Quenched and tempered steel for large-specification wind power fasteners and preparation method of quenched and tempered steel

Abstract

The invention relates to quenched and tempered steel for a large-specification wind power fastener. The fastener steel comprises the following chemical components in percentage by mass: 0.38 to 0.45 percent of C, 0.22 to 0.30 percent of Si, 1.52 to 1.60 percent of Mn, less than or equal to 0.011 percent of P, 0.008 to 0.025 percent of S, 0.55 to 0.65 percent of Ni, 1.21 to 1.31 percent of Cr, 0.50 to 0.58 percent of Mo and the balance of Fe and inevitable impurity elements. The whole technological process comprises the steps of burdening, KR molten iron pretreatment, converter or electric furnace smelting, LF refining (sulfide denaturation treatment), degassing, continuous casting, warm conveying to a heating furnace, heating, high-pressure water descaling, rolling, waste heat quenching treatment, tempering, turning, packaging and warehousing. The diameter of the fastener steel ranges from 80 mm to 130 mm, the martensite content of the core area after overall quenching reaches 90% or above, the core-surface hardness difference after quenching is controlled within 3 HRC, and the fastener steel achieves large specification, high dimensional precision and excellent comprehensive mechanical performance at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of special steel smelting, and particularly relates to a quenched and tempered steel for large-size wind power fasteners and a preparation method thereof. Background Art

[0002] Fasteners are a type of mechanical parts used for fastening connections and are extremely widely used. They are mainly used in machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, meters and daily necessities. With the decreasing non-renewable energy such as oil, new renewable green energy is receiving more and more attention. As a green energy, wind power has the advantages of no pollution, low power generation cost and short construction period of wind farms. It has gradually developed and grown at the end of the last century. With the continuous exploration of wind power projects, wind power technology has become increasingly mature, product quality is reliable, and the availability rate is over 95%. It is a safe and reliable energy source. my country has abundant wind energy resources and can learn from mature foreign technologies. Vigorously developing wind energy projects is the future development trend.

[0003] With the increase in wind turbine power, new requirements have been put forward for the load-bearing capacity of fasteners. The steel used for wind power fasteners has gradually developed towards high strength and large specifications. Fasteners bear various axial tensile loads, shear loads or bending loads, as well as impact loads; or they bear the above loads at the same time. Under the influence of environmental media, the fasteners may also cause delayed fracture. Therefore, the industry has strict requirements on the raw materials of high-strength steel used for wind power fasteners. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a large-size quenched and tempered steel for wind power fasteners and a preparation method thereof in response to the above-mentioned prior art. Based on the existing mature quenched and tempered steel for wind power fasteners, the specifications of the quenched and tempered steel for fasteners are expanded, and the comprehensive mechanical performance requirements of 10.9 grade quenched and tempered steel for fasteners are met through reasonable composition design.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problem is: a quenched and tempered steel for large-size wind power fasteners, the chemical composition of the quenched and tempered steel for fasteners is C: 0.38-0.45%, Si: 0.22-0.30%, Mn: 1.52-1.60%, P: ≤0.011%, S: 0.008-0.025%, Ni: 0.55-0.65%, Cr: 1.21-1.31%, Mo: 0.50-0.58%, and the balance is Fe and unavoidable impurity elements.

[0006] The diameter of the quenched and tempered steel is in the range of 80 to 130 mm.

[0007] The chemical composition of the quenched and tempered steel for large-size wind power fasteners of the present invention is determined as follows:

[0008] C: It is an essential element to ensure the strength and hardness of steel, but its plasticity and toughness will be worse. Considering the strength and toughness of quenched and tempered steel for fasteners, the present invention controls the carbon content to 0.38-0.45%.

[0009] Si: Adding silicon as a reducing agent and deoxidizer during the steelmaking process is beneficial to the deoxidation of molten steel, thereby improving the purity of the material; silicon dissolves in ferrite in steel to increase the strength and hardness of the steel. Too high Si will increase the brittleness of the steel. Taking all factors into consideration, the silicon content in the present invention is controlled to be 0.22-0.30%.

[0010] Mn: is an element that improves the hardenability of steel, so that the fastener product can be fully hardened during heat treatment, ensuring the uniformity of the overall mechanical properties of the material. Therefore, the Mn content of the present invention is controlled to be 1.52-1.60%.

[0011] Ni: Ni is a non-carbide forming element. Ni exists in steel in the form of solid solution, which can significantly improve the hardenability of steel. Nickel can improve the strength of steel while maintaining good plasticity and toughness. However, Ni is a precious metal. Adding too much Ni will increase the production cost of the material and reduce the market competitiveness of the product. The present invention controls its content to 0.55-0.65%.

[0012] Cr: It is a medium carbide-forming element. When heated, Cr dissolved in austenite strongly improves hardenability. Part of Cr in steel replaces iron to form alloy cementite, improving stability; part of Cr is dissolved in ferrite, playing a role of solid solution strengthening, improving the strength and hardness of ferrite. The present invention controls its content to 1.21-1.31%.

[0013] Mo: It exists in the solid solution and carbide of steel, has a solid solution strengthening effect, can improve the hardenability and tempering stability of steel, and can also refine the grains and improve the inhomogeneity of carbides, thereby improving the strength and toughness of steel. Mo is also a precious metal. Too high a content will increase the cost and reduce the market competitiveness of the product. In the present invention, the content of Mo is controlled at 0.50-0.58%.

[0014] P: It is a harmful impurity element in steel, which is easy to form defects such as segregation and inclusion. As an impurity element, it will have an adverse effect on the toughness of steel (especially the toughness of the core), and its content should be reduced as much as possible. In the present invention, P is controlled to be ≤0.011%.

[0015] S: Traditionally, S is a harmful impurity in steel. Steel with a high sulfur content is prone to brittle cracking when subjected to pressure processing at high temperatures, which is usually called hot brittleness. However, the present invention adds enough Mn, and manganese can form high-melting-point MnS with sulfur, eliminating the harmful effects of sulfur. However, the increase in sulfur content improves the cutting performance of the material, making the production of the final fastener smoother during threading. The present invention controls the S content to 0.008-0.025%.

[0016] The technical solution of the present invention to solve another technical problem is a method for manufacturing the above-mentioned large-size wind power fasteners quenched and tempered steel, the entire process flow is: batching → KR molten iron pretreatment → converter or electric furnace smelting → LF refining (sulfide modification treatment) → degassing → continuous casting → warm delivery to heating furnace → heating → high-pressure water descaling → rolling → residual temperature quenching treatment → tempering → turning → packaging → warehousing.

[0017] The specific contents of the above process steps are as follows:

[0018] The smelting raw materials are sequentially subjected to KR hot metal pretreatment, converter or electric furnace smelting, LF refining, RH or VD degassing and continuous casting to obtain ingots that meet the chemical composition requirements. In order to prevent the refining temperature from returning to P, a slag-stripping process is adopted after the converter is tapped to remove the slag on the surface of the molten steel. After the molten steel is transferred to the refining furnace, lime (main component CaO) is added to the surface of the molten steel again for further P removal. After the slag-stripping process is adopted again, refining and degassing are carried out. During refining, a sulfide modification treatment technology is adopted. During the refining process, calcium elements are added to the molten steel by feeding Ca-Si wire into the molten steel to modify the sulfides in the steel. During the solidification process of the molten steel, the high-melting-point CaS particles formed in advance can inhibit the total amount and aggregation degree of MnS generated by the molten steel in this process, and modify part or all of the MnS into CaS, that is, forming a fine, single CaS phase or a composite phase with MnS. This reduces the amount of manganese sulfide inclusions generated, and compounds fine, non-deformable CaS or calcium aluminate particles in the matrix of residual manganese sulfide inclusions, turning the originally easy-to-form strip-shaped inclusions with a large aspect ratio into inclusions with a small aspect ratio and relatively dispersed distribution, making the sulfides fine and evenly distributed in the molten steel, which is more conducive to improving the processing performance of the material; after the molten steel is continuously cast, in order to improve the production efficiency, the ingot can be warmed to the heating furnace at a temperature of 300-450℃; the preheating section temperature of the steel rolling is 650-800℃, and the heating section temperature is 900-1 050℃, the temperature of the soaking section is 1200-1270℃, and it is kept warm for 6-8 hours before being taken out of the furnace; after descaling with high-pressure water, it is rolled, the rough rolling temperature is ≥1020℃, and the final rolling temperature is 900-940℃; in order to improve production efficiency, after the final rolling, the residual temperature of the material is used for quenching, the quenching temperature is 860℃-900℃, and the quenched material must be tempered within 12 hours, the tempering temperature is 580-640℃, and it is water-cooled; the heat-treated material is lathed and polished to ensure that the dimensional accuracy of the material meets the h9 level required by the GB / T3207 standard.

[0019] Compared with the prior art, the advantages of the present invention are:

[0020] (1) The present invention adopts a brand-new composition design. On the basis of the traditional fastener steel composition, the content of alloy elements such as Mn, Ni, Mo, and Cr is greatly increased. On the one hand, the hardenability of the material is increased, and the difference in hardness between the core and the surface of the material after quenching is controlled within 3HRC. On the other hand, the addition of Ni and Mo alloys can improve the toughness of the material.

[0021] (2) For the first time, the smelting method of "twice slag removal + twice P removal" was used to produce fastener steel, which greatly reduced the P content of the material and improved the toughness of the material.

[0022] (3) Sulfide modification technology was first applied to the production of fastener steel, making the sulfides in the steel fine and evenly distributed, improving the cutting performance of the material.

[0023] (4) The residual temperature quenching method greatly improves the production efficiency of quenched and tempered materials while reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the hardness distribution diagram of the entire cross section of the 90mm material in Example 1 of the present invention after quenching.

[0025] Figure 2 This is the hardness distribution diagram of the entire cross section of the 130mm material of Example 2 of the present invention after quenching. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is described in more detail in conjunction with the preferred embodiments of the present invention. However, these embodiments are only descriptions of the preferred implementation methods of the present invention and cannot impose any limitation on the scope of the present invention.

[0027] Example 1

[0028] The diameter of the large-sized quenched and tempered steel for wind power fasteners involved in this embodiment is 90 mm, and its chemical composition is as follows by mass percentage: C: 0.42%, Si: 0.27%, Mn: 1.55%, P: 0.010%, S: 0.015%, Ni: 0.60%, Cr: 1.26%, Mo: 0.54%, and the remainder is Fe and unavoidable impurity elements.

[0029] The manufacturing process of the fastener steel is as follows: the smelting raw materials are sequentially subjected to KR molten iron pretreatment, electric furnace smelting, LF refining, VD degassing and continuous casting to obtain ingots that meet the chemical composition requirements. In order to prevent the refining temperature from returning to P, a slag-stripping process is used after the converter is tapped to remove the slag on the surface of the molten steel. After the molten steel is transferred to the refining furnace, lime (main component CaO) is added to the surface of the molten steel again for further P removal. After the slag-stripping process is used again, refining and degassing are carried out. During refining, a sulfide modification treatment technology is used to make the sulfide become fine and evenly distributed in the molten steel, which is more conducive to reducing the rebound force of the material when welding the top to ensure the stability of the weld quality. After the molten steel is continuously cast, in order to improve production efficiency, the ingot can be The billet is sent to the heating furnace at a temperature of 403°C; the preheating section temperature of the steel rolling mill is 740°C, the heating section temperature is 998°C, the soaking section temperature is 1232°C, and it is kept warm for 6.2 hours before being taken out of the furnace; it is rolled after descaling with high-pressure water, the rough rolling temperature is 1032°C, and the final rolling temperature is 922°C. In order to improve production efficiency, after the final rolling, the material is quenched using the residual temperature, and the actual quenching temperature is 890°C. The quenched material is tempered about 3 hours later, with a tempering temperature of 600°C and water cooling; the heat-treated material is lathed and polished, and the final dimensional accuracy of the material is -0.062~0mm.

[0030] The quenched and tempered material for fasteners produced by the above manufacturing process has high strength and toughness. The specific performance indicators are shown in Table 1 of the attached figure, and the hardness distribution after quenching is shown in the attached figure. Figure 1 .

[0031] Example 2

[0032] The diameter of the large-size quenched and tempered steel for wind power fasteners involved in this embodiment is 130 mm, and its chemical composition is as follows by mass percentage: C: 0.41%, Si: 0.29%, Mn: 1.54%, P: 0.009%, S: 0.013%, Ni: 0.59%, Cr: 1.24%, Mo: 0.55%, and the remainder is Fe and unavoidable impurity elements.

[0033] The manufacturing process of the fastener steel is as follows: the smelting raw materials are sequentially subjected to KR molten iron pretreatment, electric furnace smelting, LF refining, VD degassing and continuous casting to obtain ingots that meet the chemical composition requirements. In order to prevent the refining temperature from returning to P, a slag-stripping process is used after the converter is tapped to remove the slag on the surface of the molten steel. After the molten steel is transferred to the refining furnace, lime (main component CaO) is added to the surface of the molten steel again for further P removal. After the slag-stripping process is used again, refining and degassing are carried out. During refining, a sulfide modification treatment technology is used to make the sulfide become fine and evenly distributed in the molten steel, which is more conducive to reducing the rebound force of the material when welding the top to ensure the stability of the weld quality. After the molten steel is continuously cast, in order to improve production efficiency, the ingot can be The billet is sent to the heating furnace at a temperature of 405°C; the preheating section temperature of the steel rolling mill is 745°C, the heating section temperature is 992°C, the soaking section temperature is 1230°C, and it is kept warm for 6.0 hours before being taken out of the furnace; it is rolled after descaling with high-pressure water, the rough rolling temperature is 1028°C, and the final rolling temperature is 914°C. In order to improve production efficiency, after the final rolling, the material is quenched using the residual temperature, and the actual quenching temperature is 885°C. The quenched material is tempered about 4 hours later, with a tempering temperature of 600°C and water cooling; the heat-treated material is lathed and polished, and the final dimensional accuracy of the material is -0.075~0mm.

[0034] The quenched and tempered material for fasteners produced by the above manufacturing process has high strength and toughness. The specific performance indicators are shown in Table 1 of the attached figure, and the hardness distribution after quenching is shown in the attached figure. Figure 2 .

[0035] Table 1 Mechanical properties of materials (processed and sampled according to fastener standard ISO 898-1-2013)

[0036] Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A quenched and tempered steel for large-size wind power fasteners, characterized in that: The chemical composition of the fastener steel is, by mass percentage, C: 0.38-0.45%, Si: 0.22-0.30%, Mn: 1.52-1.60%, P: ≤0.011%, S: 0.008-0.025%, Ni: 0.55-0.65%, Cr: 1.21-1.31%, Mo: 0.50-0.58%, and the remainder is Fe and unavoidable impurity elements.

2. The quenched and tempered steel for large-size wind power fasteners according to claim 1, characterized in that: The diameter of the quenched and tempered steel is 80-130 mm, the martensite content of the core area after overall quenching reaches more than 90%, and the hardness difference between the core and the surface after quenching is controlled within 3HRC.

3. The quenched and tempered steel for large-size wind power fasteners according to claim 1, characterized in that: The mechanical properties of the quenched and tempered steel meet the requirements of yield strength ≥940MPa, tensile strength ≥1040Mpa, elongation ≥9%, shrinkage ≥48%, and impact energy ≥27J.

4. A method for preparing large-sized quenched and tempered steel for wind power fasteners according to claim 1, characterized in that: The method comprises the following steps: 1) The smelting raw materials are sequentially subjected to KR molten iron pretreatment, converter or electric furnace smelting, LF refining, RH or VD degassing and continuous casting to obtain a casting billet that meets the chemical composition requirements; 2) The temperature of the preheating section of the rolled steel is 650-800℃, the temperature of the heating section is 900-1050℃, the temperature of the soaking section is 1200-1270℃, and the steel is kept warm for 6-8 hours before being taken out of the furnace; 3) After descaling by high-pressure water, rolling is carried out, the rough rolling temperature is ≥1020℃, and the final rolling temperature is 900-940℃; 4) After the final rolling, the material is quenched at the residual temperature of 860℃-900℃. The quenched material must be tempered within 12 hours at a tempering temperature of 580-640℃ and water-cooled; 5) The heat-treated material is processed by lathing and polishing to ensure that the dimensional accuracy of the material meets the h9 level required by the GB / T3207 standard.

5. The method for preparing a large-sized quenched and tempered steel for wind power fasteners according to claim 4, characterized in that: After continuous casting, the molten steel is warm-transferred to a heating furnace at a temperature of 300-450°C.

6. The method for preparing a large-sized quenched and tempered steel for wind power fasteners according to claim 4, characterized in that: In order to prevent the refining temperature from returning to P, the slag removal process is used to remove the slag on the surface of the molten steel after the converter is tapped. After the molten steel is transferred to the refining furnace, lime is added to the surface of the molten steel again for further P removal. After the slag removal process is used again, refining and degassing are carried out.

7. The method for preparing a large-sized quenched and tempered steel for wind power fasteners according to claim 4, characterized in that: During the refining process, calcium is added to the molten steel by feeding Ca-Si wire into the molten steel to denature the sulfides in the steel.

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