CN109338035B

CN109338035B - Steel for wind driven generator gear box bearing and production method thereof

Info

Publication number: CN109338035B
Application number: CN201811322906.XA
Authority: CN
Inventors: 陈敏; 耿克; 许晓红; 李锋; 黄镇; 尹青; 翟蛟龙
Original assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Current assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Priority date: 2018-11-08
Filing date: 2018-11-08
Publication date: 2020-08-18
Anticipated expiration: 2038-11-08
Also published as: CN109338035A

Abstract

The invention relates to steel for a gear box bearing of a wind driven generator and a production method thereof, wherein the steel comprises the following chemical components: 0.80-1.05%, Si: 0.20 to 0.45%, Mn: 0.25-0.45%, Cr: 1.60-1.95%, S is less than or equal to 0.015%, P is less than or equal to 0.020%, and Ni: not more than 0.25%, Cu not more than 0.30%, Mo: 0.15-0.25%, Al: less than or equal to 0.05 percent, less than or equal to 0.0010 percent of Ca, less than or equal to 0.0015 percent of Ti, less than or equal to 0.0008 percent of O, less than or equal to 0.04 percent of As, less than or equal to 0.03 percent of Sn, less than or equal to 0.005 percent of Sb, less than or equal to 0.002 percent of Pb, and the balance of Fe and inevitable impurities. The production process comprises the steps of molten iron pretreatment, smelting in a converter or an electric arc furnace, LF refining, RH or VD furnace refining, large-section continuous casting CCM large continuous casting billet, continuous rolling, quick cooling and finishing.

Description

Steel for wind driven generator gear box bearing and production method thereof

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to steel for a bearing of a gearbox and a manufacturing method thereof.

Background

Wind energy is renewable energy with the greatest development prospect at present, is clean and pollution-free green energy, has the widest utilization prospect among various alternative energy sources, is more and more emphasized by various countries in the world, and has huge abundance.

The wind driven generator is a core device for wind energy utilization, and mainly comprises a paddle, a gear speed increaser, a generator, a tower, a control device and other subsystems. The gear transmission system is used as a core device of the wind driven generator. The gearbox is a transmission component for connecting a main shaft of the unit with the generator, has the main function of converting low-speed operation input of the main shaft into output required by a medium-speed or high-speed generator, and is one of important components of the wind driven generator. The bearing of the gear box has large fluctuation range of the borne torque and the rotation speed, the transmission load is easy to change suddenly, the quality of the box body and the installation space are limited, and the installation platform has flexible deformation and the like, so the bearing is far away from the application environment of the traditional heavy-load industrial gear box. Because the hoisting and the bearing replacement of the wind generating set are very inconvenient and have higher cost, the once mounting and dismounting cost is as high as hundreds of thousands to millions, the wind generating gearbox bearing has higher technical complexity, is one of the accepted technologies with the largest localization difficulty and also becomes a soft rib influencing the development of the wind power generation manufacturing industry in China.

According to special application and requirements of the wind driven generator gearbox bearing, high requirements are also put on the raw material bearing steel. At present, a bearing of a speed increaser of a wind power gear box adopts high-carbon chromium bearing steel GCrl5SiMn smelted by electroslag remelting. The steel produced by the electroslag remelting process has the quality advantages of fine and uniform non-metallic inclusion particles, high structure uniformity, high density and the like, so the quality stability is always better. However, the electroslag remelting production process has the obvious disadvantages of very low production efficiency and capacity, very high energy consumption and production cost and the like, so the market competitiveness of the electroslag remelting steel is very low. Although the continuous casting process has obvious advantages in production efficiency and cost, the current continuous casting blank has differences in purity and uniformity and cannot meet the requirements of the steel for the gearbox bearing of the wind driven generator, so that a related method for producing the steel for the gearbox bearing of the wind driven generator in a continuous casting mode in a large scale has not been reported. In addition, because GCr15SiMn adopts martensite quenching, the impact toughness of the product after quenching is relatively poor, and certain defects exist.

Disclosure of Invention

On the basis of the current production of high-carbon chromium bearing steel, the application provides a novel steel for a gearbox bearing of a wind driven generator, and the key procedures are optimized, researched and controlled by utilizing the process routes of high efficiency, large capacity and low cost of vacuum degassing, continuous casting and rolling, so that the steel can obtain high purity, high tissue uniformity and high density, the current electroslag remelting production process is replaced, and the performance of the steel can meet the requirements of the steel for the gearbox bearing of the wind driven generator.

In order to meet the requirements of purity, uniformity, compactness, wear resistance and hardenability of the steel material for the gear box bearing of the wind driven generator, which is manufactured by a novel vacuum degassing and continuous casting production technology, is designed.

Non-metallic inclusions in the steel deteriorate the continuity and uniformity of the metal. Depending on the conditions of use of the bearing, the inclusions tend to cause stress concentration under the action of alternating stress, and become sources of fatigue cracks, thereby reducing the fatigue life of the bearing. In particular for hard and brittle inclusions, e.g. Al arranged in a string or chain of points in the rolling direction₂O₃The inclusions (B type), the non-deformable point-like or spherical inclusions (D type) and the large-particle point-like or spherical inclusions (Ds type) are difficult to deform in the processing and using processes due to the fact that the inclusions do not have plasticity, stress concentration is formed, the fatigue crack initiation period is shortened, and the improvement of fatigue performance is influenced. Purity of the steel for increasing the service life of the end productCleanliness is very important and it is necessary to minimize the size and number of non-metallic inclusions, particularly non-deforming, hard and brittle inclusions, in the steel. The invention requires the microscopic brittle inclusions to be fine, and the specific requirements are shown in the following table 1. The macroscopic inclusions remarkably reduce the wear resistance of steel, cause serious stress concentration and easily cause early failure in the using process of a bearing, the macroscopic defects are detected by an SEP 1927 (water immersion ultrasonic measurement method for the purity of a forged and rolled steel bar) water immersion high-frequency flaw detection method, and the defect index is not allowed to exceed 2.5mm/dm³。

TABLE 1

The uniformity and the compactness of the macrostructure of the steel have influence on the service life of the bearing, the macrostructure adopts GB/T1979 to grade the macrostructure of the steel, and the invention requires that the center porosity is less than or equal to 1.0 grade, the general porosity is less than or equal to 1.0 grade, the ingot type segregation is less than or equal to 1.0 grade, and the center segregation is less than or equal to 1.0 grade. In order to improve steel segregation, the carbon content of the central carbon segregation region of the finished bar is required to be not more than 10% of the normal smelting carbon content.

Thirdly, the bearing steel carbide strip is formed by the crystal segregation formed in the solidification process of molten steel to form segregation strips with different carbon concentrations, and a large amount of surplus secondary carbides are separated out in a high concentration area in the cooling process after rolling extension, so that a black-white (high-low carbon) carbide strip-shaped structure is formed; the bearing steel carbide net is that in the cooling process after rolling, because the solubility of carbon in austenite is reduced, secondary carbide is separated out from excessive carbon at the grain boundary of austenite; the bearing steel liquation is characterized in that when the bearing steel is converted from a liquid state to a solid state, carbon and alloy elements in the last solidified part are enriched to generate metastable eutectic ledeburite, the liquation has high hardness and brittleness, and the liquation is broken into small blocks after hot rolling and distributed along the rolling direction, so that the wear resistance and the fatigue strength of bearing parts are obviously reduced, and quenching cracks are easily generated. The microscopic pores are one of the defects of the internal structure of the bearing steel, namely irregular cracks or pores are formed intermittently along the grain boundary, and the defects can reduce the service life of the bearing part, so that the invention requires that the existence of the microscopic pores is not allowed by adopting a metallographic detection method; and (3) detecting that the carbide liquation is less than or equal to 0 grade, the carbide banding is less than or equal to 2.0 grade and the carbide net is less than or equal to 2.5 grade by adopting a metallographic method.

And (IV) the bearing produced by the steel needs to bear large impact load, and the toughness of the traditional GCr15SiMn is poorer after martensite quenching. According to the characteristics of the steel grade, the invention can adopt a lower bainite isothermal quenching method, and the impact toughness required after the lower bainite isothermal quenching is more than or equal to 150J cm^-2。

The technical scheme adopted by the invention for solving the problems is as follows: the steel for the gear box bearing of the wind driven generator comprises the following chemical components: 0.80-1.05%, Si: 0.20 to 0.45%, Mn: 0.25-0.45%, Cr: 1.60-1.95%, S is less than or equal to 0.015%, P is less than or equal to 0.020%, and Ni: not more than 0.25%, Cu not more than 0.30%, Mo: 0.15-0.25%, Al: less than or equal to 0.05 percent, less than or equal to 0.0010 percent of Ca, less than or equal to 0.0015 percent of Ti, less than or equal to 0.0008 percent of O, less than or equal to 0.04 percent of As, less than or equal to 0.03 percent of Sn, less than or equal to 0.005 percent of Sb, less than or equal to 0.002 percent of Pb, and the balance of Fe and inevitable impurities. The steel for the gearbox bearing of the wind driven generator has the following chemical component design basis:

1) determination of C content

In high-carbon chromium bearing steel, the content of carbon is generally about 1.0 percent, and the carbon is one of the most important elements for ensuring the hardenability, the hardness and the wear resistance of the bearing steel. However, the higher the carbon content, the less the influence on the hardness, and the more likely the precipitation of large carbide particles. The content range of C in the invention is determined to be 0.80-1.05%.

2) Determination of the Si content

The addition of Si to steel can strengthen ferrite and improve strength, elastic limit and hardenability, but Si increases the susceptibility to overheating, cracking and decarburization in steel. The range of the Si content of the present invention is determined to be 0.20 to 0.45%.

3) Determination of Mn content

Mn is an element effective for steel strengthening as a deoxidizing element in the steel making process, and acts as a solid solution strengthening effect, but a high Mn content lowers the toughness of steel. The Mn content of the invention is controlled to be 0.25-0.45%.

4) Determination of the Cr content

Cr is a carbide forming element, can improve the hardenability, wear resistance and corrosion resistance of steel, but the Cr content is too high, and is combined with carbon in the steel to easily form massive carbide, the toughness of the steel is reduced by the hard-soluble carbide, the service life of a bearing is shortened, and the Cr content is determined to be 1.60-1.95%.

5) Determination of Al content

Al is added as a deoxidizing element in steel, and in addition to the purpose of reducing dissolved oxygen in molten steel, Al and N form dispersed and fine aluminum nitride inclusions to refine grains. However, when the Al content is too high, large-particle Al is easily formed in the molten steel smelting process₂O₃And the like, which reduces the purity of the molten steel and affects the service life of the finished product. The Al content of the invention is determined to be less than or equal to 0.05 percent.

6) Determination of Mo content

Molybdenum can refine the crystal grains of the steel, improve hardenability and heat strength, and maintain sufficient strength and creep resistance at high temperature. However, molybdenum is a ferrite-forming element, and when the content of molybdenum is large, a ferrite phase or other brittle phases are likely to occur, thereby lowering the toughness. The range of Mo content is determined to be 0.15-0.25%

7) Determination of Ca content

The Ca content increases the number and size of the spot-like oxides in the steel, and since the spot-like oxides have high hardness and poor plasticity, they are not deformed when the steel is deformed, and voids are easily formed at the interface, deteriorating the properties of the steel. The range of the Ca content of the invention is determined to be less than or equal to 0.001 percent.

8) Determination of the Ti content

Ti element and N element are combined to form titanium nitride inclusion, and because the titanium nitride inclusion has high hardness and is in a sharp-horn shape, stress concentration is easily caused in the bearing operation to greatly influence the service life of the bearing, so that the Ti content is determined to be less than or equal to 0.0015 percent

9) Determination of the O content

The oxygen content represents the total amount of oxide inclusions, the limitation of the oxide brittle inclusions influences the service life of a finished product, and a large number of tests show that the reduction of the oxygen content is obviously beneficial to improving the purity of steel, particularly reducing the content of the oxide brittle inclusions in steel. The oxygen content of the present invention is determined to be O.ltoreq.0.0008%.

10) P, S determination of content

The P element causes element segregation when the steel is solidified, and the P element is dissolved in ferrite to distort and coarsen crystal grains and increase cold brittleness, so that the P is determined to be less than or equal to 0.020%; s element is easy to cause hot brittleness of steel, ductility and toughness of the steel are reduced, and formed sulfide also destroys continuity of the steel, so that S is determined to be less than or equal to 0.015%.

11) Determination of As, Sn, Sb, Pb content

As, Sn, Sb, Pb and other trace elements belong to low-melting-point nonferrous metals, and exist in steel to cause the appearance of soft spots and uneven hardness on the surface of parts, so the trace elements are regarded As harmful elements in the steel, and the content ranges of the elements are determined to be less than or equal to 0.04 percent of As, less than or equal to 0.03 percent of Sn, less than or equal to 0.005 percent of Sb and less than or equal to 0.002 percent of Pb.

The other purpose of the application is to provide a production method of the steel for the gearbox bearing of the wind driven generator, which adopts a continuous casting mode to replace electroslag remelting to smelt blanks, and the manufacturing process comprises molten steel smelting, large-section continuous casting CCM large continuous casting billet, continuous rolling, finishing flaw detection and finished product warehousing.

Firstly, smelting raw materials are sequentially subjected to KR pretreatment of molten iron, smelting in an electric furnace or a converter, LF refining and RH or VD vacuum degassing to obtain molten steel with high purity and chemical components meeting the specification, in the smelting process, the molten steel meeting the chemical components of steel is smelted, and the smelting raw materials are high-quality molten iron, scrap steel, raw and auxiliary materials and high-quality refractory materials. Controlling a tapping end point C and an end point P in the smelting process of an electric furnace or a converter, wherein the end point C is as follows: 0.10-0.70 percent, the end point P is controlled to be less than or equal to 0.018 percent, the tapping temperature is 1600-1700 ℃, slag stopping and tapping are adopted to prevent tapping slag from dropping in an electric furnace or a converter, and Al is added for deoxidation in the tapping process. The slagging and deoxidation operations are enhanced in the LF refining process, the LF refining furnace adopts Al + SiC for combined deoxidation, the free oxygen content in the process is ensured to be low, and the advantage of removing impurities in the LF furnace during smelting is exerted. Stirring argon gas in the whole vacuum degassing process, degassing for 15-35min under high vacuum (133Pa), and performing long-time soft argon blowing treatment after vacuum degassing to ensure that nonmetallic inclusions float sufficiently.

The continuous casting is to cast molten steel into a rectangular continuous casting billet with the specification of 300 x 340mm or more. The continuous casting needs to be carried out by adopting anti-oxidation protection casting in the whole process, so that secondary oxidation of molten steel is prevented, and special tundish covering slag is selected to better adsorb impurities. The continuous casting adopts low superheat degree pouring, the superheat degree of the continuous casting requires 10-35 ℃, and meanwhile, the continuous casting adopts advanced process equipment of tundish induction heating, electromagnetic stirring and light pressing to control the segregation of steel.

Heating before rolling: and (3) heating the produced continuous casting slab in a stepping heating furnace, wherein the temperature of a preheating section is controlled to be 950 ℃ in 800-.

And (3) removing phosphorus from the continuous casting billet after the continuous casting billet is taken out of the heating furnace by high-pressure water, then, feeding the continuous casting billet into a rough rolling-intermediate rolling-finishing mill group, rolling the continuous casting billet into a round bar material with the diameter of 120-200, and controlling the rough rolling starting temperature to be 950-1100 ℃ so as to roll the steel material in an austenite single-phase region. In order to control the carbide net shape of the steel, the finishing rolling temperature of the steel must be more than or equal to Ar_cmAnd ensuring that the steel does not enter a secondary cementite precipitation region before rapid cooling, but if the finishing rolling temperature is too high, austenite is in a complete recrystallization state, so that the refined grains and carbide are not favorably dispersed and precipitated, the probability of net formation is further reduced, and a stronger cooling rate is needed to pass through a two-phase region, so that the finishing rolling temperature is controlled at 750-850 ℃.

In the cooling process after the final rolling, in order to rapidly jump out a large amount of precipitation areas of secondary cementite, the steel needs to be rapidly cooled after the final rolling, but in order to prevent the cooling speed from being too fast and prevent brittle bainite and martensite structures from being formed, the cooling speed is not too fast, and the surface re-reddening temperature of the steel after the final rolling is required to be controlled between 550 ℃ and 720 ℃. In addition, in the cooling process after the finish rolling, the principle of first-speed and second-speed is followed, because for large-size steel, the temperature difference between the inside and the outside is large, the surface temperature is low, the core temperature is high, the temperature return is controlled, and the core is the area with the most serious net carbon; if the cooling speed is always high, the surface cooling strength is high, the cooling rate is high, the core part is easy to enter a bainite and martensite precipitation region, a martensite structure is formed on the surface layer or the whole section, and the steel is easy to brittle fracture.

The main production process has the following characteristics:

1. chemically, the quality of the scrap steel is strictly controlled by the pretreatment of molten iron, and low-titanium alloy, deoxidizer and refractory material are preferred; the converter tapping adopts the process technologies of slag-stopping tapping, slag-removing after the converter and other controls, and solves the problem of the prior art that the contents of harmful elements such As Ti, Ca, As, Sn, Pb and Sb are higher; meanwhile, the content of O in steel is reduced to an extremely low level by adopting a core deoxidation technology and vacuum degassing, and the quantity and the size of inclusions reach the world leading level.

2. The continuous casting adopts low superheat degree pouring, and adopts tundish induction heating, soft reduction and electromagnetic stirring, so that the segregation of a casting blank and the material structure are effectively improved; the steel rolling heating high-temperature diffusion technology ensures that the central carbon segregation has enough temperature and time for diffusion, and simultaneously, the rolling adopts rough rolling under high pressure, thereby improving the low-power quality.

3. The steel rolling improves the center carbon segregation of steel through high-temperature diffusion, and the steel rolling adopts the low-temperature rolling and controlled cooling technology and the like, thereby effectively inhibiting the carbide banding and controlling the non-uniformity index of steel carbide.

4. In terms of manufacturing process, the production process of vacuum degassing and continuous casting is adopted, compared with an electroslag remelting technology, the production period is greatly shortened, the production efficiency is improved, the manufacturing cost is effectively reduced, and the large-scale production is favorable for improving the material composition and the quality stability.

5. The steel for the bearing of the gearbox of the wind driven generator, which is produced by the invention, meets the following index requirements:

the metallographic method is adopted to detect the microscopic brittle inclusions, wherein the B fine system is less than or equal to 1.5 grade, the B coarse system is less than or equal to 0.5 grade, the D fine system is less than or equal to 0.5 grade, the D coarse system is less than or equal to 0.5 grade, and the DS system is less than or equal to 1.0 grade; detecting that no microscopic pores are allowed by adopting a metallographic method; the central porosity of the macrostructure is less than or equal to 1.0 grade, the general porosity is less than or equal to 1.0 grade, ingot type segregation is less than or equal to 1.0 grade, a metallographic method is adopted to detect that the liquation of the carbide is less than or equal to 0 grade, the banding of the carbide is less than or equal to 2.0 grade, and the reticulation of the carbide is less than or equal to 2.5 grade. By usingSEP 1927 water immersion high-frequency flaw detection, the defect index is not allowed to exceed 2.5mm/dm³. The carbon content of the central carbon segregation region of the finished bar does not exceed 10% of the carbon content of normal smelting. After lower bainite austempering, the impact toughness is more than or equal to 150J cm^-2。

Detailed Description

The present invention will be described in further detail with reference to examples.

Examples of the invention the chemical composition (wt%) of the electroslag remelted GCr15SiMn used in the present invention and (as a comparison) the current market is shown in table 3.

TABLE 3

TABLE 3

The inclusions of the steels of the examples are compared in Table 4

TABLE 4

The carbide inhomogeneities and the microscopic porosity of the steels of the examples are compared in Table 5

TABLE 5

TABLE 6 impact toughness contrast values of the inventive examples after lower bainite austempering compared to the comparative steels (the comparative steels were martensitic quenching treatments according to their practical use cases)

	Impact toughness a_KU(J·cm^-2)
		Inventive example 1	156
Inventive example 2	162
		Inventive example 3	170
Comparative steel	72

The low power data of the steels of the examples are shown in Table 7

	Center porosity	Generally loose	Ingot type segregation	Center segregation
					Inventive example 1	1	1.0	1.0	1.0
Inventive example 2	1	1.0	1.0	1.0
					Inventive example 3	1	1.0	1.0	1.0
Comparative steel	1.0	1.0	1.0	1.0

The manufacturing process of the steel for the gearbox bearing of the wind driven generator in each embodiment is to produce the steel by adopting a forming process of molten iron pretreatment, top-bottom combined blown converter BOF (high power electric arc furnace EAF), ladle refining furnace LF, vacuum circulating degassing furnace RH (VD furnace), large-section continuous casting CCM (continuous casting), continuous rolling, quick cooling and finishing.

During smelting, high-quality molten iron, scrap steel, raw and auxiliary materials, high-quality deoxidizer and refractory materials are selected. In the production process of an electric furnace/converter, the tapping terminal C of the three examples is respectively controlled to be 0.10-0.70%, the terminal P is controlled to be less than or equal to 0.018%, and the continuous casting superheat degree is controlled to be within 10-35 ℃. The produced continuous casting slab is hot-fed into a stepping heating furnace to be heated and rolled into a target bar, and the processes of steel rolling heating, rolling and cooling are shown in the following table 8. And then, carrying out subsequent straightening and flaw detection on the bar to obtain a target bar finished product.

TABLE 8

As can be seen from tables 3, 4, 5, 6 and 7, the steel for the bearing of the gearbox of the wind driven generator in the embodiments of the present invention has a significantly better control level of harmful elements such as oxygen, titanium and non-metallic inclusions than the GCr15SiMn steel subjected to electroslag remelting, i.e., the purity of the steel is significantly better than that of the product produced by the electroslag remelting technology. By combining the analysis, the wind power gear box bearing steel produced by the vacuum degassing and continuous casting production process can replace the original electroslag remelting process, remarkably improve the production efficiency, reduce the production cost and remarkably enhance the product competitiveness.

In conclusion, the steel for the bearing of the gearbox of the wind driven generator, provided by the invention, has the advantages that the overall idea of improving the purity of the steel is adopted, the process routes of high efficiency, high productivity and low cost of vacuum degassing, continuous casting and rolling are adopted, the key working procedures are optimized, researched and controlled, and therefore, the steel achieves high purity, high structure uniformity and high density, and the original electroslag remelting process can be replaced.

In addition to the above embodiments, the present invention also includes other embodiments, and any technical solutions formed by equivalent transformation or equivalent replacement should fall within the scope of the claims of the present invention.

Claims

1. A production method of steel for a gearbox bearing of a wind driven generator is characterized by comprising the following steps: the process comprises

(1) Smelting molten steel: the reference chemical composition is C: 0.80-1.05%, Si: 0.20 to 0.45%, Mn: 0.25-0.45%, Cr: 1.60-1.95%, S is less than or equal to 0.015%, P is less than or equal to 0.020%, and Ni: not more than 0.25%, Cu not more than 0.30%, Mo: 0.15-0.25%, Al: not more than 0.05 percent of Ca, not more than 0.0010 percent of Ti, not more than 0.0015 percent of Ti, not more than 0.0008 percent of O, not more than 0.04 percent of As, not more than 0.03 percent of Sn, not more than 0.005 percent of Sb, not more than 0.002 percent of Pb, and the balance of Fe and inevitable impurities;

(2) continuous casting: continuously casting a rectangular continuous casting billet which has the specification of 300 multiplied by 340mm and above and conforms to the chemical composition of a steel finished product;

(3) continuous rolling: removing phosphorus from the continuous casting billet which is taken out of the heating furnace by high-pressure water, then entering a rough rolling-intermediate rolling-finishing mill set, wherein the rough rolling initial rolling temperature is 950-1100 ℃, so that rolling control is carried out in an austenite single-phase region, the initial rolling temperature is used for rolling in the austenite single-phase region, and the continuous casting billet enters a mill set to be rolled into a round bar with the diameter of 120-200 mm; controlling the finish rolling temperature at 750-850 ℃;

(4) and (3) cooling: after finish rolling, rapidly cooling the round steel bar to rapidly jump out of a large number of precipitation areas of secondary cementite, and controlling the cooling speed to avoid over-rapid cooling, wherein the surface red returning temperature of the steel after finish rolling is required to be controlled between 550 ℃ and 720 ℃; and further controlling the cooling process to follow the principle of first quick and then slow, and controlling the cooling speed to gradually or gradually reduce to avoid the core part from entering a bainite and martensite precipitation region.

2. The method for producing the steel for the gearbox bearing of the wind driven generator according to claim 1, wherein: the produced steel product adopts a metallographic method to detect microscopic brittle inclusions, and the requirements are as follows: b fine system is less than or equal to 1.5 grade, B coarse system is less than or equal to 1.0 grade, D fine system is less than or equal to 1.0 grade, D coarse system is less than or equal to 1.0 grade, and DS system is less than or equal to 1.0 grade;

adopting SEP 1927 water immersion high-frequency flaw detection to detect macroscopic defects with defect index not more than 2.5mm/dm³；

The GB/T1979 is adopted to grade the macrostructure of steel, and the requirements of central porosity less than or equal to 1.0 level, general porosity less than or equal to 1.0 level, ingot type segregation less than or equal to 1.0 level and central segregation less than or equal to 1.0 level are met; the carbon content of the central carbon segregation region of the finished bar does not exceed 10% of the carbon content of normal smelting;

detecting the existence of no microscopic gap by adopting a metallographic method; and (3) detecting that the carbide liquation is less than or equal to 0 grade, the carbide banding is less than or equal to 2.0 grade and the carbide net is less than or equal to 2.5 grade by adopting a metallographic method.

3. The method for producing the steel for the gearbox bearing of the wind driven generator according to claim 1, wherein: after lower bainite is adopted for isothermal quenching, the impact toughness is more than or equal to 150J cm^-2。

4. The method for producing the steel for the gearbox bearing of the wind driven generator according to claim 1, wherein: and (1) sequentially carrying out KR pretreatment on smelting raw materials through molten iron, smelting in an electric furnace or a converter, LF refining and RH or VD vacuum degassing.

5. The method for producing the steel for the gearbox bearing of the wind driven generator according to claim 4, wherein: controlling a tapping end point C and an end point P in the smelting process of an electric furnace or a converter, wherein the end point C is as follows: 0.10-0.70 percent, the end point P is controlled to be less than or equal to 0.018 percent, the tapping temperature is controlled to be 1600-1700 ℃, and Al is added for deoxidation during the tapping process by adopting the slag-stopping tapping process.

6. The method for producing the steel for the gearbox bearing of the wind driven generator according to claim 4, wherein: the slagging and deoxidation operations are enhanced in the LF refining process, and the LF refining furnace adopts Al + SiC for combined deoxidation, so that the free oxygen content in the process is ensured to be at a lower level, and the advantage of removing impurities in the LF furnace during smelting is exerted.

7. The method for producing the steel for the gearbox bearing of the wind driven generator according to claim 6, wherein: stirring argon in the whole vacuum degassing process, degassing for 15-35min under the high vacuum condition of less than 133Pa, and carrying out long-time soft argon blowing treatment after vacuum degassing to ensure that nonmetallic inclusions float sufficiently.

8. The method for producing the steel for the gearbox bearing of the wind driven generator according to claim 1, wherein: and (2) carrying out anti-oxidation protection pouring in the whole continuous casting process to prevent secondary oxidation of molten steel, selecting special tundish covering slag to better adsorb impurities, carrying out low-superheat-degree pouring in the continuous casting process, wherein the superheat degree of the continuous casting process is 10-35 ℃, and simultaneously carrying out advanced procedures of tundish induction heating, electromagnetic stirring and light pressing in the continuous casting process to control segregation of steel.

9. The method for producing the steel for the gearbox bearing of the wind driven generator according to claim 1, wherein: and (3) heating the continuous casting billet before rolling, wherein the temperature of a preheating section is controlled to be 800-950 ℃, the temperature of a heating section is controlled to be 1100-1250 ℃, the temperature of a soaking section is controlled to be 1150-1250 ℃, and the total heating time is controlled to be 10-20 hours.