Process Optimization of Dual-Liquid Casting and Interfacial Strength–Toughness of the Produced LAS/HCCI Bimetal

The pouring time interval is the decisive factor of dual-liquid casting for bimetallic productions. Traditionally, the pouring time interval is fully determined by the operator’s experience and on-site observation. Thus, the quality of bimetallic castings is unstable. In this work, the pouring time interval of dual-liquid casting for producing low alloy steel/high chromium cast iron (LAS/HCCI) bimetallic hammerheads is optimized via theoretical simulation and experimental verification. The relevancies of interfacial width and bonding strength to pouring time interval are, respectively, established. The results of bonding stress and interfacial microstructure indicate that 40 s is the optimum pouring time interval. The effects of interfacial protective agent on interfacial strength–toughness are also investigated. The addition of the interfacial protective agent yields an increase of 41.5% in interfacial bonding strength and 15.6% in toughness. The optimum dual-liquid casting process is used to produce LAS/HCCI bimetallic hammerheads. Samples cut from these hammerheads show excellent strength–toughness (1188 Mpa for bonding strength and 17 J/cm2 for toughness). The findings could be a reference for dual-liquid casting technology. They are also helpful for understanding the formation theory of the bimetal interface.


Introduction
Due to its excellent wear resistance, high-temperature strength, and heat resistance, high chromium cast iron (HCCI) has been regarded as the best wear-resistant material [1][2][3]. It has been widely applied in mechanical and metallurgical equipment for crushing, grinding, material handling, and so on. The main applications contain hammerheads, lining plates, grinding balls, flow passage components of mortar pumps, etc. Although components made by single HCCI have certain wear resistance and toughness under ordinary working conditions, it is difficult for them to meet the requirements of high strength, elevated wear resistance, and great security under severe conditions. The steel/high chromium cast iron (S/HCCI) bimetal composites were developed and used to prepare wear-resistant components of which the comprehensive performance is obviously improved [4][5][6].
Most S/HCCI bimetallic components are produced using casting methods. There are two kinds of casting technologies: dual-liquid and liquid-solid. Compared to the liquid-solid, the dual-liquid technology can obtain castings with a better interfacial region and performance, and have a low cost as well [7]. Thus, dual-liquid casting is the main The pouring time interval is the key factor of the interfacial bonding for dual-liquid cast bimetallic hammerheads. Currently, the pouring time interval is usually determined by observing the interfacial solidification degree during actual production. This method has obvious randomness and depends on the operator's experience. Overlong time intervals would cause a narrow and weak bonding interface. Conversely, short time intervals lead to a wide and even composition mixing layer. This results in unstable quality and performance of the hammerhead castings. In this work, the LAS/HCCI bimetallic hammerhead casting, as Figure 1 shows, is used as the research object to obtain the optimum pouring time interval. through simulating the interfacial temperature variation and solidification degree after the first pouring, the mathematical model to realize a metallurgical fusion layer can be established, and an optimum pouring time interval can be determined. LAS/HCCI bimetallic hammerheads are produced at the Handan Huiqiao Composite Material Technology Co., Ltd using dual-liquid casting technology. The self-setting resin sand process and horizontal molding-vertical pouring technology, as Figure 2a shows, are used during dual-liquid casting. Two medium-frequency fast smelting furnaces are LAS/HCCI bimetallic hammerheads are produced at the Handan Huiqiao Composite Material Technology Co., Ltd. using dual-liquid casting technology. The self-setting resin sand process and horizontal molding-vertical pouring technology, as Figure 2a shows, are used during dual-liquid casting. Two medium-frequency fast smelting furnaces are used simultaneously to melt the LAS and HCCI. The raw materials are heated to the designed pouring temperatures of 1576 • C for the LAS and 1400 • C for the HCCI. A self-made interface protective agent was added, according to the actual process, after 10 s of the first LAS pouring. The second HCCI pouring was performed after a certain time interval to the LAS. Pouring time intervals of 35, 40, 45, and 50 s were used to produce the bimetallic hammerhead. After cooling and cleaning, the bimetallic hammerhead castings underwent the following heat treatments: annealing at 1000 • C, tempering at 980 • C, and finally low temperature tempering at 260 • C. All test samples were cut from the heat-treated bimetallic hammerhead castings, as Figure 2b shows. LAS/HCCI bimetallic hammerheads are produced at the Handan Material Technology Co., Ltd using dual-liquid casting technology. T sand process and horizontal molding-vertical pouring technology, are used during dual-liquid casting. Two medium-frequency fast sm used simultaneously to melt the LAS and HCCI. The raw materials signed pouring temperatures of 1576 °C for the LAS and 1400 °C f made interface protective agent was added, according to the actual the first LAS pouring. The second HCCI pouring was performed af terval to the LAS. Pouring time intervals of 35, 40, 45, and 50 s were bimetallic hammerhead. After cooling and cleaning, the bimetallic h underwent the following heat treatments: annealing at 1000 °C, temp finally low temperature tempering at 260 °C. All test samples wer treated bimetallic hammerhead castings, as Figure 2b shows. A scanning electron microscope, SEM, was employed to observ of the bimetallic castings. An energy dispersive spectrometer, EDS, w the distribution of the alloying elements. The line and face scan of E analyze the variation in the alloying elements around interfacial regio voltage and working distance of SEM and EDS measurements were 1 respectively. The detection signal was secondary electrons for th backscattered electrons for the EDS analysis.
The interfacial bonding strength was determined using the she matic drawing and the physical photo of samples for the shear tests 3. The bulges of shearing samples are the LAS, and the body is the H A scanning electron microscope, SEM, was employed to observe the microstructure of the bimetallic castings. An energy dispersive spectrometer, EDS, was used to measure the distribution of the alloying elements. The line and face scan of EDS were adopted to analyze the variation in the alloying elements around interfacial regions. The accelerating voltage and working distance of SEM and EDS measurements were 10 KV and 6.275 mm, respectively. The detection signal was secondary electrons for the SEM images and backscattered electrons for the EDS analysis.
The interfacial bonding strength was determined using the shearing test. The schematic drawing and the physical photo of samples for the shear tests are shown in Figure 3. The bulges of shearing samples are the LAS, and the body is the HCCI. The force was loaded continuously on bulges until the fracture, while the body was supported using a special tool. A full-automatic Vickers hardness tester was utilized to measure the hardness. The total force of 1 kg was loaded onto samples and kept for 10 s. To evaluate the hardness variation, tests were performed nearby and across the interfacial region.  Charpy impact, three-point bending, and tensile tests were employed to determine the overall mechanical properties of the LAS/HCCI bimetal. These test methods were performed according to the standard of ASTM A370-22 [16]. The span of the three-point bending tests was 40 mm. Schematic drawings and physical photos of samples for these tests are shown in Figures 4-6, respectively.

Simulation Results of Interfacial Solidification for Different Pouring Time Intervals
Simulation results regarding the interfacial solidification process of the bimetal are shown, respectively, in Figures 7 and 8. The simulated temperature field results of the interface after the LAS casting ( Figure 7) show that the temperature decreases from the center to the edges of the interfacial region. Although the temperature at the edges of the interfacial region after 10 s of pouring is lower than the solidification temperature, the temperature in the central area is far higher than the solid point. As the time interval increases, the temperature in the central area decreases. While the time interval is 40 s, the temperature of the whole interfacial region is lower than the solidification point. This means that the whole interfacial region has gone through solidification already. As the time interval further increases, the temperature of the central area decreases continuously. The temperature of the central area is below 1400 • C while the time interval is 70 s. To further show the interfacial solidification process, the solid fraction in the interfacial region for different time intervals was also calculated, and the results are shown in Figure 8. The solid fraction of the central area in the interfacial region of all samples with a time interval below 40 s is lower than that of the edges. While the interval is higher than 40 s, the whole interfacial region is solidified. This is in accordance with the simulated temperature field results. Furthermore, the thickness of the solidified layer increases with the time interval. When the interval is up to 70 s, the thickness of the solidified layer increases to approximately 5 mm. Previous results [17,18] have indicated that the second casting should be performed at the moment that the interface of the first casting has just reached full solidification. So, the simulation results indicate that the optimum pouring time interval of these bimetallic hammerhead castings is 40 s.   the low alloy steel region, the interfacial region, and the high chromium cast iron region. The element diffusion would occur when the concentration difference exists between the two regions. Additionally, diffusion would become more obvious as the temperature and concentration difference increase. The contents of Cr, Mo, and C in HCCI are significantly higher than that in LAS, as Table 1 listed. Thus, these elements diffused from the HCCI side to LAS. However, the absolute content is low at 2.11 wt.% for Mo and 2.73 wt.% for C. In fact, the determination of the C content has low accuracy for ESD. Apart from Cr content, the concentration difference in the solvent element Fe between the two sides is also remarkable and can be easily detected. So, obvious changes in both the contents of Cr and Fe can be detected and shown. Observed drastic changes in elements of Fe, Cr and C in the HCCI side result from inhomogeneity and carbide precipitation. Element distribution results show the gradual changes in the content of elements, especially Fe and Cr, in the interfacial region. Therefore, the interfacial width of dual-liquid cast bimetals can be inferred by measuring the line distribution of alloy elements. Combining the EDS images and corresponding line distributions of alloy elements, the interfacial widths for different pouring time intervals can be obtained and are listed in Table 2. From the width results, it is obvious that the interfacial width decreases with an increasing pouring time interval. The maximum interfacial width is 136 µm for specimen S1, and the minimum interfacial width is 73 µm for S4. So, the interfacial width decreases with an increasing pouring time interval. The variation in the interfacial width obeys the diffusion laws. That is, the diffusion distance increases with temperature and time. Both the temperature of the first casting and the diffusion time decrease with an increasing pouring time interval. So, the diffusion distance, namely w_i here, decreases with an increasing pouring time interval. Similar results have also been shown in previous publications [12,17,18]. Based on four-point experimental w_i values in Table 2, the fitting relevant equation of interfacial width to pouring time intervals, w_i = f (∆t_p), is obtained through mathematical regression and is shown in Figure 10.
Materials 2023, 16, x FOR PEER REVIEW 6 of 15 Figure 9 shows the EDS images and line distributions of alloy elements in specimens for different pouring time intervals. EDS images show different regions for each specimen: the low alloy steel region, the interfacial region, and the high chromium cast iron region. The element diffusion would occur when the concentration difference exists between the two regions. Additionally, diffusion would become more obvious as the temperature and concentration difference increase. The contents of Cr, Mo, and C in HCCI are significantly higher than that in LAS, as Table 1 listed. Thus, these elements diffused from the HCCI side to LAS. However, the absolute content is low at 2.11 wt.% for Mo and 2.73 wt.% for C. In fact, the determination of the C content has low accuracy for ESD. Apart from Cr content, the concentration difference in the solvent element Fe between the two sides is also remarkable and can be easily detected. So, obvious changes in both the contents of Cr and Fe can be detected and shown. Observed drastic changes in elements of Fe, Cr and C in the HCCI side result from inhomogeneity and carbide precipitation. Element distribution results show the gradual changes in the content of elements, especially Fe and Cr, in the interfacial region. Therefore, the interfacial width of dual-liquid cast bimetals can be inferred by measuring the line distribution of alloy elements. Combining the EDS images and corresponding line distributions of alloy elements, the interfacial widths for different pouring time intervals can be obtained and are listed in Table 2. From the width results, it is obvious that the interfacial width decreases with an increasing pouring time interval. The maximum interfacial width is 136 μm for specimen S1, and the minimum interfacial width is 73 μm for S4. So, the interfacial width decreases with an increasing pouring time interval. The variation in the interfacial width obeys the diffusion laws. That is, the diffusion distance increases with temperature and time. Both the temperature of the first casting and the diffusion time decrease with an increasing pouring time interval. So, the diffusion distance, namely w_i here, decreases with an increasing pouring time interval. Similar results have also been shown in previous publications [12,17,18]. Based on four-point experimental w_i values in Table 2, the fitting relevant equation of interfacial width to pouring time intervals, w_i = f(∆t_p), is obtained through mathematical regression and is shown in Figure 10.   Shearing test results of bimetallic specimens produc intervals are shown in Figure 11. From the shearing stress the shearing strength, that can characterize the interfacia specimens can be determined. Thus, the interfacial bondin is, respectively, 697 MPa, 552 MPa, 400 MPa, and 329 MPa pendence on the interfacial bonding strength of the LAS mathematical regression based on values of interfacial b samples and results are shown in Figure 11b. The differen ing strength of different specimens is mainly because of th Previous publications [19−21] indicated that the interfaci depends on their interfacial width in a certain range. Acc 3.2.1, the interface width decreases with an increasing pou terfacial bonding strength decreases with an increasing p

Pouring Time Interval Dependence on Interfacial Bonding Strength
Shearing test results of bimetallic specimens produced using different pouring time intervals are shown in Figure 11. From the shearing stress vs. test time curves (Figure 11a), the shearing strength, that can characterize the interfacial bonding strength, of different specimens can be determined. Thus, the interfacial bonding strength of specimens S1 to S4 is, respectively, 697 MPa, 552 Mpa, 400 Mpa, and 329 Mpa. The pouring time interval dependence on the interfacial bonding strength of the LAS/HCCI bimetal is also fitted via mathematical regression based on values of interfacial bonding strength for those four samples and results are shown in Figure 11b. The difference between the interfacial bonding strength of different specimens is mainly because of the variation in interfacial width. Previous publications [19][20][21] indicated that the interfacial bonding strength of bimetals depends on their interfacial width in a certain range. According to the results of Section 3.2.1, the interface width decreases with an increasing pouring time interval. Thus, the interfacial bonding strength decreases with an increasing pouring time interval. Although the interfacial bonding strength increases with the decreasing pouring time interval, a too-short pouring time interval causes the excessive mixing between pairs of bimetals and unstable quality of bimetallic hammerheads, according to actual products and simulation solidification results (see Section 3.2.1). Thus, a pouring time interval of 40 s yields a high interfacial bonding strength, suitable mixing layer, and stable product quality.
To sum up, the bimetal produced by the process of a pouring time interval of 40 s has a suitable interfacial width, high interfacial bonding strength, and controllable mixing layer. Thus, the optimum pouring time interval is 40 s. To sum up, the bimetal produced by the process of a pouring time interval of 40 s has a suitable interfacial width, high interfacial bonding strength, and controllable mixing layer. Thus, the optimum pouring time interval is 40 s.

Effect of Interfacial Protective Agent on Interfacial Bonding Strength and Toughness
The typical shearing stress-time curves of the bimetallic and HCCI samples are shown in Figure 12. Where the S2 is the sign of the bimetallic specimen produced for the pouring time interval of 40 s with the addition of the interfacial protective agent, S2* is that without adding the interfacial protective agent. Both curves of S2 and HCCI have obvious yielding. However, the sample S2* fractured before yielding. The low yield shearing stress is about 455 MPa for S2, and 390 MPa for S2* and HCCI. There is a remarkable working hardening and plastic deformation in the curve of S2, but this is inapparent for S2* and HCCI. The maximum shearing stress is approximately 552 MPa for S2, and 444 MPa for HCCI. Thus, the bimetallic hammerhead casting with the addition of an interfacial protective agent has higher yield shearing stress, maximum shearing stress, and plastic deformation ability than both the bimetal without the added agent and HCCI. This means that the interfacial bonding strength is 552 MPa for S2 and 390 Mpa for S2*. An increase of approximately 41.5% in thse interfacial bonding strength is realized after adding the interfacial protective agent. The obvious increase in bonding strength for S2 originates from the cleaning effect and oxidation avoidance of the interfacial protective agent [22]. This interfacial bonding strength of 552 MPa for S2 is higher than 315 MPa for a hot diffusion compress bonded HCCI/LCS (low carbon steel) bimetal [5], but is similar to the surface liquid-phase sintered HCCI/LCS bimetal [23]. The key reasons should be the suitable interfacial width and clean interface without oxidation.

Effect of Interfacial Protective Agent on Interfacial Bonding Strength and Toughness
The typical shearing stress-time curves of the bimetallic and HCCI samples are shown in Figure 12. Where the S2 is the sign of the bimetallic specimen produced for the pouring time interval of 40 s with the addition of the interfacial protective agent, S2* is that without adding the interfacial protective agent. Both curves of S2 and HCCI have obvious yielding. However, the sample S2* fractured before yielding. The low yield shearing stress is about 455 MPa for S2, and 390 Mpa for S2* and HCCI. There is a remarkable working hardening and plastic deformation in the curve of S2, but this is inapparent for S2* and HCCI. The maximum shearing stress is approximately 552 Mpa for S2, and 444 Mpa for HCCI. Thus, the bimetallic hammerhead casting with the addition of an interfacial protective agent has higher yield shearing stress, maximum shearing stress, and plastic deformation ability than both the bimetal without the added agent and HCCI. This means that the interfacial bonding strength is 552 Mpa for S2 and 390 Mpa for S2*. An increase of approximately 41.5% in thse interfacial bonding strength is realized after adding the interfacial protective agent. The obvious increase in bonding strength for S2 originates from the cleaning effect and oxidation avoidance of the interfacial protective agent [22]. This interfacial bonding strength of 552 Mpa for S2 is higher than 315 Mpa for a hot diffusion compress bonded HCCI/LCS (low carbon steel) bimetal [5], but is similar to the surface liquid-phase sintered HCCI/LCS bimetal [23]. The key reasons should be the suitable interfacial width and clean interface without oxidation. To sum up, the bimetal produced by the process of a pouring time a suitable interfacial width, high interfacial bonding strength, and layer. Thus, the optimum pouring time interval is 40 s.

Effect of Interfacial Protective Agent on Interfacial Bonding Strength an
The typical shearing stress-time curves of the bimetallic and shown in Figure 12. Where the S2 is the sign of the bimetallic specime pouring time interval of 40 s with the addition of the interfacial pro that without adding the interfacial protective agent. Both curves of obvious yielding. However, the sample S2* fractured before yielding. T ing stress is about 455 MPa for S2, and 390 MPa for S2* and HCCI. Th working hardening and plastic deformation in the curve of S2, but th S2* and HCCI. The maximum shearing stress is approximately 552 M MPa for HCCI. Thus, the bimetallic hammerhead casting with the ad cial protective agent has higher yield shearing stress, maximum shear tic deformation ability than both the bimetal without the added age means that the interfacial bonding strength is 552 MPa for S2 and 3 increase of approximately 41.5% in thse interfacial bonding strength is ing the interfacial protective agent. The obvious increase in bonding s inates from the cleaning effect and oxidation avoidance of the interfac [22]. This interfacial bonding strength of 552 MPa for S2 is higher tha diffusion compress bonded HCCI/LCS (low carbon steel) bimetal [5], surface liquid-phase sintered HCCI/LCS bimetal [23]. The key reasons able interfacial width and clean interface without oxidation.  The impact toughness values of bimetallic and HCCI samples are listed in Table 3. The average toughness of S2* is 14.7 J/cm 2 . After adding the interfacial protective agent, the toughness of S2 is 17 J/cm 2 , an increase of approximately 15.6% to that of S2*. Thus, the addition of the interfacial protective agent can increase both interfacial bonding strength and toughness. The toughness of S2 is far higher than that of a reported LAS/HCCI bimetal (3.478 to 3.488 J/cm 2 ) that is prepared through liquid-solid casting and has a narrow interfacial region [24], and higher than 7.1 J/cm 2 of a LAS/HCCI bimetal prepared using the hot-rolling process as well [25]. The key reason for such high toughness of specimen S2 would be the suitable interface region and excellent interfacial bonding. This is also proved by the similar toughness (16.9 to 20.2 J/cm 2 ) of a carbon steel/HCCI bimetal prepared via the dual-liquid casting method [26]. For comparison, the impact results of HCCI cut from the same casting are also listed in Table 3. The toughness of S2 exceeds 3.5 times that of HCCI. The high toughness of S2 originates from the high toughness LAS and excellent interface. To summarize the abovementioned results, the process of a pouring time interval of 40 s and adding the interfacial protective agent is optimum for the production of LAS/HCCI bimetallic hammerheads.

Microstructure and Properties of the Bimetal Produced by the Optimum Process
The microstructural images of the specimen produced by the optimum process (S2) are shown in Figure 13. The microstructure image in Figure 13a also shows an evident interfacial region between the LAS and HCCI regions. Clearer than the EDS image, two different zones can be observed in the interfacial region. These are a fine white precipitation zone and a gray zone that is named a carbide-free zone [27]. Two similar interfacial zones were also reported in previous publications [4,28]. So, we measured the width of the carbide-free zone, the length of green lines, and the width of the whole interfacial region, the length of the red lines. Those green and red lines can be seen in Figure 13a. Hereafter, the markers w_g and w_r are used, respectively, for the widths of the carbide-free zone and the whole interfacial region. Both w_g and w_r, namely the length of the green lines and red lines in Figure 13a, are counted and shown in Figure 13b. The w_g varies from 44.5 µm to 53.9 µm, and the average w_g value is 49.5 µm. The measured w_r value varies from 87.8 µm to 103.2 µm, and the average value is 96.3 µm. The interfacial width from the microstructure image is in keeping with that from the EDS analysis listed in Table 2. The microstructures near the interface, of both the LAS and HCCI sides, are also shown, respectively, in Figure 13c,d. The typical microstructure of the LAS side is composed of ferrite plus pearlite, and the microstructure of the HCCI side comprises eutectic chromium carbide in the pearlite matrix. These microstructure features of the LAS/HCCI bimetal are similar to previous reports [4,14,27]. To further confirm the composition of the microstructure in the LAS/HCCI bimetal, the backscattered electron (BSD) image and element distributions of the eight elements, Fe, Cr, C, Si, Ni, Mn, and Mo, around the interface region are measured and are, respectively, shown in Figure 14a-i. The Fe content on the upper side of the EDS image is lower, but the Cr content is higher than that on the lower side. So, the upper side of the EDS image, which is the same as the upper side of Figure 13a, is the HCCI region. This comparison also shows that the dark area in Figure 13d is Cr and C rich, but Fe poor. So, this result can also prove that the dark area in Figure 13d is chromium carbide.
13d is Cr and C rich, but Fe poor. So, this result can also prove that the dark area in Figure  13d is chromium carbide.  13d is Cr and C rich, but Fe poor. So, this result can also prove that the dark area in Figure  13d is chromium carbide.  The hardness near the interface of specimen S2 was also tested. The hardness results and corresponding indentations are shown in Figure 15. The HCCI has a high hardness of about 1500 HV1. Additionally, the hardness of the LAS is approximately 500 HV1. Through the interface area, the hardness decreases gradually rather than plunges sharply. This phenomenon is very common in previous publications [14,[29][30][31]. The diffusion of elements Cr, C, and Mo from the HCCI side to LAS is the key reason for the decrement in the hardness. Element diffusion from HCCI to LAS increases the content of solute elements gradually in the interfacial region. The increased solute content can realize solid solution strengthening. Additionally, the increased solution content would induce carbide precipitation that can also enhance the hardness. Test Point 6, which is located in the interfacial region, shows a clear indentation. Previous works [32][33][34] indicated that the indentation of a hardness test can characterize the ductility of metals and alloys. The more and/or longer cracks appear, the worse the ductility of metals is. No cracks can be found around the corners of the indentation of Point 6, as Figure 15b shows. This means that the interfacial region of the cast hammerhead has good ductility. The hardness near the interface of specimen S2 was also tested. The hardness results and corresponding indentations are shown in Figure 15. The HCCI has a high hardness of about 1500 HV1. Additionally, the hardness of the LAS is approximately 500 HV1. Through the interface area, the hardness decreases gradually rather than plunges sharply. This phenomenon is very common in previous publications [14,[29][30][31]. The diffusion of elements Cr, C, and Mo from the HCCI side to LAS is the key reason for the decrement in the hardness. Element diffusion from HCCI to LAS increases the content of solute elements gradually in the interfacial region. The increased solute content can realize solid solution strengthening. Additionally, the increased solution content would induce carbide precipitation that can also enhance the hardness. Test Point 6, which is located in the interfacial region, shows a clear indentation. Previous works [32][33][34] indicated that the indentation of a hardness test can characterize the ductility of metals and alloys. The more and/or longer cracks appear, the worse the ductility of metals is. No cracks can be found around the corners of the indentation of Point 6, as Figure 15b shows. This means that the interfacial region of the cast hammerhead has good ductility. The bending force-time curves of the bimetal and HCCI are shown in Figure 16. The maximum bending force is 19.78 kN for the bimetal and 16.11 kN for HCCI. That is, the bending strength is 1188 MPa for the bimetal and 972 MPa for HCCI. The high bending strength may be because of the energy consumption and working hardening of the LAS. The bending strength of bimetallic samples in this work is far higher than that of high-Cr white cast iron and AISI4140 steel bimetallic beams (650 to 790 MPa) [35]. The fracture behavior between the bimetal and HCCI samples is also different from each other. The The bending force-time curves of the bimetal and HCCI are shown in Figure 16. The maximum bending force is 19.78 kN for the bimetal and 16.11 kN for HCCI. That is, the bending strength is 1188 MPa for the bimetal and 972 Mpa for HCCI. The high bending strength may be because of the energy consumption and working hardening of the LAS. The bending strength of bimetallic samples in this work is far higher than that of high-Cr white cast iron and AISI4140 steel bimetallic beams (650 to 790 Mpa) [35]. The fracture behavior between the bimetal and HCCI samples is also different from each other. The HCCI breaks immediately after the maximum force. However, a second increase in bending force is needed before fracturing the bimetal. This also proves that the fracture of the bimetal needs more external energy than HCCI. HCCI breaks immediately after the maximum force. However, a second increase in bend ing force is needed before fracturing the bimetal. This also proves that the fracture of the bimetal needs more external energy than HCCI. The tensile stress vs. the time curve of the bimetal from a hammerhead casting is shown in Figure 17a. The maximum tensile stress of this curve is about 515 MPa. This value is higher than 397 MPa of the high vanadium alloy steel/low carbon steel bimeta [28]. The elevated strength should result from the different raw materials and interfacia bonding strength. The photo of a typical fractured sample is also shown in Figure 17b The interface of the LAS/HCCI bimetal is nearly in the middle of the sample. However the fracture occurs on the right side, namely the HCCI side. This phenomenon proves tha the bonding strength of the bimetal is excellent and even higher than the HCCI. This frac ture phenomenon was also shown in a previous publication [28]. In brief, the bimetallic hammerhead produced by the optimum dual-liquid casting process is as follows: a pouring time interval of 40 s with the addition of an interfacia protective agent has a suitable interfacial width of approximately 96.3 μm, excellent bond ing strength, and good whole strength-toughness.

Conclusions
The effects of the pouring time interval and the interfacial protective agent of the dual-liquid casting process on the interfacial properties of the LAS/HCCI bimetal are stud ied through theoretical simulation and experiment. The microstructure and properties o The tensile stress vs. the time curve of the bimetal from a hammerhead casting is shown in Figure 17a. The maximum tensile stress of this curve is about 515 Mpa. This value is higher than 397 Mpa of the high vanadium alloy steel/low carbon steel bimetal [28]. The elevated strength should result from the different raw materials and interfacial bonding strength. The photo of a typical fractured sample is also shown in Figure 17b. The interface of the LAS/HCCI bimetal is nearly in the middle of the sample. However, the fracture occurs on the right side, namely the HCCI side. This phenomenon proves that the bonding strength of the bimetal is excellent and even higher than the HCCI. This fracture phenomenon was also shown in a previous publication [28]. HCCI breaks immediately after the maximum force. However, a second increase in bending force is needed before fracturing the bimetal. This also proves that the fracture of the bimetal needs more external energy than HCCI. The tensile stress vs. the time curve of the bimetal from a hammerhead casting is shown in Figure 17a. The maximum tensile stress of this curve is about 515 MPa. This value is higher than 397 MPa of the high vanadium alloy steel/low carbon steel bimetal [28]. The elevated strength should result from the different raw materials and interfacial bonding strength. The photo of a typical fractured sample is also shown in Figure 17b. The interface of the LAS/HCCI bimetal is nearly in the middle of the sample. However, the fracture occurs on the right side, namely the HCCI side. This phenomenon proves that the bonding strength of the bimetal is excellent and even higher than the HCCI. This fracture phenomenon was also shown in a previous publication [28]. In brief, the bimetallic hammerhead produced by the optimum dual-liquid casting process is as follows: a pouring time interval of 40 s with the addition of an interfacial protective agent has a suitable interfacial width of approximately 96.3 μm, excellent bonding strength, and good whole strength-toughness.

Conclusions
The effects of the pouring time interval and the interfacial protective agent of the dual-liquid casting process on the interfacial properties of the LAS/HCCI bimetal are studied through theoretical simulation and experiment. The microstructure and properties of In brief, the bimetallic hammerhead produced by the optimum dual-liquid casting process is as follows: a pouring time interval of 40 s with the addition of an interfacial protective agent has a suitable interfacial width of approximately 96.3 µm, excellent bonding strength, and good whole strength-toughness.

Conclusions
The effects of the pouring time interval and the interfacial protective agent of the dualliquid casting process on the interfacial properties of the LAS/HCCI bimetal are studied through theoretical simulation and experiment. The microstructure and properties of bimetallic wear-resistant hammerheads produced using the optimized dual-liquid casting process are also systematically investigated. The main conclusions are as follows.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.