Thick steel plate for large heat input welding, its manufacturing method and welding method

Abstract

The present invention relates to a thick steel plate for large heat input welding, the chemical components of which are, in weight percentages, C 0.04% to 0.10%, Si 0.1% to 0.5%, Mn 1.4% to 2.0%, P≦0.010%, S≦0.006%, Cu 0.2% to 0.5%, Ni 0.10% to 0.4%, Cr 0.10% to 0.3%, Nb 0.01% to 0.04%, Als 0.010% to 0.05%, Ti 0.01% to 0.02%, N≦0.008%, with Ti / N=2 to 4 and Ceq≦0.42; and the balance being Fe and unavoidable impurities, as well as a manufacturing method and welding method thereof. The 390 MPa class steel plate for large heat input welding according to the present invention has a thickness standard of 40 to 85 mm, can withstand welding with a heat input of 300 to 700 kJ / cm, and has good toughness in the welded joint. The present invention also provides a double-wire vertical electrogas welding method.

Description

[Technical Field]

[0001] The present invention relates to the technical field of steel manufacturing, and more particularly to a thick steel plate for large heat input welding, a manufacturing method thereof, and a welding method thereof. [Background technology]

[0002] In recent years, with the development of the economy and science and technology, the construction of structures in fields such as ships, offshore construction, oil and gas storage tanks, and bridges has become larger, and the steel materials used in the construction of these structures have become stronger, tougher, and thicker.

[0003] Welding is an important part of the construction of steel structures. Welding time accounts for 40% of the total time required to construct a structure, and welding costs account for 17% of construction costs. As the use of thick steel plates increases in various fields, welding efficiency is becoming increasingly important in structural construction. Welding steel plates using a large heat input can significantly reduce the number of welding passes and improve efficiency. For example, in shipbuilding, a typical 40mm-thick ship plate requires approximately 18 passes using a heat input of 40kJ / cm. However, welding with a heat input of 300kJ / cm can achieve the desired shape in just one pass, improving welding efficiency several dozen times over. However, generally speaking, typical steel plates can only withstand heat inputs of 50kJ / cm or less. This is because welding with a large heat input significantly coarsens the grains in the heat-affected zone (HAZ), significantly reducing the toughness of this region due to the long exposure of the weld joint to high temperatures and the slow cooling rate. Therefore, research, development, and application of steel plates suitable for large heat input welding are attracting widespread attention in many fields.

[0004] The patent with publication number CN106756541A discloses a 390 MPa-class steel for offshore platforms that can be welded with large heat input, but it can only be applied to a heat input of 100 kJ / cm.

[0005] The patent with publication number CN107164696A discloses a high-strength shipboard plate EH40 that employs a composite alloy design of Nb and Ti, has a thickness specification of 8 to 50 mm, and can withstand a maximum heat input of 150 kJ / cm, making it possible to weld with large heat input, and a method for manufacturing the same.

[0006] Patent publication number CN104404369A discloses a thick steel plate for large heat input welding that can withstand large heat input welding of 200 to 400 kJ / cm and a method for manufacturing the same. However, the technique employed, which improves the large heat input weldability of the steel plate by adding Mg, Ca and alloys thereof to form small inclusions, is difficult to implement industrially and has poor workability.

[0007] Furthermore, Patent Publication No. CN102839320A discloses a steel plate for high heat input welding manufactured by the TMCP process and capable of withstanding high heat input welding of 100 to 200 kJ / cm. Patent Publication No. CN109161671A discloses a high-strength EH36 steel plate for high heat input welding, with a maximum allowable welding heat input of 300 kJ / cm, and a manufacturing method thereof. Patent Publication No. CN108677088A discloses a low-carbon bainite steel plate for high heat input welding, suitable for high heat input welding of 100 to 300 kJ / cm, and a manufacturing method thereof. However, such a steel plate requires the addition of multiple alloying elements, which increases the manufacturing cost of the steel plate. Thus, most conventional steel plates suitable for high heat input welding can withstand a heat input between 200 and 400 kJ / cm, which is still insufficient for welding methods that use more efficient single-pass welding.

[0008] The present invention provides a method for producing steel plates for high heat input welding with a maximum thickness of 85 mm, which is an efficient welding method that enables weld formation in one pass, can withstand a maximum heat input of 700 kJ / cm, and has good joint performance after welding.The present invention also provides a double-wire vertical electrogas welding method that can be applied to the steel plates, realizes weld formation of the steel plates in one pass, ensures beautiful weld beads, is free of defects such as undercuts and slag inclusions, and significantly improves welding production efficiency. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a thick steel plate for large heat input welding that can be used for 390 MPa class steel plate for large heat input welding, has a thickness standard of 40 to 85 mm, can withstand welding with a heat input of 300 to 700 kJ / cm, and has good toughness in the welded joint, as well as a manufacturing method and welding method for the same.A further object of the present invention is to provide a double-wire vertical electrogas welding method. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention employs the following technical means. A thick steel plate for large heat input welding having chemical compositions, in weight percentages, of C 0.04%-0.10%, Si 0.1%-0.5%, Mn 1.4%-2.0%, P≦0.010%, S≦0.006%, Cu 0.2%-0.5%, Ni 0.10%-0.4%, Cr 0.10%-0.3%, Nb 0.01%-0.04%, Als 0.010%-0.05%, Ti 0.01%-0.02%, N≦0.008%, with Ti / N=2-4 and Ceq≦0.42; the remainder being Fe and unavoidable impurities.

[0011] Preferably, the chemical components in the steel sheet are, in weight percentages, C 0.05% to 0.75%, Si 0.1% to 0.3%, Mn 1.45% to 1.6%, P≦0.008%, S≦0.004%, Cu 0.3% to 0.35%, Ni 0.25% to 0.35%, Cr 0.15% to 0.25%, Nb 0.015% to 0.025%, Als 0.010% to 0.03%, Ti 0.013% to 0.018%, N 0.004% to 0.006%, with Ti / N=2.4 to 3.6, Ceq≦0.42; and the remainder being Fe and unavoidable impurities.

[0012] The steel plate has a thickness specification of 40 to 85 mm, a yield strength of 390 to 450 MPa, a tensile strength of 510 to 600 MPa, an elongation at break of 28% to 35%, and a maximum heat input that can be withstood of 700 kJ / cm.

[0013] The reasons for designing the components of the 390 MPa class thick steel plate for large heat input welding according to the present invention are as follows. C is the main element that determines the strength of steel material and is also the main element that determines the weldability of steel material. If C is less than 0.04%, it is difficult to ensure the strength of the steel plate. If C is more than 0.10%, the hard quenched structure of the weld heat affected zone increases, which is likely to lead to a rapid decrease in toughness. In the present invention, C is controlled to 0.04% to 0.10%, preferably 0.05% to 0.75%.

[0014] Si is added as a deoxidizing element to promote deoxidation of molten steel and improve the strength of steel sheets. However, solid solution strengthening by Si impairs the low-temperature impact toughness and weldability of steel sheets, and also promotes the formation and growth of MA. If the Si content is less than 0.10%, the deoxidizing effect is poor. On the other hand, if the Si content is more than 0.50%, the steel structure becomes easily embrittled and cold weld cracking and hot weld cracking are more likely to occur. In the present invention, the Si content is controlled to 0.10% to 0.50%, preferably 0.1% to 0.3%.

[0015] Mn is an important alloying element in steel. It not only improves the strength of steel sheets, but also broadens the austenite phase region, lowers the Ar3 temperature, refines ferrite grains, and improves the low-temperature toughness of steel sheets. However, Mn is prone to segregation during the solidification process of molten steel. Segregation of high Mn content with impurities such as P and S makes continuous casting difficult and also increases the likelihood of the formation of undesirable structures such as M / A islands, which affect the low-temperature toughness of welds during subsequent rolling and welding processes. MnS second-phase inclusions in steel have a significant adverse effect on both the base metal performance and the HAZ. Furthermore, excessive Mn content can easily cause center segregation in thick steel sheets. In the present invention, the Mn content is controlled to 1.4% to 2.0%, preferably 1.45% to 1.6%.

[0016] P is an impurity element that increases the brittleness of steel, impairs weldability, reduces plasticity, and deteriorates cold bending performance. Therefore, it is generally required that the P content in steel be as low as possible. In the present invention, the P content is controlled to 0.010% or less, preferably 0.008% or less.

[0017] S is also a harmful element, and if its content is high, the brittle transition temperature of the steel sheet increases, reducing the weldability of the steel. More importantly, S combines with Mn in the steel to form MnS inclusions, which tend to form long inclusion regions during the rolling process. S is also the main element that causes hot embrittlement during the hot rolling process. Therefore, its content is generally required to be low. In the present invention, the S content is controlled to 0.006% or less, preferably 0.004% or less.

[0018] Although the addition of a small amount of Cu can improve the strength of the softened zone in the weld heat affected zone, the addition of excessive copper promotes the formation of MA components and reduces the toughness of the weld heat affected zone. In the present invention, the Cu content is controlled to 0.2 to 0.5%, preferably 0.3 to 0.35%.

[0019] Ni can improve the low-temperature toughness of steel, but since it is an austenite-forming element, it also increases the stability of supercooled austenite. In order to control the number of MA components in the weld heat-affected zone, it is necessary to control the amount of Ni added so that it is not too high. In the present invention, the Ni content is controlled to 0.10 to 0.4%, preferably 0.25 to 0.35%.

[0020] Cr can improve the strength of steel, but it can also increase the ductile-brittle transition temperature of steel. If the Cr content is high, the impact toughness of steel will decrease sharply. In the present invention, the Cr content is controlled to 0.10 to 0.3%, preferably 0.15 to 0.25%.

[0021] Nb promotes grain refinement primarily during the steel rolling process and strengthens the substrate through precipitation. Nb increases the non-recrystallization temperature, promotes the formation of a low-temperature transformation structure, and can also form complex nitrides with Ti to reduce the titanium-to-nitrogen ratio and improve the performance of the heat-affected zone. However, if the Nb content is too low, the strengthening effect is insufficient, and steel with satisfactory strength may not be obtained. If the Nb content is too high, the formation of upper bainite is induced under high-heat-input welding conditions, significantly impairing the low-temperature toughness of the high-heat-input HAZ. In the present invention, the Nb content is controlled to a range of 0.01% to 0.05%, preferably 0.015% to 0.025%.

[0022] Al is a deoxidizing agent commonly used in steel, which can effectively refine crystal grains and improve the strength and toughness of steel. However, if the amount added exceeds 0.050%, large composite oxide inclusions are likely to form and agglomerate in the nozzle of the crystallizer. In the present invention, the Als content is controlled to 0.010% to 0.050%, preferably 0.010% to 0.03%.

[0023] Ti is one of the important elements in the present invention. It can form TiN with N at relatively high temperatures and TiNb(CN) with Nb. It is difficult to melt at high welding temperatures. It inhibits the growth of austenite grains and promotes ferrite nucleation, effectively improving the toughness of the heat-affected zone. The addition of Ti can also reduce the amount of solute free N and improve the weldability of the steel. At an appropriate Ti / N ratio, the effects of Ti and N can be maximized. If the Ti / N ratio is less than 2, the amount of solute N in the steel increases, resulting in reduced toughness and aging performance. If the Ti / N ratio exceeds 4, TiN particles become coarse, weakening the beneficial effect on the heat-affected zone. The amount of solute Ti increases, impairing the toughness of the base metal. Outside this range, the performance of the steel plate and the weld heat-affected zone is significantly reduced. In the present invention, the optimum Ti content range is 0.01% to 0.02%, preferably 0.013% to 0.018%.

[0024] Nitrogen (N) is an important element for ensuring the performance of joints welded with large heat input and exists in two forms in steel. One is in the form of solid solution, i.e., free nitrogen, which is detrimental to the performance of the steel, particularly the low-temperature impact resistance of the joint. The other is in the form of dispersed nitrides. The main nitrides, such as TiN, AlN, and NbN, suppress the grain growth tendency in the weld heat-affected zone and improve the performance of the weld heat-affected zone. In the present invention, the N content is controlled to 0.008% or less, preferably 0.004% to 0.006%.

[0025] The composition design of the steel for large heat input welding of the present invention makes the following two main improvements over the conventional patents and related products. (1) Regarding the challenge of improving weldability to withstand large heat input, a) do not add V element, which is detrimental to the toughness of the heat-affected zone in large heat input welding; b) reduce the C content and Ceq in the steel; c) control the contents of S element and P element low; d) control the Ti / N ratio. (2) Regarding the issue of ensuring high strength and high toughness, adding Cu and Cr elements compensates for the design with too low a C content, and strengthens the steel plate, and adding appropriate amounts of Ni and Nb elements ensures the toughness of the steel plate.

[0026] The manufacturing process for thick steel plates for large heat input welding includes the processes of hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, heating, rolling, and cooling. The rolling process uses the controlled rolling TMCP process, and specifically includes the following processes:

[0027] The smelting and continuous casting process in this invention: Before charging the molten iron into a converter, it is pre-treated by desulfurization, and molten steel is smelted according to the chemical composition of the target steel plate. The cumulative time of LF furnace refining must be more than 30 minutes, the cumulative time of further RH refining must be more than 10 minutes, and the net time of argon gas injection must be more than 5 minutes. The N content is controlled to 40-80 ppm by injecting nitrogen gas in the final stage of RH refining. The smelted molten steel is then cast into a continuous casting slab. The maximum heating temperature of the continuously cast slab is set to 1250°C or less, the soaking temperature is set to 1100 to 1180°C, and the heat retention time is set to 5 to 10 hours.

[0028] Rolling process: A two-stage rolling method is used. In the first stage of rolling, the temperature is 1150 to 1050°C, the reduction per pass is 15% or more, and the cumulative reduction is 55% or more. In the second stage of rolling, the temperature is 830 to 780°C, the reduction per pass is 10% or more, and the cumulative reduction is 50% or more. Cooling step: The cooling start temperature is set to 700°C or higher, and the material is cooled at a rate of 4 to 25°C / second until the temperature reaches 380 to 500°C.

[0029] In the manufacturing method of steel plate for high heat input welding according to the present invention, in the first stage of rolling, the final rolling temperature is controlled to 1050°C or higher, and the reduction per pass is set to 15% or higher, thereby realizing effective transmission of the rolling force and ensuring uniformity of the structure and performance in the thickness direction of the thick steel plate. Furthermore, by adding Cu and Nb to the composition design system and performing a two-stage rolling process and cooling process, it is possible to impart a uniform, fine structure and good performance to the steel plate, and also to ensure the overall toughness, particularly low-temperature toughness, of the joint after high heat input welding of the steel plate.

[0030] The welding method for thick steel plates for large heat input welding specifically includes the following steps. 1) A symmetrical V-shaped groove is made on the steel plate to be welded, and the groove position is ground with an angle grinder before welding to remove oil and rust; when welding, a ceramic backing material is attached to the base of the groove, and a copper water-cooled sliding copper pad is attached to the surface of the groove. 2) Using manual spot welding, weld and fix one "P"-shaped handle at intervals of 200 to 300 mm to the steel plate side of the base of the groove. The handle material shall be low-carbon steel, which is easy to weld. 3) Welding is performed using a double-wire vertical electrogas welding machine, with two welding torches oscillating simultaneously, and gas is supplied during the welding process for protection, and cooling water is kept circulating smoothly. 4) In double-wire vertical electrogas welding, when the wire closest to the base of the weld bead is the front wire and the other wire is the back wire, the welding process parameters for the front wire are 300-360A, 35-40V, and 340-400A, 36-42V, respectively.

[0031] The V-shaped groove has an angle of 8° to 15° on one side and a gap width at the base of 6 to 12 mm. The flow rate of the cooling water is 15 to 30 L / min. In step 3), the two welding torches are swung simultaneously with an oscillation width of 0 to ±32 mm in the plate thickness direction (vertical direction) with the origin at 1 / 2 the plate thickness position, and with an oscillation width of 0 to ±10 mm in the plate width direction (horizontal direction) with the origin at the center of the groove, and the protective gas is 100% carbon dioxide gas.

[0032] The diameter of the welding wire used is 1.6 mm to 2.0 mm, the welding speed is 2 to 5 cm / min, and the gas flow rate is 30 to 35 L / min in both cases. The welded steel plates have a joint tensile strength of 520 to 580 MPa, and the impact energy value of the heat-affected zone at -40°C is 70 J or more.

[0033] In the welding method of the present invention, (1) In process 2), the main purpose of welding one "P"-shaped handle at every 200 mm interval is to firmly fix the ceramic backing material on the back side so that the welded joint can be formed well, and to assemble the sample plate before welding. (2) In step 3), by simultaneously oscillating the two welding torches within an appropriate range during welding, the side walls are successfully fused into the welding groove during the welding process, eliminating the defect of welding undercut. (3) In step 4), by setting the welding process parameters within a predetermined range, the molten pool can be stabilized during the welding process, preventing the base of the welded sample plate from burning off and the molten iron on the surface from spilling out. (4) By making the V-shaped groove angle smaller than that normally used in the past and increasing the gap width at the base, the overall cross-sectional area of ​​the weld groove is reduced, reducing the amount of fill. This improves welding efficiency and reduces welding heat input, ensuring that the welded steel plates have a joint tensile strength of 520 to 580 MPa and an impact energy value of 70 J or more at -40°C in the heat-affected zone. (5) The flow rate of the cooling water is set to ensure a cooling rate of the sliding copper pad on the groove surface to the molten iron in the welding molten pool, and to prevent the molten iron in the molten pool from overflowing and interrupting the welding. [Effects of the Invention]

[0034] The present invention has the following advantageous effects compared to the prior art. 1) The thick steel plate for large heat input welding according to the present invention has a maximum thickness specification of 85 mm, a yield strength of 390 to 450 MPa, a tensile strength of 510 to 600 MPa, and a fracture elongation of 28% to 35%, and is particularly suitable for large heat input welding with a heat input of 50 to 700 kJ / cm. The welded steel plate has a joint tensile strength of 520 to 580 MPa, and the impact energy value of the heat affected zone at -40°C is 70 J or more. This successfully solves the problem of a significant decrease in impact toughness in the heat affected zone during large heat input welding.

[0035] 2) In the present invention, when performing double-wire vertical electrogas welding, the groove is designed to have as small an angle as possible, and the gap width at the base is adjusted to obtain a smaller cross-sectional area than the groove in conventional double-wire vertical electrogas welding. This reduces the welding heat input for the same plate thickness, ensuring better performance of the heat-affected zone of the thick steel plate for high heat input welding according to the present invention, while also saving welding material and significantly improving welding efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0036] The technical means of the present invention will be described in detail below with reference to examples. However, the following examples are merely illustrative examples for explaining and explaining the technical means of the present invention, and are not to be construed as limiting the technical means of the present invention.

[0037] Example 1 The specific chemical composition and mass percentage of the steel plate were C: 0.075%, Si: 0.30%, Mn: 1.49%, P: 0.01%, S: 0.004%, Cu: 0.2%, Ni: 0.15%, Cr: 0.2%, Nb: 0.015%, Als: 0.018%, Ti: 0.012%, N: 0.0043%, the Ti / N ratio was 2.8, Ceq was 0.387, and the balance was Fe and unavoidable impurities. The steel plate had a thickness of 40 mm.

[0038] The steelmaking and continuous casting processes were as follows. The hot metal was pre-desulfurized to a sulfur content of 0.003%, and then refined in a converter. The cumulative time for LF furnace refining was 35 min, followed by RH refining for 15 min. The net time for argon gas injection was 10 min. Nitrogen gas was injected for 1 min at the final stage of RH refining to control the N content at 43 ppm. The refined molten steel was then cast into a continuous casting slab.

[0039] Heating process: The maximum heating temperature of the continuous casting slab was 1200°C, the soaking temperature was 1180°C, and the heat retention time was 7 hours. Rolling process: A two-stage rolling method was used. In the first stage of rolling, the rolling start temperature was 1180°C, the rolling reduction per pass was 15%, and the cumulative rolling reduction was 64%; in the second stage of rolling, the rolling start temperature was 830°C, the rolling reduction per pass was 12%, and the cumulative rolling reduction was 58% or more. Cooling step: The cooling start temperature was set to 720°C, and the temperature was cooled to 450°C at a rate of 15°C / sec.

[0040] Measurements of the steel plate revealed that the tensile strength was 590 MPa, the yield strength was 440 MPa, the elongation at break was 28%, and the impact energy (longitudinal direction) values ​​at -40°C were 288 J, 267 J, and 293 J.

[0041] Double-wire vertical electrogas welding was performed, and the specific welding method and process were as follows: A V-shaped groove was drilled into the steel plate to be welded, with one side angled at 15°. The groove position was ground with an angle grinder and oil and rust were removed before welding. An 8mm-wide gap was left at the base, and a "P"-shaped handle was spot-welded to secure it. The handles were spaced 300mm apart, and a ceramic backing material was attached to the backside. The welding process was protected with 100% carbon dioxide gas, with a gas flow rate of 30 L / min. The two welding torches oscillated ±10mm in the plate thickness direction (vertical), with the origin at half the plate thickness. The welding process parameters used were as follows: the front wire welding current was 300-320 A and the welding voltage was 35-36 V; the back wire welding current was 340-360 A and the welding voltage was 36-38 V. The diameter of the welding wire used was 1.6 mm to 2.0 mm, the welding speed was 5 cm / min, the welding heat input was 273 kJ / cm, and the flow rate of the cooling water was 20 L / min. The joint performance after welding is shown in Table 1.

[0042] Example 2 The specific chemical composition and mass percentage of the steel plate were C: 0.08%, Si: 0.40%, Mn: 1.65%, P: 0.008%, S: 0.003%, Cu: 0.25%, Ni: 0.2%, Cr: 0.15%, Nb: 0.02%, Als: 0.026%, Ti: 0.016%, N: 0.0058, the Ti / N ratio was 2.8, Ceq was 0.415, and the balance was Fe and unavoidable impurities. The steel plate had a thickness of 55 mm.

[0043] The steelmaking and continuous casting processes were as follows. The hot metal was pre-desulfurized to a sulfur content of 0.0025%, and then refined in a converter. The cumulative time for LF furnace refining was 35 min, followed by RH refining for 15 min. The net time for argon gas injection was 15 min. Nitrogen gas was injected for 3 min at the final stage of RH refining to control the N content at 58 ppm. The refined molten steel was then cast into a continuous casting slab.

[0044] Heating process: The maximum heating temperature of the continuous casting slab was 1200°C, the soaking temperature was 1180°C, and the heat retention time was 6 hours. Rolling process: A two-stage rolling method was used. In the first stage of rolling, the rolling start temperature was 1180°C, the rolling reduction per pass was 17%, and the cumulative rolling reduction was 57%; in the second stage of rolling, the rolling start temperature was 820°C, the rolling reduction per pass was 12%, and the cumulative rolling reduction was 58% or more. Cooling step: The cooling start temperature was set to 700°C, and the temperature was cooled to 400°C at a rate of 10°C / second.

[0045] Measurements of the steel plate revealed that the tensile strength was 587 MPa, the yield strength was 433 MPa, the elongation at break was 29.2%, and the impact energy (longitudinal direction) values ​​at -40°C were 277 J, 289 J, and 284 J.

[0046] Double-wire vertical electrogas welding was performed, and the specific welding method and process were as follows: A V-shaped groove was drilled into the steel plate to be welded, with one side angled at 14°. The groove position was ground with an angle grinder to remove any oil or rust before welding. A 12 mm-wide gap was left at the base, and a "P"-shaped handle was spot-welded to secure the handles. The handles were spaced 280 mm apart, and a ceramic backing plate was attached to the backside. The welding process was protected with 100% carbon dioxide gas, with a gas flow rate of 30 L / min. The two welding torches had an oscillation range of ±20 mm in the plate thickness direction (vertical direction) from the origin at half the plate thickness, and ±2 mm in the plate width direction (horizontal direction) from the origin at the center of the groove. The welding process parameters used were as follows: the front wire welding current was 310–330 A, the welding voltage was 36–38 V; the back wire welding current was 350–370 A, the welding voltage was 37–39 V. The diameter of the welding wire used was 1.6 mm to 2.0 mm, the welding speed was 4.5 cm / min, the welding heat input was 360 kJ / cm, and the flow rate of the cooling water was 23 L / min. The joint performance after welding is shown in Table 1.

[0047] Example 3 The specific chemical composition and mass percentage of the steel plate were C: 0.055%, Si: 0.20%, Mn: 1.50%, P: 0.008%, S: 0.003%, Cu: 0.3%, Ni: 0.25%, Cr: 0.18%, Nb: 0.025%, Als: 0.03%, Ti: 0.015%, N: 0.0055, the Ti / N ratio was 2.7, Ceq was 0.378, and the balance was Fe and unavoidable impurities. The steel plate had a thickness of 60 mm.

[0048] The steelmaking and continuous casting processes were as follows. The hot metal was desulfurized to a sulfur content of 0.0025%, and then refined in a converter. The cumulative time of LF furnace refining was 35 min, followed by RH refining for 15 min. The net time of argon gas injection was 15 min. Nitrogen gas was injected for 2 min at the final stage of RH refining to control the N content at 55 ppm. The refined molten steel was then cast into a continuous casting slab.

[0049] Heating process: The maximum heating temperature of the continuous casting slab was 1150°C, the soaking temperature was 1120°C, and the heat retention time was 6 hours. Rolling process: A two-stage rolling method was used. In the first stage of rolling, the rolling start temperature was 1151°C, the rolling reduction per pass was 17%, and the cumulative rolling reduction was 60%; in the second stage of rolling, the rolling start temperature was 830°C, the rolling reduction per pass was 11%, and the cumulative rolling reduction was 58% or more. Cooling step: The cooling start temperature was set to 738°C, and the temperature was cooled at a rate of 8°C / sec until it reached 380°C.

[0050] Measurements of the steel plate revealed that the tensile strength was 554 MPa, the yield strength was 430 MPa, the elongation at break was 32%, and the impact energy (longitudinal direction) values ​​at -40°C were 307 J, 298 J, and 311 J.

[0051] Double-wire vertical electrogas welding was performed, and the specific welding method and process were as follows: A V-shaped groove was created in the steel plate to be welded, with one side angled at 14°. The groove position was ground with an angle grinder to remove any oil or rust before welding. A 10 mm-wide gap was left at the base, and a "P"-shaped handle was spot-welded to secure the handles. The handles were spaced 280 mm apart, and a ceramic backing plate was attached to the backside. The welding process was protected with 100% carbon dioxide gas, with a gas flow rate of 30 L / min. The two welding torches had an oscillation range of ±20 mm in the plate thickness direction (vertical direction) with the origin at half the plate thickness, and ±3 mm in the plate width direction (horizontal direction) with the origin at the center of the groove. The welding process parameters used were as follows: the front wire welding current was 310–330 A, the welding voltage was 36–38 V; the back wire welding current was 360–380 A, the welding voltage was 36–38 V. The diameter of the welding wire used was 1.6 mm to 2.0 mm, the welding speed was 4 cm / min, the welding heat input was 404 kJ / cm, and the flow rate of the cooling water was 25 L / min. The joint performance after welding is shown in Table 1.

[0052] Example 4 The specific chemical composition and mass percentage of the steel plate were C: 0.068%, Si: 0.35%, Mn: 1.60%, P: 0.007%, S: 0.004%, Cu: 0.28%, Ni: 0.23%, Cr: 0.25%, Nb: 0.028%, Als: 0.033%, Ti: 0.017%, N: 0.0055, the Ti / N ratio was 3.1, Ceq was 0.419, and the balance was Fe and unavoidable impurities. The steel plate had a thickness of 68 mm.

[0053] The steelmaking and continuous casting processes were as follows. The hot metal was desulfurized to a sulfur content of 0.0038%, and then refined in a converter. The cumulative time for LF refining was 35 min, followed by RH refining for 15 min. The net time for argon gas injection was 15 min. Nitrogen gas was injected for 2 min at the final stage of RH refining to control the N content at 55 ppm. The refined molten steel was then cast into a continuous casting slab.

[0054] Heating process: The maximum heating temperature of the continuous casting slab was 1250°C, the soaking temperature was 1190°C, and the heat retention time was 6 hours. Rolling process: A two-stage rolling method was used. In the first stage of rolling, the rolling start temperature was 1170°C, the rolling reduction per pass was 17%, and the cumulative rolling reduction was 56%; in the second stage of rolling, the rolling start temperature was 800°C, the rolling reduction per pass was 10%, and the cumulative rolling reduction was 50% or more. Cooling step: The cooling start temperature was set to 720°C, and the temperature was cooled at a rate of 7°C / sec until it reached 400°C.

[0055] Measurements of the steel plates revealed that the tensile strength was 596 MPa, the yield strength was 445 MPa, the elongation at break was 31.4%, and the impact energy (longitudinal direction) values ​​at -40°C were 330 J, 326 J, and 338 J.

[0056] Double-wire vertical electrogas welding was performed, and the specific welding method and process were as follows: A V-shaped groove was drilled into the steel plate to be welded, with one side angled at 12°. The groove position was ground with an angle grinder to remove any oil or rust before welding. An 11 mm-wide gap was left at the base, and a "P"-shaped handle was spot-welded to secure the handles. The handles were spaced 260 mm apart, and a ceramic backing material was attached to the backside. The welding process was protected with 100% carbon dioxide gas, with a gas flow rate of 30 L / min. The two welding torches had an oscillation range of ±20 mm in the plate thickness direction (vertical direction) from the origin at half the plate thickness, and ±4 mm in the plate width direction (horizontal direction) from the origin at the center of the groove. The welding process parameters used were as follows: the front wire welding current was 320–340 A, the welding voltage was 37–39 V; the back wire welding current was 360–380 A, the welding voltage was 38–40 V. The diameter of the welding wire used was 1.6 mm to 2.0 mm, the welding speed was 3.5 cm / min, the welding heat input was 488 kJ / cm, and the flow rate of the cooling water was 25 L / min. The joint performance after welding is shown in Table 1.

[0057] Example 5 The specific chemical composition and mass percentage of the steel plate were C: 0.061%, Si: 0.25%, Mn: 1.55%, P: 0.007%, S: 0.001%, Cu: 0.32%, Ni: 0.3%, Cr: 0.18%, Nb: 0.023%, Als: 0.022%, Ti: 0.014%, N: 0.0056, the Ti / N ratio was 2.5, Ceq was 0.397, and the balance was Fe and unavoidable impurities. The steel plate had a thickness of 75 mm.

[0058] The steelmaking and continuous casting processes were as follows. The hot metal was pre-desulfurized to a sulfur content of 0.002%, and then refined in a converter. The cumulative time for LF refining was 38 min, followed by RH refining for 17 min. The net time for argon gas injection was 13 min. Nitrogen gas was injected for 2 min at the final stage of RH refining to control the N content at 61 ppm. The refined molten steel was then cast into a continuous casting slab.

[0059] Heating process: The maximum heating temperature of the continuous casting slab was 1180°C, the soaking temperature was 1150°C, and the heat retention time was 6 hours. Rolling process: A three-stage rolling method was used. In the first stage of rolling, the rolling start temperature was 1150°C, the rolling reduction per pass was 17%, and the cumulative rolling reduction was 55%; in the second stage of rolling, the rolling start temperature was 800°C, the rolling reduction per pass was 13%, and the cumulative rolling reduction was 51% or more. Cooling step: The cooling start temperature was set to 720°C, and the temperature was cooled at a rate of 7.5°C / sec until the temperature reached 402°C.

[0060] Measurements of the steel plate revealed that the tensile strength was 545 MPa, the yield strength was 429 MPa, the elongation at break was 30.5%, and the impact energy (longitudinal direction) values ​​at -40°C were 327 J, 318 J, and 333 J.

[0061] Double-wire vertical electrogas welding was performed, and the specific welding method and process were as follows: A V-shaped groove was drilled into the steel plate to be welded, with one side angled at 12°. The groove position was ground with an angle grinder to remove any oil or rust before welding. A 10 mm-wide gap was left at the base, and a "P"-shaped handle was spot-welded to secure the handles. The handles were spaced 240 mm apart, and a ceramic backing plate was attached to the backside. The welding process was protected with 100% carbon dioxide gas, with a gas flow rate of 34 L / min. The two welding torches had an oscillation range of ±25 mm in the plate thickness direction (vertical direction) with the origin at half the plate thickness, and ±6 mm in the plate width direction (horizontal direction) with the origin at the center of the groove. The welding process parameters used were as follows: the front wire welding current was 340–360 A, the welding voltage was 37–39 V; the back wire welding current was 380–400 A, the welding voltage was 39–41 V. The diameter of the welding wire used was 1.6 mm to 2.0 mm, the welding speed was 3.2 cm / min, the welding heat input was 570 kJ / cm, and the flow rate of the cooling water was 28 L / min. The joint performance after welding is shown in Table 1.

[0062] Example 6 The specific chemical composition and mass percentage of the steel plate were C: 0.08%, Si: 0.2%, Mn: 1.45%, P: 0.007%, S: 0.005%, Cu: 0.2%, Ni: 0.38%, Cr: 0.28%, Nb: 0.03%, Als: 0.02%, Ti: 0.019%, N: 0.008%, the Ti / N ratio was 2.4, Ceq was 0.416, and the balance was Fe and unavoidable impurities. The steel plate had a thickness of 80 mm.

[0063] The steelmaking and continuous casting processes were as follows. The hot metal was desulfurized to a sulfur content of 0.004%, and then refined in a converter. The cumulative time for LF refining was 38 min, followed by RH refining for 17 min. The net time for argon gas injection was 13 min. Nitrogen gas was injected for 5 min at the final stage of RH refining to control the N content at 80 ppm. The refined molten steel was then cast into a continuous casting slab.

[0064] Heating process: The maximum heating temperature of the continuous casting slab was 1180°C, the soaking temperature was 1150°C, and the heat retention time was 5 hours. Rolling process: A three-stage rolling method was used. In the first stage of rolling, the rolling start temperature was 1150°C, the rolling reduction per pass was 17%, and the cumulative rolling reduction was 55%; in the second stage of rolling, the rolling start temperature was 820°C, the rolling reduction per pass was 11%, and the cumulative rolling reduction was 50% or more. Cooling step: The cooling start temperature was set to 760°C, and the temperature was cooled to 450°C at a rate of 7.5°C / sec.

[0065] Measurements of the steel plate revealed that the tensile strength was 560 MPa, the yield strength was 438 MPa, the elongation at break was 28%, and the impact energy (longitudinal direction) values ​​at -40°C were 266 J, 279 J, and 269 J.

[0066] Double-wire vertical electrogas welding was performed, and the specific welding method and process were as follows: A V-shaped groove was drilled into the steel plate to be welded, with one side angled at 10°. The groove position was ground with an angle grinder to remove any oil or rust before welding. A 12 mm-wide gap was left at the base, and a "P"-shaped handle was spot-welded to secure the handles. The handles were spaced 220 mm apart, and a ceramic backing material was attached to the backside. The welding process was protected with 100% carbon dioxide gas, with a gas flow rate of 34 L / min. The two welding torches had an oscillation range of ±25 mm in the plate thickness direction (vertical direction) with the origin at half the plate thickness, and ±8 mm in the plate width direction (horizontal direction) with the origin at the center of the groove. The welding process parameters used were as follows: the front wire welding current was 340–360 A, the welding voltage was 37–39 V; the back wire welding current was 380–400 A, the welding voltage was 39–41 V. The diameter of the welding wire used was 1.6 mm to 2.0 mm, the welding speed was 2.8 cm / min, the welding heat input was 610 kJ / cm, and the flow rate of the cooling water was 28 L / min. The joint performance after welding is shown in Table 1.

[0067] Example 7 The specific chemical composition and mass percentage of the steel plate were C: 0.047%, Si: 0.15%, Mn: 1.54%, P: 0.0069%, S: 0.002%, Cu: 0.34%, Ni: 0.28%, Cr: 0.24%, Nb: 0.022%, Als: 0.026%, Ti: 0.017%, N: 0.0057%, the Ti / N ratio was 3, Ceq was 0.393, and the balance was Fe and unavoidable impurities. The steel plate had a thickness of 84 mm.

[0068] The steelmaking and continuous casting processes were as follows. The hot metal was desulfurized to a sulfur content of 0.003%, and then refined in a converter. The cumulative time of the LF furnace refining was 40 min, followed by the cumulative time of the RH refining, which was 20 min. The net time of argon gas injection was more than 10 min. Nitrogen gas was injected for 3 min in the final stage of the RH refining to control the N content at 66 ppm. The refined molten steel was then cast into a continuous casting slab.

[0069] Heating process: The maximum heating temperature of the continuous casting slab was 1180°C, the soaking temperature was 1150°C, and the heat retention time was 5 hours. Rolling process: A two-stage rolling method was used. In the first stage of rolling, the rolling start temperature was 1080°C, the rolling reduction per pass was 18%, and the cumulative rolling reduction was 55%; in the second stage of rolling, the rolling start temperature was 810°C, the rolling reduction per pass was 12%, and the cumulative rolling reduction was 50% or more. Cooling step: The cooling start temperature was set to 750°C, and the temperature was cooled at a rate of 5°C / sec until it reached 420°C.

[0070] Measurements of the steel plate revealed that the tensile strength was 542 MPa, the yield strength was 431 MPa, the elongation at break was 31%, and the impact energy (longitudinal direction) values ​​at -40°C were 321 J, 317 J, and 344 J.

[0071] Double-wire vertical electrogas welding was performed, and the specific welding method and process were as follows: A V-shaped groove was created in the steel plate to be welded, with one side angled at 10°. The groove position was ground with an angle grinder to remove any oil or rust before welding. A 12 mm-wide gap was left at the base, and a "P"-shaped handle was spot-welded to the handle. The handles were spaced 200 mm apart, and a ceramic backing material was attached to the backside. The welding process was protected with 100% carbon dioxide gas, with a gas flow rate of 33 L / min. The two welding torches had an oscillation range of ±30 mm in the plate thickness direction (vertical direction) from the origin at half the plate thickness, and ±8 mm in the plate width direction (horizontal direction) from the origin at the center of the groove. The welding process parameters used were as follows: the front wire welding current was 320–340 A, the welding voltage was 37–39 V; the back wire welding current was 380–400 A, the welding voltage was 40–42 V. The diameter of the welding wire used was 1.6 mm to 2.0 mm, the welding speed was 2.7 cm / min, the welding heat input was 668 kJ / cm, and the flow rate of the cooling water was 30 L / min. The joint performance after welding is shown in Table 1.

[0072] Example 8 The specific chemical composition and mass percentage of the steel plate were C: 0.09%, Si: 0.25%, Mn: 1.45%, P: 0.0069%, S: 0.002%, Cu: 0.3%, Ni: 0.2%, Cr: 0.3%, Nb: 0.026%, Als: 0.028%, Ti: 0.018%, N: 0.005%, the Ti / N ratio was 3.6, Ceq was 0.417, and the balance was Fe and unavoidable impurities. The steel plate had a thickness of 85 mm.

[0073] The steelmaking and continuous casting processes were as follows. The hot metal was desulfurized to a sulfur content of 0.0015%, and then refined in a converter. The cumulative time of the LF furnace refining was 40 min, followed by the cumulative time of the RH refining, which was 20 min. The net time of argon gas injection was over 10 min, and nitrogen gas was injected for 3 min in the final stage of the RH refining to control the N content at 50 ppm. The refined molten steel was then cast into a continuous casting slab.

[0074] Heating process: The maximum heating temperature of the continuous casting slab was 1180°C, the soaking temperature was 1150°C, and the heat retention time was 5 hours. Rolling process: A two-stage rolling method was used. In the first stage of rolling, the rolling start temperature was 1080°C, the rolling reduction per pass was 18%, and the cumulative rolling reduction was 55%; in the second stage of rolling, the rolling start temperature was 780°C, the rolling reduction per pass was 10%, and the cumulative rolling reduction was 50% or more. Cooling step: The cooling start temperature was set to 710°C, and the temperature was cooled at a rate of 4°C / sec until it reached 500°C.

[0075] Measurements of the steel plate revealed that the tensile strength was 530 MPa, the yield strength was 410 MPa, the elongation at break was 31.5%, and the impact energy (longitudinal direction) values ​​at -40°C were 350 J, 332 J, and 349 J.

[0076] Double-wire vertical electrogas welding was performed, and the specific welding method and process were as follows: A V-shaped groove was created in the steel plate to be welded, with one side angled at 10°. The groove position was ground with an angle grinder to remove any oil or rust before welding. A 12 mm-wide gap was left at the base, and a "P"-shaped handle was spot-welded to secure the handles. The handles were spaced 200 mm apart, and a ceramic backing material was attached to the backside. The welding process was protected with 100% carbon dioxide gas, with a gas flow rate of 33 L / min. The two welding torches had an oscillation range of ±30 mm in the plate thickness direction (vertical direction) with the origin at half the plate thickness, and ±10 mm in the plate width direction (horizontal direction) with the origin at the center of the groove. The welding process parameters used were as follows: the front wire welding current was 340–360 A, the welding voltage was 38–40 V; the back wire welding current was 380–400 A, the welding voltage was 40–42 V. The diameter of the welding wire used was 1.6 mm to 2.0 mm, the welding speed was 3 cm / min, the welding heat input was 701 kJ / cm, and the flow rate of the cooling water was 30 L / min. The joint performance after welding is shown in Table 1.

[0077] [Table 1]

[0078] The above is merely a preferred embodiment of the present invention, and does not limit the scope of protection of the present invention. Any equivalent replacements or modifications made by those skilled in the art based on the technical means and inventive ideas of the present invention within the technical scope disclosed in the present invention shall also be included in the scope of protection of the present invention.

Claims

1. A thick steel plate for large heat input welding, characterized in that the chemical components in the steel plate are, in weight percentages, C 0.04% to 0.10%, Si 0.1% to 0.5%, Mn 1.4% to 2.0%, P≦0.010%, S≦0.006%, Cu 0.2% to 0.5%, Ni 0.10% to 0.4%, Cr 0.10% to 0.3%, Nb 0.01% to 0.04%, Als 0.010% to 0.05%, Ti 0.01% to 0.02%, N≦0.008%, with Ti / N=2 to 4 and Ceq≦0.42; and the balance being Fe and unavoidable impurities.

2. 2. The thick steel plate for large heat input welding according to claim 1, wherein the chemical components in the steel plate are, in weight percentages, C 0.05% to 0.75%, Si 0.1% to 0.3%, Mn 1.45% to 1.6%, P≦0.008%, S≦0.004%, Cu 0.3% to 0.35%, Ni 0.25% to 0.35%, Cr 0.15% to 0.25%, Nb 0.015% to 0.025%, Als 0.010% to 0.03%, Ti 0.013% to 0.018%, N 0.004% to 0.006%, with Ti / N=2.4 to 3.6, Ceq≦0.42; and the balance being Fe and unavoidable impurities.

3. The thick steel plate for large heat input welding according to claim 1 or 2, characterized in that the steel plate has a thickness standard of 40 to 85 mm, a yield strength of 390 to 450 MPa, a tensile strength of 510 to 600 MPa, an elongation at break of 28% to 35%, and a maximum heat input that can be withstood of 700 kJ / cm.

4. The method for manufacturing a thick steel plate for large heat input welding according to any one of claims 1 to 3, a step of setting the cumulative time of LF furnace refining to more than 30 min, the cumulative time of further RH refining to more than 10 min, and the net time of argon gas injection to more than 5 min; and controlling the N content to 40 to 80 ppm; A process in which the maximum heating temperature of the continuous casting slab is 1250°C or less, the soaking temperature is 1100 to 1180°C, and the temperature retention time is 5 to 10 hours; A rolling process using a two-stage rolling method including a first stage rolling at a temperature of 1150 to 1050°C, a rolling reduction per pass of 15% or more, and a cumulative rolling reduction of 55% or more, and a second stage rolling at a temperature of 830 to 780°C, a rolling reduction per pass of 10% or more, and a cumulative rolling reduction of 50% or more; and A method for manufacturing a thick steel plate for large heat input welding, comprising a cooling step in which a cooling start temperature is set to 700°C or higher and cooling is performed at a rate of 4 to 25°C / second until the temperature reaches 380 to 500°C.

5. The welding method for thick steel plates for large heat input welding according to any one of claims 1 to 3, 1) A process of forming a symmetrical V-shaped groove on a steel plate to be welded, attaching a ceramic backing material to the root of the groove during welding, and attaching a copper water-cooled sliding copper pad to the surface of the groove; 2) Manual spot welding one "P" handle at intervals of 200-300 mm to the steel plate side of the root of the groove; 3) Welding using a double-wire vertical electrogas welding machine, with two welding torches oscillating simultaneously, and flowing gas during the welding process to provide protection and ensure smooth circulation of cooling water; and 4) A welding method for thick steel plates for large heat input welding, comprising a step of setting the welding process parameters of the front wire to 300 to 360 A and the welding voltage to 35 to 40 V, and the welding current of the back wire to 340 to 400 A and the welding voltage to 36 to 42 V, when the wire of the two wires in the double-wire vertical electrogas welding that is closest to the root of the weld bead is used as the front wire and the other wire is used as the back wire.

6. The welding method for thick steel plates for large heat input welding according to claim 5, characterized in that the V-shaped groove has an angle on one side of 8° to 15° and a gap width at the base of 6 to 12 mm; and the distance between the handles is 200 to 300 mm.

7. 6. The method for welding thick steel plates for large heat input welding according to claim 5, wherein the flow rate of the cooling water is 15 to 30 L / min.

8. 6. The welding method for thick steel plates for large heat input welding according to claim 5, characterized in that in step 3), the two welding torches are swung simultaneously with an oscillation width of 0 to ±32 mm in the plate thickness direction with an origin at a position half the plate thickness, and an oscillation width of 0 to ±10 mm in the plate width direction with an origin at the center of the groove, and the protective gas is 100% carbon dioxide gas.

9. 6. The method for welding thick steel plates for large heat input welding according to claim 5, wherein the diameter of the welding wire used is 1.6 mm to 2.0 mm, the welding speed is 2 to 5 cm / min, and the gas flow rate is 30 to 35 L / min.

10. 6. The welding method for thick steel plates for large heat input welding according to claim 5, characterized in that the welded steel plates have a joint tensile strength of 520 to 580 MPa and an impact energy value of the heat-affected zone at −40°C of 70 J or more.

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