Results Of Hot Compression Tests Research Articles

Constructing processing map of M50NiL steel by artificial neural network model

The processing map for M50NiL steel was established by hot compression tests at temperatures of 950–1150 °C and strain rates of 0.002–1.0 s−1. Based on the experimental results of hot compression tests, the predictability in both reproducing experimental flow stresses and predicting flow stresses using the Arrhenius, physical-based, and artificial neural network (ANN) models was compared. The results showed that the average absolute relative errors of Arrhenius, physical-based, and ANN models in both reproducing and predicting flow stresses were 6.04 % and 8.01 %, 6.61 % and 7.78 %, and 1.91 % and 4.74 %, respectively. The ANN model had a considerably higher accuracy in reproducing and predicting flow stresses than the other two models. In addition, a processing map of M50NiL steel was established using the predicted flow stresses by the ANN model. This processing map indicated that the optimized processing parameters were 975–1050 °C/0.01–0.002 s−1. Instability occurred during deformation at 950–975 °C at 1.0 s−1 and 1075–1150 °C at 0.01 s−1. The instability prediction was verified by the microstructure evolution.

Development and Validation of Processing Maps for Hot Deformation of Modified AISI 321 Austenitic Stainless Steel

Abstract Hot deformation studies and optimization of hot working parameters and corresponding microstructure evolution were explored in a modified AISI 321 austenitic stainless steel. Hot compression tests were carried out in the temperature range of 800°C–1,100°C and five different strain rates (0.001–10 s−1). Processing maps were developed based on the results of hot compression tests, employing the principles of dynamic materials model and various domains of microstructure evolution were identified. The stable and unstable domains, as well as various domains indicating other microstructural reconstitutive mechanisms, including dynamic recrystallization (DRx), were identified with the aid of a processing map. The domain for DRx was confirmed by microstructural analysis of deformed specimens and also from the inflections in hardening curves. The processing regime for microstructural control was identified, and the results were validated by actual forging trials on a 1,000-T hydraulic forging press. The grain size of laboratory-tested hot-compressed samples and industrially forged billets exhibited excellent correlation. Constitutive equation for hot deformation was also developed for the steel based on hot compression test results.

Hot Deformation Studies and Optimization of Hot Working Parameters in Custom 465® Martensitic Precipitation Hardenable Stainless Steel

Abstract Hot deformation studies and optimization of hot working parameters and corresponding microstructure control were explored in Custom 465® ultrahigh-strength precipitation hardenable martensitic stainless steel. Hot compression tests were carried out in the temperature range of 800°C–1,100°C and at five different strain rates (0.001–10 s−1). Processing maps were developed based on the results of hot compression tests, employing principles of the Dynamic Materials Model, and various domains of microstructure evolution (in the austenite phase) were identified. The stable and unstable domains as well as domains indicating dynamic recrystallization (DRx) were identified from the processing map. The domain for DRx was confirmed by detailed microstructural investigations (prior austenite grains) of the respective water-quenched specimens, as well as from the inflections in hardening curves. The optimum conditions for processing Custom 465 steel were suggested as T = 1,075°C and ϵ˙=10−3s−1 and can be used for initial ingot breakdown (cogging) operations and T = 925°C and ϵ˙=10−3s−1 for finish forging operations to obtain grain size control. The value of the activation energy for hot deformation was calculated to be 543.88 kJ/mol for this steel.

Hot Workability of 16Cr-5Ni Stainless Steel Using Constitutive Equation and Processing Map

The hot working characteristics of 16Cr-5Ni stainless steel are studied using the results of hot compression tests. Hot compression tests were performed to a total true strain of 0.69 in the strain rate range of 0.001-10 s−1 and temperature range of 900-1100°C. Average value for activation energy is obtained as 403 kJmol−1. The processing maps were constructed based on dynamic materials model at true strain of 0.5. Stable and unstable regimes for hot working are identified and these are verified from the microstructural observations. Optimum hot working conditions associated with dynamic recrystallization are found to be in the strain rate range of 0.01-0.1 s−1 and temperature range of 1000-1100°C, which correspond to a peak power dissipation efficiency of 31%.

Hydrogen effect on compression mechanical properties of TiNb alloys at elevated temperatures

The study of this work was focused on the hydrogen effect on hot deformation behavior of hydrogen charged TiNb based alloys at three temperatures in comparison with non-charged specimens. The Ti24Nb and Ti26Nb (at.%) alloys were heat treated by three step regime in argon or hydrogen atmospheres. The hot compression tests were performed on a Gleeble 3800 machine at 800, 750 and 700°C with compression strain of 5×10-3 s-1 and deformation degree of 50 %. The microstructure resulting from heat treatment as well as from isothermal compression test was analyzed using optical and scanning electron microscopies. Measurement of microhardness revealed that higher microhardness values for Ti24Nb after thermo-hydrogen treatment corresponded to fine grained microstructure and strengthening by grain boundaries. Hydrogen contents determined using LECO RH600 analyzer showed that Ti26Nb contained higher amount of hydrogen due to the stabilization of beta phase by higher Nb concentration. Based on the hot compression test results, the plasticity at elevated temperatures was evaluated. The evolution of uniaxial compressive test curves showed the stabilization of flow stress due to the hydrogen for high deformations at lower temperatures. The differences in hot compression behavior for both niobium contents on the one hand and for hydrogen charged and non-charged specimens on the other hand were observed.

Identification and characterization of classical complement pathway inhibitors and their application to in vivo and ex vivo disease models

In this paper a set of mechanism-based unified elastic–viscoplastic constitutive equations has been used to model the mechanisms of plastic flow softening for the two-phase titanium alloy Ti-6Al-4V in hot forming conditions. Globularisation of the secondary (lamellar) alpha phase, dislocation density, plastic deformation induced temperature increase and phase transformation during deformation have been modelled. Hot compression tests were conducted on Ti-6Al-4V samples at different temperatures in a range of 1093 K–1293 K and at different strain rates in the range of 0.1 s−1–10 s−1. The material parameters were determined by using the hot compression test results and by using an Evolutionary Programming (EP)-based optimisation method. Based on the set of constitutive equations, stress–strain relationships for Ti-6Al-4V at different temperatures and strain rates were predicted. Good agreements between the experimental and computed results were obtained in steady state hot forming deformation conditions.

Modelling of dominant softening mechanisms for Ti-6Al-4V in steady state hot forming conditions

In this paper a set of mechanism-based unified elastic–viscoplastic constitutive equations has been used to model the mechanisms of plastic flow softening for the two-phase titanium alloy Ti-6Al-4V in hot forming conditions. Globularisation of the secondary (lamellar) alpha phase, dislocation density, plastic deformation induced temperature increase and phase transformation during deformation have been modelled. Hot compression tests were conducted on Ti-6Al-4V samples at different temperatures in a range of 1093K–1293K and at different strain rates in the range of 0.1s−1–10s−1. The material parameters were determined by using the hot compression test results and by using an Evolutionary Programming (EP)-based optimisation method. Based on the set of constitutive equations, stress–strain relationships for Ti-6Al-4V at different temperatures and strain rates were predicted. Good agreements between the experimental and computed results were obtained in steady state hot forming deformation conditions.

Effect of microstructure on deformation behavior of Ti–6Al–4V alloy during compressing process

In order to obtain a more quantitative understanding of the formability of Ti–6Al–4V alloys related to different initial microstructures, hot compression tests were conducted on alloys with three different initial microstructures, and Ti–6Al–4V alloy forging process for production of gear reverse idle was also studied. Three different microstructures were first established by combinations of several heat treatments for the first time. Average cooling rate obviously affects α lamellar spacing but does not strongly affect colony size. Measured flow curves for Ti–6Al–4V alloy exhibited peak flow stresses at relative low strains followed flow softening. For a given temperature and strain rate microstructures with finer lamellar spacing exhibited higher flow stresses. Flow curves for different colony sizes were almost coincident. It is concluded that α lamellar spacing strongly affects flow stress but the effect of colony size on flow stress is weak. Deformation resistances for different microstructures were predicted under various deformation conditions using hyperbolic sine law. The predicted constitutive functions coincided well with the results of hot compression tests. Dynamic recovery, dynamic recrystallization and breakage of lamellar structures result in finer microstructures and flow softening during hot forging processing. Cracks were likely to form with coarser lamellar spacing samples at lower forging temperatures.

Modeling Constitutive Relationship of BT25 Titanium Alloy During Hot Deformation by Artificial Neural Network

In this research, the constitutive relationships of BT25 titanium alloy based on regression and artificial neural network (ANN) methods were established and studied by analyzing the results of hot compression tests. The isothermal compression tests were conducted on a Gleeble 1500 thermo-mechanical simulator in the deformation temperatures ranging from 940 to 1000 °C with an interval of 20 °C and the strain rates of 0.01, 0.1, 1.0, and 10.0 s−1 with a height reduction of 60%. The average deformation activation energy of the alloy was derived as 623.26 kJ/mol at strain of 0.7 by using the non-linear regression method and assuming a hyperbolic sine equation between the stress, strain rate, and deformation temperature. On the basis of the experimental data samples, an ANN model was proposed and trained. The hot processing parameters of temperature, strain rate, and strain were used as the input variables and the flow stress as the output variable. The comparison of experimental flow stresses with predicted values by ANN model and calculated value by regression method was carried out. It was found that the predicted results by ANN are in a good agreement with the experimental values, which indicates that the predicted accuracy of the constitutive relationship established by ANN model is higher than that using the multivariable regression method.

The Effect of Deformation Heating on Restoration and Constitutive Equation of a Wrought Equi-Atomic NiTi Alloy

In this study, a set of constitutive equation corrected for deformation heating is proposed for a near equi-atomic NiTi shape memory alloy using isothermal hot compression tests in temperature range of 700 to 1000 °C and strain rate of 0.001 to 1 s−1. In order to determine the temperature rise due to deformation heating, Abaqus simulation was employed and varied thermal properties were considered in the simulation. The results of hot compression tests showed that at low pre-set temperatures and high strain rates the flow curves exhibit a softening, while after correction of deformation heating the softening is vanished. Using the corrected flow curves, the power-law constitutive equation of the alloy was established and the variation of constitutive constants with strain was determined. Moreover, it was found that deformation heating introduces an average relative error of about 9.5% at temperature of 800 °C and strain rate of 0.1 s−1. The very good agreement between the fitted flow stress (by constitutive equation) and the measured ones indicates the accuracy of the constitutive equation in analyzing the hot deformation behavior of equi-atomic NiTi alloy.

MODELING AND SIMULATION OF DYNAMIC RECRYSTALLIZATION AND GRAIN GROWTH DURING HOT WORKING OF INCONEL 783 SUPERALLOY

In this study, the modeling of recrystallization and grain growth was investigated to predict the microstructure evolution during hot working of INCONEL 783 superalloy (Alloy 783). The recrystallization model was constructed on the basis of the Avrami formation. A least-square optimization technique was used to determine several important parameters within the model from isothermal heat treatment and hot compression test results. High temperature compression tests were carried out under different temperatures, strain rates and strain conditions. The model for describing the recrystallization and grain growth behaviors of Alloy 783 was implemented onto the user-subroutine of a commercial FE code. In order to demonstrate the reliability of the model, the microstructure evolution of Alloy 783 alloy during the hot compression test was simulated and was accorded well with the experimental results.

Hot deformation behavior of low carbon advanced high strength steel (AHSS) microalloyed with boron

ABSTRACTThis research work deals the influence of boron content on the high temperature deformation behavior of a low carbon advanced high strength steel (AHSS). For this purpose high temperature tensile and compression tests are carried out at different temperatures and constant true strain rates by using an Instron testing machine equipped with a radiant cylindrical furnace. Tensile tests are carried out at different temperatures (650, 750, 800, 900 and 1000°C) at a constant true strain rate of 0.001 s-1. Uniaxial hot compression tests are also performed over a wide range of temperatures (950, 1000, 1050 and 1100°C) and constant true strain rates (10-3, 10-2 and 10-1 s-1). In general, experimental results of hot tensile tests show an improvement of the hot ductility of the AHSS microalloyed with boron, although poor ductility at low temperatures (650 and 750°C). The fracture surfaces of the AHSS tested at temperatures showing the higher ductility (800, 900 and 1000°C) indicate that the fracture mode is a result of ductile failure, whereas in the region of poor ductility the fracture mode is of the ductile-brittle type failure. On the other hand, experimental results of hot compression tests show that both peak stress and peak strain tend to decrease in the AHSS microalloyed with boron, which indicates that boron generates a sort of solid solution softening effect in similar a way to other interstitial alloying elements in steel. Likewise, hot flow curves of the AHSS microalloyed with boron show an acceleration of the onset of dynamic recrystallization (DRX) and a delay of the recrystallization kinetics. Results are discussed in terms of boron segregation towards austenitic grain boundaries and second phase particles precipitation during plastic deformation and cooling.

The prediction of hot flow behavior of Al–6%Mg alloy

In this research, the plastic flow behavior of Al–6%Mg alloy was studied by analyzing the results of hot compression tests in a range of temperature and strain rate. Then, an artificial neural network (ANN) model was trained at which the temperature, strain-rate, and strain parameters were used as the input layer and the flow stress as the output. The comparison of the predicted and experimental results of stress–strain curve proved the prediction capability of the ANN model.

Flow curve prediction of an Al-MMC under hot working conditions using neural networks

The plastic flow behaviour of a particle-reinforced aluminium alloy matrix composite (AA2618+Al2O3p) was studied by analysing the results of hot compression tests carried out in extended ranges of temperature and strain rate, typical of hot working operations. In general, for a given temperature and strain rate, the flow curves exhibit a peak, at relatively low strains, followed by flow softening; for a constant strain, the flow stress increases with increasing strain rate and decreasing temperature. The experimental data were used as an input for training artificial neural networks in order to predict the flow curves of the composite investigated. The comparison of the predicted stress–strain curves with the ones obtained by experimental testing, under conditions different from those used for the training stage, has proven the prediction generalisation capability of the artificial neural network-based models.

Influence of carbon content on high temperature response of plain carbon steels

The effect of carbon content on material hot flow behaviour of 0·06 and 0·50%C steels has been investigated. Constitutive equations for the flow behaviour, taking into account dynamic recovery and recrystallisation, have been fitted using results of hot compression tests. Validation suggests that the model describes well the stress–strain behaviour observed for various steel grades. It is found that the hardening parameter and recovery are more sensitive to forming conditions at a higher carbon content.

Improvement of hot workability of Ni 3AlCrZrB ordered alloy

The effect of minor additions of magnesium on high temperature plasticity in Ni 3AlCrZrB ordered alloy has been investigated. Results of hot compression tests in a Gleeble apparatus showed that the maximum allowable deformation of a polycrystalline alloy with an appropriate magnesium content was about 50% at 1100 °C. An applicable content of magnesium also notably increased the stress-rupture life and tensile ductility at high temperature. The improvement of high temperature properties by magnesium is caused by the magnesium mainly segregated at grain boundaries and increasing the grain boundary coherence.