A method for strengthening the heat-affected zone of thick low-carbon, low-alloy ship steel plates subjected to high heat input welding.

Abstract

This invention relates to the field of welding technology, specifically to a method for strengthening the heat-affected zone (HAZ) of thick low-carbon, low-alloy ship steel plates that withstand high heat input welding; more specifically, it relates to a method for strengthening the HAZ of thick low-carbon, low-alloy ship steel plates that withstand high heat input welding and its application. This invention uses a first flux as a printing material, which is melted onto the surface of a steel substrate via arc printing to obtain a steel billet. The first flux is mainly composed of CaF2, SiO2, MnO, and TiO2 in a mass ratio of 25–32:25–32:25–32:4–25. The steel billet is then rolled and welded. This method has advantages such as simple operation, low cost, short time consumption, and high production efficiency. Furthermore, the steel heat-affected zone prepared by this method has a large number of fine, dispersed inclusions and fine grains, greatly improving the mechanical properties of the heat-affected zone.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a method for strengthening the heat-affected zone of thick plates of low-carbon, low-alloy ship steel that can withstand high heat input during welding; more specifically, to a method for strengthening the heat-affected zone of thick plates of low-carbon, low-alloy ship steel that can withstand high heat input during welding and its application. Background Technology

[0002] Currently, low-carbon low-alloy steel is widely used in the manufacturing industry due to its excellent performance, and welding is a common method for joining materials. Among them, high heat input welding with a heat input greater than 50 kJ / cm is highly efficient and widely used in steel plate welding. However, blindly pursuing high efficiency, i.e., excessively high heat input, will lead to coarse grains and complex microstructure in the heat-affected zone of low-carbon low-alloy steel welds, thereby deteriorating the mechanical properties of the weld heat-affected zone.

[0003] Therefore, many universal methods for improving the heat-affected zone of welds have been proposed. These include preheating the material before welding or heat-treating the material after welding; and designing joint structures, such as using chamfers or gradual transitions, to reduce thermal stress concentration and thus reduce the size of the heat-affected zone. However, these methods have drawbacks such as long sample preparation time, high cost, and difficulty in operation.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a method for strengthening the heat-affected zone of thick low-carbon, low-alloy ship steel plates that can withstand high heat input welding. This method has the advantages of simple operation, low cost, short time consumption, and high production efficiency, and solves the technical problems of long preparation time, high cost, and difficulty in operation of the existing technology for preparing and studying weld heat-affected zone samples.

[0006] The second objective of this invention is to provide a method for strengthening the heat-affected zone of thick low-carbon, low-alloy ship plate steel that can withstand high heat input during welding, and its application in welding thick low-carbon, low-alloy ship plate steel.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] This invention first provides a method for strengthening the heat-affected zone of thick low-carbon, low-alloy ship steel plates that can withstand high heat input welding, comprising the following steps:

[0009] Using a first flux as the printing material, the first flux is melted onto the surface of a steel substrate by arc printing to obtain a steel billet; wherein, the first flux is mainly composed of CaF2, SiO2, MnO and TiO2 in a mass ratio of 25-32:25-32:25-32:4-25;

[0010] The steel billet is rolled and then welded.

[0011] This invention further provides the application of the method for strengthening the heat-affected zone of the high heat input welding low-carbon low-alloy ship plate thick plate in welding low-carbon low-alloy ship plate thick plate.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] (1) The method for strengthening the heat-affected zone of thick low-carbon low-alloy ship plate steel that is resistant to high heat input welding provided by the present invention has the advantages of simple operation, low cost, short time consumption and high production efficiency.

[0014] (2) The method for strengthening the heat-affected zone of thick plates of low-carbon and low-alloy ship steel that can withstand high heat input welding provided by the present invention improves the welding heat-affected zone from the perspective of "oxide metallurgy". It introduces fine and dispersed inclusions into the steel plate, promotes the nucleation of acicular ferrite, improves the microstructure of the welding heat-affected zone, and can improve the mechanical properties of the welding heat-affected zone. It solves the problem that excessive heat input leads to coarse grains and complex microstructure in the welding heat-affected zone of low-carbon and low-alloy steel, which in turn deteriorates the mechanical properties of the welding heat-affected zone.

[0015] (3) The heat-affected zone strengthening method of high heat-resistant welding of low carbon and low alloy ship plate steel provided by the present invention has a large number of fine and dispersed inclusions in the microstructure of the welded heat-affected zone, and the content of needle ferrite in the welded joint is ≥10%, with fine grains, which greatly improves the mechanical properties of the welded heat-affected zone, especially the low-temperature impact energy, wherein the low-temperature impact energy of the welded joint is ≥10J at -40℃. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 A schematic flowchart of the method for strengthening the heat-affected zone of thick low-carbon low-alloy ship plate steel for high heat input welding provided by the present invention.

[0018] Figure 2 Microstructure diagram of the weld heat-affected zone provided in Embodiment 1 of the present invention;

[0019] Figure 3 Microstructure diagram of the weld heat-affected zone provided in Embodiment 2 of the present invention;

[0020] Figure 4Microstructure diagram of the weld heat-affected zone provided in Embodiment 3 of the present invention;

[0021] Figure 5 Microstructure diagram of the weld heat-affected zone provided by Comparative Example 1 of this invention;

[0022] Figure 6 Microstructure diagram of the weld heat-affected zone provided by Comparative Example 2 of this invention;

[0023] Figure 7 Microstructure diagram of the weld heat-affected zone of Comparative Example 3 provided by the present invention;

[0024] Figure 8 Microscopic cross-sectional structural diagrams of welded joints in the heat-affected zone of Embodiments 1, 2, and 3 provided for the present invention;

[0025] Figure 9 Microscopic cross-sectional structural diagrams of welded joints in the heat-affected zone of Comparative Examples 1, 2, and 3 provided for this invention. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0027] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0028] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0029] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0030] In a first aspect, the present invention provides a method for strengthening the heat-affected zone of thick plates of low-carbon, low-alloy ship steel that are resistant to high heat input welding. (See [link to previous section]). Figure 1 As shown, it specifically includes the following steps:

[0031] Using the first flux as the printing material, the first flux is melted onto the surface of the steel substrate by electric arc printing, and a steel billet is obtained after cooling.

[0032] Arc printing refers to a printing technology that uses an electric arc as a heat source and molten metal droplets as filler material. This invention introduces flux to adjust the composition of the molten droplets, thereby controlling the composition of inclusions and promoting the formation of acicular ferrite.

[0033] The first flux is mainly composed of CaF2, SiO2, MnO and TiO2 in a mass ratio of 25-32 (including but not limited to point values ​​of any one of 25, 26, 27, 28, 29, 30, 31, 32 or a range between any two): 25-32 (including but not limited to point values ​​of any one of 25, 26, 27, 28, 29, 30, 31, 32 or a range between any two): 25-32 (including but not limited to point values ​​of any one of 25, 26, 27, 28, 29, 30, 31, 32 or a range between any two): 4-25 (including but not limited to point values ​​of any one of 4, 5, 6, 8, 10, 12, 15, 18, 20, 23, 25 or a range between any two).

[0034] After the steel billet is rolled, it is welded.

[0035] It is understood that the heat-affected zone strengthening method provided by the present invention can be used for high heat input welding, but is not limited to high heat input welding, and can also be used for low heat input welding.

[0036] The heat-affected zone strengthening method provided by the present invention has the advantages of simple operation, low cost, short time consumption and high production efficiency.

[0037] Furthermore, to better adapt low-carbon, low-alloy ship plate steel to high heat input welding, this invention improves the weld heat-affected zone from the perspective of "oxide metallurgy" (using fine, dispersed oxide particles to induce acicular ferrite nucleation and improve microstructure). It introduces fine, dispersed inclusions into the steel plate to promote acicular ferrite nucleation, improve the microstructure of the weld heat-affected zone, and thus enhance its mechanical properties. This solves the technical problem that excessive heat input leads to coarse grains and complex microstructure in the weld heat-affected zone of low-carbon, low-alloy steel, thereby deteriorating the mechanical properties of the weld heat-affected zone.

[0038] Specifically, the first flux is mainly composed of CaF2, SiO2, MnO, and TiO2, which can induce the formation of a microstructure in the heat-affected zone that is beneficial to improving mechanical properties. The reason is that the first flux, through alloy transition, allows some Ti to transition into the matrix during the printing process. Ti reacts with oxides to generate fine and dispersed inclusions, and Ti-containing inclusions are conducive to the formation of acicular ferrite.

[0039] Furthermore, this method can further supplement and enrich the proposed methods for microstructure optimization and performance enhancement in the heat-affected zone of high-strength steel welds.

[0040] In some specific embodiments, the current used for arc printing is 32–36A, including but not limited to any one of 32A, 33A, 34A, 35A, and 36A, or a range between any two; the voltage is 625–850V, including but not limited to any one of 625V, 630V, 650V, 680V, ​​700V, 730V, 750V, 780V, 800V, 830V, and 850V, or a range between any two. Using the above current and voltage is beneficial for controlling the cooling rate, and at an appropriate cooling rate, it is conducive to the formation of acicular ferrite.

[0041] In some specific embodiments, the preparation method of the first flux includes the following steps: CaF2, SiO2, MnO, and TiO2 are mixed evenly and then melted at 1500–1600°C. The resulting molten liquid is then water-quenched to obtain the first flux. The melting temperature includes, but is not limited to, any one of 1500°C, 1530°C, 1550°C, 1580°C, and 1600°C, or a range between any two. The first flux prepared by this method has advantages such as uniform particle size, easy arc initiation, intact slag shell after welding, and good weld formation.

[0042] In some specific implementations, during the arc printing process, the area covered by each subsequent print overlaps by at least one-third of the area covered by the previous print; this includes, but is not limited to, any one of the values ​​of 1 / 3, 0.35, 0.38, 0.4, 0.45, and 0.5, or any range between two of these values. This ensures that the steel plate substrate is fully covered by the printing material.

[0043] In some specific embodiments, after the arc printing is completed, the deposited metal layer formed by the first flux covers at least 80% of the surface area of ​​the top surface of the steel substrate (i.e., the surface in contact with the first flux), for example 85%, 90%, 95%, or 100%. This helps to reduce arc spatter and makes the weld formation more aesthetically pleasing.

[0044] In some specific embodiments, the steel matrix comprises low-carbon, low-alloy ship plate steel. Low-carbon, low-alloy ship plate steel has low alloy element content and high strength. Therefore, the element content in low-carbon, low-alloy ship plate steel can be changed by introducing alloying elements from the outside (first flux), thereby improving the performance of the weld heat-affected zone.

[0045] Preferably, the low-carbon low-alloy ship plate steel includes at least one of AH36 steel, DH36 steel, EH36 steel and EH420 steel.

[0046] In some specific embodiments, the rolling is carried out using a thermomechanical control process (TMCP, i.e., controlled rolling and controlled cooling technology), which is beneficial for obtaining steel plates with ideal microstructure and properties.

[0047] In some specific embodiments, the rolling process specifically includes: heating the steel billet to 1150–1250°C (including but not limited to any one of 1150°C, 1180°C, 1200°C, 1230°C, and 1250°C, or a range between any two), holding it at that temperature for 1–2 hours (e.g., 1 hour, 1.5 hours, or 2 hours), and then rolling it at 900–1200°C (including but not limited to any one of 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1180°C, and 1200°C, or a range between any two), for 2–4 rolling passes (e.g., 2, 3, or 4 passes), with a deformation of 2–4 mm per pass (e.g., 2 mm, 3 mm, or 4 mm). This achieves good plasticity, strength, and toughness in the steel plate and obtains the desired microstructure.

[0048] In some specific embodiments, the second flux used for welding is mainly composed of CaF2 and TiO2 in a mass ratio of 6 to 9 (including but not limited to any one of 6, 7, 8, 9 or any range between two): 1 to 4 (including but not limited to any one of 1, 2, 3, 4 or any range between two). The second flux is used for welding.

[0049] In some specific embodiments, the welding line energy is 30 to 90 kJ / cm, including but not limited to the point value of any one of 30 kJ / cm, 40 kJ / cm, 50 kJ / cm, 60 kJ / cm, 70 kJ / cm, 80 kJ / cm, and 90 kJ / cm, or the range between any two.

[0050] The heat-affected zone strengthening method provided by this invention can be used not only for low heat input welding but also for high heat input welding. It can improve the mechanical properties of the weld heat-affected zone and avoid the problem in the prior art where excessive heat input leads to coarse grains and complex microstructure in the weld heat-affected zone of low carbon low alloy steel, which in turn deteriorates the mechanical properties of the weld heat-affected zone.

[0051] In some specific embodiments, the acicular ferrite content in the welded joint obtained after welding is ≥10%, including but not limited to any one of 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80%, or any range between two; preferably ≥40%.

[0052] In some specific embodiments, the welded joint obtained after welding has a low-temperature impact energy of ≥10J at -40℃, including but not limited to any one of 10J, 20J, 30J, 35J, 40J, 45J, 50J, 55J, 60J, 65J, 70J, and 80J, or a range between any two; preferably ≥35J.

[0053] The welded joint obtained by the strengthening method provided by the present invention contains a large amount of acicular ferrite and has excellent mechanical properties.

[0054] In some specific implementations, the steel substrate can be of any desired size, such as a steel substrate with a length of 300 mm, a width of 150 mm, and a thickness of 25 mm, but is not limited thereto.

[0055] In some specific implementations, the number of arc printing lines is 7 to 10.

[0056] In some specific embodiments, during the arc printing process, each print pass is covered with a layer of first flux, which evenly covers the printing path, completely submerging the print nozzle. After the steel plate (steel substrate) cools, the excess material is removed, and the next print pass is performed.

[0057] In some specific implementations, the thickness of the deposited metal layer formed after the first flux is clad and cooled is 10-20 mm.

[0058] In some specific implementations, the dimensions of the steel billet obtained after arc printing can be, for example, a length of 300 mm, a width of 150 mm, and a thickness of 35–40 mm.

[0059] In some specific embodiments, the dimensions of the rolled steel billet are: length 300-350mm, width 150-200mm, and thickness 20-25mm.

[0060] In some specific embodiments, before welding, the rolled steel billet is polished and rust-removed using an angle grinder until it is shiny.

[0061] In some specific embodiments, during the welding process, the second flux is evenly distributed on the welding path.

[0062] In some specific implementations, during the welding process, the second weld is performed after the first weld has been deslag-removed, and so on.

[0063] Secondly, the present invention provides the application of the above-mentioned method for strengthening the heat-affected zone of thick plates of low-carbon and low-alloy ship steel that can withstand high heat input in welding, in the welding of thick plates of low-carbon and low-alloy ship steel.

[0064] This strengthening method introduces fine, dispersed inclusions into low-carbon, low-alloy ship plate steel, which induces the nucleation of acicular ferrite during welding, thereby improving the microstructure of the weld heat-affected zone and enhancing the mechanical properties of the welded parts.

[0065] The low-carbon, low-alloy ship plate steel includes at least one of AH36 steel, DH36 steel, EH36 steel, and EH420 steel.

[0066] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0067] The preparation method of the first flux used in the following embodiments of the present invention is as follows: CaF2, SiO2, MnO and TiO2 are mixed evenly and then melted at 1550°C. The resulting molten liquid is then poured into water for water quenching, followed by drying and sieving to obtain the first flux.

[0068] Example 1

[0069] The method for strengthening the heat-affected zone of thick low-carbon, low-alloy ship steel plates that can withstand high heat input welding provided in this embodiment includes the following steps:

[0070] (1) Steel billet fabrication using arc printing technology: A first flux, prepared from CaF2, SiO2, MnO, and TiO2 in a mass ratio of 30:30:30:10, was used as the printing material. This material was evenly and smoothly spread onto the EH36 steel substrate for arc printing. The arc printing current was 34A and the voltage was 700V. Each printing required the application of a layer of printing material to isolate the substrate from air. During the arc printing process, the area covered by each subsequent print overlapped by one-third of the area covered by the previous print. After nine prints, the molten metal layer formed by the first flux completely covered the EH36 steel substrate, resulting in the steel billet. The thickness of the molten metal layer was 6mm.

[0071] The chemical composition of the EH36 steel matrix is ​​shown in Table 1.

[0072] Table 1 Chemical composition (mass fraction) of EH36 steel matrix

[0073] element C O Si Mn Ti Al Fe Content (wt.%) 0.052 0.003 0.142 1.540 0.010 0.034 margin

[0074] (2) Rolling and welding: After preheating the steel billet obtained in step (1) to 1200℃ and holding it at that temperature for 1 hour, the steel billet is rolled using a thermomechanical control process (TMCP, controlled rolling and controlled cooling technology), wherein the rolling temperature is 1100℃, the rolling passes are 2, and the deformation amount per pass is 4mm.

[0075] The rolled steel billet was ground and polished. A second flux, made of CaF2 and TiO2 in a mass ratio of 8:2, was then evenly spread on the welding path. The current, voltage, and welding rate were adjusted to control the linear energy at 30 kJ / cm. Welding was stopped after reaching the preset position, and the workpiece was allowed to cool naturally to room temperature to obtain the welded part.

[0076] Example 2

[0077] The strengthening method for the heat-affected zone of thick low-carbon low-alloy ship plate steel provided in this embodiment is basically the same as that in embodiment 1. The difference is that the welding heat input in step (2) is controlled to be 60 kJ / cm.

[0078] Example 3

[0079] The strengthening method for the heat-affected zone of thick low-carbon low-alloy ship plate steel provided in this embodiment is basically the same as that in embodiment 1. The difference is that the welding heat-affected zone in step (2) is controlled to be 90 kJ / cm.

[0080] Example 4

[0081] The method for strengthening the heat-affected zone of thick low-carbon, low-alloy ship steel plates subjected to high heat input welding provided in this embodiment includes the following steps:

[0082] (1) Steel billet fabrication using arc printing technology: A first flux, prepared from CaF2, SiO2, MnO, and TiO2 in a mass ratio of 30:30:30:10, was used as the printing material. The printing material was spread evenly and smoothly on the DH36 steel substrate for arc printing. The arc printing current was 32A and the voltage was 625V. Each printing required the application of a layer of printing material to isolate the substrate from air. During the arc printing process, the area covered by each subsequent print overlapped by 0.35 of the area covered by the previous print. After 10 prints, the molten metal layer formed by the first flux completely covered the DH36 steel substrate, resulting in the steel billet.

[0083] (2) Rolling and welding: After preheating the steel billet obtained in step (1) to 1250℃ and holding it at that temperature for 1.5h, the steel billet is rolled using thermomechanical control process (TMCP, controlled rolling and controlled cooling technology), wherein the rolling temperature is 1000℃, the rolling passes are 3, and the deformation amount per pass is 2.5mm.

[0084] The rolled steel billet was ground and polished. A second flux, made of CaF2 and TiO2 in a mass ratio of 6:4, was then evenly spread on the welding path. The current, voltage, and welding rate were adjusted to control the linear energy at 70 kJ / cm. Welding was stopped after reaching the preset position, and the workpiece was allowed to cool naturally to room temperature to obtain the welded part.

[0085] Example 5

[0086] The method for strengthening the heat-affected zone of thick low-carbon, low-alloy ship steel plates subjected to high heat input welding provided in this embodiment includes the following steps:

[0087] (1) Steel billet fabrication using arc printing technology: A first flux, prepared from CaF2, SiO2, MnO, and TiO2 in a mass ratio of 30:30:30:10, was used as the printing material. The printing material was spread evenly and smoothly on the AH36 steel substrate for arc printing. The arc printing current was 36A and the voltage was 800V. Each printing required the application of a layer of printing material to isolate the substrate from air. During the arc printing process, the area covered by each subsequent print overlapped by 0.5 times the area covered by the previous print. After 8 prints, the molten metal layer formed by the first flux completely covered the AH36 steel substrate, resulting in the steel billet.

[0088] (2) Rolling and welding: After preheating the steel billet obtained in step (1) to 1150℃ and holding it at that temperature for 2 hours, the steel billet is rolled using a thermomechanical control process (TMCP, controlled rolling and controlled cooling technology), wherein the rolling temperature is 1000℃, the rolling passes are 4, and the deformation amount per pass is 2mm.

[0089] The rolled steel billet was ground and polished. A second flux, made of CaF2 and TiO2 in a mass ratio of 9:1, was then evenly spread on the welding path. The current, voltage, and welding rate were adjusted to control the linear energy at 80 kJ / cm. Welding was stopped after reaching the preset position, and the workpiece was allowed to cool naturally to room temperature to obtain the welded part.

[0090] Example 6

[0091] The strengthening method for the heat-affected zone of thick low-carbon low-alloy ship plate steel resistant to high heat input welding provided in this embodiment is basically the same as that in embodiment 3. The difference is that in step (1), the first flux is made of CaF2, SiO2, MnO and TiO2 in a mass ratio of 25:25:25:25.

[0092] Example 7

[0093] The strengthening method for the heat-affected zone of thick low-carbon low-alloy ship plate steel resistant to high heat input welding provided in this embodiment is basically the same as that in embodiment 3. The difference is that in step (1), the first flux is made of CaF2, SiO2, MnO and TiO2 in a mass ratio of 32:32:32:4.

[0094] Example 8

[0095] The strengthening method for the heat-affected zone of thick low-carbon low-alloy ship plate steel resistant to high heat input welding provided in this embodiment is basically the same as that in embodiment 3. The difference is that in step (1), the first flux is made of CaF2, SiO2, MnO and TiO2 in a mass ratio of 25:28:30:17.

[0096] Comparative Example 1

[0097] The strengthening method provided in this comparative example is basically the same as that in Example 1, except that step (1) is omitted and the steel billet in step (2) is replaced with EH36 steel plate (which has not been arc printed and has not been coated with the first flux).

[0098] Comparative Example 2

[0099] The strengthening method provided in this comparative example is basically the same as that in Example 2, except that step (1) is omitted and the steel billet in step (2) is replaced with EH36 steel plate (which has not been arc printed and has not been coated with the first flux).

[0100] Comparative Example 3

[0101] The strengthening method provided in this comparative example is basically the same as that in Example 3, except that step (1) is omitted and the steel billet in step (2) is replaced with EH36 steel plate (which has not been arc printed and has not been coated with the first flux).

[0102] Comparative Example 4

[0103] The strengthening method provided in this comparative example is basically the same as that in Example 1, except that the first flux is prepared from CaF2, SiO2 and MnO in a mass ratio of 40:30:30.

[0104] Comparative Example 5

[0105] The strengthening method provided in this comparative example is basically the same as that in Example 1, except that the first flux is prepared from CaF2, SiO2, MnO and TiO2 in a mass ratio of 40:25:25:10.

[0106] Comparative Example 6

[0107] The strengthening method provided in this comparative example is basically the same as that in Example 1, except that the first flux is prepared from CaF2, SiO2, MnO and TiO2 in a mass ratio of 26:35:35:4.

[0108] Experimental Example

[0109] The content of acicular ferrite in the welded joints of the welded parts obtained in each embodiment and each comparative example was detected according to the following method, and Charpy low-temperature impact test was performed on each cut welded joint. The results are shown in Table 2.

[0110] (1) Process each welded part separately: Place the welded parts obtained in each embodiment and each comparative example on the cutting table with the welding direction perpendicular to the cutting direction. Then, adjust the distance between the wire and the welded part and perform wire cutting. The length of the cut welded joint is 60mm, the width is 10mm, and the thickness is the same as the thickness of the welded part. Then, the cut welded joint is ultrasonically cleaned with ethanol for 4 minutes. After the welded joint is dried, the cross-section of the welded joint is polished in sequence with 240#, 400#, 800#, 1000#, 1200#, 1500#, and 2000# sandpaper. Then, it is mechanically polished with 0.25μm diamond polishing paste. Under a metallographic microscope at 1000x magnification, there are no visible scratches or contaminants. Next, the cross-section of the welded joint was etched with a mixture of nitric acid and alcohol using degreased cotton soaked in a solution with a volume fraction of 4% nitric acid. The sample was repeatedly wiped in the same direction for 8 times. Once the weld and heat-affected zone were visible to the naked eye, the residual corrosion solution was immediately rinsed with clean water. Ethanol was then sprayed onto the cross-section and dried for storage.

[0111] (2) Microstructure observation: The observation surface of the weld joint obtained after the above step (1) is placed on the stage. First, the heat-affected zone of the weld is found with a 100x objective lens. Then, the objective lens is adjusted until the microstructure of the heat-affected zone can be clearly observed. The stage is moved and three fields of view of the heat-affected zone of the weld are photographed. The content of different microstructures in the heat-affected zone of the weld is counted using the Monte Carlo method.

[0112] (3) Charpy low-temperature impact test: The impact specimen (i.e., the welded joint obtained after treatment in step (1) above) was kept at -40℃ with alcohol. After the temperature was reached, the specimen was immediately placed on the Charpy impact test bench. Three impact specimens were taken for each heat input, and the average value of the data was taken after three impact tests.

[0113] Table 2. Needle ferrite content and Charpy low-temperature impact test results

[0114]

[0115]

[0116] The microstructure diagram of the weld heat-affected zone in Example 1 is shown below. Figure 2 As shown. See the microstructure diagram of the weld heat-affected zone in Example 2. Figure 3 As shown. See the microstructure diagram of the weld heat-affected zone in Example 3. Figure 4 As shown. See Figure 1 for the microstructure of the weld heat-affected zone in Comparative Example 1. Figure 5 As shown. See Figure 2 for the microstructure of the weld heat-affected zone. Figure 6 As shown. See Figure 3 for the microstructure of the weld heat-affected zone. Figure 7 As shown.

[0117] See the schematic diagrams of the microscopic cross-sectional structure of the welded joints in the heat-affected zone of Examples 1, 2, and 3. Figure 8 As shown. See the schematic diagram of the microscopic cross-sectional structure of the welded joints in the heat-affected zone of Comparative Examples 1, 2, and 3. Figure 9 As shown.

[0118] From Table 2 and Figures 2-7 It is known that the heat-affected zone of low-carbon low-alloy steel produced by the strengthening method of high heat input welding of low-carbon low-alloy ship plate thick plate provided by the present invention contains a large amount of acicular ferrite in the heat-affected zone of the welded heat-affected zone in all three heat input welding processes, thereby improving the mechanical properties of the welded heat-affected zone.

[0119] However, in each comparison, the content of needle-like ferrite decreased and the mechanical properties of the weld heat-affected zone were reduced because the first flux was not clad by arc printing or the composition of the first flux was unsuitable.

[0120] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for strengthening the heat-affected zone of a thick plate of a low-carbon low-alloy ship plate steel for high heat input welding, characterized in that, Includes the following steps: Using a first flux as the printing material, the first flux is fused onto the surface of a steel substrate by arc printing to obtain a steel billet; wherein, the first flux is made of CaF2, SiO2, MnO and TiO2 in a mass ratio of 25~32:25~32:25~32:4~25; the preparation method of the first flux includes the following steps: mixing CaF2, SiO2, MnO and TiO2 evenly and then melting at 1500~1600℃, and then quenching the melt obtained after melting with water to obtain the first flux; the current of the arc printing is 32~36A and the voltage is 625~850V; The steel billet is rolled and then welded. The rolling process is carried out using a thermomechanical control process; the rolling process specifically includes: heating the steel billet to 1150~1250℃, holding it at that temperature for 1~2 hours, rolling it at a temperature of 900~1200℃, rolling it 2~4 times, and the deformation amount per pass is 2~4mm. The second flux used in the welding is made of CaF2 and TiO2 in a mass ratio of 6~9:1~4; The welding line energy is 30~90kJ / cm.

2. The method of strengthening the heat-affected zone of thick low-carbon low-alloy ship plate steel according to claim 1, characterized in that, During the arc printing process, the area covered by the subsequent printing layer shall overlap the area of ​​the previous printing layer by at least 1 / 3. And / or, after the arc printing is completed, the molten metal layer formed by the first flux covers at least 80% of the top surface area of ​​the steel substrate.

3. The method of strengthening the heat-affected zone of thick low-carbon low-alloy ship plate steel according to claim 1, characterized in that, The steel matrix includes low-carbon, low-alloy ship plate steel.

4. The method of strengthening the heat-affected zone of thick low-carbon low-alloy ship plate steel according to claim 3, characterized in that, The low-carbon, low-alloy ship plate steel includes at least one of AH36 steel, DH36 steel, EH36 steel, and EH420 steel.

5. The method of strengthening the heat-affected zone of thick low-carbon low-alloy ship plate steel according to claim 1, characterized in that, The content of acicular ferrite in the welded joint obtained after welding is ≥10%; And / or, the welded joint obtained after the welding has an impact energy of ≥10J at a low temperature of -40℃.

6. The method of strengthening the heat-affected zone of thick low-carbon low-alloy ship plate steel according to claim 1, characterized in that, The content of acicular ferrite in the welded joint obtained after welding is ≥40%; And / or, the welded joint obtained after the welding has a low-temperature impact energy of ≥35J at -40℃.

7. The method for strengthening the heat-affected zone of thick low-carbon low-alloy ship steel plates as described in any one of claims 1 to 6 is applied to the welding of thick low-carbon low-alloy ship steel plates.

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