N980cf steel for hydropower and production method therefor

Abstract

The present invention relates to the technical field of ferrous metallurgy, and in particular relates to N980CF steel for hydropower and a production method therefor. The N980CF steel for hydropower comprises the following chemical components in percentages by mass: C: 0.01-0.014%, Si: 0.10-0.30%, Mn: 1.30-1.50%, P≤0.013%, S≤0.003%, Cr: 0.30-0.50%, Ni: 1.60-1.80%, Mo: 0.30-0.60%, Nb: 0.040-0.060%, V: 0.060-0.080%, Ti: 0.008-0.030%, Al: 0.020-0.050%, B≤0.0050%, N≤0.0050%, H≤0.0002%, and the balance of Fe and inevitable impurities. In the present invention, a steel plate for hydropower with good properties including a yield strength of greater than 900 MPa, a tensile strength of 950-1130 MPa, an elongation of greater than or equal to 15% and a mean value of transverse impact at -60ºC of greater than or equal to 60 J is obtained by means of oxygen-blown converter smelting, aluminum-killed steel smelting, a low-temperature austenitic rolling process and a quenching and tempering process, and meets the requirements of the application of high-strength products to the field of hydropower.

Description

N980CF hydropower steel and production method thereof Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and in particular to N980CF hydropower steel and a production method thereof. Background Art

[0002] As the requirements of carbon neutrality and carbon peak gradually approach, the contradiction between energy and economic development becomes more and more prominent. As a representative of clean energy, hydropower is receiving more and more attention. Therefore, the development of hydropower stations is also constantly developing towards large-scale. Since 2000, 600Mpa-grade hydropower steel has been widely used in China, and the technical level has been continuously improved during the application process. With the continuous development of my country's economy, the technology of various industries has made great progress, especially the progress of steel metallurgy technology. Hydropower stations such as Baihetan and Wudongde have used 800Mpa-grade hydropower steel. With the progress of the hydropower industry, some companies have begun to trial-produce 1000Mpa hydropower steel. In order to enhance the company's position in the hydropower field, Nangang is also actively conducting 1000Mpa production trials.

[0003] The current national standard YB / T4137-2013 specifies the highest grade of hydropower steel as Q800CF, with a yield strength of ≥800 MPa and a tensile strength of 880-1050 MPa. This grade has been widely used in engineering projects, but the material standard currently does not include ultra-high-strength N980CF hydropower steel. Therefore, to ensure the strength and toughness levels required for high-strength products in the hydropower sector, this paper proposes N980CF hydropower steel and its production method.

[0004] Summary of the Invention

[0005] In response to the above technical problems, the present invention provides an N980CF hydropower steel and a production method thereof. The steel is smelted in an oxygen-blown converter, smelted in an aluminum-killed steel, and subjected to a low-temperature austenitizing rolling process. A quenching + tempering process is adopted to obtain a hydropower steel plate with excellent performance, such as a yield strength greater than 900 MPa, a tensile strength of 950 to 1130 MPa, an elongation ≥15%, and an average transverse impact value of ≥60J at -60°C, which meets the application requirements of high-strength products in the hydropower field.

[0006] In a first aspect, the present invention provides an N980CF hydropower steel, whose chemical composition and mass percentage are as follows: C: 0.01% to 0.014%, Si: 0.10% to 0.30%, Mn: 1.30% to 1.50%, P: ≤0.013%, S: ≤0.003%, Cr: 0.30 to 0.50%, Ni: 1.60% to 1.80%, Mo: 0.30 to 0.60%, Nb: 0.040 to 0.060%, V: 0.060 to 0.080%, Ti: 0.008 to 0.030%, Al: 0.020% to 0.050%, B ≤ 0.0050%, N ≤ 0.0050%, H ≤ 0.0002%, and the balance is Fe and unavoidable impurities.

[0007] The technical solutions further defined in this proposal are:

[0008] Furthermore, the chemical composition and mass percentage of the N980CF hydropower steel are as follows: C: 0.012% to 0.014%, Si: 0.10% to 0.30%, Mn: 1.30% to 1.50%, P: ≤0.013%, S: ≤0.003%, Cr: 0.30 to 0.50%, Ni: 1.60% to 1.80%, Mo: 0.30 to 0.60%, Nb: 0.040 to 0.060%, V: 0.060 to 0.080%, Ti: 0.008 to 0.030%, Al: 0.020% to 0.050%, B ≤0.0050%, N ≤0.0050%, H ≤0.0002%, and the balance is Fe and unavoidable impurities.

[0009] In a second aspect, the present invention provides a method for producing N980CF hydropower steel, which is applicable to the N980CF hydropower steel described in any one of the schemes in the first aspect, comprising the following steps:

[0010] S1. Use oxygen-blown converter for smelting, with 150-160 tons of molten iron and 20-30 tons of scrap steel;

[0011] S2. Use LF+RH for vacuum treatment, and then use continuous casting for casting after static stirring. The billet is piled and cooled for 48 hours for surface inspection and billet treatment;

[0012] S3. The billets that have passed the surface inspection are austenitized and heated to a tapping temperature of 1150-1170 degrees. Niobium, vanadium, titanium, and aluminum elements will be partially precipitated. The unprecipitated elements will play a role in solid solution strengthening, which can ensure the stability of the yield strength ratio of the product after heat treatment and achieve the strong and tough performance of the product. Conventional rolling is adopted and laminar cooling is performed to 400-500 degrees.

[0013] S4. After the steel plate is rolled, it is sent to heat treatment for quenching and tempering. The quenching temperature is 830-850 degrees, and the tempering temperature is 400-500 degrees. A lower normalizing temperature is used to ensure the refinement of the product grains and avoid the strengthening caused by element precipitation, which leads to an increase in the yield ratio. Due to the small amount of precipitated elements, low-temperature tempering is used to achieve stable strength and meet the stability of the product yield ratio. At the same time, due to the increase of solid solution elements, the ultra-low temperature impact toughness is even better.

[0014] S5. After tempering, cool to room temperature and carry out sampling, labeling and storage.

[0015] Furthermore, aluminum deoxidation is used in S1 to control the aluminum content after the furnace to 0.030-0.60%.

[0016] Furthermore, after laminar cooling in S3, if the thickness of the steel plate is greater than 20 mm, stack cooling is performed for 10 to 20 hours.

[0017] Furthermore, after the steel plate is rolled in S4, the thickness of the steel plate is controlled to be 5 to 100 mm.

[0018] The beneficial effects of the present invention are:

[0019] (1) The present invention adopts a lower carbon content, which is beneficial to ensuring the strength stability of the steel after heat treatment, improving the hardenability of the steel, and ensuring the uniformity of the structure in the thickness direction; the manganese element can refine the grains and improve the strength and plasticity of the steel; the use of chromium and molybdenum elements ensures the cooling hardenability of the steel after rolling and heat treatment, and improves the uniformity of the structure in the thickness direction of the steel plate; niobium, vanadium, titanium, and aluminum elements can effectively refine the grain size of the structure, improve toughness, and ensure the stability of the -60 degree transverse impact; the addition of nickel element can continuously dissolve with γ-iron, stably improving the strength of the steel. At the same time, the addition of nickel element can ensure the stable impact toughness of iron element under low temperature conditions, which is a key element for achieving ultra-strength hydropower steel;

[0020] (2) The present invention adopts a low-temperature austenitization process. Studies have found that the precipitation of niobium, vanadium, titanium, and aluminum elements is directly related to the austenitization temperature and also affects the size of the hardness structure grain size. The present invention adopts a steel tapping temperature of 1150 to 1170 degrees. Niobium, vanadium, titanium, and aluminum elements will be partially precipitated, and the unprecipitated elements will play a role in solid solution strengthening, which can ensure the stability of the yield strength ratio of the product after heat treatment and achieve the strong and tough performance of the product;

[0021] (3) The present invention adopts offline quenching + low-temperature tempering and adopts a lower normalizing temperature, which ensures the refinement of the product structure grains and avoids the strengthening brought by element precipitation, thereby leading to an increase in the yield strength ratio. Since there are fewer precipitated elements, low-temperature tempering is adopted to achieve stable strength. At the same time, due to the increase of solid solution elements, the ultra-low temperature impact toughness is more excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a metallographic structure diagram of N980CF hydropower steel in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] Example 1

[0024] This embodiment provides N980CF hydropower steel and a production method thereof. The chemical composition and mass percentages of N980CF hydropower steel are as follows: C: 0.013%, Si: 0.13%, Mn: 1.36%, P: 0.010%, S: 0.002%, Cr: 0.35%, Ni: 1.68%, Mo: 0.39%, Nb: 0.045%, V: 0.067%, Ti: 0.017%, Al: 0.036%, B: 0.0009%, N: 0.0031%, H: 0.00018%, and the balance is Fe and unavoidable impurities.

[0025] The production method specifically includes:

[0026] S1, using oxygen-blown converter for smelting, charging 156 tons of molten iron and 24 tons of scrap steel, using aluminum deoxidation, and the aluminum content after furnace removal is 0.045%;

[0027] S2. Use LF+RH for vacuum treatment, and then use continuous casting for casting after static stirring. The billet is piled and cooled for 48 hours for surface inspection and billet treatment;

[0028] S3. The billets that have passed the surface inspection are austenitized and heated, with a tapping temperature of 1159 degrees, conventional rolling, laminar cooling to 460 degrees, a steel plate thickness of 30 mm, and stack cooling for 16 hours;

[0029] S4. After the steel plate is rolled, it is sent to heat treatment for quenching and tempering. The quenching temperature is 839 degrees and the tempering temperature is 480 degrees.

[0030] S5. After tempering, cool to room temperature and carry out sampling, labeling and storage.

[0031] Example 2

[0032] This embodiment provides N980CF hydropower steel and its production method. The chemical composition and mass percentage of N980CF hydropower steel are as follows:

[0033] C: 0.013%, Si: 0.27%, Mn: 1.430%, P: 0.011%, S: 0.001%, Cr: 0.44%, Ni: 1.77%, Mo: 0.53%, Nb: 0.055%, V: 0.073%, Ti: 0.022%, Al: 0.042%, B: 0.0007%, N: 0.0039%, H: 0.00011%, and the balance is Fe and unavoidable impurities.

[0034] The production method specifically includes:

[0035] S1, using an oxygen-blown converter for smelting, with a molten iron charge of 153 tons and a scrap charge of 28 tons, using aluminum deoxidation, and an aluminum content of 0.051% after furnace deoxidation;

[0036] S2. Use LF+RH for vacuum treatment, and then use continuous casting for casting after static stirring. The billet is piled and cooled for 48 hours for surface inspection and billet treatment;

[0037] S3. The billets that have passed the surface inspection are austenitized and heated, with a tapping temperature of 1163 degrees. Conventional rolling is adopted, laminar cooling is performed to 470 degrees, the steel plate thickness is 42 mm, and stack cooling is performed for 18 hours.

[0038] S4. After the steel plate is rolled, it is sent to heat treatment for quenching and tempering. The quenching temperature is 842 degrees and the tempering temperature is 445 degrees.

[0039] S5. After tempering, cool to room temperature and carry out sampling, labeling and storage.

[0040] The following is a comparison table of performance parameters of hydropower steel in various embodiments of the present invention:

[0041] According to the comparison of the performance parameters of the above-mentioned hydropower steel, it can be seen that the performance of the N980CF hydropower steel of the present invention meets the technical requirements of customers, and the product performance is stable. Through the development and application of the product, the technical solution of the present invention can also be applied to lower-level hydropower steel manufacturing methods.

[0042] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection required by the present invention.

Claims

1. A N980CF hydropower steel, characterized by: Its chemical composition and mass percentage are as follows: C: 0.01%~0.014%, Si: 0.10%~0.30%, Mn: 1.30%~1.50%, P:≤0.013%, S:≤0.003%, Cr: 0.30~0.50%, Ni: 1.60%~1.80%, Mo: 0.30~0.60%, Nb: 0.040~0.060%, V: 0.060~0.080%, Ti: 0.008~0.030%, Al: 0.020%~0.050%, B≤0.0050%, N≤0.0050%, H≤0.0002%, and the balance is Fe and unavoidable impurities.

2. The N980CF hydropower steel according to claim 1, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.012%~0.014%, Si: 0.10%~0.30%, Mn: 1.30%~1.50%, P:≤0.013%, S:≤0.003%, Cr: 0.30~0.50%, Ni: 1.60%~1.80%, Mo: 0.30~0.60%, Nb: 0.040~0.060%, V: 0.060~0.080%, Ti: 0.008~0.030%, Al: 0.020%~0.050%, B≤0.0050%, N≤0.0050%, H≤0.0002%, and the balance is Fe and unavoidable impurities.

3. A method for producing N980CF hydropower steel according to claim 1 or 2, characterized in that: The following steps are involved: S1. Use oxygen-blown converter for smelting, with 150-160 tons of molten iron and 20-30 tons of scrap steel; S2. Use LF+RH for vacuum treatment, and then use continuous casting for casting after static stirring. The billet is piled and cooled for 48 hours for surface inspection and billet treatment; S3. The billets that have passed the surface inspection are austenitized and heated to a tapping temperature of 1150-1170 degrees. Conventional rolling is adopted and laminar cooling is performed to 400-500 degrees. S4. After the steel plate is rolled, it is sent to heat treatment for quenching and tempering. The quenching temperature is 830-850 degrees and the tempering temperature is 400-500 degrees. S5. After tempering, cool to room temperature and carry out sampling, labeling and storage.

4. The method for producing N980CF hydropower steel according to claim 3, characterized in that: Aluminum deoxidation is used in S1 to control the aluminum content after the furnace to 0.030-0.60%.

5. The method for producing N980CF hydropower steel according to claim 3, characterized in that: In S3, after laminar cooling, if the steel plate thickness is greater than 20 mm, stack cooling is performed for 10 to 20 hours.

6. The method for producing N980CF hydropower steel according to claim 3, characterized in that: After the steel plate is rolled in S4, the thickness of the steel plate is controlled to be 5 to 100 mm.

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