CN115852241B - Steel and bar for high-homogeneity high-hardenability wind power bolt and manufacturing method thereof - Google Patents
Steel and bar for high-homogeneity high-hardenability wind power bolt and manufacturing method thereof Download PDFInfo
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- 238000009749 continuous casting Methods 0.000 claims description 7
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
The invention discloses a high-homogeneity high-hardenability steel for wind power bolts, which contains Fe and unavoidable impurities and also contains the following chemical elements in percentage by mass: c:0.40 to 0.44 percent of Si:0.15 to 0.35 percent of Mn:0.8 to 1.0 percent of Cr:1.2 to 1.3 percent of Mo:0.20 to 0.35 percent of Ni:0.35 to 0.45 percent of Al:0.02 to 0.05 percent. Correspondingly, the invention also discloses a manufacturing method of the bar for the wind power bolt, which comprises the following steps: (1) smelting and casting; (2) heating; (3) rolling or forging; (4) solid quenching: controlling austenitizing temperature to be 850-1050 ℃, and quenching by water after austenitizing; (5) tempering: the tempering temperature is 520-640 ℃, and the air cooling or the water cooling is carried out after tempering.
Description
Technical Field
The present invention relates to steel, bar and their production process, and is especially one kind of high homogeneity and high hardenability steel, bar and their production process.
Background
In recent years, in order to improve the power generation efficiency and reduce the power generation cost, the wind power industry in China, especially large-capacity megawatt-level large-scale wind power generator sets, are rapidly developed, and more wind power equipment is gradually put into the market for use.
Most wind power equipment has a severe working environment, the adopted high-strength fastener needs to be in service in the wild for a long time, and the maintenance condition is poor, so that the performance requirement on steel materials adopted by the fastener is generally high; under normal continuous operation, the wind power bolt as a fastener is required to have a service life of more than 20 years.
Most of the fastener products on the market at present are produced according to the mechanical properties of the fastener, namely the requirements of bolts, screws and studs of ISO898-1, and the standard puts very strict requirements on the mechanical and physical properties of the fastener, wherein the difficulties are mainly the hardness difference of a core surface and the requirements on low-temperature impact toughness. The steel for producing the fastener needs to have good structure uniformity and hardenability, and enough hardening depth can be obtained during quenching, so that the martensite proportion is ensured, and the structure, hardness uniformity and toughness of the final product are ensured to be matched.
Generally, the larger the fastener product specification, the higher the requirements for structural uniformity and hardenability of the steel and the greater the difficulty of production. In the prior art, as the capacity of the fan is continuously increased and the weight of the wind tower is continuously increased, the application specification of the wind power bolt is also continuously increased, and at present, the 10.9-grade wind power bolt is generally manufactured by adopting 42CrMo steel types.
However, if the 42CrMo bolt steel is adopted to manufacture a bolt with the maximum quenching diameter of 42mm or more, the surface of the bolt has great difference with the core performance (the hardness fluctuation reaches 5-8HRC, the core toughness is lower than the index requirement of-40 ℃ or more than 27J), so that the large performance fluctuation can generate local overload in the use process, the bolt is invalid, and serious accidents are easy to cause.
Therefore, the conventional 42CrMo bolt steel used at present can cause great potential safety hazard to fans when being used for manufacturing large-size wind power bolts, and the steel cannot meet the index requirements of bolts with the size of more than 42 mm. Therefore, development of novel bolt steel capable of meeting the requirement of high hardenability of large-size wind power bolts and ensuring stable quality of bolt products is urgently needed.
Based on the problems of the large-size wind power bolt in the prior art, the invention is expected to obtain the steel and the bar for the high-homogeneity high-hardenability wind power bolt, which meet the service safety and stability of the large-size wind power bolt, and the manufacturing method thereof.
Disclosure of Invention
The invention aims to provide the high-homogeneity high-hardenability wind power bolt steel, which can meet the requirements of users on yield strength of more than or equal to 940MPa, tensile strength of more than or equal to 1040MPa, elongation of more than or equal to 10%, area shrinkage of more than or equal to 50%, impact energy Akv2 of more than or equal to 50J at minus 40 ℃ and total section hardness difference of less than or equal to 30HV 10 after tempering through reasonable chemical component design and optimized manufacturing process.
The steel for the wind power bolt has high homogeneity, high hardenability and good toughness, and has wide applicability, good use prospect and value; the steel for the wind power bolt can be used for manufacturing large-size wind power bolts and can replace steel for the wind power bolts such as 42CrMo in the prior art, so that service safety and stability are ensured, and the service life of the wind power bolts is prolonged.
In order to achieve the above object, the invention provides a high-homogeneity high-hardenability steel for wind power bolts, which contains Fe and unavoidable impurities and also contains the following chemical elements in percentage by mass:
C：0.40～0.44％、Si：0.15～0.35％、Mn：0.8～1.0％、Cr：1.2～1.3％、Mo：0.20～0.35％、Ni：0.35～0.45％、Al：0.02～0.05％。
further, in the steel for the high-homogeneity high-hardenability wind power bolt, the mass percentage of each chemical element is as follows:
C:0.40 to 0.44 percent of Si:0.15 to 0.35 percent of Mn:0.8 to 1.0 percent of Cr:1.2 to 1.3 percent of Mo:0.20 to 0.35 percent of Ni:0.35 to 0.45 percent of Al:0.02 to 0.05 percent; the balance being Fe and unavoidable impurities.
In the steel for the high-homogeneity high-hardenability wind power bolt, the design principle of each chemical element is as follows:
c: in the steel for the high-homogeneity high-hardenability wind power bolt, the C element can improve the hardenability of the steel, so that the steel forms a low-temperature phase change structure with higher hardness in the quenching and cooling process. Increasing the content of C element in steel increases the proportion of hard phases such as martensite phase and lower bainite phase of the steel, and increases the strength of the steel, but at the same time, the toughness of the steel is reduced; it should be noted that the content of C element in the steel is not too low, and when the content of C element in the steel is too low, the content of low-temperature transformation structures such as martensite and lower bainite is reduced, and the steel cannot obtain higher tensile strength. Based on the above, in the steel for the high-homogeneity high-hardenability wind power bolt, the mass percentage of the C element is controlled to be between 0.40 and 0.44 percent in consideration of the influence of the C element content on the steel performance.
Si: in the steel for the high-homogeneity high-hardenability wind power bolt, si can replace Fe atoms in the steel in a substitution mode, so that dislocation movement is blocked, and the strength of the steel is improved. In addition, the Si element can reduce the diffusion capability of the C element in ferrite, so that the addition of a proper amount of Si element during tempering can avoid the formation of coarse carbides and precipitation of coarse carbides at defects. It should be noted that the Si element content in the steel is not too high as well, and that a higher Si content lowers the impact toughness of the steel. Based on the above, in the steel for the high-homogeneity high-hardenability wind power bolt, the mass percentage of Si element is controlled to be between 0.15 and 0.35 percent.
Mn: in the high-homogeneity high-hardenability steel for the wind power bolt, mn mainly exists in a solid solution form; in the quenching process of the steel, mn element can inhibit diffusion phase transformation and improve the hardenability of the steel, so that a low-temperature phase transformation structure is formed, and the structure has higher strength. It should be noted that the content of Mn element in the steel is not too high, and too high content of Mn element can form more residual austenite, so that the yield strength of the steel is reduced. Based on the above, in the steel for the high-homogeneity high-hardenability wind power bolt, the mass percentage of Mn element is controlled to be between 0.8 and 1.0 percent.
Cr: in the steel for the high-homogeneity high-hardenability wind power bolt, the addition of a proper amount of Cr element can inhibit the diffusion phase transformation of the steel, improve the hardenability of the steel, form a hardened martensitic structure and obtain the steel with higher strength. Meanwhile, in the heating process, if Cr carbide is not completely dissolved, the effect of inhibiting the growth of austenite grains can be also achieved. It should be noted that the Cr element content in the steel is not excessively high, and when the Cr element content in the steel is excessively high, coarse carbides are formed, deteriorating the impact properties of the steel. Based on the above, in the steel for the high-homogeneity high-hardenability wind power bolt, the mass percentage of Cr element is controlled to be 1.2-1.3%.
Mo: in the steel for the high-homogeneity high-hardenability wind power bolt, mo is ferrite forming element, and the addition of a proper amount of Mo element in the steel is beneficial to improving the hardenability of the steel, so that bainite and martensite are formed in the quenching process of the steel. If the quenching speed is controlled to be faster and the tempering is controlled in a lower temperature range, mo element mainly exists in steel in a solid solution form, and the Mo element can play a solid solution strengthening effect; if tempered in a relatively high temperature range, fine carbides are formed to improve the strength of the steel. It should be noted that Mo is a noble alloying element, and the addition of higher Mo content leads to an increase in cost. Based on the above, in the steel for the high-homogeneity high-hardenability wind power bolt, the mass percentage of the Mo element is controlled to be between 0.20 and 0.35 percent in consideration of the production cost and the beneficial effects of the Mo element.
Ni: in the steel for the high-homogeneity high-hardenability wind power bolt, ni element exists in a solid solution form in the steel, and in the component system, ni exists in an FCC phase of Fe-Ni-Mn, so that the fault energy can be reduced, and the low-temperature impact performance of the steel can be improved. In addition, it should be noted that Ni is an austenite forming element, and it is not preferable to add too high a content of Ni in the steel, which results in too high a content of retained austenite in the steel, reducing the strength of the steel. In addition, the Ni element also belongs to noble metal, and the mass percent of the Ni element is controlled to be between 0.35 and 0.45 percent in the steel for the high-homogeneity high-hardenability wind power bolt, which is considered in terms of production cost.
Al: in the high-homogeneity high-hardenability steel for the wind power bolt, the Al element can form tiny AlN precipitation in the steelmaking process, and the Al element can inhibit the growth of austenite grains in the subsequent cooling process, refine the austenite grains and achieve the effect of fine grain strengthening. It should be noted that the content of Al element in the steel is not too high, which leads to formation of larger Al oxide, and coarse alumina inclusions deteriorate the fatigue properties of the steel. Based on the above, in the steel for the high-homogeneity high-hardenability wind power bolt, the mass percentage of the Al element is controlled to be between 0.02 and 0.05 percent.
Further, in the high-homogeneity high-hardenability steel for wind power bolts according to the present invention, among the unavoidable impurities, each impurity element satisfies at least one of the following: less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.0002 percent of H, less than or equal to 0.002 percent of O, less than or equal to 0.006 percent of N, less than or equal to 0.2 percent of Cu, less than or equal to 0.02 percent of V, less than or equal to 0.02 percent of Ti, less than or equal to 0.004 percent of Ca, and less than or equal to 0.0006 percent of B.
In the above technical scheme of the invention, the high-homogeneity high-hardenability steel for wind power bolts also has impurity elements P, S, H, O, cu, V, ti, ca, N, B, and the upper limit of the elements needs to be controlled in order to ensure the comprehensive mechanical properties of the steel.
Therefore, in the high-homogeneity high-hardenability steel for wind power bolts according to the present invention, it is necessary to control the upper limit of the Cu, V, ti, ca, N, B elements, that is, to control the mass percentage of the elements as follows: less than or equal to 0.2 percent of Cu, less than or equal to 0.02 percent of V, less than or equal to 0.02 percent of Ti, less than or equal to 0.004 percent of Ca, less than or equal to 0.006 percent of N, and less than or equal to 0.0006 percent of B.
Correspondingly, P, S, H and O are also impurity elements in the steel, and the content of the impurity elements in the steel should be reduced as far as possible in order to obtain the steel with better performance and better quality under the condition of technical conditions.
Wherein, the impurity element P is concentrated at the grain boundary, the bonding energy of the grain boundary can be reduced, the low-temperature impact property of the steel is deteriorated, the tempering brittleness of the steel is aggravated by the co-existence of P and Mn, the mass percentage of the chemical element P in the steel is not too high, and the P is required to be controlled to be less than or equal to 0.015 percent.
In addition, the impurity element S can be combined with Mn in steel to generate MnS, the strengthening effect of Mn is weakened, and in the molten steel solidification process, S can be subjected to segregation to form more sulfide inclusions, so that the low-temperature impact performance of the steel is endangered, and therefore, the content of the S element is controlled to be less than or equal to 0.005%.
Correspondingly, the impurity element O can form Al 2O3, tiO and the like with Al and Ti of the steel grade, and the content of the O element in the steel needs to be controlled to be less than or equal to 0.002 percent in order to ensure the uniformity of the steel structure and the low-temperature impact energy.
In addition, the impurity element H is subjected to the hydrostatic pressure field of edge dislocation in steel, and is accumulated at the defect to form hydrogen embrittlement. In steel with high tensile strength level, dislocation, subgrain boundary and other densities are high, if the content of H element in the steel is too high, more H atoms are enriched in defect parts after quenching and tempering heat treatment of the steel, H molecules are formed by H atoms aggregation, and delayed fracture of the steel is caused. Therefore, the content of H element in the present invention is controlled to be H.ltoreq.0.0002%.
Further, in the high-homogeneity high-hardenability steel for wind power bolts according to the present invention, all of the surface microstructure is tempered martensite, the core microstructure is mainly tempered martensite, and a small amount of bainite, ferrite, and pearlite structures are also present.
In the art, the microstructure of the steel for wind power bolts is generally tempered martensite throughout, and thus it is intended to ensure high hardenability. However, tempered martensite, which has a high hardenability throughout its microstructure, also gives a very high risk of cracking to the steel. Based on the above, the technical scheme is that the composition design is supplemented with the adaptive process, so that a small amount of bainite, ferrite and pearlite structures exist in the core part when all the surface microstructure is tempered martensite, and the internal stress of the steel is eliminated, thereby greatly reducing the possibility of cracking the steel.
Further, in the steel for the high-homogeneity high-hardenability wind power bolt, the volume phase proportion of the core tempered martensite exceeds 90%.
Accordingly, another object of the invention is to provide a bar for a wind power bolt, which has excellent performance, high homogeneity and high hardenability, and better toughness, wherein the yield strength of the bar for the wind power bolt is more than or equal to 940MPa, the tensile strength is more than or equal to 1040MPa, the elongation is more than or equal to 10%, the reduction of area is more than or equal to 50%, the impact energy Akv2 at-40 ℃ is more than or equal to 50J, and the total section hardness range after tempering is less than or equal to 30HV 10.
In order to achieve the above object, the invention provides a bar for a wind power bolt, which is made of the steel for a wind power bolt with high homogeneous hardenability.
Further, in the bar for the wind power bolt, the diameter is less than or equal to 90mm.
Further, in the bar for the wind power bolt, the diameter of the bar is 42-90mm.
Further, in the bar for the wind power bolt, the yield strength is more than or equal to 940MPa, the tensile strength is more than or equal to 1040MPa, the elongation is more than or equal to 10%, the area shrinkage is more than or equal to 50%, the impact energy Akv2 at minus 40 ℃ is more than or equal to 50J, and the total section hardness range after tempering is less than or equal to 30HV 10.
In addition, the invention further aims to provide a manufacturing method of the bar for the wind power bolt, which is simple to produce, and the obtained bar has excellent mechanical properties and lower production cost, and has good application prospect and application value.
In order to achieve the above object, the present invention provides a method for manufacturing the bar for a wind power bolt, comprising the steps of:
(1) Smelting and casting;
(2) Heating;
(3) Rolling or forging;
(4) Quenching: controlling austenitizing temperature to be 850-1050 ℃, and quenching by water after austenitizing;
(5) Tempering: the tempering temperature is 520-640 ℃, and the air cooling or the water cooling is carried out after tempering.
In the technical scheme of the invention, the manufacturing method adopts the quenching and high-temperature tempering heat treatment process, so that all the surface microstructure is tempered martensite, the core microstructure is mainly the tempered martensite, and a small amount of bainite, ferrite and pearlite structure exist, so that the high hardenability of the steel grade is ensured, and meanwhile, the internal stress of the steel is eliminated, and the obtained bar has good structural uniformity.
In the quenching operation of the step (4), the steel material can be heated to 850-1050 ℃ for heat preservation and then quenched after being forged or rolled. In the heating process, the carbonitrides of carbide forming elements Mn and Cr can be completely or partially dissolved, and undissolved carbonitrides spike austenite grain boundaries, so that austenite grains are prevented from being too coarse, the purpose of grain refinement after quenching is realized, and the toughness of steel is improved. In the quenching and cooling process, the alloy elements dissolved in the austenite can improve the hardenability of the steel, so that the final martensite is finer, and the structure has good toughness.
Correspondingly, in the step (5) of the invention, the quenched steel can be subjected to high-temperature tempering heat treatment at the tempering temperature of 520-640 ℃, so that the phenomenon of uneven internal stress distribution caused by the formation of bainite and martensite with larger residual austenite and defect density in the quenching process is improved to a greater extent, and the steel is ensured to have good toughness.
Further, in the manufacturing method of the invention, in the step (1), the VD high vacuum time is controlled to be more than or equal to 30 minutes, and the sedation time is controlled to be more than or equal to 30 minutes; the continuous casting adopts the end electromagnetic stirring and light pressing, the electromagnetic stirring frequency of the crystallizer is controlled to be 2.0-3.0 HZ, the current is 280-320A, the end electromagnetic stirring frequency is 6-10 HZ, the current is 550-650A, and the superheat degree during casting is controlled to be 22-38 ℃.
In the technical scheme, in the step (1), molten steel conforming to the chemical components of steel can be smelted by adopting an electric furnace or a converter, high-performance refined synthetic slag is adopted in steelmaking, the quantity and the form of various inclusions of the steel are controlled, harmful inclusions are removed, the VD high vacuum time is controlled to be more than or equal to 30 minutes, and the sedation time is controlled to be more than or equal to 30 minutes.
Accordingly, in the step (1), casting can be die casting or continuous casting, and when continuous casting is adopted, advanced terminal electromagnetic stirring and advanced equipment procedure under light pressure can be adopted, the electromagnetic stirring frequency of the crystallizer is controlled to be 2.0-3.0 HZ, the current is controlled to be 280-320A, the terminal electromagnetic stirring frequency is controlled to be 6-10 HZ, and the current is controlled to be 550-650A so as to control alloy element segregation. Meanwhile, in order to ensure the internal quality of the casting blank, the superheat degree is controlled to be 22-38 ℃ during casting.
Further, in the production method of the present invention, in the step (2), the heating temperature is controlled to 1050 to 1250 ℃.
In the above technical solution, in step (2), the heating temperature may be preferably controlled to 1050 to 1250 ℃ to heat austenitizing. During the heating process, carbide of Mn and Cr in the steel can be partially or completely dissolved in austenite; during subsequent forging or rolling and cooling, al is able to form fine carbonitrides, thereby acting to pin the austenite grain boundaries and refine the rolled structure of the steel. In addition, mn, cr and Mo elements dissolved in austenite can effectively improve the hardenability of steel; in the subsequent quenching process of step (4), mn and Cr elements dissolved in austenite can improve the martensite hardenability at the time of quenching.
Further, in the manufacturing method of the present invention, in the step (3), the finish rolling temperature is controlled to be not less than 800 ℃ or the finish forging temperature is controlled to be not less than 800 ℃.
In the technical scheme, in the step (3), the final rolling temperature is controlled to be more than or equal to 800 ℃ or the final forging temperature is controlled to be more than or equal to 800 ℃, and the steel can be recrystallized and strained to induce precipitation, so that a bainite matrix structure is formed and fine carbonitride precipitation exists.
Compared with the prior art, the steel and the bar for the high-homogeneity high-hardenability wind power bolt and the manufacturing method thereof have the following advantages:
The high-homogeneity high-hardenability wind power bolt steel can be developed through reasonable chemical component design and combination of an optimization process, has good uniformity of a full-section structure, high strength and toughness and high hardenability, and can meet the requirements of users on the wind power bolt steel with small full-section hardness difference and high low-temperature impact energy.
The steel for the high-homogeneity high-hardenability wind power bolt can meet the requirements of users on yield strength of more than or equal to 940MPa, tensile strength of more than or equal to 1040MPa, elongation of more than or equal to 10%, reduction of area of more than or equal to 50%, impact energy Akv2 of more than or equal to 50J at minus 40 ℃ and total section hardness difference of less than or equal to 30HV 10 after hardening and tempering, and can be used for replacing the steel for the wind power bolt such as 42CrMo and the like, and the service life of the bolt is prolonged.
The steel for the high-homogeneity high-hardenability wind power bolt has good hardenability, and the wind power bolt produced by the steel in batches has stable heat treatment quality, high pairing performance among parts and long service life, and has good popularization prospect and practical value.
In addition, the high-homogeneity high-hardenability steel for the wind power bolt can realize batch commercial production on a bar production line.
The bar material prepared from the high-homogeneity high-hardenability wind power bolt steel has the advantages of ensuring excellent mechanical properties, and simultaneously having lower cost, and the yield strength is more than or equal to 940MPa; tensile strength is more than or equal to 1040MPa; the elongation is more than or equal to 10 percent; the area reduction rate is more than or equal to 50 percent; impact energy Akv2 at minus 40 ℃ is more than or equal to 50J; after tempering, the hardness difference of the whole cross section is less than or equal to 30HV 10.
Correspondingly, the manufacturing method disclosed by the invention is simple in production process, and the bar obtained by the manufacturing method has excellent mechanical property and full-section structure, is low in production cost and wide in applicability, and can bring great economic benefit.
Drawings
Fig. 1 is a photograph of microstructure of a rolled core of a bar for a wind power bolt of example 1.
Fig. 2 is a photograph of the microstructure of the core of the bar for a wind power bolt of example 1 after quenching and tempering heat treatment.
Fig. 3 is a graph showing the measured hardenability of the bar for a wind power bolt of example 1 and the bar for comparison of comparative example 1.
Detailed Description
The steel for the uniform high-hardenability wind power bolt, the steel bar and the manufacturing method thereof are further explained and illustrated below by referring to the attached drawings and specific examples, but the explanation and the illustration do not limit the technical scheme of the invention in a proper way.
Examples 1 to 6 and comparative example 1
The bars for wind power bolts of examples 1 to 6 and the comparative bar of comparative example 1 were each prepared by the following steps:
(1) Smelting and casting were performed according to the chemical compositions shown in the following table 1:
Smelting by adopting an electric furnace or a converter to obtain molten steel conforming to the chemical components of steel, refining the synthetic slag with high performance in steelmaking, controlling the quantity and the form of various inclusions of the steel, simultaneously removing harmful inclusions, controlling the VD high vacuum time to be more than or equal to 30 minutes, and controlling the sedation time to be more than or equal to 30 minutes; molten steel obtained by smelting can be cast into a continuous casting blank or a steel ingot, and in the casting process, die casting or continuous casting can be adopted; the continuous casting can adopt advanced terminal electromagnetic stirring and advanced equipment working procedures under light pressure, the electromagnetic stirring frequency of a crystallizer is controlled to be 2.0-3.0 HZ, the current is 280-320A, the terminal electromagnetic stirring frequency is 6-10 HZ, the current is 550-650A, and the superheat degree during casting is controlled to be 22-38 ℃.
(2) Heating: the heating temperature is controlled to be 1050-1250 ℃.
(3) Rolling or forging: the final rolling temperature is controlled to be more than or equal to 800 ℃ or the final forging temperature is controlled to be more than or equal to 800 ℃. If forging is performed, the final dimension may be directly forged in the forging process. If rolling is performed, in the rolling process, the billet may be directly rolled to a final gauge, or the billet may be rolled to a specified intermediate billet size, and then heated and rolled to a final finished product size.
(4) Quenching: controlling austenitizing temperature at 850-1050 deg.C, and water quenching after austenitizing.
(5) Tempering: the tempering temperature is 520-640 ℃, and the air cooling or the water cooling is carried out after tempering.
In the invention, the bars for the wind power bolts of the embodiments 1-6 are prepared by adopting the steps, and the chemical components and the related technological parameters of the bars meet the control requirements of the design specification of the invention.
The comparative bars of comparative example 1 were also employed: smelting and casting, heating, forging or rolling, quenching and tempering. However, the chemical element composition of comparative example 1, which is 42CrMo of the conventional wind power bolt steel, has parameters that fail to meet the design requirements of the present invention, and the specific chemical composition thereof can be seen in the following table 1.
The bars for the wind power bolts of examples 1 to 6 are all made of the steel for the wind power bolts with high homogeneity and high hardenability according to the invention, and the bar for the comparative example 1 is made of the steel 42CrMo for the conventional wind power bolts.
Table 1 shows the mass percentages of the chemical elements of the high-homogeneity high-hardenability steel for wind power bolts used in examples 1 to 6 and the conventional steel for wind power bolts 42CrMo used in comparative example 1.
Table 1 (wt.%) Fe and other unavoidable impurities other than P, S, H, O, N, cu, V, ti, ca and B
Tables 2-1 and 2-2 list specific process parameters of bars for wind power bolts of examples 1-6 and comparative bars of comparative example 1.
Table 2-1.
Table 2-2.
The obtained bars for wind power bolts of examples 1-6 and the comparative bars of comparative example 1 were sampled respectively, and subjected to mechanical property tests, and the obtained property test results are shown in Table 3-1, respectively, and each of the bars of examples and comparative examples adopts GB/T228.1-2010 section 1 of tensile test for metallic materials: testing in a room temperature test method to obtain the tensile strength, the yield strength, the elongation and the area reduction of the bars of each example and the comparative example; the test was carried out in the manner of GB/T229-2007 "method of metal Charpy notch impact test" to detect the longitudinal impact energy of the bars of each example and comparative example.
Table 3-1 shows the results of mechanical property tests of the bars for wind power bolts of examples 1-6 and the comparative bars of comparative example 1.
Table 3-1.
Correspondingly, in order to further verify the performance of the bars for wind power bolts according to the present invention, the bars for wind power bolts of examples 1 to 6 and the comparative bars of comparative example 1 may be sampled again, and the bars of each example and comparative example may be quenched and tempered according to GB/T4340-2009 Vickers hardness test part 1: test method 90 points of hardness test were carried out with a pressure of 10Kg in two diametrical directions at an interval of 2mm each to obtain the full-section hardness and the full-section hardness of the bars of each of the examples and comparative examples were extremely poor, and the results of the related tests are shown in the following tables 3-2.
Table 3-2 shows the post-tempering full-section hardness and the full-section hardness of the bars for wind power bolts of examples 1-6 and the comparative bar of comparative example 1 are extremely poor.
Table 3-2.
As can be seen from the above Table 3-1, the wind power bolt bars of examples 1-6 all have yield strengths of 987-1065MPa, tensile strengths of 1084-1180MPa, elongation of 14.5% -18.5%, reduction of area of 58% -63%, and longitudinal impact energy Akv2 of-40 ℃ of 57-80J, and have excellent mechanical properties. As can be seen from Table 3-2, the bars for wind power bolts of examples 1-6 have a total section hardness range of 30HV 10 or less after tempering, and a total section hardness range of 22-29 and a uniform structure.
Compared with the bars for wind power bolts of the embodiments 1-6, the bars of the comparative example 1 are obviously poorer in mechanical property and uniformity of the whole cross-section structure, the impact energy Akv2 of the bars at the temperature of minus 40 ℃ is only 35J, and the whole cross-section hardness is extremely worse than that of the embodiments 1-6.
Fig. 1 is a photograph of microstructure of a rolled core of a bar for a wind power bolt of example 1.
As shown in fig. 1, in this embodiment, the microstructure of the rolled core of the bar for a wind turbine bolt according to example 1 of the present invention is mainly composed of bainite, and a small amount of martensite is present.
Fig. 2 is a photograph of the microstructure of the core of the bar for a wind power bolt of example 1 after quenching and tempering heat treatment.
As shown in fig. 2, in this embodiment, the core microstructure morphology of the bar for wind turbine bolts according to example 1 of the present invention after quenching and tempering heat treatment is mainly tempered martensite, and a small amount of bainite and ferrite pearlite structure are present.
Fig. 3 is a graph showing the measured hardenability of the bar for a wind power bolt of example 1 and the bar for comparison of comparative example 1.
As can be seen from fig. 3, in the bar for wind power bolts produced from the steel for wind power bolts having high homogeneity and high hardenability in example 1, the hardness was reduced from 57.4HRC to 47HRC and 10.4HRC from J1.5 (1.5 mm from the end) to J50 (50 mm from the end); whereas the hardness of the comparative rod of comparative example 1 was reduced from 56.6HRC to 37HRC from J1.5 to J50, 19.6HRC was reduced; the curve of example 1 has a flatter downward trend than the curve of comparative example 1 in terms of the hardenability curve, so that the hardenability of example 1 is significantly better than that of the bar of comparative example 1.
From the above, it can be seen that the high-homogeneity high-hardenability steel for wind power bolts can be developed with good uniformity of the whole-section structure, high strength and toughness and high hardenability through reasonable chemical composition design and combination of optimization process, and can meet the requirements of users on the steel for wind power bolts with small whole-section hardness difference and high low-temperature impact energy.
Meanwhile, the steel for the high-homogeneity high-hardenability wind power bolt has good hardenability, and the wind power bolt produced by the steel in batches has stable heat treatment quality, high pairing performance among parts and long service life, and has good popularization prospect and practical value.
In addition, the steel for the high-homogeneity high-hardenability wind power bolt can meet the requirements of users on the yield strength of more than or equal to 940MPa, the tensile strength of more than or equal to 1040MPa, the elongation of more than or equal to 10%, the reduction of area of more than or equal to 50%, the impact energy Akv2 of minus 40 ℃ of more than or equal to 50J and the total section hardness difference after hardening and tempering of less than or equal to 30HV 10, and can be used for replacing the steel for the wind power bolt such as 42CrMo and the like, and the service life of the bolt is prolonged.
In addition, the high-homogeneity high-hardenability steel for the wind power bolt can realize batch commercial production on a bar production line. The bar material prepared from the high-homogeneity high-hardenability wind power bolt steel has the advantages of ensuring excellent mechanical properties, and simultaneously having lower cost, and the yield strength is more than or equal to 940MPa; tensile strength is more than or equal to 1040MPa; the elongation is more than or equal to 10 percent; the area reduction rate is more than or equal to 50 percent; impact energy Akv2 at minus 40 ℃ is more than or equal to 50J; after tempering, the hardness difference of the whole cross section is less than or equal to 30HV 10.
Correspondingly, the manufacturing method disclosed by the invention is simple in production process, and the bar obtained by the manufacturing method has excellent mechanical property and full-section structure, is low in production cost and wide in applicability, and can bring great economic benefit.
It should be noted that the combination of the technical features in the present invention is not limited to the combination described in the claims or the combination described in the specific embodiments, and all the technical features described in the present invention may be freely combined or combined in any manner unless contradiction occurs between them.
It should also be noted that the above-recited embodiments are merely specific examples of the present invention. It is apparent that the present invention is not limited to the above embodiments, and similar changes or modifications will be apparent to those skilled in the art from the present disclosure, and it is intended to be within the scope of the present invention.
Claims (12)
1. The high-homogeneity high-hardenability steel for the wind power bolt contains Fe and unavoidable impurities, and is characterized by further comprising the following chemical elements in percentage by mass:
C：0.40～0.44％、Si：0.15～0.35％、Mn：0.8～1.0％、Cr：1.2～1.3％、Mo：0.20～0.35％、Ni：0.35～0.45％、Al：0.02～0.05％；
The microstructure of the surface layer is all tempered martensite, the microstructure of the core part is mainly tempered martensite, and a small amount of bainite, ferrite and pearlite structures are also present.
2. The high-homogeneity high-hardenability steel for wind power bolts according to claim 1, wherein the steel comprises the following chemical elements in percentage by mass:
C:0.40 to 0.44 percent of Si:0.15 to 0.35 percent of Mn:0.8 to 1.0 percent of Cr:1.2 to 1.3 percent of Mo:0.20 to 0.35 percent of Ni:0.35 to 0.45 percent of Al:0.02 to 0.05 percent; the balance being Fe and unavoidable impurities.
3. The high-homogeneity and high-hardenability steel for a wind power bolt according to claim 1 or 2, wherein each impurity element satisfies at least one of the following among unavoidable impurities: less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.0002 percent of H, less than or equal to 0.002 percent of O, less than or equal to 0.006 percent of N, less than or equal to 0.2 percent of Cu, less than or equal to 0.02 percent of V, less than or equal to 0.02 percent of Ti, less than or equal to 0.004 percent of Ca, and less than or equal to 0.0006 percent of B.
4. The high-homogeneity and high-hardenability steel for a wind power bolt according to claim 1, wherein the volume phase proportion of the core tempered martensite exceeds 90%.
5. A bar for wind power bolts, which is produced from the steel for high-homogeneity-hardenability wind power bolts according to any one of claims 1 to 4.
6. The bar for wind power bolts of claim 5, wherein the bar has a diameter of 90mm or less.
7. The bar for wind power bolts according to claim 6, wherein the diameter is 42-90mm.
8. The bar for wind power bolts according to claim 5, wherein the yield strength is not less than 940MPa, the tensile strength is not less than 1040MPa, the elongation is not less than 10%, the area shrinkage is not less than 50%, the impact energy Akv2 at-40 ℃ is not less than 50J, and the total section hardness range after tempering is not more than 30HV 10.
9. The method for manufacturing a bar for a wind power bolt according to any one of claims 5 to 8, comprising the steps of:
(1) Smelting and casting;
(2) Heating;
(3) Rolling or forging;
(4) Quenching: controlling austenitizing temperature to be 850-1050 ℃, and quenching by water after austenitizing;
(5) Tempering: the tempering temperature is 520-640 ℃, and the air cooling or the water cooling is carried out after tempering.
10. The method of claim 9, wherein in step (1), VD high vacuum time is controlled to 30 minutes or more and sedation time to 30 minutes or more; the continuous casting adopts the end electromagnetic stirring and light pressing, the electromagnetic stirring frequency of the crystallizer is controlled to be 2.0-3.0 HZ, the current is 280-320A, the end electromagnetic stirring frequency is 6-10 HZ, the current is 550-650A, and the superheat degree during casting is controlled to be 22-38 ℃.
11. The method according to claim 9, wherein in the step (2), the heating temperature is controlled to be 1050 to 1250 ℃.
12. The method according to claim 9, wherein in the step (3), the finish rolling temperature is controlled to not less than 800 ℃ or the finish forging temperature is controlled to not less than 800 ℃.
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