A low carbon steel and a method of making the same

Abstract

The application provides a low-carbon steel and a preparation method thereof, and belongs to the field of low-carbon steel preparation. The method comprises the following steps: heating and rolling a slab to obtain a strip steel, wherein the slab comprises the following chemical components in mass fraction: C: 0.02%-0.04%, Si: 0.02%-0.05%, Mn: 0.2%-0.5%, Cu: 0.1%-0.4%, Sn: 0.01%-0.04%, Ni: 0.02%-0.15%, Alt: 0.03%-0.05%, P≤0.01%, S≤0.01%, and N≤0.005%; wherein the Cu, the Ni and the Sn satisfy the following relationship: [Cu]+8[Sn]-[Ni]≤0.3, wherein [Cu] represents the mass fraction of Cu, [Ni] represents the mass fraction of Ni, and [Sn] represents the mass fraction of Sn; the heating temperature is 1200-1250 DEG C; and the strip steel is subjected to cold rolling, continuous hot galvanizing annealing and second coiling to obtain the low-carbon steel. By adding Cu, Sn and Ni elements satisfying the relationship [Cu]+8[Sn]-[Ni]≤0.3, the Cu solubility is improved, the Cu-rich phase is migrated to the oxide layer, the Cu enrichment at the interface between the substrate and the oxide layer is effectively reduced, and the Cu thermal embrittlement surface defects are reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of low-carbon steel preparation, and in particular to a low-carbon steel and a preparation method thereof. BACKGROUND

[0002] There are mainly two production processes in the steel industry, one is a long process of a blast furnace-converter, and the other is an electric furnace short process. Compared with converter steelmaking, electric furnace steelmaking has obvious energy-saving and emission-reducing effects, and can reduce CO2 emissions. Domestic electric furnace steelmaking is still in the early stage of development, and the proportion of electric furnace steelmaking is significantly lower than that in foreign developed countries. The main raw material for electric furnace steelmaking is scrap iron. As known, copper will cause hot brittleness problems in the process of scrap iron steelmaking. The Cu element in the scrap iron has a lower oxidation potential than iron, and is not easy to remove in the steelmaking process, and is easy to enrich at the interface of the substrate and the oxide layer and penetrate into the grain boundary in the process of high-temperature heating and rough rolling, causing high-temperature hot brittleness, and thus causing surface "hot brittleness" crack defects in the process of hot working.

[0003] Therefore, it is necessary to develop a production method of low-carbon steel capable of reducing Cu hot brittleness surface defects, so as to solve the technical problem that it is difficult to reduce the hot brittleness surface defects of low-carbon steel under the condition of high Cu content, and thus promote the sustainable development of electric furnace steelmaking in the field of the steel industry. SUMMARY

[0004] The application provides a low-carbon steel and a preparation method thereof, so as to solve the technical problem of hot brittleness surface defects of low-carbon steel which is difficult to avoid under the condition of high Cu content.

[0005] In a first aspect, the application provides a preparation method of low-carbon steel, and the method comprises the following steps:

[0006] The slab is heated, rolled and first coiled to obtain a strip steel, the slab comprises the following mass fractions of chemical components: C: 0.02% to 0.04%, Si: 0.02% to 0.05%, Mn: 0.2% to 0.5%, Cu: 0.1% to 0.4%, Sn: 0.01% to 0.04%, Ni: 0.02% to 0.15%, Alt: 0.03% to 0.05%, P≤0.01%, S≤0.01%, N≤0.005%; wherein the Cu, the Ni and the Sn satisfy the following relationship: [Cu]+8[Sn]-[Ni]≤0.3, wherein [Cu] represents the mass fraction of Cu, [Ni] represents the mass fraction of Ni, and [Sn] represents the mass fraction of Sn; the heating temperature is 1200°C to 1250°C;

[0007] The strip steel is cold-rolled, continuously hot-dip galvanized and annealed, and second coiled to obtain a low-carbon steel.

[0008] Optionally, the Cu, the Ni and the Sn satisfy the following relationship: 0.1 ≤ [Cu]+8[Sn]-[Ni] ≤ 0.3,

[0009] In the formula, [Cu] represents the mass fraction of Cu, [Ni] represents the mass fraction of Ni, and [Sn] represents the mass fraction of Sn.

[0010] Optionally, the final rolling temperature of the rolling is 870-950℃.

[0011] Optionally, the temperature of the first coiling is 600-670℃.

[0012] Optionally, the reduction of the cold rolling is 50-70%.

[0013] Optionally, the continuous hot galvanizing annealing comprises preheating, heating, holding, slow cooling, rapid cooling, galvanizing, post-galvanizing cooling, final cooling and leveling.

[0014] Optionally, the end temperature of the preheating is 200-240℃, the speed of the preheating is 8-12℃ / s; the end temperature of the heating is 780-830℃, the speed of the heating is 1.5-4℃ / s; and the holding time is 60-100s.

[0015] Optionally, the end temperature of the slow cooling is 720-760℃, the speed of the slow cooling is 8-12℃ / s; the end temperature of the rapid cooling is 450-460℃; and the end temperature of the post-galvanizing cooling is 420-430℃.

[0016] Optionally, the end temperature of the final cooling is 250-300℃, and the speed of the final cooling is 6-9℃ / s.

[0017] In a second aspect, the application provides a low-carbon steel prepared by the method of any one of the first aspect, the microstructure of the low-carbon steel comprising ferrite and pearlite, the volume fraction of the ferrite being 75-90%, and the volume fraction of the pearlite being 10-25%.

[0018] Compared with the prior art, the above technical solution provided by the embodiments of the application has the following advantages:

[0019] The application adds Cu, Sn and Ni elements satisfying the relationship [Cu]+8[Sn]-[Ni]≤0.3, improves the solubility of Cu, and makes the Cu-rich phase migrate to the oxidation layer, effectively reducing the enrichment of Cu at the interface between the substrate and the oxidation layer, thereby reducing the Cu hot short surface defects. In addition, the slab adopts an oxidation heating temperature of 1200°C or higher, which can promote selective oxidation of iron through grain boundary oxidation or internal oxidation, causing the substrate and the oxidation layer interface to be uneven, thereby causing the Cu-rich phase to migrate to the oxidation layer, reducing the enrichment of Cu at the interface, and effectively reducing the Cu hot short surface defects of low carbon steel. BRIEF DESCRIPTION OF DRAWINGS

[0020] The drawings incorporated into the specification and forming a part thereof, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, for those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative labor.

[0022] Figure 1 A flowchart of a low carbon steel preparation method according to an embodiment of the present application is shown in the figure.

[0023] Figure 2 A metallographic structure photo of the low carbon steel according to Embodiment 1 of the present application is shown in the figure. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0025] Various embodiments of the present application can exist in a range of forms; it should be understood that the description in a range form is merely for the convenience and brevity, and should not be understood as a hard limitation to the scope of the present application; therefore, it should be considered that the described range has disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single values within the described range, such as 1, 2, 3, 4, 5, and 6, which applies to any range. In addition, whenever a numerical range is indicated in the present application, it refers to any cited number (fraction or integer) within the indicated range.

[0026] In addition, in the description of the present application, the terms "include", "contain" and the like mean "include but not limited to". In the present application, the relationship terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. In the present application, "and / or" describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent the cases of A alone, A and B together, and B alone. Wherein A and B can be singular or plural. In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of the items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple.

[0027] Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0028] In a first aspect, the present application provides a method for preparing low carbon steel, please refer to Figure 1 , the method comprises:

[0029] S1, heating, rolling, first coiling a slab to obtain a strip, the slab comprising the following mass fractions of chemical components: C: 0.02% to 0.04%, Si: 0.02% to 0.05%, Mn: 0.2% to 0.5%, Cu: 0.1% to 0.4%, Sn: 0.01% to 0.04%, Ni: 0.02% to 0.15%, Alt: 0.03% to 0.05%, P≤0.01%, S≤0.01%, N≤0.005%; wherein the Cu, the Ni and the Sn satisfy the following relationship: [Cu]+8[Sn]-[Ni]≤0.3, wherein [Cu] represents the mass fraction of Cu, [Ni] represents the mass fraction of Ni, and [Sn] represents the mass fraction of Sn; the temperature of the heating is 1200°C to 1250°C;

[0030] In the embodiments of the present application, the positive effect of controlling the mass fraction of Cu to be 0.1% to 0.4% is that, within this mass fraction range, the Cu element can generate refined Cu precipitates with precipitation strengthening effect, which is beneficial to ensure the strength of the steel. When the mass fraction is greater than the maximum value of the end point of this range, the Cu content is too high, which cannot avoid Cu thermal embrittlement and affects the surface quality of the steel. When the mass fraction is less than the minimum value of the end point of this range, the Cu content is too low, which cannot achieve the Cu precipitation strengthening effect. The mass fraction of Cu can be 0.1%, 0.2%, 0.3%, 0.4%, etc.

[0031] The positive effect of controlling the mass fraction of C to be 0.03% to 0.04% is that, within this mass fraction range, the C element is the most important solid solution strengthening element in steel to ensure a certain strength. When the mass fraction is greater than the maximum value of the end point of this range, the C content is too high, which leads to excessive hardness of the steel and affects the flexibility of the steel. When the mass fraction is less than the minimum value of the end point of this range, the C content is too low, which cannot guarantee the strength of the steel. The mass fraction of C can be 0.03%, 0.035%, 0.04%, etc.

[0032] The positive effect of controlling the mass fraction of Si to be 0.02% to 0.05% and the mass fraction of Alt to be 0.03% to 0.05% is that, within this mass fraction range, both are deoxidizing elements, which improve the activity of C and are ferrite stabilizing elements. However, excessive addition of Si (Al) will generate iron oxide scale on the surface, thereby deteriorating the surface, and generate oxides in the welding process, which is prone to defects at the welding site. The mass fraction of Si can be 0.02%, 0.03%, 0.04%, 0.05%, etc., and the mass fraction of Alt can be 0.03%, 0.035%, 0.04%, 0.05%, etc.

[0033] The positive effects of controlling the mass fraction of Mn to be between 0.2% and 0.5% are as follows: Within this range, Mn is an important element for solid solution strengthening and austenite stabilization, playing a crucial role in enhancing the mechanical properties of steel. Mn also forms MnS with sulfur, fixing the sulfur and preventing edge cracks caused by low-melting-point sulfides. When the mass fraction exceeds the maximum value at the end of this range, the excessive Mn content can easily cause segregation, leading to cracking during steel forming and deteriorating the mechanical properties of the steel. Furthermore, during annealing, the segregated precipitates can accumulate on the surface, causing surface cracking. When the mass fraction is less than the minimum value at the end of this range, the insufficient Mn content will prevent effective solid solution strengthening and the inability to fix sulfur, resulting in edge cracking. The appropriate Mn mass fraction can be 0.2%, 0.3%, 0.4%, or 0.5%, etc.

[0034] The positive effects of controlling the P mass fraction to ≤0.01% include: within this range, P segregates at austenite grain boundaries in steel at high temperatures, thus mitigating Cu grain boundary enrichment. However, if P is greater than 0.10%, it readily segregates at ferrite grain boundaries formed during cooling, thereby reducing the secondary machinability of the steel sheet. The P mass fraction can be 0.001%, 0.003%, 0.006%, 0.008%, 0.01%, etc.

[0035] The positive effect of controlling the sulfur (S) mass fraction to ≤0.01% is that within this range, S, being a harmful element, combines with manganese (Mn) to form MnS, thereby deteriorating the mechanical properties of steel and increasing the risk of cracking. When the mass fraction exceeds the maximum value at the extreme end of this range, it results in excessive S content. This necessitates increasing the amount of aluminum (Al) to remove it, but also weakens the mechanical properties of the steel, further increasing the risk of cracking. The S mass fraction can be 0.001%, 0.003%, 0.006%, 0.008%, 0.01%, etc.

[0036] The positive effect of controlling the mass fraction of nitrogen (N) to ≤0.005% is that within this range, N forms precipitates that tend to accumulate at grain boundaries, leading to decreased grain boundary strength and deterioration of the material's mechanical properties, thus increasing the risk of steel cracking. Conversely, when the mass fraction exceeds the maximum value at the extreme end of this range, excessive N content results in increased precipitates, affecting the steel's performance and further increasing the risk of cracking. This N mass fraction can be 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, etc.

[0037] The positive effects of controlling the Ni mass fraction to be between 0.02% and 0.15% are as follows: Within this range, it increases the solubility of Cu and simultaneously induces internal oxidation to create irregular oxide interfaces, inducing copper enrichment to migrate from the interface to the oxide layer, thereby inhibiting Cu enrichment and reducing surface defects. However, due to the high cost of Ni, it is not advisable to add too much for economic reasons. Suitable Ni mass fractions include 0.02%, 0.04%, 0.07%, 0.12%, and 0.15%.

[0038] The positive effects of controlling the Sn mass fraction to 0.02%–0.15% include: within this range, selecting an appropriate high-temperature coiling temperature for Sn-containing low-carbon steel can achieve excellent processing performance. However, when the Sn content exceeds 0.04%, processing performance deteriorates significantly. Simultaneously, Sn reduces the solubility of Cu, promoting Cu enrichment at the interface. Suitable Sn mass fractions are 0.02%, 0.04%, 0.07%, 0.12%, and 0.15%.

[0039] The positive effects of controlling [Cu] + 2[Sn] - [Ni] ≤ 0.3: Within this mass fraction range, controlling the content relationship among the three components can increase the solubility of Cu and simultaneously allow Cu to accumulate and migrate into the oxide layer, thereby effectively reducing Cu accumulation at the substrate-oxide interface and preventing surface cracks in the steel. When the mass fraction value exceeds the endpoint of this range, interface Cu accumulation cannot be effectively controlled, thus affecting the surface quality of the steel. The values ​​of [Cu] + 2[Sn] - [Ni] can be 0.1, 0.15, 0.20, 0.25, 0.30, etc.

[0040] In some embodiments, the Cu, Ni, and Sn satisfy the following relationship: 0.1 ≤ [Cu] + 8[Sn] - [Ni] ≤ 0.3.

[0041] In the formula, [Cu] represents the mass fraction of Cu, [Ni] represents the mass fraction of Ni, and [Sn] represents the mass fraction of Sn.

[0042] In some embodiments, the heating temperature is 1200°C to 1250°C.

[0043] The positive effects of controlling the heating temperature to 1200℃~1250℃ are as follows: Within this temperature range, above 1200℃, grain boundary oxidation or internal oxidation promotes selective oxidation of iron, causing unevenness at the interface between the substrate and the oxide layer. This leads to the migration of Cu-enriched phases into the oxide layer, effectively preventing Cu enrichment at the interface. When the temperature is higher or lower than the extreme values ​​of this range, the phase transformation of the billet will be insufficient, affecting subsequent roughing and finishing rolling. The heating temperature can be 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, etc.

[0044] In some embodiments, the final rolling temperature is 870°C to 950°C.

[0045] The positive effects of controlling the final rolling temperature to 870℃~950℃ are: within this temperature range, the heat deformation resistance and elongation of the steel plate can be guaranteed to be within a suitable range, thus ensuring the smooth progress of rolling. The final rolling temperature can be 870℃, 890℃, 910℃, 930℃, 950℃, etc.

[0046] In some embodiments, the winding temperature is 600°C to 670°C.

[0047] The positive effects of controlling the coiling temperature to 600℃~670℃ are: within this temperature range, ε-Cu precipitates are ensured to precipitate as small particles, playing a precipitation strengthening role, thus guaranteeing good mechanical properties of the steel after coiling, and ensuring the smooth progress of the subsequent cold rolling stage. The coiling temperature can be 600℃, 610℃, 630℃, 650℃, 670℃, etc.

[0048] S2. The strip steel is cold rolled, continuously hot-dip galvanized and annealed, and then coiled a second time to obtain low-carbon steel.

[0049] In some embodiments, the cold rolling reduction rate is 50% to 70%.

[0050] The reduction rate of the cold rolling can be 50%, 55%, 60%, 65%, 70%, etc.

[0051] In some embodiments, the continuous hot-dip galvanizing annealing includes: preheating, heating, holding, slow cooling, rapid cooling, galvanizing, post-galvanizing cooling, final cooling and leveling.

[0052] In some embodiments, the final temperature of the preheating is 200℃~240℃, and the preheating rate is 8℃ / s~12℃ / s; the final temperature of the heating is 780℃~830℃, and the heating rate is 1.5℃ / s~4℃ / s; the holding time is 60s~100s.

[0053] In some embodiments, the endpoint temperature of the slow cooling is 720°C to 760°C, and the slow cooling rate is 8°C / s to 12°C / s; the endpoint temperature of the rapid cooling is 450°C to 460°C; and the endpoint temperature of the post-plating cooling is 420°C to 430°C.

[0054] In some embodiments, the final cooling endpoint temperature is 250°C to 300°C, and the final cooling rate is 6°C / s to 9°C / s.

[0055] During the preheating process, the cold-deformed ferrite recovers. The final temperature of the preheating can be 200℃, 210℃, 220℃, 230℃, 240℃, etc., and the preheating rate can be 8℃ / s, 9℃ / s, 10℃ / s, 11℃ / s, 12℃ / s, etc.

[0056] During the heating process, recrystallization of the cold-rolled ferrite structure is achieved, and pearlite first transforms into austenite and grows into ferrite. The endpoint temperature of this heating can be 780℃, 790℃, 800℃, 810℃, 830℃, etc., and the heating rate can be 1.5℃ / s, 2.0℃ / s, 2.5℃ / s, 3.5℃ / s, 4℃ / s, etc.

[0057] During the heat preservation process, partial austenitization is achieved, with C and Mn elements in the ferrite transferring into the austenite and being homogenized within it. The heat preservation time can be 60s, 70s, 80s, 90s, 100s, etc.

[0058] During the slow cooling process, austenite partially transforms into ferrite, and elements such as C and Mn further accumulate within the austenite. The endpoint temperature for this slow cooling can be 720℃, 730℃, 740℃, 750℃, 760℃, etc., and the slow cooling rate can be 8℃ / s, 9℃ / s, 10℃ / s, 11℃ / s, 12℃ / s, etc.

[0059] During the rapid cooling process, the strip steel is rapidly cooled to the galvanizing temperature of 450℃~460℃ by blowing air. The final temperature of this rapid cooling can be 450℃, 453℃, 456℃, 460℃, etc.

[0060] In post-galvanizing cooling, the strip steel undergoes air-knife cooling to 420℃~430℃ after galvanizing. During this process, the residence time of the strip steel in the equalization zone, furnace nose, and zinc pot is maximized to further enrich carbon in the retained austenite during the bainitic transformation, thereby improving the stability of the austenite. The final temperature for this post-galvanizing cooling can be 420℃, 423℃, 426℃, 430℃, etc.

[0061] During the final cooling process, the strip steel is cooled by a combination of front-end air cooling and rear-end air cooling between the air knife and the top roll. During this process, some unstable austenitic phases transform into martensite. The final cooling endpoint temperature can be 250℃, 260℃, 270℃, 280℃, 300℃, etc., and the final cooling rate can be 6℃ / s, 7℃ / s, 8℃ / s, 9℃ / s, etc.

[0062] Secondly, this application provides a low-carbon steel prepared by the method described in any one embodiment of the first aspect, wherein the microstructure of the low-carbon steel includes ferrite and pearlite, wherein the volume fraction of ferrite is 75-90% and the volume fraction of pearlite is 10-25%.

[0063] The low-carbon steel is achieved based on the preparation method of the low-carbon steel described above. The specific steps of the preparation method of the low-carbon steel can be referred to the above embodiments. Since the low-carbon steel adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0064] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0065] The molten steel of Examples 1-4 and Comparative Examples 1-2 was prepared and cast into slabs. The chemical composition of the slabs is shown in Table 1.

[0066] Table 1 shows the chemical composition (wt%) of each example and comparative example, with the remainder being Fe and unavoidable impurities.

[0067]

[0068]

[0069] Based on the above-mentioned chemical composition of low-carbon steel, this application provides a method for preparing low-carbon steel, the method comprising:

[0070] S11. The slab is heated, rolled, and coiled for the first time to obtain strip steel;

[0071] S21. The strip steel is cold rolled, continuously hot-dip galvanized and annealed, and then coiled a second time to obtain low-carbon steel. Please refer to Table 2 for the main process parameters.

[0072] Table 2 Main process parameters for preparing low-carbon steel

[0073]

[0074] The data from Examples 1-4 show that:

[0075] By using the method described in this application, a certain amount of Ni is added, while the content relationship between Cu, Sn, and Ni is limited, thereby effectively reducing Cu enrichment at the substrate-oxide layer interface and ensuring a low crack rate in the steel plate. Furthermore, using an oxidation heating temperature above 1200℃ can effectively promote selective oxidation, causing an uneven surface at the substrate-oxide layer interface, which leads to the migration of Cu-enriched phases to the oxide layer, thus effectively reducing Cu enrichment at the substrate-oxide layer interface and ensuring a low crack rate in the steel plate.

[0076] From the data in Comparative Examples 1-2, we can see that:

[0077] If the content relationship between Cu, Sn and Ni and the heating temperature <1200℃ are not used as defined in this application, surface cracking will occur.

[0078] Appendix Figure 2 Detailed explanation: Figure 2 The image shown is a metallographic photograph of the microstructure of an embodiment of the present invention, which consists of ferrite and pearlite. Compared with the microstructure of the comparative example, the overall microstructure is refined. Residual elements such as Cu, Ni, and Sn, as solid solution elements, have an inhibitory effect on recrystallization and grain growth, resulting in a refined microstructure.

[0079] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing low-carbon steel, characterized in that, The method includes: The slab is heated, rolled, and first coiled to obtain strip steel. The slab has the following chemical composition by mass fraction: C: 0.02%~0.04%, Si: 0.02%~0.05%, Mn: 0.2%~0.5%, Cu: 0.1%~0.4%, Sn: 0.01%~0.04%, Ni: 0.02%~0.15%, Alt: 0.03%~0.05%, P≤0.01%, S≤0.01%, N≤0.005%; wherein, Cu, Ni, and Sn satisfy the following relationship: 0.14≤[Cu]+8[Sn]-[Ni]≤0.3, where [Cu] represents the mass fraction of Cu, [Ni] represents the mass fraction of Ni, and [Sn] represents the mass fraction of Sn; the heating temperature is 1200℃~1250℃. The strip steel is subjected to cold rolling, continuous hot-dip galvanizing annealing, and a second coiling to obtain low-carbon steel; The continuous hot-dip galvanizing annealing includes: preheating, heating, heat preservation, slow cooling, rapid cooling, galvanizing, post-galvanizing cooling, final cooling and leveling; The final temperature of continuous hot-dip galvanizing annealing is 780℃~830℃; The final rolling temperature is 870℃~950℃, and the temperature of the first coil is 600℃~670℃.

2. The method according to claim 1, characterized in that, The reduction rate of the cold rolling is 50% to 70%.

3. The method according to claim 1, characterized in that, The final temperature of the preheating is 200℃~240℃, the preheating rate is 8℃ / s~12℃ / s; the heating rate is 1.5℃ / s~4℃ / s; and the holding time is 60s~100s.

4. The method according to claim 1, characterized in that, The endpoint temperature of the slow cooling is 720℃~760℃, and the slow cooling rate is 8℃ / s~12℃ / s; the endpoint temperature of the rapid cooling is 450℃~460℃; and the endpoint temperature of the post-plating cooling is 420℃~430℃.

5. The method according to claim 1, characterized in that, The final cooling endpoint temperature is 250℃~300℃, and the final cooling rate is 6℃ / s~9℃ / s.

6. A low-carbon steel prepared by the method according to any one of claims 1-5, characterized in that, The microstructure of the low-carbon steel includes ferrite and pearlite, wherein the volume fraction of ferrite is 75-90% and the volume fraction of pearlite is 10-25%.

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