Published at : 18 Sep 2024
Volume : IJtech
Vol 15, No 5 (2024)
DOI : https://doi.org/10.14716/ijtech.v15i5.6770
Nattarawee Siripath | Department of Tool and Materials Engineering, Faculty of Engineering, King Mongkut’s University of Technology, Thonburi, Bangkok, 10140, Thailand |
Surasak Suranuntchai | Department of Tool and Materials Engineering, Faculty of Engineering, King Mongkut’s University of Technology, Thonburi, Bangkok, 10140, Thailand |
Sedthawatt Sucharitpwatskul | National Science and Technology Development Agency (NSTDA), Thailand Science Park, Phahonyothin Road, Khlong Nueng, Khlong Luang, Pathum Thani, 12120, Thailand |
Utilized
the experimental data to construct models that describe DRX kinetics and the
evolution of grain size, employing the Johnson-Mehl-Avrami-Kolmogorov (JMAK)
equation, this study investigates the dynamic recrystallization (DRX)
characteristics and the microstructure evolution within BS 080M46 medium carbon
steel under high-temperature conditions. Several trials were carried out to
analyze hot compression, covering a temperature range of 900°C to 1200°C and
utilizing varying strain rates of 0.1, 1, and 10 s-1. The incorporation of
these models into QForm V10.2.1 facilitated finite element modeling (FEM)
simulation, enabling the evaluation of DRX behavior. A comparative analysis was
carried out to confirm the efficacy of the developed models, aligning the
simulation results with the data obtained through metallographic observations.
The high level of agreement between the simulation and experimental findings
related to the DRX grain size was quantified by a correlation coefficient (R)
of 0.991, along with an average absolute relative error (AARE) of 7.412%. These
results confirm the capability of the developed DRX kinetics and grain size
evolution models in accurately predicting the grain size of BS 080M46 medium
carbon steel. In addition, the study
suggests that higher temperatures or lower strain rates can result in an
increased volume fraction of dynamic recrystallization (DRX) and grain size.
This highlights the importance of Finite Element Method (FEM) as a crucial tool
for comprehending the evolution of microstructure during hot working processes.
BS 080M46 medium carbon steel; DRX behavior; Finite element modeling; Grain size; Hot compression test
BS 080M46 is a versatile medium carbon steel known for its excellent mechanical properties and ease of processing, making it ideal for high-stress applications requiring wear resistance. Its strength, toughness, and wear resistance have led to its widespread use in various machinery parts such as gears, axles, crankshafts, and connecting rods, as well as in shafts, bolts, studs, and hydraulic cylinders (Mizuguchi et al., 2009). Typically, during the hot working process of BS 080M46 medium carbon steel, the material is heated to a temperature exceeding the recrystallization temperature range. This allows for the material to be plastically shaped and formed easily using various hot working processes, including hot forging, hot rolling, and hot extrusion (Altan, 2005). Lv et al. (2018) emphasized that thermo-mechanical processing, utilized in the production of large structural components, tailors the microstructure for desired mechanical properties, necessitating predictive models due to the sensitivity of the microstructure to processing conditions, and the intricate relationship between processing parameters, material deformation behavior, and resulting microstructures.
In
the realm of metallurgy, three significant phenomena – work hardening (WH),
dynamic recovery (DRV), and dynamic recrystallization (DRX) – significantly
shape the flow behavior, microstructure, and energy required during the hot working process, occurring
concurrently during material deformation and controlling flow stress under
varying conditions (Derazkola et al., 2022; Kooiker, Perdahcioglu, and
Boogaard, 2018). These phenomena ultimately impact material
properties and behavior, playing a critical role in determining the quality of
the final product (Chen et al., 2021b). Through
these occurrences, the microstructure evolution of metals is notably influenced
by DRX. The existing coarse grains undergo notable deformation and eventually
transform into smaller, equiaxed grains, contributing to both grain refinement
and homogenization (Bharath et al., 2021; Zheng et al., 2018; Quan,
2013). Consequently, this process leads to enhanced
mechanical properties, particularly in terms of increased strength, ductility,
and toughness
(Tukiat
et
al., 2024; Zou et al., 2022; Anwar et al., 2021; Kurnia and Sofyan, 2017; Kozmel et al., 2014). The
effects of DRX on metals depend on several factors, including the composition
of the metal, the deformation temperature, the strain rate, and the processing
history (Alaneme and Okotete, 2019).
In addition, the occurrence of DRX and the resulting microstructure can also be
affected by prior cold work, which may require higher processing temperatures
or longer processing times to achieve DRX (Stefani et al., 2016; Sanrutsadakorn, Uthaisangsuk, and Suranuntchai, 2014).
Precisely characterizing the DRX behaviors and the mechanisms of grain evolution is of utmost importance for achieving the desired microstructure and mechanical properties. The construction of DRX kinetic models has involved several attempts to represent material behavior and the evolution of grain size effectively. Studies by Hu and Wang (2020) and Yang et al. (2018) have shown that flow curves can represent the hot working behaviors of BT25y titanium alloy and 5CrNiMoV steel, respectively, due to their close correlation with microstructural changes. Therefore, stress-strain data derived from isothermal compressions can be employed to formulate DRX kinetics, with the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation widely utilized to depict the correlation between the volume fraction of deformation-induced DRX, deformation temperature, and strain rate (Irani et al., 2019). For instance, Wang et al. (2016), through their research, established an Arrhenius-type constitutive equation incorporating a Zener-Hollomon parameter, along with DRX volume fraction and grain size models, all based on the JMAK equation. This comprehensive approach accurately describes the deformation behavior observed during the hot-working processes of the carburizing steel alloy 20Cr2Ni4A. Similarly, models for the DRX volume fraction and grain size, applicable to 33Cr23Ni8Mn3N heat-resistant steel, were developed by Ji et al. (2020) and integrated these models into the DEFORM-3D software. The finding stemming from microstructural observations obtained through LOM and SEM, along with finite element simulations, exhibited highly consistent, thereby validating the precision of the established DRX model. Quan et al. (2019) investigated the DRX behavior of AlCu4SiMg alloys using the JMAK equation and verified its feasibility through both FE simulations and experiments. Additionally, studies on various alloys such as Ti-5Al-5Mo-5V-3Cr-1Zr near b Titanium alloy (Lv et al., 2018), medium Mn steel (Sun et al., 2020), solution-treated Ni-based superalloy (Chen et al., 2016), Cr8 alloy (Chen et al., 2022), and TB8 Titanium alloys (Zhang et al., 2020) used FEM simulations of DRX behavior. The concordance between simulation results and microstructural observations underscores the potential of finite element simulations as valuable tools for predicting the DRX behavior across various alloys, which can be helpful in designing and optimizing manufacturing processes for these materials.
Despite extensive research
into understanding dynamic recrystallization (DRX) phenomena in various alloys,
the specific behavior of DRX in BS 080M46 medium carbon steel remains
relatively unexplored. This knowledge gap presents significant challenges in optimizing
the hot working processes of this material to achieve the desired
microstructural characteristics and mechanical properties. Furthermore, the
lack of accurate predictive models tailored to BS 080M46 medium carbon steel
further hinders process optimization efforts. Therefore, the present work aims
to address these challenges by studying the DRX behavior and microstructure
evolution of BS 080M46 medium carbon steel through hot compression testing.
Experimental data were collected to establish both a DRX kinetics model and a
grain size model based on the JMAK equation. These models were
subsequently incorporated into QForm V10.2.1 software to simulate
microstructure evolution, with a specific emphasis on grain size under
different deformation conditions. By comparing these finite element simulation
results with microstructure observations, the accuracy and reliability of the
models are verified. Providing insights into DRX behavior specific to BS 080M46
medium carbon steel and developing accurate predictive models, this study aims
to contribute to the advancement of metallurgical science and materials
engineering, facilitating enhanced process optimization and product development
in engineering applications.
The material being
studied is BS 080M46 medium carbon steel, which was supplied by S.B.-CERA Co.,
Ltd. The weight percentage (wt%) of the steel's chemical composition was
analyzed using an Emission Spectrometer (OES) and is detailed in Table 1.
Figure 1(a) illustrates the conceptual methodology diagram used in this study.
The flow curves under high temperatures required for input into the finite
element model were obtained by a hot compression test using a Baehr DIL-805
deformation dilatometer. Samples were prepared in a cylindrical shape, 5 mm in
diameter and 10 mm in height, with a thermocouple attached to the surface for
direct temperature detection during deformation. The hot compression test
covered four temperatures: 900°C, 1000°C, 1100°C, and 1200°C, along with three
strain rates: 0.1, 1, and 10 s-1, to characterize deformation
conditions. Samples were placed in a vacuum chamber filled with inert Argon gas
and heated by an induction coil to reach the deformation temperatures. The
heating rate of 1.625°C/s was maintained for 1 minute to ensure uniform
temperature distribution. Samples were then compressed using an Alumina punch
to achieve a 60% reduction in height, followed by immediate quenching in Argon
gas with a cooling rate of 40°C/s until reaching room temperature. Figure 1(b)
depicts the temperature–time path during the hot compression test.
Metallographic preparation involved cutting samples along the cylindrical axis,
mounting them on a hot press, initial polishing with 400-grit SiC abrasive
paper, followed by finer grits up to 1200 grit SiC papers and 0.3 µm Alumina
particles for final polishing. Subsequently, surfaces were etched using a 4%
picral and 3% Nital solution for 4 seconds. Microstructural observations were
conducted using Light Optical Microscopy (LOM) and scanning electron microscopy
(SEM), focusing on the central region of the sample’s cross-sections. The
initial microstructure of BS 080M46 medium carbon steel contains proeutectoid
ferrite and pearlite, as depicted in Figure 2.
Table
1 Chemical compositions (wt%) of BS 080M46 medium carbon
steel
C |
Si |
Mn |
P |
S |
Ni |
Cr |
Mo |
Cu |
0.467 |
0.194 |
0.673 |
0.027 |
0.021 |
0.068 |
0.110 |
0.016 |
0.178 |
Figure 2 Microstructure
of BS 080M46 medium carbon steel by (a) LOM and (b) SEM showing proeutectoid ferrite and pearlite
structure
3.1. Flow curve of BS 080M46 medium carbon steel
The collected experimental data is
employed to generate flow curves of BS 080M46 medium carbon steel,
systematically plotted over a range of deformation temperatures spanning from
900 to 1200°C at 100°C intervals with constant strain rates of 0.1, 1, and 10 s-1,
as illustrated in Figure 1(c) to Figure 1(e). Flow curves represent the
stress-strain relationship under well-defined deformation conditions. They
often exhibit a characteristic behavior known as dynamic recrystallization
(DRX), which starts with a peak stress and gradually declines towards a state
of steady stress, as highlighted in Mirzadeh et al. (2012) and (Mirzadeh,
2015).
3.2. Establishment of DRX
model of BS 080M46 medium carbon steel
3.2.1. Determination of Critical Strain Model
Parameters
During the hot working process, the initial stage of compressive deformation shows a rapid rise to a peak in the experimental flow curves with an increase in true strain. This is subsequently followed by a gradual reduction, ultimately leading to a consistent, steady-state stress. The strain value associated with the peak stress () is commonly denoted as the peak strain ().
The initiation of DRX is typically correlated with the dislocation accumulation, which may arise due to plastic deformation. DRX can be initiated when the dislocation density exceeds a certain critical point, commonly termed the critical strain () for DRX (Wu et al., 2018). New grains can nucleate both at the pre-existing grain boundaries and within the grains that have undergone deformation, and these newly generated grains can grow into high-angle boundaries. The work hardening rate, denoted as (MPa), is expressed as the derivative of (Chen et al., 2021a; Shafiei and Ebrahimi, 2012; Najafizadeh and Jonas, 2006). In their findings, Poliak and Jonas (2003) proposed that the inflection observed in ln plots can serve as a valuable indicator for identifying the initiation of DRX. The ln analysis was effective in providing precise values for determining critical strain (Mirzadeh and Najafizadeh, 2010a; 2010b). Applying a third-order polynomial regression method to analyze the curve until it reaches its peak facilitates the identification of the inflection point, thereby allowing for the derivation of the critical strain () corresponding to the critical stress (). Figure 3(a) displays the ln curves and their associated 3rd-order polynomial for a strain rate of 0.1 s-1. The presented data in Table 2 exhibits the values for and under various deformation conditions. These values have been computed from the experimental stress-strain curves and work hardening rate curves. According to Figure 3(b), the normalized strain can is represented by the ratio with a value of 0.478
where the constants are associated with the material. With a value of 8.314 J×K-1mol-1, R represents the universal gas constant. All deformed samples share the same initial grain size. However, the influence of grain size is subsequently taken into consideration, resulting in = 0. Obtaining the values of involves applying the natural logarithm for both sides of Equation 1, yielding in Equation 2, as depicted below:
3.2.2. Determination of DRX Kinetics Model
Parameters
Upon performing the natural logarithm on both sides of Equation 10, the values of kd and bd, are obtained, as shown:
Figure 6 versus curves at (a) 1 s-1 and (b) 1000 °C; (c) Comparing computed and experimental values for a specific deformation condition; (d) Correlation between computed and experimental values
The DRX kinetics model is applied to calculate the DRX volume fraction of
BS 080M46 medium carbon steel within a range of deformation conditions. The
plots in Figure 6(c) and Figure 6(d) illustrate the concordance between
computed and experimental values. In Figure 6(c), the comparison of the computed and experimental
values of is depicted for the hot compression
test of BS 080M46 medium carbon steel under specific conditions (1100°C and a
strain rate of 1 s-1). Meanwhile, Figure 6(d) displays a scatter
plot illustrating the correlation analysis between experimental and calculated
DRX volume fraction values across all deformation conditions. The high
correlation coefficient (R = 0.949) and low root mean square error (RMSE = 0.113) confirm the accuracy
and effectiveness of the DRX model in predicting of BS 080M46 medium carbon steel
during hot compression tests.
3.2.3. Determination of Grain size model parameters