MANUFACTURING PROCESS FOR ULTRA-HIGH HEAT INPUT WELDING STEEL

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to Chinese Patent Application No. 202310238411.3, filed to the China Patent Office on March 13, 2023 and entitled "Ultra-high Heat Input Welding Steel and Preparation Method therefor".TECHNICAL FIELD

[0002] The present application belongs to the technical field of steel rolling, and particularly relates to ultra-high heat input welding steel and a preparation method therefor.BACKGROUND

[0003] In the fields of ships, architectures, bridges and other large steel structures, welding is a key link of manufacturing, and increasing heat input may improve the welding efficiency, and shorten an engineering manufacturing cycle. Especially for thick steel plates, a conventional welding method requires multiple passes of welding molding, and requires tedious auxiliary work before welding and between layers as well, while adopting a high heat input welding method may achieve once pass molding, and the production efficiency is improved several times or dozens of times. Therefore, in each engineering field, the manufacturing of large steel welding structures tends to adopt the high heat input welding method to significantly reduce manufacturing costs and improve the production efficiency.

[0004] General high heat input welding steel may bear heat input between 100 kJ / cm and 400 kJ / cm, however, with the development of architectures, ships and other industries, further requirements are put forward for a higher heat input welding technology, and rolled steel is required to still have a high mechanical property at a 500-1500 kJ / cm ultra-high heat input, so as to ensure the safety and reliability of the engineering structure.

[0005] In the prior art, some ultra-high heat input welding high-strength steel and production methods are provided, however, a large amount of nickel elements or components with high prices such as calcium magnesium cored wires and zirconium calcium cored wires are mostly required to be added in a smelting process of rolled steel to improve low-temperature toughness of a welded joint under a high heat input welding condition, thereby greatly increasing the production cost. In addition, these technologies will improve the property of the rolled steel from the perspective of alloy compositions, it is difficult to control constituent contents on technological operation, the smelting process is prolonged, and the production efficiency is reduced.

[0006] It will have a wide application prospect in a case that a method for producing ultra-high heat input welding high-strength steel with high properties, without expensive components and with a shortened smelting process may be provided.

[0007] CN 114 703 424 A discloses a high heat input welding steel plate which comprises the following chemical components in percentage by mass: less than or equal to 0.1% of C, less than or equal to 0.15% of Si, less than or equal to 0.004% of S, 1.5-4.5% of Mn + Cr + Ni + Cu, 0.03-0.3% of Ti + Mg + Zr + Ca, 0.03-0.2% of Ti + Mg and the balance of Fe and inevitable impurities, the mass ratio of Cr to Ni to Cu is 1: 2: 1, the carbon equivalent Ceq is 0.36-0.42, and Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15. The percentage content of acicular ferrite of the steel plate is 80% or above, the size of the acicular ferrite is 15 microns or below, the yield strength is larger than or equal to 430 MPa, the tensile strength is 550-620 MPa, the ductility is larger than or equal to 25%, and the impact energy at the temperature of-40 DEG C is larger than or equal to 300 J; under the condition that the welding heat input is 600kJ / cm, the tensile strength of a welding heat affected zone is greater than or equal to 540MPa, and the impact energy at-40 DEG C is greater than 150J; and the anti-crack property Kca is greater than or equal to 8500N / mm < 1.5 >. In the manufacturing process of the steel plate, a zirconium-calcium cored wire is added during RH refining, a plate blank is formed through continuous casting after RH tapping, and the plate blank is subjected to recrystallization region rolling and non-recrystallization region rolling, so that formation of acicular ferrite can be promoted, and the crack arrest performance of the steel plate is improved. CN 104 726 787 A discloses a thick steel plate with good low temperature toughness.SUMMARY OF THE INVENTION

[0008] Therefore, the present application aims to solve the technical problem that defects such as high production cost, large control difficulty, and low production efficiency of ultra-high heat input welding steel in the prior art are overcome, so as to provide ultra-high heat input welding steel and a preparation method therefor.

[0009] Thus, the present application provides the following technical solutions: The present application provides a method for preparing ultra-high heat input welding steel, including the following steps: a steelmaking step: casting into a slab after converter smelting and LF furnace refining; a rolling step: heating the slab, two-stage rolling being adopted, wherein first-stage rolling is recrystallization zone rolling, a rolling temperature is in a range from 900°C to 1000°C, and a single pass reduction rate is greater than 20%; performing temperature-holding on a steel plate, and performing second-stage rolling when the temperature drops to 800°C or below, wherein the second-stage rolling is non-recrystallization zone rolling, and an adopted single pass reduction rate is greater than 20%; and controlling a total compression ratio in the rolling step to be 5 or above, wherein a compression ratio of the second-stage rolling accounts for 65-75% of the total compression ratio; and a cooling step: performing cooling after the rolling step is completed, wherein a finish rolling temperature of the first-stage rolling is in a range from 900°C to 950°C, and the finish rolling temperature of the rolling step is controlled within a range from 20°C to 50°C above a starting temperature Ar 3 of ferritic transformation; wherein Ar 3 =910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35(H-8), a unit of Ar 3 is °C, H is a target steel plate thickness, and a unit is mm; wherein a heating temperature of the slab is in a range from 1050°C to 1150°C, and heating time of the slab is 330 min or above; wherein a cooling speed in the cooling step is 11°C / s or above, and a finish cooling temperature is controlled within a range from 20°C to 40°C above a starting temperature B s of bainite transformation, and then is reduced to 350°Cor below through air-cooling; wherein B s =630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W, and a unit of B s is °C; wherein in a converter smelting step, a ratio of a molten iron content to clean scrap steel is (7-8):1, and a molten iron temperature is in a range from 1350°C to 1450°C; wherein in a casting step, a casting temperature is controlled at a range from 1540°C to 1560°C, and a casting speed is controlled at a range from 1.1 m / min to 1.3 m / min; wherein, in percentage by weight, chemical components of the slab comprise: 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 Fe and inevitable impurities.

[0010] Optionally, the single pass reduction rate in the first-stage rolling process is in a range from 21% to 23%; and / or, the single pass reduction rate in the second-stage rolling process is in a range from 21% to 26%.

[0011] Optionally, the heating time of the slab is in a range from 330 min to 350 min.

[0012] The action and dosage selection of components contained in the present application are specifically described below: S: as a main element generating hot shortness in a hot rolling process, should be controlled within a reasonable range; and S is combined with Mn in steel to form MnS inclusions, especially when an Mn content in the steel is high, the formed MnS is not only numerous, but also huge in size, and in the hot rolling process, the plasticity of MnS makes MnS extend in a rolling direction, so as to form an MnS inclusion belt in the rolling direction, which seriously damages low-temperature impact toughness, ductility and Z-direction property of a steel plate. Cr: being capable of effectively improving the hardenability of the steel plate, when the content is greater than 0.1%, combining with an ultra-rapid cooling technology, a structure based on fine acicular ferrite is formed, however, excessive content will also generate an adverse effect on a welding property of the steel plate. Ni: an effective element for improving strength and low-temperature toughness; however, excessive Ni content will cause difficult removal of oxide skin of the steel plate, such that the surface quality of the steel plate is affected, and Ni is expensive, which will increase manufacturing costs after being excessively added.

[0013] The present application further provides ultra-high heat input welding steel, prepared by the above preparation method.

[0014] Optionally, according to the ultra-high heat input welding steel, a yield strength of a base material is 460 Mpa or above, a tensile strength is in a range from 560 Mpa to 620 Mpa, a ductility is 26% or above, and -40°C impact energy is 280 J or above; and optionally, under the condition of welding heat input being 600 kJ / cm, a tensile strength of a welding heat affected zone is 580 Mpa or above, and -40°C impact energy is 220 J or above.

[0015] The technical solutions of the present application have the following advantages: The method for preparing the ultra-high heat input welding steel provided by the present application includes the following steps: the steelmaking step: casting into the slab after converter smelting and LF furnace refining; the rolling stage: heating the slab, two-stage rolling being adopted, wherein the first-stage rolling is recrystallization zone rolling, the rolling temperature is in a range from 900°C to 1000°C, and the single pass reduction rate is greater than 20%; performing temperature-holding on the steel plate, and performing second-stage rolling when the temperature drops to 800°C or below, wherein the second-stage rolling is non-recrystallization zone rolling, and the adopted single pass reduction rate is greater than 20%; controlling the total compression ratio in the rolling step to be 5 or above, wherein the compression ratio of the second-stage rolling accounts for 65-75% of the total compression ratio; and the cooling stage: performing cooling after rolling is completed. The present application breaks through a traditional idea of oxide metallurgy for the first time, adopts a low-temperature large reduction rolling technology to produce the ultra-high heat input welding steel, regulates and controls sizes and distribution of oxides in the steel plate by limiting the single pass reduction rate and the total compression ratio in the two-stage rolling, and the compression ratio in the second-stage rolling and combining with a TMCP technology, and solves the problem of controlling dense distribution of oxide inclusion particles in the steel plate, thereby preparing the ultra-high heat input welding steel. The method has the characteristics of low production cost, easily-controlled production process, simple operation, and suitability for scale production, meanwhile, the oxide content is not controlled by adding expensive components in the steelmaking stage, thus a rolling cycle is shortened, and the production efficiency is improved; and the method further has a high additional value, which is mainly reflected in an excellent mechanical property of the base material and an excellent welding heat affected zone property, especially under a welding condition of high heat input, low temperature toughness of the welding heat affected zone is stable, and the thus method may be widely applied to a variety of large and extra-large steel structures requiring efficient welding. From the point of view of downstream welding users, the present application further improves the welding efficiency, greatly reduces the welding labor strength, saves work welding costs of the users, greatly shortens time of the users for manufacturing steel members at the same time, and creates great value for the users.

[0016] According to the method for preparing the ultra-high heat input welding steel provided by the present application, the beneficial control technology for the oxide inclusions in the steel plate is invented, by increasing the rolling compression ratio and the single pass reduction rate, sizes of metallic oxide inclusions in the steel plate are controlled to be lower than valid grain sizes, and thus slight inclusions are fully dispersed and distributed, which promotes generation of intragranular acicular ferrite. In addition, the present application may further regulate and control the area density of oxides in the steel plate, the content and size of the acicular ferrite and the like through limitation of parameters, and then regulates and controls properties of the steel plate.

[0017] The ultra-high heat input welding steel provided by the present application is prepared by adopting the specific method of the present application. A percentage content ratio of the acicular ferrite in the prepared steel plate is 75% or above, the size of the acicular ferrite is 17 µm or below, the yield strength of the base material is 460 Mpa or above, the tensile strength is in a range from 560 Mpa to 620 Mpa, the ductility is 26% or above, and the -40°C impact energy is 280 J or above; and under the condition of welding heat input being 600 kJ / cm, the tensile strength of the welding heat affected zone is 580 Mpa or above, and -40°C impact energy is 220 J or above.DETAILED DESCRIPTION

[0018] Following examples are provided for better further understanding the present application, which is not limited to the preferable embodiment, and do not limit contents and the scope of protection of the present application.

[0019] Specific experimental procedures or conditions not indicated in the examples may be performed in accordance with operations or conditions of conventional experimental procedures described in the literature in the field. Used reagents or instruments are all conventional reagent products that can be purchased through the market if not indicated with manufactures.Example and Comparative example

[0020] A method for preparing ultra-high heat input welding steel includes the following steps:1. Component design and steelmaking technology

[0021] In percentage by weight, chemical components of a steel plate include: 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 Fe and inevitable impurities.

[0022] The steelmaking technology: a ratio of converter steelmaking molten iron content to clean scrap steel is (7-8):1, a molten iron temperature is in a range from 1350°C to 1450°C, and ferromanganese, ferrosilicon and lime are sequentially added for smelting. LF refining is mainly to control inclusions and regulate alloy components, manganese metal, ferrosilicon and the like are added to regulate components of molten steel, temperature measurement and sampling are performed after being electrified, then continuous deoxidation by diffusion and temperature regulation are performed, and finally, sampling, oxide-stabilizing and steel tapping are performed. A casting temperature is controlled at a range from 1540°C to 1560°C, a casting speed is controlled at a range from 1.1 m / min to 1.3 m / min, and then a continuous cast slab is prepared.2. Rolling technology

[0023] 1) the slab is heated, a heating temperature is controlled in a range from 1050°C to 1150°C, and heating time is controlled at a range from 330 min to 350 min. 2) the slab is rolled, two-stage control rolling is adopted, first-stage rolling is recrystallization zone rolling, a rolling temperature is controlled to be above a recrystallization critical temperature, the range is in a range from 900°C to 1000°C, a single pass reduction rate is greater than 20%, then temperature-holding is performed on the steel plate, second-stage rolling is performed when the temperature drops to 800°C or below, the second-stage rolling is non-recrystallization zone rolling, an adopted single pass reduction rate is greater than 20%, and a finish rolling temperature is controlled within a range from 20°C to 50°C above Ar 3 . 3. Cooling technology

[0024] After rolling is completed, the steel plate is immediately transported to accelerated cooling control equipment (ACC) with a largest transport speed of a roller way, a cooling speed is required to be 11°C / s or above, a finish cooling temperature is controlled within a range from 20°C to 40°C above B s , and then the steel plate is naturally air cooled to be 350°C or below.

[0025] Specific control of components and parameters in each example and comparative example is as follows: Table 1. Chemical componentsChemical components (wt%)CSiMnPSCrNiNbTiCaExample 10.080.151.550.0080.0060.150.35\0.0300.0015Example 20.070.151.600.0070.0070.200.40\0.0300.0015Example 30.080.101.550.0080.0050.150.35\0.0300.002Example 40.080.151.550.0080.0060.150.35\0.0300.0015Example 50.070.151.600.0070.0050.200.40\0.0300.0015Example 60.080.101.550.0080.0060.150.35\0.0300.002Comparative example 10.080.101.550.0080.0060.150.35\0.0300.002Comparative example 20.080.151.550.0080.0060.150.35\0.0300.0015Comparative example 30.050.201.550.0080.0050.170.35\0.0300.0015Comparative example 40.060.201.550.0080.0050.170.35\0.0300.0015Comparative example 50.080.101.550.0080.0060.150.35\0.0300.002Comparative example 60.080.101.550.0080.0060.150.35\0.0300.002 Table 2. Steelmaking technology Molten iron: scrap steelMolten iron temperatureCasting temperatureCasting speedExample 17:11350-1450°C1540-1560°C1.2m / minExample 27:11350-1450°C1540-1560°C1.2m / minExample 37:11350-1450°C1540-1560°C1.2m / minExample 47:11350-1450°C1540-1560°C1.2m / minExample 57:11350-1450°C1540-1560°C1.2m / minExample 67:11350-1450°C1540-1560°C1.2m / minComparative example 17:11350-1450°C1540-1560°C1.2m / minComparative example 27:11350-1450°C1540-1560°C1.2m / minComparative example 37:11350-1450°C1540-1560°C1.2m / minComparative example 47:11350-1450°C1540-1560°C1.2m / minComparative example 57:11350-1450°C1540-1560°C1.2m / minComparative example 67:11350-1450°C1540-1560°C1.2m / min Table 3. Rolled steel heating and cooling technologies Slab heating temperatureHeating timeCooling speedFinish cooling temperatureExample 11150°C330min11.5°C / s570°CExample 21150°C335min11.3°C / s573°CExample 31150°C332 min11.2°C / s576°CExample 41150°C330min11.5°C / s570°CExample 51150°C335min11.3°C / s572°CExample 61150°C332 min11.2°C / s575°CComparative example 11150°C332 min11.2°C / s576°CComparative example 21150°C330min11.5°C / s570°CComparative example 31150°C332 min11.2°C / s583°CComparative example 41150°C330min11.3°C / s580°CComparative example 51150°C332 min11.2°C / s575°CComparative example 61150°C332 min11.2°C / s575°C Table 4. Rolling technology Recrystallization zone start rolling temperature°CSingle pass reduction rateRecrystallization zone finish rolling temperature°CNon-recrystallization zone starting rolling temperatureSingle pass reduction rateNon-recrystallization zone finish rolling temperatureTotal compression ratioSecond-stage compression ratioExample 195021%-23%91077021%-26%75064Example 296021%-23%92076521 %-26%74564Example 395021%-23%91077021%-26%75064Example 495021%-23%91077021%-26%75075Example 596021%-23%92076521 %-26%74575Example 695021%-23%91077021%-26%75075Comparative example 195015%-20%91077010%-15%75053Comparative example 295015%-20%91077010%-15%75053Comparative example 395015%-20%92080510%-15%78653Comparative example 495015%-20%92580310%-15%78553Comparative example 595021%-23%91077021%-26%75042Comparative example 695015%-20%91077015%-20%75075 Note: Ar 3 =910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35(H-8), H is a target steel plate thickness, and each steel plate thickness is 50 mm; and B s =630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W. Table 5. Base material property of steel plate and welded joint property Type of steelBase material propertyWelded joint propertyYield strength MPaTensile strength MPaDuctility%-40°C impact energy JWelding heat input kJ / cmTensile strength MPaCGHAZ -40°Cimpact energy JExample 1EH4046356127306,301,298500563233,225,239Example 2EH4047558026316,285,301500575235,236,245Example 3EH4046458326287,298,306500571226,241,23 3Example 4EH4047359128316,321,308600583233,225,23 9Example 5EH4049561026336,325,331600595235,236,24 5Example 6EH4048460327307,328,326600591226,241,23 3Comparative example 1EH4043355425241,230,221400521124,136,11 5Comparative example 2EH4041854824222,218,247400534154,164,13 8Comparative example 3EH4042354724191,180,19840053085,64,67Comparative example 4EH4043553925202,188,19740052876,74,69Comparative example 5EH4043154424223,201,230400523134,125,14 0Comparative example 6EH4042455125201,220,211400538111,130,13 2 Table 6. Steel plate physical property Ferrite ratio, %Acicular ferrite size, µmArea density of oxides in steel plateExample 176171230Example 277161250Example 376171230Example 482141450Example 583121480Example 683121470Comparative example 16323950Comparative example 26223940Comparative example 36025920Comparative example 46025930Comparative example 56522970Comparative example 66423960

[0026] Obviously, the above examples are only intended to clearly illustrate the given instances, but do not limit embodiments. For those of ordinary skill in the art, other variations or changes in different forms may further be made within the scope of the appended claims. It is not necessary or possible to exhaust all embodiments herein. Obvious variations or changes derived therefrom still remain within the scope of the appended claims.

Claims

1. A method for preparing ultra-high heat input welding steel, comprising the following steps: a steelmaking step: casting into a slab after converter smelting and LF furnace refining; a rolling step: heating the slab, two-stage rolling being adopted, wherein first-stage rolling is recrystallization zone rolling, a rolling temperature is in a range from 900°C to 1000°C, and a single pass reduction rate is greater than 20%; performing temperature-holding on a steel plate, and performing second-stage rolling when the temperature drops to 800°C or below, wherein the second-stage rolling is non-recrystallization zone rolling, and an adopted single pass reduction rate is greater than 20%; and controlling a total compression ratio in the rolling step to be 5 or above, wherein a compression ratio of the second-stage rolling accounts for 65-75% of the total compression ratio; and a cooling step: performing cooling after the rolling step is completed; wherein a finish rolling temperature of the first-stage rolling is in a range from 900°C to 950°C, and the finish rolling temperature of the rolling step is controlled within a range from 20°C to 50°C above a starting temperature Ar3 of ferritic transformation; wherein Ar3=910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35(H-8), a unit of Ar3 is °C, H is a target steel plate thickness, and a unit is mm; wherein a heating temperature of the slab is in a range from 1050°C to 1150°C, and heating time of the slab is 330 min or above; wherein a cooling speed in the cooling step is 11°C / s or above, and a finish cooling temperature is controlled within a range from 20°C to 40°C above a starting temperature Bs of bainite transformation, and then is reduced to 350°Cor below through air-cooling; wherein Bs=630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W, and a unit of Bs is °C; wherein in a converter smelting step, a ratio of a molten iron content to clean scrap steel is (7-8):1, and a molten iron temperature is in a range from 1350°C to 1450°C; wherein in a casting step, a casting temperature is controlled at a range from 1540°C to 1560°C, and a casting speed is controlled at a range from 1.1 m / min to 1.3 m / min; wherein, in percentage by weight, chemical components of the slab comprise: 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 Fe and inevitable impurities.

2. The method for preparing ultra-high heat input welding steel according to claim 1, wherein the single pass reduction rate in the first-stage rolling process is in a range from 21% to 23%; and / or, the single pass reduction rate in the second-stage rolling process is in a range from 21% to 26%.

3. The method for preparing ultra-high heat input welding steel according to claim 1, wherein the heating time of the slab is in a range from 330 min to 350 min.