the recrystallization kinetics. Further, the microstructural evolution dependent on strain and temperature during deformation is studied with a picric acid etchant and light-optical analysis. It is shown how the microstructure of two differently alloyed ultra-high strength steels changes along with the peculiarities of the corresponding stress-strain curves including the evolution of grain size and aspect ratio of the prior austenite grain. The findings on the different recrystallization kinetics with the role of recrystallization retarding elements are further reinforced by investigations on the Zener-Hollomon parameter and the activation energy needed for dynamic recrystallization. A rolling scenario on a deformation dilatometer is simulated on a hardenable and a micro-alloyed steel to illustrate the microstructural evolution between the rolling steps. It is shown, how the two ultra-high strength steels perform different in their microstructural evolution, as the waiving of micro-alloying elements (MAE) provides finer austenite grains.

Flow Stress Behaviour and Static Recrystallization Characteristics of Hot Deformed Austenite in Microalloyed Medium-Carbon Bainitic Steels

“…Vervynckt et al [9] also examined the influence of different levels of Nb-microalloying on the SRX kinetics in low-carbon steels at 900 • C, and according to their study, 0.02% Nb alloying caused delay in the SRX kinetics only due to the solute drag effect, whereas a higher Nb alloying (0.04-0.16% Nb) resulted in both precipitation as well as the solute drag effect, respectively. The hindering effect of V and Nb on SRX kinetics in low alloy steels was also reported by Esterl et al [10]. Pereda et al [11] concluded that increasing Mo content in 0.05C-Nb steels increased the T nr essentially due to an enhanced solute drag effect in steels with low Nb content (0.03% Nb), whereas in steels with relatively higher Nb content (0.06% Nb), the acceleration of strain induced precipitation became more relevant than the solute drag.…”

“…The SRX kinetics of hot deformed austenite in C-Mn steels (with Mn < 1.5%, Si < 0.25%; hereinafter, all concentrations are in wt.%) as a function of chemical composition including the effects of V, Ti and Nb have been reported by numerous authors, for example, [6][7][8][9][10][11][12]. Medina and Quispe [13] have published experimental recrystallization-precipitation-timetemperature diagrams for various V and Nb microalloyed steels illustrating the start and finish temperatures of SRX as well as precipitation at different temperatures.…”

Influence of Microalloying Elements and Deformation Parameters on the Recrystallization and Precipitation Behavior of Two Low‐Alloyed Steels

“…The results of this work coincide well with the results of other research groups, which have described similar recrystallization behavior for different HSLA steels in the past. [17,18,20] Particularly, in this work, it was shown that the annealing temperature before deformation is decisive for an increased recrystallization-inhibiting effect of Nb-and Ti-alloyed HSLA steels. Annealing temperatures below the equilibrium solution temperature of Nb(C,N) do not ensure sufficient dissolution of Nb and, thus prevent the formation of strain-induced precipitates after deformation.…”

“…[1,16] In the past, several studies have shown that strain-induced precipitations inhibit static recrystallization, which can be seen in a deviation from Avrami-like behavior, i.e., the formation of a plateau in a recrystallization curve. [17][18][19][20] An understanding of the precipitation behavior of the microalloying elements is therefore essential for controlling the thermomechanical rolling processes.…”

Influence of V and Nb Micro‐Alloying on Direct Quenched and Tempered Ultra‐High Strength Steels

“…The second base alloy, contains an elevated amount of Cr (0.7%), which increases hardenability and enhances temper resistance . In addition, Cr acts as grain refiner, whereas its influence on recrystallization during hot rolling is negligible . The modifications of base alloy 2 are alloyed with amounts of ≈0.1% and ≈0.2% V to compare the microstructural processes during hot rolling and after tempering to the Nb variants of base alloy 1.…”