Production method for reducing flaw detection defects of wind power gear steel

Abstract

The invention discloses a production method for reducing flaw detection defects of wind power gear steel, and belongs to the technical field of ferrous metallurgy. According to the method, an electric furnace-LF-VD-continuous casting process route is adopted, the mass fraction of an aluminum element Al in molten steel is controlled to be not lower than 0.018% in the LF refining process, and the mass fraction of [Al] is controlled to be higher than 0.010% all the time in the VD vacuum treatment process. And after VD vacuum breaking, aluminum is supplemented in time, the mass fraction of Al is increased to 0.015%-0.020%, calcium treatment is reasonably carried out, and the mass fraction of Ca in molten steel is controlled to be 0.0006%-0.0009%. By accurately controlling the component change of the molten steel in the VD process, the formation of CaO-MgO-Al2O3-SiO2 inclusions with high SiO2 content is effectively inhibited, the large-size ultrasonic flaw detection defects in the wind power gear steel are remarkably reduced, and the internal quality of the steel is improved. The method is simple in process and remarkable in effect, and has a good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy and material engineering, and particularly relates to a production method for reducing flaw defects in wind power gear steel. BACKGROUND

[0002] The wind power gear steel is mainly used for manufacturing key gear components in wind power equipment, and requires excellent fatigue resistance and high internal cleanliness. In order to ensure that the gear has good strength and durability during long-term operation, the wind power gear steel puts forward extremely strict requirements for the control of internal quality defects, especially large-size inclusions. Ultrasonic flaw detection is an important means for detecting internal defects of the wind power gear steel, and the ultrasonic wave is extremely sensitive to internal defects such as cracks, holes and large-size inclusions.

[0003] In recent years, with the continuous improvement of the flaw detection standard by wind power main machine manufacturers, the flaw defect rate of some wind power gear steel products is high, which seriously affects the product quality stability and market competitiveness. Through defect analysis, it is found that the ultrasonic flaw defects in the wind power gear steel are mainly caused by the aggregation of large-size CaO-MgO-Al2O3-SiO2 inclusions, and such inclusions are mainly caused by the reaction out of control due to the too low [Al] content of the molten steel in the VD vacuum treatment process, which causes the proportion of SiO2 in the inclusions to increase, thereby forming unacceptable defects in flaw detection.

[0004] Therefore, developing a production method capable of effectively controlling the composition of the molten steel in the VD process and reducing the generation of large-size inclusions has become a key technical problem for improving the internal quality of the wind power gear steel and meeting the high-standard flaw detection requirements. SUMMARY

[0005] The purpose of the application is to provide a production method for reducing flaw defects in wind power gear steel, which accurately controls the [Al] content of the molten steel in the VD converter process to be above 0.010%, and optimally 0.015%, and controls the calcium feeding line operation after VD vacuum breaking, thereby greatly reducing the occurrence rate of large-size inclusions and improving the overall performance of the wind power gear steel.

[0006] To solve the above technical problems, the application adopts the following technical scheme:

[0007] The production method for reducing flaw defects in wind power gear steel comprises electric furnace smelting, LF refining, VD vacuum degassing and continuous casting, and is characterized in that it specifically comprises the following steps.

[0008] (1) Electric furnace smelting: the electric arc furnace is used to smelt the wind power gear steel, the temperature of the molten steel is controlled at 1600℃±10℃, the aluminum is used for deoxidation, the deoxidizer is dynamically adjusted according to the oxygen content of the molten steel to ensure the preliminary deoxidation effect, the oxygen content of the molten steel is controlled below 0.0020%, and the inclusion content of the molten steel is ensured to be low to avoid large particle oxide inclusions;

[0009] (2) LF refining: the temperature of the molten steel is controlled at 1560℃-1570℃ when entering the station; the CaO / Al2O3 ratio of the slag material is controlled at 1.2-1.4, the slag basicity is controlled at ≥2.5; the temperature is raised to 1580℃±5℃, and the temperature rising rate is controlled at 2-3℃ / min; the [Al] mass fraction is adjusted to 0.018%-0.020%, and the [O] mass fraction is controlled below 0.0015%; sampling detection is performed before the LF station to ensure that the [Al] content is not less than 0.018%;

[0010] (3) VD vacuum degassing: the temperature of the molten steel is controlled at 1570℃±5℃ before breaking the vacuum; after the VD starts, the vacuum degree is extracted to ≤10mbar, and the stirring argon flow is controlled at 20-30L / min; the vacuum treatment time is not less than 15min, the [Al] content is controlled by the intermediate control, and the [Al] mass fraction is ensured to be not less than 0.010%; the aluminum supplement is immediately performed after the VD breaks the vacuum, the aluminum supplement amount is calculated according to the measurement of the composition of the molten steel, the target [Al] mass fraction is increased to 0.015%-0.020%, and the calcium feeding is immediately performed after the aluminum supplement: the calcium feeding speed is controlled at 5-10m / min; the total amount of calcium added is controlled at 0.8-1.2kg / ton of steel; the [Ca] mass fraction in the molten steel after the calcium treatment is controlled at 0.0006%-0.0009%; during the later period of the VD operation, the light stirring argon is continuously used to ensure the mixing of the molten steel, and the stirring time is not less than 5min;

[0011] (4) Continuous casting process: the pouring temperature is controlled at 1540℃±10℃, the withdrawal speed is controlled at 0.6-1.0m / min, and the specific adjustment is made according to the section size; the low basicity and low oxide powder is used as the tundish covering agent to prevent secondary oxygen absorption; the molten steel flow is stably controlled during the pouring process to prevent the inclusion of slag, the cooling system of the secondary cooling zone is optimized, and the hot cracking is avoided.

[0012] Further, the wind power gear steel is 18CrNiMo wind power gear steel.

[0013] Further, the mass percentage content of the wind power gear steel chemical composition includes: C 0.17%~0.19%, Si 0.22%~0.34%, Mn 0.60%~0.70%, P≤0.010%, S≤0.010%, Cr 1.60%~1.72%, Mo 0.26~0.32%, Ni 1.50~1.62%, Al 0.015~0.020%, the rest is Fe and inevitable trace impurities, and the mass fraction is 100%.

[0014] Further, the mass percentage content of the wind power gear steel chemical composition includes: C 0.18%, Si 0.26%, Mn 0.65%, P 0.009%, S 0.005%, Cr 1.62%, Mo 0.28%, Ni 1.52%, Al 0.016%, the rest is Fe and inevitable trace impurities, and the mass fraction is 100%.

[0015] Further, the calcium filament diameter of the calcium feeding is 9mm.

[0016] Further, the flat bottom hole equivalent meets the standard flaw detection requirement of ≤φ0.38mm.

[0017] Further, the detection of internal inclusions meets the level of A and B≤1.5.

[0018] Chemical composition design principles:

[0019] C (carbon 0.17~0.19%) : Carbon is the main element to determine the strength and hardness of steel, and appropriate increase of C content is beneficial to obtain excellent hardenability and tempering stability, while the toughness is also considered. Controlling in 0.17%~0.19%, can ensure the fatigue strength requirements of wind power gear, and avoid brittleness caused by too high C content;

[0020] Si (silicon 0.22~0.34%) : Silicon exists as an auxiliary deoxidizer in the steelmaking process, and appropriate Si content can further reduce the oxygen content in the molten steel, promote the inclusion to float out, and improve the purity of steel. Controlling in 0.22%~0.34%, can effectively cooperate with aluminum deoxidization, and prevent excessive inclusion composition from being abnormal;

[0021] Mn (manganese 0.60~0.70%) : Manganese helps to improve the hardenability and tempering brittleness of steel, and also helps to solid solution strengthening. Controlling in this range, can improve the mechanical properties of steel, and also consider the uniformity and toughness of internal organization;

[0022] P (phosphorus ≤0.010%) : Phosphorus will seriously reduce the low temperature toughness and welding performance of steel, so it is required to be strictly controlled. Limiting to 0.010% or less, to ensure good toughness and service life of steel;

[0023] S (sulfur ≤0.010%) : Sulfur in steel can easily form brittle inclusions MnS, resulting in brittle fracture of steel. Controlling sulfur below 0.010%, helps to improve the transverse toughness and fatigue performance of steel, prevent the generation of crack source;

[0024] Cr (chromium 1.60-1.72%) : Chromium can significantly improve the hardenability, wear resistance and corrosion resistance of steel. Setting a higher Cr content, helps to improve the fatigue resistance and surface wear resistance of wind power gear steel;

[0025] Mo (molybdenum 0.26-0.32%) : Molybdenum helps to improve the hardenability of steel, prevent temper brittleness, and improve the high temperature strength of steel. Mo, Cr and Ni synergistically, further enhance the wear resistance and fatigue resistance;

[0026] Ni (nickel 1.50-1.62%) : Nickel can improve the toughness and low temperature performance of steel, and enhance the corrosion resistance of steel. Appropriate addition, helps to ensure that the wind power gear still has excellent toughness in cold environment;

[0027] Al (aluminum 0.015-0.020%) : Aluminum as the main deoxidizing element, reasonable design of aluminum content can form stable, fine Al2O3 inclusions, which is beneficial to subsequent control of inclusion evolution. Especially in the VD process, ensure that the [Al] mass fraction is not less than 0.010%, which can effectively avoid the generation of high SiO2 content inclusions.

[0028] Compared with the prior art, the beneficial technical effects of the present application are:

[0029] (1) The present application precisely controls the [Al] mass fraction of molten steel in the VD process to be higher than 0.010%, effectively avoids the formation of CaO-MgO-Al2O3-SiO2 inclusions with high SiO2 content, and reduces the ultrasonic flaw detection defect rate to below 10%, greatly improving the product flaw detection qualification rate.(2) The composition of inclusions in the molten steel of the present application is stable, the size is small and controllable, the cleanliness of the steel is significantly improved, the structure is uniform, and the strict requirements of wind power gear on high fatigue life are met.(3) The present application does not need to increase additional equipment investment, only by optimizing VD aluminum addition and calcium treatment control, it can be directly implemented on the existing LF-VD-continuous casting process, and has good process feasibility and large-scale popularization value.(4) By reducing the probability of large size flaw detection defects, significantly reducing the rework and scrap in the subsequent forging, heat treatment and processing process, greatly reducing the comprehensive production cost, improving the economic benefit of enterprises, and enhancing the competitiveness of wind power gear steel in the field of high-end equipment manufacturing. DETAILED DESCRIPTION

[0030] The present application is further described below.

[0031] The embodiment is one of the preferred embodiments in various embodiments of the application.

[0032] The production method for reducing the flaw detection of the wind power gear steel in the embodiment is: electric furnace, refining, VD vacuum degassing, and continuous casting.

[0033] The test material is 18CrNiMo wind power gear steel, and the mass percentage of the chemical components includes: C 0.18%, Si 0.26%, Mn 0.65%, P 0.009%, S 0.005%, Cr 1.62%, Mo 0.28%, Ni 1.52%, Al 0.016%, and the rest is Fe and inevitable trace impurities, and the total mass percentage is 100%.

[0034] The electric arc furnace is used to smelt the 18CrNiMo wind power gear steel, and the temperature of the molten steel is controlled at 1600°C. The aluminum is used for deoxidation, the deoxidizer is dynamically adjusted according to the oxygen content of the molten steel, the preliminary deoxidation effect is ensured, and the oxygen content of the molten steel is controlled at 0.0015%. The inclusion content of the molten steel is ensured to be low, and large particle oxide inclusions are avoided.

[0035] The molten steel is transferred into the LF for refining, and the temperature of the molten steel entering the station is controlled at 1565°C. The CaO / Al2O3 ratio of the slag material is controlled at 1.3, and the slag basicity is controlled at 2.8. The temperature is raised to 1580°C at a rate of 2.5°C / min. The [Al] mass fraction is adjusted to 0.018%, and the [O] mass fraction is controlled at 0.0014%.

[0036] The VD vacuum degassing process is used, and the temperature of the molten steel before breaking the vacuum is controlled at 1570°C. After the VD starts, the vacuum degree is extracted to 9 mbar, and the stirring argon flow is controlled at 25 L / min. The vacuum treatment time is 18 min, the [Al] content is controlled, and the [Al] mass fraction is ensured to be not less than 0.010%. The aluminum supplement operation is immediately performed after the VD breaks the vacuum, the aluminum supplement amount is calculated according to the measurement of the composition of the molten steel, the target [Al] mass fraction is increased to 0.016%, and the calcium feeding treatment is immediately performed after the aluminum supplement: the calcium feeding speed is controlled at 6 m / min, the calcium wire diameter is 9 mm, the total calcium amount is controlled at 0.9 kg / ton of steel, and the [Ca] mass fraction in the molten steel after the calcium treatment is controlled at 0.0008%. In the later period of the VD operation, the light stirring argon is continuously used to ensure the mixing of the molten steel, and the stirring time is 7 min.

[0037] The continuous casting operation is performed, the pouring temperature is controlled at 1540°C, the withdrawal speed is controlled at 0.8 m / min, and the specific adjustment is made according to the section size. The tundish covering agent is low basicity and low oxide powder, which prevents secondary oxygen absorption. The molten steel flow is stably controlled during the pouring process to prevent slag inclusion and optimize the cooling system of the secondary cooling zone to avoid hot cracking.

[0038] The sampling detection ultrasonic flaw detection defect rate is required to be flat bottom hole equivalent ≤ φ0.38 mm; the internal inclusion level is detected, and the A level and the B level are both ≤ 1.5 level. Through the above strict process parameter control, the formation of high SiO2 content CaO-MgO-Al2O3-SiO2 inclusions in the VD process can be significantly reduced, thereby reducing the ultrasonic flaw detection defects of the wind power gear steel and improving the internal quality stability of the product.

[0039] Comparative Example 1: In Comparative Example 1, the [Al] mass fraction of the molten steel is reduced to 0.006% during the VD vacuum treatment after the LF outstation, which is much lower than the standard of 0.010% or more controlled in the examples. The aluminum is not added in time after the VD breaking, resulting in a continuous low aluminum content in the molten steel. Due to the insufficient [Al] content in the molten steel, a large amount of CaO-MgO-Al2O3-SiO2 inclusions with high SiO2 content are generated in the VD process, forming large size defects, resulting in an ultrasonic flaw detection defect rate of 25%. Compared with the examples, the lack of aluminum supplement control is the main reason for the increase of the defect rate.

[0040] Comparative Example 2: In Comparative Example 2, the [Al] mass fraction is reduced to 0.009% before the VD breaking, and the aluminum supplement operation is insufficient, resulting in that the [Al] mass fraction in the molten steel cannot be effectively increased to 0.010% or more after the VD breaking. The calcium feeding operation is insufficient, and the [Ca] content in the molten steel is low, which cannot effectively modify the inclusions. Compared with the examples, due to the insufficient [Al] supplement and improper [Ca] control, the size of the inclusions in the molten steel increases, the proportion of SiO2 in the inclusions is high, and finally the ultrasonic flaw detection defect rate increases to 20%.

[0041] Comparative Example 3: In Comparative Example 3, although aluminum is added after the VD breaking, the aluminum supplement is excessive, so that the [Al] mass fraction in the molten steel reaches 0.020% or more, and at the same time, the [Ca] mass fraction is increased to 0.0015% due to the improper calcium feeding amount control, which exceeds the reasonable control range. Excessive calcium treatment leads to the generation of a large amount of coarse liquid inclusions with high Ca content in the molten steel, forming large particle CaO inclusions, increasing new flaw detection defect sources. Compared with the examples, due to the excessive aluminum supplement and calcium feeding, the morphology of the inclusions is deteriorated, resulting in that the ultrasonic flaw detection defect rate not only does not decrease, but rather increases to 22%.

[0042]

[0043] By comparing the process parameters of the above examples and the comparative examples, it can be seen that the technical scheme of the present application can effectively avoid the generation of large-size CaO-MgO-Al2O3-SiO2 inclusions caused by insufficient [Al] content or improper Ca treatment by accurately controlling the mass fraction of aluminum element [Al] in the molten steel during LF outbound and VD vacuum treatment, ensuring timely addition of aluminum to 0.015% to 0.020% after VD breaking vacuum, and reasonably controlling the mass fraction of calcium element [Ca] to 0.0006% to 0.0009% during calcium feeding. Compared with the comparative examples, the present application can significantly reduce the flaw detection defect rate in steel, improve the internal cleanliness, ensure the ultrasonic flaw detection qualified rate of wind power gear steel, and has obvious technical progress and good industrial application value.

[0044] As can be seen from the above examples and comparative examples, compared with the comparative examples, the examples of the present application have the following advantages: (1) the present application accurately adds aluminum during VD vacuum treatment to ensure that the mass fraction of [Al] in the molten steel is stable at 0.015% to 0.020%, avoiding the problem of high SiO2 of CaO-MgO-Al2O3-SiO2 inclusions caused by too low [Al], and reducing large-size inclusions from the source. (2) The present application controls the calcium feeding amount after VD breaking vacuum to keep the mass fraction of [Ca] in the molten steel at 0.0006% to 0.0009%, effectively modifying the inclusions to fine and spherical structure, and preventing new flaw detection defects caused by excessive or insufficient calcium treatment. (3) The ultrasonic flaw detection defect rate in the examples is generally reduced to about 10%, while the defect rate in the comparative examples is as high as 20% or more, fully verifying the significant effect of the present application method on improving the internal cleanliness of wind power gear steel and reducing the unqualified rate of flaw detection. (4) The present application does not need to introduce additional equipment, but only needs to optimize the aluminum addition and calcium treatment operation of the VD process, so it can be directly implemented on the existing LF-VD-continuous casting process line, has good process stability and application prospect, and can better meet the high standard requirements of high-end wind power equipment manufacturing field on material performance.

[0045] The above examples only describe the preferred mode of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical scheme of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A production method for reducing flaw detection of wind power gear steel, comprising electric furnace smelting, LF refining, VD vacuum degassing, continuous casting, characterized in that, Specifically comprising: (1) Electric furnace smelting: using electric arc furnace to smelt the wind power gear steel, and controlling the temperature of the molten steel at 1600℃±10℃ when it is discharged; using aluminum deoxidation, and dynamically adjusting the dosage of the deoxidizer according to the oxygen content of the molten steel to ensure the preliminary deoxidation effect, and controlling the oxygen content of the molten steel at less than 0.0020% when it is discharged; ensuring the low inclusion content of the molten steel when it is discharged, and avoiding large particle oxidized inclusions; (2) LF refining: controlling the temperature of the molten steel at 1560℃-1570℃ when it is fed into the LF; controlling the CaO / Al2O3 ratio of the slag material at 1.2-1.4, and the slag basicity at ≥2.5; increasing the temperature to 1580℃±5℃ at a rate of 2-3℃ / min; adjusting the [Al] mass fraction to 0.018%-0.020%, and controlling the [O] mass fraction at less than 0.0015%; sampling and detecting before the molten steel is discharged from the LF to ensure that the [Al] content is not less than 0.018%; (3) VD vacuum degassing: controlling the temperature of the molten steel at 1570℃±5℃ before breaking the vacuum; after the VD starts, the vacuum degree is extracted to ≤10mbar, and the stirring argon flow is controlled at 20-30L / min; the vacuum treatment time is not less than 15min, and the [Al] content is controlled by the intermediate control to ensure that the [Al] mass fraction is not less than 0.010%; immediately after the VD breaks the vacuum, the aluminum supplement operation is performed, the amount of the aluminum supplement is calculated according to the measurement of the composition of the molten steel, the target [Al] mass fraction is increased to 0.015%-0.020%, and immediately after the aluminum supplement, the calcium feeding treatment is performed: the calcium feeding speed is controlled at 5-10m / min; the total amount of the added calcium is controlled at 0.8-1.2kg / ton of steel; the [Ca] mass fraction in the molten steel after the calcium treatment is controlled at 0.0006%-0.0009%; in the later period of the VD operation, the light stirring argon is continuously used to ensure the mixing of the molten steel, and the stirring time is not less than 5min; (4) Continuous casting process: controlling the pouring temperature at 1540℃±10℃, and the casting speed at 0.6-1.0m / min, which is adjusted according to the section size; using low basicity and low oxide powder as the tundish covering agent to prevent secondary oxygen absorption; stably controlling the molten steel flow during the pouring process to prevent the inclusion of slag, optimizing the cooling system of the secondary cooling zone, and avoiding hot cracking.

2. The production method of reducing flaw detection of wind power gear steel according to claim 1, characterized in that, The wind power gear steel is 18CrNiMo wind power gear steel.

3. The production method of reducing flaw detection of wind power gear steel according to claim 1 or 2, characterized in that, The mass percentage of the chemical composition of the wind power gear steel comprises: C 0.17%-0.19%, Si 0.22%-0.34%, Mn 0.60%-0.70%, P ≤0.010%, S ≤0.010%, Cr 1.60%-1.72%, Mo 0.26-0.32%, Ni 1.50-1.62%, Al 0.015-0.020%, and the rest is Fe and inevitable trace impurities, and the total mass fraction is 100%.

4. The production method of reducing flaw detection of wind power gear steel according to claim 3, characterized in that, The mass percentage of the chemical composition of the wind power gear steel includes: C 0.18%, Si 0.26%, Mn 0.65%, P 0.009%, S 0.005%, Cr 1.62%, Mo 0.28%, Ni 1.52%, Al 0.016%, and the rest is Fe and inevitable trace impurities, and the total mass percentage is 100%.

5. The method of claim 1, wherein the steel is a wind turbine gear steel. The calcium filaments for feeding calcium have a diameter of 9 mm.

6. The method of claim 1, wherein the steel is a wind turbine gear steel. The flat-bottom hole equivalent is less than or equal to φ0.38 mm to meet the standard flaw detection requirements.

7. The method of claim 1, wherein the steel is a wind turbine gear steel. The detection of internal inclusions meets the requirements that the A level and the B level are less than or equal to 1.5 levels.

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