A high heat input weldable steel and a method for manufacturing the same

Abstract

The present application belongs to the technical field of steel rolling, and particularly relates to a super-large linear energy welding steel and a preparation method thereof. The present application breaks through the traditional oxide metallurgy idea for the first time, and invents a beneficial control technology of steel plate oxide inclusions. The super-large linear energy welding steel is produced by using a low-temperature large reduction rolling technology. The size and distribution of the oxide inclusions in the steel plate are controlled by controlling the rolling process, so that the super-large linear energy welding steel is prepared. The method has the characteristics of low production cost, easy control in the production process, simple operation and suitability for scale production. Meanwhile, the problem of compact distribution control of the oxide inclusion particles in the steel plate is solved. The method also has high added value, and the main performance is excellent mechanical properties and welding heat affected performance of the base material. Especially under the condition of large heat input welding, the low-temperature toughness of the welding heat affected zone is stable, so the method can be widely applied to various large and super-large steel structures which need high-efficiency welding.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of steel rolling, and particularly relates to a super-large line energy welding steel and a preparation method thereof. BACKGROUND

[0002] In the fields of large steel structures such as ships, buildings and bridges, welding is a key link in manufacturing, and increasing line energy can improve welding efficiency and shorten the engineering manufacturing cycle. In particular, for thick steel plates, conventional welding methods require multiple passes to form, and require tedious auxiliary work before and between layers, while using a large line energy welding method can form in one pass, and the production efficiency is increased by several or tens of times. Therefore, in various engineering fields, the manufacturing of large-scale welded steel structures tends to use a large line energy welding method to significantly reduce manufacturing costs and improve production efficiency.

[0003] Generally, the line energy that can be withstood by a large line energy welding steel is 100-400 kJ / cm, but with the development of the construction, shipbuilding and other industries, further requirements for higher line energy welding technology are put forward, and the steel material still has high mechanical properties under 500-1500 kJ / cm super-large line energy to ensure the safety and reliability of the engineering structure.

[0004] Some super-large line energy welding high-strength steels and production methods are provided in the prior art, but most of them need to add a large amount of nickel elements or calcium-magnesium cored wires, zirconium-calcium cored wires and other high-priced components during the smelting process of the steel to improve the low-temperature toughness of the welded joint under large heat input welding conditions, which will greatly increase the production cost. In addition, these technologies improve the performance of the steel from the alloy composition angle, and the control difficulty of the component content is large, which prolongs the smelting process and reduces the production efficiency.

[0005] If a production method of a super-large line energy welding high-strength steel without expensive components and shortening the smelting process can be provided, it will have wide application prospects. SUMMARY

[0006] Therefore, the technical problem to be solved by the present application is to overcome the defects of high production cost, large control difficulty and low production efficiency of the super-large line energy welding steel in the prior art, and to provide a super-large line energy welding steel and a preparation method thereof.

[0007] To this end, the present application provides the following technical solutions:

[0008] The present application provides a preparation method of a super-large line energy welding steel, comprising the following steps:

[0009] The steelmaking step: after converter smelting and LF furnace refining, the plate blank is poured;

[0010] Rolling step: slab heating, two-stage rolling, the first stage rolling is recrystallization zone rolling, the rolling temperature is 900-1000℃, the single pass reduction is greater than 20%; the steel plate is kept warm, when the temperature is reduced to 800℃ or below, the second stage rolling is carried out, the second stage rolling is non-recrystallization zone rolling, the single pass reduction is greater than 20%; the total compression ratio of the rolling stage is controlled to be 5 or more, and the second stage compression ratio accounts for 65-75% of the total compression ratio;

[0011] Cooling stage: after rolling is completed, cooling.

[0012] Optionally, the finish rolling temperature of the first stage rolling is 900-950℃;

[0013] And / or, the finish rolling temperature of the rolling stage is controlled to be 20-50℃ above the ferrite transformation start temperature Ar3.

[0014] Optionally, the single pass reduction during the first stage rolling is 21-23%;

[0015] And / or, the single pass reduction during the second stage rolling is 21-26%;

[0016] Optionally, the slab heating temperature is 1050-1150℃, and the slab heating time is 330min or more;

[0017] Optionally, the slab heating time is 330-350min.

[0018] Optionally, the cooling speed of the cooling step is 11℃ / s or more, the finish cooling temperature is controlled to be 20-40℃ above the bainite transformation start temperature Bs, and then air cooling is carried out to 350℃ or below.

[0019] Wherein, Ar3=910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35(H-8), H is the target steel plate thickness, unit: mm, Bs=630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W.

[0020] Optionally, in the converter smelting step, the ratio of molten iron and clean scrap steel is 7-8:1, and the molten iron temperature is 1350-1450℃.

[0021] Optionally, in the pouring step, the pouring temperature is controlled to be 1540-1560℃, and the drawing speed is controlled to be 1.1-1.3m / min.

[0022] Optionally, the slab has a chemical composition including, by weight percentage, C: 0.05-0.16%, Si: 0.1-0.4%, Mn: 0.9%-1.6%, P≤0.01%, S: 0.003-0.02%, Cr: 0.05-0.20%, Ni: 0.1-0.4%, Ti: 0.02-0.04%, Ca: 0.001-0.0025%, and the rest being Fe and inevitable impurities.

[0023] The following specifically describes the functions and dosage selection of the components contained in the present application:

[0024] S: as the main element causing hot shortness in the hot rolling process, should be controlled within a reasonable range; S combines with Mn in the steel to form MnS impurities, especially when the Mn content in the steel is high, the formed MnS is not only numerous in quantity, but also huge in size, and in the hot rolling process, the plasticity of MnS makes MnS extend along the rolling direction to form MnS impurity bands along the rolling direction, which seriously damages the low-temperature impact toughness, elongation and Z-direction performance of the steel plate.

[0025] Cr: can effectively improve the hardenability of the steel plate, when the content is greater than 0.1%, combined with ultra-fast cooling process, the microstructure with fine acicular ferrite as the matrix is formed, but too high content will adversely affect the welding performance of the steel plate.

[0026] Ni: an effective element for improving strength and low-temperature toughness; but too high Ni content will lead to difficulty in removing the oxide scale of the steel plate, thereby affecting the surface quality of the steel plate, and Ni is expensive, and excessive addition will increase the manufacturing cost.

[0027] The present application also provides a super large linear energy welding steel prepared by the above preparation method.

[0028] Optionally, the super large linear energy welding steel has a parent material yield strength of 460 MPa or more, a tensile strength of 560-620 MPa, an elongation of 26% or more, and a -40℃ impact energy of 280 J or more.

[0029] Optionally, under the condition of a welding heat input of 600 kJ / cm, the tensile strength of the welding heat affected zone is 580 MPa or more, and the -40℃ impact energy is 220 J or more.

[0030] The technical scheme of the present application has the following advantages:

[0031] The application provides a preparation method of the super-large linear energy welding steel, and comprises the following steps: a steelmaking step: through converter smelting and LF furnace refining, a slab is poured; a rolling stage: the slab is heated, two-stage rolling is adopted, the first stage rolling is recrystallization zone rolling, the rolling temperature is 900-1000 DEG C, and the single pass reduction is greater than 20 %; the steel plate is kept warm, when the temperature is reduced to below 800 DEG C, the second stage rolling is carried out, the second stage is non-recrystallization zone rolling, and the single pass reduction is greater than 20 %; the total compression ratio of the rolling stage is controlled to be greater than 5, and the second stage compression ratio accounts for 65-75 % of the total compression ratio; a cooling stage: after rolling, cooling is carried out. The application breaks through the traditional oxide metallurgy idea for the first time, adopts the low-temperature large reduction rolling technology to produce the super-large linear energy welding steel, and through the limitation of the single pass reduction and the total compression ratio in the two-stage rolling and the second stage compression ratio and the combination of the TMCP process, the oxide size and distribution in the steel plate are controlled, the dense distribution control problem of the oxide inclusions in the steel plate is solved, and the preparation of the super-large linear energy welding steel is realized. The method has the characteristics of low production cost, easy control in the production process, simple operation and suitability for scale production, meanwhile, the oxide content does not need to be controlled by adding expensive components in the steelmaking stage, the rolling cycle is shortened, and the production efficiency is improved; moreover, the method has high added value, mainly reflected in that the base material mechanical properties and the welding heat affected performance are excellent, especially under the large heat input welding condition, the low-temperature toughness of the welding heat affected zone is stable, so the method can be widely applied to various large and super-large steel structures which need high-efficiency welding. From the perspective of the downstream welding users, the welding efficiency is further improved, the welding labor intensity is greatly reduced, the labor cost of the users is saved, the time for manufacturing the steel structure of the users is greatly shortened, and great value is created for the users.

[0032] The application provides a preparation method of the super-large linear energy welding steel, and the beneficial control technology of the oxide inclusions in the steel plate is invented, the rolling compression ratio and the single pass reduction are increased, the size of the metal oxide inclusions in the steel plate is controlled to be lower than the effective grain size, the fine inclusions are fully dispersed and distributed, and the intracrystalline acicular ferrite is generated. In addition, the surface density of the oxides, the acicular ferrite content and the size in the steel plate can be controlled through the limitation of parameters, and then the performance of the steel plate is controlled.

[0033] The super-large linear energy welding steel is prepared by the specific method, the percentage of the acicular ferrite content in the prepared steel plate is more than 75 %, the size of the acicular ferrite is less than 17 μm, the yield strength of the base material is more than 460 Mpa, the tensile strength is between 560-620 Mpa, the elongation is more than 26 %, and the impact energy at-40 DEG C is more than 280 J; under the condition that the welding heat input is 600 kJ / cm, the tensile strength of the welding heat affected zone is more than 580 MPa, and the impact energy at-40 DEG C is more than 220 J. DETAILED DESCRIPTION

[0034] The following examples are provided to better enable those skilled in the art to further understand the application and are not intended to limit the scope of the application. Any product derived from the application or any combination of the application with other prior art features that is not specifically described herein is within the scope of the application.

[0035] Unless otherwise indicated, experimental procedures and conditions in the examples follow conventional procedures described in the literature. Unless otherwise indicated, reagents and instruments used are commercially available conventional reagents.

[0036] Examples and Comparative Examples

[0037] A method for preparing a high heat input welding steel includes the following steps:

[0038] 1. Component design and steelmaking process

[0039] The chemical composition of the steel plate includes, by weight percentage: C: 0.05-0.16%, Si: 0.1-0.4%, Mn: 0.9%-1.6%, P≤0.01%, S: 0.003-0.02%, Cr: 0.05-0.20%, Ni: 0.1-0.4%, Ti: 0.02-0.04%, Ca: 0.001-0.0025%, and the balance being Fe and unavoidable impurities.

[0040] The steelmaking process: the ratio of converter steelmaking molten iron and clean scrap steel is 7-8:1, the molten iron temperature is 1350-1450℃, and the molten iron is sequentially added with manganese iron, silicon iron, and lime for smelting. The LF refining mainly controls inclusions and adjusts alloy components, and metal manganese and silicon iron are added to adjust the composition of the molten steel. The temperature is measured and the sample is taken after the power is turned on, then the diffusion deoxidation and temperature adjustment are continued, and finally the sample is taken, the oxygen is determined, and the molten steel is tapped. The casting temperature is controlled at 1540-1560℃, the drawing speed is controlled at 1.1-1.3 m / min, and the continuous casting slab is prepared.

[0041] 2. Rolling process

[0042] 1) Slab heating, the heating temperature is controlled at 1050-1150℃, and the heating time is controlled at 330-350 min.

[0043] 2) slab rolling, two-stage controlled rolling, the first stage is recrystallization zone rolling, the rolling temperature is controlled above the recrystallization critical temperature, the range is 900-1000℃, single pass reduction is greater than 20%, then the steel plate is kept warm, when the temperature is reduced to below 800℃, the second stage rolling is performed, the second stage is non-recrystallization zone rolling, single pass reduction is greater than 20%, the finish rolling temperature is controlled above Ar3 20-50℃;

[0044] 3. Cooling process

[0045] After rolling, the steel plate is immediately transported to the accelerated cooling control device (ACC) at the maximum conveying speed of the roller, the cooling speed is required to be above 11℃ / s, the final cooling temperature is controlled in the range of above Bs 20-40℃, and then the steel plate is naturally air-cooled to below 350℃.

[0046] The specific control of the components and parameters in each example and comparative example is as follows:

[0047] Table 1 Chemical composition

[0048]

[0049]

[0050] Table 2 Steelmaking process

[0051] molten iron: scrap iron molten iron temperature casting temperature pulling speed Example 1 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Example 2 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Example 3 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Example 4 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Example 5 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Example 6 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Comparative Example 1 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Comparative Example 2 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Comparative Example 3 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Comparative Example 4 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Comparative Example 5 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min Comparative Example 6 7:1 1350-1450℃ 1540-1560℃ 1.2 m / min

[0052] Table 3 Steel rolling heating and cooling process

[0053] slab heating temperature heating time cooling rate final cooling temperature Example 1 1150℃ 330 min 11.5℃ / s 570℃ Example 2 1150℃ 335 min 11.3℃ / s 573℃ Example 3 1150℃ 332 min 11.2℃ / s 576℃ Example 4 1150℃ 330 min 11.5℃ / s 570℃ Example 5 1150℃ 335 min 11.3℃ / s 572℃ Example 6 1150℃ 332 min 11.2℃ / s 575℃ Comparative Example 1 1150℃ 332 min 11.2℃ / s 576℃ Comparative Example 2 1150℃ 330 min 11.5℃ / s 570℃ Comparative Example 3 1150℃ 332 min 11.2℃ / s 583℃ Comparative Example 4 1150℃ 330 min 11.3℃ / s 580℃ Comparative Example 5 1150℃ 332 min 11.2℃ / s 575℃ Comparative Example 6 1150℃ 332 min 11.2℃ / s 575℃

[0054] Table 4 Rolling process

[0055]

[0056]

[0057] 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; Bs = 630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W;

[0058] Table 5 Steel plate base material properties and welded joint properties

[0059]

[0060] Table 6 Steel plate physical properties

[0061]

[0062]

[0063] It is apparent that the above-described embodiments are merely illustrative for the sake of clarity and are not intended to limit the scope of the application. Other variations and modifications can be made by those skilled in the art based on the above description. All of the embodiments are not required to be exhaustive. The scope of the present application is defined by the appended claims rather than the embodiments described above.

Claims

1. A method of manufacturing a high heat input weldable steel, characterized in that, The method comprises the following steps: The steel plate is subjected to a second stage rolling when the temperature is reduced to below 800 DEG C, the second stage rolling is non-recrystallization zone rolling, and single pass reduction is greater than 20%; the total compression ratio of the rolling stage is controlled to be greater than 5, and the second stage compression ratio accounts for 65-75% of the total compression ratio; The cooling stage: after rolling is completed, cooling is performed; The chemical composition of the slab comprises, by weight percentage: C: 0.05~0.16%, Si: 0.1~0.4%, Mn: 0.9 %~1.6%, P≤0.01%, S: 0.003-0.02%, Cr: 0.05~0.20%, Ni: 0.1~0.4%, Ti: 0.02~0.04%, Ca: 0.001~0.0025%, and the rest is Fe and inevitable impurities. The final rolling temperature of the first stage rolling is 900-950 DEG C; And / or, the final rolling temperature of the rolling stage is controlled to be in the range of 20-50 DEG C above the ferrite transformation start temperature Ar3.

2. Process for the production of a high heat input weldable steel according to claim 1, characterized in that, The single pass reduction in the first stage rolling process is 21-23%. And / or, the single pass reduction in the second stage rolling process is 21-26%.

3. The method of manufacturing a high heat input weldable steel according to claim 1, characterized in that, The slab heating temperature is 1050-1150 DEG C, and the slab heating time is greater than 330 min. The cooling speed of the cooling stage is greater than 11 DEG C / s, the final cooling temperature is controlled to be in the range of 20-40 DEG C above the bainite transformation start temperature Bs, and then air cooling is performed to below 350 DEG C.

4. The method of manufacturing a high heat input weldable steel according to claim 1, characterized in that, In the converter smelting step, the ratio of molten iron and clean scrap steel is 7-8:1, and the molten iron temperature is 1350-1450 DEG C.

5. The method of manufacturing a high heat input weldable steel according to claim 1, characterized in that, In the pouring step, the pouring temperature is controlled to be 1540-1560 DEG C, and the drawing speed is controlled to be 1.1-1.3 m / min.

6. The method of manufacturing a high heat input weldable steel according to claim 1, characterized in that, The slab heating time is 330-350 min.

7. The method of manufacturing a high heat input weldable steel according to claim 1, characterized in that, 9. A super large heat input welding steel prepared by the preparation method of any one of claims 1-8.

8. The method of manufacturing a high heat input weldable steel according to claim 1, characterized in that, The base material yield strength is greater than 460 MPa, the tensile strength is between 560-620 MPa, the elongation is greater than 26%, and the -40 DEG C impact energy is greater than 280 J. Under the condition of a welding heat input of 600 kJ / cm, the tensile strength of the welding heat affected zone is greater than 580 MPa, and the -40 DEG C impact energy is greater than 220 J.

10. Steel for ultra-high heat input welding according to claim 9, characterized in that, ​ 11. The high heat input weldable steel according to claim 10, characterized in that, ​

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