Preparation method of engineering machinery ultrahigh-strength steel plate with yield strength of 1200 MPa for crane

Abstract

The invention discloses a preparation method of an engineering machinery ultrahigh-strength steel plate with yield strength of 1200 MPa for a crane. The steel plate comprises the following chemical components in percentage by mass: less than or equal to 0.20% of C, less than or equal to 0.80% of S i, less than or equal to 2.0% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, less than or equal to 0.5% of Cu, less than or equal to 2.0% of N i, less than or equal to 1.5% of Cr, less than or equal to 0.7% of Mo, less than or equal to 0.005% of B, less than or equal to 0.012% of V, less than or equal to 0.06% of Nb, less than or equal to 0.06% of T i and 0.030-0.050% of A l. The production technology comprises the steps of molten iron pretreatment, converter steelmaking, LF external refining, RH vacuum degassing, continuous casting, heating, phosphorus removal, rough rolling, finish rolling, cooling, straightening and off-line heat treatment. According to the steel plate base material, the yield strength Rp0.2 is larger than or equal to 1200 MPa, Rm ranges from 1250 MPa to 1600 MPa, A is larger than or equal to 9%, and the impact energy at the temperature of-40 DEG C is larger than or equal to 27 J.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgical materials, and in particular relates to a method for preparing an ultra-high-strength steel plate for cranes with a yield strength of 1200 MPa, which is mainly used in components of mobile equipment such as beam structures of engineering machinery, crane arms and bodies of dump trucks. Background Art

[0002] At present, document 1 (Development of Q620D high-strength steel plates for engineering machinery with high surface quality requirements_Chen Fuqiang) adopts a micro-alloying design of medium carbon and medium manganese, and successfully trial-produces Q620D high-strength steel plates for engineering machinery with high surface quality requirements through reasonable heating, rolling and offline tempering heat treatment processes. All mechanical performance indicators far exceed the technical requirements of engineering machinery users, but the performance is at the 620MPa level, and the specific production method of 1200MPa-level ultra-high-strength steel plates for engineering machinery is not mentioned.

[0003] Document 2 (Quenching process of Q1300E ultra-high strength steel for engineering machinery_Zhang Qingxue) uses a fully automatic tensile testing machine, a fully automatic impact testing machine, an optical microscope and a scanning electron microscope to study the mechanical properties and microstructure of Q1300E steel plates under different quenching processes. The results show that when the quenching heating time is 60 minutes and the quenching temperature is 840°C, the strength and low-temperature impact properties are the best, and the tempered mechanical properties meet the requirements. The invention also does not explain the specific smelting and rolling processes, but only provides a method for heat treatment quenching.

[0004] Reference 3 (Study on the Phase Transformation Behavior of Ultra-High Strength Steel for Engineering Machinery_Zheng Dongsheng) studied the phase transformation behavior of Cr-Mo-NiB series ultra-high strength steel for engineering machinery under continuous cooling conditions using the MMS-200 thermal simulation test machine, and analyzed the effect of cooling rate (0.5-40℃ / s) on its phase transformation temperature and microstructure through thermal expansion curve, optical microscope (OM) and scanning electron microscope (SEM). This method also does not explain the specific production method of the steel plate. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing an ultra-high-strength steel plate with a yield strength of 1200MPa for cranes, and to produce an ultra-high-strength steel plate with a yield strength of 1200MPa for cranes through micro-alloying composition design, smelting, rolling, heat treatment and other production process parameter design and small-scale industrial trial production.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The invention discloses a method for preparing an ultra-high-strength steel plate for cranes with a yield strength of 1200 MPa, characterized in that the chemical composition of the high-strength steel plate by mass percentage includes: C: ≤0.20%, Si: ≤0.80%, Mn ≤2.0%, P: ≤0.020%, S: ≤0.010%, Cu ≤0.5%, Ni ≤2.0%, Cr ≤1.5%, Mo ≤0.7%, B ≤0.005%, V ≤0.012%, Nb ≤0.06%, Ti ≤0.06%, Al: 0.030-0.050%, and the rest are Fe and unavoidable impurities, with a total mass fraction of 100%;

[0008] The production process is hot metal pretreatment - converter steelmaking - LF refining outside the furnace - RH vacuum degassing - continuous casting - heating - dephosphorization - rough rolling - finishing rolling - cooling - straightening - offline heat treatment; wherein, the heating temperature is 1250±15°C to reach the complete austenitization temperature, so that the slab structure is completely austenitized; the rough rolling adopts high temperature and large reduction rolling to ensure that the columnar crystals are fully crushed; the final rolling temperature is 900±15°C to ensure that the finishing rolling is rolled in the completely non-recrystallization temperature area, so that the austenite will not recrystallize and grow, but the grains are elongated and fragmented, thereby obtaining uniform and fine austenite grains; heat treatment: quenching temperature 910±10°C, heat preservation 10-30min, tempering temperature 480-520°C, heat preservation 40-60min, and finally obtain tempered martensite structure;

[0009] Furthermore, the chemical composition of the high-strength steel plate by mass percentage includes: C: 0.07%, Si: 0.06%, Mn: 1.50%, P: 0.003%, S: 0.005%, Ni: 0.50%, Cr: 0.30%, Mo: 0.30%, Nb: 0.050%, Ti: 0.015%, B: 0.0014%, Al: 0.045%, V: 0.04%, and the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

[0010] Furthermore, C: 0.07%, Si: 0.06%, Mn: 1.60%, P: 0.003%, S: 0.005%, Ni: 0.50%, Cr: 0.30%, Mo: 0.30%, Nb: 0.060%, Ti: 0.015%, B: 0.0014%, Al: 0.045%, V: 0.04%, and the rest are Fe and unavoidable impurities, and the mass fraction totals 100%.

[0011] Furthermore, C: 0.07%, Si: 0.06%, Mn: 1.60%, P: 0.003%, S: 0.005%, Ni: 0.50%, Cr: 0.30%, Mo: 0.30%, Nb: 0.050%, Ti: 0.015%, B: 0.0014%, Al: 0.045%, V: 0.04%, and the rest are Fe and unavoidable impurities, and the mass fraction totals 100%.

[0012] Further, the specific production process is as follows:

[0013] (1) Hot metal pretreatment: After hot metal desulfurization pretreatment, the S content is ≤ 0.003%;

[0014] (2) Converter steelmaking: The converter adopts single slag process to ensure the successful carbon extraction in one go; the steel tapping process adopts bottom blowing argon operation. To ensure the effect, the bottom blowing mode of nitrogen and argon switching is adopted; the steel tapping temperature is less than 1670℃;

[0015] (3) LF refining: mainly for the addition of Si, Mn, Nb, V, Ti, Cr, Mo, and adding appropriate amounts of alloy according to the requirements of internal control components; LF refining is carried out for no less than 40 minutes;

[0016] (4) RH refining: vacuum treatment is performed for no less than 30 minutes in the RH stage; 50 kg of rare earth alloy is added for microalloying in the later stage of RH treatment; the molten steel after RH treatment is first subjected to soft argon blowing to ensure uniform composition and sufficient floating of inclusions for more than 15 minutes, and then allowed to stand and steel is added, wherein the standing time is no less than 15 minutes;

[0017] (5) Continuous casting: electromagnetic stirring and light pressure are used to ensure the quality of the casting;

[0018] (6) Heating process: The slab is cold loaded into the furnace, the furnace time is not less than 300 min, and the furnace temperature is 1250°C;

[0019] (7) Hot rolling process: The starting temperature of the rough rolling of the slab is 1230±15℃. Considering that the steel plate is relatively thin, two-stage controlled rolling is not adopted. The final rolling temperature of the steel plate is set to 900±15℃. In addition, the chemical composition design has ensured good hardenability. Under the condition of low cooling rate, the rolled steel plate will also obtain tempered martensite structure. Considering that ACC acceleration is easy to cause poor shape of thin gauge steel plate, the steel plate is not cooled after rolling and is cooled naturally in air.

[0020] (8) Heat treatment process: quenching heating temperature 910℃, keep warm for 10min; temper the steel plate within 24 hours after quenching; tempering temperature of steel plate 480℃, keep warm for 40min.

[0021] Further, the specific production process is as follows:

[0022] (1) Hot metal pretreatment: After hot metal desulfurization pretreatment, the S content is ≤ 0.003%;

[0023] (2) Converter steelmaking: The converter adopts single slag process to ensure the successful carbon extraction in one go; the steel tapping process adopts bottom blowing argon operation. To ensure the effect, the bottom blowing mode of nitrogen and argon switching is adopted; the steel tapping temperature is less than 1670℃;

[0024] (3) LF refining: mainly for the addition of Si, Mn, Nb, V, Ti, Cr, Mo, and adding appropriate amounts of alloy according to the requirements of internal control components; LF refining is carried out for no less than 40 minutes;

[0025] (4) RH refining: vacuum treatment is performed for no less than 30 minutes in the RH stage; 50 kg of rare earth alloy is added for microalloying in the later stage of RH treatment; the molten steel after RH treatment is first subjected to soft argon blowing to ensure uniform composition and sufficient floating of inclusions for more than 15 minutes, and then allowed to stand and steel is added, wherein the standing time is no less than 15 minutes;

[0026] (5) Continuous casting: electromagnetic stirring and light pressure are used to ensure the quality of the casting;

[0027] (6) Heating process: The slab is cold loaded into the furnace, the furnace time is not less than 300 min, and the furnace temperature is 1250°C;

[0028] (7) Hot rolling process: The starting temperature of the rough rolling of the slab is 1230±15℃. Considering that the steel plate is relatively thin, two-stage controlled rolling is not adopted. The final rolling temperature of the steel plate is set to 900±15℃. In addition, the chemical composition design has ensured good hardenability. Under the condition of low cooling rate, the rolled steel plate will also obtain tempered martensite structure. Considering that ACC acceleration is easy to cause poor shape of thin gauge steel plate, the steel plate is not cooled after rolling and is cooled naturally in air.

[0029] (8) Heat treatment process: quenching heating temperature 910℃, keep warm for 30min; tempering within 24 hours after quenching; tempering temperature 500℃, keep warm for 40min.

[0030] Further, the specific production process is as follows:

[0031] (1) Hot metal pretreatment: After hot metal desulfurization pretreatment, the S content is ≤ 0.003%;

[0032] (2) Converter steelmaking: The converter adopts single slag process to ensure the successful carbon extraction in one go; the steel tapping process adopts bottom blowing argon operation. To ensure the effect, the bottom blowing mode of nitrogen and argon switching is adopted; the steel tapping temperature is less than 1670℃;

[0033] (3) LF refining: mainly for the addition of Si, Mn, Nb, V, Ti, Cr, Mo, and adding appropriate amounts of alloy according to the requirements of internal control components; LF refining is carried out for no less than 40 minutes;

[0034] (4) RH refining: vacuum treatment is performed for no less than 30 minutes in the RH stage; 50 kg of rare earth alloy is added for microalloying in the later stage of RH treatment; the molten steel after RH treatment is first subjected to soft argon blowing to ensure uniform composition and sufficient floating of inclusions for more than 15 minutes, and then allowed to stand and steel is added, wherein the standing time is no less than 15 minutes;

[0035] (5) Continuous casting: electromagnetic stirring and light pressure are used to ensure the quality of the casting;

[0036] (6) Heating process: The slab is cold loaded into the furnace, the furnace time is not less than 300 min, and the furnace temperature is 1250°C;

[0037] (7) Hot rolling process: The starting temperature of the rough rolling of the slab is 1230±15℃. Considering that the steel plate is relatively thin, two-stage controlled rolling is not adopted. The final rolling temperature of the steel plate is set to 900±15℃. In addition, the chemical composition design has ensured good hardenability. Under the condition of low cooling rate, the rolled steel plate will also obtain tempered martensite structure. Considering that ACC acceleration is easy to cause poor shape of thin gauge steel plate, the steel plate is not cooled after rolling and is cooled naturally in air.

[0038] (8) Heat treatment process: quenching heating temperature 880℃, keep warm for 10min; tempering within 24 hours after quenching; tempering temperature 520℃, keep warm for 30min.

[0039] Compared with the prior art, the beneficial technical effects of the present invention are:

[0040] The present invention designs and develops an ultra-high strength steel plate for cranes with a yield strength of 1200 MPa-level engineering machinery that meets standard requirements by adding microalloy elements alone or in combination.

[0041] The steel plate base material meets the following requirements: yield strength Rp0.2 ≥ 1200MPa, Rm: 1250-1600MPa, A ≥ 9%, -40℃ impact energy ≥ 27J. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described below in conjunction with the accompanying drawings.

[0043] Figure 1 For example 1 organization;

[0044] Figure 2 For Example 2 organization;

[0045] Figure 3 Organized as in Example 3. DETAILED DESCRIPTION

[0046] Embodiment 1:

[0047] (1) The embodiment includes the following chemical compositions in weight percentage: The present invention relates to an ultra-high strength steel plate for crane with a yield strength of 1200 MPa for engineering machinery and a preparation method thereof, characterized in that the chemical composition is C: 0.07%, Si: 0.06%, Mn: 1.50%, P: 0.003%, S: 0.005%, Ni: 0.50%, Cr: 0.30%, Mo: 0.30%, Nb: 0.060%, Ti: 0.015%, B: 0.0014%, Al: 0.045%, V: 0.04%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

[0048] (2) Hot metal pretreatment: After hot metal desulfurization pretreatment, the S content is ≤0.003%.

[0049] (3) Converter steelmaking: The converter adopts the single slag process to ensure the success of carbon extraction in one go. The steel tapping process adopts bottom blowing argon operation. To ensure the effect, the bottom blowing mode of nitrogen and argon switching is adopted. The steel tapping temperature is less than 1670℃.

[0050] (4) LF refining: mainly for the addition of Si, Mn, Nb, V, Ti, Cr, Mo, and the addition of appropriate amount of alloy according to the requirements of internal control components. LF refining is carried out for no less than 40 minutes.

[0051] (5) RH refining: The vacuum treatment time in the RH stage is not less than 30 minutes. In the later stage of RH treatment, 50 kg of rare earth alloy is added for micro-alloying treatment. The molten steel after RH treatment must first be soft-blown with argon to ensure uniform composition and sufficient floating of inclusions for more than 15 minutes, and then allowed to stand and steel is added, with the standing time being not less than 15 minutes.

[0052] (6) Continuous casting: Electromagnetic stirring and light pressure are used to ensure the quality of the casting.

[0053] (7) Heating process: The slab is cold loaded into the furnace, the time in the furnace is not less than 300 min, and the furnace temperature is 1250°C.

[0054] (8) Hot rolling process: The starting temperature of the rough rolling of the slab is 1230±15℃. Considering that the steel plate is relatively thin, two-stage controlled rolling is not adopted. The final rolling temperature of the steel plate is set to 900±15℃. In addition, the chemical composition design of this steel grade has ensured good hardenability, and the tempered martensite structure of the rolled steel plate can be obtained under low cooling rate conditions. Considering that ACC acceleration can easily cause poor shape of thin gauge steel plate, the steel plate is not subjected to controlled cooling after rolling, and natural cooling in air is adopted.

[0055] (9) Heat treatment process: quenching heating temperature 910℃, keep warm for 10 minutes. After quenching, the steel plate is tempered within 24 hours. Since this steel has high hardness and its microstructure is tempered martensite, the steel plate is tempered at 480℃ and kept warm for 40 minutes.

[0056] Embodiment 2:

[0057] (1) The embodiment includes the following chemical compositions in weight percentage: The present invention relates to an ultra-high strength steel plate for crane with a yield strength of 1200 MPa for engineering machinery and a preparation method thereof, characterized in that the chemical composition is C: 0.07%, Si: 0.06%, Mn: 1.60%, P: 0.003%, S: 0.005%, Ni: 0.50%, Cr: 0.30%, Mo: 0.30%, Nb: 0.060%, Ti: 0.015%, B: 0.0014%, Al: 0.045%, V: 0.04%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

[0058] (2) Hot metal pretreatment: After hot metal desulfurization pretreatment, the S content is ≤0.003%.

[0059] (3) Converter steelmaking: The converter adopts the single slag process to ensure the success of carbon extraction in one go. The steel tapping process adopts bottom blowing argon operation. To ensure the effect, the bottom blowing mode of nitrogen and argon switching is adopted. The steel tapping temperature is less than 1670℃.

[0060] (4) LF refining: mainly for the addition of Si, Mn, Nb, V, Ti, Cr, Mo, and the addition of appropriate amount of alloy according to the requirements of internal control components. LF refining is carried out for no less than 40 minutes.

[0061] (5) RH refining: The vacuum treatment time in the RH stage is not less than 30 minutes. In the later stage of RH treatment, 50 kg of rare earth alloy is added for micro-alloying treatment. The molten steel after RH treatment must first be soft-blown with argon to ensure uniform composition and sufficient floating of inclusions for more than 15 minutes, and then allowed to stand and steel is added, with the standing time being not less than 15 minutes.

[0062] (6) Continuous casting: Electromagnetic stirring and light pressure are used to ensure the quality of the casting.

[0063] (7) Heating process: The slab is cold loaded into the furnace, the time in the furnace is not less than 300 min, and the furnace temperature is 1250°C.

[0064] (8) Hot rolling process: The starting temperature of the rough rolling of the slab is 1230±15℃. Considering that the steel plate is relatively thin, two-stage controlled rolling is not adopted. The final rolling temperature of the steel plate is set to 900±15℃. In addition, the chemical composition design of this steel grade has ensured good hardenability, and the tempered martensite structure of the rolled steel plate can be obtained under low cooling rate conditions. Considering that ACC acceleration can easily cause poor shape of thin gauge steel plate, the steel plate is not subjected to controlled cooling after rolling, and natural cooling in air is adopted.

[0065] (9) Heat treatment process: quenching heating temperature 910℃, keep warm for 30min. After quenching, the steel plate is tempered within 24 hours. Tempering temperature 500℃, keep warm for 40min.

[0066] Embodiment 3:

[0067] (1) The embodiment includes the following chemical compositions in weight percentage: The present invention relates to an ultra-high strength steel plate for crane with a yield strength of 1200 MPa for engineering machinery and a preparation method thereof, characterized in that the chemical composition is C: 0.07%, Si: 0.06%, Mn: 1.60%, P: 0.003%, S: 0.005%, Ni: 0.50%, Cr: 0.30%, Mo: 0.30%, Nb: 0.050%, Ti: 0.015%, B: 0.0014%, Al: 0.045%, V: 0.04%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

[0068] (2) Hot metal pretreatment: After hot metal desulfurization pretreatment, the S content is ≤0.003%.

[0069] (3) Converter steelmaking: The converter adopts the single slag process to ensure the success of carbon extraction in one go. The steel tapping process adopts bottom blowing argon operation. To ensure the effect, the bottom blowing mode of nitrogen and argon switching is adopted. The steel tapping temperature is less than 1670℃.

[0070] (4) LF refining: mainly for the addition of Si, Mn, Nb, V, Ti, Cr, Mo, and the addition of appropriate amount of alloy according to the requirements of internal control components. LF refining is carried out for no less than 40 minutes.

[0071] (5) RH refining: The vacuum treatment time in the RH stage is not less than 30 minutes. In the later stage of RH treatment, 50 kg of rare earth alloy is added for micro-alloying treatment. The molten steel after RH treatment must first be soft-blown with argon to ensure uniform composition and sufficient floating of inclusions for more than 15 minutes, and then allowed to stand and steel is added, with the standing time being not less than 15 minutes.

[0072] (6) Continuous casting: Electromagnetic stirring and light pressure are used to ensure the quality of the casting.

[0073] (7) Heating process: The slab is cold loaded into the furnace, the time in the furnace is not less than 300 min, and the furnace temperature is 1250°C.

[0074] (8) Hot rolling process: The starting temperature of the rough rolling of the slab is 1230±15℃. Considering that the steel plate is relatively thin, two-stage controlled rolling is not adopted. The final rolling temperature of the steel plate is set to 900±15℃. In addition, the chemical composition design of this steel grade has ensured good hardenability, and the tempered martensite structure of the rolled steel plate can be obtained under low cooling rate conditions. Considering that ACC acceleration can easily cause poor shape of thin gauge steel plate, the steel plate is not subjected to controlled cooling after rolling, and natural cooling in air is adopted.

[0075] (9) Heat treatment process: quenching heating temperature 880℃, keep warm for 10 minutes. After quenching, the steel plate is tempered within 24 hours. Tempering temperature 520℃, keep warm for 30 minutes.

[0076] The mechanical properties of each embodiment are shown in Table 1.

[0077] Table 1 Mechanical properties of steel plates in various examples

[0078]

[0079] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing an ultra-high strength steel plate for cranes with a yield strength of 1200 MPa for engineering machinery, characterized in that: The chemical composition of the high-strength steel plate by mass percentage includes: C: ≤0.20%, Si: ≤0.80%, Mn ≤2.0%, P: ≤0.020%, S: ≤0.010%, Cu ≤0.5%, Ni ≤2.0%, Cr ≤1.5%, Mo ≤0.7%, B ≤0.005%, V ≤0.012%, Nb ≤0.06%, Ti ≤0.06%, Al: 0.030-0.050%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%; The process of molten iron pretreatment - converter steelmaking - LF refining - RH vacuum degassing - continuous casting - heating - dephosphorization - rough rolling - finishing rolling - cooling - straightening - offline heat treatment is adopted for production; wherein, the heating temperature is 1250±15°C to reach the complete austenitization temperature, so that the slab structure is completely austenitized; the rough rolling adopts high temperature and large reduction rolling to ensure that the columnar crystals are fully crushed; the final rolling temperature is 900±15°C to ensure that the finishing rolling is rolled in the completely non-recrystallization temperature region, so that the austenite will not recrystallize and grow, but the grains will be elongated and fragmented, thereby obtaining uniform and fine austenite grains; heat treatment: quenching temperature is 910±10°C, heat preservation is 10-30min, tempering temperature is 480-520°C, heat preservation is 40-60min, and finally a tempered martensite structure is obtained.

2. The method for preparing the ultra-high strength steel plate for crane with a yield strength of 1200 MPa for engineering machinery according to claim 1, characterized in that: The chemical composition of the high-strength steel plate by mass percentage includes: C: 0.07%, Si: 0.06%, Mn: 1.50%, P: 0.003%, S: 0.005%, Ni: 0.50%, Cr: 0.30%, Mo: 0.30%, Nb: 0.050%, Ti: 0.015%, B: 0.0014%, Al: 0.045%, V: 0.04%, and the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

3. The method for preparing the ultra-high strength steel plate for crane with a yield strength of 1200 MPa for engineering machinery according to claim 1, characterized in that: C: 0.07%, Si: 0.06%, Mn: 1.60%, P: 0.003%, S: 0.005%, Ni: 0.50%, Cr: 0.30%, Mo: 0.30%, Nb: 0.060%, Ti: 0.015%, B: 0.0014%, Al: 0.045%, V: 0.04%, and the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

4. The method for preparing the ultra-high strength steel plate for crane with a yield strength of 1200 MPa for engineering machinery according to claim 1, characterized in that: C: 0.07%, Si: 0.06%, Mn: 1.60%, P: 0.003%, S: 0.005%, Ni: 0.50%, Cr: 0.30%, Mo: 0.30%, Nb: 0.050%, Ti: 0.015%, B: 0.0014%, Al: 0.045%, V: 0.04%, and the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

5. The method for preparing the ultra-high strength steel plate for crane with a yield strength of 1200 MPa for engineering machinery according to claim 2, characterized in that: The specific production process is as follows: (1) Hot metal pretreatment: After hot metal desulfurization pretreatment, the S content is ≤ 0.003%; (2) Converter steelmaking: The converter adopts single slag process to ensure the successful carbon extraction in one go; the steel tapping process adopts bottom blowing argon operation. To ensure the effect, the bottom blowing mode of nitrogen and argon switching is adopted; the steel tapping temperature is less than 1670℃; (3) LF refining: mainly for the addition of Si, Mn, Nb, V, Ti, Cr, and Mo, and adding appropriate amounts of alloys according to the requirements of internal control components; LF refining is carried out for no less than 40 minutes; (4) RH refining: vacuum treatment is performed for no less than 30 minutes in the RH stage; 50 kg of rare earth alloy is added for microalloying in the later stage of RH treatment; the molten steel after RH treatment is first subjected to soft argon blowing to ensure uniform composition and sufficient floating of inclusions for more than 15 minutes, and then allowed to stand and steel is added, wherein the standing time is no less than 15 minutes; (5) Continuous casting: electromagnetic stirring and light pressure are used to ensure the quality of the casting; (6) Heating process: The slab is cold loaded into the furnace, the furnace time is not less than 300 min, and the furnace temperature is 1250°C; (7) Hot rolling process: The starting temperature of the rough rolling of the slab is 1230±15℃. Considering that the steel plate is relatively thin, two-stage controlled rolling is not adopted. The final rolling temperature of the steel plate is set to 900±15℃. In addition, the chemical composition design has ensured good hardenability. Under the condition of low cooling rate, the rolled steel plate will also obtain tempered martensite structure. Considering that ACC acceleration is easy to cause poor shape of thin gauge steel plate, the steel plate is not cooled after rolling and is cooled naturally in air. (8) Heat treatment process: quenching heating temperature 910℃, keep warm for 10min; temper the steel plate within 24 hours after quenching; tempering temperature of steel plate 480℃, keep warm for 40min.

6. The method for preparing the ultra-high strength steel plate for crane with a yield strength of 1200 MPa for engineering machinery according to claim 3, characterized in that: The specific production process is as follows: (1) Hot metal pretreatment: After hot metal desulfurization pretreatment, the S content is ≤ 0.003%; (2) Converter steelmaking: The converter adopts single slag process to ensure the successful carbon extraction in one go; the steel tapping process adopts bottom blowing argon operation. To ensure the effect, the bottom blowing mode of nitrogen and argon switching is adopted; the steel tapping temperature is less than 1670℃; (3) LF refining: mainly for the addition of Si, Mn, Nb, V, Ti, Cr, and Mo, and adding appropriate amounts of alloys according to the requirements of internal control components; LF refining is carried out for no less than 40 minutes; (4) RH refining: vacuum treatment is performed for no less than 30 minutes in the RH stage; 50 kg of rare earth alloy is added for microalloying in the later stage of RH treatment; the molten steel after RH treatment is first subjected to soft argon blowing to ensure uniform composition and sufficient floating of inclusions for more than 15 minutes, and then allowed to stand and steel is added, wherein the standing time is no less than 15 minutes; (5) Continuous casting: electromagnetic stirring and light pressure are used to ensure the quality of the casting; (6) Heating process: The slab is cold loaded into the furnace, the furnace time is not less than 300 min, and the furnace temperature is 1250°C; (7) Hot rolling process: The starting temperature of the rough rolling of the slab is 1230±15℃. Considering that the steel plate is relatively thin, two-stage controlled rolling is not adopted. The final rolling temperature of the steel plate is set to 900±15℃. In addition, the chemical composition design has ensured good hardenability. Under the condition of low cooling rate, the rolled steel plate will also obtain tempered martensite structure. Considering that ACC acceleration is easy to cause poor shape of thin gauge steel plate, the steel plate is not cooled after rolling and is cooled naturally in air. (8) Heat treatment process: quenching heating temperature 910℃, keep warm for 30min; tempering within 24 hours after quenching; tempering temperature 500℃, keep warm for 40min.

7. The method for preparing the ultra-high strength steel plate for crane with a yield strength of 1200 MPa for engineering machinery according to claim 4, characterized in that: The specific production process is as follows: (1) Hot metal pretreatment: After hot metal desulfurization pretreatment, the S content is ≤ 0.003%; (2) Converter steelmaking: The converter adopts single slag process to ensure the successful carbon extraction in one go; the steel tapping process adopts bottom blowing argon operation. To ensure the effect, the bottom blowing mode of nitrogen and argon switching is adopted; the steel tapping temperature is less than 1670℃; (3) LF refining: mainly for the addition of Si, Mn, Nb, V, Ti, Cr, and Mo, and adding appropriate amounts of alloys according to the requirements of internal control components; LF refining is carried out for no less than 40 minutes; (4) RH refining: vacuum treatment is performed for no less than 30 minutes in the RH stage; 50 kg of rare earth alloy is added for microalloying in the later stage of RH treatment; the molten steel after RH treatment is first subjected to soft argon blowing to ensure uniform composition and sufficient floating of inclusions for more than 15 minutes, and then allowed to stand and steel is added, wherein the standing time is no less than 15 minutes; (5) Continuous casting: electromagnetic stirring and light pressure are used to ensure the quality of the casting; (6) Heating process: The slab is cold loaded into the furnace, the furnace time is not less than 300 min, and the furnace temperature is 1250°C; (7) Hot rolling process: The starting temperature of the rough rolling of the slab is 1230±15℃. Considering that the steel plate is relatively thin, two-stage controlled rolling is not adopted. The final rolling temperature of the steel plate is set to 900±15℃. In addition, the chemical composition design has ensured good hardenability. Under the condition of low cooling rate, the rolled steel plate will also obtain tempered martensite structure. Considering that ACC acceleration is easy to cause poor shape of thin gauge steel plate, the steel plate is not cooled after rolling and is cooled naturally in air. (8) Heat treatment process: quenching heating temperature 880℃, keep warm for 10min; tempering within 24 hours after quenching; tempering temperature 520℃, keep warm for 30min.

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