Large-thickness steel plate for high heat input welding, and preparation method and welding method therefor

Abstract

The present invention relates to a large-thickness steel plate for high heat input welding, and a preparation method and a welding method therefor. The steel plate comprises the following chemical components in percentages by weight: 0.04%-0.10% of C, 0.1%-0.5% of Si, 1.4%-2.0% of Mn, P≤0.010%, S≤0.006%, 0.2%-0.5% of Cu, 0.10%-0.4% of Ni, 0.10%-0.3% of Cr, 0.01%-0.04% of Nb, 0.010%-0.05% of Als, 0.01%-0.02% of Ti, and N≤0.008%, wherein Ti / N is 2-4, and Ceq≤0.42, with the balance being Fe and inevitable impurities. The 390 MPa grade steel plate of the present invention can be used for high heat input welding; the thickness specification of the steel plate can reach 40-85 mm; the steel plate can bear heat input welding of 300-700 kJ / cm; and a welding joint area has good toughness. In addition, provided is a double-wire electro-gas welding method.

Description

A steel plate for large thickness and high line energy welding, and its preparation method and welding method Technical Field

[0001] The present invention relates to the technical field of steel manufacturing, and in particular to a steel plate for large-thickness and high-heat-line welding, and a preparation method and a welding method thereof. Background Art

[0002] In recent years, with the development of economy and technology, the structural construction in industries such as ships, marine engineering, oil and gas storage tanks, and bridges has been increasingly moving towards large-scale construction. At the same time, the steel used to build these structures is also developing towards high strength, high toughness, and large thickness.

[0003] Welding is a critical step in steel structure construction. Welding hours can account for 40% of the total construction time, and welding costs can account for 17% of the total cost. Therefore, with the increasing application of thick steel plates in various fields, welding efficiency has become an increasingly prominent constraint on structural construction. Using high heat input welding for steel plates can significantly reduce the number of welding passes and improve efficiency. For example, in the shipbuilding industry, welding a 40mm thick plate using a 40kJ / cm heat input requires approximately 18 passes. However, using a high heat input welding method with a heat input of 300kJ / cm can achieve a single pass, significantly increasing welding efficiency by tens of times. However, ordinary steel plates can generally only withstand heat inputs below 50kJ / cm. This is because when welding with higher heat inputs, the weld joint spends longer at high temperatures and cools more slowly, resulting in severe grain coarsening in the heat-affected zone (HAZ), significantly reducing toughness in this area. Therefore, the development and application of steel plates suitable for high heat input welding has attracted widespread attention in various fields.

[0004] The invention patent with publication number CN106756541A discloses a 390 MPa-grade steel for high-energy-input welding of offshore platforms, but it is only applicable to an energy-input of 100 kJ / cm.

[0005] The invention patent with publication number CN107164696A discloses a high-strength ship plate EH40 that can be welded with high linear energy and its production method. The composition design adopts Nb and Ti composite alloying. The developed EH40 ship plate has a thickness specification of 8-50mm and can withstand a maximum linear energy input value of 150kJ / cm.

[0006] Patent publication number CN104404369A discloses a method for welding thick steel plates at high heat inputs of 200-400 kJ / cm and its manufacturing method. However, the method employs a technique for adding Mg, Ca, and their alloys to produce small inclusions, thereby improving the high heat input weldability of the steel plates. This technique is difficult to implement in industry and has limited operability.

[0007] In addition, patent publication number CN102839320A discloses a steel plate for high-heat input welding produced using the TMCP process, which can withstand high-heat input welding of 100-200 kJ / cm. Patent publication number CN109161671A discloses a high-strength EH36 steel plate for high-heat input welding and a manufacturing method thereof, which allows a maximum welding heat input of 300 kJ / cm. Patent publication number CN108677088A discloses a low-carbon bainitic steel plate for high-heat input welding and a manufacturing method thereof, which is suitable for high-heat input welding of 100-300 kJ / cm. The addition of multiple alloying elements to the steel plate increases the production cost of the steel plate. Therefore, most existing steel plates suitable for high-heat input welding can withstand heat inputs between 200 and 400 kJ / cm, which is far from sufficient for the more efficient one-shot welding method.

[0008] The present invention provides a process for preparing steel plates for high-heat input welding with a maximum thickness of 85 mm. This steel plate can be welded in a single pass using an efficient welding method, can withstand a maximum heat input of 700 kJ / cm, and exhibits excellent weld joint performance. Furthermore, the present invention provides a twin-wire electrogas vertical welding method applicable to this steel plate. This method enables single-pass welding of the steel plate, ensures a beautiful weld bead without defects such as undercuts and slag inclusions, and significantly improves welding production efficiency.

[0009] Summary of the Invention

[0010] The present invention provides a thick, high-heat input welding steel plate, a preparation method, and a welding method thereof. The steel plate can be used for high-heat input welding of 390 MPa-grade steel plates with thicknesses ranging from 40 to 85 mm, can withstand welding heat inputs of 300 to 700 kJ / cm, and exhibits good toughness in the weld joint area. A twin-wire electrogas vertical welding method is also provided.

[0011] To achieve the above objectives, the present invention adopts the following technical solutions:

[0012] A steel plate for large-thickness and high-heat-input welding has the following chemical compositions by weight: 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%, Ti / N ratio is 2-4, Ceq≤0.42; the remainder is Fe and unavoidable impurities.

[0013] Preferably, the chemical composition of the steel plate is as follows by weight: 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%, and Ti / N is 2.4 to 3.6, Ceq ≤ 0.42; the remainder is Fe and unavoidable impurities.

[0014] The steel plate has a thickness of 40 to 85 mm, a yield strength of 390 to 450 MPa, a tensile strength of 510 to 600 MPa, an elongation after fracture of 28% to 35%, and can withstand a maximum linear energy of 700 kJ / cm.

[0015] The composition design principle of a thick 390MPa grade steel plate suitable for high input energy welding of the present invention is as follows:

[0016] Carbon (C) is a key element in determining both steel strength and weldability. When C content is below 0.04%, the strength of the steel plate is difficult to maintain. When C content is above 0.10%, the weld heat-affected zone (HAZ) exhibits a high concentration of hardened microstructure, which can lead to a rapid decrease in toughness. In the present invention, C content is controlled within a range of 0.04% to 0.10%, preferably 0.05% to 0.75%.

[0017] Si is added as a deoxidizing element, promoting deoxidation of molten steel and increasing steel plate strength. However, solid solution strengthening through Si impairs the steel plate's low-temperature impact toughness and weldability, while also promoting the formation and growth of MA. When Si content is less than 0.10%, the deoxidation effect is poor; however, when Si content exceeds 0.50%, the steel structure becomes brittle and increases sensitivity to cold and hot cracking during welding. In the present invention, Si content is controlled within a range of 0.10% to 0.50%, preferably 0.1% to 0.3%.

[0018] Mn is an important alloying element in steel. It not only improves the strength of steel plates, but also expands the austenite phase, lowers the Ar3 point temperature, refines ferrite grains, and improves the low-temperature toughness of steel plates. However, Mn is prone to segregation during the solidification process of molten steel. High Mn content easily segregates with impurities such as P and S, making continuous casting difficult. It also easily produces undesirable structures such as M / A islands during subsequent rolling and welding, which affect the low-temperature toughness of welds. MnS second-phase inclusions in steel have a serious adverse effect on both base material properties and the HAZ. Furthermore, excessive Mn content can easily cause central segregation in thick steel plates. The present invention controls the Mn content to 1.4% to 2.0%, with a preferred Mn content of 1.45% to 1.6%.

[0019] Phosphorus (P) is an impurity element that increases steel's brittleness, impairs weldability, reduces plasticity, and worsens cold bending properties. Therefore, it is generally desirable to keep the P content in steel as low as possible. In the present invention, the P content is controlled to ≤ 0.010%, preferably ≤ 0.008%.

[0020] S is also a harmful element. A high sulfur content increases the brittle transition temperature of steel plates and reduces their weldability. More importantly, S combines with Mn in steel to form MnS inclusions, which easily form long strips of inclusions during rolling. S is also the primary element causing hot brittleness during hot rolling, so its content is generally required to be low. In the present invention, the S content is required to be controlled at ≤ 0.006%, preferably ≤ 0.004%.

[0021] The addition of a small amount of Cu can improve the strength of the softening zone of the weld heat affected zone, but the addition of too much copper will promote the formation of MA components and reduce the toughness of the weld heat affected zone. The Cu content of the present invention is required to be controlled within 0.2-0.5%, preferably 0.3%-0.35%.

[0022] Ni can improve the low-temperature toughness of steel, but Ni is an austenite-forming element that improves the stability of supercooled austenite. To control the amount of MA components in the heat-affected zone of the weld, its addition level should be controlled and not too high. In the present invention, the Ni content is required to be controlled within a range of 0.10% to 0.4%, preferably 0.25% to 0.35%.

[0023] Cr can increase the strength of steel, but it also raises the ductile-brittle transition temperature. At higher Cr contents, the impact toughness of steel decreases dramatically. In the present invention, the Cr content is controlled within a range of 0.10% to 0.3%, preferably 0.15% to 0.25%.

[0024] Niobium primarily promotes grain refinement during steel rolling and strengthens the matrix through precipitation. It raises the pre-recrystallization temperature and promotes the formation of low-temperature phase transformation structures. It also forms complex nitrides with Ti, reducing the titanium-nitrogen ratio and improving heat-affected zone properties. However, if the niobium content is too low, the strengthening effect is minimal, and the steel's strength often falls short of requirements. Excessive niobium content can induce the formation of upper bainite under high-heat-input welding conditions, severely impairing the low-temperature toughness of the high-heat-input HAZ. In the present invention, the niobium content is controlled within the range of 0.01% to 0.05%, preferably 0.015% to 0.025%.

[0025] Al: It is a common deoxidizer in steel and can effectively refine the grain elements and improve the strength and toughness of steel. However, when the addition amount is greater than 0.050%, it is easy to form large composite oxide inclusions and easily form nodules at the water nozzle of the crystallizer. In the present invention, Als is controlled at 0.010% to 0.050%, preferably 0.010% to 0.03%.

[0026] Ti is a key element in this invention. At higher temperatures, Ti combines with nitrogen to form TiN and, simultaneously, with Nb, TiNb(CN). This metal is less soluble at high welding temperatures, limiting austenite grain growth and promoting ferrite nucleation, effectively improving the toughness of the heat-affected zone (HAZ). The addition of Ti also reduces the solute content of free nitrogen, improving the weldability of the steel. An appropriate Ti / N ratio maximizes the effects of both Ti and N. When the Ti / N ratio is less than 2, the steel contains a high amount of solute nitrogen, resulting in lower toughness and aging properties. When the Ti / N ratio is greater than 4, the TiN particles coarsen, weakening their beneficial effects on the HAZ. Meanwhile, the amount of solute Ti increases, compromising the toughness of the base material. Exceeding this range significantly reduces the performance of the steel plate and the HAZ. The optimal Ti content in this invention is 0.01%-0.02%, preferably 0.013%-0.018%.

[0027] Nitrogen is an important element for ensuring the performance of high-heat-input welded joints. Nitrogen exists in two forms in steel. One is solid solution, that is, in the form of free nitrogen, which is detrimental to the performance of the steel, especially the low-temperature impact performance of the joint. The other is in the form of dispersed nitrides. The main nitrides such as TiN, AlN and NbN can reduce the growth trend of grains in the heat-affected zone of the weld and improve the performance of the heat-affected zone of the weld. In the present invention, the nitrogen content is controlled to N≤0.008%, preferably 0.004% to 0.006%.

[0028] The steel composition design for high heat input welding of the present invention is improved with respect to existing patents and related products, mainly in the following two aspects:

[0029] (1) Improvement of the weldability with high heat input: ① Do not add V element which is detrimental to the toughness of the heat affected zone of high heat input welding; ② Reduce the C content and Ceq in the steel; ③ Control the low S and P content; ④ Control the Ti / N ratio.

[0030] (2) Guarantee of high strength and high toughness: The low C content is designed to be compensated by adding Cu and Cr elements for strengthening, and an appropriate amount of Ni and Nb elements are added to ensure the toughness of the steel plate.

[0031] A method for preparing a steel plate for large thickness and high heat input welding includes the following steps: molten iron pretreatment, converter smelting, LF refining, RH refining, continuous casting, heating, rolling, and cooling; the rolling step adopts a controlled rolling TMCP process; and specifically includes the following steps:

[0032] The smelting and continuous casting process of the present invention involves desulfurization pretreatment of the molten iron before entering the converter, followed by smelting of the steel according to the target chemical composition of the steel plate. The cumulative refining time in the LF furnace should be greater than 30 minutes, the cumulative deep refining time in the RH refining should be greater than 10 minutes, and the net argon purge time should be greater than 5 minutes. Nitrogen content is controlled by blowing nitrogen at the end of the RH refining to maintain a nitrogen content of 40-80 ppm. The smelted molten steel is then cast into continuously cast ingots.

[0033] The maximum heating temperature of continuous casting slab is not higher than 1250℃, the soaking temperature is 1100~1180℃, and the holding time is 5~10h;

[0034] Rolling process: adopt two-stage rolling method, the first stage rolling temperature is 1150-1050℃, the single pass reduction is ≥15%, and the cumulative reduction rate is ≥55%; the second stage rolling temperature is 830-780℃, the single pass reduction is ≥10%, and the cumulative reduction rate is ≥50%;

[0035] Cooling process: the starting cooling temperature is ≥700℃, and the temperature is cooled to 380~500℃ at a speed of 4~25℃ / s.

[0036] In the present method for producing steel plates for high-heat input welding, the final rolling temperature is controlled above 1050°C during the first rolling stage, ensuring a single-pass reduction of no less than 15%. This effectively transmits the rolling force and ensures uniformity of the structure and properties of the thick steel plates through the thickness. Furthermore, the addition of Cu and Nb elements to the compositional design system, combined with the two-stage rolling and cooling processes, results in a uniform, fine structure and excellent properties. This ensures the overall toughness of the joints after high-heat input welding, particularly low-temperature toughness.

[0037] A method for welding thick steel plates for high heat input welding, comprising the following steps:

[0038] 1) A symmetrical V-shaped groove is processed on the steel plate to be welded. Before welding, the groove is polished with cornea to remove oil and rust. During welding, a ceramic liner is installed at the root of the groove and a copper water-cooled copper slider is installed on the surface of the groove.

[0039] 2) Use manual spot welding to fix a "П" type iron on one side of the steel plate at the root of the groove every 200 to 300 mm; the iron is made of low-carbon steel that is easy to weld.

[0040] 3) Use a double-wire gas-electric vertical welding machine for welding, with two welding guns swinging at the same time. Use gas for protection during welding to keep the cooling water circulation unobstructed;

[0041] 4) In double-wire gas-electric vertical welding, the double wire close to the weld root is called the front wire, and the other one is called the rear wire. The corresponding welding process parameters are: the front wire welding current is 300~360A, and the welding voltage is 35~40V; the rear wire welding current is 340~400A, and the welding voltage is 36~42V.

[0042] The angle of the V-shaped groove is 8° to 15° on one side, and the root gap is 6 to 12 mm.

[0043] The cooling water flow rate is 15 to 30 L / min.

[0044] The two welding guns in the above step 3) swing simultaneously. In the plate thickness direction (longitudinal direction) with the 1 / 2 plate thickness position as the origin, the swing amplitude of the welding gun is 0 to ±32 mm, and in the plate width direction (transverse direction) with the groove center as the origin, the swing amplitude of the welding gun is 0 to ±10 mm, and the shielding gas is 100% carbon dioxide gas.

[0045] The diameter of the welding wire used is 1.6mm~2.0mm, the welding speed is 2~5cm / min, and the gas flow rate is 30~35L / min.

[0046] The tensile strength of the steel plate joint after welding is 520~580MPa, and the impact energy value of the heat affected zone at -40℃ is ≥70J.

[0047] In the welding method of the present invention:

[0048] (1) In step 2), the main purpose of welding a "П" type iron every 200mm is to fasten the ceramic liner on the back and assemble the test plate before welding to ensure that the weld joint is well formed.

[0049] (2) During welding in step 3), the two welding guns are simultaneously swung within an appropriate range to ensure good side wall fusion in the welding groove and eliminate welding undercut defects during the welding process.

[0050] (3) The welding process parameter range given in step 4) can ensure that the molten pool remains stable during the welding process and eliminate the burn-through of the root of the welding test plate or the overflow of molten iron on the surface.

[0051] (4) The angle of the V-groove is smaller than the commonly used groove angle, and the root gap is increased, the overall cross-sectional area of ​​the weld groove is reduced, and the filling volume is reduced. While improving welding efficiency, the welding heat input is reduced, thereby ensuring that the tensile strength of the steel plate joint after welding is 520-580MPa and the impact energy value of the heat-affected zone at -40°C is ≥70J.

[0052] (5) The cooling water flow rate is to ensure the cooling speed of the copper slider on the groove surface to the molten iron in the welding pool, and to prevent the molten iron in the pool from overflowing and causing welding interruption.

[0053] Compared with the existing technology, the beneficial effects of the present invention are:

[0054] 1) The present invention's high-thickness, high-heat input welding steel plate has a maximum thickness of 85 mm, a yield strength of 390-450 MPa, a tensile strength of 510-600 MPa, and an elongation of 28%-35%. It is particularly suitable for high-heat input welding at energy inputs of 50-700 kJ / cm. The welded steel plate joint has a tensile strength of 510-580 MPa, and an impact energy value of 70 J or greater at -40°C in the heat-affected zone. This successfully addresses the problem of severely reduced impact toughness in the heat-affected zone during high-heat input welding.

[0055] 2) When using double-wire gas-electric vertical welding, the groove design in the present invention minimizes the groove angle and adjusts the root gap, obtaining a smaller groove cross-sectional area than that in conventional double-wire gas-electric vertical welding. The welding line energy is reduced under the same plate thickness, ensuring that the heat-affected zone performance of the steel plate for large thickness and high line energy welding in the present invention is better, while also saving welding materials and greatly improving welding efficiency. DETAILED DESCRIPTION

[0056] The technical solutions of the present invention are described in detail below through examples. The following examples are merely exemplary for explaining and illustrating the technical solutions of the present invention and are not to be construed as limiting the technical solutions of the present invention.

[0057] Example 1

[0058] The specific chemical composition and mass percentage of the steel plate are: 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%, Ti / N ratio is 2.8, Ceq is 0.387, and the rest are Fe and unavoidable impurity elements; the steel plate thickness is 40 mm

[0059] The steelmaking and continuous casting process is as follows: molten iron undergoes desulfurization pretreatment to a sulfur content of 0.003%, followed by converter smelting. The LF furnace refining process lasts for 35 minutes, the RH refining deep treatment process lasts for 15 minutes, the net argon purge lasts for 10 minutes, and the nitrogen content is controlled at 43 ppm by a 1-minute nitrogen purge at the end of the RH refining. The smelted molten steel is then cast into continuous casting billets.

[0060] Heating process: The maximum heating temperature of the continuous casting billet is 1200℃, the soaking temperature is 1180℃, and the holding time is 7h.

[0061] Rolling process: A two-stage rolling method is adopted. The first stage rolling temperature is 1180℃, the single pass reduction is 15%, and the cumulative reduction rate is 64%; the second stage rolling temperature is 830℃, the single pass reduction is 12%, and the cumulative reduction rate is ≥58%.

[0062] Cooling process: start cooling at 720℃ and cool to 450℃ at a rate of 15℃ / s.

[0063] After testing, the steel plate had a tensile strength of 590 MPa, a yield strength of 440 MPa, an elongation at break of 28%, and impact energy (longitudinal) values ​​of 288 J, 267 J, and 293 J at -40°C.

[0064] Double-wire gas-electric vertical welding is used for welding. The specific welding method and process are as follows:

[0065] The steel plates to be welded were V-grooved with a single-sided 15° groove angle. Before welding, the grooves were ground with corneal polishing, degreasing, and rust removal. An 8mm gap was reserved at the root, and "П"-shaped irons were spot-welded for fixation, spaced 300mm apart, with ceramic backing. The welding process was shielded with 100% CO2 gas at a flow rate of 30 L / min. The two welding torches were positioned longitudinally, with the origin at half the thickness of the plate, and the torches swung within ±10 mm. The welding parameters used were: a leading wire welding current of 300-320 A and a welding voltage of 35-36 V; a trailing wire welding current of 340-360 A and a welding voltage of 36-38 V. The wire diameter ranged from 1.6 to 2.0 mm, the welding speed was 5 cm / min, and the welding energy input was 273 kJ / cm. The cooling water flow rate was 20 L / min.

[0066] The properties of the welded joint are shown in Table 1.

[0067] Example 2

[0068] The specific chemical composition and mass percentage of the steel plate are: 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, Ti / N ratio is 2.8, Ceq is 0.415, and the rest are Fe and unavoidable impurity elements; the steel plate thickness is 55 mm.

[0069] The steelmaking and continuous casting process is as follows: After desulfurization pretreatment, the molten iron has a sulfur content of 0.0025%, followed by converter smelting. The LF furnace refining process lasts for 35 minutes, the RH refining deep treatment process lasts for 15 minutes, and the net argon purge time is 15 minutes. At the end of the RH refining, nitrogen is purged for 3 minutes to control the nitrogen content to 58 ppm. The smelted molten steel is then cast into continuous casting billets.

[0070] Heating process: The maximum heating temperature of the continuous casting billet is 1200℃, the soaking temperature is 1180℃, and the holding time is 6h.

[0071] Rolling process: A two-stage rolling method is adopted. The first stage rolling temperature is 1180℃, the single pass reduction is 17%, and the cumulative reduction rate is 57%; the second stage rolling temperature is 820℃, the single pass reduction is 12%, and the cumulative reduction rate is ≥58%.

[0072] Cooling process: Start cooling at 700℃ and cool to 400℃ at a rate of 10℃ / s.

[0073] After testing, the steel plate had a tensile strength of 587 MPa, a yield strength of 433 MPa, an elongation at break of 29.2%, and -40°C impact energy (longitudinal) values ​​of 277 J, 289 J, and 284 J.

[0074] Double-wire gas-electric vertical welding is used for welding. The specific welding method and process are as follows:

[0075] The steel plates to be welded have a V-shaped groove with a single-sided 14° groove angle. Before welding, the groove is ground with a cornea to remove oil and rust. A 12mm gap is reserved at the root, and "П"-shaped irons are spot welded for fixation, with the irons spaced 280mm apart and backed with a ceramic backing. The welding process uses 100% carbon dioxide gas shielding with a gas flow rate of 30L / min. The two welding guns swing within ±20mm in the plate thickness direction (longitudinal direction) with the 1 / 2 plate thickness position as the origin. The welding gun swings within ±2mm in the plate width direction (transverse direction) with the groove center as the origin. The welding process parameters used are: front wire welding current of 310-330A, welding voltage of 36-38V; rear wire welding current of 350-370A, welding voltage of 37-39V. 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 line energy was 360 kJ / cm, and the cooling water flow rate was 23 L / min.

[0076] The properties of the welded joint are shown in Table 1.

[0077] Example 3

[0078] The specific chemical composition and mass percentage of the steel plate are: 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, Ti / N ratio is 2.7, Ceq is 0.378, and the rest are Fe and unavoidable impurity elements; the steel plate thickness is 60 mm

[0079] The steelmaking and continuous casting process is as follows: molten iron undergoes desulfurization pretreatment to a sulfur content of 0.0025%, followed by converter smelting. The LF furnace refining process lasts for 35 minutes, the RH refining deep treatment process lasts for 15 minutes, and the net argon purge lasts for 15 minutes. At the end of the RH refining, nitrogen is purged for 2 minutes to control the nitrogen content to 55 ppm. The smelted molten steel is then cast into continuous casting ingots.

[0080] Heating process: The maximum heating temperature of the continuous casting billet is 1150℃, the soaking temperature is 1120℃, and the holding time is 6h.

[0081] Rolling process: A two-stage rolling method is adopted. The first stage rolling temperature is 1151℃, the single pass reduction is 17%, and the cumulative reduction rate is 60%; the second stage rolling temperature is 830℃, the single pass reduction is 11%, and the cumulative reduction rate is ≥58%.

[0082] Cooling process: start cooling at 738℃ and cool to 380℃ at a rate of 8℃ / s.

[0083] After testing, the steel plate had a tensile strength of 554 MPa, a yield strength of 430 MPa, an elongation at break of 32%, and impact energy (longitudinal) values ​​of 307 J, 298 J, and 311 J at -40°C.

[0084] Double-wire gas-electric vertical welding is used for welding. The specific welding method and process are as follows:

[0085] The steel plates to be welded were V-grooved with a single-sided 14° groove angle. Before welding, the groove was ground with corneal polishing, degreasing, and rust removal. A 10mm gap was reserved at the root, and "П"-shaped irons were spot-welded for fixation, spaced 280mm apart, with a ceramic backing. The welding process was shielded with 100% CO2 gas at a flow rate of 30 L / min. The two welding torches swung within ±20mm in the longitudinal direction, with the origin at half the thickness of the plate, and ±3mm in the transverse direction, with the origin at the center of the groove. The welding process parameters used were: a leading wire welding current of 310-330A and a welding voltage of 36-38V; a trailing wire welding current of 360-380A and a welding voltage of 36-38V. The diameter of the welding wire used was 1.6 mm to 2.0 mm, the welding speed was 4 cm / min, the welding line energy was 404 kJ / cm, and the cooling water flow rate was 25 L / min.

[0086] The properties of the welded joint are shown in Table 1.

[0087] Example 4

[0088] The specific chemical composition and mass percentage of the steel plate are: 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, Ti / N ratio is 3.1, Ceq is 0.419, and the rest are Fe and unavoidable impurity elements; the steel plate thickness is 68mm

[0089] The steelmaking and continuous casting process is as follows: After desulfurization pretreatment, the molten iron has a sulfur content of 0.0038%, followed by converter smelting. The LF furnace refining process lasts for 35 minutes, the RH refining deep treatment process lasts for 15 minutes, and the net argon purge lasts for 15 minutes. At the end of the RH refining, nitrogen is purged for 2 minutes to control the nitrogen content to 55 ppm. The smelted molten steel is then cast into continuous casting billets.

[0090] Heating process: The maximum heating temperature of the continuous casting billet is 1250℃, the soaking temperature is 1190℃, and the holding time is 6h.

[0091] Rolling process: A two-stage rolling method is adopted. The first stage rolling temperature is 1170℃, the single pass reduction is 17%, and the cumulative reduction rate is 56%; the second stage rolling temperature is 800℃, the single pass reduction is 10%, and the cumulative reduction rate is ≥50%.

[0092] Cooling process: start cooling at 720℃ and cool to 400℃ at a rate of 7℃ / s.

[0093] After testing, the steel plate had a tensile strength of 596 MPa, a yield strength of 445 MPa, an elongation at break of 31.4%, and impact energy (longitudinal) values ​​of 330 J, 326 J, and 338 J at -40°C.

[0094] Double-wire gas-electric vertical welding is used for welding. The specific welding method and process are as follows:

[0095] The steel plates to be welded have a V-shaped groove with a single-sided 12° groove angle. Before welding, the groove is ground with a cornea to remove oil and rust. An 11mm gap is reserved at the root, and "П"-shaped irons are spot welded for fixation, with the irons spaced 260mm apart and backed with a ceramic backing. The welding process uses 100% carbon dioxide gas shielding with a gas flow rate of 30L / min. The two welding torches swing within ±20mm in the plate thickness direction (longitudinal direction) with 1 / 2 of the plate thickness as the origin. In the plate width direction (transverse direction), the welding torches swing within ±4mm with the groove center as the origin. The welding process parameters used are: 320-340A welding current and 37-39V welding voltage for the front wire; 360-380A welding current and 38-40V welding voltage for the rear wire. 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 line energy was 488 kJ / cm, and the cooling water flow rate was 25 L / min.

[0096] The properties of the welded joint are shown in Table 1.

[0097] Example 5

[0098] The specific chemical composition and mass percentage of the steel plate are: 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, Ti / N ratio is 2.5, Ceq is 0.397, and the rest is Fe and unavoidable impurity elements; the steel plate thickness is 75mm

[0099] The steelmaking and continuous casting process is as follows: molten iron undergoes desulfurization pretreatment to a sulfur content of 0.002%, followed by converter smelting. The LF furnace refining process lasts for 38 minutes, the RH refining deep treatment process lasts for 17 minutes, and the net argon purge process lasts for 13 minutes. A nitrogen purge is performed at the end of the RH refining process for 2 minutes to control the nitrogen content to 61 ppm. The smelted molten steel is then cast into continuous casting ingots.

[0100] Heating process: The maximum heating temperature of the continuous casting billet is 1180℃, the soaking temperature is 1150℃, and the holding time is 6h.

[0101] Rolling process: A three-stage rolling method is adopted. The first stage rolling temperature is 1150℃, the single pass reduction is 17%, and the cumulative reduction rate is 55%; the second stage rolling temperature is 800℃, the single pass reduction is 13%, and the cumulative reduction rate is ≥51%.

[0102] Cooling process: start cooling at 720℃ and cool at a rate of 7.5℃ / s to a temperature of 402℃.

[0103] After testing, the steel plate had a tensile strength of 545 MPa, a yield strength of 429 MPa, an elongation at break of 30.5%, and impact energy (longitudinal) values ​​of 327 J, 318 J, and 333 J at -40°C.

[0104] Double-wire gas-electric vertical welding is used for welding. The specific welding method and process are as follows:

[0105] The steel plates to be welded have a V-groove with a single-sided 12° groove angle. Before welding, the groove is ground with a cornea and degreased. A 10mm gap is reserved at the root. "П"-shaped irons are spot-welded for fixation, spaced 240mm apart, and backed with ceramic backing. The welding process utilizes 100% CO2 shielding at a flow rate of 34 L / min. The two welding torches oscillate within ±25mm in the longitudinal direction, with the origin at half the thickness, and ±6mm in the transverse direction, with the origin at the center of the groove. The welding process parameters used are: a leading wire current of 340-360A and a voltage of 37-39V; a trailing wire current of 380-400A and a voltage of 39-41V. The wire diameter ranges from 1.6mm to 2.0mm, and the welding speed is 3.2cm / min. The welding line energy is 570kJ / cm2 and the cooling water flow rate is 28L / min.

[0106] The properties of the welded joint are shown in Table 1.

[0107] Example 6

[0108] The specific chemical composition and mass percentage of the steel plate are: 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%, Ti / N ratio is 2.4, Ceq is 0.416, and the rest are Fe and unavoidable impurity elements; the steel plate thickness is 80mm

[0109] The steelmaking and continuous casting process is as follows: After desulfurization pretreatment, the molten iron has a sulfur content of 0.004%, followed by converter smelting. The LF furnace refining process lasts for 38 minutes, the RH refining deep treatment process lasts for 17 minutes, and the net argon purge process lasts for 13 minutes. A nitrogen purge is performed at the end of the RH refining process for 5 minutes to control the nitrogen content to 80 ppm. The smelted molten steel is then cast into continuous casting billets.

[0110] Heating process: The maximum heating temperature of the continuous casting billet is 1180℃, the soaking temperature is 1150℃, and the holding time is 5h.

[0111] Rolling process: A three-stage rolling method is adopted. The first stage rolling temperature is 1150℃, the single pass reduction is 17%, and the cumulative reduction rate is 55%; the second stage rolling temperature is 820℃, the single pass reduction is 11%, and the cumulative reduction rate is ≥50%.

[0112] Cooling process: start cooling at 760℃ and cool to 450℃ at a rate of 7.5℃ / s.

[0113] After testing, the steel plate had a tensile strength of 560 MPa, a yield strength of 438 MPa, an elongation at break of 28%, and impact energy (longitudinal) values ​​of 266 J, 279 J, and 269 J at -40°C.

[0114] Double-wire gas-electric vertical welding is used for welding. The specific welding method and process are as follows:

[0115] The steel plates to be welded have a V-groove with a single-sided 10° groove angle. Before welding, the groove is ground with a cornea and degreased. A 12mm gap is reserved at the root. "П"-shaped irons are spot-welded for fixation, spaced 220mm apart, and backed with ceramic backing. The welding process utilizes 100% CO2 shielding at a flow rate of 34 L / min. The two welding torches oscillate within ±25mm in the longitudinal direction, with the origin at half the thickness, and ±8mm in the transverse direction, with the origin at the center of the groove. The welding process parameters used are: a leading wire welding current of 340-360A and a welding voltage of 37-39V; a trailing wire welding current of 380-400A and a welding voltage of 39-41V. The wire diameter ranges from 1.6mm to 2.0mm, and the welding speed is 2.8cm / min. The welding line energy is 610kJ / cm2 and the cooling water flow rate is 28L / min.

[0116] The properties of the welded joint are shown in Table 1.

[0117] Example 7

[0118] The specific chemical composition and mass percentage of the steel plate are: 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%, Ti / N ratio is 3, Ceq is 0.393, and the rest are Fe and unavoidable impurity elements; the steel plate thickness is 84 mm.

[0119] The steelmaking and continuous casting process is as follows: molten iron undergoes desulfurization pretreatment to a sulfur content of 0.003%, followed by converter smelting. The LF furnace refining process lasts for 40 minutes, the RH refining deep treatment process lasts for 20 minutes, and the net argon purge lasts for more than 10 minutes. At the end of the RH refining, nitrogen is purged for 3 minutes to control the nitrogen content to 66 ppm. The smelted molten steel is then cast into continuous casting billets.

[0120] Heating process: The maximum heating temperature of the continuous casting billet is 1180℃, the soaking temperature is 1150℃, and the holding time is 5h.

[0121] Rolling process: A two-stage rolling method is adopted. The first stage rolling temperature is 1080℃, the single pass reduction is 18%, and the cumulative reduction rate is 55%; the second stage rolling temperature is 810℃, the single pass reduction is 12%, and the cumulative reduction rate is ≥50%.

[0122] Cooling process: start cooling at 750℃ and cool to 420℃ at a rate of 5℃ / s.

[0123] After testing, the steel plate had a tensile strength of 542 MPa, a yield strength of 431 MPa, an elongation at break of 31%, and impact energy (longitudinal) values ​​of 321 J, 317 J, and 344 J at -40°C.

[0124] Double-wire gas-electric vertical welding is used for welding. The specific welding method and process are as follows:

[0125] The steel plates to be welded have a V-shaped groove with a single-sided 10° groove angle. Before welding, the groove is ground with a cornea to remove oil and rust. A 12mm gap is reserved at the root, and "П"-shaped irons are spot welded for fixation, with the irons spaced 200mm apart and backed with a ceramic backing. The welding process uses 100% carbon dioxide gas shielding with a gas flow rate of 33L / min. The two welding guns swing within ±30mm in the plate thickness direction (longitudinal direction) with the 1 / 2 plate thickness position as the origin. The welding gun swings within ±8mm in the plate width direction (transverse direction) with the center of the groove as the origin. The welding process parameters used are: front wire welding current of 320-340A, welding voltage of 37-39V; rear wire welding current of 380-400A, welding voltage of 40-42V. 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 line energy was 668 kJ / cm, and the cooling water flow rate was 30 L / min.

[0126] The properties of the welded joint are shown in Table 1.

[0127] Example 8

[0128] The specific chemical composition and mass percentage of the steel plate are: 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%, Ti / N ratio is 3.6, Ceq is 0.417, and the rest are Fe and unavoidable impurity elements; the steel plate thickness is 85 mm.

[0129] The steelmaking and continuous casting process is as follows: molten iron undergoes desulfurization pretreatment to a sulfur content of 0.0015%, followed by converter smelting. The LF furnace refining process lasts for 40 minutes, the RH refining deep treatment process lasts for 20 minutes, and the net argon purge lasts for more than 10 minutes. At the end of the RH refining, nitrogen is purged for 3 minutes to control the nitrogen content to 50 ppm. The smelted molten steel is then cast into continuous casting billets.

[0130] Heating process: The maximum heating temperature of the continuous casting billet is 1180℃, the soaking temperature is 1150℃, and the holding time is 5h.

[0131] Rolling process: A two-stage rolling method is adopted. The first stage rolling temperature is 1080℃, the single pass reduction is 18%, and the cumulative reduction rate is 55%; the second stage rolling temperature is 780℃, the single pass reduction is 10%, and the cumulative reduction rate is ≥50%.

[0132] Cooling process: start cooling at 710℃ and cool to 500℃ at a rate of 4℃ / s.

[0133] After testing, the steel plate had a tensile strength of 530 MPa, a yield strength of 410 MPa, an elongation at break of 31.5%, and impact energy (longitudinal) values ​​of 350 J, 332 J, and 349 J at -40°C.

[0134] Double-wire gas-electric vertical welding is used for welding. The specific welding method and process are as follows:

[0135] The steel plates to be welded have a V-groove with a single-sided 10° groove angle. Before welding, the groove is ground with corneal polishing, degreasing, and rust removal. A 12mm gap is reserved at the root, and "П"-shaped irons are spot-welded for fixation, spaced 200mm apart, with a ceramic backing. The welding process utilizes 100% CO2 shielding at a flow rate of 33 L / min. The two welding torches oscillate within ±30mm in the longitudinal direction, with the origin at half the thickness. In the transverse direction, the torches oscillate within ±10mm, with the origin at the center of the groove. The welding process parameters used are: a leading wire welding current of 340-360A and a welding voltage of 38-40V; a trailing wire welding current of 380-400A and a welding voltage of 40-42V. The diameter of the welding wire used was 1.6 mm to 2.0 mm, the welding speed was 3 cm / min, the welding line energy was 701 kJ / cm, and the cooling water flow rate was 30 L / min.

[0136] The properties of the welded joint are shown in Table 1.

[0137] Table 1 Performance of welded joints after welding

[0138] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A steel plate for large thickness and high heat input welding, characterized in that: The chemical composition of the steel plate is as follows by weight: 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%, and Ti / N is 2-4, Ceq≤0.42; the rest is Fe and unavoidable impurities.

2. The steel plate for large thickness and high heat input welding according to claim 1, characterized in that: The chemical composition of the steel plate is as follows by weight: 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%, and Ti / N is 2.4 to 3.6, Ceq≤0.42; the remainder is Fe and unavoidable impurities.

3. A steel plate for large thickness and high heat input welding according to claim 1 or 2, characterized in that: The steel plate has a thickness of 40 to 85 mm, a yield strength of 390 to 450 MPa, a tensile strength of 510 to 600 MPa, an elongation after fracture of 28% to 35%, and can withstand a maximum linear energy of 700 kJ / cm.

4. A method for preparing a thick and high heat input welding steel plate according to any one of claims 1 to 3, characterized in that: The specific methods include the following: The cumulative refining time of LF furnace is greater than 30 minutes, the cumulative refining deep treatment time of RH furnace is greater than 10 minutes, and the net argon blowing time is greater than 5 minutes; the nitrogen content is controlled at 40-80ppm; The maximum heating temperature of continuous casting slab is not higher than 1250℃, the soaking temperature is 1100~1180℃, and the holding time is 5~10h; Rolling: adopt two-stage rolling method, the first stage rolling temperature is 1150~1050℃, the single pass reduction is ≥15%, and the cumulative reduction rate is ≥55%; the second stage rolling temperature is 830~780℃, the single pass reduction is ≥10%, and the cumulative reduction rate is ≥50%; Cooling: The starting cooling temperature is ≥700℃, and the temperature is cooled to 380~500℃ at a speed of 4~25℃ / s.

5. A method for welding thick steel plates for high heat input welding according to any one of claims 1 to 3, characterized in that: The specific method steps include: 1) A symmetrical V-shaped groove is processed on the steel plate to be welded. During welding, a ceramic liner is installed at the root of the groove and a copper water-cooled copper slider is installed on the surface of the groove; 2) Use manual spot welding to weld a "П" type iron every 200-300mm on one side of the steel plate at the root of the groove to fix it; 3) Use a double-wire gas-electric vertical welding machine for welding, with two welding guns swinging at the same time. Use gas for protection during welding to keep the cooling water circulation unobstructed; 4) In double-wire gas-electric vertical welding, the double wire close to the weld root is called the front wire, and the other one is called the rear wire. The corresponding welding process parameters are: the front wire welding current is 300~360A, and the welding voltage is 35~40V; the rear wire welding current is 340~400A, and the welding voltage is 36~42V.

6. The method for welding thick steel plates for high heat input welding according to claim 5, characterized in that: The angle of the V-shaped groove is 8° to 15° on one side, and the root gap is 6 to 12 mm; the spacing between the handles is 200 to 300 mm.

7. The method for welding thick steel plates for high heat input welding according to claim 5, characterized in that: The cooling water flow rate is 15 to 30 L / min.

8. The method for welding thick steel plates for high heat input welding according to claim 5, characterized in that: The two welding guns in the above step 3) swing simultaneously, with the 1 / 2 plate thickness position as the origin, and the swing amplitude of the welding gun is 0 to ±32 mm. In the plate width direction, with the groove center as the origin, the swing amplitude of the welding gun is 0 to ±10 mm, and the shielding gas is 100% carbon dioxide gas.

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

10. The method for welding thick steel plates for high heat input welding according to claim 5, characterized in that: The tensile strength of the steel plate joint after welding is 520~580MPa, and the impact energy value of the heat affected zone at -40℃ is ≥70J.

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