An ultra-high strength crack-arrest steel suitable for high heat input welding and a method of manufacturing the same

Abstract

The application discloses a high-heat-input-welding suitable ultrahigh-strength crack-arrest steel and a manufacturing method thereof, and belongs to the technical field of low-alloy ship steel manufacturing. The high-heat-input-welding suitable ultrahigh-strength crack-arrest steel has the following chemical components and percentage by weight: C: 0.030%-0.070%, Si: 0.10%-0.50%, Mn: 1.80%-2.00%, P: 0.012% or less, S: 0.005% or less, Al: 0.005%-0.04%, Ti: 0.004%-0.015%, Ni: 0.65%-0.80%, Cu: 0.25%-0.50%, Ca: 0.020%-0.050%, Mg: 0.001%-0.005%, Zr: 0.002%-0.010%, Cr: 0.15%-0.30%, Mo: 0.10%-0.30%, V: 0.01%-0.07%, Re: 0.01%-0.050%, and the balance of Fe and inevitable impurities. Through the adoption of a component system suitable for high-heat-input welding, metallurgical process design, fine organization control and other means, an ultrahigh-strength, high-heat-input-welding suitable super-thick crack-arrest steel with a heat input of 180 KJ / cm or more is prepared, and the steel meets the demand of steel used in key structural parts of super-large container ships, ocean platforms and the like.

Description

Technical Field

[0001] This invention belongs to the field of low-alloy shipbuilding steel manufacturing technology, specifically relating to an ultra-high strength crack-arresting steel suitable for high heat input welding and its manufacturing method. Background Technology

[0002] High-strength low-alloy steel, as a crucial engineering structural material, is widely used in the construction of ships, marine engineering, bridges, buildings, and other equipment and engineering projects. Increased material strength often leads to a decrease in toughness. However, for steel used in ships and offshore platforms, which require higher safety levels, international standards and specifications dictate that toughness requirements increase with strength to ensure structural safety during service. In the construction of large equipment and engineering projects, welding is the primary connection method and a key factor affecting construction efficiency. For example, welding processes account for approximately 80% of all shipbuilding time, especially as shipbuilding trends towards larger scale and lower costs. Adopting efficient welding is crucial for achieving high-efficiency shipbuilding and reducing manufacturing costs; therefore, shipyards have a stronger demand for shipbuilding steel that meets high heat input requirements. Currently, large shipyards have widely adopted high-heat-input welding equipment such as multi-wire submerged arc welding, FCB, and gas-electric vertical welding to achieve high-efficiency shipbuilding.

[0003] Welding with a heat input of 50 kJ / cm or higher is generally referred to as high heat input welding. During the welding process, the heat-affected zone of steel plates undergoes changes in microstructure and properties due to the welding thermal cycle, especially a significant reduction in low-temperature toughness. To ensure the quality of welded joints in steel structures, traditional structural steel generally requires strict limits on welding heat input, adherence to weld bead layout, control of interpass temperature, and sometimes preheating. While strict standardized procedures can effectively ensure the reliability of welded structural components, they also significantly limit welding efficiency, thereby limiting the construction efficiency of the structure.

[0004] As one of the three major ship types, container ships have seen a year-on-year increase in orders. In particular, key components such as hatch coamings utilize thick steel plates, and improved welding efficiency significantly shortens the shipbuilding cycle, bringing considerable profits to shipyards. Faced with the increasing workload of welding thick steel plates, existing technologies have developed some high-energy welding steels. Patent CN112746158 A discloses "A Low-Cost, High-Crack-Arrest and High-Weldability YP460MPa Grade Thick Steel Plate and Its Manufacturing Method," which uses low-C-low-Si-medium-high Mn-Nb low-alloy steel as a base, with micro-Ti treatment, Ca treatment, and a Ca / S ratio controlled between 1.0 and 3.0. It exhibits an impact energy ≥100J at -50℃ and a Kca (-20℃) ≥6000N / mm². 3 / 2However, it cannot meet the requirements for high heat input welding. The invention patent with publication number CN 109321815A discloses "A manufacturing method for high-strength thick steel plates resistant to high heat input welding". The strength grade of the steel plate prepared is 36kg, which is only suitable for ordinary ship structures. In addition, in the implementation of high heat input welding, Ti alloying is used. However, due to the preferential oxidation of C, Si, Mn and Al caused by RH oxygen blowing, the composition is lost. Moreover, the particle size of the secondary oxidation products formed by this method is uncontrollable, and the particle size and distribution of the obtained inclusions are unreliable. The invention patent with publication number CN 112458365 A, entitled "A Vanadium-Free Normalized High-Strength and Tough Thick Ship Plate with a Thickness ≥ 60mm and its Production Method," describes a method that adjusts the content of inexpensive elements such as silicon and titanium (e.g., increasing silicon and titanium content) and eliminates the addition of vanadium. It achieves the production of high-strength and tough thick ship plate steel with a thickness ≥ 60mm and a yield strength ≥ 380MPa through optimized billet heating, rolling, and normalizing processes. However, this method is only suitable for ordinary ship hull structures and cannot meet the crack-arresting toughness requirements of container ships. In summary, while these manufacturing methods can produce ultra-high-strength steel plates, the aforementioned existing technologies cannot meet the key characteristics of high heat input welding and thus cannot meet the high-efficiency construction requirements of ultra-large container ships. Summary of the Invention

[0005] In response to the various key performance requirements for crack-arresting steel during the efficient construction of large container ships, the present invention aims to provide an ultra-high strength crack-arresting steel suitable for high heat input welding and its manufacturing method. This invention, through the adoption of a suitable composition system and metallurgical process design for high heat input welding, and precise microstructure control, produces an extra-thick crack-arresting steel of 60–90 mm with ultra-high strength, high crack-arresting toughness (BCA2 grade), and a suitable heat input of over 180 KJ / cm. This solves the problem of matching high strength, excellent low-temperature toughness, resistance to brittle fracture, and high heat input welding performance.

[0006] The objective of this invention is achieved through the following means:

[0007] This invention provides an ultra-high strength crack-arresting steel suitable for high heat input welding, with the following chemical composition and weight percentages: C: 0.030%–0.070%, Si: 0.10%–0.50%, Mn: 1.80%–2.00%, P≤0.012%, S≤0.005%, Al: 0.005%–0.04%, Ti: 0.004%–0.015%, Ni: 0.65%–0.80%, Cu: 0.25%–0.50%, Ca: 0.020%–0.050%, Mg: 0.001%–0.005%, Zr: 0.002%–0.010%, Cr: 0.15%–0.30%, Mo: 0.10%–0.30%, V: 0.01%–0.07%, Re: 0.01%–0.050%, with the balance being Fe and unavoidable impurities.

[0008] Based on the above technical solution, furthermore, the chemical composition and weight percentage of the ultra-high strength crack-arresting steel are as follows: C: 0.035%–0.065%, Si: 0.30%–0.50%, Mn: 1.80%–2.00%, P: 0.003%–0.012%, S≤0.005%, Al: 0.005%–0.04%, Ti: 0.004%–0.015%, Ni: 0.65%. %~0.80%, Cu: 0.25%~0.50%, Ca: 0.020%~0.050%, Mg: 0.001%~0.002%, Zr: 0.002%~0.005%, Cr: 0.15%~0.30%, Mo: 0.15%~0.25%, V: 0.01%~0.06%, Re: 0.01%~0.025%, balance being Fe and unavoidable impurities.

[0009] Based on the above technical solution, the ultra-high strength crack-arresting steel has a thickness range of 60-90mm, a yield strength ≥500MPa, a tensile strength of 600-700MPa, an elongation after fracture ≥20%, a low-temperature impact energy at -40℃ ≥200J, a weld with a high heat input of 180kJ / cm or more and a low-temperature impact energy at -40℃ ≥140J, and a crack-arresting toughness Kca ≥8000N / mm. 3 / 2 .

[0010] The following details the mechanism of action of each alloy component in the crack-arresting steel of this invention, where the percentage symbol % represents a weight percentage:

[0011] Carbon (C) is the most effective strengthening alloying element, improving hardenability while also increasing the ductile-brittle transition temperature. To maintain strength, minimizing C content is beneficial for lowering the ductile-brittle transition temperature. For ultra-high-strength steel plates, a content above 0.03% is acceptable. However, exceeding a certain level significantly worsens the material's low-temperature toughness, crack-arresting toughness, and weldability. Furthermore, increasing C content also increases the tendency for retained austenite to form during cooling; therefore, the upper limit is 0.07%. The preferred C content is controlled between 0.035% and 0.065%.

[0012] Si is the main deoxidizing component in steelmaking. To achieve sufficient deoxidation, it must contain more than 0.10%. However, if it exceeds the upper limit, it will reduce the toughness of the base material and the weld. Si in solid solution form can increase strength and also increase the ductile-brittle transition temperature. Therefore, the Si content should be 0.10% to 0.50%.

[0013] Mn is an essential element for ensuring the strength and toughness of steel. Mn combines with S to form MnS, preventing hot cracking caused by FeS formation at grain boundaries. Mn is also a good deoxidizer. While manganese is a low-cost strengthening and toughening element, its content is too low to guarantee the material's strength. However, when the Mn content exceeds 2.00%, it exacerbates segregation in the cast billet and worsens the low-temperature toughness of the coarse-grained heat-affected zone (CGHAZ). Therefore, the preferred Mn content is 1.80%–2.00%.

[0014] P (phosphorus): An unavoidable impurity element in steel, it deteriorates the steel's toughness and weldability. Studies have shown that when the P content is higher than 0.02%, its embrittlement properties are significantly improved; therefore, the upper limit is preferably 0.012%.

[0015] If the sulfur (S) content exceeds 0.01%, it will form a large number of MnS inclusions in the steel. The formation of MnS inclusions and the resulting anisotropy severely reduce the toughness, plasticity, and weldability of the steel plate. Simultaneously, increasing the S content will increase the tendency of hot-rolled steel plates to hot crack. Therefore, measures are taken during the smelting process to minimize the S content in the steel. In this invention, the upper limit of the S content is determined to be 0.005%.

[0016] Al (Al): As a deoxidizing and grain-refining element, its content is generally above 0.005%, but exceeding 0.05% easily leads to hot cracking in the cast billet. Furthermore, the solid-state phase transformation product of Al-deoxidized steel is a small amount of PF + a large amount of BU. Ferrite laths grow without any restrictions, growing very easily and eventually intersecting at the original austenite grain center, resulting in very long lath bundles, essentially half the grain width. The presence of high-carbon MA components and carbides between these lath bundles leads to high brittleness and reduces the toughness of the welded steel plate. Therefore, the upper limit of Al content is 0.05%, with a preferred range of 0.005% to 0.04%.

[0017] Ni: As an austenite stabilizing element, increasing Ni can improve the solid solution strengthening effect. Nickel can lower the ferrite phase transformation temperature, refine the ferrite grain size, and play a role in grain refinement strengthening. In addition, it can promote the formation of acicular ferrite, which, while generating phase transformation strengthening, can also increase the grain boundary area, improve fracture toughness and crack arrest ability. Therefore, the preferred Ni content is between 0.65% and 0.80%.

[0018] Cu can significantly improve the hardenability and corrosion resistance of steel plates. It is also an austenite stabilizing element in steel. Appropriate addition can refine the microstructure of TMCP steel plates and improve low-temperature toughness. However, excessive addition will cause a tendency for "copper embrittlement", making it easy for cracks to appear on the surface and inside of the billet, reducing the mechanical properties of the rolled steel plate, and reducing toughness, causing the steel plate to become embrittled. Therefore, the Cu content in this invention is controlled at 0.25% to 0.50%.

[0019] Mg / Zr composite addition: Mg / Zr has a strong affinity for O and is a typical oxide-forming element. The small-sized dispersed metal compounds can become nucleation sites that induce ferrite phase transformation. During high heat input welding, it can effectively suppress grain coarsening and improve the low-temperature toughness of the material after welding. The preferred Mg content range is 0.0010% to 0.0020%, and the Zr content range is 0.0020% to 0.0050%.

[0020] Ti: Trace amounts of titanium combine with C and N in steel to form fine and stable C and N compound particles. During the slab heating process, it can effectively prevent austenite grain coarsening. During welding, it can suppress the coarsening of weld heat-affected grains and improve the low-temperature toughness of the matrix structure and the heat-affected zone of the weld.

[0021] V: V is a precipitation strengthening element, especially at lower controlled rolling temperatures, where it can achieve good precipitation strengthening effects. In the welding thermal cycle, the combination of V and N is also an important means to inhibit grain boundary growth and migration. In this invention, a medium-low temperature TMCP final rolling and final cooling temperature is used to give full play to the strengthening effect of V, while its VN and other particles also play a good role in promoting high heat input welding. The preferred V content in this invention is 0.01% to 0.06%.

[0022] Mo: Mo can dissolve in ferrite and austenite and combine with C to form carbides of various compositions. Molybdenum can improve the hardenability of steel, and its effect is stronger than chromium but slightly weaker than manganese. It is an effective strengthening element and is beneficial to improving the cooling effect of thick steel plates. At the same time, as an effective element to promote the transformation of microstructure at medium and low temperatures, Mo also has a certain grain refinement effect. However, adding a large amount of Mo will not only increase the carbon equivalent and impair weldability, but also increase the cost of steel plates. Therefore, its content should be controlled at 0.15% to 0.25%.

[0023] Ca: Calcium treatment modifies inclusions. CaO combines with Al2O3 inclusions to form calcium aluminate, which floats into the slag. Simultaneously, Ca combined with S to form CaS, which can coat alumina into spherical shapes, reducing the proportion of MnS formation and thus improving the transverse properties of the steel plate. In this invention, the formation of CaS and fine-sized CaO mainly obtains austenite intragranular mass transfer-induced phase deformation nuclei, which can refine grains and improve material toughness. Therefore, the preferred Ca content is 0.020%–0.050%, Ca / S ≥ 5, and the ratio of remaining Ca to S after combination needs to be greater than 1.5.

[0024] Cr: Chromium is a weak carbide-forming element. Adding a certain amount of Cr can improve the hardenability of steel plates and promote the formation of strengthening structures represented by bainite. It can replace some of the strengthening elements such as C and Mn, reducing the toughness deterioration caused by the former's increased strength. However, adding a high amount of Cr can also lead to the deterioration of weldability. Therefore, under the TMCP process, the preferred Cr content range is between 0.15% and 0.30%.

[0025] Re: Rare earth elements can significantly reduce the deterioration caused by the segregation of low-melting-point elements at grain boundaries in steel, thereby improving strength and toughness by purifying grain boundaries; they can also change the distribution and morphology of sulfides in steel, especially MnS inclusions in steel that are prone to forming fine strips during hot rolling, resulting in obvious directionality of the steel and severely deteriorating transverse properties. The preferred content is 0.01% to 0.025%.

[0026] This invention also provides a method for manufacturing the aforementioned ultra-high strength crack-arresting steel suitable for high heat input welding, mainly including smelting, refining, continuous casting, heating, rolling, cooling, and slow cooling stacking processes; wherein,

[0027] The heating temperature during the heating process is 1100–1150℃, and the holding time is 0.8–1.5 min / mm. This temperature setting is because temperatures below 1100℃ are insufficient to allow alloying elements to completely dissolve into the austenite, making it impossible to guarantee the final rolling temperature required for hot rolling. Temperatures above 1150℃, on the other hand, cause significant coarsening of the original austenite grains, which reduces the low-temperature toughness of the steel plate.

[0028] The rolling process is divided into two stages: the first stage rolling is carried out in the austenite recrystallization zone, and the second stage rolling is carried out in the non-recrystallization zone.

[0029] The cooling process is laminar flow cooling, with an initial cooling temperature of over 690℃ and a final cooling temperature of under 570℃, and the cooling rate is controlled at 2-5℃ / s.

[0030] During the slow cooling process of stacking, the initial slow cooling temperature is between 350 and 450°C, and the stacking time is not less than 48 hours.

[0031] Based on the above technical solution, further, the heating temperature during the heating process is 1100~1145℃, and the holding time is 1.0~1.2min / mm.

[0032] Based on the above technical solution, further, the initial rolling temperature of the first stage rolling is 1000℃~1050℃, and the cumulative reduction is not less than 50%; the initial rolling temperature of the second stage rolling is 770℃~810℃, the final rolling temperature is 730℃~760℃, the cumulative reduction is not less than 50%, and the thickness of the intermediate billet is 2 to 3 times the thickness of the finished product.

[0033] Based on the above technical solution, the initial cooling temperature is 690–760℃, and the final cooling temperature is 530–570℃.

[0034] Based on the above technical solution, the smelting process is further carried out in a top-and-bottom combined blowing converter, using low-carbon / low-aluminum molten iron with C≤0.12% and Al≤0.05%.

[0035] Based on the above technical solution, the smelting process further adopts a high-pulling carbon single-point blowing method for production.

[0036] Based on the above technical solution, the refining process is further carried out in a vacuum refining furnace. Zr, Mg, and Ca are added to the steel by wire feeding, and the amount of Mg added to the molten steel is controlled to be 15-30 ppm, the amount of Zr added to be 30-60 ppm, and the amount of Ca added to be 300-500 ppm. During the vacuum treatment, FeOx cored wire is fed in to increase oxygen, and the amount of oxygen added to the molten steel is controlled to be 7-16 ppm. Argon gas is blown into the molten steel through the argon gas hole at the bottom of the tank to stir it. The argon blowing flow rate is controlled to make the surface of the molten steel slightly tumble, and the diameter of the exposed surface of the molten steel is ≤70 mm. The stirring time is 5-8 min. After stirring is completed, the steel is poured into the furnace within 15 min.

[0037] Based on the above technical solution, further, the superheat during the continuous casting process is ≤25℃, dynamic light reduction and electromagnetic stirring at the end of the crystallizer are adopted, the light reduction is 5~15mm, the secondary cooling adopts segmented cooling, the front section is strong cooling with a cooling rate of 15~40℃ / s, the rear section is weak cooling with a cooling rate of 10~20℃ / s, the continuous casting billet pulling speed is 0.6~1.0m / min, and the casting slab thickness is 300~360mm.

[0038] The advantages of this invention over the prior art are as follows:

[0039] 1) This invention, through the adoption of a suitable composition system and metallurgical process design for high-heat-input welding, and through precise microstructure control, obtains thick crack-arresting steel plates with ultra-high strength, brittle fracture crack-arresting toughness, and high heat input welding characteristics (FCB and gas-electric vertical welding) with a welding heat input of over 180 kJ / cm. The thickness ranges from 60 to 90 mm, with a yield strength ≥ 500 MPa, tensile strength 600–700 MPa, elongation after fracture ≥ 20%, and a low-temperature impact energy of ≥ 200 J at -40℃. The weld after high-heat-input welding with a heat input of over 160 kJ / cm has a low-temperature impact energy of ≥ 140 J at -40℃, and a crack-arresting toughness Kca ≥ 8000 N / mm². 3 / 2 It meets the requirements of key structural components such as ultra-large container ships and offshore platforms, and is suitable for the manufacturing of large equipment with high fracture toughness and high heat input welding requirements.

[0040] 2) The composition system of this invention is controlled by low C and low Mn, i.e. low carbon equivalent composition, to ensure the weldability and low-temperature toughness of the material. Low carbon and appropriate toughening elements are used to improve the low-temperature toughness of the material. Elements such as Mg / Zr, Ti and Ca are combined with O and N to form nitrogen oxides that inhibit the growth and coarsening of austenite grains. The grains are refined by promoting the nucleation of acicular ferrite during the austenite transformation process, thus solving the problem of matching strength and toughness in high heat input welding.

[0041] 3) This invention achieves a comprehensive effect of fine grain, precipitation and phase transformation strengthening by adding appropriate amounts of toughening elements and using precise smelting and TMCP processes. Appropriate amounts of strengthening elements such as Ni, Cu, and Cr are added to compensate for the insufficient strength caused by low carbon content, and to avoid the deterioration of low-temperature toughness, crack arrest performance and weldability.

[0042] 4) The crack-arresting steel obtained by the present invention has a microstructure mainly composed of fine lath B+ acicular ferrite, and the average grain size of the obtained base material is less than 10μm, which realizes effective control of grain size and thus ensures the matching of strength and toughness. Attached Figure Description

[0043] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0044] Figure 1 This is a microstructure image of the ultra-high strength crack-arresting steel prepared in Example 3 of the present invention.

[0045] Figure 2 The image shows the HAZ microstructure of the ultra-high strength crack-arresting steel prepared in Example 3 after welding at 230 KJ / cm. Detailed Implementation

[0046] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0047] Examples 1-5

[0048] This embodiment provides a method for manufacturing BCA2 type ultra-high strength crack arresting steel suitable for high heat input welding. The chemical composition and weight percentage of the ultra-high strength crack arresting steel are shown in Table 1.

[0049] Table 1. Chemical composition and weight percentage (%) of the ultra-high strength crack-arresting steels in Examples 1-5

[0050]

[0051] Includes the following steps:

[0052] (1) Smelting: Low-carbon / low-aluminum clean molten iron is used as raw material. The smelting process adopts high-carbon one-time blowing method. The main elements of steel are adjusted to the range of Table 1 in the converter, and other alloy components are added as required for smelting.

[0053] (2) Refining: The molten steel from the converter is subjected to secondary refining to further reduce the content of harmful impurities such as O, S, and non-metallic inclusions; Zr, Mg and Ca are added to the steel by wire feeding, and the amount of Mg added to the molten steel is controlled to be 15-30 ppm, the amount of Zr added to be 30-60 ppm, and the amount of Ca added to be 300-500 ppm; FeOx cored wire is fed into the molten steel ladle during vacuum treatment to increase oxygen, and the amount of oxygen added to the molten steel is controlled to be 7-16 ppm; Argon gas is blown into the molten steel through the argon gas hole at the bottom of the ladle to stir, and the argon blowing flow rate is controlled to make the surface of the molten steel tumble slightly, the diameter of the exposed surface of the molten steel is ≤70 mm, and the stirring time is 5-8 min; after stirring is completed, it is poured into the machine within 15 min.

[0054] (3) Continuous casting: The superheat of the molten steel in the tundish needs to be controlled at ≤25℃. Dynamic light pressure of 5~15mm and electromagnetic stirring at the end of the crystallizer are adopted. The secondary cooling adopts segmented cooling, with strong cooling in the front section and a cooling rate of 15~40℃ / s, and weak cooling in the back section and a cooling rate of 10~20℃ / s. The continuous casting billet pulling speed is 0.6~1.0m / min, and the thickness of the cast slab is 300~360mm.

[0055] (4) Heating: The above slab is heated. The heating temperature and holding time are shown in Table 2.

[0056] (5) Rolling: First, rolling is carried out in the austenite recrystallization zone, and then rolling is carried out in the non-recrystallization zone. The rolling is controlled in two stages. The initial rolling temperature, the second rolling temperature, the final rolling temperature and the thickness of the intermediate billet are shown in Table 2. The cumulative reduction of each stage of rolling is not less than 50%.

[0057] (6) Cooling: The cooling method is laminar flow cooling. The start-up cooling temperature, final cooling temperature and cooling rate are shown in Table 2.

[0058] (7) Stacking and slow cooling: After the steel plates are off the production line, they should be stacked and slow cooled. The starting temperature for slow cooling should be between 350 and 450°C, and the stacking time should be no less than 48 hours.

[0059] Table 2. Preparation process parameters of ultra-high strength crack-arresting steel in Examples 1-5

[0060]

[0061] The welding process parameters of the ultra-high strength crack-arresting steels in Examples 1-5 are shown in Table 3, and the mechanical properties of the ultra-high strength crack-arresting steels in each example are shown in Table 4.

[0062] Table 3 Welding processes for ultra-high strength crack-arresting steels in Examples 1-5

[0063]

[0064] Table 4 Mechanical properties of ultra-high strength crack-arresting steels in Examples 1-5

[0065]

[0066] As shown in Table 4, the BCA2 type ultra-high strength crack-arresting toughness steel prepared by this invention has an impact energy of ≥210J in the base material at -40℃, and an impact energy of ≥140J in the weld heat-affected zone after welding with a high heat input of ≥180KJ / cm, both of which exceed the requirements of the International Classification Society standard.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-strength crack-arresting steel suitable for high heat input welding, characterized in that, The chemical composition and weight percentage are as follows: C: 0.030%~0.070%, Si: 0.10%~0.50%, Mn: 1.80%~2.00%, P≤0.012%, S≤0.005%, Al: 0.005%~0.04%, Ti: 0.004%~0.015%, Ni: 0.65%~0.80%, Cu: 0.25%~0.50%, Ca: 0.020%~0.050%, Mg: 0.001%~0.005%, Zr: 0.002%~0.010%, Cr: 0.15%~0.30%, Mo: 0.10%~0.30%, V: 0.01%~0.07%, RE: 0.01%~0.050%, with the balance being Fe and unavoidable impurities; The ultra-high strength crack-arresting steel has a thickness range of 60~90mm, yield strength ≥500 MPa, tensile strength 600~700 MPa, elongation after fracture ≥20%, low-temperature impact energy at -40℃ ≥200J, weld impact energy at -40℃ after high heat input of 180kJ / cm or more ≥140J, and crack-arresting toughness Kca ≥8000N / mm 3 / 2 ; The manufacturing method of the ultra-high strength crack-arresting steel suitable for high heat input welding includes smelting, refining, continuous casting, heating, rolling, cooling, and slow cooling stacking processes; wherein, The heating temperature during the heating process is 1100~1150℃, and the holding time is 0.8~1.5min / mm; The rolling process is divided into two stages: the first stage rolling is carried out in the austenite recrystallization zone, and the second stage rolling is carried out in the non-recrystallization zone. The cooling process is laminar flow cooling, with an initial cooling temperature of over 690℃ and a final cooling temperature of under 570℃, and the cooling rate is controlled at 2-5℃ / s. During the slow cooling process of stacking, the initial slow cooling temperature is between 350 and 450°C, and the stacking time is not less than 48 hours.

2. The ultra-high strength crack-arresting steel suitable for high heat input welding according to claim 1, characterized in that, The chemical composition and weight percentage of the ultra-high strength crack-arresting steel are as follows: C: 0.035%~0.065%, Si: 0.30%~0.50%, Mn: 1.80%~2.00%, P: 0.003%~0.012%, S≤0.005%, Al: 0.005%~0.04%, Ti: 0.004%~0.015%, Ni: 0.65%~0.80%, Cu: 0.25%~0.50%, Ca: 0.020%~0.050%, Mg: 0.001%~0.002%, Zr: 0.002%~0.005%, Cr: 0.15%~0.30%, Mo: 0.15%~0.25%, V: 0.01%~0.06%, RE: 0.01%~0.025%, with the balance being Fe and unavoidable impurities.

3. The ultra-high strength crack-arresting steel suitable for high heat input welding according to claim 1, characterized in that, The heating temperature during the heating process is 1100~1145℃, and the holding time is 1.0~1.2min / mm.

4. The ultra-high strength crack-arresting steel suitable for high heat input welding according to claim 1, characterized in that, The initial rolling temperature for the first stage is 1000℃~1050℃, and the cumulative reduction is not less than 50%. The initial rolling temperature for the second stage is 770℃~810℃, and the final rolling temperature is 730℃~760℃, with a cumulative reduction of not less than 50%. The thickness of the intermediate billet is 2 to 3 times the thickness of the finished product.

5. The ultra-high strength crack-arresting steel suitable for high heat input welding according to claim 1, characterized in that, The initial cooling temperature is 690~760℃, and the final cooling temperature is 530~570℃.

6. The ultra-high strength crack-arresting steel suitable for high heat input welding according to claim 1, characterized in that, The smelting process is carried out in a top-and-bottom combined blowing converter, using low-carbon / low-aluminum molten iron with C≤0.12% and Al≤0.05%.

7. The ultra-high strength crack-arresting steel suitable for high heat input welding according to claim 1, characterized in that, The refining process is carried out in a vacuum refining furnace. Zr, Mg, and Ca are added to the steel by wire feeding, and the amount of Mg added to the molten steel is controlled to be 15~30ppm, the amount of Zr added to be 30~60ppm, and the amount of Ca added to be 300~500ppm. During the vacuum treatment, FeOx cored wire is fed in to increase oxygen, and the amount of oxygen added to the molten steel is controlled to be 7~16ppm. Argon gas is blown into the molten steel through the argon gas hole at the bottom of the tank to stir it. The argon flow rate is controlled to make the surface of the molten steel slightly tumble, and the diameter of the exposed surface of the molten steel is ≤70mm. The stirring time is 5~8min. After stirring is completed, the steel is poured into the machine within 15min.

8. The ultra-high strength crack-arresting steel suitable for high heat input welding according to claim 1, characterized in that, During the continuous casting process, the superheat is ≤25℃. Dynamic light reduction and electromagnetic stirring at the end of the crystallizer are adopted. The light reduction is 5~15mm. The secondary cooling adopts segmented cooling. The first segment is strong cooling with a cooling rate of 15~40℃ / s, and the second segment is weak cooling with a cooling rate of 10~20℃ / s. The continuous casting billet pulling speed is 0.6~1.0m / min, and the casting slab thickness is 300~360mm.

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