WO2023217022A1 - Ultralow-carbon cold-rolled high-strength steel applicable to electrostatic dry powder enamel, and manufacturing method therefor - Google Patents

Abstract

Disclosed in the present invention are an ultralow-carbon cold-rolled high-strength steel applicable to electrostatic dry powder enamel, and a manufacturing method therefor. The ultra-low carbon cold-rolled high-strength steel of the present invention contains Fe, inevitable impurity elements and the following chemical elements by mass percentages: 0.002~0.010% of C, Si≤0.05%, 0.25~1.0% of Mn, 0.04~0.08% of P, 0.01~0.04% of S, 0.01~0.05% of Al, 0.02~0.08% of Cu, 0.05~0.12% of Ti, 0.02~0.10% of Mo and 0.004~0.012% of N, each chemical element satisfying at least one of the following formulas: M*＞0, M*＝Ti-S×1.5-N×3.4-C×4＞0, N*≥0.012, and N*＝(Mn+P)×Mo. The ultra-low carbon cold-rolled high-strength steel of the present invention can meet the requirements of electrostatic dry powder double-sided enamel for fish-scaling resistance performance, enamel adherence performance and enamel surface quality.

Description

Ultra-low carbon cold-rolled high-strength steel suitable for electrostatic dry powder enamel and manufacturing method thereof Technical field

The present invention relates to a steel plate and a manufacturing method thereof, in particular to a low-carbon cold-rolled high-strength steel plate and a manufacturing method thereof.

Background technique

As we all know, enamel products are made of metal and glassy inorganic materials fired at high temperatures. It combines two materials with completely different properties, metal and glassy inorganic materials, and becomes a whole to eliminate their respective shortcomings. Compensate each other to better reflect their respective strengths.

For example: when the enamel layer of an enamel product is impacted by the outside world, the metal has high strength and can withstand this external force, so that the product is protected from damage or damaged. When the enamel product is chemically corroded, the enamel layer can It plays a protective role to prevent metal materials from being damaged or scrapped due to corrosion. Therefore, enamel products have the excellent properties of a series of metal and glassy inorganic materials.

Enamel steel products are a composite material formed by cladding glassy inorganic materials on the surface of steel plates. In recent years, they have been widely used in light industry, home appliances, environmental protection and construction industries, and are used to prepare ovens, water heaters, bathtubs, etc. , denitrification equipment (SCR), air preheater (APH) and flue gas heater (GGH) for thermal power plants, building decorative panels, various enamel plate assembled storage tanks and other products.

In the current preparation of enameled steel, the enamel coating methods are mainly divided into two types: wet enamel coating and dry enamel coating. Among them, the coating method of applying glaze slurry on the metal body is called wet coating. There are three basic methods of wet coating: dip coating, spray coating and flow coating. Dry enamel coating mainly refers to electrostatic dry powder enamel coating. This method uses the high-voltage generation principle through an electrostatic spray gun. Under a voltage of 70 to 100kV, the gun head forms a negatively charged electrostatic field. The workpiece to be sprayed is grounded and the workpiece is in the spray room. When it passes through the spray gun, the spray gun starts spraying powder. The positively charged workpiece and the negatively charged powder are attracted to each other to form a powder coating.

Among the above-mentioned enamel coating methods, the surface quality of enamel steel made by electrostatic dry powder enamel is the best, but this process also has higher requirements for the base steel plate.

This is because the porcelain layer obtained by the enamel method of electrostatic dry powder enamel is more dense. The hydrogen generated during the process is more difficult to escape, so scale explosion defects are more likely to occur. In addition, because the electrostatic dry powder enamel layer is thin (usually less than 200 μm), defects such as bubbles and pinholes are prone to appear on the enamel surface, which affects the surface quality. Therefore, during design and development, steel plates suitable for electrostatic dry powder enamel need to have excellent resistance to scale explosion, pinholes and bubble defects.

In addition, it should be noted that in addition to excellent anti-scaling performance, anti-pinhole and bubble defect performance, the steel plates used to prepare enamel products also need to have high yield strength and durability in specific applications. The strength decreases slightly after high-temperature enameling. This is because, with the continuous progress of the enamel industry, the quality of enamel products is also constantly improving. For example, in the field of manufacturing enamel steel plates for building decorative panels, in order to reduce splicing and improve aesthetics, larger format enamel steel plates need to be produced. However, because this type of enamel steel plate has strict requirements on the shape of the plate, and the larger the size of the workpiece, the more likely it is to have deformation problems during the high-temperature enameling process. This requires that the steel plate for enamel as the substrate must have sufficient resistance to high-temperature deformation. , to ensure that no serious deformation occurs after high temperature enameling at 840~870℃.

To this end, in order to meet the current market demand, the present invention hopes to obtain an ultra-low carbon cold-rolled high-strength steel suitable for electrostatic dry powder enamel. This ultra-low carbon cold-rolled high-strength steel can meet the various uses of electrostatic dry powder double-sided enamel. The requirements are that there will be no scale defects after enamelling, and the porcelain layer and the steel plate are closely adhered to each other, and the enamel surface quality is excellent. At the same time, this ultra-low carbon cold-rolled high-strength steel has a yield strength of more than 200MPa. After high-temperature calcination at 840-870°C, the yield strength decreases within 10%, which can avoid deformation problems after high-temperature calcination and significantly improve the final result. Improve the strength of enamel products, obtain excellent performance, and extend the service life of enamel products.

In the prior art, although there are already some manufacturing technologies for cold-rolled enamel steel suitable for electrostatic dry powder enamel, they are still different from the steel with specific strength and performance requirements of the present invention, and their chemical composition design is still different. There are significant differences.

For example: the publication number is CN101356295A, the publication date is January 28, 2009, and the Chinese patent document titled "A continuously cast enamel steel plate with significantly excellent scale explosion resistance and its manufacturing method" discloses a scale-resistant steel plate. The chemical element composition of the continuously cast enamel steel plate with significantly excellent explosiveness and its manufacturing method is designed to be: C: 0.010% or less, Mn: 0.03 to 1.30%, Si: 0.100% or less, Al: 0.030% or less, N: 0.0055 % or less, P: 0.035% or less, S: 0.08% or less, O: 0.005 to 0.085%, B: 0.0003 to 0.0250%, there are non-integrated or integrated oxides with different mass concentrations of B or Mn in the steel plate.

Another example: the public number is CN105518174A, the public date is April 20, 2016, and the name is The Chinese patent document "A cold-rolled steel plate for enamel, its manufacturing method and enamel products" discloses a cold-rolled steel plate for enamel, its manufacturing method and enamel products. Its chemical element composition is designed to be: C: 0.0005~0.0050% , Mn: 0.05～1.50%, Si: 0.001～0.015%, Al: 0.001～0.01%, N: 0.0010～0.0045%, O: 0.0150～0.0550%, P: 0.04～0.10%, S: 0.0050～0.050%, Nb: 0.020 to 0.080%, Cu: 0.015 to 0.045%, and the balance is Fe and impurities.

Another example: the publication number is CN106560523A, the publication date is April 12, 2017, and the Chinese patent document titled "Cold-rolled steel plate for enamel and its manufacturing method" discloses a cold-rolled steel plate for enamel and its manufacturing method. Its chemical element composition is designed to be: C: 0.005% or less (except 0%), Mn: 0.05% to 0.3%, Al: 0.005% or less (0% excluded), P: 0.03% or less (0% excluded), S: 0.02% or less (excluding 0%), Si: 0.01% or less (excluding 0%), Ti: 0.005% to 0.01%, Y: 0.01% to 0.02%, N: 0.003% or less (excluding 0%), the balance is Fe and other inevitable impurities.

Contents of the invention

One of the purposes of the present invention is to provide an ultra-low carbon cold-rolled high-strength steel suitable for electrostatic dry powder enamel. This ultra-low carbon cold-rolled high-strength steel can meet the various usage requirements of electrostatic dry powder double-sided enamel. There are no scale defects, and the porcelain layer and the steel plate are closely adhered to each other, and the enamel surface quality is excellent. At the same time, this ultra-low carbon cold-rolled high-strength steel has a yield strength of more than 200MPa. After high-temperature calcination at 840-870°C, the yield strength decreases within 10%, which can avoid deformation problems after high-temperature calcination and significantly improve the final result. Improve the strength of enamel products, obtain excellent performance, and extend the service life of enamel products.

The ultra-low carbon cold-rolled high-strength steel of the present invention can be widely used in large-format architectural decorative enamel panels, bathtubs, and other products that require electrostatic dry powder enamel and have high yield strength performance requirements after enamelling, and has very significant application value. .

In order to achieve the above object, the present invention provides an ultra-low carbon cold-rolled high-strength steel suitable for electrostatic dry powder enamel, which contains Fe and inevitable impurity elements, and also contains the following chemical elements in the following mass percentages:

C: 0.002～0.010%, Si≤0.05%, Mn: 0.25～1.0%, P: 0.04～0.08%, S: 0.01～0.04%; Al: 0.01～0.05%, Cu: 0.02～0.08%, Ti: 0.05 ~0.12%, Mo: 0.02~0.10%, N: 0.004~0.012%;

Each chemical element satisfies at least one of the following formulas:

M*>0, where M*=Ti-S×1.5-N×3.4-C×4;

N*≥0.012, where N*=(Mn+P)×Mo;

Each chemical element in the formula is substituted into the value before the mass percentage sign of the chemical element.

Further, in the ultra-low carbon cold-rolled high-strength steel of the present invention, the mass percentage content of each chemical element is:

C: 0.002～0.010%, Si≤0.05%, Mn: 0.25～1.0%, P: 0.04～0.08%, S: 0.01～0.04%; Al: 0.01～0.05%, Cu: 0.02～0.08%, Ti: 0.05 ~0.12%, Mo: 0.02~0.10%, N: 0.004~0.012%; the balance is Fe and inevitable impurity elements;

Each chemical element satisfies at least one of the following formulas:

M*>0, where M*=Ti-S×1.5-N×3.4-C×4;

N*≥0.012, where N*=(Mn+P)×Mo;

Each chemical element in the formula is substituted into the value before the mass percentage sign of the chemical element.

In the ultra-low carbon cold-rolled high-strength steel of the present invention, the design principles of each chemical element are as follows:

C: In the ultra-low carbon cold-rolled high-strength steel of the present invention, all C elements can be combined with strong carbide-forming elements such as Ti or Nb to form fine and dispersed precipitated phases. These precipitated phases can effectively improve the hydrogen storage performance of the steel plate, thereby playing the role of the enamel in resisting scale explosion. At the same time, nanoscale TiC and other precipitated phases can also play a precipitation strengthening role. However, it should be noted that the content of C element should not be too high, and its addition amount should not be excessive relative to the alloying elements. This is because when enamel is fired, excess free carbon will cause a large amount of CO and other gases to be generated during the enamel firing process. These gases will cause poor bubble structure in the enamel layer, resulting in defects such as pinholes and bubbles, which will affect the surface quality of the enamel. In the electrostatic dry powder enamel process, this effect is even greater. Therefore, considering the influence of C element content on steel properties, in the ultra-low carbon cold-rolled high-strength steel of the present invention, the mass percentage content of C element is controlled between 0.002% and 0.010%.

Si: In the ultra-low carbon cold-rolled high-strength steel of the present invention, the Si element is a residual element. When the Si element content in the steel is too high, the plasticity of the steel will deteriorate. In addition, during the enamel process, higher Si element content will also affect the adhesion between the steel plate and the enamel. Therefore, in the ultra-low carbon cold-rolled high-strength steel of the present invention, the mass percentage content of Si element is controlled to Si≤0.05%. In some embodiments, the mass percentage of Si is 0.01-0.05% or 0.01-0.045%.

Mn, P: In the ultra-low carbon cold-rolled high-strength steel of the present invention, both Mn and P elements are the main solid solution strengthening elements. Usually, in steels with high content of Ti and P elements, TiFe(P) precipitate phase will be formed, and this precipitate phase will tend to segregate and precipitate at the ferrite grain boundaries, resulting in poor mechanical properties of the material. In the technical solution of the present invention, the TiFe(P) phase is avoided by controlling the hot rolling final rolling temperature and coiling temperature. precipitation temperature range, thereby avoiding the occurrence of this situation and allowing the P element to only play a solid solution strengthening role. At the same time, it should also be considered that too high a P element will lead to the formability and secondary brittleness of the material. Therefore, in the ultra-low carbon cold-rolled high-strength steel of the present invention, the mass percentage of the Mn element is limited to Between 0.25% and 1.0%, the mass percentage of P element is limited to between 0.04% and 0.08%.

S: Usually in steel with more Mn elements added, the S element will combine with the Mn element to form strips and linear MnS inclusions. Such inclusions will cause the mechanical properties of the material to deteriorate. In the ultra-low carbon cold-rolled high-strength steel of the present invention, because a higher content of Ti element is added, the Ti element will promote the formation of spherical or polygonal TiMn(S) inclusions, which will instead improve the Mechanical properties of materials. In addition, in this technical solution, the S element mainly combines with Ti and C in steel to form Ti4C2S2 and TiS precipitated phases or inclusions. These precipitated phases or inclusions formed in steel can serve as irreversible hydrogen storage traps and play a role in enamel's resistance to scale explosion. Therefore, in order to exert the beneficial effects of S element, in the present invention, the mass percentage content of S element is controlled between 0.01% and 0.04%.

Mo: In the ultra-low carbon cold-rolled high-strength steel of the present invention, molybdenum can be solid dissolved in ferrite, austenite and carbide to play a solid solution strengthening effect; in addition, molybdenum can also improve TiC and NbC The stability of carbides can be reduced by reducing the aggregation and coarsening of carbide precipitates caused by high-temperature enameling (usually the enameling temperature reaches 840 to 870°C), thereby improving the high-temperature stability of steel and preventing The problem of a significant decrease in the yield strength of steel plates due to weakened precipitation strengthening. However, it should be noted that the content of Mo element in steel should not be too high. Adding excessive Mo element will significantly increase the manufacturing cost. Therefore, in the ultra-low carbon cold-rolled high-strength steel of the present invention, the mass percentage of Mo element is limited to between 0.02% and 0.10%.

Al: In the ultra-low carbon cold-rolled high-strength steel of the present invention, Al is a strong deoxidizing element. In order to keep the O content in the steel at a low value, Al is often used for deoxidation in medium-low carbon steel. In addition, the dissolved Al element in the steel can also combine with free nitrogen to precipitate A1N. Its precipitation temperature is relatively high, which can refine the austenite grains and is beneficial to grain refinement and fine grain strengthening. Therefore, in order to exert the beneficial effects of Al element, in the present invention, the mass percentage content of Al element is limited to between 0.01% and 0.05%.

Ti: In the ultra-low carbon cold-rolled high-strength steel of the present invention, Ti is the main element that enables the steel to obtain good hydrogen storage performance. The Ti element in the steel can form fine, dispersed particles under appropriate controlled rolling and cooling processes. TiC and Ti (C, N) precipitated phases, these precipitated phases act as irreversible hydrogen storage traps and can improve the hydrogen storage performance of the steel plate, thus exerting the anti-scaling effect of enamel. However, too high Ti element in steel will cause the material to form The performance deteriorates and the cost increases. Therefore, taking into account the mechanical properties and cost factors of the steel, in the ultra-low carbon cold-rolled high-strength steel of the present invention, the mass percentage of the Ti element is limited to between 0.05 and 0.12%. .

Cu: In the ultra-low carbon cold-rolled high-strength steel of the present invention, the Cu element will be deposited at the bonding interface between the enamel and the steel during the high-temperature enameling process, thereby improving the adhesion between the steel and the enamel and thereby improving the steel material. Anti-scaling properties. However, the Cu element content in steel should not be too high. When the Cu element content in steel is too high, it will also lead to poor formability of the material and increased cost. Therefore, taking into account the mechanical properties and cost factors of steel, in the present invention, the mass percentage content of Cu element is limited to 0.02-0.08%.

N: In the ultra-low carbon cold-rolled high-strength steel of the present invention, the main function of the N element is to form inclusions such as TiN, NbN or Ti (C, N), Nb (C, N) and other alloying elements such as Ti and Nb. substances or precipitated phases, thereby playing the role of enamel's hydrogen storage trap in resisting scale explosion. In addition, the nitride inclusions will be partially broken during the cold rolling process, thereby forming tiny holes around them, which are also very important and effective hydrogen storage traps. Based on this, in order to exert the beneficial effects of the N element, the mass percentage of the N element in the ultra-low carbon cold-rolled high-strength steel of the present invention is limited to 0.004 to 0.012%.

In the above technical solution of the present invention, while controlling the mass percentage of a single chemical element in the steel, the present invention can also control the elements in the steel to satisfy "M*>0, where M*=Ti-S×1.5-N ×3.4-C×4” limited relationship. The inventor found through experimental research that when the element content in the steel meets the above-mentioned limiting relationship, it can ensure that the C and N interstitial atoms in the steel are completely fixed, thereby ensuring that the structure of the steel is a single ferrite. After the steel plate with this structural characteristic is electrostatic dry powder enamel, the enamel surface quality is excellent and there are no defects such as pinholes or bubbles. In some embodiments, 0.001≤M*≤0.02. In some embodiments, 0.001≤M*≤0.013.

Correspondingly, while controlling the mass percentage of a single chemical element in steel, the present invention can also control the elements in the steel plate for pressure vessels to satisfy the requirement of "N*≥0.012, where N*=(Mn+P)×Mo" Qualified relationship. The inventor found through experimental research that when this limiting relationship is satisfied, the steel plate can be guaranteed to have a yield strength of more than 200MPa, and after high-temperature enamel treatment, the steel plate still maintains a higher yield strength value, which is higher than the original strength. The decline is within 10%. In some embodiments, 0.012≤N*≤0.10. In some embodiments, 0.012≤N*≤0.06.

Furthermore, the ultra-low carbon cold-rolled high-strength steel of the present invention may also contain: B≤0.003%, and Nb≤0.06%.

Furthermore, in the ultra-low carbon cold-rolled high-strength steel of the present invention, its chemical elements also contain at least one of the following items: B: 0.0006~0.003%; Nb: 0.02~0.06%.

In the present invention, in order to obtain ultra-low carbon cold-rolled high-strength steel with better performance, in some embodiments, appropriate amounts of B and Nb elements can be further added.

Nb: In the technical solution of the present invention, the Nb element can be combined with C and N elements to form fine NbC, NbN and other precipitated phases. Of course, Nb can also be attached to the previously formed TiC precipitated phase to form (Nb, Ti) Phase C. These precipitated phase particles can serve as irreversible hydrogen storage traps, play a role in enamel's resistance to scale explosion, and can also play a role in precipitation strengthening. In addition, these precipitate phase particles can effectively inhibit the deformation recrystallization of austenite and prevent its grain growth during the hot rolling process, thus playing a role in grain refinement and strengthening. Therefore, in order to exert the beneficial effects of Nb element, a small amount of Nb can be preferably added to the ultra-low carbon cold-rolled high-strength steel of the present invention, and the mass percentage of Nb element is limited to between 0.02 and 0.06%. .

B: In the technical solution of the present invention, adding an appropriate amount of B element can form B (C, N) in the steel plate, increase the second phase particles, and increase the number of hydrogen traps, thereby improving the scale explosion resistance of the steel plate. performance. In addition, B (C, N) can also play the role of crystal nucleation, which is beneficial to the formation of equiaxed crystals and prevents grain growth, which is beneficial to improving the coating performance and mechanical properties of the steel plate. Therefore, in the ultra-low carbon cold-rolled high-strength steel of the present invention, a small amount of B can be preferably added, and the mass percentage of the B element is controlled between 0.0006 and 0.003%.

Further, in the ultra-low carbon cold-rolled high-strength steel according to the present invention, the microstructure is single ferrite.

In the ultra-low carbon cold-rolled high-strength steel designed by the present invention, the matrix of the microstructure is single ferrite, and TiN, TiC, Ti(C, N), Nb(C, N) are dispersed in the matrix. ) and other inclusions or precipitated phases.

Further, in the ultra-low carbon cold-rolled high-strength steel of the present invention, the ferrite grain size is 9 to 11 levels.

Further, in the ultra-low carbon cold-rolled high-strength steel according to the present invention, the thickness is 0.7 to 3.5 mm.

Furthermore, in the ultra-low carbon cold-rolled high-strength steel of the present invention, its properties meet the following requirements: yield strength ≥ 200MPa, tensile strength ≥ 400MPa, elongation ≥ 30%, and yield after being calcined at high temperature of 840 to 870°C. The decrease in intensity is less than 10%.

Further, in the ultra-low carbon cold-rolled high-strength steel according to the present invention, its performance satisfies: yield strength ≥220MPa, tensile strength ≥410MPa, elongation ≥34%. After enamelling at 840~870℃ for 5 minutes, the yield strength decreases by less than 6.5%.

Further, in the ultra-low carbon cold-rolled high-strength steel of the present invention, after enameling at 840-870°C for 5 minutes, its properties meet: yield strength ≥ 210 MPa, tensile strength ≥ 370 MPa, elongation ≥ 34% .

Accordingly, another object of the present invention is to provide a method for manufacturing ultra-low carbon cold-rolled high-strength steel plates suitable for electrostatic dry powder enamel. The manufacturing method has a simple production process and can effectively prepare the above-mentioned ultra-low carbon steel plates of the present invention. Carbon cold-rolled high-strength steel plate has good adaptability to enamel coating and can be effectively applied to electrostatic dry powder enamel.

In order to achieve the above object, the present invention proposes a manufacturing method of the above-mentioned ultra-low carbon cold-rolled high-strength steel, which includes the steps:

(1) Smelting and casting;

(2) Heating of cast slab;

(3) Hot rolling;

(4) Laminar cooling: control the cooling rate to 10~30°C/s to cool the steel plate to the coiling temperature;

(5) Coiling: The coiling temperature is 600~680℃, and then air cooled to room temperature;

(6) Pickling;

(7) Cold rolling;

(8) Annealing;

(9) Smooth.

In the present invention, the casting process of the above-mentioned step (1) can be implemented by a continuous casting process, which can ensure uniform internal composition of the cast slab and good surface quality. Of course, in some other embodiments, the mold casting process can also be used for casting, and the molded steel ingot also needs to be rolled by a blooming mill to form a steel billet.

Further, in the manufacturing method of the present invention, in step (2), the heating temperature is controlled to be 1180-1260°C.

Further, in the manufacturing method of the present invention, in step (3), the heated billet is first rough rolled into an intermediate billet, and then the intermediate billet is finished rolled, wherein the rough rolling temperature is controlled at 900°C. Above, such as 900~1080℃; the opening temperature of finishing rolling is 900~1050℃, and the finishing temperature of finishing rolling is 860~940℃.

In the manufacturing method designed by the present invention, by controlling the hot rolling controlled rolling and controlled cooling process of step (3) and step (4), it can be ensured that the steel material of the present invention obtains a fine ferrite grain structure, so as to Improve the yield strength of steel plates through grain refinement strengthening. In addition, it is also beneficial to obtain finely dispersed precipitation phases of alloy elements such as Ti and Nb, thereby improving the scale resistance of the steel plate. In addition, it can also effectively avoid the formation of TiFe(P) precipitate phase, which tends to segregate and precipitate at the ferrite grain boundaries and will lead to poor mechanical properties of the material.

Furthermore, in the manufacturing method of the present invention, in step (7), the cold rolling reduction rate is controlled to be 70 to 95%.

In the above step (7), the cold rolling reduction rate can be controlled between 70 and 95%. As the cold rolling reduction rate increases, on the one hand, the recrystallization temperature of the steel can be reduced, and on the other hand, it is beneficial to Tiny cavities are formed around the inclusions or precipitated phases in the steel, which increases the hydrogen storage performance of the steel and thereby improves the enamel scale explosion resistance of the steel plate.

Further, in the manufacturing method of the present invention, in step (8), continuous annealing is used, and the annealing temperature is 770 to 830°C.

Further, in the manufacturing method of the present invention, in step (8), bell annealing is adopted, and the annealing temperature is 690 to 740°C.

In the present invention, the annealing process can adopt a continuous annealing process or a bell annealing process as needed. When the continuous annealing process is adopted, the continuous annealing temperature can be controlled to be 770-830°C; and when the bell annealing process is adopted, the cover annealing process can be controlled. The formula annealing temperature is 690~740℃. This can ensure sufficient recrystallization and texture development, which is conducive to obtaining good processing and forming properties of the steel plate.

Accordingly, after completing the annealing process in step (8), the steel plate or steel strip needs to be flattened to improve the shape and surface quality of the steel plate or steel strip.

Compared with the existing technology, the ultra-low carbon cold-rolled high-strength steel and its manufacturing method suitable for electrostatic dry powder enamel according to the present invention have the following advantages and beneficial effects:

Compared with the existing technology, in the present invention, the inventor designed a brand-new chemical composition design, which uses a specific composition ratio of P, Mn, and Mo, and a composition of Ti alloy elements and C, S, and N. Distribution ratio, combined with a specific hot rolling controlled rolling and cooling process, as well as cold rolling and annealing processes, can effectively prepare an ultra-low carbon cold-rolled high-strength steel suitable for electrostatic dry powder enamel. This ultra-low carbon cold-rolled high-strength steel can While having high yield strength performance, it can also meet the anti-scaling performance, enamel adhesion performance, and enamel surface quality requirements of electrostatic dry powder double-sided enamel.

The ultra-low carbon cold-rolled high-strength steel prepared using the technical solution of the present invention has a yield strength of more than 200MPa, and after being enameled at a high temperature of 840 to 870°C, the yield strength decreases within 10%, which can avoid high-temperature enamelling. It solves the problem of steel plate deformation after firing, significantly improves the strength of the final enamel product, and extends the service life of the enamel product.

In summary, it can be seen that the ultra-low carbon cold-rolled high-strength steel designed in the present invention can be widely used in large-format architectural decorative enamel panels that require electrostatic dry powder enamel and have high yield strength performance requirements after enamelling. product, which has very significant application value.

Description of the drawings

Figure 1 is a photo of the metallographic structure of the ultra-low carbon cold-rolled high-strength steel in Example 1.

Figure 2 is a photograph of the precipitation phase in the ultra-low carbon cold-rolled high-strength steel of Example 1.

Detailed ways

The ultra-low carbon cold-rolled high-strength steel suitable for electrostatic dry powder enamel and its manufacturing method according to the present invention will be further explained and described below in conjunction with specific embodiments and description drawings. However, this explanation and description do not limit the scope of the present invention. The technical solution constitutes an inappropriate restriction.

Examples 1-8 and Comparative Examples 1-2

The ultra-low carbon cold-rolled high-strength steel plates of Examples 1-8 of the invention and the comparative steel plates of Comparative Examples 1-2, which are suitable for electrostatic dry powder enamel, are prepared by the following steps:

(1) Smelting and casting according to the chemical composition shown in Table 1-1 and Table 1-2: The smelted molten steel is subjected to vacuum degassing and then continuously cast to obtain a continuous casting billet.

(2) Cast slab heating: Heat the obtained continuous cast slab and control the heating temperature to 1180~1260°C.

(3) Hot rolling: First, the heated billet is roughly rolled into an intermediate billet, and then the intermediate billet is finished. The rough rolling temperature is controlled to be above 900°C, the finishing rolling opening temperature is 900~1050°C, and the finishing rolling temperature is controlled to be above 900°C. The final rolling temperature is 860~940℃.

(4) Laminar flow cooling: Perform laminar flow water cooling and control the cooling rate to 10~30°C/s to cool the steel plate to the coiling temperature.

(5) Coiling: Control the coiling temperature to 600~680℃, and then air cool to room temperature.

(6) Pickling: remove the oxide scale on the surface of the steel plate.

(7) Cold rolling: Control the cold rolling reduction rate to 70 to 95%.

(8) Annealing: Use continuous annealing or bell annealing for annealing. When continuous annealing is used, the annealing temperature is controlled between 770 and 830°C; when bell annealing is used, the annealing temperature is controlled between 690 and 740°C. between ℃.

It should be noted that in the present invention, the chemical composition design and related processes of the ultra-low carbon cold-rolled high-strength steel designed by the inventor in Examples 1-8 all meet the design specification requirements of the present invention. Although the comparative steel plates of Comparative Examples 1-2 were also prepared using the above-mentioned steps (1)-(8), there are parameters in the chemical composition design and related processes that do not meet the design requirements of the present invention.

Table 1-1 and Table 1-2 list the mass percentages of each chemical element in the ultra-low carbon cold-rolled high-strength steel of Example 1-8 and the comparative steel plate of Comparative Example 1-2.

Table 1-1. (wt%, the balance is Fe and other unavoidable impurities)

Table 1-2.

Note: In the above table, the calculation formula of M* is "M*=Ti-S×1.5-N×3.4-C×4", and the calculation formula of N* is "N*=(Mn+P)×Mo". In the above two relational expressions, the elements in the formula are substituted into the value before the percentage sign of the mass percentage of the element.

Table 2 lists the specific process parameters of the ultra-low carbon cold-rolled high-strength steel of Examples 1-8 and the comparative steel plate of Comparative Examples 1-2 in steps (1)-(8) of the above manufacturing method.

Table 2.

In order to further prove the performance of the ultra-low carbon cold-rolled high-strength steel plates of Examples 1-8 of the present invention suitable for electrostatic dry powder enamel and the comparative steel plates of Comparative Examples 1-2 after enameling. The inventor took samples of the ultra-low carbon cold-rolled high-strength steel of Examples 1-8 and the comparative steel plate of Comparative Examples 1-2 obtained through the above process steps, and performed enamel treatment.

The enamel treatment includes: performing double-sided electrostatic dry powder enamel treatment on the sample steel plates of each example and comparative example: using Flow Company's TR1042 enamel, and controlling the enamel temperature to 840-870°C, holding for 5 minutes, and then air-cooling to obtain the enamel The final enameled steel plate. In the present invention, the ultra-low carbon cold-rolled high-strength steel of Examples 1-8 and the comparative steel plate of Comparative Examples 1-2 can be subjected to enamel treatment to obtain corresponding enamel steel plates.

After completing the above operations, observe and test the enameled steel plates of Examples 1-8 and Comparative Examples 1-2 that have been enameled. That is, let the enameled steel plates stand for 48 hours to observe the enamel surface quality; use a drop weight test. The adhesion performance between the steel plate and the enamel is verified and rated; a tensile test is used to determine the room temperature tensile properties of the steel plates of each example and comparative example before and after enameling.

Relevant performance testing methods and means are as follows:

(1) Tensile test: Conduct the tensile test in accordance with GB/T 228.1-2010 "Metal Materials Tensile Test Method at Room Temperature", use the SCL233 normal temperature tensile testing machine to conduct the test, control the tensile speed to 3mm/min, and perform the tensile test. The samples are JIS5 tensile specimens to test and obtain the yield strength, tensile strength and elongation of each example and comparative example.

It should be noted that when conducting the above tensile test, two test groups were designed. One group of plates was the enameled steel plates obtained after enameling in Examples 1-8 and Comparative Examples 1-2, and the other group was the enameled steel plates of the present invention. The original ultra-low carbon cold-rolled high-strength steel of Examples 1-8 and the comparative steel plate of Comparative Examples 1-2 were prepared. Through these two test groups, the room temperature tensile properties of the steel plates of each example and comparative example before and after enameling can be measured.

(2) Drop weight test and adhesion performance rating: According to the drop weight test method described in the European standard BS EN 10209-1996, use the corresponding drop weight test device to test Examples 1-8 and Comparative Example 1 obtained after enameling -2 enamel steel plates are tested and rated for enamel adhesion performance.

Table 3 lists the mechanical properties of the plates of Examples 1-8 and Comparative Examples 1-2 before enamel treatment, as well as the test results of the enamel properties and mechanical properties of the enameled steel plates obtained after enamel treatment of each Example and Comparative Example.

table 3.

As shown in Table 3 above, in the present invention, the yield strength of the original plate of the ultra-low carbon cold-rolled high-strength steel in Examples 1-8 is between 223 and 246 MPa, its tensile strength is between 418 and 449 MPa, and its elongation Rate A50 is between 34-38%. These ultra-low carbon cold-rolled high-strength steels of Examples 1-8 after high-temperature calcination treatment The mechanical properties are still excellent, the yield strength decreases between 3.04 and 6.38%, and the yield strength is still above 200MPa and between 212-230MPa.

Correspondingly, when the enamel surface of the enamel steel plates of Examples 1-8 was observed after 48 hours, it was found that no scale explosion occurred in any of these enamel steel plates, and no pinholes or bubble defects occurred on the surface. In addition, in accordance with the European standard BS EN 10209:2013, the drop weight test of the enamel steel plates prepared corresponding to Examples 1-8 found that the adhesion between the steel plate and the porcelain layer was excellent, reaching A1 level.

However, the performance of the comparative steel plate of Comparative Example 1-2 is significantly inferior to that of the ultra-low carbon cold-rolled high-strength steel plate of Example 1-8. The composition of the comparative steel in Comparative Example 1 does not meet the N* value design requirements of the present invention. Its yield strength before and after enamelling is relatively low. The yield strength before enamelling is 183MPa. After high-temperature enamelling, the yield strength decreases by 12.57%. %, reduced to 160MPa. At the same time, the composition of the steel in Comparative Example 2 did not meet the M* value design requirements of the present invention, and its enamel surface quality was poor, with a large number of pinholes and bubble defects (>200/m ² ).

Figure 1 is a photo of the metallographic structure of the ultra-low carbon cold-rolled high-strength steel in Example 1.

As shown in Figure 1, in this embodiment, the metallographic structure of the ultra-low carbon cold-rolled high-strength steel of Example 1 is a ferrite structure with the characteristics of IF steel structure, and the grain size of its ferrite is according to The GB/T 6394-2017 standard evaluation is level 10.

Figure 2 is a photograph of the precipitation phase in the ultra-low carbon cold-rolled high-strength steel of Example 1.

It can be seen from Figure 2 that the morphology and distribution of the precipitated phases in the matrix of the ultra-low carbon cold-rolled high-strength steel of Example 1. As shown in Figure 2, in this embodiment, there are a large number of finely dispersed precipitates such as TiC, Ti(C, N), Nb(C, N) in the ultra-low carbon cold-rolled high-strength steel of Example 1, and their distribution in steel matrix.

It should be noted that the combination of each technical feature in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All the technical features recorded in this case can be freely combined in any way or combination, unless there is a conflict between them.

It should also be noted that the embodiments listed above are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and subsequent similar changes or deformations that those skilled in the art can directly derive from the disclosed content of the present invention or can easily associate them should all fall within the protection scope of the present invention. .

Claims (15)

1. An ultra-low carbon cold-rolled high-strength steel suitable for electrostatic dry powder enamel contains Fe and inevitable impurity elements. It is characterized in that it also contains the following chemical elements in the following mass percentages:

   C: 0.002～0.010%, Si≤0.05%, Mn: 0.25～1.0%, P: 0.04～0.08%, S: 0.01～0.04%; Al: 0.01～0.05%, Cu: 0.02～0.08%, Ti: 0.05 ~0.12%, Mo: 0.02~0.10%, N: 0.004~0.012%;

   Each chemical element satisfies at least one of the following formulas:

   M*>0, where M*=Ti-S×1.5-N×3.4-C×4>0;

   N*≥0.012, where N*=(Mn+P)×Mo;

   Each chemical element in the formula is substituted into the value before the mass percentage sign of the chemical element.
2. The ultra-low carbon cold-rolled high-strength steel as claimed in claim 1, characterized in that the mass percentage of each chemical element is:

   C: 0.002～0.010%, Si≤0.05%, Mn: 0.25～1.0%, P: 0.04～0.08%, S: 0.01～0.04%; Al: 0.01～0.05%, Cu: 0.02～0.08%, Ti: 0.05 ~0.12%, Mo: 0.02~0.10%, N: 0.004~0.012%; preferably, Si: 0.01%-0.045%; the balance is Fe and inevitable impurity elements;

   Each chemical element satisfies at least one of the following formulas:

   M*>0, where M*=Ti-S×1.5-N×3.4-C×4>0;

   N*≥0.012, where N*=(Mn+P)×Mo;

   Each chemical element in the formula is substituted into the value before the mass percentage sign of the chemical element.
3. The ultra-low carbon cold-rolled high-strength steel according to claim 1 or 2, characterized in that its chemical elements also contain at least one of the following items: B: 0.0006~0.003%; Nb: 0.02~0.06%.
4. The ultra-low carbon cold-rolled high-strength steel according to claim 1 or 2, characterized in that its microstructure is single ferrite.
5. The ultra-low carbon cold-rolled high-strength steel according to claim 4, characterized in that the ferrite grain size is 9 to 11.
6. The ultra-low carbon cold-rolled high-strength steel according to claim 1 or 2, characterized in that its thickness is 0.7 to 3.5 mm.
7. The ultra-low carbon cold-rolled high-strength steel according to claim 1 or 2, characterized in that its performance satisfies: The yield strength is ≥200MPa, the tensile strength is ≥400MPa, and the elongation is ≥30%. After enamelling at 840-870°C, the decrease in yield strength is less than 10%. Preferably, the enamel holding time is 5 minutes.
8. The ultra-low carbon cold-rolled high-strength steel according to claim 7, characterized in that its performance satisfies: yield strength ≥ 220MPa, tensile strength ≥ 410MPa, elongation ≥ 34%, and is enameled at 840-870°C for 5 minutes. Afterwards, the yield strength decreased by less than 6.5%.
9. The ultra-low carbon cold-rolled high-strength steel according to claim 1 or 2, characterized in that, after being enameled at a temperature of 840-870°C for 5 minutes, its properties meet: yield strength ≥ 210 MPa, tensile strength ≥ 370 MPa, elongation ≥34%.
10. The manufacturing method of ultra-low carbon cold-rolled high-strength steel according to any one of claims 1-9, characterized in that it includes the steps:

    (1) Smelting and casting;

    (2) Heating of cast slab;

    (3) Hot rolling;

    (4) Laminar cooling: control the cooling rate to 10~30°C/s to cool the steel plate to the coiling temperature;

    (5) Coiling: The coiling temperature is 600~680℃, and then air cooled to room temperature;

    (6) Pickling;

    (7) Cold rolling;

    (8) Annealing;

    (9) Smooth.
11. The manufacturing method according to claim 10, characterized in that in step (2), the heating temperature is controlled to be 1180-1260°C.
12. The manufacturing method according to claim 10, characterized in that, in step (3), the heated slab is first rough rolled into an intermediate billet, and then the intermediate billet is finished rolled, wherein the rough rolling temperature is controlled at 900 ℃ or above, preferably 900 to 1080 ℃, the finishing rolling starting temperature is 900 to 1050 ℃, and the finishing rolling temperature is 860 to 940 ℃.
13. The manufacturing method according to claim 10, characterized in that in step (7), the cold rolling reduction rate is controlled to be 70-95%.
14. The manufacturing method according to claim 8, characterized in that in step (8), continuous annealing is adopted, and the annealing temperature is 770-830°C.
15. The manufacturing method according to claim 10, characterized in that, in step (8), bell annealing is adopted, and the annealing temperature is 690-740°C.