Effect Of Hot Deformation Parameters Research Articles

Effect of hot deformation parameters on microstructure evolution mechanism and workability in a wear-resistance steel of machinery equipment

Hot compression experiments were conducted to study the flow behavior and hot workability of NM400 wear-resistance steel. A new Zener-Hollomon parameter ( Z) model is developed for coupling strain into the conventional Z model. The NM400 exhibits excellent resistance to instability owing to its low sensitivity to unsafe regions. Conversely, the peak efficiency of the power dissipation (EPD) region expands to the direction of low temperature with increasing of strain. The dynamic recrystallization (DRX) is facilitated at elevated temperatures and lower strain rates. DRX becomes the dominant softening mechanism with the increasing of temperature. Finally, 1050–1175 °C and 0.11–1.82 s−1 are recommended to be the optimal window. The optimal ln Z values for different strains are provided by the new Z model.

Hot Deformation Behavior of Free-Al 2.43 wt.% Si Electrical Steel Strip Produced by Twin-Roll Strip Casting and Its Effect on Microstructure and Texture.

Twin-roll strip casting (TRSC) technology has unique advantages in the production of non-oriented electrical steel. However, the hot deformation behavior of high-grade electrical steel produced by TRSC has hardly been reported. This work systematically studied the hot deformation behavior of free-Al 2.43 wt.% Si electrical steel strip produced by twin-roll strip casting. During the simulated hot rolling test, deformation reduction was set as 30%, and the ranges of deformation temperature and strain rate were 750~950 °C and 0.01~5 s-1, respectively. The obtained true stress-strain curves show that the peak true stress decreased with an increase in the deformation temperature and with a decrease in the strain rate. Then, the effect of hot deformation parameters on microstructure and texture was analyzed using optical microstructure observation, X-ray diffraction, and electron backscattered diffraction examination. In addition, based on the obtained true stress-strain curves of the strip cast during hot deformation, the constitutive equation for the studied silicon steel strip was established, from which it can be found that the deformation activation energy of the studied steel strip is 83.367 kJ/mol. Finally, the kinetics model of dynamic recrystallization for predicting the recrystallization volume percent was established and was verified by a hot rolling experiment conducted on a rolling mill.

Effect of Hot Deformation Parameters on Heat-Treated Microstructures and Mechanical Properties of 300M Steel.

The high strength of 300M steel originates from the heat treatment process after forging, but how hot deformation affects the heat-treated microstructure and mechanical properties is unclear. In this study, compression tests under different hot deformation parameters and post-deformation heat treatment experiments were carried out, and the martensite transformation process was investigated using in situ observation. The results show that the grain size of the specimen deformed at low temperature and high strain rate is smaller, and annealing twins will be formed. Both austenite grain boundaries and twin boundaries hinder the growth of martensite blocks, reducing the size of martensite units after heat treatment and thus resulting in higher yield strength. Besides, the mathematical models were established to describe the relationship between hot deformation parameters and grain size after deformation, martensite packet size and martensite block width, respectively, after heat treatment. The relationship between yield strength and hot deformation parameters was also analyzed. According to the results and models, the hot deformation parameters would be optimized more reasonably to improve the final mechanical properties of 300M steel forgings.

Correction to: Effect of Hot Deformation Parameters on the Dissolution of γ′ Precipitates for As-Cast Ni-Based Superalloys

Correction to: Effect of Hot Deformation Parameters on the Dissolution of γ′ Precipitates for As-Cast Ni-Based Superalloys

Effect of Hot Deformation Parameters on the Dissolution of γ′ Precipitates for As-Cast Ni-Based Superalloys

Effect of Hot Deformation Parameters on the Dissolution of γ′ Precipitates for As-Cast Ni-Based Superalloys

Damage and Cracking Prediction of AISI 410 Martensitic Stainless Steel at Elevated Temperatures

Combining Gleeble hot compression and tensile tests with finite‐element (FE) simulations, this study delivers a robust assessment of the elevated temperature damage and cracking of AISI 410 martensitic stainless steel. The effects of hot deformation parameters on the macroscopic flow and deformation behaviors as well as microscopic damage and fracture characteristics are discussed, determining the critical damage values with the aid of FE calculations. Furthermore, a novel critical damage value model is proposed using the Zener–Hollomon parameter to establish the normalized Oyane fracture criterion coupling hot deformation parameters. The results reveal that the flow stress and tensile load both increase, as the strain rate increases and the temperature decreases and vice versa. The occurrence of localized necking and internal damage cracking causes the tensile load to decline drastically. The hot deformation parameters manipulate not only the plat and dimple fractures, each caused by intergranular and transgranular fractures, but also the internal damage cracking before the final fracture. The established criterion predicts outcomes in good agreement with experimental results. This work provides essential information and a model for the cracking prediction of AISI 410 steel at elevated temperatures, helping to derive a rational hot forming design to prevent cracking.

Effect of Hot Deformation Parameters on the Evolution of Microstructure and Texture of β Phase in TC18 Titanium Alloy

Effect of Hot Deformation Parameters on the Evolution of Microstructure and Texture of β Phase in TC18 Titanium Alloy

The Effects of Hot Deformation Parameters on the Size of Dynamically Recrystallised Austenite Grains of HSLA Steel

The Effects of Hot Deformation Parameters on the Size of Dynamically Recrystallised Austenite Grains of HSLA Steel

A modified kinetics model and softening behavior for static recrystallization of 12Cr ultra-super-critical rotor steel

In this paper, the static recrystallization (SRX) of 12Cr ultra-super-critical (USC) rotor steel was investigated by a series of hot compression tests on a Gleeble1500D thermal simulator. Double-hit hot deformation tests were conducted at temperatures of 1223K–1323 K and strain rates of 0.001 s−1–0.1 s−1 with inter-pass times of 10s–180 s. A conventional kinetics model of SRX was established based on flow curves obtained by regression analysis under different deformation conditions. However, a significant deviation resulted between predicted and experimental values for the SRX fraction, and therefore a modified kinetics equation was proposed by analysing the SRX characteristics and possession of the capability to accurately predict SRX softening behaviour was confirmed. Effects of hot deformation parameters on SRX softening behaviour and SRX grain size were discussed. Furthermore, microstructure deforming was observed at different inter-pass times with an optical microscope (OM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). Analysis showed that recovery was the main softening mechanism and the fundamental nucleation mechanism for SRX was bulging at the grain boundary.

The Coarse Microstructure of Medium‐Carbon Microalloyed Steel Crankshafts: Formation Mechanism and Finish Forging Control

The effect of hot deformation parameters on microstructure coarsening of the medium‐carbon microalloyed steel is studied by means of hot compression experiments. The effective strain of finish forging in a crankshaft is simulated by means of finite element numerical simulations. The microstructure and properties of the crankshaft are also analyzed. The hot compression experiments result shows that with the deformation increasing from 2% to 18%, the austenite grain size first increases and then decreases, and it reaches the maximum when the deformation is 6%. The microstructure coarsening is mainly caused by critical deformation. With the increase in deformation temperature and the decrease in strain rate, the austenite grains can also be coarsened. When the effective strain of finish forging exceeds 0.2 in the main journal section of the crankshaft, the microstructure is refined significantly, and mechanical properties are improved. To avoid coarse microstructure, the reduction of finish forging should reach 15–20 mm.

Effect of hot deformation conditions on magnetic properties of rare earth free magnetic Mn-Al-C alloy

Abstract The effect of hot deformation parameters on the magnetic properties of Mn51Al47C2 (at%) alloy was investigated. The hysteresis loops of cylindrical samples hot compressed to 50% of initial height at temperatures of 600 °C, 650 °C and 700 °C with strain rates 0.001 S−1 and 0.1 S−1 were obtained by means of vibrating sample magnetometer. In order to find the effect of strain on the magnetic properties, hot compressed samples to 30%, 45%, 60% and 75% in a specific temperature and strain rate were investigated. It was found that by increasing strain and strain rate, the coercivity increases and the highest coercivity gained at the temperature of 650 °C. Moreover, by further straining, the developed texture changed and higher remanent magnetization was obtained in axial direction for lower strains and in radial direction for higher strains.

Evolution of microstructure and microtexture during hot deformation in an advanced P/M nickel base superalloy

In the present study, the effect of hot deformation parameters on the microstructural evolution is investigated for an experimental powder metallurgy nickel superalloy. The hot isostatically pressed (HIPed) alloy is isothermally hot compressed at constant true strain rate over wide temperatures (1000 °C, 1050 °C, 1100 °C, 1150 °C) and strain rates (0.001 s−1, 0.01 s−1, 0.1 s−1, 1 s−1) regimes. Electron Back-Scattered Diffraction (EBSD) characterization of the hot deformed samples is carried out to evaluate the microstructural evolution, grain boundary characteristics, and microtextural behaviour. The strong dependence of dynamic recrystallization characteristics on the hot deformation conditions is divulged through EBSD derived colour inverse pole figure maps endorsed by grain/twin boundary characteristics and misorientation gradient. Dynamic recrystallization (DRX) is maximized at higher deformation temperatures, whereas limited DRX is observed at lower deformation temperatures, especially at higher strain rates. The dominance of discontinuous dynamic recrystallization (DDRX) is manifested through bulged/serrated grain boundaries resulting in the formation of necklace microstructure corroborated by grain boundary cumulative misorientation gradient. Although random microtexture is revealed in both deformed and recrystallized microstructures, the tendency towards the formation of 〈110〉 fiber compression texture is apparently evident.

Investigation on the hot deformation characteristics of Ni-Cr-Fe-Ti alloy

The hot deformation characteristics of Ni-Cr-Fe-Ti alloy were researched by the isothermal compression tests in temperatures range of 880–1030 °C and strain rates range of 0.01–10s−1. The hot deformation conditions have vital effect on hot deformation behaviors of Ni-Cr-Fe-Ti alloy. Based on experimental study and dynamic materials model (DMM), the processing map of the studied alloy was established. The deformation mechanisms of the studied alloy at various deformation parameters were verified according to microstructure evolution during hot deformation. When the strain is 0.3, a stable domain can be found in the strain rates range of 0.01–0.15s−1 and the temperatures range of 930–1030 °C. A mathematic model was established to research the dynamic recrystallization behavior of Ni-Cr-Fe-Ti alloy. The effects of hot deformation parameters on DRX behavior were studied according to the established dynamic recrystallization kinetics model. The corresponding recrystallization volume fraction, strain and peaks stress were investigated to validate the kinetic models for DRX. There is perfect match between the calculated results and the experimental data. Thus, in view of the analysis above, it can be concluded that the kinetic models can provide accurate prediction of the DRX behavior of Ni-Cr-Fe-Ti alloy.

Deformation Mechanism and Hot Workability of Extruded Magnesium Alloy AZ31

Using the flow stress curves obtained by Gleeble thermo-mechanical testing, the processing map of extruded magnesium alloy AZ31 was established to analyze the hot workability. Stress exponent and activation energy were calculated to characterize the deformation mechanism. Then, the effects of hot deformation parameters on deformation mechanism, microstructure evolution and hot workability of AZ31 alloy were discussed. With increasing deformation temperature, the operation of non-basal slip systems and full development of dynamic recrystallization (DRX) contribute to effective improvement in hot workability of AZ31 alloy. The influences of strain rate and strain are complex. When temperature exceeds 350 °C, the deformation mechanism is slightly dependent of the strain rate or strain. The dominant mechanism is dislocation cross-slip, which favors DRX nucleation and grain growth and thus leads to good plasticity. At low temperature (below 350 °C), the deformation mechanism is sensitive to strain and strain rate. Both the dominant deformation mechanism and inadequate development of DRX deteriorate the ductility of AZ31 alloy. The flow instability mainly occurs in the vicinity of 250 °C and 1 s−1.

Effect of Hot Deformation Parameters on Flow Behavior and Microstructure of Ti-6Al-4V-0.2O Alloy

Isothermal compression tests were conducted to investigate the effect of hot deformation parameters on flow behavior and microstructure of Ti-6Al-4V-0.2O alloy. The experimental results show that the strain rate and height reduction have little effect on the volume fraction of primary α at a deformation temperature of 860 ̊C. At a deformation temperature of 940 ̊C, the volume fraction of primary α at a high strain rate (10s-1) is about 10% less than that at low strain rates (0.01s-1~1s-1). It may be one of the reasons for the significantly discontinuous yielding phenomenon. Another reason is that the dislocation density decreased suddenly due to the dynamic recovery. With the increasing strain rate and the decreasing deformation temperature, the volume fraction of irregular secondary α increases and lamellar secondary α decreases. And with height reduction increasing, the irregular secondary α increases firstly and then tends to be steady because of dynamic recovery and recrystallization.

Experimental study and numerical simulation of dynamic recrystallization behavior of TiAl-based alloy

An Avrami-type equation was used to investigate the dynamic recrystallization (DRX) behavior of a TiAl-based alloy during hot compression tests. The effects of hot deformation parameters on DRX behavior of samples were determined based on the established dynamic recrystallization kinetics model. The nucleation mechanism of dynamic recrystallization and the microstructure evolution of the deformed samples were studied using electron backscatter diffraction (EBSD). Discontinuous dynamic recrystallization (DDRX) is subsequently identified by obvious nucleation and grain growth. It was indicated that the DRX volume fraction and grain size decrease with the decrease of deformation temperature or the increase of strain rate. The TEM images show that the deformation twinning of γ-phase is formed during hot deformation which can provide more nucleation sites for DDRX and promote the occurrence of DRX significantly. Furthermore, the determined kinetics model was programmed into finite element codes to investigate the DRX behavior of the TiAl-based alloy during hot deformation. The equivalent strain distribution and DRX volume fraction evolution calculated by simulated approach can well demonstrate the experiment results.

New constitutive model for high-temperature deformation behavior of inconel 718 superalloy

Abstract Hot deformation behavior of an aged inconel 718 superalloy is investigated by isothermal compression tests over wide ranges of strain rate and deformation temperature. In this study, the effects of hot deformation parameters (deformation temperature and strain rate) on flow stress are analyzed. It is found that the flow stress of the studied superalloy is significantly affected by deformation temperature and strain rate. The flow stress decreases with the decrease of strain rate or the increase of deformation temperature. Based on the experimental results, a new constitutive model is developed to describe the hot deformation behavior. For the work hardening-dynamic recovery stage, an isotropic internal variable is used to represent the plastic deformation resistance, and a viscoplastic constitutive model is developed to describe the work hardening and dynamic recovery behavior. For the dynamic softening stage, the phenomenological constitutive models, which consider the coupled effects of deformation temperature, strain rate and strain on hot deformation behavior, are developed. The predicted flow stresses are in a good agreement with the experimental ones, indicating that the developed models can accurately characterize the hot deformation behavior of the studied Ni-based superalloy.

Microstructure Evolution and Processing Map of Superalloy GH720Li during Isothermal Compression

sothermal compression tests for superalloy GH720Li were conducted to investigate the effect of hot deformation parameters on microstructure evolution. The changing characteristics of flow stress during hot deformation were also studied. The flow instability area was calculated based on Prasad Plastic Instability Criterion and the hot processing map was obtained. The results showed that dynamic recrystallization was the main softening mechanism of GH720Li alloy during hot deformation. The peak and steady stress decreased significantly with an increase of test temperature and a decrease of the strain rate. Finally, three unstable areas have been found from the processing map.

Directly spheroidizing during hot deformation in GCr15 steels

The spheroidizing heat treatment is normally required prior to the cold forming in GCr15 steel in order to improve its machinability. In the conventional spheroidizing process, very long annealing time, generally more than 10 h, is needed to assure proper spheroidizing. It results in low productivity, high cost, and especially high energy consumption. Therefore, the possibility of directly spheroidizing during hot deformation in GCr15 steel is preliminarily explored. The effect of hot deformation parameters on the final microstructure and hardness is investigated systematically in order to develop a directly spheroidizing technology. Experimental results illustrate that low deformation temperature and slow cooling rate is the favorite in directly softening and/or spheroidizing during hot deformation, which allows the properties of asrolled GCr15 to be applicable for post-machining without requirement of prior annealing.

Characterization of Dynamic Globularization Behavior during Hot Working of Ti-6Al-4V Alloy

The dynamic globularization behavior during hot working of Ti-6Al-4V alloy was investigated by high temperature torsion tests. The torsion tests were carried out to investigate microstructure evolution occurring during dynamic globularization in Ti-6Al-4V alloy. The torsion tests were performed under a wide range of temperatures and strain rates with true strain up to 2. The flow curves revealed that the amount of flow softening for the fine alpha-lamellae structure was higher than that for the coarse alpha-lamellae structure under the temperature of 900oC. The effects of hot deformation parameters and initial microstructures on the dynamic globularization were analyzed.