Hot Flow Stress Research Articles

Numerical analysis of alpha-beta brass by constitutive model for prediction of hot flow stress

Numerical analysis of alpha-beta brass by constitutive model for prediction of hot flow stress

Delineating the role of dynamic and static recrystallization during hot working of nickel-based superalloy (IN600)

In the presented research, the dynamic working of nickel-based (IN600) superalloy was performed and the micro-mechanisms affecting the deformation behaviour were closely monitored, particularly the role of static and dynamic recrystallization. Hot deformation flow stress response indicated an increase in the true stress value with an increase in strain rate and decrease in temperature. The constitutive calculations indicated that deformation progressed mainly due to dislocation climb motion. The hot workability map indicated a peak power dissipation efficiency (PDE) of 0.39 in two working domains. The microstructural evolution in the hot deformed specimens depicted a consistent increase in dynamic softening at temperature ≥ 1000 °C, whereas, a steady decline in the extent of dynamic softening is observed with increase in strain rate from 0.01 s−1 to 1 s−1. The mechanism for microstructural evolution in this range (0.01–1 s−1) was identified as discontinuous dynamic recrystallization (DDRX). Moreover, at the highest strain rate of 10 s−1, a sudden surge in the recrystallization fraction was observed, which was attributed to the combined effect of DDRX and static recrystallization (SRX). Additionally, this study shows that the presence of twin boundaries (TBs) contributes to dynamic softening by serving as sites for nucleation of strain-free grains.

Study on the Constitutive Modeling of (2.5 vol%TiB + 2.5 vol%TiC)/TC4 Composites under Hot Compression Conditions.

The hot deformation behavior of titanium matrix composites plays a crucial role in determining the performance of the formed components. Therefore, it is significant to establish an accurate constitutive relationship between material deformation parameters and flow stress. In this study, hot compression experiments were conducted on a (2.5 vol%TiB + 2.5 vol%TiC)/TC4. The experiments were performed under temperatures ranging from 1013.15 to 1133.15 K and strain rates ranging from 0.001 to 0.1 s-1. Based on the stress-strain data obtained from the experiment, the constitutive models were established by using the Arrhenius model and the BP neural network algorithm, respectively. Considering the relationship between strain rate, hot working temperature, and flow stress, a comparative analysis was conducted to evaluate the prediction accuracy of two different constitutive models. The research results indicate that the flow stress of (2.5 vol%TiB + 2.5 vol%TiC)/TC4 increases with decreasing temperature and increasing strain rate, and the stress-strain curve shows obvious work hardening and softening behaviors. Both the Arrhenius model and the BP neural network algorithm are effective in predicting the hot compression flow stress of (2.5 vol%TiB + 2.5 vol%TiC)/TC4, but the average relative error and root mean square error of the BP neural network algorithm are smaller and the correlation coefficient is higher, thus possessing higher accuracy and reliability.

Hot Deformation Behavior and Processing Maps of 26CrMo7S Steel Used in Oil Exploration.

The hot deformation behavior and flow stress characteristics of experimental 26CrMo7S steel were analyzed using a thermal simulator under a range of conditions, including a strain rate range of 0.01~10 s-1, a temperature range of 850~1250 °C, and a maximum deformation amount of 70%. The Arrhenius constitutive model was built for the corresponding conditions, and the model's accuracy was verified through error analysis. Additionally, hot processing maps were constructed to analyze the processing zone of the steel under different hot deformation conditions. Finally, the microstructure of the processing zones was observed and verified using the electron backscattered diffraction (EBSD). The results indicate that the interaction of work hardening and dynamic softening influences the hot deformation behavior of 26CrMo7S steel. The Arrhenius constitutive equation with a value of the correlation coefficient (r = 0.99523) accurately predicts the flow behavior of 26CrMo7S steel under different strains. The optimal processing zone obtained with the hot processing maps is within a deformation range of 1010~1190 °C and a strain rate range of 0.01~10-1.5 s-1, and the obtained microstructure is in good agreement with the analysis results.

Hot deformation behavior and flow stress modeling of coarse-grain nickel-base GH4151 superalloy ingot materials in cogging

Due to the high deformation resistance and poor thermal ductility of the new cast GH4151 alloy ingots, cracks are easy to occur during cogging process. For clarifying the effects of deformation parameters on microstructural evolution and dynamic recrystallization (DRX) nucleation mechanisms. In this work, the causes of crack formation and extension were first investigated using SEM and EBSD. The study revealed that the reasons for crack formation and propagation are the MC carbides at the original grain boundaries, large-size γ′ phase, residual eutectic phases, and tiny pores near the grain boundaries. Subsequently, a series of hot compression tests were performed using a Thermecamastor-Z thermo-mechanical simulator at temperatures ranging from 1080 °C to 1160 °C and a strain rate range of 0.01–10 s−1. The constitutive equation of the Arrhenius model and the hot working map was established, determining activation energy(Q) of 1086.58 kJ·mol−1. Large-size γ′ is coherent with the matrix. For the γ+γ′ dual-phase region, heterogeneous strain-induced dynamic recrystallization (HDRX) occurs, and discontinuous dynamic recrystallization (DDRX) is the main nucleation mechanism for DRX. However, for γ single-phase region, DDRX plays a more significant role. Furthermore, the MC phase (>1 μm) has different crystal orientations with the γ matrix and acts as sites for recrystallization through particle-stimulated nucleation (PSN). Finally, a fine and uniform grain structure can be obtained in the temperature range of 1120–1135 °C and the strain rate range of 0.1 s−1 to 1 s−1.

Thermal Deformation Behavior and Dynamic Softening Mechanisms of Zn-2.0Cu-0.15Ti Alloy: An Investigation of Hot Processing Conditions and Flow Stress Behavior.

Through isothermal hot compression experiments at various strain rates and temperatures, the thermal deformation behavior of Zn-2.0Cu-0.15Ti alloy is investigated. The Arrhenius-type model is utilized to forecast flow stress behavior. Results show that the Arrhenius-type model accurately reflects the flow behavior in the entire processing region. The dynamic material model (DMM) reveals that the optimal processing region for the hot processing of Zn-2.0Cu-0.15Ti alloy has a maximum efficiency of about 35%, in the temperatures range (493-543 K) and a strain rate range (0.01-0.1 s-1). Microstructure analysis demonstrates that the primary dynamic softening mechanism of Zn-2.0Cu-0.15Ti alloy after hot compression is significantly influenced by temperature and strain rate. At low temperature (423 K) and low strain rate (0.1 s-1), the interaction of dislocations is the primary mechanism for the softening Zn-2.0Cu-0.15Ti alloys. At a strain rate of 1 s-1, the primary mechanism changes to continuous dynamic recrystallization (CDRX). Discontinuous dynamic recrystallization (DDRX) occurs when Zn-2.0Cu-0.15Ti alloy is deformed under the conditions of 523 K/0.1 s-1, while twinning dynamic recrystallization (TDRX) and CDRX are observed when the strain rate is 10 s-1.

High Cycle Fatigue Behaviour of 316L Stainless Steel Produced via Selective Laser Melting Method and Post Processed by Hot Rotary Swaging.

This paper deals with a study of additively manufactured (by the Selective Laser Melting, SLM, method) and conventionally produced AISI 316L stainless steel and their comparison. With the intention to enhance the performance of the workpieces, each material was post-processed via hot rotary swaging under a temperature of 900 °C. The samples of each particular material were analysed regarding porosity, microhardness, high cycle fatigue, and microstructure. The obtained data has shown a significant reduction in the residual porosity and the microhardness increase to 310 HV in the sample after the hot rotary swaging. Based on the acquired data, the sample produced via SLM and post-processed by hot rotary swaging featured higher fatigue resistance compared to conventionally produced samples where the stress was set to 540 MPa. The structure of the printed samples changed from the characteristic melting pools to a structure with a lower average grain size accompanied by a decrease of a high fraction of high-angle grain boundaries and higher geometrically necessary dislocation density. Specifically, the grain size decreased from the average diameters of more than 20 µm to 3.9 µm and 4.1 µm for the SLM and conventionally prepared samples, respectively. In addition, the presented research has brought in the material constants of the Hensel-Spittel formula adapted to predict the hot flow stress evolution of the studied steel with respect to its 3D printed state.

Hot workability characteristics of two A335 P92 steels for power plant application: A comparative study

The article reports on the workability of two P92 steels having a chromium content of 8.29 and 9.48 wt%. Constitutive equations were used to calculate material parameters describing the hot deformation flow stress. Hot deformation tests were conducted using the Gleeble® 3500 thermomechanical facility. Test conditions were: temperature of 850-1000°C and strain rate of 0.1-10s-1 to a strain of 0.5. The flow stress curve results show that dynamic recovery was the only softening mechanism. A comparative study of the two steels revealed that Cr content had a marginal significance on the flow stress behaviour. Constitutive analysis results of the material parameters were: a stress exponent of 9.0 (P92-A), and 11.0 (P92-B), while the activation energy was 369 kJmol-1 (P92-A), and 472 kJmol-1 (P92-B). A brief explanation of the material parameter results is in this article. A flow stress model was developed to predict the flow stress behaviour of the two P92 steels investigated. The results show that the model accurately predicts the flow stress at all the deformation conditions applied. The statistical parameters showed a good correlation between the predicted and the experimental data. Therefore, this model can be used to develop metal forming schedules for industrial applications.

Influence of different homogenization heat treatments on the microstructure and hot flow stress of the aluminum alloy AA6082

Proper design of the homogenization heat treatment of 6000 series Al wrought alloys is crucial for processes such as hot rolling and extrusion. Important aspects are the precipitation and growth of dispersoids and the dissolution and re-precipitation of Mg-Si-precipitates. Studying these processes is laborious and experimentally demanding, limiting the feasibility of systematic study of variations in the homogenization regime. We conducted in situ differential scanning calorimetry (DSC) experiments of homogenization of AA6082 at different soak temperatures and cooling rates. The resultant heating and cooling curves were interpreted to obtain information on dispersoid number density and Mg-Si-phase dissolution and re-precipitation. Microstructural differences have been evaluated by scanning electron microscopy analysis. The results elucidate the complex relations between dissolution of primary Mg-Si-precipitates, dispersoid precipitation and growth, Mg-Si-re-precipitation, and hot forming behavior while reducing experimental effort compared to semi-industrial furnace trials. Overall, the homogenization soak temperature had the largest influence on these microstructural phenomena while differences due to the cooling rate were less pronounced in an industrially relevant range. In conclusion, in situ DSC can be used as a tool for rapid and inexpensive investigation of homogenization parameters • In-depth analysis of heating and cooling DSC curves. • Use of industry-relevant heating rates and homogenization soak temperatures/times. • Experimental effort is reduced compared to furnace trials. • Advanced SEM characterization of constituents, dispersoids, and Mg-Si-phases. • Microstructure after homogenization is discussed with regards to hot flow stress.

Shallow and deep learning of an artificial neural network model describing a hot flow stress Evolution: A comparative study

In recent years, the utilization of artificial neural networks (ANNs) as regression models to solve the issue of hot flow stress forecasting has become a standard approach. In a connection with this kind of regression issue, employed ANNs are usually learned via a shallow learning technique while only limited attention has been paid to a deep learning method. In the frame of the submitted research, the shallow learning approach is thoroughly compared to the deep learning techniques which are based on the use of a Restricted Boltzmann Machine (RBM) and an Auto-Encoder (AE). To do so, these learning techniques are applied on a feed-forward multi-layer ANN describing the experimental hot flow curve dataset of micro-alloyed medium carbon steel. In comparison with the shallow learning method, both deep learning approaches provided higher accuracy in the network response – especially in the case of a higher number of hidden layers. The results have also shown that neither the RBM-based deep learning method nor the AE-based method had a significant effect on the duration of the necessary calculations. However, it turned out that the RBM-based method can, under certain conditions, lead to a more reliable network performance.

Flow Characteristics and Structure Optimization of a Baffle Plate Heat Exchanger

In this study, a theoretical model of the hot and cold fluid flow, heat transfer, and thermal stress coupling in a baffle plate heat exchanger is established, and numerical simulation is carried out. The flow field in the heat exchanger and the deformation of the heat exchange tube bundles in the baffle plate heat exchanger are studied. The optimization effect of the diversion grid on the flow field at the inlet of the variable section is emphasized. The influence of grid arrangement on the flow field and the performance of the tube bundles are analyzed and discussed. The results show that the backflow situation can be effectively improved and the vortex intensity in the straight section of the cold fluid inlet can be greatly reduced by adding the grid. The deformation of the heat exchange tube bundles illustrates the maximum deformation with 1.39 mm at the position of the strongest backflow. The deformation can be reduced by 26% due to the arrangement of the diversion grid, which is helpful to improve the safety of the device.

Hot Deformation Behavior and Strain Rate Sensitivity of α+β Brass Sheet by Uniaxial Material Constitutive Equations

The present work proposes a systematic procedure for evaluation of high temperatures deformation and formability of α+β Brass undergoing the uniaxial tensile test conditions. Firstly, uniaxial tensile tests were conducted on Universal Testing Machine (UTM) with loading capacity of 100 KN at temperature of 773K, 873K and 973K with a quasi-static strain rates of 0.001s-1, 0.01 s-1 and 0.1s-1. Hot tensile flow stress behaviors have been affected significantly by test temperatures and strain rates for Brass. Drop-in yield and ultimate tensile strength have been observed at approximately 58 % and 68 % with a rise in test temperature from 773 K to 973 K. Around 30% improvement has been observed in % elongation with rise in test temperature. Further, flow stress has been predicted by most popular Johnson Cook (JC) uniaxial constitutive model at wide range of temperatures (773K, 873K and 973K) and strain rates (0.001s-1,0.01 s-1 and 0.1s-1). Further, yield loci have been plotted at various temperatures using Hill 1948 and Barlat 1989 yield function. Barlat 1989 has followed experimental results correctly in all test temperatures.

Hot Ductility Analysis and Flow Stress Prediction of (C-Mn-S-Al-Nb-V-Ti) Micro-alloyed Steel

The objective of this work is to study the hot ductility of (C-Mn-S-Al-Nb-V-Ti) micro-alloy steel of industrial production whose initial structural state is rolling stock. To simulate the thermomechanical treatments imposed we have deformed by pulling our samples after subjecting them to a solution treatment at 1200 °C and a precipitation treatment cycle before deformation. Hot deformations were carried out at temperatures from 700 °C and 1150 °C and deformation rates ranging between 10-2 s-1 and 5.10-4 s-1. The results show a decrease in hot ductility. Minimum values of hot ductility are determined at 800°C, and another decrease in hot ductility was observed at 900°C. Ferrite precipitation is observed at austenitic grain boundaries in the intercritical temperature range, causing intergranular embrittlement. Precipitation makes the hot ductility curve wider and deeper around 900°C. Hot ductility losses can explain by the presence of precipitates in the austenitic region and the presence of the two-phase structure in the intercritical region. Finally, based on experimental stress-deformation data, artificial neuron network (ANN) methods were used to predict flow stress of (C-Mn-S-Al-Nb-V-Ti) micro-alloy steel. This model is more effective in predicting flow stress and results can also be used in the mathematical simulation of hot metal formation processes.

Constitutive modelling of hot deformation behaviour of metallic materials

The complexity of hot deformation behaviours of metallic materials is acknowledged in decades of study. The present work uses a new constitutive model by Zhu-Ou-Popov (ZOP model) and its modifications to predict the hot deformation behaviours of metals. The ZOP model and its modifications are introduced firstly. The basic idea of these models is centred on a set of piecewise and transition functions: the piecewise functions are used to predict flow stress at different strain ranges, whilst the transition functions enable a smooth shifting from small strain to large strain ranges. The methods for identification of four variant models are developed and given in detail. Hot compressive flow stress curves of 42CrMo at different strain rates and temperatures are used to show the validity of these models. Results show that, all of the developed models are able to predict the hot compressive behaviour of 42CrMo. Using the Arrhenius type equation and modified Zener-Holloman parameter to predict the flow stress from the yield point, the Modified model Ⅲ gives the most favourable prediction accuracy with R2 of 0.9569, whilst other models are also effective with R2 higher than 0.91. The modifications of the ZOP model can be used to predict the yield stress and to reflect the peak stress. In addition, the applicability and advancement of the presented constitutive models are discussed. The models are considered to be effective in reflecting the occurrence and completion of dynamic recrystallization (DRX) in hot deformation of metallic materials. It is shown that the studied models are capable of predicting the peak strain and completion strain of DRX, with comparable results obtained to experimental data.

Processing Workability and Artificial Neural Network of AA1070 to the Prediction of Hot Flow Stress

Processing Workability and Artificial Neural Network of AA1070 to the Prediction of Hot Flow Stress

Hot deformation behavior and flow stress modeling of a novel CoNi-based wrought superalloy

The thermal deformation behavior and flow stress modeling of a novel CoNi-based wrought superalloy after forging was investigated at γ' sub-solvus temperature (1050 °C and 1075 °C) and γ' super-solvus temperature (1100 °C and 1125 °C) with strain rate range from 0.001 s−1 to 0.1 s−1 under a 50% strain. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques were used to characterize the microstructures and explain the flow behavior. The results show that the flow stress increases with decreasing temperature and increasing strain rate. Dynamic recrystallization (DRX) occurs under all deformation conditions. When the alloy was deformed sub-solvusly at 1075 °C/0.01 s−1 and 0.001 s−1 conditions, the γ' phase dissolved resulting in substantial grain growth. The constitutive equations were established via the flow stress data with the respect to the γ' phase dissolution. The activation energies for the γ + γ' dual-phase region and the γ single-phase region of the studied alloy are about 650 and 390 kJ/mol, respectively, which is comparable with traditional Ni-based superalloys.

Modelling of Hot Flow Stress of Duplex Steel in Dependence of Microstructure Using the Rule of Mixture

The ferrite fraction and phase distribution of duplex steels depend strongly on the temperature evolution during hot deformation and are correlated to different mechanical behaviors during hot deformation as well as cold deformation. Therefore, the control of microstructure evolution during hot forming is relevant for target-oriented material design. In flow stress modelling for hot forming, the influence of microstructure beyond the ferrite fraction is often neglected. In the present work, a new method is demonstrated to also consider the influence of grain size in flow stress modelling. For this purpose, different initial microstructures with different ferrite fractions and phase distribution were tested in compression tests at 1100 °C and 0.1 s−1. The microstructure was analyzed before and after forming and it was observed that the differences in ferrite fractions vanished during the compression tests. Those microstructure data were used in a model including a rule of mixture and Hall–Petch relationship to extract the single-phase flow curves of ferrite and austenite. Based on the flow stress of the single phases, in combination with ferrite fraction and individual grain size, the flow curves of the different material conditions were calculated and the concurrent influence of ferrite fraction and phase distance on the mechanical behavior was discussed.

Hot Deformation Behavior of a Co-Spray-Formed Al-Si/7075 Bimetallic Gradient Alloy

In this paper, we report the results obtained from the hot compression behaviour of co-spray-formed Al-Si/7075 bimetallic gradient alloys by investigating the five selected layers divided evenly from top to bottom. It was found that with a decrease in the strain rate and an increase in temperature, the hot compression flow stress of deposited alloys decreases gradually, as expected. The relationship between flow stress, temperature and strain rate follows the Arrhenius relationship. The deformation activation energy of the co-spray formed gradient alloy gradually increases from bottom to top in the height direction, which are 100.15, 167.35, 185.54, 208.78 and 220.83 KJ/mol, indicating that the degree of difficulty in the deformation of the alloy is affected by changes in the silicon content of the alloy. Finally, the flow stress constitutive equation is calculated for each layer of alloy material, which is instructive for the subsequent study of the densification process of co-spray-formed gradient alloys.

Analysis of Tensile Deformation Behaviour of Dual Phase -590 Steel at Different Temperatures and Strain Rates

ABSTRACT An accurate uniaxial constitutive model is necessary to analyse the plastic deformation behaviour of metal and for reliable finite element simulations in sheet metal forming operations. In the present study, the hot uniaxial tensile flow stress analysis of dual phase (DP590) steel thin sheet has been carried out under a quasi-static strain rates of 0.1–0.001/s at the temperature range of 723–1073 K. The flow stress behaviour is significantly affected by test temperatures, strain rates and sheet orientations. Further, the Fields–Backofen constitutive flow relationship has been used to investigate the flow stress behaviour. This predicted flow stress curves shows a good fit to the experimentally measured stress at the work-hardening stage. Furthermore, a modified Fields–Backofen constitutive equation with a softening term has been considered to predict the flow behaviour. The capability of models has been evaluated based on the correlation coefficient (R), average absolute error AAE (Δavg) and root mean square error (RMSE). A better prediction of flow stress behaviour is observed by modified modified Fields–Backofen model with R = 0.9552, Δ = 0.034 and s = 0.0564.

Analysis of material properties and strain hardening behaviour of brass at different temperature and quasi-static strain rate conditions

ABSTRACT The α-Brass alloy is gaining special attention for electrical and thermal conductivity applications because of being easily formed/workability and retaining high strength after forming. This makes crucial to understand the plastic deformation behaviour and work hardening behaviour of a material for reliable finite element simulations. In present study, the hot uniaxial tensile flow stress analysis of α-Brass alloy thin sheet has been carried out under a quasi-static strain rates of 0.1–0.001/s at the temperature range of 300 K–773 K. Flow stress behaviour has significantly affected with test temperatures, strain rates and sheet orientations. Anisotropy in terms of yield stress variation and % elongation by in-plane anisotropy and Anisotropy index have been evaluated. Further, stress–strain relation has been analysed by popular empirical strain hardening equation namely, Hollomon and Swift. The work hardening behaviour of alloy has been well-defined by Swift relationship compare to Hollomon empirical relation.