CN112522566B

CN112522566B - Thin-specification patterned steel plate/strip and manufacturing method thereof

Info

Publication number: CN112522566B
Application number: CN201910889368.0A
Authority: CN
Inventors: 吴建春
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2019-09-19
Filing date: 2019-09-19
Publication date: 2022-10-21
Anticipated expiration: 2039-09-19
Also published as: CN112522566A; WO2021052429A1

Abstract

A thin specification pattern steel plate/belt and its manufacturing method, selectively add micro-alloy elements such as B in the steel; controlling the alkalinity of slag, the type and melting point of inclusions in steel, the content of free oxygen in molten steel and the content of acid-soluble aluminum Als in the smelting process; then, performing double-roller thin-strip continuous casting to cast strip steel with the thickness of 1.5-3mm, directly entering a lower closed chamber with non-oxidizing atmosphere after the strip steel exits from a crystallization roller, and entering an online rolling mill for hot rolling under the closed condition; the rolled strip steel is cooled by adopting an air atomization cooling mode, and the air atomization cooling mode can effectively reduce the thickness of oxide skins on the surface of the strip steel, improve the temperature uniformity of the strip steel and improve the surface quality of the strip steel. The finally produced steel coil can be directly used as a hot-rolled checkered plate/belt, can also be used as a finishing checkered plate/belt after edge cutting and flattening, and can be widely applied to the fields of building, mechanical manufacturing, automobiles, bridges, traffic, shipbuilding and the like.

Description

Thin-specification patterned steel plate/strip and manufacturing method thereof

Technical Field

The invention belongs to a continuous casting process and a product in the metallurgical industry, and particularly relates to a thin-specification patterned steel plate/strip and a manufacturing method thereof.

Background

The traditional thin strip steel is produced by casting blanks with the thickness of 70-200mm through multi-pass continuous rolling, and the traditional hot rolling process flow is as follows: continuous casting, casting blank reheating and heat preservation, rough rolling, finish rolling, cooling and coiling, namely firstly, a casting blank with the thickness of about 200mm is obtained through continuous casting, the casting blank is reheated and heat preserved, then rough rolling and finish rolling are carried out to obtain a steel strip with the thickness generally larger than 2mm, and finally laminar cooling and coiling are carried out to the steel strip to complete the whole hot rolling production process. The difficulty is relatively great if steel strip with a thickness of less than 1.5mm inclusive is to be produced, which is usually done by subsequent cold rolling and annealing of the hot rolled strip. And the process flow is long, the energy consumption is high, the number of unit equipment is large, the capital construction cost is high, and the production cost is high.

The thin slab continuous casting and rolling process flow is as follows: continuous casting, heat preservation and soaking of a casting blank, hot continuous rolling, cooling and coiling. The main differences between the process and the traditional process are as follows: the thickness of a casting blank in the thin slab process is greatly reduced to 50-90mm, and because the casting blank is thin, the casting blank can be reduced to the required specification before finish rolling only by carrying out 1-2 times of rough rolling (when the thickness of the casting blank is 70-90 mm) or not carrying out the rough rolling (when the thickness of the casting blank is 50 mm) on the casting blank, while the casting blank in the traditional process can be repeatedly rolled for multiple times; and the casting blank of the thin slab process directly enters a soaking pit furnace for soaking and heat preservation without cooling or a small amount of temperature compensation, so the thin slab process greatly shortens the process flow, reduces the energy consumption and the investment, and further reduces the production cost. However, the continuous casting and rolling of thin slabs can lead to the improvement of the strength of steel and the yield ratio due to the faster cooling speed, thereby increasing the rolling load, so that the thickness specification of the hot rolled products which can be economically produced cannot be too thin, generally being more than or equal to.5 mm, see Chinese patents CN200610123458.1, CN200610035800.2 and CN200710031548.2.

The ESP realizes the continuous casting of the plate blank, eliminates a heating furnace with the functions of flame cutting, heat preservation, soaking and plate blank transition, greatly shortens the length of the whole production line to about 190 meters, ensures that the plate blank continuously cast by a continuous casting machine has the thickness of 90-110mm and the width of 1100-1600mm, ensures that the continuously cast plate blank plays the role of heat preservation, soaking and heating through a section of induction heating roller table, and then sequentially enters the procedures of rough rolling, finish rolling, layer cooling and coiling to obtain the hot rolled plate. The process is rapidly developed and popularized at present, and a plurality of ESP production lines are operated and produced in the world at present.

The process flow shorter than the thin slab continuous casting and rolling is a thin strip continuous casting and rolling process, the thin strip continuous casting technology is a leading-edge technology in the fields of metallurgy and material research, the emergence of the technology brings a revolution to the steel industry, the production process of steel strips in the traditional metallurgy industry is changed, continuous casting, rolling, even heat treatment and the like are integrated into a whole, the produced thin slab is subjected to online hot rolling once to form a thin steel strip, the production process is greatly simplified, the production period is shortened, and the length of the process line is only about 50 m; the equipment investment is correspondingly reduced, the product cost is obviously reduced, and the method is a low-carbon and environment-friendly hot-rolled thin strip production process. The twin-roll thin strip continuous casting process is a main form of the thin strip continuous casting process and is the only thin strip continuous casting process for realizing industrialization in the world.

The typical process flow of twin roll strip casting is shown in fig. 1, molten steel in a ladle 1 is directly poured into a molten pool 7 surrounded by two relatively rotating and rapidly cooled crystallizing

rollers

8a, 8b and side sealing devices 6a, 6b through a ladle long nozzle 2, a tundish 3, a submerged nozzle 4 and a distributor 5, the molten steel is solidified on the circumferential surfaces of the rotating crystallizing

rollers

8a, 8b to form solidified shells and gradually grows, a steel strip 11 with the thickness of 1-5mm is formed at the minimum clearance (nip point) of the two crystallizing rollers, the steel strip is guided by a guide plate 9 to a pinch roller 12 and is fed into a rolling mill 13 to be rolled into 0.7-2.5mm thin strips, then the thin strips are cooled by a cooling device 14, cut ends by a flying shear device 16 and finally fed into a coiler 19 to be coiled.

In the face of the severe market situation of iron and steel enterprises, expanding the product structure and improving the economic benefit and competitiveness are the only way for the survival and development of the enterprises, and each large steel mill needs to produce products with higher competitiveness. The checkered plate is a hot-rolled steel plate with patterns on the surface, is used as a special hot-rolled plate strip product, is widely applied to the fields of buildings, mechanical manufacturing, automobiles, bridges, traffic, shipbuilding and the like, and has large market demand, particularly the market demand of the thin checkered plate is larger. As the requirements of the extremely thin checkered plate (less than or equal to 1.5 mm) on the rolling stability of a rolling mill and the shape of a coil of a coiling machine are high, domestic manufacturers are few, and the market price of the thin hot-rolled checkered plate is directly 120-200 yuan/ton higher than that of the checkered plate with the thickness of more than 2.0 mm. The product types mainly comprise a round bean-shaped checkered plate, a diamond-shaped checkered plate, a hyacinth bean-shaped checkered plate and the like, the hyacinth bean-shaped checkered plate is the main bean shape of the checkered plate due to the characteristics of wear resistance, attractiveness, skid resistance, no oil and water storage, easiness in cleaning, steel saving and the like, the application occasion and market demand are large, the price is high, the pattern becomes a high value-added benefit variety and a typical product of a hot continuous rolling enterprise, and all large steel mills are in competitive development and production.

When the hot-rolled strip steel is used as a thin hot-rolled plate product, the requirement on the surface quality of the strip steel is high. It is generally required that the thinner the scale on the surface of the strip, the better the scale formation, and it is necessary to control the scale formation in the subsequent stages of the strip casting, such as in the typical process of twin roll strip casting, a closed chamber device is used from the crystallization roll to the entrance of the rolling mill to prevent the oxidation of the strip, and the thickness of the scale on the surface of the strip can be controlled by adding hydrogen gas into the closed chamber device as in US6920912 and controlling the oxygen content to be less than 5% in US 20060182989. However, there are few patents on how to control the thickness of the scale during the transport from the rolling mill to the coiling, and particularly, in the cooling of the strip by laminar cooling or spray cooling, the strip at high temperature is in contact with cooling water, and the scale thickness on the surface of the cast strip increases rapidly. Meanwhile, the contact between the high-temperature strip steel and the cooling water also brings about a plurality of problems: firstly, water spots (rusty spots) are formed on the surface of strip steel, and the surface quality is influenced; secondly, cooling water for laminar cooling or spray cooling easily causes uneven local cooling on the surface of the strip steel and uneven microstructure inside the strip steel, thereby causing uneven performance of the strip steel and influencing the product quality; thirdly, the local cooling of the surface of the strip steel is uneven, which causes the deterioration of the plate shape and influences the quality of the plate shape.

However, the continuous strip casting has the fast solidification process characteristics, so that the produced steel generally has the problems of uneven structure, low elongation, high yield ratio and poor formability; meanwhile, the austenite grains of the cast strip have obvious nonuniformity, which can cause the structure of a final product obtained after austenite phase transformation to be nonuniform, thereby causing the performance of the product to be unstable. Therefore, the thin strip continuous casting production line is adopted to produce the checkered plate with high strength and thin specification, certain difficulty is achieved, certain challenge is achieved, traditional component technology cannot be used for production, and breakthroughs in components and technology are needed.

Disclosure of Invention

The invention aims to provide a thin-specification patterned steel plate/strip and a manufacturing method thereof, which can save complex intermediate processes such as slab heating, multi-pass repeated hot rolling and the like, and have the advantages of shorter production flow, higher efficiency and greatly reduced production line investment cost and production cost by adopting a double-roller thin strip continuous casting and one-pass online hot rolling process; the hot-rolled thin-specification patterned steel plate/strip produced by the process of the invention can be directly supplied to the market for use without further rolling, the cost performance of the plate/strip is obviously improved, and the hot-rolled thin-specification patterned steel plate/strip can be widely applied to the fields of buildings, machine manufacturing, automobiles, bridges, traffic, shipbuilding and the like.

In order to achieve the purpose, the technical scheme of the invention is as follows:

in the invention, microalloy elements such as B and the like are selectively added into steel; controlling the alkalinity of slag, the type and melting point of inclusions in steel, the content of free oxygen in molten steel and the content of acid-soluble aluminum Als in the smelting process; then, performing double-roller thin-strip continuous casting to cast strip steel with the thickness of 1.5-3mm, directly entering a lower closed chamber with non-oxidizing atmosphere after the strip steel exits from a crystallization roller, and entering an online rolling mill for hot rolling under the closed condition; the rolled strip steel is cooled by adopting an air atomization cooling mode, and the air atomization cooling mode can effectively reduce the thickness of oxide skins on the surface of the strip steel, improve the temperature uniformity of the strip steel and improve the surface quality of the strip steel. The finally produced steel coil can be directly used as a hot-rolled checkered plate/belt, and can also be used as a finishing checkered plate/belt after edge cutting and flattening.

Specifically, the thin-specification patterned steel plate/strip provided by the invention comprises the following chemical components in percentage by weight: c: not more than 0.06%, not more than 0.5% of Si, not more than 1.7% of Mn, not more than 0.04% of P, not more than 0.007% of S, N:0.004-0.010%, als:<0.001%, B:0.001-0.006% of total oxygen [ O ]] _T ：0.007-0.020％，Mn/S>250 of (a); the balance being Fe and other unavoidable impurities.

The pattern height h of the patterned steel plate/strip reaches more than 20% of the thickness a of the base plate strip, namely h is more than or equal to 0.2a.

The microstructure of the figured steel plate/belt is a mixed microstructure of block ferrite, acicular ferrite and pearlite. The yield strength of the patterned steel plate/strip reaches more than 235MPa, the tensile strength reaches more than 340MPa, and the elongation rate reaches more than 26%.

In the component design of the thin specification pattern steel plate/strip of the invention:

c: c is the most economical and basic strengthening element in steel, and enhances the strength of steel by solid solution strengthening and precipitation strengthening. C is an essential element for precipitating cementite during austenite transformation, so the strength level of the steel is determined to a great extent by the content of C, namely, higher C content corresponds to higher strength level. However, since interstitial solid solution and precipitation of C are harmful to the plasticity and toughness of steel, and an excessively high C content is disadvantageous to welding performance, the C content cannot be excessively high, and the strength of steel is compensated by appropriate addition of alloying elements. Meanwhile, for conventional slab continuous casting, casting in a peritectic reaction region is easy to generate surface cracks of a casting blank, and steel leakage accidents can happen in severe cases. The same is true for thin strip casting, where casting a cast strip in the peritectic reaction zone is prone to surface cracking and, in severe cases, strip breakage. Therefore, strip casting of Fe — C alloys also requires avoidance of the peritectic reaction zone. Therefore, the content range of C adopted by the invention is less than or equal to 0.06 percent.

Si: si acts as a solid solution strengthening in steel, and addition of Si to steel improves steel purity and deoxidation, but too high a Si content leads to deterioration of weldability and toughness in weld heat affected zone. Therefore, the Si content range adopted by the invention is less than or equal to 0.5 percent.

Mn: mn is one of the cheapest alloy elements, can improve the hardenability of steel, has considerable solid solubility in the steel, improves the strength of the steel through solid solution strengthening, basically has no damage to the plasticity and the toughness of the steel, is the most main strengthening element for improving the strength of the steel, and can play a role in deoxidizing in the steel. However, too high Mn content results in deterioration of weldability and toughness of weld heat-affected zone. Therefore, the Mn content range adopted by the invention is less than or equal to 1.7 percent.

P: high content of P is easy to be segregated in grain boundary, increases cold brittleness of steel, deteriorates welding performance, reduces plasticity and deteriorates cold bending performance. In the thin strip continuous casting process, the solidification and cooling rates of the cast strip are extremely high, and the segregation of P can be effectively inhibited, so that the disadvantages of P can be effectively avoided, and the advantages of P can be fully exerted. Therefore, in the invention, the P content is higher than that in the traditional process, the content of the P element is properly relaxed, the dephosphorization procedure is eliminated in the steelmaking procedure, in the actual operation, the dephosphorization procedure is not required to be carried out intentionally, and no extra phosphorus is required to be added, and the range of the P content is less than or equal to 0.04 percent.

S: in general, S is a harmful element in steel, causes hot brittleness of steel, reduces ductility and toughness of steel, and causes cracks during rolling. S also reduces weldability and corrosion resistance. Therefore, in the present invention, S is also controlled as an impurity element, and the content range thereof is 0.007% or less. And Mn/S >250.

And Als: in order to control inclusions in steel, the invention requires that Al cannot be used for deoxidation, and in the use of the refractory, the extra introduction of Al is avoided as much as possible, and the content of acid-soluble aluminum Als is required to be as follows: <0.001%.

N: similar to C element, N element can improve the strength of steel through interstitial solid solution, and the invention needs to generate a BN precipitated phase by utilizing the action of N and B in the steel and needs a certain content of N in the steel. However, the interstitial solid solution of N has great harm to the plasticity and toughness of the steel, and the existence of free N can improve the yield ratio of the steel, so that the content of N cannot be too high. The content range of N adopted by the invention is 0.004-0.010%.

B: the significant role of B in steel is: the hardenability of the steel can be multiplied by trace B, the B can preferentially precipitate coarse BN particles in high-temperature austenite so as to inhibit the precipitation of fine AlN, weaken the pinning effect of the fine AlN on grain boundaries, and improve the growth capability of grains, so that austenite grains are coarsened and homogenized, the recrystallization after rolling is facilitated, the improvement of the yield ratio of a product is facilitated after the austenite grains are coarsened and homogenized, and the forming performance of the product can be improved; in addition, the combination of B and N can effectively prevent the grain boundary low melting point phase B ₂ O ₃ Is present.

B is an active segregation-prone element and is easy to segregate in a grain boundary, and the content of B is generally controlled to be very strict and is generally about 0.001-0.003% when B-containing steel is produced by a traditional process; in the thin-strip continuous casting process, the solidification and cooling rates are high, the segregation of B can be effectively inhibited, and more B content is dissolved, so that the content of B can be properly widened; coarse BN particles can be generated through reasonable process control, and the precipitation of fine AlN is inhibited, so that the nitrogen fixation effect is achieved. Therefore, in the present invention, a higher B content is used than in the conventional process, in the range of 0.001-0.006%.

The invention relates to a method for manufacturing a thin-specification pattern steel plate/strip, which comprises the following steps:

1) Smelting of

Smelting according to the components, wherein the basicity of slagging in the steelmaking process is a = CaO/SiO ₂ Control in a<1.5, preferably a<1.2, or a =0.7-1.0; obtaining low melting point MnO-SiO in molten steel ₂ -Al ₂ O ₃ MnO/SiO in ternary inclusions ₂ The content is controlled to be 0.5 to 2, preferably 1 to 1.8; free oxygen [ O ] in molten steel] _Free The contents are as follows: 0.0005-0.005%; the control of Mn and S in molten steel must satisfy the following relational expression: mn/S>250；

2) Continuous casting

Adopting double-roller thin strip continuous casting, wherein molten steel forms a cast strip with the thickness of 1.5-3mm at the position with the minimum gap between two crystallizing rollers; the diameter of the crystallization roller is 500-1500mm, preferably 800mm, the inner part of the crystallization roller is cooled by water, and the casting speed of the casting machine is 60-150m/min; a two-stage steel water distribution system is adopted for continuous casting flow distribution, namely a tundish and a flow distributor;

3) Lower enclosed chamber protection

After the cast strip is taken out of the crystallization roller, the temperature of the cast strip is 1420-1480 ℃, the cast strip directly enters a lower closed chamber, non-oxidizing gas is introduced into the lower closed chamber, the oxygen concentration in the lower closed chamber is controlled to be less than 5%, and the temperature of the cast strip at the outlet of the lower closed chamber is 1150-1300 ℃;

4) In-line hot rolling

Conveying the cast strip to a rolling mill in a lower closed chamber through a pinch roll, and rolling into a checkered plate with the thickness of 0.8-2.5mm, wherein the rolling temperature is 1100-1250 ℃, the hot rolling reduction is controlled to be 10-50%, preferably, the hot rolling reduction is 15-35%, and the thickness of the hot rolled steel strip is 0.8-2.5mm, preferably, the thickness is 1.0-1.6mm;

5) Cooling after rolling

Cooling the strip steel after the online hot rolling, wherein the cooling adopts an air atomization cooling mode, and the cooling rate is 20-100 ℃/s;

6) Strip steel coiling

And directly coiling the cooled hot-rolled strip steel into coils after cutting off the head with poor quality, and controlling the coiling temperature to be 600-700 ℃.

Preferably, in the step 1), the molten steel is smelted by adopting electric furnace steelmaking or converter steelmaking, or enters the refining procedures of an LF furnace, a VD/VOD furnace and an RH furnace for component adjustment.

Preferably, in step 3), the non-oxidizing gas comprises N ₂ Ar, or CO obtained by sublimation on dry ice ₂ A gas.

Preferably, in the step 4), the roller for rolling the patterned steel plate/plate comprises an upper roller and a lower roller, wherein the upper roller is a patterned roller, and the lower roller is a flat roller; the surface appearance of the pattern roller is hyacinth bean shape, and the roller diameter of the upper roller pattern roller is 0.3-3mm larger than that of the lower roller flat roller.

Preferably, in the step 4), the lower roller is a flat roller, the roller diameter at the center is 0.15-0.22mm smaller than the roller diameters at two ends by taking the central line of the roller body as a reference, and a smooth transition parabolic roller shape is formed.

Preferably, in the step 5), the gas-water ratio of the gas atomization cooling is 15:1 to 10:1, the air pressure is 0.5-0.8 MPa, and the water pressure is 1.0-1.5 MPa.

Preferably, in the step 5), 1-2 pairs of high-pressure side air injection nozzles for blowing accumulated water on the surface of the patterned steel plate/strip are arranged at the atomized cooling outlet of the patterned steel plate/strip, the pressure of the nozzles is 0.5-0.8 MPa, and the flow rate is 20-200m ³ /h。

Preferably, in step 6), the coiling is performed in a double coiler format or a carrousel coiling format.

In the manufacturing method of the present invention:

in order to improve the castability of thin-strip continuous casting molten steel, the alkalinity a = CaO/SiO of slagging in the steel-making process ₂ Is controlled at a<1.5, preferably a<1.2, or a =0.7-1.0.

To improve the castability of thin strip continuous casting molten steel, it is necessary to obtain MnO-SiO of low melting point ₂ -Al ₂ O ₃ Ternary inclusions, e.g. shaded areas of FIG. 2, mnO-SiO ₂ -Al ₂ O ₃ MnO/SiO in ternary inclusions ₂ The concentration is controlled to be 0.5-2, preferably 1-1.8.

In order to improve the castability of thin strip continuous casting molten steel in which O is an essential element for forming oxide inclusions, the present invention requires formation of MnO-SiO with a low melting point ₂ -Al ₂ O ₃ The ternary inclusions of (2) require free oxygen [ O ] in molten steel] _Free The range is as follows: 0.0005-0.005%.

In order to improve the castability of the thin strip continuous casting molten steel, the Mn and S of the above components should satisfy the following relation: mn/S >250.

And (3) casting a metal casting strip with the thickness of 1.5-3mm by using a double-roller thin strip casting machine. After the cast strip exits the crystallization roller, the cast strip is heated to 1420-1480 deg.C and directly enters a lower sealed chamber into which a non-oxidizing gas, such as CO sublimated from dry ice, is introduced ₂ Gas, etc., the oxygen concentration in the lower sealed chamber is controlled<5 percent. The lower closed chamber protects the cast strip from oxidation to the mill inlet. The temperature of the cast strip at the outlet of the lower closed chamber is 1150-1300 ℃.

The theoretical basis of BN precipitated phase involved in the lower sealing process of the cast strip is as follows:

the thermodynamic equation of boron with nitrogen, aluminum and nitrogen in gamma-Fe in steel is as follows:

BN＝B+N；Log[B][N]＝-13970/T+5.24 (1)

AlN＝Al+N；Log[Al][N]＝-6770/T+1.03 (2)

as shown in FIG. 3, the initial precipitation temperature of BN in the steel is about 1280 ℃ and the precipitation of BN at 980 ℃ is in equilibrium, but the precipitation of AlN is just started (the precipitation temperature of AlN is about 980 ℃), and the precipitation of BN is thermodynamically preferred to AlN. The invention completes the combination of B and N in the lower closed chamber to generate coarse BN particles, thereby inhibiting the precipitation of fine AlN, weakening the pinning effect of the fine AlN on grain boundaries, improving the growth capability of crystal grains and further coarsening austenite crystal grainsThe austenite grains are more uniform, which is beneficial to effectively reducing the yield ratio of the product and improving the product performance; in addition, the combination of B and N can effectively prevent the grain boundary low-melting-point phase B ₂ O ₃ Is present.

The roller used for the checkered plate is an upper roller, the surface appearance of the checkered roller is in a hyacinth bean shape, in order to ensure that the rolled strip steel does not stick to the roller and ensure the stability of strip discharging, the roller diameter of the upper roller checkered roller is 0.3-3mm larger than that of a lower roller plain roller. Because the checkered roller has no roller shape, in order to ensure the plate shape of the checkered plate after rolling and avoid the generation of middle waves, when the lower roller is manufactured, the central line of the roller body of the roller is taken as a reference, the roller diameter at the center is 0.15-0.22mm smaller than the roller diameters at two ends, and a smoothly-transitional parabolic roller shape is formed. Due to the higher rolling temperature of the method, the pattern height h of the checkered plate can reach 20% or more of the thickness a of the substrate, namely h is more than or equal to 0.2a.

The strip steel after the online hot rolling is cooled after being rolled, and the strip steel is cooled by adopting an air atomization cooling mode, so that the thickness of oxide scale on the surface of the strip steel can be effectively reduced, the temperature uniformity of the strip steel is improved, and the surface quality of the strip steel is improved. The gas-water ratio of gas atomization cooling is 15:1 to 10:1, the air pressure is 0.5-0.8 MPa, and the water pressure is 1.0-1.5 MPa. High-pressure water mist is formed after gas atomization and sprayed on the surface of a steel strip, so that on one hand, the temperature of the steel strip is reduced, on the other hand, the water mist can form a compact air film to coat on the surface of the steel strip, the anti-oxidation effect of the steel strip is achieved, and the growth of oxide skin on the surface of the hot-rolled steel strip is effectively controlled. The cooling mode can avoid the problems caused by the traditional spraying or laminar cooling, so that the surface temperature of the strip steel is uniformly reduced, the temperature uniformity of the strip steel is improved, and the effect of homogenizing the internal microstructure is achieved; meanwhile, the cooling is uniform, so that the shape quality and the performance stability of the strip steel can be improved; effectively reducing the thickness of oxide scale on the surface of the strip steel. The cooling rate of the gas atomization cooling is in the range of 20-100 ℃/s.

Because the upper surface of the patterned steel plate is provided with raised patterns, accumulated water easily exists on the upper surface after cooling, 1-2 pairs of nozzles for jetting air at a high pressure side are arranged at an atomization cooling outlet of the strip steel, the pressure of the nozzles is 0.5-0.8 MPa, and the flow rate is 20-200m ³ H for blowing the surface of the checkered plateWater is accumulated in the tank.

And cutting the head of the cooled hot-rolled strip steel by using a cutting head to remove the head with poor quality, and directly coiling the hot-rolled strip steel into coils. The coiling temperature is controlled to be 600-700 ℃, so that the rolled high-temperature austenite structure is converted into a mixed microstructure of bulk ferrite, acicular ferrite and pearlite.

Through the manufacturing process, the performance yield strength of the final thin-specification pattern steel plate/strip reaches more than 235MPa, the tensile strength reaches more than 340MPa, and the elongation rate reaches more than 26%. FIG. 4 is a diagram of a checkered plate produced by the present invention.

The invention is distinguished and improved from the prior art:

the most obvious characteristic of the invention which is different from the prior thin strip continuous casting technology is the roller diameter of the crystallization roller and the corresponding distribution mode. The EUROSTRIP technology is characterized in that the crystallization roller with a large roller diameter of 1500mm phi is large, the molten steel capacity of a molten pool is large, the distribution is easy, and the manufacturing cost and the operation cost of the crystallization roller are high. The CASTIP technology is characterized in that a crystallization roller with a small roller diameter of 500mm phi is small, the molten steel capacity of a molten pool is small, the distribution is very difficult, but the manufacturing, operation and maintenance costs of casting machine equipment are low. CASTIP adopts a three-level steel water distribution system (tundish, transition ladle and distributor) to solve the problem of uniform distribution of small molten pools. Because a three-level flow distribution system is adopted, the cost of the refractory material is directly increased; more importantly, the three-stage flow distribution system enables the flowing path of the molten steel to be lengthened, the temperature drop of the molten steel is large, and in order to meet the temperature of molten steel in a molten pool, the tapping temperature needs to be greatly increased. The increase of the tapping temperature causes problems such as increase of steel-making cost, increase of energy consumption, and shortening of the life of refractory.

The crystallization roller with the diameter of 800mm is preferably selected, and a two-stage steel water distribution system (a tundish and a flow distributor) is adopted. Molten steel flowing out of the flow distributor forms different flow distribution modes along the roller surface and the two end surfaces, and flows in two paths without mutual interference. Because the two-stage flow distribution system is adopted, compared with a three-stage flow distribution system, the cost of refractory materials is greatly reduced; the reduction of the flow path of the molten steel reduces the temperature drop of the molten steel, and can reduce the tapping temperature by 30-50 ℃ compared with a three-level flow distribution system. The steel tapping temperature is reduced, so that the steel making cost can be effectively reduced, the energy consumption is saved, and the service life of refractory materials is prolonged. The invention is matched with the crystallization roller with the optimal diameter of 800mm, and adopts a two-stage molten steel distribution system, thereby not only realizing the requirement of stable molten steel distribution, but also realizing the aims of simple structure, convenient operation and low processing cost.

There are many patents for producing thin strip products and processes by strip continuous casting, but there is no direct report on producing thin specification pattern steel plate/strip containing B by strip continuous casting, but the following patents/documents and this patent are considered to have certain comparability in product process control and equipment, and detailed description is as follows:

chinese patent CN107716552A discloses a method for producing checkered plates with the thickness of 1.4mm by using a CSP process. The method adopts a CSP short-process production line to produce the checkered plate with thin specification, the weight reduction rate is not lower than 10%, and the plate shape quality is excellent. The invention adopts a more advanced thin strip continuous casting and rolling process, and can realize the production of the checkered plate with the thinnest thickness of 1.0 mm.

Chinese patent CN108486476A discloses a 700Mpa vanadium-containing hot-rolled pattern steel plate and a production method thereof. The patent adopts the traditional hot rolling process flow to produce a microalloyed checkered plate product with higher strength, the thickness range of the microalloyed checkered plate product is 1.5-8.0mm, the continuous production of batch ultrathin specifications cannot be realized, and the continuous production difficulty is higher. The invention adopts the thin strip continuous casting process for production, and the thickness, the strength grade and the process realization mode of the product are obviously different.

The document 'trial rolling and process improvement of a thin checkered plate' mainly solves the process problem of a checkered plate with the thickness of 2.3mm, and does not relate to the process and the thickness specification of the invention. In the document 'research and application of new technology for rolling extreme thin pattern plates', the thickness of the thin pattern plates mainly produced by adopting an ESP short-flow process is about 1.8mm, and satisfactory results are obtained, but the process route and the thickness specification related to the invention are different.

The main advantages of the invention are:

1. the invention adopts the thin strip continuous casting technology, reasonably adds trace element boron (B) into steel to produce the thin specification pattern steel plate/strip, and has not been reported so far.

2. The invention omits the complex processes of slab heating, multi-pass repeated hot rolling and the like, and has the advantages of shorter production flow, higher efficiency and greatly reduced production line investment cost and production cost by adopting the working procedures of double-roller thin-strip continuous casting and one-pass online hot rolling.

3. The invention omits a plurality of complex intermediate steps in the traditional process production, and compared with the traditional production process of the figured steel plate/strip, the production energy consumption and CO are reduced ₂ Greatly reduces the emission, and is a green and environment-friendly product.

4. The invention adopts the thin strip continuous casting process to produce the hot-rolled thin-specification patterned steel plate/strip, the thickness of the cast strip is thinner, the thin-specification product is produced to the thickness of the expected product through online hot rolling, the thin-specification product is directly supplied to the market for use without further rolling, the purpose of supplying the thin-specification hot rolled plate is achieved, and the cost performance of the plate/strip can be obviously improved.

5. According to the invention, trace boron is added, and coarse BN particles are preferentially precipitated in high-temperature austenite, so that the precipitation of fine AlN is inhibited, the pinning effect of fine AlN on grain boundaries is weakened, the growth capability of grains is improved, and therefore, austenite grains are coarsened and homogenized, and the product performance is favorably improved.

6. The invention adopts the air atomization cooling mode of the rolled strip steel, can avoid the problems brought by the traditional spray or laminar cooling, uniformly reduces the surface temperature of the strip steel, improves the temperature uniformity of the strip steel, thereby achieving the effect of homogenizing the internal microstructure; meanwhile, the cooling is uniform, so that the shape quality and the performance stability of the strip steel can be improved; effectively reducing the thickness of the oxide scale on the surface of the strip steel.

7. In the traditional process, alloy elements are separated out in the cooling process of the plate blank, and the utilization rate of the alloy elements is reduced because the re-dissolution of the alloy elements is insufficient when the plate blank is reheated. In the thin strip continuous casting process, the high-temperature cast strip is directly hot-rolled, and the added alloy elements mainly exist in a solid solution state, so that the alloy utilization rate can be improved.

8. The checkered plate product with low cost and thin specification produced by the invention has the characteristics of rapid solidification of thin strip continuous casting, has guaranteed strength, can meet the requirements of light weight (weight reduction) of the product in the current market, and can effectively save material cost for downstream users; if the product is used in the occasions of moving automobiles, ships and the like, the light weight can also bring the advantages of saving fuel or electricity consumption (new energy automobiles), reducing exhaust emission and the like for the users.

9. According to the invention, the hot rolled steel strip carrousel coiling machine is selected, so that the length of a production line is effectively shortened; meanwhile, the control precision of the coiling temperature can be greatly improved by the co-position coiling, and the stability of the product performance is improved.

Drawings

FIG. 1 is a schematic diagram of a process arrangement for a twin roll strip casting process;

FIG. 2 shows MnO-SiO ₂ -Al ₂ O ₃ Ternary phase diagram (shaded area: low melting point region);

FIG. 3 is a schematic diagram of a thermodynamic curve of BN, alN precipitation;

FIG. 4 is a diagram of a checkered plate produced by the present invention.

Detailed Description

The invention is further illustrated by the following examples, which are not intended to limit the invention in any way. Any variations in the practice of the invention that may occur to those skilled in the art and which are made in the light of the teachings of this specification are intended to be within the scope of the following claims.

Referring to fig. 1, molten steel designed according to the chemical composition of the present invention is directly poured into a molten pool 7 surrounded by two

crystallization rollers

8a, 8b which rotate relatively and can be rapidly cooled and side closing plate devices 6a, 6b through a ladle 1, a tundish 2, a tundish 3, a submerged nozzle 4 and a distributor 5, the molten steel is solidified on the circumferential surfaces of the rotation of the

crystallization rollers

8a, 8b, thereby forming solidified shells and gradually growing, and then a casting strip 11 with the thickness of 1.5-3mm is formed at the minimum clearance (nip point) between the two crystallization rollers; the diameter of the crystallization roller is 500-1500mm, preferably 800mm; the interior of the cooling tower is cooled by water. The casting speed of the casting machine ranges from 60 to 150m/min according to the thickness of the cast strip.

After the cast strip 11 exits the crystallization rolls 8a, 8b, the cast strip temperature is 1420-1480 ℃ and enters directly into the lower closed chamberIn 10, the lower closed chamber 10 is filled with inert gas to protect the strip steel, so as to realize the anti-oxidation protection of the strip steel, the atmosphere of the anti-oxidation protection can be N2, ar or other non-oxidizing gas, such as CO obtained by sublimation of dry ice ₂ Gas, etc., the oxygen concentration in the lower sealed chamber 10 is controlled to be<5 percent. Lower enclosed chamber 10 protects against oxidation of cast strip 11 to the entrance of rolling mill 13. The temperature of the cast strip at the outlet of the lower closed chamber 10 is 1150-1300 ℃. Then the cast strip is sent to a hot rolling mill 13 through a swinging guide plate 9 and a pinch roll 12, a hot rolled strip with the thickness of 0.8-2.5mm is formed after hot rolling, and the temperature uniformity of the strip steel is improved by cooling after rolling in an air atomization cooling mode. After the head is cut by the flying shear device 16, the head falls into the flying shear pit 18 along the flying shear guide plate 17, and the hot rolled strip after the head is cut enters the coiler 19 for coiling. And taking the steel coil off the coiling machine, and naturally cooling to room temperature. The finally produced steel coil can be directly used as a hot-rolled checkered plate/belt, and can also be used as a finishing checkered plate/belt after edge cutting and flattening.

The chemical compositions of the examples of the invention are shown in table 1, and the balance of the compositions is Fe and other unavoidable impurities. The process parameters of the manufacturing method of the invention are shown in table 2, and the properties of the finally obtained hot rolled strip are shown in table 3.

In conclusion, the final thin-specification patterned steel plate/strip produced by the strip continuous casting process technology according to the design range of the steel components provided by the invention has the performance yield strength of more than 235MPa, the tensile strength of more than 340MPa, the elongation of more than 26 percent and qualified cold-working bending performance, and can be widely applied to the fields of building, mechanical manufacturing, automobiles, bridges, traffic, shipbuilding and the like.

Table 1 chemical composition (wt.%) of the example steels

	C	Si	Mn	P	S	N	O	Als	B
										Example 1	0.03	0.13	1.35	0.008	0.004	0.0077	0.0093	0.0009	0.004
Example 2	0.04	0.10	0.90	0.013	0.003	0.0051	0.0110	0.0006	0.001
										Example 3	0.02	0.24	1.28	0.015	0.004	0.0059	0.0150	0.0004	0.003
Example 4	0.05	0.36	1.10	0.023	0.006	0.0088	0.0130	0.0008	0.005
										Example 5	0.03	0.44	0.65	0.009	0.002	0.0054	0.0120	0.0007	0.004
Example 6	0.05	0.42	0.67	0.012	0.002	0.0048	0.0070	0.0008	0.005
										Example 7	0.06	0.28	0.85	0.015	0.003	0.0040	0.0100	0.0005	0.004
Example 8	0.02	0.17	1.00	0.014	0.005	0.0100	0.0085	0.0006	0.003
										Example 9	0.03	0.26	0.84	0.018	0.003	0.0068	0.0200	0.0003	0.004
Example 10	0.04	0.44	0.40	0.040	0.001	0.0065	0.0125	0.0004	0.006
										Example 11	0.05	0.50	0.65	0.030	0.002	0.0080	0.0090	0.0005	0.004
Example 12	0.02	0.27	1.70	0.022	0.007	0.0075	0.0118	0.0003	0.002
										Example 13	0.06	0.48	1.37	0.038	0.004	0.0065	0.0132	0.0006	0.006
Example 14	0.045	0.23	1.40	0.017	0.003	0.0064	0.0075	0.0005	0.004

TABLE 2 Process parameters of the examples

TABLE 3 Properties of the steels of the examples

The thin-strip continuous casting process is adopted to produce the thin-specification checkered plate, and has strong manufacturing and cost advantages for thin-specification hot-rolled high-strength products with the thickness of less than 1.5mm (inclusive) due to the thin thickness. The product specification characteristic thickness of the thin checkered plate directly supplied in a hot rolling state is 1.0-1.6mm, and the product is produced by adopting the traditional production line process due to the fact that the product is thin, the problem of product plate shape can occur, and the product cannot be produced; the thin slab continuous casting and rolling process is adopted for production, the roller consumption of the roller is obviously increased, and the production cost of the thin-specification checkered plate is undoubtedly increased by the production process. Therefore, the thin-strip continuous casting process is adopted to produce the thin-specification checkered plate product, so that the requirements of the market on thin specification and light weight can be met, the production cost can be reduced, and the profit level and the competitiveness of the product are improved.

Claims

1. A thin specification pattern steel plate/belt comprises the following chemical components in percentage by weight: c: not more than 0.06%, not more than 0.5% of Si, not more than 1.7% of Mn, not more than 0.04% of P, not more than 0.007% of S, N:0.004-0.010%, als:<0.001%, B:0.001-0.006% of total oxygen [ O ]] _T ：0.007-0.020％，Mn/S>250 of (a); the balance of Fe and other unavoidable impurities;

the microstructure of the patterned steel plate/strip is a mixed microstructure of massive ferrite, acicular ferrite and pearlite;

the yield strength of the patterned steel plate/strip reaches above 235-270 MPa, the tensile strength reaches above 340MPa, and the elongation rate reaches above 26%.

2. The thin gauge steel plate/strip as claimed in claim 1, wherein the height h of the pattern of said steel plate/strip is 20% or more of the thickness a of the base plate strip, i.e. h is 0.2a or more.

3. The method for manufacturing a thin gauge pattern steel plate/strip as claimed in claim 1 or 2, comprising the steps of:

1) Smelting

Smelting according to the composition of claim 1, wherein the basicity of slagging in the steelmaking process is a = CaO/SiO ₂ Control at a =0.7-1.0; obtaining low melting point MnO-SiO in molten steel ₂ -Al ₂ O ₃ MnO/SiO in ternary inclusions ₂ Controlling the temperature to be 0.5-2; free oxygen [ O ] in molten steel] _Free The contents are as follows: 0.0005-0.005%; the control of Mn and S in molten steel must satisfy the following relational expression: mn/S>250；

2) Continuous casting

Adopting twin-roll thin strip continuous casting, and forming a cast strip with the thickness of 1.5-3mm at the minimum position of a gap between two crystallizing rolls by molten steel; the diameter of the crystallization roller is 500-1500mm, water is introduced into the crystallization roller for cooling, and the casting speed of the casting machine is 60-150m/min; the continuous casting flow distribution adopts a two-stage steel water distribution system, namely a tundish and a flow distributor;

3) Lower sealed chamber protection

4) In-line hot rolling

Conveying the cast strip to a rolling mill through a pinch roll in a lower closed chamber, and rolling into a checkered plate with the thickness of 0.8-2.5mm, wherein the rolling temperature is 1100-1250 ℃, the hot rolling reduction rate is controlled to be 10-50%, and the thickness of the hot rolled steel strip is 0.8-2.5mm;

5) Cooling after rolling

6) Strip steel coiling

And directly coiling the cooled hot-rolled strip steel after cutting off the head with poor quality, and controlling the coiling temperature to be 600-700 ℃.

4. The method for manufacturing a thin gauge pattern steel plate/strip as claimed in claim 3, wherein in the step 1), the molten steel is smelted by electric furnace steelmaking, converter steelmaking, or refining in LF furnace, VD/VOD furnace, RH furnace, and the composition adjustment is performed.

5. The method for manufacturing thin gauge steel plate/strip as claimed in claim 3, wherein in step 3), said non-oxidizing gas comprises N ₂ Ar, or CO obtained by sublimation on dry ice ₂ A gas.

6. The method for manufacturing a thin gauge pattern steel plate/strip as claimed in claim 3, wherein in the step 4), the rolls for rolling the pattern steel plate/plate comprise an upper roll and a lower roll, the upper roll is a pattern roll, and the lower roll is a flat roll; the surface appearance of the patterned roller is hyacinth bean-shaped, and the diameter of the patterned roller is 0.3-3mm larger than that of the flat roller.

7. The method for manufacturing a thin gauge steel plate/strip as claimed in claim 6, wherein in step 4), the flat rolls have a roll diameter at the center which is 0.15-0.22mm smaller than the roll diameters at both ends with respect to the center line of the roll body and form a smoothly transiting parabolic roll shape.

8. The method for manufacturing a thin gauge pattern steel plate/strip as claimed in claim 3, wherein the air-water ratio of the air-atomized cooling in the step 5) is 15:1 to 10:1, the air pressure is 0.5-0.8 MPa, and the water pressure is 1.0-1.5 MPa.

9. The method for manufacturing a thin gauge pattern steel plate/strip as claimed in claim 3, wherein in the step 5), 1 to 2 pairs of high pressure side air injection nozzles for blowing accumulated water on the surface of the pattern steel plate/strip are provided at the pattern steel plate/strip atomization cooling outlet, the nozzle pressure is 0.5 to 0.8MPa, and the flow rate is 20 to 200m ³ /h。

10. The method for manufacturing a thin gauge textured steel plate/strip as claimed in claim 3, wherein in step 6), the coiling is performed in a double coiler type or a carrousel coiling type.

11. The method for manufacturing a thin gauge pattern steel plate/strip as claimed in claim 3, wherein in step 1), said low melting point MnO-SiO is ₂ -Al ₂ O ₃ MnO/SiO in ternary inclusions ₂ The control is 1 to 1.8.

12. The method for manufacturing a thin gauge pattern steel plate/strip as claimed in claim 3, wherein in the step 2), the diameter of the crystallization roll is 800mm.

13. The method for manufacturing a thin gauge pattern steel plate/strip as claimed in claim 3, wherein said hot rolling reduction in step 4) is 15-35%.

14. The method for manufacturing a thin gauge pattern steel sheet/strip as claimed in claim 3 or 13, wherein the thickness of the hot rolled steel strip in the step 4) is 1.0 to 1.6mm.