Steel plate and method for manufacturing the same

Abstract

This invention provides steel sheets and methods for manufacturing the same, relating to the field of alloy technology. The steel sheet employs a corrosion-resistant alloying component system with Ce+Sn+Cu composite additives. The addition of Ce not only improves the corrosion resistance of the steel sheet, but Ce also readily combines with oxygen to form spherical oxides, which have the ability to induce needle-shaped ferrite nucleation within grains, thereby improving the weldability of the steel sheet. Based on the comprehensive design of the chemical composition, precise control of process parameters in the rolling and cooling processes yields a marine atmospheric corrosion-resistant, ultra-high heat input weldable steel sheet with excellent overall performance.

Description

Technical Field

[0001] This application is filed based on the Chinese patent application with application number CN202311040927.3 and filing date August 17, 2023, and claims the priority of the Chinese patent application. All the contents of the above patent application are incorporated into this application for reference.

[0002] The present invention relates to the field of alloy technology, and more specifically to steel plates and their manufacturing methods.

Background Art

[0003] Steel plates for ocean engineering are required to have relatively high corrosion resistance and excellent low-temperature impact performance. At the same time, since the steel plates are required to have good welding performance, the quality requirements for the steel plates are very high.

[0004] Under ocean atmospheric environmental conditions, water vapor in the ocean atmosphere adheres to the rust layer on the steel surface under the influence of capillary action, adsorption action, chemical condensation action, etc., leading to an increase in the corrosion rate. Corrosion-resistant steels usually add alloying elements such as Cr, Ni, Cu, etc. to improve corrosion resistance, but the addition of these alloying elements usually deteriorates welding performance.

[0005] High-heat-input welding steel plates can improve the heat input during the welding process, thereby improving the welding efficiency, and are thus widely applied in the field of ocean engineering. High-heat-input welding steel plates have the characteristic that the low-temperature toughness of the welding HAZ can still remain stable under high heat input welding conditions. By adopting oxide metallurgy technology and TMCP process, the low-temperature toughness problem of the heat-affected zone under high heat input welding conditions can be solved. However, when the welding heat input exceeds 600 kJ / cm, basically the stability of the welding HAZ performance cannot be guaranteed. Ultra-high heat input welding steels can achieve a welding heat input of 600 kJ / cm or more through low-carbon, low-alloy component design and inclusion adjustment technology based on oxide metallurgy, thereby meeting the one-pass welding requirements for steel plates with a thickness specification of 40 mm or more. However, this type of steel generally does not have corrosion resistance.

[0006] Therefore, there is an urgent need to develop corrosion-resistant, ultra-high heat input welded steel with superior overall performance.

[0007] References to prior art in this specification do not constitute confirmation or suggestion that such prior art constitutes part of common knowledge in any jurisdiction, or that such prior art will be understood, considered relevant, and / or reasonably expected to be combined with other prior art by those skilled in the art. [Overview of the project]

[0008] The object of the present invention is to provide a steel sheet and a method for manufacturing the same.

[0009] The method for manufacturing steel sheets according to the present invention is: The chemical composition of the steel sheet is as follows by mass percentage: Ce: 0.05-0.5%, Sn: 0.05-0.5%, Cu: 0.1-0.5%, Si: 0.1-0.4%, C: ≤0.12%, Mn: <2.0%, with the remainder being Fe and unavoidable impurities. A process to obtain molten steel by sequentially performing a converter smelting process, an LF refining process, and an RH refining process according to the mixing ratio of the above chemical components, A step of casting the molten steel by a continuous casting process to form a continuous cast slab, A rolling process to obtain a steel sheet by heating the aforementioned continuous casting slab and then rolling it, wherein rough rolling and finish rolling are sequentially employed, the finish rolling stage is non-recrystallized region rolling, the cumulative reduction ratio is controlled to 50% or more, the single-pass reduction ratio is controlled to 15% or more, and the finish rolling temperature is controlled to 780°C or less. The process includes a cooling step for cooling the steel plate, The obtained steel plate showed an average corrosion weight loss rate of <1.2 g / (m²) in a periodic immersion corrosion test. 2 Under the conditions of ×h) and a welding heat input of 600kJ / cm or more, the -40°C impact value of the heat-affected zone of the steel plate is ≥ 200J.

[0010] As a further improvement of the present invention, the Ce content in the steel sheet is 0.1 to 0.5% by mass, and the Sn content in the steel sheet is 0.1 to 0.5% by mass.

[0011] As a further improvement of the present invention, the converter smelting process is: This process involves adding clean steel and scrap in a ratio of (5-6):1, controlling the molten iron temperature to 1350-1450°C, and sequentially adding and dissolving ferromanganese, ferrosilicon, and lime into the molten iron.

[0012] As a further improvement of the present invention, the LF refining process is: The LF refining process includes bottom-blowing argon throughout the entire process, stirring the molten steel, and keeping the molten steel covered.

[0013] As a further improvement of the present invention, the RH refining process is: The RH refining process includes adding more than 800m of rare earth flux-filled wire at a speed of 4-5 meters / second, and adding carbide rice husks for heat retention before tapping.

[0014] As a further improvement of the present invention, the continuous casting process is: This includes controlling the casting temperature to 1540-1560°C and the continuous casting speed to 1.1-1.3 m / min to obtain a 320 mm thick continuously cast slab.

[0015] As a further improvement of the present invention, the cooling step is: This process includes first water-cooling the rolled steel sheet, controlling the water cooling rate to 12°C / s or higher, controlling the cooling stop temperature to 480-540°C, and then air-cooling it to 350°C or lower after water cooling.

[0016] In another view, the present invention provides a steel sheet. The chemical composition of the steel sheet is, by mass percentage, Ce: 0.05-0.5%, Sn: 0.05-0.5%, Cu: 0.1-0.5%, Si: 0.1-0.4%, C: ≤0.12%, Mn: <2.0%, with the remainder being Fe and unavoidable impurities.

[0017] As a further improvement of the present invention, the present invention also provides a steel plate, which is manufactured by the above-mentioned method for manufacturing a steel plate.

[0018] As a further improvement of the present invention, the content of Ce in the steel plate is 0.1 to 0.5% by mass percentage, and the content of Sn in the steel plate is 0.1 to 0.5% by mass percentage.

[0019] As a further improvement of the present invention, in the cyclic immersion corrosion test, the average corrosion loss rate of the steel plate < 1.2 g / (m 2 ×h).

[0020] As a further improvement of the present invention, under the condition that the welding heat input is 600 kJ / cm or more, the impact value (impact absorption energy) at -40°C in the heat-affected zone of the steel plate is ≧ 200 J.

Advantages of the Invention

[0021] The beneficial effects of the present invention are as follows. The steel plate provided by the present invention adopts a corrosion-resistant alloying component system with composite addition of Ce + Sn + Cu compared with existing steel for resisting marine atmospheric corrosion. The addition of Ce not only improves the corrosion resistance of the steel plate, but Ce is also easy to combine with oxygen to form spherical oxides and has the ability to induce acicular ferrite nucleation within grains, thereby improving the welding performance of the steel plate. Based on the comprehensive design of chemical components and through precise control of process parameters in the rolling and cooling processes, a steel plate for resisting marine atmospheric corrosion and with excellent welding performance for large heat input is obtained.

[0022] As used herein, the terms "comprising", "including", and variations thereof such as "includes" do not exclude other features, components, elements or steps unless the context explicitly requires otherwise.

Brief Description of the Drawings

[0023] [Figure 1] It is a schematic diagram of the steps of the method for manufacturing a steel plate in an embodiment of the present invention.

Embodiments for Carrying out the Invention

[0024] To more clearly illustrate the objectives, technical solutions, and advantages of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments of the present invention and the corresponding drawings. Of course, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative labor shall also be included in the protection scope of the present invention.

[0025] This embodiment provides a steel plate and a manufacturing method thereof. Compared with existing steels resistant to marine atmospheric corrosion, the steel plate adopts a corrosion-resistant alloying component system with composite addition of Ce + Sn + Cu. The addition of Ce not only improves the corrosion resistance of the steel plate, but Ce is also easy to combine with oxygen to form spherical oxides and has the ability to induce the formation of intragranular acicular ferrite nuclei, thereby improving the welding performance of the steel plate. Based on the comprehensive design of chemical components and through precise control of process parameters in the rolling and cooling processes, a steel plate resistant to marine atmospheric corrosion and with excellent welding performance for large heat input is obtained.

[0026] The chemical composition of the steel plate is in mass percentage, including Ce: 0.05 - 0.5%, Sn: 0.05 - 0.5%, Cu: 0.1 - 0.5%, Si: 0.1 - 0.4%, C: ≤ 0.12%, Mn: < 2.0%, and the balance consists of Fe and inevitable impurities.

[0027] Preferably, the content of Ce in the steel plate is 0.1 - 0.5% in mass percentage, and the content of Sn in the steel plate is 0.1 - 0.5% in mass percentage.

[0028] Specifically, the design principle of the chemical composition of the steel plate is as follows. When the Ce:Ce content exceeds 0.05%, in terms of improving corrosion resistance, Ce tends to segregate at grain boundaries. Ce segregated at grain and phase boundaries reduces the free energy at the interface, mitigating corrosion caused by high-energy interfacial corrosion and thereby improving the corrosion resistance of the grain boundaries. Rare earth elements segregated at the free surface also act to passivate the rust layer. Furthermore, Ce can also improve the pitting corrosion resistance of steel. In terms of improving welding performance, Ce readily combines with oxygen to form spheroidal oxides. Ce has the ability to induce acicular ferrite nucleation within grains. The large-angle grain boundaries formed by the acicular ferrites and their surrounding structure suppress crack expansion and increase the energy of crack expansion, thereby improving the low-temperature toughness of the heat-affected zone of the weld and enhancing welding performance. However, if the Ce content exceeds 0.5%, the amount of segregation at the grain boundaries becomes excessive, affecting the low-temperature toughness and weldability of the steel sheet. Therefore, considering performance and cost factors comprehensively, this invention controls the Ce content to 0.05-0.50%, thereby ensuring good low-temperature toughness and weldability of the steel sheet while maintaining its corrosion resistance.

[0029] Sn:Sn also tends to segregate at grain boundaries, effectively improving the corrosion resistance of the grain boundaries. Sn forms a dense SnO2 protective rust layer on the surface of the steel, thereby improving corrosion resistance. When the Sn content is excessive, the improvement effect is not clear and it affects the low-temperature toughness and weldability of the steel sheet. Therefore, in this invention, the Sn content is controlled to 0.05-0.50%, and while maintaining corrosion resistance, good low-temperature toughness and weldability of the steel sheet are guaranteed.

[0030] Cu:Cu also tends to segregate at grain boundaries, effectively improving the corrosion resistance of the grain boundaries. Furthermore, Cu inhibits the crystallization of the rust layer, promotes the formation of α-FeOOH and amorphous Fe3O4, and accumulates in the weak parts of the rust layer, forming oxides during the corrosion process. This tightly bonds the rust layer to the steel substrate, reducing cracks and voids in the rust layer and improving pitting corrosion resistance. In addition, the Cu element has the effect of activating the cathode, passivating the steel substrate and reducing the corrosion rate. However, a high Cu content is detrimental to the welding performance of the steel plate. Therefore, in this invention, the Cu content is controlled to 0.1-0.5% to improve corrosion resistance without affecting welding performance.

[0031] Carbon (C:C) is a strengthening element, and its C content significantly affects the microstructure of the steel material, thereby directly impacting the strength of the steel sheet. However, a high C content increases the pearlite content, further worsening the low-temperature toughness and weldability of the steel sheet. Therefore, in this invention, the C content is controlled to C:≦0.12%, and combined with the overall design of other elements, not only is the strengthening effect guaranteed, but the low-temperature toughness and weldability of the steel sheet can also be improved, eliminating the need to use a special protective slag in the continuous casting process to resolve the problem of large fluctuations in the molten metal level.

[0032] Si:Si is mainly used for oxygen removal in the molten steel smelting process and can improve the strength of steel sheets, but it is detrimental to weld performance. In particular, under extremely high heat input welding conditions, Si not only promotes the formation of MA islands, but the size and distribution of the formed MA islands are coarse and uneven, severely damaging the low-temperature toughness of the heat-affected zone. Therefore, the Si content in steel should be controlled to be as low as possible. Accordingly, in this invention, the Si content is controlled to 0.1-0.4%, and while assuming that it does not affect the low-temperature toughness and weldability of the steel sheet, the deoxidation effect is guaranteed, and strength and corrosion resistance are improved.

[0033] Mn: Mn is a solid solution strengthening element that improves the hardenability of steel sheets, thereby increasing their strength. At the same time, Mn can combine with the harmful element S to reduce the thermal brittleness of steel sheets. However, excessive Mn worsens the segregation of elements such as P, Sb, and Sn, further weakening the corrosion resistance of the steel sheet and degrading the low-temperature toughness and weldability of the steel sheet core. Therefore, in this invention, the Mn content is controlled to ≤2.0%, which ensures the strength of the steel sheet on the one hand, and reduces the impact of segregation on the corrosion resistance, low-temperature toughness, and weldability of the steel sheet.

[0034] In summary, this implementation employs a composite additive of Ce+Sn+Cu elements, primarily segregating them at grain boundaries to reduce the free energy at the interface, thereby mitigating corrosion caused by high-energy interfacial corrosion, improving the corrosion resistance of the grain boundaries, and consequently improving the overall corrosion resistance of the steel sheet. Due to the addition of Ce and the low-Si design, the steel sheet has excellent weldability.

[0035] As shown in Figure 1, the present invention also provides a method for manufacturing the steel sheet described above. In this embodiment, the manufacturing method includes the following steps. S1: Molten steel is obtained by sequentially performing converter smelting, LF refining, and RH refining according to the mixing ratio of chemical components.

[0036] S2: The molten steel is cast by a continuous casting process to form a continuous cast slab.

[0037] S3: A rolling process to obtain a steel sheet by heating the continuous casting slab and then rolling it, wherein rough rolling and finish rolling are sequentially employed. The finish rolling stage is non-recrystallized region rolling, in which the cumulative reduction rate is controlled to 50% or more, the single-pass reduction rate is controlled to 15% or more, and the finish rolling temperature is controlled to 780°C or less.

[0038] S4: Cool the steel plate.

[0039] In step S1, the converter smelting process includes adding clean steel and scrap in a ratio of (5-6):1, controlling the molten iron temperature to 1350-1450°C, and sequentially adding and dissolving ferromanganese, ferrosilicon, and lime into the molten iron.

[0040] Of these, clean steel is steel that has undergone refining and purification treatment, while scrap is steel that is recovered and reused. In converter smelting, the temperature of molten iron is controlled between 1350 and 1450°C. An appropriate temperature ensures the smooth progress of the smelting reaction and is also favorable for the dissolution and reaction of additives. The addition of ferromanganese improves the manganese content of the steel, improving its strength, toughness, and wear resistance. The addition of ferrosilicon increases the silicon content in the steel, affecting the deoxidation and composition adjustment of the steel. The addition of lime captures impurities such as sulfur, thereby reducing the sulfur content in the steel.

[0041] The LF refining process includes bottom-blowing argon throughout the entire process to agitate the molten steel and keep it covered.

[0042] Bottom-blowing argon generates bubbles, causing the molten steel to rise and exchange gases. This promotes the oxidation and removal of unstable elements, reduces the impurity content in the molten steel, and improves the purity of the steel. In addition, argon can cool the molten steel and control its temperature. The agitator generates bubbles and propels them from the bottom to the top, creating a swirling motion in the molten steel and uniformly mixing various elements and impurities within it.

[0043] The RH refining process includes adding 800m or more of rare earth flux-filled wire during the RH refining process, and adding carbide rice husks for heat retention before tapping.

[0044] RH smelting furnaces are primarily used to reduce the oxygen content and impurities in molten steel, thereby improving the purity and quality of the steel. Before tapping, insulating material is usually added to the RH furnace to maintain a stable temperature for the molten steel and prevent excessive heat loss. In this implementation, carbonized rice husks are used. This is a type of commonly used insulating material, produced by specially treating rice husks to provide excellent heat retention. By adding carbonized rice husks to the surface of the molten steel in the RH furnace, an insulating layer is formed to cover the surface of the molten steel, thereby preventing the molten steel from rapidly losing heat and maintaining the temperature of the molten steel within a certain range, preparing it for the subsequent continuous casting process.

[0045] In step S2, the continuous casting process includes controlling the casting temperature to 1540-1560°C and the continuous casting speed to 1.1-1.3 m / min to obtain a 320 mm thick continuously cast slab by continuous casting.

[0046] By controlling the casting temperature of the molten steel within the range of 1540 to 1560°C, an appropriate solidification rate is achieved, ensuring a uniform and dense internal structure of the slab, while simultaneously helping to avoid surface quality problems. By controlling the continuous casting rate within the range of 1.1 to 1.3 m / min, an appropriate draw rate is achieved, allowing the slab to solidify gradually and maintain its proper shape, thereby resulting in a uniform internal structure and good surface quality.

[0047] In step S3, during the rough rolling stage, the slab thickness is gradually reduced through multiple rolling passes, while simultaneously undergoing rudimentary plastic deformation and shape adjustment. During this process, the internal structure of the slab gradually changes, forming the necessary metal flow and grain reorganization.

[0048] In the finishing rolling stage, non-recrystallized region rolling is performed. Non-recrystallized region rolling refers to a process in which the steel sheet is held within a certain temperature range during the rolling deformation process to avoid the occurrence of recrystallization. By holding the steel sheet within a temperature range above room temperature but below the recrystallization temperature, plastic deformation does not occur in the steel sheet during the deformation process. As a result, the original grain structure is maintained, and the steel sheet maintains a cold deformation state even after deformation, thereby obtaining higher hardness, strength, and deformation resistance.

[0049] By controlling the cumulative reduction ratio to 50% or more during the finish rolling stage, sufficient deformation of the slab can be ensured, improving its internal grain structure and performance. Controlling the single-pass reduction ratio to 15% or more increases the degree of deformation in each rolling pass, which is advantageous for achieving grain refinement and plastic deformation. By controlling the finish rolling temperature to 780°C or below, deformation is completed in a cold deformation state, while simultaneously avoiding recrystallization, thereby maintaining the cold deformation state of the slab.

[0050] In step S4, the cooling process includes first water-cooling the rolled steel sheet, controlling the water-cooling rate to 12°C / s or higher, controlling the cooling stop temperature to 480-540°C, and then air-cooling it to 350°C or lower after water-cooling.

[0051] During the water cooling phase, rapid cooling quickly solidifies the exterior of the steel plate, thereby preserving its internal plastic deformation and refined grain structure. The cooling stop temperature is controlled to 480-540°C, and within this temperature range, the steel plate is continuously and gradually cooled, the grains continue to refine, and internal stresses are gradually relieved.

[0052] Specifically, the performance characteristics of the final steel sheet are as follows: In periodic immersion corrosion tests, the average corrosion weight loss rate of steel plates was <1.2 g / (m²). 2 h) Of these, the periodic immersion corrosion test shall refer to the standard test conditions of GB / T 24195-2009 "Corrosion of metals and alloys - Accelerated cyclic tests with exposure to acidified salt spray, “dry” and “wet” conditions".

[0053] In terms of welding performance, the impact value of the heat-affected zone at -40°C is 200J or higher under conditions of a welding heat input of 600kJ / cm or more, referencing the standard test conditions of GB / T 2650-2008 "Impact test methods on welded joints".

[0054] In summary, the steel sheet employs a corrosion-resistant alloying component system with a Ce+Sn+Cu composite additive. The addition of Ce not only improves the corrosion resistance of the steel sheet, but Ce also readily combines with oxygen to form spherical oxides, which have the ability to induce needle-shaped ferrite nucleation within the grain, thereby improving the weldability of the steel sheet. Based on the comprehensive design of the chemical composition, precise control of process parameters during the rolling and cooling processes yields a steel sheet with excellent overall performance, resistant to marine and atmospheric corrosion, and capable of ultra-high heat input welding.

[0055] The following sections will further introduce specific embodiments of the present invention through nine specific examples and three comparative examples.

[0056] Examples 1-9 and Comparative Examples 1-3 all provide steel sheets. The chemical composition of the steel sheets is shown in Table 1.

[0057] [Table 1]

[0058] The steel sheets in Examples 1-9 and Comparative Examples 1-3 were produced according to the above manufacturing method. The flux-cored wires for steelmaking and the joining process are shown in Table 2, and the rolling process parameters are shown in Table 3.

[0059] [Table 2]

[0060] [Table 3]

[0061] A standard periodic immersion corrosion tester was used to detect the corrosion resistance of the steel plates of Examples 1-9 and Comparative Examples 1-3. The average corrosion weight loss rate and welding performance of Examples 1-9 and Comparative Examples 1-3 are shown in Table 4.

[0062] Table 4 shows that the average corrosion weight loss rate of the steel plates in Examples 1 to 9 was <1.2 g / (m²) in all cases. 2 h) is the case. Comparative Example 1 did not meet the corrosion resistance requirement, and Comparative Examples 2 and 3 did not meet the low-temperature toughness requirement.

[0063] [Table 4]

[0064] Combining this with the above detection results, it can be seen that the corrosion-resistant, ultra-high heat input welded steel sheet provided by the present invention is not only cost-controllable and has a simple and highly efficient process flow, but also has excellent corrosion resistance, low-temperature toughness, and weldability, making it advantageous for widespread application.

[0065] Although this specification is described according to embodiments, each embodiment does not necessarily include only a single technical solution. This style of description is solely for clarity, and those skilled in the art should understand the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that are understandable to those skilled in the art.

[0066] The series of detailed descriptions listed above are merely specific descriptions of possible embodiments of the present invention and do not limit the scope of protection of the present invention. Equivalent embodiments or modifications made without departing from the technical spirit of the present invention are all included within the scope of protection of the present invention.

Claims

1. A method for manufacturing steel plates, The chemical composition of the steel sheet is, by mass percentage, Ce: 0.05-0.5%, Sn: 0.05-0.5%, Cu: 0.1-0.5%, Si: 0.1-0.4%, C: ≤0.12%, Mn: <2.0%, with the remainder being Fe and unavoidable impurities. A process to obtain molten steel by sequentially carrying out a converter smelting process, an LF refining process, and an RH refining process according to the mixing ratio of the above chemical components, A step of casting the molten steel by a continuous casting process to form a continuous cast slab, A rolling process to obtain a steel sheet by heating the aforementioned continuous casting slab and then rolling it, wherein rough rolling and finish rolling are sequentially employed, the finish rolling stage is non-recrystallized region rolling, the cumulative reduction ratio is controlled to 50% or more, the single-pass reduction ratio is controlled to 15% or more, and the finish rolling temperature is controlled to 780°C or less. The process includes a cooling step for cooling the steel plate, The obtained steel plate showed an average corrosion weight loss rate < 1.2 g / (m²) in a periodic immersion corrosion test. ２ Under the conditions of ×h) and a welding heat input of 600 kJ / cm or more, the -40°C impact value of the heat-affected zone of the steel plate is ≥ 200 J. A method for manufacturing steel plates.

2. The steel sheet contains 0.1 to 0.5% by mass of Ce, and the steel sheet contains 0.1 to 0.5% by mass of Sn. The method for manufacturing a steel plate according to claim 1.

3. The aforementioned converter smelting process is, This process involves adding clean steel and scrap in a ratio of (5-6):1, controlling the molten iron temperature to 1350-1450°C, and sequentially adding and dissolving ferromanganese, ferrosilicon, and lime into the molten iron. The method for manufacturing a steel plate according to claim 1.

4. The LF refining process is as follows: The LF refining process includes bottom-blowing argon throughout the entire process to agitate the molten steel and keep it covered. The method for manufacturing a steel plate according to claim 1.

5. The RH refining process described above is: The RH refining process includes adding more than 800m of rare earth flux-filled wire at a speed of 4-5 meters / second, and adding carbide-filled rice husks for heat retention before tapping. The method for manufacturing a steel plate according to claim 1.

6. The continuous casting process described above is: This includes controlling the casting temperature to 1540-1560°C, controlling the continuous casting speed to 1.1-1.3 m / min, and obtaining a 320 mm thick continuously cast slab by continuous casting. The method for manufacturing a steel plate according to claim 1.

7. This process includes first water-cooling the rolled steel sheet, controlling the water cooling rate to 12°C / s or higher, controlling the cooling stop temperature to 480-540°C, and then air-cooling it to 350°C or lower after water cooling. The method for manufacturing a steel plate according to claim 1.

8. It is a steel plate, The chemical composition of the steel sheet is, by mass percentage, Ce: 0.05-0.5%, Sn: 0.05-0.5%, Cu: 0.1-0.5%, Si: 0.1-0.4%, C: ≤0.12%, Mn: <2.0%, with the remainder being Fe and unavoidable impurities.

9. The steel sheet contains 0.1 to 0.5% by mass of Ce, and the steel sheet contains 0.1 to 0.5% by mass of Sn. The steel plate according to claim 8.

10. In periodic immersion corrosion tests, the average corrosion weight loss rate of the steel plate was < 1.2 g / (m²). ２ • h) The steel plate according to claim 8.

11. Under conditions of a welding heat input of 600 kJ / cm or more, the -40°C impact value of the heat-affected zone of the steel plate during welding is ≥ 200 J. The steel plate according to claim 8.

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