Microhardness control method for high-speed welding ship plate steel

Abstract

The invention provides a microhardness control method for high-speed welding ship plate steel, which comprises the following steps: S1, cutting two ship steel plates to a preset size, and overlapping and fixing according to a T-shaped mode; and S2, a preset welding wire is selected for double-wire welding according to the preset welding speed. By limiting the chemical components of the welding wire, on the premise that the low-alloy high-strength ship plate steel does not need to be preheated before welding, the welding seam is attractive in forming, the macroscopic structure is compact and free of defects, and detection items such as the microhardness of a fusion area meet the classification society and corresponding detection specifications and standards. And double-wire common-molten-pool welding is adopted, so that the fillet weld welding quality is guaranteed, and the welding efficiency is remarkably improved. And the preheating procedure can be omitted, the welding procedures are reduced, and the applicability and the high efficiency of double-wire welding are further improved.

Description

Technical Field

[0001] The present application relates to the technical field of shipbuilding, and in particular to a method for controlling the microhardness of high-speed welded ship plate steel. Background Art

[0002] The rapid development of the shipbuilding industry has put forward higher requirements for welding technology. Welding is an important way to connect ship plate steel. Therefore, welding technology is one of the main factors affecting the production efficiency of large ships. Studies have shown that the welding work cycle accounts for 30%-40% of the total time of shipbuilding work, and the welding cost accounts for about 30%-50% of the overall shipbuilding process. Therefore, improving welding efficiency has become a key breakthrough direction for large medium and thick ship plate welding technology.

[0003] Fillet welds account for a very large proportion in the shipbuilding process and are the main form of shipbuilding technology, which has a significant impact on the overall construction cost and quality control of the ship. In block construction, the amount of welding materials used for fillet welds accounts for about 50% of the total amount of welding materials; calculated by the unit length of the weld, the total length of the fillet weld type accounts for about 80% of the welds in the entire shipbuilding. Therefore, the welding efficiency of fillet welds has a significant impact on the entire shipbuilding cycle.

[0004] During the welding process of fillet welds, when the thickness of the ship plate is greater than 12mm and the welding speed is greater than 50cm / min, in order to reduce the occurrence of welding cracks, the steel plate needs to be preheated before welding. The preheating slows down the cooling rate of the heat-affected zone during the cooling process to prevent the formation of hardened structures. However, preheating before welding will reduce welding efficiency and production cycle, and increase energy consumption, which is very unfavorable for speeding up production and saving costs. If preheating before welding is not performed, martensite and MA components are easily formed in the fusion zone, resulting in a microhardness exceeding 350HV, which does not meet the classification society specifications.

[0005] In summary, it is necessary to provide an improved technical solution to address the above-mentioned deficiencies in the prior art. Summary of the invention

[0006] The purpose of the embodiment of the present application is to provide a method for controlling the microhardness of high-speed welded ship plate steel, which can perform high-speed welding on ship plate steel, the fillet weld is beautiful and defect-free, and the maximum microhardness requirement of the joint fusion zone meets the specifications and standards of the classification society.

[0007] The present application specifically provides a method for controlling the microhardness of high-speed welded ship plate steel, comprising the following steps:

[0008] S1. Cut two ship steel plates to the predetermined size, overlap and fix them in a T-shaped manner;

[0009] S2. Select a predetermined welding wire and perform twin-wire welding at a predetermined welding speed.

[0010] In an implementable manner, in step S2, the requirements for the elemental contents of the predetermined welding wire are as follows:

[0011] The carbon C content is between 0.03% and 0.05%, the silicon Si content is less than or equal to 0.45%, the manganese Mn content is between 0.90% and 1.20%, the sulfur S content is less than or equal to 0.015%, the phosphorus P content is less than or equal to 0.015%, the copper Cu content is less than or equal to 0.10%, the nickel Ni content is less than or equal to 0.15%, the chromium Cr content is less than or equal to 0.10%, the molybdenum Mo content is less than or equal to 0.05%, and the vanadium V content is less than or equal to 0.08%.

[0012] In an implementable manner, the maximum carbon equivalent value in the predetermined welding wire is determined according to the cold crack sensitivity coefficient P cm for determination.

[0013] In an implementable manner, in step S2, during twin-wire welding, the welding speed is 80 - 150 cm / min.

[0014] In an implementable manner, the thickness of the ship steel plate is 12 - 25 mm.

[0015] In an implementable manner, the elemental contents in the ship steel plate are as follows:

[0016] The carbon content is less than or equal to 0.18%, the silicon content is between 0.90% and 1.60%, the sulfur content is less than or equal to 0.015%, the phosphorus content is less than or equal to 0.015%, the aluminum content is less than or equal to 0.02%, the vanadium content is between 0.05% and 0.10%, the niobium content is between 0.02% and 0.05%, the titanium content is less than or equal to 0.015%, the magnesium content is less than or equal to 0.005%, and iron is the main matrix element in the alloy, and the iron content is the remaining part.

[0017] In an implementable manner, in step S1, the area to be welded is polished with a grinding wheel, cleaned with acetone and dried.

[0018] In an implementable manner, the twin-wire welding gun includes a front wire and a rear wire. The front wire and the rear wire are arranged front and rear along the welding direction; the ends of the front wire and the rear wire are both inclined towards the axis of the twin-wire welding gun; the angle between the axis of the twin-wire welding gun and the vertical direction is 30 - 40°, the twin-wire dry elongation of the twin-wire welding gun is 10 - 15 mm, and the twin-wire spacing is 8 - 12 mm.

[0019] In an implementable manner, in step S2, the welding parameters during welding at least include the following:

[0020] The current of the front wire is 265 - 320A, the current of the rear wire is 260 - 300A, the voltage of the front wire is 36 - 39.5V, the voltage of the rear wire is 35 - 38.5V, the wire feeding speed of the front wire is 15.5 - 18m / min, and the wire feeding speed of the rear wire is 11.5 - 17.5m / min.

[0021] In an implementable manner, in step S2, the shielding gas used during welding is 99.99% carbon dioxide gas, and the gas flow rate is 16 - 24L / min.

[0022] Compared with the prior art, the beneficial effects of this application are as follows:

[0023] In the technical solution of this application, by limiting the chemical composition of the welding wire, it is possible to achieve beautiful weld formation, dense and defect - free macroscopic structure, and meet the requirements of classification societies and corresponding inspection specifications and standards for inspection items such as the micro - hardness of the fusion zone on the premise of not pre - heating the low - alloy high - strength ship plate steel before welding. By adopting double - wire common - molten - pool welding, the welding quality of fillet welds is ensured, and the welding efficiency is significantly improved, at least 2 - 4 times that of the existing single - wire welding efficiency. At a high welding speed of 80 - 150cm / min and without pre - heating before welding, the fillet weld formation is beautiful and the structure is defect - free. The maximum micro - hardness of the fusion zone of the low - alloy high - strength ship plate steel weld is lower than 350HV, meeting the specifications and standards of classification societies. This application can also eliminate the pre - heating process, reduce the welding process, and further improve the applicability and efficiency of double - wire welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flowchart of the method for controlling the micro - hardness of high - speed welding ship plate steel according to an embodiment of the present invention.

[0025] Figure 2 is a micro - structure diagram of the fusion zone of test plate 1 in the method for controlling the micro - hardness of high - speed welding ship plate steel according to an embodiment of the present invention.

[0026] Figure 3 is a micro - structure diagram of the fusion zone of test plate 2 in the method for controlling the micro - hardness of high - speed welding ship plate steel according to an embodiment of the present invention.

[0027] Figure 4 is a micro - structure diagram of the fusion zone of comparative test plate 2 in the method for controlling the micro - hardness of high - speed welding ship plate steel according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The following further elaborates on the specific embodiments of the present invention in conjunction with the accompanying drawings. These embodiments are only for illustrative purposes of the present invention and do not limit the present invention.

[0029] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0030] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] In addition, in the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0032] See Figure 1 , the present application provides a method for controlling the microhardness of high-speed welded ship plate steel, including the following steps:

[0033] S1. Before the start of the welding test, cut two ship steel plates to a predetermined size, clean the welding area to be welded of the ship steel plates, and lap and fix the two ship steel plates in a T shape.

[0034] S2. Select a predetermined welding wire and perform twin-wire welding at a predetermined welding speed. In the prior art, when single-wire welding is used for welding, the penetration and formation of the weld seam are contradictory and difficult to balance. Therefore, the welding speed of a single wire is limited. If the welding speed is increased, there will be insufficient heat input to melt the base material, and the formation of the weld seam cannot be guaranteed. By using twin-wire welding in the present application, while ensuring a high welding speed, it can also have a large amount of metal cladding and penetration, ensuring the formation and arc stability. The two wires can be melted in the same molten pool, and the heat generated by the two wires is borrowed from each other, that is, the heat dissipated by the front wire is used to melt the rear wire, and the heat generated by the rear wire in turn accelerates the melting speed of the front wire, forming a cycle to further increase the cladding amount, reducing the heat input to the base material while increasing the cladding amount and improving the welding quality.

[0035] In an implementable manner, in step S2, the content requirements of each element of the predetermined welding wire are as follows:

[0036] The carbon C content is between 0.03% and 0.05%, the silicon Si content is less than or equal to 0.45%, the manganese Mn content is between 0.90% and 1.20%, the sulfur S content is less than or equal to 0.015%, the phosphorus P content is less than or equal to 0.015%, the copper Cu content is less than or equal to 0.10%, the nickel Ni content is less than or equal to 0.15%, the chromium Cr content is less than or equal to 0.10%, the molybdenum Mo content is less than or equal to 0.05%, and the vanadium V content is less than or equal to 0.08%.

[0037] In this application, by limiting the content of each element in the predetermined welding wire, the carbon equivalent is controlled to adjust the type and efficiency of phase transformation, promote the phase transformation of bainite, and make the microstructure mainly composed of upper bainite and ferrite formed in the fusion zone, avoiding the formation of conventional hardened structures, martensite and M-A constituents. Therefore, in this application, the microhardness is controlled by controlling the microstructure. When using the predetermined welding wire for high-speed welding, the microhardness can be controlled not to exceed the standard; moreover, it can replace the pre-welding heat treatment process and improve the welding efficiency on the premise of ensuring the welding quality.

[0038] In an implementable manner, the carbon equivalent in the predetermined welding wire is evaluated using the cold crack sensitivity coefficient P cm as follows: Considering that this application mainly controls the microhardness of ship plate steel by controlling the carbon equivalent, by using the cold crack sensitivity coefficient P cm to evaluate the carbon equivalent, the accuracy of the obtained carbon equivalent can be guaranteed.

[0039] As the main constituent element and strengthening element in steel, an increase in the C content can increase the hardenability of the weld metal, thereby increasing the tendency of martensite transformation. Therefore, in this application, the C content is controlled at 0.03 - 0.05%. When the C content is less than 0.03%, the difference in carbon content between the welding wire and the base metal increases, and the weld strength cannot be guaranteed; when the C content is higher than 0.05%, the hardening tendency increases, and martensite is easily formed, and the microhardness of the fusion zone cannot be guaranteed. An excessive Si content will increase the thermal cracking tendency of the weld metal. In this application, the Si content of the welding wire is controlled to be less than or equal to 0.45%. Mn is one of the most effective elements for increasing the strength of steel, and its function is similar to that of the C element. In this application, the Mn content is controlled at 0.90 - 1.20%. Adding a small amount of Cu can improve the corrosion resistance of the weld of the low-alloy steel joint. When the content is relatively high, the thermal cracking tendency increases. In this application, the Cu content is controlled to be less than or equal to 0.10%. An excessive Ni content will lead to a decrease in the hot crack resistance of the weld and an increase in cost. In this application, the Ni content is controlled to be less than or equal to 0.15%. A small amount of Cr element plays a solid solution strengthening effect, improves the weld performance, and is beneficial to the formation of a passive film on the surface to improve the corrosion resistance. An increase in the content will reduce the weldability of the low-alloy steel. In this application, the Cr content is controlled to be less than or equal to 0.10%. A small amount of Mo not only increases the weld strength but also improves the toughness and promotes the formation of a ferrite structure. In this application, the Mo content is controlled to be less than or equal to 0.05%. Adding a small amount of V refines the structure and grains, increases the weld strength, and improves the welding performance. In this application, the V content is controlled to be less than or equal to 0.08%. The synergistic effect of different alloying elements not only improves the weld performance but also improves the weldability.

[0040] Specifically, in this embodiment, the carbon equivalent should be less than or equal to 0.15%.

[0041] It should be noted that in step S2, when performing twin-wire welding, the welding speed is 80 - 150 cm / min. This application can omit the preheating procedure before welding and directly adopt high-speed welding. By designing the chemical composition of the welding wire, the microstructure mainly composed of upper bainite and ferrite is regulated in the weld fusion zone, so that the weld formation and mechanical properties both meet the requirements.

[0042] In an implementable manner, in step S1, at least the following is further included: grinding the area to be welded with a grinding wheel to remove the primer and rust, and then cleaning and drying it with acetone. In this embodiment, the size of the ship steel plate is 1000 mm × 150 mm, and the thickness is t. In this application, the thickness t of the ship steel plate is 12 - 25 mm.

[0043] It should be noted that the ship plate steel in this embodiment is a low-alloy high-strength ship plate steel in the thermo-mechanical control rolling state, and the requirements for the content of each element in the low-alloy high-strength ship plate steel are as follows:

[0044] The carbon C content is less than or equal to 0.18%, the silicon Si content is less than or equal to 0.50%, the manganese Mn content is between 0.90% and 1.60%, the sulfur S content is less than or equal to 0.015%, the phosphorus P content is less than or equal to 0.015%, the aluminum Al content is less than or equal to 0.02%, the vanadium V content is between 0.05% and 0.10%, the niobium Nb content is between 0.02% and 0.05%, the titanium Ti content is less than or equal to 0.015%, the magnesium Mg content is less than or equal to 0.005%, and iron Fe is the main matrix element in the alloy, and the iron Fe content is the remaining part.

[0045] In this embodiment, DH36 ship plate steel is selected, and the specific numerical values of the various element contents of DH36 ship plate steel are as follows:

[0046] The carbon C content is 0.08%, the silicon Si content is 0.19%, the manganese Mn content is 1.49%, the sulfur S content is 0.002%, the phosphorus P content is 0.009%, the aluminum Al content is 0.018%, the niobium Nb content is 0.022%, the titanium Ti content is 0.012%, and the magnesium Mg content is 0.005%.

[0047] In an implementable manner, the twin-wire welding torch includes a front wire and a rear wire, and the front wire and the rear wire are arranged front and back along the welding direction; the ends of the front wire and the rear wire are inclined towards the axis of the twin-wire welding torch; the angle between the axis of the twin-wire welding torch and the vertical direction is 30 - 40°, the twin-wire dry elongation of the twin-wire welding torch is 10 - 15 mm, and the twin-wire spacing is 8 - 12 mm.

[0048] The torch angle, twin-wire dry elongation, and twin-wire spacing in this application are interrelated to ensure stable arc, the twin wires melt to form a single molten pool, and the heat is concentrated; beyond this range, the arc is unstable, prone to spatter, and a single molten pool cannot be guaranteed, resulting in a reduction in the cladding efficiency.

[0049] In this embodiment, the angle between the twin-wire welding torch and the vertical direction is 35°, the twin-wire dry elongation of the twin-wire welding torch is 12 mm, and the twin-wire spacing is 10 mm.

[0050] In an implementable manner, in step S2, the welding parameters during welding at least include the following content:

[0051] The current of the front wire is 265 - 320 A, the current of the rear wire is 260 - 300 A, the voltage of the front wire is 36 - 39.5 V, the voltage of the rear wire is 35 - 38.5 V, the wire feeding speed of the front wire is 15.5 - 18 m / min, and the wire feeding speed of the rear wire is 11.5 - 17.5 m / min. The welding current, welding voltage and wire feeding speed in this application are matched, influencing each other and controlling the weld formation. During high-speed welding, if the welding current is too small, the penetration depth cannot be achieved, the heat input is low, and the cladding rate decreases; if the welding current is too large, the spatter increases, the weld formation is poor, the microstructure is coarse, and the comprehensive performance decreases.

[0052] In an implementable manner, in step S2, the shielding gas used during welding is 99.99% carbon dioxide gas, and the gas flow rate is 16 - 24 L / min.

[0053] Specifically, in this embodiment, the gas flow rate of the shielding gas is 22 L / min.

[0054] In this embodiment, test plates one, two, three, and comparison test plates one, two, three, and four are respectively set up for welding tests. Specifically as follows:

[0055] Select the DH36 ship plate steel with a thickness t of 16 mm as test plate one and perform welding according to steps S1 and S2. During welding, the current of the front wire is 265 A, the current of the rear wire is 275 A, the voltage of the front wire is 36 V, the voltage of the rear wire is 37 V, the wire feeding speed of the front wire is 15.5 m / min, and the wire feeding speed of the rear wire is 14.5 m / min.

[0056] It should be noted that the welding speed of test plate one is 80 cm / min, and the selected welding wire is a flux-cored wire with a diameter of 1.2 mm. The chemical composition is 0.05% carbon content, 0.45% silicon content, 1.20% manganese content, 0.008% sulfur content, 0.012% phosphorus content, 0.10% copper content, 0.15% nickel content, 0.10% chromium content, 0.05% molybdenum content, and 0.08% vanadium content. The carbon equivalent is 0.15%.

[0057] Select the DH36 ship plate steel with a thickness t of 16 mm as test plate two and perform welding according to steps S1 and S2. The current of the front wire is 290 A, the current of the rear wire is 300 A, the voltage of the front wire is 36.5 V, the voltage of the rear wire is 38 V, the wire feeding speed of the front wire is 16.5 m / min, and the wire feeding speed of the rear wire is 16.5 m / min.

[0058] It should be noted that the welding speed of test plate two is 100 cm / min. Similar to test plate one, the selected welding wire is a flux-cored wire with a diameter of 1.2 mm, and its chemical composition is: carbon content 0.05%, silicon content 0.45%, manganese content 1.20%, sulfur content 0.008%, phosphorus content 0.012%, copper content 0.10%, nickel content 0.15%, chromium content 0.10%, molybdenum content 0.05%, vanadium content 0.08%. The carbon equivalent is 0.15%.

[0059] Select DH36 ship plate steel with a thickness t of 20 mm as test plate three and carry out welding according to steps S1 and S2. The current of the front wire is 310 A, the current of the rear wire is 300 A, the voltage of the front wire is 39 V, the voltage of the rear wire is 38 V, the wire feeding speed of the front wire is 16.5 m / min, and the wire feeding speed of the rear wire is 14.8 m / min.

[0060] It should be noted that the welding speed of test plate three is 150 cm / min. Similar to test plate one, the selected welding wire is a flux-cored wire with a diameter of 1.2 mm, and its chemical composition is: carbon content 0.05%, silicon content 0.45%, manganese content 1.20%, sulfur content 0.008%, phosphorus content 0.012%, copper content 0.10%, nickel content 0.15%, chromium content 0.10%, molybdenum content 0.05%, vanadium content 0.08%. The carbon equivalent is 0.15%.

[0061] Select DH36 ship plate steel with a thickness t of 16 mm as comparative test plate one and carry out welding according to steps S1 and S2. The current of the front wire is 320 A, the current of the rear wire is 300 A, the voltage of the front wire is 39.5 V, the voltage of the rear wire is 38.5 V, the wire feeding speed of the front wire is 16.5 m / min, and the wire feeding speed of the rear wire is 14 m / min.

[0062] It should be noted that the welding speed of comparative test plate one is 160 cm / min. Similar to test plate one, the selected welding wire is a flux-cored wire with a diameter of 1.2 mm, and its chemical composition is: C: 0.045%, Si: 0.45%, Mn: 1.19%, S: 0.008%, P: 0.012%, Cu: 0.02%, Ni: 0.03%, Cr: 0.05%, Mo: 0.003%, V: 0.01%. The carbon equivalent is 0.125%.

[0063] Select DH36 ship plate steel with a thickness t of 16 mm as comparative test plate two and carry out welding according to steps S1 and S2. The current of the front wire is 305 A, the current of the rear wire is 285 A, the voltage of the front wire is 38 V, the voltage of the rear wire is 36 V, the wire feeding speed of the front wire is 16.5 m / min, and the wire feeding speed of the rear wire is 14 m / min. The shielding gas is 80% argon and 20% carbon dioxide gas.

[0064] It should be noted that the welding speed of the second comparison test plate is 160 cm / min. The selected welding wire is a flux-cored wire with a diameter of 1.2 mm. Different from the first test plate, the chemical composition of the welding wire is C: 0.075%, Si: 0.86%, Mn: 1.50%, S: 0.008%, P: 0.015%, Cu: 0.24%, Ni: 0.02%, Cr: 0.03%, Mo: 0.003%, V: 0.006%. The carbon equivalent is 0.19%.

[0065] Select a DH36 ship plate steel with a thickness t of 16 mm as the third comparison test plate and perform welding according to steps S1 and S2. The current of the front wire is 305 A, the current of the rear wire is 285 A, the voltage of the front wire is 38 V, the voltage of the rear wire is 36 V, the wire feeding speed of the front wire is 16.5 m / min, and the wire feeding speed of the rear wire is 14 m / min. The shielding gas is 80% argon and 20% carbon dioxide gas.

[0066] It should be noted that the welding speed of the third comparison test plate is 120 cm / min. Different from the first test plate, the selected welding wire is a metal-cored wire with a diameter of 1.2 mm, and the chemical composition is C: 0.07%, Si: 0.58%, Mn: 1.43%, S: 0.007%, P: 0.011%, Cu: 0.11%, Ni: 0.02%, Cr: 0.035%, Mo: 0.003%, V: 0.008%. The carbon equivalent is 0.169%.

[0067] Select a DH36 ship plate steel with a thickness t of 16 mm as the fourth comparison test plate and perform welding according to steps S1 and S2. The current of the front wire is 305 A, the current of the rear wire is 285 A, the voltage of the front wire is 38 V, the voltage of the rear wire is 36 V, the wire feeding speed of the front wire is 16.5 m / min, and the wire feeding speed of the rear wire is 14 m / min. The shielding gas is 80% argon and 20% carbon dioxide gas.

[0068] It should be noted that the welding speed of the fourth comparison test plate is 60 cm / min. Different from the first test plate, the selected welding wire is a metal-cored wire with a diameter of 1.2 mm, and the chemical composition is C: 0.07%, Si: 0.58%, Mn: 1.43%, S: 0.007%, P: 0.011%, Cu: 0.11%, Ni: 0.02%, Cr: 0.035%, Mo: 0.003%, V: 0.008%. The carbon equivalent is 0.169%.

[0069] The fillet welds of test plate 1, test plate 2, test plate 3, test plate 4, comparison test plate 1, comparison test plate 2, comparison test plate 3 and comparison test plate 4 were inspected. Among them, the penetrant inspection was carried out according to the standard of CB / T 3958-2004 "Magnetic particle inspection and penetrant inspection process and quality classification for steel welds of ships"; the macroscopic metallographic evaluation standard was based on EN ISO 5817:2014 "Welding - Fusion welded joints of steels, nickel, titanium and their alloys (except beam welding) - Quality levels for imperfections"; the fracture test was evaluated according to the standard of CB / T3692-2016 "Method for fillet weld fracture test"; the microhardness of the fusion zone was based on the standard of GB / T2654-2008 "Test method for hardness of welded joints". The microhardness of the fusion zone of the fillet welds of test plate 1, test plate 2, test plate 3, test plate 4, comparison test plate 1, comparison test plate 2, comparison test plate 3 and comparison test plate 4 was measured ten times with a load of 10 Kg. The test results are shown in Table 1.

[0070] Table 1

[0071]

[0072] Test plate 1, test plate 2 and test plate 3 were welded using the predetermined welding wire provided by this application and welded within the predetermined welding speed. By controlling the carbon, silicon and manganese contents in the welding wire, the type and efficiency of phase transformation were affected, which was conducive to promoting bainite phase transformation. It was possible to control the microstructure of the fusion zone to be mainly upper bainite and ferrite, and avoid the formation of hardened structures such as martensite and M-A constituents, as Figure 2 and Figure 3 shown.

[0073] The fillet welds of test plate 1, test plate 2 and test plate 3 had beautiful forming, dense macro and microstructures, and no defects. The maximum microhardness of the fusion zone of the fillet weld of test plate 1 was 292 HV, the minimum was 225 HV, and the average was 263 HV, meeting the specifications and standards of the classification society. The maximum microhardness of the fusion zone of the fillet weld of test plate 2 was 304 HV, the minimum was 259 HV, and the average was 287 HV, meeting the specifications and standards of the classification society. The maximum microhardness of the fusion zone of the fillet weld of test plate 3 was 341 HV, the minimum was 298 HV, and the average was 331 HV, meeting the specifications and standards of the classification society.

[0074] Comparison test plate 1 was welded using the predetermined welding wire provided by this application, but the welding speed was greater than 150 cm / min. The maximum microhardness of the fusion zone of the fillet weld of comparison test plate 1 was 362 HV, the minimum was 260 HV, and the average was 307 HV. The maximum value exceeded 350 HV, not meeting the specifications and standards of the classification society.

[0075] The second reference test plate was welded at the predetermined welding speed provided by the present application, but the carbon equivalent of the solid wire was 0.19%. The microstructure in the fusion zone was mainly composed of hardened structures such as martensite and M-A, as Figure 4 shown. The reason is that the increase in the contents of carbon, silicon, and manganese in the solid wire increases the hardening tendency, resulting in the easy formation of martensite in the heat-affected zone of the weld. The maximum microhardness of the fillet weld fusion zone of the second reference test plate was 399 HV, the minimum was 351 HV, and the average was 374 HV. The maximum value exceeded 350 HV, which did not meet the specifications and standards of the classification society.

[0076] The third reference test plate was welded at the predetermined welding speed provided by the present application, but the carbon equivalent of the flux-cored wire was 0.169%. The maximum microhardness of the fillet weld fusion zone of the third reference test plate was 383 HV, the minimum was 350 HV, and the average was 368 HV. The maximum value exceeded 350 HV, which did not meet the specifications and standards of the classification society.

[0077] The welding speed of the fourth reference test plate was less than 80 cm / min, and the carbon equivalent of the flux-cored wire was 0.169%. The maximum microhardness of the fillet weld fusion zone of the fourth reference test plate was 357 HV, the minimum was 331 HV, and the average was 342 HV. The maximum value exceeded 350 HV, which did not meet the specifications and standards of the classification society.

[0078] In summary, in the prior art, when welding DH36 ship plate steel with a thickness greater than or equal to 12 mm, when the welding speed is greater than or equal to 50 cm / min, preheating before welding is required to ensure that the hardness of the fusion zone does not exceed the standard. The present application limits the chemical composition of the wire, selects a wire with a carbon equivalent less than or equal to 0.15% for high-speed welding, and improves the welding efficiency on the premise of ensuring the welding quality.

[0079] According to the method for controlling the microhardness of high-speed welding ship plate steel provided by the present application, by limiting the chemical composition of the wire, it is possible to achieve beautiful weld formation, dense and defect-free macrostructure, and meet the classification society and corresponding inspection specifications and standards for inspection items such as the microhardness of the fusion zone on the premise of not preheating before welding low-alloy high-strength ship plate steel. By adopting double-wire common molten pool welding, the welding quality of the fillet weld is ensured, and the welding efficiency is significantly improved, at least 2-4 times that of the existing single-wire welding efficiency. At a high welding speed of 80-150 cm / min and without preheating before welding, the fillet weld has a beautiful formation and defect-free structure. The maximum microhardness of the fusion zone of the low-alloy high-strength ship plate weld is lower than 350 HV, meeting the specifications and standards of the classification society. The present application can also eliminate the preheating procedure, reduce the welding process, and further improve the applicability and efficiency of double-wire welding.

[0080] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and substitutions can be made, and these improvements and substitutions should also be regarded as the protection scope of the present invention.

Claims

1. A method for controlling the microhardness of high-speed welding ship plate steel, characterized in that, It includes the following steps: S1. Cut two pieces of ship steel plates to a predetermined size, lap and fix them in a T-shaped manner; S2. Select a predetermined welding wire and perform twin-wire welding at a predetermined welding speed.

2. The microscopic hardness control method of the high-speed welding ship plate steel according to claim 1, wherein, In step S2, the requirements for the element contents of the predetermined welding wire are as follows: The carbon C content is between 0.03% and 0.05%, the silicon Si content is less than or equal to 0.45%, the manganese Mn content is between 0.90% and 1.20%, the sulfur S content is less than or equal to 0.015%, the phosphorus P content is less than or equal to 0.015%, the copper Cu content is less than or equal to 0.10%, the nickel Ni content is less than or equal to 0.15%, the chromium Cr content is less than or equal to 0.10%, the molybdenum Mo content is less than or equal to 0.05%, and the vanadium V content is less than or equal to 0.08%.

3. The microscopic hardness control method of the high-speed welding ship plate steel according to claim 2, characterized in that, The carbon equivalent in the predetermined welding wire is evaluated by the cold crack sensitivity coefficient P cm The calculation of the cold crack sensitivity coefficient P cm is as follows:

4. The microscopic hardness control method of the high-speed welding ship plate steel according to claim 1, characterized in that, In step S2, when performing twin-wire welding, the welding speed is 80 - 150 cm / min.

5. The microscopic hardness control method of the high-speed welding ship plate steel according to claim 1, characterized in that, The thickness of the ship steel plate is 12 - 25 mm.

6. The method for controlling the microhardness of high-speed welded ship plate steel according to claim 5, characterized in that, The element contents in the ship steel plate are as follows: The carbon content is less than or equal to 0.18%, the silicon content is between 0.90% and 1.60%, the sulfur content is less than or equal to 0.015%, the phosphorus content is less than or equal to 0.015%, the aluminum content is less than or equal to 0.02%, the vanadium content is between 0.05% and 0.10%, the niobium content is between 0.02% and 0.05%, the titanium content is less than or equal to 0.015%, the magnesium content is less than or equal to 0.005%, and iron is the matrix main element in the alloy, and the iron content is the remaining part.

7. The microscopic hardness control method of the high-speed welding ship plate steel according to claim 1, characterized in that, In step S1, grind the area to be welded with a grinding wheel, clean it with acetone and dry it.

8. The microscopic hardness control method of the high-speed welding ship plate steel according to claim 1, characterized in that, The twin-wire welding gun includes a front wire and a rear wire, and the front wire and the rear wire are arranged front and rear along the welding direction; the ends of the front wire and the rear wire are inclined towards the axis of the twin-wire welding gun; the angle between the axis of the twin-wire welding gun and the vertical direction is 30 - 40°, the twin-wire dry elongation of the twin-wire welding gun is 10 - 15 mm, and the twin-wire spacing is 8 - 12 mm.

9. The method for controlling the microhardness of high-speed welded ship plate steel according to claim 8, characterized in that, In step S2, the welding parameters during welding at least include the following contents: The front wire current is 265 - 320 A, the rear wire current is 260 - 300 A, the front wire voltage is 36 - 39.5 V, the rear wire voltage is 35 - 38.5 V, the wire feeding speed of the front wire is 15.5 - 18 m / min, and the wire feeding speed of the rear wire is 11.5 - 17.5 m / min.

10. The microscopic hardness control method for high-speed welded ship plate steel according to claim 9, characterized in that, In step S2, the shielding gas used during welding is 99.99% carbon dioxide gas, and the gas flow rate is 16 - 24 L / min.

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