Steel for ultra-high heat input welding and its manufacturing method

Abstract

The manufacturing method of ultra-large heat input welding steel and the manufactured welding steel adopt advantageous control of oxide-based inclusions in steel plate, adopt low-temperature large reduction rolling to produce, and control the rolling process to control the size and distribution of oxides in the steel plate, thereby achieving the manufacturing of ultra-large heat input welding steel. The method has low production costs, easy-to-control production process, simple operation, is suitable for mass production, and has excellent mechanical properties and welding heat effect properties of the base material.

Description

[Technical field]

[0001] The present application belongs to the technical field of steel rolling, and specifically relates to a steel for ultra-high heat input welding and a method for producing the same.

[0002] This application claims priority to a Chinese patent application filed with the China Patent Office on March 13, 2023, bearing application number 202310238411.3 and entitled "Steel for ultra-high heat input welding and manufacturing method thereof," the entire contents of which are incorporated herein by reference. [Background technology]

[0003] In the fields of large steel structures such as ships, buildings, and bridges, welding is a key manufacturing process, and increasing heat input can improve welding efficiency and shorten the manufacturing cycle of construction works. Especially for thick steel plates, traditional welding methods require multiple passes of welding and cumbersome auxiliary work before welding and between layers, but by adopting a high heat input welding method, it can be formed in one pass, and the production efficiency is improved by several or even tens of times. Therefore, in various construction fields, the manufacturing of large steel welded structures tends to adopt a high heat input welding method, which significantly reduces manufacturing costs and improves production efficiency.

[0004] General steel for high heat input welding can withstand a heat input of 100 to 400 kJ / cm. However, with the development of industries such as construction and ships, there is a growing demand for welding techniques with greater heat input. In order to ensure the safety and reliability of construction structures, steel materials are required to have high mechanical properties even with an ultra-high heat input of 500 to 1500 kJ / cm.

[0005] In the prior art, some high-strength steels for ultra-large heat input welding and manufacturing methods have been provided, but most of them need to add a large amount of expensive components such as nickel element or calcium magnesium core wire or zirconium calcium core wire during the smelting of steel to improve the low-temperature toughness of the welded joint under the high heat input welding conditions, thus greatly increasing the production cost. In addition, these technologies all improve the performance of steel in terms of alloy composition, and in the operation of the process, it is difficult to control the content of components, which makes the smelting process longer and reduces the production efficiency.

[0006] If it were possible to provide a method for producing high-strength steel for ultra-high heat input welding that does not require expensive components and shortens the smelting process, the future would be promising. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the technical problem to be solved by the present application is to provide a steel for ultra-high heat input welding and a manufacturing method thereof by solving the defects of the prior art, such as high production cost, high control difficulty, and low production efficiency of the steel for ultra-high heat input welding. [Means for solving the problem]

[0008] Therefore, the present application provides the following technical solutions: The present application, The steelmaking step involves converting smelting into steel and refining into steel using an LF furnace, followed by casting of slabs; A rolling step in which the slab is heated and two-stage rolling is adopted, the first stage rolling is the rolling of the recrystallized region with a rolling temperature of 900-1000°C and a rolling reduction rate per pass of more than 20%, and the steel plate is allowed to stand for a certain temperature. When the temperature drops to 800°C or lower, the second stage rolling is the rolling of the non-recrystallized region, and the rolling reduction rate per pass is greater than 20%. The total compression ratio of the rolling steps is controlled to 5 or more, and the compression ratio of the second stage rolling accounts for 65-75% of the total compression ratio. and a cooling step after the rolling step is completed.

[0009] Optionally, the final rolling temperature of the first rolling step is 900 to 950° C.; and / or The final rolling temperature in the rolling step is controlled to be within a range of 20 to 50° C. higher than the ferrite transformation start temperature Ar3.

[0010] Optionally, the reduction rate per pass in the first rolling step is 21 to 23%, and / or The reduction rate per pass in the second rolling stage is 21-26%.

[0011] Optionally, the slab heating temperature is 1050-1150° C., and the slab heating time is 330 min or more.

[0012] Optionally, the slab heating time is 330-350 min.

[0013] Optionally, the cooling rate in the cooling step is 11° C. / s or more, and the final cooling temperature is controlled within a range of 20 to 40° C. above the bainite transformation start temperature Bs, and then air-cooled to 350° C. or less.

[0014] Here, Ar3=910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35(H-8), the unit of Ar3 is °C, and H is the target steel sheet thickness in mm.

[0015] Optionally, in the converter smelting step, the ratio of hot metal to clean iron scrap is 7-8:1, and the hot metal temperature is 1350-1450°C.

[0016] Optionally, in the casting step, the casting temperature is controlled to 1540 to 1560° C., and the drawing speed is controlled to 1.1 to 1.3 m / min.

[0017] Optionally, the chemical composition of the slab includes C: 0.05-0.16 wt%, Si: 0.1-0.4 wt%, Mn: 0.9-1.6 wt%, P≦0.01 wt%, S: 0.003-0.02 wt%, Cr: 0.05-0.20 wt%, Ni: 0.1-0.4 wt%, Ti: 0.02-0.04 wt%, Ca: 0.001-0.0025 wt%, and the remainder is Fe and unavoidable impurities.

[0018] The actions of the components contained in the present application and the selection of the amounts used will be specifically explained below. S: S is the main element that causes hot brittleness during hot rolling and should be controlled within a reasonable range. S combines with Mn in steel to form MnS inclusions. Especially when the Mn content in steel is high, the formed MnS is not only large in number but also large in size. During hot rolling, MnS elongates along the rolling direction due to plasticity, and MnS inclusion bands are formed along the rolling direction, which seriously impairs the low-temperature impact toughness, elongation and Z-direction properties of the steel plate. Cr: Cr can effectively improve the hardenability of steel plate. When its content is greater than 0.1%, it can form a microstructure based on fine needle ferrite when combined with the rapid cooling process. However, if its content is too high, it will have a negative effect on the welding performance of the steel plate. Ni: Ni is an effective element for improving strength and low-temperature toughness. However, if the Ni content is too high, the scale of the steel plate is difficult to remove, thereby affecting the surface quality of the steel plate. Moreover, since Ni is expensive, adding too much of it increases the production cost.

[0019] The present application further provides a steel for ultra-high heat input welding produced by the above production method.

[0020] Optionally, in the ultra-high heat input welding steel, the base metal has a yield strength of 460 MPa or more, a tensile strength of 560 to 620 MPa, an elongation of 26% or more, and a -40°C impact energy of 280 J or more.

[0021] Selectively, under the condition of welding heat input of 600 kJ / cm, the tensile strength of the welded heat affected zone is 580 MPa or more, and the -40°C impact energy is 220 J or more. Effect of the Invention

[0022] The technical solution of the present application has the following advantages:

[0023] The method for producing steel for ultra-large heat input welding according to the present application includes a steelmaking step of performing converter smelting and LF furnace refining and casting a slab, a rolling step of heating the slab and employing two-stage rolling, in which the first stage of rolling is rolling of the recrystallized region at a rolling temperature of 900-1000°C and a reduction rate per pass of more than 20%, waiting for the temperature of the steel sheet, and when the temperature drops to 800°C or lower, performing a second stage of rolling which is rolling of the unrecrystallized region, with a reduction rate per pass of more than 20%, controlling the total compression ratio of the rolling steps to 5 or more, and making the compression ratio of the second stage of rolling account for 65-75% of the total compression ratio of the rolling steps, and a cooling step after completion of rolling. This application is the first to overturn the traditional concept of oxide metallurgy and adopt low-temperature large reduction rolling technology to produce steel for ultra-large heat input welding, and by limiting the reduction rate per pass and total compression ratio in two-stage rolling, and the compression ratio of the second-stage rolling, combined with the TMCP process, the size and distribution of oxides in the steel plate are controlled, solving the difficult problem of controlling the dense distribution of oxide inclusion particles in the steel plate, and realizing the production of steel for ultra-large heat input welding. This method not only has the characteristics of low production cost, easy-to-control production process, simple operation, and suitable for mass production, but also does not need to control the oxide content by adding expensive components in the steelmaking stage, shortens the rolling cycle, improves production efficiency, and has high added value, mainly excellent in the mechanical properties of the base material and the performance of the welded heat affected zone, and especially under the welding conditions of large heat input, the low-temperature toughness of the welded heat affected zone is stable, so that it can be widely applied to various large and ultra-large steel structures that require high-efficiency welding. From the perspective of downstream welding users, the present application further improves welding efficiency, greatly reduces the burden of welding work, saves the users' welding labor costs, and also greatly shortens the users' time to manufacture steel members, bringing huge value to the users.

[0024] The manufacturing method of steel for ultra-high heat input welding according to the present application invents a technology for advantageously controlling oxide-based inclusions in steel plate, and by increasing the compression ratio of rolling and the reduction per pass, the size of metal oxide inclusions in the steel plate is controlled to be smaller than the effective grain size, fine inclusions are sufficiently dispersed and distributed, and the formation of needle ferrite within the grains is promoted. In addition, the present application also makes it possible to control the areal density of oxides in the steel plate, the content and size of needle ferrite, etc., by limiting parameters, and further realizes control over the performance of the steel plate.

[0025] The steel for ultra-high heat input welding according to the present application is manufactured by a specific method according to the present application, and in the manufactured steel plate, the needle ferrite has a content of 75% or more and a size of 17 μm or less, and the base material has a yield strength of 460 MPa or more, a tensile strength of 560 to 620 MPa, an elongation of 26% or more, and a -40°C impact energy of 280 J or more, and under the condition of a welding heat input of 600 kJ / cm, the weld heat affected zone has a tensile strength of 580 MPa or more, and a -40°C impact energy of 220 J or more. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The following examples are provided for a better understanding of the present application, and are not limited to the above-mentioned best embodiment, and are not intended to limit the content and scope of protection of the present application. Any products identical or similar to those of the present application that someone obtains by combining the teachings of the present application or the features of the present application with other prior art are within the scope of protection of the present application.

[0027] In the examples, unless specific experimental steps or conditions are specified, the procedures or conditions of conventional experimental steps described in the literature in the field may be followed. Unless the manufacturers are specified, the reagents or equipment used are all ordinary reagent products available from commercial sources. Examples and Comparative Examples

[0028] The manufacturing method of steel for ultra-high heat input welding includes the following steps.

[0029] 1. Component design and steelmaking process The chemical composition of the steel plate includes C: 0.05-0.16 wt%, Si: 0.1-0.4 wt%, Mn: 0.9-1.6 wt%, P≦0.01 wt%, S: 0.003-0.02 wt%, Cr: 0.05-0.20 wt%, Ni: 0.1-0.4 wt%, Ti: 0.02-0.04 wt%, Ca: 0.001-0.0025 wt%, and the remainder is Fe and unavoidable impurities. Steelmaking process: In the converter steelmaking step, the ratio of the amount of molten iron to clean iron scrap is 7-8:1, and the temperature of the molten iron is 1350-1450℃. Ferromanganese, ferrosilicon, and lime are added in sequence to melt the molten iron. In the LF refining, the main focus is on controlling inclusions and adjusting the alloy components, adding metal manganese, ferrosilicon, etc. to adjust the molten steel components, measuring the temperature after current application, sampling, then continuing diffusion deoxidation and temperature adjustment, finally sampling, measuring the oxygen content, and tapping. The casting temperature was controlled at 1540-1560℃, and the drawing speed was controlled at 1.1-1.3m / min to produce a continuous cast slab.

[0030] 2.Rolling process 1) Slab heating The heating temperature was controlled to 1050° C. to 1150° C., and the heating time was controlled to 330 to 350 min. 2) Slab rolling A two-stage controlled rolling was adopted, in which the first stage rolling was performed in the recrystallized region, where the rolling temperature was controlled above the recrystallization critical temperature, in the range of 900-1000°C, and the reduction rate per pass was greater than 20%. After that, the steel plate was allowed to cool, and when the temperature dropped to 800°C or below, the second stage rolling was performed, which was the rolling of the unrecrystallized region, with the reduction rate per pass being greater than 20% and the final rolling temperature being controlled in the range of 20-50°C higher than Ar3.

[0031] 3. Cooling process Immediately after the rolling is completed, the steel plate is transported to the accelerated cooling control device (ACC) at the maximum transport speed of the roller table, and the cooling rate is set to 11℃ / s or more, and the final cooling temperature is set to B s The temperature was controlled to within a range of 20 to 40°C higher than the initial temperature, and the steel plate was then naturally air-cooled to 350°C or lower.

[0032] The components and parameters in each of the examples and comparative examples are specifically controlled as follows.

[0033] [Table 1] JPEG2025513040000002.jpg106155

[0034] [Table 2]

[0035] [Table 3]

[0036] [Table 4] JPEG2025513040000006.jpg132155 Note: Ar3=910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35(H-8), H is the target steel plate thickness, the steel plate thickness is 50mm, and Bs=630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W.

[0037] [Table 5] JPEG2025513040000008.jpg160156

[0038] [Table 6]

[0039] Obviously, the above examples are merely illustrative and are not intended to limit the embodiments. Those skilled in the art can make various other changes or modifications based on the above description. It is not necessary and impossible to list all the embodiments here. Any obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for producing steel for ultra-high heat input welding, comprising the steps of: A steelmaking step of performing converter smelting and LF furnace refining and casting a slab; a rolling step in which the slab is heated and two-stage rolling is adopted, the first stage rolling is performed in a recrystallized region with a rolling temperature of 900-1000°C and a rolling reduction rate per pass of more than 20%, and the steel sheet is allowed to cool. When the temperature drops to 800°C or lower, the second stage rolling is performed in a non-recrystallized region, and the rolling reduction rate per pass is made greater than 20%. The total compression ratio of the rolling step is controlled to 5 or more, and the compression ratio of the second stage rolling accounts for 65-75% of the total compression ratio; and a cooling step after the rolling step is completed.

2. The final rolling temperature of the first stage rolling is 900 to 950° C. And / or, the final rolling temperature of the rolling step is set to the ferrite transformation start temperature Ar ３ 2. The method for producing steel for ultra-high heat input welding according to claim 1, wherein the temperature is controlled to be within a range of 20 to 50° C. higher than the temperature at which the welding is started.

3. Ar ３ = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35 (H-8), Ar ３ 3. The method for producing steel for ultra-high heat input welding according to claim 2, characterized in that the unit of is °C, and H is the target steel plate thickness in mm.

4. The reduction rate per pass in the first rolling step is 21 to 23%. and / or the reduction rate per pass in the second rolling step is 21 to 26%.

5. 2. The method for producing steel for ultra-high heat input welding according to claim 1, wherein the slab heating temperature is 1050 to 1150° C., and the slab heating time is 330 min or more.

6. The method for producing steel for ultra-high heat input welding according to claim 5, characterized in that the slab heating time is 330 to 350 min.

7. The cooling rate in the cooling step is 11 ° C. / s or more, 2. The method for producing steel for ultra-large heat input welding according to claim 1, characterized in that the final cooling temperature is controlled to within a range of 20 to 40° C. higher than the bainite transformation start temperature Bs, and then air-cooled to 350° C. or lower.

8. 8. The method for producing steel for ultra-high heat input welding according to claim 7, wherein Bs=630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W, and the unit of Bs is °C.

9. The method for producing steel for ultra-large heat input welding as claimed in claim 1, characterized in that in the converter smelting step, the ratio of the amount of molten iron to the amount of clean iron scrap is 7-8:1, and the temperature of the molten iron is 1350-1450°C.

10. The method for producing steel for ultra-high heat input welding according to claim 1, characterized in that, in the casting step, the casting temperature is controlled to 1540 to 1560°C, and the drawing speed is controlled to 1.1 to 1.3 m / min.

11. The method for producing steel for ultra-large heat input welding according to any one of claims 1 to 10, characterized in that the chemical components of the slab include C: 0.05-0.16 wt%, Si: 0.1-0.4 wt%, Mn: 0.9-1.6 wt%, P≦.0.01 wt%, S: 0.003-0.02 wt%, Cr: 0.05-0.20 wt%, Ni: 0.1-0.4 wt%, Ti: 0.02-0.04 wt%, Ca: 0.001-0.0025 wt%, and the remainder being Fe and unavoidable impurities.

12. A steel for ultra-high heat input welding, A steel for ultra-high heat input welding, characterized in that it is produced by the production method according to any one of claims 1 to 11.

13. The steel for ultra-high heat input welding according to claim 12, characterized in that the base material has a yield strength of 460 MPa or more, a tensile strength of 560 to 620 MPa, an elongation of 26% or more, and a -40°C impact energy of 280 J or more.

14. The steel for ultra-high heat input welding according to claim 13, characterized in that, under the condition of a welding heat input of 600 kJ / cm, the tensile strength of the welded heat affected zone is 580 MPa or more and the -40°C impact energy is 220 J or more.

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