Method for calibrating rare earth inclusions in high-temperature laser confocal experiment of rare earth microalloyed steel

Abstract

The invention discloses a method for calibrating rare earth inclusions in a rare earth microalloyed steel high-temperature laser confocal experiment. The method comprises the following steps: (1) preparing and cutting a rare earth microalloyed steel plate to prepare a cylindrical sample, and pretreating the sample to obtain an experimental steel sample; (2) dividing the to-be-observed surface of the experimental steel sample into n areas and marking; (3) placing the marked experimental steel sample under a scanning electron microscope to observe inclusions; judging an area where the target rare earth inclusion is located according to the mark and determining coordinates of the area; and (4) the experimental steel sample is placed in a high-temperature laser confocal scanning laser microscope, the target rare earth inclusion is found according to the coordinates, and a heating-cooling program is started to melt the experimental steel sample to complete in-situ observation of the target rare earth inclusion. The method can solve the problem that an existing inclusion observation means cannot ensure that original inclusions and changes of the original inclusions cannot be observed when a high-temperature confocal experiment is carried out.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy steel inclusion calibration, in particular to a method for calibrating rare earth inclusions in a high-temperature laser confocal experiment of rare earth microalloyed steel. Background Art

[0002] High-temperature confocal scanning laser microscopy (CSLM) is widely used to observe inclusions and phase changes in steel. Using CSLM observations can effectively monitor changes in sample surfaces at high temperatures, providing valuable insights into the formation of inclusions in molten steel and their precipitation during solidification. Conventional methods for observing alloy steel inclusions using CSLM include finding inclusions of similar morphology and size for observation under a high-temperature laser confocal microscope, or observing inclusions floating on the surface of melted test samples under a 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 disadvantages: it is impossible to determine whether the inclusions found directly under high-temperature confocal microscopy are the type of inclusions that need to be observed, or the observed inclusions may actually be contaminated impurities, resulting in the disappearance or change of inclusions / impurities floating on the sample surface after heating to melt. Therefore, it cannot be used as data on the changes of rare earth inclusions during the heating and cooling process of high-temperature laser confocal microscopy experiments.

[0004] Therefore, the existing inclusion observation methods cannot guarantee that the original inclusions and their changes can be easily observed during high-temperature confocal experiments, and the existing alloy steel inclusion observation methods need to be improved. Summary of the Invention

[0005] To this end, 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 the in-situ observation of inclusions in alloy steel more convenient, simple to operate, and highly feasible.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for calibrating rare earth inclusions in a high-temperature laser confocal experiment of rare earth microalloyed steel comprises the following steps: Step (1): preparing a rare earth microalloyed steel plate, cutting and preparing an experimental steel sample from the rare earth microalloyed steel plate; Step (2): Divide the surface of the experimental steel sample to be observed into n areas, where n is greater than or equal to 4; and make different marks on each of the n areas; 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 mark, and use the ruler function of the scanning electron microscope to determine the coordinates of the target rare earth inclusion; Step (4): Place the experimental steel sample in a high-temperature laser confocal scanning laser microscope and find 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.

[0007] In the above method for calibrating rare earth inclusions in a high-temperature laser confocal experiment on rare earth microalloyed steel, in step (1): the preparation method of the rare earth microalloyed steel plate is: Step (1-1): preparing alloy raw materials according to the chemical composition content of the rare earth microalloyed steel plate; Step (1-2): placing the alloy raw materials in a smelting furnace, smelting and casting to obtain a steel ingot; Steps (1-3): heating and descaling the steel ingot in sequence; Step (1-4): The descaling ingot is subjected to two-stage controlled rolling, and the rolling process is completed to obtain a rare earth microalloyed steel plate.

[0008] The method for calibrating rare earth inclusions in a high-temperature laser confocal experiment of rare earth microalloyed steel, in step (1-1): the rare earth microalloyed steel plate is a Q370qNHE steel plate containing rare earth elements; the Q370qNHE steel plate has a carbon content of 0.06-0.08wt%, a silicon content of 0.15-0.18wt%, a manganese content of 1.0-1.2wt%, a phosphorus content of 0.010-0.015wt%, a sulfur content of less than or equal to 0.002wt%, an aluminum content of 0.03-0.04wt%, a chromium content of 0.5-0.6wt%, a copper content of 0.3-0.4wt%, a niobium content of 0.03-0.04wt%, a nickel content of 0.3-0.4wt%, and a rare earth element content of 0.004-0.005wt%; In step (1-2): the alloy raw material is smelted at a temperature of 1520-1600°C for 20-40 minutes; after smelting, it is refined in a converter, and the refined alloy liquid is cast into a shape at 1540-1570°C; In step (1-3), the heating treatment method is: heating to 1200-1250°C at a heating rate of 10-15°C / min and keeping warm for 2-3 hours; the descaling method is: descaling with high-pressure water at a water pressure of 20-25 MPa; In step (1-4): the two-stage controlled rolling includes a rough rolling stage and a finishing rolling stage; the starting rolling temperature of the rough rolling stage is 1180-1200°C, the total rolling reduction is 70-80%, the rolling passes are 3-4 passes, and the reduction of each pass is controlled within the range of 30-40 mm; the starting rolling temperature of the finishing rolling stage is 890-910°C, the final rolling temperature is 815-835°C, the total rolling reduction is 50-70%, the rolling passes are 5-6 passes, and the reduction of each pass is controlled within the range of 5-6 mm; after the finishing rolling is completed, the steel is cooled to 550-580°C at a cooling rate of 9-11°C / s, and then naturally cooled to room temperature.

[0009] The method for calibrating rare earth inclusions in a high-temperature laser confocal laser experiment on rare earth microalloyed steel includes the following steps: selecting a cross section perpendicular to the rolling direction from the rare earth microalloyed steel plate, performing wire cutting to obtain a cylindrical specimen with a diameter of 5 mm and a height of 4 mm, and pre-treating the cylindrical specimen; The pretreatment method of the cylindrical specimen is: first grinding and then polishing; the grinding method is: using 200 to 2000 mesh metallographic sandpaper to grind to a surface roughness of 0.3-0.6 μm; the polishing method is: using 2.5 μm diamond suspension on a velvet polishing cloth to polish the surface to be observed to a surface roughness of 0.05-0.10 μm, then cleaning in an ultrasonic cleaner and blowing dry.

[0010] In the above method for calibrating rare earth inclusions in a high-temperature laser confocal experiment on rare earth microalloyed steel, in step (2): a blade is used to mark an XY coordinate axis on the surface to be observed of the experimental steel sample, and the XY coordinate axis divides the surface to be observed into four areas, which are marked as area A, area B, area C and area D in a clockwise direction; when marking, areas A and C are marked by dots, and areas B and D are marked by short lines.

[0011] In the above method for calibrating rare earth inclusions in a high-temperature laser confocal experiment of rare earth microalloyed steel, in step (3): when the target rare earth inclusion is observed, the magnification of the target rare earth inclusion is recorded, and then the ruler function of the scanning electron microscope is used to make a ruler from the position of the target rare earth inclusion vertically to the foot position of the perpendicular axis and the Y axis, and then to the origin of the X and Y coordinate axes. The distances displayed by the ruler from the target inclusion to the foot position and from the foot position to the origin are recorded respectively, thereby determining the coordinates of the target rare earth inclusion.

[0012] In the above method for calibrating rare earth inclusions in high-temperature laser confocal microalloying experiments of rare earth microalloyed steel, in step (4), the heating-cooling procedure is as follows: first, heating to 200-300°C at a heating rate of 30-50°C / min, then heating to 700-750°C at a heating rate of 250-300°C / min, then heating to 1200-1300°C at a heating rate of 15-25°C / min, then heating to 1600-1650°C at a heating rate of 100-150°C / min and holding for 5-7 minutes, then cooling to 1200-1300°C at a cooling rate of 15-20°C / min, and finally cooling to 20-30°C at a cooling rate of 25-30°C / min.

[0013] When conducting a high-temperature laser confocal experiment, the present invention first adopts a lower heating rate (30-50°C / min) to heat the sample from room temperature to 200-300°C, and then adopts a high heating rate (250-300°C / min) to continue heating the sample to 700-750°C. This can avoid sample deformation caused by internal stress generated in the sample during the heating process, is conducive to tracking and observing target rare earth inclusions, and reduces the influence of sample deformation on the floating path of target inclusions; when heating from 700-750°C to 1200-1300°C, a lower heating rate of 15-25°C / min is adopted to ensure that there is sufficient time to intuitively observe the morphological change characteristics of target rare earth inclusions during the heating process and their influence mechanism on the growth process of original austenite grains, thereby avoiding deformation of the sample caused by too fast a heating rate and deviation of the position of target rare earth inclusions; when heating from 1200-1300°C to 1600- At 1650℃, a relatively high heating rate of 100-150℃ / min can quickly increase the temperature and effectively shorten the observation experiment time. Since the observation of rare earth inclusions in rare earth-containing Q370qNHE steel has been basically completed in the previous stage, the purpose of this stage is mainly to fully melt the sample at 1600-1650℃, so as to facilitate the subsequent observation of the changes of rare earth inclusions in the solidification process of the molten steel. After that, the temperature is cooled to 1200-1300℃ at a smaller cooling rate of 15-20℃ / min, and the changes of inclusions from the solidification of the molten steel into ingots and at the start rolling temperature can be observed. If the cooling rate is too fast at this stage, the change behavior of the inclusions will deviate far from the actual processing production. Finally, the temperature is cooled to 20℃ at a larger cooling rate of 25℃ / min, and the changing characteristics of the inclusions in the entire casting process and the influence mechanism of the inclusions on the microstructure transformation and recrystallization grain nucleation during the cooling process can be observed. The present invention adopts the above-mentioned heating-cooling procedure to accurately observe the details of the changing behavior of inclusions in Q370qNHE steel plates containing rare earth elements at various production stages.

[0014] In the above method for calibrating rare earth inclusions in high-temperature laser confocal microscopy experiments of rare earth microalloyed steel, in step (4), the heating-cooling procedure is as follows: first, heating to 200°C at a heating rate of 50°C / min, then heating to 700°C at a heating rate of 300°C / min, then heating to 1200°C at a heating rate of 15°C / min, then heating to 1600°C at a heating rate of 100°C / min and holding for 5 minutes, then cooling to 1200°C at a cooling rate of 15°C / min, and finally cooling to 20°C at a cooling rate of 25°C / min.

[0015] In the above method for calibrating rare earth inclusions in a high-temperature laser confocal experiment on rare earth microalloyed steel, in step (4): 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%.

[0016] In the above method for calibrating rare earth inclusions in a high-temperature laser confocal experiment on rare earth microalloyed steel, in step (1): the preparation method of the rare earth microalloyed steel plate is: Step (1-1): preparing alloy raw materials according to the chemical composition content of a 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 carbon content is 0.065wt%, the silicon content is 0.152wt%, the manganese content is 1.04wt%, the phosphorus content is 0.0111wt%, the sulfur content is less than or equal to 0.002wt%, the aluminum content is 0.039wt%, the chromium content is 0.534wt%, the copper content is 0.323wt%, the niobium content is 0.037wt%, the nickel content is 0.318wt%, and the cerium content is 0.0049wt%; Step (1-2): placing the alloy raw material in a melting furnace and smelting at 1600°C for 30 minutes, refining in a converter after smelting, and casting the refined alloy liquid at 1570°C to obtain a steel ingot; Steps (1-3): The steel ingot is subjected to heating treatment and descaling treatment in sequence; the heating treatment method is: heating to 1250°C at a heating rate of 15°C / min and keeping the temperature for 2 hours; the descaling method is: using high-pressure water for descaling, the water pressure is 22MPa; Step (1-4): the descaling ingot is subjected to two-stage controlled rolling, and the rolling treatment is completed to obtain a rare earth microalloyed steel plate; the starting rolling temperature of the rough rolling stage is 1200°C, the total rolling reduction is 80%, the rolling passes are 4, and the reduction of each pass is controlled within the range of 30-40 mm; the starting rolling temperature of the finishing rolling stage is 900°C, the final rolling temperature is 825°C, the total rolling reduction is 60%, the rolling passes are 5, and the reduction of each pass is controlled within the range of 5-6 mm; after the finishing rolling is completed, the steel is cooled to 550°C at a cooling rate of 10°C / s, and then naturally cooled to room temperature; A cross section perpendicular to the rolling direction was selected from the rare earth microalloyed steel plate, and cylindrical specimens with a diameter of 5 mm and a height of 4 mm were obtained by wire cutting. The pretreatment method of the cylindrical specimen is: first grinding and then polishing; the grinding method is: using 200-2000 mesh metallographic sandpaper to grind to a surface roughness of 0.6 μm; the polishing method is: using 2.5 μm diamond suspension on a velvet polishing cloth to polish the surface to be observed to a surface roughness of 0.1 μm, then cleaning in an ultrasonic cleaner and drying; In step (2): use a blade to draw an XY coordinate axis on the surface to be observed of the experimental steel sample. The XY coordinate axis divides the surface to be observed into four areas. The four areas are marked as area A, area B, area C and area D in a clockwise direction. When marking, areas A and C are marked by dots, and areas B and D are marked by short lines. In step (3): when the target rare earth inclusion is observed, the magnification of the target rare earth inclusion is recorded, and then the ruler function of the scanning electron microscope is used to make a ruler from the position of the target rare earth inclusion vertically to the foot position of the X-axis and Y-axis, and then from the foot position to the origin of the XY coordinate axis. The distances shown by the rulers from the target inclusion to the foot position and from the foot position to the origin are recorded respectively, thereby determining the coordinates of the target rare earth inclusion; In step (4): the heating-cooling procedure is: first, heating to 200°C at a heating rate of 50°C / min, then heating to 700°C at a heating rate of 300°C / min, heating to 1200°C at a heating rate of 15°C / min, then heating to 1600°C at a heating rate of 100°C / min and keeping warm for 5 minutes, then cooling to 1200°C at a cooling rate of 15°C / min, and finally cooling to 20°C at a cooling rate of 25°C / min; during the entire high-temperature laser confocal experiment, argon gas was introduced into the heating chamber of the high-temperature laser confocal scanning laser microscope for protection, and the purity of pure argon gas was greater than or equal to 99.99%.

[0017] The technical solution of the present invention achieves the following beneficial technical effects: 1. The method for calibrating rare earth inclusions in a high-temperature laser confocal experiment of rare earth microalloyed steel of the present invention divides the surface of the experimental steel sample of the rare earth microalloyed steel plate to be observed into coordinate zones, preliminarily determines the approximate position of the target rare earth inclusion, and then uses the ruler function of the scanning electron microscope to lock the precise position of the target rare earth inclusion, providing a basis for rapid calibration of the target rare earth inclusion in subsequent high-temperature laser confocal experiments, thereby making the in-situ observation of the target rare earth inclusion more convenient, simple to operate, and highly feasible.

[0018] 2. The present invention has innovatively designed the heating and cooling procedures in the high-temperature laser confocal experiment of rare earth microalloyed steel, which can enable the in-situ observation of the target rare earth inclusions in the high-temperature laser confocal experiment to more accurately restore 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Inclusion distribution and morphology in 1# experimental steel in the embodiment of the present invention; Figure 2 Energy spectrum analysis diagram of inclusions in 1# experimental steel in the embodiment of the present invention; Figure 3 Inclusion distribution and morphology in 2# experimental steel in the embodiment of the present invention; Figure 4 Energy spectrum analysis diagram of inclusions in 2# experimental steel in the embodiment of the present invention; Figure 5 Austenitization process diagram of 1# experimental steel in the embodiment of the present invention; Figure 6 Austenitization process diagram of 2# experimental steel in the embodiment of the present invention; Figure 7 Figure 1 shows the evolution of the phenomenon of inclusions hindering grain growth in experimental steel No. 1 according to an embodiment of the present invention; Figure 8 Figure 2 shows the evolution of the phenomenon of inclusions hindering grain growth in the 2# experimental steel according to the embodiment of the present invention; Figure 9 A diagram of the precipitation process of inclusions during the solidification process of experimental steel No. 1 in an embodiment of the present invention; Figure 10 A diagram of the inclusion precipitation process during the solidification process of the 2# experimental steel in the embodiment of the present invention; Figure 11 A diagram showing changes in inclusions during subsequent cooling under CSLM in the 1# experimental steel according to an embodiment of the present invention; Figure 12 A diagram showing changes in inclusions during subsequent cooling under CSLM of the 2# experimental steel in the embodiment of the present invention; Figure 13Distribution and morphology of marked inclusions in 1# experimental steel in the embodiment of the present invention; Figure 14 Energy spectrum analysis diagram of inclusions marked in 1# experimental steel in the embodiment of the present invention; Figure 15 Distribution and morphology of marked inclusions in 2# experimental steel in the embodiment of the present invention; Figure 16 Energy spectrum analysis diagram of the marked inclusions in 2# experimental steel in the embodiment of the present invention. DETAILED DESCRIPTION

[0020] 1. Method for calibrating rare earth inclusions in high-temperature laser confocal micro-alloyed steel The method for calibrating rare earth inclusions in a high-temperature laser confocal laser experiment on rare earth microalloyed steel in this embodiment includes the following steps: Step (1): preparing a rare earth microalloyed steel plate, cutting a cylindrical specimen from the rare earth microalloyed steel plate, and pretreating the cylindrical specimen to obtain an experimental steel sample; the rare earth microalloyed steel plate prepared in this embodiment is a Q370qNHE steel plate containing rare earth elements, and the preparation method of the rare earth microalloyed steel plate is: Step (1-1): preparing alloy raw materials according to the chemical composition content of the rare earth microalloyed steel plate; in the rare earth microalloyed steel plate, the carbon content is 0.065wt%, the silicon content is 0.152wt%, the manganese content is 1.04wt%, the phosphorus content is 0.0111wt%, the sulfur content is less than or equal to 0.002wt%, the aluminum content is 0.039wt%, the chromium content is 0.534wt%, the copper content is 0.323wt%, the niobium content is 0.037wt%, the nickel content is 0.318wt%, and the cerium content is 0.0049wt%; Step (1-2): placing the alloy raw material in a melting furnace and smelting at 1600°C for 30 minutes, refining in a converter after smelting, and casting the refined alloy liquid at 1570°C to obtain a steel ingot; Steps (1-3): The steel ingot is subjected to heating treatment and descaling treatment in sequence; the heating treatment method is: heating to 1250°C at a heating rate of 15°C / min and keeping the temperature for 2 hours; the descaling method is: using high-pressure water for descaling, the water pressure is 22MPa; Step (1-4): the descaling ingot is subjected to two-stage controlled rolling, and the rolling treatment is completed to obtain a rare earth microalloyed steel plate; the starting rolling temperature of the rough rolling stage is 1200°C, the total rolling reduction is 80%, the rolling passes are 4, and the reduction of each pass is controlled within the range of 30-40 mm; the starting rolling temperature of the finishing rolling stage is 900°C, the final rolling temperature is 825°C, the total rolling reduction is 60%, the rolling passes are 5, and the reduction of each pass is controlled within the range of 5-6 mm; after the finishing rolling is completed, the steel is cooled to 550°C at a cooling rate of 10°C / s, and then naturally cooled to room temperature; A cross section perpendicular to the rolling direction was selected from the rare earth microalloyed steel plate, and cylindrical specimens with a diameter of 5 mm and a height of 4 mm were obtained by wire cutting. The cylindrical specimens were pretreated by grinding and then polishing. The grinding method was to use 200-2000 mesh metallographic sandpaper to a surface roughness of 0.6 μm. The polishing method was to use a 2.5 μm diamond suspension on a velvet polishing cloth to polish the surface to be observed to a surface roughness of 0.1 μm, and then cleaned in an ultrasonic cleaner and blown dry. Step (2): Divide the surface to be observed of the experimental steel sample into n areas, and mark each of the n areas with a different mark, where n is greater than or equal to 4. In this embodiment, a blade is used to mark an XY coordinate axis on the surface to be observed of the experimental steel sample. The XY coordinate axis divides the surface to be observed into four areas, and the four areas are marked as area A, area B, area C, and area D in a clockwise direction. When marking, areas A and C are marked by dots, and areas B and D are marked by short lines. 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 based on the mark, and use the ruler function of the scanning electron microscope to determine and record the coordinates of the target rare earth inclusion; When the target rare earth inclusion is observed, record the magnification of the target rare earth inclusion. Then use the ruler function of the scanning electron microscope to make a ruler from the position of the target rare earth inclusion vertically to the foot position of the X-axis and Y-axis. Then make a ruler from the foot position to the origin of the XY coordinate axis. Record the distances shown on the rulers 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): Place the experimental steel sample in a high-temperature laser confocal scanning laser microscope and find 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.

[0021] The heating-cooling procedure of this embodiment is as follows: first, the temperature is increased to 200°C at a heating rate of 50°C / min, then to 700°C at a heating rate of 300°C / min, then to 1200°C at a heating rate of 15°C / min, then to 1600°C at a heating rate of 100°C / min and held for 5 minutes, then to 1200°C at a cooling rate of 15°C / min, and finally to 20°C at a cooling rate of 25°C / min. During the entire high-temperature laser confocal scanning laser microscope experiment, argon gas with a purity greater than or equal to 99.99% was introduced into the heating chamber of the high-temperature laser confocal scanning laser microscope for protection.

[0022] A high-temperature laser confocal microscopy experiment was conducted on an experimental steel sample of Q370qNHE steel plate (2#) containing rare earth elements using this embodiment, and a high-temperature laser confocal microscopy experiment was conducted on a Q370qNHE steel plate (1#) without rare earth elements using the same method as this embodiment as a control. The experimental results are analyzed as follows.

[0023] 2. Experimental results 2.1. Inclusion morphology and energy spectrum analysis on the surface of the test sample to be observed in situ from Figures 1 to 2 ,as well as Figures 3 and 4 It can be seen that the inclusions in experimental steel #2, after adding Ce, were modified to spherical or ellipsoidal shapes. Compared to the inclusions in experimental steel #1 (MnS / Al2O3), the inclusions modified with Ce exhibited improved mechanical properties. Irregular Al2O3 inclusions and elongated MnS inclusions exhibit significant differences in hardness and plasticity from the steel matrix, generating significant stress concentrations when subjected to stress. This can lead to gaps and microcracks at the interface between the inclusions and the steel matrix. During subsequent rolling, the significantly different thermal expansion coefficients of the MnS / Al2O3 inclusions and the steel matrix disrupt the continuity of the steel matrix, resulting in a decrease in the mechanical properties of the experimental steel. The mechanical properties and thermal expansion coefficients of the Ce-OS / Ce-Al-O (Mn / Ti-O) inclusions formed after adding Ce are similar to those of the steel matrix. The spherical or ellipsoidal inclusions are also less prone to stress concentration when subjected to stress, resulting in improved mechanical properties of the experimental steel.

[0024] 2.2 CSLM in situ observation experiment The inclusions of the two test steels observed under the scanning electron microscope were used as the observation origin under CSLM, as shown in Figure 5 、 Figure 6The phenomena of the beginning and end of austenitization in the two experimental steels are respectively shown. Compared with the 1# experimental steel, the Ac1 phase transition temperature of the 2# experimental steel with the addition of Ce element is reduced by 24.3℃ and the Ac3 phase transition temperature is increased by 13.2℃. The chemical properties of the Ce element are active and the inclusions formed in the steel are evenly distributed. Using rare earth inclusions as nucleation particles can reduce the energy required for the critical nucleation of austenite, so the Ac1 phase transition temperature of the 2# experimental steel is reduced. At the same time, rare earth elements have the effect of inhibiting the diffusion of carbon elements in austenite. Figure 6 In (b), carbon precipitates on the surface of the test steel to form a nanoscale carbon film. This, combined with the surface enrichment of Ce and its reaction with trace impurities, results in darkening during optical observation. The transformation of the steel matrix to austenite requires more activation energy, resulting in a decrease in the austenitization rate of the steel matrix. Consequently, the Ac3 transition temperature of test steel #2 increases. The addition of Ce increases the austenite nucleation rate in the test steel and reduces the driving force for austenite growth, hindering austenite grain growth. This results in a reduction in the original austenite grain size of test steel #2 and an improvement in the overall mechanical properties of the steel matrix.

[0025] The phenomenon of the inclusions hindering grain growth in the two experimental steels was observed under CSLM, such as Figure 7 , Figure 8 As shown in the figure, it is obvious that the inclusions in the two experimental steels play a certain role in hindering the growth of grains, which helps to prevent the grains from growing further during the actual heat treatment process. Figure 7 As can be seen from the curves (ac), A2, A3, and A4 inclusions have little effect on hindering grain growth in the steel matrix above 1088.6°C. However, for the inclusions in experimental steel #2, B2 and B3 have a significant impact on hindering grain boundary movement. This indirectly suggests that the addition of Ce helps hinder grain growth in actual production.

[0026] Figure 9 and Figure 10 The solidification temperature of the two experimental steels and the changes in inclusions during the solidification process are given. For the 1# experimental steel, due to the high precipitation temperature, there are only a few Al2O3 inclusions on the steel surface as nucleation particles before solidification, so the solidification temperature is relatively low. Compared with the 2# experimental steel, due to the addition of Ce elements, there are a large number of Ce-OS slag on the surface of the molten steel as nucleation particles, and the solidification temperature of the molten steel is increased by 23.1°C compared with the 1# experimental steel. When the molten steel solidifies, the solute elements (S, O) are discharged into the liquid phase due to the distribution coefficient K < 1, which causes solute elements such as S and O to be concentrated in the interdendritic gaps. In the later stage of solidification, when the concentration product of solute elements such as S and O between the dendrites exceeds the solubility product, the S element combines with alloying elements such as Mn to form chain or granular MnS and impurities precipitate, as shown in the following example. Figure 9As shown in (h) and (i), it is consistent with the characteristics of MnS inclusions in the molten steel precipitating at about 1400℃. Due to the presence of a large number of nucleation particles in the 2# test steel, the number of nucleated grains is greatly increased. The large number of rare earth inclusions in the matrix will hinder the subsequent movement of grain boundaries and hinder the growth of grains, such as Figure 10 This indicates that the addition of Ce can refine the austenite grain size in the subsequent rolling process, thereby improving the comprehensive performance of the test steel.

[0027] The marked inclusions in the two groups of experimental steels during the subsequent cooling process were observed, e.g. Figure 11 and Figure 12 As shown in the figure, it can be seen that the inclusions subsequently precipitated in the 1# experimental steel are dispersed near the grain boundaries. This is because S and O are enriched in the interdendritic gaps at the end of solidification or during solid-state cooling, so they will also precipitate at the grain boundaries of the grains growing in the interdendritic gaps. The Ce element added to the 2# experimental steel combines with elements such as S and O to form high-melting-point rare earth oxysulfides, which purifies the molten steel. No dispersed inclusions precipitate during the subsequent solidification process. The grain boundaries are cleaner than those of the 1# experimental steel, and the grain size is also refined.

[0028] 2.3 Analysis results of inclusions marked by CSLM experiments The morphology and element distribution of the marked inclusions in the two groups of experimental steels were analyzed by SEM-EDS. The results are as follows: Figure 13 and Figure 14 ,as well as Figure 15 and Figure 16 As shown in the figure, the first image in the SEM-EDS analysis results is an EDS layered image, showing the segregation of various elements in real inclusions. The results show that due to the addition of Ce, the S and O elements in the 2# test steel react with Ce to form rare earth oxysulfides. Compared with the 1# test steel, the inclusion morphology is more regularized, and there are no NbN inclusions. The presence of NbN inclusions at the grain boundaries of the 1# test steel indicates the segregation of N at the grain boundaries. Compared with the 2# test steel, the addition of Ce reduces the segregation of N at the grain boundaries.

[0029] Analysis revealed that the primary inclusions in the two experimental steels were MnS, Al2O3, CeS, Ce3S4, Ce2O2S, and CeAlO3. Comparing the elastic moduli of the inclusions with those of the steel matrix revealed that the elastic moduli of Al2O3 and CeAlO3 were significantly higher than those of the Fe matrix. Under external forces, these inclusions do not deform synchronously with the steel matrix, leading to stress concentration between the matrix and the inclusions. This leads to microcracks forming between the steel matrix and these inclusions when subjected to stress, resulting in reduced toughness and increased brittleness. Inclusions such as Ce2O3, Ce2O2S, CeS, and Ce3S4 have lower elastic moduli than the steel matrix. These inclusions deform prior to the matrix under stress, alleviating stress concentration to a certain extent and positively impacting the material's toughness.

[0030] The presence of inclusions affects the toughness of steel. Rare earth inclusions Ce3S4 and Ce2O2S exhibit toughness, while Ce2O3 and CeS exhibit slight brittleness. In contrast, Al2O3, MnS, and CeAlO3 inclusions exhibit pronounced brittleness. This suggests that in actual engineering applications, inclusions such as Al2O3, MnS, and CeAlO3 have weak bonds with the steel matrix, making them prone to forming crack sources. When cracks propagate to these inclusions, their inherent brittleness may prevent them from effectively hindering crack propagation, reducing the material's mechanical properties.

[0031] Furthermore, Al2O3, MnS, and CeAlO3 inclusions have much higher hardness than the matrix, while Ce3S4 inclusions have the lowest hardness. Ce2O3, CeS, and Ce2O2S have similar hardness to the matrix. In actual engineering applications, when friction and wear occur on the steel surface, inclusions with much higher hardness than the matrix will protrude from the matrix surface, increasing the friction coefficient and reducing the material's wear resistance.

[0032] 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 when the steel is subjected to stress, reducing the mechanical properties of the steel matrix. With the addition of Ce, with the exception of the CeAlO3 inclusions, which have significant differences in hardness and elastic modulus from the matrix, the resulting inclusions, such as Ce2O3, CeS, and Ce2O2S, have relatively small differences in elastic modulus, hardness, and toughness. This helps delay crack initiation and improves the consistency of plastic deformation between the steel matrix and the inclusions, thereby significantly improving the overall mechanical properties of the steel matrix.

Claims

1. A method for calibrating rare earth inclusions in high-temperature laser confocal micro-alloyed steel experiments, characterized in that: The steps include: Step (1): preparing a rare earth microalloyed steel plate, cutting and preparing an experimental steel sample from the rare earth microalloyed steel plate; Step (2): Divide the surface of the experimental steel sample to be observed into n areas, where n is greater than or equal to 4; and make different marks on each of the n areas; 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 mark, and use the ruler function of the scanning electron microscope to determine the coordinates of the target rare earth inclusion; Step (4): Place the experimental steel sample in a high-temperature laser confocal scanning laser microscope and find 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.

2. The method for calibrating rare earth inclusions in high-temperature laser confocal microalloyed steel experiments according to claim 1, characterized in that: In step (1): the preparation method of the rare earth microalloyed steel plate is: Step (1-1): preparing alloy raw materials according to the chemical composition content of the rare earth microalloyed steel plate; Step (1-2): placing the alloy raw materials in a smelting furnace, smelting and casting to obtain a steel ingot; Steps (1-3): heating and descaling the steel ingot in sequence; Step (1-4): The descaling ingot is subjected to two-stage controlled rolling, and the rolling process is completed to obtain a rare earth microalloyed steel plate.

3. The method for calibrating rare earth inclusions in high-temperature laser confocal microalloyed steel experiments according to claim 2, characterized in that: In step (1-1), 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%; In step (1-2): the alloy raw material is smelted at a temperature of 1520-1600°C for 20-40 minutes; after smelting, it is refined in a converter, and the refined alloy liquid is cast into a shape at 1540-1570°C; In step (1-3), the heating treatment method is: heating to 1200-1250°C at a heating rate of 10-15°C / min and keeping warm for 2-3 hours; the descaling method is: descaling with high-pressure water at a water pressure of 20-25 MPa; In step (1-4): the two-stage controlled rolling includes a rough rolling stage and a finishing rolling stage; the starting rolling temperature of the rough rolling stage is 1180-1200°C, the total rolling reduction is 70-80%, the rolling passes are 3-4 passes, and the reduction of each pass is controlled within the range of 30-40 mm; the starting rolling temperature of the finishing rolling stage is 890-910°C, the final rolling temperature is 815-835°C, the total rolling reduction is 50-70%, the rolling passes are 5-6 passes, and the reduction of each pass is controlled within the range of 5-6 mm; after the finishing rolling is completed, the steel is cooled to 550-580°C at a cooling rate of 9-11°C / s, and then naturally cooled to room temperature.

4. The method for calibrating rare earth inclusions in high-temperature laser confocal microalloyed steel experiments 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, and a cylindrical specimen with a diameter of 5 mm and a height of 4 mm is obtained by wire cutting, and the cylindrical specimen is pretreated; The pretreatment method of the cylindrical specimen is: first grinding and then polishing; the grinding method is: using 200 to 2000 mesh metallographic sandpaper to grind to a surface roughness of 0.3-0.6 μm; the polishing method is: using 2.5 μm diamond suspension on a velvet polishing cloth to polish the surface to be observed to a surface roughness of 0.05-0.10 μm, then cleaning in an ultrasonic cleaner and blowing dry.

5. The method for calibrating rare earth inclusions in high-temperature laser confocal microalloyed steel experiments according to claim 1, characterized in that: In step (2): use a blade to draw an XY coordinate axis on the surface to be observed of the experimental steel sample. The XY coordinate axis divides the surface to be observed into four areas. The four areas are marked as area A, area B, area C and area D in a clockwise direction. When marking, areas A and C are marked by dots, and areas B and D are marked by short lines.

6. The method for calibrating rare earth inclusions in high-temperature laser confocal microalloyed steel experiments according to claim 1, characterized in that: In step (3): when the target rare earth inclusion is observed, the magnification of the target rare earth inclusion is recorded, and then the ruler function of the scanning electron microscope is used to make a ruler from the position of the target rare earth inclusion vertically to the foot position of the X-axis and Y-axis, and then to the origin of the XY coordinate axis. The distances displayed by the ruler from the target inclusion to the foot position and from the foot position to the origin are recorded respectively, thereby determining the coordinates of the target rare earth inclusion.

7. The method for calibrating rare earth inclusions in high-temperature laser confocal microalloyed steel experiments according to claim 1, characterized in that: In step (4): the heating-cooling procedure is: first, heat the temperature to 200-300°C at a heating rate of 30-50°C / min, then heat the temperature to 700-750°C at a heating rate of 250-300°C / min, then heat the temperature to 1200-1300°C at a heating rate of 15-25°C / min, then heat the temperature to 1600-1650°C at a heating rate of 100-150°C / min and keep warm for 5-7 minutes, then cool the temperature to 1200-1300°C at a cooling rate of 15-20°C / min, and finally cool the temperature to 20-30°C at a cooling rate of 25-30°C / min.

8. The method for calibrating rare earth inclusions in high-temperature laser confocal microalloyed steel experiments according to claim 7, characterized in that: In step (4): the heating-cooling procedure is as follows: first, heat the temperature to 200°C at a heating rate of 50°C / min, then heat the temperature to 700°C at a heating rate of 300°C / min, heat the temperature to 1200°C at a heating rate of 15°C / min, then heat the temperature to 1600°C at a heating rate of 100°C / min and keep it at that temperature for 5 minutes, then cool it to 1200°C at a cooling rate of 15°C / min, and finally cool it to 20°C at a cooling rate of 25°C / min.

9. The method for calibrating rare earth inclusions in high-temperature laser confocal experiments on rare earth microalloyed steel according to any one of claims 1 to 8, characterized in that: In step (4): 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%.

10. The method for calibrating rare earth inclusions in high-temperature laser confocal microalloyed steel experiments according to claim 9, characterized in that: In step (1): the preparation method of the rare earth microalloyed steel plate is: Step (1-1): preparing alloy raw materials according to the chemical composition content of the rare earth microalloyed steel plate; The rare earth microalloyed steel plate is a Q370qNHE steel plate containing rare earth elements; the Q370qNHE steel plate has a carbon content of 0.065 wt%, a silicon content of 0.152 wt%, a manganese content of 1.04 wt%, a phosphorus content of 0.0111 wt%, a sulfur content of less than or equal to 0.002 wt%, an aluminum content of 0.039 wt%, a chromium content of 0.534 wt%, a copper content of 0.323 wt%, a niobium content of 0.037 wt%, a nickel content of 0.318 wt%, and a cerium content of 0.0049 wt%. Step (1-2): placing the alloy raw material in a melting furnace and smelting at 1600°C for 30 minutes, refining in a converter after smelting, and casting the refined alloy liquid at 1570°C to obtain a steel ingot; Steps (1-3): The steel ingot is subjected to heating treatment and descaling treatment in sequence; the heating treatment method is: heating to 1250°C at a heating rate of 15°C / min and keeping the temperature for 2 hours; the descaling method is: using high-pressure water for descaling, the water pressure is 22MPa; Step (1-4): the descaling ingot is subjected to two-stage controlled rolling, and the rolling treatment is completed to obtain a rare earth microalloyed steel plate; the starting rolling temperature of the rough rolling stage is 1200°C, the total rolling reduction is 80%, the rolling passes are 4, and the reduction of each pass is controlled within the range of 30-40 mm; the starting rolling temperature of the finishing rolling stage is 900°C, the final rolling temperature is 825°C, the total rolling reduction is 60%, the rolling passes are 5, and the reduction of each pass is controlled within the range of 5-6 mm; after the finishing rolling is completed, the steel is cooled to 550°C at a cooling rate of 10°C / s, and then naturally cooled to room temperature; A cross section perpendicular to the rolling direction was selected from the rare earth microalloyed steel plate, and cylindrical specimens with a diameter of 5 mm and a height of 4 mm were obtained by wire cutting. The pretreatment method of the cylindrical specimen is: first grinding and then polishing; the grinding method is: using 200-2000 mesh metallographic sandpaper to grind to a surface roughness of 0.6 μm; the polishing method is: using 2.5 μm diamond suspension on a velvet polishing cloth to polish the surface to be observed to a surface roughness of 0.1 μm, then cleaning in an ultrasonic cleaner and drying; In step (2): use a blade to draw an XY coordinate axis on the surface to be observed of the experimental steel sample. The XY coordinate axis divides the surface to be observed into four areas. The four areas are marked as area A, area B, area C and area D in a clockwise direction. When marking, areas A and C are marked by dots, and areas B and D are marked by short lines. In step (3): when the target rare earth inclusion is observed, the magnification of the target rare earth inclusion is recorded, and then the ruler function of the scanning electron microscope is used to make a ruler from the position of the target rare earth inclusion vertically to the foot position of the X-axis and Y-axis, and then from the foot position to the origin of the XY coordinate axis. The distances shown by the rulers from the target inclusion to the foot position and from the foot position to the origin are recorded respectively, thereby determining the coordinates of the target rare earth inclusion; In step (4): the heating-cooling procedure is: first, heating to 200°C at a heating rate of 50°C / min, then heating to 700°C at a heating rate of 300°C / min, heating to 1200°C at a heating rate of 15°C / min, then heating to 1600°C at a heating rate of 100°C / min and keeping warm for 5 minutes, then cooling to 1200°C at a cooling rate of 15°C / min, and finally cooling to 20°C at a cooling rate of 25°C / min; during the entire high-temperature laser confocal experiment, argon gas was introduced into the heating chamber of the high-temperature laser confocal scanning laser microscope for protection, and the purity of the argon gas was greater than or equal to 99.99%.

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