CN115627414A - Phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality and production method thereof - Google Patents
Phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality and production method thereof Download PDFInfo
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- 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
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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 automobile steel manufacturing. 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 to 0.70%, P: 0.02-0.06%, S is less than or equal to 0.009%, als:0.03 to 0.04%, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance of Fe and inevitable impurities; and Nb and C are required to meet the requirement, and C-Nb/7.74 is more 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 IF high-strength steel in the traditional technical scheme, the steel does not contain B, ti, and the addition amount of Nb is less than that of the traditional IF high-strength steel and the cost is lower through the accurate control of solid solution C.
Description
Technical Field
The invention belongs to the field of manufacturing of steel 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 requirement of the automobile industry on the corrosion resistance, the galvanized high-strength IF steel is widely applied to the automobile industry due to excellent corrosion resistance, strength and deep drawing performance. The high-strength IF steel is based on ultra-low carbon steel components, micro-alloying elements Nb, ti and V are added compositely to eliminate C, N solid solution atoms, and Si, mn and P are added to realize solid solution strengthening so as to reach corresponding strength level. When P element is added into steel, secondary processing brittleness of a steel plate can be caused, and the prior art improves the secondary processing brittleness of phosphorus-containing IF steel by adding B element. However, when B is added to steel, it may segregate on the surface of the steel sheet as an oxide before hot dip coating after annealing, and also induce segregation of Mn and P oxides on the surface of the steel, resulting in a plating leakage defect on the hot dip galvanized surface, and failing to meet the requirements of the automobile exterior panel for the quality of the panel surface. On the other hand, B segregated in the grain boundary may diffuse into the grain again to cause dislocation pinning, resulting in aging, and the steel sheet may be aged at room temperature before stamping. The current technical scheme limits the further application of the galvanized high-strength IF steel on the automobile outer plate. The demand is high, and the secondary processing brittleness problem of the hot-dip galvanized phosphorus-containing IF steel can be solved, and the surface quality and the deep drawing performance are excellent.
Through search, the application with the Chinese patent application number of 201210119462.6 discloses a steel containing P for an IF automobile panel and a production method thereof, wherein the secondary brittleness of the steel is improved by adding B, but B is segregated on the surface in an annealing furnace and easily causes plating leakage defects, so the method is more suitable for cold-rolled outer plates and has certain limitation when producing hot-dip galvanized outer plates.
For another example, the application of the chinese patent application No. 201810684401.1 discloses a method for preparing an IF steel strip, wherein the IF steel strip in the application comprises the following components in percentage by mass: c:0.0005 to 0.008 percent, mn:0.15 to 0.8%, si: 0.02 to 0.1%, B:0.01 to 0.02%, V:0.04 to 0.09%, P:0.005 to 0.08%, N: less than or equal to 0.005 percent, less than or equal to 0.002 percent of O, less than or equal to 0.002 percent of S and the balance of Fe. The preparation method is used for producing continuous annealing coils, and the Si element added by the preparation method is up to 0.1 percent, so that the wettability of the surface of a steel plate to zinc liquid can be deteriorated, and surface defects can be caused. Meanwhile, the C content is 0.008% at most, which may result in too high strength of the finished product and is not suitable for outer plates with high requirements on deep drawing performance.
For another example, the application of the chinese patent application No. 202011344974.3 discloses 220 MPa-grade hot-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 to 0.058 percent; nb:0.01 to 0.02 percent; ti:0.015 to 0.025 percent; and Als: 0.020-0.045%; a restriction element S: less than 0.003%; n: less than 0.003% and Fe for the rest. In the application, the precipitation of FePTiNb is avoided by controlling the addition amounts of Nb and Ti, and the technical problem of poor secondary processing brittleness resistance of high-strength IF steel in the prior art is solved or partially solved. However, the problem of secondary brittleness caused by P segregation in grain boundaries in the application is not fundamentally solved, and the application of the method is limited.
Disclosure of Invention
1. Problems to be solved
Aiming at least some problems in the prior art, the invention provides the phosphorus-containing IF steel plate with the secondary processing brittleness resistance and excellent surface quality and the production method thereof.
2. Technical scheme
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%, si: less than or equal to 0.02 percent, mn:0.24 to 0.70%, P: 0.02-0.06%, S is less than or equal to 0.009%, als:0.03 to 0.04%, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance of Fe and inevitable impurities; and Nb and C are required to meet the requirement, and C-Nb/7.74 is more than or equal to 1PPM and less than or equal to 5PPM.
Furthermore, the secondary processing brittleness SWET of the IF steel plate is less than or equal to-50 ℃, and the plating leakage defect degree on the steel surface is grade 2 and above.
Furthermore, r of the IF steel is more than or equal to 1.8, delta r is less than or equal to 0.25, n is more than or equal to 0.2, AI is 0, and Ra is 0.7-1.5 mu m.
The invention relates to a method for producing a phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality, which comprises the following process steps: steel making, continuous casting, hot rolling, pickling, cold rolling, continuous annealing, hot dip galvanizing and finishing rolling, wherein the chemical components of steel tapping after steel making are calculated according to the weight percentage, C:0.0010 to 0.0030%, si: less than or equal to 0.02%, mn:0.24 to 0.70%, P: 0.02-0.06%, S is less than or equal to 0.009%, als:0.03 to 0.04%, nb:0.006 to 0.020 percent, less than or equal to 0.003 percent of N, and the balance of Fe and inevitable impurities, wherein Nb and C meet the requirement that C-Nb/7.74 is less than or equal to 5PPM and is more than or equal to 1 PPM.
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 finishing temperature Ar3+30 ℃, the coiling temperature is 640-680 ℃, the descaling water state is full open, and the descaling water pressure is more than or equal to 150Bar.
Further, in the pickling and cold rolling step, the total cold rolling reduction is 75-85%.
Further, in the steps of continuous annealing and hot dip galvanizing, the temperature of RTF and SF in the annealing section is 770-800 ℃, the temperature of a zinc pot is 450-460 ℃, the temperature of the zinc pot is lower than the temperature of a strip steel in the pot and lower than the temperature of the zinc pot plus 10 ℃, and the dew point temperature is less than or equal to minus 50 ℃; al in the zinc pot: 0.20 to 0.30 percent;
furthermore, the alloying temperature of the zinc-iron alloy coating steel plate is 520-550 ℃.
Furthermore, in the step of finishing rolling, the roughness of a working roll of the finishing machine is 1.5-2.5 μm, 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) According to the phosphorus-containing IF steel plate with the secondary processing brittleness resistance and the excellent surface quality, under the condition that B element is not added, C and Nb in steel components meet the requirements, and C-Nb/7.74 is more than or equal to 1PPM and less than or equal to 5PPM; when the steel contains more than 1PPM and less than 5PPM of solid solution C, the solid solution C is preferentially segregated to a grain boundary in the annealing process, so that the distortion energy of the grain boundary is reduced, and the segregation of a P element in the grain boundary is inhibited, thereby solving the problem of secondary processing brittleness caused by the addition of P; on the other hand, a production method adopts a process of high-temperature tapping, finishing temperature near critical Ar3, low Wen Juanqu and low-temperature annealing, so that the final structure is a fine ferrite structure, when fine grains are subjected to external force, plastic deformation can be dispersed in more grains, the plastic deformation is uniform, the stress concentration is small, in addition, the grains are thinner, the grain boundary area is larger, the grain boundary is more tortuous, the crack expansion is more difficult, and finally the secondary processing brittleness SWET of the phosphorus-containing IF steel plate is less than or equal to-50 ℃.
(2) According to the phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality, when solid solution atoms C are used for replacing solid solution atoms B under the condition of not adding B elements, the C enriched on the surface can be changed into CO or CO 2 Gas, the surface plating leakage defect of the hot dip plated steel plate caused by B element precipitation in the annealing process of the steel plate can not be caused, and in addition, the casting blank is subjected to flame cleaning in the production to control the internal quality defectIn the hot rolling stage, descaling water is controlled to avoid oxygen pressing, low-temperature coiling is used to reduce the generation of iron scale, the dew point of an annealing furnace is controlled to be less than or equal to-50 ℃ in the annealing stage to control the Mn and P elements to be separated out on the surface, the temperature of a zinc pot, the Al content and the temperature of strip steel entering the pot are limited, so that a coating with excellent quality is obtained, and the finally obtained steel surface plating leakage defect degree is 2 grade or more.
(3) According to the production method of the phosphorus-containing IF steel plate with the secondary processing brittleness resistance and the excellent surface quality, annealing is carried out within the temperature range of 770-800 ℃, nbC particles cannot be dissolved at the temperature, namely the content of solid solution C in the steel cannot be increased, and as the matrix only contains 1-5 PPM of solid solution C, the dislocation pinning effect cannot occur at normal temperature, so that the room temperature aging does not occur 6 months after the steel plate is produced.
(4) Compared with IF high-strength steel of the traditional technical scheme, the production method of the phosphorus-containing IF steel plate with secondary processing brittleness resistance and excellent surface quality does not add B, ti element, and the addition amount of Nb is less than that of the traditional IF high-strength steel and the cost is lower through the accurate control of solid solution C.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is a schematic representation of the metallographic structure of a steel plate matrix according to the invention;
FIG. 3 is a schematic diagram of the product state at-55 ℃ in the example of the present invention;
FIG. 4 is a schematic diagram showing a state of a product of a comparative example of the present invention at-50 ℃;
FIG. 5 is a schematic view of a plating through defect in a comparative example of the present invention;
FIG. 6 is a schematic diagram of a defect free from plating omission in an embodiment of the present 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%, si: less than or equal to 0.02 percent, mn:0.24 to 0.70%, P: 0.02-0.06%, S is less than or equal to 0.009%, als:0.03 to 0.04%, nb:0.006 to 0.020 percent, less than or equal to 0.003 percent of N, and the balance of Fe and inevitable impurities, wherein Nb and C meet the formula, and C-Nb/7.74 is less than or equal to 5PPM and is more than or equal to 1 PPM. Wherein the content of the first and second substances,
c: 0.0010-0.0030 percent, when the content of C is less than 0.0010 percent, the RH steel-making deep decarburization time is prolonged, the decarburization time is more than 25min, and the production efficiency is influenced. When the C content is more than 0.0030 percent, in order to satisfy the formula, 1PPM is less than or equal to C-Nb/7.74 is less than or equal to 5PPM, more Nb needs to be added, which is not favorable for cost control and can also deteriorate the deep drawing performance of the material.
Si: not more than 0.02% by weight, si is one of the alloying elements of steel, and in the present invention, the Si addition amount is strictly controlled so that the upper limit of the Si element is 0.02%, and Si added in an amount exceeding 0.02% may cause surface defects of a hot-dip galvanized steel sheet.
Mn:0.24 to 0.70%, mn is an important solid solution strengthening element of the high strength IF steel, and IF the Mn content is less than 0.24%, the strength of the steel may not be satisfactory, and IF the Mn content is more than 0.7%, the yield strength of the steel may be excessively high, and excessive Mn may cause significant surface segregation, thereby deteriorating the surface quality of the hot-dip galvanized steel sheet.
P: 0.02-0.06%, P is an important solid solution strengthening element of the high-strength IF steel, the increment of the tensile strength of the P solid solution strengthening to the steel is larger than the increment of the yield strength to the steel, the deep drawing performance of the steel is strong, and the minimum addition amount of P is determined to be 0.02% in order to fully exert the solid solution strengthening effect of the P. However, when the amount of P in the steel is too large, even if a certain amount of solid solution C is present in the steel, the concentration of P becomes too high, which may increase the tendency of grain boundary segregation, leading to cold embrittlement of the steel, and also to too high strength of the steel, deteriorating the deep drawability of the steel, so the P content in 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 elements cause edge cracking defects in the steel during hot rolling, and sulfide inclusions also deteriorate the deep drawability of the steel sheet, and for the steel of the present invention, S must be limited to less than 0.009%.
Acid-soluble aluminum (Als): 0.03-0.04%, als in the steel 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 easily caused, deep drawing performance of the steel plate is deteriorated, and when Als is more than 0.04%, excessive Als can cause more inclusions in a steel matrix and can cause the defect of punching cracking.
Nb: 0.006-0.020%, nb is the key element of the invention steel, on one hand, nb is taken as a strong carbide forming element, and Nb and C form NbC precipitate in the hot rolling process, and the precipitate can inhibit the disordered growth of recrystallized grains in the subsequent annealing process, thereby being beneficial to the uniform structure of the annealed steel plate and the isotropy of the steel plate performance. On the other hand, the relationship between Nb and C satisfies the formula, C is more than or equal to 1PPM and less than or equal to 5PPM, and by the method, the secondary processing brittleness of the phosphorus-containing IF steel can be obviously improved even IF B element is not added into the steel. Therefore, the lower limit of the amount of Nb added to achieve the above effect is 0.006%, while if the amount of Nb added exceeds 0.020%, the growth of recrystallized grains is suppressed, and the deep drawability of the steel sheet may be deteriorated.
N: less than or equal to 0.003 percent, N is a limiting element in the steel grade of the invention, and the lower N is better when the N is controlled under possible conditions, but the lower N increases the steelmaking cost, so the upper limit of the N content is limited to 0.003 percent, and simultaneously 0.03 to 0.04 percent of Als is matched, N atoms can be effectively converted into AlN precipitates, thereby being beneficial to smooth rolling in the hot rolling process and reducing the recrystallization annealing temperature.
In addition, ti is not added, the anisotropy of the finished product is larger than that of Nb-added high-strength IF steel due to the high-strength IF steel added with Ti or the IF steel only added with Ti, and meanwhile, when the high-strength IF steel added with Ti is annealed, ti elements can segregate on the surface of the steel, so that the quality of hot-dip galvanized steel is influenced. For the steel plate with the zinc-iron alloying coating, excessive Ti is added to cause the alloying coating to have alloying stripes, 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: steel making, continuous casting, hot rolling, acid pickling, cold rolling, continuous annealing, hot dip galvanizing and finishing rolling.
Steel making: through steelmaking, the chemical composition C of the steel in percentage by weight: 0.0010 to 0.0030%, si: less than or equal to 0.02 percent, mn:0.24 to 0.70%, P: 0.02-0.06%, S is less than or equal to 0.009%, als:0.03 to 0.04%, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance is Fe and inevitable impurities, wherein Nb and C satisfy the formula, and C-Nb/7.74 is less than or equal to 5PPM and is more than or equal to 1 PPM.
The desulfurization treatment is carried out in the molten iron pretreatment process, so that the final component S of the molten iron pretreatment is less than or equal to 0.009 percent. Through converter smelting and RH furnace smelting, the C content in the steel is controlled to be 0.0010-0.0030%, nb and C meet the formula, C-Nb/7.74 is more than or equal to 1PPM and less than or equal to 5PPM, and 1-5 PPM of excess C is ensured in the steel. The C atom and the B atom are adjacent elements in the same period, the atomic radii of the C and the B are equivalent, the electronegativity is equivalent, the C and the B can play a similar role when being dissolved in steel, a certain amount of surplus C can be used for replacing the B preferentially at the grain boundary, and the P segregation at the grain boundary is restrained, 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 because the defects of slag inclusion, air holes and the like are easy to exist within the depth range of 2mm on the surface of the casting blank, the defects are amplified after subsequent hot rolling and cold rolling processes and are brought to the surface of a finished product, so that poor surface quality and stamping cracking can be caused.
Hot rolling: when the high furnace-out temperature is 1230-1260 ℃, carbide and nitride in the casting blank can be fully dissolved, nucleation particles can not be provided for dynamic recrystallization in the subsequent hot rolling stage, and the abnormal growth of austenite grains in the rolling process can be controlled; the finishing temperature Ar3+30 ℃ is adopted, and a second phase is generated by strain induction during finishing at the temperature close to the critical Ar3 temperature, so that the effect of refining grains is achieved; when the coiling temperature is lower than 640-680 ℃, fine grains can be obtained, and the obtained hot coil has thinner iron scale thickness. Meanwhile, descaling water is fully opened and the pressure is more than or equal to 150Bar during rough rolling and finish rolling, so that the oxygen pressing defect can be avoided to the maximum extent.
Acid pickling and cold rolling: the hot rolled coil is subjected to cold rolling after acid pickling, the total reduction rate of the cold rolling is 75-85%, when the total reduction rate is less than 75%, a strong {111} favorable texture and a high r value are not easily obtained after annealing, and when the total reduction rate is more than 85%, the equipment load is large, so that the continuous stability of production is not facilitated.
Continuous annealing and hot dip coating: the annealing RTF and SF temperatures of the steel are 770-800 ℃, when the temperature is less than 770 ℃, recrystallization growth of a cold rolled structure is insufficient, deep drawing performance is possibly deteriorated, when the temperature is more than 800 ℃, nbC is possibly dissolved, nbC particles in the steel are reduced, recrystallization grain growth unbalance is caused, and anisotropy of a steel plate is possibly increased, namely delta r of the steel plate is more than or equal to 0.20. On the other hand, if the amount of the solid-solution C atoms in the steel increases beyond a certain amount, room-temperature aging may occur before use, resulting in surface defects 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 low at an extremely low dew point, the precipitation 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 ℃, and the temperature of the zinc pot<The temperature of the strip steel in the zinc pot is less than the temperature of the zinc pot plus 10 ℃, and the ratio of Al in the zinc pot: 0.20-0.30%, wherein the above limitation is performed to ensure that uniform Fe is formed on the surface of the strip steel substrate when the strip steel runs in a zinc pot 2 Al 5 The inhibiting layer ensures good adhesion between the strip coating and the substrate, ensures that Fe-Zn compound bottom slag is not generated in the zinc pot, and avoids violent Fe-Zn reaction, thereby being beneficial to obtaining high surface quality. For the zinc-iron alloy coating steel plate, alloying treatment is carried out after hot dip galvanizing is finished, and 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 process is limited, so that the Ra of the band steel after finishing rolling is 0.7-1.5 mu m, good plate shape can be obtained, a yield platform of finished steel can be eliminated after finishing rolling, the 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 ductile-brittle transition temperature of the steel, the lower the temperature is, the stronger the secondary processing brittleness resistance of the steel is represented, and the automotive steel can possibly be used under extremely cold conditions, generally, the SWET temperature is less than or equal to-50 ℃, so that the universal requirement can be met, the SWET temperature of the steel is less than or equal to-50 ℃, and the steel 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, the larger the r value and the n value, the better the deep drawing performance of the steel is, 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 requirement of the phosphorus-containing IF steel outer plate of the automobile at present is met.
The index for evaluating the room temperature aging resistance of the steel plate is an aging index AI, and when the aging index AI is 0, the steel plate can not be subjected to room temperature aging. Although the steel has a certain amount of solid solution C, when Nb and C satisfy the formula, and C-Nb/7.74 is less than or equal to 5PPM and is more than or equal to 1PPM, the AI =0 of the steel plate can be ensured, and the room temperature aging can not occur.
The size of the plating leakage defect of the galvanized plate is 0.2 mm-0.8 mm. And (4) grading the plating-missing defects according to the number of the plating-missing defects in any specified area on the steel strip, wherein the grade of the plating-missing defects of the steel is more than or equal to grade 2. The standard of the plating missing defect level on the surface of the steel plate is shown in Table 1.
TABLE 1 determination method of the levels of plating-missing defects on the surface of a steel sheet
| 3m 2 Number of area skip plating defects | Grade of plating missing defects on steel plate surface |
| ≤1 | Level 1 |
| ≤3 | Stage 2 |
| ≤5 | Grade 3 |
| ≤10 | 4 stage |
| ＞10 | Grade 4 and above |
The present invention will be described in more detail with reference to the following examples, which are provided only for illustrating the present invention and are not intended to limit the scope of the present invention.
Table 2 shows chemical compositions of steel 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 composition of the billet
The following table shows the main process parameters for the production of the steel of examples and comparative examples, wherein examples 5 and 6 belong to the alloyed hot-dip galvanized steel sheet, and the remainder are hot-dip galvanized steel sheets.
TABLE 3 Main Process parameters of the examples and comparative examples
Steel sheets were produced from the steel slabs having the compositions shown in table 2 by the production processes shown in table 3, and the results of evaluation of tensile strength, yield strength, elongation, and deep drawability index r, n, and Δ r, time resistance room temperature effect index AI, secondary work embrittlement SWET temperature, surface roughness, and surface quality grade of the steel sheets are shown in table 4.
TABLE 4 various performance indexes of the steels
Examples 1 to 6 were carried out according to the method of the invention, and all the properties required by the invention were met, the steel sheets having a SWET of ≦ 50 ℃ according to GB/T24173-2016 "Experimental method for Secondary work embrittlement of Steel sheets" Standard test. The experimental results of examples and comparative examples can be referred to fig. 3 and 4. Wherein FIG. 3 shows the example product conducted at-55 deg.C, and FIG. 4 shows the comparative example product conducted at-50 deg.C.
The degree of the plating leakage defect on the surface of the steel plate is 2 grade or above, and the judging method of the grade of the plating leakage defect on the surface of the steel plate is shown in table 1.
The r value of the steel plate is more than or equal to 1.8 and delta r is less than or equal to 0.25 according to the GB/T5027 standard of the determination of the plastic strain ratio (r value) of the metal material sheet and the thin strip.
The measured n value of the steel plate is more than or equal to 0.2 according to GB/T5028 determination of the tensile strain hardening index (n value) of the metal sheet and the thin strip. The aging index AI (100 ℃ heat preservation 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 do not satisfy the method of the present invention and do not satisfy any one or more of the characteristics required in the present invention. Wherein, the relation between C and Nb in the comparative examples 1-2 does not conform to the formula, 1PPM is not less than C-Nb/7.74 is not more than 5PPM, and C-Nb/7.74 is less than 1PPM, the obtained SWET is > -50 ℃, and the SWET which does not meet the requirements of the invention steel is less than-50 ℃. The relation between C and Nb in the comparative example 3 does not conform to the formula, C-Nb/7.74 is not less than 1PPM and not more than 5PPM, C-Nb/7.74 is more than 5PPM, the room temperature aging index AI is more than 0, room temperature aging is possible, and the requirement of the invention steel AI =0 is not met. The annealing RTF and SF temperatures of comparative example 4 were 825 deg.C, and the solid solution C in the steel was increased due to the dissolution of NbC at this temperature, even though the relation of C and Nb in the steel slab satisfied 1 PPM. Ltoreq.C-Nb/7.74. Ltoreq.5PPM, and the AI index was > 0. Meanwhile, when the annealing temperature is too high, mn and P elements are precipitated on the surface, which deteriorates the surface quality. The steel slabs of comparative examples 5 and 6 have Mn and P contents exceeding the upper limit of the inventive steel, resulting in excessively high strength, r values lower than the lower limit of 1.8, deep drawability not satisfying the requirements of the inventive steel, and surface segregation occurring during annealing due to high Mn and P contents, deteriorating the surface quality of the steel sheet.
The present invention and its embodiments have been described above schematically, and the description is not intended to be limiting, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, without departing from the spirit of the present invention, a person of ordinary skill in the art should understand that the present invention shall not be limited to the embodiments and the similar structural modes without creative design.
Claims (10)
1. A phosphorus-containing IF steel sheet resistant to secondary work embrittlement and excellent in surface quality, 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 to 0.70%, P: 0.02-0.06%, S is less than or equal to 0.009%, als:0.03 to 0.04%, nb: 0.006-0.020%, N is less than or equal to 0.003%, and the balance of Fe and inevitable impurities; and Nb and C are required to meet the requirement, and C-Nb/7.74 is more than or equal to 1PPM and less than or equal to 5PPM.
2. The phosphorus-containing IF steel sheet having resistance to secondary work embrittlement and excellent surface quality as claimed in claim 1, wherein: the secondary processing brittleness SWET of the IF steel plate is less than or equal to minus 50 ℃, and the plating leakage defect degree on the steel surface is grade 2 and above.
3. The IF-containing steel sheet as set forth in claim 2, which is resistant to secondary work embrittlement and has excellent surface quality, wherein: the r of the IF steel is more than or equal to 1.8, delta r is less than or equal to 0.25, n is more than or equal to 0.2, AI is 0, and Ra is 0.7-1.5 mu m.
4. A method for producing a phosphorus-containing IF steel plate resistant to secondary processing brittleness and excellent in surface quality is characterized by comprising the following steps: the method comprises the following process steps: steel making, continuous casting, hot rolling, pickling, cold rolling, continuous annealing, hot dip galvanizing and finishing rolling, wherein the chemical components of steel tapping after steel making are calculated according to the weight percentage, C:0.0010 to 0.0030%, si: less than or equal to 0.02%, mn:0.24 to 0.70%, P: 0.02-0.06%, S is less than or equal to 0.009%, als:0.03 to 0.04%, nb:0.006 to 0.020 percent, less than or equal to 0.003 percent of N, and the balance of Fe and inevitable impurities, wherein Nb and C meet the requirement that C-Nb/7.74 is less than or equal to 5PPM and is more than or equal to 1 PPM.
5. The method for producing a phosphorus-containing IF steel sheet having resistance to secondary work embrittlement and excellent surface quality as claimed in claim 4, wherein: in the continuous casting step, the casting blank is subjected to flame cleaning, and the cleaning depth is more than or equal to 2mm.
6. The method for producing a phosphorus-containing IF steel sheet having resistance to secondary work embrittlement and excellent surface quality as claimed in claim 5, wherein: in the hot rolling step, the hot rolling tapping temperature is 1230-1260 ℃, the final rolling temperature is Ar3+30 ℃, the coiling temperature is 640-680 ℃, the descaling water state is full open, and the descaling water pressure is more than or equal to 150Bar.
7. The method for producing a phosphorus-containing IF steel sheet having resistance to secondary work embrittlement and excellent surface quality as set forth in claim 6, wherein: in the pickling and cold rolling steps, the total cold rolling reduction is 75-85%.
8. The method for producing a phosphorus-containing IF steel sheet resistant to secondary work embrittlement and excellent in surface quality as claimed in claim 7, wherein: in the steps of continuous annealing and hot dip galvanizing, the temperature of RTF and SF at the annealing section is 770-800 ℃, the temperature of a zinc pot is 450-460 ℃, the temperature of the zinc pot is lower than the temperature of a strip steel entering the pot and is lower than the temperature of the zinc pot plus 10 ℃, and the dew point temperature is lower than or equal to minus 50 ℃; al in the zinc pot: 0.20 to 0.30 percent.
9. The method for producing a phosphorus-containing IF steel sheet having resistance to secondary work embrittlement and excellent surface quality as claimed in claim 8, wherein: for the zinc-iron alloy coating steel plate, the alloying temperature is 520-550 ℃.
10. The method for producing a phosphorus-containing IF steel sheet resistant to secondary work embrittlement and excellent in surface quality as claimed in claim 8 or 9, wherein: in the step of finishing rolling, the roughness of a working roll of the finishing machine is 1.5-2.5 mu m, and the rolling elongation is 1.0-1.4%.
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