Preparation method of wind power fastener steel, wind power fastener steel and wind power fastener

Abstract

The present application discloses a preparation method of a wind power fastener steel, the wind power fastener steel and a wind power fastener. The preparation method includes: selecting a small bloom for rolling, and the chemical composition of the small bloom is: Ti ≤ 40 ppm, Al S / Ti ≥ 4.0, 7.0 ≥ Al / N ≥ 4.0; controlling the cross-sectional hardness difference of the wind power fastener steel ≤ 1.5 HRC; performing differential temperature rolling on the surface of the continuous casting billet; controlling the size range of the normal grains of the wind power fastener steel to be 10 μm to 15 μm, the size of the abnormal grains of the wind power fastener steel ≤ 35 μm, and the area percentage of the abnormal grains ≤ 2%. Through the technical solution of the present application, it is possible to roll a wind power fastener steel with high strength, toughness and plasticity by using a small bloom, reducing the production cost and energy consumption.

Description

Technical Field

[0001] This application belongs to the technical field of steel rolling, and particularly relates to a preparation method of wind power fastener steel, wind power fastener steel and wind power fasteners. Background Art

[0002] At present, the requirements for high strength, toughness, strength and plasticity of wind power fastener steel materials are getting higher and higher. In the prior art, the rectangular billet blooming process is usually used to produce wind power fastener steel, and this production method has the disadvantages of high cost and high energy consumption. Summary of the Invention

[0003] Embodiments of this application provide a preparation method of wind power fastener steel, wind power fastener steel and wind power fasteners, which can utilize small square billets to roll wind power fastener steel with high strength, toughness, strength and plasticity, reducing production costs and energy consumption.

[0004] Other characteristics and advantages of this application will become apparent through the following detailed description, or be learned partially through the practice of this application.

[0005] According to the first aspect of the embodiments of this application, a preparation method of wind power fastener steel is provided, and the preparation method includes:

[0006] Select a small square billet for rolling, and the chemical composition of the small square billet is: Ti≤40ppm, Al S / Ti≥4.0, 7.0≥Al / N≥4.0;

[0007] Control the cross-sectional hardness difference of the wind power fastener steel ≤1.5HRC;

[0008] Perform differential temperature rolling on the surface of the continuous casting billet;

[0009] Control the size range of normal grains of the wind power fastener steel to be 10μm~15μm, the size of abnormal grains of the wind power fastener steel ≤35μm, and the area percentage of abnormal grains ≤2%.

[0010] In some embodiments of this application, based on the foregoing solution, the wind power fastener steel is a round steel with a diameter greater than 60mm.

[0011] In some embodiments of this application, based on the foregoing solution, the area range of the small square billet is 150mm 2 ~200mm 2 .

[0012] In some embodiments of this application, based on the foregoing solution, the control of the cross-sectional hardness difference of the wind power fastener steel ≤1.5HRC includes:

[0013] Control the segregation degree of Cr-Mn-Mo alloying elements in the core of the continuous casting billet to be ≤0.5, so that the cross-sectional hardness difference of the rolled round steel after heat treatment is ≤1.5 HRC.

[0014] In some embodiments of the present application, based on the foregoing solution, controlling the segregation degree of Cr-Mn-Mo alloying elements in the core of the continuous casting billet to be ≤0.5 includes:

[0015] Control the parameters of the secondary cooling and electromagnetic stirring of the bloom continuous casting to control the segregation degree of the Cr-Mn-Mo alloying elements to be ≤0.5.

[0016] In some embodiments of the present application, based on the foregoing solution, the differential temperature rolling of the surface of the continuous casting billet includes:

[0017] Control the surface temperature drop of the continuous casting billet by single-pass high-pressure water cooling to be ≥200°C, and the reduction per pass at the start of rolling to be ≥25%.

[0018] In some embodiments of the present application, based on the foregoing solution, the surface temperature drop of the continuous casting billet by single-pass high-pressure water cooling is 200°C, and the reduction per pass at the start of rolling is 30%.

[0019] In some embodiments of the present application, based on the foregoing solution, controlling the area percentage of abnormal grains of the wind power fastener steel to be ≤2% includes:

[0020] Control the area percentage of abnormal grains in the edge or core of the wind power fastener steel to be ≤2%.

[0021] According to the second aspect of the embodiments of the present application, there is provided a wind power fastener steel, which is produced according to the above-mentioned preparation method of the wind power fastener steel.

[0022] According to the third aspect of the embodiments of the present application, there is provided a wind power fastener, which includes the above-mentioned wind power fastener steel.

[0023] In the present application, by selecting a bloom for rolling, the chemical composition of the bloom is: Ti ≤ 40 ppm, Al S / Ti ≥ 4.0, 7.0 ≥ Al / N ≥ 4.0; control the cross-sectional hardness difference of the wind power fastener steel to be ≤1.5 HRC; perform differential temperature rolling on the surface of the continuous casting billet; control the size range of normal grains of the wind power fastener steel to be 10 μm to 15 μm, the size of abnormal grains of the wind power fastener steel to be ≤35 μm, and the area percentage of abnormal grains to be ≤2%. Through the technical solution of the present application, it is possible to roll a wind power fastener steel with high strength, toughness and plasticity by using a bloom, reducing production costs and energy consumption.

[0024] It should be understood that the above general description and the following detailed description are merely exemplary and explanatory, and do not limit this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings herein are incorporated into the specification and form a part of this specification, showing embodiments consistent with this application, and are used together with the specification to explain the principles of this application. Obviously, the drawings in the following description are only some embodiments of this application, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts. In the drawings:

[0026] Figure 1 is a schematic flow chart of a preparation method of wind power fastener steel in one embodiment;

[0027] Figure 2 is a schematic flow chart of a preparation method of wind power fastener steel in another embodiment;

[0028] Figure 3 is the central segregation structure of a wind power fastener with a specification of 80 mm after quenching and tempering heat treatment in the comparative example of this application;

[0029] Figure 4 is the microscopic segregation photograph of Cr-Mn-Mo alloy elements at the center of a wind power fastener with a specification of 80 mm after quenching and tempering heat treatment in the embodiments and comparative example of this application;

[0030] Figure 5 is an abnormal grain picture with a size of 55 μm at the center of a wind power fastener with a specification of 80 mm after quenching in the comparative example of this application;

[0031] Figure 6 is the equivalent strain diagram from the surface to the center of a 200-square billet differential temperature rolled round steel with a specification of 80 mm. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The following will specifically describe this application in combination with specific embodiments and examples, and the advantages and various effects of this application will be presented more clearly therefrom. Those skilled in the art should understand that these specific embodiments and examples are used to illustrate this application, rather than to limit this application.

[0033] Throughout the specification, unless otherwise specifically stated, the terms used in this application should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used in this application have the same meaning as the general understanding of those skilled in the art to which this application belongs. In case of conflict, this specification shall prevail.

[0034] Unless otherwise specified, all kinds of raw materials, reagents, instruments, equipment, etc. used in this application can be obtained through market purchase or can be prepared by existing methods.

[0035] Figure 1 is a schematic flow chart of the preparation method of wind power fastener steel in an embodiment.

[0036] As Figure 1 shown, the embodiment of the present application provides a preparation method of wind power fastener steel, and the preparation method includes:

[0037] Step 101, select a small billet for rolling, and the chemical composition of the small billet is: Ti≤40ppm, Al S / Ti≥4.0, 7.0≥Al / N≥4.0.

[0038] In specific implementation, the area of the small billet can be 150mm 2 ~200mm 2 , and the wind power fastener steel can be a round steel with a diameter greater than 60mm, such as a round steel with a diameter of 60mm~80mm.

[0039] It should be understood that when rolling large-sized round steel from small billets in the prior art, problems such as large cross-section hardness fluctuations, poor consistency, and poor low-temperature toughness at -40°C will occur, resulting in the rolled round steel being unable to meet the processing and use of high-strength fastener products above 1000Mpa. Therefore, at present, wind power fastener steel is produced by using a rectangular billet blooming process with high cost and high energy consumption. In this embodiment, by controlling the content and ratio of chemical components Al S , Ti, the matching of Al and N content, the cross-section hardness difference of the round steel, improving the penetration of the central deformation amount through differential temperature rolling during the rolling process, and controlling the normal grain size and abnormal grain size of the cross-section of the round steel, the rolling of large-sized round steel with small billets is realized, and the rolled round steel has the characteristics of small cross-section hardness fluctuations, good consistency, and good low-temperature toughness at -40°C, and can meet the processing and use of high-strength fastener products above 1000Mpa.

[0040] Specifically, since the chemical composition of the small billet is Ti≤40ppm, Al S / Ti≥4.0, 7.0≥Al / N≥4.0, and the wind power fastener steel is rolled from the small billet, the chemical composition of the wind power fastener steel is Ti≤40ppm, Al S / Ti≥4.0, 7.0≥Al / N≥4.0.

[0041] Based on the requirements of the large-scale wind turbines, the specification range of wind power fasteners is usually 35mm - 80mm. The reduction ratio of small bloom rolling large-sized round steel is small, so it is necessary to refine the grains to make up for the small reduction ratio. At the same time, it is necessary to control the grain size to be uniform and avoid mixed grains. In this embodiment, by controlling Al S / Ti≥4.0 and Ti≤40ppm, and using AlN precipitation to refine grains, fine and uniform grains can be formed, and large-sized TiN particles can be avoided.

[0042] If Al S / Ti<4.0 and Ti>40ppm, Ti and N in the steel will form TiN during the liquid state, and large-sized grains and large-sized TiN particles are likely to form during the steel rolling process, and the low-temperature impact energy will be greatly reduced. By matching the Al content with the N content in the steel, that is, when 7.0≥Al / N≥4.0, after dissolution during the heating process in the heating furnace, fine and dispersed grains will precipitate during the rolling process. When Al / N>7.0, the precipitated grains are too fine, which will affect the hardenability of the steel and cannot achieve full-section hardening; when Al / N<4.0, the precipitation of Al element is insufficient, resulting in a low utilization rate of Al element.

[0043] Step 102, control the cross-section hardness difference of the wind power fastener steel ≤1.5HRC.

[0044] In a specific implementation, the segregation degree of Cr-Mn-Mo alloy elements in the center of the continuous casting billet can be controlled ≤0.5, so that the cross-section hardness difference of the rolled round steel after heat treatment ≤1.5HRC.

[0045] It should be understood that the wind power fasteners require full-section hardening and a high cross-section consistency. For large-sized fasteners with a specification above 60mm, alloy element segregation will cause tissue differences and large fluctuations in the cross-section hardness difference. If the segregation degree of Cr-Mn-Mo alloy elements >0.5, element segregation will cause the formation of soft phases of proeutectoid ferrite during the quenching heat treatment process, and the cross-section hardness difference will be greater than 1.5HRC. Therefore, in this embodiment, by controlling the segregation degree of Cr-Mn-Mo alloy elements in the center of the continuous casting billet ≤0.5, after the heat treatment process, the cross-section hardness difference ≤1.5HRC.

[0046] In a specific implementation, the segregation degree of Cr-Mn-Mo alloy elements can be controlled ≤0.5 by controlling the parameters of small bloom continuous casting cooling and electromagnetic stirring.

[0047] Among them, the parameters of small bloom continuous casting cooling include continuous casting speed, water cooling intensity and pressure, etc., and this embodiment does not limit them.

[0048] The parameters of electromagnetic stirring include frequency and current, etc., and this embodiment does not limit them.

[0049] Step 103: Perform differential temperature rolling on the surface of the continuous casting billet.

[0050] Performing differential temperature rolling on the surface of the continuous casting billet can be achieved by controlling the surface temperature drop of the continuous casting billet during single-pass high-pressure water cooling and the reduction per single pass during the first rolling pass. Specifically, the surface temperature drop of the continuous casting billet during single-pass high-pressure water cooling can be controlled to be ≥200°C, and the reduction per single pass during the first rolling pass can be controlled to be ≥25%.

[0051] It should be understood that for the rolling of small square billets with a size of 150 mm 2 ~200 mm 2 into round steel with a specification of more than 60 mm, the compression ratio is less than 10, the core deformation is 0.3 mm / mm, the grain recrystallization is insufficient, the grain size is large, and the matching performance of strength and toughness and toughness and plasticity is poor. In this embodiment, rapid surface quenching is designed to form a hardened layer on the surface layer, and the deformation is transmitted through the hardened layer to increase the core deformation. When the surface temperature of the continuous casting billet during single-pass high-pressure water cooling drops by more than 200°C and the reduction per single pass during the first rolling pass is more than 25%, the equivalent strain of the core can be increased by 0.15 mm / mm. When the surface temperature of the continuous casting billet during single-pass high-pressure water cooling drops by 200°C and the reduction per single pass during the first rolling pass is 30%, the equivalent strain of the core can be increased by 0.18 mm / mm.

[0052] Step 104: Control the normal grain size range of the wind power fastener steel to be 10 μm to 15 μm, the abnormal grain size of the wind power fastener steel to be ≤35 μm, and the area percentage of the abnormal grains to be ≤2%.

[0053] It should be understood that the uniformity of the grain size of the wind power fastener steel and the coordinated matching of multiple grains during cold upsetting deformation are directly related to the cold deformation ability of the material. During continuous hot rolling, it is difficult to achieve complete uniformity of the grain size, and there is a quantitative relationship between the uniformity of the grain size and the critical deformation amount of the material.

[0054] For the round steel with a specification of 60 mm to 80 mm in the wind power fastener steel, the normal grain size range is 20 μm to 30 μm, the size range of the abnormal single crystal grains in the abnormal structure is usually 40 μm to 60 μm, and the maximum can reach 100 μm. Non-uniform grain size will significantly reduce the coordinated deformation ability of multiple grains during cold upsetting, but the coordinated deformation ability is closely related to the proportion of the abnormal structure area, the critical deformation amount of the material processed into products, and the abnormal grain size, etc. When the size of the abnormal grains is greater than 35 μm, it is difficult to match with the normal grains of 10 μm to 15 μm during cold deformation, and the proportion of cold upsetting cracking increases significantly. Therefore, to be used for normal cold upsetting, the size of the abnormal grains must be controlled to be ≤35 μm.

[0055] Among them, the area percentage of the abnormal grains refers to the percentage of the area of the abnormal grains to the area of all grains (including abnormal grains and normal grains).

[0056] Furthermore, the area percentage of abnormally coarse structures (i.e., abnormal grains) in the edge or core of the wind power fastener steel can be controlled to be ≤2%, and the cold heading deformation can reach the critical allowable deformation amount of the material. If the area percentage of the coarse structure is >2%, the critical deformation amount of the material for cold heading will be significantly reduced, and the cold heading cracking rate will be significantly increased.

[0057] In this embodiment, by selecting small square billets for rolling, the chemical composition of the small square billets is: Ti ≤ 40 ppm, AlS / Ti ≥ 4.0, 7.0 ≥ Al / N ≥ 4.0; controlling the cross-section hardness difference of the wind power fastener steel to be ≤1.5 HRC; performing differential temperature rolling on the surface of the continuous casting billet; controlling the size range of the normal grains of the wind power fastener steel to be 10 μm to 15 μm, the size of the abnormal grains of the wind power fastener steel to be ≤35 μm, and the area percentage of the abnormal grains to be ≤2%. Through the technical solution of the present application, it is possible to roll wind power fastener steel with high strength, toughness and plasticity by using small square billets, reducing production costs and energy consumption.

[0058] Figure 2 It is a schematic flow chart of the preparation method of wind power fastener steel in another embodiment.

[0059] As Figure 2 shown, the preparation method of the wind power fastener steel may include the following steps:

[0060] Step 201, select small square billets for rolling, and the chemical composition of the small square billets is: Ti ≤ 40 ppm, Al S / Ti ≥ 4.0, 7.0 ≥ Al / N ≥ 4.0.

[0061] Step 202, control the segregation degree of Cr-Mn-Mo alloy elements in the core of the continuous casting billet to be ≤0.5, so that the cross-section hardness difference after heat treatment of the rolled round steel is ≤1.5 HRC.

[0062] Step 203, control the surface temperature drop of the continuous casting billet cooled by high-pressure water in a single pass to be ≥200 °C, and the reduction in a single pass at the start of rolling to be ≥25%.

[0063] Step 204, control the size range of the normal grains of the wind power fastener steel to be 10 μm to 15 μm, the size of the abnormal grains of the wind power fastener steel to be ≤35 μm, and the area percentage of the abnormal grains in the edge or core of the wind power fastener steel to be ≤2%.

[0064] Figure 3 is the core segregation structure of the 80-mm specification wind power fastener after quenching and tempering heat treatment in the comparative example of the present application, Figure 4 is the microscopic segregation photo of Cr-Mn-Mo alloy elements at the core position of the 80-mm specification wind power fasteners after quenching and tempering heat treatment in the embodiment (after optimization) and the comparative example (before optimization) of the present application. From Figure 3 andFigure 4 It can be seen that after quenching and tempering heat treatment, the segregation degree of Cr-Mn-Mo alloy elements at the core of the wind power fastener in the embodiment of the present application is small.

[0065] Figure 5 This is an abnormal grain picture of 55μm at the core of an 80mm specification wind power fastener after quenching and tempering in the comparative example of the present application. When the size of the abnormal grain is 55μm, the proportion of cold heading cracking will increase significantly.

[0066] Figure 6 This is the equivalent strain diagram from the surface to the core of a round steel with a specification of 80mm obtained by differential temperature rolling of a 200-square billet. Figure 6 It can be seen that when differential temperature rolling is performed on the billet, if the temperature drop is greater than 200°C, the equivalent strain at the core will increase significantly.

[0067] In specific implementation, small square billets can be selected for rolling. The chemical composition of the small square billet includes Al S / Ti = 8.0, Ti = 38ppm, Al / N = 5.5. Furthermore, the chemical composition in the steel includes Al S / Ti = 8.0, Ti = 38ppm, Al / N = 5.5; control the segregation degree of Cr-Mn-Mo alloy elements at the core of the billet to be 0.45, and the hardness difference of the cross-section after heat treatment of the rolled round steel is 1.2HRC; use a billet with a specification of 200mm 2 to roll a round steel with a diameter of 80mm, control the surface temperature drop of 200°C during single-pass high-pressure water cooling of the billet, and the reduction per pass during the start of rolling is 30% to achieve an increase in the equivalent strain at the core of 0.18mm / mm; control the size of the normal grains of the round steel to be 12.5μm, the size of the largest abnormal grains to be 30μm, and the area percentage of the abnormal grains to be 1.5%.

[0068] Next, the preparation method of a wind power fastener steel of the present application under various experimental conditions will be summarized in combination with examples, comparative examples, and experimental data. The detailed data is shown in Table 1.

[0069]

[0070] Table 1

[0071] As can be seen from Table 1 above, compared with the comparative example, the round steel prepared according to the embodiment of the present application has a higher impact energy Akv (-40°C), that is, it has better toughness at a low temperature of -40°C and can meet the requirements of the low-temperature service performance of the wind power industry with an impact energy at -40°C.

[0072] The embodiment of the present application also provides a wind power fastener steel prepared by the above preparation method.

[0073] The embodiment of the present application also provides a wind power fastener including the above wind power fastener steel.

[0074] Finally, it should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or apparatus comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or apparatus.

[0075] The flowcharts shown in the accompanying drawings are only illustrative and do not necessarily include all the content and operations / steps, nor are they necessarily executed in the order described. For example, some operations / steps can be decomposed, while some operations / steps can be combined or partially combined, so the actual execution order may be changed according to the actual situation.

[0076] The above are only the embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A preparation method of a wind power fastener steel, characterized in that, the preparation method includes: Select a small bloom for rolling. The chemical composition of the small bloom is: Ti ≤ 40 ppm, Al S / Ti ≥ 4.0, 7.0 ≥ Al / N ≥ 4.0; controlling the cross-section hardness difference of the wind power fastener steel ≤ 1.5 HRC; performing differential temperature rolling on the surface of the continuous casting billet; controlling the size range of normal grains of the wind power fastener steel to be 10 μm - 15 μm, the size of abnormal grains of the wind power fastener steel ≤ 35 μm, and the area percentage of the abnormal grains ≤ 2%.

2. The preparation method of the wind power fastener steel according to claim 1, characterized in that, the wind power fastener steel is a round steel with a diameter greater than 60 mm.

3. The preparation method of the wind power fastener steel according to claim 2, characterized in that, The area range of the said billet is 150mm 2 ~200mm 2 .

4. The preparation method of the wind power fastener steel according to claim 3, characterized in that, the controlling the cross-section hardness difference of the wind power fastener steel ≤ 1.5 HRC includes: controlling the segregation degree of Cr-Mn-Mo alloy elements in the core of the continuous casting billet ≤ 0.5, so that the cross-section hardness difference ≤ 1.5 HRC after heat treatment of the rolled round steel.

5. The preparation method of the wind power fastener steel according to claim 4, characterized in that, the controlling the segregation degree of Cr-Mn-Mo alloy elements in the core of the continuous casting billet ≤ 0.5 includes: controlling the parameters of small billet continuous casting cooling and electromagnetic stirring to control the segregation degree of Cr-Mn-Mo alloy elements ≤ 0.

5.

6. The preparation method of the wind power fastener steel according to claim 4, characterized in that, the performing differential temperature rolling on the surface of the continuous casting billet includes: controlling the surface temperature drop of the continuous casting billet by high-pressure water single-pass cooling ≥ 200 °C, and the reduction per pass at the start of rolling ≥ 25%.

7. The preparation method of the wind power fastener steel according to claim 6, characterized in that, the surface temperature drop of the continuous casting billet by high-pressure water single-pass cooling is 200 °C, and the reduction per pass at the start of rolling is 30%.

8. The preparation method of the wind power fastener steel according to any one of claims 1 to 7, characterized in that, the controlling the area percentage of abnormal grains of the wind power fastener steel ≤ 2% includes: controlling the area percentage of abnormal grains at the edge or in the core of the wind power fastener steel ≤ 2%.

9. A wind power fastener steel, characterized in that, the wind power fastener steel is produced according to the preparation method of the wind power fastener steel according to any one of claims 1 to 8.

10. A wind power fastener, characterized in that, it includes the wind power fastener steel according to claim 9.

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