The Deformation Microstructure and Recrystallization Behavior of Warm Rolled Steels.

Abstract

The deformation microstructure of various warm (ferritic) rolled steels was characterized and its influence upon the subsequent annealing behavior determined. The materials investigated included three interstitialfree (IF) steels (stabilized with either titanium or niobium), an extra low carbon (ELC) steel, and four experimental low carbon chromium steels with varying levels of boron, nitrogen and phosphorus. Single pass rolling experiments were conducted in a pilot mill at temperatures between 440 and 850°C and the asrolled microstructures were examined using optical microscopy. Particular attention was paid to the nature and intensity of the in-grain shear bands produced. Partial annealing was conducted to examine the nucleation of recrystallization in the deformed microstructure. Shear bands of moderate intensity were usually formed in the IF steels, which tended to be insensitive to rolling temperature. For the ELC steel, intense shear bands were formed at low rolling temperatures, but at higher temperatures this intensity was found to be drastically reduced. The development of shear bands at the higher rolling temperatures was significantly enhanced by alloying with chromium. The differences in shear band frequency and intensity are explained in terms of the dynamic strain aging behaviors of the various materials. Recrystallized grains were found to nucleate preferentially on the shear bands during annealing, regardless of their morphology or intensity.

Influence of Microalloying Elements on Recrystallization Texture of Warm-Rolled Interstitial Free Steels

“…It is clear that, according with calculations, the whole amount of P and a significant amount of Ti remains in solid solution in the ferrite. However, it has been profusely reported in literature 25,26) that in presence of Ti, P forms FeTiP phosphide which leads to the deterioration of both drawability and loss of strength. The FeTiP precipitates present in IF-HR steel (Fig.…”

Prediction of Flow Behavior during Warm Working

“…18) ................. (13) where k s is the shear yield stress, v r the relative velocity between the tool and the deforming metal, m the friction factor, and a is a positive constant of the order of 10 Ϫ4 . Equations (2), (10) and (11) should be solved simultaneously to have the temperature distribution, the velocity field and the kinetics of dynamic recovery. In order to solve the heat conduction and the energy equations, a two dimensional finite element analysis utilizing four-node isoparametric elements 19) are employed and Newton-Raphson and direct iteration methods are used to solve the nonlinear system of…”

“…Flow stress modelling under warm rolling conditions has been carried out by Huang et al 9) In this research, two grades of commercial Ti-Nb stabilized interstitial free steels were investigated and a flow stress model with regard to dynamic recovery and recrystallization was developed to predict flow behavior of steels during warm rolling. The microstructure and recrystallization kinetics after warm rolling was studied by Liu et al 10) They have shown that dynamic strain aging could be responsible for the formation of moderate and intense shear bands in IF and low carbon steels, respectively.…”

“…There have been many studies on the behavior of low carbon steels during warm working. [2][3][4][5][6][7][8][9][10] Suitable conditions for warm working by forging and rolling have been considered by Hawkins. 2) Dynamic strain aging during wire drawing and its effect on flow behavior was investigated by Taheri et al 3) They employed an upper bound approach using spherical velocity field to analyze plastic deformation during wire drawing. The results show that dynamic strain aging may occur in the deformation zone and leads to localized flow.…”

Effect of Chromium, Boron and Manganese Additions on the Deformation and Recrystallization Textures of Warm Rolled Low Carbon Steels

“…The dependence of shear band morphology and intensity on rolling temperature in these steels has been described in detail in Ref. 21). Barnett and Jonas 1,22) stressed that this dependence can be linked directly to the DSA behaviors of these materials.…”