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Philippe Maugis - One of the best experts on this subject based on the ideXlab platform.
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Effects of cementite size and chemistry on the kinetics of Austenite Formation during heating of a high-formability steel
Computational Materials Science, 2020Co-Authors: Arthur Marceaux Dit Clément, Josée Drillet, Véronique Hébert, Khalid Hoummada, Philippe MaugisAbstract:To understand how Austenite forms in high-formability steels during the heating step of intercritical annealing, calculations based on atomic diffusion and local equilibrium assumption were used to simulate the transFormation kinetics. It appears that chromium must be considered in the calculations to allow for a good fit with the Austenite Formation kinetics obtained by dilatometry. Indeed, Cr has a strong delaying effect on this kinetics, even though it is a minor element in the steel chemistry. The parametric study reveals that cementite initial radius is the most influential parameter on transFormation kinetics. Mn and Cr enrichments also prove to be important parameters to consider.
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Atom probe tomography study of Austenite Formation during heating of a high-formability steel
Journal of Materials Science, 2020Co-Authors: Arthur Marceaux Dit Clément, Josée Drillet, Véronique Hébert, Khalid Hoummada, Philippe MaugisAbstract:Controlling Austenite Formation kinetics and its mean chemistry during annealing are two ways to act on the in-use and mechanical properties of high-carbon high-formability steels. Indeed, these characteristics influence Austenite stability at room temperature after cooling and are therefore at the origin of potential TRIP effects under mechanical loading. Atom probe tomography analyses and Thermo-Calc/DICTRA calculations were used to understand how Austenite forms during 1 °C/s heating of a 0.2 wt% C high-formability steel. The proposed analysis is conducted in the quaternary FeCMnCr system. It is shown that the transFormation kinetics can be rationalized from the evolution of interfacial compositions, which are imposed by the operative tie-lines positions in the relevant phase diagrams. This analysis method helps to gain insight on the evolution of phases chemistries upon heating. Good agreement is found between experimental and calculated kinetics, but also between APT-measured and calculated phases chemistries. Mn and Cr partitioning between ferrite and Austenite is confirmed during heating. APT also allows for the characterization of segregation on $$\alpha /\gamma$$ α / γ interphase boundary, showing that Mn segregation already occurred at 750 °C.
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Ferrite recrystallization and Austenite Formation during annealing of cold-rolled advanced high-strength steels: In situ synchrotron X-ray diffraction and modeling
Materials Characterization, 2019Co-Authors: Marion Bellavoine, Myriam Dumont, Moukrane Dehmas, Andreas Stark, Norbert Schell, Josée Drillet, Véronique Hébert, Philippe MaugisAbstract:Ferrite recrystallization and Austenite Formation occurring during annealing of cold-rolled advanced high-strength steels are key mechanisms as they largely determine the final microstructure and mechanical properties. However, the influence of processing parameters on these mechanisms and their interactions is still not fully understood. This is particularly the case for Dual-Phase steels having an initial cold-rolled microstructure con-sisting of ferrite and martensite before annealing, which were scarcely investigated compared to ferrite-pearlite initial microstructures. In situ synchrotron X-ray diffraction experiments together with post-mortem metallo-graphic analysis allowed clarifying both ferrite recrystallization and Austenite Formation during annealing of a ferrite-martensite initial microstructure depending on the process parameters of the annealing cycle. Results showed a major influence of recrystallization state on Austenite Formation, leading to an unexpected effect of heating rate on Austenite Formation kinetics. A modeling approach was undertaken to rationalize the influence of heating rate on Austenite Formation by taking into account the bi-phased ferrite-martensite initial microstructure and the effect of ferrite recrystallization state.
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Influence of Heating Rate on Ferrite Recrystallization and Austenite Formation in Cold-Rolled Microalloyed Dual-Phase Steels
Metallurgical and Materials Transactions A, 2017Co-Authors: C. Philippot, Marion Bellavoine, Myriam Dumont, Josée Drillet, Véronique Hébert, Khalid Hoummada, Philippe MaugisAbstract:Compared with other dual-phase (DP) steels, initial microstructures of cold-rolled martensite-ferrite have scarcely been investigated, even though they represent a promising industrial alternative to conventional ferrite-pearlite cold-rolled microstructures. In this study, the influence of the heating rate (over the range of 1 to 10 K/s) on the development of microstructures in a microalloyed DP steel is investigated; this includes the tempering of martensite, precipitation of microalloying elements, recrystallization, and Austenite Formation. This study points out the influence of the degree of ferrite recrystallization prior to the Austenite Formation, as well as the importance of the cementite distribution. A low heating rate giving a high degree of recrystallization, leads to the Formation of coarse Austenite grains that are homogenously distributed in the ferrite matrix. However, a high heating rate leading to a low recrystallization degree, results in a banded-like structure with small Austenite grains surrounded by large ferrite grains. A combined approach, involving relevant multiscale microstructural characterization and modeling to rationalize the effect of the coupled processes, highlights the role of the cold-worked initial microstructure, here a martensite-ferrite mixture: recrystallization and Austenite Formation commence in the former martensite islands before extending in the rest of the material.
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Austenite Formation in a ferrite/martensite cold-rolled microstructure during annealing of advanced high-strength steels
Metallurgical Research & Technology, 2014Co-Authors: C. Philippot, Véronique Hébert, Josée Drillet, Philippe Maugis, Myriam DumontAbstract:From a ferrite/martensite cold-rolled microstructure, the interaction between ferrite recrystallization and Austenite Formation is investigated. It is observed that a slow heating rate promotes the ferrite recrystallization and a homogeneous microstructure, whereas a fast heating rate delays the recrystallization and leads to heterogeneously dis- tributed Austenite islands.
Lijian Rong - One of the best experts on this subject based on the ideXlab platform.
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the influence of tempering temperature on the reversed Austenite Formation and tensile properties in fe 13 cr 4 ni mo low carbon martensite stainless steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: Yuanyuan Song, Lijian RongAbstract:The influence of tempering temperature on the reversed Austenite Formation and tensile properties are investigated in Fe-13%Cr-4%Ni-Mo low carbon martensite stainless steel in the temperature range of 550-950 degrees C. It is found that at the temperatures below 680 degrees C, the reversed Austenite Formation occurs by diffusion. Amount of the reversed Austenite is determined I:IN the tempering temperature and the holding time. The segregation of Ni is the main reason for the stability of the reversed Austenite. When the temperatures are above 680 degrees C, the reversed Austenite Formation proceeds by diffusionless. The reversed Austenite will transform back to martensite after cooled to room temperature. The tensile properties are most strongly influenced by the amount of the reversed Austenite obtained at room temperature. The excellent combination of good strength and ductility is at 610 degrees C. (C) 2011 Elsevier B.V. All rights reserved.
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The influence of tempering temperature on the reversed Austenite Formation and tensile properties in Fe–13%Cr–4%Ni–Mo low carbon martensite stainless steels
Materials Science and Engineering: A, 2011Co-Authors: Yuanyuan Song, Lijian RongAbstract:The influence of tempering temperature on the reversed Austenite Formation and tensile properties are investigated in Fe-13%Cr-4%Ni-Mo low carbon martensite stainless steel in the temperature range of 550-950 degrees C. It is found that at the temperatures below 680 degrees C, the reversed Austenite Formation occurs by diffusion. Amount of the reversed Austenite is determined I:IN the tempering temperature and the holding time. The segregation of Ni is the main reason for the stability of the reversed Austenite. When the temperatures are above 680 degrees C, the reversed Austenite Formation proceeds by diffusionless. The reversed Austenite will transform back to martensite after cooled to room temperature. The tensile properties are most strongly influenced by the amount of the reversed Austenite obtained at room temperature. The excellent combination of good strength and ductility is at 610 degrees C. (C) 2011 Elsevier B.V. All rights reserved.
Xiaoying Hou - One of the best experts on this subject based on the ideXlab platform.
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Austenite Formation and mechanical behavior of a novel TRIP- assisted steel with ferrite/martensite initial structure
Materials Science and Engineering: A, 2021Co-Authors: Xu Wang, Rendong Liu, Fei Peng, Hongliang Liu, R.d.k. Misra, Xiaoying HouAbstract:Abstract A newly developed TRIP-assisted steel with ferrite/martensite initial structure was designed to investigate the microstructural evolution during overall annealing cycle. The results were compared with the traditional cold-rolled TRIP steel. The characteristic of Austenite Formation from different initial microstructure was clarified based on combining the experiments and modeling. Results indicated that the new Austenite obtained during intercritical annealing was fine-grained and uniformly-distributed. It comprised of acicular structure formed in pre-existing martensite (Mpre) matrix and blocky structure occurred at phase interfaces or prior Austenite grain boundaries. The kinetics of Austenite Formation in specimens involving Mpre are similar in the early heating stage, and then decreased with decreasing Mpre content at temperatures greater than 770 °C. Both experimental and DICTRA results indicated that the Austenite fractions of specimens with 90% and 100% Mpre fraction attained almost the maximum at the end of heating, and decreased with isothermal holding time during the intercritical annealing. Moreover, the retained Austenite at interfaces of ferrite and pre-existing phase followed the Kurdjumov-Sachs (K–S) relationship with adjacent tempered martensite, while only part of the retained Austenite had identical relationship with neighboring ferrite. In addition, the amount of retained Austenite increased with Mpre content, although their stability against martensite transFormation during tensile testing was similar and greater than that of cold-rolled specimen. As a consequence, the yield strength was increased from 590 MPa to 753 MPa and the tensile strength increased slightly from 995 MPa to 1046 MPa with Mpre fraction increasing from 50% to 100%, and the total elongation was ~30%, similar to the third generation advanced high strength steels.
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Austenite Formation and mechanical behavior of a novel trip assisted steel with ferrite martensite initial structure
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2020Co-Authors: Xu Wang, Rendong Liu, Fei Peng, Hongliang Liu, R.d.k. Misra, Xiaoying HouAbstract:Abstract A newly developed TRIP-assisted steel with ferrite/martensite initial structure was designed to investigate the microstructural evolution during overall annealing cycle. The results were compared with the traditional cold-rolled TRIP steel. The characteristic of Austenite Formation from different initial microstructure was clarified based on combining the experiments and modeling. Results indicated that the new Austenite obtained during intercritical annealing was fine-grained and uniformly-distributed. It comprised of acicular structure formed in pre-existing martensite (Mpre) matrix and blocky structure occurred at phase interfaces or prior Austenite grain boundaries. The kinetics of Austenite Formation in specimens involving Mpre are similar in the early heating stage, and then decreased with decreasing Mpre content at temperatures greater than 770 °C. Both experimental and DICTRA results indicated that the Austenite fractions of specimens with 90% and 100% Mpre fraction attained almost the maximum at the end of heating, and decreased with isothermal holding time during the intercritical annealing. Moreover, the retained Austenite at interfaces of ferrite and pre-existing phase followed the Kurdjumov-Sachs (K–S) relationship with adjacent tempered martensite, while only part of the retained Austenite had identical relationship with neighboring ferrite. In addition, the amount of retained Austenite increased with Mpre content, although their stability against martensite transFormation during tensile testing was similar and greater than that of cold-rolled specimen. As a consequence, the yield strength was increased from 590 MPa to 753 MPa and the tensile strength increased slightly from 995 MPa to 1046 MPa with Mpre fraction increasing from 50% to 100%, and the total elongation was ~30%, similar to the third generation advanced high strength steels.
Matthias Militzer - One of the best experts on this subject based on the ideXlab platform.
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HSLA Steels 2015, Microalloying 2015 & Offshore Engineering Steels 2015: Conference Proceedings - Development of Processing Maps for Intercritical Annealing Using the Phase Field Approach
HSLA Steels 2015 Microalloying 2015 & Offshore Engineering Steels 2015, 2016Co-Authors: Benqiang Zhu, Matthias MilitzerAbstract:A phase field model has been developed to simulate microstructure evolution during intercritical annealing. The model describes ferrite recrystallization, intercritical Austenite Formation and decomposition. In particular, the overlap of ferrite recrystallization and Austenite Formation for sufficiently fast line speeds has been taken into account in the model. The model has been benchmarked and validated with experimental data for a DP600 steel. Further, simulations have been performed with a systematic variation of processing parameters, i.e. line speed and intercritical holding temperature. Processing maps have been constructed based on these simulations providing martensite fraction and ferrite grain size as a function of line speed and intercritical temperature for the investigated DP600 steel. This study demonstrates the phase field approach as a promising tool to develop through-process models for advanced high strength steels.
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development of processing maps for intercritical annealing using the phase field approach
hsla, 2016Co-Authors: Benqiang Zhu, Matthias MilitzerAbstract:A phase field model has been developed to simulate microstructure evolution during intercritical annealing. The model describes ferrite recrystallization, intercritical Austenite Formation and decomposition. In particular, the overlap of ferrite recrystallization and Austenite Formation for sufficiently fast line speeds has been taken into account in the model. The model has been benchmarked and validated with experimental data for a DP600 steel. Further, simulations have been performed with a systematic variation of processing parameters, i.e. line speed and intercritical holding temperature. Processing maps have been constructed based on these simulations providing martensite fraction and ferrite grain size as a function of line speed and intercritical temperature for the investigated DP600 steel. This study demonstrates the phase field approach as a promising tool to develop through-process models for advanced high strength steels.
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A Microstructure Evolution Model for Intercritical Annealing of a Low-carbon Dual-phase Steel
ISIJ International, 2014Co-Authors: Mykola Kulakov, Warren J. Poole, Matthias MilitzerAbstract:A model was developed to describe the microstructure evolution during intercritical annealing of a lowcarbon steel suitable for industrial production of DP600 grade dual-phase steel on a hot-dip galvanizing line. The microstructure evolution model consists of individual submodels for ferrite recrystallization, Austenite Formation and decomposition constructed using the Johnson-Mehl-Avrami-Kolmogorov approach and the additivity principle. The submodels for recrystallization and Austenite Formation are adopted from a previous study. The present paper provides a detailed analysis of the model development for the decomposition of intercritical Austenite. The overall microstructure evolution model is validated using simulated industrial thermal paths for intercritical annealing. Model validation is expedited by in-situ measurements of the recrystallization completion temperature using laser ultrasonics and the intercritical Austenite Formation and decomposition using dilatometry.
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The Effect of the Initial Microstructure on Recrystallization and Austenite Formation in a DP600 Steel
Metallurgical and Materials Transactions A, 2013Co-Authors: M. Kulakov, Warren J. Poole, Matthias MilitzerAbstract:The effects of initial microstructure and thermal cycle on recrystallization, Austenite Formation, and their interaction were studied for intercritical annealing of a low-carbon steel that is suitable for industrial production of DP600 grade. The initial microstructures included 50 pct cold-rolled ferrite–pearlite, ferrite–bainite–pearlite and martensite. The latter two materials recrystallized at similar rates, while slower recrystallization was observed for ferrite–pearlite. If heating to an intercritical temperature was sufficiently slow, then recrystallization was completed before Austenite Formation, otherwise Austenite formed in a partially recrystallized microstructure. The same trends as for recrystallization were found for the effect of initial microstructure on kinetics of Austenite Formation. The recrystallization–Austenite Formation interaction accelerated austenization in all the three starting microstructures by providing additional nucleation sites and enhancing growth rates, and drastically altered morphology and distribution of Austenite. In particular, for ferrite–bainite–pearlite and martensite, the recrystallization–Austenite Formation interaction resulted in substantial microstructural refinement. Recrystallization and Austenite Formation from a fully recrystallized state were successfully modeled using the Johnson–Mehl–Avrami–Kolmogorov approach.
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Austenite Formation in plain low carbon steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2011Co-Authors: Hamid Azizializamini, Matthias Militzer, W J PooleAbstract:In this study, Austenite Formation from hot-rolled (HR) and cold-rolled (CR) ferrite-pearlite structures in a plain low-carbon steel was investigated using dilation data and microstructural analysis. Different stages of microstructural evolution during heating of the HR and CR samples were investigated. These stages include Austenite Formation from pearlite colonies, ferrite-to-Austenite transFormation, and final carbide dissolution. In the CR samples, recrystallization of deformed ferrite and spheroidization of pearlite lamellae before transFormation were evident at low heating rates. An increase in heating rate resulted in a delay in spheroidization of cementite lamellae and in recrystallization of ferrite grains in the CR steel. Furthermore, a morphological transition is observed during austenitization in both HR and CR samples with increasing heating rate. In HR samples, a change from blocky Austenite grains to a fine network of these grains along ferrite grain boundaries occurs. In the CR samples, Austenite Formation changes from a random spatial distribution to a banded morphology.
Roumen Petrov - One of the best experts on this subject based on the ideXlab platform.
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Study of carbide dissolution and Austenite Formation during ultra–fast heating in medium carbon chromium molybdenum steel
Metals, 2018Co-Authors: Spyros Papaefthymiou, Marianthi Bouzouni, Roumen PetrovAbstract:In this study, UltraFast Heat Treatment (UFHT) was applied to a soft annealed medium carbon chromium molybdenum steel. The specimens were rapidly heated and subsequently quenched in a dilatometer. The resulting microstructure consists of chromium-enriched cementite and chromium carbides (in sizes between 5–500 nm) within fine (nano-sized) martensitic and bainitic laths. The dissolution of carbides in Austenite (γ) during ferrite to Austenite phase transFormation in conditions of rapid heating were simulated with DICTRA. The results indicate that fine (5 nm) and coarse (200 nm) carbides dissolve only partially, even at peak (austenitization) temperature. Alloying elements, especially chromium (Cr), segregate at Austenite/carbide interfaces, retarding the dissolution of carbides and subsequently Austenite Formation. The sluggish movement of the Austenite/carbide interface towards Austenite during carbide dissolution was attributed to the partitioning of Cr nearby the interface. Moreover, the undissolved carbides prevent Austenite grain growth at peak temperature, resulting in a fine-grained microstructure. Finally, the simulation results suggest that ultrafast heating creates conditions that lead to chemical heterogeneity in Austenite and may lead to an extremely refined microstructure consisting of martensite and bainite laths and partially dissolved carbides during quenching.
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study of carbide dissolution and Austenite Formation during ultra fast heating in medium carbon chromium molybdenum steel
Metals, 2018Co-Authors: Spyros Papaefthymiou, Marianthi Bouzouni, Roumen PetrovAbstract:In this study, UltraFast Heat Treatment (UFHT) was applied to a soft annealed medium carbon chromium molybdenum steel. The specimens were rapidly heated and subsequently quenched in a dilatometer. The resulting microstructure consists of chromium-enriched cementite and chromium carbides (in sizes between 5–500 nm) within fine (nano-sized) martensitic and bainitic laths. The dissolution of carbides in Austenite (γ) during ferrite to Austenite phase transFormation in conditions of rapid heating were simulated with DICTRA. The results indicate that fine (5 nm) and coarse (200 nm) carbides dissolve only partially, even at peak (austenitization) temperature. Alloying elements, especially chromium (Cr), segregate at Austenite/carbide interfaces, retarding the dissolution of carbides and subsequently Austenite Formation. The sluggish movement of the Austenite/carbide interface towards Austenite during carbide dissolution was attributed to the partitioning of Cr nearby the interface. Moreover, the undissolved carbides prevent Austenite grain growth at peak temperature, resulting in a fine-grained microstructure. Finally, the simulation results suggest that ultrafast heating creates conditions that lead to chemical heterogeneity in Austenite and may lead to an extremely refined microstructure consisting of martensite and bainite laths and partially dissolved carbides during quenching.
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The Effect of Heating Rate on the Microstructure of a Soft‐Annealed Medium Carbon Steel
steel research international, 2017Co-Authors: Spyros Papaefthymiou, C. Goulas, Felipe Manuel Castro Cerda, Nico Geerlofs, Roumen PetrovAbstract:A comparative study on the microstructural changes after conventional (20 °C s−1) and ultrafast (300 °C s−1) heating is performed on a medium carbon steel in the soft annealed condition. Continuous-heating dilatometry experiments are carried out. The phase transFormations and the volume phase fraction of Austenite are determined among other microstructural changes. The microstructure is first observed using Optical Microscopy (OM), further characterized by Scanning (SEM), and detailed analyzed by Transmission Electron Microscopy (TEM). The effect of heating rate on the kinetics of cementite dissolution and Austenite Formation is rationalized. The experimental results are compared with Dictra calculations, and the possible effects on the kinetics of diffusion-controlled Austenite Formation are rationalized as well. Metallographic observations indirectly suggest the enhanced nucleation of Austenite above Am.
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Austenite Formation in 0 2 c and 0 45 c steels under conventional and ultrafast heating
Materials & Design, 2017Co-Authors: Ilchat Sabirov, C. Goulas, Jilt Sietsma, Alberto Monsalve, Roumen Petrov, F Castro M CerdaAbstract:Abstract The Austenite Formation in 0.2% C and 0.45% C steels with the initial microstructure of ferrite and pearlite has been studied. The effect of conventional (10 °C/s), fast (50 °C/s–100 °C/s) and ultrafast heating rates (> 100 °C/s) on the Austenite nucleation and growth mechanisms is rationalized. Scanning Electron Microscopy (SEM), and Electron BackScatter Diffraction (EBSD) analyses provide novel experimental evidence of the Austenite nucleation and growth mechanisms operating at ultrafast heating rates. Two mechanisms of Austenite Formation are identified: diffusional and massive. It is demonstrated that at conventional heating rates the Austenite Formation kinetics are determined by carbon diffusion, whereas at ultrafast heating rates Formation of Austenite starts by carbon diffusion control, which is later overtaken by a massive mechanism. Comprehensive thermodynamic and kinetic descriptions of Austenite nucleation and growth are developed based on experimental results.
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Austenite Formation in 0.2% C and 0.45% C steels under conventional and ultrafast heating
Materials & Design, 2017Co-Authors: F. M. Castro Cerda, Ilchat Sabirov, C. Goulas, Jilt Sietsma, Alberto Monsalve, Roumen PetrovAbstract:Abstract The Austenite Formation in 0.2% C and 0.45% C steels with the initial microstructure of ferrite and pearlite has been studied. The effect of conventional (10 °C/s), fast (50 °C/s–100 °C/s) and ultrafast heating rates (> 100 °C/s) on the Austenite nucleation and growth mechanisms is rationalized. Scanning Electron Microscopy (SEM), and Electron BackScatter Diffraction (EBSD) analyses provide novel experimental evidence of the Austenite nucleation and growth mechanisms operating at ultrafast heating rates. Two mechanisms of Austenite Formation are identified: diffusional and massive. It is demonstrated that at conventional heating rates the Austenite Formation kinetics are determined by carbon diffusion, whereas at ultrafast heating rates Formation of Austenite starts by carbon diffusion control, which is later overtaken by a massive mechanism. Comprehensive thermodynamic and kinetic descriptions of Austenite nucleation and growth are developed based on experimental results.
