A method for calibrating rare earth inclusions in a high-temperature laser confocal experiment of a rare earth microalloyed steel

Abstract

The application discloses a method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel, which comprises the following steps: (1) preparing and cutting a rare earth microalloyed steel plate to obtain a cylindrical sample, and pre-treating the sample to obtain an experimental steel sample; (2) dividing the surface to be observed of the experimental steel sample into n regions and marking the regions; (3) placing the marked experimental steel sample under a scanning electron microscope to observe inclusions; determining the region where a target rare earth inclusion is located and determining the coordinates of the target rare earth inclusion according to the mark; and (4) placing the experimental steel sample in a high-temperature laser confocal scanning laser microscope, finding the target rare earth inclusion according to the coordinates, starting a heating-cooling program to melt the experimental steel sample, and completing in-situ observation of the target rare earth inclusion. The application can solve the problem that existing inclusion observation methods cannot guarantee that the original inclusions and changes thereof are observed in high-temperature confocal experiments.

Description

Technical Field

[0001] This invention relates to the field of alloy steel inclusion calibration technology. Specifically, it is a method for calibrating rare earth inclusions in high-temperature laser confocal experiments on rare earth microalloyed steel. Background Technology

[0002] High-temperature confocal scanning laser microscopy (CSLM) is widely used for observing inclusions and phase transformations in steel. CSLM observation can effectively observe changes on the sample surface at high temperatures, providing valuable insights for observing the formation of inclusions in molten steel and the precipitation of inclusions during solidification. The conventional practice for CSLM observation of inclusions in alloy steel is as follows: locate inclusions with similar morphology and size under the high-temperature laser confocal microscope for observation, or observe inclusions that float on the surface of the melted sample under the high-temperature laser confocal microscope, using these inclusions as observation points for subsequent in-situ observation experiments.

[0003] However, this observation method has the following drawbacks: the inclusions found directly under high-temperature confocal microscopy cannot be determined to be the type of inclusions to be observed, or the inclusions to be observed may actually be contaminated impurities, causing the inclusions / impurities floating on the sample surface to disappear or change after being heated to melt. Therefore, they cannot be used as data on the changes in rare earth inclusions during the heating and cooling process of high-temperature laser confocal microscopy experiments.

[0004] Therefore, existing methods for observing inclusions cannot guarantee that the original inclusions and their changes can be easily observed during high-temperature confocal experiments, and improvements are needed to the existing methods for observing inclusions in alloy steel. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel, so as to solve the problem that existing inclusion observation methods cannot guarantee that the original inclusions and their changes can be easily observed during high-temperature confocal experiments, making in-situ observation of inclusions in alloy steel more convenient, simple to operate, and highly feasible.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for calibrating rare earth inclusions in high-temperature laser confocal experiments on rare earth microalloyed steel includes the following steps:

[0008] Step (1): Prepare rare earth microalloyed steel plates, cut and prepare experimental steel samples from the rare earth microalloyed steel plates;

[0009] Step (2): Divide the surface of the experimental steel sample into n regions, where n is greater than or equal to 4; mark each of the n regions differently.

[0010] Step (3): Place the marked experimental steel sample under a scanning electron microscope for observation. When the target rare earth inclusion is observed, determine the area where the target rare earth inclusion is located based on the marking, and use the scale function of the scanning electron microscope to determine the coordinates of the target rare earth inclusion.

[0011] Step (4): Place the experimental steel sample in a high-temperature laser confocal scanning laser microscope and locate the target rare earth inclusions according to the determined coordinates; start the heating-cooling program to melt the experimental steel sample and complete the in-situ observation of the target rare earth inclusions.

[0012] The above method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel, in step (1): the preparation method of the rare earth microalloyed steel plate is as follows:

[0013] Step (1-1): Prepare alloy raw materials according to the chemical composition content of rare earth microalloyed steel plates;

[0014] Steps (1-2): Place the alloy raw materials in a melting furnace to melt and cast them into steel ingots;

[0015] Steps (1-3): The steel ingots are subjected to heat treatment and descaling treatment in sequence;

[0016] Steps (1-4): The descaled steel ingot is rolled in a two-stage controlled process. After the rolling process is completed, rare earth microalloyed steel plate is obtained.

[0017] In the above method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel, step (1-1) involves the following: the rare earth microalloyed steel plate is a Q370qNHE steel plate containing rare earth elements; in the Q370qNHE steel plate, the carbon content is 0.06-0.08wt%, the silicon content is 0.15-0.18wt%, the manganese content is 1.0-1.2wt%, the phosphorus content is 0.010-0.015wt%, the sulfur content is less than or equal to 0.002wt%, the aluminum content is 0.03-0.04wt%, the chromium content is 0.5-0.6wt%, the copper content is 0.3-0.4wt%, the niobium content is 0.03-0.04wt%, the nickel content is 0.3-0.4wt%, and the rare earth element content is 0.004-0.005wt%.

[0018] In steps (1-2): the alloy raw materials are melted at 1520-1600℃ for 20-40 minutes; after melting, they are refined in a converter, and the refined alloy liquid is cast into shape at 1540-1570℃.

[0019] In steps (1-3): the heating treatment method is to heat to 1200-1250℃ at a heating rate of 10-15℃ / min and hold for 2-3 hours; the descaling treatment method is to use high-pressure water to descale, with a water pressure of 20-25MPa.

[0020] In steps (1-4): the two-stage controlled rolling includes a roughing stage and a finishing stage; the initial rolling temperature of the roughing stage is 1180-1200℃, the total rolling reduction rate is 70-80%, the number of rolling passes is 3-4, and the reduction per pass is controlled within the range of 30-40mm; the initial rolling temperature of the finishing stage is 890-910℃, the final rolling temperature is 815-835℃, the total rolling reduction rate is 50-70%, the number of rolling passes is 5-6, and the reduction per pass is controlled within the range of 5-6mm; after finishing rolling, the temperature is cooled to 550-580℃ at a cooling rate of 9-11℃ / s, and then naturally cooled to room temperature.

[0021] The above method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel includes step (1): a section perpendicular to the rolling direction is selected from the rare earth microalloyed steel plate, and a cylindrical sample with a diameter of 5 mm and a height of 4 mm is obtained by wire cutting, and the cylindrical sample is pretreated.

[0022] The pretreatment method for cylindrical samples is as follows: first grinding and then polishing. The grinding method is to use 200-2000 grit metallographic sandpaper to grind the surface until the surface roughness is 0.3-0.6μm. The polishing method is to use 2.5μm diamond suspension on a velvet polishing cloth to polish the surface to be observed until the surface roughness is 0.05-0.10μm, and then clean it in an ultrasonic cleaner and blow it dry.

[0023] In the above method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel, step (2) involves: using a blade to draw the XY coordinate axis on the surface to be observed of the experimental steel sample, dividing the surface to be observed into 4 regions, which are then labeled as region A, region B, region C and region D in clockwise order; when marking, regions A and C are marked by dot marking, while regions B and D are marked by short lines.

[0024] The above method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel includes the following steps (3): When the target rare earth inclusion is observed, record the magnification of the observed target rare earth inclusion. Then, use the scale function of the scanning electron microscope to make a scale from the position of the target rare earth inclusion perpendicular to the foot of the X-axis and Y-axis, and make a scale from the foot of the vertical to the origin of the XY coordinate axis. Record the distances shown by the scales from the target inclusion to the foot of the vertical and from the foot of the vertical to the origin, thereby determining the coordinates of the target rare earth inclusion.

[0025] The above method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel, in step (4): the heating-cooling procedure is as follows: first, heat up to 200-300℃ at a heating rate of 30-50℃ / min, then heat up to 700-750℃ at a heating rate of 250-300℃ / min, then heat up to 1200-1300℃ at a heating rate of 15-25℃ / min, then heat up to 1600-1650℃ at a heating rate of 100-150℃ / min and hold for 5-7min, then cool down to 1200-1300℃ at a cooling rate of 15-20℃ / min, and finally cool down to 20-30℃ at a cooling rate of 25-30℃ / min.

[0026] In this invention, during high-temperature laser confocal experiments, a lower heating rate (30-50℃ / min) is first used to raise the temperature from room temperature to 200-300℃, followed by a higher heating rate (250-300℃ / min) to 700-750℃. This avoids sample deformation caused by internal stress during heating, facilitating the tracking and observation of target rare earth inclusions and reducing the impact of sample deformation on the upward path of the inclusions. When heating from 700-750℃ to 1200-1300℃, a smaller heating rate of 15-25℃ / min is used to ensure sufficient time for direct observation of the morphological changes of the target rare earth inclusions during heating and their impact on the growth mechanism of the original austenite grains. This avoids excessively rapid heating causing sample deformation and deviation of the target rare earth inclusions' position. The heating rate from 1200-1300℃ to 1600℃ is further controlled. At 1650℃, a relatively high heating rate of 100-150℃ / min can quickly raise the temperature and effectively shorten the observation time. Since the previous stage has basically completed the observation of rare earth inclusions in Q370qNHE steel containing rare earth, the purpose of this stage is mainly to fully melt the sample at 1600-1650℃ to facilitate subsequent observation of the changes of rare earth inclusions during the solidification process of the molten steel. Then, cooling to 1200-1300℃ at a smaller cooling rate of 15-20℃ / min allows observation of the changes of inclusions from the solidification of the molten steel into an ingot and at the initial rolling temperature. If the cooling rate is too fast in this stage, the behavior of the inclusions will deviate significantly from the actual processing and production. Finally, cooling to 20℃ at a larger cooling rate of 25℃ / min allows observation of the changes of inclusions throughout the casting process and the influence mechanism of inclusions on the microstructure transformation and recrystallization grain nucleation during the cooling process. The present invention employs the aforementioned heating-cooling process, which enables accurate observation of the details of inclusion changes in Q370qNHE steel plates containing rare earth elements at each production stage.

[0027] The above method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel, in step (4): the heating-cooling procedure is as follows: first, the temperature is raised to 200℃ at a heating rate of 50℃ / min, then raised to 700℃ at a heating rate of 300℃ / min, then raised to 1200℃ at a heating rate of 15℃ / min, then raised to 1600℃ at a heating rate of 100℃ / min and held for 5min, then cooled to 1200℃ at a cooling rate of 15℃ / min, and finally cooled to 20℃ at a cooling rate of 25℃ / min.

[0028] In the above method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel, step (4) involves: during the entire high-temperature laser confocal experiment, argon gas is introduced into the heating chamber of the high-temperature laser confocal scanning laser microscope for protection, and the purity of the argon gas is greater than or equal to 99.99%.

[0029] The above method for calibrating rare earth inclusions in high-temperature laser confocal experiments of rare earth microalloyed steel, in step (1): the preparation method of the rare earth microalloyed steel plate is as follows:

[0030] Step (1-1): Prepare alloy raw materials according to the chemical composition of the rare earth microalloyed steel plate; the rare earth microalloyed steel plate is a Q370qNHE steel plate containing rare earth elements; in the Q370qNHE steel plate, the content of carbon is 0.065wt%, the content of silicon is 0.152wt%, the content of manganese is 1.04wt%, the content of phosphorus is 0.0111wt%, the content of sulfur is less than or equal to 0.002wt%, the content of aluminum is 0.039wt%, the content of chromium is 0.534wt%, the content of copper is 0.323wt%, the content of niobium is 0.037wt%, the content of nickel is 0.318wt%, and the content of cerium is 0.0049wt%.

[0031] Steps (1-2): Place the alloy raw material in a melting furnace and melt it at 1600℃ for 30 minutes. After melting, refine it in a converter. Cast the refined alloy liquid at 1570℃ to obtain steel ingots.

[0032] Steps (1-3): The steel ingot is subjected to heat treatment and descaling treatment in sequence; the heat treatment method is to heat to 1250℃ at a heating rate of 15℃ / min and hold for 2 hours; the descaling treatment method is to use high-pressure water descaling at a water pressure of 22MPa.

[0033] Steps (1-4): The descaled steel ingot is subjected to two-stage controlled rolling. After the rolling process is completed, rare earth microalloyed steel plate is obtained. The initial rolling temperature of the rough rolling stage is 1200℃, the total rolling reduction rate is 80%, and the rolling passes are 4, with the reduction per pass controlled within the range of 30-40mm. The initial rolling temperature of the finish rolling stage is 900℃, the final rolling temperature is 825℃, the total rolling reduction rate is 60%, and the rolling passes are 5, with the reduction per pass controlled within the range of 5-6mm. After the finish rolling is completed, the ingot is cooled to 550℃ at a cooling rate of 10℃ / s, and then allowed to cool naturally to room temperature.

[0034] A cylindrical sample with a diameter of 5 mm and a height of 4 mm was obtained by wire cutting a section perpendicular to the rolling direction from a rare earth microalloyed steel plate.

[0035] The pretreatment method for cylindrical specimens is as follows: first grinding and then polishing. The grinding method is as follows: use 200-2000 grit metallographic sandpaper to grind until the surface roughness is 0.6 μm. The polishing method is as follows: use 2.5 μm diamond suspension on a velvet polishing cloth to polish the surface to be observed until the surface roughness is 0.1 μm. Then clean it in an ultrasonic cleaner and blow it dry.

[0036] In step (2): Use a blade to draw the XY coordinate axis on the surface of the experimental steel sample to be observed. The XY coordinate axis divides the surface to be observed into 4 regions. The 4 regions are marked as region A, region B, region C and region D in clockwise order. When marking, region A and region C are marked by dot marking, and region B and region D are marked by short lines.

[0037] In step (3): When the target rare earth inclusion is observed, record the magnification of the observed target rare earth inclusion. Then, use the scale function of the scanning electron microscope to make a scale from the position of the target rare earth inclusion perpendicular to the foot of the X-axis and Y-axis. Make a scale from the foot of the perpendicular to the origin of the XY coordinate axis. Record the distances shown by the scale from the target inclusion to the foot of the perpendicular and from the foot of the perpendicular to the origin, respectively, so as to determine the coordinates of the target rare earth inclusion.

[0038] In step (4), the heating-cooling procedure is as follows: first, the temperature is increased to 200℃ at a heating rate of 50℃ / min, then increased to 700℃ at a heating rate of 300℃ / min, then increased to 1200℃ at a heating rate of 15℃ / min, then increased to 1600℃ at a heating rate of 100℃ / min and held for 5 min, then decreased to 1200℃ at a cooling rate of 15℃ / min, and finally decreased to 20℃ at a cooling rate of 25℃ / min. During the entire high-temperature laser confocal experiment, argon gas is introduced into the heating cavity of the high-temperature laser confocal scanning laser microscope for protection. The purity of the pure argon gas is greater than or equal to 99.99%.

[0039] The technical solution of the present invention achieves the following beneficial technical effects:

[0040] 1. The present invention provides a method for calibrating rare earth inclusions in high-temperature laser confocal microscopy experiments of rare earth microalloyed steel. By dividing the surface of the experimental steel sample of the rare earth microalloyed steel plate into coordinate partitions, the approximate location of the target rare earth inclusion is initially determined. Then, the scale function of the scanning electron microscope is used to lock the precise location of the target rare earth inclusion, providing a basis for rapid calibration of the target rare earth inclusion in subsequent high-temperature laser confocal microscopy experiments. This makes in-situ observation of the target rare earth inclusion more convenient, simple to operate, and highly feasible.

[0041] 2. This invention innovatively designs the heating and cooling procedures in the high-temperature laser confocal experiment of rare earth microalloyed steel, which enables the in-situ observation of the target rare earth inclusions in the high-temperature laser confocal experiment to more accurately reproduce the actual evolution process of the inclusions in the steel matrix, thereby obtaining observation results that are more consistent with the actual state of the inclusions in the steel matrix. Attached Figure Description

[0042] Figure 1 Distribution and morphology of inclusions in experimental steel #1 in this embodiment of the invention;

[0043] Figure 2 Energy dispersive spectroscopy (EDS) analysis diagram of inclusions in experimental steel #1 in this embodiment of the invention;

[0044] Figure 3 Distribution and morphology of inclusions in experimental steel #2 in this embodiment of the invention;

[0045] Figure 4 Energy dispersive spectroscopy (EDS) analysis diagram of inclusions in experimental steel #2 in this embodiment of the invention;

[0046] Figure 5 A diagram illustrating the austenitizing process of experimental steel #1 in this embodiment of the invention;

[0047] Figure 6 A diagram illustrating the austenitizing process of experimental steel #2 in this embodiment of the invention;

[0048] Figure 7 A diagram illustrating the evolution of the phenomenon of inclusions hindering grain growth in experimental steel #1 of this invention.

[0049] Figure 8 Schematic diagram of the evolution process of inclusions hindering grain growth in experimental steel #2 in this embodiment of the invention;

[0050] Figure 9 A diagram illustrating the inclusion precipitation process during the solidification of experimental steel #1 in this embodiment of the invention;

[0051] Figure 10 A diagram illustrating the inclusion precipitation process during the solidification of experimental steel #2 in this embodiment of the invention;

[0052] Figure 11 A diagram showing the changes in inclusions during the subsequent cooling process of experimental steel #1 under CSLM in this embodiment of the invention;

[0053] Figure 12 A diagram showing the changes in inclusions in experimental steel #2 under CSLM during the subsequent cooling process in this embodiment of the invention.

[0054] Figure 13 Distribution and morphology of marked inclusions in experimental steel #1 in this embodiment of the invention;

[0055] Figure 14 Energy dispersive spectroscopy (EDS) analysis of inclusions marked on experimental steel #1 in this embodiment of the invention;

[0056] Figure 15 Distribution and morphology of marked inclusions in experimental steel #2 in this embodiment of the invention;

[0057] Figure 16 Energy dispersive spectroscopy (EDS) analysis of inclusions marked on experimental steel #2 in this embodiment of the invention. Detailed Implementation

[0058] 1. A method for calibrating rare earth inclusions in high-temperature laser confocal experiments on rare earth microalloyed steel.

[0059] The method for rare earth inclusion calibration in high-temperature laser confocal experiments on rare earth microalloyed steel, as described in this embodiment, includes the following steps:

[0060] Step (1): Prepare rare earth microalloyed steel plate, cut cylindrical samples from the rare earth microalloyed steel plate, and pretreat the cylindrical samples to obtain experimental steel samples; the rare earth microalloyed steel plate prepared in this embodiment is Q370qNHE steel plate containing rare earth elements, and the preparation method of the rare earth microalloyed steel plate is as follows:

[0061] Step (1-1): Prepare alloy raw materials according to the chemical composition of rare earth microalloyed steel plates; in rare earth microalloyed steel plates, the content of carbon is 0.065wt%, the content of silicon is 0.152wt%, the content of manganese is 1.04wt%, the content of phosphorus is 0.0111wt%, the content of sulfur is less than or equal to 0.002wt%, the content of aluminum is 0.039wt%, the content of chromium is 0.534wt%, the content of copper is 0.323wt%, the content of niobium is 0.037wt%, the content of nickel is 0.318wt%, and the content of cerium is 0.0049wt%.

[0062] Steps (1-2): Place the alloy raw material in a melting furnace and melt it at 1600℃ for 30 minutes. After melting, refine it in a converter. Cast the refined alloy liquid at 1570℃ to obtain steel ingots.

[0063] Steps (1-3): The steel ingot is subjected to heat treatment and descaling treatment in sequence; the heat treatment method is to heat to 1250℃ at a heating rate of 15℃ / min and hold for 2 hours; the descaling treatment method is to use high-pressure water descaling at a water pressure of 22MPa.

[0064] Steps (1-4): The descaled steel ingot is subjected to two-stage controlled rolling. After the rolling process is completed, rare earth microalloyed steel plate is obtained. The initial rolling temperature of the rough rolling stage is 1200℃, the total rolling reduction rate is 80%, and the rolling passes are 4, with the reduction per pass controlled within the range of 30-40mm. The initial rolling temperature of the finish rolling stage is 900℃, the final rolling temperature is 825℃, the total rolling reduction rate is 60%, and the rolling passes are 5, with the reduction per pass controlled within the range of 5-6mm. After the finish rolling is completed, the ingot is cooled to 550℃ at a cooling rate of 10℃ / s, and then allowed to cool naturally to room temperature.

[0065] A section perpendicular to the rolling direction was selected from a rare-earth microalloyed steel plate, and a cylindrical sample with a diameter of 5 mm and a height of 4 mm was obtained by wire cutting. The pretreatment method of the cylindrical sample was: first grinding and then polishing. The grinding method was: grinding with 200-2000 grit metallographic sandpaper until the surface roughness was 0.6 μm. The polishing method was: polishing the surface to be observed with 2.5 μm diamond suspension on a velvet polishing cloth until the surface roughness was 0.1 μm, and then cleaning in an ultrasonic cleaner and drying.

[0066] Step (2): Divide the surface of the experimental steel sample into n regions and mark each of the n regions differently, where n is greater than or equal to 4. In this embodiment, use a blade to draw the XY coordinate axis on the surface of the experimental steel sample. The XY coordinate axis divides the surface into 4 regions, which are then labeled as region A, region B, region C, and region D in clockwise order. When marking, regions A and C are marked with dots, while regions B and D are marked with short lines.

[0067] Step (3): Place the marked experimental steel sample under a scanning electron microscope to observe the inclusions on the surface to be observed; when the target rare earth inclusion is observed, determine the area where the target rare earth inclusion is located according to the marking, and use the scale function of the scanning electron microscope to determine and record the coordinates of the target rare earth inclusion;

[0068] When observing the target rare earth inclusions, record the magnification of the observed rare earth inclusions. Then, use the scale function of the scanning electron microscope to draw a scale from the position of the target rare earth inclusions perpendicular to the foot of the X and Y axes, and draw a scale from the foot of the perpendicular to the origin of the X and Y coordinate axes. Record the distances shown by the scales from the target inclusions to the foot of the perpendicular and from the foot of the perpendicular to the origin, respectively, so as to determine the coordinates of the target rare earth inclusions.

[0069] Step (4): Place the experimental steel sample in a high-temperature laser confocal scanning laser microscope and locate the target rare earth inclusions according to the recorded coordinates; start the heating-cooling program to melt the experimental steel sample and complete the in-situ observation of the target rare earth inclusions.

[0070] The heating-cooling procedure in this embodiment is as follows: first, the temperature is increased to 200°C at a heating rate of 50°C / min; then, it is increased to 700°C at a heating rate of 300°C / min; next, it is increased to 1200°C at a heating rate of 15°C / min; then, it is increased to 1600°C at a heating rate of 100°C / min and held for 5 minutes; then, it is cooled to 1200°C at a cooling rate of 15°C / min; and finally, it is cooled to 20°C at a cooling rate of 25°C / min. Throughout the high-temperature laser confocal experiment, argon gas is introduced into the heating chamber of the high-temperature laser confocal scanning laser microscope for protection; the purity of the pure argon gas is greater than or equal to 99.99%.

[0071] This embodiment uses high-temperature laser confocal microscopy to conduct experiments on the experimental steel sample of Q370qNHE steel plate (2#) containing rare earth elements, and uses the same method to conduct high-temperature laser confocal microscopy experiments on Q370qNHE steel plate (1#) without rare earth elements as a control; the experimental results are analyzed as follows.

[0072] 2. Experimental Results

[0073] 2.1 Morphology and energy dispersive spectroscopy analysis of inclusions on the surface of the test samples to be observed in situ.

[0074] from Figures 1 to 2 ,as well as Figures 3 to 4It can be seen that the inclusions in experimental steel #2, with the addition of Ce, were modified into spherical or ellipsoidal shapes. Compared with the inclusions (MnS / Al2O3) in experimental steel #1, the Ce-modified inclusions exhibited improved mechanical properties. Irregular Al2O3 inclusions and elongated MnS inclusions have significant differences in hardness and plasticity compared to the steel matrix, leading to greater stress concentration under stress. This can cause gaps and microcracks at the interface between the inclusions and the steel matrix. In subsequent rolling, the significant difference in the coefficient of thermal expansion between the MnS / Al2O3 inclusions and the steel matrix disrupts the continuity of the steel matrix, resulting in a decrease in the mechanical properties of the experimental steel. The Ce-OS / Ce-Al-O (Mn / Ti-O) inclusions formed after the addition of Ce have mechanical properties and coefficients of thermal expansion similar to the steel matrix. The spherical or ellipsoidal inclusions are also less prone to stress concentration under stress, thus improving the mechanical properties of the experimental steel.

[0075] 2.2 CSLM in-situ observation experiment

[0076] Using the inclusions of the two types of test steel observed under a scanning electron microscope as the observation origin under CSLM, such as... Figure 5 , Figure 6 The austenitization process in two experimental steels was demonstrated from start to finish. Compared to experimental steel #1, experimental steel #2, with the addition of Ce, showed a 24.3℃ decrease in the Ac1 phase transformation temperature and a 13.2℃ increase in the Ac3 phase transformation temperature. The chemically active nature of Ce resulted in a uniform distribution of inclusions in the steel. Using rare earth inclusions as nucleation sites reduces the energy required for critical austenite nucleation, thus lowering the Ac1 phase transformation temperature of experimental steel #2. Simultaneously, rare earth elements inhibit the diffusion of carbon within austenite. Figure 6 In (b), carbon precipitation on the surface of the experimental steel forms a nanoscale carbon film, which, combined with the surface enrichment of Ce and the reaction of trace impurities, leads to darkening in optical observation. The transformation of the steel matrix to austenite requires more phase transformation activation energy, resulting in a lower austenitization rate and thus an increased Ac3 phase transformation temperature for experimental steel #2. The addition of Ce increases the austenite nucleation rate in the experimental steel and reduces the driving force for austenite growth, hindering austenite grain growth. This reduces the initial austenite grain size in experimental steel #2, improving the overall mechanical properties of the steel matrix.

[0077] The effect of inclusions in two types of test steels on hindering grain growth was observed under CSLM, such as... Figure 7 , Figure 8 As shown in the figure, it is clear that the inclusions in both experimental steels played a role in hindering grain growth, which helps to prevent further grain growth during actual heat treatment. However, from... Figure 7As can be seen from (ac), inclusions A2, A3, and A4 have a negligible effect on hindering grain growth in the steel matrix at temperatures above 1088.6℃. However, for inclusions in experimental steel #2, inclusions B2 and B3 have a significant effect on hindering grain boundary movement. This indirectly suggests that the addition of Ce element helps to hinder grain growth in actual production.

[0078] Figure 9 and Figure 10 The solidification temperatures and inclusion changes during solidification of two experimental steels are presented. For experimental steel #1, due to the high precipitation temperature, only a small number of Al2O3 inclusions exist on the steel surface as nucleation sites before solidification, resulting in a lower solidification temperature. In contrast, for experimental steel #2, the addition of Ce led to a large number of Ce-OS slag particles on the surface of the molten steel acting as nucleation sites, increasing the solidification temperature by 23.1℃ compared to #1. During solidification, solute elements (S, O) are discharged into the liquid phase due to their partition coefficient K < 1. This causes solute elements like S and O to concentrate in the dendrite interstices. In the later stages of solidification, when the concentration product of solute elements such as S and O in the dendrite interstices exceeds the solubility product, S combines with alloying elements such as Mn to form chain-like or granular MnS and other impurities that precipitate out. Specifically, as shown... Figure 9 As shown in (h) and (i), this is consistent with the characteristic of MnS inclusions precipitating in molten steel at approximately 1400℃. Due to the presence of numerous nucleation particles, the number of nucleated grains in test steel #2 is significantly increased. The large number of rare earth inclusions in the matrix hinders subsequent grain boundary movement and impedes grain growth. Figure 10 As shown in (g)~(i). This indicates that the addition of Ce can refine the austenite grain size in the subsequent rolling process, thereby improving the overall performance of the experimental steel.

[0079] The marked inclusions in the two groups of experimental steels were observed during the subsequent cooling process, such as... Figure 11 and Figure 12 As shown, the inclusions that precipitated later in experimental steel #1 were dispersed near the grain boundaries. This is because S and O were enriched in the interdendritic spaces during the final stage of solidification or solid-state cooling, and thus precipitated later at the grain boundaries where the dendrites grew. In experimental steel #2, the Ce element added combined with S, O and other elements to form high-melting-point rare earth oxysulfides, purifying the molten steel. No dispersed inclusions precipitated during the subsequent solidification process, and the grain boundaries were cleaner than those in experimental steel #1, with finer grain sizes.

[0080] 2.3 Results of inclusion analysis of CSLM-labeled samples

[0081] The morphology and elemental distribution of the marked inclusions in the two groups of experimental steels were analyzed by SEM-EDS, and the results are as follows: Figure 13 and Figure 14 ,as well as Figure 15and Figure 16 As shown, the first image in the SEM-EDS analysis results is an EDS layered image, demonstrating the segregation of various elements in the actual inclusions. The results indicate that due to the addition of Ce, the S and O elements in test steel #2 react with Ce to form rare earth oxysulfides. Compared to test steel #1, the inclusion morphology in #2 is more regular, and no NbN inclusions are present. The presence of NbN inclusions at the grain boundaries in test steel #1 indicates the segregation of N elements at the grain boundaries. In contrast, the addition of Ce reduces the degree of N element segregation at the grain boundaries in test steel #2.

[0082] Analysis revealed that the main inclusions in the two experimental steels were MnS, Al2O3, CeS, Ce3S4, Ce2O2S, and CeAlO3. Comparison of the elastic moduli of the inclusions and the steel matrix showed that the elastic moduli of Al2O3 and CeAlO3 were significantly higher than those of the Fe matrix. Under external force, these two inclusions did not deform synchronously with the steel matrix, leading to stress concentration between the matrix and the inclusions. This resulted in the formation of microcracks in the steel matrix under stress, leading to decreased toughness and increased brittleness. Inclusions such as Ce2O3, Ce2O2S, CeS, and Ce3S4 had lower elastic moduli than the steel matrix. These inclusions deformed preferentially under stress compared to the matrix, which could alleviate stress concentration to some extent and positively impact the material's toughness.

[0083] The presence of inclusions affects the toughness of steel. Rare earth inclusions Ce3S4 and Ce2O2S exhibit toughness, while Ce2O3 and CeS show slight brittleness. In contrast, Al2O3, MnS, and CeAlO3 inclusions exhibit significant brittleness. This indicates that in practical engineering applications, inclusions such as Al2O3, MnS, and CeAlO3 have weak bonding with the steel matrix and are prone to forming crack initiation sites. When cracks propagate to these inclusions, their inherent brittleness may prevent them from effectively inhibiting crack propagation, thus reducing the mechanical properties of the material.

[0084] Furthermore, the hardness values ​​of Al2O3, MnS, and CeAlO3 inclusions are much higher than those of the matrix, while Ce3S4 inclusions have the lowest hardness. The hardness values ​​of Ce2O3, CeS, and Ce2O2S inclusions are similar to those of the matrix. In practical engineering applications, when friction and wear occur on the steel surface, inclusions with a hardness much higher than the matrix will protrude from the matrix surface, increasing the coefficient of friction and reducing the material's wear resistance.

[0085] The addition of Ce improves the segregation of hard phase inclusions such as MnS and Al2O3 at grain boundaries. These inclusions are prone to initiating microcracks in the steel matrix under stress, reducing the mechanical properties of the steel matrix. After the addition of Ce, except for the CeAlO3 inclusion which has a large difference in hardness and elastic modulus from the matrix, the resulting inclusions such as Ce2O3, CeS, and Ce2O2S have smaller differences in elastic modulus, hardness, and toughness. This helps to delay crack initiation, improve the consistency of plastic deformation between the steel matrix and inclusions, and thus significantly improve the overall mechanical properties of the steel matrix.

Claims

1. A method for calibrating rare earth inclusions in high temperature laser confocal experiments of rare earth microalloyed steel, characterized in that, The method comprises the following steps: Step (1): preparing a rare earth micro-alloyed steel plate, cutting and preparing an experimental steel sample from the rare earth micro-alloyed steel plate; Step (2): drawing an XY coordinate axis on the surface to be observed of the experimental steel sample with a blade, the XY coordinate axis divides the surface to be observed into four regions, and the four regions are respectively marked as region A, region B, region C and region D in clockwise order; when marking, region A and region C are marked by dotting, and region B and region D are marked by drawing short lines; Step (3): placing the experimental steel sample with the marking treatment under a scanning electron microscope, when a target rare earth inclusion is observed, determining the region where the target rare earth inclusion is located according to the marking, and determining the coordinates of the target rare earth inclusion by using the scale function of the scanning electron microscope; that is, when the target rare earth inclusion is observed, recording the magnification at which the target rare earth inclusion is observed, then using the scale function of the scanning electron microscope to make a scale from the position of the target rare earth inclusion to the foot position of the perpendicular of the X axis and the Y axis, and then making a scale from the foot position to the origin of the XY coordinate axis, and recording the distances displayed by the scales from the target inclusion to the foot position and from the foot position to the origin position respectively, so as to determine the coordinates of the target rare earth inclusion; Step (4): placing the experimental steel sample in a high-temperature laser confocal scanning laser microscope, finding the target rare earth inclusion according to the determined coordinates, starting a heating-cooling program to melt the experimental steel sample, and completing in-situ observation of the target rare earth inclusion; the heating-cooling program is as follows: firstly, increasing the temperature to 200-300 DEG C at a temperature increasing rate of 30-50 DEG C / min, secondly, increasing the temperature to 700-750 DEG C at a temperature increasing rate of 250-300 DEG C / min, then increasing the temperature to 1200-1300 DEG C at a temperature increasing rate of 15-25 DEG C / min, next, increasing the temperature to 1600-1650 DEG C at a temperature increasing rate of 100-150 DEG C / min and keeping the temperature for 5-7 min, then decreasing the temperature to 1200-1300 DEG C at a temperature decreasing rate of 15-20 DEG C / min, and finally decreasing the temperature to 20-30 DEG C at a temperature decreasing rate of 25-30 DEG C / min; the preparation method of the rare earth micro-alloyed steel plate in step (1) is as follows: Step (1-1): preparing alloy raw materials according to the chemical composition content of the rare earth micro-alloyed steel plate; the rare earth micro-alloyed steel plate is a Q370qNHE steel plate containing rare earth elements; in the Q370qNHE steel plate, the content of carbon element is 0.06-0.08wt%, the content of silicon element is 0.15-0.18wt%, the content of manganese element is 1.0-1.2wt%, the content of phosphorus element is 0.010-0.015wt%, the content of sulfur element is less than or equal to 0.002wt%, the content of aluminum element is 0.03-0.04wt%, the content of chromium element is 0.5-0.6wt%, the content of copper element is 0.3-0.4wt%, the content of niobium element is 0.03-0.04wt%, the content of nickel element is 0.3-0.4wt%, and the content of rare earth element is 0.004-0.005wt%; Step (1-2): The alloy raw materials are placed in a smelting furnace for smelting and casting forming to obtain a steel ingot; the alloy raw materials are smelted at a temperature of 1520-1600 ℃ for 20-40 min; after smelting, converter refining is performed, and the alloy liquid after refining is cast into a shape at a temperature of 1540-1570 ℃; Step (1-3): The steel ingot is sequentially subjected to heating treatment and descaling treatment; the heating treatment method is as follows: heating at a temperature increasing rate of 10-15 ℃ / min to 1200-1250 ℃, and maintaining for 2-3 h; the descaling treatment method is as follows: high-pressure water descaling is adopted, and the water pressure is 20-25 MPa; Step (1-4): The steel ingot after descaling treatment is subjected to two-stage controlled rolling, and a rare earth microalloyed steel plate is obtained after rolling treatment; the two-stage controlled rolling includes a rough rolling stage and a finish rolling stage; the rough rolling stage has an opening rolling temperature of 1180-1200 ℃, a total rolling reduction of 70-80%, and 3-4 rolling passes, and the controlled reduction amount of each pass is in the range of 30-40 mm; the finish rolling stage has an opening rolling temperature of 890-910 ℃, a finish rolling temperature of 815-835 ℃, a total rolling reduction of 50-70%, and 5-6 rolling passes, and the controlled reduction amount of each pass is in the range of 5-6 mm; after finish rolling, the steel plate is cooled to 550-580 ℃ at a cooling rate of 9-11 ℃ / s, and then naturally cooled to room temperature.

2. The method for calibration of rare earth inclusions in high temperature laser confocal experiments on rare earth microalloyed steels according to claim 1, characterized in that, In step (1), a cross section perpendicular to the rolling direction is selected from the rare earth microalloyed steel plate, a cylindrical sample with a diameter of 5 mm and a height of 4 mm is obtained by wire cutting, and the cylindrical sample is pretreated; The pretreatment method of the cylindrical sample is as follows: polishing treatment is performed after grinding treatment; the grinding treatment method is as follows: 200-mesh to 2000-mesh metallographic sandpaper is used for grinding until the surface roughness is 0.3-0.6 μm; the polishing treatment method is as follows: 2.5 μm diamond suspension is used to polish the surface to be observed on a velvet polishing cloth until the surface roughness is 0.05-0.10 μm, and then the sample is cleaned in an ultrasonic cleaning machine and dried.

3. The method for calibration of rare earth inclusions in high temperature laser confocal experiments on rare earth microalloyed steels according to claim 1, characterized in that, In step (4), the heating-cooling program is as follows: first, heating at a rate of 50 ℃ / min to 200 ℃, then heating at a rate of 300 ℃ / min to 700 ℃, heating at a rate of 15 ℃ / min to 1200 ℃, then heating at a rate of 100 ℃ / min to 1600 ℃ for 5 min, then cooling at a rate of 15 ℃ / min to 1200 ℃, and finally cooling at a rate of 25 ℃ / min to 20 ℃.

4. The method for calibrating rare earth inclusions in high temperature laser confocal experiments on rare earth microalloyed steels according to any one of claims 1 to 3, characterized in that, In step (4), during the entire high-temperature laser confocal experiment, argon gas is introduced into the heating cavity of the high-temperature laser confocal scanning laser microscope for protection, and the purity of the argon gas is greater than or equal to 99.99%.

5. The method for calibration of rare earth inclusions in high temperature laser confocal experiments on rare earth microalloyed steels according to claim 4, characterized in that, In step (1), the preparation method of the rare earth microalloyed steel plate is as follows: Step (1-1): The alloy raw materials are prepared according to the chemical composition content of the rare earth microalloyed steel plate; In the Q370qNHE steel plate, the content of carbon element is 0.065wt%, the content of silicon element is 0.152wt%, the content of manganese element is 1.04wt%, the content of phosphorus element is 0.0111wt%, the content of sulfur element is less than or equal to 0.002wt%, the content of aluminum element is 0.039wt%, the content of chromium element is 0.534wt%, the content of copper element is 0.323wt%, the content of niobium element is 0.037wt%, the content of nickel element is 0.318wt%, and the content of cerium element is 0.0049wt%; Step (1-2): the alloy raw material is placed in a smelting furnace and smelted at 1600℃ for 30min, then converter refining is carried out after smelting, and the alloy liquid after refining is cast into a steel ingot at 1570℃; Step (1-3): the steel ingot is sequentially subjected to heating treatment and descaling treatment; the heating treatment method is: heating to 1250℃ at a heating rate of 15℃ / min, and holding for 2h; the descaling treatment method is: high-pressure water descaling, with a water pressure of 22MPa; Step (1-4): the steel ingot after descaling treatment is subjected to two-stage controlled rolling, and a rare earth microalloyed steel plate is obtained after rolling treatment; the rough rolling stage is opened at 1200℃, the total rolling reduction is 80%, and the rolling passes are 4, with the controlled reduction amount in each pass being in the range of 30-40mm; the finish rolling stage is opened at 900℃, the finish rolling temperature is 825℃, the total rolling reduction is 60%, and the rolling passes are 5, with the controlled reduction amount in each pass being in the range of 5-6mm; after finish rolling, the cooling rate is 10℃ / s to 550℃, and then natural cooling to room temperature; A cross section perpendicular to the rolling direction is selected from the rare earth microalloyed steel plate, and a cylindrical sample with a diameter of 5mm and a height of 4mm is obtained by wire cutting; The pretreatment method of the cylindrical sample is: polishing treatment after grinding treatment; the grinding treatment method is: polishing with 200-2000 mesh metallographic sandpaper until the surface roughness is 0.6μm; the polishing treatment method is: polishing the surface to be observed on the silk polishing cloth with 2.5μm diamond suspension, polishing to a surface roughness of 0.1μm, and then cleaning in an ultrasonic cleaning machine and blowing dry; In step (4): the heating-cooling program is: first heating to 200℃ at a heating rate of 50℃ / min, then heating to 700℃ at a heating rate of 300℃ / min, heating to 1200℃ at a heating rate of 15℃ / min, then heating to 1600℃ at a heating rate of 100℃ / min and holding for 5min, then cooling to 1200℃ at a cooling rate of 15℃ / min, and finally cooling to 20℃ at a cooling rate of 25℃ / min; during the whole high-temperature laser confocal experiment, argon gas is introduced into the heating cavity of the high-temperature laser confocal scanning laser microscope for protection, and the purity of the argon gas is greater than or equal to 99.99%.

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