Wind power fastener steel and production method thereof

Abstract

The invention belongs to the technical field of steel manufacturing in the metallurgical industry, and particularly relates to wind power fastener steel and a production method thereof. The wind power fastener steel comprises the following components in percentage by weight: 0.38 to 0.45 percent of C, 0.50 to 0.80 percent of Mn, 0.17 to 0.37 percent of Si, 0.15 to 0.25 percent of Mo, 0.90 to 1.20 percent of Cr, 0.30 to 0.50 percent of Ni, less than or equal to 0.020 percent of P, less than or equal to 0.020 percent of S, less than or equal to 0.20 percent of Cu and the balance of Fe. The method comprises the steps of smelting, refining, vacuum degassing, continuous casting, continuous rolling and wind power fastener steel machining. The Ni element is creatively added, technological operation is combined, the impact energy of the wind power fastener steel material is 50 J or above, the highest impact energy reaches 72.7 J and far exceeds the low-temperature impact energy of a conventional material, the remarkable technical effect is achieved, and wide market application prospects are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel manufacturing in the metallurgical industry, and specifically relates to a wind power fastener steel and a production method thereof. Background Art

[0002] The chemical composition of steel used to manufacture wind power fasteners is generally designed to be CrMo alloy steel. The representative steel grade is GB / T3077-2015 standard 42CrMoA. The chemical composition of 42CrMoA is designed to be C: 0.38~0.45%, Mn: 0.50~0.80%, Si: 0.17~0.37%, Mo: 0.15~0.25%, Cr: 0.90~1.20%, Ni: ≤0.30%, P: ≤0.020%, S: ≤0.020%, Cu: ≤0.20%, and the rest is Fe and unavoidable impurities.

[0003] However, the low-temperature impact energy -45℃ and AKV2 of materials produced by the current composition design can generally only reach about 27-35J (the average value is 30J) after tempering heat treatment. For users with high requirements for low-temperature impact energy (low-temperature impact energy -45℃ AKV2 ≥ 35J), it is difficult to meet the needs of users with GB / T 3077-2015 standard 42CrMoA composition design. Wind power fastener heat treatment plants are often required to rescue unqualified materials through secondary tempering heat treatment, which not only causes a large waste of costs, but also greatly reduces the production efficiency of fastener plants, becoming a pain point in the wind power fastener industry. Summary of the invention

[0004] The purpose of the present invention is to overcome the technical defects existing in the prior art and provide a wind power fastener steel and a production method thereof, which improves the uniformity of material structure, increases the stacking fault energy of the material, improves the notch sensitivity of the material, and thereby improves the low-temperature impact performance of the material through chemical composition design.

[0005] In order to achieve the above objectives, the present invention adopts the following scheme:

[0006] Firstly, a wind power fastener steel is provided, which is composed of the following components in weight percentage:

[0007] C: 0.38-0.45%, Mn: 0.50-0.80%, Si: 0.17-0.37%, Mo: 0.15-0.25%, Cr: 0.90-1.20%, Ni: 0.30-0.50%, P: ≤0.020%, S: ≤0.020%, Cu: ≤0.20%, and the rest is Fe and unavoidable impurities; the low-temperature impact energy of the wind power fastener steel is -45°C and AKV2 is not less than 50J.

[0008] The composition design of the present invention is to creatively add Ni element on the basis of the composition of 42CrMoA product standard GB / T 3077-2015, and further control the Ni element content to be 0.30% to 0.50%. Nickel is the most effective element for improving the low-temperature toughness of steel; nickel and iron can be infinitely solid-dissolved, and are elements that form and stabilize austenite, which can improve the hardenability of steel, improve the uniformity of the material structure after steel quenching and tempering heat treatment, and improve the low-temperature toughness of the material. At the same time, nickel can improve the stacking fault energy of the material, promote the cross-slip of spiral dislocations at low temperatures, increase the work consumed by crack expansion, and improve the impact toughness of steel under low temperature conditions. Moreover, nickel can also strengthen ferrite and refine and increase pearlite, improve the strength of steel, and do not significantly reduce the plasticity of steel. However, too high a nickel content will also reduce the stability of carbonitrides and reduce tempering resistance; at the same time, nickel is a relatively expensive metal, and too high a dosage will also increase the cost of steel. Therefore, the preferred content of Ni in the present invention is 0.30% to 0.50%.

[0009] The present invention improves the low-temperature impact energy of the material by increasing the hardenability of the material, improving the uniformity of the material structure, and increasing the stacking fault energy of the material through the Ni element, thereby achieving unexpected technical effects.

[0010] In addition, impurity elements such as P and S tend to segregate at grain boundaries, greatly increasing the brittleness of steel and reducing the impact toughness of the material. This effect is more serious in a low-temperature environment, and its content needs to be reduced as much as possible. The present invention has implemented more stringent control over P and S.

[0011] The present invention also provides a method for producing wind power fastener steel, comprising the following steps:

[0012] (1) Converter smelting:

[0013] The smelting is carried out in a top and bottom combined blowing basic converter, and the converter smelting endpoint is controlled, with target S≤0.015%; target P≤0.015%; and target tapping temperature≥1600℃;

[0014] (2) Refining:

[0015] Based on step (1), the molten steel after converter smelting is refined in an LF refining furnace, and after the submerged arc is stable, lime and fluorite are added to adjust the slag fluidity; the white slag retention time is ≥20min;

[0016] The amount of lime and fluorite added is calculated based on the total amount of refined molten steel, and the relevant additives are as follows: lime 0-2kg / t, fluorite 0-2kg / t.

[0017] (3) VD vacuum degassing:

[0018] After LF refining in step (2), vacuum degassing is performed using VD degassing equipment, with a vacuum degree of ≤67pa and a holding time of ≥10min; ensuring that [H]≤1.5ppm and [O]≤20ppm when breaking the air; and the soft blowing time is not less than 15 minutes;

[0019] (4) Continuous casting:

[0020] After the VD vacuum degassing treatment in step (3), a continuous casting machine is used to protect the casting throughout the whole process, and the molten steel is controlled to absorb air, and the nitrogen increase during the continuous casting process is ≤3ppm; electromagnetic stirring of the crystallizer and electromagnetic stirring of the end are used to maintain a constant casting speed, and the casting speed is controlled to be ≤0.05m / min; the amount of molten steel remaining in the large ladle casting is ≥2.5 tons, and the amount of molten steel remaining in the medium ladle casting is >3.5 tons, and finally a steel billet is obtained after continuous casting; the steel billet is piled and cooled in a windproof pile for ≥36 hours;

[0021] Among them, crystallizer electromagnetic stirring and end electromagnetic stirring are adopted, the crystallizer electromagnetic stirring frequency is 2Hz, and the end electromagnetic stirring frequency is 10Hz.

[0022] (5) Continuous rolling:

[0023] The continuous casting billet obtained by continuous casting in step (4) is charged into a heating furnace for heating, wherein the preheating section temperature is ≤750°C, the heating section temperature is 950-1050°C, the heating section temperature is 1150-1220°C, the soaking section temperature is 1160-1220°C, the total heating time is ≥180min, and the heating section and soaking section time are ≥100min in total; the furnace discharge temperature is 1160-1220°C, the final rolling temperature is ≥850°C; the rolling compression ratio is ≥12; the round steel after continuous rolling is stacked in the middle of other hot steel products, and is sheltered from wind and slowly cooled for not less than 36h to obtain continuously rolled steel products;

[0024] (6) Processing of wind power fasteners:

[0025] After the steel billet is continuously rolled, the continuously rolled round steel is subjected to quenching and tempering treatment to obtain the final material; wherein the quenching temperature is in the range of 845°C to 855°C, and the tempering temperature is in the range of 550°C to 610°C.

[0026] Preferably, the target temperature range of the steel tapping in step (1) is 1620-1660°C;

[0027] Preferably, the soft blowing time in step (3) is controlled to be 20-25 minutes.

[0028] Preferably, in step (5), the temperature of the preheating section is 660°C, the temperature of the first heating section is 970°C, the temperature of the second heating section is 1180°C, the temperature of the soaking section is 1180°C, and the temperature out of the furnace is 1160°C.

[0029] Preferably, the time for slow cooling in step (5) is 40-48 hours.

[0030] The advantages and technical effects of the present invention are:

[0031] (1) The present invention optimizes the components to make the Ni content reach 0.30% to 0.50%; nickel is the most effective element for improving the low-temperature toughness of steel. Nickel and iron can be infinitely dissolved in solid solution, and are elements that form and stabilize austenite. They can improve the hardenability of steel, improve the uniformity of the material structure after steel quenching and tempering heat treatment, and improve the low-temperature toughness of the material. Nickel can also increase the stacking fault energy of the material, promote the cross-slip of spiral dislocations at low temperatures, increase the work consumed by crack propagation, and improve the impact toughness of steel under low temperature conditions. Nickel can also strengthen ferrite and refine and increase pearlite, thereby improving the strength of steel without significantly reducing the plasticity of steel. The present invention improves the low-temperature impact energy of the material by increasing the hardenability of the material, improving the uniformity of the material structure, and increasing the stacking fault energy of the material through the Ni element, and achieves unexpected technical effects.

[0032] (2) The low-temperature impact energy -45°C and AKV of the materials produced by the current composition design after quenching and tempering heat treatment can generally only reach about 27-35J, with an average value of 30J, and rarely reaching 35J. The advantage of the present invention is that the impact energy is significantly improved. The present invention produces 9 furnace compositions (Examples 1-9), and these 9 furnace compositions are rolled into 45.3mm round steel. After quenching and tempering heat treatment, the round steel has an impact energy of -45°C and AKV2 of more than 50J, and the highest reaches 72.7J; the impact energy of -45°C and AKV2 of the original technology is improved by 28.6 to 42.7J, which is far greater than the low-temperature impact energy -45°C and AKV2 ≥ 35J required by high-end users, and has achieved very significant technical effects. DETAILED DESCRIPTION

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art in the art to which the present invention relates.

[0035] Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0036] It will be apparent to those skilled in the art that many modifications and variations can be made to the particular embodiments of the invention described herein without departing from the scope or spirit of the invention.

[0037] Other embodiments will be apparent to the skilled person from the description of the present invention.The description and examples of the present invention are intended to be exemplary only.

[0038] Comparative Example 1:

[0039] The chemical composition of 42CrMoA steel currently used in China for wind power fasteners is shown in Table 1.

[0040] The following production process is used for preparation:

[0041] 1) Converter smelting: Blowing is carried out in a top and bottom combined basic converter, the auxiliary gun determines the composition, and the infrared slag detection + slide mechanism is used to control the slag to prevent the P return of the steel. The P of the steel is controlled to be ≤0.010%. The aluminum deoxidizer and high-purity alloy are pre-deoxidized and the composition is initially adjusted. The target [C] is 0.12-0.20%, and the target temperature of the steel is ≥1600℃;

[0042] 2) Refining: Based on step (1), the molten steel after converter smelting is refined in a LF refining furnace. After the arc is stabilized, 0-2 kg / t lime and 0-2 kg / t fluorite are added to the total amount of refined molten steel to adjust the slag fluidity; the white slag retention time is ≥ 20 min, and no aluminum, alloy or auxiliary materials shall be added 5 min before transfer, and the temperature rise range shall not be greater than 15°C; the refining process is strengthened to remove sulfur and inclusions;

[0043] 3) VD vacuum degassing: After LF refining, use VD degassing equipment for vacuum degassing, and keep it under high vacuum of vacuum degree ≤67pa for more than 15 minutes to ensure that [H]≤1.5ppm and [O]≤20ppm when breaking the air; Soft blowing: soft blowing treatment is carried out, and the flow rate and pressure are automatically monitored throughout the process. The soft blowing time is 15-25 minutes;

[0044] 4) Continuous casting: After the VD vacuum degassing treatment in step (3), a continuous casting machine is used to protect the casting throughout the whole process, control the air absorption of the molten steel, and increase the nitrogen in the continuous casting process by ≤3ppm; a crystallizer + secondary cooling + terminal electromagnetic stirring is used, the pulling speed is controlled to ≤0.05m / min, and the casting speed is maintained constant. The large ladle casting residue is ≥2.5 tons, and the medium ladle casting residue is >3.5 tons to obtain a steel billet; the steel billet is cooled in a windproof pile for ≥36 hours; wherein, the crystallizer electromagnetic stirring and the terminal electromagnetic stirring are used, the crystallizer electromagnetic stirring frequency is 2Hz, and the terminal electromagnetic stirring frequency is 10Hz, so as to achieve a small component segregation.

[0045] 5) Continuous rolling: the continuous casting billet obtained by continuous casting in step (4) is charged into a heating furnace for heating, the preheating section temperature is ≤750°C, the heating section temperature is 950-1050°C, the heating section temperature is 1150-1220°C, the soaking section temperature is 1160-1220°C, the total heating time is ≥180min, and the heating section and soaking section time are ≥110min in total; the furnace discharge temperature is 1160-1220°C, the final rolling temperature is ≥850°C; the rolling compression ratio is ≥12; the round steel after continuous rolling is stacked in the middle of other hot steel products, and is sheltered from wind and slowly cooled for not less than 36h to obtain continuously rolled steel products;

[0046] 6) Processing

[0047] The continuously rolled round steel obtained after continuous rolling of the steel billet is subjected to quenching (quenching temperature 850±5°C, oil) + tempering (temperature 580±30°C) treatment to obtain the wind power fastener material.

[0048] The process conditions not limited in the above preparation method can refer to the conventional technology in the art, are well known in the art, and will not be introduced in detail.

[0049] Table 1 Chemical composition of 42CrMoA steel commonly used in wind power fasteners

[0050]

[0051] Embodiment 1:

[0052] 1. The chemical composition is as follows:

[0053] C: 0.42%, Si: 0.20%, Mn: 0.60%, S: 0.005%, P: 0.015%, Cr: 1.10%, Mo: 0.17%, Ni: 0.35%, Cu: 0.10%, and the rest is Fe.

[0054] 2. Prepared by the following production process: Same as the comparative example;

[0055] Embodiment 2:

[0056] 1. The chemical composition is as follows:

[0057] C: 0.41%, Si: 0.25%, Mn: 0.61%, S: 0.005%, P: 0.014%, Cr: 1.11%, Mo: 0.17%, Ni: 0.41%, Cu: 0.10%, and the rest is Fe.

[0058] 2. Prepared by the following production process: Same as the comparative example.

[0059] Embodiment 3:

[0060] 1. The chemical composition is as follows:

[0061] C: 0.42%, Si: 0.22%, Mn: 0.62%, S: 0.004%, P: 0.012%, Cr: 1.11%, Mo: 0.16%, Ni: 0.41%, Cu: 0.09%, and the rest is Fe.

[0062] 2. Prepared by the following production process: Same as the comparative example.

[0063] Embodiment 4:

[0064] 1. The chemical composition is as follows:

[0065] C: 0.41%, Si: 0.23%, Mn: 0.63%, S: 0.005%, P: 0.015%, Cr: 1.13%, Mo: 0.18%, Ni: 0.42%, Cu: 0.15%, and the rest is Fe.

[0066] 2. Prepared by the following production process: Same as the comparative example.

[0067] Embodiment 5:

[0068] 1. The chemical composition is as follows:

[0069] C: 0.41%, Si: 0.22%, Mn: 0.62%, S: 0.003%, P: 0.014%, Cr: 1.13%, Mo: 0.17%, Ni: 0.40%, Cu: 0.11%, and the rest is Fe.

[0070] 2. Prepared by the following production process: Same as the comparative example.

[0071] Embodiment 6:

[0072] 1. The chemical composition is as follows:

[0073] C: 0.40%, Si: 0.25%, Mn: 0.61%, S: 0.005%, P: 0.014%, Cr: 1.11%, Mo: 0.17%, Ni: 0.40%, Cu: 0.08%, and the rest is Fe.

[0074] 2. Prepared by the following production process: Same as the comparative example.

[0075] Embodiment 7:

[0076] 1. The chemical composition is as follows:

[0077] C: 0.41%, Si: 0.22%, Mn: 0.61%, S: 0.002%, P: 0.015%, Cr: 1.11%, Mo: 0.17%, Ni: 0.43%, Cu: 0.12%, and the rest is Fe.

[0078] 2. Prepared by the following production process: Same as the comparative example.

[0079] Embodiment 8:

[0080] 1. The chemical composition is as follows:

[0081] C: 0.41%, Si: 0.22%, Mn: 0.61%, S: 0.005%, P: 0.016%, Cr: 1.13%, Mo: 0.17%, Ni: 0.42%, Cu: 0.13%, and the rest is Fe.

[0082] 2. Prepared by the following production process: Same as the comparative example.

[0083] Embodiment 9:

[0084] 1. The chemical composition is as follows:

[0085] C: 0.42%, Si: 0.22%, Mn: 0.65%, S: 0.004%, P: 0.016%, Cr: 1.12%, Mo: 0.17%, Ni: 0.42%, Cu: 0.11%, and the rest is Fe.

[0086] 2. Prepared by the following production process: Same as the comparative example.

[0087] The results of Examples 1-9 are shown in Table 2;

[0088] Table 2 Impact energy test data of wind power fastener materials prepared by the scheme of the present invention

[0089] Example (Sample) Test methods Specification, mm Impact energy (-45℃AKV2), J 1 GB / T 229 45.3 63.3 2 GB / T 229 45.3 58.6 3 GB / T 229 45.3 56.6 4 GB / T 229 45.3 53.2 5 GB / T 229 45.3 72.7 6 GB / T 229 45.3 63.4 7 GB / T 229 45.3 58 8 GB / T 229 45.3 67.6 9 GB / T 229 45.3 50.6

[0090] Note: AKV2: impact absorption energy of V-notch specimen with a depth of 2 mm;

[0091] At present, the low-temperature impact energy -45℃ and AKV of the materials produced by the composition design after quenching and tempering heat treatment can generally only reach about 27-35J, with an average value of 30J, and rarely reaching 35J. It can be seen from Table 2 that the advantage of the present invention is that the impact energy is significantly improved. The present invention produces 9 furnace compositions (Examples 1-9), and these 9 furnace compositions are rolled into 45.3mm round steel. After quenching and tempering heat treatment, the round steel has an impact energy of -45℃ and AKV2 of more than 50J, and the highest reaches 72.7J; the impact energy of -45℃ and AKV2 of the original technology is improved by 28.6~42.7J, which is far greater than the low-temperature impact energy -45℃ and AKV2≥35J requirements of high-end users, and has achieved very significant technical effects.

[0092] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; therefore, although this specification has described the present invention in detail with reference to the above embodiments, a person skilled in the art should understand that the present invention can still be modified or replaced by equivalents; and all technical solutions and improvements thereof that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A wind power fastener steel, characterized in that: It is composed of the following components in percentage by mass: C: 0.38-0.45%, Mn: 0.50-0.80%, Si: 0.17-0.37%, Mo: 0.15-0.25%, Cr: 0.90-1.20%, Ni: 0.30-0.50%, P: ≤0.020%, S: ≤0.020%, Cu: ≤0.20%, and the rest is Fe and unavoidable impurities; the low-temperature impact energy of the wind power fastener steel is -45°C and AKV2 is not less than 50J.

2. A wind power fastener steel according to claim 1, characterized in that: The low-temperature impact energy of the wind power fastener steel is -45°C and AKV2 is 50.6 to 72.7J.

3. A method for producing wind power fastener steel according to claim 1 or 2, characterized in that: The following steps are involved: (1) Converter smelting: The steel is blown in a top and bottom combined blowing basic converter, and the converter smelting endpoint is controlled, with target S≤0.015%; target P≤0.015%; target tapping temperature≥1600℃; and the target tapping temperature range is 1600~1680℃; (2) Refining: Based on step (1), the molten steel after converter smelting is refined in an LF refining furnace, and after the submerged arc is stable, lime and fluorite are added to adjust the slag fluidity; the white slag is kept for ≥20 min; The amount of lime and fluorite added is calculated based on the total amount of refined molten steel, and the amount of relevant additives is as follows: lime 0-2kg / t, fluorite 0-2kg / t; (3) VD vacuum degassing: After LF refining in step (2), vacuum degassing is performed using VD degassing equipment, with a vacuum degree of ≤67 Pa and a holding time of ≥10 min; ensuring that [H] is ≤1.5 ppm and [O] is ≤20 ppm when breaking the air; and the soft blowing time is not less than 15 minutes; (4) Continuous casting: After the VD vacuum degassing treatment in step (3), a continuous casting machine is used to protect the casting throughout the whole process, and the molten steel is controlled to absorb air, and the nitrogen increase during the continuous casting process is ≤3ppm; electromagnetic stirring of the crystallizer and electromagnetic stirring of the end are used to maintain a constant casting speed, and the casting speed is controlled to be ≤0.05m / min; the amount of molten steel remaining in the large ladle casting is ≥2.5 tons, and the amount of molten steel remaining in the medium ladle casting is >3.5 tons, and finally a steel billet is obtained after continuous casting; the steel billet is cooled in a windproof pile for ≥36 hours; wherein, electromagnetic stirring of the crystallizer and electromagnetic stirring of the end are used, the electromagnetic stirring frequency of the crystallizer is 2Hz, and the electromagnetic stirring frequency of the end is 10Hz; (5) Continuous rolling: The continuous casting billet obtained by continuous casting in step (4) is charged into a heating furnace for heating, wherein the preheating section temperature is ≤750°C, the heating section temperature is 950-1050°C, the heating section temperature is 1150-1220°C, the soaking section temperature is 1160-1220°C, the total heating time is ≥180min, and the heating section and soaking section time are ≥100min in total; the furnace discharge temperature is 1160-1220°C, the final rolling temperature is ≥850°C; the rolling compression ratio is ≥12; the round steel after continuous rolling is stacked in the middle of other hot steel products, and is sheltered from wind and slowly cooled for not less than 36h to obtain continuously rolled steel products; (6) Processing of wind power fasteners: After the steel billet is continuously rolled, the continuously rolled round steel is subjected to quenching and tempering treatment to obtain the final material; wherein the quenching temperature is in the range of 840°C to 860°C, and the tempering temperature is in the range of 540°C to 580°C.

4. The method for producing wind power fastener steel according to claim 3, characterized in that: The target temperature range of the steel tapping in step (1) is 1620-1660°C.

5. The method for producing wind power fastener steel according to claim 3, characterized in that: The soft blowing time in step (3) is controlled to be 20-25 minutes.

6. The method for producing wind power fastener steel according to claim 3, characterized in that: In step (5), the temperature of the preheating section is 660°C, the temperature of the first heating section is 970°C, the temperature of the second heating section is 1180°C, the temperature of the soaking section is 1180°C, and the temperature out of the furnace is 1160°C.

7. The method for producing wind power fastener steel according to claim 3, characterized in that: The time for sheltering from wind and slow cooling in step (5) is 40-48 hours.

Images