阅读说明：本技术 表面质量优良的水轮发电机转子磁轭用钢及生产方法 (Steel with excellent surface quality for hydraulic generator rotor yoke and production method thereof ) 是由 宋畅 魏兵 高智平 黄大伟 熊飞 何亚元 刘斌 刘志勇 徐进桥 张俊鹏 于 2021-05-26 设计创作，主要内容包括：表面质量优良的水轮发电机转子磁轭用钢,其化学成分及wt%：C：0.03～0.07%,Si：≤0.05%,Mn：1.85～2.0%,P：≤0.015%,S：≤0.002%,Nb：0.075～0.095%,V：0.03～0.07%,Mo：0.10～0.20%,Als：0.02～0.10%,N：≤0.010%；生产方法：经转炉冶炼后连铸成坯；对铸坯加热；经除鳞后热轧；层流冷却；卷取进行罩式退火；自然冷却至室温。本发明屈服强度≥800MPa,抗拉强度≥850MPa,磁感性能B50≥1.5T的前提下,还能使表面粗糙度≤1.6μm,满足单机容量≥100万千瓦水轮发电机转子的需求。(The steel for the magnetic yoke of the hydro-generator rotor with excellent surface quality comprises the following chemical components in percentage by weight: c: 0.03 to 0.07%, Si: less than or equal to 0.05 percent, Mn: 1.85-2.0%, P: less than or equal to 0.015 percent, S: less than or equal to 0.002%, Nb: 0.075-0.095%, V: 0.03 to 0.07%, Mo: 0.10-0.20%, Als: 0.02-0.10%, N: less than or equal to 0.010 percent; the production method comprises the following steps: smelting in a converter and then continuously casting into a blank; heating a casting blank; hot rolling after descaling; laminar cooling; coiling and performing cover annealing; naturally cooling to room temperature. The invention can ensure that the surface roughness is less than or equal to 1.6 mu m under the premise that the yield strength is more than or equal to 800MPa, the tensile strength is more than or equal to 850MPa and the magnetic induction property B50 is more than or equal to 1.5T, thereby meeting the requirement that the capacity of a single machine is more than or equal to 100 ten thousand kilowatts of hydraulic generator rotors.)

1. The steel for the magnetic yoke of the hydro-generator rotor with excellent surface quality comprises the following chemical components in percentage by weight: c: 0.03 to 0.07%, Si: less than or equal to 0.05 percent, Mn: 1.85-2.0%, P: less than or equal to 0.015 percent, S: less than or equal to 0.002%, Nb: 0.075-0.095%, V: 0.03 to 0.07%, Mo: 0.10-0.20%, Als: 0.02-0.10%, N: less than or equal to 0.010 percent, and the balance of Fe and inevitable impurities.

2. The steel for a rotor yoke of a hydro-generator having excellent surface quality according to claim 1, wherein: the Nb accounts for 0.079-0.091 wt%.

3. The steel for a rotor yoke of a hydro-generator having excellent surface quality according to claim 1, wherein: the weight percentage content of V is 0.039-0.065%.

4. A method for manufacturing a steel for a rotor yoke of a hydro-generator having excellent surface quality as claimed in claim 1, comprising the steps of:

1) smelting in a converter and then continuously casting into a blank;

2) heating a casting blank at 1180-1220 ℃;

3) performing two-stage hot rolling after descaling, and controlling the finish rolling speed at 12-14 m/s and the finish rolling temperature at 880-920 ℃;

4) carrying out laminar flow, and cooling to the coiling temperature at the cooling speed of 20 ℃/s;

5) coiling, wherein the coiling temperature is controlled to be 500-550 ℃;

6) performing cover annealing, annealing in a full hydrogen atmosphere, controlling the annealing temperature at 500-550 ℃, and preserving the heat for 10-15 h at the temperature;

7) naturally cooling to room temperature.

5. The method for producing a steel for a rotor yoke of a hydro-generator having excellent surface quality as set forth in claim 4, wherein: the coiling temperature is 508-536 ℃.

6. The method for producing a steel for a rotor yoke of a hydro-generator having excellent surface quality as set forth in claim 4, wherein: the annealing temperature is 507-542 ℃, and the temperature is kept for 11-14 h at the temperature.

Technical Field

The invention relates to steel for a motor and a production method thereof, in particular to steel for a magnetic yoke of a hydraulic generator rotor with excellent surface quality and a production method thereof, which are more suitable for the hydraulic generator rotor in a unit with the capacity of more than or equal to 100 kilo-kilowatts.

Background

The rotor magnetic yoke in the hydraulic generator structure is one of the most core components, and the main function of the hydraulic generator structure is to generate rotational inertia and hang and install magnetic poles, and is also a part of a magnetic circuit. High strength, high precision and good magnetic properties are required. With the large-scale development of hydroelectric engineering, the rotor volume is continuously increased, and the safety performance requirement is continuously improved, so that higher requirements are provided for the surface quality. Defects such as pits on the surface of the steel plate directly affect the appearance of the steel plate, and the surface pits increase the surface roughness so as to reduce the fatigue limit. The surface quality is improved, and the method has important significance for prolonging the service life and reliability of the generator rotor and reducing the maintenance cost.

Prior to the present invention application, patent documents of inventions having chinese patent nos. ZL201711083951.x, ZL201611103749.4 and ZL201510921787.x describe "a high strength steel sheet having excellent magnetic properties and a method for producing the same", and "a high strength steel sheet for a yoke of a hydraulic generator" respectively. The three documents respectively introduce hot-rolled magnetic yoke steel produced by a controlled rolling and controlled cooling method, the Ti content of the patents is 0.08-0.18%, 0.20-0.25% and 0.035-0.075%, because the TiC solid solution temperature of Ti carbide is high, the casting blank needs to be heated at high temperature before rolling, the heating process is 1350-1400 ℃, 1300-1350 ℃ (heat preservation for 3 hours) and 1280-1350 ℃ (soaking time for 100-150 min), the heating temperature is high, the heat preservation time is long, thick iron scale is easy to generate, the subsequent process is difficult to remove, and the surface quality of the final steel plate is not good.

In addition, the invention patent documents of Chinese patent numbers ZL201510921794.X and ZL201510921789.9 respectively describe 'high-strength high-toughness hot-rolled yoke steel with 550MPa grade yield strength and a manufacturing method thereof' and 'high-strength high-toughness hot-rolled yoke steel with 650MPa grade yield strength and a manufacturing method thereof', because the rolling speed is not controlled, the steel plate forms a thicker iron sheet in the high-temperature rolling process, the later period is difficult to remove, and because an annealing process is not carried out, the surface of the steel plate is not bright, and the surface roughness is influenced.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a magnetic induction performance B for a rotor magnetic yoke of a single-machine hydraulic generator with the capacity of more than or equal to 100 ten thousand kilowatts, wherein the yield strength is more than or equal to 800MPa, the tensile strength is more than or equal to 850MPa and the magnetic induction performance B is₅₀A magnet yoke steel with a surface roughness not more than 1.0 μm and not more than 1.5T and a production method thereof.

The measures for realizing the aim are as follows:

the steel for the magnetic yoke of the hydro-generator rotor with excellent surface quality comprises the following chemical components in percentage by weight: c: 0.03 to 0.07%, Si: less than or equal to 0.05 percent, Mn: 1.85-2.0%, P: less than or equal to 0.015 percent, S: less than or equal to 0.002%, Nb: 0.075-0.095%, V: 0.03 to 0.07%, Mo: 0.10-0.20%, Als: 0.02-0.10%, N: less than or equal to 0.010 percent, and the balance of Fe and inevitable impurities.

Preferably: the Nb accounts for 0.079-0.091 wt%.

Preferably: the weight percentage content of V is 0.039-0.065%.

The production method of the steel with excellent surface quality for the magnetic yoke of the hydro-generator rotor comprises the following steps:

1) smelting in a converter and then continuously casting into a blank;

2) heating a casting blank at 1180-1220 ℃;

3) performing two-stage hot rolling after descaling, and controlling the finish rolling speed at 12-14 m/s and the finish rolling temperature at 880-920 ℃;

4) carrying out laminar cooling, and cooling to the coiling temperature at the cooling speed of 20 ℃/s;

5) coiling, wherein the coiling temperature is controlled to be 500-550 ℃;

6) performing cover annealing, annealing in a full hydrogen atmosphere, controlling the annealing temperature at 500-550 ℃, and preserving the heat for 10-15 h at the temperature;

7) naturally cooling to room temperature.

Preferably: the coiling temperature is 508-536 ℃.

Preferably: the annealing temperature is 507-542 ℃, and the temperature is kept for 11-14 h at the temperature.

The action and mechanism of each element and main process in the invention

Carbon (C) in the present invention: carbon is one of indispensable elements for improving the strength of steel in steel, and can form microalloy carbide under the action of Nb, V and Ti in the steel to play a role in precipitation strengthening, and the magnetic induction performance of the steel is influenced by the over-high content of the carbon. The carbon content is limited to 0.03-0.07%, so that the strength of the steel can be improved, and the magnetic induction performance of the steel can be ensured.

Silicon (Si) in the present invention: si is an important deoxidizer, and has a solid-solution strengthening effect to improve the strength of the steel sheet. However, Si readily forms SiO with O₂SiO during heating in a heating furnace₂Is easy to form fayalite Fe with iron oxide FeO₂SiO₄，Fe₂SiO₄Embedded into the steel sheet structure, is tightly combined with the matrix and is difficult to remove subsequently, thereby causing surface defects, and therefore, the Si content is controlled to be less than or equal to 0.05 percent.

Manganese (Mn) in the present invention: manganese can reduce the phase transition temperature of austenite transformed into ferrite, expand the hot working temperature area, be beneficial to refining the ferrite grain size and improve the yield strength and tensile strength of steel. Therefore, the Mn content is controlled to be 1.85-2.0%.

Phosphorus (P) and sulfur (S) in the present invention: phosphorus is easy to cause segregation in steel, sulfur is easy to combine with manganese to generate MnS inclusions, and the uniform strength is unfavorable. Therefore, the invention should reduce the adverse effects of phosphorus and sulfur elements on the magnetic property and strength of the steel as much as possible, and the content of phosphorus and sulfur is controlled by means of deep desulfurization pretreatment and the like on the molten iron, so that the adverse effects are reduced.

Niobium (Nb) in the invention: nb, V and Ti are the most effective microalloy elements, but Ti is active in chemical property, is easy to combine with O, S, N, C in steel, forms coarse TiN and other impurities in the steel and is unfavorable for performance, and meanwhile, the solid solution temperature of Ti is high, high-temperature heating is needed, and the surface quality control is unfavorable, so that Ti is not additionally added in the invention. Nb has more stable chemical properties, can effectively refine the austenite grain size by inhibiting recrystallization and preventing grain growth, is favorable for improving the strength of the steel plate, and has lower solid solution temperature and favorable for surface quality control. However, if the lower limit is less than the defined lower limit, the strength may be insufficient; however, if the content is higher than the upper limit, the grain boundary segregation is increased to increase the risk of slab cracking, and therefore, the content is controlled to 0.075 to 0.095%, preferably 0.079 to 0.091%.

Vanadium (V) in the present invention: v has stronger grain refining and precipitation strengthening effects, the heat dissipation of the edge part is faster than that of the middle part in the cooling and coiling process of the steel plate, so that the precipitation of Nb at the edge part is insufficient compared with that of the middle part, but the precipitation temperature of V is slightly lower than that of Nb, so that the Nb is suitable for precipitation at the edge part, the strength insufficiency of the edge part is well compensated, and the performance uniformity of the whole plate surface is ensured. However, if the lower limit is less than the defined lower limit, the strength may be insufficient; however, if the content is higher than the upper limit, the segregation at the grain boundary is increased to increase the risk of the occurrence of slab cracking, and therefore, the content is controlled to 0.03 to 0.07%, preferably 0.039 to 0.065%.

Molybdenum (Mo) in the present invention: mo exists in solid solution and carbide of steel, and has the function of solid solution strengthening. When Mo and Nb are added simultaneously, Mo can increase the inhibition on austenite recrystallization in the controlled rolling process, and further promote the refinement of an austenite microstructure, thereby improving the strength of the steel plate.

The heating temperature of the casting blank is controlled to be 1180-1220 ℃. Because the heating temperature is an important factor influencing the surface iron sheet because the fayalite Fe₂SiO₄The melting point is about 1170 ℃, and the molten state is formed, so that the molten state can invade into the iron sheet and the matrix in a wedge shape, and the later stage is extremely difficult to remove. Therefore, the temperature needs to be heated to 1180-1220 ℃, and the subsequent descaling temperature is ensured to be Fe₂SiO₄The melting point is higher than the melting point, so that the removal is convenient, the complete solid solution of the alloy elements can be ensured, and the excessive coarsening of austenite grains and the coarsening of precipitates caused by the overhigh heating temperature can be avoided.

The invention controls the hot rolling speed to be 12-14 m/s, because the rapid rolling can avoid the steel plate from generating thicker iron scale due to longer retention time at high temperature.

The temperature of the hot rolling and the finish rolling is controlled to be 880-920 ℃ so as to obtain the required strength.

The invention controls the coiling temperature to be 500-550 ℃ so as to be beneficial to the precipitation of carbo-nitride of Nb and V, obtain the required strength and simultaneously reduce the further oxidation of the steel plate.

The annealing temperature is controlled to be 500-550 ℃, and the steel plate surface is subjected to a reduction reaction by keeping the temperature for 10-15 hours, so that the surface is clean and bright.

Compared with the prior art, the invention ensures that the yield strength is more than or equal to 800MPa, the tensile strength is more than or equal to 850MPa, and the magnetic induction property B₅₀On the premise of not less than 1.5T, the surface roughness can be not more than 1.6 mu m, and the requirement of steel for the rotor yoke of the hydraulic generator with the single-machine capacity of not less than 100 ten thousand kilowatts can be completely met.

Detailed Description

The present invention is described in detail below:

table 1 is a list of values of the components of each example and comparative example of the present invention;

table 2 shows the values of the process parameters of the examples and comparative examples of the present invention;

table 3 is a table of experimental results of examples and comparative examples of the present invention.

The preparation method comprises the following steps:

1) smelting in a converter and then continuously casting into a blank;

2) heating a casting blank at 1180-1220 ℃;

3) performing two-stage hot rolling after descaling, and controlling the finish rolling speed at 12-14 m/s and the finish rolling temperature at 880-920 ℃;

4) carrying out laminar flow, and cooling to the coiling temperature at the cooling speed of 20 ℃/s;

5) coiling, wherein the coiling temperature is controlled to be 500-550 ℃;

6) performing cover annealing, annealing in a full hydrogen atmosphere, controlling the annealing temperature at 500-550 ℃, and preserving the heat for 10-15 h at the temperature;

7) naturally cooling to room temperature.

TABLE 1 list of chemical compositions (wt%) of inventive and comparative examples

TABLE 2 List of the main process parameters for the examples of the invention and the comparative examples

TABLE 3 results of performance tests of examples of the present invention and comparative examples

As can be seen from the results in the above Table 3, the steel plate of the invention can achieve yield strength of more than or equal to 800MPa, tensile strength of more than or equal to 850MPa and magnetic induction property B₅₀The surface roughness is less than or equal to 1.0 mu m and is more than or equal to 1.5T, and the use requirement of a single-machine capacity hydroelectric generating set with the capacity of more than or equal to 100 ten thousand kilowatts can be completely met.

The above examples are merely preferred examples and are not intended to be exhaustive of the invention.