The Dynamic, Static and Metadynamic Recrystallization of a Nb-microalloyed Steel.

Abstract

Using hot torsion tests, the dynamic (DRX), static (SRX) and metadynamic (MDRX) recrystallization characteristics of a Nb-microalloyed steel were studied. The torsion tests were carried out at temperatures in the range 850 to 1 050°C with strain rates ranging from 0.5 to 5/sec. At the higher temperatures, the Nb remained in solution, while precipitation was underway in the lower temperature range. The results indicate that Nb precipitation has little influence on the value of the critical strain (e c ) for dynamic recrystallization. The peak strain/Zener-Hollomon parameter equation is derived and the effect of austenite grain size on the peak strain is considered. The times for 50 % recrystallization for static and metadynamic recrystallization were established by means of interrupted torsion tests and are compared. The rate of metadynamic recrystallization increases with strain rate and temperature and is observed to be independent of the pass strain; this contrasts sharply with the observations for static recrystallization. Finally, an example is given of an industrial rolling process in which DRX/MDRX can play important roles. Here, the occurrence of dynamic/ metadynamic recrystallization causes the load to drop or else to increase less rapidly than in the case of pure strain accumulation in the absence of SRX.

The Static and Metadynamic Recrystallization Behaviour of an X60 Nb Microalloyed Steel

“…The rate of softening decreased with a decrease in the applied strain due to a lower dislocation density which provides the driving force for SRX (that is a nucleation and growth process). 15) The SRX, in agreement with previous studies 5,15) was observed in all annealing conditions for the alloy used in this work (Figs. 4 and 5).…”

“…A number of authors 13,15) have even suggested discontinuities between conventional static and metadynamic recrystallization. This is clear from Fig.…”

Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

“…They then become supersaturated when the temperature is lower than the critical temperature because of the difference between the amount of microalloying elements being dissolved after reheating and microalloying elements dissolution limit in equilibrium condition at various temperatures. The degree of supersaturation is the potential for precipitation and it can be described by a factor, supersaturation ratio [35,[89][90][91][92][93][94][95][96]. The supersaturation ratio is calculated by the solubility product of different microalloying elements at different temperatures using the following equation:…”

A mean field model of dynamic and post-dynamic recrystallization predicting kinetics, grain size and flow stress

“…and after deformation, however, limited studies have been reported on the microstructural evolution in terms of recrystallized volume fraction and grain size. A large group of these models are based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation approach [15][16][17][18][19][20][21]. However, the ideal JMAK behavior is rarely exhibited by real materials.…”