Thermal Deformation Conditions Research Articles

Adjustment of the Hot Rolling Technology of Micro-Alloyed Pipe Steel Using a Digital Twin to Provide the Targeted Structure and Properties of the Metal

The results of computer and physical modeling of pipe steel hot rolling on a continuous rolling mill 2000 are presented. The moment of growth of austenite grains and the reasons for their growth are determined. The possibility of grinding the microstructure of the metal before controlled cooling, and the thermal deformation conditions conducive to grinding are investigated. It is shown that Nb (C,N) are not a factor in stopping the growth of austenite grains, but only inhibit the growth processes.

Hot Formability Study of Cr5 Alloy Steel by Integration of FEM and 3D Processing Maps.

Microstructure is an important factor that affects the mechanical properties and service life of forgings. Through the full study of the formability of the material, the internal microstructure of the material can be effectively controlled. In order to accurately describe the formability of materials during thermal processing, 3D hot processing maps containing strains were established in this paper, and the 3D hot processing maps were coupled with the finite element method for simulation calculation. The Cr5 alloy steel was subjected to unidirectional thermal compression at a strain rate of 0.005–5 s−1 and temperature range of 900–1200 °C on a Gleeble-1500D thermal simulation machine, in order to obtain the date of true stress and strain. Based on the dynamic material model (DMM), the 3D processing maps of Cr5 alloy steel was established, and the 3D processing maps were associated with the analysis of microstructure evolution during hot deformation. The results show that the optimum thermal deformation conditions are as follows: temperature of 1000–1125 °C, strain rate of 0.01–0.2 s−1, and peak power dissipation of 0.41. The 3D processing maps were coupled with the finite element software FORGE® to simulate the hot working process, and the distribution and change of power dissipation and flow instability domain on the metal deformation under different thermal deformation conditions were obtained. The comparison between the simulation results and metallographic images of typical regions of metal deformation shows that they are in good agreement. This method can effectively predict and analyze the formability of materials during hot processing and provide guidance for practical industrial production.

Study on static softening behavior and hot working performance of Fe-0.2C-7Mn steel

Static softening behavior and hot working performance of medium Mn steel (Fe-0.2C-7Mn) are studied by 2-step and interrupt hot compression test with a Gleeble-3500 thermal-mechanical simulator. The results show that static softening behavior of the steel exhibits obvious sensitivity to the deformation temperature, inter-pass time and strain rate. But deformation temperature has a more significant effect on the static recrystallization (SRX) grain size than strain rate. 3D hot working processing maps are established, that low temperature and medium strain rate (850 °C ∼ 925 °C and 0.02 s−1 ∼ 0.3 s−1) are the preferred thermal deformation conditions for the test steel. Microstructure observations indicate that both static recovery (SRV) and SRX occur within inter-pass time, and SRV is the predominant mechanism in determining softening fraction. The microstructure is composed of film-like α at room temperature, and most of the nucleation of SRX preferably take place at triple junctions of grains or prior grain boundaries. Besides, high-angle grain boundaries (HAGBs) migration produce twin boundaries during grain growth and the main nucleation mechanism of the SRX is strain-induced boundary migration. The kinetics model of static softening is established and the experimental values are consistent with predicted ones, which proves the reliability of the model.

Microalloying effects on structure-forming processes during hot plastic deformation

The kinetics of austenite grains' growth upon heating has been investigated, and the processes of dynamic and static recrystallization occurring under different modes of plastic deformation (reduction pattern, deformation temperature) of high-strength steels with various microalloying complexes have been studied. The research made it possible to reveal the thermal deformation conditions for the formation of a finely dispersed homogeneous structure of steel. Technological recommendations have been developed for the production of high-strength steels depending on their microalloying (vanadium, niobium).

Влияние увеличения содержания никеля и молибдена в аустенитной стали на термодеформационные условия достижения пороговой степени деформации

Влияние увеличения содержания никеля и молибдена в аустенитной стали на термодеформационные условия достижения пороговой степени деформации

The Flow Stress Behavior and Constitutive Model of Cr8Mo2SiV Tool Steel during Hot Deformation

The uniaxial hot compression tests of Cr8Mo2SiV tool steel are conducted by thermomechanical simulator in a wide strain rate range of 0.005–5 s−1 and temperature range of 900–1150 °C to predict the hot deformation behavior. It is found that flow stress strongly depends on deformation temperature and strain rate under the mechanisms of dynamic softening and work hardening. Second, the Johnson–Cook model and modified Arrhenius‐type equation considering the compensation of strain are proposed for the estimation of flow stress of the tool steel. Subsequently, the validity of the established constitutive models is verified by standard statistical parameters including correlation coefficient (R) and average absolute relative error (AARE). Finally, the hot deformed microstructure is analyzed using the constitutive model with strong predictive ability. With the decrease in lnZ (Z is the Zener–Hollomon [Z–H] parameter) value from 43.5 to 32.7 s−1, microstructure evolution indicates that a remarkable increase in the high‐angle grain boundaries (misorientation more than 15°) from 19.1% to 32.6%, which also reflects the reliability of Z–H map in predicting dynamic recrystallization behavior under most thermal deformation conditions.

Studying the Influence of Radial-Shear Rolling on Thermal Deformation Conditions of A1050 Processing

The analysis of the influence exerted by the deformation techniques on the conditions of radial-shear rolling (RSR) of commercial purity aluminum A1050 is carried out. Based on finite-element modeling (FEM), the temperature change at various feed angles and elongation in the first and last passes is obtained. The increase in feed angle slightly raises the temperature variations in the surface layer due to the increase in reduction per pass but does not significantly influence total deformation heating during the RSR process. The finishing deformation temperature can be controlled by varying a reduction ratio. In this case, it is necessary to take into account the initial temperature of heating, dimensions of rolled products obtained, and elongation per pass. The dimensions of a workpiece have a significant effect on thermal changes in the RSR process. In the last pass, when the diameters are 20–14 mm, deformation heating is almost completely compensated for by rod cooling upon contact between the environment and the tool and begins to prevail, with an increase in elongation ratio of more than 1.2. An analysis of effective strain (eeff) at various deformation modes shows that the difference in eeff values over the cross section of the rod decreases with an increasing feed angle. A comparison of the data with the hardness and microstructure of the rolled A1050 samples shows that eeff has a significant impact on the change in the structure and properties to a certain value, which is confirmed by the distribution of the microhardness over the cross section of the rods. The mechanical properties of the rods correspond to the properties of commercial purity aluminum in the work-hardened state (σeff ~ 115 MPa, σ0.2 ~ 110 MPa, δ ~ 1%, HV ~ 40–43).

Hot Workability of Ultra-Supercritical Rotor Steel Using a 3-D Processing Map Based on the Dynamic Material Model.

As a new-type of ultra-supercritical HI-IP rotor steel, X12CrMoWVNbN10-1-1 alloy steel has excellent integrative performance, which can effectively improve the power generation efficiency of the generator set. In this paper, uniaxial thermal compression tests were carried out over a temperature range of 950–1200 °C and strain rates of 0.05–5 s−1 with a Gleeble-1500D thermal simulation testing machine. Moreover, based on hot compression experimental data and the theory of processing diagrams, in combination with the dynamic material model, a three-dimensional (3-D) thermal processing map considering the effect of strain was constructed. It was concluded that optimum thermal deformation conditions were as follows: the temperature range of 1150–1200 °C, the strain rate range of 0.05–0.634 s−1. Through secondary development of the finite element (FE) software FORGE®, three-dimensional thermal processing map data were integrated into finite element software FORGE®. The distributions of instability coefficient and power dissipation coefficient were obtained over various strain rates and temperatures of the Ø 8 × 12 mm cylinder specimen by using finite element simulation. It is shown that simulation results are consistent with the microstructure photos. The method proposed in this paper, which integrates the three-dimensional processing map into the finite element software FORGE® (Forge NxT 2.1, Transvalor, Nice, France), can effectively predict the formability of X12CrMoWVNbN10-1-1 alloy steel.

Fretting Wear Properties of Thermally Deformed Inconel 625 Alloy

The effect of microstructure on fretting wear behavior of Inconel 625 alloy was studied after different thermal deformation conditions (strain rate and temperature). The results show that grain size and microhardness have a significant influence on the fretting wear. As thermal deformation temperature increases and strain rate decreases, grain size increases and microhardness decreases. The oxide formed on the surface of Inconel 625 helps to reduce wear, but oxidative wear is the main wear mechanism. In the thermal deformation temperature range of 900–1000 °C and strain rate of 0.1–1 s−1, grain size is less than 4.5 μm, and the hardness is greater than 252.9 HV. Under these conditions, the coefficient of friction is the highest and the wear volume is the lowest. This paper proposes to improve the fretting wear resistance of the workpiece by adjusting the strain rate and temperature during the thermal deformation process.

Metadynamic recrystallization behaviors of SA508Gr.4N reactor pressure vessel steel during hot compressive deformation

The two-pass isothermal hot compression method was used to study the effect of different thermal deformation conditions on static recrystallization behavior in Ni–Cr–Mo series SA508Gr.4N low alloy steel with interval holding time ranging from 1 to 300 s, temperature ranging from 950 to 1150 °C, strain rate ranging from 0.01 to 1 s−1, true strains ranging from 0.1 to 0.2, and initial austenite grain size ranging from 175 to 552 μm. It can be concluded that the static recrystallization volume fraction gradually increases with the increase in the deformation temperature, strain rate, strain and pass interval, and the decrease in the initial grain size, which is mainly due to the increase in the deformation energy storage and dislocations. Moreover, strain-induced grain boundary migration is the nucleation mechanism for static recrystallization of SA508Gr.4N low alloy steel. Based on the stress–strain curve, the predicted value obtained from the established static recrystallization kinetics model is in good consistence with the experimental value, and the static recrystallization thermal activation energy of SA508Gr.4N steel was calculated as 264,225.99 J/mol.

Hot deformation characteristics and dynamic recrystallization mechanisms of a Co–Ni-based superalloy

The hot deformation behavior of a Co–Ni-based superalloy was systematically investigated using thermal compression tests. Stress–strain curves showed a typical dynamic softening after peak stress, especially at high temperatures and low strain rates. An Arrhenius-type constitutive equation was developed to reveal the relationship between the flow stress, strain rate, and temperature, while a processing map was constructed based on the calculations from the stress-strain curves combined with microstructural observations to determine the optimum thermal deformation conditions. The extent of recrystallization was found to increase with increasing temperature, a decreasing strain rate, or an increasing strain. A complete dynamic recrystallization (DRX) condition was reached at 1050 °C/0.01 s−1/0.7. In addition, pre-existing annealing twins were replaced by discontinuous dynamic recrystallization (DDRX) grains along the twin boundaries and the twin-DRX (TDRX) grains in the twin interior. In the case of an un-twinned matrix, a combined DDRX and continuous DRX (CDRX) process occurred at high strain rates, in contrasted with a single DDRX process taking place at low strain rates.

Hot Deformation Behavior and Microstructure Evolution of Cu-Ni-Co-Si Alloys.

The Cu-1.7Ni-1.4Co-0.65Si (wt%) alloy is hot compressed by a Gleeble-1500D machine under a temperature range of 760 to 970 °C and a strain rate range of 0.01 to 10 s−1. The flow stress increases with the extension of strain rate and decreases with the rising of deformation temperature. The dynamic recrystallization behavior happens during the hot compression deformation process. The hot deformation activation energy of the alloy can be calculated as 468.5 kJ/mol, and the high temperature deformation constitutive equation is confirmed. The hot processing map of the alloy is established on the basis of hot deformation behavior and hot working characteristics. With the optimal thermal deformation conditions of 940 to 970 °C and 0.01 to 10 s−1, the fine equiaxed grain and no holes are found in the matrix, which can provide significant guidance for hot deformation processing technology of Cu–Ni–Co–Si alloy.

Classification of pressure welding methods depending on thermal deformation conditions

In this study, a classification of welding methods is proposed, based on the peculiarities of metal gripping under various heat-deformation conditions for the implementation of welding processes. The theoretical basis of the developed classification is the hypothesis of the critical sizes of active centers. The main approaches to the classification of welding methods are considered, and four groups of pressure welding methods are proposed, depending on the mechanism of formation of stable centres of gripping: mechanical welding methods with low plastic deformation rate; mechanical methods of welding with a high plastic deformation rate; thermo-mechanical welding methods, in which, in addition to heating by deformation, additional sources of thermal energy are used to increase the temperature in the zone of joint formation; thermal pressure welding methods that envisage only a thermal activation channel.

Research of Recrystallization Processes in Low-Carbon Low-Alloy Steel in Modeling High-Temperature Rolling

Abstract—The processes of dynamic and static recrystallization occurring under various types of plastic deformation (compression pattern, deformation temperature) of low-carbon low-alloy steel are studied. Modeling of thermomechanical processing followed by a comprehensive analysis of the microstructure was performed on a Gleeble 3800. The studies performed revealed the thermal deformation conditions for the formation of a finely dispersed homogeneous steel structure. The results of industrial testing of the developed modes of hot rolling of sheet metal are given.

Simulation and experimental investigations of complex thermal deformation behavior of wire electrical discharge machining of the thin-walled component of Inconel 718

The geometric error is very important to the component performance in wire electric discharge machining (WEDM) process, yet few studies have focused on the geometric error caused by thermal deformation. This work mainly describes the complex thermal deformation phenomenon and its corresponding cause during the WEDM processing the thin-walled component of Inconel 718. Firstly, the thermo-physical model is developed to explore the thermal deformation by calculating the temperature distribution of workpiece and surface residual stress. Then a number of experiments are conducted to investigate the effect of pulse-on time, pulse current, water pressure, and wire speed on the thermal deformation of thin-walled samples. By the comparison of experimental and simulation results, it was confirmed the reliability and accuracy of thermo-physical model while experimental results revealed that the effects of process parameters of WEDM on the surface integrity as well as thermal deformation scale. Furthermore, we presented their variations of residual stress and surface characteristics including surface topography, micro-hardness, surface elemental composition, and recast layer thickness under different thermal deformation conditions. It can be concluded that the variations of residual stress and surface integrity are almost consistent with that of the thermal deformation.

Radial-Shear Rolling of Titanium Alloy VT-8 Bars with Controlled Structure for Small Diameter Ingots (≤200 mm)

Experimental studies are made of the technological possibilities of radial-shear rolling in order to prepare titanium alloy VT-8 bars with a controlled structure and mechanical properties for small diameter ingots. The effects of rolling routes and thermal deformation conditions on macro- and microstructure are studied for the bars obtained, and also on mechanical properties. The possibility is demonstrated of preparing bar with structure and properties satisfying standard specifications for bars 200 mm in diameter solely by radial-shear rolling. A production scheme proved by experiment in RSR mills may be proposed as a basis for high-tech mini-rolled product manufacture with a flexible production program.

热变形条件对激光增材制造TC18钛合金组织及变形行为的影响

热变形条件对激光增材制造TC18钛合金组织及变形行为的影响

Influence of thermal deformation conditions on the microstructure and mechanical properties of boron steel

The influence of thermal deformation conditions on the microstructure and mechanical properties of B1500HS boron steel was investigated based on a series of isothermal uniaxial tensile tests. The relationship model between work hardening rate and temperature and strain rate was established on the basis of Johnson Cook constitutive model. Moreover, the equation of the temperature rise caused by plastic deformation was modified by introducing the conversion efficiency of deformation work to heat. Next, the effects of deformation conditions (temperature and strain rate) on the volume fraction of martensite and ferrite were studied by metallographic observation. It was found that a higher strain rate brought out the martensite lath with a shorter length and thus a better ductility, and the ferrite transformation was restrained at the higher strain rate. Finally, the hardness and dislocation densities of the boron steel were detected by Vickers micro-hardness and X-ray diffraction (XRD) tests, respectively. The dislocation densities of the boron steel were quantitatively characterized by analyzing the XRD peak profiles according to the Williamson–Hall (WH) method. The results show that deformation temperature and strain rate have a similar influence on the dislocation density and micro-hardness, and hence the relationship of dislocation density and micro-hardness was deduced.

Study on Thermal Deformation Behavior of Cu-P Weathering Steel

Using thermal simulator (Gleeble 1500D), the thermal deformation behavior of Cu-P weathering steel containing Cr, Ni, Mo under the conditions of various deformation temperatures and strain rates was studied. The true stress-true strain curves at various thermal deformation conditions were got, and the thermal deformation equation was established. Then the microstructure features of the steel under various deformation temperatures and strain rates were analyzed when the true strains were same. The results show that with the same strains and strain rates, the higher the deformation temperature, the easier the recrystallization occurs, and the greater the size of the recrystal grains. And with the same strains and deformation temperatures, the lower the strain rate, the easier the recrystallization occurs, and the greater the proportion and size of the recrystal grains. Keywords:Weathering steel, Deformation temperature, Strain rate, Thermal deformation equation, Recrystallization

Effects of Temperature and Strain Rate on Thermal Deformation-Behaviour of Cu-P Weathering Steel

The effects of temperature and strain rate on the thermal deformation-behavior of Cu-P weathering steel were studied by using thermal simulator. And the true stress-true strain curves at different thermal deformation conditions were got. Then the features of the microstructure of the steel under different temperatures and strain rates were analyzed. The results show that with the same deformation dimensions and strain rates, when the deformation temperatures were higher, the recrystallization would proceed much easier, and the size of the recrystal grains could be also larger. And with the same deformation dimensions and temperatures, when the strain rates were lower, the recrystallization could also occur easier, and the proportion and size of the recrystal grains were larger.