Steel plate and production method therefor

Abstract

The present invention relates to the technical field of alloys. Provided are a steel plate and a production method therefor. The steel plate adopts a corrosion-resistant alloying component system with compound addition of Ce+Sn+Cu. The addition of Ce can improve the corrosion resistance of the steel plate, and Ce is easy to combine with oxygen to generate a spherical oxide; and the steel plate has the capacity of inducing acicular ferrite nucleation in crystals, thereby improving the welding performance of the steel plate. On the basis of the comprehensive design of chemical components, by means of accurate control over process parameters of a rolling and cooling process, a super-large-heat-input steel plate, which is resistant to marine atmospheric corrosion and has good comprehensive performance, is obtained.

Description

Steel plate and production method thereof

[0001] This application is based on the Chinese patent application with application number CN202311040927.3 and application date of August 17, 2023, and claims the priority of the Chinese patent application. The entire content of the above patent application is hereby introduced into this application as a reference. Technical Field

[0002] The present invention relates to the technical field of alloys, and in particular to a steel plate and a production method thereof. Background Art

[0003] Steel plates used in marine engineering are required to have high corrosion resistance and excellent low-temperature impact resistance, as well as good welding performance, so the quality requirements for steel plates are very high.

[0004] Under marine atmospheric conditions, water vapor in the marine atmosphere adheres to the rust layer on the steel surface due to capillary action, adsorption, and chemical condensation, leading to an increase in corrosion rate. Corrosion-resistant steels are usually improved by adding alloying elements such as Cr, Ni, and Cu, but the addition of these alloying elements usually deteriorates weldability.

[0005] High-energy-input steel plates are widely used in marine engineering because they can increase the welding energy input during the welding process, thereby improving welding efficiency. High-energy-input steel plates maintain stable low-temperature toughness in the HAZ under high-heat-input welding conditions. The low-temperature toughness problem of the heat-affected zone under high-heat-input welding conditions is addressed by adopting oxide metallurgy technology and the TMCP process. However, when the welding heat input exceeds 600kJ / cm, the stability of the HAZ performance is basically unguaranteed. Ultra-high-energy-input welding steels can achieve welding energy inputs exceeding 600kJ / cm through low-carbon, low-alloy composition design and inclusion control technology based on oxide metallurgy, thus meeting the single-pass welding requirements of steel plates with a thickness of 40mm or more. However, this type of steel generally does not have corrosion resistance.

[0006] Therefore, it is urgent to develop a corrosion-resistant ultra-high heat input welding steel with excellent comprehensive performance.

[0007] The reference to any prior art in the specification is not an acknowledgement or suggestion that the prior art forms part of the common general knowledge in any jurisdiction, or that it could reasonably be expected that the person skilled in the art would understand, consider relevant and / or combine with other prior art. Summary of the Invention

[0008] The object of the present invention is to provide a steel plate and a production method thereof.

[0009] The present invention provides a steel plate production method, comprising the steps of:

[0010] The chemical composition of the steel plate includes, 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%, and the remainder is Fe and unavoidable impurities;

[0011] According to the above chemical composition ratio, molten steel is obtained by smelting in a converter, LF refining and RH refining in sequence;

[0012] Casting the molten steel into a continuous casting slab through a continuous casting process;

[0013] The continuous casting slab is heated and then rolled to obtain a steel plate, wherein the rolling process sequentially adopts rough rolling and finish rolling, wherein the finish rolling stage is rolling in the non-recrystallization zone, the cumulative reduction rate is controlled to be above 50%, the single-pass reduction rate is controlled to be above 15%, and the final rolling temperature is controlled to be below 780°C;

[0014] performing a cooling process on the steel plate;

[0015] The average corrosion weight loss rate of the steel plate obtained in the periodic immersion corrosion test is less than 1.2g / (m 2 ×h), under the condition that the welding heat input is not less than 600kJ / cm, the impact energy of the welding heat affected zone of the steel plate at -40°C is ≥200J.

[0016] As a further improvement of the present invention, the Ce content in the steel plate is 0.1-0.5% by mass, and the Sn content in the steel plate is 0.1-0.5% by mass.

[0017] As a further improvement of the present invention, the converter smelting process specifically includes:

[0018] Add clean steel and scrap steel in a ratio of (5~6):1, control the molten iron temperature to 1350~1450℃, and add ferromanganese, ferrosilicon and lime to the molten iron in sequence for smelting.

[0019] As a further improvement of the present invention, the LF refining process specifically includes:

[0020] During the LF refining process, argon is blown from the bottom and the molten steel is stirred to keep it covered.

[0021] As a further improvement of the present invention, the RH refining process specifically includes:

[0022] During the RH refining process, more than 800m of rare earth cored wire is added at a speed of 4-5m / s, and carbonized rice husks are added for heat preservation before tapping.

[0023] As a further improvement of the present invention, the continuous casting process specifically includes:

[0024] The casting temperature is controlled at 1540~1560℃, the continuous casting speed is controlled at 1.1~1.3m / min, and a 320mm thick continuous casting slab is obtained by continuous casting.

[0025] As a further improvement of the present invention, the cooling process specifically includes:

[0026] The rolled steel plate is first water-cooled, the water cooling rate is controlled at above 12℃ / s, the final cooling temperature is controlled at 480~540℃, and after water cooling, it is air-cooled to below 350℃.

[0027] The present invention also provides a corrosion-resistant ultra-high heat input welding steel plate, the chemical composition of which includes, 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%, and the rest being Fe and unavoidable impurities.

[0028] As a further improvement of the present invention, the steel plate is manufactured using the above-mentioned steel plate production method.

[0029] As a further improvement of the present invention, the Ce content in the steel plate is 0.1-0.5% by mass, and the Sn content in the steel plate is 0.1-0.5% by mass.

[0030] As a further improvement of the present invention, in the periodic immersion corrosion test, the average corrosion weight loss rate of the steel plate is less than 1.2g / (m 2 ×h).

[0031] As a further improvement of the present invention, under the condition that the welding heat input is not less than 600 kJ / cm, the impact energy of the welding heat affected zone of the steel plate at -40°C is ≥200 J.

[0032] The beneficial effects of the present invention are as follows: Compared to existing marine atmospheric corrosion-resistant steels, the steel plate provided by the present invention utilizes a corrosion-resistant alloying component system comprising Ce, Sn, and Cu. The addition of Ce not only improves the steel plate's corrosion resistance but also readily combines with oxygen to form spherical oxides, inducing the nucleation of acicular ferrite within the grains, thereby enhancing the steel plate's weldability. Based on a comprehensive design of the chemical composition and precise control of the rolling and cooling process parameters, a marine atmospheric corrosion-resistant, ultra-high heat input steel plate with excellent overall performance is achieved.

[0033] As used herein, the term "comprise" and variations of the term, such as "comprises," "comprised," "comprising," "including," and "containing" do not exclude other features, components, elements, or steps unless the context clearly requires otherwise. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a schematic diagram of the steps of a steel plate production method in one embodiment of the present invention. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0036] This embodiment provides a steel plate and a production method thereof. Compared to existing marine atmospheric corrosion-resistant steel, this steel plate utilizes a corrosion-resistant alloying composition system comprising Ce, Sn, and Cu. The addition of Ce not only improves the steel plate's corrosion resistance but also readily combines with oxygen to form spherical oxides, inducing the nucleation of acicular ferrite within the grains, thereby enhancing the steel plate's weldability. Based on a comprehensive design of chemical composition and precise control of rolling and cooling process parameters, a marine atmospheric corrosion-resistant, ultra-high heat input steel plate with excellent overall performance is achieved.

[0037] The chemical composition of the steel plate includes 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%, the rest is Fe and unavoidable impurities

[0038] Preferably, the Ce content in the steel plate is 0.1-0.5% by mass, and the Sn content in the steel plate is 0.1-0.5% by mass.

[0039] Specifically, the design principles of the chemical composition of the steel plate are described as follows:

[0040] Ce: When the Ce content is greater than 0.05%, Ce tends to segregate at grain boundaries to improve corrosion resistance. Ce segregated at grain and phase boundaries can reduce the free energy of the interface, alleviating corrosion caused by high interface energy, thereby improving grain boundary corrosion resistance. Rare earth elements segregated at the free surface will passivate the rust layer. Ce can also improve the steel's resistance to pitting corrosion. In terms of improving welding performance, Ce easily combines with oxygen to form spherical oxides. Ce also has the ability to induce the nucleation of acicular ferrite within the grain. The high-angle grain boundaries formed by acicular ferrite and its surrounding tissues can inhibit crack propagation and increase the energy for crack expansion, thereby improving the low-temperature toughness of the heat-affected zone and enhancing welding performance. However, when the Ce content exceeds 0.5%, its excessive segregation at the grain boundaries will affect the low-temperature toughness and welding performance of the steel plate. Therefore, considering performance and cost factors, in the present invention, the Ce content is controlled within 0.05-0.50%, thereby ensuring good low-temperature toughness and welding performance of the steel plate while ensuring the corrosion resistance of the steel plate.

[0041] Sn: Sn also readily segregates at grain boundaries, effectively improving their corrosion resistance. Furthermore, Sn forms a dense, protective SnO2 rust layer on the steel surface, thereby enhancing corrosion resistance. Excessive Sn content can have a limited improvement and can affect the low-temperature toughness and weldability of the steel. Therefore, in this invention, the Sn content is controlled within a range of 0.05% to 0.50%, ensuring good low-temperature toughness and weldability without compromising corrosion resistance.

[0042] Cu: Cu also tends to segregate at grain boundaries, effectively improving the corrosion resistance of grain boundaries. Furthermore, Cu can hinder the crystallization of the rust layer and promote the formation of α-FeOOH and amorphous Fe3O4. Cu can be enriched in weak areas of the rust layer, forming oxides during the corrosion process, tightly connecting the rust layer and the steel matrix, reducing cracks and voids in the rust layer, and improving pitting resistance. Furthermore, the Cu element has the effect of activating the cathode, passivating the steel matrix and reducing the corrosion rate. However, a high Cu content is detrimental to the welding performance of the steel plate. Therefore, in the present invention, the Cu content is controlled at 0.1-0.5%, which not only improves corrosion resistance but also does not affect welding performance.

[0043] C: C is a strengthening element. Its content significantly affects the microstructure of steel and thus directly impacts the strength of the steel plate. However, high C content increases the pearlite content, which in turn deteriorates the steel plate's low-temperature toughness and weldability. Therefore, in the present invention, the C content is controlled to ≤ 0.12%. Combined with the overall design of other elements, this not only ensures the strengthening effect but also improves the steel plate's low-temperature toughness and weldability. This also eliminates the need for specialized mold slag in the continuous casting process to address the problem of large liquid level fluctuations.

[0044] Si: Si is primarily used to remove oxygen during the steelmaking process. While it can improve steel plate strength, it has a detrimental effect on weldability. Especially under extremely high heat input welding conditions, Si not only promotes the formation of MA islands, but also creates large, unevenly distributed MA islands, severely impairing the low-temperature toughness of the weld heat-affected zone. Therefore, the Si content in steel should be kept as low as possible. Therefore, in the present invention, the Si content is controlled to 0.1-0.4%, ensuring a deoxidation effect and improving strength and corrosion resistance without compromising the low-temperature toughness and weldability of the steel plate.

[0045] Mn: Mn is a solid solution strengthening element that improves the hardenability of steel plates, thereby increasing their strength. It also combines with the harmful element S to reduce their hot brittleness. However, excessive Mn can exacerbate the segregation of elements like P, Sb, and Sn, further weakening the steel's corrosion resistance and deteriorating its core's low-temperature toughness and weldability. Therefore, in the present invention, the Mn content is controlled to less than 2.0%. This not only maintains the steel's strength, but also mitigates the effects of segregation on its corrosion resistance, low-temperature toughness, and weldability.

[0046] In summary, in this embodiment, the composite addition of Ce, Sn, and Cu primarily segregates them at grain boundaries, reducing interfacial free energy, alleviating corrosion caused by high interfacial energy, and improving grain boundary corrosion resistance, thereby enhancing the overall corrosion resistance of the steel plate. The addition of Ce and the low-Si design provide the steel plate with excellent weldability.

[0047] As shown in FIG1 , the present invention further provides a method for producing the aforementioned steel plate. In this embodiment, the production method includes the following steps:

[0048] S1: According to the chemical composition ratio, molten steel is obtained by smelting in a converter, LF refining and RH refining in sequence.

[0049] S2: Casting the molten steel into a continuous casting slab through a continuous casting process.

[0050] S3: The continuous casting slab is heated and then rolled to obtain a steel plate. In the rolling process, rough rolling and finish rolling are sequentially adopted. The finish rolling stage is rolling in the non-recrystallization zone. The cumulative reduction rate is controlled at more than 50%, the single-pass reduction rate is controlled at more than 15%, and the final rolling temperature is controlled at less than 780°C.

[0051] S4: Cooling the steel plate.

[0052] In step S1, the converter smelting process specifically includes: adding clean steel and scrap steel in a ratio of (5~6):1, controlling the temperature of the molten iron to 1350~1450℃, and adding ferromanganese, ferrosilicon and lime to the molten iron in sequence for smelting.

[0053] Clean steel is steel that has been refined and purified, while scrap steel is steel that has been recycled and reused. During converter smelting, the temperature of the molten iron is controlled between 1350°C and 1450°C. This appropriate temperature ensures smooth smelting reactions and facilitates the melting and reaction of additives. Adding ferromanganese increases the manganese content of the steel, improving its strength, toughness, and wear resistance. Adding ferrosilicon increases the silicon content of the steel, impacting deoxidation and composition adjustment. Lime is added to capture impurities such as sulfur, thereby reducing the sulfur content in the steel.

[0054] The LF refining process specifically includes: during the LF refining process, argon is blown from the bottom and the molten steel is stirred to keep the molten steel covered.

[0055] Bottom-blown argon creates bubbles that propel the molten steel upward and exchange with the gas, thereby promoting the oxidation and expulsion of unstable elements, reducing impurities in the molten steel and improving its purity. Argon also cools the molten steel and controls its temperature. The agitator creates bubbles and propels them upward from the bottom, creating a vortex-like motion in the molten steel, uniformly mixing the various elements and impurities in the molten steel.

[0056] The RH refining process specifically includes: adding more than 800m of rare earth cored wire during the RH refining process, and adding carbonized rice husks for heat preservation before tapping.

[0057] The RH refining furnace is mainly used to reduce the oxygen content and impurities in molten steel to improve the purity and quality of the steel. Before tapping, some insulation material is usually added to the RH furnace to maintain a stable temperature of the molten steel and prevent excessive heat loss. In this embodiment, carbonized rice husks are used, which are a commonly used insulation material made from specially treated rice husks and have good thermal insulation properties. Carbonized rice husks are added to the surface of the molten steel in the RH furnace, covering the surface of the molten steel to form an insulation layer, thereby preventing the molten steel from losing heat too quickly and keeping the temperature of the molten steel within a certain range for the subsequent continuous casting process.

[0058] In step S2, the continuous casting process specifically includes: controlling the casting temperature to 1540-1560°C, controlling the continuous casting speed to 1.1-1.3 m / min, and continuously casting to obtain a 320 mm thick continuous casting slab.

[0059] Controlling the molten steel casting temperature within the range of 1540-1560°C achieves an appropriate solidification rate, ensuring a uniform and dense internal structure of the slab while also helping to avoid surface quality issues. Controlling the continuous casting drawing speed within the range of 1.1-1.3 m / min achieves an appropriate drawing speed, allowing the slab to gradually solidify and maintain an appropriate morphology, resulting in a uniform internal structure and good surface quality.

[0060] In step S3, during the rough rolling phase, the slab thickness is gradually reduced through multiple rolling passes, while undergoing preliminary plastic deformation and shape adjustment. During this process, the internal structure of the slab gradually changes, resulting in the desired metal flow and grain reorganization.

[0061] During the finishing rolling stage, rolling is performed in the non-recrystallized zone. Non-recrystallized zone rolling refers to maintaining the steel plate within a certain temperature range during the rolling deformation process to prevent recrystallization. The steel plate is maintained within a temperature range below its recrystallization temperature but above room temperature during plastic deformation. This prevents grain rearrangement and refinement during deformation, thereby preserving the original grain structure and allowing the steel plate to remain in a cold-deformed state after deformation, resulting in higher hardness, strength, and deformation resistance.

[0062] During the finishing rolling stage, controlling the cumulative reduction to above 50% ensures sufficient deformation of the slab to improve its internal grain structure and properties. Keeping the reduction per pass above 15% results in a relatively high degree of deformation during each rolling pass, which is beneficial for grain refinement and plastic deformation. Keeping the final rolling temperature below 780°C facilitates deformation in the cold-deformed state while preventing recrystallization, thereby maintaining the slab's cold-deformed state.

[0063] In step S4, the cooling process specifically includes: first water cooling the rolled steel plate, controlling the water cooling rate to be above 12°C / s, controlling the final cooling temperature to be between 480°C and 540°C, and then air cooling to below 350°C after water cooling.

[0064] During the water cooling stage, the steel plate's exterior solidifies rapidly through rapid cooling, thereby preserving its internal plastic deformation and refined grain structure. The final cooling temperature is controlled between 480 and 540°C. Within this temperature range, the steel plate continues to cool gradually, the grains continue to refine, and internal stresses are gradually relieved.

[0065] Specifically, the performance characteristics of the finally obtained steel plate are as follows:

[0066] In the cyclic immersion corrosion test, the average corrosion weight loss rate of the steel plate was less than 1.2 g / (m 2 ×h), where the cyclic immersion corrosion test refers to the standard test conditions of GB / T 24195-2009 "Test method for corrosion resistance of metals and alloys in corrosive environments - Cyclic immersion corrosion test".

[0067] In terms of welding performance, the standard test conditions of GB / T 2650-2008 "Charpy Pendulum Impact Test Method for Metallic Materials" are referred to. Under the condition that the welding heat input is not less than 600kJ / cm, the impact energy of the welding heat affected zone at -40℃ is more than 200J.

[0068] In summary, the steel plate adopts a corrosion-resistant alloying component system with a composite addition of Ce+Sn+Cu. The addition of Ce not only improves the corrosion resistance of the steel plate, but also easily combines with oxygen to form spherical oxides and has the ability to induce the nucleation of acicular ferrite within the grains, thereby improving the weldability of the steel plate. Based on the comprehensive design of chemical composition and the precise control of the process parameters during rolling and cooling, a high-heat input steel plate with excellent comprehensive performance and resistance to marine atmospheric corrosion is obtained.

[0069] The following nine specific examples and three comparative examples further introduce the specific implementation methods of the present invention.

[0070] Examples 1 to 9 and Comparative Examples 1 to 3 all provide a steel plate, and the chemical composition of the steel plate is shown in Table 1.

[0071] Table 1

[0072]

[0073] The steel plates in Examples 1 to 9 and Comparative Examples 1 to 3 were produced according to the above production method. The cored wire used for steelmaking and the addition process are shown in Table 2. The rolling process parameters are shown in Table 3.

[0074] Table 2

[0075]

[0076] Table 3

[0077]

[0078] The corrosion resistance of the steel plates of Examples 1 to 9 and Comparative Examples 1 to 3 was tested using a standard periodic immersion corrosion tester. The average corrosion weight loss rates and welding properties of Examples 1 to 9 and Comparative Examples 1 to 3 are shown in Table 4.

[0079] As shown in Table 4, the average corrosion weight loss rate of the steel plates in Examples 1 to 9 is less than 1.2 g / (m 2 ×h). Comparative Example 1 does not meet the corrosion resistance requirement, and Comparative Examples 2 and 3 do not meet the low-temperature toughness requirement.

[0080] Table 4

[0081]

[0082] Combined with the above test results, it can be seen that the steel plate provided by this embodiment is not only cost-controllable and has a simple and efficient process flow, but also has excellent corrosion resistance, low-temperature toughness and welding performance, which is conducive to promotion and application.

[0083] It should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation method can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0084] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for producing a steel plate, characterized in that: Includes steps: The chemical composition of the steel plate includes, 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%, and the rest is Fe and unavoidable impurities; According to the above chemical composition ratio, molten steel is obtained by smelting in a converter, LF refining and RH refining in sequence; Casting the molten steel through a continuous casting process to form a continuous casting slab; The continuous casting slab is heated and then rolled to obtain a steel plate, wherein rough rolling and finish rolling are sequentially adopted in the rolling process, wherein the finish rolling stage is rolling in the non-recrystallization zone, the cumulative reduction rate is controlled to be above 50%, the single-pass reduction rate is controlled to be above 15%, and the final rolling temperature is controlled to be below 780°C; performing a cooling process on the steel plate; The average corrosion weight loss rate of the steel plate obtained in the periodic immersion corrosion test is less than 1.2g / (m 2 ×h), under the condition that the welding heat input is not less than 600kJ / cm, the impact energy of the welding heat affected zone of the steel plate at -40°C is ≥200J.

2. The method for producing a steel plate according to claim 1, characterized in that: The Ce content in the steel plate is 0.1-0.5% by mass, and the Sn content in the steel plate is 0.1-0.5% by mass.

3. The method for producing a steel plate according to claim 1, characterized in that: The converter smelting process specifically includes: Add clean steel and scrap steel in a ratio of (5~6):1, control the molten iron temperature to 1350~1450℃, and add ferromanganese, ferrosilicon and lime in turn to the molten iron for smelting.

4. The method for producing a steel plate according to claim 1, characterized in that: The LF refining process specifically includes: During the LF refining process, argon is blown from the bottom and the molten steel is stirred to keep it covered.

5. The method for producing a steel plate according to claim 1, characterized in that: The RH refining process specifically includes: During the RH refining process, more than 800m of rare earth cored wire is added at a speed of 4-5m / s, and carbonized rice husk is added for heat preservation before steelmaking.

6. The method for producing a steel plate according to claim 1, characterized in that: The continuous casting process specifically includes: The casting temperature is controlled at 1540~1560℃, the continuous casting speed is controlled at 1.1~1.3m / min, and a 320mm thick continuous casting slab is obtained by continuous casting.

7. The method for producing a steel plate according to claim 1, characterized in that: The cooling process specifically includes: The rolled steel plate is first water-cooled, the water cooling rate is controlled at above 12°C / s, the final cooling temperature is controlled at 480~540°C, and then air-cooled to below 350°C after water cooling.

8. A steel plate, characterized in that: The chemical composition of the steel plate includes, 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%, and the rest is Fe and unavoidable impurities.

9. The steel plate according to claim 8, characterized in that: The Ce content in the steel plate is 0.1-0.5% by mass, and the Sn content in the steel plate is 0.1-0.5% by mass.

10. The steel plate according to claim 8, characterized in that In the periodic immersion corrosion test, the average corrosion weight loss rate of the steel plate is less than 1.2g / (m 2 ×h).

11. The steel plate according to claim 8, characterized in that Under the condition that the welding heat input is not less than 600kJ / cm, the impact energy of the welding heat affected zone of the steel plate at -40℃ is ≥200J.

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