CN112522595B

CN112522595B - High-strength thin-specification fire-resistant weather-resistant steel plate/steel belt and production method thereof

Info

Publication number: CN112522595B
Application number: CN201910889392.4A
Authority: CN
Inventors: 吴建春; 方园; 张丰
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: CN112522595A

Abstract

A high-strength thin-specification fire-resistant weather-resistant steel plate/steel belt and a production method thereof are disclosed, wherein the steel plate/steel belt comprises the following chemical components in percentage by weight: 0.02-0.06% of C, 0.1-0.55% of Si, 0.4-1.7% of Mn, less than or equal to 0.03% of P, less than or equal to 0.007% of S, 0.30-0.80% of Cr, 0.20-0.60% of Mo, 0.01-0.08% of Nb, 0.004-0.010% of N, als<0.001% of total oxygen [ O ]] _T :0.007-0.020%, and the balance of Fe and inevitable impurities, which simultaneously satisfy: also contains one or two elements of 0.10-0.60% of Cu or 0.005-0.04% of Sn; mn/S>250 of (a); pcm is less than or equal to 0.27 percent. The method utilizes residual Sn, cu and other elements in the scrap steel to smelt the molten steel, and selectively adds Mo/Nb/Cr and other microalloy elements; controlling the slag alkalinity, the type and melting point of inclusions in steel, the free oxygen content in molten steel and the content of acid-soluble aluminum Als; and then casting a cast strip by adopting a twin-roll thin strip continuous casting method, directly passing the cast strip through a lower closed chamber, performing online hot rolling, and cooling the rolled strip steel in an air atomization cooling mode.

Description

High-strength thin-specification fire-resistant weather-resistant steel plate/steel belt and production method thereof

Technical Field

The invention relates to a manufacturing technology of fire-resistant weather-resistant steel, in particular to a high-strength thin-specification fire-resistant weather-resistant steel plate/steel belt and a production method thereof.

Background

In the traditional steel production flow, tin (Sn) and copper (Cu) are typical residual elements or harmful elements in steel, the Sn and the Cu are difficult and expensive to remove fully in the steel making process, once the steel contains the Sn and the Cu, the Sn and the Cu cannot be completely eliminated basically, and the contents of the Sn and the Cu can be reduced only by diluting molten steel, which causes the increase of the smelting cost of steel products.

In recent years, as scrap steel is continuously recycled, scrap steel resources are more and more, electricity prices are continuously reduced, domestic scrap-based short-flow electric furnace steel making is increasingly started, so that the content of residual elements such as Sn and Cu in steel is gradually increased, sn and Cu in steel are easy to segregate and are easy to concentrate in grain boundaries to cause defects such as cracks, and the like, so that the content of Sn and Cu elements in the traditional process is strictly controlled, and in common structural steel, the content of Sn and Cu has clear requirements: sn (wt%) is less than or equal to 0.005%; cu (wt%) is less than or equal to 0.2%.

Therefore, if the residual elements such as Sn, cu and the like in steel (particularly scrap steel) can be reasonably utilized, the 'harm into benefit' can generate positive influence on the whole metallurgical industry; the method can realize the effective utilization of the prior steel scraps or low-quality inferior ore resources (high-tin ore and high-copper ore), promote the recycling of steel, reduce the production cost and realize the sustainable development of the steel industry.

The traditional thin strip steel is produced by continuously rolling a casting blank with the thickness of 70-200mm for multiple times, 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 strips with a thickness of less than 1.5mm inclusive are 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 the casting blank is thin, so that 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 in the traditional process through repeated multi-pass rolling; 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 strength of steel is improved and the yield ratio is improved due to the faster cooling speed of the sheet billet continuous casting and rolling, so that the rolling load is increased, and the thickness specification of a hot rolled product which can be economically produced cannot be too thin, generally more than or equal to 1.5mm, see Chinese patents CN200610123458.1, CN200610035800.2 and CN200710031548.2, and the patents do not relate to Sn and Cu.

The ESP realizes the continuous casting of the slab continuously, cancels the slab flame cutting and the heating furnace with the functions of heat preservation, soaking and slab transition, and greatly shortens the length of the whole production line to about 190 meters. The thickness of a plate blank continuously cast by the continuous casting machine is 90-110mm, the width of the plate blank is 1100-1600mm, the plate blank continuously cast by the continuous casting machine plays a role in heat preservation and soaking through a section of induction heating roller way, and then the plate blank sequentially enters the working procedures of rough rolling, finish rolling, layer cooling and coiling to obtain a hot rolled plate. The process realizes endless rolling, can obtain the hot rolled plate with the thinnest thickness of 0.8mm, expands the specification range of the hot rolled plate, and has the output of a single production line reaching 220 kiloton per year. At present, the process is rapidly developed and popularized, 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 technology changes the production process of steel strips in the traditional metallurgy industry, integrates continuous casting, rolling, even heat treatment and the like into a whole, and the produced thin slab is subjected to online hot rolling once to form a thin steel strip, so that 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 cast strip 11 with the thickness of 1-5mm is formed at the position (nip point) where the roll gaps of the two crystallizing

rollers

8a, 8b are minimum, the cast strip 11 is fed into a rolling mill 13 through a guide plate 9 to be rolled into a thin strip with the thickness of 0.7-2.5mm, then is cooled through a cooling device 14, is cut by a flying shear device 16, and is finally fed into a coiler 19 to be coiled.

In recent years, with the continuous emergence of large buildings and high-rise buildings at home and abroad, in order to avoid the collapse of the buildings caused by the sudden decrease of the strength of the building steel due to the heating when the buildings are in fire, and great loss of lives and properties of residents, the fire protection process design of the building steel is widely regarded by people internationally, and the fire protection process design of the building steel becomes one of necessary measures for ensuring the building safety. The strength and the bearing capacity of the steel for the common building are rapidly reduced when the steel is heated, and the requirement of fire safety cannot be met. In order to improve the fire resistance of the building constructed by the common construction steel, the measures such as spraying a fire-resistant coating or covering a fire-proof plate and the like are required in the prior common method, but the fire-resistant steel is greatly used at present, so that the fire-resistant coating or the fire-proof plate can be thinned or omitted, the steel can be ensured to keep higher strength level at high temperature, the construction period can be shortened, the quality of the building is reduced, the safety of the building is improved, the construction cost is reduced, and the economic benefit and the social benefit are obvious. Meanwhile, most of the constructional steel is exposed in the air, and the service life is long, so that the steel has weather resistance on the basis of fire resistance, and a brand-new fire-resistant weather-resistant steel product is derived. Under the large application background, the existing fire-resistant weather-resistant steel plate/belt is increasingly applied to industries and fields of building steel with fire protection requirements, tower and mast columns, engineering machinery, industrial structures and the like, and is particularly widely applied to places with high fire safety requirements, such as high-rise buildings, large public buildings, high-grade houses and the like.

The fire-resistant weathering steel is required to have good high-temperature performance, but is different from the heat-resistant steel which is used at high temperature for a long time, and the heat-resistant steel is required to have good high-temperature strength and high-temperature stability, and generally adopts high alloy steel. The fire-resistant weather-resistant steel is loaded at normal temperature, but is required to keep higher yield strength under the short-time (usually 1-3 h) high-temperature condition of fire hazard, and can gain precious time for safe evacuation of personnel, so that the steel belongs to the category of low-alloy structural steel, and the composition design of the steel is not suitable for adding excessive expensive alloy elements.

The safety design specifications of the steel structure of Japan specify: 2/3 of the yield strength of steel at normal temperature corresponds to the long-term allowable stress value of the material, and when a fire breaks out, if the yield point of the fire-resistant weathering steel can still keep the value, the building can not collapse. Therefore, the yield strength of the fire-resistant weathering steel at a certain high temperature is required to be not less than 2/3 of the yield strength at room temperature. In order to improve the seismic resistance of steel structures, it is always desirable to improve the seismic energy absorbing capacity of steel as much as possible. If the yield ratio (σ) of the steel _s /σ _b ) When the earthquake occurs, local stress concentration and local large deformation can be generated, and at the moment, the steel structure can only absorb less energy, so that the low yield ratio is beneficial to improving the energy absorbed by the building structure when the earthquake occurs, and the yield ratio of the anti-seismic fire-resistant weathering steel is generally required to be less than or equal to 0.8.

One of the keys to the development of fire resistant weathering steel is to set the fire temperature at which it is desired to achieve high temperature strength. Mo-containing steel resistant to high temperatures of 900-1 000 ℃ has been studied in European Creusot-Loire steelworks, but is not popularized due to too high cost. In order to determine the fire-resistant temperature which is optimally matched with the reduction of the production cost and the reduction of the consumption of the fire-resistant materials, the high-temperature tensile test is carried out on several typical steels with the tensile strength of 400-780MPa in the Xinri iron, and the test shows that: yield strength (σ) of all test steels _s ) Sharply decreases in the range of 500-600 deg.C, and sigma at 700 deg.C or above 700 deg.C _s Reducing the pressure to below 50 MPa. If the handle is guaranteedIf the temperature of the strength is set to 700 ℃, a large amount of alloy elements must be added, so that the good weldability is difficult to ensure, and the cost is greatly increased. If the temperature for ensuring the strength is set at a lower temperature of 500 ℃, the thickness of the refractory coating can be only slightly reduced, which is not in accordance with the original purpose of using refractory weathering steel. Therefore, the fire resistance temperature of the fire resistant weathering steel was set to 600 ℃.

In view of the above, and in accordance with the general requirements of the construction steel, the performance indexes of the fire-resistant weathering steel are determined as follows:

(1) Fire resistance: sigma _s，600℃ ≥(2/3)σ _s，20℃ ；

(2) The room temperature mechanical property and other quality indexes meet the requirements of the standard of common construction steel;

(3) Shock resistance: sigma at room temperature _s /σ _b Less than or equal to 0.8, and the fluctuation range of the yield strength is as small as possible;

(4) The weldability is good, equal to or better than common construction steel;

(5) Weather resistance: compared with Q345B, the relative corrosion rate is less than or equal to 60 percent by adopting the standard TB/T2375-1993 measurement.

The high-strength fire-resistant weather-resistant steel plate/strip is produced by adopting a strip continuous casting process, and due to the sub-rapid solidification characteristic of the strip continuous casting process, a fine crystal layer with a certain thickness can be naturally formed on the surface of the strip steel, so that the produced steel has weather resistance; meanwhile, the novel LED lamp has certain manufacturing and cost advantages in thin-specification use occasions. The specification characteristic thickness of the thin-specification high-strength fire-resistant weather-resistant steel plate/strip is 1.2-2.0mm, and because the product thickness is thin, if the production is difficult by adopting a traditional continuous casting and hot continuous rolling production line, the roll consumption of a roll is large even if the thin slab continuous casting and rolling production is adopted, and the production cost of the thin-specification high-strength fire-resistant weather-resistant steel plate/strip is increased by the production process.

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 should be controlled in the subsequent stages of the strip casting, that the oxidation of the strip be prevented by using a closed chamber device in the crystallization rolls up to the entrance of the rolling mill, that the thickness of the scale on the surface of the strip be controlled by adding hydrogen in the closed chamber device, for example, 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 (rusts) are formed on the surface of strip steel, which affects the surface quality; 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 unevenness, which can cause the uneven structure of the final product obtained after austenite phase transformation, thereby causing the instability of the performance of the product, particularly the forming performance. Therefore, the method for producing the high-strength fire-resistant weather-resistant steel plate/strip product by adopting the thin-strip continuous casting process has certain difficulty and challenge, and needs to make a breakthrough in composition and process.

Chinese patent CN200610123458.1 discloses a method for producing 700MPa grade high strength weathering steel by Ti micro alloying process based on thin slab continuous casting and rolling process, the chemical components of the weathering steel plate manufactured by the method are: c:0.03 to 0.07%, si:0.3-0.5%, mn:1.2-1.5, P is less than or equal to 0.04%, S is less than or equal to 0.008%, al:0.025-0.05%, cr:0.3-0.7%, ni:0.15-0.35%, cu:0.2-0.5%, ti:0.08 to 0.14 percent of the total weight of the alloy, less than or equal to 0.008 percent of N and the balance of Fe and inevitable impurities. The yield strength of the steel plate is more than or equal to 700MPa, the tensile strength is more than or equal to 775MPa, and the elongation is more than or equal to 21 percent. In the patent, the phosphorus is controlled according to impurity elements, the content is less than or equal to 0.04 percent, and is less than or equal to 0.025 percent compared with the traditional process, which is relaxed.

Chinese patent CN200610035800.2 discloses a method for producing 700MPa V-N microalloying weathering steel based on a thin slab continuous casting and rolling process, and the chemical components of the weathering steel plate manufactured by the method are as follows: c is less than or equal to 0.08%, si:0.25-0.75%, mn:0.8-2, P is less than or equal to 0.07-0.15%, S is less than or equal to 0.04%, cr:0.3-1.25%, ni: less than or equal to 0.65%, cu:0.25-0.6%, V:0.05-0.2%, N:0.015 to 0.03 percent, and the balance of Fe and inevitable impurities. The yield strength of the steel plate is more than or equal to 700MPa, the tensile strength is more than or equal to 785MPa, and the elongation is more than or equal to 21%. In this patent, phosphorus is controlled according to elements for improving weather resistance, and the content is 0.07-0.15%; the copper content is 0.25-0.6%, and the lower limit and the upper limit are respectively 0.2% and 0.55% higher than the lower limit and the upper limit of the copper content of the traditional process.

Chinese patent CN1633509A discloses a method for producing copper-containing carbon steel products by strip casting, which emphasizes that the strip is subjected to heat treatment processes such as annealing and tempering at 400-700 ℃ to precipitate or recrystallize copper elements in the strip. The manufacturing method of the high-copper low-alloy thin strip mentioned in the patent US2008264525/CN200580009354.1 is technically characterized in that the strip steel is cooled to be lower than 1080 ℃ in non-oxidizing atmosphere before entering a rolling mill so as to prevent the strip steel from generating the phenomenon of hot brittleness.

These patents all relate to the weather resistance of steel, but do not relate to the effect of fire resistance, and the present invention is a steel grade specifically proposed for the fire and weather resistance characteristics.

Disclosure of Invention

The invention aims to provide a high-strength thin-specification fire-resistant weather-resistant steel plate/steel belt and a production method thereof, the produced fire-resistant weather-resistant steel plate/steel belt can ensure that the steel keeps higher strength level at high temperature, the quality of a building can be reduced, the safety of the building is improved, and the construction cost is reduced; meanwhile, by utilizing the technological characteristics of thin-strip continuous casting, the surface of the produced fire-resistant weather-resistant steel plate/strip naturally forms a fine grain layer with a certain thickness on the basis of fire resistance, so that the product has weather resistance; the product has excellent earthquake resistance and excellent fire resistance, is an ideal material in the field of steel for earthquake resistance and fire prevention, can be widely applied to industries and fields of construction steel with fireproof and earthquake resistance requirements, tower and mast column, engineering machinery, industrial structures and the like, and is particularly applied to places with higher fire safety requirements such as high-rise buildings, large public buildings, high-grade houses and the like.

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

the method utilizes residual elements such as Sn, cu and the like in the scrap steel to smelt the molten steel, and selectively adds microalloy elements such as Mo/Nb/Cr and the like into the steel; in the smelting process, the alkalinity of slag, the type and melting point of inclusions in steel, the free oxygen content in molten steel and the content of acid-soluble aluminum Als are controlled; 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 plate/strip, and can also be used as a finishing plate/strip after edge cutting and flattening.

Specifically, the high-strength thin-specification fire-resistant weather-resistant steel plate/steel strip comprises the following chemical components in percentage by weight: c:0.02 to 0.06%, si:0.1-0.55%, mn:0.4-1.7%, P: less than or equal to 0.03%, S: less than or equal to 0.007%, cr:0.30-0.80%, mo:0.20-0.60%, nb:0.01-0.08%, N:0.004-0.010%, als:<0.001%, total oxygen [ O ]] _T :0.007-0.020%, the balance being Fe and other unavoidable impurities, and, simultaneously:

further contains Cu:0.10-0.60%, or Sn:0.005-0.04% of one or two elements;

Mn/S>250；

Pcm≤0.27％，Pcm＝C+Si/30+Mn/20+Cu/20+Cr/20+Mo/15+5B。

according to the invention, the microstructure of the fire-resistant weather-resistant steel plate/steel strip is a mixed microstructure of block ferrite, pearlite and acicular ferrite, or a mixed microstructure of block ferrite, pearlite and lower bainite.

The invention relates to a high-strength fire-resistant weather-resistant steel plate/belt, which comprises the following chemical components in the design:

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 greatly impair the plasticity and toughness of steel, and an excessively high C content is disadvantageous in weldability, the C content cannot be excessively high, and the strength of steel is compensated by appropriate addition of alloy 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 0.02-0.06%.

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 0.1-0.55%.

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 0.4-1.7%.

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 0.03 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, al is avoided from being additionally introduced as much as possible in the use of refractory materials, and the content of acid-soluble aluminum Als is strictly controlled as follows: <0.001%.

N: similar to the element C, the element N can improve the strength of the steel through interstitial solid solution, but the interstitial solid solution of the element N has great harm to the plasticity and the toughness of the steel, and the yield ratio of the steel can be improved due to the existence of free N, so that the content of the element N cannot be too high. The content range of N adopted by the invention is 0.004-0.010%.

Cr: the Cr is added into the fire-resistant weathering steel, so that the high-temperature strength and creep strength of the steel are improved, the weather resistance of the steel is improved, and the corrosion resistance of the steel can be obviously improved. However, the welding property is seriously deteriorated by too high a content thereof, and the Cr content is limited to 0.30 to 0.80% in the present invention.

Nb: in the refractory steel, nb is mainly used to improve the high-temperature strength of the steel by precipitation strengthening of NbC in ferrite. Meanwhile, in the strip continuous casting process, due to the unique characteristics of rapid solidification and rapid cooling, the added alloy element Nb can exist in the steel strip in a solid solution state more, and the Nb element which is in solid solution in the steel can play a role in solid solution strengthening. The content range of Nb designed by the invention is 0.01-0.08%.

Mo: the solid solution in the ferrite strengthens the ferrite matrix, and the diffusion speed of Mo in the ferrite is slow at high temperature, so that the high-temperature strength and creep strength of the steel can be obviously improved. Research shows that the solid-dissolved Mo is easy to segregate on the grain boundary, and plays a role in improving the high-temperature strength of the steel; mo can also increase the stability of super-cooled austenite, and the volume fraction of bainite in steel is increased after Mo is added; the bainite structure with high dislocation density enables the refractory weathering steel to obtain good high-temperature performance. Mo precipitates in steel to form carbide, which improves the high-temperature strength of the steel. Research shows that better precipitation strengthening effect can be generated after Nb and Mo are added in a composite way: the 1 st view is that in the composite addition, in addition to the strengthening effect of adding Nb and Mo separately, mo can be enriched on an NbC/matrix interface, so that the coarsening of NbC particles is prevented, and the high-temperature strength of the steel is further improved; the 2 nd view suggests that Mo reduces the driving force for NbC precipitation, hinders the diffusion nucleation process of NbC, delays the NbC precipitation, promotes bainite transformation in steel, increases the dislocation density, and increases the NbC nucleation sites. These result in a better precipitation strengthening effect, which in turn improves the high temperature strength of the steel. Too high Mo increases the raw material smelting cost of the steel. Therefore, the content range of Mo designed by the invention is 0.20-0.60%.

Cu: the Cu is an element for improving the weather resistance, and the Cu is an easily-segregated element, so that the Cu content is generally strictly controlled in the traditional process flow. The invention improves the upper limit of Cu to 0.60% by applying the rapid solidification effect of thin strip continuous casting. The improvement of the Cu content can fully utilize the scrap steel in a certain sense, and screening can be omitted when the scrap steel raw material is prepared, so that the smelting operation rate is improved, the cost is reduced, the recycling of the steel is promoted, and the purpose of sustainable development is realized; and the effective utilization of copper in poor-quality ore resources (such as high copper ore) can be realized.

Sn: the Sn element is one of main residual elements in scrap steel and is generally recognized as a harmful element in steel, because Sn is an easily segregated element, a small amount of Sn is enriched in grain boundaries, and defects such as cracks occur, so that the content of the Sn element is strictly controlled in the conventional process. Due to the characteristic of rapid solidification, segregation of elements among dendrites is greatly reduced, and the solid solution amount of the elements can be greatly improved, so that the range of Sn elements can be expanded under the condition of a strip continuous casting process, and the steelmaking cost can be greatly reduced. Fig. 2 is a relationship between Sn element and average heat flux density. As can be seen from fig. 2, when the Sn addition is less than 0.04%, the influence on the heat flux density is not great, i.e., the ribbon solidification process is not affected. FIG. 3 is a relationship between Sn content and surface roughness. Since cracks on the surface of the cast strip usually occur at the uneven folds on the surface of the cast strip, the surface roughness is used to characterize the occurrence of surface cracks. If the roughness is large, the probability of occurrence of cracks is high. As is clear from FIG. 3, the increase in Sn content does not adversely affect the surface quality of the cast strip under the rapid solidification conditions. From the results of fig. 2 and 3, it is clear that Sn does not adversely affect the solidification and surface quality of the cast strip. Therefore, in the present invention, the requirement for Sn content can be further relaxed, and the Sn content is designed to be in the range of 0.005-0.04%.

In order to ensure the welding performance of the steel grade, the elements are designed to satisfy the following relational expression:

Pcm(％)＝C+Si/30+Mn/20+Cu/20+Cr/20+Mo/15+5B≤0.27。

the invention relates to a production method of a high-strength thin-specification fire-resistant weather-resistant steel plate/steel strip, which comprises the following steps:

1) Smelting of

Smelting according to the chemical composition requirements, wherein the slagging alkalinity a = CaO/SiO in the steelmaking process ₂ Is controlled at 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%; in molten steel composition, mn/S>250；

2) Continuous casting

The continuous casting adopts double-roller thin strip continuous casting, and a casting strip with the thickness of 1.5-3mm is formed at the minimum position of a gap between two crystallizing rollers; the diameter of the crystallization roller is 500-1500mm, and the preferred diameter is 800mm; cooling the crystallization roller by introducing water, wherein 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 enclosed chamber protection

The temperature of the cast strip after the cast strip is taken out of the crystallization roller is 1420-1480 ℃, the cast strip directly enters a lower closed chamber, non-oxidizing gas is introduced into the lower closed chamber, and the oxygen concentration in the lower closed chamber is controlled to be less than 5%; 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 through pinch rolls in a lower closed chamber, and rolling the cast strip into strip steel, wherein the rolling temperature is 1100-1250 ℃, and the hot rolling reduction is controlled to be 10-50%, preferably 30-50%; the thickness of the hot rolled steel strip is 0.8-2.5mm, and the preferable thickness is 1.2-2.0mm;

5) Cooling after rolling

Cooling the strip steel after the online hot rolling, and cooling the strip steel by adopting an air atomization cooling mode after rolling at a cooling rate of 20-100 ℃/s;

6) Strip steel coiling

And cutting the head of the cooled hot-rolled strip steel to remove the head with poor quality, and directly coiling the hot-rolled strip steel into coils at the coiling temperature of 500-600 ℃.

Further, the method also comprises a step 7), wherein the steel coil is directly used as a hot rolled plate/strip or used as a finishing plate/strip after edge cutting and flattening.

Preferably, in the step 1), 100% of all-waste steel can be selected as smelting raw materials, pre-screening is not needed, and electric furnace steelmaking is adopted for molten steel smelting; or, the smelting adopts a converter for steelmaking, the scrap steel is added into the converter according to the proportion of more than 20 percent of the smelting raw materials, and pre-screening is not needed; then refining in an LF furnace, a VD/VOD furnace or an RH furnace.

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

Preferably, the gas-water ratio of the gas atomization 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.

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

In the production 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 Control 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. red shaded areas, mnO-SiO, FIG. 4 ₂ -Al ₂ O ₃ MnO/SiO in ternary inclusions ₂ The content is controlled to be 0.5 to 2, and further 1 to 1.8.

In order to improve the castability of thin strip continuous casting molten steel, oxygen (O) in the steel is an essential element for forming oxide inclusions, and 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.

The molten steel can be smelted by an electric furnace or a converter and then enters necessary refining processes, such as an LF furnace, a VD/VOD furnace, an RH furnace and the like.

In order to save investment cost and production cost, modern iron and steel production enterprises actively carry out technical innovation on the prior production process flow. Aiming at the problems of long process, more equipment and complexity of the existing hot strip steel production process, a plurality of manufacturers tightly combine the continuous casting and rolling technology with the traditional process so as to meet the requirements of the continuous casting and rolling technology.

When converter steelmaking is adopted to provide molten steel, production plants and furniture are required to be provided with molten iron providing conditions, and blast furnace ironmaking equipment or non-blast furnace ironmaking equipment is required under the general condition, so that the method belongs to the current long-flow steel production mode. However, nowadays, the steel scrap resource is increasingly abundant, the country advocates improving the steel scrap ratio of the converter so as to achieve the purposes of energy saving, consumption reduction and cost reduction, the average level of the steel scrap ratio of the converter is about 8 percent in the past, and the steel scrap ratio of the converter is 15-25 percent in the present and future. The converter scrap ratio of the invention reaches more than 20 percent.

When molten steel is provided by electric steelmaking, the steel scrap is used as a main raw material, and the solidification cooling speed of the traditional process such as die casting or thick plate continuous casting is only 10 ^-1 10 ℃/s, the residual elements in the steel scrap can generate grain boundary segregation during the solidification process, deteriorate the performance and quality of the steel, and directly generate cracking and breaking phenomena in severe cases, so that in the traditional process, the harmful elements need to be strictly controlled, in the selection of the steel scrap raw materials, some pre-screening needs to be carried out, and in the steel-making process, some special treatment needs to be carried out, such as adding some fine materials for dilution, and the like, which undoubtedly increases the production operation cost. Because the components of steel need to be controlled, certain quality requirements are required for the adopted steel scrap raw materials, and the steel scrap needs to be pre-screened and classified under general conditions. In order to improve the production efficiency of some domestic electric steel mills, concentrated materials such as outsourcing sponge iron, iron carbide and the like are selectively added into the raw material composition to dilute harmful elements which are difficult to remove in the scrap steel, so that the quality of molten steel is improved. Some domestic steel mills with blast furnaces and electric furnaces simultaneously utilize self-produced molten iron to be added into the electric furnaces as raw materials of the electric furnaces to improve the production efficiency of the electric furnaces, thereby greatly shortening the tapping time of the electric furnaces, and the molten iron blending ratio in the electric furnaces can reach 30-50%.

The adoption of twin-roll thin-strip casting technology is a typical sub-rapid solidification process, and the solidification cooling speed is as high as 10 ² -10 ⁴ The residual harmful elements in the scrap steel, such as Cu, sn, P and the like, can be dissolved in the matrix of the steel to the maximum extent without generating grain boundary segregation, so that 100 percent of total scrap steel smelting can be realized, pre-screening is not needed, and the raw material cost is greatly reduced. The residual elements can also play a role in solid solution strengthening, so that ultrathin hot rolled strip steel with excellent performance is produced. Realizes the comprehensive utilization of the production of inferior steel scrap resources, and has the effects of turning harmful into beneficial and utilizing waste on the harmful residual elements in the steel scrap.

After the strip casting strip steel is taken out of the crystallization roller, the temperature of the strip casting is 1420-1480 ℃, the strip casting directly enters a lower closed chamber, the strip steel is protected by non-oxidizing gas in the lower closed chamber, the strip steel is protected against oxidation, the atmosphere of the oxidation protection can be N2, ar or other non-oxidizing gases, such as CO2 gas obtained by sublimation of dry ice, and the oxygen concentration in the lower closed chamber is controlled to be less than 5%. The lower closed chamber protects the cast strip from oxidation to the inlet of the rolling mill, and the temperature of the cast strip at the outlet of the lower closed chamber is 1150-1300 ℃.

And cooling the strip steel after the online hot rolling, and cooling the strip steel by adopting an air atomization cooling mode after the strip steel is rolled, wherein the air atomization cooling mode can effectively reduce the thickness of the oxide scale 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 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 the 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 be coated 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.

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 of the hot rolled strip was controlled to 500-600 ℃, and the high temperature austenite structure after rolling was transformed into a mixed microstructure of bulk ferrite + pearlite + acicular ferrite, or a mixed microstructure of bulk ferrite + pearlite + lower bainite, as shown in fig. 5. The coiler adopts a double-coiling form and a carrousel coiling form to ensure the continuous production of the strip steel.

Through the manufacturing process, the performance of the final high-strength fire-resistant weather-resistant steel plate/belt can reach the following levels: the yield strength at room temperature is more than or equal to 410MPa, the tensile strength is more than or equal to 590MPa, and the elongation is more than or equal to 17 percent; yield ratio sigma _s /σ _b Less than or equal to 0.8; the yield strength at 600 ℃ is more than or equal to 275MPa and sigma _s，600℃ /σ _s，20℃ Not less than 0.67; the relative corrosion rate is less than or equal to 60 percent.

The invention has the main advantages that:

the invention utilizes the thin strip continuous casting technology to produce the high-strength fire-resistant weathering steel containing tin (Sn), copper (Cu)/tin (Sn) and copper (Cu), and reports are not found so far, and the advantages are summarized as follows:

1. 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.

2. The invention omits a plurality of complex intermediate steps in the production of the traditional process, and compared with the traditional production process, the energy consumption and CO2 emission of the production are greatly reduced, thus the invention is a green and environment-friendly product.

3. The invention adopts the thin strip continuous casting process to produce the hot-rolled thin high-strength fire-resistant weathering steel, and because of the sub-rapid solidification characteristic of the thin strip continuous casting process, a fine crystal layer with a certain thickness can be naturally formed on the surface of the strip steel, so that the produced steel grade has weather resistance; meanwhile, the thickness of the cast strip is thin, and the thin-specification product can be directly supplied to the market for use by online hot rolling to the desired product thickness, so that the purpose of supplying the thin-specification hot rolled plate is achieved, and the cost performance of the plate strip can be obviously improved.

4. The electric furnace is adopted for smelting, the smelting raw materials can realize 100 percent of all-scrap steel smelting in the true sense, pre-screening is not needed, and the raw material cost is greatly reduced; if the converter is adopted for smelting steel, the scrap steel is added into the converter according to the proportion accounting for more than 20 percent of smelting raw materials, and pre-screening is not needed, so that the scrap steel ratio of the converter is improved to the maximum extent, and the smelting cost and the energy consumption are greatly reduced.

5. The invention utilizes the scrap steel containing Cu and Sn to turn the Cu and Sn in the steel into harmful and beneficial, realizes the full utilization of the existing scrap steel or low-quality inferior ore resources (high-tin ore and high-copper ore), promotes the recycling of the scrap steel, reduces the production cost and realizes the sustainable development of the steel industry.

6. The invention adopts the gas atomization rapid quenching mode of the rolled strip steel, can avoid the problems brought by the traditional spraying or laminar cooling, uniformly reduces the surface temperature of the strip steel, and improves the temperature uniformity of the strip steel, thereby achieving the effect of homogenizing the internal microstructure and improving the yield ratio of the material; 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, the alloy elements are precipitated 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. According to the invention, a hot rolled steel strip carrousel coiler 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.

9. 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. CASTRIP adopts a three-stage molten steel 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.

10. The diameter of the crystallization roller is 500-1500mm, preferably the diameter of the crystallization roller is 800mm, 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 a two-stage flow distribution system is adopted, compared with a three-stage flow distribution system, the cost of the refractory material is greatly reduced; the flow path of the molten steel is shortened, so that the temperature drop of the molten steel is reduced, the tapping temperature can be reduced, and compared with a three-level flow distribution system, the tapping temperature can be reduced by 30-50 ℃. 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.

Drawings

Fig. 1 is a schematic layout of a twin roll strip casting process;

FIG. 2 is a graph showing the relationship between Sn content and average heat flux density;

FIG. 3 is a schematic representation of the relationship between Sn content and surface roughness of a cast strip;

FIG. 4 shows MnO-SiO ₂ -Al ₂ O ₃ Ternary phase diagram (shaded area: low melting point region);

FIG. 5 is a photograph showing the microstructure of the steel according to the example of the present invention.

Detailed Description

The invention will be further elucidated by the following examples and figures, which are by no means limitative in any way. Any variations in the practice of the invention which may occur to those skilled in the art and which fall within the scope of the appended claims will be deemed to fall within the scope of the invention.

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, and water is introduced into the crystallization roller for cooling. 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 comes out of the crystallization rollers 8a and 8b, the cast strip is at 1420-1480 deg.C and directly enters the lower closed chamber 10, the lower closed chamber 10 is filled with non-oxidizing gas to protect the cast strip 11, so as to realize the oxidation prevention protection of the cast strip 11, and the atmosphere of the oxidation prevention protection can be N ₂ 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, the lower closed chamber 10 protects the casting strip 11 from oxidation to the inlet of a rolling mill 13, and the temperature of the casting strip at the outlet of the lower closed chamber 10 is 1150-1300 ℃; then the cast strip 11 is sent to a rolling mill 13 through a swing guide plate 9 and a pinch roll 12, hot rolling is carried out to form a hot rolled strip steel with the thickness of 0.8-2.5mm, and the rolled strip steel is cooled by adopting an air atomization cooling mode to improve the temperature uniformity of the strip steel; 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 down from the coiling machine, and naturally cooling to room temperature. The finally produced steel coil can be directly used as a hot rolled plate/strip, and can also be used as a finishing plate/strip 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 manufacturing method of the invention has the process parameters shown in the table 2, and the mechanical properties of the finally obtained hot rolled strip are shown in the table 3.

The corrosion resistance of the example steels was tested: a72 h period infiltration cycle corrosion test is carried out according to a 72h period infiltration corrosion test method (TB/T2375-1993) by taking a common carbon steel Q345B as a comparison sample. And calculating the corrosion weight loss of the sample in unit area to obtain the average corrosion rate and further obtain the relative corrosion rate of the steel grade. The test results are shown in Table 4.

In conclusion, the high-strength thin-specification fire-resistant weather-resistant steel plate/strip manufactured by the thin-strip continuous casting process technology according to the design range of the steel grade components provided by the invention has the room-temperature yield strength of more than or equal to 410MPa, the tensile strength of more than or equal to 590MPa and the elongation of more than or equal to 17 percent; yield ratio sigma _s /σ _b Less than or equal to 0.8; the yield strength at 600 ℃ is more than or equal to 275MPa and sigma _s，600℃ /σ _s，20℃ Not less than 0.67; and the cold-processing bending performance is qualified.

The comparison result of the corrosion resistance also shows that the relative corrosion rate of the steel grade is less than or equal to 60 percent. The material meets and exceeds the performance requirements of fire-resistant and weather-resistant steel, can realize the supply of thin hot-rolled products, greatly reduces the production cost, has low yield ratio of materials, excellent earthquake resistance and excellent fire resistance, and is an ideal material in the field of earthquake-resistant and fire-resistant steel.

Claims

1. A production method of a high-strength thin-specification fire-resistant weather-resistant steel plate/steel strip comprises the following chemical components in percentage by weight: c:0.02-0.06%, si:0.1-0.55%, mn:0.4-1.7%, P: less than or equal to 0.03%, S: less than or equal to 0.007 percent, cr:0.30-0.80%, mo:0.20-0.60%, nb:0.01-0.08%, N:0.004-0.010%, als:<0.001%, total oxygen [ O ]] _T :0.007-0.020%, the balance being Fe and other unavoidable impurities, and, simultaneously:

further contains Cu:0.10-0.60%, or Sn:0.005-0.04% of one or two elements;

Mn/S>250；

Pcm≤0.27％，Pcm＝C+Si/30+Mn/20+Cu/20+Cr/20+Mo/15+5B；

the microstructure of the high-strength thin-specification fire-resistant weather-resistant steel plate/steel strip is a mixed microstructure of massive ferrite, pearlite and acicular ferrite, or a mixed microstructure of massive ferrite, pearlite and lower bainite;

the performance of the high-strength thin-specification fire-resistant weather-resistant steel plate/belt reaches: the yield strength at room temperature is 410-443 MPa, the tensile strength is more than or equal to 590MPa, and the elongation is more than or equal to 17 percent; yield ratio sigma _s /σ _b Less than or equal to 0.8; the yield strength at 600 ℃ is more than or equal to 275MPa and sigma _s，600℃ /σ _s，20℃ Not less than 0.67; the relative corrosion rate is less than or equal to 60 percent;

the method specifically comprises the following steps:

1) Smelting of

Smelting according to the chemical composition requirement, wherein the alkalinity a = CaO/SiO of slagging in the steelmaking process 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 to 0.005 percent; in molten steel composition, mn/S>250；

2) Continuous casting

The continuous casting adopts double-roller thin strip continuous casting, and a casting strip with the thickness of 1.5-3mm is formed at the minimum position of a gap between two crystallizing rollers; the diameter of the crystallization roller is 500-1500 mm; cooling the crystallization roller by introducing water, wherein 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 enclosed chamber protection

4) In-line hot rolling

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

5) Cooling after rolling

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

6) Strip steel coiling

2. The method for producing a high-strength thin-gauge fire-resistant and weather-resistant steel plate/strip as claimed in claim 1, further comprising a step 7) of using the steel coil as a hot-rolled plate/strip directly or as a finished plate/strip after trimming and flattening.

3. The method for producing the high-strength thin-specification fire-resistant weather-resistant steel plate/strip as claimed in claim 1, wherein in the step 1), 100% of all scrap steel is selected as the smelting raw material, pre-screening is not required, and electric furnace steelmaking is adopted for smelting molten steel; or, the smelting adopts a converter for steelmaking, the scrap steel is added into the converter according to the proportion of more than 20 percent of the smelting raw materials, and pre-screening is not needed; then refining in an LF furnace, a VD/VOD furnace or an RH furnace.

4. The method for producing a high-strength thin-gauge fire-resistant and weather-resistant steel sheet/strip as claimed in claim 1, wherein the non-oxidizing gas of step 3) is N ₂ CO obtained by sublimation of Ar or dry ice ₂ A gas.

5. The method for producing a high-strength thin-gauge fire-resistant and weather-resistant steel plate/strip as claimed in claim 1, wherein the gas-water ratio of the gas-atomization cooling in 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.

6. The method for producing a high-strength thin-gauge fire and weather resistant steel plate/strip as claimed in claim 1, wherein in the step 6), the coiling is performed in a twin-coiler type or a carrousel coiling type.

7. The method for producing a high-strength thin-gauge fire-resistant and weather-resistant steel sheet/strip as claimed in claim 1, wherein in the step 1), a low melting point is obtained in the molten steelPoint MnO-SiO ₂ -Al ₂ O ₃ MnO/SiO in ternary inclusions ₂ The temperature is controlled to be 1-1.8.

8. The method for producing a high-strength thin-gauge fire and weather resistant steel plate/strip as claimed in claim 1, wherein in the step 2), the diameter of the crystallizing roller is 800mm.

9. The method for producing a high-strength thin-gauge fire and weather resistant steel plate/strip as claimed in claim 1, wherein the hot rolling reduction in the step 4) is 30 to 50%.

10. The method for producing a high-strength thin-gauge fire and weather resistant steel plate/strip as claimed in claim 1 or 9, wherein in the step 4), the thickness of the hot-rolled steel strip is 1.2 to 2.0mm.