US20130224064A1 - Non-oriented electrical steel plate without corrugated fault and production method thereof - Google Patents

Non-oriented electrical steel plate without corrugated fault and production method thereof Download PDF

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US20130224064A1
US20130224064A1 US13/823,311 US201113823311A US2013224064A1 US 20130224064 A1 US20130224064 A1 US 20130224064A1 US 201113823311 A US201113823311 A US 201113823311A US 2013224064 A1 US2013224064 A1 US 2013224064A1
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slab
temperature
oriented electrical
electrical steel
planishing
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Feng Zhang
Xiao Chen
Wei Cao
Yezhong Sun
Changsong Ma
Jianru Zhu
Zhuolei Chen
Xiandong Liu
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Baoshan Iron and Steel Co Ltd
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Baoshan Iron and Steel Co Ltd
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Assigned to BAOSHAN IRON & STEEL CO., LTD. reassignment BAOSHAN IRON & STEEL CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CAO, WEI, CHEN, XIAO, CHEN, ZHUOLEI, LIU, XIANDONG, MA, Changsong, SUN, YEZHONG, ZHANG, FENG, ZHU, JIANRU
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D25/00—Special casting characterised by the nature of the product
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/18—Controlling or regulating processes or operations for pouring
    • B22D11/181—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level
    • B22D11/182—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level by measuring temperature
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
    • B22D11/225—Controlling or regulating processes or operations for cooling cast stock or mould for secondary cooling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties involving a particular fabrication or treatment of ingot or slab
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
    • C21D8/1222—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
    • C21D8/1233—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
    • C21D8/1272—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1277—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties involving a particular surface treatment
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
    • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
    • H01F1/16—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of sheets
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2201/00—Treatment for obtaining particular effects
    • C21D2201/05—Grain orientation

Definitions

  • the present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof, especially to a middle steel grade non-oriented electrical steel sheet without corrugated defect, which has an excellent magnetism, and a manufacturing method thereof.
  • corrugated defect For a non-oriented electrical steel sheet having a high extent of silicon, in the surface of a finished strip, accidented waves, similar to corrugations, appear in a direction of rolling, which is generally called “corrugated defect”. This defect will reduce a stacking coefficient of the finished strip notably, making the magnetism of the finished strip worse and the electrical resistance between insulating film layers decreased, thus reducing the service performance and life of terminal production. Therefore, almost all of users have a definite demand that a finished strip having corrugated defects is not allowed.
  • the mechanism of the generation of the corrugated defects may be explained as follows: the equiaxed crystal ratio in the slab is low, whereas the columnar crystal is gross and growing.
  • the growing direction of the columnar crystal ⁇ 001> which is the normal direction of (001), is the direction in which the heat flux gradient is the largest. In such a hot rolling process, the gross columnar crystal can not thoroughly break due to dynamic recovery and slow re-crystallization.
  • the slab columnar crystals are easy to grow in the direction of heat flux, and form gross columnar crystals having a certain orienting relation, resulting in inhomogeneous deformations in a rolling process, the center in sheet thickness is fiber texture primarily after hot rolling process, and austenite and ferrite have no phase transition in subsequent process, and will not re-crystallize in the following cold rolling and annealing process, which does not make the homogeneity of the texture eliminated, and leaving behind to the finished product, finally forming accidented corrugated defects.
  • the conventional methods for treating corrugated defects are mainly as follows: by utilizing electromagnetic stirring, the equiaxed crystal ratio in the slab may be improved, for example, in Japanese Patent Application Laid-open No. 49-39526; by adding the contents of carbon and manganese into steel, the phase transiting temperature in hot rolling process may be reduced, for example, in Japanese Patent Application Laid-open No. 48-49617, Chinese Patent Application CN10127519, CN1548569 and CN101139681 etc.; by utilizing low temperature pouring, the equiaxed crystal ratio in the slab may be improved, for example, in Japanese Patent Application Laid-open No. 53-14609 and No.
  • the strip may re-crystallize sufficiently, for example, in Japanese Patent Application Laid-open No. 49-27420, No. 49-38813, No. 53-2332, No. 61-69923, Chinese Patent Application CN 1611616 and CN1548569; and by utilizing a normalized process, the strip may re-crystallize sufficiently, for example, in Japanese Patent Application Laid-open No. 61-127817, etc.
  • the equiaxed crystal ratio in the slab may be improved.
  • This method utilizes electromagnetic stirring, the columnar crystals may break under electromagnetic force, and therefore, the effect thereof is the most effective.
  • This method will remarkably reduce the columnar crystal ratio in the slab and improve the equiaxed crystal ratio in the slab, especially when utilizing electromagnetic stirring twice or more, and will effectively prohibit a secondary columnar crystal in the central area as well.
  • the main disadvantage of this method is that the stirring effect depends on the content of silicon in steel and the electromagnetic stirring number.
  • the equiaxed crystal in the slab is relatively easy to conglomerate, grow, and form a gross columnar crystal once again, therefore, it is necessary to utilize electromagnetic stirring twice or more and control the solidification effect of liquid steel strictly. Also, the manufacturing cost of the electromagnetic stirring is high.
  • phase transiting temperature in hot rolling process may be reduced.
  • This method is mainly conducted by adding the contents of carbon and manganese in steel, a phase transition occurs to the slab in the heating up and hot rolling process, accelerating dynamic recovery and re-crystallization, so as to eliminate gross deformation crystal grains.
  • the main disadvantage of this method is that it is necessary to decarburize in annealing process, which is easy to produce inner oxide layer and inner nitration layer, making the magnetism of steel worse.
  • the equiaxed crystal ratio in the slab may be improved.
  • This method decreases the columnar crystal ratio in the slab and improves the ratio that the equiaxed crystal accounts for mainly by reducing the superheat of the liquid steel in the pouring process.
  • the main disadvantage of this method is that it is demanded that the superheat scope of the liquid steel is very low, which is hard to control effectively, and which affects the normal control in the continuous casting process.
  • the strip By increasing furnace tap temperature of the slab, adjusting heating-up speed of the slab, controlling end-rolling temperature in a planishing process, and controlling the degrees of reduction of the first and the last pass in the hot rolling process, the strip may re-crystallize sufficiently.
  • This method is mainly conducted by increasing the furnace tap temperature of the slab, adjusting the heating-up speed of the slab, controlling the end-rolling temperature in a planishing process, and controlling the degrees of reduction of the first and the last pass in the hot rolling process, the gross columnar crystals in the slab may break, so as to prohibit the development of the gross deformation crystal grains as well as to make the strip re-crystallized sufficiently.
  • the main disadvantage of this method is that increasing the furnace tap temperature of the slab will make the impurities such as MnS, MN etc., solutionized intensively, thus make the magnetism of the finished strip worse. Meanwhile, in order to ensure the re-crystallization effect of the strip, the contents of impurity elements such as S, N etc., in steel are strictly demanded. Also, improving the degrees of reduction of the first and the last pass in the hot rolling process is restricted by self-capability of a rolling mill.
  • the strip may re-crystallize sufficiently.
  • the steel grade that has a high content of silicon needs to carry out the normalized process, one of the objects is to increase the re-crystallizing ratio in the hot rolling sheet, so as to avoid the generation of the corrugated defects.
  • the main disadvantage of this method is that the manufacturing cost is very high, which is not applied in low or middle steel grade silicon steel of which the additional value is relatively low.
  • the object of the present invention is to provide a non-oriented electrical steel sheet without the corrugated defect and a manufacturing method thereof.
  • the manufacture of a middle steel grade non-oriented electrical steel sheet without corrugated defect can be accomplished, which has advantages of easy operation, low cost, energy conservation and environmental protection, and excellent magnetism, by strictly controlling the cooling speed of the slab in continuous casting and pouring process, the temperature difference in the length direction of the slab in the heating furnace, and by controlling the temperature drop before planishing the slab.
  • the casting speed of the slab in continuous casting and pouring process is normal, so that the relatively high superheat of the liquid steel can be maintained, and the relatively low furnace tap temperature of the slab, and normal end-rolling temperature and coiling temperature etc., can be maintained in the hot rolling and steel reheating process, so that the strip in the hot rolling process does not need to carry out a normalized process.
  • a middle steel grade non-oriented electrical steel sheet without the corrugated defect wherein the weight percentage of the chemical composition thereof is that C is no more than 0.005%, Si is 1.2-2.2%, Mn is 0.2-0.4%, P is no more than 0.2%, S is no more than 0.005%, Al is 0.2-0.6%, N is no more than 0.005%, O is no more than 0.005%, and a balance substantially being Fe and inevitable impurities.
  • C is no more than 0.005%.
  • C is an element for strongly inhibiting the growth of crystal grains, which is easy to result in the increase of iron loss of a strip, producing the serious magnetic aging. Meanwhile, C may further widen ⁇ phase, and increase the transition amount between ⁇ phase and ⁇ phase when in the normalized process, so as to reduce Acl point notably, and to fine crystallizing structure. Therefore, C is necessary to be controlled to no more than 0.005%.
  • Si is 1.2%-2.2%.Si is an effective element for increasing the electrical resistivity of the steel. If the content of Si is lower than 1.2%, the electromagnetic performance of the steel is not good, whereas if the content of Si is higher than 2.2%, phase change will not occur in the hot rolling process, and the cold-working performance is not good.
  • Al is 0.2%-0.6%.Al is an effective element for increasing the electrical resistivity of the steel. If the content of Al is lower than 0.2%, the electromagnetic performance is not stable, whereas if the content of Al is higher than 0.6%, the smelting and pouring process will become difficult, thus increasing the manufacturing cost.
  • Mn is 0.2%-0.4%.Like the elements Si and Al, Mn may increase the electrical resistivity of the steel, as well as improve the surface state of the electrical steel, so it is necessary to add no less than 0.2% of Mn. While the content of Mn is higher than 0.4%, the smelting and pouring process will become difficult, thus increasing the manufacturing cost.
  • P is no more than 0.2%. Adding some phosphorus into steel can improve the workability of steel sheet, but if the content of phosphorus is more than 0.2%, it instead makes the cold rolling workability of steel plate deteriorated.
  • S is no more than 0.005%. If the content of S is more than 0.005%, the deposition amount of sulfide such as MnS, will increase greatly, thus strongly preventing crystal grains growing and making iron loss worse.
  • N is no more than 0.005%. If the content of N is more than 0.005%, the deposition amount of nitride such as AlN, will increase greatly, thus strongly preventing crystal grains growing and making iron loss worse.
  • O is no more than 0.005%. If the content of O is more than 0.005%, the impurity amount of oxidate such as Al 2 O 3 , will increase greatly, thus strongly preventing crystal grains growing and making iron loss worse.
  • a method for manufacturing a non-oriented electrical steel sheet without corrugated defect of the present invention comprises the following steps:
  • the middle steel grade non-oriented electrical steel sheet without corrugated defect of the present invention and the manufacturing method thereof comprise the following steps:
  • the average superheat of liquid steel in the pouring process is controlled to 10-45° C.
  • the water flowrate of cooling water is adjusted to 100-190 l/min, so as to improve the equiaxed crystal ratio in the slab, avoiding columnar crystals in the slab gross and growing.
  • the temperature difference between the random two points in the length direction when the slab is heated is controlled to be lower than 25° C.; the temperature difference between the watermark points of the slab is limited within 25° C., meanwhile the residence time of the slab in after-firing zone should be no less than 45 min, so as to ensure uniform heating, making the temperatures of both surfaces of the slab close.
  • the furnace tap temperature of the slab can be reduced to no higher than 1150° C., avoiding the impurities such as MnS, AlN etc., solutionized intensively, which thus making the magnetism of the finished strip worse.
  • Hot rolling sheet is rolled to have a thickness of 2.0 mm-2.8 mm.
  • the entry temperature in the planishing process is controlled to no lower than 970° C. so as to facilitate sufficient re-crystallization, and the end-rolling temperature is controlled to about 850° C., the coiling temperature is controlled to about 600° C.
  • the hot rolling is rolled to thick strip that has a thickness of 0.5 mm, and then is annealed continuously in a dry atmosphere.
  • the electromagnetic performance of the steel is further improved by warming up the finished strip quickly in a preheating zone, in which the heat-up speed is no less than 1000° C./min, and by controlling the atmosphere mode in furnace.
  • the content of silicon when the content of silicon is less than 2.2%, the content of silicon does not affect the growth of the columnar crystal as greatly as the cooling speed of the slab, therefore, the water flowrate of cooling water in the continuous casting process can be adjusted to reduce the heat flux gradient of the slab in the growing direction of the columnar crystal, so that the ratio of gross and growing columnar crystals can be reduced effectively.
  • the temperature of the slab at the location where the slab contacts the roller table is relatively low in the slab heating process, which affects the re-crystallization of the fiber texture in the interior of the slab, not making the homogeneity of the texture eliminated and leaving behind to the finished product, therefore, it is necessary to strictly control the temperature of the watermark point of the slab.
  • the main reason on improving the entry temperature in the planishing process is to facilitate the break and elimination of the columnar crystals in the rolling process and improve the re-crystallization ratio of the fiber texture in the hot rolling strip.
  • the content of silicon is no more than 1.2%, the phase change from ⁇ phase to ⁇ phase in the hot rolling process is sufficient, the corrugated defects will not occur in the surface of the subsequent finished product.
  • the columnar crystals in the slab may be broken due to highly electromagnetic stirring force, as possible as to transit to fine equiaxed crystals, so as to improve the equiaxed crystal ratio in the slab greatly; or the phase change from ⁇ phase to ⁇ phase happens in the interior of the slab by increasing the furnace tap temperature of the slab in the heat process greatly, meanwhile the re-crystallization of the slab is improved by utilizing high temperature status to enlarge the re-crystallizing structure in the interior of the slab.
  • the electromagnetic stirring technology is hard to match the superheat of the liquid steel precisely, if the superheat of the liquid steel is controlled improperly, the controlling effect of the electromagnetic stirring is not stable, which is hard to obtain the expecting effect; and by increasing the furnace tap temperature of the slab, the heating load distribution in the heating furnace will forward, making high temperature time zone relatively long, which affects the magnetism of the finished strip.
  • This method is easy to result in mass defect at the edge of the strip with respect to high-silicon steel grade.
  • the water flowrate of cooling water in the continuous casting process can be adjusted to reduce the heat flux gradient of the slab in the growing direction of the columnar crystal, so that the ratio of gross and growing columnar crystals can be reduced effectively. It is more important that this method is substantially affected by the change in the superheat of the liquid steel, so the range of application is relatively wide. Meanwhile, the adjustment on the water flowrate of cooling water is very simple and controllable, so the difficulty in implementation is low, the stability is good. Further, the equipment load may be reduced by utilizing lower furnace tap temperature of the slab, avoiding the deposition of fine impurities in the steel and affecting the magnetism of final product.
  • the temperature at the watermark points in the slab may be adjusted to increase re-crystallizing ratio of the fiber texture of the slab in the hot rolling process, and to improve the homogeneity of the texture of the slab in the hot rolling strip, which facilitates to the corrugated defects in the surface of the finished strip.
  • FIG. 1 is a schematic view of the relation between the water flowrate of the cooling water and the equiaxed crystal ratio in the slab.
  • FIG. 2 is a schematic view of the relation between the entry temperature in the hot rolling and planishing process and the incidence of the corrugated defects in a finished product.
  • FIG. 3 is a schematic view of the relation between the furnace tap temperature of the slab and the magnetism of the finished product.
  • FIG. 4 is a picture of a metallographic structure of a strip in hot rolling process corresponding to a watermark point temperature of 20° C.
  • FIG. 5 is a picture of a metallographic structure of a strip in hot rolling process corresponding to a watermark point temperature of 35° C.
  • the chemical composition of the tundish liquid steel in the continuous casting process is controlled as follows: C is 0.001%, Si is 1.22%, Mn is 0.25%, P is 0.02%, S is 0.003%, Al is 0.33%, N is 0.001%, O is 0.004%, and a balance substantially being Fe and inevitable impurities.
  • the average superheat of the liquid steel is 34.6° C.
  • the casting speed is 1.07 m/min
  • the water flowrate of the cooling water is 185 l/min
  • the temperature drop speed of the slab is 11.6min/° C.
  • the surface temperature of the slab at the outlet of a caster is 710° C.
  • the equiaxed crystal ratio is 43%.
  • the temperature difference between the watermark points is 22° C.
  • the residence time in after-firing zone of the slab is 46 minutes.
  • the rolling process will be carried out after heating for 3 h at 1125° C.
  • the temperature at the inlet in planishing process is 978° C.
  • the end-rolling temperature is 856° C.
  • the coiling temperature is 567° C.
  • the hot rolling sheet is rolled to 0.5 mm thickness of strip with the single cold rolling method, and then is annealed continuously in a dry atmosphere. Corrugated defects are not generated in the surface of the finished strip, the iron loss is 4.743 W/kg, and the magnetic induction is 1.727 T.
  • the chemical composition of the tundish liquid steel in the continuous casting process is controlled as follows: C is 0.002%, Si is 1.42%, Mn is 0.30%, P is 0.06%, S is 0.002%, Al is 0.25%, N is 0.002%, O is 0.002%, and a balance substantially being Fe and inevitable impurities.
  • the average superheat of the liquid steel is 31.4° C.
  • the casting speed is 1.04 m/min
  • the water flowrate of the cooling water is 175 l/min
  • the temperature drop speed of the slab is 9.6 min/° C.
  • the surface temperature of the slab at the outlet of a caster is 680° C.
  • the temperature difference between the watermark points is 22 ° C.
  • the residence time in after-firing zone of the slab is 48 minutes.
  • the rolling process will be carried out after heating for 3 h at 1135° C.
  • the temperature at the inlet in planishing process is 973° C.
  • the end-rolling temperature is 853° C.
  • the coiling temperature is 563° C.
  • the hot rolling sheet is rolled to 0.5 mm thickness of strip with the single cold rolling method, and then is annealed continuously in a dry atmosphere. Corrugated defects are not generated in the surface of the finished strip, the iron loss is 3.130 W/kg, and the magnetic induction is 1.741 T.
  • the chemical composition of the tundish liquid steel in the continuous casting process is controlled as follows: C is 0.002%, Si is 1.49%, Mn is 0.49%, P is 0.02%, S is 0.003%, Al is 0.59%, N is 0.001%, O is 0.002%, and a balance substantially being Fe and inevitable impurities.
  • the average superheat of the liquid steel is 28.7° C.
  • the casting speed is 0.99 m/min
  • the water flowrate of the cooling water is 189 l/min
  • the temperature drop speed of the slab is 8.7 min/° C.
  • the surface temperature of the slab at the outlet of a caster is 660° C.
  • the temperature difference between the watermark points is 24 ° C.
  • the residence time in after-firing zone of the slab is 53 minutes.
  • the rolling process will be carried out after heating for 3 h at 1102° C.
  • the temperature at the inlet in planishing process is 983° C.
  • the end-rolling temperature is 854° C.
  • the coiling temperature is 575° C. .
  • the hot rolling sheet is rolled to 0.5 mm thickness of strip with the single cold rolling method, and then is annealed continuously in a dry atmosphere. Corrugated defects are not generated in the surface of the finished strip, the iron loss is 3.559 W/kg, and the magnetic induction is 1.737 T.
  • the chemical composition of the tundish liquid steel in the continuous casting process is controlled as follows: C is 0.001%, Si is 2.12%, Mn is 0.25%, P is 0.01%, S is 0.002%, Al is 0.36%, N is 0.001%, O is 0.004%, and a balance substantially being Fe and inevitable impurities.
  • the average superheat of the liquid steel is 31.2° C.
  • the casting speed is 0.95 m/min
  • the water flowrate of the cooling water is 173 l/min
  • the temperature drop speed of the slab is 13.2 min/° C.
  • the temperature difference between the watermark points is 20° C.
  • the residence time in after-firing zone of the slab is 48 minutes.
  • the rolling process will be carried out after heating for 3 h at 1097° C.
  • the temperature at the inlet in planishing process is 972° C.
  • the end-rolling temperature is 844° C.
  • the coiling temperature is 583° C.
  • the hot rolling sheet is rolled to 0.5 mm thickness of strip with the single cold rolling method, and then is annealed continuously in a dry atmosphere. Corrugated defects are not generated in the surface of the finished strip, the iron loss is 2.833 W/kg, and the magnetic induction is 1.726 T.
  • the chemical composition of the tundish liquid steel in the continuous casting process is controlled as follows: C is 0.001%, Si is 1.47%, Mn is 0.32%, P is 0.02%, S is 0.003%, Al is 0.25%, N is 0.002%, O is 0.002%, and a balance substantially being Fe and inevitable impurities.
  • the average superheat of the liquid steel is 28.9° C.
  • the casting speed is 1.03m/min
  • the water flowrate of the cooling water is 257 l/min
  • the temperature drop speed of the slab is 17.4 min/° C.
  • the surface temperature of the slab at the outlet of a caster is 580° C.
  • the equiaxed crystal ratio is 28%.
  • the temperature difference between the watermark points is 37° C.
  • the residence time in after-firing zone of the slab is 41 minutes.
  • the rolling process will be carried out after heating for 3 h at 1153° C.
  • the temperature at the inlet in planishing process is 947° C.
  • the end-rolling temperature is 847° C.
  • the coiling temperature is 567° C.
  • the hot rolling sheet is rolled to 0.5 mm thickness of strip with the single cold rolling method, and then is annealed continuously in a dry atmosphere.
  • the percentage of the generation of corrugated defects in the surface of the finished strip is as high as no less than 90%, the iron loss is 3.273 W/kg, and the magnetic induction is 1.736 T.
  • FIG. 1 shows the relation between the water flowrate of the cooling water and the equiaxed crystal ratio in the slab.
  • the equiaxed crystal ratio in the slab may be controlled when the superheat of the liquid steel is relatively high.
  • the equiaxed crystal ratio in the slab when the water flowrate of the cooling water is 173 l/m, the equiaxed crystal ratio in the slab is up to 59%, in the comparative example, when the water flowrate of the cooling water is 257 l/min, the equiaxed crystal ratio in the slab is only 28%. Also, in the third embodiment, the control of the equiaxed crystal ratio in the slab is better, up to 63%.
  • FIG. 2 shows the relation between the entry temperature in the hot rolling and planishing process and the incidence of the corrugated defects in a finished product. It is indicated in accordance with the statistical results that by increasing the entry temperature in the hot rolling and planishing process and up to more than 970° C., because the re-crystallizing ratio of the fiber texture of the slab in the hot rolling process is increased remarkably, the incidence of the corrugated defects in the finished strip may be reduced greatly.
  • the entry temperatures in the hot rolling and planishing process of most of strips are less than 970° C.
  • the percentage of the generation of corrugated defects in the surface of the finished strip is as high as no less than 90%.
  • most of the entry temperatures in the hot rolling and planishing process of strips are more than 970° C., corrugated defects are not generated in the surface of the finished strip, respectively.
  • FIG. 3 shows the relation between the furnace tap temperature of the slab and the magnetism of the finished product. The higher the furnace tap temperature of the slab is, the worse the magnetism of the finished product is.
  • FIGS. 4 and 5 are metallographic structures of strips in hot rolling process corresponding to different watermark point temperatures.
  • the watermark point temperatures are all less than 25° C. in the first to fourth embodiments, so re-crystallizing structures of the strips in the hot rolling process are very homogeneous, the fiber textures disappear completely, whereas in the comparative example, the temperature at the watermark point is as high as 37° C., the fiber texture of the strip in the hot rolling process is clear, which is hard to re-crystallized in the period of the subsequent cold rolling and annealing process, not being able to destroy the homogeneity of the structures and leaving behind to the finished product, finally forming accidented corrugated defects.

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