Continuous hot-rolled strip steel and manufacturing method thereof

Abstract

The invention discloses continuous hot-rolled strip steel which comprises a hot-rolled base plate, the upper surface and the lower surface of the hot-rolled base plate are each provided with a pretreatment layer, and the pretreatment layer of at least one surface is further covered with a primer coating. The pretreatment layer is formed by coating treatment liquid containing resin molecules on the surface of the hot-rolled substrate, so that the resin molecules in the treatment liquid enter the interior of oxide skin on the surface of the hot-rolled substrate, and a self-crosslinking reaction is carried out in the interior and on the surface of the oxide skin. The invention further discloses a manufacturing method of the strip steel, which comprises the following steps of: obtaining a hot-rolled substrate, and arranging hot-rolled oxide skin on the surface of the hot-rolled substrate; the upper surface and the lower surface of the hot-rolled substrate are coated with treating fluid containing resin molecules, so that the resin molecules in the treating fluid enter the hot-rolled oxide skin, a self-crosslinking reaction is carried out in the oxide skin and on the surface of the oxide skin, and a pretreatment layer is formed; and coating primer on the pretreatment layer on the upper surface of the hot-rolled substrate and / or the pretreatment layer on the lower surface of the hot-rolled substrate to form a primer coating.

Description

Technical Field

[0001] The present invention relates to a steel material and a manufacturing method thereof, and particularly to a hot-rolled strip steel and a manufacturing method thereof. Background Art

[0002] The hot rolling of steel plates is a high-temperature process. The surface of the steel material continuously forms scale due to oxidation. This black scale with a thickness of several micrometers to dozens of micrometers can provide protection for the hot-rolled steel during production, storage, and transportation, and can slow down the rusting of the product. Currently, the main directions of hot-rolled steel are two aspects: one is to be used as cold-rolled raw materials after pickling; the other is to be directly supplied to users after pickling or without pickling.

[0003] There are more and more environmental protection constraints for pickling or shot blasting and peening treatment after the steel plates leave the factory. At the same time, users also have to pay the price in terms of cost, efficiency, and warehousing management. Moreover, in the context where pickling is becoming increasingly difficult to implement, shot blasting or peening treatment of steel plates is a helpless choice that more and more users have to make. However, shot blasting will still be restricted by environmental protection due to dust pollution.

[0004] At the same time, whether it is shot blasting or peening treatment, it will have a significant impact on the plate shape of the steel plate. Among them, the impact of peening treatment is particularly obvious. The treatment of steel plates with a thickness of less than 4 mm will significantly affect the subsequent processing accuracy and increase the difficulty of weld alignment; for hot-rolled plates with a thickness of less than 2 mm, even shot blasting needs to be particularly cautious. Although pickling the steel plates at the steel mill before leaving the factory can well avoid the above problems, if the steel plates lose the protection of the scale during storage and transportation and are not properly protected during storage and transportation, they are extremely prone to rust, and the consequence is that users have to perform secondary rust removal.

[0005] Most of the existing hot-rolled plate surface coating technologies are carried out after pickling or shot blasting and peening treatment of the hot-rolled plates. In the prior art, almost all hot-rolled plates need to be treated to remove the scale, and it is impossible to avoid the environmental protection, cost, and quality problems brought by shot blasting and descaling.

[0006] For example: In the Chinese patent document with the publication number CN101249605B, the publication date of April 14, 2010, and the name of "Method for Continuously Producing Rust Inhibiting Primer Coated Steel Plate", a method for continuously producing rust inhibiting primer coated steel plate is disclosed. This method continuously coats a primer coating on the surface of the hot-rolled strip steel, reduces intermediate links, and can provide temporary protection for the hot-rolled strip steel during production, storage, and transportation. However, this method has complex processes and requires pickling the hot-rolled plate to remove the scale.

[0007] For another example, a Chinese patent document with the publication number CN101724806A, publication date of June 9, 2010, and title "Manufacturing Method of Continuously Hot-Sprayed Metal Anticorrosion Coating Hot-Rolled Plate" discloses a manufacturing technology for obtaining a corrosion-resistant coating by online sandblasting and hot spraying on the surface of a steel plate in a hot-rolling production line. This technology can be applied online in a hot-rolling production line, and there are no problems with welding and forming for the formed corrosion-resistant alloy coating. However, for the hot spraying process adopted by this technology, on the one hand, the efficiency is relatively low and it is difficult to meet the conditions of high-speed continuous online production in hot rolling. On the other hand, continuous long-term online hot spraying places extremely high requirements on the nozzle, making it difficult to ensure the stability of continuous production. Summary of the Invention

[0008] One object of the present invention is to provide a continuously hot-rolled strip steel, the surface of which is covered with a primer paint and a pretreatment layer formed based on mill scale, so as to provide stronger protection for the product, avoid rusting during service, and meet the requirements for surface anti-corrosion and simple painting of hot-rolled products.

[0009] To achieve the above object, the present invention provides a continuously hot-rolled strip steel, which includes: a hot-rolled substrate, pretreatment layers are provided on both the upper and lower surfaces of the hot-rolled substrate, and a primer coating is further covered on at least one surface of the pretreatment layer; the pretreatment layer is formed by coating a treatment liquid containing resin molecules on the surface of the hot-rolled substrate, so that the resin molecules in the treatment liquid enter the interior of the mill scale on the surface of the hot-rolled substrate and undergo a self-crosslinking reaction inside and on the surface of the mill scale.

[0010] It should be noted that in the present invention, the pretreatment layer penetrates into the mill scale and seals the cracks and holes in the mill scale to improve the toughness and adhesion of the mill scale, so that the modified mill scale also becomes a part of the pretreatment layer.

[0011] In the present invention, both the pretreatment layer and the primer coating have excellent adhesion, and the overall coating can achieve an adhesion better than grade 1 (cross-cut method) on the premise of avoiding sandblasting and descaling.

[0012] Further, in the continuously hot-rolled strip steel of the present invention, primer coatings are covered on the pretreatment layers on both the upper and lower surfaces of the hot-rolled substrate.

[0013] Further, in the continuously hot-rolled strip steel of the present invention, the single-sided thickness of the primer coating is 10 - 50 μm.

[0014] In some embodiments, controlling the single-sided thickness of the primer coating between 10 - 50 μm can provide long-term anti-corrosion on the surface and ensure that the surface has no rust during long-term outdoor service.

[0015] Further, in the continuous hot-rolled strip steel of the present invention, the primer coating is formed based on an applied epoxy primer.

[0016] Further, in the continuous hot-rolled strip steel of the present invention, the epoxy primer includes at least one of the following: linear epoxy primer, epoxy iron red primer, epoxy zinc-rich primer, high-solids epoxy primer, waterborne epoxy primer, fusion-bonded epoxy primer.

[0017] Further, in the continuous hot-rolled strip steel of the present invention, the single-sided thickness of the pretreatment layer is 1 - 20 μm.

[0018] Further, in the continuous hot-rolled strip steel of the present invention, the resin molecules are selected from at least one of the following: acrylic acid, polyurethane, styrene-acrylic, silicone-acrylic, hydroxypropyl, epoxy, alkyd, and modified resins of the above.

[0019] In this embodiment, the resin molecules undergo a self-crosslinking reaction inside the scale to seal the cracks and pores in the scale, enhancing its corrosion resistance. Even without the aid of a surface coating, a rust resistance of more than 12 months can be achieved in an indoor environment. Additionally, it can enhance its toughness and the bonding force with the steel plate, and at the same time improve the surface state of the scale, making it easier to achieve good adhesion with the epoxy primer.

[0020] Another object of the present invention is to provide a method for manufacturing a continuous hot-rolled strip steel, which can form a pretreatment layer and a primer coating, thereby providing stronger protection for the product, avoiding rust during service, and meeting the requirements for surface anti-corrosion and simple painting of hot-rolled products.

[0021] Based on the above invention object, the present invention also provides a method for manufacturing a continuous hot-rolled strip steel, including the steps of:

[0022] Obtain a hot-rolled substrate, the surface of the hot-rolled substrate having hot-rolled scale;

[0023] Coat a treatment liquid containing resin molecules on the upper and lower surfaces of the hot-rolled substrate, so that the resin molecules in the treatment liquid enter the inside of the hot-rolled scale and undergo a self-crosslinking reaction inside and on the surface of the scale to form a pretreatment layer;

[0024] Apply a primer on the pretreatment layer on the upper surface of the hot-rolled substrate and / or the pretreatment layer on the lower surface of the hot-rolled substrate to form a primer coating.

[0025] In the present invention, the treatment liquid contains a large number of resin molecules, and the resin molecules can be cured into a film through a self-crosslinking reaction in the air; at the same time, when the treatment liquid penetrates into the scale, the surface area can be rapidly increased to shorten the film-forming time. The film-forming time of a 1 - μm-thick coating film in room-temperature air is within about 20 seconds.

[0026] It should be noted that after obtaining the hot-rolled substrate and before the coating treatment, the manufacturing method of the continuous hot-rolled strip of the present invention can perform surface cleaning on the hot-rolled substrate. The surface cleaning only needs to clean the floating ash, oxide particles or oil stains on the surface of the hot-rolled substrate to obtain a clean surface, without the need for complex pre-coating treatment processes such as pickling and phosphating.

[0027] Furthermore, in the manufacturing method of the continuous hot-rolled strip of the present invention, the treatment liquid further includes: one or several of a film-forming auxiliary agent, a fluorescent color developer, a preservative, an anti-flash rust agent, a pH regulator, and a substrate wetting agent.

[0028] Furthermore, in the manufacturing method of the continuous hot-rolled strip of the present invention, the viscosity of the treatment liquid < 100 mPa·s.

[0029] Furthermore, in the manufacturing method of the continuous hot-rolled strip of the present invention, in the step of forming the pretreatment layer, flowing air is also used to blow and cure the surface of the hot-rolled substrate coated with the treatment liquid.

[0030] Furthermore, in the manufacturing method of the continuous hot-rolled strip of the present invention, flowing air with a wind pressure of 0.1 to 1000 Kpa, a temperature of room temperature to 150 °C, and a relative humidity of less than 70% is used for the blowing and curing.

[0031] In this embodiment, by adopting the above process, the curing time of the pretreatment layer can be shortened to within 10 seconds, further improving the curing speed of the pretreatment layer.

[0032] Furthermore, in the manufacturing method of the continuous hot-rolled strip of the present invention, in the step of forming the primer coating, hot air blowing or baking is also used to cure the surface of the hot-rolled substrate coated with the primer.

[0033] The continuous hot-rolled strip and its manufacturing method of the present invention have the following advantages and beneficial effects compared with the prior art:

[0034] The continuous hot-rolled strip of the present invention is coated with a primer, which can significantly reduce the user's painting. As the inner wall of the equipment, it can be paint-free, and the outer surface can achieve simple painting; at the same time, the hot-rolled strip has good corrosion resistance, can effectively avoid rust during production, storage and transportation, can realize product transportation without packaging, reduce the packaging and unpackaging links, and is more economical, environmentally friendly, simple and easy to use.

[0035] In addition, the primer coating of the continuous hot-rolled strip steel of the present invention has good compatibility with other conventional topcoats and can be directly further coated during the subsequent use by users. At the same time, the hot-rolled strip steel does not affect subsequent cutting and can match conventional mechanical, laser, plasma or water jet cutting methods. Moreover, for this hot-rolled strip steel, after grinding the coating in the weld area, the welding process is basically not affected.

[0036] The manufacturing method of the continuous hot-rolled strip steel of the present invention realizes sandblasting-free coating for users, can save sandblasting, shot peening or pickling processes, is more energy-saving and environmentally friendly, and has higher economy. At the same time, it can avoid the problems of black ash and rust of the strip steel during production, storage and transportation, and reduce the adverse effects on the quality of steel, the production environment of users and the physical health of personnel. The above manufacturing method can also reduce user coating, simplify the process, facilitate use and is green and environmentally friendly.

[0037] The manufacturing method of the continuous hot-rolled strip steel of the present invention integrates the production steps of uncoiling, straightening, surface cleaning, online scale modification treatment, transverse cutting, primer coating and baking curing, surface inspection, trimming, packing, printing and tail gas treatment, so that all processes of strip steel surface cleaning, scale modification treatment, primer coating and curing, shearing and packaging are automatically completed online, and can meet the requirements of continuous automated production at a speed of 3 - 100 meters per minute.

[0038] In the surface cleaning step of the hot-rolled substrate in the manufacturing method of the continuous hot-rolled strip steel of the present invention, only the floating ash, oxide particles or oil stains on the strip steel surface need to be cleaned to obtain a clean strip steel surface, without the complex pre-coating treatment processes such as pickling and phosphating, which can greatly simplify the process, reduce costs, and reduce environmental pollution and resource consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematically shows the interlayer structure of the continuous hot-rolled strip steel of the present invention.

[0040] Figure 2 Schematically shows the implementation system structure diagram of the manufacturing method of the continuous hot-rolled strip steel of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The following will further explain and illustrate the continuous hot-rolled strip steel and its manufacturing method of the present invention in combination with specific embodiments and the accompanying drawings of the specification. However, this explanation and illustration do not unduly limit the technical solution of the present invention.

[0042] Figure 1 Schematically shows the interlayer structure of the continuous hot-rolled strip steel of the present invention.

[0043] As Figure 1As shown, the continuous hot-rolled strip steel includes a hot-rolled substrate 1, with pretreatment layers on both the upper and lower surfaces of the hot-rolled substrate, and a primer coating 4 is further covered on at least one surface of the pretreatment layer; the pretreatment layer is formed by coating a treatment liquid containing resin molecules on the surface of the hot-rolled substrate 1, so that the resin molecules in the treatment liquid enter the scale 2 on the surface of the hot-rolled substrate and undergo a self-crosslinking reaction inside and on the surface of the scale 2 to form, Figure 1 The label "3" in Figure 1 represents the film formed by the curing of the treatment liquid outside the scale. The pretreatment layer of the present invention includes

[0044] the sum of these two parts, namely the label "3" and the label "2" in

[0045] This is because the treatment liquid penetrates into the scale 2 and seals the cracks and pores in the scale, improving the toughness and adhesion of the scale, so that the modified scale 2 also becomes a part of the pretreatment layer.

[0046] Figure 2 Schematically shows the implementation system structure diagram of the manufacturing method of the continuous hot-rolled strip steel of the present invention.

[0047] As Figure 2 shown, in some embodiments, the manufacturing method of the continuous hot-rolled strip steel of the present invention can be implemented by using this implementation system. This implementation system includes: a pretreatment section a, which includes a welding device a2 for welding the strip steel a1 to be processed and a straightening machine a3; a surface cleaning section b, which includes a surface cleaning device b1 for surface cleaning; a surface pretreatment section c, which includes a coating device c1; an air drying and curing section d, which includes an air drying and curing device d1; a transverse cutting section e, which includes a shearing machine e1; a primer spraying section f, which includes a primer spraying device f1; a primer curing section g, which includes a baking or hot air device g1 and a tail gas incineration treatment device g2; a surface detection section h, which includes an on-line surface detector h1; a packing and warehousing section I, which includes a printing device I1 and a stacking and packing device I2.

[0048] In some embodiments, the hot-rolled continuous strip steel is obtained based on the following steps:

[0049] S1: Obtain a hot-rolled substrate with scale on the surface based on the following steps:

[0050] Uncoiling and straightening: The head of the hot-rolled strip a1 to be processed and the tail of the previous coil are welded and connected by a welding device a2. After the hot-rolled strip a1 to be processed is uncoiled, it is sent into a straightening machine a3 for straightening to optimize the shape of the strip to be processed, so as to ensure that the surface flatness of the hot-rolled strip meets the requirements of subsequent surface treatment operations.

[0051] Surface cleaning: The floating dust, oxide particles and oil stains on the surface of the straightened strip are cleaned by a surface cleaning device b1 to ensure that the surface cleanliness of the strip meets the surface treatment requirements. In the present invention, there is no need to pickle the strip to remove the scale, so the surface of the hot-rolled strip in the present invention has scale.

[0052] In some more specific embodiments, the floating dust and oxide particles on the surface of the strip can be cleaned and removed by means of high-pressure water jet flushing or compressed air blowing. If there is oil stain on the surface of the strip, a degreasing agent is used for degreasing.

[0053] S2: A treatment liquid containing resin molecules is coated on the upper and lower surfaces of the hot-rolled substrate, so that the resin molecules in the treatment liquid enter the interior of the hot-rolled scale and undergo a self-crosslinking reaction inside and on the surface of the scale to form a pretreatment layer; specifically, it may include:

[0054] First, it is confirmed that the surface of the strip meets the treatment requirements, and then the treatment liquid is evenly coated on the surface of the hot-rolled strip by a coating device c1 by means of spraying, brushing or roll coating.

[0055] In some embodiments, the treatment liquid is naturally cured at room temperature to form a pretreatment layer. The treatment liquid contains a large number of resin molecules, and the resin molecules can be cured into a film through a self-crosslinking reaction in the air. The resin molecules include, but are not limited to, acrylic acid, polyurethane, styrene-acrylic, silicone-acrylic, hydroxypropyl, epoxy, alkyd, and modified resins of the above. In this way, the film-forming time of a 1um-thick coating film in the air at room temperature is about within 20 seconds.

[0056] In some other embodiments, an air drying and curing device d1 can also be used to blow and cure the surface of the hot-rolled substrate coated with the treatment liquid with flowing air at a wind pressure of 0.1 to 1000 KPa, a temperature from room temperature to 150 degrees, and a relative humidity of less than 70%. By using this method, the curing time of the pretreatment layer can be shortened to within 10 seconds, realizing the rapid curing of the pretreatment layer.

[0057] In some more embodiments, the treatment liquid includes resin molecules, and in addition, it may also include: one or several of a film-forming auxiliary agent, a fluorescent color developer, a preservative, an anti-flash rust agent, a pH regulator, and a substrate wetting agent.

[0058] Preferably, the viscosity of the treatment liquid < 100 mPa·s.

[0059] After the pretreatment layer is cured, the continuous hot-rolled substrate can be trimmed by a shearing machine e1 and cross-cut as required.

[0060] S3: Apply a primer on the pretreatment layer on the upper surface of the hot-rolled substrate and / or the pretreatment layer on the lower surface of the hot-rolled substrate through a primer spraying device f1 to form a primer coating.

[0061] In some embodiments, a baking or hot air device g1 can be used to cure the surface of the hot-rolled substrate coated with the primer, and a tail gas incineration treatment device g2 is used to incinerate the tail gas.

[0062] In some other embodiments, the steps may further include:

[0063] S4: Surface inspection: Inspect the curing degree, thickness, coverage rate, etc. of the scale modification layer and the treatment liquid protection coating to ensure its complete curing and prevent interlayer adhesion during coiling and stacking, and ensure that the strip steel is effectively covered and the thickness is within the ideal range. Among them, the curing degree can be detected and judged by sampling the surface hardness or by methods such as finger touch method, blowing cotton ball method, and pressing filter paper method. The thickness of the scale modification layer and the treatment liquid protection coating can be estimated based on the consumption of raw materials. The coverage of the scale modification layer and the treatment liquid protection coating is irradiated with a ultraviolet lamp to make the coating added with a fluorescent color developer show color. In some embodiments, an on-line surface detector h1 can be used to detect the coverage.

[0064] S5: Trimming and packing: Trim the continuous hot-rolled strip with a scale modification layer and a treatment liquid protection coating, and cut, pack, and store it according to the requirements of the delivery form. If the delivery form is a steel coil, the strip is longitudinally slit after trimming, and according to the surface inspection results, the unqualified parts of the strip surface are recorded for repair or directly downgraded, and then re-coiled, spray-coded, and packed for storage. If the delivery form is a steel plate, after trimming the strip, it is bevelled and cut to size, spray-coded through a printing device I1, and packed and stored through a stacking and packing device I2.

[0065] To verify the implementation effect of this case, the present invention sets preferred Examples 1-6, and Examples 1-6 all use BS960E hot-rolled strip. Table 1 lists the product structure characteristic parameters of the continuous hot-rolled strip formed in Examples 1-6.

[0066] Table 1.

[0067]

[0068] Table 2 lists the specific process parameters for forming the pretreatment layer and the primer coating in the manufacturing method of the continuous hot-rolled strip in Examples 1-6.

[0069] Table 2.

[0070]

[0071]

[0072] It should be noted that although Examples 1-6 only show a single type of resin molecule used in each example, in other ways, it is also feasible to use these resin molecules in combination, and it is also feasible to use modified resins of these resin molecules.

[0073] Likewise, although Examples 1-6 only show a single type of primer used in each example, in other embodiments, it is also feasible to use these primers in combination.

[0074] In order to verify the effect of the present invention, various performances of the hot-rolled steel strip samples of each embodiment prepared by the following method were tested.

[0075] The hot-rolled steel strip samples of Examples 1-6 were subjected to a salt spray test (ASTM B117). After 480 hours of the salt spray test, no obvious rust was found on the surface.

[0076] The cross-cut method (GB / T 9286-2021) was used to test the adhesion of the samples, and all of them reached the optimal level. The optimal level can also be achieved after applying epoxy topcoat or polyurethane topcoat.

[0077] It should be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with by those skilled in the art from the contents disclosed in the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A continuous hot-rolled strip steel, characterized in that, it comprises: a hot-rolled substrate, both the upper and lower surfaces of the hot-rolled substrate have a pretreatment layer, and at least one surface of the pretreatment layer is further covered with a primer coating; the pretreatment layer is formed by coating a treatment liquid containing resin molecules on the surface of the hot-rolled substrate, so that the resin molecules in the treatment liquid enter the scale inside the surface of the hot-rolled substrate, and self-crosslinking reaction occurs inside and on the surface of the scale.

2. The continuous hot-rolled strip steel according to claim 1, characterized in that, primer coatings are covered on both the upper and lower surface pretreatment layers of the hot-rolled substrate.

3. The continuous hot-rolled strip steel according to claim 1, characterized in that, the single-sided thickness of the primer coating is 10 - 50 μm.

4. The continuous hot-rolled strip steel according to claim 1, characterized in that, the primer coating is formed based on an epoxy primer applied.

5. The continuous hot-rolled strip steel according to claim 4, characterized in that, the epoxy primer includes at least one of the following: linear epoxy primer, epoxy iron red primer, epoxy zinc-rich primer, high-solids epoxy primer, waterborne epoxy primer, fused epoxy primer.

6. The continuous hot-rolled strip steel according to claim 1, characterized in that, the single-sided thickness of the pretreatment layer is 1 - 20 μm.

7. The continuous hot-rolled strip steel according to claim 1, characterized in that, the resin molecules are selected from at least one of the following: acrylic acid, polyurethane, styrene-acrylic, silicone-acrylic, hydroxypropyl, epoxy, alkyd, and modified resins of the above.

8. A manufacturing method of the continuous hot-rolled strip steel according to any one of claims 1 - 7, characterized in that, it includes steps: obtaining a hot-rolled substrate, the surface of the hot-rolled substrate has hot-rolled scale; coating a treatment liquid containing resin molecules on the upper and lower surfaces of the hot-rolled substrate, so that the resin molecules in the treatment liquid enter the scale inside the hot-rolled substrate, and self-crosslinking reaction occurs inside and on the surface of the scale to form a pretreatment layer; coating a primer on the pretreatment layer on the upper surface of the hot-rolled substrate and / or the pretreatment layer on the lower surface of the hot-rolled substrate to form a primer coating.

9. The manufacturing method according to claim 8, characterized in that, the treatment liquid further includes: one or several of a film-forming auxiliary agent, a fluorescent color developer, a preservative, an anti-flash rust agent, a pH regulator, a substrate wetting agent.

10. The manufacturing method according to claim 8, characterized in that, the viscosity of the treatment liquid < 100 mPa·s.

11. The manufacturing method according to claim 8, characterized in that, in the step of forming the pretreatment layer, the surface of the hot-rolled substrate coated with the treatment liquid is also purged and cured with flowing air.

12. The manufacturing method according to claim 11, characterized in that, the purging and curing is carried out with flowing air having a wind pressure of 0.1 to 1000 Kpa, a temperature of room temperature to 150 °C, and a relative humidity of less than 70%.

13. The manufacturing method according to claim 8, characterized in that, in the step of forming the primer coating, the surface of the hot-rolled substrate coated with the primer is also cured by hot air purging or baking.

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