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Chengsi Zheng - One of the best experts on this subject based on the ideXlab platform.
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mechanical behavior of ultrafine grained Eutectoid Steel containing nano cementite particles
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Chengsi ZhengAbstract:Abstract A Eutectoid Steel with an ultrafine-grained ferrite ( α ) + submicron/Nano-cementite particle ( θ ) structure was formed by combining warm deformation of martensite to a strain of 0.36 at 0.1 s −1 at 500 °C with subsequent annealing at 500 °C for 6 h. The characteristics of the microstructure were investigated by means of a scanning electronic microscope and transmission electron microscope, and the corresponding mechanical behavior was analyzed in comparison with that of the Eutectoid Steel with a typical ultrafine-grained α + θ structure. The results show that both ferrite matrix and cementite particles of the ultrafine-grained α + submicron/Nano- θ Steel are finer than that of the ultrafine-grained α + θ Steel, i.e., the average size of approximately 0.54 µm vs. 1.0 µm and 0.20 µm vs. 0.56 µm, accompanying with a continuous yielding and a discontinuous yielding, respectively. The yield strength of the ultrafine-grained α + submicron/Nano- θ Steel is 264 MPa higher that of the ultrafine-grained α + θ Steel, i.e., 884 MPa vs. 620 MPa, resulting from the enhancement caused by refined ferrite grains and cementite particles. The intragranular cementite particles within the ultrafine-grained α + submicron/Nano- θ Steel are in Nano-scale, i.e., an average size of approximately 60 nm, resulting in plenty of geometrically necessary dislocations (GNDs) to bring its work-hardening rate higher than that of the ultrafine-grained α + θ Steel during uniform deformation. As a result, the stress increments caused by work-hardening are 89 MPa and 155 MPa for the ultrafine-grained α + θ Steel and the ultrafine-grained α + submicron/Nano- θ Steel, respectively, and their interval length of uniform strain range are nearly equal, i.e., a true strain of approximately 0.08. The work-hardening rate of the ultrafine-grained α + θ Steel decline continuously with the increase of tensile strain during uniform deformation. However, the ultrafine-grained α + submicron/Nano- θ Steel shows that the work-hardening rate decrease rapidly at the initial stage of work-hardening and then raise within a small strain range, then following by a slowly continuous decline to necking, and, namely, there has a peak of work-hardening rate. Furthermore, the work-hardening rate curve were divided into three stages, and the work-hardening behavior of Stage I, II and III were discussed in view of the evolution of dislocation substructures and the analytical model based on the Kocks-Mecking model.
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effect of microstructure on mechanical behavior for Eutectoid Steel with ultrafine or fine grained ferrite cementite structure
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Chengsi ZhengAbstract:A Eutectoid Steel with various ultrafine- or fine-grained ferrite matrix (α)+cementite particle (θ) structures was fabricated to explore the effects of the microstructural features on the mechanical behavior of hard particle-strengthened two-phase alloys. The effect of microstructure on the parameters of an analytical model and the mechanical behavior for the Eutectoid Steel with ultrafine- or fine-grained α+θ structure were analyzed basing on statistical data and physical metallurgy. The results showed that the rate of dislocation-storage caused by ferrite grain boundaries and cementite particles is approximately a microstructural constant and is proportional to the dislocation mean free path. The larger ferrite grains and the larger volume fraction of intragranular cementite particles are beneficial to obtaining a lower rate of dynamic recovery when ultrafine- or fine-grained α+θ structures with an equal dislocation mean free path, and the uniform elongation increases with the decrease in the rate of dynamic recovery. Moreover, the ultimate strength is closely related to the effective dislocation mean free path including both roles of the storage and the recovery of dislocations. It is feasible to design a microstructure consisting of ultrafine- or fine-grained ferrite matrix and tiny cementite particles mainly within grain interior to possess an enhanced strength-plasticity synergy for the Eutectoid Steel.
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Effect of microstructure on mechanical behavior for Eutectoid Steel with ultrafine- or fine-grained ferrite+cementite structure
Materials Science and Engineering: A, 2017Co-Authors: Chengsi ZhengAbstract:A Eutectoid Steel with various ultrafine- or fine-grained ferrite matrix (α)+cementite particle (θ) structures was fabricated to explore the effects of the microstructural features on the mechanical behavior of hard particle-strengthened two-phase alloys. The effect of microstructure on the parameters of an analytical model and the mechanical behavior for the Eutectoid Steel with ultrafine- or fine-grained α+θ structure were analyzed basing on statistical data and physical metallurgy. The results showed that the rate of dislocation-storage caused by ferrite grain boundaries and cementite particles is approximately a microstructural constant and is proportional to the dislocation mean free path. The larger ferrite grains and the larger volume fraction of intragranular cementite particles are beneficial to obtaining a lower rate of dynamic recovery when ultrafine- or fine-grained α+θ structures with an equal dislocation mean free path, and the uniform elongation increases with the decrease in the rate of dynamic recovery. Moreover, the ultimate strength is closely related to the effective dislocation mean free path including both roles of the storage and the recovery of dislocations. It is feasible to design a microstructure consisting of ultrafine- or fine-grained ferrite matrix and tiny cementite particles mainly within grain interior to possess an enhanced strength-plasticity synergy for the Eutectoid Steel.
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Micromechanical behavior of Eutectoid Steel quantified by an analytical model calibrated by in situ synchrotron-based X-ray diffraction
Materials Science and Engineering: A, 2015Co-Authors: Chengsi Zheng, Yandong Wang, Wangyue Yang, Zuqing SunAbstract:Abstract A Eutectoid Steel with three types of ferrite ( α )+cementite particle ( θ ) microstructures, i.e., a coarse-grained α + θ structure, a fine-grained α + θ structure and an ultrafine-grained α + θ structure, was fabricated to explore the effects of the microstructural features on the micromechanical behavior of hard particle-strengthened two-phase alloys. An analytical model based on the Kocks–Mecking model was established to elucidate the evolution of the geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs) in the hard particle-strengthened alloys and, hence, to predict the stress partitioning for each phase and the enhancement in the work hardening during uniform plastic deformation. In situ synchrotron-based X-ray diffraction was used to verify the stress partitioning and the important material parameters predicted by our analytical model. Our results showed that a decrease in the geometric slip distance leads to an appreciable increase in the GND density, whereas an increase in the grain size of the ferrite causes an increase in the SSD density under uniform plastic deformation for Eutectoid Steel with an α + θ structure. Both the stresses for the individual phase and the difference in stress between the two phases for Eutectoid Steel with various α + θ structures were closely related to the change in the GND density near the phase interfaces. The GND density also played an important role in determining the work-hardening rate for Eutectoid Steel with various α + θ structures.
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microstructure evolution and mechanical properties of Eutectoid Steel with ultrafine or fine ferrite cementite structure
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Chengsi Zheng, Wangyue Yang, Zuqing SunAbstract:Abstract Eutectoid Steel with the ultrafine or fine-grained ferrite (α)+cementite (θ) particles structure was formed by hot deformation of undercooled austenite at 0.1 s−1 or 5 s−1 at 650 °C using a Gleeble 1500 hot simulator and subsequent annealing. The microstructural evolution of fine (α+θ) structure was investigated by means of a scanning electronic microscope, electron backscattered diffraction and transmission electron microscope, and the mechanical properties of fine (α+θ) Steel were analyzed in comparison with that of ultrafine (α+θ) Steel. The results show that only dynamic transformation of undercooled austenite into proEutectoid ferrite occurs during hot deformation at 650 °C at 5 s−1. During water quenching, lamellar pearlite with small colony sizes is formed and the average size of pearlite colonies decreases with increasing the strain. By subsequent annealing at 650 °C for 30 min, the spheroidization of lamellar pearlite takes place, resulting in the formation of fine (α+θ) structure consisting of ferrite matrix with the average size of about 4.9 μm and fine cementite particles mainly within ferrite grains. In comparison with ultrafine (α+θ) Steel consisting of ferrite matrix with the average size of about 1.8 μm and relatively large cementite particles mostly located at grain boundaries, the yield strength, tensile strength, uniform elongation, total elongation and work-hardening capability of fine (α+θ) Steel improve markedly.
Won Jong Nam - One of the best experts on this subject based on the ideXlab platform.
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Effects of Wire Drawing and Annealing Conditions on Torsional Ductility of Cold Drawn and Annealed Hyper-Eutectoid Steel Wires
Metals, 2020Co-Authors: Jin Young Jung, Pyeong Yeol Park, Won Jong NamAbstract:The effects of microstructural features on torsional ductility of cold drawn and annealed hyper-Eutectoid Steel wires were investigated. The patented wire rods were successively dry drawn to ε = 0.79 (54.7%) ~ 2.38 (90.7%). To examine the effects of hot-dip galvanizing conditions on torsional ductility, Steel wires with ε = 1.95 were annealed at 500 °C for 30 s for ~1 h in a salt bath. In cold drawn wires, the number of turns to failure increased steadily, showing the maximum peak, and then decreased with drawing strain. During the post-deformation annealing at 500 °C, torsional ductility of Steel wires decreased with annealing time, except for the rapid drop due to the occurrence of delamination for 10 s annealing. The decrease of the number of turns to failure would be attributed to the microstructural evolutions, accompanying the spheroidization and growth of cementite particles and the recovery of ferrite in cold drawn Steel wires. From the relationship between microstructural evolution and torsional ductility, it was found that among microstructural features, the shape and orientation of lamellar cementite showed the significant effect on torsional ductility of cold drawn and annealed hyper-Eutectoid Steel wires.
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Effects of Alloying Elements, Si and Cr, on Aging and Delamination Behaviors in Cold-Drawn and Subsequently Annealed Hyper-Eutectoid Steel Wires
Metals and Materials International, 2019Co-Authors: Shinwoong Joung, Won Jong NamAbstract:The effects of alloying elements, Cr and Si, and the conditions of hot-dip galvanizing on the aging behaviors and their related tensile and torsional properties in cold drawn hyper-Eutectoid Steel wires were investigated. The Cr and Si additions were found to increase tensile strength, but decrease the limit of drawing strain without delamination in cold drawn Steel wires. The Cr and Si additions encouraged the suppression of age hardening and age softening during annealing. The increased amount of deformation in cold drawn Steel wires made age hardening occur at the lower annealing temperature and shorter annealing time, and expanded the delamination region to high temperature during annealing. The additions of Cr and Si did not show the noticeable improvement of tensile strength without delamination in cold drawn Steel wires, but increased the upper limit of tensile strength without delamination in cold drawn and annealed Steel wires.
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aging behavior and delamination in cold drawn and post deformation annealed hyper Eutectoid Steel wires
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: S W Joung, U G Kang, Seungpyo Hong, Youngwoon Kim, Won Jong NamAbstract:Abstract The effects of drawing strains and post-deformation annealing conditions on the aging behavior and the occurrence of delamination in cold drawn hyper-Eutectoid Steel wires were studied. At low annealing temperatures the increased tensile strength for a short annealing time would be attributed to age hardening, which came from the decomposition of the unstable cementite in deformed pearlite. The decrease of tensile strength at the high annealing temperature was due to age softening, which would be attributed to the decreased carbon content in lamellar ferrite through the spheroidization or the re-precipitation of cementite, and recovery or recrystallization of ferrite. The extent for the occurrence of delamination during annealing expanded to the high temperature region with the increased amount of deformation in Steel wires. At high annealing temperatures, the decreased carbon content dissolved in lamellar ferrite due to age softening would result in the decrease of tensile strength and suppress the occurrence of delamination. The total magnitude of carbon content dissolved in lamellar ferrite either by the partial dissolution of lamellar cementite during wire drawing or by the partial decomposition of lamellar cementite during post-deformation annealing would control the occurrence of delamination in cold drawn Steel wires.
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The prediction of the occurrence of the delamination in cold drawn hyper-Eutectoid Steel wires
Journal of Materials Processing Technology, 2007Co-Authors: D. B. Park, Eui Goo Kang, Won Jong NamAbstract:Abstract The effects of mechanical properties and microstructural features such as interlamellar spacing on the occurrence of the delamination in cold drawn hyper-Eutectoid Steel wires were investigated. Since the cementite dissolution occurred during wire drawing would become one of the main reasons to cause the occurrence of the delamination, the dependence of the occurrence of the delamination on mechanical properties was examined using tensile test and scanning electron microscopy. The results showed that tensile strength would become a proper parameter to predict the occurrence of the delamination in hyper-Eutectoid pearlitic carbon Steels and Cr-added Steels. It was found that while the initial interlamellar spacing showed little influence on the occurrence of the delamination, the Cr addition would improve tensile strength of cold drawn pearlitic Steel wires without the occurrence of the delamination.
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Effect of alloying elements on work hardening behavior in cold drawn hyper-Eutectoid Steel wires
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Hyung Rak Song, Eui Goo Kang, Won Jong NamAbstract:Abstract The effects of alloying elements, Cr and Ni, and transformation temperature on strength and work hardening behavior of cold drawn hyper-Eutectoid Steel wires were investigated. The Cr addition effectively increased strength and work hardening rate, k /(2 λ 0 ) 1/2 by refining interlamellar spacing and increasing the Hall–Petch parameter, k . However, the Ni addition caused little change in mechanical properties of strength, work hardening rate and ductility. It was also found that the Hall–Petch parameter, controlling work hardening behavior, was not affected by interlamellar spacing but by the addition of alloying elements. Additionally, the refinement of interlamellar spacing due to low transformation temperature and the Cr addition caused the increase of reduction of area in drawn pearlitic Steels.
Zuqing Sun - One of the best experts on this subject based on the ideXlab platform.
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Mechanical Properties of Plain Carbon Steels with Ultrafine (α+θ)
2016Co-Authors: Haiyan Zhu, Wangyue Yang, Zuqing SunAbstract:Abstract. Mechanical properties of a medium-carbon Steel with the ultrafine (α+θ) microstructures obtained by hot deformation of undercooled austenite and annealing were investigated by tensile tests, in comparison with that of a Eutectoid Steel. The results indicated that in the case of hot deformation of undercooled austenite to strain of 1.61 at 650°C at 0.01s-1 and annealing at 650°C for 30min, the ultrafine (α+θ) microstructures consisting of ultrafine ferrite grains and dispersed cementite particles were similar in the medium-carbon Steel and the Eutectoid Steel, but the mechanical properties of the Eutectoid Steel were better that maybe be attributed to the relatively coarser size and the higher amount of cementite particles. With the increase of temperature for hot deformation of undercooled austenite to 700°C, the ultrafine (α+θ) microstructure of the medium-carbon Steel changed obviously with the presence of some spheroidized pearlite colonies, and demonstrated the best balance of strength and elongation, the yield strength of about 545MPa, the tensile strength of about 635MPa, and the total elongation of about 35%
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Micromechanical behavior of Eutectoid Steel quantified by an analytical model calibrated by in situ synchrotron-based X-ray diffraction
Materials Science and Engineering: A, 2015Co-Authors: Chengsi Zheng, Yandong Wang, Wangyue Yang, Zuqing SunAbstract:Abstract A Eutectoid Steel with three types of ferrite ( α )+cementite particle ( θ ) microstructures, i.e., a coarse-grained α + θ structure, a fine-grained α + θ structure and an ultrafine-grained α + θ structure, was fabricated to explore the effects of the microstructural features on the micromechanical behavior of hard particle-strengthened two-phase alloys. An analytical model based on the Kocks–Mecking model was established to elucidate the evolution of the geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs) in the hard particle-strengthened alloys and, hence, to predict the stress partitioning for each phase and the enhancement in the work hardening during uniform plastic deformation. In situ synchrotron-based X-ray diffraction was used to verify the stress partitioning and the important material parameters predicted by our analytical model. Our results showed that a decrease in the geometric slip distance leads to an appreciable increase in the GND density, whereas an increase in the grain size of the ferrite causes an increase in the SSD density under uniform plastic deformation for Eutectoid Steel with an α + θ structure. Both the stresses for the individual phase and the difference in stress between the two phases for Eutectoid Steel with various α + θ structures were closely related to the change in the GND density near the phase interfaces. The GND density also played an important role in determining the work-hardening rate for Eutectoid Steel with various α + θ structures.
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microstructure evolution and mechanical properties of Eutectoid Steel with ultrafine or fine ferrite cementite structure
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Chengsi Zheng, Wangyue Yang, Zuqing SunAbstract:Abstract Eutectoid Steel with the ultrafine or fine-grained ferrite (α)+cementite (θ) particles structure was formed by hot deformation of undercooled austenite at 0.1 s−1 or 5 s−1 at 650 °C using a Gleeble 1500 hot simulator and subsequent annealing. The microstructural evolution of fine (α+θ) structure was investigated by means of a scanning electronic microscope, electron backscattered diffraction and transmission electron microscope, and the mechanical properties of fine (α+θ) Steel were analyzed in comparison with that of ultrafine (α+θ) Steel. The results show that only dynamic transformation of undercooled austenite into proEutectoid ferrite occurs during hot deformation at 650 °C at 5 s−1. During water quenching, lamellar pearlite with small colony sizes is formed and the average size of pearlite colonies decreases with increasing the strain. By subsequent annealing at 650 °C for 30 min, the spheroidization of lamellar pearlite takes place, resulting in the formation of fine (α+θ) structure consisting of ferrite matrix with the average size of about 4.9 μm and fine cementite particles mainly within ferrite grains. In comparison with ultrafine (α+θ) Steel consisting of ferrite matrix with the average size of about 1.8 μm and relatively large cementite particles mostly located at grain boundaries, the yield strength, tensile strength, uniform elongation, total elongation and work-hardening capability of fine (α+θ) Steel improve markedly.
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Enhancement of mechanical properties by changing microstructure in the Eutectoid Steel
Materials Science and Engineering: A, 2012Co-Authors: Chengsi Zheng, Wangyue Yang, Zuqing SunAbstract:Abstract The different microstructures of Eutectoid Steel were analyzed with SEM and its corresponding room-temperature tensile tests were carried out. The results show that the ultrafine ( α + θ ) duplex structure consisting of ferrite matrix ( α ) with grain size of about 1 μm and dual-size distributed cementite particles ( θ ) could be formed by hot deformation of undercooled austenite and subsequent annealing. Moreover, the mixed microstructures consisting of polygonal ferrite grains with size of about 2 μm and fine pearlite colonies could be also obtained by this process under different conditions. Although the yield strength and total elongation of ultrafine ( α + θ ) duplex structure increase markedly, its tensile strength decrease obviously comparing to that of lamellar pearlite. The lower work-hardening rate at the beginning of uniform plastic deformation is probably responsible for tensile strength decrease in the ultrafine ( α + θ ) duplex structure. Moreover, the tensile strengths and total elongations of mixed microstructures are both larger than that of ultrafine ( α + θ ) duplex structure and lamellar pearlite due to their well work-hardening capabilities.
H. Rastegari - One of the best experts on this subject based on the ideXlab platform.
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Constitutive Modeling of Warm Deformation Flow Curves of an Eutectoid Steel
Journal of Materials Engineering and Performance, 2017Co-Authors: H. Rastegari, M. Rakhshkhorshid, Mahesh C. Somani, David PorterAbstract:The capabilities of the commonly encountered Johnson-Cook and Arrhenius-type constitutive equations to describe the warm deformation flow curves of an Eutectoid Steel undergoing dynamic spheroidization have been compared based on the warm compression test data. Warm compression tests were conducted over the temperature range 620-770 °C and strain rates in the range of 0.01-10 s−1. The average absolute relative error values for the Johnson-Cook and Arrhenius-type constitutive equations were 44.03 and 6.50%, respectively, thereby showing that the Arrhenius-type constitutive equation is to be preferred. It is also shown that in contrast to the Arrhenius-type constitutive equation, the softening caused by dynamic spheroidization cannot be modeled using the Johnson-Cook equation.
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Exponential-type Constitutive Equation in Order to Use in Modeling the Warm Deformation of a Eutectoid Steel
international journal of iron and steel society of iran, 2016Co-Authors: M. Rakhshkhorshid, H. RastegariAbstract:The main contribution of the present work is to investigate the capability of exponential-type constitutive equationto model the warm deformation flow curves of a Eutectoid Steel in the temperature range of 620-770 °C andat the strain rates in the range of 0.01-10 s-1 conducted on a Gleeble-1500 thermomechanical simulator. Warmdeformation in this temperature range facilitates the occurrence of dynamic spheroidization of cementite lamellaeas a softening process as well as some instabilities and microstructural defects. The prediction capability of theexamined model was assessed using the average absolute relative error (AARE) criterion. The obtained AAREwith the value of 7.39% for warm deformation modeling of the tested Steel showed the acceptable performance ofthe examined model.
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Effect of initial microstructure on the work hardening behavior of plain Eutectoid Steel
Materials Science and Engineering: A, 2015Co-Authors: H. Rastegari, Ahmad Kermanpur, Abbas NajafizadehAbstract:Abstract Work hardening capability and tensile properties of the plain Eutectoid Steel rods are the key factors in the wire drawing process to fabricate high strength wire rods with a minimum failure. In the present research, the work hardening behavior of Eutectoid Steel with different initial microstructures of bainite, duplex bainite+pearlite, pearlite, partially spheroidized and spheroidized pearlite was assessed in terms of instantaneous work hardening exponent ( n value) and work hardening rate ( θ ) using room temperature tensile test. The results show an inverse parabolic behavior for variation of instantaneous n value versus true strain, i.e., work hardening exponent initially increases up to a maximum value and then decreases. The bainitic microstructure exhibits the lowest n value, whereas the spheroidized pearlitic one shows the highest. It is shown that the fine pearlitic microstructure containing partially spheroidized regions exhibited the best combination of tensile properties, n value and work hardening rate.
Abbas Najafizadeh - One of the best experts on this subject based on the ideXlab platform.
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Effect of initial microstructure on the work hardening behavior of plain Eutectoid Steel
Materials Science and Engineering: A, 2015Co-Authors: H. Rastegari, Ahmad Kermanpur, Abbas NajafizadehAbstract:Abstract Work hardening capability and tensile properties of the plain Eutectoid Steel rods are the key factors in the wire drawing process to fabricate high strength wire rods with a minimum failure. In the present research, the work hardening behavior of Eutectoid Steel with different initial microstructures of bainite, duplex bainite+pearlite, pearlite, partially spheroidized and spheroidized pearlite was assessed in terms of instantaneous work hardening exponent ( n value) and work hardening rate ( θ ) using room temperature tensile test. The results show an inverse parabolic behavior for variation of instantaneous n value versus true strain, i.e., work hardening exponent initially increases up to a maximum value and then decreases. The bainitic microstructure exhibits the lowest n value, whereas the spheroidized pearlitic one shows the highest. It is shown that the fine pearlitic microstructure containing partially spheroidized regions exhibited the best combination of tensile properties, n value and work hardening rate.
