A high-strength and high-magnetic-induction cold-rolled magnetic pole steel and its production method and application

Abstract

The present invention provides a high-strength and high-magnetic induction cold-rolled magnetic pole steel and its production method and application, the composition: C: 0.07-0.09%, Si: 0.20-0.40%, Mn: 0.50-0.70%, P: 0.03-0.06%, S: 0.0040-0.0060%, N: 0.0090-0.0120%, Ti: ≤0.0016%, V: 0.01-0.012%; B = 0.78N-0.22V; the rest is Fe and inevitable impurities. Compared with the prior art, the present invention obtains a production process suitable for component design matching through component control, obtains a certain bainite structure, ensures the mechanical performance strength of the product, and does not need to add precious metals such as Cr, Ni, Nb, etc., has low cost, and the product performance can meet the high requirements of large-scale hydroelectric generator manufacturing.

Description

Technical Field

[0001] The present invention belongs to the field of cold-rolled magnetic pole steel production, and specifically relates to a high-strength and high-magnetic induction cold-rolled magnetic pole steel and a production method and application thereof. The yield strength of the product is not less than 550Mpa, and the magnetic induction intensity B 50 ≥1.65T, B 100 ≥1.80T, B 150 ≥1.88T, stacking coefficient ≥0.98, can be used in the manufacture of large hydroelectric generators. Background Art

[0002] Among power generation equipment, hydropower is the cleanest and most environmentally friendly. As hydropower generators become larger, the required material performance is getting higher and higher. The magnetic pole is a key component of the rotor body of the hydro-turbine generator and is installed on the outer ring of the hydro-turbine generator. Due to the large size of large hydro-turbine generators, the linear speed during power generation is very high and is subject to very large centrifugal force. In addition, the Lorentz force on the magnetic poles during power generation is also very large. Therefore, in addition to requiring the magnetic properties of the steel used to manufacture the magnetic poles to be very high, the mechanical properties of the steel are required to be higher and higher in strength. In addition, the increase in the strength of the magnetic pole steel greatly increases the difficulty of controlling the shape of the steel plate, and the large size of the large hydro-turbine generator is large and the lamination is high, so there are also strict requirements on the plate shape.

[0003] In order to obtain higher magnetic induction intensity and strength index, the British patent GB1351884 increases the carbon, manganese and silicon content by alloying, but although high strength is obtained, the magnetic induction intensity is significantly lower. Chinese patents CN200610019771.0, CN200610019772.5, CN201310226025.9, CN201310226038.6, CN201310226044.1, CN201310227270.1 obtain high mechanical strength and high magnetic induction intensity by adding different amounts of manganese, niobium and titanium microalloying elements and controlling appropriate hot rolling and cold rolling annealing processes, but the large amount of alloying elements undoubtedly increases the production cost. Summary of the invention

[0004] The purpose of the present invention is to provide a high-strength and high-magnetic induction cold-rolled magnetic pole steel and a production method thereof, which can achieve high mechanical strength and magnetic induction intensity with low alloy cost and appropriate process adjustment, and the yield strength of the product is ≥550MPa, the yield strength ratio is stable at 0.80-0.90, and the magnetic induction intensity B 50 ≥1.65T, B 100 ≥1.80T, B 150 ≥1.88T, no precious metals are added, which significantly improves product competitiveness.

[0005] The present invention also provides an application of high-strength and high-magnetic induction cold-rolled magnetic pole steel for the manufacture of large-scale hydroelectric generators. The product has high strength and high magnetic induction intensity and can meet the high requirements for the manufacture of large-scale hydroelectric generators.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A high-strength and high-magnetic-induction cold-rolled magnetic pole steel, comprising the following components in percentage by mass:

[0008] C: 0.07~0.09%, Si: 0.20~0.40%, Mn: 0.50~0.70%, P: 0.03~0.06%, S: 0.0040~0.0060%, N: 0.0090~0.0120%, Ti: ≤0.0016%, V: 0.01~0.012%; B=0.78N-0.22V; the rest is Fe and unavoidable impurities.

[0009] B=0.78N-0.22V, the calculation result is rounded to 4 decimal places.

[0010] Ti has a strong ability to combine with C and N and forms a stable TiN or Ti(C, N) precipitate phase. This precipitate phase seriously deteriorates the magnetic induction intensity index B under low magnetic field strength. 50 , and for this strength level of magnetic pole steel, B 50 It is also a critical indicator, so the Ti content needs to be controlled in the present invention. At the same time, since Ti is an element that is ubiquitous in molten iron and difficult to remove, in order to reduce the smelting cost, only the upper limit of Ti is required and controlled.

[0011] The structure of the high-strength and high-magnetic-induction cold-rolled magnetic pole steel is a bainite structure, which contains the mechanical property strength that is guaranteed for the product.

[0012] The yield strength of the high-strength and high-magnetic induction cold-rolled magnetic pole steel is ≥550MPa, the yield strength ratio is stable at 0.80-0.90, and the magnetic induction intensity B 50 ≥1.65T, B 100 ≥1.80T, B 150 ≥1.88T, stacking coefficient ≥0.98.

[0013] In the present invention, the matching of C, Si, V and Mn can ensure sufficient austenite content in the hot rolling process, which is conducive to the smooth progress of hot rolling. On the other hand, the carbon equivalent of this matching can ensure a sufficient amount of cementite Fe3C in the finished product to ensure strength. Too high alloy content will significantly deteriorate magnetic induction and increase alloy cost; the addition of P can properly improve strength, and on the other hand, P segregation along the grain boundary can increase {100} component and reduce {111} component, which is beneficial to the improvement of magnetic induction intensity, but too high P content will become brittle and deteriorate cold workability; S combines with Mn to form fine MnS particles, which will inhibit the growth of grains during annealing and improve strength, but excessive S will increase the hot brittleness tendency and is not conducive to the smooth progress of hot rolling; the matching of B, N and V can form BN, VN and V (N, C) particles, which will inhibit the growth of grains during annealing and improve strength. In addition, Ti is an impurity element that is difficult to remove in molten iron, and the production control cost is low at this content. V is a microalloying element that is infinitely dissolved in ferrite. It is easy for N to form VN particles dispersed in the steel, which strongly hinders the grain growth and dislocation movement during annealing, and has a significant effect on improving strength. B preferentially forms BN with N in austenite, which can serve as the nucleation core of other precipitated particles, which helps to evenly distribute the precipitated phase and evenly inhibits the growth of grains and improves the mechanical strength. In addition, B has a small atomic radius and is easy to be segregated and dissolved along the grain boundary, which can increase the {100} component and reduce the {111} component, which is beneficial to the improvement of magnetic induction intensity (especially the magnetic induction intensity in low magnetic fields) and inhibit the generation of magnetic aging.

[0014] The present invention provides a method for producing high-strength and high-magnetic-induction cold-rolled magnetic pole steel, comprising the following process flow:

[0015] Molten steel smelting → continuous casting → heating of ingot → hot rolling → pickling and cold rolling → annealing → leveling → finishing and packaging.

[0016] The continuous casting uses electromagnetic stirring of the crystallizer, and the thickness of the continuous casting billet is 200-260 mm, so that the equiaxed crystal ratio of the billet is ≥60%. If the equiaxed crystal ratio is too low, the finished product will have corrugated surface defects.

[0017] The ingot is heated at a temperature of 1120-1220°C.

[0018] The hot rolling has a hot rolling thickness of 2.8 to 3.2 mm, a final rolling temperature of 870 to 920° C., and a coiling temperature of 500 to 550° C. The reduction ratio between the hot rolling thickness and the ingot thickness can ensure that the columnar crystals in the ingot are fully broken to avoid corrugation defects on the surface of the finished product, and can ensure a {100} component texture with sufficient strength on the other hand. The final rolling temperature can ensure that the hot rolling is carried out in the austenite phase region to ensure a stable and smooth hot rolling process. The coiling temperature can ensure that the deformed grains after hot rolling can be fully recrystallized into equiaxed grains, which is beneficial to subsequent cold rolling. In addition, at the lower coiling temperature, a large amount of BN is precipitated to inhibit the grain growth during the subsequent annealing of the finished product and improve the mechanical strength.

[0019] The pickling and cold rolling process may meet the requirements of general cold-rolled products.

[0020] The annealing is carried out at 650-750°C in a reducing atmosphere for 0.5-1h. This temperature can ensure that the deformed structure after cold rolling is partially recovered and recrystallized, thereby ensuring the yield strength ratio (the ratio of yield strength to tensile strength), providing sufficient safety margin for subsequent use in generators.

[0021] The flattening process adopts a plate shape control mode to control the elongation rate to 0.3-0.5%, eliminate the wave shape, improve the plate shape of the finished product and ensure the stacking coefficient.

[0022] The present invention provides an application of high-strength and high-magnetic induction cold-rolled magnetic pole steel for manufacturing large-scale hydroelectric generators. The product has high strength and high magnetic induction intensity, a yield strength of ≥550MPa, a yield strength ratio stable between 0.80 and 0.90, and a magnetic induction intensity B 50 ≥1.65T, B 100 ≥1.80T, B 150 ≥1.88T, stacking coefficient ≥0.98, which can meet the high requirements of large-scale hydroelectric generator manufacturing.

[0023] Compared with the prior art, the present invention obtains a production process suitable for component design through component control, obtains a certain bainite structure, ensures the mechanical strength of the product, and does not need to add precious metals such as Cr, Ni, Nb, etc., and can obtain cold-rolled magnetic pole steel products with excellent performance on the basis of ordinary carbon steel. It has the following advantages: the yield strength of the cold-rolled magnetic pole steel product produced according to the technical solution of the present invention is ≥550MPa, and the yield strength ratio is stable between 0.80 and 0.90, which provides sufficient strength safety margin for subsequent use in generators; the magnetic induction intensity B of the cold-rolled magnetic pole steel product produced according to the technical solution of the present invention is 50 ≥1.65T, B 100 ≥1.80T, B 150 ≥1.88T, stacking coefficient ≥0.98, which provides guarantee for the efficiency of subsequent generators. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the organization diagram of Example 1, which is a bainite organization;

[0025] Figure 2 is the organization diagram of comparative example 1, which is pearlite organization;

[0026] The strength of the steel having a bainite structure in Example 1 is higher than that of the steel having a pearlite structure in Comparative Example 1. DETAILED DESCRIPTION

[0027] Example 1

[0028] A method for producing high-strength and high-magnetic-induction cold-rolled magnetic pole steel includes the following process flow:

[0029] Molten steel smelting → continuous casting → heating of ingot → hot rolling → pickling and cold rolling → annealing → leveling → finishing and packaging.

[0030] Specifically: the composition of molten steel is smelted according to mass percentage: C: 0.07%, Si: 0.20%, Mn: 0.50%, P: 0.06%, S: 0.0060%, N: 0.012%, Ti: 0.0015%, V: 0.01%, B: 0.0072%, and the rest is Fe and unavoidable impurities. The smelted molten steel is then continuously cast into a 200mm thick continuous casting billet with an equiaxed crystal ratio of 60%. The billet is then heated in a heating furnace at 1120°C for 3h, and then hot rolled to 2.8mm, with the final rolling temperature at 870°C and the coiling temperature at 500°C. The hot-rolled coil is then pickled and cold-rolled to an ordered thickness of 1.0mm, and the cold-rolled coil is annealed. The annealing process is to maintain the temperature at 650°C in a reducing atmosphere for 0.5h. Finally, the annealed coil is flattened and lightly pressed according to the plate type mode (elongation 0.5%).

[0031] The cold-rolled magnetic pole steel product produced according to the technical solution of Example 1 has a yield strength of 579 MPa, a yield strength ratio of 0.88, and a magnetic induction intensity B 50 =1.66T, B 100 =1.81T, B 150 =1.89T, stacking coefficient is 0.99.

[0032] Embodiment 2:

[0033] A method for producing high-strength and high-magnetic-induction cold-rolled magnetic pole steel includes the following process flow:

[0034] Molten steel smelting → continuous casting → heating of ingot → hot rolling → pickling and cold rolling → annealing → leveling → finishing and packaging.

[0035] Specifically: the composition of molten steel is smelted according to mass percentage: C: 0.09%, Si: 0.40%, Mn: 0.70%, P: 0.03%, S: 0.0040%, N: 0.012%, Ti: 0.0010%, V: 0.012%, B: 0.0067%, and the rest is Fe and unavoidable impurities. Then the smelted molten steel is continuously cast into a continuous casting billet with a thickness of 260 mm. The proportion of equiaxed crystals in the billet is 62%. The billet is then heated in a heating furnace at 1220°C for 3 hours, and then hot rolled to 3.2 mm. The final rolling temperature is controlled at 920°C and the coiling temperature is 550°C. The hot-rolled coil is then pickled and cold-rolled to an order thickness of 1.0 mm. The cold-rolled coil is then annealed. The annealing process is to maintain the temperature at 750°C in a reducing atmosphere for 0.5 hours. Finally, the annealed coil is flattened and lightly pressed according to the plate shape mode (elongation 0.5%). The yield strength of the cold-rolled magnetic pole steel product produced in Example 2 is 572 MPa, the yield strength ratio is 0.81, and the magnetic induction intensity B 50 =1.67T, B 100 =1.80T, B 150 =1.88T, stacking coefficient is 0.99.

[0036] Example 3

[0037] A method for producing high-strength and high-magnetic-induction cold-rolled magnetic pole steel includes the following process flow:

[0038] Molten steel smelting → continuous casting → heating of ingot → hot rolling → pickling and cold rolling → annealing → leveling → finishing and packaging.

[0039] Specifically: The composition of molten steel is smelted according to mass percentage: C: 0.08%, Si: 0.20%, Mn: 0.50%, P: 0.03%, S: 0.0041%, N: 0.0090%, Ti: 0.0010%, V: 0.01%, B: 0.0048%, and the rest is Fe and inevitable impurities. Then the smelted molten steel is continuously cast into a 200mm thick continuous casting billet, and the proportion of equiaxed crystals in the billet is 60%. Then the billet is heated in a heating furnace at 1120℃ for 3h, and then hot rolled to 2.8mm, and the final rolling temperature is controlled at 890℃ and the coiling temperature is 550℃; then the hot-rolled coil is pickled and cold-rolled to the order thickness of 0.5mm, and then the cold-rolled coil is annealed. The annealing process is to keep it at 750℃ in a reducing atmosphere for 1h, and finally the annealed coil is flattened and lightly pressed according to the plate type mode (elongation 0.3%). The cold-rolled magnetic pole steel product produced according to the technical solution of Example 3 has a yield strength of 566 MPa, a yield strength ratio of 0.83, and a magnetic induction intensity B 50 =1.66T, B 100 =1.81T, B 150 =1.88T, stacking coefficient is 0.98.

[0040] Example 4

[0041] A method for producing high-strength and high-magnetic-induction cold-rolled magnetic pole steel includes the following process flow:

[0042] Molten steel smelting → continuous casting → heating of ingot → hot rolling → pickling and cold rolling → annealing → leveling → finishing and packaging.

[0043] Specifically: the composition of molten steel is smelted according to mass percentage: C: 0.08%, Si: 0.40%, Mn: 0.70%, P: 0.06%, S: 0.0047%, N: 0.010%, Ti: 0.0016%, V: 0.012%, B: 0.0052%, and the rest is Fe and unavoidable impurities. Then the smelted molten steel is continuously cast into a continuous casting billet with a thickness of 260 mm. The proportion of equiaxed crystals in the billet is 61%. The billet is then heated in a heating furnace at 1200°C for 3 hours, and then hot rolled to 3.2 mm. The final rolling temperature is controlled at 890°C and the coiling temperature is 500°C. The hot-rolled coil is then pickled and cold-rolled to an order thickness of 0.5 mm. The cold-rolled coil is then annealed. The annealing process is to maintain the temperature at 700°C in a reducing atmosphere for 0.8 hours. Finally, the annealed coil is flattened and lightly pressed according to the plate shape mode (elongation 0.3%). The yield strength of the cold-rolled magnetic pole steel product produced according to the technical solution of Example 4 is 587 MPa, the yield strength ratio is 0.87, and the magnetic induction intensity B 50 =1.65T, B 100 =1.81T, B 150 =1.89T, stacking coefficient is 0.98.

[0044] Comparative Example 1:

[0045] A production method for cold-rolled magnetic pole steel includes the following process flow:

[0046] Molten steel smelting → continuous casting → heating of ingot → hot rolling → pickling and cold rolling → annealing → leveling → finishing and packaging.

[0047] Specifically: The composition of molten steel is smelted according to mass percentage: C: 0.07%, Si: 0.20%, Mn: 0.10%, P：0.02％、 S: 0.0060%, N: 0.012%, Ti: 0.0050% , V: 0.01%, no boron B, the rest is Fe and inevitable impurities. Then the smelted molten steel is continuously cast into a 200mm thick continuous casting billet, the equiaxed crystal ratio in the billet is 60%, and then the billet is heated in a heating furnace at 1120℃ for 3h, and then hot rolled to 2.8mm, and the final rolling temperature is controlled at 870℃. Coiling temperature 650℃; After that, the hot-rolled coil is pickled and cold-rolled to the order thickness of 1.0 mm, and then the cold-rolled coil is annealed. The annealing process is to maintain the temperature at 650°C in a reducing atmosphere for 0.5 hours. Finally, the annealed coil is flattened and lightly pressed according to the plate shape mode (elongation 0.5%). The cold-rolled magnetic pole steel product produced according to the technical scheme of comparative example 1 Yield strength is 539MPa , yield strength ratio 0.88, magnetic induction intensity B 50 =1.64T , B 100 =1.80T, B 150 =1.87T , the stacking coefficient is 0.99. In comparative example 1, B is not contained, and the reduction of Mn and P content and the increase of Ti content are unfavorable to the magnetic induction, but the precipitation strengthening effect of the higher Ti content also maintains a higher mechanical strength.

[0048] Comparative Example 2:

[0049] A production method for cold-rolled magnetic pole steel includes the following process flow:

[0050] Molten steel smelting → continuous casting → heating of ingot → hot rolling → pickling and cold rolling → annealing → leveling → finishing and packaging.

[0051] Specifically: The composition of molten steel is smelted according to mass percentage: C: 0.09%, Si: 0.40%, Mn: 0.30% , P: 0.03%, S: 0.0040%, N: 0.012%, Ti: 0.0050% , V：0.03％ , without adding boron B, the rest is Fe and inevitable impurities. Then the smelted molten steel is continuously cast into a 260mm thick continuous casting billet, the equiaxed crystal ratio in the billet is 62%, and then the billet is heated in a heating furnace at 1220℃ for 3h, and then hot rolled to 3.2mm, and the final rolling temperature is controlled at 920℃. Coiling temperature 700℃ ; After that, the hot-rolled coil is pickled and cold-rolled to the order thickness of 1.0mm, and then the cold-rolled coil is annealed. The annealing process is to keep it at 750℃ in a reducing atmosphere for 0.5h. Finally, the annealed coil is flattened and lightly pressed according to the plate shape mode (elongation 0.5%). The yield strength of the cold-rolled magnetic pole steel product produced according to the technical scheme of comparative example 2 is 610MPa and the yield strength ratio is 0.93 , magnetic induction intensity B 50 =1.62T、B 100 =1.78T , B 150 =1.88T, The stacking coefficient is 0.91 The large amount of V and Ti added greatly improves the mechanical strength, but also worsens the magnetic induction and increases the difficulty of controlling the plate shape; the coiling temperature at this alloy content cannot be too low, otherwise more precipitation phases will precipitate and cold rolling cannot be carried out.

[0052] Comparative Example 3:

[0053] A production method for cold-rolled magnetic pole steel includes the following process flow:

[0054] Molten steel smelting → continuous casting → heating of ingot → hot rolling → pickling and cold rolling → annealing → leveling → finishing and packaging.

[0055] Specifically: The composition of molten steel is smelted according to mass percentage: C: 0.08%, Si: 0.20%, Mn: 0.10% , P: 0.03%, S: 0.0041%, N: 0.0090%, Ti: 0.0010%, V: 0.010%, B：0.0048％， The remainder is Fe and unavoidable impurities. The smelted molten steel is then continuously cast into a 200mm thick continuous casting billet, with an equiaxed crystal ratio of 60%. The billet is then heated in a heating furnace at 1120°C for 3 hours, and then hot rolled to 2.8mm, with the final rolling temperature at 890°C and the coiling temperature at 530°C. The hot-rolled coil is then pickled and cold-rolled to an order thickness of 0.5mm, and then the cold-rolled coil is annealed. The annealing process is to maintain the temperature at 750°C in a reducing atmosphere for 1 hour, and finally the annealed coil is cut according to the plate pattern. (elongation 0.1%) The cold-rolled magnetic pole steel product produced according to the technical solution of Comparative Example 3 is Yield strength is 535MPa , yield strength ratio 0.83, magnetic induction intensity B 50 =1.66T, B 100 =1.81T, B 150 =1.88T, The stacking factor is 0.96. The elongation is equivalent to slight cold rolling, which has the function of improving the plate shape. At the same time, work hardening will also increase the yield strength by a small amount. In the comparison example, the elongation is lower, the strength is slightly reduced, the plate shape is poor, and the stacking coefficient is low.

[0056] The present specification uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A high-strength and high-magnetic-induction cold-rolled magnetic pole steel, characterized in that: The high-strength and high-magnetic-induction cold-rolled magnetic pole steel comprises the following components in percentage by mass: C: 0.07~0.09%, Si: 0.20~0.40%, Mn: 0.50~0.70%, P: 0.03~0.06%, S: 0.0040~0.0060%, N: 0.0090~0.0120%, Ti: ≤0.0016%, V: 0.01~0.012%; B=0.78N-0.22V; the rest is Fe and unavoidable impurities; The production method of the high-strength and high-magnetic-induction cold-rolled magnetic pole steel comprises the following process flow: smelting molten steel→continuous casting→heating of ingots→hot rolling→pickling and cold rolling→annealing→flattening→finishing and packaging; The continuous casting uses electromagnetic stirring of the crystallizer, and the thickness of the continuous casting billet is 200-260 mm, so that the equiaxed crystal ratio of the billet is ≥60%; The casting is heated at a temperature of 1120-1220°C; The hot rolling has a hot rolling thickness of 2.8-3.2 mm, a final rolling temperature of 870-920° C., and a coiling temperature of 500-550° C.; The annealing is carried out at a temperature of 650-750° C. in a reducing atmosphere for 0.5-1 h.

2. The high-strength and high-magnetic-induction cold-rolled magnetic pole steel according to claim 1, characterized in that: The yield strength of the high-strength and high-magnetic induction cold-rolled magnetic pole steel is ≥550MPa, and the yield strength ratio is stable at 0.80~0.90; the magnetic induction intensity B 50 ≥1.65T, B 100 ≥1.80T, B 150 ≥1.88T, stacking coefficient ≥0.

98.

3. A method for producing the high-strength and high-magnetic-induction cold-rolled magnetic pole steel according to claim 1 or 2, characterized in that: The production method comprises the following process flow: smelting molten steel→continuous casting→heating of ingots→hot rolling→pickling and cold rolling→annealing→flattening→finishing and packaging; The continuous casting uses electromagnetic stirring of the crystallizer, and the thickness of the continuous casting billet is 200-260 mm, so that the equiaxed crystal ratio of the billet is ≥60%; The casting is heated at a temperature of 1120-1220°C; The hot rolling has a hot rolling thickness of 2.8-3.2 mm, a final rolling temperature of 870-920° C., and a coiling temperature of 500-550° C.; The annealing is carried out at a temperature of 650-750° C. in a reducing atmosphere for 0.5-1 h.

4. The production method according to claim 3, characterized in that: The flatness controls the elongation to be 0.3-0.5%.

5. An application of the high-strength and high-magnetic-induction cold-rolled magnetic pole steel according to claim 1 or 2, characterized in that: Used in the manufacture of large hydroelectric generators.

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