Preparation method of cold-rolled high-strength enameled steel, cold-rolled high-strength enameled steel and application thereof

Abstract

The present application discloses a preparation method of cold-rolled high-strength enameled steel, cold-rolled high-strength enameled steel and application. The preparation method comprises: providing molten steel: C: 0.02%-0.08%, Si≤0.5%, Mn: 0.2%-0.8%, P≤0.03%; S≤0.03%, Al≥0.015%, Ti: 0.02%-0.08%, Nb: 0.005%-0.03%, N≤0.01%, Ti-3.4×N-1.5×S≤0, Cu≤0.05%, the remainder being Fe and unavoidable impurities; continuously heating the molten steel; Casting to obtain a continuous casting billet; heating the continuous casting billet to 1100-1300°C, hot rolling, the final rolling temperature of hot rolling is 850-950°C; coiling the hot-rolled steel, the coiling temperature is 650-750°C; cold rolling the coiled steel, the cold rolling reduction rate is 50%-80%; annealing the cold-rolled steel, the annealing temperature is 640-720°C; leveling the annealed steel, the leveling reduction rate is 1.5%-2.5%. The preparation method can obtain high-strength, low yield strength drop rate after 860°C enameling and low thickness cold-rolled high-strength enameled steel, and use it in the inner tank of the water heater, reducing the weight of the inner tank of the water heater, and reducing the manufacturing cost and transportation cost of the water heater.

Description

Technical Field

[0001] The present application relates to the technical field of steel smelting, and in particular to a preparation method of cold-rolled high-strength enameled steel, cold-rolled high-strength enameled steel and applications thereof. Background Art

[0002] In recent years, water heaters have developed rapidly. However, due to increasingly fierce market competition and increased labor costs, manufacturers of water heater tanks are under pressure from production costs and need to design water heater tanks to be lightweight. This allows the water heater tanks to be appropriately thinned based on the thickness of existing steel, ultimately achieving the goal of reducing the weight of the water heater tank and reducing costs.

[0003] The processing technology of the water heater tank is mainly to first punch, punch holes, and trim the end caps, then roll, weld, and expand the barrel wall, and then weld the end caps and barrel wall together to make the water heater tank, and then enamelled the water heater tank on one side. The enameled water heater tank needs to undergo pressure resistance test and fatigue test. Therefore, the steel used to manufacture the water heater tank must not only meet the requirements of water heater forming and enameling, but also meet its service condition test.

[0004] Therefore, how to prepare low-thickness enameled steel while meeting the requirements of high strength and low yield strength drop rate after 860°C enameling has become an urgent problem to be solved. Summary of the invention

[0005] The embodiments of the present application provide a preparation method of cold-rolled high-strength enameled steel, cold-rolled high-strength enameled steel and applications, which can obtain low-thickness cold-rolled high-strength enameled steel with high strength and low yield strength drop rate after 860°C enameling, and use the cold-rolled high-strength enameled steel for the inner tank of a water heater, thereby reducing the weight of the inner tank of the water heater and reducing the manufacturing cost and transportation cost of the water heater.

[0006] In the first aspect, the embodiment of the present application proposes a method for preparing cold-rolled high-strength enameled steel, the preparation method comprising: providing molten steel with the following components, with the total mass of the molten steel being 100%, the chemical composition of the molten steel being: C: 0.02%-0.08%, Si≤0.5%, Mn: 0.2%-0.8%, P≤0.03%; S≤0.03%, Al≥0.015%, Ti: 0.02%-0.08%, Nb: 0.005%-0.03%, N≤0.01%, Ti-3.4×N-1.5×S≤0, Cu≤0.05%, the remainder being Fe and unavoidable impurities The method comprises the following steps: continuously casting the molten steel to obtain a continuous casting billet; heating the continuous casting billet to 1100-1300°C and hot rolling the billet to obtain a hot rolled steel product, wherein the final rolling temperature of the hot rolling process is 850-950°C; coiling the hot rolled steel product at a coiling temperature of 650-750°C; cold rolling the coiled steel product at a reduction rate of 50%-80%; annealing the cold rolled steel product at a temperature of 640-720°C; leveling the annealed steel product at a reduction rate of 1.5%-2.5%.

[0007] According to one aspect of the embodiment of the present application, the hot rolling process is performed in a single-phase austenite region.

[0008] According to one aspect of an embodiment of the present application, the preparation method further includes a pickling treatment after the coiling treatment.

[0009] According to one aspect of an embodiment of the present application, the annealing process adopts hood annealing, and the hood annealing adopts a full hydrogen purge mode.

[0010] According to one aspect of an embodiment of the present application, the annealing treatment time is 8-11 hours.

[0011] According to one aspect of an embodiment of the present application, the preparation method further includes re-rolling, oiling and splitting the rolls after the flattening treatment.

[0012] In the second aspect, an embodiment of the present application proposes a cold-rolled high-strength enameled steel, which is prepared by the preparation method of the first aspect of the present application. Taking the total mass of the cold-rolled high-strength enameled steel as 100%, the chemical composition of the cold-rolled high-strength enameled steel is: C: 0.02%-0.08%, Si≤0.5%, Mn: 0.2%-0.8%, P≤0.03%; S≤0.03%, Al≥0.015%, Ti: 0.02%-0.08%, Nb: 0.005%-0.03%, N≤0.01%, Ti-3.4×N-1.5×S≤0, Cu≤0.05%, and the remainder is Fe and unavoidable impurities.

[0013] According to another aspect of the embodiment of the present application, the yield strength of the cold-rolled high-strength enameled steel is ≥330MPa, the tensile strength of the cold-rolled high-strength enameled steel is ≥430MPa, the elongation of the cold-rolled high-strength enameled steel is ≥20%, and the yield strength decrease rate of the cold-rolled high-strength enameled steel after 860°C enameling is ≤5%.

[0014] According to another aspect of the embodiment of the present application, the thickness of the cold-rolled high-strength enameled steel is less than 1.8 mm.

[0015] In a third aspect, the embodiments of the present application propose a preparation method of the first aspect of the present application or an application of the cold-rolled high-strength enameled steel of the second aspect of the present application in the preparation of a water heater tank.

[0016] The embodiment of the present application designs the chemical composition of molten steel, heats the continuous casting ingot to 1100-1300°C, controls the final rolling temperature of the hot rolling treatment within the range of 850-950°C, controls the temperature of the coiling treatment within the range of 650-750°C, controls the reduction rate of the cold rolling treatment within the range of 50%-80%, controls the temperature of the annealing treatment within the range of 640-720°C, and controls the reduction rate of the flattening treatment within the range of 1.5%-2.5%, thereby obtaining high-strength and low-thickness cold-rolled high-strength enameled steel with a low yield strength drop rate after 860°C enameling, and uses the cold-rolled high-strength enameled steel for the water heater inner tank, thereby reducing the weight of the water heater inner tank, thereby reducing the manufacturing cost and transportation cost of the water heater. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The features, advantages and technical effects of exemplary embodiments of the present application will be described below with reference to the accompanying drawings.

[0018] Figure 1 A schematic diagram of the preparation method provided in the embodiment of the present application;

[0019] Figure 2 This is a photo of the water heater tank prepared in accordance with an embodiment of the present application.

[0020] in:

[0021] 11. End cover; 12. Barrel wall. DETAILED DESCRIPTION

[0022] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0023] It should be noted that, in this application, the term "comprises" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprises..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0024] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application). Unless otherwise specified, the test temperature of the parameters mentioned in this application is 25° C. and the test pressure is standard atmospheric pressure.

[0025] It should be noted that the water heater tank in the embodiments of the present application is taken as an example of a 50L household water heater.

[0026] The water heater tank made of ordinary cold-rolled low-carbon enameled steel prepared by cold rolling needs to have a thickness of more than 1.8mm in order to meet the pressure test and fatigue test of the water heater tank. As the steel used is thicker, the weight of the water heater tank is also heavier, resulting in higher production and transportation costs.

[0027] When hot rolling is used to produce water heater tanks, if the thickness of the produced steel is above 1.8 mm, the same problem as the cold rolling method will be encountered. In addition, when the thickness of the steel produced by hot rolling is less than 1.8 mm, the thickness of the hot-rolled steel is close to the hot-rolling limit specification, which further increases the production cost.

[0028] Figure 1 Schematic diagram of the preparation method provided in the embodiment of the present application. Figure 1 As shown, the present application embodiment proposes a method for preparing cold-rolled high-strength enameled steel. The preparation method comprises the following steps:

[0029] S10: providing molten steel of the following composition, with the total mass of the molten steel being 100%, the chemical composition of the molten steel being: C: 0.02%-0.08%, Si≤0.5%, Mn: 0.2%-0.8%, P≤0.03%; S≤0.03%, Al≥0.015%, Ti: 0.02%-0.08%, Nb: 0.005%-0.03%, N≤0.01%, Ti-3.4×N-1.5×S≤0, Cu≤0.05%, and the remainder being Fe and unavoidable impurities;

[0030] S20: continuously casting the molten steel to obtain a continuously cast billet;

[0031] S30: heating the continuous casting billet to 1100-1300° C. and performing hot rolling treatment to obtain hot-rolled steel, wherein the final rolling temperature of the hot rolling treatment is 850-950° C.;

[0032] S40: coiling the hot-rolled steel at a temperature of 650-750°C;

[0033] S50: cold rolling the coiled steel, with a reduction rate of 50% to 80%;

[0034] S60: annealing the cold-rolled steel at a temperature of 640-720°C;

[0035] S70: The annealed steel is flattened, and the reduction rate of the flattening process is 1.5%-2.5%.

[0036] The embodiment of the present application designs the chemical composition of molten steel, heats the continuous casting ingot to 1100-1300°C, controls the final rolling temperature of the hot rolling treatment within the range of 850-950°C, controls the temperature of the coiling treatment within the range of 650-750°C, controls the reduction rate of the cold rolling treatment within the range of 50%-80%, controls the temperature of the annealing treatment within the range of 640-720°C, and controls the reduction rate of the flattening treatment within the range of 1.5%-2.5%, thereby obtaining high-strength and low-thickness cold-rolled high-strength enameled steel with a low yield strength drop rate after 860°C enameling, and uses the cold-rolled high-strength enameled steel for the water heater inner tank, thereby reducing the weight of the water heater inner tank, thereby reducing the manufacturing cost and transportation cost of the water heater.

[0037] The composition of molten steel and the specific control principles of each step in the preparation method provided in the embodiment of the present application will be described in detail below.

[0038] Carbon is an element that ensures the strength and anti-phosphorus explosion performance of steel. Carbon exists in the form of interstitial atoms and cementite in steel. It can improve the anti-phosphorus explosion performance of steel while ensuring that the steel has a certain strength. However, too high a carbon content will reduce the formability of the steel. Therefore, the carbon content should be controlled within the range of 0.02%-0.06%.

[0039] Silicon is a strengthening element that improves the strength of steel. The higher the silicon content, the higher the strength of the steel. However, when the silicon content is too high, it is easy to generate iron oxide scale that is difficult to pickle, affecting the quality of the steel surface. Therefore, the silicon content should be controlled within the range of ≤0.5%.

[0040] Manganese is also a strengthening element for steel. Adding a small amount of manganese to steel is conducive to improving strength. At the same time, adding a certain amount of manganese can combine with sulfur to form MnS, avoiding the problem of hot brittleness. However, adding too much manganese is not conducive to stamping processing. Therefore, the mass content of manganese should be controlled within the range of 0.2%-0.8%.

[0041] Phosphorus can improve the strength of steel, but the increase in phosphorus content will cause the steel to become cold and brittle. Therefore, the phosphorus content should be as low as possible and should be controlled within the range of ≤0.03%.

[0042] Sulfur can increase the strength of steel, reduce plasticity and improve formability. At the same time, sulfur can cause hot brittleness and affect the surface quality of steel. In addition, if the sulfur content is too high, sulfur will combine with manganese in steel to produce too many MnS inclusions, which can easily become the starting point of corrosion and perforation. Therefore, the sulfur content should be as low as possible and should be controlled within the range of ≤0.03%. By reducing the sulfur content, the generation of MnS inclusions can also be reduced, thereby reducing the adverse effects of MnS on fatigue properties.

[0043] Aluminum can be added as a deoxidizer during steel smelting. When the mass content of aluminum is less than 0.015%, it will lead to an increase in inclusions in the steel and deterioration of stamping processing performance. Therefore, the mass content of Al should be controlled within the range of ≥0.015%.

[0044] Titanium is an important additive element in the molten steel of the embodiment of the present application. Titanium is a strong carbonitride-forming element. It can prevent the growth of austenite grains during the heating process of the slab, which is conducive to obtaining a uniform and fine structure after rolling, so as to achieve the purpose of refining grains and improving strength. In addition, during the enameling process, TiN, TiS, and TiC particles in the steel act as traps for hydrogen absorption, which can reduce the occurrence of scale explosion, but increasing the mass content of titanium will increase costs. Therefore, the mass content of titanium is controlled within the range of 0.02%-0.08%.

[0045] Niobium is also an important additive element in the molten steel of the embodiment of the present application. Niobium is a strong carbonitride-forming element. It will prevent grain growth during hot rolling, coiling and annealing, which is conducive to obtaining a uniform and fine structure, so as to achieve the purpose of refining grains and improving strength. In addition, during the enamelling process, Nb (NC) and NbC particles in the steel act as traps for hydrogen absorption, which can reduce the occurrence of scale explosion. However, adding too much niobium will increase costs. Therefore, the mass content of niobium is controlled within the range of 0.005%-0.03%.

[0046] Nitrogen and titanium will combine to form large TiN precipitates, which is not conducive to grain refinement and improvement of fatigue test performance. Therefore, the mass content of nitrogen should be controlled within the range of ≤0.01%.

[0047] Copper is one of the elements that improve the strength of steel. However, the increase in copper content will cause copper brittleness and easily segregate at the grain boundary, reducing the fatigue test performance of steel. Therefore, the copper content should be controlled within the range of ≤0.05%.

[0048] In order to further reduce the weight of the water heater tank, thereby reducing the production cost of the water heater, this application adopts the design idea of ​​reducing the mass content of carbon in molten steel to ensure that the steel has certain forming properties. However, when the strength of the steel reaches a certain level, its production cost will increase significantly, and it cannot reduce the manufacturing cost of the water heater tank. Therefore, alloy elements such as manganese, niobium and titanium within the above mass content range are added to improve the strength of the steel, resistance to deformation and fatigue test performance. Adding alloy elements can also improve the steel's resistance to phosphorus explosion. Thereby meeting the pressure test and pulse test requirements of the water heater tank made after the steel is thinned.

[0049] If the hot rolling temperature is too high, the scale will not be easy to pickle, affecting the surface quality of the steel. If the hot rolling temperature is too low, the steel will enter the two-phase region and mixed crystals will appear, and snowflake defects will be produced during stamping, affecting the appearance of the enamel product. Therefore, in the embodiment of the present application, the final rolling temperature of the hot rolling treatment is controlled at 850-950°C.

[0050] Increasing the coiling temperature is conducive to the precipitation of precipitates and improves the anti-phosphorus explosion performance. However, if the coiling temperature is too high, the iron scale on the surface of the steel will be seriously difficult to pickle, affecting the quality of the steel. Therefore, the coiling temperature is controlled within the range of 650-750℃.

[0051] Increasing the reduction rate of cold rolling can reduce the recrystallization temperature, but too large a reduction rate of cold rolling will increase the difficulty of cold rolling. Therefore, the reduction rate of cold rolling should be controlled between 50% and 80%. It should be noted that the reduction rate of cold rolling in the embodiment of the present application is a cumulative reduction rate.

[0052] The purpose of annealing is to eliminate the work hardening effect of cold rolling and make the steel have excellent plasticity, that is, formability. If the annealing temperature is too high, it will cause abnormal grain growth and produce stamping orange peel or raindrop defects. Therefore, the annealing temperature should be controlled within the range of 640-720℃.

[0053] The purpose of flattening is to eliminate the yield platform of steel and avoid tensile strain mark defects during the stamping process, which will affect the appearance quality of enamel products. If the reduction rate of flattening is too low, the yield platform of steel cannot be eliminated. If the reduction rate of flattening is too high, the steel will be hardened and the plasticity and processing performance of steel will be reduced. Therefore, the reduction rate of flattening is controlled within the range of 1.5%-2.5%.

[0054] In the embodiment of the present application, by controlling the process parameters in each step, that is, the hot rolling adopts the control process of high temperature final rolling and high temperature coiling, the cold rolling adopts a large reduction rate, and the complete recrystallization annealing control process, the product performance can be guaranteed and the phosphorus explosion resistance of the steel can be improved, thereby obtaining a low-thickness cold-rolled high-strength enameled steel with high strength and a low yield strength drop rate after 860°C enameling.

[0055] In some optional embodiments, the hot rolling process is performed in a single-phase austenite region.

[0056] In some optional embodiments, the preparation method may further include a pickling process after the coiling process.

[0057] Pickling can remove the scale and rust on the surface of steel, making the surface of steel smooth and clean. Pickling can also improve the quality and service life of steel. The conditions for pickling can be conventional pickling conditions, for example, the surface of steel can be cleaned with dilute sulfuric acid.

[0058] In some optional embodiments, the annealing process may be performed by hood annealing, and the hood annealing may be performed in a full hydrogen purge mode.

[0059] Hood annealing has slow heating and cooling rates, which allows sufficient time for carbide precipitation and grain growth. Hood annealing can be carried out in a full hydrogen purge mode. Hydrogen is light in weight and has strong penetration ability. It can penetrate into the interlayer of steel coils, give full play to the characteristics of high thermal conductivity, and significantly improve the heat transfer efficiency. Using hydrogen as a reducing gas can reduce FeO to iron at high temperatures and greatly reduce the rolling oil brought by the cold rolling mill. Using hydrogen as a protective atmosphere can make recrystallization more uniform and the mechanical properties of annealed steel more uniform.

[0060] In some optional embodiments, the annealing time may be 8-11 hours.

[0061] In some optional embodiments, the preparation method may further include re-rolling, oiling and splitting the rolls after the flattening treatment.

[0062] Re-rolling and oiling the steel can make the surface of the steel less likely to rust.

[0063] In the second aspect, an embodiment of the present application proposes a cold-rolled high-strength enameled steel, which is prepared by the preparation method of the first aspect of the present application. Taking the total mass of the cold-rolled high-strength enameled steel as 100%, the chemical composition of the cold-rolled high-strength enameled steel is: C: 0.02%-0.08%, Si≤0.5%, Mn: 0.2%-0.8%, P≤0.03%; S≤0.03%, Al≥0.015%, Ti: 0.02%-0.08%, Nb: 0.005%-0.03%, N≤0.01%, Ti-3.4×N-1.5×S≤0, Cu≤0.05%, and the remainder is Fe and unavoidable impurities.

[0064] The chemical composition of the cold-rolled high-strength enameled steel in the embodiment of the present application is the same as the chemical composition of molten steel, that is, the chemical composition of the molten steel does not change during the entire preparation process. Therefore, the control principle of the chemical composition in the cold-rolled high-strength enameled steel is the same as the control principle of the chemical composition in the molten steel, and will not be repeated here.

[0065] The preparation method of the embodiment of the present application significantly improves the yield strength, tensile strength and elongation of the cold-rolled high-strength enameled steel, and the yield strength decrease rate of the cold-rolled high-strength enameled steel after 860°C enameling is relatively low.

[0066] In some optional embodiments, the yield strength of the cold-rolled high-strength enameled steel is ≥330MPa, the tensile strength of the cold-rolled high-strength enameled steel is ≥430MPa, the elongation of the cold-rolled high-strength enameled steel is ≥20%, and the yield strength drop rate of the cold-rolled high-strength enameled steel after 860°C enameling is ≤5%.

[0067] In some optional embodiments, the thickness of the cold-rolled high-strength enameled steel is less than 1.8 mm.

[0068] Illustratively, the thickness of the cold-rolled high-strength enameled steel prepared in the embodiment of the present application can be 1.6 mm.

[0069] In a third aspect, the embodiments of the present application propose a preparation method of the first aspect of the present application or an application of the cold-rolled high-strength enameled steel of the second aspect of the present application in the preparation of a water heater tank.

[0070] Figure 2 This is a photo of the water heater tank prepared in the embodiment of the present application, such as Figure 2 As shown, the end covers 11 are arranged at both ends of the barrel wall 12 .

[0071] Since the thickness of the steel used for the water heater tank is reduced, the strength of the steel needs to be increased to meet the service conditions of the water heater tank, such as the pressure test and fatigue test. However, while increasing the strength of the steel, its forming performance will be reduced. Considering that the deformation of the water heater end cover is large, the thinning amount during the forming process is greater than that of the barrel wall, and the forming performance requirements are higher. Therefore, in the process of preparing the water heater tank, the cold-rolled high-strength enameled steel prepared in the embodiment of the present application can be used as the barrel wall of the water heater tank, and the end cover part of the water heater tank can still use the cold-rolled low-carbon enameled steel produced by conventional methods.

[0072] Example

[0073] The following examples describe the disclosure of the present application in more detail, and these examples are for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present application are apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are commercially available.

[0074] Example 1

[0075] Provide molten steel with the following composition. Based on the total mass of the molten steel as 100%, the chemical composition of the molten steel is: C: 0.0456%, Si: 0.0263%, Mn: 0.2395%, P: 0.0095%, S: 0.0107%, Al: 0.0373%, N: 0.0048%, Cu: 0.0467%, Ti: 0.0364%, Nb: 0.0178%, and the remainder is Fe and unavoidable impurities.

[0076] The molten steel is continuously cast to obtain a continuously cast billet; the continuously cast billet is heated to 1228°C in a heating furnace and hot rolled to obtain hot rolled steel, the final rolling temperature of the hot rolling is 909°C; the hot rolled steel is coiled at a coiling temperature of 695°C to obtain a steel with a thickness of 3.5 mm; the coiled steel is cold rolled and pickled to form a 1.6 mm thick hard rolled coil, the cold rolling reduction is 54%; the cold rolled steel is annealed at a temperature of 680°C and for 8 hours; the annealed steel is cooled and then leveled on a leveling machine, the leveling reduction is 1.8%, and the leveled steel is coiled on a rewinding line for oiling.

[0077] Example 2

[0078] Provide molten steel with the following composition. Based on the total mass of the molten steel as 100%, the chemical composition of the molten steel is: C: 0.0533%, Si: 0.0272%, Mn: 0.4501%, P: 0.0091%, S: 0.009%, Al: 0.0336%, N: 0.0051%, Cu: 0.0279, Ti: 0.0446%, Nb: 0.0199%, and the remainder is Fe and unavoidable impurities.

[0079] The molten steel is continuously cast to obtain a continuously cast billet; the continuously cast billet is heated to 1180°C in a heating furnace and hot rolled to obtain hot rolled steel, the final rolling temperature of the hot rolling is 895°C; the hot rolled steel is coiled at a coiling temperature of 714°C to obtain a steel with a thickness of 4 mm; the coiled steel is cold rolled and pickled to form a 1.6 mm thick hard rolled coil, the cold rolling reduction is 60%; the cold rolled steel is annealed at a temperature of 710°C for 8 hours; the annealed steel is cooled and then leveled on a leveling machine, the leveling reduction is 1.6%, and the leveled steel is coiled on a rewinding line for oiling.

[0080] Example 3

[0081] Provide molten steel with the following composition. Based on the total mass of the molten steel as 100%, the chemical composition of the molten steel is: C: 0.0349%, Si: 0.0357%, Mn: 0.2909%, P: 0.0135%, S: 0.0106%, Al: 0.0253%, N: 0.0076%, Cu: 0.0368%, Ti: 0.0617%, Nb: 0.0164%, and the remainder is Fe and unavoidable impurities.

[0082] The molten steel is continuously cast to obtain a continuously cast billet; the continuously cast billet is heated to 1233°C in a heating furnace and hot rolled to obtain hot rolled steel, the final rolling temperature of the hot rolling is 918°C; the hot rolled steel is coiled at a coiling temperature of 672°C to obtain a steel with a thickness of 4 mm; the coiled steel is cold rolled and pickled to form a 1.6 mm thick hard rolled coil, the cold rolling reduction is 60%; the cold rolled steel is annealed at a temperature of 690°C and for 10 hours; the annealed steel is cooled and then leveled on a leveling unit, the leveling reduction is 2%, and the leveled steel is coiled on a rewinding line for oiling.

[0083] Example 4

[0084] Provide molten steel with the following composition. Based on the total mass of the molten steel as 100%, the chemical composition of the molten steel is: C: 0.0599%, Si: 0.0121%, Mn: 0.5396%, P: 0.01%, S: 0.017%, Al: 0.03%, N: 0.0046%, Cu: 0.0311%, Ti: 0.0377%, Nb: 0.0236%, and the remainder is Fe and unavoidable impurities.

[0085] The molten steel is continuously cast to obtain a continuously cast billet; the continuously cast billet is heated to 1175°C in a heating furnace and hot rolled to obtain hot rolled steel, the final rolling temperature of the hot rolling is 889°C; the hot rolled steel is coiled at a coiling temperature of 688°C to obtain a steel with a thickness of 3.5 mm; the coiled steel is cold rolled and pickled to form a 1.6 mm thick hard rolled coil, the cold rolling reduction is 54%; the cold rolled steel is annealed at a temperature of 700°C and for 8 hours; the annealed steel is cooled and then leveled on a leveling unit, the leveling reduction is 1.8%, and the leveled steel is coiled on a rewinding line for oiling.

[0086] Comparative Example 1

[0087] Provide molten steel with the following composition. Based on the total mass of the molten steel as 100%, the chemical composition of the molten steel is: C: 0.0504%, Si: 0.0215%, Mn: 0.1432%, P: 0.0104%, S: 0.0039%, Al: 0.0355%, N: 0.008%, and the remainder is Fe and unavoidable impurities.

[0088] The molten steel is continuously cast to obtain a continuously cast billet; the continuously cast billet is heated to 1205°C in a heating furnace and hot rolled to obtain hot rolled steel, the final rolling temperature of the hot rolling is 902°C; the hot rolled steel is coiled at a coiling temperature of 675°C to obtain a steel with a thickness of 4.8mm; the coiled steel is cold rolled and pickled to form a 1.8mm thick hard rolled coil, the cold rolling reduction is 62.5%; the cold rolled steel is annealed at a temperature of 700°C and for 11h; the annealed steel is cooled and then leveled on a leveling machine, the leveling reduction is 1.2%, and the leveled steel is coiled on a rewinding line for oiling.

[0089] Comparative Example 2

[0090] Provide molten steel with the following composition. Based on the total mass of the molten steel as 100%, the chemical composition of the molten steel is: C: 0.0526%, Si: 0.0149%, Mn: 0.1814%, P: 0.0234%, S: 0.0029%, Al: 0.0211%, N: 0.0055%, and the remainder is Fe and unavoidable impurities.

[0091] The molten steel is continuously cast to obtain a continuously cast billet; the continuously cast billet is heated to 1232°C in a heating furnace and hot rolled to obtain hot rolled steel, the final rolling temperature of the hot rolling is 896°C; the hot rolled steel is coiled at a coiling temperature of 692°C to obtain a steel with a thickness of 4.8mm; the coiled steel is cold rolled and pickled to form a 1.6mm thick hard rolled coil, the cold rolling reduction is 67%; the cold rolled steel is annealed at a temperature of 690°C for 8h; the annealed steel is cooled and then leveled on a leveling machine, the leveling reduction is 1.2%, and the leveled steel is coiled on a rewinding line for oiling.

[0092] The yield strength, tensile strength, elongation, yield strength after 860°C enameling and yield strength reduction rate after 860°C enameling of the steels prepared in Examples 1-4 and Comparative Examples 1-2 of the present application are shown in Table 1.

[0093] Table 1

[0094]

[0095] The enamel performance, service performance and thickness of the water heater inner tank prepared in Examples 1-4 and Comparative Examples 1-2 of the present application are shown in Table 2.

[0096] Table 2

[0097]

[0098]

[0099] It can be seen from Table 1 and Table 2 that the cold-rolled high-strength enameled steel prepared in Examples 1-4 of the present application can improve the yield strength, tensile strength and elongation of the steel. The yield strength decrease rate after enameling at 860°C is low. The thickness of the steel can also be reduced. Using the cold-rolled high-strength enameled steel for the barrel wall of the water heater tank can make the water heater tank meet the enameling performance and service performance tests, reduce the weight of the water heater tank, and thus reduce the manufacturing cost and transportation cost of the water heater.

[0100] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing cold-rolled high-strength enameled steel, characterized in that: The preparation method comprises: Provide molten steel with the following composition, based on the total mass of the molten steel being 100%, the chemical composition of the molten steel is: C: 0.02%-0.0599%, Si≤0.5%, Mn: 0.2%-0.8%, P≤0.03%; S≤0.03%, Al≥0.015%, Ti: 0.02%-0.08%, Nb: 0.005%-0.03%, N≤0.01%, Ti-3.4×N-1.5×S≤0, Cu≤0.05%, and the balance is Fe and unavoidable impurities; The molten steel is continuously cast to obtain a continuous casting billet; The continuous casting billet is heated to 1100-1300° C. and hot rolled to obtain a hot-rolled steel product, wherein the final rolling temperature of the hot rolling process is 850-950° C.; The hot-rolled steel is coiled at a temperature of 650-750°C; The coiled steel is cold-rolled, wherein the reduction ratio of the cold-rolling process is 50%-80%; Annealing the cold-rolled steel at a temperature of 640-720° C. using hood annealing in a full hydrogen purge mode; The annealed steel is flattened, wherein the reduction rate of the flattening process is 1.5%-2.5%; The thickness of the cold-rolled high-strength enameled steel is less than 1.8 mm, and the yield strength reduction rate of the cold-rolled high-strength enameled steel after being enameled at 860° C. is less than or equal to 5%.

2. The preparation method according to claim 1, characterized in that: The hot rolling process is performed in a single-phase austenite region.

3. The preparation method according to claim 1, characterized in that: The preparation method further includes a pickling process after the coiling process.

4. The preparation method according to claim 1, characterized in that: The annealing treatment time is 8-11 hours.

5. The preparation method according to claim 1, characterized in that: The preparation method further comprises re-rolling, oiling and splitting the rolls after the flattening treatment.

6. A cold-rolled high-strength enameled steel, characterized in that: Prepared by the preparation method according to any one of claims 1 to 5, based on the total mass of the cold-rolled high-strength enameled steel being 100%, the chemical composition of the cold-rolled high-strength enameled steel is: C: 0.02%-0.0599%, Si≤0.5%, Mn: 0.2%-0.8%, P≤0.03%; S≤0.03%, Al≥0.015%, Ti: 0.02%-0.08%, Nb: 0.005%-0.03%, N≤0.01%, Ti-3.4×N-1.5×S≤0, Cu≤0.05%, the balance is Fe and unavoidable impurities; The thickness of the cold-rolled high-strength enameled steel is less than 1.8 mm, and the yield strength reduction rate of the cold-rolled high-strength enameled steel after being enameled at 860° C. is less than or equal to 5%.

7. The cold-rolled high-strength enameled steel according to claim 6, characterized in that: The yield strength of the cold-rolled high-strength enameled steel is ≥330MPa, the tensile strength of the cold-rolled high-strength enameled steel is ≥430MPa, and the elongation of the cold-rolled high-strength enameled steel is ≥20%.

8. Use of the preparation method according to any one of claims 1 to 5 or the cold-rolled high-strength enameled steel according to any one of claims 6 to 7 in the preparation of a water heater tank.

Images