Dynamic recrystallization analysis of reduction pretreatment process by multi-phase field method

Dynamic recrystallization behavior of the equiatomic FeCoCrNi high-entropy alloy during high temperature deformation

Effect of initial grain size on dynamic recrystallization in high purity austenitic stainless steels

Oxygen free high conductivity (OFHC) and electrolytic tough pitch (ETP) copper specimens of different grain sizes (10–800 μm) were tested at various constant true strain rates in a modified Instron testing machine. The temperature range investigated was 725–1075 K. The effect of initial grain size on the transition from multiple to single peak flow was studied. The dependence of the stable dynamic grain size on the temperature corrected strain rate and the steady state stress was determined, as were the density of twins and of deformation bands. The density of twins decreased as the initial grain size was increased and when the recrystallization mechanism changed from static to dynamic. The density of deformation bands increased markedly with initial grain size. As the deformation bands are preferential nucleation sites for new dynamic grains, the results indicate that the initial effective grain size D o * </mm...

The effect of composition on the dynamic recrystallization behavior of plain carbon steels has been examined in the temperature range 850 to 1300 °C and the strain-rate range 6 × 10-6 to 2 × 10-2 s-1. With increasing solute content, the onset of dynamic recrystallization is delayed and the rate of recrystallization is decreased. At 1000 °C the elements can be ranked in order of increasing effectiveness as C, Ni, Mn, Si, P. At higher temperatures the effect of composition is complicated by its effect on grain coarsening, which itself postpones the onset and slows the rate of recrystallization. Similarly, for steels in which precipitation may occur, a fine-grain structure can promote the earlier onset and faster rate of recrystallization. Thus, out of an examination of the effect of composition comes an appreciation of the influence of initial grain size. Another factor which can complicate any explanation of the compositional dependence of dynamic recrystallization is grain-boundary segregation, which is probably responsible for the strong retarding influence of phosphorus.

Axisymmetric hot compression experiments of Mg–Al–Zn specimens in intervals of temperature 250–450 °С and deformation rate (10-3-5)·10–1 s–1 were carried out. Structure formation was studied by optical microscopy. Macroscopically localized strain of cylindrical specimens depending on temperature, strain rates and initial grain size (400 μm and 1400 μm) are investigated. Localized strain diagrams for different initial grain size can be used for development and optimization of hot processing technology parameters are plotting. It is shown that increase of the grain size direct to strain localization increment tendency.

The effects of two initial grain sizes of 15 and 40μm on the dynamic recrystallization behavior of a type 304 stainless steel have been investigated at temperatures of 950–1100°C and strain rates of 0.005–0.5s−1 using hot compression testing. Microstructural investigations showed that the dimensionless parameter of Z/A can be used to express in which conditions dynamic recrystallization progressed via a necklace structure. Electron backscattered diffraction maps exhibited some evidence that confirmed the dynamic recrystallization mechanism changed from discontinuous to continuous with a decrease in the initial grain size. Results showed that the coarse grained material produced finer and more homogeneous metadynamic recrystallized grains, possibly due to the uniform substructure observed in the grains interior.

The hot deformation and dynamic recrystallization (DRX) behaviors of 40Cr steel were studied by hot compression tests over a wide range of deformation temperature (1023 K–1323 K) and strain rate (0.01 s−1–10 s−1). The constitutive relationship, DRX kinetics and DRXed grain size were modelled, and numerical simulation was performed to verify their predicting accuracy. Moreover, the effects of deformation parameters on martensite structure after hot compression and quenching were analyzed. The results show that the strain compensated Arrhenius can accurately predict the flow stress with the average absolute relative error of 3.89% and correlation coefficient of 0.992. The fraction and grain size of DRX are strongly related to deformation conditions, and low strain rate and high temperature are beneficial for the occurrence of DRX. Moreover, the equation of DRX fraction was developed based on Avrami model, and the relationship between DRXed grain size and Zener-Holloman parameter was also established. The simulated results of true strain, DRX fraction and grain size agree well with experimental findings. Finally, it was found that the size of martensite packet became larger under high strain rate, while the aspect ratio of martensite lath increases at higher deformation temperature.

High temperature deformation and microstructural evolution were studied in tension using single phase polycrystalline Ni3Al doped with boron. The samples with grain sizes from 3.0 to 18 μm were rapidly H2 gas-quenched immediately after straining in order to examine deformed structures and to elucidate the mechanism of superplastic deformation. A stress peak appears at a strain of less than 0.1 more remarkably with increasing initial grain size, and with increasing strain rate or decreasing temperature. Dynamic recrystallization (DRX) initiates along prior grain boundaries at near the peak stress and develops toward grain interiors on further deformation, leading to the evolution of necklace structures. A rapid decrease in flow stress after the peak is mainly due to grain boundary sliding at interfaces between DRX grains. In contrast, work hardening takes place at low and moderate strains for samples with smaller initial grain sizes, when they are deformed at lower strain rates or higher temperatures. Under these conditions, grain boundary sliding occurs predominantly accompanied with grain coarsening due to DRX. Superplastic elongation appears in specimens exhibiting no significant behavior of work softening or work hardening. It is concluded that work softening or hardening behavior depends sensitively on the relative difference between the initial grain size and the stable DRX grain size evolved at high strains, and high temperature deformation of Ni3Al can be controlled by grain boundary sliding assisted by DRX.

A review of dynamic recrystallization phenomena in metallic materials

Initial grain size effects on dynamic recrystallization (DRX) of pure nickel were studied by means of tensile testing and microstructural observation over the range of strain rates from 10−5 s−1 to 10−1 s−1 and at temperatures between 923 K and 1123 K. The flow curves were categorized in terms of three types of shapes; (i) single peak type at high Z (=\dotεexp(Q⁄RT)), (ii) multiple peak type at medium Z, and (iii) the third type which showed a sharp stress dip following a stress peak and then strain hardening with serrations in stress at lower Z. The grain structural changes by DRX as well as the flow curves were affected sensitively by initial grain size Do. The coarse grained sample was refined continuously during single peak flow until the stable size Ds was attained. The fine grained one underwent some grain refinement at the first peak strain, even though it eventually coarsened up to the same size Ds during multiple peak flow. The critical value of Zc (or the first peak stress σpc at Zc), at which the flow curve shape changed from multiple to single peak type, depended on Do. The relationship between σpc and Do approximately overlapped that of σp vs. 2Ds, and thus the critical condition in question was expressed by the relation of Do=2Ds. These results were analyzed by using the relative grain size model for DRX.

Effect of initial state on hot deformation and dynamic recrystallization of Ni-Fe based alloy GH984G for steam boiler applications

A comprehensive model for the recrystallization kinetics is proposed which incorporates both microstructure and the textural components in the deformed state. The model is based on the single-grain approach proposed previously. The influence of the as-deformed grain orientation, which affects the stored energy via subgrain size and sub-boundary misorientation, is taken into account. The effects of the deformed grain geometry, the nucleation-site density, and the initial grain size prior to deformation on the recrystallization kinetics are assessed. The model is applied to the recrystallization kinetics of a cold-rolled AA1050 alloy.

In this paper, the static recrystallization behavior of X20Cr13 martensitic stainless steel was studied based on the hot compression test. The experimental results show that when the strain of the first pass is less than the critical strain of dynamic recrystallization, the main static softening mechanism is static recrystallization. The effects of prestrain, initial austenite grain size, deformation temperature and strain rate on the microstructure during static recrystallization were analyzed in detail.

A combination of phase-field and cellular automata methods is used to study the effect of initial grain size and laser power density on heat-affected zone (HAZ) formation during laser surface melting. Also, an analytical model is developed to estimate the depth of HAZ as a function of initial grain size and process parameters. Both analytical and numerical results indicate that the size of HAZ, as measured with respect to the changes in the grain structure, is inversely proportional to the initial grain size. They also show how increasing the laser power leads to an increase in the extent of HAZ. The proposed models thus provide a basis for the prediction and control of HAZ in laser surface melting.

Modelling the Effect of Initial Grain Size on Dynamic Recrystallization Using a Modified Cellular Automata and a Adaptive Response Surface Method