WO2024222944A1 - Online modification method for surface scale of hot-rolled product and hot-rolled product - Google Patents

Abstract

Disclosed in the present invention is an online modification method for the surface scale of a hot-rolled product, comprising steps: acquiring a hot-rolled substrate, wherein the surface of the hot-rolled substrate is provided with a hot-rolled scale; and coating the surface of the hot-rolled substrate with a treatment liquid containing resin particles, so as to enable the resin particles in the treatment liquid to enter the interior of the hot-rolled scale, and carrying out a self-crosslinking reaction on the interior and surface of the scale to form a film. Correspondingly, further disclosed in the present invention is a hot-rolled product prepared by means of the method. According to the present invention, a scale modified layer formed by compounding a layer of scale and a treatment liquid is formed on the surface of a hot-rolled product, so that effective protection is provided for the hot-rolled product in production and storage and transportation links, and scale shedding and strip steel surface corrosion can be prevented, thereby reducing adverse effects on user production and environment. Additionally, the scale modified layer and a treatment liquid layer almost have no obvious impact on the subsequent processes of cutting, welding, forming, coating and the like of the hot-rolled product.

Description

Online modification method for surface oxide scale of hot-rolled product and hot-rolled product Technical Field

The invention relates to a hot-rolled product and a manufacturing method thereof, and in particular to an online modification method for surface oxide scale of a hot-rolled product and a product thereof.

Background Art

Affected by the increasingly fierce market competition and increasingly stringent environmental pressure, more and more hot-rolled products are used directly without pickling, which puts higher requirements on their surface oxide scale. The oxide scale generated by the conventional hot rolling process is brittle and is easily broken into fine black oxide scale powder (black ash) during production, storage, transportation and processing, causing pollution and affecting the quality of coating. In addition, the oxide scale formed during production often has many holes or cracks, which is prone to corrosion during production, storage and transportation, generating red rust, affecting the appearance of the product and the quality of coating. The material is prone to spatter during the welding process, and the spatter is easy to combine with the oxide scale on the surface of the steel, which is extremely difficult to remove and affects the quality of coating. Mechanical cleaning must be carried out after welding, which affects the production rhythm and increases the processing cost.

In the prior art, one method to solve the above-mentioned black ash and red rust problems is to adjust the hot rolling, cooling and coiling process of steel to improve the scale structure on the surface of steel, enhance the density and flexibility of the scale, reduce the shedding of scale particles and delay the generation of red rust. However, this adjustment often inevitably affects the on-site production rhythm, product organization and mechanical properties, etc., and the improvement in the protective performance of the scale is limited, which may not meet the needs of users. Another method is to improve the corrosion resistance of steel through some protective measures, such as using anti-rust paper packaging, or applying anti-rust oil. However, anti-rust oil will have a serious impact on product welding and painting, and it needs to be removed by degreasing and other methods later. Anti-rust paper packaging has requirements for packaging integrity and sealing, and it will quickly fail once it is damaged or unpacked.

For another example, the Chinese patent document with publication number CN104845416A, publication date August 19, 2015, and titled "A protective coating for steel billets in hot rolling heating furnaces" discloses that the coating contains: 10-30% magnesium-aluminum composite material, 40-60% dead-burned magnesia, 10-30% aluminum silicate, 1-3% borax, 1-3% calcium phosphate, 4-10% bentonite, 1-5% powder thickener, and 40-50% of the total amount of water added. It can react with the oxides generated by the slab itself at high temperature to obtain a protective layer with different melting points, protecting The layer can effectively isolate the slab from the atmosphere in the heating furnace. It can effectively reduce the oxidation and burning of conventional carbon manganese steel, low carbon aluminum killed steel, low alloy steel, micro alloy steel and some alloy steels in the temperature range of 1000-1400℃. This type of technology belongs to the special protective coating in the rolling production process of hot rolled products. It is costly and its function is to reduce the high temperature oxidation and burning in the production process. It is not helpful for the rust problem in the storage and transportation process.

Conventional coating technology usually regards hot-rolled scale as a negative factor in coating, so it must be removed. Whether it is pickling or mechanical removal of scale, it will inevitably increase costs and carbon emissions, either there will be problems with waste acid emissions or cause dust and noise pollution, and it will also have an adverse effect on the plate shape. The hot-rolled scale itself is mainly composed of iron oxides, which have excellent corrosion resistance and are corrosion-resistant fillers for many coatings. The reason why hot-rolled products are prone to rust is often not because the scale itself is not corrosion-resistant enough, but because the scale has holes and cracks, which cause water and corrosive media to pass through the scale and enter the interior of the steel substrate, causing corrosion.

Based on this, it is hoped to provide an online modification method and product for the surface oxide scale of hot-rolled products, which can modify the hot-rolled oxide scale through online processing, enhance the toughness of the oxide scale, change its loose and porous structure, close the cracks and holes in the oxide scale, etc., prevent the entry of water and corrosive media, and solve the problems of black ash and red rust in one fell swoop.

Summary of the invention

One of the purposes of the present invention is to provide an online modification method for the surface oxide scale of a hot-rolled product. The method comprises the following steps: applying a water-based treatment liquid containing resin particles on the surface of the hot-rolled product online, so that the resin particles with a smaller diameter can penetrate into the interior of the hot-rolled oxide scale, and can rapidly undergo a self-crosslinking reaction to form a film after contacting the air, thereby sealing the oxide scale cavities and cracks, and finally forming an oxide scale modified layer containing oxide scale and resin, which completely changes the loose and porous structure of the oxide scale, and at the same time firmly fixes the oxide scale on the surface of the steel plate, which not only prevents the oxide scale from falling off, but also greatly delays surface corrosion, thereby providing process protection for the hot-rolled products during production, transportation and storage, avoiding impact on user production and the environment, and at the same time will not have a significant impact on the user's use processes such as cutting, welding, forming and painting.

In order to achieve the above object, the present invention provides an online modification method for the surface oxide scale of a hot-rolled product, which comprises the steps of:

Obtaining a hot-rolled substrate, wherein the hot-rolled substrate has a hot-rolled oxide scale on its surface;

A water-based treatment liquid containing resin particles is applied to the surface of the hot-rolled substrate so that the resin particles in the treatment liquid The particles enter the hot-rolled oxide scale and undergo self-crosslinking reaction inside and on the surface of the oxide scale to form a film.

Herein, the hot rolled product may be a hot rolled steel strip, preferably a continuously hot rolled steel strip.

Furthermore, in the online modification method for the oxide scale on the surface of hot-rolled products of the present invention, the particle size of the resin particles is less than or equal to 1.0 μm. Here, a Malvern laser particle size analyzer is used to measure the particle size of the resin particles.

More preferably, the particle size of the resin particles is less than or equal to 0.20 μm.

In some embodiments, the particle size of the resin particles is between 0.01 and 0.1 μm.

Furthermore, in the online modification method of hot-rolled product surface oxide scale described in the present invention, the resin is selected from at least one of the following: epoxy resin, polyurethane resin, alkyd resin, acrylic resin, styrene acrylic resin, silicone acrylic resin, and modified resins of the above items.

Herein, the epoxy resin, polyurethane resin, alkyd resin, acrylic resin, styrene acrylic resin, silicone acrylic resin and modified resins thereof may be various resins well known in the art.

For example, the epoxy resin can be a glycidyl ether epoxy resin, a glycidyl ester epoxy resin, a glycidyl amine epoxy resin, a linear aliphatic epoxy resin, an alicyclic epoxy resin, etc., which are well known in the art. Commonly used epoxy resins include but are not limited to bisphenol A epoxy resin, brominated bisphenol A epoxy resin or phenolic epoxy resin.

Polyurethane resin can be polyether type, polyester type, polyimide type or polyurea type polyurethane. The main raw materials of polyurethane include diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI) and polypropylene glycol (PPG) etc.

Alkyd resins may include drying short oil alkyd resins, drying medium oil alkyd resins, non-drying oil alkyd resins, long oil alkyd resins, very long oil alkyd resins, and the like.

Acrylic resins generally include thermosetting acrylic resins and thermoplastic acrylic resins. The former are infusible acrylic polymers with acrylic monomers (such as methyl acrylate, ethyl acrylate, n-butyl acrylate and methyl methacrylate, n-butyl methacrylate, etc.) as basic components and cross-linked into a network structure. The latter are a type of thermoplastic resin made by polymerization of acrylic acid, methacrylic acid and their derivatives (such as esters, nitriles, amides).

Styrene acrylic resin is obtained by emulsion copolymerization of styrene and acrylate monomers, and the viscosity of the emulsion is usually in the range of 80 to 2000 mPa.s. Silicone acrylic resin is a copolymer emulsion of organosiloxane and acrylate, and the viscosity is generally in the range of 150 to 350 mPa.s.

The modification of the above resins can be carried out by methods well known in the art, including but not limited to acrylic acid modification, Organic fluorine modification, organic silicon modification, nano material modification, epoxy resin modification, bio-based material modification and cross-linking modification, etc. For example, the modification of polyurethane includes but is not limited to acrylic acid modification, organic fluorine modification, organic silicon modification, nano material modification, epoxy resin modification, bio-based material modification and cross-linking modification, etc. The modified resins of alkyd resin include acrylic acid modified alkyd resin, organic silicon modified alkyd resin, styrene modified alkyd resin, nano modified alkyd resin, etc.

It should be understood that the resin used herein is a resin that can self-crosslink at room temperature without human intervention. A suitable resin can be selected to implement the present invention according to specific production conditions, as long as the particle size of the resin meets the requirements of the present application.

Optionally, in the online modification method of the oxide scale on the surface of hot-rolled products described in the present invention, the treatment liquid also includes: one or more of a film-forming aid, a fluorescent color developer, a preservative, an anti-flash rust agent and a pH adjuster. Various film-forming aids, fluorescent color developers, preservatives, anti-flash rust agents and pH adjusters well known in the art can be used to prepare the treatment liquid of the present application. Those skilled in the art can select a suitable film-forming aid and its dosage according to the type of resin used. For fluorescent color developers, preservatives and anti-flash rust agents, their dosage can be conventional dosages. For pH adjusters, their dosage should be sufficient to adjust the pH range of the treatment liquid to 6 to 9.

Preferably, the treatment liquid of the present application is an aqueous emulsion and does not require a special curing agent.

Further, in the online modification method of the hot-rolled product surface oxide scale of the present invention, the treatment liquid satisfies at least one of the following items: solid content is 1% to 60wt%; viscosity ≤2000mPa.s; pH value is 6 to 9; VOC content <100g/l. In some embodiments, the solid content of the treatment liquid is 10% to 60%. In some embodiments, the solid content of the treatment liquid is 20% to 60%. In some embodiments, the solid content of the treatment liquid is 1% to 30%. In some embodiments, the solid content of the treatment liquid is 10% to 30%. In some embodiments, the viscosity of the treatment liquid is 1 to 2000mPa.s. In some embodiments, the viscosity of the treatment liquid is 1 to 200mPa.s.

In some embodiments, in the online modification method of hot-rolled product surface oxide scale of the present invention, the self-crosslinking reaction time (which may be the time required to generate a 1 micron coating and dry the surface at room temperature without human intervention) is within 10 minutes.

In some other embodiments, the method for online modification of oxide scale on the surface of hot-rolled products of the present invention further comprises the step of: using compressed air to purge and solidify the surface of the hot-rolled substrate coated with the treatment liquid.

Furthermore, the purging and curing can be carried out using compressed air with a temperature of 20 to 100° C., a pressure of 0.1 to 1 MPa, and a dew point of less than or equal to -18° C.

Furthermore, when compressed air is used to blow the surface of the hot-rolled substrate coated with the treatment liquid, During curing, the time for film formation and surface drying is less than 10s.

Furthermore, when compressed air is used to blow and solidify the surface of the hot-rolled substrate coated with the treatment liquid, the time for the film to dry on the surface is 2 to 5 seconds.

In some embodiments, the strip speed during blowing is 10 to 100 m/min.

In the online modification method for the surface oxide scale of hot-rolled products described in the present invention, the obtained hot-rolled substrate is not subjected to complicated steps of removing the surface oxide scale such as sandblasting, shot peening, pickling, and descaling, but is directly subjected to the hot-rolled oxide scale surface to ensure that there is no dust, debris, or oil on the oxide scale surface.

In some embodiments of the present invention, coating the treatment liquid on the surface of the hot-rolled substrate is performed by an online continuous treatment method.

In some embodiments of the present invention, coating the treatment liquid on the surface of the hot-rolled substrate may be performed after the last surface treatment of the hot-rolled product, such as after the last straightening.

In some embodiments of the present invention, the treatment liquid coverage can also be detected by a surface tester or ultraviolet light irradiation.

Another object of the present invention is to provide a hot-rolled product whose oxide scale is not easy to fall off and whose surface is not easy to rust.

Based on the above-mentioned invention purpose, the present invention also provides a hot-rolled product, which is obtained by the online modification method of the surface oxide scale of the hot-rolled product as described above, and the hot-rolled product includes, from the inside to the outside in the thickness direction: a hot-rolled substrate, an oxide scale modified layer formed after the hot-rolled oxide scale is cross-linked and cured by the resin particles in the treatment liquid, and a treatment liquid protective coating.

In the hot-rolled product of the present invention, the oxide scale modified layer is a combination of resin particles and hot-rolled oxide scale. The resin particles penetrate into the oxide scale, seal the holes and cracks of the oxide scale through self-crosslinking reaction, and finally combine with the oxide scale and solidify into a film, forming an oxide scale modified layer containing resin particles and hot-rolled oxide scale. In addition, there is an extremely thin treatment liquid protective coating on the oxide scale modified layer, which is a resin film layer formed by the treatment liquid alone.

Furthermore, in the hot-rolled product described in the present invention, the thickness of the treatment liquid protective coating on the oxide scale modified layer is ≤3 microns.

Furthermore, in the hot-rolled product of the present invention, the oxide scale on the surface of the product after modification is not only enriched with Fe and O elements, but also has a C element enrichment significantly higher than that of conventional hot-rolled products due to the resin particles entering the oxide scale and forming a film.

Furthermore, in the hot-rolled product of the present invention, the enrichment degree of C element on the surface of the product is far It is higher than conventional hot-rolled products and much lower than conventional continuous organic coatings. After the treated steel plate is heated to above 500°C, the carbon volatilized from its surface is measured by high-frequency infrared absorption spectroscopy. Conventional hot-rolled plates with clean surfaces usually have less than 1 mg/ ^dm2 of carbon, and conventional continuous organic coatings can reach a minimum of 40 mg/ ^dm2 or more. The total carbon content in the surface oxide scale modification layer and the treatment liquid protective layer of the product obtained by the technical solution of the present application is 5-30 mg/ ^dm2 .

More preferably, the total carbon content in the scale modification layer and the treatment liquid protection layer of the hot-rolled product obtained by adopting the technical solution of the present application is 10-20 mg/dm ² .

The online modification method of the hot-rolled product surface oxide scale and the hot-rolled product of the present invention have the following advantages and beneficial effects:

The hot-rolled product described in the present invention has an oxide scale modified layer formed by oxide scale and treatment liquid on its surface. The oxide scale modified layer can fix the loose oxide scale particles on the surface of the strip to prevent the oxide scale from falling off, which can effectively slow down or even prevent the occurrence of rust on the surface of the strip, and will not affect subsequent welding, forming and further coating treatment.

Therefore, compared with conventional hot-rolled products, the hot-rolled products of the present invention can achieve:

The strip steel will not have black oxide particles falling off during normal handling and indoor storage, and can be touched by hand without pollution or residue. The strip steel has good corrosion resistance and will not have red rust or oxide scale falling off for 18 months in a conventional indoor storage environment. However, products that have not been modified usually have obvious rust in just 3 to 6 months.

The effect on welding is small. Under the premise of ensuring that there is no coating and scale on the welding surface, the coating has no significant effect on the welding quality. Compared with the parent material, the tensile strength decreases by no more than 5%. In addition, welding spatter does not adhere to the surface of the treated steel plate and can be easily removed without grinding, which can greatly reduce the workload of post-weld cleaning.

The protective layer formed by the oxide scale modification layer and the protective coating has a certain flexibility, can be tightly bonded to the surface of the strip, and can be bent 180° with the strip without breaking.

The protective layer has good compatibility with other treatment fluids and can be directly further coated during subsequent user use.

The protective layer thickness of the hot-rolled product of the present invention is extremely thin, and can be flame-cut without generating obvious smoke and odor, and does not affect laser cutting. While ensuring that the welding surface is free of coating, the joint quality is equivalent to that of the hot-rolled plate without coating.

In some preferred embodiments, the hot-rolled product of the present invention can be rapidly cured to form a film. The time may be less than 5 seconds, for example 2-5 seconds.

The present invention can avoid the problem of rust caused by the shedding of oxide scale during the production, storage and transportation of hot-rolled products, reduce the adverse effects on steel quality, user production environment and personnel health, and the temporary protective layer does not have a significant impact on the subsequent user use process, is easy to remove, and is more flexible to use.

In addition, compared with other protective measures in the storage and transportation of hot-rolled products, the present invention has the advantages of being easy to use and having good anti-rust effects. For example, conventional anti-rust oil requires the user to add a degreasing process; although anti-rust paper packaging can also delay rust, it will become ineffective once the packaging is removed, which places high demands on product use management.

Compared with conventional coating, the present invention does not need to remove the oxide scale and has better cost advantages. Not only that, conventional coating has extremely high requirements for welding, forming, handling, etc., and the coating must be repaired once it is damaged. The technical solution advocated by this patent has no special requirements for welding and forming. Because there is a subsequent coating operation, it is not sensitive to damage caused during the transportation process and is very easy to use. Not only that, the use of this patented technology can also realize continuous online processing of continuous strip steel on the hot rolling production line. There is no additional transportation, sandblasting and other links of conventional offline coating, which can greatly improve efficiency and save costs. At the same time, it can also avoid rusting of the product during transportation to the coating location, and realize continuous corrosion protection of hot-rolled products.

In addition, compared with conventional coating, the present invention is more green and low-carbon. Conventional coating regards hot-rolled oxide scale as a negative factor of coating, so it must be removed. Whether it is pickling or mechanical removal of oxide scale, it will inevitably increase carbon emissions and have an adverse effect on the plate shape. The hot-rolled oxide scale itself is mainly composed of iron oxides and has excellent corrosion resistance. It is only because of the holes and cracks on the surface that water and corrosive media pass through the oxide scale and enter the interior of the steel substrate that corrosion occurs. The method advocated by the present invention makes full use of the characteristics of hot-rolled oxide scale. Only a small amount of treatment liquid is required to penetrate into the interior of the oxide scale. After the emulsion is cured, the holes and cracks in the oxide scale are sealed, which makes up for the corrosion loopholes of the oxide scale, thereby achieving a multiplier effect. Since there is no need for pickling or sandblasting and shot blasting to remove scale, it has better low-carbon and environmental protection advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the continuous production equipment used in the online modification method of the oxide scale on the surface of hot-rolled products according to the present invention.

FIG. 2 schematically shows the structure of the hot rolled product according to the present invention.

FIG3 shows a photograph of the weld of Example 3.

FIG4 shows a photograph of the weld of Comparative Example 2.

DETAILED DESCRIPTION

The online modification method of the hot-rolled product surface oxide scale and the hot-rolled product described in the present invention will be further explained and illustrated below in conjunction with specific embodiments and the accompanying drawings of the specification. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

The hot-rolled products in Examples 1-6 of the present invention are prepared using the equipment shown in FIG1 based on the following steps:

S1: Obtain the hot-rolled substrate: The head of the hot-rolled product to be processed and the tail of the previous coil are welded together by a welding device 2, the hot-rolled product to be processed is uncoiled 1 and sent to a straightening machine 3 for straightening, and the plate shape of the strip to be processed is optimized to ensure that the surface flatness of the hot-rolled product meets the requirements of subsequent surface treatment operations.

Surface cleaning: The floating dust, oxide particles and oil stains on the surface of the straightened steel strip are cleaned by the surface cleaning device 4 to ensure that the surface cleanliness of the steel strip meets the surface treatment requirements. The present invention does not require pickling to remove oxide scale from the steel strip, and in most cases there is no oil stain on the surface of the hot-rolled product.

Specifically, in some embodiments, high-pressure water flow flushing or compressed air blowing can be used to clean and remove floating dust and oxide particles on the surface of the steel strip. If there is oil on the surface of the steel strip, a degreasing agent is used for degreasing.

It can be seen that the present invention eliminates the need for complex pre-coating treatment processes such as pickling and phosphating, which is beneficial to simplifying the process, reducing costs, reducing environmental pollution, and reducing resource consumption.

S2: Spraying and squeezing or roller coating the treatment liquid on the upper and lower surfaces of the hot-rolled substrate, which may include:

First, confirm that the surface of the strip meets the treatment requirements, then use the coating device 5 to evenly apply the treatment liquid on the surface of the hot-rolled product by spraying, brushing or roller coating, and use the squeeze roller 6 to help the treatment liquid penetrate into the oxide scale to form an oxide scale modified layer, and further spread on the surface of the oxide scale modified layer to form an extremely thin treatment liquid protective coating, the thickness of the treatment liquid protective coating does not exceed 3 microns. In this way, the resin particles in the treatment liquid enter the hot-rolled oxide scale, and self-crosslinking reaction occurs inside and on the surface of the oxide scale to form a film. In this embodiment, the time of the self-crosslinking reaction (i.e., the film formation time) is within 10 minutes.

In some embodiments, after applying the treatment liquid, the method may further include the following steps:

S3: Air drying and curing, using continuous air knife to continuously blow the upper and lower surfaces to promote rapid film formation.

In some more specific embodiments, clean compressed air 7 with a temperature of 20 to 100° C., a dew point below -18° C., and a pressure of 0.1 to 1 MPa can be used to continuously blow the surface of the steel strip to promote rapid solidification of the surface coating into a film. Such as Examples 1, 3, 4 and 6.

In some other embodiments, the method may further include the steps of:

S4: Surface detection: The curing degree, thickness, coverage, etc. of the oxide scale modified layer and the treatment liquid protective coating are detected to ensure that they are completely cured and no interlayer adhesion is formed during the winding and stacking process, so as to ensure that the strip is effectively covered and the thickness is within the ideal range. Among them, the degree of curing can be detected and judged by sampling the surface hardness or by finger touch method, cotton ball blowing method, and filter paper pressing method. The thickness of the oxide scale modified layer and the treatment liquid protective coating can be calculated based on the consumption of raw materials. The coverage of the oxide scale modified layer and the treatment liquid protective coating is irradiated by ultraviolet light to make the coating with added fluorescent color developer develop color. In some embodiments, an online surface detector 8 can be used to detect the coverage.

S5: Trimming and packaging: The hot-rolled products with the scale modification layer and the treatment liquid protective coating are trimmed, and the products are cut, packaged and stored according to the delivery form. If the delivery form is a steel coil, the strip is cut into strips after trimming. According to the surface inspection results of step 4, the unqualified parts of the strip surface inspection are recorded, repaired or directly downgraded, and then re-reeled, coded, packaged and stored. If the delivery form is a steel plate, the strip is trimmed, chamfered and trimmed to a fixed length. According to the surface inspection results, the unqualified parts of the strip surface inspection are cut off, and the cross-cutting is completed by the cross-cutting device 9, and the coding is performed by the printing device 10. The strip is packaged and stored through the stacking and packaging device 11, and the cut parts of the strip surface inspection that are unqualified are treated as waste.

In addition, the strip steel with the scale modification layer and the treatment liquid protective coating is no longer straightened before being shipped out of the warehouse to the user.

FIG2 schematically shows the structure of the hot-rolled product of the present invention. As shown in FIG2 , the hot-rolled product includes a hot-rolled substrate a, an oxide scale modified layer b formed by the combination of the hot-rolled oxide scale and the treatment liquid, and a treatment liquid protective coating c formed by the treatment liquid. Among them, the thickness of the treatment liquid protective coating c located on the outermost side is within 3 microns, for example, it can be 0.1-3 microns, and its function is to prevent water and other corrosive media from entering the interior. In addition, it can also stabilize the oxide scale to prevent it from falling off and forming black ash, and finally it can also avoid the adhesion of welding spatter. Inside the treatment liquid protective coating c is the oxide scale modified layer b formed by the combination of the oxide scale and the treatment liquid, which is the main body of the corrosion resistance, and the thickness can be from a few microns to tens of microns, which can provide the corrosion protection requirements of the hot-rolled product for indoor storage for 18 months. The innermost is the hot-rolled substrate c that needs to be protected.

The hot-rolled substrates used in Examples 1 to 6 of the present invention are all BS960E hot-rolled products. Table 1 lists the basic mechanical properties of BS960E hot-rolled products.

Table 1

Examples 1 to 6 respectively use treatment liquids made from different resin particles for coating. Table 2 lists the manufacturing process parameters used in Examples 1 to 6.

Table 2

Note: All components in the treatment solution are commercially available. 1-film-forming aid (alcohol ester film-forming aid), 2-fluorescent color developer (FW-200 water-based fluorescent color developer), 3-preservative (Kasong bactericidal preservative), 4-anti-flash rust agent (Tianyu D1600 anti-flash rust agent), 5-pH adjuster (AMP-95 pH adjuster).

It should be noted that, although not listed in the above embodiments 1-6, in other embodiments, it is also feasible to prepare the treatment liquid using one or a combination of epoxy, polyurethane, alkyd, acrylic, styrene acrylic, silicone acrylic and their modified resins. In addition, the film-forming aids, fluorescent color developers, preservatives, anti-flash rust agents and pH adjusters listed in the embodiments are only exemplary, and those skilled in the art can make conventional selections based on the actual resin used and actual production conditions.

In order to verify the effect of the present invention, various properties of the hot-rolled product samples of each embodiment prepared by the following method were tested.

1. Coating removal experiment

Take the hot-rolled product samples of Examples 1-6 and perform the following operations respectively: cut samples with a side length of 10 cm*10 cm by laser cutting, and divide each sample into a left area and a right area, that is, each area is 5 cm*10 cm. Use a wire brush to carefully remove the coating on the right area, and continuously use a UV lamp to irradiate and test during the process to ensure that the original oxide scale is just exposed.

The test results are: Since the coating is extremely thin, the flexible coating can be easily removed by manually scraping it with a wire brush dipped in water. Therefore, in practical applications, if you need to ensure good welding quality, you can use this method to clean the coating on the surface near the weld. The method of ultraviolet light irradiation can make the coating very clear. After observation, even in the exposed oxide scale after grinding, a very small amount of fluorescent bright spots or fluorescent thin lines of the coating can be seen under the irradiation of ultraviolet light with a magnifying glass, proving that the coating can penetrate into the oxide scale very well and fill the holes and cracks inside the oxide scale.

2. Oxide scale powder shedding test

After the above coating removal experiment, the right area surface of each sample is the exposed original oxide scale, and the left area surface is the coating. Then the following operations are performed: two white erasers are used to rub the right area and the left area respectively until a large amount of eraser crumbs appear.

The test results are: the rubber remains white and not contaminated, and the rubber crumbs are also white and not contaminated. This proves that the protective layer can effectively prevent the oxide scale powder from falling off the surface of the strip. For the uncoated sample, the same test was done, and the rubber turned black, and the rubber crumbs turned black, indicating that the oxide scale is very easy to fall off.

3. Coating thickness and surface carbon residue test

After the above-mentioned oxide scale powder shedding test, the sample was tested with a German FISCHER handheld coating thickness gauge to measure the thickness of the sample surface covering, that is, the left area is the total thickness of the treatment liquid protective coating and the oxide scale modified layer, and the right area is the thickness of the oxide scale modified layer (also known as the oxide scale). The measurement adopts the five-point averaging method, that is, the upper left, upper right, lower left, lower right and middle areas of the measurement area are averaged. The average thickness of the protective coating of the treatment liquid is estimated based on the difference between the mean thickness of the left area and the right area.

Another BS960 steel plate produced in the same manner but not treated with the treatment solution was taken as comparative example 1. The other production processes were exactly the same as those of the steel plate substrate in the example for comparison. The average thickness of the surface oxide scale was measured by the same method as above using a five-point average method.

Another BS960 steel plate produced in the same manner but not treated was taken. The other production processes were exactly the same as those of the steel plate substrate in the example. A single coat of Hempel 15280 shop primer was sprayed on its surface. This sample was used as comparative example 2. The average thickness of the shop primer and the oxide scale on the steel plate surface was measured by the same method as above.

Next, the carbon residue on the surface of all the above-mentioned examples and comparative example samples was measured at 500 degrees Celsius using a LECORC-412 multiphase carbon water analyzer. The above-mentioned thickness measurement results are shown in Table 3.

Table 3

It can be seen from Table 3 that the thickness of the treatment liquid protective coating of the hot-rolled product with the corrosion-resistant layer according to the present invention is ≤3 μm.

The sample plates 16 of Examples 1, 2, and 5 were bent 180° in the vertical direction using an elbow with a diameter of 5 mm. The left area has a corrosion-resistant layer (i.e., including an oxide scale modification layer and a treatment liquid protective coating), and the right area is an exposed oxide scale. When observing the bend in the left area of the sample, no damage or peeling of the flexible coating was found.

Subsequently, the samples of Examples 1-6 were exposed and placed indoors. After 18 months, no obvious surface corrosion was found in the area where the adhesion test was not performed, and slight corrosion was found in the area where the outermost water-based coating was removed after the adhesion test. This shows that the corrosion-resistant layer can effectively slow down and prevent the generation and development of corrosion.

4. Welding performance test

The hot-rolled products of Examples 1 to 6 were taken again and butt-welded. The welding process was as follows: the groove was a 60° V-shaped groove, the gap width at the bottom of the groove was 1.5-2 mm, the blunt edge height was about 1.5 mm, argon-enriched gas shielded welding was adopted, the shielding gas was 80% Ar+20% CO ₂ , the burrs on the cut were cleaned before welding, but the oxide scale and protective coating on other surfaces were retained, and the welding wire was an ultra-high strength argon-enriched gas shielded welding wire. During the welding process, no significant effect of the coating on the welding was found, there was no smoke or odor during the process, and the welding spatter did not adhere and was easy to remove.

The performance of the welded joints of the welded plates obtained above was evaluated by the following method:

(1) Appearance inspection: According to the requirements of ISO 15614, the appearance of the welded joints was inspected. The inspection results showed that the welds of all weld plates were well formed, and there were no visible cracks, undercuts, pores, poor fusion and other defects on the front and root of the welds.

(2) Tensile test: According to ISO 15614, the welded joints were tested. Two tensile, bending and impact test pieces were processed for each weld plate, and the welds were reinforced and polished. Table 4 lists the tensile test results of the welded joints obtained in each embodiment.

Table 4

It can be seen from Table 4 that the tensile properties of the welded joints of the hot-rolled products with corrosion-resistant layers have no significant change, the joints are all broken in the welding heat-affected zone, and the tensile strength value is not less than 95% of the minimum value of the parent material. According to the NB/T47016 standard, the test results of the welded joints are all qualified.

(3) Bending test. All welded joints were then subjected to a 180-degree bending test using a 6a bending diameter according to ISO 15614. All welded joints were found to be qualified without cracking.

(4) Impact test. The welded joints were subjected to CVN impact tests according to ISO 15614. The test temperature was -40°C and the test results met the standard requirements.

This proves that applying treatment liquid on the surface of hot-rolled products has almost no significant effect on the butt welding performance of the hot-rolled products, and the quality of the welded joints can also meet the relevant requirements of ISO 15614.

In order to compare and verify the influence on welding, the welding experiment with coating on the groove was carried out on the samples of Examples 1 to 6 and Comparative Example 1. The specific method is: take the samples of Examples 1 to 6 and Comparative Examples 1 and 2, first open the groove, and then treat the groove position according to Table 2 respectively. The thickness of the protective coating at the groove of the embodiment is 0.5 to 1.5um, the groove of Comparative Example 1 is uncoated, and the thickness of Hempel 15280 shop primer of Comparative Example 2 is 10 to 15um. Then, butt welding is carried out according to the above method, and then the appearance is observed, and tensile, bending and impact tests are carried out.

After observation, no abnormality was found in the welds of Examples 1 to 6 and Comparative Example 1, no abnormality was found in the molten pool, no salt spray odor was found during welding, and no bubbles were visible to the naked eye on the weld surface. FIG3 is a photograph of the weld of Example 3.

For comparison, two samples of comparative example 2 were overlapped and welded, and the surface coating of the overlapped steel plates was not polished. Obvious smoke appeared during welding, a large number of bubbles appeared in the molten pool, and multiple bubbles of about 10 mm appeared in the weld, making it difficult to weld, as shown in Figure 4.

Comparative Example 2 has lost the significance of tensile, bending and impact tests, so only the joints of all examples and Comparative Example 1 were subjected to relevant experiments. The tensile test results of all examples showed no abnormality, no obvious strength reduction, and the fracture positions were all in the heat-affected zone, which was consistent with Comparative Example 1 without any treatment. The welded joints of all examples and Comparative Example 1 were subjected to 6a bending core diameter according to ISO 15614 requirements. In the 180-degree bending test, all welded joints did not crack and were qualified. All welded joints except for comparative example 2 were subjected to CVN impact tests according to ISO 15614 requirements, with the test temperature at -40°C, and the test results all met the standard requirements.

In summary, the comparative example 2 represents a conventional coating of extremely thin specifications, but it still has a significant and fatal effect on welding without grinding. On the contrary, the steel plate treated by the technology of the present application has no significant effect on welding without grinding. In terms of weldability, the technical solution of the present application is significantly better than even the thinnest conventional shop primer and significantly better than the existing coating solution.

The above test results prove that the hot-rolled product with a corrosion-resistant layer described in the present invention provides effective protection for the hot-rolled product in the production, storage and transportation links by forming an oxide scale modified layer composed of an oxide scale and a treatment liquid on the surface of the hot-rolled product, which can prevent the oxide scale from falling off and the strip surface from rusting, thereby reducing the adverse effects on user production and the environment. At the same time, the oxide scale modified layer and the treatment liquid protective coating have almost no obvious effect on the subsequent welding, forming, painting and other processes of the hot-rolled product, and can partially replace the pretreatment workshop primer in some application scenarios, saving costs for users.

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 (15)

A hot-rolled product, characterized in that the hot-rolled product comprises, from inside to outside in the thickness direction: a hot-rolled substrate, an oxide scale modified layer formed after the hot-rolled oxide scale is modified by resin cross-linking and curing, and a protective coating formed by resin on the surface of the oxide scale modified layer; preferably, the hot-rolled product is a hot-rolled strip, more preferably a continuously hot-rolled strip. The hot-rolled product according to claim 1 is characterized in that the resin is selected from at least one of the following: epoxy resin, polyurethane resin, alkyd resin, acrylic resin, styrene acrylic resin, silicone acrylic resin, and modified resins of the above. The hot-rolled product according to claim 1 or 2, characterized in that the thickness of the scale modification layer is 1.0 to 30.0 microns, and/or the thickness of the protective coating is 0.1 to 3.0 microns. The hot rolled product according to claim 1 or 2, characterized in that the hot rolled product has the following characteristics: after heating it to 500°C, the amount of carbon volatilized from its surface measured by high frequency infrared absorption spectroscopy is 5-30 mg/ ^dm2 . A method for online modification of oxide scale on the surface of hot-rolled products, characterized in that it comprises the steps of: Obtaining a hot-rolled substrate, wherein the hot-rolled substrate has a hot-rolled oxide scale on its surface; A treatment liquid containing resin particles is coated on the surface of the hot-rolled substrate, so that the resin particles in the treatment liquid enter the hot-rolled oxide scale and undergo a self-crosslinking reaction inside and on the surface of the oxide scale to form a film. The method for online modification of surface oxide scale of hot-rolled products as described in claim 5 is characterized in that the particle size of the resin particles is less than or equal to 1 μm, preferably less than or equal to 0.2 μm. The online modification method of the surface oxide scale of hot-rolled products as described in claim 5 is characterized in that the resin particles are selected from at least one of the following: epoxy resin, polyurethane resin, alkyd resin, acrylic resin, styrene acrylic resin, silicone acrylic resin, and modified resins of the above. The method for online modification of hot-rolled product surface oxide scale as described in claim 5 is characterized in that the treatment liquid also includes: one or more of a film-forming aid, a fluorescent color developer, a preservative, an anti-flash rust agent, and a pH adjuster. The method for online modification of the surface scale of hot-rolled products according to claim 5 is characterized in that the treatment liquid satisfies at least one of the following conditions: solid content is 1% to 60%, preferably 10% to 60%, preferably 20% to 60% or 1% to 30%; viscosity is ≤ 2000 mPa.s, preferably 1 to 2000 mPa.s, more preferably 1-200 mPa.s; pH value is 6-9. The method for online modification of hot-rolled product surface oxide scale as described in claim 5 is characterized in that the surface drying time of the treatment liquid for self-crosslinking reaction is within 10 minutes without human intervention. The method for online modification of the oxide scale on the surface of hot-rolled products as described in claim 5 is characterized in that it also includes the step of using compressed air to blow and solidify the surface of the hot-rolled substrate coated with the treatment liquid. The online modification method of the oxide scale on the surface of hot-rolled products as described in claim 11 is characterized in that the purging and curing is carried out using compressed air with a temperature of 20 to 100°C, a pressure of 0.1 to 1 MPa, and a dew point of less than or equal to -18°C. The method for online modification of the oxide scale on the surface of a hot-rolled product as described in claim 11 or 12 is characterized in that when compressed air is used to blow and solidify the surface of the hot-rolled substrate coated with the treatment liquid, the surface drying time of the film is less than 10 seconds, preferably 2 to 5 seconds. A hot-rolled product, characterized in that it is obtained by the online modification method of the surface oxide scale of the hot-rolled product as described in any one of claims 5 to 13, and the hot-rolled product comprises, from the inside to the outside in the thickness direction: a hot-rolled substrate, an oxide scale modified layer formed after the hot-rolled oxide scale is cross-linked and cured by resin particles in a treatment liquid, and a treatment liquid protective coating. The hot-rolled product according to claim 14, characterized in that the thickness of the treatment liquid protective coating is ≤ 3 microns.