CN109554529B - Hot-rolled strip steel iron scale reduction method based on reduction pretreatment process - Google Patents

Hot-rolled strip steel iron scale reduction method based on reduction pretreatment process Download PDF

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CN109554529B
CN109554529B CN201811548376.0A CN201811548376A CN109554529B CN 109554529 B CN109554529 B CN 109554529B CN 201811548376 A CN201811548376 A CN 201811548376A CN 109554529 B CN109554529 B CN 109554529B
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CN109554529A (en
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刘振宇
李志峰
曹光明
王皓
崔春圆
李成刚
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Northeastern University China
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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
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
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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
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    • 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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    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • 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
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Abstract

The invention relates to a hot-rolled strip steel iron scale reduction method based on a reduction pretreatment process, which comprises the following steps: rapidly heating the hot-rolled strip steel to 400-550 ℃ at a speed of 80-150 ℃/s, carrying out isothermal reduction for 30-600 s, obtaining a reduction product which is multi-gap sponge iron, carrying out intermediate cooling, heating to 700-1100 ℃ at the speed of 80-150 ℃/s, reducing the temperature for 30-600 s at an isothermal temperature, bonding iron particles in the multi-gap sponge iron, growing crystal grains, through material transmission, gaps, air holes and crystal boundaries in a reduction product are gradually reduced, the total volume is shrunk, a compact polycrystalline pure iron layer with a microstructure is formed, and reduction of the iron scale is completed.

Description

Hot-rolled strip steel iron scale reduction method based on reduction pretreatment process
The technical field is as follows:
the invention belongs to the technical field of metallurgy, and particularly relates to a hot-rolled strip steel iron scale reduction method based on a reduction pretreatment process.
Background art:
at present, hydrochloric acid or sulfuric acid is generally adopted in the method for removing the iron scale of various large iron and steel enterprises at home and abroad, the pickling technology can provide an ideal metal surface, and long-time and intensive use of acid liquor can easily cause air pollution and underground water pollution and cause great harm to the ecological environment. In view of environmental protection requirements, domestic and foreign enterprises and scientific research institutes are carrying out acid-washing-free descalingThe technique has been extensively studied and a gas (H) has been proposed2CO) reduction to replace acid cleaning to remove the iron scale on the surface of the hot rolled steel product, namely the acid cleaning-free reduction descaling technology of the hot rolled steel iron scale. The gas reduction descaling technology for hot rolled steel is originally originated from the field of pyrometallurgical smelting of iron ores, and is a process for extracting metals from oxides. The main technological process is that under the specific reduction temperature, the combustible gas (H)2Or CO) is used as a reducing agent, and the oxide is reduced to obtain crude metal or alloy. The gas reduction process of the oxide scale of the hot rolled steel is similar to that of the gas reduction of iron ore, and the oxide scale on the surface of the hot rolled strip steel is reduced into pure Fe to replace pickling in a continuous annealing furnace by introducing reducing atmosphere. The process has the characteristics of cleanness, high efficiency and high quality, and is widely concerned by the steel industry once being put forward.
Hot-rolled strip steel scale quilt H2Or the CO reduction process is carried out thermodynamically stepwise. First the lower oxides and finally elemental Fe. Fe is used as a transition metal element, and three oxides, namely FeO and Fe, appear during high-temperature oxidation3O4And Fe2O3. Under the action of O, the sequence of oxide formation follows the principle of stepwise transformation. Meanwhile, 570 ℃ is used as the critical temperature of the disproportionation reaction of FeO, and different transformation sequences exist above or below the critical temperature, so that the reduction of the iron scale is gradual. At different temperatures, H2The reaction process for reducing the iron scale is shown in the following equation, the CO reduction process and H2The same is true.
When the reaction temperature is above 570 ℃:
3Fe2O3+H2＝2Fe3O4+H2O(g)
Fe3O4+H2＝3FeO+H2O(g)
FeO+H2＝Fe+H2O(g)
when the reaction temperature is below 570 ℃:
3Fe2O3+H2＝2Fe3O4+H2O(g)
Figure BDA0001909962550000011
however, in production practice and laboratory theoretical studies, the "pickling-free" technique of removing scale by gas reduction also faces several problems:
(1) the reducing agent is selected, CO is a toxic gas, and the safety cost needs to be increased in the using process; reaction product CO2Environmental pollution is caused, and a tail gas filtering and recovering device needs to be built; c in the reducing agent enters the surface of the matrix to form cementite during reaction, and the final mechanical property of the material is influenced. In contrast to CO, H2Has stronger diffusion and transmission capability and quicker reaction efficiency. The reduction product is water vapor, has no pollution to the environment, can reduce the investment of tail gas treatment equipment, and is green energy H2The advantage of reducing efficiency makes it the reducing agent of choice in gas reduction descaling process, but because of H2Belongs to explosive gas and needs safe cost investment in the using process.
(2) Concentration of reducing agent, in order to raise safety coefficient, H in mixed gas adopted in annealing furnace at present2The concentration is low (less than or equal to 8 percent), so that the reduction reaction efficiency is slow, and the time required for the complete reduction of the iron scale is too long, thus being not suitable for the application of an actual production line.
(3) The reduction temperature and the temperature system of the reduction annealing furnace are unreasonable set, the annealing furnace adopts single-section heating at present, the temperature in the furnace chamber is generally lower than 750 ℃, the diffusion rate of the reducing agent is slow, and the reduction reaction efficiency is low.
(4) The reducing agent reacts with the iron scale on the surface layer of the steel, the reduction product on the surface layer is metallic iron, the metallic iron can nucleate and grow at high temperature to form a compact pure iron layer, once the compact pure iron layer is formed too early, the diffusion rate of H to the inside of the iron scale can be delayed, and the reduction reaction rate is reduced.
The invention content is as follows:
the invention aims at solving the problems of the prior art that the acid pickling-free reduction annealing hot galvanizing technology is adoptedThe method for reducing the iron scale of the hot-rolled strip steel based on the reduction pretreatment process is provided, and the eutectoid tissue of the polycrystalline boundaries in the iron scale is utilized to reduce the H-shaped iron scale in the hot-rolled strip steel2The reduction characteristic in the process is that a reduction pretreatment section with rapid heating is additionally arranged in front of a high-temperature reduction section, and the acid-washing-free hot-dip galvanized plate with high surface quality and good forming performance is prepared, so that a new thought is provided for industrial popularization and application, the iron oxide scales on the surface of the hot-rolled strip steel can be reduced into a compact pure iron layer at a higher speed, the investment cost of a continuous annealing furnace is reduced, and the adhesiveness and the forming performance of the hot-dip galvanized plate are improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a hot-rolled strip steel iron scale reduction method based on a reduction pretreatment process comprises the following steps:
step 1, preheating:
heating the hot-rolled strip steel to 200-300 ℃, and completing preheating;
step 2, reduction pretreatment:
(1) and (3) rapid heating: heating the preheated strip steel to 400-550 ℃ at a heating rate of 80-150 ℃/s;
(2) reduction pretreatment: carrying out isothermal reduction on the heated strip steel to generate pre-reduced strip steel; wherein the reduction temperature is 400-550 ℃, the reduction time is 30-600 s, and the reduction atmosphere is H2And N2In which H is2The volume concentration of (A) is 5-50%;
step 3, intermediate cooling:
cooling the pre-reduced strip steel to 300-500 ℃ at a cooling rate of 10-20 ℃/s to obtain cooled strip steel;
and 4, high-temperature reduction:
(1) and (3) rapid heating: after cooling, the strip steel is heated to 700-1100 ℃ at a heating rate of 80-150 ℃/s;
(2) high-temperature reduction: after the temperature is raised, the isothermal reduction is carried out on the strip steel to finishReducing the iron scale and cooling to room temperature; wherein the reduction temperature is 700-1100 ℃, the reduction time is 30-600 s, and the reduction atmosphere is H2And N2In which H is2The volume concentration of (A) is 5-100%.
In the step 1, the hot-rolled strip steel comprises, by weight, 0.03-0.10% of C, 0.04-0.60% of Si, 0.15-2.5% of Mn, less than or equal to 0.015% of S, less than or equal to 0.019% of P, 0.2-1.0% of Cr, 0.015-0.045% of Als, less than or equal to 0.08% of Ti, less than or equal to 0.08% of Nb, and the balance of Fe and inevitable impurities during smelting.
In the step 1, the thickness of the hot rolled strip steel is 1.3-3.0 mm, the initial rolling temperature of the hot rolled strip steel is 950-1050 ℃, the final rolling temperature is 800-900 ℃, the coiling temperature is 350-500 ℃, the thickness of the iron scale is 4-8 mu m, the cooling rate is 0.01-0.05 ℃/s, and the Fe in-iron scale lamellar eutectoid tissue is Fe3O4The proportion of/α -Fe is 60-100%.
In the step 1, the preheating mode adopts a radiant tube for heating.
In the step 1, the heating rate is 30-60 ℃/s.
In the step 2(1), the original eutectoid structure (Fe) in the iron scale is prevented by controlling the heating rate3O4/α -Fe) to generate reverse phase transformation, so that the proportion of lamellar eutectoid tissue is kept between 60 and 100 percent.
In the step 2(2), the tissue structure of the pre-reduced band steel obtained after the reduction pretreatment is multi-gap sponge iron.
In the step 4(1), the reduction product on the surface of the strip steel after cooling is still multi-gap sponge iron.
In the step 4(2), after isothermal reduction, iron particles in the reduction product multi-gap sponge iron on the surface of the strip steel are bonded with each other, crystal grains grow up, and a compact polycrystalline pure iron layer with a microstructure is finally formed by gradually reducing gaps, air holes and crystal boundaries in the material transmission reduction product and shrinking the total volume.
In the step 4(2), after the reduction of the iron scale, the strip steel is used for preparing the galvanized sheet, and the specific process comprises the following steps:
(1) cooling the strip steel reduced by the iron scale to 450-480 ℃ at the speed of 10-30 ℃/s, and then immersing the strip steel into zinc liquid for hot galvanizing; wherein the temperature of the zinc liquid is 450-480 ℃, the zinc liquid comprises components with the weight percentage of Al0.4-6.0%, Sb less than or equal to 0.07%, and the balance of pure Zn;
(2) and cooling the galvanized strip steel by adopting a conventional mode of combining forced cooling and natural cooling after galvanization to prepare the galvanized plate.
In the invention, in order to improve the reduction efficiency, intermediate cooling is carried out between the reduction pretreatment and the high-temperature reduction operation, the reduction process is controlled by respectively adopting methods of controlling the combustion speed and the temperature in the reduction pretreatment and the high-temperature reduction section, the temperature of the strip steel is reduced by 50-100 ℃ in the intermediate cooling stage, and because the shrinkage rates of the substrate and the reduction product are different when being cooled, a large number of microcracks can be formed on the surface of the reduction product, and a diffusion channel can be provided for the inward diffusion of the reduction gas and the outward diffusion of the water vapor of the reduction product.
In the step 2 and the step 4, in the reduction pretreatment and high-temperature reduction processes, the dew point value is controlled to be below-70 ℃, and the specific operation is as follows: measuring water vapor content in the furnace cavity by using a gas dew point meter, and controlling the water vapor content (C + H) in the furnace by using high-temperature graphite2O＝CO+H2) The dew point value is controlled below-70 ℃, and the content of CO in the furnace atmosphere is kept between 5 and 30 percent.
The invention relates to a high-efficiency reduction method for the oxide scale of hot-rolled strip steel based on a reduction pretreatment process, the thickness specification of the adopted hot-rolled strip steel is 1.3-3.0 mm, and at present, steel products with the thickness specification are produced in a plate rolling mode finally. In order to prevent the excessive thickness of the iron scale on the surface of the adopted hot-rolled strip steel, a high-temperature fast rolling process is adopted during production, and the thickness of the iron scale is controlled to be 4-8 mu m. The temperature range of the strip steel product during coiling is 400-700 ℃, the cooling rate is slow because the strip steel is cooled in a coiling way, and according to a Fe-O phase diagram, FeO in the iron scale can generate phase change below 570 ℃ and is converted into pre-eutectoid Fe3O4Or eutectoid structure (Fe)3O4α -Fe). therefore, the cooling process setting of the hot rolled steel will affect the final scale structure, and the control of the scale structure will have a great influence on the reduction efficiency in the continuous annealing furnace due to the large performance difference between different structures3O4The proportion of/α -Fe is controlled to be 60-100%.
The method of the present invention is different from the above-described method of reducing scale using a sectional type. To suppress reverse eutectoid transformation in scale and prevent Fe3O4The temperature of the reduction pretreatment section is 350-550 ℃, and meanwhile, a rapid heating mode is adopted, and the temperature rise rate is most suitable to be 80-150 ℃/s. The purpose of adopting the reduction temperature is to control the temperature of reduction pretreatment below the critical temperature (570 ℃) of phase transformation so as to ensure eutectoid tissue (Fe)3O4α -Fe), during reduction, H can diffuse through grain boundaries, eutectoid structure is a polycrystalline boundary structure which can provide more diffusion channels for diffusion, and meanwhile, the contact area of H and oxide is increased, so that the iron scale can be rapidly reduced into porous iron.
As is apparent from the Fe-Zn binary alloy phase diagram, when hot-dip galvanizing is performed in a zinc bath containing no Al, Fe-Zn phases such as η, ζ, σ and the like are formed in the coating, and since the metal compound is hard and brittle as compared with pure zinc, the coating performance is deteriorated, which is disadvantageous in the coating formability, and therefore, in order to improve the adhesion and workability of the coating, Al is added to the zinc bath in a mass fraction of 0.15 to 0.20%, so that Fe is formed on the surface of the substrate first when the substrate enters the zinc pot2Al5The layer has an inhibiting effect on Fe-Zn reaction and inhibits the generation of Fe-Zn brittle phase. The invention is based on reduction pretreatmentThe high-efficiency reduction method of the oxide scale of the hot-rolled strip steel adopts H2The reduction replaces the pickling to remove the iron scale, the surface of the iron scale can form a compact pure iron layer after being reduced in a continuous annealing furnace, the surface roughness is increased, and the distribution of Al and Fe in a coating can be influenced2Al5Inhibit the formation of a layer, and further destroy the uniformity and adhesiveness of the coating structure. Therefore, the mass percent of Al in the zinc liquid is designed to be 0.4-6.0%.
The invention has the beneficial effects that:
(1) the method greatly improves the reduction reaction efficiency of the iron scale by means of the characteristic of solid phase change of the iron scale, so that the iron scale can be reduced into pure iron in a short time;
(2) the invention adopts high-temperature graphite to absorb the water vapor of the reduction product, and the obtained reaction product CO can continuously play the role of a reducing agent in the furnace, namely, the dew point in the furnace is effectively controlled, and the use amount of hydrogen is also reduced.
Description of the drawings:
FIG. 1 is a surface SEM topography of a pre-reduced strip steel obtained after reduction pretreatment in example 1 of the present invention;
FIG. 2 is a surface SEM topography of a strip steel after being subjected to intermediate cooling in example 1 of the present invention;
FIG. 3 is a process diagram of a hot rolled strip iron scale reduction method based on a reduction pretreatment process according to example 1 of the present invention, in which ① -preheating, ② -rapid heating, ③ -reduction pretreatment, ④ -intermediate cooling, ⑤ -secondary rapid heating, ⑥ high temperature reduction, ⑦ -cooling, T-cooling1At a temperature of 200 to 300 ℃ and T2At 400-550 ℃ and T3Is 300-500 ℃ and T4700-1100 ℃;
FIG. 4 is a SEM sectional morphology of a hot-rolled strip steel scale in example 1 of the present invention;
FIG. 5 is a surface SEM topography of a reduced product obtained after reduction in example 1 of the present invention;
FIG. 6 is a sectional SEM topography of a reduced product obtained after reduction in example 1 of the present invention;
FIG. 7 is a photograph of a curved surface of a hot-dip galvanized sheet formed with a steel strip after the reduction of iron scale in example 1 of the present invention;
FIG. 8 is a SEM sectional morphology of a hot-rolled strip steel scale in example 2 of the present invention;
FIG. 9 is a SEM topography of the surface of a reduced product obtained after reduction in example 2 of the present invention;
FIG. 10 is a sectional SEM topography of a reduced product obtained after reduction in example 2 of the present invention;
FIG. 11 is a photograph of a curved surface of a hot-dip galvanized sheet formed with a steel strip after the reduction of iron scales in example 2 of the present invention;
FIG. 12 is a SEM topography of the surface of a reduced product obtained after reduction in example 3 of the present invention;
FIG. 13 is a sectional SEM topography of a reduced product obtained after reduction in example 3 of the present invention;
FIG. 14 is a photograph of a curved surface of a hot-dip galvanized sheet formed with steel strip after the reduction of iron scale in example 3 of the present invention;
FIG. 15 is a photograph of a curved surface of a hot-dip galvanized sheet formed with a steel strip after completion of reduction of iron scales in example 4 of the present invention; wherein: a-steel matrix, B-eutectoid structure, C-iron scale and D-reduction product.
The specific implementation mode is as follows:
the present invention will be described in further detail with reference to examples.
The hot-rolled strip steel in the embodiment of the invention comprises, by weight, 0.03-0.10% of C, 0.04-0.60% of Si, 0.15-2.5% of Mn, less than or equal to 0.015% of S, less than or equal to 0.019% of P, 0.2-1.0% of Cr, 0.015-0.045% of Als, less than or equal to 0.08% of Ti, less than or equal to 0.08% of Nb, and the balance of Fe and inevitable impurities during smelting.
In the embodiment of the invention, the thickness of the hot rolled strip steel is 1.3-3.0 mm, the initial rolling temperature of the hot rolled strip steel is 950-1050 ℃, the final rolling temperature is 800-900 ℃, the coiling temperature is 350-500 ℃, the thickness of the iron scale is 4-8 mu m, the cooling rate is 0.01-0.05 ℃/s, and the iron scale middle-sheet lamellar eutectoid structure Fe3O4The proportion of/α -Fe is 60-100%.
In the embodiment of the invention, the hot rolled strip steel sequentially passes through five stages in the continuous annealing furnace, namely a preheating stage, a reduction pretreatment stage for rapid heating, an intermediate cooling stage, a high-temperature reduction stage for rapid heating and a cooling stage.
In the embodiment of the invention, the rapid heating rate of the hot-rolled strip steel in the reduction pretreatment section and the high-temperature reduction section is 80-150 ℃/s.
In the embodiment of the invention, a gas dew point tester is adopted in the reduction pretreatment section and the high-temperature reduction section of the continuous annealing furnace to measure the water vapor content in the furnace cavity, and high-temperature graphite is used to control the water vapor content (C + H) in the continuous annealing furnace2O＝CO+H2) The dew point value is controlled below-70 ℃, and the content of CO in the furnace atmosphere is kept at 5-30%.
In the embodiment of the invention, the weight percentage of Al in the zinc liquid is controlled to be 0.4-6.0%, the weight percentage of Sb is less than or equal to 0.07%, and the balance is pure Zn.
Example 1
A hot-rolled strip steel iron scale reduction method based on a reduction pretreatment process is shown in a process diagram of figure 3 and comprises the following steps:
(1) taking a hot-rolled strip steel, heating to 200 ℃ at the temperature of 30 ℃/S, and preheating, wherein the hot-rolled strip steel comprises 0.03% of C, 0.04% of Si, 0.15% of Mn, 0.015% of S, 0.019% of P, 0.2% of Cr, 0.015% of Als and the balance of Fe and inevitable impurities during smelting according to the weight percentage. The thickness of the hot-rolled strip steel is 1.3mm, the section microscopic morphology of the iron scale is shown in figure 4, the thickness of the iron scale is 6 mu m, and the lamellar eutectoid structure Fe in the iron scale3O4The proportion of/α -Fe is 95%;
(2) a reduction pretreatment section with rapid heating, wherein the temperature is rapidly raised to 550 ℃ at the speed of 150 ℃/s, and H2The volume concentration of the strip steel is 50%, isothermal reduction is carried out for 30s, and the surface SEM topography of the pre-reduced strip steel obtained after reduction pretreatment is shown in figure 1;
(3) after the strip steel is subjected to reduction pretreatment, the temperature is reduced by 100 ℃ at a cooling rate of 20 ℃/s, and an SEM (scanning electron microscope) appearance picture of the surface of the cooled strip steel is obtained and is shown in figure 2;
(4) the high-temperature reduction section with rapid heating rapidly heats up to 800 ℃ at the speed of 150 ℃/s, and H2The volume concentration of the steel is 20 percent, isothermal reduction is carried out for 180s, reduction of iron scales is completed, the surface and section microscopic appearances of the reduced strip steel are respectively shown in fig. 5 and 6, the reduction product is a compact polycrystalline pure iron layer, and a large number of microcracks exist on the surface; in a continuous annealing furnace, the strip steel after finishing the reduction of the iron scale is cooled to 450 ℃ at the speed of 30 ℃/s, then is immersed into a zinc pot for hot galvanizing, the weight percentage of Al in the zinc liquid is controlled to be 0.4 percent, and the balance is pure Zn to prepare a hot galvanized plate, a 180-degree cold bending experiment is carried out on the produced hot galvanized plate by adopting a universal mechanical testing machine, the bending surface is shown in figure 7, and the hot galvanized plate has bright, flat and flawless coating surface and better forming performance.
Example 2
A hot-rolled strip steel iron scale reduction method based on a reduction pretreatment process comprises the following steps:
(1) taking hot-rolled strip steel, heating to 300 ℃ at the speed of 60 ℃/s, and preheating, wherein: the hot rolled strip steel comprises, by weight, 0.10% of C, 0.60% of Si, 1.0% of Mn, 0.015% of S, 0.019% of P, 0.5% of Cr, 0.045% of Als, 0.08% of Ti, and the balance of Fe and inevitable impurities during smelting. The thickness of the hot-rolled strip steel is 1.5mm, the section microscopic morphology of the iron scale is shown in figure 8, the thickness of the iron scale is 6 mu m, and the lamellar eutectoid structure Fe in the iron scale3O4The proportion of/α -Fe is 60%;
(2) a reduction pretreatment section with rapid heating, the temperature is rapidly raised to 500 ℃ at 100 ℃/s, H2The volume concentration of (3) is 30 percent, and isothermal reduction is carried out for 60 s;
(3) after the reduction pretreatment of the strip steel, the temperature is reduced by 80 ℃ at the cooling rate of 15 ℃/s;
(4) the high-temperature reduction section with rapid heating rapidly heats up to 900 ℃ at a speed of 120 ℃/s, H2The volume concentration of the steel is 5 percent, the isothermal reduction is 600s, the reduction of the iron scale is completed, the surface and section microscopic appearances of the reduced strip steel are respectively shown in figures 9 and 10, the reduction product is a compact polycrystalline pure iron layer and is shown on the surfaceA large number of micro cracks exist on the surface; in a continuous annealing furnace, the strip steel after finishing the reduction of the iron scale is cooled to 480 ℃ at the speed of 10 ℃/s, then is immersed into a zinc pot for hot galvanizing, the weight percentage of Al in the zinc liquid is controlled to be 1.5 percent, and the rest is pure Zn to prepare a hot galvanized plate, a 180-degree cold bending experiment is carried out on the produced hot galvanized plate by adopting a universal mechanical testing machine, the bending surface is shown in figure 11, and the hot galvanized plate has bright, flat and flawless coating surface and better forming performance.
Example 3
A hot-rolled strip steel iron scale reduction method based on a reduction pretreatment process comprises the following steps:
(1) taking hot-rolled strip steel, heating to 300 ℃ at a speed of 45 ℃/s, and preheating, wherein: the hot rolled strip steel comprises, by weight, 0.05% of C, 0.30% of Si, 0.5% of Mn, 0.009% of S, 0.010% of P, 1.0% of Cr, 0.045% of Als, 0.045% of Ti, 0.08% of Nb, and the balance of Fe and inevitable impurities during smelting. The thickness of the hot-rolled strip steel is 2.0mm, the thickness of the iron scale is 6.5 mu m, and the lamellar eutectoid structure Fe in the iron scale3O4The proportion of/α -Fe is 70%;
(2) a reduction pretreatment section with rapid heating, the temperature is rapidly raised to 450 ℃ at the speed of 80 ℃/s, H2The volume concentration of (2) is 5%, and isothermal reduction is carried out for 600 s;
(3) after the reduction pretreatment of the strip steel, the temperature is reduced by 50 ℃ at the cooling rate of 10 ℃/s;
(4) the high-temperature reduction section with rapid heating rapidly heats up to 1100 ℃ at a speed of 100 ℃/s, and H2The volume concentration of the steel is 100 percent, isothermal reduction is carried out for 30s, the reduction of the iron scale is completed, the surface appearance and the section microscopic appearance of the reduced strip steel are respectively shown in figures 12 and 13, the reduction product is a compact polycrystalline pure iron layer, and a large number of microcracks exist on the surface; cooling the strip steel after finishing the reduction of the iron scale to 460 ℃ at 20 ℃/s in a continuous annealing furnace, then soaking the strip steel into a zinc pot for hot galvanizing, controlling the weight percentage of Al in zinc liquid to be 3.0 percent, and the balance being pure Zn to prepare a hot galvanized plate, and carrying out a 180-degree cold bending experiment on the produced hot galvanized plate by adopting a universal mechanical testing machine, wherein the bending surface is shown as figure 14, and the surface is shown asThe surface of the bright coating is bright, flat and free of defects, and the hot-dip galvanized plate has better forming performance.
Example 4
A hot-rolled strip steel iron scale reduction method based on a reduction pretreatment process comprises the following steps:
(1) taking a hot-rolled strip steel, heating to 300 ℃ at the temperature of 60 ℃/S, and preheating, wherein the hot-rolled strip steel comprises 0.045% of C, 0.18% of Si, 0.2% of Mn, 0.009% of S, 0.010% of P, 0.4% of Cr, 0.045% of Als, 0.025% of Ti, 0.045% of Nb and the balance of Fe and inevitable impurities during smelting according to the weight percentage. The thickness of the hot-rolled strip steel is 3.0mm, the thickness of the iron scale is 8 mu m, and the lamellar eutectoid structure Fe in the iron scale3O4The proportion of/α -Fe is 60%;
(2) a reduction pretreatment section with rapid heating, the temperature is rapidly raised to 400 ℃ at the speed of 120 ℃/s, H2The volume concentration of (2) is 20%, and isothermal reduction is carried out for 120 s;
(3) after the reduction pretreatment of the strip steel, the temperature is reduced by 60 ℃ at the cooling rate of 10 ℃/s;
(4) in the high-temperature reduction section of rapid heating, the temperature is rapidly raised to 700 ℃ at the speed of 80 ℃/s, the volume concentration of H2 is 75%, isothermal reduction is carried out for 60s, iron scale reduction is completed, the strip steel after the iron scale reduction is completed is cooled to 470 ℃ at the speed of 20 ℃/s in a continuous annealing furnace, then the strip steel is immersed into a zinc pot for hot galvanizing, the weight percentage of Al in zinc liquid is controlled to be 6%, the weight percentage of Sb is controlled to be 0.07%, and the balance is pure Zn, a hot-dip galvanized plate is prepared, a 180-degree cold bending experiment is carried out on the produced hot-dip galvanized plate by adopting a universal mechanical testing machine, the bending surface is shown in figure 15, the surface of the plated layer is bright and flat without defects, and the.
Example 5
A hot-rolled strip steel iron scale reduction method based on a reduction pretreatment process comprises the following steps:
(1) taking hot-rolled strip steel, heating to 200 ℃ at the speed of 60 ℃/s, and preheating, wherein: the hot rolled strip steel comprises, by weight, 0.03% of C, 0.04% of Si, 0.15% of Mn, 0.007% of S, 0.008% of P, 0.2% of Cr, and 0.045% of AlsThe balance of Fe and inevitable impurities during smelting. The thickness of the hot-rolled strip steel is 1.3mm, the thickness of the iron scale is 4 mu m, and the lamellar eutectoid structure Fe in the iron scale3O4The proportion of/α -Fe is 100 percent;
(2) a reduction pretreatment section with rapid heating, the temperature is rapidly raised to 500 ℃ at 150 ℃/s, H2The volume concentration of (a) is 20%, and isothermal reduction is carried out for 100 s;
(3) after the reduction pretreatment of the strip steel, the temperature is reduced by 50 ℃ at the cooling rate of 10 ℃/s;
(4) the high-temperature reduction section with rapid heating rapidly heats up to 900 ℃ at the speed of 150 ℃/s, and H2The volume concentration of the zinc is 50 percent, isothermal reduction is carried out for 120s, reduction of iron scales is completed, strip steel subjected to reduction of the iron scales is cooled to 450 ℃ at the speed of 30 ℃/s in a continuous annealing furnace, then the strip steel is immersed into a zinc pot for hot galvanizing, the weight percentage of Al in zinc liquid is controlled to be 5 percent, the weight percentage of Sb is controlled to be 0.02 percent, and the balance is pure Zn, so that the hot galvanized plate is prepared, a 180-degree cold bending experiment is carried out on the produced hot galvanized plate by adopting a universal mechanical testing machine, and the hot galvanized plate is shown to be bright, flat and free of defects on the surface of the plated layer and has.

Claims (5)

1. A hot-rolled strip steel iron scale reduction method based on a reduction pretreatment process is characterized by comprising the following steps:
step 1, preheating:
heating a hot-rolled strip steel to 200-300 ℃, and completing preheating, wherein the hot-rolled strip steel comprises, by weight, 0.03-0.10% of C, 0.04-0.60% of Si, 0.15-2.5% of Mn, less than or equal to 0.015% of S, less than or equal to 0.019% of P, 0.2-1.0% of Cr, 0.015-0.045% of Als, less than or equal to 0.08% of Ti, less than or equal to 0.08% of Nb, and the balance of Fe and inevitable impurities during smelting; the thickness of the hot rolled strip steel is 1.3-3.0 mm, the initial rolling temperature of the hot rolled strip steel is 950-1050 ℃, the final rolling temperature is 800-900 ℃, the coiling temperature is 350-500 ℃, the thickness of the iron scale is 4-8 mu m, the cooling rate is 0.01-0.05 ℃/s, and the middle-sheet lamellar eutectoid structure Fe of the iron scale3O4The proportion of/α -Fe is 60-100%;
step 2, reduction pretreatment:
(1) and (3) rapid heating: heating the preheated strip steel to 400-550 ℃ at a heating rate of 80-150 ℃/s;
(2) reduction pretreatment: carrying out isothermal reduction on the heated strip steel to generate pre-reduced strip steel; wherein the reduction temperature is 400-550 ℃, the reduction time is 30-600 s, and the reduction atmosphere is H2And N2In which H is2The volume concentration of (A) is 5-50%;
step 3, intermediate cooling:
cooling the pre-reduced strip steel to 300-500 ℃ at a cooling rate of 10-20 ℃/s to obtain cooled strip steel;
and 4, high-temperature reduction:
(1) and (3) rapid heating: after cooling, the strip steel is heated to 700-1100 ℃ at a heating rate of 80-150 ℃/s;
(2) high-temperature reduction: after the temperature is raised, the strip steel is subjected to isothermal reduction to complete the reduction of iron scales, and is cooled; wherein the reduction temperature is 700-1100 ℃, the reduction time is 30-600 s, and the reduction atmosphere is H2And N2In which H is2The volume concentration of (A) is 5-100%.
2. The hot-rolled strip steel scale reduction method based on the reduction pretreatment process as claimed in claim 1, wherein the temperature rise rate in step 1 is 30-60 ℃/s.
3. The hot-rolled strip iron oxide scale reduction method based on the reduction pretreatment process as claimed in claim 1, wherein in the step 2, the tissue structure of the pre-reduced strip obtained after the reduction pretreatment is multi-gap sponge iron.
4. The hot-rolled strip iron scale reduction method based on the reduction pretreatment process as claimed in claim 1, wherein in the step 2, the dew point value is controlled to be below-70 ℃ in the reduction pretreatment and high-temperature reduction processes, and the specific operation is as follows: a gas dew point tester is adopted to measure the water vapor content in the furnace cavity, high-temperature graphite is used to control the water vapor content in the furnace, the dew point value is controlled below-70 ℃, and the CO content in the furnace atmosphere is kept at 5-30%.
5. The hot-rolled strip steel iron scale reduction method based on the reduction pretreatment process as claimed in claim 1, wherein in the step 4, the strip steel is used for preparing galvanized plates after iron scale reduction, and the specific process is as follows:
(1) cooling the strip steel reduced by the iron scale to 450-480 ℃ at the speed of 10-30 ℃/s, and then immersing the strip steel into zinc liquid for hot galvanizing; wherein the temperature of the zinc liquid is 450-480 ℃, the zinc liquid comprises components with the weight percentage of Al0.4-6.0%, Sb less than or equal to 0.07%, and the balance of pure Zn;
(2) and cooling the galvanized strip steel by adopting a conventional mode of combining forced cooling and natural cooling after galvanization to prepare the galvanized plate.
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