CN115627414B - Secondary processing brittleness resistance and excellent surface quality phosphorus-containing IF steel plate and production method thereof - Google Patents
Secondary processing brittleness resistance and excellent surface quality phosphorus-containing IF steel plate and production method thereof Download PDFInfo
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- 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention discloses a phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality and a production method thereof, belonging to the field of steel manufacturing for automobiles. The IF steel plate comprises the following chemical components in percentage by weight: 0.0010 to 0.0030 percent, si: less than or equal to 0.02 percent, mn:0.24 to 0.70 percent, P:0.02 to 0.06 percent, S is less than or equal to 0.009 percent, als:0.03 to 0.04 percent, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance is Fe and unavoidable impurities; and Nb and C also need to be satisfied, wherein C-Nb/7.74 is less than or equal to 1PPM and less than or equal to 5PPM. The steel plate has excellent secondary processing brittleness, excellent deep drawing performance and good surface quality. Compared with the IF high-strength steel in the traditional technical scheme, the steel does not contain B, ti elements, the addition amount of Nb is less than that of the traditional IF high-strength steel through the accurate control of solid solution C, and the cost is lower.
Description
Technical Field
The invention belongs to the field of steel manufacturing for automobiles, and particularly relates to a phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality and a production method thereof.
Background
With the improvement of the requirements of the automobile industry on the corrosion resistance, the galvanized high-strength IF steel has excellent corrosion resistance, strength and deep drawing performance, and is widely applied to the automobile industry. The high-strength IF steel is based on ultra-low carbon steel components, and is prepared by removing C, N solid solution atoms by compounding and adding microalloying elements Nb, ti and V, and achieving solid solution strengthening by adding Si, mn and P elements. The secondary work embrittlement of the steel sheet may occur when the P element is added to the steel, and the prior art improves the secondary work embrittlement of the phosphorus-containing IF steel by adding the B element. However, after the B element is added into the steel, the B element can be segregated on the surface of the steel plate in an oxide mode before hot dip plating after annealing, meanwhile, the segregation of Mn and P oxides on the surface of the steel can be induced, so that the hot dip galvanizing surface has a missing plating defect, and the requirements of the automobile outer plate on the quality of the plate surface can not be met. On the other hand, aging may occur due to re-diffusion of B, which is segregated at grain boundaries, into the crystal and pinning of dislocations, and thus the steel sheet may undergo room temperature aging before stamping. The current technical proposal limits the further application of the galvanized high-strength IF steel on the automobile outer plate. There is a need for a hot dip galvanised phosphorus IF steel that solves the problem of secondary work brittleness while having excellent surface quality and deep drawing properties.
Through searching, the application of Chinese patent application No. 201210119462.6 discloses steel for IF automobile panels containing P and a production method thereof, wherein the application improves the secondary brittleness of the steel by adding B, but B segregates on the surface of an annealing furnace, and the defect of plating omission is easily caused, so the method is relatively suitable for cold-rolled outer plates, and has certain limitation when producing hot-dip galvanized outer plates.
For another example, the application of Chinese patent application number 201810684401.1 discloses a preparation method of an IF steel thin strip, wherein the IF steel thin strip comprises the following components in percentage by mass: c:0.0005 to 0.008 percent, mn:0.15 to 0.8 percent, si: 0.02 to 0.1 percent, B:0.01 to 0.02 percent, V:0.04 to 0.09 percent, P: 0.005-0.08%, N: less than or equal to 0.005%, less than or equal to 0.002% of O, less than or equal to 0.002% of S, and the balance of Fe. The preparation method is used for producing continuous annealed rolls, and Si element is added up to 0.1%, which may deteriorate wettability of the steel sheet surface to zinc liquid, resulting in surface defects. Meanwhile, the highest C content is 0.008%, which possibly leads to the excessively high strength of the finished product and is not suitable for the outer plate with high deep drawing performance requirement.
As another example, the application of chinese patent application No. 202011344974.3 discloses a 220 MPa-grade hot dip galvanized high strength IF steel and a preparation method thereof, wherein the IF steel comprises the following chemical components in percentage by weight: c:0.0008 to 0.003 percent; si: 0.07 to 0.10 percent; mn:0.35 to 0.45 percent; p: 0.048-0.058%; nb:0.01 to 0.02 percent; ti:0.015 to 0.025 percent; als:0.020 to 0.045 percent; restriction element S: less than 0.003%; n: less than 0.003%, and the balance being Fe. In the application, the precipitation of FePTiNb is avoided by controlling the addition amount of Nb and Ti, so that the technical problem of poor secondary processing brittleness resistance of the high-strength IF steel in the prior art is solved or partially solved. However, the problem of secondary brittleness caused by segregation of P at grain boundaries in this application is not fundamentally solved, and its application has limitations.
Disclosure of Invention
1. Problems to be solved
Aiming at least some problems existing in the prior art, the invention provides a phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality and a production method thereof.
2. Technical proposal
In order to solve the problems, the technical scheme adopted by the invention is as follows:
the invention relates to a phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality, which comprises the following chemical components in percentage by weight: 0.0010 to 0.0030 percent, si: less than or equal to 0.02 percent, mn:0.24 to 0.70 percent, P:0.02 to 0.06 percent, S is less than or equal to 0.009 percent, als:0.03 to 0.04 percent, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance is Fe and unavoidable impurities; and Nb and C also need to be satisfied, wherein C-Nb/7.74 is less than or equal to 1PPM and less than or equal to 5PPM.
Further, the secondary processing brittleness SWET of the IF steel plate is less than or equal to-50 ℃, and the degree of the missing plating defect on the surface of the steel plate is 2 grade or more.
Further, the IF steel has r not less than 1.8, Δr not less than 0.25, n not less than 0.2, AI of 0, and Ra of 0.7-1.5 μm.
The invention relates to a production method of a phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality, which comprises the following process steps: steelmaking, continuous casting, hot rolling, pickling and cold rolling, continuous annealing and hot dip galvanization and finishing rolling, wherein the chemical components of steel tapping after steelmaking are calculated in percentage by weight: 0.0010 to 0.0030 percent, si: less than or equal to 0.02 percent, mn:0.24 to 0.70 percent, P:0.02 to 0.06 percent, S is less than or equal to 0.009 percent, als:0.03 to 0.04 percent, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance is Fe and unavoidable impurities, wherein Nb and C meet the requirement of 1PPM to less than or equal to C-Nb/7.74 to less than or equal to 5PPM.
Further, in the continuous casting step, the casting blank is subjected to flame cleaning, and the cleaning depth is more than or equal to 2mm.
Further, in the hot rolling step, the hot rolling tapping temperature is 1230-1260 ℃, the final rolling temperature is Ar < 3+ > 30 ℃, the coiling temperature is 640-680 ℃, the descaling water state is fully opened, and the descaling water pressure is more than or equal to 150Bar.
Further, in the pickling and cold rolling steps, the total rolling reduction is 75-85%.
Further, in the continuous annealing and hot dip galvanizing step, the temperature of an annealing section RTF and SF is 770-800 ℃, the temperature of a zinc pot is 450-460 ℃, the temperature of the zinc pot is less than the temperature of a strip steel entering the zinc pot and less than the temperature of the zinc pot plus 10 ℃, and the dew point temperature is less than or equal to-50 ℃; al in zinc pot: 0.20 to 0.30 percent;
further, for zinc-iron alloy coated steel sheet, the alloying temperature is 520-550 ℃.
Further, in the finishing rolling step, the roughness of a working roller of the finishing machine is 1.5-2.5 mu m, and the rolling elongation is 1.1-1.4%.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
(1) The phosphorus-containing IF steel plate with the secondary processing brittleness resistance and excellent surface quality meets the conditions that C and Nb in steel components are not more than 1PPM and not more than C-Nb/7.74 and not more than 5PPM under the condition that B element is not added; when the steel contains more than 1PPM and less than 5PPM of solid solution C, the solid solution C is segregated to a grain boundary preferentially in the annealing process, so that the deformation energy of the grain boundary is reduced, the segregation of P element in the grain boundary is inhibited, and the problem of secondary processing brittleness caused by the addition of P is solved; on the other hand, the production method adopts a process of finishing temperature, low-temperature coiling and low-temperature annealing near the critical Ar3 of high Wen Chulu to ensure that the final structure is a fine ferrite structure, fine grains can be dispersed in more grains when the fine grains are subjected to external force, the plastic deformation is uniform, the stress concentration is smaller, in addition, the finer the grains are, the larger the area of the grain boundary is, the more tortuous the grain boundary is, the more unfavorable the crack expansion is, and finally the secondary processing brittleness SWET of the phosphorus-containing IF steel plate is less than or equal to-50 ℃.
(2) The phosphorus-containing IF steel plate with the secondary processing brittleness resistance and excellent surface quality can change C enriched on the surface into CO or CO when solid solution atoms C are used for replacing solid solution atoms B under the condition of not adding B element 2 In addition, flame cleaning is carried out on a casting blank in production to control internal quality defects, scale removal water is controlled to avoid oxygen pressing in a hot rolling stage, low-temperature coiling is used to reduce generation of iron scales, the dew point of an annealing furnace is controlled to be less than or equal to-50 ℃ in an annealing stage to control Mn and P elements to be separated out on the surface, and the temperature of a zinc pot, the Al content and the temperature of strip steel entering the pot are limited, so that a plating layer with excellent quality is obtained, and finally the degree of the obtained steel surface plating leakage defects is 2 grade or more.
(3) The production method of the phosphorus-containing IF steel plate with the secondary processing brittleness resistance and the excellent surface quality is annealed at the temperature of 770-800 ℃, nbC particles cannot be dissolved at the temperature, namely the content of solid solution C in steel cannot be increased, and because the matrix only contains 1-5 PPM solid solution C, dislocation pinning effect cannot occur at normal temperature, and room temperature aging cannot occur 6 months after the steel plate is produced.
(4) Compared with the IF high-strength steel in the traditional technical scheme, the production method of the phosphorus-containing IF steel plate with the secondary processing brittleness resistance and excellent surface quality has the advantages that B, ti elements are not added, the addition amount of Nb is less than that of the traditional IF high-strength steel through precise control of solid solution C, and the cost is lower.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is a schematic diagram of a metallographic structure of a steel sheet matrix according to the present invention;
FIG. 3 is a schematic diagram showing the state of a product at-55℃in accordance with an embodiment of the present invention;
FIG. 4 is a schematic representation of the state of the product of the comparative example of the present invention at-50 ℃;
FIG. 5 is a schematic illustration of a missing plating defect in a comparative example of the present invention;
FIG. 6 is a schematic diagram showing no missing plating defect in an embodiment of the invention.
Detailed Description
The invention relates to a phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality, which comprises the following chemical components in percentage by weight: 0.0010 to 0.0030 percent, si: less than or equal to 0.02 percent, mn:0.24 to 0.70 percent, P:0.02 to 0.06 percent, S is less than or equal to 0.009 percent, als:0.03 to 0.04 percent, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance is Fe and unavoidable impurities, wherein Nb and C satisfy the formula, and C-Nb/7.74 is less than or equal to 1PPM and less than or equal to 5PPM. Wherein, the liquid crystal display device comprises a liquid crystal display device,
c: when the C content is less than 0.0010%, the RH steelmaking deep decarburization time is prolonged, and the decarburization time is more than 25 minutes, so that the production efficiency is affected. When the C content is more than 0.0030%, 1PPM is less than or equal to C-Nb/7.74 is less than or equal to 5PPM to meet the formula, more Nb is required to be added, the cost control is not facilitated, and the deep drawing performance of the material is possibly deteriorated.
Si: less than or equal to 0.02%, si is one of the alloying elements of the steel, and in the present invention, the Si addition amount is strictly controlled to be limited to 0.02%, and the addition of Si exceeding 0.02% may cause surface defects of the hot dip galvanized steel sheet.
Mn:0.24 to 0.70 percent of Mn is an important solid solution strengthening element of the high-strength IF steel, when the Mn content is less than 0.24 percent, the strength of the steel possibly cannot meet the requirement, when the Mn content is more than 0.7 percent, the yield strength of the steel possibly is excessively high, excessive Mn can generate obvious surface segregation, and the surface quality of the hot-dip galvanized steel sheet is deteriorated.
P:0.02 to 0.06 percent, P is an important solid solution strengthening element of the high-strength IF steel, and the increment of tensile strength of the P solid solution strengthening on the steel is larger than the increment of yield strength of the steel, which is powerful on the deep drawing performance of the steel, and the minimum adding amount of P is set to be 0.02 percent in order to fully exert the solid solution strengthening effect of the P. However, when too much P is contained in the steel, even if a certain amount of solid solution C is contained in the steel, the concentration of P is too high, which increases the grain boundary segregation tendency, and may cause cold embrittlement of the steel, and the strength of the steel is too high, which deteriorates the deep drawability of the steel, so that the P content of the present invention is limited to 0.06%.
S: less than or equal to 0.009%, S is a harmful element in steel, compounds formed by S, mn and Fe can cause edge crack defects of the steel in the hot rolling process, sulfide inclusions can also deteriorate the deep drawing performance of the steel plate, and for the steel of the invention, the S is limited to be less than 0.009%.
Acid soluble aluminum (Als): 0.03-0.04%, als plays an important role in fixing N atoms, when acid-soluble aluminum (Als) is less than 0.03%, als cannot completely fix N atoms, room-temperature aging is easy to cause, deep drawing performance of a steel plate is deteriorated, and when Als is more than 0.04%, excessive Als can cause more inclusions in a steel matrix, and stamping cracking defects can be caused.
Nb: 0.006-0.020%, nb is a key element of the steel, on one hand, nb is used as a strong carbide forming element, nb and C form NbC precipitates in the hot rolling process, and the precipitates can inhibit disordered growth of recrystallized grains in the subsequent annealing process, thereby being beneficial to obtaining uniform structure of the annealed steel plate, namely isotropy of the steel plate performance. On the other hand, the relation between Nb and C satisfies the formula, and C-Nb is not less than 1PPM and not more than 5PPM, and by the method, even IF B element is not added in the steel, the secondary processing brittleness of the phosphorus-containing IF steel can be obviously improved. Therefore, in order to achieve the above effect, the lower limit of the addition amount of Nb is 0.006%, while if the addition amount of Nb exceeds 0.020%, the grain growth to recrystallization is suppressed, and the deep drawability of the steel sheet may be deteriorated.
N: in the steel grade of the invention, N is a limiting element, and under the possible conditions, the lower N is controlled to be better, but the lower N increases the steelmaking cost, so that the upper limit of the N content is limited to 0.003 percent, and simultaneously, the N atoms can be effectively converted into AlN precipitates by being matched with 0.03 to 0.04 percent of Als, thereby being beneficial to smooth rolling in the hot rolling process and reducing the recrystallization annealing temperature.
In addition, the invention does not add Ti, and because the high-strength IF steel added with Ti or the IF steel only added with Ti has larger anisotropy than the high-strength IF steel added with Nb, the Ti element can segregate on the surface of the steel during annealing of the high-strength IF steel added with Ti, and the quality of the hot dip galvanized steel is affected. For the zinc-iron alloy coated steel sheet, the addition of excessive Ti causes the alloy coating to develop alloying streaks, so that the product cannot be used for an outer plate.
The application provides a production method of the inventive steel, which comprises the following process steps: steelmaking, continuous casting, hot rolling, pickling and cold rolling, continuous annealing and hot dip galvanizing, and finishing rolling.
Steelmaking: through steelmaking, the chemical composition of the steel C:0.0010 to 0.0030 percent, si: less than or equal to 0.02 percent, mn:0.24 to 0.70 percent, P:0.02 to 0.06 percent, S is less than or equal to 0.009 percent, als:0.03 to 0.04 percent, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance is Fe and unavoidable impurities, wherein Nb and C satisfy the formula, and C-Nb/7.74 is less than or equal to 1PPM and less than or equal to 5PPM.
Desulfurizing treatment is carried out in the molten iron pretreatment process, so that the final component S of molten iron pretreatment is less than or equal to 0.009%. C content in steel is controlled to be 0.0010-0.0030 percent through converter smelting and RH furnace smelting, nb and C meet a formula, C-Nb/7.74 is less than or equal to 1PPM and less than or equal to 5PPM, and surplus C of 1-5 PPM is ensured in the steel. C atoms and B atoms are adjacent element elements with the same period, the atomic radiuses of the C atoms and the B atoms are equivalent, the electronegativity is equivalent, the C atoms and the B atoms can play a similar role when being dissolved in steel, a certain amount of excessive C can be used for replacing B to preferentially act on grain boundaries, and the segregation of P on the grain boundaries is inhibited, so that the secondary processing brittleness of the steel is improved.
Continuous casting: the surface of the casting blank is subjected to flame cleaning with the depth of more than or equal to 2mm, and the defects such as slag inclusion, air holes and the like are easy to exist in the depth range of 2mm of the surface of the casting blank, and after the subsequent hot rolling and cold rolling processes, the defects are amplified and brought to the surface of a finished product, so that poor surface quality and stamping cracking can be caused.
And (3) hot rolling: when the higher tapping temperature is 1230-1260 ℃, carbide and nitride in the casting blank can be fully dissolved, nucleation points can not be provided for dynamic recrystallization in the subsequent hot rolling stage, and abnormal growth of austenite grains in the rolling process can be controlled; adopting a finishing rolling temperature Ar < 3+ > 30 ℃, and generating strain to induce precipitation of a second phase during finishing rolling near the critical Ar < 3+ > temperature, thereby playing a role in refining grains; the adoption of the lower coiling temperature of 640-680 ℃ is beneficial to obtaining fine grains, and the obtained hot coil has thinner oxide scale thickness. Meanwhile, the descaling water is fully opened during rough rolling and finish rolling, the pressure is more than or equal to 150Bar, and the oxygen pressing defect can be avoided to the greatest extent.
Pickling and cold rolling: the hot rolled coil is subjected to cold rolling after pickling, the total rolling reduction is 75% -85%, when the total rolling reduction is less than 75%, the strong {111} favorable texture and the high r value are not easy to obtain after annealing, and when the total rolling reduction is more than 85%, the equipment load is larger, so that the continuous and stable production is not facilitated.
Continuous annealing and hot dip plating: the annealing RTF and SF temperatures of the steel are 770-800 ℃, when the temperature is less than 770 ℃, the recrystallization growth of a cold rolled structure is insufficient, the deep drawing performance is possibly deteriorated, when the temperature is more than 800 ℃, nbC is possibly dissolved, nbC particles in the steel are reduced, the growth unbalance of the recrystallization crystal grains is possibly caused, and the anisotropy of the steel plate is possibly increased, namely the delta r of the steel plate is more than or equal to 0.20. On the other hand, if the number of solid solution C atoms in the steel increases beyond a certain level, room temperature aging may occur before use, resulting in defects in the surface of the steel sheet. The dew point temperature is controlled to be less than or equal to minus 50 ℃, the oxygen partial pressure is extremely small at the extremely low dew point, the separation of oxides of Mn and P on the surface is favorably inhibited, and a substrate with excellent surface quality is provided for hot dip galvanizing. The temperature of the zinc pot is 450-460 DEG C<The temperature of the strip steel entering the zinc pot is less than +10deg.C, and Al in the zinc pot: 0.20 to 0.30 percent, and the aim of limiting is to ensure that the steel belt is in a zinc potDuring operation, the surface of the strip steel substrate forms uniform Fe 2 Al 5 The inhibiting layer ensures good adhesion between the strip coating and the substrate, ensures that no Fe-Zn compound bottom slag is generated in the zinc pot, and is beneficial to obtaining high surface quality because the Fe-Zn reaction is avoided. And (3) carrying out alloying treatment on the zinc-iron alloy coated steel plate after hot dip galvanizing is finished, wherein the alloying temperature is 520-550 ℃.
Finishing and rolling: the roughness of the working roll is 1.5-2.5 mu m, the rolling elongation is 1.0-1.4%, and the limitation of the process can ensure that the Ra of the strip steel after finishing rolling is 0.7-1.5 mu m on one hand, and can obtain good plate shape at the same time, and on the other hand, the yield platform of the finished steel can be eliminated after finishing rolling, rp0.2 of the steel plate can be improved, and the deep drawing performance of the steel plate can be improved.
The secondary processing brittleness index of the steel plate is SWET temperature, namely the ductile-brittle transition temperature of the steel, the lower the temperature is, the stronger the secondary processing brittleness resistance of the steel is, and because the steel for the automobile is likely to be in service under extremely cold conditions, the SWET temperature is generally less than or equal to-50 ℃, the general requirement of the steel can be met, and the SWET of the steel is less than or equal to-50 ℃ and has good secondary processing brittleness resistance.
The deep drawing performance index of the steel plate is characterized by a plastic strain ratio, namely an r value and a strain hardening index, namely an n value, and the greater the r value and the n value, the better the deep drawing performance of the steel is indicated, the r value of the steel is more than or equal to 1.8, and the n value is more than or equal to 2.0, so that the requirements of the current automobile phosphorus-containing IF steel outer plate are met.
The index for evaluating the room temperature aging resistance of the steel sheet is an aging index AI, and when the aging index AI is 0, it is indicated that the steel sheet does not undergo room temperature aging. The steel of the invention has a certain amount of solid solution C, but when Nb and C satisfy the formula, C-Nb/7.74 is less than or equal to 5PPM, AI=0 of the steel plate can be ensured, and room temperature aging can not occur.
The size of the plating leakage defect of the galvanized plate is 0.2 mm-0.8 mm. According to the number of the missing plating defects in any specified area on the steel strip, the missing plating defects are rated, and the missing plating defect level of the steel is more than or equal to level 2. The standards of the surface plating omission defect level of the steel plate are shown in table 1.
TABLE 1 determination method for grade of missing plating defect on surface of steel plate
| 3m 2 Number of area miss-plating defects | Grade of missing plating defect on surface of steel plate |
| ≤1 | Level 1 |
| ≤3 | Level 2 |
| ≤5 | 3 grade |
| ≤10 | Grade 4 |
| ＞10 | Class 4 and above |
The present invention will be described more specifically by way of examples, which are given by way of illustration only and are not intended to limit the scope of the claims.
Table 2 shows chemical compositions of billets in examples and comparative examples, wherein examples 5 and 6 are alloyed hot-dip galvanized steel sheets, and the balance is hot-dip galvanized steel sheets.
Table 2 chemical compositions of billets
The following table shows the main process parameters for the production of example and comparative steel, wherein example 5 and example 6 belong to alloyed hot-dip galvanized steel sheets, the remainder being hot-dip galvanized steel sheets.
Table 3 major process parameters for examples and comparative examples
Steel sheets were produced by using the billets having the compositions shown in table 2 under the production process shown in table 3, and the tensile strength, yield strength, elongation, and deep drawing performance index r value, n value, and Δr value, the room temperature resistance performance index AI value, and the evaluation results of the secondary work brittleness SWET temperature, surface roughness, and surface quality grade are shown in table 4.
Table 4 various performance indices of steels
Examples 1 to 6 are carried out according to the process of the invention, satisfying all the characteristics required by the invention, the steel sheet being SWET < 50℃according to the test of GB/T24173-2016 Standard for embrittlement experiments for Secondary working of Steel sheets. The experimental results of the examples and comparative examples can be referred to fig. 3 and 4. Wherein FIG. 3 shows the example product at-55deg.C and FIG. 4 shows the comparative example product at-50deg.C.
The degree of the missing plating defect on the surface of the steel plate is 2 grade or more, and the judging method of the missing plating defect grade on the surface of the steel plate is shown in table 1.
The measured r value of the steel plate is more than or equal to 1.8 and the delta r is less than or equal to 0.25 according to GB/T5027 standard for measuring the plastic strain ratio (r value) of a metal material sheet and a thin strip.
The measured n value of the steel plate is more than or equal to 0.2 according to GB/T5028 determination of tensile strain hardening index (n value) of metal sheets and thin strips. The aging index AI (heat preservation at 100 ℃ for 60 min) of the steel is 0, and the roughness of the steel is Ra 0.7-1.5 mu m.
Comparative examples 1 to 6 did not satisfy any one or more of the characteristics required in the present invention because they did not satisfy the method of the present invention. Wherein, the relation between C and Nb in comparative examples 1-2 does not accord with the formula, C-Nb/7.74 is less than or equal to 1PPM and less than or equal to 5PPM, C-Nb/7.74 is less than 1PPM, and the obtained SWET is > -50 ℃ and does not meet the SWET < -50 ℃ required by the invention steel. The relation between C and Nb in comparative example 3 does not conform to the formula, C-Nb/7.74 is less than or equal to 1PPM and less than or equal to 5PPM, C-Nb/7.74 is more than 5PPM, the room temperature aging index AI is more than 0, room temperature aging can occur, and the requirement of the invention steel AI=0 is not met. The annealing RTF and SF temperatures of comparative example 4 were 825 ℃, at which NbC dissolved, increased the solid solution C in the steel, and the AI index was > 0 even if the relationship between C and Nb in the steel slab satisfied 1 PPM.ltoreq.C-Nb/7.74.ltoreq.5 PPM. Meanwhile, the surface quality is deteriorated due to precipitation of Mn and P elements on the surface caused by too high annealing temperature. The comparative examples 5 and 6 have Mn and P contents exceeding the upper limit of the inventive steel, thus resulting in excessively high strength, r-value lower than the lower limit of 1.8 of the inventive steel, failing to satisfy the inventive steel in deep drawability, and surface segregation occurs during annealing due to the higher Mn and P contents, deteriorating the surface quality of the steel sheet.
The invention and its embodiments have been described above by way of illustration and not limitation, and the invention is illustrated in the accompanying drawings and described in the drawings in which the actual structure is not limited thereto. Therefore, if one of ordinary skill in the art is informed by this disclosure, the structural mode and the embodiments similar to the technical scheme are not creatively designed without departing from the gist of the present invention.
Claims (8)
1. A phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality is characterized in that: the IF steel plate comprises the following chemical components in percentage by weight: 0.0010 to 0.0030%, si: less than or equal to 0.02 percent, mn: 0.24-0.70%, P: 0.02-0.06%, S is less than or equal to 0.009%, als: 0.03-0.04%, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance is Fe and unavoidable impurities; and Nb and C are required to be satisfied, wherein the content of C-Nb is more than or equal to 1ppm and less than or equal to 7.74 ppm and less than or equal to 5ppm;
the secondary processing brittleness SWET of the IF steel plate is less than or equal to-50 ℃, and the degree of the missing plating defect on the surface of the steel is 2 grade or more;
the IF steel has r more than or equal to 1.8, deltar less than or equal to 0.25, n more than or equal to 0.2, AI of 0 and Ra of 0.7-1.5 mu m.
2. The method for producing a phosphorus-containing IF steel sheet resistant to secondary working embrittlement and excellent in surface quality as claimed in claim 1, characterized by: the method comprises the following process steps: steelmaking, continuous casting, hot rolling, pickling and cold rolling, continuous annealing and hot dip galvanization and finishing rolling, wherein the chemical components of steel tapping after steelmaking are calculated in percentage by weight: 0.0010 to 0.0030%, si: less than or equal to 0.02 percent, mn: 0.24-0.70%, P: 0.02-0.06%, S is less than or equal to 0.009%, als: 0.03-0.04%, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance is Fe and unavoidable impurities, wherein Nb and C meet 1ppm less than or equal to C-Nb/7.74 ppm less than or equal to 5ppm.
3. The method for producing a phosphorus-containing IF steel sheet having excellent surface quality and resistance to secondary working embrittlement according to claim 2, characterized by: in the continuous casting step, the casting blank is subjected to flame cleaning, and the cleaning depth is more than or equal to 2mm.
4. The method for producing a phosphorus-containing IF steel sheet resistant to secondary working embrittlement and excellent in surface quality as claimed in claim 3, characterized by: in the hot rolling step, the hot rolling tapping temperature is 1230-1260 ℃, the final rolling temperature is Ar < 3+ > 30 ℃, the coiling temperature is 640-680 ℃, the descaling water state is fully opened, and the descaling water pressure is more than or equal to 150Bar.
5. The method for producing a phosphorus-containing IF steel sheet having excellent surface quality and resistance to secondary working embrittlement as defined in claim 4, wherein: in the pickling and cold rolling steps, the total rolling reduction is 75% -85%.
6. The method for producing a phosphorus-containing IF steel sheet having excellent surface quality and resistance to secondary working embrittlement according to claim 5, characterized by: in the continuous annealing and hot dip galvanizing step, the temperature of an annealing section RTF and SF is 770-800 ℃, the temperature of a zinc pot is 450-460 ℃, the temperature of the zinc pot is less than the temperature of entering strip steel into the zinc pot and less than the temperature of the zinc pot plus 10 ℃, and the dew point temperature is less than or equal to-50 ℃; al in zinc pot: 0.20-0.30%.
7. The method for producing a phosphorus-containing IF steel sheet resistant to secondary working embrittlement and excellent in surface quality according to claim 6, characterized in that: for the zinc-iron alloy coated steel plate, the alloying temperature is 520-550 ℃.
8. The method for producing a phosphorus-containing IF steel sheet having excellent surface quality and resistance to secondary working embrittlement according to claim 7, characterized by: in the finishing rolling step, the roughness of a working roller of the finishing machine is 1.5-2.5 mu m, and the rolling elongation is 1.0-1.4%.
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