Recrystallization Behavior Of Austenite Research Articles

A comprehensive method to identify the kinetics of static recrystallization using the hot torsion test results with an inverse solution

Many difficulties exist in directly following the static recrystallization of metals, particularly during hot working. Indirect measurement of static recrystallization has been extensively performed in the literature where, for example, the recrystallization behavior of austenite in steels has commonly been measured indirectly using the fractional softening method. This method relies on the yield stress changes during recrystallization which are physically simulated by hot torsion or compression tests. However, the inherent heterogeneity of deformation during a mechanical test leads to a non-uniform static recrystallization distribution in the test sample. This, in turn, poses a serious question concerning the reliability of the measurement since the stress calculation techniques during recrystallization are not adequately developed in the existing literature.This paper develops a computer-based method to account for heterogeneous deformation during fractional softening measurements based on the hot torsion test data. The importance of the fractional softening gradient in determining the kinetics is emphasized and deficiencies in our understanding of the basic mechanisms are highlighted. A computer-based method is introduced to generate the experimental and computational components in a cost function. The cost function is then utilized by an inverse solution to calibrate the design parameters in a static recrystallization model.A

The Dynamic Recrystallization of Hot-Deformed Austenite in a Micro-Alloyed Steel

As the dynamic recrystallization (DRX) behavior of hot-deformed austenite is the basis of determining controlled rolling schedule for steel, in the present work, the dynamic recrystallization behavior of austenite of a 0.22%C-1.30%Mn-0.04%Nb micro-alloyed steel was investigated by means of high temperature compression tests on the Thermecmastor-Z simulator. By the analysis of true stress-strain curves at different deformation stages, the hot deformation equation of austenite was established for the steel. As a result, the energy to induce recrystallization of austenite for the steel is 419.1 kJmol-1, as it was influenced by the drag effect of micro-alloyed element Nb in solid solution. The ratio (σc/σp) of critical stress σc (where DRX occurs) to peak stress σp is 0.93 while the ratio (εc/εp) of critical strain εc to peak stress εp is 0.52 for the steel. The austenite grain size of dynamic recrystallization of the micro-alloyed steel is refined by decreasing the deformation temperature and improving the stain rate.

Analysis of work hardening and recrystallization during the hot working of steel using a statistically based internal variable model

A mathematical model has been developed which describes the hot deformation and recrystallization behavior of austenite using a single internal variable: dislocation density. The dislocation density is incorporated into equations describing the rate of recovery and recrystallization. In each case no distinction is made between static and dynamic events, and the model is able to simulate multideformation processes. The model is statistically based and tracks individual populations of the dislocation density during the work-hardening and softening phases. After tuning using available data the model gave an accurate prediction of the stress–strain behavior and the static recrystallization kinetics for C–Mn steels. The model correctly predicted the sensitivity of the post deformation recrystallization behavior to process variables such as strain, strain rate and temperature, even though data for this were not explicitly incorporated in the tuning data set. In particular, the post dynamic recrystallization (generally termed metadynamic recrystallization) was shown to be largely independent of strain and temperature, but a strong function of strain rate, as observed in published experimental work.

Effect of vanadium and molybdenum addition on high temperature recovery, recrystallization and precipitation behavior of niobium-based microalloyed steels

The effects of multiple microalloy additions on the dynamic recovery and recrystallization behavior of austenite were investigated in a series of 0.05% C-l.25% Mn steels. The steels contained one or more of 0.30% Mo, 0.035% Nb or 0.115% V, and a reference plain carbon steel was also tested. Constant strain rate compression tests were conducted in the temperature range 1150°–875°C, that is, above and below the relevant carbonitride solution temperatures ( T sol ). Dynamic recrystallization-time-temperature (RTT) curves were developed from the flow curves at 5.6 × 10 −3 and 3.7 × 10 −2 s −1. At the higher strain rate, only the solute retardation of recrystallization was detected for the vanadium, Nb-V, Nb-1.9 Mn and No-Mo steels. An additional delay due to the dynamic precipitation of Nb(CN) was observed in the Nb-1.25 Mn steel, where there was a break to the right in the RTT curve. These breaks were seen in the results for all the steels at the lower strain rate. They appeared about 50°–100°C below the calculated T sol for the particular carbonitride, and coincided with the intersection of the RTT and PTT (precipitation-time-temperature) curves. The solute retarding potential of each element was normalized to 0.1 at.% with a solute retarding parameter (SRP). The SRP for niobium, molybdenum and vanadium when added singly, was 63, 10 and 3% respectively. In the multiply alloyed steels, the SRP attributable to each element was smaller than when it was present alone. Possible explanations for this negative interaction are advanced. Dynamic PTT curves for the precipitation of carbonitrides are presented for the Nb-1.25 Mn, Nb-1.9 Mn, Nb-Mo, Nb-V and Nb-Mo-V steels. The addition of molybdenum, vanadium or manganese is seen to retard the dynamic precipitation of Nb(CN). These delays are explained in terms of the decrease in T sol resulting from the reduction in the carbon and nitrogen activity coefficients in the joint presence of the former elements. An empirical formulation for the effect of manganese on NbC solubility is deduced from results reported in the literature which is consistent with the present observations.