CN117344215A - 590 MPa-level low-cost pickling-free structural steel plate and manufacturing method thereof - Google Patents

590 MPa-level low-cost pickling-free structural steel plate and manufacturing method thereof Download PDF

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CN117344215A
CN117344215A CN202210759497.XA CN202210759497A CN117344215A CN 117344215 A CN117344215 A CN 117344215A CN 202210759497 A CN202210759497 A CN 202210759497A CN 117344215 A CN117344215 A CN 117344215A
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equal
pickling
less
steel
percent
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刘生
赵振伟
张华�
胡晓萍
李建新
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Baoshan Iron and Steel Co Ltd
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Baoshan Iron and Steel Co Ltd
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    • 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
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

A590 MPa-grade low-cost pickling-free structural steel and a manufacturing method thereof comprise the following components in percentage by mass: c:0.04 to 0.16 percent, si is less than or equal to 0.05 percent, mn:0.3 to 1.2 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.01 percent, ti:0.03 to 0.16 percent, nb:0.006 to 0.035 percent, and the balance of Fe and other unavoidable impurities, and the requirements are as follows: 0.251Ti+1.12Nb is more than or equal to 0.032, and C+Mn/6 is less than or equal to 0.23. The yield strength of the steel plate is more than or equal to 500MPa, the tensile strength is more than or equal to 590MPa, the elongation is more than or equal to 19%, D=1.5a is bent for 180 degrees and does not crack; meanwhile, the invention adopts low-cost component design, the manufacturing process flow is simple, and the production cost is low.

Description

590 MPa-level low-cost pickling-free structural steel plate and manufacturing method thereof
Technical Field
The invention relates to the field of structural steel, in particular to a 590 MPa-level low-cost pickling-free structural steel plate and a manufacturing method thereof.
Background
Along with the continuous improvement of the national requirements on environmental protection, the development of green and high quality has become the main melody of various industries, and users also put forward the requirements on high performance, high quality, low cost and the like on steel products. Many hot rolled structural steel products are usually subjected to an acid washing method to remove iron scales on the surface of a steel plate before being coated and used, so that the generated waste acid seriously pollutes the environment.
In order to solve the above problems, it is thought that the state of the scale is brought to a pickling-free state by improving the state and structure of the scale on the surface of the steel, thereby reducing the pollution of the waste acid discharge to the environment. There are many techniques currently available for hot rolling scale control, such as:
the Chinese patent CN201010235928.X discloses a production method of environment-friendly high-surface-quality pickling-free automobile girder steel, which introduces a method for producing high-surface-quality pickling-free automobile girder steel by adopting a high-temperature heating, high-temperature rolling and low-temperature coiling control of an oxide skin structure on the surface of the automobile girder steel.
Chinese patent CN201110307238.5 discloses a "temperature control method for solving black ash on the surface of a hot rolled automotive girder steel sheet", which describes a method for solving black ash on the surface of a girder steel by reducing the heating temperature of a slab, adopting double descaling treatment, increasing the finishing temperature and coiling temperature to improve the oxide skin component.
The Chinese patent CN201210176422.5 discloses a pickling-free steel coil with uniform surface iron sheet and a manufacturing method thereof, which introduces a method for producing the pickling-free steel coil with uniform surface iron sheet by adopting micro-medium waves and lubrication finish rolling, coating oxidation-resistant glass powder on the surfaces of two ends of the steel coil after rolling and forcibly cooling the steel coil.
Chinese patent CN201310057003.4 discloses "steel for high-strength girder with stable oxide layer free from acid washing and manufacturing method thereof", which introduces a method of cooling by adopting the post-stage: the method for producing the pickling-free girder steel with the stable oxide layer comprises the steps of relaxation cooling for 10-30 s after the strip steel is discharged from a finishing mill, cooling to 420-550 ℃ at a cooling speed of 10-40 ℃/s, coiling, preserving the heat of a steel coil for 6-10 h after coiling, and cooling to room temperature.
Chinese patent CN201610486480.6 discloses a high surface quality pickling-free hot rolled strip steel and a manufacturing method thereof, which introduces a method for producing the high surface quality pickling-free hot rolled strip steel by controlling the content of Si and Mn elements in the steel and high coiling temperature and forming a pure iron layer on the surface of the strip steel by utilizing the internal oxidation of Si and Mn after coiling.
Chinese patent CN201810003351.6 discloses a method for preventing scale from scaling off in hot-rolled pickling-free automobile girder steel, which introduces a method for adjusting Fe in the scale by controlling the content of Si element (0.28-0.3 wt%) in steel, adding 0.2-0.225 wt% Cr and adding a fan in the coiling process to improve the cooling rate 3 O 4 And FeO composition ratio to produce the method for preventing the powder flaking of the girder steel iron scale.
The production method of the hot-rolled pickling-free steel plate with tensile strength levels of 400MPa, 490MPa, 510MPa, 560MPa and 610MPa is respectively introduced, wherein the hot-rolled steel plate with the pickling-free automobile structure and the production method thereof are disclosed in China patent CN201510778750.6, the production method of the hot-rolled pickling-free steel plate with the 490MPa is disclosed in China patent CN201010298939.2, the hot-rolled pickling-free steel plate with the automobile structure and the production method thereof are disclosed in China patent CN201711190855.5, the hot-rolled pickling-free steel plate with the 560MPa is disclosed in China patent CN201711190852.1, the production method of the hot-rolled pickling-free steel plate with the 610MPa is disclosed in China patent CN 201711190853.6.
The technical characteristics of the patents are the same, the components are designed by adopting C, si and Mn+ (Nb and Ti), the content of C is 0.04-0.11%, the content of Si is 0.05-0.27%, the content of Mn is 0.7-1.5%, and the addition amount of Ti is below 0.03. The heating temperature is controlled between 1210 and 1240 ℃ in the process, the heating time is 1.2 to 1.8 hours, the finishing temperature is 860 to 890 ℃, the coiling temperature is 560 to 590 ℃, and the hot-rolled pickling-free steel plates with different strength grades are finally obtained through the matching of components and the process.
Disclosure of Invention
The invention aims to provide 590 MPa-grade low-cost pickling-free structural steel and a manufacturing method thereof, wherein the yield strength of the steel is more than or equal to 355MPa, the tensile strength is more than or equal to 510MPa, the elongation is more than or equal to 24%, the cold bending performance is excellent, and D=1a is bent for 180 degrees and does not crack; the surface oxide skin of the steel plate is smooth and compact, has good deformation and peeling resistance, and realizes no acid washing; meanwhile, the invention adopts low-cost component design, the manufacturing process flow is simple, and the production cost is low.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
a590 MPa-grade low-cost pickling-free structural steel comprises the following components in percentage by mass: c: 0.03 to 0.15 percent, si is less than or equal to 0.05 percent, mn:0.2 to 1.0 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.01 percent, ti:0.03 to 0.15 percent, and the balance of Fe and other unavoidable impurities, and the requirements are as follows: C+Mn/6 is less than or equal to 0.2.
The balance being Fe and other unavoidable impurities.
Further, the alloy also comprises one or more than one of Mo less than or equal to 0.2%, nb less than or equal to 0.05%, cr less than or equal to 0.2%, V less than or equal to 0.15%, ni less than or equal to 0.1% and Ca less than or equal to 0.015%.
The structure of the pickling-free structural steel is polygonal ferrite and/or quasi-polygonal ferrite plus a small amount of pearlite.
The yield strength of the pickling-free structural steel is more than or equal to 355MPa, the tensile strength is more than or equal to 510MPa, the elongation is more than or equal to 24%, and the structural steel is not cracked when being bent for 180 degrees by D=1a.
In the composition design of the pickling-free structural steel, the invention comprises the following steps:
c: c is a basic element in steel and is also the most important strengthening element in the invention. C is a central atom in steel and plays a very important role in improving the strength of steel. In the invention, C can also form a precipitated phase with Ti, so that the yield strength and the tensile strength of the steel are improved. However, a higher C content deteriorates the weldability and low-temperature toughness of the steel and more voids are formed in the scale, so that the C content needs to be controlled within a proper range, and the C content is controlled within a range of 0.04 to 0.16% in the present invention.
Si: si can increase the strength of steel in the form of solid solution strengthening and suppress or retard Fe 3 C formation. But Si content is too high, fe is formed in the heating process of the heating furnace 2 SiO 4 The descaling is not clean, resulting in deterioration of the surface quality of the steel sheet, and the increase of Si content results in deterioration of the uniformity of the scale. Therefore, the Si content in the present invention is controlled to 0.05% or less.
Mn: mn is an important toughening element, can enlarge an austenite phase region, stabilize austenite, delay the transformation from austenite to pearlite, reduce the critical cooling speed of martensite transformation, and greatly improve the hardenability; meanwhile, mn has a certain solid solution strengthening effect, and is beneficial to improving the strength of the steel plate. However, too high a Mn content results in too high hardenability of the steel, which is disadvantageous for fine control of the material. In addition, as environmental conditions become more severe, the price of Mn raw materials is greatly increased, and too much Mn is not added to the steel due to cost consideration. Therefore, the Mn content in the present invention is controlled to be 0.3 to 1.2%.
P: p is an impurity element in steel. P is easily biased to form eutectic compound Fe with low melting point with Fe on grain boundary 2 P reduces the plasticity and toughness of the steel, and the lower the solid content is, the better is, and the content is generally controlled within 0.02 percent.
S: s is an impurity element in steel. S in the steel is usually combined with Mn to form MnS inclusion, the MnS has certain plasticity, is deformed along the rolling direction in the rolling process, breaks the continuity of a matrix, and reduces the transverse performance of the steel plate, so that the lower the S content in the steel is, the better the lower the S content is, and the actual production is usually controlled within 0.01%.
Ti: ti is a strong carbonitride forming element, undissolved carbonitride of Ti can effectively pin an austenite grain boundary when steel is heated, austenite grain growth is controlled, tiN and TiC separated out during rough rolling in a high-temperature austenite area can effectively inhibit austenite grain growth, and fine TiC second-phase particles separated out in ferrite can prevent dislocation movement so as to greatly improve the strength of the steel plate. Therefore, the Ti content in the invention is controlled to be 0.03-0.16%.
Nb: nb is a strong carbonitride forming element, and increases the strength of steel by fine grain strengthening and precipitation strengthening. Nb can raise the austenite recrystallization temperature and realize austenite non-recrystallization rolling at a higher temperature, so that rolling deformation of a rolled piece can be completed at a higher temperature and a fine structure can be obtained. However, since Nb is expensive compared with the prior art, the content of Nb in the present invention is controlled to be 0.006 to 0.035%.
The invention adopts the component design of low C, low Si, low Mn, ti and Nb. The low C and low Mn (C+Mn/6 is less than or equal to 0.23) are used for reducing the hardenability of the steel and facilitating the accurate control of the steel plate structure, if the content of C, mn is too high, the hardenability of the steel is high, ferrite phase transformation is inhibited in the finish rolling post-layer cooling process, and bainite or martensite structures can appear in the final structure of the steel plate, so that the steel plate has too high strength and low elongation. And when the hardenability of the steel plate is larger, polygonal ferrite and/or quasi-polygonal ferrite structures are not easy to obtain, and the precipitation strengthening effect of second phases such as TiC, nbC and the like is not easy to play. Meanwhile, the lower C can reduce the generation of hollow holes in the oxide skin, the compactness of the oxide skin is improved, and the higher the compactness of the oxide skin is, the better the toughness of the oxide skin is, so that the acid washing-free use is realized. Lower Mn content is beneficial to reduce alloy cost.
Because the contents of C, si and Mn in the steel are very low, a certain amount of Ti and Nb are added to ensure that the steel plate reaches the required strength index. The purpose of adding Ti is to form TiC second phase particles in the steel, and the strength of the steel plate is improved by the TiC second phase. The purpose of adding Nb is two:
1. refining grains, and improving the strength and toughness of the steel plate;
2. the strength of the steel sheet is improved by forming NbC second phase particles. In order to fully exert the precipitation strengthening effect of Ti and the fine grain strengthening and precipitation strengthening effect of Nb, the mechanical properties of the steel plate reach the index requirements, and the Ti and Nb are required to satisfy: 0.251Ti+1.12Nb is more than or equal to 0.032.
The invention relates to a manufacturing method of 590 MPa-level low-cost pickling-free structural steel, which comprises the following steps:
1) Smelting and casting
Smelting, refining and continuously casting into casting blanks or cast ingots according to the chemical components;
2) Heating the cast slab or ingot
Heating the casting blank or the cast ingot in a heating furnace at 1250-1300 ℃ for 2-5 hours;
3) Hot rolling
The descaling water of the descaling box is opened before rough rolling, the primary scale is removed, the descaling is put in the rough rolling pass, the outlet temperature of rough rolling is less than or equal to 1010 ℃, and then finished steel coils are formed through finish rolling by a plurality of frames; the descaling water of the descaling box is opened before finish rolling, secondary oxide skin is removed, the descaling water between the finish rolling F1 and F2 frames is put in, the finish rolling temperature is 870-920 ℃, and the threading speed is more than or equal to 7m/s; cooling by adopting a pre-cooling process after rolling, wherein the coiling temperature is 600-650 ℃;
4) Post-roll cooling control
Cooling the coiled steel coil by adopting a fan after coil unloading, cooling to 520-550 ℃ at a cooling rate of more than or equal to 2 ℃/s, and then cooling down the coiled steel coil to a heat preservation wall or a hot coil pile at a cooling rate of less than or equal to 0.5 ℃/s to room temperature.
Preferably, the finish rolling of the hot rolling in the step 3) adopts a six-stand or seven-stand finishing mill.
In the manufacturing method of the present invention:
the invention adopts higher heating temperature to ensure that the casting blank (ingot) is fully austenitized and the second phases of Ti and Nb contained in the steel blank are fully redissolved, and the redissolved Ti and Nb are separated out in the form of second phases of TiC, nbC and the like in the subsequent rolling and layer cooling processes so as to improve the strength of the steel plate.
The invention adopts more descaling water to fully remove primary and secondary oxide skin during rough rolling, can ensure lower rough rolling outlet temperature and reduce the generation of oxide skin during the steel swinging process of billets. The finish rolling uses a large amount of descaling water to reduce the formation of triple scale. The main purpose of the descaling water in the process is to reduce the generation of oxide scale, control the thickness of the oxide scale, and when the thickness of the oxide scale is too thick, the thermal stress in the oxide scale is large, cracks are easy to generate, the toughness of the oxide scale and the binding force with a matrix are reduced, and conditions are created for realizing pickling-free of the final steel plate. The purpose of adopting higher finishing temperature is to utilize the plasticity of the oxide skin at high temperature, so that the oxide skin is fully expanded and deformed through rolling and is not broken at the same time, thereby improving the uniformity, toughness and binding force with a steel matrix of the oxide skin and creating conditions for pickling-free of the final steel plate.
The invention adopts a fast threading speed and a front-stage cooling process to enable the strip steel to be reduced to a low temperature as soon as possible, less oxidation after rolling is carried out, and the thickness of oxide skin on the surface of the final steel plate is reduced. And coiling at a higher coiling temperature to ensure that the oxide scale on the surface of the strip steel still exists in a form of FeO. After rolling, the mixture was rapidly cooled to a temperature of 520 to 550 ℃ (FeO decomposition temperature: 570 ℃).
After rolling, adopting a pre-cooling process, namely a pre-stage cooling process, namely cooling the strip steel by boiled water from a first valve after entering a layer cooling roller way, and automatically calculating and determining a layer cooling valve which needs to be continuously opened from the first cooling valve according to a final rolling temperature, a strip steel speed, a laminar roller way length and a coiling temperature target value by a system model.
The method is characterized in that a post-cooling process is adopted, namely, boiled water is not boiled firstly after strip steel enters a layer cooling roller way, the strip steel is air cooled, and a system model automatically calculates and determines which valve is to start to continuously start a cooling valve from the last valve according to the final rolling temperature, the strip steel speed, the laminar roller way length and the coiling temperature target value.
The rapid cooling is to restrain FeO decomposition in the cooling process, and the lower rapid cooling stop temperature ensures a certain supercooling degree of FeO decomposition and increases the driving force of FeO decomposition. The steel coil is transported to the heat preservation wall or the middle of the hot coil pile after reaching the cooling stop temperature to reduce the cooling speed of the steel coil, so that the steel coil is kept at 520-550 ℃ for a sufficient time to fully decompose FeO into Fe and Fe 3 O 4 . See fig. 1. The surface oxide scale of the final steel plate mainly consists of Fe and Fe 3 O 4 Two phases are composed, and the toughness of the two phases is the best among all Fe-O compounds, and the binding force between the two phases and an iron matrix is the strongest. The oxide skin formed by the two phases has good binding force with the steel matrix, so that the oxide skin can be deformed along with the steel matrix without breaking and peeling, and the purpose of no acid washing is achieved.
Compared with the prior art, the invention has the following differences and advantages:
the Chinese patents CN201010235928.X, CN201110307238.5, CN201210176422.5 and CN201310057003.4 are special processes for improving the uniformity of oxide skin on the surface of the steel plate, and mainly emphasize that the production process is not considered on the economy and convenience of the component design of the steel plate. For example, chinese patent CN201110307238.5 adopts double dephosphorization process, chinese patent CN201210176422.5 adopts coating of anti-oxidation glass powder on two end surfaces of the rolled steel coil, which affects normal production efficiency and increases production cost. The Chinese patent CN201310057003.4 needs to use a heat preservation cover to carry out heat preservation treatment on coiled steel coils, which is equipment not provided in the conventional hot continuous rolling production line and is not beneficial to the convenient production of pickling-free steel.
The present invention considers both the economy of component design and the convenience of the steel sheet production process, in contrast to the above-mentioned patents.
Chinese patents CN201610486480.6 and CN201810003351.6 both control the structure of the oxide scale by adding specific amounts of Si and Mn or Cr to the steel, so as to achieve the purpose of improving the quality of the oxide scale on the surface of the steel sheet.
The invention has no Cr and Si content lower than that of the two patents, and the adopted technical scheme for controlling the composition of the oxide scale is different from that of the two patents.
The Chinese patents CN201510778750.6, CN201010298939.2, CN201711190855.5, CN201711190852.1 and CN201711190853.6 have the same technical characteristics, the components adopt C, si and Mn+Ti designs, the content of C is 0.04-0.11%, the content of Si is 0.05-0.27%, the content of Mn is 0.7-1.5%, and the addition amount of Ti is below 0.03. The heating temperature is controlled between 1210 and 1240 ℃ in the process, the heating time is 1.2 to 1.8 hours, the finishing temperature is 860 to 890 ℃, the coiling temperature is 560 to 590 ℃, and the hot-rolled pickling-free steel plates with different strength grades are finally obtained through the matching of components and the process.
Compared with the above patent, the Si content is controlled below 0.05%, the Ti addition amount is above 0.03%, the heating time is 2-5 hours, the coiling temperature is 600-650 ℃, and the technical scheme is obviously different by adopting the cooling control after coiling.
Compared with the prior patent, the steel grade adopts low-cost component design, and the phase composition and the form of the iron scale on the surface of the steel plate are regulated and controlled by controlling the rolling process and the cooling process after coiling, so that the purposes of improving the toughness of the iron scale and the binding force with a steel substrate and realizing no acid washing are achieved. This is not known from other known patents at present, and is specifically as follows:
1. the micro-alloying elements added by the invention are few in variety and low in content, and especially, noble alloying elements such as Mo, V, ni and the like are not added, so that the production cost is greatly reduced.
2. According to the invention, ti precipitation strengthening is fully utilized, the yield strength of the steel plate is more than or equal to 500MPa, the tensile strength is more than or equal to 590MPa, the elongation is more than or equal to 19%, the cold bending performance is excellent, and the steel plate is bent for 180 degrees by D=1.5a without cracking.
3. The steel grade surface oxide skin is uniform and compact, has good anti-stripping performance, can reduce falling and ash generation in the processing and using process of a user, and improves the working environment of the user.
4. The steel grade of the invention has simple production process, wide process window and simple manufacturing process flow, and can be directly produced on the existing hot continuous casting production line.
Drawings
FIG. 1 is a diagram of Fe-O phase.
Fig. 2 is a photograph of the poor resistance of the scale to bending and peeling.
FIG. 3 is a photograph showing the general resistance of the scale to bending and peeling.
Fig. 4 is a photograph showing that the scale has good bending and peeling resistance.
Detailed Description
The invention is further described below with reference to examples and figures.
The chemical compositions of the steel sheet examples and comparative examples of the present invention are shown in Table 1, and the balance contains Fe and other unavoidable impurities. Components I through IX are within the claimed invention and components X and XI are not within the claimed invention.
The production process of the embodiment of the invention comprises the following steps: smelting by adopting a converter after deep desulfurization of molten iron, refining outside the converter, and continuously casting to form a plate blank; heating the slab to 1250-1300 ℃, preserving heat for 2-5 hours, wherein the rough rolling finishing temperature is less than or equal to 1010 ℃, the finish rolling finishing temperature is 870-920 ℃, cooling to 600-650 ℃ by adopting a pre-cooling process after rolling, coiling, and controlling cooling of the steel coil after coiling. Example process parameters are shown in table 2. Table 3 shows the performance parameters of the steels according to the examples of the present invention.
In all the examples and comparative example steels, 2 groups of descaling water before rough rolling are fully opened, 3 groups of descaling water before rough rolling are fully opened, 2 groups of descaling water before finish rolling are fully opened, and the descaling water between the F1 and F2 racks is fully opened.
Cooling after coiling, namely fast cooling and slow cooling after coiling and uncoiling the steel coil, cooling the steel coil to 520-550 ℃ by a fan (more than or equal to 2 ℃/s), and then lifting the steel coil to a heat-insulating wall or a hot coil pile to cool the steel coil to room temperature at a cooling speed less than or equal to 0.5 ℃/s; the natural cooling refers to the natural cooling of the coiled steel coil which is transported to a steel coil warehouse by the transportation quantity after coiling and uncoiling.
In examples 1 to 13, the steel sheet components and the process are within the design range of the invention, the steel sheet performance meets the requirements, the surface quality of the steel sheet is also 'good', and the surface quality requirement of the pickling-free steel is met.
Comparative examples 1 and 2, the steel sheet composition was within the range of the present invention, but the comparative example 1 was lower in coiling temperature than the range of the present invention, and the steel sheet surface quality grade was "general".
The rolling process of comparative example 2 falls within the process designed by the invention, but the cooling rate after the coil of steel is not controlled, and the performance of the steel plate meets the requirements, but the surface quality is poor.
Comparative examples 3 and 4, in which the composition of the steel sheet is not within the scope of the present invention, the process of comparative example 3 is different from the process of the present invention, and the properties of the steel sheet meet the requirements, but the surface quality of the steel sheet is "poor".
The process of comparative example 4 falls within the process range designed by the invention, but the steel plate composition and the invention patent claim have great difference, the surface quality of the final steel plate is general, the tensile strength does not reach 590MPa minimum requirement, and the surface quality requirement of the pickling-free steel is not met.
Note that: the bending and peeling resistance of the oxide layer was evaluated by examining the peeling of the oxide scale on the outer surface after bending the steel sheet. The specific method comprises the following steps: and bending the steel plate with the oxide skin by d=2a and 90 degrees, attaching a transparent adhesive tape to the outer R angle after bending, tearing off and transferring the transparent adhesive tape to white paper, and observing the condition of the oxide skin falling off. The scale bending and peeling resistance is classified into three grades of "good", "general" and "poor" according to the scale peeling degree, see fig. 2 to 4.

Claims (7)

1. A590 MPa-grade low-cost pickling-free structural steel comprises the following components in percentage by mass: c:0.04 to 0.16 percent, si is less than or equal to 0.05 percent, mn:0.3 to 1.2 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.01 percent, ti:0.03 to 0.16 percent, nb:0.006 to 0.035 percent, and the balance of Fe and other unavoidable impurities, and the requirements are as follows: 0.251Ti+1.12Nb is more than or equal to 0.032, and C+Mn/6 is less than or equal to 0.23.
2. 590 MPa-grade low-cost pickling-free structural steel according to claim 1, characterised in that the balance is Fe and other unavoidable impurities.
3. The 590 MPa-level low-cost pickling-free structural steel of claim 1 or 2, further comprising one or more of Mo less than or equal to 0.2%, cr less than or equal to 0.2%, V less than or equal to 0.15%, ni less than or equal to 0.1%, ca less than or equal to 0.015%.
4. A 590 MPa-grade low-cost pickling-free structural steel according to claim 1 or 2 or 3, characterized in that the structure of the pickling-free structural steel is polygonal ferrite and/or quasi-polygonal ferrite + small amount of pearlite.
5. The 590 MPa-level low-cost pickling-free structural steel according to claim 1, 2, 3 or 4, wherein the yield strength of the pickling-free structural steel is greater than or equal to 500MPa, the tensile strength is greater than or equal to 590MPa, the elongation is greater than or equal to 19%, and the d=1.5 a is bent 180 ° without cracking.
6. The method for manufacturing 590 MPa-level low-cost pickling-free structural steel according to any one of claims 1 to 5, characterized by comprising the following steps:
1) Smelting and casting
Smelting, refining and continuously casting into casting blanks or ingots according to the components of claim 1, 2 or 3;
2) Heating the cast slab or ingot
Heating the casting blank or the cast ingot in a heating furnace at 1250-1300 ℃ for 2-5 hours;
3) Hot rolling
The descaling water of the descaling box is opened before rough rolling, the primary scale is removed, the descaling is put in the rough rolling pass, the outlet temperature of rough rolling is less than or equal to 1010 ℃, and then finished steel coils are formed through finish rolling by a plurality of frames; the descaling water of the descaling box is opened before finish rolling, secondary oxide skin is removed, the descaling water between the finish rolling F1 and F2 frames is put in, the finish rolling temperature is 870-920 ℃, and the threading speed is more than or equal to 7m/s; cooling by adopting a pre-cooling process after rolling, wherein the coiling temperature is 600-650 ℃;
4) Post-roll cooling control
Cooling the coiled steel coil by adopting a fan after coil unloading, cooling to 520-550 ℃ at a cooling rate of more than or equal to 2 ℃/s, and then cooling down the coiled steel coil to a heat preservation wall or a hot coil pile at a cooling rate of less than or equal to 0.5 ℃/s to room temperature.
7. The method for manufacturing 590MPa low-cost pickling-free structural steel according to claim 6, wherein the finish rolling in the step 3) is performed by using a six-stand or seven-stand finishing mill.
CN202210759497.XA 2022-06-29 2022-06-29 590 MPa-level low-cost pickling-free structural steel plate and manufacturing method thereof Pending CN117344215A (en)

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