CN112813345A

CN112813345A - Non-quenched and tempered steel for cold machining engineering machinery hydraulic piston rod and preparation method

Info

Publication number: CN112813345A
Application number: CN202011585062.5A
Authority: CN
Inventors: 张振民; 李硕; 马恒春; 杨国; 冶廷全; 苗红生; 方光锦; 尚大军; 王海龙; 赵海东
Original assignee: XINING SPECIAL STEEL CO Ltd; Qinghai Xigang Special Steel Technology Development Co ltd
Current assignee: XINING SPECIAL STEEL CO Ltd; Qinghai Xigang Special Steel Technology Development Co ltd
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2021-05-18

Abstract

The invention provides a non-quenched and tempered steel for cold-working engineering machinery hydraulic piston rods and a preparation method. 0.010～0.030%, V 0.12～0.14%, Ti 0.010～0.020%, Cr 0.16～0.18%, Al 0.010～0.050%, N 110～130ppm, Fe balance. The present invention also relates to the preparation method of the aforementioned non-quenched and tempered steel. The high-strength and high-toughness non-quenched and tempered steel for the hydraulic piston rod prepared by the method of the invention has the mechanical properties meeting the requirements for the use of the hydraulic piston rod in the hot-rolled state, and the overall segregation degree of the steel is good, which is beneficial to friction welding for users and direct turning of the steel. The post-processing is a hydraulic piston rod, which can be processed without quenching, tempering and straightening as in the past, which can save production costs by 28%-35%.

Description

Non-quenched and tempered steel for cold machining engineering machinery hydraulic piston rod and preparation method

Technical Field

The invention belongs to the field of metal material smelting; in particular to non-quenched and tempered steel for a hydraulic piston rod of cold working engineering machinery and a preparation method thereof.

Background

The non-quenched and tempered steel is prepared by adding vanadium, titanium and niobium microalloying elements on the basis of medium carbon manganese steel, so that the vanadium, titanium and niobium microalloying elements are dissolved in austenite in the heating process, and the solid solubility of the vanadium, titanium and niobium in the austenite is reduced along with cooling. The microalloying elements vanadium, titanium and niobium will precipitate in the form of fine carbides and nitrides in the previously precipitated ferrite and pearlite. These precipitates are in a coherent relationship with the parent phase, and strengthen the steel. The mechanical properties of the steel in a hot rolled state, a forged state or a normalized state reach or exceed the level of quenched and tempered steel. Therefore, the heat treatment process and the heat treatment equipment are reduced, waste products caused by deformation or quenching cracks generated in the heat treatment process are avoided, the labor condition is improved, the pollution caused by heat treatment is reduced, the cost is saved by 30 percent compared with quenched and tempered steel, the production period is shortened, and the energy is saved. Referred to as "green steel".

The non-quenched and tempered steel is developed successfully by the German Teddle Steel company in 1972, 49MnVS3 represents the steel type, and the non-quenched and tempered steel is rapidly developed and popularized due to the advantages of energy conservation, material conservation and cost reduction, and is particularly widely applied to the automobile industry. In recent years, through the research and study on companies such as Nissan Toyota, Sumitomo and Ormura forging stocks, the results show that: at present, more than 90 percent of crankshafts and connecting rods in Japan are forged by non-quenched and tempered steel, such as Sumitomo metal S43CV, S45CV and S50CV which are used for forging automobile connecting rods; in addition, according to data introduction, Germany mass automobile factories adopt non-quenched and tempered steel 27MnSiVS6 to manufacture automobile connecting rods, and the annual production is 250 ten thousand pieces; 25000 tons of non-heat-treated steel are consumed annually by the company Volvo, sweden for the manufacture of automotive parts. According to statistics, except for a few high-performance racing cars at present, almost more than 80 percent of automobile crankshaft forgings are made of non-quenched and tempered steel.

China also obtains a series of achievements in the aspects of development and application of non-quenched and tempered steel, in recent years, relevant forging plants in Shanghai cooperate with a steel research institute, the non-quenched and tempered steel and the forging control-cooling control technology thereof are applied to actual production in a large-scale and batch mode, and corresponding cooling control production lines are established to be respectively used for producing car crankshafts and connecting rods. However, the production of cold-working non-quenched and tempered steel for engineering machinery is at the beginning stage at present in China.

Disclosure of Invention

The invention aims to provide non-quenched and tempered steel for a hydraulic piston rod of cold machining engineering machinery and a preparation method thereof. The invention successfully develops the non-quenched and tempered steel for the hydraulic piston rod of the large-size cold-working engineering machinery with the diameter of phi 90-phi 140mm, the tensile strength of the non-quenched and tempered steel in a hot rolling state reaches more than 820MPa, and the surface of the non-quenched and tempered steel isThe shrinkage rate is more than or equal to 30 percent, and the steel is subjected to cold corrosion

(D is the rolled stock diameter).

The invention is realized by the following technical scheme:

in a first aspect, the invention relates to non-quenched and tempered steel for a hydraulic piston rod of a cold working engineering machine, which comprises the following components in percentage by weight:

preferably, the diameter of the non-quenched and tempered steel is phi 90mm to phi 140 mm.

Preferably, the ferrite network grain size of the non-quenched and tempered steel is more than or equal to grade 5.

Preferably, the tensile strength of the non-quenched and tempered steel in the hot rolling state is more than or equal to 820 MPa; the yield strength is more than or equal to 545MPa, and the elongation is more than or equal to 15 percent; the reduction of area is more than or equal to 30 percent.

Preferably, the non-heat treated steel is cold-etched

Wherein D is the diameter of the rolled stock.

In a second aspect, the invention also relates to a preparation method of the non-quenched and tempered steel for the hydraulic piston rod of the cold working engineering machinery, which comprises the following steps:

the preparation method of the 1106 steel comprises the following steps: the method comprises the following steps of component design, Consteel electric furnace primary smelting, LF refining, VD vacuum degassing, LF refining, continuous casting, casting blank heat preservation, rolling process blank, continuous rolling, controlled cooling, pit entering heat preservation, flaw detection, inspection and packaging.

Preferably, the preparation method of the non-quenched and tempered steel for the hydraulic piston rod of the cold working engineering machinery comprises the following specific steps:

(1) composition design

In order to improve the effects of V, Ti and Al of the microalloy and accurately control N, on one hand, precipitation strengthening is enhanced, on the other hand, the fine-grain strengthening effect is achieved, and the requirements of high strength and high toughness of steel are met; and the cold processing performance is improved by applying the S control technology.

(2) Initial smelting of Consteel electric furnace

In the smelting period, electroless oxygen blowing smelting is adopted, and CaO and dolomite are added in batches for slagging, so that on one hand, effective P removal is carried out at a favorable time in a forward and reverse reaction direction under the control of the molten steel at a lower temperature, and on the other hand, the decarbonization amount of the molten steel is ensured.

In the steel tapping period, in order to ensure the temperature from the steel ladle to an LF station, the steel tapping temperature of the electric furnace is required to be more than or equal to 1620 ℃, in order to prevent slag falling caused by the excessively high steel tapping speed of the molten steel, the steel tapping time is less than or equal to 120S, and the post-furnace deoxidation work and the large ladle alloying work are carried out after steel tapping. And the sequence of adding the large-package deoxidizer and the alloy during electric furnace tapping is as follows: aluminum ingot or steel core aluminum → composite deoxidizer, pre-melted slag powder → alloy → slag charge; the alloy types are metal manganese, high-carbon ferrochrome, nickel plates and steel-cored aluminum, and the content of the alloy in the obtained crude steel-making water is as follows: 0.10-0.30% of C, 0.10-0.20% of Si, 0.70-0.80% of Mn, less than or equal to 0.020% of S, less than or equal to 0.20% of V, less than or equal to 0.20% of Cr, less than or equal to 0.20% of Ni, 0.030-0.050% of Al, less than or equal to 0.10% of Mo, less than or equal to 0.015% of N, and the balance of Fe.

(3) LF refining

The temperature of the molten steel entering an LF refining station is more than or equal to 1520 ℃, and the time from tapping to entering the refining station is controlled within 15 minutes; before power supply, the argon flow is 200-400NL/min, stirring is 2-3min, and the argon flow is controlled to be 100-400NL/min in the LF refining process; after the slag is placed in a tank, 400Kg of lime 200 and 400Kg of silicon-aluminum-calcium powder 100 +/-10 Kg are added according to the slag condition, and the total slag amount is controlled according to 1000-1100 Kg.

Controlling aluminum in an LF refining process: when the alloy enters an LF refining station, the Al content is required to be 0.030-0.040%; if the Al content is not between 0.030 and 0.040 percent, feeding Al for one time according to the target of 0.040 percent in the early stage of LF refining; adjusting the Al content in the steel after vacuum to 0.025-0.035% by adopting a wire feeding mode;

slag adjustment in the LF refining process: CaO and fluorite can be added according to the sulfur content and slag condition in the steel for slag regulation, and SiC powder or Al powder is added in the refining furnace for diffusion deoxidation; after the slag is whitened, adding a small amount of SiC powder and C powder in batches, wherein the total adding amount is controlled to be 1.0-2.0kg/t, and the refining time of the white slag is more than or equal to 45 minutes. Sampling and analyzing chemical components after LF refining, and entering a VD vacuum degassing station when the chemical components of the alloy meet the control target requirement and the temperature is 1620-;

the alloy has the chemical composition control target requirements of 0.43-0.45% of C, 0.20-0.30% of Si, 1.10-1.16% of Mn, 0.16-0.18% of Cr, less than or equal to 0.08% of Ni, 0.025-0.035% of Al, less than or equal to 0.05% of Mo and 0.010-0.015% of Ti.

(4) VD vacuum degassing:

vacuum degassing: the holding time is more than or equal to 18 minutes under the vacuum degree of less than or equal to 0.5 torr; argon control during degassing operation: the argon flow is 50-100NL/min in vacuum, and the argon flow is 100-200NL/min in extreme vacuum; the steam pressure is more than or equal to 0.90Mpa, the steam temperature is more than or equal to 175 ℃, and the water temperature is less than or equal to 30 ℃.

After the vacuum is broken, heating the molten steel to 1570-.

Weak argon stirring with slag surface fluctuation of 50-100 mm is carried out according to the temperature condition of the molten steel, the time is more than 20 minutes, and finally the components of the molten steel are as follows: 0.43-0.45% of C, 0.20-0.30% of Si, 1.10-1.16% of Mn, 0.010-0.030% of S, 0.16-0.18% of Cr, less than or equal to 0.08% of Ni, 0.025-0.035% of Al, less than or equal to 0.05% of Mo, 0.010-0.015% of Ti, 0.010-0.013% of N and the balance of Fe.

(5) Continuous casting

The temperature of the molten steel is 1540-1560 ℃, the steel ladle is hung into a continuous casting platform for casting, a long water gap and an immersion water gap are required to be sealed in the continuous casting process to prevent secondary oxidation of the molten steel, secondary cooling of a continuous casting billet is weak cooling, M-EMS/F-EMS electromagnetic stirring is adopted, the superheat degree of the molten steel is 15-25 ℃, and the casting blank drawing speed is 0.38M/min.

(6) Casting blank heat preservation

And (3) preserving the heat of the casting blank after the continuous casting is finished, wherein the heat preservation time is more than or equal to 48 hours, and obtaining a semi-finished casting blank with O, N content and endogenous inclusions meeting the standard requirement of high-quality steel.

(7) Rolling process billet

Rolling a process blank: heating a 410 × 530mm billet → dephosphorizing → 1250 rolling mill rolls a 210 × 210mm + -5 mm billet.

Controlling the heating process: the temperature of the preheating section is less than or equal to 850 ℃, the temperature of the first heating section is 1000-; the total heating time of the continuous casting billet is 8-13 h, and the high-temperature diffusion time is more than or equal to 4 h;

and (3) descaling control: water is adopted for descaling, and the hydraulic pressure requirement is more than or equal to 23 MPa.

And (3) rolling: the initial rolling temperature of rough rolling is more than or equal to 1050 ℃, and the final rolling temperature is more than or equal to 990 DEG C

(8) Continuous rolling

And (3) continuous rolling process: square billet of 210mm by 210mm → steel airing temperature control → 8 frame flat rolling mill rolling → water penetration → cooling bed blowing cooling → pit entry heat preservation.

Airing steel and controlling temperature: after the rolling of the process blank is finished, the blank is kept on a roller way, so that the temperature of the steel blank is reduced by 870-890 ℃.

Rolling by 8 horizontal and vertical rolling mills: the initial rolling temperature is 870-890 ℃.

Water penetration: after rolling, the rolled steel enters a water tank, and the water tank uniformly sprays water to the steel, wherein the temperature of the steel is required to be reduced to 80-100 ℃.

(9) Controlled cooling

Air blowing of a cooling bed: the temperature of the steel on the cooling bed is required to be more than or equal to 650 ℃, the steel is cooled by blowing air by a fan, and the steel is naturally cooled when the temperature of the steel is reduced to 550 ℃.

(10) Entering a pit for heat preservation: the pit entry temperature of the steel is more than or equal to 300 ℃, and the heat preservation is carried out for 48 hours

(11) Flaw detection: the surface defect is less than or equal to 0.2mm, and the equivalent of a single internal flaw is less than or equal to phi 2.8 mm.

(12) And (6) inspecting and packaging.

The preparation principle of the method is as follows:

the first, the application of precise control of N and micro-alloying (V, Ti, Al) technology. The gaseous N is used for replacing an alloy Si-N line to control N, the N adding cost is reduced, and the N content is accurately controlled within +/-30 ppm; by reasonably controlling the content proportion of the added vanadium, titanium, aluminum and nitrogen elements, the carbon and the nitride of the vanadium and the titanium elements are fully precipitated, and the optimal matching of the obdurability of the steel is ensured by precipitation strengthening.

Secondly, C, Mn optimization technology is applied, the addition amount of C, Mn is finely controlled according to the requirements of steel performance, and the situation that the blanking straightening of a user is difficult due to high stress strength is avoided under the condition that the normal use performance of the steel is ensured.

And thirdly, a control technology of a continuous casting pouring process is applied, the superheat degree of the pouring process is controlled to be 15-25 ℃, the reasonable drawing speed and the optimal matching of tail end electromagnetic stirring are realized, and the segregation degree of the core part of the continuous casting billet is reduced.

Fourthly, a new generation of controlled rolling and controlled cooling technology, namely a cooling path control technology, is adopted, and the controlled cooling operation before finish rolling and after rolling is carried out, so that the steel has the advantages of fine grain size, uniform structure, high strength and good toughness.

The invention has the following advantages:

1. the V, Ti and Al alloy added into the medium-carbon structural carbon steel has rich resources in China, small addition amount, greatly reduced cost and rich mature experience of the N-controlled smelting technology at present.

2. The invention utilizes the low superheat degree pouring and constant drawing speed control in the continuous casting process to finally solve the problem of the core segregation of the continuous casting billet;

3. the invention adopts the application of the on-line controlled rolling and controlled cooling technology, and the mechanical hot rolling performance index of the steel reaches the performance level of quenched and tempered steel;

4. the large-compression-ratio (the compression ratio is more than or equal to 14) product of the large continuous casting billet (the end surface is 410mm multiplied by 530mm) adopted by the invention ensures the homogenization and the stable performance of the steel.

5. The steel prepared by the method is directly subjected to cold machining to produce the hydraulic piston rod; compared with the traditional method, the process does not need quenching and high-temperature tempering procedures, thereby not only saving the process steps; but also saves heat treatment equipment, simplifies the production process, reduces the energy consumption, improves the utilization rate of materials, improves the quality of parts, reduces the manufacturing cost by 25 to 38 percent, and has good economic benefit and social benefit.

Drawings

FIG. 1 is a structural diagram of an edge microstructure of high-strength high-toughness non-quenched and tempered steel for a hydraulic piston rod of a large-specification cold-working engineering machine, according to the invention;

FIG. 2 is a 1/2R microstructure structural diagram of high-strength high-toughness non-quenched and tempered steel for a hydraulic piston rod of a large-specification cold-working engineering machine, provided by the invention;

FIG. 3 is a structural diagram of a central microstructure of high-strength high-toughness non-quenched and tempered steel for a hydraulic piston rod of a large-specification cold-working engineering machine, according to the invention;

FIG. 4 is a low-magnification 'black-heart' photo of high-strength high-toughness non-quenched and tempered steel for a hydraulic piston rod of a large-specification cold-working engineering machine.

Detailed Description

The present invention will be described in detail with reference to specific examples. It should be noted that the following examples are only illustrative of the present invention, but the scope of the present invention is not limited to the following examples.

Example 1

The embodiment relates to a production method of high-strength high-toughness non-quenched and tempered steel for a hydraulic piston rod of large-size cold machining engineering machinery, which specifically comprises the following steps:

(1) composition design

(2) Initial smelting of Consteel electric furnace

(3) LF refining

(4) VD vacuum degassing:

After the vacuum is broken, heating the molten steel to 1570-.

(5) Continuous casting

(6) Casting blank heat preservation

(7) Rolling process billet

(8) Continuous rolling

(9) Controlled cooling

(12) And (6) inspecting and packaging.

The chemical components of the high-strength high-toughness non-quenched and tempered steel for the hydraulic piston rod of the large-size cold-working engineering machinery prepared according to the steps of the embodiment 1 are as follows: 0.43-0.45% of C, 0.20-0.30% of Si, 1.10-1.16% of Mn, 0.010-0.030% of S, 0.16-0.18% of Cr, less than or equal to 0.08% of Ni, 0.025-0.035% of Al, less than or equal to 0.05% of Mo, 0.010-0.015% of Ti, 0.010-0.013% of N and the balance of Fe.

The high-strength high-toughness non-quenched and tempered steel for the hydraulic piston rod of the large-size cold-working engineering machinery is prepared and obtained in the embodiment, and the related drawings are as follows: FIG. 1 is a structural diagram of an edge microstructure of high-strength high-toughness non-quenched and tempered steel for a hydraulic piston rod of a large-specification cold-working engineering machine, according to the invention; FIG. 2 is a 1/2R microstructure structural diagram of high-strength high-toughness non-quenched and tempered steel for a hydraulic piston rod of a large-specification cold-working engineering machine, provided by the invention; FIG. 3 is a structural diagram of a central microstructure of high-strength high-toughness non-quenched and tempered steel for a hydraulic piston rod of a large-specification cold-working engineering machine, according to the invention; FIG. 4 is a low-magnification 'black-heart' photo of the high-strength high-toughness non-quenched and tempered steel for the hydraulic piston rod of the large-specification cold-working engineering machine.

Comparative example 1

The comparative example 1 relates to a production process of high-strength high-toughness non-quenched and tempered steel for a hydraulic piston rod of large-size cold machining engineering machinery, and specifically comprises the following steps: 110 ton Consteel smelting +70 ton LF refining + VD degassing → continuous casting machine continuous casting 410mm multiplied by 530mm blank → slow cooling → inspection, coping → steel rolling industry large rod operation area 1250 rolling mill cogging → 8 frame continuous rolling production material → controlled cooling (water penetration) → cold bed cooling → pit entry slow cooling → straightening → surface cleaning → flaw detection → inspection, inspection → packaging and handing over.

Mechanical properties of the high-strength high-toughness non-quenched and tempered steel 4 furnace for the hydraulic piston rod of the cold working engineering machinery with phi 90-phi 140mm prepared in the example 1 are sampled and detected, mechanical properties of steel materials with different specifications meet the mechanical properties, and specific detection data are shown in table 1 (the mechanical properties of the high-strength high-toughness non-quenched and tempered steel for the piston rod).

TABLE 1

The data from table 1 show: the sampling detection shows that: a, B, C, D types of non-metallic inclusions and DS in the high-strength high-toughness non-quenched and tempered steel for the hydraulic piston rod are both less than or equal to 2.0 grades, and are shown in table 2 (detection data of the non-metallic inclusions in the high-strength high-toughness non-quenched and tempered steel for the hydraulic piston rod).

TABLE 2

The black core of the non-quenched and tempered steel is tested, and the detection result is shown in table 3 (detection data of the black core of the high-strength high-toughness non-quenched and tempered steel for the hydraulic piston rod).

TABLE 3

Furnace number	Steel grade	Specification of	Diameter of black heart
				L19X33379	1106	Ф140mm	2.0
L19X33379	1106	Ф140mm	2.0
				20EB07517	1106	φ120mm	1.5
20EB07517	1106	φ120mm	1.0
				20EA02024	1106	φ100mm	1.5
20EA02024	1106	φ100mm	1.5
				20EB07517	1106	φ90mm	1.0
20EB07517	1106	φ90mm	1.0

The ferrite network grain grade of the high-strength high-toughness non-quenched and tempered steel for the hydraulic piston rod is obtained through sampling detection, and the ferrite network structure of the high-strength high-toughness non-quenched and tempered steel for the hydraulic piston rod obtained by the invention is refined and homogenized: the rolled material ferrite network crystal grain is more than or equal to grade 6, the cross section ferrite network crystal grain range is less than or equal to grade 1.5, and the specific detection data is shown in table 4 (detection data of the ferrite network crystal grain grade of the high-strength high-toughness non-quenched and tempered steel for the hydraulic piston rod).

TABLE 4

Therefore, the high-strength high-toughness non-quenched and tempered steel for the hydraulic piston rod, which is prepared by the method, has the mechanical properties meeting the use requirements of the hydraulic piston rod in a hot rolling state, has better integral segregation degree of steel, is beneficial to friction welding of users, can be processed into the hydraulic piston rod after being directly turned, can be processed without quenching, tempering and straightening the steel in the past, and can save the production cost by 28-35%.

The high-strength high-toughness non-quenched and tempered steel prepared by the method disclosed by the invention is processed into a piston rod mounting machine, and all properties of the piston rod mounting machine reach the level of quenched and tempered steel.

The method is a pioneer for saving energy and reducing cost in order to ensure the welding performance of products, accelerate the use and popularization of non-quenched and tempered steel for cold machining in the field of engineering machinery in China. The non-adjustable steel complete production technology is formed, the core technology of independent intellectual property rights is formed, the quality of the real object reaches the level of similar products at home and abroad, the product quality is stable, and the capacity of batch production is realized.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims

1. a non-quenched and tempered steel for cold working engineering machinery hydraulic piston rod, is characterized in that, this non-quenched and tempered steel is made up of each composition of following weight percentage:

2 . The non-quenched and tempered steel for cold working hydraulic piston rods of construction machinery according to claim 1 , wherein the diameter of the non-quenched and tempered steel is φ90mm-φ140mm. 3 .

3 . The non-quenched and tempered steel for cold working hydraulic piston rods of construction machinery according to claim 1 , wherein the non-quenched and tempered steel has a ferrite network grain size ≥ grade 5. 4 .

4. The non-quenched and tempered steel for cold-working hydraulic piston rods of construction machinery according to claim 1, wherein the non-quenched and tempered steel has mechanical properties and tensile strength ≥ 820 MPa in a hot-rolled state; yield strength ≥ 545 MPa, Elongation ≥ 15%; section shrinkage ≥ 30%.

5. The non-quenched and tempered steel for cold-working hydraulic piston rods of construction machinery according to claim 1, wherein the non-quenched and tempered steel is cold-etched

Where D is the diameter of the rolled material.

6. the preparation method of the non-quenched and tempered steel for cold working construction machinery hydraulic piston rod as claimed in claim 1, is characterized in that, comprises the following steps:

Specifically refers to the preparation method of 1106 steel, including: composition design - Consteel electric furnace initial refining - LF refining - VD vacuum degassing - LF refining - continuous casting - casting billet insulation - rolling process billet - continuous rolling - controlled cooling - pit insulation - Flaw detection - Inspection packaging.

7. the preparation method of the non-quenched and tempered steel used for cold working engineering machinery hydraulic piston rod as claimed in claim 6, is characterized in that, described step is specifically:

(1) Ingredient design

Precisely control N to enhance the effect of microalloys V, Ti, Al;

(2) Consteel electric furnace primary refining

During the smelting period, electroless oxygen blowing is used for smelting, and CaO and dolomite are added in batches to make slag;

During the tapping period, the tapping temperature of the electric furnace is greater than or equal to 1620°C, and the tapping time is less than or equal to 120S. During the tapping of the electric furnace, the order of adding the deoxidizer and alloy to the ladle is: aluminum ingot or steel core aluminum → composite deoxidizer, pre-melting slag powder → alloy → Slag material; the alloy types are metal manganese, high carbon ferrochromium, nickel plate, steel core aluminum, and the alloy content in the obtained rough molten steel should meet the following standards: C 0.10~0.30%, Si0.10~0.20%, Mn 0.70 ~0.80%, S≤0.020%, V≤0.20%, Cr≤0.20%, Ni≤0.20%, Al0.030-0.050%, Mo≤0.10%, N≤0.015%, Fe balance;

(3) LF refining

The temperature of molten steel entering the LF refining station is greater than or equal to 1520 °C, and the time from the end of tapping to entering the refining station is controlled within 15 minutes; the flow of argon gas is 200-400NL/min before power supply, and the stirring is 2-3min; during the LF refining process, control argon The air flow is 100-400NL/min; after entering the tank, add lime 200-400Kg, silicon aluminum calcium powder 100±10Kg, and the total slag volume is controlled by 1000-1100Kg;

Aluminum control in the LF refining process: the Al content is 0.030-0.040% when entering the LF refining station; when the Al content is not between 0.030-0.040%, Al is fed once at a target of 0.040% in the early stage of LF refining; The Al content is adjusted to 0.025%-0.035% by feeding the wire;

Slag adjustment in the LF refining process: according to the sulfur content in the steel and the slag condition, add CaO and fluorite to adjust the slag, add SiC powder or Al powder by diffusion and deoxidation in the refining furnace; after the slag turns white, add SiC powder and C powder in small batches, and The total amount added should be controlled at 1.0-2.0kg/t, and the refining time of white slag should be ≥45 minutes; after LF refining, take samples to analyze the chemical composition. ;

The alloy chemical composition control target requirements of this station are C 0.43～0.45%, Si 0.20～0.30%, Mn 1.10～1.16%, Cr 0.16～0.18%, Ni≤0.08%, Al 0.025～0.035%, Mo≤0.05, Ti 0.010～0.015%;

(4) VD vacuum degassing:

Vacuum degassing: holding time ≥ 18 minutes under vacuum degree ≤ 0.5 Torr; vacuum argon flow rate during degassing operation is 50-100NL/min, and argon gas flow rate in extreme vacuum is 100-200NL/min; steam pressure ≥ 0.90Mpa, steam Temperature≥175℃, water temperature≤30℃;

After breaking the vacuum, heat the molten steel at the LF station to 1570-1580°C for N blowing, and the N content is controlled at 0.011% to 0.013%;

According to the molten steel temperature, the weak argon stirring with the slag surface fluctuation of 50-100mm is carried out for more than 20 minutes. The final composition of the molten steel is as follows: C 0.43-0.45%, Si 0.20-0.30%, Mn 1.10-1.16%, S 0.010-0.030 %, Cr 0.16～0.18%, Ni≤0.08%, Al 0.025～0.035%, Mo≤0.05, Ti 0.010～0.015%, N0.010～0.013%, Fe balance;

(5) Continuous pouring:

The temperature of molten steel is 1540-1560°C, the ladle is hoisted into the continuous casting platform for pouring, the long nozzle and the submerged nozzle are sealed during the continuous casting process to prevent the secondary oxidation of molten steel, and the second cooling of the continuous casting billet adopts weak cooling and M-EMS/F -EMS electromagnetic stirring, the superheat of molten steel is 15-25℃, and the casting speed is 0.38m/min;

(6) Insulation of casting billet;

After the continuous casting is completed, the casting billet is kept warm, and the holding time is ≥48h, and the semi-finished billet with O, N content and endogenous inclusions meeting the requirements of high-quality steel standards is obtained;

(7) Rolling process billet: mainly includes: 410×530mm billet heating→phosphorus removal→1250 rolling mill rolling 210×210mm±5mm billet;

The process control parameters of 410×530mm billet heating are: preheating section temperature ≤850℃, heating first section temperature 1000-1150℃, heating second section temperature 1180-1200℃, soaking first section temperature 1160-1200℃, soaking second section temperature 1150-1200℃; the total heating time of continuous casting slab is 8～13h, and the high temperature diffusion time is ≥4h;

The control parameters for descaling are: water descaling, water pressure requirement ≥ 23MPa;

The process of rolling 210×210mm±5mm billet in 1250 rolling mill: the rough rolling temperature is ≥1050℃, and the final rolling temperature is ≥990℃;

(8) Continuous rolling

The process of continuous rolling is: 210×210mm billet → temperature control of steel drying → rolling with 8 vertical rolling mills → water penetration → cooling bed blowing and cooling → pit insulation;

Among them, the temperature control of the air-drying steel: the billet stays on the roller table after the rolling process, so that the temperature of the billet drops by 870℃-890℃;

The rolling parameters of the 8 vertical rolling mills are: the rolling temperature is 870℃-890℃;

The water penetration is as follows: the steel enters the water tank after rolling, the water tank sprays water evenly on the steel, and the temperature of the steel is required to drop to 80-100 °C;

(9) Controlled cooling:

The cooling bed blowing cooling is as follows: the temperature of the cooling bed on the steel is required to be ≥650°C, the fan blows for cooling, and the steel temperature drops to 550°C for natural cooling;

(10) Insulation in the pit: The parameters are: the temperature of the steel entering the pit is ≥ 300 °C, and the insulation is 48h;

(11) Flaw detection: surface defect ≤ 0.2mm, internal flaw detection single defect equivalent ≤ φ2.8mm;

(12) Inspection packaging.