The present investigation is dealing with the evolution of simultaneous Dynamic and metaDynamic Recrystallization (DRX)& (MDRX) phenomena by physical simulation for a 4-strock hot compression process, where flow curves were presented for each stroke. The primary alloy is a penetrator steel containing 0.3% C in addition to some Cr, Mo, Ni and 1.63 W. Calculated grain size after the onest of DRX & occurrence of MDRX decreases continuously with the increase of cumulative strain reaching to 0.289 µm. However, Electron Backscatter Diffraction (EBSD) investigation established that 99% of the grains, after the last compression stroke, were detected as <1.0 μm, with an average grain size 0.31 μm. Microstructure after simulation presents fine lath martensitic structure, coexisting with Cr-W carbides, which are crammed at the inter- martensite laths. Furthermore, 56% of the grains showed grain boundaries misoriention creating High Angle Grain Boundaries (HAGBs), which are promoting MDRX. The flow curve of each stroke definitely contains two complementary microstructure events, namely a DRX , and a MDRX phenomenon, where the peak stress (σp) of DRX is inversely proportional to the mean temperature of stroke.

Determination of critical points on hot stress-strain curve of metals is crucial in thermo-mechanical processes design. In this investigation a mathematical modeling is given to illustrate the behavior of metal during hot deformation processes such as hot rolling. The critical strain for the onset of Dynamic Recrystallization has been obtained as a function of strain at the maximum stress. In addition, the transition strain from static Recrystallizationto full metaDynamic Recrystallization has been presented to form an equation as a function of peak strain, peak stress and steady-state stress. The results of this mathematical modeling are in a good agreement with the experimental data.

Dynamic Recrystallization, DRX, behaviour of a precipitation hardened, PH, stainless steel was studied in connection with microstructural developments in a compression test, The experimental results showed that the dominant mechanism of softening is DRX, but at high strain rates and low temperatures,, high Zener-Holman parameter, Z. work hardening and Dynamic recovery, DRV, produced a pancked structure. When Z values decreased, the flow curves displayed DRX in two ways: single peak behavior observed at low Z values and multiple peak behavior at the lowest ones. In addition, the peak strain, ep, necessary for DRX is also determined as a function of peak , Stress sp, and Z. according to the observed and calculated data, at low sp values, ep is directly proportional to sp while in higher sp p values, ep rarely depends on it. Besides, ep expotenentially depends on Z.

Strain induced precipitation in HSLA-100 steel was investigated by conducting hot compression and relaxation tests at temperature range of 850oC to 1100oC and strain rate of 0.001 s-1 to 1s-1. The absence of Dynamic Recrystallization at temperatures below 1000oC was attributed to the influence of Dynamic precipitation. The stress relaxation tests showed that strain induced precipitation is possible over a wide range of temperatures from 850oC to 1050oC. The starting and finishing times of precipitation were sensitive to temperature than strain rate. At temperature range of 950-1000oC and strain rate of 0.1s-1 the lowest times for precipitation were observed. The combination of precipitation-time-temperature and Recrystallization-time temperature diagrams showed that at high temperatures and low strain rates, precipitation precedes Dynamic Recrystallization, whereas at the opposite condition, Dynamic Recrystallization goes in advance. The starting and finishing times for Dynamic precipitation were approximated about 40 percent lower that those for strain induced precipitation.

The study of nucleation mechanism of new grains during severe plastic deformation of magnesium alloys is of great importance to control the characteristics of final microstructures. To investigate the role of discontinuous Recrystallization, a wrought AZ31 magnesium alloy was deformed by accumulative back extrusion process at 330oC. The obtained microstructures were studied using optical and field emission microscopy as well as electron back scattered diffraction techniques. The results demonstrated that the fine and ultrafine grains formed along the prior grain boundaries yielding a bimodal structure. The EBSD analysis showed that the new grains exhibit a similar basal texture to deformed grains, which may confirm the operation of strain induced boundary migration mechanism.

The aim of this study is to investigate the nucleation of new grains by neck lacing mechanism during DynamicRecrystallization (DRX). The material used is 316 stainless steel. In order to modeling the deformation behavior during hot rolling, one-hit compression tests were performed at temperature range of 950-1100°C with strain rates of 0.01-1s-1 The result shows that at the temperature of 1000°C with the strain rate of 0.1s-1 DRX developed by necklace mechanism, it is far from completeness over the steady state stress. By contrast the hardness increased by development of DRX. The final microstructure is very heterogeneous and comprises of very fine and coarse grains due to the occurrence of partial DRX. The results also show that the necklace structure developed by increasing Zener-Hollomonparameter (Z).

In this paper the hot deformation behavior of Al-5083 commercial alloy is investigated. The aim is to investigate the formability of this alloy in hot tension under Dynamic Recrystallization. For this purpose, the material is thermo-mechanically processed. Then hot tensile tests are carried out at various temperatures and strain rates. Velocity jump tests are performed to determine stress-strain rate curves at various temperatures and strains. The microstructures are studied by optical and electron microscopy (SEM). It is found that the thermo–mechanical process resulted in a homogeneous distribution of fine precipitates. Dynamic Recrystallization occurs during hot deformation of the AA5083. Maximum elongation about 250% is obtained at 450 oC and strain rate of 0.005 s-1. Maximum strain rate sensitivity (m) is 0.3. The failure surface is narrow and failure occurs by necking.

In this research, the hot deformation behavior of API X70 steel was investigated by hot compression tests. A temperature range between 950 and 1150 oC was used for experiments with different strain rates of 0.01, 0.1 and 1 s-1. The work hardening rate versus stress curves were used to reveal if Dynamic Recrystallization (DRX) occurred. The application of constitutive equations to determine the hot working constants for the tested steel was discussed. Using regression analysis, the stress multiplier (a), the apparent stress exponent (n), and the activation energy (Qd) for DRX were calculated as 0.016 and 4.420, and 382 kJ/mol, respectively. Furthermore, the effect of Zener–Hollomon parameter (Z) on the characteristic points of flow curves was investigated using the obtained relations. The Dynamic Recrystallization (DRX) kinetics of API X70 steel was also studied and its governing equation was derived.