CN102766748B - Production method of low-temperature steel plate capable of being welded at high heat input - Google Patents

Abstract

The invention relates to a production method of a low-temperature steel plate that can be welded with large heat input. The production method includes: molten iron pretreatment→re-blowing converter smelting→LF refining→RH refining→wire feeding→continuous casting, LF refining to produce white slag, titanium Iron is added at the RH station, and when the molten steel temperature reaches 1570-1600°C and the dissolved oxygen content of the molten steel reaches 20-80ppm, break through and feed 200-400 meters of magnesium alloy or The calcium alloy cored wire is continuously cast to obtain a continuous casting slab. After the continuous casting slab is reheated and kept warm, the low temperature steel plate that can be welded with large heat input can be obtained through controlled rolling and controlled cooling. The steel plate has excellent low-temperature toughness, Charpy impact energy at -80°C > 47J, and Charpy impact energy at -60°C in the heat-affected zone after welding with a heat input of 500-600kJ/cm > 47J, and can be widely used in ships and low-temperature pressure vessels. , offshore platforms and other energy construction engineering fields.

Description

A production method of a low-temperature steel plate that can be welded with large heat input

technical field

The invention belongs to the field of manufacturing low-temperature steel medium-thick plates with excellent welding performance, and in particular relates to a production method of low-temperature steel plates that can be welded with large heat input.

Background technique

Due to the continuous improvement of energy demand, the demand for low-temperature steel in the fields of shipbuilding, bridges, natural gas pipelines, and offshore platforms is also increasing; the use of welding steel plates with a large heat input (≥200kJ/cm) can significantly improve welding efficiency and shorten construction. Therefore, low-temperature steel that can be welded with large heat input has been widely used in the field of energy construction.

Industrial mass production of steel plates that can be welded with large heat input usually includes processes such as molten steel smelting and finished steel plate rolling (or including heat treatment). The process flow usually used in molten steel smelting is: molten iron pretreatment→converter smelting, adding aluminum block during the tapping process of the converter to carry out deep deoxidation of molten steel→LF refining, adding and fine-tuning alloy elements→RH vacuum treatment, purifying molten steel→continuous casting, And obtain the continuous casting slab that meets the requirements of subsequent rolling. Prior art (such as JP 2007-293648, JP 2007-235974, CN100519809C, CN100447278C) involves adding strong oxide forming elements such as Ti/Ca/Zr/Mg/REM in the LF refining process, the purpose is to Form uniform and dense fine oxide particles, and then use these oxide particles to pin the grain boundaries to inhibit the growth of austenite grains in high temperature environments, thereby improving the low temperature impact performance of the welding heat affected zone, and achieving improved steel plate The purpose of welding performance. However, the above-mentioned technology has the following disadvantages:

1) The most important process parameters in this technology are not studied, such as the type of alloy to be added, the way of alloy addition, the order of alloy addition, the timing of alloy addition (namely, the temperature of molten steel before alloy addition, the dissolved oxygen content in molten steel ), etc.; the above process parameters directly determine the type, size and areal density of the final oxide, which in turn directly determines the welding performance of the final steel plate product.

2) Deep deoxidation is done by adding aluminum blocks in converter tapping, which will introduce a certain amount of solid solution aluminum in molten steel; since aluminum is a strong deoxidizing element, and its affinity with oxygen is greater than that of other alloy elements, the existence of aluminum in molten steel has a serious impact on The chemical reaction between the addition of strong deoxidizer and molten steel leads to the formation of larger alumina or alumina-based composite oxides in molten steel, which loses the purpose of improving the welding performance of steel plates by pinning austenite grain boundaries.

Another way to improve welding performance is to increase the process of feeding silicon-calcium wire between RH treatment and continuous casting. The principle is to form a certain amount of Sulfides, oxides and composite oxysulfide particles in a dispersed distribution (JP 2004-176100, JP 2004-10951, JP 2003-286540, JP 2005-220379, JP 2005-68478, JP 2010 -77494, CN101545077B), these fine and dense particles can improve the welding performance of the final steel plate by hindering the grain boundary movement and inhibiting the growth of austenite at high temperature. However, since this technology requires a certain amount of S, it is easy to cause coarse sulfides and deteriorate the toughness.

Contents of the invention

The object of the present invention is to provide a production method capable of welding low-temperature steel plates with large heat input. The steel plate produced according to this process has excellent impact toughness at -80°C (Akv-80°C>47J). Under the condition of welding heat input as high as 500-600kJ/cm, it can ensure that the welding heat-affected zone meets the impact toughness requirements of -60°C ( Akv-60°C > 47J). It makes it possible to complete the welding of steel plates with a thickness of 50mm and below in a single pass, which greatly improves the welding efficiency and can meet the needs of structural steel for ships and offshore platforms in cold regions. While ensuring structural safety, it can greatly improve construction efficiency.

In order to realize the above-mentioned purpose of the invention, the present invention has adopted following technical scheme:

The molten steel smelting process is as follows: molten iron pretreatment → reblowing converter smelting → LF refining → RH refining → wire feeding → continuous casting. The goals of the pretreatment of the molten iron are: the temperature of the molten iron ≥ 1350°C, the S ≤ 0.003% in weight percentage, and the slag removal rate ≥ 95%. During the smelting process of the converter, the ratio of the amount of molten iron used for charging to the scrap steel should be greater than 7, the basicity of the slag should be controlled between 3.5 and 4.5, and the MgO should be controlled between 8.0 and 10.0%. When the converter tapping accounts for 10-20% of the total capacity of the converter, ferromanganese, ferrosilicon and lime are added in sequence, and aluminum blocks are not used for deoxidation. White slag is produced during the LF refining process. At the same time, oxygen is fixed for molten steel, ferroboron is added, diffusion deoxidation is carried out, and molten steel samples are taken for composition fine-tuning. The tapping temperature is between 1610 and 1640 °C. In the RH vacuum treatment stage, the degassing time is ≥10 minutes. After oxygen measurement, when the dissolved oxygen in molten steel meets 10-100ppm, add ferrotitanium. After alloying, the net cycle time is ≥5 minutes, and when the molten steel temperature is 1570-1600℃ and Dissolved oxygen content of 20-80ppm is satisfied at the same time before breaking the air. After breaking the air, feed 200-400 meters of magnesium alloy or calcium alloy cored wire into the molten steel at a speed of 4-6 m/s. The diameter of the cored wire is 10 ~ 14mm, and then ensure that the soft stirring time is not less than 5 minutes. Before the ladle is hoisted away, add ultra-low carbonized rice husk to keep it warm. The casting temperature is 1570-1590° C., and the casting speed of the continuous casting slab is 1.0-1.4 m/s to obtain the continuous casting slab.

The components (percentage by weight) of the obtained continuous casting slab are: C≤0.07%, Si＜0.10%, Mn1.40～1.80%, Ti0.007～0.017%, Al＜0.01%, B0.0005～0.003%, P≤ 0.009%, S≤0.005%, and one or two of 0.0002-0.002% Mg, 0.0002-0.002% Ca, and the rest are iron and unavoidable impurity elements.

The billet rolling process is as follows: reheating in the heating furnace → rolling in the wide and thick plate rolling mill → cooling in the accelerated cooling system → air cooling on the roller table to room temperature.

The billet is reheated at a temperature of 1150-1200°C and heat-preserved for 2-3 hours. The rolling process adopts two-stage controlled rolling, in which the cumulative reduction rate in the first stage is ≥50%; the rolling temperature in the second stage is ≤860°C, and the reduction rate is ≥60%. After rolling, enter the accelerated cooling device and water-cool at a rate of 10-30°C/s to 350-500°C, and then air-cool to room temperature to obtain the target steel plate.

Compared with the prior art, the advantages of the present invention are at least:

1) For the first time, Mg/Ca strong deoxidizer was added by feeding the cored wire technology, and the speed, amount and timing of adding the cored wire (the temperature of the molten steel before feeding the wire, the content of dissolved oxygen), etc. were clearly stipulated. A large number of densely distributed fine oxide particles (area density of oxide particles with a size ≤ 2 μm ≥ 3000/mm ² ) are obtained in molten steel and continuous casting slab, which significantly improves the weldability of the final steel plate.

2) The smelting process excludes the use of Al deoxidation, reduces the content of solid-solution Al in molten steel, eliminates its interference with the reaction between the added strong deoxidizer and molten steel, enhances the reaction between the deoxidizer and molten steel, and significantly improves the target oxide The number of particles improves the weldability of the final steel plate.

3) The rolling process with low temperature and large reduction (cumulative reduction rate ≥ 80%) and the rapid cooling process (10-30°C/s) not only significantly improve the strength of the steel plate, but also ensure its low-temperature impact at -80°C Toughness, yield strength of final steel plate>400MPa, Akv-80℃>47J

Description of drawings

Fig. 1 is the base metal microstructure figure of steel embodiment 3 of the present invention;

Fig. 2 is a microstructure diagram of the coarse-grained heat-affected zone of Steel Example 3 of the present invention under the welding heat input of 500-600 kJ/cm.

specific implementation plan

The present invention will be further described below in conjunction with specific embodiment:

Example 1:

The molten steel smelting process is as follows:

Hot metal pretreatment→180t combined blowing converter smelting→LF refining→RH refining→wire feeding→continuous casting. During the converter smelting process, the ratio of the amount of molten iron for furnace charging to clean steel scrap is 7.5, the temperature of molten iron is 1400°C, S≤0.003% by weight, the basicity of slag is 3.5, and the ratio of MgO is 9.0%; Ferromanganese, ferrosilicon, lime. White slag is produced during the LF refining process. At the same time, the molten steel is oxygenated, ferroboron is added, diffusion deoxidized, and molten steel samples are taken for composition fine-tuning. In the RH vacuum treatment stage, measure oxygen and control the oxygen content at 10-100ppm before adding ferrotitanium. After the net circulation, the temperature of the molten steel is 1570-1600°C and the oxygen content is 20-80ppm. Feed 400 meters of magnesium alloy cored wire into the water, the diameter of the cored wire is 10mm, and then softly stir for 8 minutes. The casting temperature is controlled at 1570-1590° C., and the casting speed of the continuous casting slab is 1.1 m/s to obtain the continuous casting slab.

The chemical composition (percentage by weight) of the continuous casting billet includes C 0.03%, Si 0.08%, Mn 1.52%, Ti0.012%, Als 0.005%, B 0.0012%, Mg 0.0015%, P 0.007%, S 0.003%.

Billet rolling process is as follows:

Reheat the continuous casting slab with the above composition to 1180°C and keep it warm for 2 hours. After the furnace is released, the rough rolling start temperature is 1100°C, the thickness reduction is 220→100mm, and the cumulative reduction rate is 0.55; temperature; the start temperature of finish rolling is 860°C, the finish rolling temperature is 820°C, the thickness reduction is 100→40mm, and the cumulative reduction rate is 0.60; after rolling, the rolled plate is cooled to 500°C at a speed of 12°C/s and then air-cooled to room temperature. The thickness specification is the target steel plate of 40mm.

Physical performance of rolled plate

The yield strength of the rolled plate is 445MPa, the tensile strength is 542MPa, the elongation after fracture is 25.6%, and Akv-80℃=298J. The oxide particles in the rolled sheet are mainly titanium-magnesium composite oxide particles, and the surface density of oxide particles with a size ≤ 2 μm is ≥ 3100/mm ² .

The welding properties of the rolled plates are shown in Table 1.

Example 2:

The molten steel smelting process is as follows:

Hot metal pretreatment→180t combined blowing converter smelting→LF refining→RH refining→wire feeding→continuous casting. During the converter smelting process, the ratio of the amount of molten iron used for charging to clean steel scrap is 7, the temperature of molten iron is 1450°C, S≤0.003% by weight, the basicity of slag is 3.5, and the ratio of MgO is 9.0%; Ferromanganese, ferrosilicon, lime. During the LF refining process, white slag is produced, and ferroboron is added. At the same time, the molten steel is subjected to constant oxygen, diffusion deoxidation, and liquid steel samples are taken to fine-tune the composition. The tapping temperature is controlled at 1620-1640°C. In the stage of RH vacuum treatment, when the oxygen content of the molten steel meets the requirements of 10-100ppm, add ferrotitanium, and then measure the oxygen. Feed 350 meters of magnesium alloy cored wire with a diameter of 14mm into the molten steel at a speed of 2 seconds, and then softly stir for 6 minutes. The casting temperature is controlled at 1570-1590° C., and the casting speed of the continuous casting slab is 1.3 m/s to obtain the continuous casting slab.

The chemical composition of continuous casting billet is: C 0.03%, Si 0.09%, Mn 1.62%, Ti 0.012%, Als0.004%, B 0.0016%, Mg 0.0012%, P 0.007%, S 0.002%.

Billet rolling process is as follows:

Heat the continuous casting slab with the above composition to 1200°C and keep it warm for 2 hours. After coming out of the furnace, the rough rolling start temperature is 1080°C, the thickness reduction is 320→160mm, and the cumulative reduction rate is 0.50; The finish rolling start temperature is 850°C, the final rolling temperature is 810°C, the thickness reduction is 160→60mm, and the cumulative reduction rate is 0.63; after rolling, the rolled plate is cooled to 460°C at a speed of 15°C/s and then air-cooled to room temperature. The target steel plate with a thickness specification of 60mm.

Physical performance of rolled plate

The yield strength of the rolled plate is 427MPa, the tensile strength is 511MPa, the elongation after fracture is 26.5%, and Akv-80℃=288J. The oxide particles in the rolled sheet are mainly titanium-magnesium composite oxide particles, and the surface density of oxide particles with a size ≤ 2 μm is ≥ 3220/mm ² .

The welding properties are shown in Table 1.

Example 3:

The molten steel smelting process is as follows:

Hot metal pretreatment→180t combined blowing converter smelting→LF refining→RH refining→wire feeding→continuous casting. During the converter smelting process, the ratio of the amount of molten iron used for charging to clean steel scrap is 8, the temperature of the molten iron is 1430°C, S≤0.003% by weight, and the basicity of the slag is 3.5; ferromanganese and ferrosilicon are added sequentially when tapping about 35 tons of steel ,lime. White slag is produced during the LF refining process. At the same time, oxygen is fixed for molten steel, ferroboron is added, and the composition is fine-tuned. The tapping temperature is controlled at 1620-1640 °C. In the RH vacuum stage, when the oxygen content of the molten steel meets the requirements of 10-100ppm, add ferrotitanium, and then measure the oxygen. After the oxygen content of the molten steel meets 20-80ppm, feed it into the molten steel for 380 meters at a speed of 4.5 m/s. A length of calcium alloy cored wire with a diameter of 12 mm cored wire was then soft stirred for 9 minutes. The casting temperature is controlled at 1570-1590° C., and the casting speed of the continuous casting slab is 1.2 m/s to obtain the continuous casting slab.

The chemical composition (percentage by weight) of the continuous casting billet is: C 0.05%, Si 0.05%, Mn 1.65%, Ti0.011%, Als 0.0065%, B 0.0014%, Ca 0.0014%, P 0.006%, S 0.002%.

Billet rolling process is as follows:

Heat the continuous casting slab with the above composition to 1200°C and keep it warm for 2 hours. After being out of the furnace, the rough rolling start temperature is 1120°C, the thickness reduction is 320→150mm, and the cumulative reduction rate is 0.53; The starting temperature of finish rolling is 870°C, the final rolling temperature is 800°C, the thickness reduction is 150→60mm, and the cumulative reduction rate is 0.60; after rolling, the rolled plate is cooled to 420°C at a speed of 18°C/s and then air-cooled to room temperature. The target steel plate with a thickness specification of 60mm.

Physical performance of rolled plate

The yield strength of the rolled plate is 418MPa, the tensile strength is 508MPa, the elongation after fracture is 28.3%, and Akv-80℃=268J. The oxide particles in the rolled sheet are mainly titanium-calcium composite oxide particles, and the surface density of oxide particles with a size ≤ 2 μm is ≥ 3220/mm ² .

The welding properties are shown in Table 1.

The invention can produce low-temperature steel plates that can be welded with large heat input on the existing large-scale production platform of the steel plant through detailed and accurate smelting process control, controlled rolling and controlled cooling process of continuous casting blanks, and the yield strength of the steel plate is >400MPa , -80°C Charpy impact energy > 47J, and high heat input (500 ~ 600kJ/cm) welding can still ensure that the toughness of HAZ at -60°C meets the requirements. According to the production method of the present invention, it is possible to stably and continuously produce steel plates for low-temperature welding with large heat input required in fields such as energy construction projects (ships, offshore platforms) in cold regions.

Table 1 embodiment steel plate weldability

Claims (4)

1. A production method of a low-temperature steel plate that can be welded with large heat input, adopts molten iron pretreatment, converter smelting, LF refining, RH refining, wire feeding and continuous casting process, and is rolled by the usual pure steel process, characterized in that, In the smelting process, the ratio of molten iron for converter charging to steel scrap is greater than 7, and ferromanganese, ferrosilicon and lime are added in sequence when tapping; LF refining makes white slag, adding ferroboron, and the tapping temperature is 1610-1640°C; RH station, Guaranteed degassing time ≥ 10 minutes, when the dissolved oxygen content of the molten steel is 10-100ppm, add ferrotitanium, and when the molten steel temperature is 1570-1600℃ and the dissolved oxygen content of the molten steel is 20-80ppm at the same time, break the air and feed magnesium alloy into the molten steel And/or calcium alloy cored wire, then softly stirred for more than 5 minutes, and finally obtained continuous casting slab through continuous casting; the obtained continuous casting slab composition in weight percentage is: C≤0.07%, Si<0.10%, Mn 1.40～ 1.80%, Ti 0.007～0.017%, Al＜0.01%, B 0.0005～0.003%, P≤0.009%, S≤0.005%, and one or both of 0.0002～0.002%Mg, 0.0002～0.002%Ca, The rest is iron and unavoidable impurity elements; In the rolling process, the reheating temperature of the continuous casting slab is 1150-1200°C and heat preservation treatment for 2-3 hours, followed by controlled rolling and controlled cooling, wherein the cumulative rolling reduction rate in the rolling stage is ≥80%, and the two-stage rolling Temperature ≤ 860°C, two-stage rolling reduction rate ≥ 60%; after rolling, the steel plate is water-cooled to 350-500°C at a rate of 10-30°C/s, and then air-cooled to room temperature. 2. The production method of a low-temperature steel plate that can be welded with large heat input as claimed in claim 1, wherein the argon blowing control valve at the bottom of the ladle is opened before tapping the converter, and when the tapping of the converter accounts for 10 to 20% of the total capacity of the converter Add ferromanganese, ferrosilicon and lime in turn. 3. The method for producing low-temperature steel plates that can be welded with large heat input as claimed in claim 1, characterized in that 200-400 meters of magnesium alloy is fed into the molten steel at a speed of 4-6 m/s during the wire feeding process Or calcium alloy cored wire. 4. The production method of low-temperature steel plate that can be welded with large heat input as claimed in claim 3, characterized in that the diameter of the magnesium alloy or calcium alloy cored wire is 10-14 mm.

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