Ultrahigh-strength steel plate with yield strength of 1,500 MPa for engineering machinery and manufacturing method of ultrahigh-strength steel plate

Abstract

The invention belongs to the field of engineering materials, and discloses an ultrahigh-strength steel plate with yield strength of 1500 MPa for engineering machinery and a manufacturing method of the ultrahigh-strength steel plate. Through reasonable component design and combination with proper rolling reduction, finish rolling temperature and quenching temperature, the microalloying effect of Nb, V and Ti is fully utilized, ultra-fine grain martensite is obtained, the effects of fine grain strengthening, precipitation strengthening and dislocation strengthening are fully exerted, the effects of C and alloy are exerted, and the Q1500 steel plate with the low carbon equivalent CEV is obtained. By means of the process, the high-strength steel plate which is good in production performance, easy to weld, 5-20 mm thick, 1500 MPa in yield strength and used for engineering machinery can be stably produced, and the high-strength steel plate is widely applied to large engineering machinery equipment such as crawler cranes and wheeled cranes.

Description

Technical Field

[0001] The present invention relates to the technical field of engineering materials, and in particular to an ultra-high-strength steel plate with a yield strength of 1500 MPa for engineering machinery and a manufacturing method thereof. Background Art

[0002] my country has become a major manufacturer of construction machinery, with production and sales ranking first globally. Low-alloy, high-strength structural steel is a key raw material for construction machinery. In recent years, with the rapid development of the national economy, resource and energy constraints have become increasingly prominent, and environmental issues have become increasingly severe. The construction machinery industry has developed in the direction of larger, lighter, and heavier loads, requiring lighter structural components and greater load-bearing capacity, placing higher demands on the steel used in construction machinery. To achieve lightweight construction equipment while simultaneously increasing its load-bearing capacity, more and higher-grade structural steel plates are required, and the need for raw material upgrades is urgent. The trend for structural steel used in construction machinery to develop towards higher strength, higher toughness, easier formability, and weldability has become inevitable.

[0003] Patent publication number CN119372426A discloses "a 900MPa grade high-strength steel, its preparation method and application", which achieves a yield strength of 900MPa through complex hot rolling, cooling, coiling, reciprocating cold rolling and heat treatment processes, but its yield strength is still lower than 1300MPa.

[0004] Patent publication number CN117344201B discloses "a high-plasticity 1500MPa-grade ultra-high-strength steel and its preparation method", whose components by weight percentage are: C: 0.35-0.40%; Si: 1.0-1.8%; Mn: 1.5-2.0%; Cr: 0.3-0.6%; Al: 0.02-0.05%; Ti: 0.02-0.05%; B: 0.002-0.02%; through controlled rolling and heat treatment processes, a high-strength steel with a microstructure of 10%-15% ferrite + 70%-80% martensite + retained austenite is obtained. The tensile strength of the ultra-high-strength steel is ≥1500MPa, and the elongation at break is ≥18%. However, the maximum yield strength of the invented steel is at the 1300MPa level, which is relatively low.

[0005] The patent with publication number CN119351871A discloses "a low-cost 1500MPa grade hot-rolled high-strength steel and a preparation method", the chemical components are as follows in mass percentage: C 0.20-0.24%, Mn 2.4-2.8%, Al 1.4-1.8%, Si 0.3-0.4%, P≤0.01%, S≤0.01%, by selecting and adjusting the content of alloying elements, combining hot rolling and critical annealing treatment, and controlling the air cooling cooling rate, a 4-8mm thick low-cost 1500MPa grade hot-rolled high-strength steel is prepared. The tensile strength is not less than 1500MPa, although the resource utilization rate is high, the production cost is low, the process is short, easy to operate and efficient, but the yield strength can only be guaranteed to be not less than 750MPa.

[0006] The high-strength structural steel with yield strength of 1300 MPa and below is widely used in the current engineering machinery industry, and the organization thereof is usually tempered sorbite or tempered martensite, which has relatively good plastic forming performance and welding performance, but the strength thereof cannot fully meet the manufacturing requirements of lightweight engineering machinery. In order to obtain good strength and plasticity, high-strength steel generally adds more C and other alloying elements, which increases the carbon equivalent and reduces the welding performance of the steel plate. The present application fully utilizes the effects of Nb, V and Ti micro-alloying by reasonable composition design combined with accurate reduction, finishing temperature and quenching temperature control, obtains ultra-fine grain martensite, fully plays the roles of fine-grain strengthening, precipitation strengthening and dislocation strengthening, maximizes the roles of C and alloy, and obtains a low-carbon equivalent yield strength of 1500 MPa grade ultra-high strength steel plate. SUMMARY

[0007] The present application aims to provide a yield strength of 1500 MPa grade engineering machinery ultra-high strength steel plate and its manufacturing method, by reasonable composition design combined with suitable compression ratio, finishing temperature and quenching temperature, fully utilizing the effects of Nb, V and Ti micro-alloying, obtaining ultra-fine grain martensite, fully playing the roles of fine-grain strengthening, precipitation strengthening and dislocation strengthening, maximizing the roles of C and alloy, and obtaining a low-carbon equivalent Q1500 steel plate, to realize stable production of 5-20 mm thick yield strength of 1500 MPa grade engineering machinery high-strength steel plate with good performance and easy welding.

[0008] The technical solution of the present invention is as follows: an ultra-high-strength steel plate for engineering machinery with a yield strength of 1500 MPa is smelted according to the following chemical composition; the chemical composition is as follows in percentage by weight: C: 0.20%-0.30%; Si: 0.20%-0.40%; Mn: 0.90%-1.20%; S≤0.002; P≤0.008; Cr: 0.40%-1.00%; Ni: 0.50%-1.20%; Mo: 0.50%-0.80%; Nb: 0.02%-0.05%; V: 0.03%-0.08%; Ti: 0.001%-0.02%; the balance is Fe and unavoidable impurity elements; an ultra-low nitrogen design is adopted, and N is strictly controlled to be ≤40 ppm.

[0009] The thickness of ultra-high-strength steel plates for engineering machinery with a yield strength of 1500 MPa is 5mm to 25mm.

[0010] A method for manufacturing an ultra-high-strength steel plate for engineering machinery with a yield strength of 1500 MPa, comprising the following specific steps: converter smelting, LF and VD refining, protective casting, stacking and slow cooling, continuous casting billet heating, controlled rolling and controlled cooling, and heat treatment;

[0011] After LF and VD refining, sliding slag blocking technology is used in the tapping process before protective casting, and slag washing is performed during the tapping process. High-basicity refined slag is used for smelting in the LF refining process, and vacuum degassing is performed in the VD refining process. Low superheat pouring technology is used in the continuous casting process, combined with electromagnetic stirring, dynamic secondary cooling water distribution, and soft pressing at the end of solidification.

[0012] A wide plate mill is used in the controlled rolling and controlled cooling stages, and the rolling process adopts two-stage controlled rolling, hot rolling to a thickness of 5-20 mm;

[0013] The starting temperature of finishing rolling in the controlled rolling and controlled cooling stage is 900℃-1040℃, and the finishing temperature of finishing rolling is 830℃-880℃. The finishing temperature of the finishing rolling stage is guaranteed, and the cumulative reduction rate of finishing rolling accounts for 50%-60% of the total reduction rate; after rolling, it is ultra-fast cooled to between 550℃-600℃, and then air-cooled to room temperature.

[0014] The quenching temperature of the heat treatment is 830°C-880°C, the heating time is 20 min-70 min, the tempering temperature is 160°C-260°C, and the heating time is 45 min-120 min.

[0015] During smelting, the contents of harmful elements N, S, P, O and H are strictly controlled, with N ≤ 40 ppm, S ≤ 0.002%, P ≤ 0.010%, total oxygen ≤ 13 ppm and H ≤ 1.2 ppm. Protective casting is used in the continuous casting process to obtain 350 mm thick continuous casting billets, which are then opened according to the thickness of the finished plate.

[0016] The rolling process utilizes a two-stage controlled rolling process with a total reduction exceeding 80%. The reduction in the two passes after rough rolling is above 20%. Increasing the total reduction is intended to achieve a finer, original austenite grain size. However, if the reduction is too high, the steel plate will be longer during finish rolling, and for thinner plates, the temperature drop will be more rapid, hindering precise temperature control. Rough rolling occurs above the recrystallization temperature and beyond the critical deformation. Greater deformation increases the number of recrystallization nucleation sites and results in finer recrystallized grains. A reduction of greater than 20% in the two passes after the roughing stage achieves even better grain refinement.

[0017] The starting temperature for finishing rolling is 900°C-1040°C, and the final rolling temperature is 830°C-880°C. The cumulative reduction during finishing accounts for 50%-60% of the total reduction. Keeping the final rolling temperature below the recrystallization temperature produces flattened austenite grains. This, combined with a large cumulative deformation, facilitates the creation of numerous nucleation sites, allowing for refinement of the original austenite during subsequent reheating and quenching. The cumulative reduction during finishing is also limited. If it is too low, the roughing reduction will be excessive, preventing further grain refinement. If it is too high, the number of finishing passes will increase, leading to a greater temperature drop and potentially exceeding the mill's load capacity.

[0018] A controlled cooling process is used after rolling to ensure ultra-rapid cooling to between 550°C and 600°C, followed by air cooling to room temperature. Ultra-rapid cooling is intended to retain more distortion energy while suppressing carbide coarsening, resulting in finely dispersed precipitates of Nb, V, and Ti, maximizing the precipitation strengthening and grain refinement effects of Nb, V, and Ti.

[0019] After controlled rolling and controlled cooling, the steel undergoes an offline heat treatment process with a quenching temperature of 830-880°C for a heating time of 20-70 minutes, and a tempering temperature of 160-260°C for a heating time of 45-120 minutes. The low quenching temperature allows for complete austenitic hardening while simultaneously obtaining an ultrafine, original austenitic structure, fully maximizing the effects of grain refinement.

[0020] The present invention has the following beneficial effects: Through rational composition design combined with appropriate reductions, finishing temperatures, and quenching temperatures, the effects of Nb, V, and Ti microalloying are fully utilized to obtain ultrafine-grained martensite. This process leverages the effects of grain refinement, precipitation strengthening, and dislocation strengthening, as well as the effects of carbon and alloying, resulting in Q1500 steel plates with a low carbon equivalent (CEV). This process enables the stable production of high-strength steel plates with a yield strength of 1500 MPa, 5-20 mm thick, excellent performance, and ease of welding for engineering machinery. These plates are widely used in large-scale engineering equipment such as crawler cranes and wheeled cranes. DETAILED DESCRIPTION

[0021] Example 1: The chemical composition of the present invention, by weight percentage, is as follows: C: 0.25; Si: 0.31; Mn: 0.99; Cr: 0.45; Ni: 0.50; Mo: 0.50; Nb: 0.025; V: 0.040; Ti: 0.020; the balance being Fe and unavoidable impurities. Smelting was performed according to the above composition. During smelting, the contents of the harmful elements N, S, P, O, and H were strictly controlled: N: 40 ppm, S: 0.0013%, P: 0.007%, total oxygen: 11 ppm, and H: 1.0 ppm. A 350 mm thick continuous casting slab was produced using protective casting and then opened to a thickness of 120 mm.

[0022] The steel was hot-rolled to a thickness of 7 mm using a wide plate mill, using a two-stage controlled rolling process. The total reduction was 94.2%. The two subsequent roughing passes had reductions of 20.5% and 22.5%, respectively. Finishing was performed at a starting temperature of 1020°C and a final temperature of 830°C, with the cumulative reduction accounting for 58% of the total reduction. After rolling, the steel was ultra-rapidly cooled to approximately 580°C, followed by air cooling to room temperature.

[0023] After rolling, offline heat treatment is carried out with a low quenching temperature of 840 °C, a heating time of 22 min, and a tempering temperature of 180 °C, a heating time of 50 min.

[0024] The mechanical property test results of Example 1 are shown in Table 1: the yield strength is 1521 MPa, the tensile strength is 1820 MPa, the elongation is 11.5%, and the original austenite grain size is 5.2 μm.

[0025] The high-strength steel plate for engineering machinery with a yield strength of 1500 MPa produced in this Example 1 can be cold-bent 180° without cracking under the condition of a bending head diameter D=6a; after laser composite welding with a heat input of 0.22 kJ / mm, the tensile strength of the weld is 1460 MPa, and the average impact absorption energy KV2 at the center of the weld at -40°C is 42 J.

[0026] Example 2: The chemical composition of the present invention, by weight, is as follows: C: 0.25; Si: 0.31; Mn: 0.99; Cr: 0.45; Ni: 0.50; Mo: 0.50; Nb: 0.025; V: 0.040; Ti: 0.020; the balance being Fe and unavoidable impurities. Smelting was performed according to the above composition. During smelting, the contents of the harmful elements N, S, P, O, and H were strictly controlled: N: 40 ppm, S: 0.0013%, P: 0.007%, total oxygen: 11 ppm, and H: 1.0 ppm. A 350 mm thick continuous casting slab was produced using protective casting and then opened to a thickness of 120 mm.

[0027] The steel was hot-rolled to a thickness of 7 mm using a wide plate mill, employing a two-stage controlled rolling process. The steel achieved a total reduction of 94.2%. The two subsequent roughing passes achieved reductions of 20.5% and 22.5%, respectively. Finishing was performed at a starting temperature of 960°C and a final temperature of 830°C, with the cumulative reduction accounting for 58% of the total reduction. After rolling, the steel was ultra-rapidly cooled to approximately 580°C, followed by air cooling to room temperature.

[0028] After rolling, offline heat treatment is carried out with a low quenching temperature of 840 °C, a heating time of 22 min, and a tempering temperature of 180 °C, a heating time of 50 min.

[0029] The mechanical property test results of Example 2 are shown in Table 1: the yield strength is 1529 MPa, the tensile strength is 1824 MPa, the elongation is 11.6%, and the original austenite grain size is 4.7 μm.

[0030] The high-strength steel plate for engineering machinery with a yield strength of 1500 MPa produced in this Example 2 can be cold-bent 180° without cracking under the condition of a bending head diameter D=6a; after laser composite welding with a heat input of 0.22 kJ / mm, the tensile strength of the weld is 1469 MPa, and the average impact absorption energy KV2 at the center of the weld at -40°C is 40 J.

[0031] Example 3: The chemical composition of the present invention, by weight, is as follows: C: 0.25; Si: 0.31; Mn: 0.99; Cr: 0.45; Ni: 0.50; Mo: 0.50; Nb: 0.025; V: 0.040; Ti: 0.020; the balance being Fe and unavoidable impurities. Smelting was performed according to the above composition. During smelting, the contents of the harmful elements N, S, P, O, and H were strictly controlled: N: 40 ppm, S: 0.0013%, P: 0.007%, total oxygen: 11 ppm, and H: 1.0 ppm. A 350 mm thick continuous casting slab was produced using protective casting and then opened to a thickness of 120 mm.

[0032] The steel was hot-rolled to a thickness of 10 mm using a wide plate mill, employing a two-stage controlled rolling process. The steel achieved a total reduction of 91.7%. The two subsequent roughing passes achieved reductions of 20.5% and 22.5%, respectively. Finishing was performed at a starting temperature of 960°C and a final temperature of 830°C, with the cumulative reduction accounting for 58% of the total reduction. After rolling, the steel was ultra-rapidly cooled to approximately 580°C, followed by air cooling to room temperature.

[0033] After rolling, offline heat treatment is carried out with a low quenching temperature of 840 °C, a heating time of 22 min, and a tempering temperature of 180 °C, a heating time of 50 min.

[0034] The mechanical property test results of Example 3 are shown in Table 1: the yield strength is 1505 MPa, the tensile strength is 1795 MPa, the elongation is 13.0%, and the original austenite grain size is 6.1 μm.

[0035] The high-strength steel plate for engineering machinery with a yield strength of 1500 MPa produced in this Example 3 can be cold-bent 180° without cracking under the condition of a bending head diameter D=6a; after laser composite welding with a heat input of 0.22 kJ / mm, the tensile strength of the weld is 1429 MPa, and the average impact absorption energy KV2 at the center of the weld at -40°C is 39 J.

[0036] Example 4: The chemical composition of the present invention, by weight, is as follows: C: 0.25; Si: 0.31; Mn: 0.99; Cr: 0.45; Ni: 0.50; Mo: 0.50; Nb: 0.025; V: 0.040; Ti: 0.020; the balance being Fe and unavoidable impurities. Smelting was performed according to the above composition. During smelting, the contents of the harmful elements N, S, P, O, and H were strictly controlled: N: 40 ppm, S: 0.0013%, P: 0.007%, total oxygen: 11 ppm, and H: 1.0 ppm. A 350 mm thick continuous casting ingot was produced using protective casting.

[0037] The steel was hot-rolled to a thickness of 20 mm using a wide plate mill, employing a two-stage controlled rolling process. The steel achieved a total reduction of 83.3%. The two subsequent roughing passes had reductions of 20.5% and 22.5%, respectively. Finishing was performed at a starting temperature of 930°C and a final temperature of 830°C, with the cumulative reduction accounting for 58% of the total reduction. After rolling, the steel was ultra-rapidly cooled to approximately 580°C, followed by air cooling to room temperature.

[0038] After rolling, offline heat treatment is carried out with a low quenching temperature of 840 °C, a heating time of 22 min, and a tempering temperature of 180 °C, a heating time of 50 min.

[0039] The mechanical property test results of Example 4 are shown in Table 1: the yield strength is 1517 MPa, the tensile strength is 1803 MPa, the elongation is 12.5%, and the original austenite grain size is 5.8 μm.

[0040] The high-strength steel plate for engineering machinery with a yield strength of 1500 MPa produced in this Example 4 can be cold-bent 180° without cracking under the condition of a bending head diameter D=6a; after laser composite welding with a heat input of 0.22 kJ / mm, the tensile strength of the weld is 1439 MPa, and the average impact absorption energy KV2 at the center of the weld at -40°C is 44 J.

[0041] Comparative Example 1: The chemical composition of the present invention, by weight percentage, is as follows: C: 0.25; Si: 0.31; Mn: 0.99; Cr: 0.45; Ni: 0.50; Mo: 0.50; Nb: 0.025; V: 0.040; Ti: 0.020; the balance being Fe and unavoidable impurities. Smelting was performed according to the above composition. During smelting, the contents of the harmful elements N, S, P, O, and H were strictly controlled: N: 40 ppm, S: 0.0013%, P: 0.007%, total oxygen: 11 ppm, and H: 1.0 ppm. A 350 mm thick continuous casting slab was produced using protective casting and then slabbed to a thickness of 120 mm.

[0042] The steel was hot-rolled to a thickness of 25 mm using a wide plate mill, employing a two-stage controlled rolling process. The steel achieved a total reduction of 79.2%. The two subsequent roughing passes achieved reductions of 20.5% and 22.5%, respectively. Finishing was performed at a starting temperature of 1020°C and a final temperature of 830°C, with the cumulative reduction accounting for 58% of the total reduction. After rolling, the steel was ultra-rapidly cooled to approximately 580°C, followed by air cooling to room temperature.

[0043] After rolling, offline heat treatment is carried out with a low quenching temperature of 840 °C, a heating time of 22 min, and a tempering temperature of 180 °C, a heating time of 50 min.

[0044] The mechanical property test results of Comparative Example 1 are shown in Table 1, where the yield strength is 1452 MPa, the tensile strength is 1767 MPa, the elongation is 13.5%, and the original austenite grain size is 10.1 μm.

[0045] Comparative Example 2: The chemical composition of the present invention, by weight percentage, is C: 0.25; Si: 0.31; Mn: 0.99; Cr: 0.45; Ni: 0.50; Mo: 0.50; Nb: 0.025; V: 0.040; Ti: 0.020; the balance being Fe and unavoidable impurities. Smelting was performed according to the above composition. During smelting, the contents of the harmful elements N, S, P, O, and H were strictly controlled to: N: 40 ppm, S: 0.0013%, P: 0.007%, total oxygen: 11 ppm, and H: 1.0 ppm. A 350 mm thick continuous casting slab was produced using protective casting and then slabbed to a thickness of 120 mm.

[0046] The steel was hot-rolled to a thickness of 7 mm using a wide plate mill, employing a two-stage controlled rolling process. The total reduction was 94.2%. The two subsequent roughing passes had reductions of 20.5% and 22.5%, respectively. Finishing was performed at a starting temperature of 1100°C and a final temperature of 900°C, with the cumulative reduction accounting for 58% of the total. After rolling, the steel was ultra-rapidly cooled to approximately 580°C, followed by air cooling to room temperature.

[0047] After rolling, offline heat treatment is carried out with a low quenching temperature of 840 °C, a heating time of 22 min, and a tempering temperature of 180 °C, a heating time of 50 min.

[0048] The mechanical property test results of Comparative Example 2 are shown in Table 1, where the yield strength is 1473 MPa, the tensile strength is 1791 MPa, the elongation is 13.0%, and the original austenite grain size is 8.9 μm.

[0049] Comparative Example 3: The chemical composition of the present invention, by weight percentage, is C: 0.25; Si: 0.31; Mn: 0.99; Cr: 0.45; Ni: 0.50; Mo: 0.50; Nb: 0.025; V: 0.040; Ti: 0.020; the balance being Fe and unavoidable impurities. Smelting is performed according to the above composition. During smelting, the contents of the harmful elements N, S, P, O, and H are strictly controlled: N: 40 ppm, S: 0.0013%, P: 0.007%, total oxygen: 11 ppm, and H: 1.0 ppm. A 350 mm thick continuous casting slab was produced using protective casting and then slabbed to a thickness of 120 mm.

[0050] The steel was hot-rolled to a thickness of 7 mm using a wide plate mill using a two-stage controlled rolling process, with a total reduction of 94.2%. The reductions in the two subsequent roughing passes were 20.5% and 22.5%, respectively. Finishing was performed at a start temperature of 1020°C and a final temperature of 830°C, with the cumulative reduction accounting for 58% of the total reduction. After rolling, the steel was air-cooled to room temperature.

[0051] After rolling, offline heat treatment is carried out with a low quenching temperature of 840 °C, a heating time of 22 min, and a tempering temperature of 180 °C, a heating time of 50 min.

[0052] The mechanical property test results of Comparative Example 3 are shown in Table 1, where the yield strength is 1458 MPa, the tensile strength is 1785 MPa, the elongation is 13.0%, and the original austenite grain size is 9.1 μm.

[0053] Comparative Example 4: The chemical composition of the present application is C: 0.25; Si: 0.31; Mn: 0.99; Cr: 0.45; Ni: 0.50; Mo: 0.50; Nb: 0.025; V: 0.040; Ti: 0.020; the balance is Fe and inevitable impurity elements, smelting according to the above composition. The contents of harmful elements N, S, P, O and H are strictly controlled during smelting, N: 40 ppm, S: 0.0013%, P: 0.007%, total oxygen: 11 ppm and H: 1.0 ppm; a 350 mm thick continuous casting billet is obtained by protective casting, and is broken down to 120 mm thick.

[0054] A wide plate mill is used, and the rolling process is two-stage controlled rolling hot rolling to 7 mm thick, and the total reduction is 94.2%; the reduction of the two passes after rough rolling is 20.5% and 22.5% respectively. The rough rolling temperature is 1020 ℃, the finish rolling temperature is 830 ℃, and the cumulative reduction of finish rolling accounts for 58% of the total reduction. After rolling, ultra-fast cooling is performed to between 580 ℃, and then air cooling is performed to room temperature.

[0055] After rolling, offline heat treatment is performed, and a low quenching temperature is used, the quenching temperature is 890 ℃, the heating time is 22 min, the tempering temperature is 180 ℃, and the heating time is 50 min.

[0056] The mechanical property test results of Comparative Example 4 are shown in Table 1, the yield strength is 1479 MPa, the tensile strength is 1801 MPa, the elongation is 13.0%, and the original austenite grain size is 8.7 μm.

[0057] The mechanical property test results and grain size of the steel plates obtained by Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 and Example 1, Example 2, Example 3, Example 4 are shown in Table 1.

[0058] The above examples and comparative examples show that the 5-20 mm thick yield strength 1500 MPa grade high-strength steel plate for engineering machinery according to the present application has good strength and plasticity matching by fine control of rolling and cooling process, and the offline heat treatment process window is wide, which is particularly suitable for producing large engineering machinery equipment parts, and has important significance for improving the carrying capacity of engineering machinery equipment, large-scale lightweight design and prolonging the service life, and has a wide application prospect in the field of engineering machinery.

[0059] Table 1 Mechanical properties of steel plates

[0060]

[0061] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. An ultra-high strength steel plate for engineering machinery with a yield strength of 1500 MPa, characterized in that: Smelting is carried out according to the following chemical composition; the chemical composition is as follows in percentage by weight: C: 0.20%-0.30%; Si: 0.20%-0.40%; Mn: 0.90%-1.20%; S≤0.002; P≤0.008; Cr: 0.40%-1.00%; Ni: 0.50%-1.20%; Mo: 0.50%-0.80%; Nb: 0.02%-0.05%; V: 0.03%-0.08%; Ti: 0.001%-0.02%; the balance is Fe and unavoidable impurity elements; ultra-low nitrogen design is adopted, and N is strictly controlled to be ≤40 ppm.

2. The ultra-high strength steel plate for engineering machinery with a yield strength of 1500 MPa according to claim 1, characterized in that: The thickness of ultra-high strength steel plates for engineering machinery with a yield strength of 1500 MPa is 5mm to 25mm.

3. A method for manufacturing an ultra-high-strength steel plate for engineering machinery with a yield strength of 1500 MPa as claimed in claim 1 or 2, characterized in that: The specific steps are as follows: converter smelting, LF and VD refining, protective casting, stacking slow cooling, continuous casting billet heating, controlled rolling and controlled cooling and heat treatment; After LF and VD refining, sliding slag blocking technology is used in the tapping process before protective casting, and slag washing is performed during the tapping process. High-basicity refined slag is used for smelting in the LF refining process, and vacuum degassing is performed in the VD refining process. Low superheat pouring technology is used in the continuous casting process, combined with electromagnetic stirring, dynamic secondary cooling water distribution, and soft pressing at the end of solidification. A wide plate mill is used in the controlled rolling and cooling stages, and the rolling process adopts two-stage controlled rolling, hot rolling to a thickness of 5-20 mm; The start rolling temperature of the finishing rolling in the controlled rolling and controlled cooling stage is 900℃-1040℃, and the final rolling temperature of the finishing rolling is 830℃-880℃. The final rolling temperature of the finishing rolling stage is guaranteed, and the cumulative reduction rate of the finishing rolling accounts for 50%-60% of the total reduction rate. After rolling, the steel is ultra-fast cooled to between 550℃-600℃, and then air-cooled to room temperature. The quenching temperature of the heat treatment is 830°C-880°C, the heating time is 20 min-70 min, the tempering temperature is 160°C-260°C, and the heating time is 45 min-120 min.

4. The manufacturing method according to claim 3, characterized in that During smelting, the contents of harmful elements N, S, P, O and H are strictly controlled, with N ≤ 40 ppm, S ≤ 0.002%, P ≤ 0.010%, total oxygen ≤ 13 ppm and H ≤ 1.2 ppm. Protective casting is used in the continuous casting process to obtain 350 mm thick continuous casting billets, which are then opened according to the thickness of the finished plate.

5. The manufacturing method according to claim 3, characterized in that The rolling process adopts two-stage controlled rolling with a total reduction rate of more than 80%; the reduction rates of the two passes after rough rolling are more than 20%.

6. The manufacturing method according to claim 3, characterized in that The starting temperature of finishing rolling is 900℃-1040℃, the final rolling temperature of finishing rolling is 830℃-880℃, and the cumulative reduction rate of finishing rolling accounts for 50%-60% of the total reduction rate.

7. The manufacturing method according to claim 3, characterized in that The post-rolling controlled cooling process is adopted to ensure ultra-fast cooling to between 550℃-600℃ after rolling, and then air cooling to room temperature.

8. The manufacturing method according to claim 3, characterized in that After controlled rolling and controlled cooling, an offline heat treatment process is carried out with a quenching temperature of 830-880 °C, a heating time of 20 min-70 min, a tempering temperature of 160 °C-260 °C, and a heating time of 45 min-120 min.

Images