Control method for hot-rolled scale of hot-based galvanized deep-drawing steel, strip steel, hot-based galvanized deep-drawing steel and preparation method of hot-based galvanized deep-drawing steel

Abstract

The invention provides a control method for hot-rolled scale of hot-based galvanized deep-drawing steel, strip steel, hot-based galvanized deep-drawing steel and a preparation method of the hot-rolled scale. According to the control method for the hot-rolled oxide scale of the steel for hot-based galvanization deep drawing, the chemical composition is controlled, the hot rolling procedure adopts the means of rough rolling high-temperature rolling, full-pass descaling, finish rolling low-temperature rolling, high-speed finish rolling, layer cooling front-section dense water cooling and the like, the technological conditions are controlled, and thinning of an acid pickling raw material oxide layer is achieved; the generation of microcracks on the III scale is promoted. The structural composition of a surface oxide layer is a proeutectoid Fe3O4 + small-amount eutectoid structure (Fe + Fe3O4), the oxide layer does not contain Fe2O3, the thickness of the oxide layer is 7-9 microns, and obvious oxide scale microcracks exist on the surface of the strip steel. And the acid pickling oxide scale removal effect is effectively promoted. The hot-rolled strip steel for hot-based galvanizing deep drawing produced by the method is good in surface quality and technical and economic indexes of a finished product, and the thickness and the structure of an oxide layer completely meet the technical indexes.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a control method for hot-rolled oxide scale of hot-base galvanized deep-drawing steel, strip steel, hot-base galvanized deep-drawing steel and a preparation method thereof. Background Art

[0002] Hot rolled strip is an important metal material, which is widely used in industrial production. In order to improve the surface quality of the strip after cold deformation, the hot rolled strip must be subjected to online continuous pickling or shot blasting. There is generally a serious red iron oxide scale on the surface of conventional pickling raw materials. The FeO phase in the oxide layer structure has the highest reaction efficiency with hydrochloric acid, followed by the Fe3O4 phase, and the Fe2O3 phase has the lowest reaction efficiency with hydrochloric acid. It is extremely difficult to remove it. Fe2O3 should be avoided as much as possible in the production process. The presence of Fe2O3 in the surface oxide layer. In addition, the thicker the iron scale, the slower the reaction rate. The iron oxide scale defect of hot rolled strip is one of the most common defects in the quality of hot rolled products.

[0003] In order to improve the corrosion resistance of cold-rolled thin plates, online hot-dip galvanizing or chemical plating is usually used to form a thin passivation layer or corrosion-resistant coating on the surface of the strip, thereby improving the corrosion resistance of the basic metal materials. The hot-rolling-pickling-hot-dip galvanizing process, which is improved on the basis of the conventional hot-rolling-pickling-cold-rolling-hot-dip galvanizing process, is the hot-based galvanizing process technology. Due to the technical advantages of thick specifications and thick coatings, the cold rolling process is reduced and the manufacturing cost is reduced. The hot-based galvanized strip produced has a good market promotion prospect. In terms of iron scale control, hot-rolled strip steel for hot-based galvanizing at home and abroad mainly adopts the production technology of reduced pickling steel with the oxide layer structure adjusted to FeO, the control technology of improving the proportion of Fe3O4 in the iron scale structure and reducing the adhesion between the iron scale and the substrate, and the relatively fast reaction rate of FeO in the oxide layer with hydrochloric acid is used to increase the pickling rate. In terms of process technology, the core is to control the pressure of the oxide scale of the strip steel, and adopt odd-pass descaling, adding water to the rolls to prevent spalling, lubrication rolling and other measures. After rolling, the cooling rate of the upper and lower headers is 70% and 50% (cooling rate 5-10℃ / s). The surface oxide layer structure is composed of pro-eutectoid Fe3O4+a small amount of eutectoid structure (Fe+Fe3O4)+a small amount of Fe2O3, and the oxide layer thickness is 9-11μm. However, the existing technology is still not ideal for controlling the oxide scale defects of hot-rolled strip steel. Summary of the invention

[0004] In view of this, the present invention provides a control method for hot-rolled oxidized iron scale of hot-dip galvanized deep-drawing steel, a strip steel, a hot-dip galvanized deep-drawing steel and a preparation method thereof. The method provided by the present invention can obtain a steel strip with a thin oxidized iron scale layer, an oxidized layer structure without Fe2O3, and excellent surface quality after pickling, and the thickness and structure of the oxidized layer fully meet the technical indicators.

[0005] The present invention provides a method for controlling hot-rolled oxide scale of hot-base galvanized deep-drawing steel, comprising the following steps:

[0006] A) Molten steel:

[0007] The blast furnace molten iron and metallurgical auxiliary materials are smelted in an oxygen top-blown converter to obtain molten steel; then, the steel is tapped into a molten steel tank;

[0008] B) LF refining:

[0009] LF refining treatment is performed on the molten steel in the molten steel tank;

[0010] C) RH treatment:

[0011] The molten steel tank is transported to the RH vacuum treatment furnace for decarburization, deoxidation and alloying to obtain molten steel;

[0012] In terms of mass percentage, the molten steel obtained in step C) comprises:

[0013] C: ≤0.01%;

[0014] Si: 0%~0.01%;

[0015] Mn: 0.10%~0.20%;

[0016] P: 0%~0.015%;

[0017] S: 0%~0.010%;

[0018] Ti: 0.04%~0.06%;

[0019] Als: 0.015%~0.060%;

[0020] Fe and inevitable impurity elements: balance;

[0021] D) Continuous Casting:

[0022] Casting the molten steel obtained in step C) through a slab continuous casting machine to obtain a slab;

[0023] E) Hot rolling:

[0024] hot rolling the slab obtained in step D);

[0025] The hot rolling process includes: reheating and soaking treatment, rough rolling, finish rolling and cooling;

[0026] in,

[0027] The reheating soaking temperature of the hot rolling is 1180-1210°C, and the time is 0.5-1.0h;

[0028] The rough rolling temperature is 1175-1200°C, the descaling water pressure is 25MPa, and the rough rolling dephosphorization sequence is full-pass dephosphorization;

[0029] The start rolling temperature of the finishing rolling is 1010-1040°C, the rolling speed is 1.30-1.70 m / s, the final rolling temperature is 900-930°C, and the thickness rolling reduction ratios of the last two stands of the rolling mill are ≤13% and ≤10% respectively;

[0030] The cooling adopts a front-stage intensive cooling, middle-stage air cooling and rear-stage temperature adjustment mode; wherein the length of the front-stage intensive cooling is 5 to 15 m, the length of the middle section is 15 to 60 m, and the length of the rear section is 5 to 10 m;

[0031] F) Pickling:

[0032] The steel strip obtained in step E) is pickled online to obtain a hot-dip galvanized substrate raw material.

[0033] Preferably, in step E), the water pressure of the dense upper and lower headers in the front section is 0.8 MPa; the cooling rates of the dense upper and lower headers in the front section are 90% and 75% respectively.

[0034] Preferably, in step E), the front-stage intensive cooling rate is 10-25° C. / s.

[0035] Preferably, in step E), the water pressure of the upper and lower headers of the rear-stage temperature adjustment is 0.8 MPa; the cooling rate of the upper and lower headers of the rear-stage temperature adjustment is 30%.

[0036] Preferably, in step E), the steel sheet is cooled to a coiling temperature of 700-730° C. before coiling.

[0037] Preferably, in step F), the pickling process section speed is 280-320 mm / min, and the tensile elongation is 0.80%-1.50%.

[0038] Preferably, in step A), when 1 / 3 of the steel is tapped, an aluminum-iron alloy is added to the molten steel tank for pre-deoxidation, and the molten steel tank is subjected to bottom blowing of argon; wherein the argon pressure of the bottom blowing is 200-400 Pa, and the time is 4-10 min;

[0039] In step B), during LF refining, argon is introduced into the bottom of the molten steel tank; the pressure of the argon is 200-400 Pa, and the time of passing the argon is 4-6 minutes; the termination temperature of LF refining is 1610-1640°C; alloying is not performed in the LF refining process, and the oxygen concentration at the exit is 350-450ppm.

[0040] The present invention also provides a steel strip produced by the method described in the above technical solution.

[0041] The present invention also provides a method for preparing hot-dip galvanized deep-drawing steel, wherein the strip steel used is the strip steel described in the above technical solution.

[0042] The present invention also provides a hot-dip galvanized deep-drawing steel produced by the preparation method described in the above technical solution.

[0043] The control method of hot-rolled scale of hot-dip galvanized deep-drawing steel provided by the present invention controls the chemical composition, and the hot-rolling process adopts rough rolling high-temperature rolling-full-pass descaling-finishing rolling low-temperature rolling-high-speed final rolling-intensive water cooling in the front section of layer cooling and other means and controls the process conditions, so as to achieve the thinning of the oxide layer of the pickling raw material and promote the generation of microcracks of the third-order scale. The surface oxide layer structure is composed of pre-eutectoid Fe3O4+a small amount of eutectoid structure (Fe+Fe3O4), the oxide layer has no Fe2O3, the oxide layer thickness is 7-9μm, and there are obvious scale microcracks on the surface of the strip. It effectively promotes the removal effect of pickling scale. The surface quality and finished product technical and economic indicators of the cold-rolled strip for hot-dip galvanized deep-drawing produced by the method are good, and the thickness and structure of the oxide layer fully meet the technical indicators. After thinning the oxide layer thickness and adjusting the oxide layer structure, the pickling surface quality is excellent, and the defects such as scale indentation and insufficient pickling are significantly reduced. The surface quality of the steel strip is excellent, which can effectively meet the demand of the galvanizing unit for raw materials. The method of the present invention improves the yield rate of the pickling process of hot-dip galvanized deep-drawing steel on the one hand, and improves the pickling quality of the strip steel on the other hand, which has a significant promoting effect on reducing the surface quality defects of the strip steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0045] Figure 1 is a morphology diagram of the oxide layer of the hot-rolled steel strip obtained after hot rolling in step E) in Example 1;

[0046] Figure 2 is a morphology diagram of the oxide layer of the hot-rolled steel strip obtained after hot rolling in step E) in Example 2;

[0047] Figure 3 This is a morphology of the oxide layer of the hot-rolled steel strip obtained after hot rolling in step E) in Comparative Example 1. DETAILED DESCRIPTION

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0049] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0050] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0051] Herein, when it comes to numerical ranges, unless otherwise specified, the numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0052] In this article, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 15~25min means that the units of the left endpoint "15" and the right endpoint "25" are both min.

[0053] The present invention provides a method for controlling hot-rolled oxide scale of hot-base galvanized deep-drawing steel, comprising the following steps:

[0054] A) Molten steel:

[0055] The blast furnace molten iron and metallurgical auxiliary materials are smelted in an oxygen top-blown converter to obtain molten steel; then, the steel is tapped into a molten steel tank;

[0056] B) LF refining:

[0057] LF refining treatment is performed on the molten steel in the molten steel tank;

[0058] C) RH treatment:

[0059] The molten steel tank is transported to the RH vacuum treatment furnace for decarburization, deoxidation and alloying to obtain molten steel;

[0060] In terms of mass percentage, the molten steel obtained in step C) comprises:

[0061] C: ≤0.01%;

[0062] Si: 0%~0.01%;

[0063] Mn: 0.10%~0.20%;

[0064] P: 0%~0.015%;

[0065] S: 0%~0.010%;

[0066] Ti: 0.04%~0.06%;

[0067] Als: 0.015%~0.060%;

[0068] Fe and inevitable impurity elements: balance;

[0069] D) Continuous Casting:

[0070] Casting the molten steel obtained in step C) through a slab continuous casting machine to obtain a slab;

[0071] E) Hot rolling:

[0072] hot rolling the slab obtained in step D);

[0073] The hot rolling process includes: reheating and soaking treatment, rough rolling, finish rolling and cooling;

[0074] in,

[0075] The reheating soaking temperature of the hot rolling is 1180-1210°C, and the time is 0.5-1.0h;

[0076] The rough rolling temperature is 1175-1200°C, the descaling water pressure is 25MPa, and the rough rolling dephosphorization sequence is full-pass dephosphorization;

[0077] The start rolling temperature of the finishing rolling is 1010-1040°C, the rolling speed is 1.30-1.70 m / s, the final rolling temperature is 900-930°C, and the thickness rolling reduction ratios of the last two stands of the rolling mill are ≤13% and ≤10% respectively;

[0078] The cooling adopts a front-stage intensive cooling, middle-stage air cooling and rear-stage temperature adjustment mode; wherein the length of the front-stage intensive cooling is 5 to 15 m, the length of the middle section is 15 to 60 m, and the length of the rear section is 5 to 10 m;

[0079] F) Pickling:

[0080] The steel strip obtained in step E) is pickled online to obtain a hot-dip galvanized substrate raw material.

[0081] The method provided by the present invention can obtain a steel strip with a thin iron oxide layer, an oxide layer structure without Fe2O3, and excellent surface quality after pickling, and the oxide layer thickness and structure fully meet the technical indicators.

[0082] [About Step A]:

[0083] A) Molten steel making: Molten iron from blast furnace and metallurgical auxiliary materials are smelted in oxygen top-blown converter to obtain molten steel; then, the steel is tapped into a molten steel tank.

[0084] In the present invention, the equipment for smelting molten steel is a top-blown converter, and the molten iron after vanadium extraction from the blast furnace iron is used as the raw material. In addition to the above raw materials, metallurgical auxiliary materials are also added for smelting. The types of the auxiliary materials are not particularly limited, and they can be auxiliary materials commonly used in steelmaking in this field, and the ingredients can be prepared according to the chemical composition of the target molten steel. Smelting to 1660-1680°C, specifically 1660, 1670, 1680°C. Then, tapping.

[0085] In the present invention, when 1 / 3 to 1 / 2 of the steel is tapped, preferably 1 / 3, aluminum-iron alloy is added to the molten steel tank for pre-deoxidation, and the molten steel tank is subjected to bottom blowing of argon. Among them, 1 / 3 of the steel tapping means that 1 / 3 of the molten steel (the amount is measured by mass) is poured out when the converter taps the steel, that is, the ratio of the amount of molten steel poured out / the total amount of molten steel = 1 / 3. Among them, the argon pressure of the bottom blowing argon is preferably 350Pa. The time of the bottom blowing argon is preferably 4 to 10 minutes, more preferably 4 minutes.

[0086] [About step B]:

[0087] B) LF refining: The molten steel in the steel tank is subjected to LF refining treatment.

[0088] In the present invention, during LF refining, argon is introduced into the bottom of the molten steel tank, and the pressure of the argon is preferably 200-400Pa, specifically 200Pa, 250Pa, 300Pa, 350Pa, 400Pa. The time for passing argon is preferably 4-10min, more preferably 5min. The argon flow rate is based on the molten steel not turning over. The termination temperature of LF refining is preferably 1610-1640℃, specifically 1610℃, 1615℃, 1620℃, 1625℃, 1630℃, 1635℃, 1640℃. No alloying is performed in the LF process, and the oxygen content at the exit is 350-450ppm.

[0089] [About Step C]:

[0090] C) RH treatment: The molten steel tank is transported to the RH vacuum treatment furnace for decarburization, deoxidation and alloying treatment to obtain molten steel.

[0091] In the present invention, the molten steel tank is transported to the RH vacuum treatment furnace for decarburization, final deoxidation and alloying. The RH treatment time is preferably 15 to 25 minutes, specifically 15 minutes, 20 minutes, and 25 minutes. The outlet temperature of the RH treatment is preferably 1590 to 1610°C, specifically 1590°C, 1595°C, 1600°C, 1605°C, and 1610°C.

[0092] After RH treatment, the composition of the obtained molten steel is as follows:

[0093] C: ≤0.01%;

[0094] Si: 0%~0.01%;

[0095] Mn: 0.10%~0.20%;

[0096] P: 0%~0.015%;

[0097] S: 0%~0.010%;

[0098] Ti: 0.04%~0.06%;

[0099] Als: 0.015%~0.060%;

[0100] Fe and inevitable impurity elements: balance

[0101] In one embodiment of the present invention, the composition of molten steel is as follows: C: 0.0030%, Si: 0.01%, Mn: 0.18%, P: 0.010%, S: 0.005%, Ti: 0.055%, Als: 0.037%, and the rest is Fe and inevitable impurities. In another embodiment of the present invention, the composition of molten steel is as follows: C: 0.0031%, Si: 0%, Mn: 0.16%, P: 0.010%, S: 0.003%, Ti: 0.050%, Als: 0.035%, and the rest is Fe and inevitable impurities. Among them, Als is a well-known concept in the art, i.e., acid-soluble aluminum.

[0102] [About Step D]:

[0103] D) Continuous casting: The molten steel obtained in step C) is cast through a slab continuous casting machine to obtain a slab.

[0104] The continuous casting is specifically to cast the refined molten steel into a pre-baked tundish, and cast the slab into a slab by a slab continuous casting machine with full process protection. After casting, it is preferably cooled, for example, naturally cooled at room temperature. In the present invention, the thickness of the slab is preferably 230±5 mm.

[0105] [About Step E]:

[0106] E) Hot rolling: The slab obtained in step D) is subjected to hot rolling.

[0107] In the present invention, the hot rolling treatment includes: reheating and soaking treatment, rough rolling, finish rolling and cooling.

[0108] The hot rolling step is to reheat the cast slab and then roll it to adjust its thickness and width.

[0109] The hot rolling treatment includes a reheating soaking treatment. After the slab is obtained by continuous casting, the slab is sent to a heating furnace for heating, which is a reheating soaking treatment. The temperature of the reheating soaking refers to the rolling temperature of the steel billet out of the furnace. Soaking at this temperature can fully dissolve the micro-alloying elements and eliminate the chemical element segregation caused by the dendrite bias of the casting. In the present invention, the temperature of the reheating soaking treatment is 1180-1210°C, specifically 1180°C, 1190°C, 1200°C, and 1210°C. The time of the reheating soaking treatment is 0.5-1.0h, specifically 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, and 1.0h.

[0110] After the above-mentioned reheating and soaking treatment, rough rolling is carried out. Specifically, it is first descaled by high-pressure water and then enters the rough rolling mill for preliminary rolling. Among them, the descaling water pressure is 25MPa. The dephosphorization sequence is full-pass dephosphorization. The above-mentioned descaling treatment can remove the furnace-generated iron scale and secondary iron scale on the surface of the strip at high temperature. The rough rolling temperature is 1175-1200℃, specifically 1175℃, 1178℃, 1180℃, 1185℃, 1190℃, 1195℃, 1200℃.

[0111] After the above-mentioned rough rolling, finishing rolling is carried out. Specifically, the rough-rolled billet enters the finishing mill for finishing rolling. Wherein, the start rolling temperature of the finishing rolling is 1010-1040°C, specifically 1010°C, 1015°C, 1020°C, 1025°C, 1030°C, 1035°C, 1040°C. The rolling speed of the finishing rolling is 1.30-1.70m / s, specifically 1.30m / s, 1.40m / s, 1.50m / s, 1.60m / s, 1.70m / s. The final rolling temperature of the finishing rolling (referring to the temperature of the strip exiting the finishing rolling mill) is 900-930°C, specifically 900°C, 905°C, 910°C, 915°C, 920°C, 925°C, 930°C. The thickness rolling reduction rates of the last two stands of the rolling mill are ≤13% (corresponding to the second to last stand) and ≤10% (corresponding to the last stand), respectively; wherein, the former reduction rate can be specifically 11%, and the latter reduction rate can be specifically 8%. The present invention controls the above-mentioned start rolling temperature to remove the FeO·Fe2SiO4 or FeO·Fe3(PO4)2 compounds with low melting points on the surface of the slab, and prevents the formation of Fe2O3 which is not conducive to pickling after cooling; controlling the above-mentioned rolling speed and start rolling temperature to match is conducive to reducing the thickness of the finished product oxide layer; controlling the above-mentioned final rolling temperature can make the thickness and mechanical properties of the finished product uniform and avoid the formation of Fe2O3 phase during the finishing rolling process. Controlling the reduction rates of the last two stands of the rolling mill can prevent the edge-broken FeO from transforming into the Fe2O3 phase.

[0112] After the above-mentioned finishing rolling, cooling is carried out, specifically laminar cooling. In the present invention, the cooling adopts the mode of intensive cooling in the front section + air cooling in the middle section + temperature adjustment in the rear section. Among them, the length of the intensive cooling in the front section is 5 to 15m, specifically 5m, 6m, 7m, 8m, 9m, 10m, 11m, 12m, 13m, 14m, 15m. The water pressure of the upper and lower manifolds in the front section is preferably 0.8MPa; the cooling rate of the upper and lower manifolds in the front section is preferably 90% and 75%, respectively. The above cooling rate is expressed as the proportion of water passing through. In actual production, the cooling rate is adjusted by switching the cooling manifold nozzle. The percentage expression method is well known in the industry. For example, the full-open mode is 100%, that is, 100% of the 0.8MPa water pressure is directly sprayed on the surface of the strip. The present invention controls the cooling rates of the upper and lower headers to 90% and 75% respectively. If the cooling rate is too high, the grain size of the hot-rolled microstructure will be too fine, which will affect the subsequent hot-based galvanizing process. At the same time, there are too many cracks in the surface oxide layer prefabricated iron sheet, and pitting defects are prone to occur if pickling is not timely. The rate of the above-mentioned front-stage intensive cooling is 10-25°C / s, specifically 10°C / s, 15°C / s, 20°C / s, and 25°C / s. The length of the air cooling in the middle section is preferably 15-60m, specifically 15m, 20m, 25m, 30m, 35m, 40m, 45m, 50m, 55m, and 60m. The air cooling process is not particularly limited, and it can be a conventional air cooling method in the field. The length of the temperature adjustment in the rear section is preferably 5-10m, specifically 5m, 6m, 7m, 8m, 9m, and 10m. The water pressure of the upper and lower headers of the rear stage temperature adjustment is preferably 0.8MPa; the cooling rate of the upper and lower headers of the rear stage temperature adjustment is preferably 30%. The steel strip coming out of the rolling mill must be prefabricated with oxide layer cracks at a very high cooling rate in a very short time and cooled to the coiling temperature for coiling. Cooling to the coiling temperature of 700-730℃, specifically 700℃, 705℃, 710℃, 715℃, 720℃, 725℃, 730℃. In order to improve the mechanical properties of the finished product, it is necessary to use high-temperature coiling in hot rolling to promote the precipitation of Ti(C,N) and AlN particles, and the continuous recrystallization annealing of the hot-based galvanizing process uses Ti(C,N) and AlN particles to inhibit F growth, and improves the steel strength through fine grain strengthening and second phase strengthening mechanisms; in addition, in order to obtain an oxide layer rich in microcracks, the present invention adopts the above-mentioned three-stage cooling method and controls its conditions, and controls the coiling temperature to achieve the above-mentioned effect.

[0113] In the present invention, after the hot rolling process, the oxide layer thickness of the obtained steel strip is 7 to 9 μm, the oxide layer structure is pro-eutectoid Fe3O4 + a small amount of eutectoid structure (Fe+Fe3O4), and the oxide layer has no Fe2O3; the proportion of pro-eutectoid Fe3O4 is 80 to 90%, the proportion of eutectoid structure is 10 to 20%, and microcracks exist in the oxide layer, which can effectively promote the removal effect of pickling oxide scale.

[0114] The thickness of the oxide layer (i.e., iron oxide scale) can be measured by a method known to those skilled in the art. The test sample can be a polished or corroded metallographic sample. The sample corrosive agent is a 1-2% hydrochloric acid alcohol solution. The corrosion time is 5-8s, such as the metallographic method of GB / T 6394. The structure of the oxide layer can be measured by a method known to those skilled in the art. The test sample can be a polished or corroded metallographic sample. The sample corrosive agent is a 1-2% hydrochloric acid alcohol solution. The corrosion time is 5-8s, such as the metallographic method of GB / T 6394.

[0115] [About Step F]:

[0116] F) Pickling: The steel strip obtained in step E) is pickled online to obtain a hot-dip galvanized substrate raw material product.

[0117] Pickling is usually continuous online pickling, and the present invention has no special restrictions on it, and it can be carried out in a conventional manner in the art. Usually, the thin steel strip rolled by hot rolling is welded at the head of the pickling unit to form a continuous steel strip, and is rolled after straightening, tensioning and phosphorus removal, pickling, alkali washing, drying, and trimming. In the present invention, the tensioning elongation of the pickling section is preferably 0.80% to 1.50%, and can be specifically 0.80%, 0.90%, 1.00%, 1.10%, 1.20%, 1.30%, 1.40%, 1.50%. The pickling section speed is preferably 280 to 320 mm / min, and can be specifically 280 mm / min, 290 mm / min, 300 mm / min, 310 mm / min, and 320 mm / min. After the above pickling, the surface oxide scale is removed and the surface quality is improved. By controlling the preceding process, the higher pickling process unit speed is obtained, thus avoiding the defects of oxidation pressing and insufficient pickling in the prior art. The surface quality after pickling is excellent, the technical and economic indicators are good, and the prospect of promotion and use is good.

[0118] The control method of hot-rolled iron scale of hot-dip galvanized deep-drawing steel provided by the present invention is essentially a method for producing steel strips, which mainly controls the chemical composition and the hot rolling process (including hot rolling soaking temperature, finishing rolling start temperature, descaling water pressure, rough rolling descaling sequence, final rolling temperature, layer cooling system, coiling temperature, etc.), and the obtained steel strip has a thickness of 7-9 μm, an oxide layer structure of pre-eutectoid Fe3O4+a small amount of eutectoid structure (Fe+Fe3O4), and no Fe2O3 in the oxide layer; the proportion of pre-eutectoid Fe3O4 is 80-90%, the proportion of eutectoid structure is 10-20%, and microcracks exist in the oxide layer. Through the control of the preceding process section, a higher pickling process section unit speed can be used in the pickling process section to achieve an effective pickling effect, avoid defects such as oxidation pressing defects and under-pickling defects, and the surface quality after pickling is excellent.

[0119] The control method of hot-rolled scale of hot-dip galvanized deep-drawing steel provided by the present invention controls the chemical composition, and the hot-rolling process adopts rough rolling high-temperature rolling-full-pass descaling-finishing rolling low-temperature rolling-high-speed final rolling-intensive water cooling in the front section of layer cooling and other means and controls the process conditions, so as to achieve the thinning of the oxide layer of the pickling raw material and promote the generation of microcracks of the third-order scale. The surface oxide layer structure is composed of pre-eutectoid Fe3O4+a small amount of eutectoid structure (Fe+Fe3O4), the oxide layer has no Fe2O3, the oxide layer thickness is 7-9μm, and there are obvious scale microcracks on the surface of the strip. It effectively promotes the removal effect of pickling scale. The surface quality and finished product technical and economic indicators of the cold-rolled strip for hot-dip galvanized deep-drawing produced by the method are good, and the thickness and structure of the oxide layer fully meet the technical indicators. After thinning the oxide layer thickness and adjusting the oxide layer structure, the pickling surface quality is excellent, and the defects such as scale indentation and insufficient pickling are significantly reduced. The surface quality of the steel strip is excellent, which can effectively meet the demand of the galvanizing unit for raw materials. The method of the present invention improves the yield rate of the pickling process of hot-dip galvanized deep-drawing steel on the one hand, and improves the pickling quality of the strip steel on the other hand, which has a significant promoting effect on reducing the surface quality defects of the strip steel.

[0120] The present invention also provides a steel strip produced by the method described in the above technical solution.

[0121] The present invention also provides a method for preparing hot-dip galvanized deep-drawing steel, wherein the strip steel used is the strip steel described in the above technical solution. Hot-dip galvanized deep-drawing steel is a method for preparing hot-dip galvanized deep-drawing steel by hot-dip galvanizing the strip steel to form a galvanized layer on the strip steel. The present invention has no special restrictions on the method of hot-dip galvanizing, and any conventional method in the art can be used.

[0122] The present invention also provides a hot-dip galvanized deep-drawing steel produced by the preparation method described in the above technical solution.

[0123] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0124] Example 1

[0125] A) Molten steel:

[0126] The smelting equipment is a top-blown converter. The molten iron from the blast furnace after vanadium extraction is used as the raw material. The temperature is 1350℃. Steelmaking auxiliary materials are added to melt to 1670℃ and the steel is tapped into the molten steel tank. When 1 / 3 of the steel is tapped, 200Kg of aluminum iron is added for pre-deoxidation. The molten steel tank is bottom-blown with argon at a pressure of 350Pa for 4 minutes.

[0127] B) LF refining:

[0128] A certain pressure (300Pa) of argon is introduced into the bottom of the molten steel tank for 5 minutes. The argon flow rate is based on the condition that the molten steel does not overturn. The LF treatment termination temperature is 1620℃. No alloying is performed in the LF process, and the oxygen content is 400ppm at the exit.

[0129] C) RH treatment:

[0130] The molten steel tank was transported to the RH vacuum treatment furnace for decarburization, deoxidation and alloying treatment. The RH vacuum treatment time was 20 minutes and the exit temperature was 1595°C. The composition of the molten steel was: C: 0.0030%, Si: 0.01%, Mn: 0.18%, P: 0.010%, S: 0.005%, Ti: 0.055%, Als: 0.037%, and the rest was Fe and unavoidable impurity elements.

[0131] D) Continuous Casting:

[0132] The molten steel tank is transported to the casting position, and the bottom of the molten steel tank slides the Al stopper rod, and the molten steel automatically flows into the tundish, passes through the Al stopper rod, and is drained to the crystallizer for continuous casting. The whole process uses protective slag for protective casting, and after casting, it is cooled into a hot-rolled slab with a thickness of 230mm.

[0133] E) Hot rolling:

[0134] The continuous casting slab is sent to the heating furnace for reheating and soaking treatment, the soaking temperature is 1210℃, and the soaking time is 30min; then, it is descaled by high-pressure water, the descaling pressure is 25MPa, and the dephosphorization sequence is full-pass dephosphorization; after that, it is sent to the rough rolling mill for preliminary rolling, and the rough rolling temperature is 1178℃. After the rough rolling is completed, it enters the finishing mill for finishing rolling; the finishing rolling start temperature is 1040℃, the start rolling speed is 1.6m / s, the thickness reduction rates of the last two rolling mill stands are 11% and 8% respectively, and the final rolling temperature is 925℃. Among them, the thickness after rough rolling is 46mm, the number of finishing rolling passes is 7, and the thickness after finishing rolling is 3.5mm.

[0135] After the above-mentioned finishing rolling, laminar cooling is carried out, using the mode of front-stage intensive cooling + middle-stage air cooling + rear-stage temperature adjustment; the length of the front-stage intensive cooling is 10m, and the cooling rates of the upper and lower headers (water pressure is 0.8MPa) are 90% and 75% respectively (intensive cooling rate is 20℃ / min); the length of the middle-stage air cooling is 30m; the length of the rear-stage temperature adjustment is 8m, and the cooling rates of the upper and lower headers (water pressure is 0.8MPa) are 30%. Cool to the coiling temperature of 730℃ for coiling.

[0136] F) Pickling:

[0137] The steel strip obtained in step E) is pickled online, wherein the thickness of the steel strip after the pickling unit is 3.5 mm, the elongation of the pickling unit is 0.8%, and the process section speed is 300 m / min.

[0138] test:

[0139] The strip obtained in step E) was subjected to oxide layer structure and thickness test. The results showed that the oxide layer thickness on the strip surface was 7 μm, the oxide layer structure was pro-eutectoid Fe3O4 + a small amount of eutectoid structure, there was no Fe2O3 phase in the oxide layer, the proportion of pro-eutectoid Fe3O4 was 85%, the proportion of eutectoid structure was 15%, and microcracks existed in the oxide layer structure, such as Figure 1 The surface quality of the steel strip after pickling is good, and there is no residual pickling scale defect, which meets the technical requirements of pickling raw materials for hot-dip galvanized deep drawing steel strip.

[0140] Example 2

[0141] Implement according to Example 1, except that:

[0142] In step C), the composition of the molten steel is: C: 0.0031%, Si: 0%, Mn: 0.16%, P: 0.010%, S: 0.003%, Ti: 0.050%, Als: 0.035%, and the rest is Fe and unavoidable impurity elements.

[0143] In step E), the conditions are as follows: soaking temperature is 1200°C, soaking time is 35min; rough rolling temperature is 1180°C; finishing rolling start temperature is 1035°C, start rolling speed is 1.5m / s, and final rolling temperature is 920°C. Among them, the thickness after rough rolling is 46mm, the number of finishing rolling passes is 7, and the thickness after finishing rolling is 3.5mm. In laminar cooling, the intensive cooling rate is 15°C / min, and the coiling is carried out by cooling to a coiling temperature of 720°C. The remaining conditions are the same as those in Example 1, and the thickness of the slab after rough rolling and finishing rolling is also the same as in Example 1.

[0144] In step F), the thickness of the steel strip after the pickling unit is 3.5 mm, the elongation of the pickling unit is 0.8%, and the process section speed is 280 m / min.

[0145] test:

[0146] The strip steel obtained in step E) was subjected to oxide layer structure and thickness test. The results showed that the oxide layer thickness on the strip steel surface was 8 μm, the oxide layer structure was pro-eutectoid Fe3O4 + a small amount of eutectoid structure, there was no Fe2O3 phase in the oxide layer, the proportion of pro-eutectoid Fe3O4 was 90%, the proportion of eutectoid structure was 10%, and microcracks existed in the oxide layer structure, such as Figure 2 The surface quality of the steel strip after pickling is good, and there is no residual pickling scale defect, which meets the technical requirements of pickling raw materials for hot-dip galvanized deep drawing steel strip.

[0147] Comparative Example 1

[0148] Implement according to Example 1, except that:

[0149] In step C), the composition of the molten steel is: C: 0.0035%, Si: 0.01%, Mn: 0.20, P: 0.011, S: 0.003, Ti: 0.055, Als: 0.028, and the rest are Fe and unavoidable impurity elements.

[0150] In step E), the conditions are as follows: soaking temperature is 1220°C; rough rolling temperature is 1130°C; finishing rolling start temperature is 1078°C, start rolling speed is 1.2m / s, thickness reduction ratios of the last two rolling mill stands are 17% and 13% respectively, final rolling temperature is 920°C, and the thickness after finishing rolling is 3.5mm. In laminar cooling, front-stage laminar cooling is adopted, and the cooling rates of the upper and lower manifolds are 60% and 50% (cooling rate 10°C / s), and the coiling is carried out after cooling to a coiling temperature of 720°C. The remaining conditions are the same as those in Example 1, and the thickness of the slab after rough rolling and finishing rolling is also the same as in Example 1.

[0151] In step F), the thickness of the steel strip after the pickling unit is 3.5 mm, the elongation of the pickling unit is 0.8%, and the process section speed is 210 m / min.

[0152] test:

[0153] The strip obtained in step E) was tested for oxide layer structure and thickness. The results showed that the oxide layer thickness on the strip surface was 12 μm, the oxide layer structure was Fe2O3+eutectoid Fe3O4+eutectoid structure (Fe+Fe3O4), the ratio of pre-eutectoid Fe3O4 was greater than 95%, the ratio of eutectoid structure was less than 5%, and there were no microcracks in the oxide layer structure. Figure 3 The surface quality of the steel strip after pickling is poor, with many pickling scale defects remaining, which does not meet the technical requirements for pickling raw materials for hot-dip galvanized stamping steel strips.

[0154] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for controlling hot-rolled oxide scale of hot-dip galvanized deep-drawing steel, characterized in that: The following steps are involved: A) Molten steel: The blast furnace molten iron and metallurgical auxiliary materials are smelted in an oxygen top-blown converter to obtain molten steel; then, the steel is tapped into a molten steel tank; B) LF refining: LF refining treatment is performed on the molten steel in the molten steel tank; C) RH treatment: The molten steel tank is transported to the RH vacuum treatment furnace for decarburization, deoxidation and alloying to obtain molten steel; In terms of mass percentage, the molten steel obtained in step C) comprises: C：≤0.01％； Si: 0%~0.01%; Mn: 0.10%~0.20%; P：0％～0.015％； S：0％～0.010％； Ti: 0.04%~0.06%; Als: 0.015%~0.060%; Fe and inevitable impurity elements: balance; D) Continuous Casting: Casting the molten steel obtained in step C) through a slab continuous casting machine to obtain a slab; E) Hot rolling: hot rolling the slab obtained in step D); The hot rolling process includes: reheating, soaking treatment, rough rolling, finishing rolling and cooling; in, The reheating soaking temperature of the hot rolling is 1180-1210°C, and the time is 0.5-1.0h; The rough rolling temperature is 1175-1200°C, the descaling water pressure is 25MPa, and the rough rolling dephosphorization sequence is full-pass dephosphorization; The start rolling temperature of the finishing rolling is 1010-1040°C, the rolling speed is 1.30-1.70 m / s, the final rolling temperature is 900-930°C, and the thickness rolling reduction ratios of the last two stands of the rolling mill are ≤13% and ≤10% respectively; The cooling adopts a front-stage intensive cooling, middle-stage air cooling and rear-stage temperature adjustment mode; wherein the length of the front-stage intensive cooling is 5 to 15 m, the length of the middle section is 15 to 60 m, and the length of the rear section is 5 to 10 m; F) Pickling: The steel strip obtained in step E) is pickled online to obtain a hot-dip galvanized substrate raw material.

2. The method according to claim 1, characterized in that In step E), the water pressure of the dense upper and lower headers in the front section is 0.8 MPa; the cooling rates of the dense upper and lower headers in the front section are 90% and 75% respectively.

3. The method according to claim 1 or 2, characterized in that: In step E), the front-stage intensive cooling rate is 10-25° C. / s.

4. The method according to claim 1, characterized in that: In step E), the water pressure of the upper and lower headers of the rear stage temperature adjustment is 0.8 MPa; the cooling rate of the upper and lower headers of the rear stage temperature adjustment is 30%.

5. The method according to claim 1, characterized in that In step E), the steel sheet is cooled to a coiling temperature of 700-730° C. and then coiled.

6. The method according to claim 1, characterized in that In step F), the pickling process section speed is 280-320 mm / min, and the tensile elongation is 0.80%-1.50%.

7. The method according to claim 1, characterized in that In step A), when 1 / 3 of the steel is tapped, aluminum-iron alloy is added to the molten steel tank for pre-deoxidation, and the molten steel tank is subjected to bottom blowing of argon; wherein the argon pressure of the bottom blowing is 200-400 Pa, and the time is 4-10 minutes; In step B), during LF refining, argon is introduced into the bottom of the molten steel tank; the pressure of the argon is 200-400 Pa, and the time of passing the argon is 4-6 minutes; the termination temperature of LF refining is 1610-1640°C; alloying is not performed in the LF refining process, and the oxygen concentration at the exit is 350-450ppm.

8. A steel strip produced by the method according to any one of claims 1 to 7.

9. A method for preparing hot-dip galvanized deep-drawing steel, characterized in that: The strip steel used is the strip steel described in claim 8.

10. A hot-dip galvanized deep-drawing steel produced by the production method according to claim 9.

Images