900mpa-grade magnetic pole steel for pumped storage hydroelectric generating unit and production method thereof

Abstract

A kind of 900MPa grade magnetic pole steel for pumped storage hydroelectric generating set, its component and wt% are as follows: C: 0.25~0.30%, Si: 0.10~0.20%, Mn: 1.1~1.5%, Cr: 0.3~0.4%, Ti: 0.2~0.3%, B: 0.0025~0.0030%, P: ≤0.015%, S: ≤0.010%, Als: 0.02~0.10%; production method: after conventional smelting, cast into blank; the cast blank is heated; adopt 7 passes hot rolling to product thickness; laminar flow cooling is carried out; coiling; annealing; straightening is carried out.The application does not contain valuable alloy elements such as Nb, Mo, etc., and its yield strength is greater than or equal to 900MPa, elongation A is greater than or equal to 12%, magnetic induction performance B 50 ≥1.60T, can fully meet the demand of 900MPa grade magnetic pole steel for pumped storage hydroelectric generator rotor suitable for rated speed of 600r / min, product thickness is not more than 2mm, and cost can be reduced by 600~900 yuan / ton of steel compared with prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of motor steel and production method, exactly belongs to a kind of 900MPa grade magnetic pole steel and production method for pumped storage hydroelectric generating set. BACKGROUND

[0002] Pumped storage power station is the most mature technology, the most optimal economy, the most large-scale development conditions of green low-carbon clean flexible regulating power source of electric power system, and wind power, solar power generation, nuclear power, thermal power etc. Better cooperation.

[0003] Magnetic pole steel is used in the rotor magnetic pole part of pumped storage generator structure, is the main component for generating magnetic field of hydroelectric generator, belongs to rotating component, requires good electromagnetic performance and mechanical property, generally thickness≤2.0mm. With the increase of rated speed of unit, the required strength of magnetic pole steel plate also increases, thus for the pumped storage hydroelectric generating set with rated speed of 600r / min, the demand of yield strength≥900MPa, thickness≤2.0mm extremely thin gauge magnetic pole steel is proposed.

[0004] Through retrieval:

[0005] The document of Chinese patent application No.CN201210165348.7 discloses "a kind of high magnetic induction low-cost 250MPa grade cold-rolled magnetic pole steel manufacturing method", and its process includes: heating slab to 1200-1260℃, and keeping warm;Hot rolling: final rolling temperature is 850-900℃, coiling temperature is 550-630℃, and cooling mode adopts jet type water cooling mode;Cooling to 60-80℃ for pickling, and cooling mode adopts air cooling mode;Cold rolling: cold rolling reduction is 50-75%;Continuous annealing: soaking temperature is 720-780℃, and soaking time is 60~200s;0.8-1.4% flatness extension rate is adopted for flattening, and 250MPa grade cold-rolled magnetic pole steel is prepared. But the yield strength of the produced magnetic pole steel is only 250MPa grade.

[0006] The document with Chinese patent application number CN200910049782.7 discloses "a manufacturing method of 500MPa grade cold-rolled magnetic pole steel", the main chemical components of the slab are as follows: C: 0.07-0.10%, Si: 0.18-0.31%, Mn: 1.00-1.50%, P: ≤0.02%, S: ≤0.007%, O ≤0.004%, N ≤0.004%, Nb: 0.046-0.060%, Ti: ≤0.003%, V: 0.050-0.070%, and the balance is Fe and inevitable impurities. It is prepared by the following steps: (1) heating the slab to 1200-1260℃, then rolling the slab into a thin steel plate, the final rolling temperature is 830-890℃, and the slab is cooled to 550-600℃ by laminar cooling mode for coiling; (2) cooling by air cooling mode, pickling; (3) cold rolling; (4) continuous annealing: the temperature of the soaking section of the annealing furnace is controlled at 740-760℃, the speed of the annealing process section is controlled at 120-125m / min, and the soaking section time is controlled at 230-239s; (5) flattening. But the yield strength of the product can only reach 570MPa.

[0007] The document with Chinese patent application number ZL202110575161.3 discloses "tensile strength ≥850MPa magnetic yoke steel with excellent fatigue resistance", the chemical components and weight percentage content are as follows: C: 0.03-0.07%, Si: ≤0.15%, Mn: 0.5-1.0%, P: ≤0.015%, S: ≤0.002%, Nb: 0.075-0.095%, V: 0.015-0.025%, Mo: 0.20-0.30%, Als: 0.02-0.10%, N: ≤0.010%, and the balance is Fe and inevitable impurities. The yield strength is ≥800MPa, but there are Mo, Nb and other precious metals, and the alloy cost is high. SUMMARY

[0008] The present application aims to overcome the shortcomings of the prior art, and provides a 900MPa grade magnetic pole steel for pumped storage hydroelectric generating set, which has a yield strength ≥900MPa, an elongation A ≥12%, a magnetic induction performance B 50 ≥1.6T, and a product thickness ≤2.0mm, and a production method thereof.

[0009] The measures to achieve the above-mentioned purposes are as follows:

[0010] A kind of 900MPa grade magnetic pole steel for pumped storage hydroelectric generating set, its component and weight percentage content are as follows: C: 0.25~0.30%, Si: 0.10~0.20%, Mn: 1.1~1.5%, Cr: 0.3~0.4%, Ti: 0.2~0.3%, B: 0.0025~0.0030%, P: ≤0.015%, S: ≤0.010%, Als: 0.02~0.10%, the rest is Fe and inevitable inclusion.

[0011] Preferably: the weight percentage content of Cr is 0.33~0.37%.

[0012] Preferably: the weight percentage content of Ti is 0.20~0.25%.

[0013] A kind of 900MPa grade magnetic pole steel steel for pumped storage hydroelectric generating set is produced, and the steps are as follows:

[0014] 1) after conventional smelting, it is poured into blank, in the process, control the thickness of casting blank to be 60~85mm;

[0015] 2) the casting blank is heated, control the soaking temperature to be 1150~1200℃, and control the soaking time to be no less than 30min;

[0016] 3) using 7 passes hot rolling to product thickness: control the rolling temperature to be no less than 1050℃, and the finish rolling temperature is 850~900℃;

[0017] 4) laminar cooling is carried out, and the cooling rate is 70~90℃ / s, and cooling to coiling temperature;

[0018] 5) coiling is carried out, and the coiling temperature is controlled to be 300~400℃.

[0019] 6) annealing is carried out, control the annealing heating temperature to be 550~600℃, and the holding time is 3~6h;

[0020] 7) straightening is carried out.

[0021] Preferably: the soaking temperature of casting blank is 1157~1192℃.

[0022] Preferably: the rolling temperature is no less than 1058℃, and the finish rolling temperature is 868~892℃.

[0023] Preferably: the coiling temperature is 340~390℃.

[0024] The role and mechanism of each element and main process in the application

[0025] The carbon (C) content of this invention is 0.25% to 0.30%, as carbon is the most economical strengthening element. However, if the carbon content is between 0.07% and 0.15%, peritectic reaction will occur in the molten steel during casting, increasing the risk of leakage during continuous casting. Furthermore, excessively high carbon content will reduce magnetic properties. Therefore, limiting the carbon content to 0.25% to 0.30% can improve the strength of the steel while ensuring its magnetic properties, and at the same time significantly reduce the addition of alloying elements, thus reducing costs.

[0026] The manganese (Mn) content of the present invention is 1.1% to 1.5%. Manganese can reduce the phase transformation temperature of austenite to ferrite, expand the hot working temperature range, and is beneficial to refine the ferrite grain size and improve the yield strength of steel.

[0027] The chromium (Cr) content of this invention is 0.3% to 0.4%. Chromium is a carbide-forming element with a strong affinity for carbon, which can hinder the diffusion of carbon atoms. Cr is beneficial for refining ferrite grains and improving the strength of steel plates, but excessive Cr content is detrimental to magnetic properties. In this invention, the chromium content is controlled at 0.3% to 0.4%, preferably: the weight percentage of Cr is 0.30% to 0.35%.

[0028] The titanium (Ti) content of this invention is 0.2% to 0.3%. Ti is a strong carbide and nitride forming element. The formed carbon and nitride particles can prevent austenite grain growth during steel reheating and high-temperature austenitic rough rolling, thus refining the grains and improving the toughness of the steel. The fine, dispersed TiC precipitated during the coiling stage can have a significant precipitation strengthening effect, thereby effectively improving the strength of the steel plate. This invention selects a Ti content of 0.2% to 0.3%, preferably: the weight percentage content of Ti is 0.20% to 0.25%.

[0029] The silicon (Si) content of this invention is 0.10% to 0.20%. Si has a solid solution strengthening effect, which can improve the strength of steel and is beneficial to magnetic properties. When the silicon content exceeds a certain range, it will be detrimental to the surface quality. Therefore, this invention controls the Si content to 0.10% to 0.20%.

[0030] The phosphorus (P) content of this invention is ≤0.015%, and the sulfur (S) content is ≤0.010%. Phosphorus in steel has adverse effects such as easily causing segregation and reducing magnetic properties. Sulfur readily combines with manganese to form MnS inclusions, affecting the magnetic properties and plasticity of steel. Therefore, this invention aims to minimize the adverse effects of phosphorus and sulfur on steel properties by controlling the phosphorus and sulfur content through deep desulfurization pretreatment of molten iron, thereby mitigating their adverse effects.

[0031] The boron (B) content of this invention is 0.0025% to 0.0030%. The main function of B is as a surface-active element, adsorbing onto the austenite grain boundaries to delay the transformation of austenite to ferrite, thereby refining the final microstructure and achieving a strengthening effect. Furthermore, B is extremely inexpensive, significantly contributing to cost control. However, excessively high B content can lead to the formation of low-melting-point eutectics, concentrated at grain boundaries, causing hot brittleness. Therefore, the boron content of this invention ranges from 0.0025% to 0.0030%.

[0032] The reason why the homogenization temperature of the billet is controlled at 1150-1200℃ in this invention is to ensure that the alloying elements are completely dissolved and fully austenitized, while improving the temperature uniformity of the billet, reducing the deformation resistance and rolling load, which is beneficial for rolling thin-gauge magnetic yoke steel.

[0033] The purpose of controlling the final rolling temperature at 850–900℃, the cooling rate at 70–90℃ / s, and the coiling temperature at 300–400℃ in this invention is to obtain a bainitic structure using a high cooling rate, thereby fully utilizing the structural strengthening and grain refinement effects. At the same time, the annealing temperature of 550–600℃ allows TiC particles to fully precipitate, thereby fully utilizing the precipitation strengthening effect and improving the strength of the steel plate.

[0034] This invention does not contain precious alloying elements such as Nb and Mo, and has a yield strength ≥900MPa, elongation A ≥12%, and magnetic induction properties B. 50 With a strength of ≥1.60T, it fully meets the requirements for 900MPa grade magnetic pole steel for pumped storage hydroelectric generator rotors, which are suitable for rated speeds of 600r / min, have a product thickness of no more than 2mm, and can reduce costs by 600-900 yuan / ton of steel compared to existing technologies. Detailed Implementation

[0035] The present invention will now be described in detail:

[0036] Table 1 is a list of component values ​​for each embodiment and comparative example of the present invention;

[0037] Table 2 is a list of process parameter values ​​and performance tests for each embodiment and comparative example of the present invention.

[0038] Each embodiment of the present invention is produced according to the following steps:

[0039] 1) After conventional smelting, the billet is cast into a billet, during which the thickness of the billet is controlled between 60 and 85 mm;

[0040] 2) Heat the billet, control the homogenization temperature at 1150-1200℃, and control the homogenization time at no less than 30 minutes;

[0041] 3) Use 7 passes of hot rolling to achieve the desired product thickness: control the initial rolling temperature to be no less than 1050℃ and the final rolling temperature to be between 850℃ and 900℃;

[0042] 4) Perform laminar flow cooling at a rate of 70–90°C / s until the winding temperature is reached;

[0043] 5) Perform winding and control the winding temperature at 300-400℃.

[0044] 6) Perform annealing, controlling the annealing heating temperature at 550-600℃ and the holding time at 3-6 hours;

[0045] 7) Straighten the object.

[0046] Table 1. List of chemical components (wt%) of various embodiments and comparative examples of the present invention.

[0047]

[0048] Table 2. List of main process parameters for each embodiment and comparative example of the present invention.

[0049]

[0050]

[0051] Table 3. List of mechanical property test results for each embodiment and comparative example of the present invention.

[0052]

[0053] As can be seen from Table 3, embodiments 1 to 8 meet the requirements of yield strength ≥ 900 MPa, elongation A ≥ 12%, and magnetic properties B. 50 With a requirement of ≥1.60T, the thickness of its hot-rolled plate is ≤2.0mm, which fully meets the market demand.

[0054] This specific embodiment is merely a best example and is not intended to limit the implementation of the technical solution of the present invention.

Claims

1. A 900MPa grade magnetic pole steel for pumped storage hydroelectric generators, comprising the following components and weight percentages: C: 0.25-0.30%, Si: 0.10-0.20%, Mn: 1.45-1.5%, Cr: 0.3-0.4%, Ti: 0.2-0.3%, B: 0.0025-0.0030%, P: ≤0.015%, S: ≤0.010%, Als: 0.02-0.10%, with the remainder being Fe and unavoidable inclusions; Production method: 1) After conventional smelting, the billet is cast into a billet, during which the thickness of the billet is controlled between 60 and 85 mm; 2) Heat the billet, control the homogenization temperature at 1150~1200℃, and control the homogenization time at no less than 30min; 3) Use 7 passes of hot rolling to achieve the product thickness: control the initial rolling temperature to be no less than 1050℃ and the final rolling temperature to be between 850℃ and 900℃; 4) Perform laminar flow cooling at a rate of 70~90℃ / s until the winding temperature is reached; 5) Perform winding and control the winding temperature at 300-400℃; 6) Perform annealing, controlling the annealing heating temperature at 550-600℃ and the holding time at 3-6 hours; 7) Straighten.

2. The 900MPa grade magnetic pole steel for pumped storage hydroelectric generators as described in claim 1, characterized in that: The weight percentage content of Cr is between 0.33% and 0.37%.

3. The 900MPa grade magnetic pole steel for pumped storage hydroelectric generators as described in claim 1, characterized in that: The weight percentage content of Ti is 0.20-0.25%.

4. A method for producing 900MPa grade magnetic pole steel for pumped storage hydroelectric generators as described in claim 1, comprising the following steps: 1) After conventional smelting, the billet is cast into a billet, during which the thickness of the billet is controlled between 60 and 85 mm; 2) Heat the billet, control the homogenization temperature at 1150~1200℃, and control the homogenization time at no less than 30min; 3) Use 7 passes of hot rolling to achieve the product thickness: control the initial rolling temperature to be no less than 1050℃ and the final rolling temperature to be between 850℃ and 900℃; 4) Perform laminar flow cooling at a rate of 70~90℃ / s until the winding temperature is reached; 5) Perform winding and control the winding temperature at 300-400℃; 6) Perform annealing, controlling the annealing heating temperature at 550-600℃ and the holding time at 3-6 hours; 7) Straighten.

5. The method for producing a 900MPa grade magnetic pole steel for pumped storage hydroelectric generators as described in claim 4, characterized in that: The homogenization temperature of the billet is between 1157 and 1192℃.

6. The method for producing a 900MPa grade magnetic pole steel for pumped storage hydroelectric generators as described in claim 4, characterized in that: The initial rolling temperature shall not be lower than 1058℃.

7. The method for producing a 900MPa grade magnetic pole steel for pumped storage hydroelectric generators as described in claim 4, characterized in that: The winding temperature is between 340 and 390°C.

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