Kinetics Of Metadynamic Recrystallization Research Articles

The metadynamic recrystallization behavior of ultrahigh-strength stainless steel: effects of precipitates and shear bands

The metadynamic recrystallization behavior of Cr-Co-Ni-Mo ultrahigh-strength martensitic stainless steel was studied in a double-pass isothermal compression test, and a metadynamic recrystallization kinetics model for softening was established. The results showed that the metadynamic recrystallization softening rate of the steel not only depended on the deformation temperature and strain rate but was also related to the dynamic precipitation and the local shear bands in the steel. When the deformation temperature was below 1050 °C, the dynamically precipitated M6C carbides pinned the grain boundaries and hindered metadynamic recrystallization. When the steel was deformed at a deformation temperature of 1000∼1050 °C and a strain rate of 1.0∼5.0 s−1, a large number of local shear bands were generated. The local shear bands increased the number of nucleation sites for dynamic recrystallization and enhanced the softening rate of metadynamic recrystallization.

Features of Formation of the Structure of Nitrogenous Steel during High Temperature Thermomechanical Treatment

The study of formation of the structure of austenitic nitrogenous steel obtained from physical simulation of the processes of hot deformation with a Gleeble-3800 installation by various modes is considered in the work. The kinetics of metadynamic recrystallization within the interdeformation interval under multipass deformation implemented under different schemes is studied. As a result, it was established that, depending on the deformation scheme, the recrystallization runs with varying degree and intensity.

Metadynamic Recrystallization Kinetics of Twin Roll Cast AZ31 Alloy during Hot Deformation

Metadynamic recrystallization takes place during isothermal annealing of materials in which an incomplete dynamic recrystallization occurred. In magnesium alloys this question has been investigated less until now. The metadynamic recrystallization behavior of twin-roll-cast and annealed AZ31 strip after hot deformation was investigated under conditions corresponding to hot strip rolling process of twin-roll-cast Mg coils. Plane strain compression tests were performed using double hit compression tests at temperatures of 250 - 400 oC, strain rates of 0.1 - 5 s-1 and interpass time of 0.5 – 10 s. Based on the experimental results, the kinetic equations and grain size model were established. Results show the effects of deformation parameters, including forming temperature and strain rate, on metadynamic recrystallization softening fractions and grain size in the two-pass hot deformed AZ31 alloy. Results also reveal that the pre-strain (beyond the peak strain) has little influence on the metadynamic recrystallization behavior in AZ31 alloy. Comparisons between the experimental and the predicted results were carried out. A good agreement between the experimental and the predicted results was obtained.

Characteristics of metadynamic recrystallization of a high Nb containing TiAl alloy

Stress relaxation tests were applied to measure the kinetics of metadynamic recrystallization (MDRX) of a high Nb containing TiAl alloy subsequent to plane strain compression tests executed in the temperature range of 1050–1150°C and the strain rate range of 0.01–1s−1. The results showed that MDRX behavior of the alloy was almost independent on pre-strain and deformation temperature, but significantly dependent on strain rate. The Avrami exponents under different deformation conditions were identified to be about 0.40–0.52. The low Avrami exponents indicate a low MDRX rate during interpass annealing, and these low values are mainly ascribed to the weak driving force for MDRX. Moreover, high Nb additions and multiple phases can further decrease the MDRX rate.

Activation Energy in Hot Forming and Recrystallization Models for Magnesium Alloy AZ31

Kinetics of the dynamic, as well as postdynamic recrystallization of the wrought magnesium alloy AZ31, was ascertained. Continuous compression tests associated with the study of dynamic recrystallization were realized at temperatures from 523 to 723 K and at the strain rates from 0.001 to 10 s−1. The activation energy in hot forming was determined as Q = 158 kJ/mol for stress-strain curves of conventional shape, or Q = 146 kJ/mol for stress-strain curves with the concave initial phase affected by twinning. If the Zener-Hollomon parameter Z > 9.1 × 1012 s−1 the deformation necessary for the initiation of dynamic recrystallization is almost independent on the forming parameters. Using the results of the stress relaxation tests, equations describing the kinetics of metadynamic recrystallization and the grain size originated in such a way were developed and the effect of individual variables was evaluated.

A new method to predict the metadynamic recrystallization behavior in 2124 aluminum alloy

The metadynamic recrystallization behaviors in deformed 2124 aluminum alloy were investigated by isothermal interrupted hot compressive tests, which were carried out at the deformation temperatures of (653–743) K, strain rates of (0.01–10) s−1 and inter-stage delay time of (30–180) s. A new approach, “peak stress method”, is proposed to calculate the softening fractions induced by the rapid metadynamic recrystallization. The kinetic equations were developed to predict the metadynamic recrystallization behaviors in hot compressed 2124 aluminum alloy. Both the experimental and predicted results show that the effects of deformation parameters, including strain rate, deformation degree and temperature, on the softening behaviors in the two-pass hot compressed 2124 aluminum alloy are significant. A good consistency between the experimental and predicted results indicates that the proposed kinetic equations can precisely estimate the softening behaviors and metadynamic recrystallization kinetics of the hot compressed 2124 aluminum alloy.

Modeling of metadynamic recrystallization kinetics after hot deformation of low-alloy steel Q345B

Based on the steady-state strain measured by single-pass hot compression tests, the method by a double-pass hot compression testing was developed to measure the metadynamic-recrystallization kinetics. The metadynamic recrystallization behavior of low-alloy steel Q345B during hot compression deformation was investigated in the temperature range of 1 000–1 100 °C, the strain rate range of 0.01–0.10 s−1 and the interpass time range of 0.5–50 s on a Gleeble-3500 thermo-simulation machine. The results show that metadynamic recrystallization during the interpass time can be observed. As the deformation temperature and strain rate increase, softening caused by metadynamic recrystallization is obvious. According to the data of thermo-simulation, the metadynamic recrystallization activation energy is obtained to be Q md=100.674 kJ/mol and metadynamic recrystallization kinetics model is set up. Finally, the error analysis of metadynamic recrystallization kinetics model proves that the model has high accuracy (correlation coefficient R=0.988 6).

Kinetics of Metadynamic Recrystallization in Microalloyed Hypereutectoid Steels

The isothermal kinetics of the recrystallization processes of vanadium microalloyed high carbon steels has been measured and modelled. The overall softening data were obtained by double hit compression tests performed at temperatures between 900 to 1 050°C, strain rates of 0.01 to 1 s -1 , and inter-pass times of 0.1 to 30 s. The recrystallization behavior above and below and the critical strain for dynamic recrystallization was investigated. The results show that there is a transition strain region between where both static and metadynamic recrystallization take place during the inter-pass time. The results also revealed that V and Si have a strong solute drag effect, on the kinetics of metadynamic recrystallization. A kinetic model is proposed which takes the V and Si concentrations into account.

Transition between static and metadynamic recrystallization kinetics in coarse Nb microalloyed austenite

Abstract The recrystallization behaviour of a Nb microalloyed steel, under deformation conditions corresponding to the initial stands of a thin slab hot rolling process which is characterized by coarse initial austenite grain sizes and large strains per pass, has been investigated. A range of strain levels were studied ranging from below the critical strain for the onset of dynamic recrystallization, e c , well into the steady state for dynamic recrystallization, e > e ss . There is a transition strain, e c e T e ss , separating the post-dynamic softening strain-dependent range from that which is strain-independent. At strains above e T , the kinetics of recrystallization is independent of strain but strongly dependent on strain rate. Under these conditions, metadynamic recrystallization operates as the prime softening mechanism and the kinetics have been derived. At strains between e c and e T , both metadynamic and classical static recrystallization are involved in post-dynamic softening. A model is derived to predict the evolution of softening as a function of the holding time for different strain ranges, based on the contributions of the individual components to the overall softening.

Effect of alloying elements on metadynamic recrystallization in HSLA steels

By means of interrupted torsion tests, the kinetics of metadynamic recrystallization (MDRX) were studied in a Mo, a Nb, and a Ti microalloyed steel at temperatures ranging from 850 °C to 1000 °C and strain rates from 0.02 to 2 s1. Quenches were also performed after full MDRX. In contrast to the case of static recrystallization (SRX), the kinetics of MDRX are shown to be highly sensitive to a change of an order of magnitude in strain rate and are relatively insensitive to temperature changes within the range of values applicable to industrial hot-rolling practice. A similar algebraic dependence of the MDRX grain size on strain rate and temperature was found in the three steels. The kinetics of MDRX were slower in the Nb than in the Mo steel, and those of the Ti steel were slower than in the Nb and Mo steels. Above 900 °C and 950 °C, the retardation of MDRX in the Nb and Ti steels, respectively, is due to solute drag. Models predicting the start time for Nb and Ti carbonitride precipitation showed that MDRX is delayed below these temperatures by this mechanism. Comparison of the MDRX and precipitation start times in the Nb steel indicated that a temperature of “no-MDRX” could not be defined, in contrast to the well-definedT nr (no recrystallization temperature) of SRX. By means of torsion simulations composed of multiple interruptions, it is shown that MDRX is retarded decreasingly as the accumulated strain is increased. This appears to be due to the promotion of precipitate coarsening by the continuing deformation.