High hardness, lamellar tear resistant steel plate and method of production thereof

Abstract

The present application relates to a kind of high-hardness anti-laminated tearing steel plate and its production method, the chemical composition in steel is C:0.27%~0.31%, Si:0.85%~0.95%, Mn:0.8%~1.0%, Nb:0.015%~0.030%, Ni:0.45%~0.55%, W:0.40%~0.50%, Al:0.04%~0.07%, B:0.0005%~0.0020%, RE:0.0015%~0.0035%, and 1.25%≤W+Mn≤1.45%, the balance is Fe and impurity;With Nb micro-alloying, replace Mo with W, ensure quenching and prevent the precipitation of harmful oxide at grain boundary;Add rare earth element RE to purify steel liquid, modify inclusion and reduce the segregation of P, S and B at grain boundary, utilize controlled rolling and controlled cooling to refine and homogenize the original structure of steel plate, utilize longer time tempering heat treatment to fully release residual stress, finally produce high-hardness anti-laminated tearing low-alloy steel plate with thickness specification of 30~60mm, HB500 grade.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel plate production, in particular to a high-hardness layered tearing resistant steel plate with a thickness specification of 30-60mm and a surface hardness of HB500 level and a production method thereof. BACKGROUND

[0002] Low-alloy wear-resistant steel plates with a surface hardness of HB500 level are widely used in the fields of engineering machinery and mining machinery for manufacturing wear-resistant components, and generally adopt a heat treatment process of quenching and tempering, and the structure is mainly low-carbon martensite.

[0003] Wear-resistant steel plates with a thickness of 30mm or more often have layered tearing phenomenon when welded or subjected to Z-direction stress, which is a phenomenon of layered cracking of steel along the thickness direction, seriously threatening the safety of components. In recent years, with the development of the field of engineering machinery, the performance requirements for high-strength steel plates are increasingly stringent. For example, key parts of engineering machinery such as coal mine scraper conveyors require not only a hardness of HB500 level, but also excellent Z-direction performance.

[0004] A Chinese patent application with the publication number CN115369303A discloses a "wear-resistant steel NM500 preparation method", the steel contains C: 0.22-0.25%, Si: 0.30-0.40%, Mn: 1.30-1.40%, P: ≤0.015%, S: ≤0.005%, Als: 0.020-0.040%, Nb: 0.020-0.030%, Ti: 0.015-0.025%, Cr: 0.80-1.0%, Mo: 0.35-0.45%, Ni: 0.30-0.40%, B: 0.0010-0.0020%, Ce: ≤0.0030%, and the rest is Fe and unavoidable inclusions; a 25kg steel ingot is smelted by a vacuum electric furnace, heated to 1200℃ by an electric heating furnace for 60min, rolled by a 750mm×550mm two-high reversing mill, the final rolling temperature is 820±20℃, the rolled steel plate is water-cooled to 680±20℃, and then placed in a cooling bed for air cooling to room temperature; after cooling, the steel plate is placed in an electric heating furnace and heated to 860±10℃ for 25min, and then taken out for water quenching to room temperature. The quenched steel plate is placed in an electric heating furnace and heated to 200±10℃ for 90min, and then taken out for air cooling to room temperature. The application smelts, rolls and heat treats by a vacuum electric furnace, a two-high reversing mill and an electric heating furnace to produce wear-resistant steel NM500, and the steel plate performance meets the requirements and has good low-temperature toughness. However, it does not involve the problem of preventing layered tearing of thick wear-resistant steel plates.

[0005] Chinese patent application CN116855835A discloses a method for producing thick, heat-treated, high-strength steel plates resistant to lamellar tearing. The steel's chemical composition by weight percentage is: C=0.11–0.16, Si=0.15–0.35, Mn=0.80–1.30, P≤0.010, S≤0.002, Nb=0.015–0.025, V=0.02–0.06, Ti≤0.005, Al=0.07–0.09, Cr=0.30–0.80, Mo=0.35–0.65, Ni=0.30–1.20, B=0.001–0.002, CEV≤0.70, with the balance being Fe and unavoidable impurities. The process route is BOF-LF-VD-continuous casting-slab heating-rolling-stacking-heat treatment-performance testing. The billet is heated to 1180–1230℃, with a soaking time of ≥60 min. Rolling is a two-stage process: the roughing stage has a rolling temperature of ≥1120℃, with the last three passes controlling a reduction of ≥35 mm per pass; the finishing stage has a rolling temperature of ≤900℃. The rolled steel plate is cooled to 250–300℃ on a cooling bed and then stacked for slow cooling for ≥48 h. After slow cooling, the steel plate undergoes quenching and tempering in a continuous heat treatment furnace, with a quenching temperature of 900–930℃ and a tempering temperature of 620–680℃. The matrix structure of the steel plate is tempered sorbite + lower bainite, and no TiN or MnS inclusions affecting resistance to lamellar tearing were detected in the core of the steel plate. It employs a Ti-removing and Al-adding composition design, along with an optimized Ca treatment process, to eliminate the impact of TiN and MnS inclusions on the Z-axis properties of the steel plate. During continuous casting, a combination of light reduction and convex roller reduction is used to improve core porosity, while a reasonable steel plate cooling and dehydrogenation process is implemented. Under the condition that other alloying elements are not adjusted and the steelmaking and rolling production rhythm is not affected, the pass rate of the anti-laminated tear performance of 100-150mm Q550 and Q690 grade high-strength steel is consistently maintained at ≥98.0%. However, the strength level of the finished steel plate is only 690MPa, which cannot reach the HB500 level hardness. Furthermore, the high Al content easily leads to continuous casting nozzle blockage and excessive inclusions, and also affects low-temperature toughness.

[0006] Chinese patent application CN115747657A discloses "a high-strength HY950CF steel plate for hydropower engineering and its production method." The steel plate has a thickness of 50-120 mm and contains the following chemical composition (wt%): C: 0.09-0.12, Si: 0.15-0.25, Mn: 0.30-0.60, P≤0.010, S≤0.003, Al s: 0.020~0.040, Nb: 0.02~0.03, V: 0.04~0.1, Cr: 1.2~1.6, Ni: 2.4~2.8, Cu: 0.8~1.0, Mo: 0.2~0.3, Re: 0.0015~0.0025, others are Fe and residual elements, carbon equivalent Ceq < 0.7, microstructure is bainitic tempered microstructure, longitudinal and transverse V-notch impact energy at -60℃ ≥127J. The production process is ingot casting, primary heating, billet rolling, secondary heating and rolling, heat treatment, using high temperature quenching + critical quenching + tempering heat treatment, after quenching, it is placed in a quenching furnace for tempering at 650±20℃, and air-cooled to room temperature. It adopts a rolling-instead-of-forging process, and the heat treatment process involves multiple quenchings to ensure hardenability while refining austenite grains, and tempering to improve the uniformity of the mechanical properties of the whole plate. The finished steel plate possesses high strength, high toughness, fatigue resistance, resistance to lamellar tearing, as well as good weldability and corrosion resistance. However, it requires the production of large-thickness steel ingots, and the high Cr and Ni content in the steel makes continuous casting impossible.

[0007] Chinese patent application CN108642390A discloses "a high-strength thick steel plate with a thickness-direction property Z of 35-50% and a production method thereof." The composition and wt% of the thick steel are as follows: C: 0.10-0.18%, Si: 0.10-0.40%, Mn: 1.20-1.60%, P≤0.010%, S≤0.005%, Cr: 0.10-0.50%, Mo: 0.45-0.75%, Ni: 0.05-0.20%, Nb+Ti+V sum of 0.040-0.06%, B: 0.0008-0.0020%, H≤2ppm. The production steps include: smelting clean steel and continuously casting it into billets; rough rolling after heating the billets; finish rolling; quenching; tempering; and natural cooling to room temperature. Its main purpose is to address the problem of high-strength steel exhibiting low stress under 107 cyclic fatigue conditions, leading to lamellar tearing after welding or under stress. The finished steel plate has a yield strength of 900–1000 MPa, tensile strength ≥1000 MPa, elongation A ≥15%, and a thickness-direction property Z-value of 35%–50%. No lamellar tearing was observed after welding or 107 cyclic fatigue testing. However, the hardness of the finished steel plate is lower than HB500, and it requires high-temperature tempering heat treatment.

[0008] Chinese patent application CN116583610A discloses an "extremely thick steel plate for steam boiler drum with excellent surface quality and resistance to lamellar tearing, and a method for manufacturing the same." The steel plate composition and microstructure are as follows: C: 0.2% to 0.3%, Si: 0.05% to 0.5%, Mn: 1.0% to 2.0%, Al: 0.005% to 0.1%, P: 0.01% or less, S: 0.015% or less, Nb: 0.001% to 0.02%, V: 0.001% to 0.03%, Ti: 0.001% to 0.03%, Cr: 0.01% to 0.3%, Mo: 0.01% to 0.12%, Cu: 0.01% to 0.4%, Ni: 0.05% to 0.4%, Ca: 0.0005% to 0.004%, with the balance being Fe and other unavoidable impurities. Ceq is in the range of 0.5 to 0.6; the slab is first heated at a temperature of 1100°C to 1300°C; the first intermediate material is second heated at a temperature of 1000°C to 1200°C; the second intermediate material is third heated at a temperature of 1000°C to 1200°C; and normalizing heat treatment is performed after hot rolling. The thickness of the steel is 133 mm to 250 mm. The tensile strength of the steel is 550 MPa to 690 MPa. The reduction of area (ZRA) is 35% or greater. However, the production process of this steel plate requires multiple heating and heat treatments, making the production process complex.

[0009] In summary, the existing production of high-strength anti-lamellar tear steel plates has the following shortcomings: 1. The hardness of the finished steel plate is lower than HB500; 2. The production process is complex; 3. The alloy content is high, making continuous casting impossible; 4. Z-axis performance cannot be guaranteed. Summary of the Invention

[0010] This invention provides a high-hardness, lamellar tear-resistant steel plate and its production method. It employs a novel chemical composition and production process design, using W instead of Mo for Nb microalloying to ensure hardenability while suppressing the precipitation of harmful oxides at grain boundaries. The addition of rare earth element RE purifies the molten steel, reduces impurities and the segregation of P, S, and B grain boundaries. Controlled rolling and cooling refine and homogenize the original microstructure of the steel plate, and prolonged tempering heat treatment fully releases residual stress. The combination of these techniques significantly reduces the risk of lamellar tear initiation. Ultimately, it produces high-hardness, lamellar tear-resistant low-alloy steel plates with a thickness of 30–60 mm and an HB500 grade.

[0011] To achieve the above objectives, the present invention employs the following technical solution:

[0012] A high-hardness, tear-resistant steel plate, wherein the chemical composition of the steel, by weight percentage, is: C: 0.27%–0.31%, Si: 0.85%–0.95%, Mn: 0.8%–1.0%, Nb: 0.015%–0.030%, Ni: 0.45%–0.55%, W: 0.40%–0.50%, Al: 0.04%–0.07%, B: 0.0005%–0.0020%, RE: 0.0015%–0.0035%, and 1.25% ≤ W + Mn ≤ 1.45%, with the balance being Fe and unavoidable impurities; the impurity elements in the steel are controlled as follows: P ≤ 0.009%, S ≤ 0.0010%, [N] ≤ 0.0030%, [H] ≤ 0.00010%, [O] ≤ 0.0010%, and the retained austenite content is 3%–5%.

[0013] The finished steel plate has a surface hardness of HB≥500, tensile strength ≥1400MPa, longitudinal impact energy Akv≥40J at -40℃, elongation A≥10%, 180° cold bending D=8a is qualified, and thickness direction Z≥15%.

[0014] The thickness of the finished steel plate is 30-60mm.

[0015] A method for producing high-hardness, tear-resistant steel plate, comprising the following processes: converter smelting, refining, continuous casting, billet heating and slow cooling, slab heating, controlled rolling, controlled cooling, stacking and slow cooling / high-temperature tempering, quenching, and tempering heat treatment; wherein the following processes are controlled:

[0016] 1) Refining: LF+RH refining process is adopted, and the RH refining vacuum cycle time is ≥24min; after RH vacuum treatment, RE alloy is added by wire feeding under argon protection;

[0017] 2) Continuous casting: The billet casting speed is 0.8~1.0m / min, and the target superheat of the tundish is controlled below 20℃; the entire process is protected during casting, and electromagnetic stirring is used; the center segregation of the billet is controlled below C1.0 grade;

[0018] 3) Slow cooling of billet: The initial heating temperature is ≥550℃, and the billet is heated to 620~650℃ at a heating rate of ≤50℃ / h. After holding at this temperature for 30~40h, the billet is slowly cooled in the furnace to below 400℃ and then removed from the furnace and air-cooled to room temperature.

[0019] 4) Slab heating: The temperature of the soaking zone is 1160~1200℃, and the soaking time is 2~2.5h;

[0020] 5) Controlled rolling: Two-stage controlled rolling is adopted, with the compression ratio (i.e., billet thickness / finished plate thickness) controlled to be ≥4; the upper and lower roll speed ratio controlled to be 1.1:1 to 1.3:1; the roughing rolling start temperature ≥1000℃, the roughing rolling finish temperature ≥960℃; the finishing rolling start temperature is 850~880℃, the finishing rolling reduction rate is ≥60%, and the finishing rolling finish temperature is 800~850℃.

[0021] 6) Controlled cooling: Ultra-fast cooling or laminar flow cooling is adopted after rolling, with an initial cooling temperature ≥760℃ and a final cooling temperature of 660~680℃;

[0022] 7) Stacking and slow cooling / high temperature tempering: When the slab temperature is >400℃, stacking and slow cooling is carried out for ≥28h; when the slab temperature is ≤400℃, high temperature tempering is carried out, with a tempering heating temperature of 600~650℃ and a holding time of 3.5~4.5min / mm.

[0023] 8) Quenching and tempering heat treatment: Quenching temperature 850~880℃, holding time 3.0~3.5min / mm; Low temperature stress relief tempering temperature 200~220℃, holding time 8~10min / mm.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1) A new chemical composition and production process design is adopted, with W replacing Mo and Nb microalloying to ensure hardenability while inhibiting the precipitation of harmful oxides at grain boundaries; rare earth element RE is added to purify the molten steel, reduce the inclusions and grain boundary segregation of P, S and B; controlled rolling and cooling are used to refine and homogenize the original microstructure of the steel plate; and a longer tempering heat treatment is used to fully release residual stress. The combination of the above technologies greatly reduces the risk of lamellar tearing; finally, high-hardness, lamellar tear-resistant low-alloy steel plates with a thickness of 30-60mm and HB500 grade are produced.

[0026] 2) Finished steel plate surface hardness ≥ HB500, tensile strength ≥ 1400MPa; impact energy Akv ≥ 40J at -40℃; elongation A ≥ 10%, 180° cold bending D=8a qualified, thickness direction Z ≥ 15%.

[0027] 3) The chemical composition design of the steel plate is characterized by low carbon, tungsten, niobium, boron and rare earth synergistic microalloying. The alloy content is relatively low, which makes it easy to realize smelting and continuous casting, and the production process is simple. Detailed Implementation

[0028] The present invention discloses a high-hardness, anti-lamellar tear steel plate, the chemical composition of which, by weight percentage, is: C: 0.27%–0.31%, Si: 0.85%–0.95%, Mn: 0.8%–1.0%, Nb: 0.015%–0.030%, Ni: 0.45%–0.55%, W: 0.40%–0.50%, Al: 0.04%–0.07%, B: 0.0005%–0.0020%, RE: 0.0015%–0.0035%, and 1.25% ≤ W + Mn ≤ 1.45%, with the balance being Fe and unavoidable impurities; the impurity elements in the steel are controlled as follows: P ≤ 0.009%, S ≤ 0.0010%, [N] ≤ 0.0030%, [H] ≤ 0.00010%, [O] ≤ 0.0010%, and the retained austenite content is 3%–5%.

[0029] The rationale for the chemical composition design of the high-hardness, tear-resistant steel plate described in this invention is as follows:

[0030] C: A carbide-forming element, C ensures that the steel plate achieves a strength of HB500 after quenching and improves the hardenability of thick steel plates, ensuring uniform performance along the thickness direction. However, excessive carbon content reduces the plasticity and low-temperature toughness of the steel plate, and also easily leads to center segregation in the cast billet after continuous casting, which acts as a crack initiation point after rolling, causing a decrease in the Z-axis properties of the steel plate. Therefore, this invention controls the C content to be between 0.27% and 0.31%.

[0031] Si is a non-carbide-forming element, whose main function is to inhibit carbide precipitation and stabilize the content of retained austenite in steel. During Z-axis tension, the retained austenite acts as a soft phase, which can inhibit the formation and propagation of lamellar cracks. However, excessive Si will reduce toughness and weldability. Therefore, this invention controls the Si content to be between 0.85% and 0.95%.

[0032] Mn plays a role in deoxidation and solid solution strengthening, ensuring the strength of steel plates. It can also delay the transformation of austenite to ferrite and pearlite, and improve hardenability. However, Mn is prone to forming central segregation in steel, which can lead to lamellar cracks in the center of the steel plate thickness. Therefore, this invention controls the Mn content at 0.8% to 1.0%.

[0033] Nitrogen (Nb): The most effective element for refining grains and achieving controlled rolling. During two-stage controlled rolling, it forms carbonitrides, inhibiting austenite recrystallization, refining austenite grains, and after quenching, forming refined martensite lath bundles, thus effectively preventing lamellar cracks in steel plates. Nb can also work synergistically with titanium (W) to delay boron diffusion to grain boundaries and avoid the formation of the brittle B2O3 phase that triggers lamellar cracks; however, excessive Nb content will result in the precipitation of too many carbonitrides, affecting the steel plate's resistance to lamellar tearing. Therefore, this invention controls the Nb content to 0.015%–0.030%.

[0034] Al (Al) is an effective element for deoxidation and nitrogen fixation. Deoxidation reduces oxide inclusions in steel and purifies the steel. After deoxidation, nitrogen fixation ensures that boron (B) does not combine with nitrogen (N), thus enhancing hardenability. When its content is less than 0.03%, the effect is minimal; excessively high content will form a large number of Al₂O₃ inclusions in the steel, which can easily become the initiation point for lamellar tearing under Z-axis stress. Therefore, this invention controls the Al content to 0.04%–0.07%.

[0035] W effectively inhibits the segregation of P at grain boundaries, thereby improving Z-axis properties. W works synergistically with Nb to delay B diffusion towards grain boundaries, preventing the formation of the brittle B2O3 phase. Furthermore, WC and NbC precipitate coherently, resulting in finer carbides under the same processing conditions, significantly enhancing the dislocation pinning effect and further suppressing P segregation at grain boundaries. W also strengthens through solid solution and refines grains. Additionally, W significantly improves hardenability and promotes martensitic transformation. Compared to Mo, W carbides are more stable and have a better effect on improving hardenability. Therefore, this invention controls the W content to 0.40%–0.50%. Because both W and Mn improve hardenability, excessive addition increases the risk of lamellar cracks; therefore, the content is required to be 1.25% ≤ W + Mn ≤ 1.45%.

[0036] Ni (Ni): It can improve the low-temperature toughness, hardenability, and resistance to lamellar tearing of steel. It can form FeNi compounds with Fe. When the steel plate is subjected to low-temperature impact load at low temperatures, the Ni in solid solution will increase the low-temperature impact absorption energy. Ni and W work synergistically to shift the CCT curve to the right and improve hardenability. Ni can also reduce the segregation of impurity elements such as P and S at grain boundaries and improve the ability to resist lamellar tearing. However, Ni is relatively expensive. The addition of 0.45% to 0.55% Ni to the steel of this invention can ensure the mechanical properties of the steel plate, especially the low-temperature toughness at -40℃, without significantly increasing the production cost, making the product competitive in the market.

[0037] RE (reinforcing iron): Adding 0.0015%–0.0035% RE is mainly used for morphology control of inclusions in steel, modifying elongated sulfides (Mns) and oxides (Al2O3) into spherical inclusions, preventing them from becoming Z-axis crack initiation sites, thereby improving Z-axis properties. Simultaneously, RE atoms segregate at austenite grain boundaries, delaying proeutectoid ferrite precipitation, inhibiting grain boundary adsorption of harmful elements such as P and S, and reducing temper brittleness. RE below 0.0010% has no effect, while excessively high content will form coarse oxides, reducing Z-axis properties.

[0038] B: Even trace amounts of boron in steel can inhibit the formation of proferrite and greatly improve hardenability. When the boron content is too high (≥0.0025%), it tends to accumulate at grain boundaries, reducing the grain boundary bonding energy, and thus forming lamellar fracture under Z-direction stress. Therefore, this invention controls the boron content to be between 0.0005% and 0.0020%.

[0039] Retained austenite: 3% to 5% retained austenite acts as a hydrogen trap, which can prevent the formation and propagation of lamellar tears. However, if the content of retained austenite is too high, it will reduce the strength of the steel plate.

[0040] Impurity elements: P and S tend to segregate at grain boundaries or form segregation in the core of the steel plate, which seriously affects low-temperature toughness and Z-axis properties; H accumulates at metallurgical defects in the steel plate and can become the initiation source of lamellar tearing; in addition, strip-shaped sulfides, oxides and sharp-angled nitrides in the steel can cause local stress concentration and significantly reduce the crack arrest ability of lamellar cracks in the steel plate; in order to ensure good Z-axis properties, this invention controls P ≤ 0.009%, S ≤ 0.0010%, [N] ≤ 0.0030%, [H] ≤ 0.00010%, and [O] ≤ 0.0010% in the steel.

[0041] The present invention discloses a method for producing high-hardness, tear-resistant steel plates. The production process includes converter smelting, refining, continuous casting, billet heating and slow cooling, slab heating, controlled rolling, controlled cooling, stacking and slow cooling / high-temperature tempering, quenching, and tempering heat treatment; wherein the following processes are controlled:

[0042] 1) Refining: LF+RH refining is adopted, with RH refining vacuum circulation time ≥24min; through long-term vacuum treatment, the [N] in the molten steel is controlled to be ≤0.0030%, [O] ≤0.0010%, and [H] ≤0.00010%. After RH vacuum treatment, RE alloy is added to the wire feed under argon protection; the purpose is to prevent rare earth oxidation, improve the yield, and add rare earth modification treatment to reduce the harm of sulfides and oxide inclusions.

[0043] 2) Continuous casting: The billet casting speed is 0.8 to 1.0 m / min, and the target superheat of the tundish is controlled below 20°C; the entire process is protected during casting to prevent the molten steel from oxidizing and hydrogen from entering the tundish; electromagnetic stirring is used during continuous casting; the center segregation of the billet is controlled below C1.0 grade; the purpose is to reduce center segregation and prevent center segregation from becoming the initiation point of lamellar cracks.

[0044] 3) Slow cooling of billet: The initial heating temperature is ≥550℃, and the billet is heated to 620~650℃ at a heating rate of ≤50℃ / h. After holding at this temperature for 30~40h, it is slowly cooled in the furnace to below 400℃ and then air-cooled to room temperature. Heating reduces the degree of segregation in the core of the billet and can also reduce the hydrogen content and casting internal stress in the billet.

[0045] 4) Slab heating: The temperature of the soaking zone is 1160~1200℃, and the soaking time is 2~2.5h; the purpose is to prevent rare earth elements from oxidizing during slab heating due to prolonged heating in the soaking zone.

[0046] 5) Controlled Rolling: A two-stage controlled rolling process, consisting of roughing and finishing, is employed to fully refine and homogenize the rolled microstructure. To ensure deep core deformation, the compression ratio (slab thickness / finished plate thickness) is controlled to be ≥4; the upper and lower roll speed ratio is controlled to be 1.1:1 to 1.3:1; differential speed rolling (using different roll speeds for the upper and lower rolls) introduces asymmetric deformation in the thickness direction, creating a shear strain gradient and thus improving Z-axis properties. The roughing rolling start temperature is ≥1000℃, and the roughing rolling finish temperature is ≥960℃; the finishing rolling start temperature is 850~880℃, the finishing rolling reduction rate is ≥60%, and the finishing rolling finish temperature is 800~850℃.

[0047] 6) Controlled cooling: After rolling, ultra-fast cooling or laminar flow cooling is adopted, with an initial cooling temperature of ≥760℃ and a final cooling temperature of 660~680℃; the purpose of controlled cooling is to prevent grain growth and to prevent premature precipitation of W carbides.

[0048] 7) Stacking and slow cooling / high-temperature tempering: When the slab temperature after rolling is >400℃, stacking and slow cooling is carried out for ≥28h; when the slab temperature after rolling is ≤400℃, high-temperature tempering is carried out, with a tempering heating temperature of 600~650℃ and a holding time of 3.5~4.5min / mm; the purpose of stacking and slow cooling / high-temperature tempering is to remove hydrogen inside the steel plate and at the same time remove the internal stress caused by uneven rolling and cooling of the steel plate.

[0049] 8) Quenching and Tempering Heat Treatment: Quenching temperature 850–880℃, holding time 3.0–3.5 min / mm; the purpose of quenching is to obtain a martensitic structure to ensure the steel plate hardness reaches HB500 level. Using a lower temperature and a longer quenching time aims to allow core elements to diffuse and improve core segregation without excessive grain growth. Low-temperature stress-relieving tempering temperature is 200–220℃, holding time 8–10 min / mm. The purpose of prolonged low-temperature tempering after quenching is to fully remove the internal stress formed during quenching and further improve resistance to lamellar tearing.

[0050] The finished steel plate has a surface hardness of HB≥500, tensile strength ≥1400MPa, longitudinal impact energy Akv≥40J at -40℃, elongation A≥10%, 180° cold bending D=8a is qualified, and thickness direction Z≥15%.

[0051] The thickness of the finished steel plate is 30-60mm.

[0052] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0053] Example:

[0054] The chemical composition of the steel in each embodiment is shown in Table 1, the smelting process parameters are shown in Table 2, the rolling process parameters are shown in Table 3, the post-rolling slow cooling process parameters are shown in Table 4, the heat treatment process parameters are shown in Table 5, and the performance test results of the finished steel plates are shown in Table 6.

[0055] Table 1 Chemical composition of steel, wt%

[0056]

[0057] Table 2 Smelting process parameters

[0058]

[0059] Table 3 Rolling process parameters

[0060]

[0061] Table 4 Post-rolling slow cooling process parameters

[0062]

[0063] Table 5 Heat treatment process parameters

[0064]

[0065] Table 6 Performance test results of finished steel plates

[0066]

[0067] As can be seen, the steel plate produced in this embodiment has high hardness, good plasticity and toughness, qualified cold bending performance, Z-direction performance ≥15%, and good resistance to lamellar tearing.

[0068] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for producing a high-hardness, tear-resistant steel plate, characterized in that, The chemical composition of the steel, by weight percentage, is: C: 0.27%–0.31%, Si: 0.85%–0.95%, Mn: 0.8%–1.0%, Nb: 0.015%–0.030%, Ni: 0.45%–0.55%, W: 0.40%–0.50%, Al: 0.04%–0.07%, B: 0.0005%–0.0020%, RE: 0.0015%–0.0035%, with 1.25% ≤ W + Mn ≤ 1.45%, and the balance being Fe and unavoidable impurities. Impurity element control in the steel is as follows: P ≤ 0.009%, S ≤ 0.0010%, [N] ≤ 0.0030%, [H] ≤ 0.00010%, [O] ≤ 0.0010%, and retained austenite content 3%–5%. The production process includes converter smelting, refining, continuous casting, billet heating and slow cooling, slab heating, controlled rolling, controlled cooling, stacking and slow cooling / high-temperature tempering, quenching and tempering heat treatment; among which the following processes are controlled: 1) Refining: LF+RH refining process is adopted, and the RH refining vacuum cycle time is ≥24min; after RH vacuum treatment, RE alloy is added by wire feeding under argon protection; 2) Continuous casting: The billet casting speed is 0.8~1.0m / min, and the target superheat of the tundish is controlled below 20℃; the entire process is protected during casting, and electromagnetic stirring is used; the center segregation of the billet is controlled below C1.0 grade; 3) Slow cooling of billet: The initial heating temperature is ≥550℃, and the billet is heated to 620~650℃ at a heating rate of ≤50℃ / h. After holding at this temperature for 30~40h, the billet is slowly cooled in the furnace to below 400℃ and then removed from the furnace and air-cooled to room temperature. 4) Slab heating: The temperature of the soaking zone is 1160~1200℃, and the soaking time is 2~2.5h; 5) Controlled rolling: Two-stage controlled rolling is adopted, with the compression ratio (i.e., billet thickness / finished plate thickness) controlled to be ≥4; the upper and lower roll speed ratio controlled to be 1.1:1 to 1.3:1; the roughing rolling start temperature ≥1000℃, the roughing rolling finish temperature ≥960℃; the finishing rolling start temperature is 850~880℃, the finishing rolling reduction rate is ≥60%, and the finishing rolling finish temperature is 800~850℃. 6) Controlled cooling: Ultra-fast cooling or laminar flow cooling is adopted after rolling, with an initial cooling temperature ≥760℃ and a final cooling temperature of 660~680℃; 7) Stacking and slow cooling / high temperature tempering: When the slab temperature is >400℃, stacking and slow cooling is carried out for ≥28h; when the slab temperature is ≤400℃, high temperature tempering is carried out, with a tempering heating temperature of 600~650℃ and a holding time of 3.5~4.5min / mm. 8) Quenching and tempering heat treatment: Quenching temperature 850~880℃, holding time 3.0~3.5min / mm; Low temperature stress relief tempering temperature 200~220℃, holding time 8~10min / mm.

2. The method for producing a high-hardness, tear-resistant steel plate according to claim 1, characterized in that, The finished steel plate has a surface hardness of HB≥500, tensile strength ≥1400MPa, longitudinal impact energy Akv≥40J at -40℃, elongation A≥10%, 180° cold bending D=8a is qualified, and thickness direction Z≥15%.

3. The method for producing a high-hardness, tear-resistant steel plate according to claim 1, characterized in that, The thickness of the finished steel plate is 30-60mm.

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