High-strength steel with yield strength of 1200 MPa grade for lightweight engineering machinery and preparation method of high-strength steel

Abstract

The invention relates to the technical field of high-strength steel for engineering machinery, and discloses light-weight high-strength steel with the yield strength of 1200 MPa for engineering machinery and a preparation method of the light-weight high-strength steel. The high-strength steel for the engineering machinery comprises the following components in percentage by weight: 0.170 to 0.190 percent of C, 0.02 to 0.15 percent of Si, 1.15 to 1.25 percent of Mn, less than or equal to 0.015 percent of P, 0.025 to 0.050 percent of Alt, 0.010 to 0.020 percent of Nb, 0.010 to 0.025 percent of Ti, 0.20 to 0.30 percent of Ni, 0.25 to 0.33 percent of Cr, 0.40 to 0.50 percent of Mo, 0.048 to 0.055 percent of V, 0.0010 to 0.0025 percent of B and 0.0010 to 0.0030 percent of Ca. The high-strength steel plate for the lightweight engineering machinery is thinner, and has higher strength, high percentage elongation after fracture and high longitudinal impact energy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-strength steel for engineering machinery, and particularly relates to a high-strength steel with a yield strength of 1200 MPa for lightweight engineering machinery and a preparation method thereof. BACKGROUND

[0002] The high-strength steel with a yield strength of 1200 MPa for lightweight engineering machinery is mainly used for a crane boom. The high-strength and easy-to-weld structural steel is used to manufacture the crane boom of the engineering machinery, and the crane boom is required to reduce the weight of the equipment, reduce fuel consumption and improve work efficiency. With the intensification of international competition, it has become a trend to use the high-strength and easy-to-weld structural steel to manufacture the crane boom of the crane. Due to the development requirements of high performance, large size and lightweight of the engineering machinery, the strength grade of the steel for engineering machinery is higher, and the steel is more widely used.

[0003] The high-strength steel for engineering machinery has strict requirements on the quality of the steel due to its harsh use environment and stress conditions. In terms of performance, in order to ensure the use safety during loading, the strength performance and impact performance of the steel are required to be high. The heat treatment process requires uniform temperature and uniform cooling, the finishing and straightening process can eliminate or greatly reduce the deformation that has been generated, and the internal stress is balanced and reduced, etc. In addition, the welding performance of the steel plate and the post-weld deformation are strictly required, and the post-weld deformation of the crane boom is required to be not more than 4 mm.

[0004] The existing high-strength steel for engineering machinery cannot well balance the high strength, easy weldability and low cost. Some high-cost special alloys are added, and the cost is high. The mechanical properties such as yield strength and tensile strength of some steel are not high.

[0005] Chinese patent application CN201110098008.2 discloses a yield strength 960 MPa grade ultra-high strength steel and its production method. The chemical composition is as follows: C: 0.07-0.09%; Si: 0.15-0.25%; Mn: 1.00-1.20%; Cr: 1.05-1.15%; Mo: 0.15-0.20%; Al: 0.01-0.06%; P: ≤0.02%; S: ≤0.01%; N: ≤0.008%; the rest is Fe and inevitable impurities. The production method is as follows: smelting and casting into billet; heating to 1150-1250 °C; final rolling temperature is 840-900 °C; final cooling temperature is 640-700 °C; quenching and tempering treatment, quenching heating temperature is 880-920 °C, holding time is 20-60 min, tempering heating temperature is 150-450 °C, holding time is 90-180 min. The material reaches the performance requirements of 960 MPa ultra-high strength steel, and has good elongation and impact toughness. According to the examples, the yield strength of the material is 960-1010 MPa, the tensile strength is not more than 1120 MPa, and the impact energy at -40 °C is not more than 35 J. The yield strength, tensile strength and longitudinal impact energy at -40 °C are relatively low.

[0006] Chinese patent application CN201110096170.0 discloses a yield strength 1100-1200 MPa grade ultra-high strength steel and its production method. The chemical composition (wt%) is as follows: C: 0.15-0.18%; Si: 0.20-0.25%; Mn: 0.85-1.25%; Cr: 0.20-0.60%; Mo: 0.45-0.65%; V: 0.035-0.060%; Nb: 0.015-0.020%; Ni: 0-0.55%; Cu: 0-0.035%; Al: 0.01-0.06%; P: ≤0.015%; S: ≤0.01%; N: ≤0.008%, the rest is Fe and inevitable impurities. The production method is as follows: smelting and casting into billet; heating the billet to 1150-1250 °C, final rolling temperature is 860-920 °C; coiling temperature is 650-750 °C; quenching heating temperature is 880-930 °C, holding time is 20-90 min, tempering heating temperature is 100-450 °C, holding time is more than 90 min, slow cooling or air cooling to room temperature. The steel plate produced according to the composition and process has yield strength of 1150-1230 MPa, tensile strength of 1250-1340 MPa, elongation of 11-13.5%, and impact energy at -40 °C of 21-34 J. The yield strength and impact energy at -40 °C are relatively low, and cannot meet the long-term service requirements in extremely cold weather.

[0007] Chinese patent application CN201210430148.X discloses a production method of ultra-high strength steel plate, which adopts a process route of converter steelmaking, secondary refining, continuous casting, heating, rolling, accelerated cooling and heat treatment. The chemical composition of the steel plate is as follows: C=0.25-0.27, Si=0.75-0.85, Mn=1.45-1.55, P≤0.015, S≤0.010, Alt≤0.020, Nb=0.02-0.03, V=0.05-0.06, Ti=0.045-0.060, Mo=0.55-0.65 and B=0.0017-0.0022. The component design of the steel plate is simple, no large amount of alloy elements are added, and the production cost of the ultra-high strength steel plate is reduced. The welding performance of the steel plate is improved by adopting Ti oxide metallurgy technology. The microstructure of the steel plate after Q+P treatment is ultra-fine lath martensite, nano-scale lath residual austenite and precipitated complex carbide, the comprehensive performance of the strength and plasticity of the steel plate is better than that of dual-phase steel, TRIP steel and general martensite steel. The plate shape of the steel plate after roller quenching is good. The process is simple and easy to implement, and solves the problem that traditional quenching and tempering cannot produce ultra-high strength steel plate, and realizes batch production of 1600MPa grade ultra-high strength steel plate. The component system and process are different, and the cost is higher. The Si, Mn, Mo, Nb, V and Ti components are much higher than those of the present application, and the alloy cost is higher.

[0008] Chinese patent application CN201210429983.1 discloses a production process of ultra-high strength steel plate, adopting process route of steelmaking→refining→continuous casting→heating→rolling→cooling→heat treatment, the mass percentage of the steel is C=0.18-0.20, Si=0.35-0.42, Mn=1.30-1.40, P≤0.015, S≤0.010, Al=0.03-0.06, Nb=0.02-0.03, V=0.05-0.06, Ti=0.035-0.045, Mo=0.25-0.35, B=0.0017-0.0022. The component design of the steel plate is simple, without adding a large amount of alloy elements, reducing the production cost of the ultra-high strength steel plate; the Ti added in the component of the steel plate improves the welding performance of the steel plate; the steel plate is treated by Q+P, the organization of the steel plate is ultra-fine lath martensite+nanometer lath residual austenite and precipitated complex carbide, the comprehensive performance of the strength and plasticity of the steel plate is superior to that of dual-phase steel, TRIP steel and general martensite steel; the steel plate is quenched by a roller quenching machine, the plate shape is good; the process is simple and easy to realize, solves the problem that the traditional quenching and tempering cannot produce the ultra-high strength steel plate, and realizes batch production of 1100MPa grade ultra-high strength steel plate. According to the embodiments, the steel plate is thick, the yield strength of the 20mm steel plate is 1271MPa, the yield strength of the 40mm steel plate is 1164MPa, and the yield strength of the 60mm steel plate is 1185MPa, the steel plate is too thick to meet the lightweight requirement of the engineering machinery.

[0009] Chinese patent application CN201410300731.8 discloses a low-cost and high-performance ultra-high strength steel for engineering machinery and a manufacturing method thereof, the weight percentage of the components is as follows: C: 0.18%-0.22%, Si: ≤0.10%, Mn: 1.30%-1.60%, P: ≤0.013%, S: ≤0.0030%, Cr: 0.30%-0.60%, Mo: 0.10%-0.30%, B: 0.0010%-0.0020%, Ti: 0.008%-0.018%, Nb: 0.010%-0.030%, Al: 0.030%-0.070%, N: ≤0.0050%, O≤0.0030%, Mg: 0.001%-0.004%, and the rest is iron and inevitable inclusions. According to the embodiments, the thickness of the steel plate is 15-40mm, the steel plate is too thick to meet the lightweight requirement of the engineering machinery. SUMMARY

[0010] The present application aims at overcoming the problem that the prior high-strength steel for engineering machinery cannot well balance high strength, light weight and low cost, and provides a light-weight high-strength steel for engineering machinery with a yield strength of 1200 MPa and a preparation method thereof, which has a thin steel plate, high strength, high elongation after fracture and high longitudinal impact energy with a small amount of noble metal added, high safety factor and light weight.

[0011] To achieve the above-mentioned purpose, the present application provides a light-weight high-strength steel for engineering machinery with a yield strength of 1200 MPa, which contains the following chemical components by weight percentage: C: 0.170-0.190%, Si: 0.02-0.15%, Mn: 1.15-1.25%, P: ≤0.015%, S: ≤0.002%, Alt: 0.025-0.050%, Nb: 0.010-0.020%, Ti: 0.010-0.025%, Ni: 0.20-0.30%, Cr: 0.25-0.33%, Mo: 0.40-0.50%, V: 0.048-0.055%, B: 0.0010-0.0025%, Ca: 0.0010-0.0030%, N ≤0.0050%, T[O] ≤0.0030%, H ≤0.00025%, and the balance is Fe and unavoidable inclusions.

[0012] Preferably, the light-weight high-strength steel for engineering machinery satisfies a safety factor: K1=C+Si / 27+Mn / 12+V / 3+Nb / 2.5+Ti / 5+Cr / 6+Mo / 9+9B, and K1 is 0.38-0.47%.

[0013] Preferably, the light-weight high-strength steel for engineering machinery has a yield strength of 1200-1300 MPa, a tensile strength of 1250-1350 MPa, an elongation after fracture A ≥10%, and a longitudinal impact energy KV2 at -40 ℃ ≥50 J.

[0014] Preferably, the light-weight high-strength steel for engineering machinery has a steel plate thickness of 3-6 mm.

[0015] The present application provides a method for preparing the light-weight high-strength steel for engineering machinery with a yield strength of 1200 MPa described above, which comprises KR hot metal desulfurization, converter smelting, argon blowing at the bottom of the argon blowing station, LF refining, RH vacuum treatment, CaSi treatment, continuous casting, slab heating, rolling, cooling, coiling and heat treatment. In the RH vacuum treatment process, the vacuum circulation time is 27-37 minutes, the vacuum degree is controlled at ≤12 Pa, and the vacuum end temperature is controlled at 1551-1561℃; In the CaSi treatment process, CaSi wire is fed for calcium treatment, and the addition amount of CaSi wire is 0.72-0.90 kg / t.s; In the heat treatment process, the quenching temperature is 900-920℃, the quenching holding time is 10-12 min; the tempering temperature is 210-230℃, and the tempering holding time is 20-25 min.

[0016] Preferably, in the KR molten iron desulfurization process, more than twice of slag skimming treatment is carried out, and the residence time between every two times of slag skimming is not less than 6 min; the exposed surface of molten iron after slag skimming is not less than 95%; and the S in the molten iron after desulfurization is ≤0.0008%.

[0017] Preferably, in the converter smelting process, the smelting end temperature is controlled at 1590-1608℃, and the smelting end oxygen is controlled at 0.040-0.065%; aluminum iron is added for deoxidization when the converter is tapped, and the Alt in the molten steel is controlled at 0.046-0.060%.

[0018] Preferably, in the bottom argon blowing process of the argon blowing station, the Alt in the molten steel at the end of argon blowing is controlled at 0.060-0.070%.

[0019] Preferably, in the LF furnace refining process, the S in the molten steel at the end of LF furnace refining is controlled at ≤0.0015%, and the Alt is controlled at 0.045-0.065%.

[0020] Preferably, in the continuous casting process, the protective slag is used for continuous casting, the basicity of the protective slag is 1.27-1.37, the viscosity at 1300℃ is 0.08-0.18 Pa·S, and the melting point is 1100-1160℃.

[0021] Preferably, in the continuous casting process, the taper of the crystallizer is 1.25-1.35%, the wide surface cooling water flow of the crystallizer is 3200-3350 L / min, and the narrow surface cooling water flow of the crystallizer is 600-620 L / min.

[0022] Preferably, in the continuous casting process, the superheat degree is controlled at 15-25℃, and the tundish temperature is controlled at 1526-1536℃.

[0023] Preferably, in the continuous casting process, the casting speed is controlled at 1.0-1.2 m / min, and the fluctuation of the liquid steel surface of the crystallizer is controlled within ±3 mm.

[0024] Preferably, the slab heating temperature is 1240-1300℃.

[0025] Preferably, in the rolling process, the rough rolling temperature is 1120-1140℃, and the finish rolling temperature is 920-940℃.

[0026] Preferably, the coiling temperature is 650-680℃.

[0027] Compared with the prior art, the present application has at least the following technical effects: The present application has high strength, high elongation after fracture (plasticity) and high longitudinal impact energy (toughness) by strictly controlling the components and contents in the high-strength steel for engineering machinery and adding a small amount of noble metal elements, and the safety factor of the steel is high.

[0028] In addition, the steel prepared in the prior art has high strength but thick steel plate, and cannot meet the lightweight requirement. Generally, it is difficult for a steel plate to simultaneously meet thinness and high strength, and the present application realizes thinness and high strength of the steel by controlling the components and contents in the steel and ensuring the purity of the molten steel, and obtains the lightweight high-strength steel for engineering machinery. DETAILED DESCRIPTION

[0029] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0030] The endpoints of the ranges and any values in the ranges disclosed herein are not limited to the precise values stated. The endpoints and ranges should be construed as being open-ended unless expressly stated otherwise. It is to be understood that beyond the endpoints lie other values and within the range lies other values not expressly stated. The endpoints of the ranges and any values in the ranges are included in the ranges themselves. Any numerical value, however, can explicitly exclude any value outside that range.

[0031] The present application provides a lightweight high-strength steel for engineering machinery with a yield strength of 1200MPa, containing the following weight percentages of chemical components: C: 0.170-0.190%, Si: 0.02-0.15%, Mn: 1.15-1.25%, P: ≤0.015%, S: ≤0.002%, Alt: 0.025-0.050%, Nb: 0.010-0.020%, Ti: 0.010-0.025%, Ni: 0.20-0.30%, Cr: 0.25-0.33%, Mo: 0.40-0.50%, V: 0.048-0.055%, B: 0.0010-0.0025%, Ca: 0.0010-0.0030%, N ≤0.0050%, T[O] ≤0.0030%, H ≤0.00025%, the balance being Fe and unavoidable inclusions.

[0032] The high-strength steel for engineering machinery with the specific chemical components and contents has high strength, excellent plasticity and toughness, and low noble metal content. Specifically, the yield strength of the lightweight high-strength steel for engineering machinery is 1200-1300 MPa, the tensile strength is 1250-1350 MPa, the elongation A after fracture is ≥10%, and the longitudinal impact energy KV2 at -40°C (low temperature) is ≥50 J, Further, the steel provided by the application is not only high in strength, but also thin. Specifically, the thickness of the lightweight high-strength steel for engineering machinery is 3-6 mm.

[0033] Because the safety of the high-strength steel for engineering machinery mainly depends on its resistance to cracks generated during machining and service period, and fatigue resistance, the safety factor K1 is set in the application. The inventors found that the safety of the high-strength steel for engineering machinery is proportional to the main elements Si, Mn, V, Nb, Ti, Cr, Mo, and B, and the contribution of each element is different. The inventors found through research that the contribution coefficients of Si, Mn, V, Nb, Ti, Cr, Mo, and B to the high-strength steel for engineering machinery are 1 / 27, 1 / 12, 1 / 3, 1 / 2.5, 1 / 5, 1 / 6, 1 / 9, and 9, respectively. When the safety factor K1 is lower than 0.38%, the safety performance cannot meet the safety requirements of the high-strength steel for engineering machinery for long-term service. When the safety factor K1 is higher than 0.47%, the performance is excessive and the alloy cost is high, resulting in waste of alloy cost. Specifically, the high-strength steel for engineering machinery satisfies the safety factor: K1 = C + Si / 27 + Mn / 12 + V / 3 + Nb / 2.5 + Ti / 5 + Cr / 6 + Mo / 9 + 9B, and K1 is 0.38-0.47%. When the safety factor K1 satisfies the above range, the safety requirement for service for more than 15 years can be met.

[0034] The action mechanism of various elements in the application will be described in detail below.

[0035] Carbon (C): The carbon element strengthens the structure of the steel by forming carbides with iron, significantly improves the yield strength and tensile strength, and meets the demand of engineering machinery for high strength. The addition of carbon improves the hardness of the steel and enhances the wear resistance of the material, prolonging the service life. An appropriate amount of carbon content helps to improve the cutting performance of the steel, making it easier to machine. However, too much carbon will reduce plasticity and impact toughness, so the amount of carbon added is controlled to be 0.170-0.190%.

[0036] Manganese (Mn): Manganese reacts with oxygen and sulfur during the steelmaking process, reducing impurities and improving the purity of the steel, thereby improving its mechanical properties. Manganese dissolves in the steel matrix, increasing its strength through lattice distortion, significantly increasing yield strength and tensile strength. Manganese increases the hardenability of steel, resulting in a more uniform internal structure after quenching, stable performance, and the ability to withstand high stress and impact. However, high manganese content reduces the plasticity and weldability of steel. Therefore, the addition of manganese is controlled at 1.15~1.25%.

[0037] Silicon (Si): Silicon dissolves in ferrite, increasing the strength of steel through solid solution strengthening, increasing yield strength and tensile strength to meet the needs of high-strength steel. Appropriate silicon can improve the toughness and impact performance of steel, reduce the risk of brittle fracture, and enhance the reliability of the material. Silicon improves the oxidation resistance of steel, reduces the scale, and improves the hot rolling surface quality; at the same time, it optimizes the welding performance and reduces the crack tendency. However, too much silicon will reduce the plasticity and weldability, so the addition of silicon is controlled at 0.02~0.15%.

[0038] Niobium (Nb): Niobium can effectively refine the grain structure of steel, thereby improving the strength and toughness of the material. Grain refinement is usually achieved by inhibiting grain growth, which is particularly important during high-temperature processing. Niobium forms fine precipitates in steel that hinder dislocation movement, thereby enhancing the strength of the material. Niobium helps to improve the stability of steel at high temperatures, preventing the material from softening or deforming in high-temperature environments, which is crucial for the performance of engineering machinery in complex working conditions. However, too much niobium will reduce the toughness of the steel, resulting in uneven carburized layer. Therefore, the addition of niobium is controlled at 0.010~0.020%.

[0039] Titanium (Ti): Ti can combine with C or N in steel to form compounds such as TiC or TiN. These compounds act as nuclei to promote grain refinement, thereby improving the strength and toughness of the material. The addition of Ti helps to improve the corrosion resistance of the material, especially in harsh environments, enhancing the durability of engineering machinery. Ti forms stable compounds during heat treatment, improving the thermal stability of the material. In welding, Ti helps to reduce cracks and improve joint performance. Ti interacts with elements such as Cr and Mo to form complex compounds, further optimizing material performance. However, too much Ti will reduce the toughness of the steel. Therefore, the addition of titanium is controlled at 0.010~0.025%.

[0040] Nickel (Ni): Ni increases the lattice distortion through solid solution strengthening, thereby increasing the yield strength and tensile strength of the material. The addition of Ni enhances the toughness and impact toughness of the steel, especially at low temperatures, reducing the risk of brittle fracture. Ni forms a dense oxide film that prevents the penetration of corrosive media, improving the corrosion resistance of the material in harsh environments. Ni helps to refine the grain structure of the steel, thereby increasing the strength and toughness of the material. Therefore, the addition of nickel is controlled at 0.20-0.30%.

[0041] Chromium (Cr): Cr dissolves in the iron matrix, causing lattice distortion, thereby increasing the strength of the material. Cr promotes the formation of fine precipitates, hindering dislocation movement, further enhancing material strength. Cr forms a dense oxide film that prevents further oxidation and corrosion, especially in humid or corrosive environments, extending the service life. However, too high a Cr content will increase the risk of brittleness and welding cracks. Therefore, the addition of chromium is controlled at 0.25-0.35%.

[0042] Molybdenum (Mo): Molybdenum significantly increases the yield strength and tensile strength of the steel through solid solution strengthening and precipitation strengthening mechanisms, meeting the high strength requirements of engineering machinery. Molybdenum can improve the hardenability and thermal strength, improve the tempering stability of the steel, prevent temper brittleness, and improve the plasticity of the steel. Molybdenum changes the electrochemical properties of the steel, forms a passivation film, and enhances the corrosion resistance, adapting to harsh working environments. Molybdenum enhances the fatigue resistance of the material, prolonging the service life of the engineering machinery parts. Therefore, the addition of molybdenum is controlled at 0.40-0.50%.

[0043] Vanadium (V): Vanadium can refine the grain structure of the steel, thereby increasing the strength and toughness of the material. Fine grain structure not only enhances strength, but also reduces crack propagation path. The addition of vanadium helps to improve the toughness of the steel, preventing brittle fracture under impact load, ensuring the reliability of the material in high stress environments. Vanadium affects the phase transformation behavior and tempering process of the steel, promoting the formation of beneficial precipitates, optimizing the overall performance of the steel. However, too high a vanadium content will cause the appearance of aggregated carbides, reducing the strength, and the precipitation of carbides in the grain will reduce the toughness. Therefore, the addition of vanadium is controlled at 0.045-0.055%.

[0044] Boron (B): Boron enhances the hardenability of the steel, enabling sufficient hardness and strength inside during the quenching process. Boron affects the formation of martensite, optimizing the microstructure and improving the performance of the material. Boron cooperates with elements such as manganese and nickel to further improve the overall performance of the steel. However, too much boron will easily accumulate at the grain boundaries, reducing the grain boundary binding energy, making the steel plate more prone to intergranular fracture under impact load, and reducing the low temperature impact energy of the steel plate. Therefore, the addition of boron is controlled at 0.0010-0.0025%.

[0045] Aluminum (Al): Aluminum can play a role in refining the grain and the common effect of precipitation strengthening, significantly improve the mechanical properties of steel, meet the needs of the construction machinery for high strength and high toughness. Al in the steelmaking process as a deoxidizer, reduce the oxygen content in the steel, avoid defects, improve the quality of steel. But the aluminum content in the steel more than 0.05%, easy to lead to the obvious increase of aluminum oxide inclusions, reduce the cleanliness of steel, the toughness of steel. Therefore, the amount of aluminum added to control 0.025~0.050%.

[0046] Phosphorus, sulfur (P, S): P will lead to brittle steel at low temperature, affect its toughness and impact resistance, increase the risk of fracture. Sulfur in the steel to form sulfide inclusions, especially at the grain boundary, leading to material at high temperature, affect the welding performance and structural safety. Therefore, should try to reduce the content of phosphorus, sulfur in steel.

[0047] Nitrogen, oxygen, hydrogen (N, O, H): nitrogen, oxygen, hydrogen is an important indicator of the purity of molten steel, nitrogen, oxygen, hydrogen is easy to form inclusions, porosity, leading to steel cracks, affect the service life of steel. Therefore, should try to reduce the content of nitrogen, oxygen, hydrogen in steel.

[0048] Calcium (Ca): calcium treatment is mainly used for the modification of the inclusions in the steel can not be removed, change the morphology of high melting point of aluminum oxide inclusions, form low melting point of calcium-aluminum compound, improve the purity of molten steel, reduce the influence of inclusions on the performance of steel. Improve the casting performance of molten steel.

[0049] The method for preparing the high-strength steel for engineering machinery with yield strength of 1200 MPa provided in the application comprises KR molten iron desulfurization, converter smelting, bottom argon blowing in argon blowing station, LF refining, RH vacuum treatment, CaSi treatment, continuous casting, slab heating, rolling, cooling, coiling and heat treatment.

[0050] In the method, during KR molten iron desulfurization, more than twice of slag removal treatment is carried out, i.e., before slag removal and after slag removal, and the residence time between every two times of after-slag-removal is not less than 6 min; the bare surface of molten iron after slag removal is not less than 95%; and the S content in molten iron after desulfurization is not more than 0.0008%. The molten iron desulfurization and clean slag removal are to reduce the S content of molten iron entering the converter and prevent the molten steel from being resulfurized due to incomplete slag removal.

[0051] In the application, after converter smelting, the converter smelting end temperature is controlled to be 1590-1608℃, the converter smelting end oxygen is controlled to be 0.040-0.065%, aluminum iron is added for deoxidization when the converter is tapped, and the Alt content in molten steel after deoxidization is controlled to be 0.046-0.060%. The converter is deoxidized, and the Alt content is controlled, so that the reduction slag is prepared in advance for subsequent desulfurization, and the reduction property of the slag is required for subsequent desulfurization.

[0052] In the present application, the molten steel is argon-bubbled from the bottom of the argon-bubbling station, and the Alt in the molten steel at the end of argon bubbling is controlled to be 0.060-0.070%. The control of Alt in the argon-bubbling station is to make the reduction slag in advance for the subsequent desulfurization, and the reduction property of the slag must be required for the subsequent desulfurization.

[0053] In the LF refining process, the molten steel is subjected to deep desulfurization treatment in a ladle furnace, and the S in the molten steel at the end of LF refining is controlled to be ≤0.0015%, and the Alt is controlled to be 0.045-0.065%.

[0054] In the RH vacuum treatment process of the present application, the molten steel is subjected to cyclic degassing and deslagging treatment in a vacuum furnace, and the composition and temperature are fine-tuned by alloying. In some embodiments, the vacuum cycle time can be 27-37 minutes, the vacuum degree can be controlled to be ≤12 Pa, and the vacuum end temperature can be controlled to be 1551-1561℃. Strict control of the vacuum cycle time and the vacuum degree parameters in the RH vacuum treatment process in the above range can further reduce the nitrogen content in the steel, further remove harmful impurities and gases, and improve the purity of the molten steel, thereby improving the strength of the steel.

[0055] In the present application, CaSi treatment is performed after the end of the RH vacuum treatment. In the CaSi treatment process, CaSi wire is fed for calcium treatment, and the addition amount of the CaSi wire is 0.72-0.90 kg / t.s, wherein 0.72-0.90 kg / t.s means that 0.72-0.90 kg of CaSi wire is added per ton of steel. The main purpose of calcium treatment is to change the morphology of inclusions to improve the performance of the steel. An appropriate amount of CaSi wire addition ensures sufficient calcium content to achieve effective inclusion modification, thereby improving the strength and toughness of the steel. If the addition amount of CaSi wire is less than 0.72 kg / t.s, the expected effect of changing the morphology of inclusions cannot be achieved; if the addition amount of CaSi wire is more than 0.90 kg / t.s, the calcium treatment reaction is intense and the reaction time is long, which can introduce too many impurities, affect the quality of the steel, and waste costs. Therefore, this range is a balance point found between ensuring the effect and avoiding negative effects.

[0056] In the continuous casting stage, a high-alkalinity, low-viscosity, and low-melting-point mold powder for medium-carbon steel is used in the mold powder during continuous casting, wherein the alkalinity of the mold powder is 1.27-1.37, the viscosity at a temperature of 1300℃ is 0.08-0.18 Pa·S, and the melting point is 1100-1160℃.

[0057] Further, during continuous casting, the taper of the mold can be 1.25-1.35%, the wide-face cooling water flow rate of the mold can be 3200-3350 L / min, and the narrow-face cooling water flow rate of the mold can be 600-620 L / min.

[0058] Further, the superheat during continuous casting can be controlled to be low, and the superheat during continuous casting is controlled to be 15-25℃, and the tundish temperature is controlled to be 1526-1536℃. Due to the low superheat, the center segregation can be well controlled during casting, but too low superheat and tundish temperature close to the liquidus temperature of the molten steel can cause the molten steel to solidify to be interrupted during casting, and therefore the superheat is controlled to be in the foregoing range.

[0059] In an embodiment, the withdrawal speed during continuous casting can be controlled to be 1.0-1.2 m / min, and the meniscus fluctuation of the crystallizer can be controlled to be within ±3 mm.

[0060] In the present application, the slab heating temperature can be 1240-1300℃. The high-strength steel for engineering machinery needs to have high strength and good toughness after rolling. In the temperature range of 1240-1300℃, the austenite structure of the steel can be fully formed, while avoiding excessive grain growth, so as to ensure that the microstructure of the material after rolling is uniform and the mechanical properties are excellent. The hot rolling process needs the billet to have good plasticity at high temperature, so that it can be deformed smoothly during rolling. The temperature range of 1240-1300℃ can ensure that the billet has sufficient plasticity, while avoiding grain coarsening and performance degradation due to excessively high temperature. If the heating temperature is too high (more than 1300℃), overheating or overburning of the billet will occur, which will cause grain coarsening, mechanical property degradation, surface oxidation and other problems, so as to prevent the deterioration of the material performance. Excessively high heating temperature will increase energy consumption, while excessively low temperature will lead to rolling difficulty. The temperature range of 1240-1300℃ can ensure the material performance, and also realize the efficiency and economy of the hot rolling process. Further, during rolling, the rough rolling temperature can be 1120-1140℃, and the finish rolling temperature can be 920-940℃.

[0061] In an embodiment, the coiling temperature can be 650-680℃. The coiling temperature is controlled in this range in order to obtain better uniformity of the structure, which is beneficial to the yield strength stability control of the finished product performance.

[0062] During the heat treatment process, the quenching temperature can be controlled at 900-920 DEG C, and the quenching holding time can be 10-12 min; the tempering temperature can be controlled at 210-230 DEG C, and the tempering holding time can be 20-25 min. The quenching temperature of the present application is controlled at 900-920 DEG C, and the quenching holding time is controlled at 10-12 min, because under this process, better quenching organization and quenching plate shape can be ensured, when the quenching temperature is lower than 900 DEG C, ferrite will exist in the final organization, so that the strength decreases, and when the quenching temperature is higher than 920 DEG C, the original austenite grain is easy to be coarse, and the toughness will be deteriorated sharply. The tempering temperature of the present application is controlled at 210-230 DEG C, and the tempering holding time is controlled at 20-25 min, because when the tempering temperature is lower than 210 DEG C or the tempering time is lower than 20 min, the tempering effect is poor, and the improvement ability of the plate shape and internal stress is weak, when the tempering temperature is higher than 230 DEG C or the tempering time is higher than 25 min, the supersaturated carbon in sorbite is easy to precipitate, the solid solubility decreases, the strength and hardness are greatly affected, and the performance is not good.

[0063] The present application will be described in detail through examples below, but the protection scope of the present application is not limited to this.

[0064] Example 1 The yield strength 1200 MPa grade high-strength steel for lightweight engineering machinery prepared in this example contains the following chemical components by weight percentage: C: 0.17%, Si: 0.02%, Mn: 1.15%, Nb: 0.01%, Ti: 0.01%, Ni: 0.20%, Cr: 0.25%, Mo: 0.4%, V: 0.048%, B: 0.001%, Ca: 0.0012%, Alt: 0.025%, P: 0.012%, S: 0.0011%, N: 0.0035%, T[O]: 0.0021%, H: 0.0002%, the balance is Fe and unavoidable inclusions, safety factor: K1 is 0.384.

[0065] The preparation method of the yield strength 1200 MPa grade high-strength steel for lightweight engineering machinery includes the following steps: KR hot metal desulphurization, converter smelting, bottom argon blowing in argon blowing station, LF refining, RH vacuum treatment, CaSi treatment, continuous casting, slab heating, rolling, cooling, coiling and heat treatment; During the KR hot metal desulphurization, more than twice slagging treatment is carried out, that is, before and after slagging, and the residence time between every two times of after slagging is 8 min; the exposed surface of the hot metal after slagging is 95%; the S content in the hot metal after desulphurization is 0.0007%; The converter smelting is carried out, the converter end temperature is 1595℃, the converter end oxygen is 0.042%; after the converter tapping deoxidization, the Alt in the molten steel is 0.047%; The molten steel is blown by the bottom argon blowing station, the Alt in the molten steel is 0.061% when the argon blowing is finished; The molten steel is treated by the ladle furnace deep desulfurization, the content of S in the molten steel is 0.0009% and the Alt is 0.049% when the ladle furnace (LF furnace refining) is finished; During the RH vacuum treatment process, the vacuum circulation time is 35 minutes, the vacuum degree is 11Pa, and the vacuum end temperature is 1554℃; after the RH vacuum treatment is finished, the CaSi wire is fed to carry out calcium treatment, and the addition amount of the CaSi wire is 0.72kg / t.s; During the continuous casting process, the high basicity, low viscosity and low melting point mold powder for medium carbon steel is used, wherein the basicity of the mold powder is 1.37, the viscosity at 1300℃ is 0.08Pa·S, the melting point is 1108℃, the taper of the mold is 1.26%, the cooling water flow of the wide surface of the mold is 3206L / min, the cooling water flow of the narrow surface of the mold is 606L / min, the overheat degree of the continuous casting is 18℃, the tundish temperature is 1529℃, the continuous casting speed is 1.1m / min, and the mold liquid surface fluctuation is-2mm; The slab heating temperature is 1265℃, the rough rolling temperature is 1127℃, the finish rolling temperature is 928℃, and the coiling temperature is 658℃; During the heat treatment process, the quenching temperature is 905℃, the quenching holding time is 10min; the tempering temperature is 215℃, and the tempering holding time is 22min.

[0066] Examples 2-10 and Comparative Examples 1-2 are carried out according to the process of Example 1, except that the chemical composition of the steel and the main steelmaking process parameters are different, see Tables 1-5.

[0067] Table 1 Component values of examples and comparative examples Table 2 Table 3 Table 4 Table 5 Test Example The yield strength, tensile strength, elongation and longitudinal impact energy at-40℃ of the high-strength steel for engineering machinery prepared in the test examples and comparative examples are tested, and the results are shown in Table 6.

[0068] Table 6 From the above, it can be seen that the yield strength, tensile strength, elongation and longitudinal impact energy at -40 DEG C of the high-strength steel for engineering machinery prepared by the method of the present application are much higher than those of the comparative examples, the thickness of the steel plate is thinner, the light weight requirement of the high-strength steel for engineering machinery is met, and the safety factor K1 is 0.38-0.47%, which can meet the safety requirement of service for more than 15 years.

[0069] It should be understood that the parts not elaborated in the specification are all prior art.

[0070] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and belong to the protection scope of the present application.

Claims

1. A high-strength steel for lightweight engineering machinery with a yield strength of 1200 MPa, characterized by, The high-strength steel for engineering machinery contains the following chemical components by weight percentage: C: 0.170~0.190%, Si: 0.02~0.15%, Mn: 1.15~1.25%, P: ≤0.015%, S: ≤0.002%, Alt: 0.025~0.050%, Nb: 0.010~0.020%, Ti: 0.010~0.025%, Ni: 0.20~0.30%, Cr: 0.25~0.33%, Mo: 0.40~0.50%, V: 0.048~0.055%, B: 0.0010~0.0025%, Ca: 0.0010~0.0030%, N ≤0.0050%, T[O] ≤0.0030%, H ≤0.00025%, the balance being Fe and unavoidable inclusions.

2. The high-strength steel for light-weight construction machinery according to claim 1, characterized by, The high-strength steel for lightweight engineering machinery satisfies a safety factor: K1= C + Si / 27 + Mn / 12 + V / 3 + Nb / 2.5 + Ti / 5 + Cr / 6 + Mo / 9 + 9B, and K1 is 0.38~0.47%.

3. The high-strength steel for light-weight construction machinery according to claim 1 or 2, characterized by, The high-strength steel for lightweight engineering machinery has a yield strength of 1200-1300MPa, a tensile strength of 1250-1350MPa, an elongation A≥10%, and a longitudinal impact energy KV2≥50J at -40℃. And / or, the high-strength steel for lightweight engineering machinery has a plate thickness of 3-6mm.

4. A method of producing the high-strength steel for lightweight engineering machinery of the yield strength 1200 MPa grade according to claim 1 or 2, characterized by, The method comprises KR molten iron desulfurization, converter smelting, bottom argon blowing at an argon blowing station, LF refining, RH vacuum treatment, CaSi treatment, continuous casting, slab heating, rolling, cooling, coiling, and heat treatment. In the RH vacuum treatment process, the vacuum cycle time is 27~37 minutes, the vacuum degree is controlled to be ≤12Pa, and the vacuum end temperature is controlled to be 1551~1561℃. In the CaSi treatment process, CaSi wire is fed for calcium treatment, and the addition amount of the CaSi wire is 0.72~0.90kg / t.s. In the heat treatment process, the quenching temperature is 900~920℃, the quenching holding time is 10~12min, the tempering temperature is 210~230℃, and the tempering holding time is 20~25min.

5. The method of claim 4, wherein, In the KR molten iron desulfurization process, more than twice of slag removal treatment is performed, and the residence time between every two times of slag removal is not less than 6min; the exposed surface of the molten iron after slag removal is not less than 95%; and the S in the molten iron after desulfurization is ≤0.0008%.

6. The method according to claim 4 or 5, characterized in that, In the converter smelting process, the smelting end temperature is controlled to be 1590~1608℃, and the smelting end oxygen is controlled to be 0.040~0.065%; aluminum iron is added for deoxidization when the converter is tapped, and the Alt in the molten iron is controlled to be 0.046~0.060%.

7. The method of claim 4, wherein, In the bottom argon blowing at the argon blowing station, the Alt in the molten iron at the end of argon blowing is controlled to be 0.060~0.070%. And / or, in the LF furnace refining process, the S in the molten iron at the end of LF furnace refining is controlled to be ≤0.0015%, and the Alt is controlled to be 0.045~0.065%.

8. The method of claim 4, wherein, In the continuous casting process, the casting protection slag is used for continuous casting, the basicity of the protection slag is 1.27-1.37, the viscosity at 1300℃ is 0.08-0.18Pa·S, and the melting point is 1100-1160℃; And / or, when the continuous casting is carried out, the taper of the crystallizer is 1.25-1.35%, the cooling water flow of the wide surface of the crystallizer is 3200-3350L / min, and the cooling water flow of the narrow surface of the crystallizer is 600-620L / min; And / or, the superheat degree is controlled to be 15-25℃ when the continuous casting is carried out, and the tundish temperature is controlled to be 1526-1536℃; And / or, the casting speed is controlled to be 1.0-1.2m / min when the continuous casting is carried out, and the liquid surface fluctuation of the crystallizer is controlled to be within ±3mm.

9. The method of claim 4, wherein, The slab heating temperature is 1240-1300℃.

10. The method of claim 4, wherein, In the rolling process, the rough rolling temperature is 1120-1140℃, and the finish rolling temperature is 920-940℃; And / or, the coiling temperature is 650-680℃.

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