1. A1200 MPa-grade magnetic yoke steel for manufacturing a hydraulic generator rotor comprises the following chemical components in percentage by weight: c: 0.15 to 0.25%, Si: 0.35-0.45%, Mn: 1.40-1.80%, P: less than or equal to 0.015 percent, S: less than or equal to 0.002%, Nb: 0.01-0.023%, B: 0.002-0.003%, Als: 0.02-0.10%, RE: 0.20 to 0.30% and the balance of Fe and inevitable impurities.

2. A 1200MPa grade yoke steel for manufacturing a hydro-generator rotor according to claim 1, wherein: the weight percentage of RE is 0.23-0.30%.

3. A 1200MPa grade yoke steel for manufacturing a hydro-generator rotor according to claim 1, wherein: the weight percentage of Mn is 1.43-1.73%.

4. A 1200MPa grade yoke steel for manufacturing a hydro-generator rotor according to claim 1, wherein: the weight percentage of Nb is 0.013-0.023%.

5. A method for producing 1200MPa grade yoke steel for manufacturing a hydro-generator rotor according to claim 1, comprising the steps of:

1) continuously casting into a blank after smelting in a converter and refining by LF and RH;

2) heating a casting blank at 1230-1265 ℃;

3) carrying out hot rolling after descaling, and carrying out finish rolling at the finish rolling temperature of 850-900 ℃ by adopting the traditional two-stage rolling;

4) carrying out laminar flow, and cooling to the coiling temperature at the cooling speed of 20-30 ℃/s;

5) coiling, wherein the coiling temperature is controlled to be 550-600 ℃;

6) quenching, wherein the quenching temperature is controlled to be 910-930 ℃;

7) tempering is carried out, the tempering temperature is controlled to be 350-400 ℃, and the temperature is kept for 20-50 min at the temperature;

8) naturally cooling to room temperature.

6. The production method of 1200MPa grade yoke steel for manufacturing a hydro-generator rotor according to claim 5, characterized in that: the heating temperature of the casting blank is 1242-1270 ℃.

7. The production method of 1200MPa grade yoke steel for manufacturing a hydro-generator rotor according to claim 5, characterized in that: the coiling temperature is 550-590 ℃.

8. The production method of 1200MPa grade yoke steel for manufacturing a hydro-generator rotor according to claim 5, characterized in that: the tempering temperature is 350-386 ℃.

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 also continuously improved, so that higher requirements are also provided for the strength of the magnetic yoke steel.

After retrieval: chinese patent application No. ZL201711087052.7 describes 'ultrahigh strength magnet yoke steel and a manufacturing method thereof', and the ultrahigh strength magnet yoke steel comprises the following chemical components in percentage by weight: 0.10 to 0.15, Si: less than or equal to 0.15, Mn: 1.85-2.00, P: 0.015 or less, S: less than or equal to 0.010, Ti: 0.20 to 0.30, Nb: 0.05 to 0.07, Mo: 0.35-0.55, B: 0.001 to 0.003, Als: 0.02-0.10, N: less than or equal to 0.010 percent, and the balance of Fe and inevitable impurities. After the steel plate is subjected to controlled rolling and controlled cooling treatment, the yield strength of the steel plate can only reach 900MPa, and the requirement of a hydraulic generator rotor with 120 ten thousand kilowatts of unit capacity on 1200MPa ultrahigh-strength magnet yoke steel cannot be met.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a magnetic induction property B with the yield strength of more than or equal to 1200MPa, the tensile strength of more than or equal to 1250MPa, the elongation of more than or equal to 10 percent₅₀The yield strength 1200MPa grade magnetic yoke steel which is more than or equal to 1.46T and is used for manufacturing a hydraulic generator rotor with the single-machine capacity of 120 ten thousand kilowatts and a production method thereof.

The measures for realizing the aim are as follows:

a1200 MPa-grade magnetic yoke steel for manufacturing a hydraulic generator rotor comprises the following chemical components in percentage by weight: c: 0.15 to 0.25%, Si: 0.35-0.45%, Mn: 1.40-1.80%, P: less than or equal to 0.015 percent, S: less than or equal to 0.002%, Nb: 0.01-0.023%, B: 0.002-0.003%, Als: 0.02-0.10%, RE: 0.20 to 0.30% and the balance of Fe and inevitable impurities.

Preferably: the weight percentage of RE is 0.23-0.30%.

Preferably: the weight percentage of Mn is 1.43-1.73%.

Preferably: the weight percentage of Nb is 0.013-0.023%.

A production method of 1200 MPa-level magnetic yoke steel for manufacturing a hydraulic generator rotor comprises the following steps:

1) continuously casting into a blank after smelting in a converter and refining by LF and RH;

2) heating a casting blank at 1230-1265 ℃;

3) carrying out hot rolling after descaling, and carrying out finish rolling at the finish rolling temperature of 850-900 ℃ by adopting the traditional two-stage rolling;

4) carrying out laminar cooling, and cooling to the coiling temperature at the cooling speed of 20-30 ℃/s;

5) coiling, wherein the coiling temperature is controlled to be 550-600 ℃;

6) quenching, wherein the quenching temperature is controlled to be 910-930 ℃;

7) tempering is carried out, the tempering temperature is controlled to be 350-400 ℃, and the temperature is kept for 20-50 min at the temperature;

8) naturally cooling to room temperature.

Preferably: the heating temperature of the casting blank is 1242-1270 ℃.

Preferably: the coiling temperature is 550-590 ℃.

Preferably: the tempering temperature is 350-386 ℃.

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

The content of carbon (C) is 0.15-0.25%, carbon is one of indispensable elements for improving the strength of steel in steel, and the magnetic induction performance of the steel is influenced by the excessively high content of carbon. The carbon content is limited to 0.15-0.25%, so that the strength of the steel can be improved, and the magnetic induction performance of the steel can be ensured.

The content of silicon (Si) is 0.35-0.40%, Si has solid solution strengthening effect and can improve hardenability. Si can reduce the diffusion speed of carbon in ferrite, so that carbide precipitated during tempering is not easy to aggregate, the tempering stability is improved, the strength and the hardness of steel are improved along with the increase of silicon, and when the content of silicon exceeds a certain range, crystal grains are coarsened, so that the content of Si is controlled to be 0.35-0.40 percent.

The content of manganese (Mn) is 1.40-1.80%, the 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. However, if the Mn content is too high, the temper brittleness and center segregation of the steel are increased, so the Mn content is controlled to be 1.40-1.80 percent by the invention.

The content of niobium (Nb) is 0.01-0.023%, and a trace amount of niobium can obviously refine grains and improve the tensile strength of the steel. In the controlled rolling process, niobium can improve the recrystallization temperature of steel, reduce the load of a rolling mill and facilitate the control of plate shape. Meanwhile, the austenite grain size can be refined by inhibiting recrystallization and preventing grain growth. In the cooling process after rolling, the small particles of NbC and NbN are separated out, and can play a role in strengthening precipitation.

The content of phosphorus (P) is less than or equal to 0.015 percent, the content of sulfur (S) is less than or equal to 0.002 percent, phosphorus is easy to cause segregation in steel, and sulfur is easy to combine with manganese to generate MnS inclusions which are all unfavorable for strength. Therefore, the invention should minimize the adverse effects of phosphorus and sulfur on the magnetic properties and strength of the steel, and the P, S content of the steel is controlled as P: 0.015 or less, S: less than or equal to 0.002.

The content of boron (B) is 0.002% -0.003%, B has the main function of improving the hardenability of steel, and boron is taken as a surface active element, is adsorbed on austenite grain boundaries, delays the transformation from austenite to ferrite, and is segregated in the austenite grain boundaries to block the nucleation of ferrite, thereby being beneficial to the formation of martensite and further improving the structure strengthening effect. However, the B content is too high, the hardenability is lowered, and eutectic crystals having a low melting point are formed and concentrated on the grain boundaries, thereby causing hot brittleness. Therefore, the boron content range of the invention is 0.002% -0.003%.

Rare Earth (RE) in the present invention: the rare earth has obvious solid solution strengthening effect, the solid solution rare earth is mainly distributed in a crystal boundary, the interfacial tension and the interfacial energy are reduced, and the driving force for the growth of crystal grains is reduced, so that the growth of austenite crystal grains is inhibited, and the crystal grains are refined. Meanwhile, the rare earth can promote the precipitation of microalloy elements, enhance the precipitation strengthening effect, and enrich the grain boundary through a diffusion mechanism, thereby reducing the segregation of impurity elements in the grain boundary and strengthening the grain boundary. In addition, the rare earth has better magnetism, the magnetic property of the steel plate can be effectively improved, and the RE content range is 0.20-0.30% by comprehensive consideration.

The method limits the heating temperature of the casting blank to 1230-1280 ℃, preferably 1242-1270 ℃, so as to ensure complete solid solution and full austenitization of alloy elements, improve the temperature uniformity of the plate blank, reduce the deformation resistance and rolling load and be beneficial to rolling the thin-gauge magnet yoke steel.

The final rolling temperature is limited to 850-900 ℃, the coiling temperature is 550-600 ℃, preferably the coiling temperature is 550-590 ℃, and the refined austenite grains are mainly used, so that the strength of the steel after heat treatment is improved.

The invention limits the quenching heating temperature to 910-930 ℃, namely Ac3+ (70-90) DEG C, and mainly coarsens original austenite grains, reduces the barrier effect of austenite grain boundaries on magnetic domain walls, obtains good magnetic performance, and simultaneously avoids oversize structures, thereby obtaining refined quenched martensite structures and improving the strength of steel.

The tempering heating temperature is limited to 350-400 ℃, preferably 350-386 ℃, and the holding time is 20-50 min. The method is characterized in that supersaturated carbon atoms in the quenched martensite are desolventized to form fine carbide particles through a tempering process, the strength of the steel plate is further improved, the plasticity of the steel is improved, and the carbide particles grow rapidly when the tempering temperature is too high or the heat preservation time is too long, so that the yield strength of the steel plate can be remarkably reduced. And comprehensively considering the strength and the plasticity, finally setting the tempering heating temperature to be 350-400 ℃, and keeping the temperature for 20-50 min.

Compared with the prior art, the invention has the yield strength of more than or equal to 1200MPa, the tensile strength of more than or equal to 1250MPa, the elongation of more than or equal to 10 percent and the magnetic induction property B₅₀The steel is more than or equal to 1.46T, has simple elements and lower production cost, and can completely meet the requirement of the steel for the rotor yoke of the hydraulic generator with the single-machine type capacity of 120 ten thousand kilowatts and the required yield strength of over 12000 MPa.

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 is a list of process parameter values and performance tests for each example and comparative example of the present invention.

The preparation method comprises the following steps:

1) continuously casting into a blank after smelting in a converter and refining by LF and RH;

2) heating a casting blank at 1230-1265 ℃;

3) carrying out hot rolling after descaling, and carrying out finish rolling at the finish rolling temperature of 850-900 ℃ by adopting the traditional two-stage rolling;

4) carrying out laminar cooling, and cooling to the coiling temperature at the cooling speed of 20-30 ℃/s;

5) coiling, wherein the coiling temperature is controlled to be 550-600 ℃;

6) quenching, wherein the quenching temperature is controlled to be 910-930 ℃;

7) tempering is carried out, the tempering temperature is controlled to be 350-400 ℃, and the temperature is kept for 20-50 min at the temperature;

8) naturally cooling to room temperature.

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

TABLE 2 Main Process parameters and Performance test List for inventive and comparative examples

As can be seen from the results in the above Table 2, the yield strength of the steel of the invention is not less than 1200MPa, the tensile strength is not less than 1250MPa, the elongation is not less than 10%, and the magnetic induction property B₅₀The pressure is more than or equal to 1.46T, and the requirement of manufacturing a hydraulic generator rotor with the capacity of 120 ten thousand kilowatts of a single machine is completely met.

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