CN115261732B - 350 MPa-grade low-cost high-magnetic-induction cold-rolled magnetic pole steel and manufacturing method thereof - Google Patents
350 MPa-grade low-cost high-magnetic-induction cold-rolled magnetic pole steel and manufacturing method thereof Download PDFInfo
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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Abstract
The invention discloses 350 MPa-level low-cost high-magnetic-induction cold-rolled magnetic pole steel, which comprises the following chemical components in percentage by weight: c:0.01 to 0.03 percent of Mn:0.3 to 0.5 percent, si:0.3 to 0.6 percent, als:0.050 to 0.10%, P: less than or equal to 0.02 percent, S: less than or equal to 0.0020 percent, N: less than or equal to 0.005 percent, cu: less than or equal to 0.02, ti: less than or equal to 0.02-0.04%, T [ O ] less than or equal to 0.002%, and the balance being Fe and unavoidable impurities; the microstructure of the product is ferrite and a small amount of pearlite, and the thickness of the finished product is 0.6 mm-2.0 mm; the manufacturing method comprises the steps of converter steelmaking, LF refining, RH refining, continuous casting, hot rolling, coiling, straightening, pickling, cold rolling, electrolytic degreasing, full hydrogen gas hood annealing and leveling; the yield strength Rp0.2 of the obtained product is more than or equal to 350MPa, the tensile strength is more than or equal to 450MPa, and the magnetic induction strength B50 is more than or equal to 1.65T.
Description
Technical Field
The invention belongs to the technical field of metallurgy, and particularly relates to 350 MPa-level low-cost high-magnetic-induction cold-rolled magnetic pole steel and a manufacturing method thereof.
Background
The magnetic pole is an important component of the generator rotor, and in order to ensure stable high-speed operation of the unit, the steel plate is required to have good mechanical property and magnetic property and good dimensional accuracy. The magnetic induction intensity is an important index for measuring the performance of the magnetic pole steel, and the magnetic pole steel is required to have excellent magnetic induction intensity in order to reduce the energy conversion loss of the generator set, namely, to reduce eddy current loss.
In order to increase the strength of the magnetic pole steel, the strength of the material is usually increased by adding an alloy element, but the increase in strength is usually accompanied by a decrease in magnetic properties, that is, magnetic induction strength B50. And along with the increasing competition of homogenization of steel factories, how to green and low-cost produce high-performance steel materials also becomes the research and development direction of various enterprises.
The patent application No. CN200610018662.5 discloses a manufacturing method of 350MPa grade cold-rolled magnetic pole steel, which comprises the following steps: (1) heating the slab to 1160-1230 ℃; (2) a step of hot rolling; the initial rolling temperature is 1050-1100 ℃, and the final rolling temperature is 130-180 ℃; cooling to 620-610 ℃ and coiling; (3) cooling to below 60 ℃ and pickling; (4) a step of cold rolling; (5) bell furnace annealing; the annealing temperature is controlled to be 650-660 ℃; (6) flattening to prepare 350MPa grade cold-rolled magnetic pole steel; the slab comprises the following main chemical components in percentage by weight: 0.05-0.10% of C, 0.10-0.30% of Si, 0.50-1.10% of Mn, 0.020-0.040% of Nb, 0.020-0.040% of Ti, 0.02-0.06% of Als, less than or equal to 0.025% of P, less than or equal to 0.010% of S and the balance of Fe. The cold-rolled magnetic pole steel produced by the method has good matching of the steel plate strength and the magnetic induction strength, has no strict requirements on rolling equipment and process control, and has low cost, and the magnetic induction strength B50 is more than 1.58T.
Patent application number CN201510331665.8 discloses a cold-rolled magnetic pole steel with high magnetic induction and low cost and high yield strength of 450MPa and a manufacturing method thereof, wherein the steel comprises the following chemical components in percentage by mass: c:0.05 to 0.08 percent, mn:0.65 to 1.15 percent, P is less than or equal to 0.025 percent, S is less than or equal to 0.01 percent, al:0.015 to 0.05 percent, N is less than or equal to 0.01 percent, nb: 0.005-0.02%, ti:0.05 to 0.08 percent, and the balance of Fe and unavoidable impurities, and the requirements are that: ti is more than or equal to 0.03% +3.43 x N. The steel has simple chemical components, low cost is greatly reduced by adding low-cost Ti, the uniformity of the product performance is obviously improved by adopting a continuous annealing mode, the lower yield strength ReL of the manufactured magnetic pole steel is more than or equal to 450MPa, the magnetic induction strength B50 is more than or equal to 1.6T, the steel plate strength and the magnetic induction strength are well matched, and the product has better comprehensive performance.
The method in the two published patents adds more Mn and Nb elements with higher cost, and the magnetic induction intensity B50 is more than 1.58T/B50 is more than or equal to 1.6T, and the magnetic induction intensity is lower.
How to produce 350Mpa grade cold rolled magnetic pole steel with good magnetic property and low cost is a problem to be solved.
Disclosure of Invention
In order to obtain a magnetic pole steel plate with low cost and 350MPa grade and good magnetic performance, the magnetic pole steel plate is usually reinforced by adding C, si, mn, nb, ti and other alloy elements into the magnetic pole steel, the addition of manganese plays a role in solid solution strength, the strength of the steel can be obviously improved, but the magnetic performance is influenced by excessive Mn; the element C is the most economical strengthening element, mainly exists in a steel base in the form of solid solution or carbide, and the magnetic induction intensity of the element C is influenced by excessive C. Si can improve the strength of the steel and reduce the magnetic resistance, but strip scale defects are easy to form on the surface along with the increase of the addition amount. Nb and Ti can play a role in strengthening fine crystals, and can form NbC/TiC with redundant carbon to play a role in solidifying C. The cost of raw materials of ferromanganese and ferroniobium is high, and excessive addition leads to the increase of alloy cost, and the magnetic induction intensity B50 of 350 Mpa-level magnetic pole steel in the current search patent is more than 1.6T.
Aiming at the defects of the existing magnetic pole steel component design and the whole process production process, the invention provides a manufacturing method of low-cost high-magnetic induction magnetic pole steel, which comprises the steps of new components, hot rolling and cold rolling, and the 350 MPa-level magnetic pole steel based on the hood-type annealing process is obtained, wherein the yield strength Rp0.2 is more than or equal to 350MPa, the tensile strength is more than or equal to 450MPa, and the magnetic induction strength B50 is more than or equal to 1.65T.
In order to achieve the above purpose, the following technical scheme is adopted:
a350 MPa-grade low-cost high-magnetic-induction cold-rolled magnetic pole steel comprises the following chemical components in percentage by weight: c:0.01 to 0.03 percent of Mn:0.3 to 0.5 percent, si:0.3 to 0.6 percent, als:0.050 to 0.10%, P: less than or equal to 0.02 percent, S: less than or equal to 0.0020 percent, N: less than or equal to 0.005 percent, cu: less than or equal to 0.02, ti: less than or equal to 0.02-0.04%, T [ O ] less than or equal to 0.002%, and the balance being Fe and unavoidable impurities; the microstructure of the product is ferrite and a small amount of pearlite, and the thickness of the finished product is 0.6 mm-2.0 mm.
The manufacturing method of the 350 MPa-level cold-rolled magnetic pole steel comprises the steps of converter steelmaking, LF refining, RH refining, continuous casting, hot rolling, coiling, straightening, pickling, cold rolling, electrolytic degreasing, full hydrogen cover annealing and leveling.
According to the scheme, the heating temperature of the hot rolled plate blank is 1150-1250 ℃, the initial rolling temperature is 1030-1010 ℃, the final rolling finishing temperature is 110-830 ℃, and the coiling temperature is 600-600 ℃.
According to the scheme, the straightening machine stretches by 0.6-1.2%.
According to the scheme, the concentration of the pickling hydrochloric acid is 100-250 ml/L, the pickling belt speed is 10-150 m/min, and the pickling temperature is 60-80 ℃.
According to the scheme, the total rolling reduction rate is 65-10%; the rolling reduction rate of one-time cold rolling is 40-50%.
According to the scheme, the full hydrogen hood type annealing adopts two-section heating; comprises primary heating, heat preservation, secondary heating, heat preservation and cooling of the steel coil; wherein the primary heat preservation temperature is 350-450 ℃ and the heat preservation time is 2-6 h; the secondary heat preservation temperature is 600-630 ℃ of hot spot temperature, the heat preservation time is 10-20 h, the cold spot temperature is 620-600 ℃, then the furnace cooling is carried out, and the protective atmosphere adopts full hydrogen.
According to the scheme, the flattening rolling reduction is 0.1-2.0%, and the corresponding flattening elongation is set according to the thickness of the finished product: when the thickness of the finished product is less than or equal to 1.2mm, the leveling elongation is 0.1-1.2%; when the thickness of the finished product is more than 1.2mm, the flat elongation is 1.2-2.0%.
The main elements and the action and mechanism of the process in the invention are as follows:
c: the addition of carbon can effectively improve the strength of steel, but the plasticity and the formability of the steel plate can be reduced along with the obvious increase of the strength of the steel plate, and the magnetic property of the magnetic pole steel is not facilitated no matter the C is in solid solution in a steel base or exists in a carbide form, the control of the lower carbon content is beneficial to reducing the precipitation of solid solution C and cementite in a grain boundary, so that the C content in the steel is selected to be 0.01% -0.03%.
Mn: mn is a solid solution strengthening element. The Mn content is increased to reduce the toughness of the product, weaken the elongation, reaming and cold bending properties, and the magnetic property is weakened along with the increase of the Mn content, so that the Mn content in the invention is 0.3-0.5%.
Si: si is a solid solution strengthening element, so that the strength of the steel can be obviously improved, the magnetic resistance is reduced, the steel is easier to magnetize, but iron scale of fayalite is easy to form on the surface of the steel plate in the hot rolling process with the excessively high Si content, hot rolling descaling is difficult to remove, and the Si content is not too high, so that the Si content is 0.3-0.6 percent in the hot rolling process.
Als: al is a deoxidizer, reduces the oxygen content in steel, reduces inclusions in steel, improves the toughness of steel, but the Al content is too high to form coarse AlN particles, and reduces the toughness of steel, so the Al content is 0.050-0.10%.
P: p is an impurity element in steel, is easy to gather at grain boundaries and affects the toughness and magnetic performance of products, so that the lower the content is, the better the content is, and the content is controlled below 0.02 percent according to the practical control level and cost factors.
S: s is an impurity element in steel, is liable to cause segregation at grain boundaries, and forms sulfide inclusions with Fe and Mn in steel at a low melting point, and is controlled to be at a low level, so that S is controlled to be 0.002% or less.
N: n is an impurity element in steel, and decreases the toughness of steel, so that the content thereof should be controlled to 0.005% or less as much as possible.
Cu: cu can improve the corrosion resistance of steel, and the increase of Cu content can increase the strength of steel, especially the yield ratio, so the Cu content is less than or equal to 0.02 percent.
Ti: ti can play a role in precipitation strengthening, refine structure grains, reduce anisotropy of a structure, and form TiC second phase particles with C, so that the content of carbide dissolved and precipitated in steel is reduced, but too high Ti content also increases the strength of the material and the production cost, so that the Ti content is less than or equal to 0.02-0.04%.
T [ O ]: the content of oxide inclusion is high, so that it should reduce the content of T [ O ] in steel, and the T [ O ] in the invention is less than or equal to 0.002%.
The main process reason analysis in the invention is as follows:
the S and O content in the steel can be reduced by LF refining, the sulfide and oxide content in the steel can be reduced, and the toughness of the product can be improved.
The RH vacuum can reduce the content of C, N, H and other elements in molten steel, reduce the content of carbide, nitride and harmful gas in the steel, improve the purity of the steel, and is favorable for improving the magnetic performance.
Austenite rolling is adopted in hot rolling, the strip steel is in a gamma phase region before entering a finishing mill, and the higher finishing temperature avoids the condition that the finishing temperature is lower than Ar 3 Entering a two-phase region, and finishing rolling from the beginning to the finish rolling is in an austenite phase region, so that the mixed crystal phenomenon caused by rolling in the two-phase region is avoided. The hot rolling coiling temperature is 600-600 ℃, high-temperature coiling is beneficial to the control of hot rolled plate shape, the plate shape fluctuation caused by low coiling temperature is avoided, wave-shaped phenomena are avoided, but coarse grains are easy to form too high, so 600-600 ℃ is selected.
The straightening machine stretches 0.6-1.2%, the pickling hydrochloric acid concentration is 100-250 ml/L, the pickling belt speed is 10-150 m/min, the pickling temperature is 60-80 ℃, a certain amount of Si is added into steel, si is an element easy to form oxide scale, proper stretching is favorable for breaking and falling off of the oxide scale, the acid liquor has larger contact area during pickling, the pickling is insufficient, the residual oxygen scale on the surface of the hot rolled plate is inherited to the post-process to form surface defects, and the process ensures the effective removal of the oxide scale on the surface.
The high cold rolling reduction rate is adopted in the cold rolling process, so that the structure in steel is thinned, and the crystal grains with certain size are kept, so that the total cold rolling reduction rate is 65-10%.
The rolling of five frames is adopted in the cold rolling, the primary rolling reduction rate in the process is 40-50%, the structure in steel can be fully refined, the deformation of a single frame in the subsequent four frames is smaller, and better surface and dimensional accuracy is obtained, so that the primary rolling reduction rate in the invention is 40-50%.
In the hood-type annealing process, a two-stage heating mode is adopted. The method comprises the steps of primary heating and heat preservation of the steel coil, secondary heating and heat preservation, cooling and the like. The primary heat preservation temperature is 350-450 ℃, the heat preservation time is 2-6 h, the secondary heat preservation temperature is 600-630 ℃ and the heat preservation time is 10-20 h, the cold spot temperature is 620-600 ℃, the two-stage heat preservation heating mode can lead the radial and width directions of the strip steel coil to be heated more uniformly, the temperature difference between the inside and the outside of the steel coil is smaller, the temperature unevenness and the brought internal stress are avoided, the crystal grains at each part are ensured to be fully grown, and the non-uniformity is eliminated.
The production is carried out by adopting the all-hydrogen type hood-type annealing furnace, and the hydrogen is taken as a protective atmosphere by adopting the all-hydrogen type hood-type annealing furnace because the surface quality requirement of the magnetic pole steel plate is higher, so that the hydrogen has reducibility and a better surface state is obtained.
The invention adopts the wet leveling process, the rolling force required by the wet leveling process is smaller than that required by the dry leveling process, the energy consumption is reduced, the elimination of the steel plate yield platform is facilitated, and the surface quality of the finished product is better. And adopting the flattening elongation of 0.1-2.0% to finally obtain the magnetic pole steel with good surface and dimensional accuracy.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a low-cost high-magnetic-induction 350 MPa-grade cold-rolled magnetic pole steel and a manufacturing method thereof, wherein the product consists of ferrite and a small amount of pearlite, the yield strength of the product is more than or equal to 350MPa, the tensile strength is more than or equal to 450MPa, and the magnetic induction B50 is more than or equal to 1.65T.
The hood-type annealing two-section heating and heat preservation process is beneficial to the uniformity of the structure of the steel coil in the radial direction and the width direction, eliminates the internal stress and obtains uniform performance.
The product of the invention adopts a cover-removing production line with low cost of alloy element addition and flexible production variety rhythm, and realizes the production of magnetic pole steel products with the yield strength of 350 Mpa.
Drawings
Fig. 1: metallographic structure diagram of example 1.
Detailed Description
The following examples further illustrate the technical aspects of the present invention, but are not intended to limit the scope of the present invention.
The specific embodiment provides 350 MPa-level low-cost high-magnetic-induction cold-rolled magnetic pole steel, which comprises the following chemical components in percentage by weight: c:0.01 to 0.03 percent of Mn:0.3 to 0.5 percent, si:0.3 to 0.6 percent, als:0.050 to 0.10%, P: less than or equal to 0.02 percent, S: less than or equal to 0.0020 percent, N: less than or equal to 0.005 percent, cu: less than or equal to 0.02, ti: less than or equal to 0.02-0.04%, T [ O ] less than or equal to 0.002%, and the balance being Fe and unavoidable impurities; the microstructure of the product is ferrite and a small amount of pearlite, and the thickness of the finished product is 0.6 mm-2.0 mm.
The specific embodiment also provides a manufacturing method of the 350 MPa-grade cold-rolled magnetic pole steel, and the main process flow comprises converter steelmaking, LF refining, RH refining, continuous casting, hot rolling, coiling, straightening, pickling, cold rolling, electrolytic degreasing, all-hydrogen gas hood annealing, wet leveling and finished product production. Specifically, desulphurized refined molten iron is adopted, and smelting and casting are carried out according to preset components to form a plate blank;
heating the slab, and then carrying out hot rolling, wherein the heating temperature of the hot rolled slab is 1150-1250 ℃; the initial rolling temperature is 1030-1010 ℃, the final rolling finishing temperature is 110-830 ℃, and the coiling temperature is 600-600 ℃;
the straightening machine stretches by 0.6 to 1.2 percent after withdrawal and straightening.
The concentration of the pickling hydrochloric acid is 100-250 ml/L, the pickling belt speed is 10-150 m/min, and the pickling temperature is 60-80 ℃.
The total rolling reduction rate is 65-10%; the rolling reduction rate of one-time cold rolling is 40-50%.
The whole hydrogen hood type annealing adopts two-section heating; comprises primary heating, heat preservation, secondary heating, heat preservation and cooling of the steel coil; wherein the primary heat preservation temperature is 350-450 ℃ and the heat preservation time is 2-6 h; the secondary heat preservation temperature is 600-630 ℃ of hot spot temperature, the heat preservation time is 10-20 h, the cold spot temperature is 620-600 ℃, then the furnace cooling is carried out, and the protective atmosphere adopts full hydrogen.
The flattening rolling rate is 0.1-2.0%, and the corresponding flattening elongation rate is set according to the thickness of the finished product: when the thickness of the finished product is less than or equal to 1.2mm, the leveling elongation is 0.1-1.2%; when the thickness of the finished product is more than 1.2mm, the flat elongation is 1.2-2.0%.
Table 1 shows the chemical composition list (wt%) of each example and comparative example of the present invention;
table 2 is a list of the main process parameters for each example and comparative example of the present invention;
table 3 shows a list of performance tests for each example and comparative example of the present invention.
TABLE 1
| Sequence number | C | Si | Mn | Als | N | P | S | Cu | Ti | T[O] |
| Example 1 | 0.026 | 0.56 | 0.44 | 0.06 | 0.0042 | 0.010 | 0.0010 | 0.014 | 0.030 | 0.0013 |
| Example 2 | 0.024 | 0.41 | 0.48 | 0.08 | 0.0031 | 0.011 | 0.0012 | 0.015 | 0.038 | 0.0014 |
| Example 3 | 0.011 | 0.50 | 0.42 | 0.01 | 0.0033 | 0.012 | 0.0010 | 0.016 | 0.033 | 0.0015 |
| Example 4 | 0.028 | 0.56 | 0.38 | 0.06 | 0.0034 | 0.008 | 0.0008 | 0.015 | 0.035 | 0.0016 |
| Example 5 | 0.016 | 0.51 | 0.41 | 0.01 | 0.0034 | 0.001 | 0.0001 | 0.016 | 0.032 | 0.0010 |
| Comparative example | 0.06 | 0.11 | 1.00 | 0.06 | 0.0062 | 0.013 | 0.0015 | 0.001 | 0.016 | 0.0020 |
TABLE 2
Continuous table 2
TABLE 3 Table 3
As can be seen from examples 1-5 of Table 3, the properties were all targeted, while the properties remained stable for the steel sheets of different finished thickness, and FIG. 1 is a metallographic structure diagram of example 1.
Claims (1)
1. A350 MPa-grade low-cost high-magnetic-induction cold-rolled magnetic pole steel is characterized by comprising the following chemical components in percentage by weight: c:0.01 to 0.03 percent of Mn:0.3 to 0.5 percent, si:0.3 to 0.6 percent, als:0.050 to 0.10%, P: less than or equal to 0.02 percent, S: less than or equal to 0.0020 percent, N: less than or equal to 0.005 percent, cu: less than or equal to 0.02, ti: less than or equal to 0.02-0.04%, T [ O ] less than or equal to 0.002%, and the balance being Fe and unavoidable impurities; the microstructure of the product is ferrite and a small amount of pearlite, and the thickness of the finished product is 0.6 mm-2.0 mm; the steel is prepared by a converter steelmaking, LF refining, RH refining, continuous casting, hot rolling, coiling, straightening, pickling, cold rolling, electrolytic degreasing, full hydrogen hood annealing and leveling process;
wherein the heating temperature of the hot rolled plate blank is 1150-1250 ℃, the initial rolling temperature is 1030-1080 ℃, the final rolling finishing temperature is 880-930 ℃, and the coiling temperature is 600-700 ℃;
stretching and straightening by 0.6-1.2% of the straightener;
the concentration of the pickling hydrochloric acid is 100-250 ml/L, the pickling belt speed is 80-150 m/min, and the pickling temperature is 70-90 ℃;
the total rolling reduction rate is 65-80 percent; the rolling reduction rate of the primary cold rolling is 40-50%;
the whole hydrogen hood type annealing adopts two-section heating; comprises primary heating, heat preservation, secondary heating, heat preservation and cooling of the steel coil; wherein the primary heat preservation temperature is 350-450 ℃ and the heat preservation time is 2-6 h; the secondary heat preservation temperature is 600-730 ℃ of hot spot temperature, the heat preservation time is 10-20 h, the cold spot temperature is 620-700 ℃, then the furnace cooling is carried out, and the protective atmosphere adopts full hydrogen;
the flattening rolling rate is 0.8-2.0%, and the corresponding flattening elongation rate is set according to the thickness of the finished product: when the thickness of the finished product is less than or equal to 1.2mm, the leveling elongation is 0.8-1.2%; when the thickness of the finished product is more than 1.2mm, the flat elongation is 1.2-2.0%.
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| CN100392133C (en) * | 2006-07-31 | 2008-06-04 | 武汉钢铁(集团)公司 | Production method of 350 MPa grade cold rolled magnetic pole steel |
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