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).

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.

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 the current study, the RECRYSTALLIZATION behavior of 75% cold-rolled Fe-22Mn-10Al-1. 4C steel during annealing at 750, 770, 790, 810, and 830° C was studied. X-ray diffraction patterns and optical microscopy were used to characterize microstructures. The Vickers Micro-hardness test was used to characterize RECRYSTALLIZATION KINETICS during annealing. Johnson-Mehl-Avrami-Kolmogorov (JMAK) model was used to evaluate the experimental data. The ashomogenized microstructure illustrated only austenite with a high fraction of annealing twins, and austenite to martensite phase transformation was not observed after quenching at a high temperature and also until high thickness reduction. Avrami exponent was decreased from 0. 76 to 0. 42, with increasing the annealing temperature from 750 to 830° C. The activation energy value was determined to be ~175 kJ/mol, which was slightly higher than the diffusion activation energy of carbon in austenite.

In this research, RECRYSTALLIZATION behavior and coarsening KINETICS of 7075 alloy were investigated during conventional and newly modified SIMA processes. The conventional SIMA process consisted of applying 10-55% uniaxial compression strain at ambient temperature and subsequent semi-solid treatment at various temperatures and times. A new modified SIMA process was developed by introducing repetitive upsetting-extrusion (RUE) for the first time for semi-solid processing of 7075 Al alloy. Specimens of 7075 alloy were subjected to different RUE cycles at 250 ° C, and then the semi-solid treatment was carried out. Microstructural studies revealed that the RECRYSTALLIZATION rate is accelerated, the average grain size is reduced considerably and the sphericity of solid grains is improved by the newly modified SIMA process. Lifshitz-Slyozov-Wagner (LSW) theory was used to describe the coarsening process of the semi-solid slurries. Coarsening rate of the solid grains in the newly modified SIMA process was slower than the conventional SIMA process.