Adaptability optimization treatment process for hot dipping of hot-rolled strip steel

Abstract

The invention belongs to the technical field of post-treatment processes of hot-rolled strip steel, and relates to a hot-rolled strip steel hot dipping suitability optimization treatment process which comprises the following steps: performing acid-free phosphorus removal treatment on hot-rolled strip steel to remove surface oxide skin and rust, and preliminarily regulating and controlling the surface roughness of the hot-rolled strip steel; carrying out impact plating treatment on the hot-rolled strip steel subjected to acid-free phosphorus removal treatment so as to further regulate and control the surface roughness of the hot-rolled strip steel; and carrying out hot dipping treatment on the hot-rolled strip steel subjected to the impact plating treatment. Through cooperation of the acid-free phosphorus removal treatment process and the impact plating treatment process, the hot-rolled strip steel can be directly used for hot dipping, the cold rolling procedure is omitted, the short process is achieved, and meanwhile hot dipping of the thick strip steel is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of post-processing technology of hot-rolled strip steel, and relates to an adaptability optimization processing technology for hot-dip plating of hot-rolled strip steel. Background Art

[0002] Cold-rolled sheets have good surface quality and can be directly used for hot-dip coating. However, due to the thickness and cost of cold-rolled sheets, they can no longer meet the demand for anti-corrosion performance of thick steel plates in photovoltaic brackets, agricultural animal husbandry, underground pipe galleries and other fields. Hot-rolled strip steel is cheap and easy to obtain, and has excellent machinability and is suitable for bending. In addition, the thickness of hot-rolled strip steel is thicker than that of cold-rolled sheets. Hot-dip coating can meet the demand for thicker and more corrosion-resistant steel plates.

[0003] However, the oxide film on the surface of the hot-rolled strip covers the surface of the steel plate, so it cannot be directly subjected to post-processing processes such as painting, electroplating, and hot-dip plating. The removal of the oxide scale on the surface of the hot-rolled strip is mainly done by pickling, which will produce waste acid, waste gas, and solid waste during the process, thereby polluting the environment and increasing the carbon emissions of the steel plant; and the pickling process will also produce typical process defects such as over-pickling, under-pickling, parking spots, and hydrogen embrittlement; in addition, after pickling, oxide scale marks will still be left on the edge of the surface, which cannot be completely covered by the coating after hot-dip plating, resulting in surface color difference defects; as a result, if the hot-rolled strip wants to improve the coating performance and surface quality through further post-processing, it needs to be pickled or further cold rolled, but this undoubtedly increases the equipment cost and post-processing cost, and pollutes the environment.

[0004] The surface quality and thickness of the hot-dip coating are directly affected by the surface state of the substrate, especially the wettability and bonding strength of the substrate to the coating. 2 Al 5 Poor formation of the inhibition layer causes surface defects such as dezincification and missed plating. The current methods for dephosphorization of hot-rolled strip before hot-dip plating include pickling and hydrogen reduction. U.S. Patent No. US20140377585A1 discloses high-manganese hot-rolled galvanized steel sheet and its manufacturing method. Low-aluminum hot-dip galvanizing is performed on 5%-35% high-Mn steel hot-rolled strip. The inner oxide layer of different thicknesses is obtained by controlling the coiling temperature of the hot-rolled coil, but the subsequent pickling process is also required for hot-dip plating. U.S. Patent No. US6258186B1 discloses a high-speed manufacturing method for hot-rolled galvanized steel sheet without pickling. The surface oxide of the hot-rolled strip is rapidly cooled in the middle and reduced with hydrogen to obtain an FeO content of more than 20% in the oxide, and then hot-dip plating is performed. However, in this patent, Al is limited to 0.2-5wt.% in order to form Fe-Al-Zn compounds, so it is only suitable for low-aluminum coating dip plating. At the same time, since the main component of the oxide scale of the hot-rolled strip is Fe 3 O4 Therefore, the hydrogen reduction time is long and the production efficiency cannot keep up with the production line speed. The surface roughness after hydrogen reduction is high, and the active inhibition layer cannot be formed during the subsequent hot dip plating, so the bonding strength of the coating is poor.

[0005] With the improvement of anti-corrosion performance, the coating composition of hot dip plating is constantly developing. Low aluminum coating can no longer meet the demand. Medium aluminum and high aluminum coatings are more and more widely used because of their better corrosion resistance and mechanical properties. However, the pickling and hydrogen reduction methods of hot dip plating of hot rolled strip are only applicable to the low aluminum series. Therefore, it is urgent to propose a new adaptability optimization treatment process for hot dip plating of hot rolled strip. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide an adaptability optimized treatment process for hot dip plating of hot rolled strip, which directly performs hot dip plating after acid-free surface dephosphorization and impact plating of the hot rolled strip, thereby reducing the cold rolling process, thereby realizing a short process for post-processing of the strip, and making the hot rolled steel plate product have both the high formability of the hot rolled steel plate and the high corrosion resistance of the coated steel plate.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A process for optimizing the adaptability of hot-dip galvanizing of hot-rolled strip steel comprises the following steps:

[0009] The hot-rolled steel strip is subjected to acid-free dephosphorization treatment to remove the surface scale and rust, and the surface roughness of the hot-rolled steel strip is preliminarily adjusted;

[0010] The hot-rolled steel strip after the acid-free dephosphorization treatment is subjected to impact plating treatment to further control the surface roughness of the hot-rolled steel strip;

[0011] The hot-rolled steel strip after the impact plating treatment is subjected to hot-dip plating treatment.

[0012] The present invention performs acid-free dephosphorization on the hot-rolled strip to remove oxide scale and rust on the surface of the hot-rolled strip, and selects an adaptive impact plating process according to the roughness obtained by the acid-free dephosphorization process to improve the metallurgical reaction between the substrate (the surface of the hot-rolled strip) and the plating solution, inhibit the dissolution and diffusion of the substrate into the plating solution, and improve the wettability of hot-dip plating and the bonding strength of the coating.

[0013] Furthermore, the hot-rolled steel strip is formed by flattening and welding the hot-rolled steel coil.

[0014] Furthermore, the plate thickness of the hot-rolled steel coil is 0.6 mm-30 mm.

[0015] Further, according to the composition, oxide scale thickness and oxide morphology of the hot-rolled steel strip, one or more of the dephosphorization technologies selected from the group consisting of plasma dephosphorization technology, water + abrasive mixed jet dephosphorization technology, grinding roller scouring dephosphorization technology and wet shot blasting dephosphorization technology are used to perform acid-free dephosphorization on the hot-rolled steel strip, and the surface roughness grade of the hot-rolled steel strip after the acid-free dephosphorization treatment is controlled to be Ra 1-4, and the surface has no work hardening. In view of the different thickness of the oxide scale on the surface of the hot-rolled steel strip, any one or more combinations of the above acid-free dephosphorization technologies can be selected.

[0016] The chemical composition of hot rolled steel strip has a significant impact on the thickness, type and morphology of its oxide scale. For example, when the steel strip contains chromium (Cr), the chromium element can react chemically with oxygen to form chromium trioxide (Cr 2 O 3 ). The chromium trioxide can inhibit the formation and growth of oxide scale, thereby reducing the thickness of the oxide scale. In addition, the chromium trioxide will further react with iron (Fe) oxide to form iron chromium oxide (FeCr 2 O 4 ), this substance can further improve the density of the oxide scale and enhance the bonding force between the oxide scale and the strip steel matrix. For this type of chromium-containing strip steel, when choosing acid-free phosphorus removal technology, it is advisable to adopt a phosphorus removal process with a large mechanical force to effectively destroy the bonding force between the oxide scale and the coating and achieve efficient phosphorus removal. When the strip steel contains silicon (Si) elements, during the oxidation process of the strip steel, the silicon elements will segregate to the interface between the oxide scale and the strip steel matrix, and react with iron oxides to form a complex silicate phase. The formation of these silicate phases will promote the growth of the oxide scale, resulting in an increase in the thickness of the oxide scale. At the same time, the silicate phase and the iron oxide are intertwined, which increases the brittleness of the oxide scale. For the oxide scale of strip steel containing silicon elements, plasma phosphorus removal technology can be used. This technology is suitable for small-batch production. Although the production rhythm is slightly slow, it can meet the production needs with high requirements for the surface quality of the strip steel.

[0017] Furthermore, when performing acid-free phosphorus removal, the operating speed of the unit is 10-200 m / min.

[0018] Further, according to the different surface roughness of the hot-rolled strip after the acid-free dephosphorization treatment and the different dephosphorization speed during the acid-free dephosphorization treatment, the impact plating treatment is performed by using a nickel impact plating process, an iron impact plating process or an iron alloy impact plating process, and the current density of the impact plating is 1-40A / dm 2 ; According to the different surface roughness of the hot-rolled strip after dephosphorization, the different oxide forms and the difference in the coating composition of the hot-dip plating, the adaptability of the impact plating process is selected, and the current density, plating time and operating speed of the production line are selected.

[0019] According to the different surface roughness of the hot-rolled steel coil after dephosphorization and the different coating composition, the adaptability of the impact plating process is selected. After the steel plate is treated with acid-free dephosphorization technology, its surface roughness varies due to differences in process parameters, treatment time and the material of the steel plate itself. The surface roughness essentially reflects the degree of fluctuation of the microscopic surface of the steel plate. This fluctuation is directly related to the interaction between the hot-dip plating solution and the steel plate substrate during the hot-dip plating process. When the surface roughness of the steel plate is high, the fluctuation of its microscopic surface forms a large number of microscopic gullies and protrusions, which greatly increases the actual contact area between the impact plating and the substrate. From the perspective of chemical reaction kinetics, a larger contact area means more active sites, and the reaction activity between the metal ions in the plating solution and the steel plate substrate is significantly enhanced. In this case, the selection of a rapid deposition impact plating process has obvious advantages. As the deposition process continues, these rapidly deposited metal atoms gradually fill the microscopic gullies on the surface, making the surface gradually flat, thereby effectively reducing the roughness of the steel plate surface. At the same time, a certain coating thickness can be achieved in a relatively short time, meeting the requirements for coating thickness and surface quality for subsequent use. On the contrary, for steel plates with lower surface roughness, their microscopic surfaces are relatively smooth, the contact area between the impact plating solution and the substrate is relatively small, and the reaction activity is relatively weak. In this case, if a fast deposition impact plating process is used, the diffusion speed of the plating solution on the surface cannot keep up with the deposition speed, resulting in uneven coating, and even local accumulation or leakage of the coating. Therefore, for steel plates with lower roughness, it is more appropriate to choose an impact plating process with a slow deposition speed. This process can be achieved by reducing the metal ion concentration in the plating solution, reducing the plating solution temperature, or reducing the current density. In the slow deposition process, the plating solution has enough time to diffuse and react evenly on the surface of the steel plate, and the metal ions can be deposited on the substrate surface more orderly, thereby obtaining a smoother coating surface. At the same time, the slow deposition process is also conducive to the formation of a dense and uniform coating structure, improving the corrosion resistance and adhesion of the coating.

[0020] Furthermore, the hot-dip coating treatment is hot-dip galvanizing, alloyed galvanizing, hot-dip galvanized aluminum-magnesium or hot-dip aluminum-zinc.

[0021] Furthermore, the hot-rolled steel strip after the hot-dip galvanizing treatment is subjected to passivation and spraying treatment.

[0022] The beneficial effects of the present invention are:

[0023] The present invention provides an adaptability optimization treatment process for hot-dip plating of hot-rolled strip steel. Through the coordination of an acid-free dephosphorization treatment process and an impact plating treatment process, the hot-rolled strip steel can be directly used for hot-dip plating, thereby eliminating the cold rolling process, realizing a short process, and realizing hot-dip plating of thick-gauge strip steel.

[0024] Secondly, by adjusting the parameters of the acid-free dephosphorization and impact plating processes, the wettability and bonding strength of the hot-dip coating can be regulated, thereby achieving hot-dip plating of various coating components to meet diversified anti-corrosion needs;

[0025] Finally, the acid-free dephosphorization process uses physical methods to remove surface oxide scale and attachments without the use of harmful chemicals such as strong acids. The treatment process is more environmentally friendly, with no waste acid, waste gas or solid waste generated, and saves the investment in environmental protection equipment. The cleaned steel coils do not have typical process defects of pickling such as over-pickling, under-pickling, parking spots, hydrogen embrittlement, etc., thereby ensuring the product quality of hot-rolled strip after hot-dip galvanizing.

[0026] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 The present invention is a continuous production process in which the hot-rolled steel strip is directly used for hot-dip plating;

[0029] Figure 2 This is one of the continuous production flow charts of hot-rolled steel strip for hot-dip coating in the embodiment;

[0030] Figure 3 This is the second continuous production flow chart of hot-rolled strip for hot-dip coating in the embodiment. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0032] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0033] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0034] See also Figure 1 , which is an adaptability optimization treatment process for hot-dip galvanizing of hot-rolled strip steel, specifically comprising the following steps:

[0035] S001. The hot-rolled steel coil is flattened and welded to form a hot-rolled strip;

[0036] In this step, the hot-rolled steel coil is placed on the unwinding machine, so that the coil is continuously unwound and welded to form a hot-rolled steel strip. In addition, in this embodiment, the hot-rolled steel coil raw material requires: the plate thickness is between 0.6mm-30mm.

[0037] S002. Perform acid-free dephosphorization on the hot-rolled strip to remove the surface scale and rust, and preliminarily adjust the surface roughness of the hot-rolled strip;

[0038] In this embodiment, one or more dephosphorization technologies including plasma dephosphorization technology, water + abrasive mixed jet dephosphorization technology, grinding roller scouring dephosphorization technology, and wet shot blasting dephosphorization technology can be used to perform acid-free dephosphorization on the hot-rolled strip according to the state of the hot-rolled strip and the limitations of the production line.

[0039] S003. Impact plating treatment of the hot-rolled strip after dephosphorization;

[0040] In this embodiment, the surface of the hot-rolled strip after acid-free dephosphorization is relatively smooth, which solves the problem of uneven surface of the previous hot-rolled strip. However, when the surface roughness is too large, it will affect the distribution of Al in the coating and the formation of the inhibition layer, thereby affecting the uniformity and adhesion of the coating structure. At this time, matching the impact plating process can further regulate the surface roughness of the hot-rolled strip and improve the wettability of the hot-dip plating solution and the strip, thereby reducing the surface defects of the hot-dip plating and greatly affecting the surface quality and performance. In addition, for hot-dip plating components with a higher aluminum content, the impact plating can prevent the formation of surface oxides at high temperatures and improve the quality and performance of the coating.

[0041] S004. hot-dip galvanizing the hot-rolled strip after impact galvanizing;

[0042] In this embodiment, the hot-dip coating of the hot-rolled steel sheet after impact plating can be selected from one of hot-dip zinc, zinc-iron, zinc-aluminum and zinc-magnesium-aluminum;

[0043] S005 performs subsequent passivation, spraying and other treatments on the hot-dip galvanized hot-rolled strip.

[0044] Specifically, the surface roughness level after acid-free dephosphorization is Ra 1-4, and there is no work hardening on the surface;

[0045] Optionally, according to the different characteristics of the hot-rolled strip dephosphorization device, the running speed of the hot-rolled strip is different, and different impact plating processes are selected for adaptability selection; in this embodiment, the running speed of the unit is 10-200m / min;

[0046] The hot-rolled steel strip after dephosphorization is subjected to impact plating treatment, wherein the impact plating treatment includes an impact nickel plating process, an impact iron plating process and an impact iron alloy plating process, and different grain sizes, thicknesses and surface roughnesses are obtained by selecting different current densities and plating times;

[0047] Preferably, in this embodiment, the current density of the impact plating is 1-40A / dm 2 The current density is changed from large to small to achieve the grain size change, so that the surface roughness of the hot-rolled strip after impact plating can be selected; through the matching of acid-free dephosphorization and impact plating processes, the inhibition layer of the hot-dip coating can be regulated, thereby regulating the thickness of the hot-dip coating.

[0048] Example 1

[0049] See also Figure 2 , in order to optimize the adaptability of hot-rolled steel strip for hot-dip galvanizing directly, the process steps are to flatten and weld the hot-rolled steel coil to obtain the hot-rolled steel strip, then perform plasma dephosphorization, then perform impact plating, and then enter the hot-dip galvanizing process;

[0050] In this embodiment, the surface roughness of the hot-rolled steel strip after dephosphorization by plasma dephosphorization is Ra3, and the nickel plating process is combined with the impact plating process, and the current density of the nickel plating process is 20A / dm 2 , thereby reducing the overall surface roughness of the hot-rolled strip to Ra1.9, and then performing a hot-dip coating process, and the hot-dip coating process is hot-dip galvanizing and aluminum coating.

[0051] Specifically, in the present embodiment, the power of the plasma in the plasma dephosphorization method is 30 kW, a mixed gas of argon and hydrogen is used with a volume ratio of 9:1 to bombard the hot-rolled silicon steel coil, and the speed of the plasma dephosphorization is 10 m / min.

[0052] Example 2

[0053] See also Figure 3 , in order to optimize the adaptability of hot-rolled steel strip directly for hot-dip plating, the process steps are to flatten and weld the hot-rolled steel coil, then perform a grinding roller scouring and dephosphorization method, then perform an impact plating process, and then enter the hot-dip plating process step;

[0054] In this embodiment, the surface roughness of the hot-rolled steel strip after dephosphorization by grinding roller scouring is Ra1.5, and the current density of the iron plating process is 10A / dm 2 , thereby reducing the overall surface roughness to Ra1.0, and then performing a hot dip plating process, and the hot dip plating process is hot dip plating of low aluminum zinc aluminum magnesium.

[0055] Specifically, in this embodiment, the grinding roller scouring dephosphorization method uses a tungsten carbide grinding roller, and the roller speed is adjusted to 1500rpm and the pressure is 15N / m 2 , the phosphorus removal speed is 15m / min.

[0056] Example 3

[0057] In order to optimize the adaptability of hot-rolled steel strip directly for hot-dip galvanizing, the process steps are to flatten and weld the hot-rolled steel coil, then perform wet shot blasting and dephosphorization, then perform impact galvanizing, and then enter the hot-dip galvanizing process;

[0058] In this embodiment, the wet shot blasting dephosphorization process is to use a mixture of 0.8 mm ceramic shot and water to spray the oxide scale of the hot-rolled steel coil of the structural steel. The spraying speed is 80 m / s, the spraying pressure is 0.5 MPa, the spraying time is 40 s, and the surface roughness of the steel plate after spraying is Ra1. The nickel plating process of the impact plating is matched, and the process current density is 5 A / dm 2 , thereby reducing the overall surface roughness to Ra0.8, and then performing a hot dip coating process, and the hot dip coating process is hot dip coating of aluminum zinc aluminum magnesium.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A process for optimizing the adaptability of hot-dip galvanizing of hot-rolled steel strip, characterized in that: The following steps are involved: The hot-rolled steel strip is subjected to acid-free dephosphorization treatment to remove the surface scale and rust, and the surface roughness of the hot-rolled steel strip is preliminarily adjusted; The hot-rolled steel strip after the acid-free dephosphorization treatment is subjected to impact plating treatment to further control the surface roughness of the hot-rolled steel strip; The hot-rolled steel strip after the impact plating treatment is subjected to hot-dip plating treatment.

2. The process for optimizing the adaptability of hot-dip galvanizing of hot-rolled steel strip according to claim 1, characterized in that: The hot-rolled steel strip is formed by flattening and welding the hot-rolled steel coil.

3. The process for optimizing the adaptability of hot-dip plating of hot-rolled steel strip according to claim 2, characterized in that: The plate thickness of the hot-rolled steel coil is 0.6 mm-30 mm.

4. The process for optimizing the adaptability of hot-dip plating of hot-rolled steel strip according to claim 1, characterized in that: According to the composition, oxide thickness and oxide morphology of the hot-rolled strip, one or more dephosphorization technologies including plasma dephosphorization technology, water + abrasive mixed jet dephosphorization technology, grinding roller scouring dephosphorization technology and wet shot blasting dephosphorization technology are used to carry out acid-free dephosphorization treatment on the hot-rolled strip, and the surface roughness grade of the hot-rolled strip after the acid-free dephosphorization treatment is controlled to be Ra 1-4, and there is no work hardening on the surface.

5. The process for optimizing the adaptability of hot-dip plating of hot-rolled steel strip according to claim 4, characterized in that: When performing acid-free phosphorus removal, the unit operates at a speed of 10-200m / min.

6. The process for optimizing the adaptability of hot-dip plating of hot-rolled steel strip according to claim 4, characterized in that: According to the different surface roughness of the hot-rolled strip after acid-free dephosphorization treatment and the different dephosphorization speed during the acid-free dephosphorization treatment, one of the impact nickel plating process, the impact iron plating process or the impact iron alloy plating process is used for impact plating treatment, and the current density of the impact plating is controlled to be 1-40A / dm 2 .

7. The process for optimizing the adaptability of hot-dip plating of hot-rolled steel strip according to claim 4, characterized in that: The hot-dip treatment is hot-dip galvanizing, alloyed galvanizing, hot-dip galvanized aluminum-magnesium or hot-dip aluminum-zinc.

8. The process for optimizing the adaptability of hot-dip plating of hot-rolled steel strip according to claim 1, characterized in that: The hot-rolled strip after hot-dip galvanizing is passivated and sprayed.

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