Cold-rolled enameled steel sheet for deep-drawing inner pot and its manufacturing method

Abstract

The present invention discloses a cold-rolled enameling steel for deep-drawing inner pots containing the following chemical elements in the following mass percentages: C: 0.02 - 0.06%, 0 < Si ≤ 0.08%, Mn: 0.1 - 0.7%, P ≤ 0.055%, S ≤ 0.03%, Al: 0.01 - 0.07%, N: 0.002 - 0.010%, B: 0.002 - 0.009%, Ti: 0.002 - 0.015%, Nb: 0.002 - 0.012%, Cr: 0.01 - 0.08%, and at least one of Cu, Ni, and Mo; Cu + Ni + Mo ≤ 0.40%. The cold-rolled enameling steel for deep-drawing inner pots according to the present invention adopts reasonable chemical composition and process design, and thus has good formability, high strength after high-temperature cloisonné, excellent welding performance, and excellent anti-chipping performance.

Description

[Technical field]

[0001] The present invention relates to a metal material and a method for producing the same, in particular enameled steel. board And the present invention relates to a method for producing the same. [Background technology]

[0002] There are two types of structures for enameled kettle, including two-stage and three-stage, which are mainly distinguished by the forming and welding process. The two-stage kettle is made by welding two circular plates by deep drawing, so there is only one annular weld seam on the whole kettle, while the three-stage kettle is made by welding two end caps and one kettle body, so the end caps are stamped and the kettle body is edge-rolled, so there are two annular weld seams and one straight seam on the whole kettle.

[0003] In recent years, in industrial production, two-stage enameled inner kettle has been rapidly developed from the viewpoint of improving product quality and reducing overall costs. In the forming process of two-stage inner kettle, a high degree of forming is performed by deep drawing and ironing die processing (for example, for a typical 80L inner kettle, when the diameter is 382mm, the press processing depth is about 430mm), so the steel plate of the two-stage enameled inner kettle is required to have good formability. In addition, the finished enameled inner kettle must undergo high-pressure circulating water pressure tests more than 20,000 times, so if the strength of the steel plate after sintering is insufficient, the inner kettle will deform during the pressure process and the enamel will peel off, so the steel plate used for the two-stage enameled inner kettle is required to have high strength even after cloisonné.

[0004] In addition, the nail-pop defect is one of the most important problems in the quality of enamel products, and the occurrence of the nail-pop defect is related to the solubility of hydrogen atoms in steel. There are three sources of hydrogen: hydrogen dissolved in the base steel sheet; hydrogen generated during pickling and firing; and most importantly, hydrogen generated during firing by the reaction between the steel sheet and the steam in the furnace or the crystal water of the glaze polishing additive. During the high-temperature sintering process, hydrogen atoms generated by the chemical reaction between water and the iron and carbon atoms of the steel sheet enter the steel sheet and exist near the structures of the steel sheet, such as dislocations, crystal boundaries, voids, impurities, and precipitates. As the steel sheet cools, the solubility of hydrogen atoms in the steel decreases and they gather at the interface between the steel sheet and the enamel layer. When the pressure of the hydrogen gas exceeds the tensile strength of the enamel layer, it breaks through the glaze layer and causes the so-called nail-pop defect. Under the strict production conditions of a certain water heater manufacturer, all open ends of vertical units face downward during the cloisonné process, which is unfavorable for the evaporation of water vapor. Therefore, in order to meet the high requirements for resistance to nail chipping, the steel plate itself needs to have sufficient areas to absorb hydrogen.

[0005] In order to ensure that the two-stage enamel inner kettle fits well in terms of forming, pressure resistance, welding, and glazing, the steel plate used in the two-stage enamel inner kettle must have good deep drawing performance, high strength after cloisonné, good welding performance, excellent glazing performance, and especially excellent resistance to nail chipping.

[0006] The characteristics of conventional cold-rolled deep-drawing enamel steels are all based on ultra-low carbon, high sulfur and nitrogen content, and the addition of appropriate alloying elements (most commonly titanium). Titanium can fix free carbon, nitrogen and sulfur atoms, reduce the amount of solid solution of impurity elements, and improve the press-forming performance of the steel sheet; on the other hand, titanium can combine with carbon, nitrogen and sulfur to form inclusions or second phases, which can act as effective hydrogen storage traps to enhance the hydrogen storage capacity of the steel sheet. However, it should be noted that although this design can simultaneously improve the deep-drawing performance and anti-flicking performance of the steel sheet, the yield strength of the substrate is low, and the yield strength after high-temperature sintering is further reduced, so the pressure resistance requirements of the enamel inner kettle cannot be met, and the manufacturing cost is high due to the addition of a large amount of alloying elements in this design. Summary of the Invention [Problem to be solved by the invention]

[0007] At present, there is not much specialized development in China regarding steel plates specifically for two-stage enameled kettles. The steel for two-stage enameled kettles used by Chinese electric water heater manufacturers is mainly ordinary steel SPCC, which does not contain alloy elements such as titanium, niobium, or boron, and has only finely adjusted elements such as carbon and manganese, resulting in some problems in terms of glazing quality and welding quality. [Means for solving the problem]

[0008] One of the objectives of the present invention is to develop a cold-rolled enamel steel for deep drawing inner kettles, which is made by adding an appropriate amount of boron, nitrogen, and trace amounts of titanium and niobium to a basic low carbon steel, and also by adding alloying elements such as copper and chromium, which improve the adhesion performance of the enamel, to obtain a uniform and fine microstructure of ferrite + lamellar and pseudo-pearlite. board Pearlite has the effect of strengthening the substrate, and the cementite pellets in the pearlite act as irreversible hydrogen traps to improve the anti-fracture performance of the steel. In designing the chemical components, adding an appropriate amount of boron and nitrogen to the steel not only allows the BN pellets generated and dispersedly precipitated by the combination of the two to significantly improve the anti-fracture performance of the steel as an effective hydrogen trap, but also effectively enhances the growth ability of ferrite and gives the steel good formability. A small amount of titanium added to the steel can replace some of the boron and combine with nitrogen to generate TiN particles, reducing the risk of cracking of continuously cast slabs due to BN, while also being advantageous for welding performance.

[0009] Cold-rolled enamel steel for the above deep-drawn inner pot boardIt has a ferrite crystal grain size of grade 7.5 - 8, a yield strength of 220 - 280 MPa, an elongation rate of 38 - 43%, a hydrogen penetration time ≥ 8 min, and a yield strength ≥ 200 MPa after performing high-temperature cloisonné firing at at least 850°C for at least 12 min. It has good formability, high strength after high-temperature cloisonné firing, excellent welding performance, and excellent anti-chip-flight performance, and can be effectively applied to enamel inner pots of electric water heaters with high forming requirements, etc.

[0010] To achieve the above object, the present invention provides cold-rolled enamel steel for deep-drawing inner pots containing the following chemical elements in the following mass percentages board as follows: C: 0.02 - 0.06%, 0 < Si ≤ 0.08%, Mn: 0.1 - 0.7%, P ≤ 0.055%, S ≤ 0.03%, Al: 0.01 - 0.07%, N: 0.002 - 0.010%, B: 0.002 - 0.009%, Ti: 0.002 - 0.015%, Nb: 0.002 - 0.012%, Cr: 0.01 - 0.08%, and at least one of Cu, Ni, and Mo; Cu + Ni + Mo ≤ 0.40%. In the above formula, Cu, Ni, and Mo respectively represent the mass percentage contents of their respective elements.

[0011] Furthermore, for the cold-rolled enamel steel for deep-drawing inner pots according to the present invention board the mass percentages of each chemical element are: C: 0.02 - 0.06%, 0 < Si ≤ 0.08%, Mn: 0.1 - 0.7%, P ≤ 0.055%, S ≤ 0.03%, Al: 0.01 - 0.07%, N: 0.002 - 0.010%, B: 0.002 - 0.009%, Ti: 0.002 - 0.015%, Nb: 0.002 - 0.012%, Cr: 0.01 - 0.08%, and at least one of Cu, Ni, and Mo; Cu + Ni + Mo ≤ 0.40%; the balance is Fe and other inevitable impurities.

[0012] For the cold-rolled enamel steel for deep-drawing inner pots according to the present invention board the design principle of each chemical element is as follows: C: For the cold-rolled enamel steel for deep-drawing inner pots according to the present invention boardAmong them, C is the most basic strengthening element in steel, and carbon mainly exists in the form of a small amount of lamellar and pseudo-pearlite in the steel of the present invention. The cementite pellets in pearlite serve as suitable hydrogen storage traps to reinforce the anti-peeling performance of the steel plate. On the other hand, a small amount of lamellar and pseudo-pearlite generates a very small amount of CO and CO2 gases during high-temperature cloisonné firing, greatly reducing the bubbles or pinhole defects in the enamel layer, which is beneficial for improving the quality of the glaze layer. However, it should be noted that as the percentage content of C in the steel increases, the strength of the steel increases, while the plasticity and toughness decrease correspondingly. The steel plate of the present invention is used for the steel of the deep-drawing inner pot of the enamel inner pot board Therefore, it is preferable that the mass percentage of C is not too high. Therefore, the cold-rolled enamel steel for the deep-drawing inner pot according to the present invention board sets the mass percentage of C to 0.02 - 0.06%.

[0013] In a preferred embodiment, the mass percentage of C may also be 0.02 - 0.04%. Si: In the cold-rolled enamel steel for the deep-drawing inner pot according to the present invention board Among them, Si does not form carbides in the steel and exists in the form of a solid solution. Therefore, it has the effect of solid solution strengthening, and at the same time, it can reduce the plasticity and toughness of the steel to a certain extent. Si can also affect the adhesion performance of the enamel steel. The SiO2 thin film formed during the high-temperature cloisonné firing process from an appropriate amount of Si is beneficial for the penetration and infiltration of the glaze onto the steel. However, if the Si content is too high, the chemical reaction between the glaze and the metal interface will be inhibited. In addition, if the Si content is too high, peeling defects are likely to occur in the product. Therefore, considering the forming performance, enamel adhesion performance, and anti-peeling performance, in the cold-rolled enamel steel for the deep-drawing inner pot according to the present invention board sets the mass percentage of Si to 0 < Si ≤ 0.08%.

[0014] In a preferred embodiment, the mass percentage of Si may also be 0 < Si ≤ 0.05%. In a preferred embodiment, the mass percentage of Si may also be 0.005 - 0.08%, preferably 0.005 - 0.05%.

[0015] Mn: Cold-rolled enamel steel for deep-drawing inner kettle according to the present invention board In the above, the addition of Mn to steel has the effect of solid solution strengthening. Mn has the effect of deoxidizing and desulfurizing during steelmaking, and can remove FeO and FeS from the steel. At the same time, the generated MnO and MnS act as effective "hydrogen traps" and can reduce the nail jump sensitivity to some extent. Furthermore, the mixed precipitation of MnO and MnS can improve the elongated shape of MnS to a spindle or ellipse shape, thereby avoiding the adverse effect on the lateral formability of the steel sheet caused by the precipitation of MnS alone. However, it should be noted that if the Mn content in the steel exceeds 0.7%, the plasticity, welding performance, and enamel adhesion performance of the steel may be reduced. Therefore, the cold rolled enamel steel for deep drawing inner pots according to the present invention is board Then, the mass percentage of Mn is 0.1-0.7%.

[0016] In a preferred embodiment, the mass percentage of Mn may be 0.2-0.5%. P: Cold-rolled enamel steel for deep-drawing inner pots according to the present invention board In the present invention, P is an inevitable impurity element, and although it can improve the strength and hardness of steel, its severe segregation increases temper brittleness and reduces the plasticity and toughness of steel; it also has a negative effect on welding performance. It is necessary to strictly control the content. Therefore, in the present invention, board In the above, the mass percentage of P is P≦0.055%.

[0017] In a preferred embodiment, the mass percentage of P may be P≦0.035%. S: Cold-rolled enamel steel for deep-drawing inner pots according to the present invention board In the above, S is a harmful element in ordinary steels, and the S element remaining in the steel inevitably reacts with Fe to form FeS, which causes the steel to become hot brittle and reduces the ductility and toughness of the steel. S is also detrimental to the welding performance of the steel and reduces the corrosion resistance of the steel. For this reason, the cold-rolled enamel steel for deep drawing inner kettles according to the present invention is board In the above, the mass percentage of S is set to S≦0.03%.

[0018] In a preferred embodiment, the mass percentage of S may be S≦0.015%. Al: Cold-rolled enamelled steel for deep-drawing inner kettles according to the invention board In the present invention, however, since the nitride-forming element B is added, the main effect of Al is to deoxidize or adjust the oxygen content. Cold-rolled enamel steel for deep-drawing inner pot according to the present invention. board Then, the mass percentage of Al is set to 0.01-0.07%.

[0019] In a preferred embodiment, the mass percentage of Al may be 0.01-0.04%.

[0020] B and N: Cold-rolled enamelled steel for deep-drawing inner kettle according to the present invention board In the formula, B is a strong nitride-forming element. In the present invention, B preferentially forms BN particles with N. There is a strong affinity between the BN pellets and hydrogen atoms. Meanwhile, the large amount of voids generated around the BN pellets after cold rolling can also effectively store hydrogen atoms, and BN strongly affects the diffusion and capacity of hydrogen atoms in steel, and can significantly improve the anti-claw-flying performance of the steel sheet. At the same time, the preferentially precipitated BN pellets suppress the precipitation of fine AlN, so that the growth ability of crystal grains is enhanced, the size of ferrite crystal grains is increased, and the enamel steel can have good deep drawing performance. It should be noted that B also has the effect of suppressing high-temperature deformation of the steel sheet, so that the cold-rolled enamel steel for deep drawing inner pots according to the present invention can be used in a wide range of applications. board Therefore, the cold-rolled enameled steel for deep-drawing inner pots according to the present invention can be effectively prevented from being deformed at high temperatures during welding and glazing after forming. board In the above, the mass percentage of B is 0.002-0.009%, and the mass percentage of N is 0.002-0.010%.

[0021] In a preferred embodiment, the mass percentage of B may be 0.0025-0.0065% and the mass percentage of N may be 0.003-0.008%.

[0022] Ti: Cold-rolled enamel steel for deep-drawing inner kettle according to the present invention board In the above, Ti is a strong carbon and nitride forming element. In low carbon steel, Ti has a large effect on the strength of the steel sheet. Since the enamel steel according to the present invention requires good formability, a trace amount of titanium is treated. A trace amount of Ti can combine with N at high temperature to form dispersed TiN pellets, which consumes some N and prevents the formation of too many BN pellets, effectively reducing the risk of transverse cracks occurring at the corners of the continuously cast slab. At the same time, the stable and dispersed TiN pellets can control the size of the austenite grains in the welding heat affected zone and improve the welding performance of the steel. It should also be noted that the dispersed precipitated TiN pellets can further improve the claw-flying resistance of the steel. Therefore, the cold rolled enamel steel for deep drawing inner pot according to the present invention has a high degree of mechanical properties. board Then, the mass percentage of Ti is 0.002-0.015%.

[0023] In a preferred embodiment, the mass percentage of Ti may be 0.002-0.008%.

[0024] Nb: Cold-rolled enamel steel for deep-drawing inner kettle according to the present invention board In the present invention, the addition of a small amount of Nb effectively improves the performance of the steel sheet in the 45° direction, reduces the anisotropy of the steel sheet, reduces earring defects in the steel sheet after deep drawing, and is easy to increase production efficiency and product yield. In addition, Nb exists in the form of solid solution Nb and NbC, and has the effects of solid solution tension and precipitation pinning in the recrystallization process, so that fine crystal grains can be obtained and the strength of the steel sheet after high-temperature cloisonné tempering can be effectively ensured. Therefore, the cold rolled enamel steel for deep drawing inner pots according to the present invention is board Then, the mass percentage of Nb is 0.002-0.012%.

[0025] In a preferred embodiment, the mass percentage of Nb may be 0.002-0.006%.

[0026] Cr: Cold-rolled enamel steel for deep-drawing inner pots according to the present invention board In the present invention, an appropriate amount of Cr can adjust the unevenness of the steel sheet surface during production and effectively increase the bonding strength between the steel sheet substrate and the enamel glaze. If the Cr content in the steel is too low, the effect of improving enamel adhesion cannot be achieved, but if the Cr content in the steel is too high, not only does the production cost increase, but the pickling process progresses slowly and it is difficult to obtain a rough surface. Therefore, the cold rolled enamel steel for deep drawing inner pots according to the present invention is board In this case, the mass percentage of Cr is 0.01-0.08%.

[0027] In a preferred embodiment, the mass percentage of Cr may be 0.02-0.08%.

[0028] Cu, Ni and Mo: Cold-rolled enamelled steel for deep-drawing inner kettle according to the invention board In the enamel steel, the presence of one or more of Cu, Ni and Mo is unavoidable, and all of these elements have an effect on the adhesion performance of enamel. In the high-temperature cloisonné process, the appropriate content of Cu, Ni and Mo can promote the infiltration of the glaze into the metal, and promote the dissolution of iron and iron oxide in the glaze, so as to form a good transition layer structure in which the metal and the enamel layer are closely bonded. In addition, nickel oxide is favorable for the formation of a relatively uniform bubble structure by the enamel layer, and improves the quality of the enamel layer. However, it should be noted that if the content of Cu, Ni and Mo is too high, not only will the alloy cost increase, but also the bonding strength between the metal and the glaze will decrease. Therefore, the cold-rolled enamel steel for deep-drawing inner pot according to the present invention board In this case, Cu+Ni+Mo≦0.40%.

[0029] In a preferred embodiment, the mass percentages of Cu, Ni and Mo may be Cu+Ni+Mo≦0.25%. In a more preferred embodiment, the mass percentages of Cu, Ni and Mo may be Cu+Ni+Mo≦0.10%, more preferably ≦0.05%.

[0030] In one embodiment, the mass percentage of Cu is 0.005-0.02%. In one embodiment, the mass percentage of Ni is ≦0.02%, preferably ≦0.01%. In one embodiment, the mass percentage of Mo is ≦0.02%, preferably ≦0.01%. In one embodiment, the cold rolled enamel steel for deep drawing inner kettle according to the present invention is board contains Cu 0.005-0.02%; Ni ≦0.02%, preferably ≦0.01%; and Mo ≦0.02%, preferably ≦0.01%. Preferably, Cu+Ni+Mo≦0.05%.

[0031] Furthermore, the present invention provides a cold-rolled enamel steel for deep-drawing inner pots. board In the formula, the mass percent contents of B and N satisfy B / N=0.8-1.5, where B and N each represent the mass percent content of the respective elements.

[0032] In the above technical solution, the cold-rolled enamel steel for deep drawing inner kettle according to the present invention board In this method, the content of each element is controlled, and at the same time, the mass percent content of B and N is controlled to satisfy B / N=0.8-1.5. This is because B is an element that is easily burned off during the steelmaking process, and it is difficult to control it stably. The higher the B content, the more difficult it is to control. If the B / N ratio is too high, that is, if too much B is added, fine Fe 23 Because (CB)6 is formed, the growth of crystal grains is inhibited, and the deep drawing performance of the steel sheet is impaired. And if the ratio of B / N is too low, the resistance to finger-breaking of the steel is poor.

[0033] Furthermore, the present invention provides a cold-rolled enamel steel for deep-drawing inner pots. board wherein each chemical element satisfies at least one of the following formulas: 0.4≦B×N×10 5 ≦10; -2≦Ti×(N-14 / 11B)×10 5 ≦12; In the above formula, B, Ti and N each represent the mass percent content of each element.

[0034] In the technical solution of the present invention, the cold-rolled enamel steel for deep drawing inner pot according to the present invention is board The synergistic relationship between B, Ti and N in steel sheet affects the performance of the steel sheet. B and N are 0.4≦B×N×10 5 If the ratio is not less than 10, a small amount of BN cannot improve the anti-crack performance of the steel plate because BN is an effective irreversible hydrogen trap in steel, whereas an excessive amount of BN pellets precipitates at the grain boundaries of austenite, and these particles are subjected to stress during the continuous casting process. When the stress is concentrated, the formation and expansion of cracks will be accelerated, and finally the corner transverse cracks of the continuously cast slab will occur. This will increase the edge cut amount of the steel plate and reduce the product rate.

[0035] B, Ti and N are -2≦Ti×(N-14 / 11B)×10 5 If the Ti content is too low, the risk of the corner cracking problem of the continuous casting slab caused by the BN pellets will increase significantly; the larger the solid solubility product of Ti and N, the easier it is to form coarse TiN pellets in the molten steel. The coarse TiN pellets cannot inhibit the growth of crystal grains, which is disadvantageous to both the welding performance and the strength after high-temperature cloisonné. The larger the TiN pellets, the smaller the effective surface area around them, which means there is less space available for storing hydrogen atoms, which is disadvantageous to improving the nail-breaking resistance. Therefore, the cold-rolled enamel steel for deep drawing inner kettle according to the present invention board In the above, when the B element, Ti element and N element satisfy the above relationship, it is easy to realize an appropriate amount, fine and dispersed distribution of BN and TiN pellets in the steel. 5 <=0.

[0036] Furthermore, the present invention provides a cold-rolled enamel steel for deep-drawing inner pots. boardIn this case, the mass percentage content of each chemical element satisfies at least one of the following items: C: 0.02 - 0.04%, 0 < Si ≤ 0.05%, Mn: 0.2 - 0.5%, P ≤ 0.035%, S ≤ 0.015%, Al: 0.01 - 0.04%, N: 0.003 - 0.008%, B: 0.0025 - 0.0065%, Ti: 0.002 - 0.008%, Nb: 0.002 - 0.006%, Cr: 0.02 - 0.08%, and at least one of Cu, Ni, and Mo, Cu + Ni + Mo ≤ 0.25%; preferably, Cu 0.005 - 0.02%; Ni ≤ 0.02%, preferably ≤ 0.01%; Mo ≤ 0.02%, preferably ≤ 0.01%, and preferably, Cu + Ni + Mo ≤ 0.05%.

[0037] Furthermore, the cold-rolled enameling steel for deep-drawing inner pots according to the present invention board In this case, its microstructure is uniform and fine ferrite, lamellar pearlite, and pseudo-pearlite, and the phase ratio (volume ratio) of pearlite < 3%; there are a large number of voids between the cementite pellets and ferrite in the above pearlite (including lamellar pearlite and pseudo-pearlite). The above voids are generated during the cold rolling process and are determined by the number, size of the second-phase particles, and the magnitude of the cold rolling reduction ratio. The more, finer the second-phase particles and the larger the cold rolling reduction ratio, the more voids are generated.

[0038] Furthermore, the cold-rolled enameling steel for deep-drawing inner pots according to the present invention board In this case, the lamellar pearlite is located at the grain boundary triple line of ferrite, and the cementite pellets in the pseudo-pearlite are located at the ferrite grain boundaries or inside the ferrite grains.

[0039] Furthermore, the cold-rolled enameling steel for deep-drawing inner pots according to the present invention board In this case, the crystal grain size of ferrite is grade 7.5 - 8.

[0040] Furthermore, the cold-rolled enameling steel for deep-drawing inner pots according to the present invention boardThe performance satisfies at least one of the following requirements: yield strength 220-280 MPa, elongation 38-43%, hydrogen permeation time ≥ 8 min, and yield strength ≥ 200 MPa after high temperature cloisonné at least 850°C for at least 12 min. In one embodiment, the cold rolled enamel steel for deep drawing inner pot according to the present invention. board The tensile strength is 320-390MPa.

[0041] Another object of the present invention is to provide a cold-rolled enamel steel for deep drawing inner pots. board This manufacturing method uses appropriate rolling control and cooling control processes and a high-temperature rapid continuous annealing process to achieve a dispersed distribution of boron, titanium and niobium carbonitrides in the steel, and obtains a uniform and fine ferrite + small amount of lamellar and pseudo-pearlite structure. The cold-rolled enamel steel for deep drawing inner kettles manufactured by this manufacturing method is board The ferrite grain size is 7.5-8 grade, the yield strength is 220-280MPa, the elongation is 38-43%, the hydrogen permeation time is ≥ 8min, and the yield strength after high-temperature cloisonné at least 850℃ for at least 12min is ≥ 200MPa. It has good formability, high strength after high-temperature cloisonné, excellent welding performance and excellent resistance to nail chipping, and is suitable for making enameled inner kettles of electric water heaters and other products which have high requirements for forming.

[0042] In order to achieve the above object, the present invention provides the above-mentioned cold-rolled enamel steel for deep drawing inner pot, which comprises the following steps: board Providing a practical manufacturing method: (1) Smelting, refining and continuous casting activities; (2) Heat the slab; (3) Hot rolling and coiling; (4) Pickling; (5) Cold rolling: cold rolling reduction is 60-70%; (6) Continuous annealing: soaking temperature is 800-830℃, soaking time is 100-150s, overaging temperature is 350-450℃, overaging time is 250-350s; (7)Level up.

[0043] Cold-rolled enamelled steel for deep-drawing inner pots according to the present invention board In the manufacturing method of the present invention, the smelting and refining operations in step (1) can remove harmful gases such as nitrogen gas and hydrogen gas from the molten steel, realize decarbonization and deoxidization, and ultimately homogenize the composition and temperature of the molten steel. In the continuous casting operation in step (1), the molten steel is sent to a rotating table and passes through equipment such as an intermediate tank, a crystallizer, a secondary cooling stage, and a tension leveler to obtain a continuously cast slab with good shape, surface quality, and internal structure.

[0044] In the manufacturing method according to the present invention, the pickling in the above step (4) can remove the oxide scale on the surface of the hot-rolled steel strip, which can facilitate the subsequent operations.

[0045] In the cold rolling operation of step (5), the cold rolling reduction affects the formability and anti-claw snapping performance of the steel. Usually, the larger the reduction, the larger the deformation storage energy of the steel sheet, and the easier it is for recrystallization to occur during annealing, and the easier it is for the recrystallization structure to fully develop. The second phase pellets are crushed during the cold rolling process, and voids are formed between the periphery and the ferrite substrate, which makes it easier for hydrogen atoms to diffuse, and the larger the cold rolling reduction, the more voids there are, and the stronger the anti-claw snapping performance. If the cold rolling reduction is less than 60%, it is difficult to obtain good formability, and if the cold rolling reduction exceeds 70%, the deformation resistance of the cold rolled strip steel is too large and exceeds the support capacity of the mechanical system. Therefore, in step (5) of the manufacturing method according to the present invention, the cold rolling reduction is 60-70%. In one embodiment, the thickness of the cold rolled sheet may be in the range of 1.5-2.5 mm, for example, 1.5-2.0 mm.

[0046] Meanwhile, the above step (6) uses a high-temperature rapid continuous annealing process, with a soaking temperature of 800-830°C, soaking time of 100-150s, overaging temperature of 350-450°C, and overaging time of 250-350s. Combined with the cold rolling process, it can realize the formation and development of recrystallized structure, obtain uniform and fine ferrite grains, promote the simultaneous improvement of the strength and plasticity of the steel sheet, and at the same time, the cementite pellets can be re-dissolved and precipitated during the annealing process, so that the steel sheet is more likely to exhibit its anti-claw performance.

[0047] Furthermore, in the manufacturing method according to the present invention, the heating temperature in step (2) is 1100-1250°C.

[0048] Cold-rolled enamelled steel for deep-drawing inner pots according to the present invention board In the manufacturing method, when the heating temperature in step (2) is 1100-1250°C, a uniform austenite structure is obtained. When the heating temperature is lower than 1100°C, the deformation resistance of the steel is large, and hot rolling is difficult to proceed. In addition, when the heating temperature exceeds 1250°C, problems such as decarbonization of the steel slab and thick oxide scale are likely to occur during the heating process. The heating time in step (2) may be 120-200 minutes, for example 130-180 minutes.

[0049] Furthermore, in the manufacturing method according to the present invention, in step (3), the finish rolling temperature in the hot rolling is 880-920°C, and the coiling temperature is 680-720°C.

[0050] Cold-rolled enamelled steel for deep-drawing inner pots according to the present invention board In the manufacturing method of the above, in step (3), the finish rolling temperature of the hot rolling is 880-920°C. If the finish rolling temperature is less than 880°C, the finish rolling falls in the two-phase region, resulting in a fine ferrite mixed structure formed by transition from massive pro-eutectoid ferrite and deformed austenite, which has a negative effect on the mechanical properties of the steel sheet. If the finish rolling temperature exceeds 920°C, the deformed austenite is easily restored, which is disadvantageous for refining the ferrite grains.

[0051] In addition, the present invention uses a high coiling temperature. When the coiling temperature is set to 680-720°C, not only is the formability of the steel sheet easily improved, but the second phase pellets are easily dispersed and precipitated, and the resistance to finger chipping of the steel can be effectively improved.

[0052] Furthermore, in the manufacturing method according to the present invention, the leveling reduction in step (7) is 0.8-1.2%.

[0053] In the above-mentioned embodiment, when leveling is performed in step (7) with a leveling reduction rate of 0.8-1.2%, not only can the flatness and surface gloss of the steel sheet be improved, but also a "yield shelf" is not generated when the steel sheet is pressed after a certain storage time. Effect of the Invention

[0054] Cold-rolled enamelled steel for deep-drawing inner pots according to the present invention board And the manufacturing method thereof has the following advantages and beneficial effects compared with the prior art: Cold-rolled enamelled steel for deep-drawing inner pots according to the present invention board In the steel, an appropriate amount of boron, nitrogen, and trace amounts of titanium and niobium are added to the basic low carbon steel, and alloy elements such as copper and chromium, which improve the adhesion of enamel, are also added, resulting in a uniform and fine ferrite + lamellar and pseudo-pearlite microstructure. Pearlite has the effect of strengthening the substrate, and the cementite pellets in the pearlite act as irreversible hydrogen traps to improve the nail-flying resistance of the steel. In the design of the chemical composition, by adding an appropriate amount of boron and nitrogen to the steel, the BN pellets formed and dispersed and precipitated by the combination of the two not only significantly improve the nail-flying resistance of the steel as an effective hydrogen trap, but also effectively increase the growth ability of ferrite, giving the steel good formability. The trace amount of titanium added to the steel can replace some of the boron and combine with nitrogen to form TiN particles, which reduces the risk of cracking of continuous casting slabs due to BN, and is also advantageous for welding performance.

[0055] Cold-rolled enamel steel for the above deep-drawn inner pot board The ferrite grain size is 7.5-8 grade, the yield strength is 220-280MPa, the elongation is 38-43%, the hydrogen permeation time is ≥8min, and the yield strength after high-temperature cloisonné at least 850℃ for at least 12min is ≥200MPa. It has good formability, high strength after high-temperature cloisonné, excellent welding performance and excellent anti-toeing performance, and can be effectively applied to the enamel inner pot of electric water heater, which has high forming requirements.

[0056] In addition, the manufacturing method of the present invention uses an appropriate rolling control / cooling control process and a high-temperature rapid continuous annealing process to realize a dispersed distribution of carbon nitrides of boron, titanium and niobium. As a result, the cold-rolled enamel steel for deep drawing inner kettles obtained by the manufacturing method of the present invention can be obtained. board The result is a uniform and fine ferrite + small amount of lamellar and pseudo-pearlite structure. The lamellar pearlite is located at the ferrite grain boundary triple line, and the cementite pellets of the pseudo-pearlite are located at the ferrite grain boundary and inside the grains. board It has properties such as high strength after high-temperature cloisonné firing, high formability, and excellent resistance to chipping. [Brief description of the drawings]

[0057] [Figure 1] FIG. 1 is a microstructure diagram of the cold-rolled enameled steel sheet for deep drawing inner kettle of Example 1. [Diagram 2] FIG. 2 shows a typical pearlite morphology in the microstructure of the cold-rolled enameled steel sheet for deep drawing inner kettle of Example 1. [Diagram 3] FIG. 3 shows the pseudo-pearlite morphology in the microstructure of the cold-rolled enameled steel sheet for deep drawing inner kettle of Example 1. [Figure 4] FIG. 4 shows the location of boron element in the cold-rolled enamel steel sheet for deep drawing inner kettle of Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] Hereinafter, the cold-rolled enamel steel for deep drawing inner pot according to the present invention will be described with reference to specific examples and drawings. board And the manufacturing method thereof will be described in more detail, but the description does not limit the technical solution of the present invention.

[0059] Examples 1-6 and Comparative Examples 1-2 Table 1 shows the cold-rolled enamel steel for deep drawing inner pot of Examples 1-6. board and the enameled steel of Comparative Example 1-2 board The mass percentage of each chemical element in the sample is shown.

[0060] [Table 1]

[0061] Cold-rolled enamel steel for deep drawing inner pot of Examples 1-6 according to the present invention board and the enameled steel of Comparative Example 1-2 board Each was prepared by the following steps: (1) Smelting, refining and continuous casting activities; (2) Slab heating: The heating temperature is set to 1100-1250°C, the heating time is controlled, and the slab is fully austenitized before being hot-rolled; (3) Hot rolling and coiling: the finishing rolling temperature of hot rolling is 880-920℃, and after rolling, the strip is water-cooled, air-cooled or slowly cooled, and then the coiling temperature is 680-720℃, and the strip is coiled; (4) Pickling; (5) Cold rolling: cold rolling reduction is 60-70%; (6) Continuous annealing: soaking temperature is 800-830℃, soaking time is 100-150s, overaging temperature is 350-450℃, overaging time is 250-350s; (7) Leveling: The leveling reduction ratio is 0.8-1.2%.

[0062] Tables 2-1 and 2-2 show the cold-rolled enamel steel for deep drawing inner pots of Examples 1-6. board The specific process parameters of the enameled steel of comparative cold 1-2 are shown below.

[0063] [Table 2-1]

[0064] [Table 2-2]

[0065] It should be noted that in the actual operation process, the overaging temperature changes and is not stable as a fixed value. During the overaging time, the temperature gradually decreases, so the overaging temperature in step (6) of Table 2-2 does not indicate a single value but a range of values ​​in each example and comparative example.

[0066] Cold-rolled enamel steel for deep drawing inner pot of Example 1-6 board and the enameled steel of Comparative Example 1-2 board Each performance test was carried out on the following items. The specific test methods are as follows: Cold-rolled enamel steels of Examples 1-6 and Comparative Examples 1-2 board A high-temperature simulated cloisonné test was conducted on this material, with the cloisonné temperature set to 850°C and the in-furnace time set to 12 minutes. The mechanical properties were measured and the results are shown in Table 3.

[0067] The cold-rolled enamelled steels of Examples 1-6 and Comparative Examples 1-2 were prepared using a wet glazing process. First, the steel sheets were pretreated to obtain a surface suitable for glazing. Then, the steel sheets coated with glaze were placed in a drying oven at 110°C and dried. Finally, they were fired in a high-temperature oven. The cloisonné temperature was 850°C and the time in the oven was 12 minutes. The enamelled steel sheets were air-cooled to room temperature, and then the adhesion performance was measured according to the European standard EN 10209-2013. A steel ball was dropped from a height of 750 mm and collided with the enamelled steel sheet surface. The adhesion level was determined by observing the degree of bonding between the glaze and the steel sheet, and the enamelled steel sheets were left for 72 hours or more to observe the condition of chipping. Furthermore, to evaluate the nail-breaking resistance of the steel sheets, the hydrogen permeation values ​​of the steel sheets were measured according to the European standard EN 10209-2013 and converted into hydrogen permeation times at a thickness of 1 mm, where the yield strength and tensile strength were measured according to GB / T 228.1-2010, and the elongation was measured according to GB / T 228.1-2010.

[0068] Table 3 shows the cold-rolled enamel steel for deep drawing inner pot of Examples 1 to 6. board and the enameled steel of Comparative Example 1-2 board The measurement results of each performance are shown below.

[0069] [Table 3]

[0070] As can be seen from Tables 1 to 3, the cold-rolled enamel steel of Comparative Example 1 has a low B content, so the number of effective hydrogen traps in the steel sheet is insufficient, and the nail-fly resistance cannot be effectively improved. In particular, in special equipment where all openings face downward, nail-fly defects are likely to occur during high-temperature cloisonné. The cold-rolled enamel steel of Comparative Example 2 has a high Ti content, so in addition to the formation of coarse TiN and TiS pellets, finely dispersed TiC also precipitates, resulting in an increase in strength and a decrease in elongation. In addition, Ti is prone to form TiO2 at high temperatures, so the adhesion level of the steel sheet is significantly reduced.

[0071] As can be seen from Table 3, the cold-rolled enamel steel for deep drawing inner pots of Examples 1-6 of the present invention board In the present invention, the phase ratio of pearlite is <3%, the grain size of ferrite is 7.5-8 grade, the longitudinal yield strength is 220-280MPa, the elongation is 38.0-43.0%, and the yield strength after high-temperature cloisonné annealing at 850℃ for at least 12min is ≧200MPa. In addition, the steel sheet after wet glazing on one side has a good bonding degree between the enamel layer and the steel sheet, which is A1 grade, and no nail-popping phenomenon occurs even after long-term storage. When measured, the hydrogen permeability of the steel sheet (converted to 1mm thickness) is ≧8min, exceeding the threshold value of 6.7min specified in the European standard EN 10209-2013. The cold-rolled enamel steel for deep drawing inner pots of each embodiment of the present invention is board Even when glazed on both sides, no chipping occurred, demonstrating excellent chipping resistance.

[0072] FIG. 1 shows the cold-rolled enamel steel for deep drawing inner pot of Example 1. board FIG. As shown in FIG. 1, the cold-rolled enamel steel for deep drawing inner pot of Example 1 according to the present invention is board In the present study, the microstructure is composed of polygonal ferrite and a small amount of lamellar and pseudo-pearlite, the lamellar pearlite is distributed at the grain boundary triple line of ferrite, and the cementite pellets of the pseudo-pearlite are distributed at the ferrite grain boundaries and inside the grains.

[0073] FIG. 2 shows the cold-rolled enamel steel for deep drawing inner pot of Example 1. board The typical pearlite morphology in the microstructure is shown.

[0074] FIG. 3 shows the cold-rolled enamel steel for deep drawing inner pot of Example 1. board The pseudo-pearlite morphology in the microstructure of the specimen is shown.

[0075] As can be seen by taking FIG. 2 and FIG. 3 together, the cold-rolled enamel steel for deep drawing inner pot of Example 1 according to the present invention is boardIn the steel, pearlite contains not only typical lamellar pearlite but also pseudo-pearlite structure. The cementite is not continuous but tends to be elliptical or rectangular. This may be because the addition of B reduces the content of solute carbon in the steel, which prevents the formation of a complete lamellar pearlite structure. As can be seen from Figure 3, the pseudo-pearlite cementite pellets exist at the ferrite grain boundaries and inside the grains. Research has shown that BN or boron carbide segregates at the grain boundaries and inhibits the precipitation of carbides at the grain boundaries, which tend to precipitate on the substrate.

[0076] FIG. 4 shows the cold-rolled enamel steel for deep drawing inner pot of Example 1. board The location of boron in the

[0077] Cold-rolled enamel steel for deep drawing inner kettle according to embodiment 1 of the present invention board In the steel, the B element does not exist in the form of a single atom, but combines with the N element or the C element to form a complex compound BN or boron carbide pellet, which segregates on the grain boundary or on the cementite within the crystal.

[0078] It should be noted that the above-mentioned embodiments are only specific embodiments of the present invention, and the present invention is not limited to the above-mentioned embodiments, and similar changes and modifications can be directly obtained or easily conceived by those skilled in the art from the disclosure of the present invention, and therefore, they are within the protection scope of the present invention.

Claims

1. A cold-rolled enamelled steel sheet for deep drawing inner kettles, the mass percentages of chemical elements being: C: 0.02-0.06%, 0<Si≦0.08%, Mn: 0.1-0.7%, P≦0.055%, S≦0.03%, Al: 0.01-0.07%, N: 0.002-0.010%, B: 0.002-0.009%, Ti: 0.002-0.015%, Nb: 0.002-0.0097%, Cr: 0.01-0.08%, and at least one of Cu, Ni and Mo; Cu+Ni+Mo≦0.40%; the balance being Fe and other unavoidable impurities, The chemical elements contained in the cold rolled enameled steel sheet for deep drawing inner kettle satisfy the following formulas: B / N=0.8-1.5; 0.4≦B×N×10 ５ ≦10; -2≦Ti×(N-14 / 11B)×10 ５ ≦12; The cold-rolled enameled steel sheet for deep drawing inner pots has a microstructure which is uniform and fine ferrite, lamellar pearlite and pseudo-pearlite, the total phase ratio of the lamellar pearlite and the pseudo-pearlite being <3%; voids exist between the cementite pellets in the pearlite and the ferrite, and the crystal grain size of the ferrite is 7.5-8 class.

2. The cold rolled enamel steel sheet for deep drawing inner pots according to claim 1, wherein the mass percent content of each of the chemical elements satisfies at least one of the following items: C: 0.02-0.04%, 0<Si≦0.05%, Mn: 0.2-0.5%, P≦0.035%, S≦0.015%, Al: 0.01-0.04%, N: 0.003-0.008%, B: 0.0025-0.0065%, Ti: 0.002-0.008%, Nb: 0.002-0.006%, Cr: 0.02-0.08%, and at least one of Cu, Ni and Mo; Cu+Ni+Mo≦0.25%.

3. 2. The cold-rolled enameled steel sheet for deep drawing inner pots according to claim 1, wherein the lamellar pearlite is located at the triple grain boundary line of ferrite, and the cementite pellets in the pseudo-pearlite are located at the ferrite grain boundaries or inside the grains.

4. The cold-rolled enameled steel sheet for deep drawing inner kilns according to claim 1, wherein the cold-rolled enameled steel sheet for deep drawing inner kilns satisfies at least one of the following properties: yield strength 220-280 MPa, elongation 38-43%, hydrogen permeation time ≥ 8 min, and yield strength ≥ 200 MPa after high-temperature cloisonné annealing at at least 850°C for at least 12 min.

5. The cold-rolled enamel steel sheet for deep drawing inner pots according to claim 1, wherein Cu: 0.005-0.02%, Ni: ≦0.02%, Mo: ≦0.02%, and Cu + Ni + Mo ≦0.05%.

6. A manufacturing method for manufacturing the cold-rolled enameled steel sheet for a deep drawing inner kettle according to any one of claims 1 to 5, comprising the following steps: (1) Smelting, refining and continuous casting activities; (2) Heat the slab; (3) hot rolling and coiling; (4) Pickling; (5) Cold rolling: cold rolling reduction ratio is 60-70%; (6) Continuous annealing: soaking temperature is 800-830°C, soaking time is 100-150s, overaging temperature is 350-450°C, and overaging time is 250-350s; (7) Leveling is performed.

7. The method according to claim 6, wherein in step (2), the heating temperature is 1100-1250°C.

8. The method according to claim 6, wherein in step (3), the finish rolling temperature of the hot rolling is 880-920°C, and the coiling temperature is 680-720°C.

9. The method according to claim 6, wherein in step (7), the leveling reduction is 0.8-1.2%.

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