High-strength steel with low residual internal stress and preparation method thereof

Abstract

The invention provides high-strength steel with low residual internal stress and a preparation method thereof, and the high-strength steel with low residual internal stress comprises the following chemical components in percentage by mass: 0.10-0.16% of C, 0.09-0.18% of Si, 1.0-1.5% of Mn, 0.4-0.6% of Cr, 0.05-0.08% of Cu, 0.05-0.1% of Ni, 0.03-0.05% of Al, less than or equal to 0.008% of P, less than or equal to 0.008% of S, 0.5-0.7% of Mo and the balance of Fe and inevitable impurities. Wherein the Brinell hardness of the high-strength steel with low residual internal stress is 200-350 HB. The preparation method of the low-residual-internal-stress high-strength steel is simple, convenient to operate, capable of reducing the production cost and energy consumption and suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of high-strength steel production technology, and particularly relates to a high-strength steel with low residual internal stress and its preparation method. Background Technology

[0002] In recent years, high-strength steel has been widely used in automobiles, construction machinery, and other fields due to its excellent mechanical properties. However, sheet shape quality issues have become a core bottleneck restricting its industrial application. The essence of sheet shape defects lies in the presence of large residual internal stresses within the steel sheet and their severely uneven distribution, leading to uncontrollable deformation during subsequent processing or use. Statistics show that there are significant problems with the sheet shape quality of high-strength steel sheets. The main sheet shape quality issues include both the sheet shape itself and the shape during processing and use, specifically manifested as warping, curling, dovetail patterns, wavy lines, and transverse folds. These problems not only affect the aesthetics of the product but, more importantly, impact its processing and performance.

[0003] In existing technologies, the residual internal stress problem of low-alloy high-strength steel plates is mainly solved by leveling and straightening processes, but the corresponding mechanical properties are not ideal. For cooling high-strength steel plates, laminar flow, atomization, or ultra-fast cooling methods are commonly used for post-rolling controlled cooling to improve the steel plate's strength. However, this easily leads to inhomogeneity in microstructure and mechanical properties, resulting in significant residual internal stress. Based on this, this invention proposes a low-residual-stress high-strength steel and its preparation method. Summary of the Invention

[0004] The main objective of this invention is to provide a high-strength steel with low residual internal stress and its preparation method, aiming to solve the technical problems of internal stress deformation and high cost in the processing of high-strength steel plates in the prior art.

[0005] To achieve the above objectives, the present invention provides a high-strength steel with low residual internal stress. The chemical composition of the high-strength steel with low residual internal stress, by mass fraction, includes: C 0.10-0.16%, Si 0.09-0.18%, Mn 1.0-1.5%, Cr 0.4-0.6%, Cu 0.05-0.08%, Ni 0.05-0.1%, Al 0.03-0.05%, P≤0.008%, S≤0.008%, Mo 0.5-0.7%, with the remainder being Fe and unavoidable impurities.

[0006] The Brinell hardness of the low residual internal stress high-strength steel is 200-350 HB.

[0007] According to the embodiments of this application, the yield strength of the low residual internal stress high-strength steel is 800-1200 MPa, the tensile strength is 1000-1400 MPa, the elongation is 10-25%, and the impact toughness is 15-25 J.

[0008] According to an embodiment of this application, the fatigue strength of the low residual internal stress high-strength steel is 50-60% of its tensile strength.

[0009] According to an embodiment of this application, the thickness of the low residual internal stress high-strength steel is 3 to 10 mm.

[0010] The present invention also provides a method for preparing the above-mentioned high-strength steel with low residual internal stress, the steps of which include:

[0011] The continuously cast billet is heated, rough rolled, finish rolled, cooled to room temperature, coiled, quenched, straightened, subjected to the first shot blasting treatment, tempered, and subjected to the second shot blasting treatment.

[0012] The chemical composition of the continuously cast billet is the same as that of the low residual internal stress high-strength steel.

[0013] The quenching process includes heating, holding, and laminar flow cooling steps. In the quenching step, the speed of the conveyor rollers is 0.30 to 0.50 m / min, the heating temperature is 870 to 925°C, and the holding time is 10 to 15 min.

[0014] The laminar flow cooling adopts a laminar water cooling method, with a water temperature of 15-25℃ and a laminar flow cooling rate of 55-60℃·s. -1 .

[0015] The tempering temperature is 550–630°C, and the tempering holding time is 30–40 minutes.

[0016] According to an embodiment of this application, the water flow rate for laminar cooling is 2200–2800 m³ / h. 3 / h, the ratio of the upper and lower water flow rates for laminar flow cooling is (1.15:1) to (1.35:1).

[0017] According to an embodiment of this application, in the quenching heating step, the oxygen content of the heating atmosphere is 800-1000 ppm, and the pressure of the heating atmosphere is 15-25 Pa.

[0018] In the laminar flow cooling step of quenching, the water pressure is 0.9–1.0 MPa.

[0019] According to the embodiments of this application, the heating temperature of the continuously cast billet is 1270-1290℃; the roughing temperature is 1000-1220℃; the finishing temperature is 950-1050℃; and the coiling temperature is 600-650℃.

[0020] According to the embodiments of this application, the roughing mill has 7 to 9 rolling passes, and the single-pass reduction rate of the roughing mill is ≥13%.

[0021] Finishing rolling includes a first rolling pass, a second rolling pass, and a third rolling pass. The finishing rolling has 6 to 8 rolling passes. The single-pass reduction rate of the first rolling pass is 20 to 25%, the single-pass reduction rate of the second rolling pass is 15 to 20%, and the single-pass reduction rate of the third rolling pass is 10 to 15%.

[0022] According to the embodiments of this application, the current of the first shot blasting process and the second shot blasting process are 30-40A, the speed of the first shot blasting process and the second shot blasting process are 5-7m / min, and the particle size of the shot in the first shot blasting process and the second shot blasting process is 0.4-0.8mm.

[0023] The beneficial effects of this invention are:

[0024] The low residual internal stress high-strength steel of this invention achieves homogenization of the internal microstructure and reduction of residual internal stress through optimized chemical composition and synergistic control of process parameters. This results in a Brinell hardness of 200–350 HB, high strength, and good wear resistance. Specifically, the introduction of alloying elements such as Cr, Mo, and W, under controlled process parameters, promotes the formation of alloy cementite (e.g., Cr...). 23 C6) filling analysis reveals synchronicity with the martensitic phase transformation, reducing the internal stress difference in the microstructure, thus refining the microscopic internal stress concentration and reducing residual internal stress. It can also reduce the segregation of grain boundary carbides and inhibit the decomposition of residual austenite during service, avoiding dimensional changes. Simultaneously, Mo and W elements preferentially occupy grain boundaries, purifying impurities in the grain boundary region. This dual effect prevents temper brittleness and improves impact toughness.

[0025] The above-mentioned method for preparing high-strength steel with low residual internal stress is simple, easy to operate, reduces production costs and energy consumption, and is suitable for large-scale production. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 This is a photograph of the high-strength steel with low residual internal stress obtained in Example 1 of the present invention.

[0028] Figure 2 The images show the actual high-strength steels obtained in Comparative Examples 1 and 2 of this invention; wherein, (a) the roller speed is 0.26 m / min, and (b) the roller speed is 0.55 m / min.

[0029] Figure 3 This is a distribution diagram of different test points in the rolling and transverse directions according to an embodiment of the present invention.

[0030] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0033] To achieve the above objectives, the present invention provides a high-strength steel with low residual internal stress. The chemical composition of the high-strength steel with low residual internal stress, by mass fraction, includes: C 0.10-0.16%, Si 0.09-0.18%, Mn 1.0-1.5%, Cr 0.4-0.6%, Cu 0.05-0.08%, Ni 0.05-0.1%, Al 0.03-0.05%, P≤0.008%, S≤0.008%, Mo 0.5-0.7%, with the remainder being Fe and unavoidable impurities.

[0034] The Brinell hardness of the low residual internal stress high-strength steel is 200-350 HB.

[0035] Carbon is the main element that improves the strength and hardness of high-strength steel with low residual internal stress, but it also reduces plasticity and toughness. In high-strength steel, the carbon content is usually controlled at a low level to maintain good toughness and plasticity. Meanwhile, carbon and chromium can form alloy cementite (such as Cr...). 23 C6) improves the hardness and wear resistance of high-strength steel with low residual internal stress.

[0036] Silicon plays a deoxidizing role in the smelting process, helping to reduce impurities in high-strength steel with low residual internal stress. Its introduction can inhibit cementite coarsening and significantly improve yield strength and tempering stability.

[0037] Manganese is an important element for improving the hardenability and toughness of steel. It can refine grains and enhance the strength and hardness of steel. Manganese combines with sulfur to form manganese sulfide, reducing the harmful effects of sulfur.

[0038] The introduction of chromium contributed to the growth of Cr. 23 The analysis of C6 revealed that it refined the microscopic internal stress concentration and reduced residual internal stress. It also formed a dense chromium oxide film, significantly improving the corrosion resistance of the steel.

[0039] When copper and phosphorus are used together, the strength and yield ratio of steel can be improved, and the introduction of copper can improve the steel's resistance to atmospheric corrosion.

[0040] Nickel improves the strength and toughness of steel.

[0041] Aluminum acts as a deoxidizer, helping to reduce oxide inclusions in steel and improve its purity. At the same time, aluminum can refine grains, increasing the strength of the steel.

[0042] Molybdenum can improve the hot strength of steel, refine the grains, and improve the tempering stability of martensite. When combined with chromium and nickel, it can significantly improve hardenability and toughness.

[0043] This invention, through the regulation of the above chemical components and combined with the process, achieves homogenization of the internal structure of the material and reduces residual internal stress, resulting in a high-strength steel with a Brinell hardness of 200–350 HB. Specifically, by introducing alloying elements such as Cr, Mo, and W, and under the control of process parameters, the alloy cementite (e.g., Cr) can be promoted. 23 C6) filling analysis reveals synchronicity with the martensitic phase transformation, reducing the internal stress difference in the microstructure, thus refining the microscopic internal stress concentration and reducing residual internal stress. It can also reduce the segregation of grain boundary carbides and inhibit the decomposition of residual austenite during service, avoiding dimensional changes. Simultaneously, Mo and W elements preferentially occupy grain boundaries, purifying impurities in the grain boundary region. This dual effect prevents temper brittleness and improves impact toughness.

[0044] In some embodiments, the yield strength of the low residual internal stress high-strength steel is 800-1200 MPa, the tensile strength is 1000-1400 MPa, the elongation is 10-25%, and the impact toughness is 15-25 J.

[0045] In some embodiments, the yield strength of low residual internal stress high-strength steel is 800–1200 MPa, enabling it to withstand large loads without easily deforming, thus contributing to improved structural stability. Tensile strength indicates high load-bearing capacity, making it suitable for applications requiring high tensile forces. High elongation indicates good plasticity, allowing the material to absorb energy and undergo plastic deformation without easily fracturing. Impact toughness reflects the material's ability to reduce the risk of fracture when subjected to impact or vibration, thus improving safety.

[0046] In some embodiments, the fatigue strength of the low residual internal stress high-strength steel is 50-60% of its tensile strength.

[0047] In some embodiments, if the tensile strength of the low residual internal stress high-strength steel is 1000 MPa, then the fatigue strength is 500–600 MPa.

[0048] In some embodiments, the thickness of the low residual internal stress high-strength steel is 3 to 10 mm.

[0049] In some embodiments, by optimizing the thickness of high-strength steel with low residual internal stress, uneven deformation during the rolling process can be reduced and the plate shape can be improved, effectively controlling and reducing residual internal stress, thereby improving the mechanical properties of high-strength steel with low residual internal stress.

[0050] The present invention also provides a method for preparing the above-mentioned high-strength steel with low residual internal stress, the steps of which include:

[0051] The continuously cast billet is heated, rough rolled, finish rolled, cooled to room temperature, coiled, quenched, straightened, subjected to the first shot blasting treatment, tempered, and subjected to the second shot blasting treatment.

[0052] The chemical composition of the continuously cast billet is the same as that of the low residual internal stress high-strength steel.

[0053] The quenching process includes heating, holding, and laminar flow cooling steps. In the quenching step, the speed of the conveyor rollers is 0.30 to 0.50 m / min, the heating temperature is 870 to 925°C, and the holding time is 10 to 15 min.

[0054] The laminar flow cooling adopts a laminar water cooling method, with a water temperature of 15-25℃ and a laminar flow cooling rate of 55-60℃·s. -1 .

[0055] The tempering temperature is 550–630°C, and the tempering holding time is 30–40 minutes.

[0056] In some implementations, the furnace exit temperature of the continuously cast billet after heating is 1270–1290°C.

[0057] After heating, the continuously cast billet undergoes rough descaling using high-pressure water to remove iron oxide scale and impurities from its surface, improving surface quality. Rough rolling at 1000–1220℃ initially reduces the billet's thickness and width, facilitating subsequent finish rolling. Shearing removes irregular portions of the billet, ensuring dimensional accuracy during rolling. High-pressure water descaling further removes residual oxide scale from rough rolling, ensuring a clean surface. Finish rolling at 950–1050℃ controls the final thickness and width of the steel to achieve the desired dimensions. After finish rolling, the billet is cooled to room temperature and then coiled for storage and transportation. Finally, the coils are packaged for protection against damage during transport and storage.

[0058] The winding temperature is 600–650℃, and the coiled coil is then quenched. The quenching process includes heating, holding, and laminar flow cooling steps; the heating temperature for quenching is 870–925℃, and the holding time for quenching is 10–15 minutes.

[0059] The laminar flow cooling adopts a laminar water cooling method, with a water temperature of 15-25℃ and a laminar flow cooling rate of 55-60℃·s. -1 .

[0060] In some embodiments, the quenching process easily generates two types of internal stress. One is thermal internal stress, where the surface layer of the steel cools and contracts first, while the core remains expanded, forming tensile internal stress on the surface and compressive internal stress in the core. The other is structural internal stress, where the surface layer of the steel expands due to volume expansion, transforming into martensite first, while the core remains austenite, forming compressive internal stress on the surface and tensile internal stress in the core. When these two types of internal stress are superimposed, uneven cooling during quenching can lead to localized stress concentration, resulting in high residual internal stress. Therefore, this invention employs laminar flow cooling. By controlling various parameters during the quenching process, the initial residual internal stress is kept at a low level. Specifically, the internal stress is reduced by 30-40% compared to traditional quenching. Furthermore, by controlling the holding time, carbides are fully precipitated, reducing or eliminating residual internal stress while ensuring performance strength.

[0061] In some embodiments, during the quenching heating step, the oxygen content of the heating atmosphere is 800–1000 ppm, and the pressure of the heating atmosphere is 15–25 Pa.

[0062] In the laminar flow cooling step of quenching, the water pressure is 0.9–1.0 MPa.

[0063] In some embodiments, the quenching includes heating the quenching furnace and cooling the furnace using a quenching machine. The oxygen content inside the quenching furnace is 800–1000 ppm, the heating temperature for heat treatment quenching is 870–925°C, the holding time is 10–15 min, and the furnace pressure is 15–25 Pa.

[0064] In some embodiments, the laminar flow cooling water flow rate is 2200–2800 m³ / h. 3 / h, the ratio of the upper and lower water flow rates for laminar flow cooling is (1.15:1) to (1.35:1).

[0065] In some embodiments, the quenching machine operates at a high pressure of 0.9–1.0 MPa, with a water-to-water ratio of 1.15–1.35, and a water flow rate of 2200–2800 m³ / h in high-pressure mode. 3 / h.

[0066] By controlling the flow rate of laminar cooling water during the quenching process, cooling water is sprayed onto the steel surface under pressure, allowing it to penetrate the oxide film on the steel surface. This ensures uniform cooling rate across the entire cross-section of the steel, reducing the temperature gradient between the surface and core, and minimizing differences in thermal stress. The high flow rate of laminar cooling water guarantees complete quenching and prevents localized cooling delays caused by insufficient water flow, which could affect the shape and properties of the steel.

[0067] The ratio of the upper and lower water flow rates for laminar cooling is adjusted to (1.15:1) to (1.35:1) to ensure uniform cooling of the upper and lower surfaces of the steel and prevent warping deformation and additional internal stress caused by uneven cooling rates of the upper and lower surfaces of the steel.

[0068] In some embodiments, the quenching machine roller speed is 0.30 to 0.50 m / min. Adjusting the appropriate roller speed allows the steel to remain in the quenching process for a sufficient time (2 to 3 min), which, combined with laminar flow cooling, enables the synchronous transformation of the martensitic phase and reduces the difference in internal stress.

[0069] In some embodiments, by adjusting the tempering parameters, the tempering brittle zone is avoided, ensuring both stress relief and preventing a decrease in impact toughness. Furthermore, at this tempering temperature, the alloy cementite (such as Cr)... 23 The precipitation temperature of C6 is higher than that of ordinary Fe3C, which ensures the full precipitation of cementite in the alloy. At the same time, the introduction of Mo and W elements can suppress the segregation of grain boundary impurities and avoid temper brittleness.

[0070] In some embodiments, according to the Johnson-Mehl equation, the half-cycle for cementite precipitation at 550°C is 15 min; at 30 min, 80% of the peak amount of cementite precipitation is reached; and at 40 min, granulation is essentially complete. If the tempering holding time is >40 min, it will lead to carbide coarsening (size >1 μm). Although the internal stress is completely eliminated, it will reduce the strength of the steel. Furthermore, by adjusting the tempering parameters, internal stress can be eliminated in a shorter time, with residual internal stress ≤50 MPa.

[0071] In some embodiments, the roughing mill has 7 to 9 rolling passes, and the single-pass reduction rate of the roughing mill is ≥13%.

[0072] In some embodiments, the rolling process includes roughing and finishing. The roughing process involves 7 to 9 rolling passes, and the finishing process has an inlet temperature of 950 to 1050°C.

[0073] Finishing rolling includes a first rolling pass, a second rolling pass, and a third rolling pass. The finishing rolling has 6 to 8 rolling passes. The single-pass reduction rate of the first rolling pass is 20 to 25%, the single-pass reduction rate of the second rolling pass is 15 to 20%, and the single-pass reduction rate of the third rolling pass is 10 to 15%.

[0074] In some embodiments, the first rolling pass of the finishing mill consists of the first 2 to 3 rolling passes, with a reduction rate of 20 to 25% per pass. The second rolling pass is an intermediate pass, and the third rolling pass is the last 1 to 2 rolling passes, with a reduction rate of 10 to 15%, in order to refine the grains and improve the surface quality of the steel.

[0075] In some embodiments, the currents for the first shot blasting and the second shot blasting are 30-40A, the speeds for the first shot blasting and the second shot blasting are 5-7m / min, and the particle sizes of the shot for the first shot blasting and the second shot blasting are 0.4-0.8mm.

[0076] In some embodiments, after the steel plate is tempered at high temperature, shot blasting is performed to relieve internal stress. The shot particle size is 0.4 to 0.8 mm, and the shot blasting process uses light shot blasting with an upper and lower current of 30 to 40 A and a shot blasting speed of 5 to 7 m / min.

[0077] In some embodiments, current regulation of the first and second shot blasting processes ensures uniform shot blasting speed. Speed ​​regulation of the first and second shot blasting processes helps accommodate steels of different thicknesses, achieving good surface treatment results. It prevents excessively high or low processing speeds from affecting the surface quality of the steel. The selection of shot particle size for the first and second shot blasting processes allows for finer processing to achieve optimal cleaning or strengthening effects.

[0078] In some embodiments, the first shot blasting treatment can remove oxides from the steel surface, effectively removing scale, rust, paint, and other contaminants, reducing the adsorption of corrosive media, and improving the corrosion resistance of the steel. The second shot blasting treatment can generate compressive stress on the steel surface, which helps to reduce or eliminate internal residual stress.

[0079] The above-mentioned method for preparing high-strength steel with low residual internal stress is simple, easy to operate, reduces production costs and energy consumption, and is suitable for large-scale production.

[0080] To further illustrate the present invention, the following examples are provided:

[0081] Example 1

[0082] A high-strength steel with low residual internal stress is provided, with a length of 10000 mm, a width of 1850 mm, and a thickness of 8 mm. The chemical composition of this high-strength steel, by mass fraction, includes: C 0.14%, Si 0.11%, Mn 1.2%, Cr 0.5%, Cu 0.06%, Ni 0.08%, Al 0.04%, P≤0.008%, S≤0.008%, Mo 0.6%, with the remainder being Fe and unavoidable impurities.

[0083] The preparation process is rigorous and orderly, proceeding as follows: heating the continuously cast billet, rough rolling, finish rolling, cooling to room temperature, coiling, quenching, straightening, first shot blasting, tempering, and second shot blasting. The process parameters for each key step are set as follows: billet heating temperature is 1280℃; rough rolling temperature is 1200℃, with 9 rolling passes; finish rolling temperature is 1000℃; coiling temperature is maintained at 630℃; quenching heating temperature is 900℃, holding time is 15 min, quenching machine roll speed is 0.40 m / min, and laminar flow cooling rate is 58℃·s. -1 The tempering temperature is 570℃, and the tempering holding time is 35 minutes.

[0084] Tests showed that the low residual internal stress high-strength steel had a Brinell hardness of 280HB, a yield strength of 850MPa, a tensile strength of 980MPa, an elongation of 15%, and an impact toughness of 80J, exhibiting excellent comprehensive mechanical properties.

[0085] Comparative Example 1

[0086] Compared to Example 1, the roller speed of the quenching machine was changed.

[0087] The quenching machine roller speed was 0.26 m / min. Other steps were the same as in Example 1, resulting in high-strength steel.

[0088] Tests showed that the high-strength steel had a Brinell hardness of 270 HB, a yield strength of 830 MPa, a tensile strength of 950 MPa, an elongation of 16%, and an impact toughness of 75 J. However, the corresponding internal stress distribution was uneven, affecting the product's sheet shape.

[0089] Comparative Example 2

[0090] Compared to Example 1, the roller speed of the quenching machine was changed.

[0091] The quenching machine roller speed is 0.55 m / min. Other steps are the same as in Example 1, and high-strength steel is obtained.

[0092] Tests showed that the high-strength steel had a Brinell hardness of 275HB, a yield strength of 840MPa, a tensile strength of 960MPa, an elongation of 15.5%, and an impact toughness of 78J. However, the corresponding internal stress was relatively large and unevenly distributed.

[0093] Comparative Example 3

[0094] Compared to Example 1, no second shot blasting treatment was performed.

[0095] The other steps were the same as in Example 1, and high-strength steel was obtained.

[0096] Tests showed that the high-strength steel had a Brinell hardness of 280 HB, a yield strength of 850 MPa, a tensile strength of 1050 MPa, an elongation of 15%, and an impact toughness of 20 J. However, the uneven distribution of internal stress in the steel plate affected its subsequent performance.

[0097] Table 1 shows the internal stress data at different test points in the transverse direction corresponding to the absence of a second shot blasting treatment. Table 2 shows the internal stress test data for different test points corresponding to different quenching machine roller speeds in this invention for testing the internal stress data of high-strength steel with low residual internal stress.

[0098] It should be noted that the test content includes: selecting high-strength steel with low residual internal stress to be tested with the following specifications: length 10000mm, width 1850mm, and thickness 8mm. Taking the rolling direction of point 1 as an example, in the width direction of the steel plate, a distance of 50mm from one edge of the steel plate is selected as the edge point of the steel plate, and then 1 / 8, 1 / 4, 3 / 8, and 1 / 2 of the plate width are selected as test points, marked as test positions of point 1.

[0099] Taking point 1 in the horizontal direction as an example, along the length of the steel plate, a distance of 200mm from one edge of the steel plate is selected as the edge test point, and then test points are set at intervals of 2000mm along the length direction.

[0100] During the testing process, a zero-stress specimen with dimensions of 100*50*4mm was used as the test benchmark, providing an accurate reference standard for stress measurement. Ultrasonic testing was combined to ensure that the high-strength steel was not damaged during the testing process, maintaining its original stress state. Furthermore, a large number of measurement points were completed in a short time, reducing the impact of environmental factors (such as temperature fluctuations) on the measurement results. Good repeatability allowed for cross-verification of multiple measurement results, ensuring the accuracy and reliability of the data.

[0101] Table 1 shows the internal stress data at different test points in the transverse direction for cases without a second shot blasting treatment.

[0102]

[0103] Table 2. Internal stress data at different test points corresponding to different quenching machine roller speeds.

[0104]

[0105]

[0106] in, Figure 1 This is a photograph of the high-strength steel with low residual internal stress obtained in Example 1 of the present invention. Figure 2 The images show the actual high-strength steels obtained in Comparative Examples 1 and 2 of this invention; wherein, (a) the roller speed is 0.26 m / min, and (b) the roller speed is 0.55 m / min. Figure 3 This is a distribution diagram of different test points in the rolling and transverse directions according to an embodiment of the present invention.

[0107] This invention, by testing the internal stress at different test points, taking Example 1 as an example, and by selecting appropriate chemical compositions and process parameters, produced a high-strength steel with low residual internal stress, exhibiting a Brinell hardness of 280 HB, a yield strength of 850 MPa, a tensile strength of 1050 MPa, an elongation of 15%, and an impact toughness of 20 J, demonstrating excellent comprehensive mechanical properties. According to the data in Table 1, the internal stress is higher and unevenly distributed in the area without the second shot blasting treatment, affecting subsequent performance. According to the data in Table 2, the quenching machine roller speed in Example 1 is 0.4 m / min, resulting in a lower level of residual internal stress. The internal stress data at different test points fluctuate less and are more evenly distributed, effectively ensuring the stability of the steel during subsequent use and contributing to improved service performance under complex working conditions.

[0108] Furthermore, in the testing of high-strength steel, test points were selected at the edge, 1 / 8, 1 / 4, 3 / 8, and 1 / 2 of the steel plate, respectively, to comprehensively cover different parts of the steel plate. During processing, the edge of the steel plate is prone to stress concentration due to shearing, rolling, and other processes, while the stress distribution in the central area is relatively complex. This layout allows for the complete capture of stress changes from the edge to the center, avoiding omissions of key stress distribution areas and ensuring that the obtained stress data reflects the overall stress state of the steel plate.

[0109] Measuring points are selected at specific proportional locations such as the edge, 1 / 8, and 1 / 4 of the steel plate, as these locations are typical and representative. For example, the 1 / 4 and 1 / 2 points are key locations for assessing the stress in the central region of the steel plate, while the 1 / 8 and 3 / 8 points can help analyze the transition of stress from the edge to the center. By measuring these typical locations, the overall stress distribution of the steel plate can be inferred based on limited measurement data, thus improving the representativeness of the data for the overall stress condition.

[0110] During the rolling process, the internal microstructure of high-strength steel exhibits a distinct directionality along the rolling direction, resulting in differences in mechanical properties and stress distribution between the rolling and transverse directions. Simultaneously collecting and monitoring stress data in both the rolling and transverse directions allows for a more comprehensive assessment of the stress characteristics of high-strength steel in different directions. This provides a basis for rationally selecting the material's application direction in engineering applications, avoiding evaluation biases caused by unidirectional stress analysis.

[0111] By setting each longitudinal test point 2000mm apart, the system balances data validity with testing efficiency and cost. For large high-strength steel plates, overly dense test point arrangements increase testing time and cost, while overly sparse arrangements may fail to accurately reflect stress distribution characteristics. The 2000mm interval effectively captures the longitudinal stress variation trend of the steel plate in most cases, ensuring representative measurement data that reflects the stress distribution pattern over a long distance, providing reliable data support for macroscopic stress analysis.

[0112] During the testing process, a zero-stress specimen with dimensions of 100*50*4mm was used as the test benchmark, providing an accurate reference standard for stress measurement. The zero-stress specimen eliminates the interference of the material's initial stress on the measurement results, ensuring that the obtained stress data truly reflects the stress changes generated during the processing and use of the high-strength steel. When comparing and analyzing stress data from different locations, the zero-stress benchmark ensures the accuracy and comparability of the data, effectively reducing measurement errors and improving the reliability of the test results.

[0113] Furthermore, ultrasonic testing, which is non-destructive, rapid, and highly repeatable, is combined with the aforementioned measurement design to further enhance data accuracy. The non-destructive testing characteristics ensure that the high-strength steel remains undamaged during testing, maintaining its original stress state; rapid testing enables the completion of measurements at numerous points in a short time, reducing the impact of environmental changes (such as temperature fluctuations) on the measurement results; and excellent repeatability allows for cross-verification of multiple measurement results, ensuring accurate and reliable data.

[0114] In summary, this invention, through optimized chemical composition and synergistic control of process parameters, achieves homogenization of the internal microstructure and reduces residual internal stress, resulting in a high-strength steel with a Brinell hardness of 200–350 HB, exhibiting high strength and good wear resistance. It reduces the difference in internal stress within the microstructure, refining microscopic stress concentration and lowering residual internal stress. It also reduces the segregation of grain boundary carbides and inhibits the decomposition of residual austenite during service, preventing dimensional changes. Simultaneously, Mo and W elements preferentially occupy grain boundaries, purifying impurities in the grain boundary region. This dual effect prevents temper brittleness and improves impact toughness.

[0115] The above-mentioned method for preparing high-strength steel with low residual internal stress is simple, convenient to operate, reduces production costs and energy consumption, and is suitable for large-scale production. In summary, the above technical solutions of this invention are merely preferred embodiments and do not limit the patent scope of this invention. Any equivalent structural transformations made using the description and drawings of this invention under the technical concept of this invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this invention.

Claims

1. A high-strength steel with low residual internal stress, characterized in that, The chemical composition of the low residual internal stress high-strength steel, by mass fraction, includes: C 0.10-0.16%, Si 0.09-0.18%, Mn 1.0-1.5%, Cr 0.4-0.6%, Cu 0.05-0.08%, Ni 0.05-0.1%, Al 0.03-0.05%, P≤0.008%, S≤0.008%, Mo 0.5-0.7%, with the remainder being Fe and unavoidable impurities; The Brinell hardness of the low residual internal stress high-strength steel is 200-350 HB.

2. The high-strength steel with low residual internal stress according to claim 1, characterized in that, The low residual internal stress high-strength steel has a yield strength of 800-1200 MPa, a tensile strength of 1000-1400 MPa, an elongation of 10-25%, and an impact toughness of 15-25 J.

3. The high-strength steel with low residual internal stress according to claim 2, characterized in that, The fatigue strength of the low residual internal stress high-strength steel is 50-60% of its tensile strength.

4. The high-strength steel with low residual internal stress according to claim 1, characterized in that, The thickness of the low residual internal stress high-strength steel is 3-10 mm.

5. A method for preparing high-strength steel with low residual internal stress as described in any one of claims 1 to 4, characterized in that, step include: The continuous casting billet is heated, rough rolled, finish rolled, cooled to room temperature, coiled, quenched, straightened, subjected to first shot blasting, tempered and second shot blasting. The chemical composition of the continuously cast billet is the same as that of the low residual internal stress high-strength steel. The quenching process includes heating, holding, and laminar flow cooling steps; in the quenching step, the speed of the conveyor rollers is 0.30 to 0.50 m / min; the heating temperature for quenching is 870 to 925℃, and the holding time for quenching is 10 to 15 min. The laminar flow cooling adopts a laminar water cooling method, with a water temperature of 15-25℃ and a laminar flow cooling rate of 55-60℃·s. -1 ; The tempering temperature is 550–630°C, and the tempering holding time is 30–40 minutes.

6. The method for preparing high-strength steel with low residual internal stress according to claim 5, characterized in that, The laminar flow cooling water flow rate is 2200–2800 m³ / h. 3 / h, the ratio of the upper and lower water flow rates for laminar flow cooling is (1.15:1) to (1.35:1).

7. The method for preparing high-strength steel with low residual internal stress according to claim 5, characterized in that, In the quenching heating step, the oxygen content of the heating atmosphere is 800-1000 ppm, and the pressure of the heating atmosphere is 15-25 Pa. In the laminar flow cooling step of quenching, the water pressure is 0.9–1.0 MPa.

8. The method for preparing high-strength steel with low residual internal stress according to claim 5, characterized in that, The continuous casting billet is heated at a temperature of 1270–1290°C; the roughing rolling temperature is 1000–1220°C; the finishing rolling temperature is 950–1050°C; and the coiling temperature is 600–650°C.

9. The method for preparing high-strength steel with low residual internal stress according to claim 5, characterized in that, The roughing mill has 7 to 9 rolling passes, and the single-pass reduction rate of the roughing mill is ≥13%. Finishing rolling includes a first rolling pass, a second rolling pass, and a third rolling pass. The finishing rolling has 6 to 8 rolling passes. The single-pass reduction rate of the first rolling pass is 20 to 25%, the single-pass reduction rate of the second rolling pass is 15 to 20%, and the single-pass reduction rate of the third rolling pass is 10 to 15%.

10. The method for preparing high-strength steel with low residual internal stress according to claim 5, characterized in that, The current for the first shot blasting treatment and the second shot blasting treatment are 30-40A, the speed for the first shot blasting treatment and the second shot blasting treatment are 5-7m / min, and the particle size of the shot for the first shot blasting treatment and the second shot blasting treatment is 0.4-0.8mm.

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