CN112522638B

CN112522638B - Fire-resistant weather-resistant steel plate/belt and production method thereof

Info

Publication number: CN112522638B
Application number: CN201910889382.0A
Authority: CN
Inventors: 吴建春; 秦波; 方园
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: CN112522638A

Abstract

A fire-resistant weather-resistant steel plate/belt and a production method thereof are disclosed, which 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 is less than or equal to 0.03%, S is less than or equal to 0.007%, cr:0.30-0.80%, cu:0.10-0.60%, mo:0.20-0.60%, N:0.004-0.010% of Als<0.001% of total oxygen [ O ]] _T :0.007-0.020%, the balance of Fe and other inevitable impurities, and Mn/S>250 of (a); pcm is less than or equal to 0.27 percent. The fire-resistant weather-resistant steel plate/strip produced by the invention can ensure that the steel keeps higher strength level at high temperature, also can lighten the quality of a building, increase the safety of the building and reduce the construction cost; meanwhile, by utilizing the technological characteristics of thin strip continuous casting, the produced fire-resistant weather-resistant steel plate/strip naturally forms a fine crystal layer with a certain thickness on the surface of the strip steel on the basis of the fire resistance, so that the product has weather resistance.

Description

Fire-resistant weather-resistant steel plate/belt and production method thereof

Technical Field

The invention belongs to a twin-roll thin strip continuous casting process, and particularly relates to a fire-resistant weather-resistant steel plate/strip and a production 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, after the casting blank is reheated and heat preserved, 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 process flow of the thin slab continuous casting and rolling comprises the following steps: 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 supplementing a small amount of heat, so that the thin slab process greatly shortens the process flow, reduces the energy consumption and the investment, thereby reducing the production cost. However, the strength of steel and the yield ratio of the sheet billet can be improved due to the faster cooling speed in the continuous casting and rolling of the sheet billet, 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.

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 the continuously cast plate blank of the continuous casting machine is 90-110mm, the width of the continuously cast plate blank is 1100-1600mm, the continuously cast plate blank plays a role in heat preservation and uniform heating on the plate blank through a section of induction heating roller way, and then the continuously cast 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 0.8mm thickness, expands the specification range of the hot rolled plate, and has the output of a single production line reaching 220 ten thousand tons 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 large ladle 1 is directly poured into a molten pool 7 surrounded by two oppositely rotating and rapidly cooled crystallizing

rolls

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

rolls

8a and 8b, then a casting strip 11 with the thickness of 1-5mm is formed at the minimum gap (nip point) between the two crystallizing rolls, the casting strip is guided to a pinch roll 12 through a guide plate 9 and is fed into a rolling mill 13 to be rolled into a thin strip with the thickness of 0.7-2.5mm, then the thin strip is cooled through a cooling device 14 and is cut by a flying shear device 16 and then is 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 plates/belts are increasingly applied to industries and fields such as construction steel with fire-proof requirements, tower and mast columns, engineering machinery, industrial structures and the like, and are particularly widely applied to places with high fire-fighting 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 weathering steel is loaded at normal temperature, but is required to maintain higher yield strength under the short-time (usually 1-3 h) high-temperature condition of fire, and can gain precious time for the safe evacuation of personnel, so that the fire-resistant weathering steel belongs to the category of low-alloy structural steel, and excessive expensive alloy elements are not suitable to be added in the component design.

The safety design specifications for the steel structure in Japan stipulate: 2/3 of the yield strength of the steel at normal temperature is equivalent to the long-term allowable stress value of the material, and when a fire disaster occurs, 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 (sigma) of the steel _s /σ _b ) Higher, will be generated when earthquake occursThe local stress concentrates and the local large deformation, and at the moment, the steel structure can only absorb less energy, so the low yield ratio is beneficial to improving the energy absorbed by the building structure when earthquake occurs, and the yield ratio of the earthquake-resistant, fire-resistant and weather-resistant steel is generally required to be less than or equal to 0.8.

One of the keys to the development of fire resistant weathering steels is to set the fire temperature at which it is desired to achieve high temperature strength. Mo-containing steel which can resist the high temperature of 900-1000 ℃ has been researched in European Creusot-Loire steel works, but the Mo-containing steel is not popularized and applied due to high cost. In order to determine the fire-resistant temperature which is best matched with the reduction of the production cost and the consumption of the fire-resistant materials, the new-day iron is subjected to high-temperature tensile tests on several typical steels with the tensile strength of 400-780MPa, and the tests show 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 temperature for ensuring the strength is set at 700 ℃, a large amount of alloy elements must be added, which makes it difficult to ensure good weldability and greatly increases the cost. 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 conclusion, according to 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 that of 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 thin-gauge cable has certain manufacturing and cost advantages in thin-gauge 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 at each stage of the subsequent casting of the strip, and in the twin roll strip casting process, the closed chamber is used up to the entrance of the rolling mill for the crystallization 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 in the closed chamber 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 high temperature strip comes into contact with the 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 on the surface of the strip steel is not uniform, 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 instability of the performance, particularly the forming performance, of the product. Therefore, the method for producing the fire-resistant weather-resistant steel plate/strip product by adopting the thin strip continuous casting process has certain difficulty and challenge, needs to make a breakthrough in composition and process, and effectively improves the uniformity of the structure by reasonable cooling measures after rolling to achieve the aim of reducing the yield ratio.

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, so that the phosphorus content is relaxed.

Chinese patent CN200610035800.2 discloses a method for producing 700MPa grade V-N microalloyed weathering steel based on thin slab continuous casting and rolling process, the chemical components of the weathering steel plate manufactured by the method are: c: less than or equal to 0.08 percent, si:0.25-0.75%, mn:0.8-2, P: less than or equal to 0.07-0.15 percent, S: less than or equal to 0.04 percent, 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 weathering resistance of the steel, but none relate to the effect of fire resistance.

Disclosure of Invention

The invention aims to provide a fire-resistant weather-resistant steel plate/belt and a production method thereof, the produced fire-resistant weather-resistant steel plate/belt can ensure that 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 produced fire-resistant weather-resistant steel plate/strip naturally forms a fine crystal layer with a certain thickness on the surface of the strip steel on the basis of the 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 resistance, can be widely applied to industries and fields of construction steel with fireproof and earthquake resistance requirements, tower column columns, 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:

in the invention, microalloy elements such as Mo/Cr and the like and B elements are selectively added into 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.

the fire-resistant weather-resistant steel plate/belt 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 is less than or equal to 0.03%, S is less than or equal to 0.007%, cr:0.30-0.80%, cu:0.10-0.60%, mo:0.20-0.60%, N:0.004-0.010%, als<0.001% of total oxygen [ O ]] _T :0.007 to 0.020 percent, and the balance of Fe and other inevitable impurities; and simultaneously satisfies:

Mn/S>250；

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

in the chemical composition design of the fire-resistant weather-resistant steel plate/belt, the following steps are carried out:

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 grade of the steel is determined to a large extent by the C content, i.e. higher C content corresponds to higher strength grade. 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 a steel leakage accident 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, the thin strip casting of Fe-C alloy also needs to avoid the peritectic reaction zone. Therefore, the C content range 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 a 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 segregate in grain boundary, increases the cold brittleness of steel, deteriorates the welding performance, reduces the plasticity and deteriorates the 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, which causes hot brittleness, decreases ductility and toughness, 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 refractory materials, the additional introduction of Al is avoided as much as possible, and the content of acid-soluble aluminum Als is strictly controlled: <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.

Mo: solid solution in ferrite strengthens the ferrite matrix, and Mo has a low diffusion speed in the ferrite 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 fire-resistant weathering steel to obtain good high-temperature performance. Mo precipitates in steel to form carbide, which improves the high-temperature strength of the steel. Too high Mo increases the raw material smelting cost of the steel. In the present invention, the Mo content is limited to 0.20 to 0.60%.

Cu: the Cu is also an element for improving 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.

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

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

the invention relates to a production method of a fire-resistant weather-resistant steel plate/belt, which comprises the following steps:

a) Smelting

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

b) 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 position with the minimum 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; a two-stage steel water distribution system is adopted for continuous casting flow distribution, namely a tundish and a flow distributor;

c) 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 ℃;

d) In-line hot rolling

The cast strip which is taken out of the lower closed chamber is sent to a rolling mill through a pinch roll and rolled into strip steel with the thickness of 0.8-2.5mm, the rolling temperature is 1100-1250 ℃, and the hot rolling reduction rate is 10-50%;

e) Cooling after rolling strip steel

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

f) Strip steel coiling

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, wherein the coiling temperature of the hot-rolled strip steel is controlled to be 580-680 ℃.

Further, the method also comprises a step g) of directly using a steel coil formed after the strip steel is coiled as a hot rolled plate/strip or using the steel coil as a finishing plate/strip after edge cutting and flattening.

In a preferred step c), the non-oxidizing gas comprises: n is a radical of hydrogen ₂ Ar, or CO obtained by sublimation on dry ice ₂ A gas.

Preferably, the hot rolling reduction rate of the step d) ranges from 30 to 50 percent, and the thickness of the strip steel is 0.8 to 2.5mm or 1.2 to 2.0mm.

Preferably, in the step e), 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, the step f) take-up is in the form of a twin winder or in the form of a carrousel take-up.

In the production method of the present invention:

in order to improve the castability of the strip-cast molten steel, the basicity of the slagging in the steel-making process a = CaO/SiO ₂ Control in 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. grey shaded area in FIG. 2, mnO-SiO ₂ -Al ₂ O ₃ MnO/SiO in ternary inclusions ₂ The concentration is controlled to be 0.5 to 2, preferably 1 to 1.8.

In order to improve the castability of thin strip cast 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 control of Mn and S in the components must satisfy: mn/S >250.

And cooling the strip steel after the online hot rolling, wherein the strip steel after the online hot rolling is cooled by adopting an air atomization cooling mode, and the cooling rate range of the air atomization cooling is 20-100 ℃/s.

The gas atomization cooling mode can effectively reduce the thickness of 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 the oxide scale on the surface of the strip steel.

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 is controlled to be 580-680 ℃, so that the rolled high-temperature austenite structure is transformed into a mixed microstructure of bulk ferrite + pearlite + acicular ferrite, or a mixed microstructure of bulk ferrite + pearlite + lower bainite, as shown in figure 3.

The invention is suitable for pouring metal cast steel strips with the thickness of 1.5-3mm by using a double-roller type thin strip continuous casting machine, in particular to hot-rolled fireproof weather-resistant steel plates/strips.

The invention has the main advantages that:

1. the invention adopts the thin strip continuous casting process to produce the fire-resistant weather-resistant steel plate/strip, and has certain manufacturing and cost advantages in thin-specification use occasions. The thin-specification fire-resistant weather-resistant steel plate/strip has the product specification characteristic thickness of 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 the roll is large even if the thin slab continuous casting and rolling production is adopted, and the production cost of the thin-specification fire-resistant weather-resistant steel plate/strip is increased by the production flow.

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 production of the traditional process, and compared with the traditional production process, the energy consumption and CO of the production 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 fire-resistant weather-resistant 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 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.

The improvement of the Cu content can fully utilize the scrap steel in a certain sense, and screening is not needed when the scrap steel raw material is prepared, so that the smelting operation rate is improved, the cost is reduced, the recycling of 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.

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 and reducing 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, 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 carrousel coiling machine is adopted for coiling, 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 flow 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 in tapping temperature leads to an increase in steel-making cost, an increase in energy consumption, a reduction in the life of refractory, and the like.

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 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.

Drawings

FIG. 1 is a schematic view of 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 photograph showing the microstructure of the steel according to the example of 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.

As 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 seals 6a, 6b through a ladle shroud 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 a solidified shell and gradually grows to form a solidified shell and then gradually grows to form a strip 11 with a thickness of 1.5-3mm at the minimum clearance (nip point) between the two crystallizing rollers.

Referring to fig. 1, the production method of the invention designs smelting according to the chemical components of the invention, and the molten steel can be smelted by an electric furnace or a converter, and then enters necessary refining procedures such as an LF furnace, a VD/VOD furnace, an RH furnace and the like; then, the molten steel is directly poured into a molten pool 7 which is surrounded by two relatively rotating and rapidly-cooled

crystallizing rollers

8a and 8b and side sealing plate devices 6a and 6b through a ladle 1, a tundish long nozzle 2, a tundish 3, a submerged nozzle 4 and a flow distributor 5, the molten steel is solidified on the circumferential surfaces of the

rotating crystallizing rollers

8a and 8b, so that solidified shells are formed and gradually grow, and then a casting belt 11 with the thickness of 1.5-3mm is formed at the minimum clearance (nip point) of the two crystallizing rollers, wherein the diameters of the crystallizing

rollers

8a and 8b are 500-1500mm in the embodiment, and water is introduced for cooling. According to different thicknesses of the casting belts, the casting speed of the casting machine is 60-150m/min; after the casting belt 11 comes out of the crystallizing rollers 8a and 8b, the casting belt temperature is 1420-1480 ℃, the casting belt directly enters the lower closed chamber 10, the lower closed chamber 10 is filled with non-oxidizing gas to protect the casting belt 11, so as to realize the anti-oxidation protection of the casting belt 11, and the atmosphere of the anti-oxidation 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 cast strip 11 from oxidation to the inlet of a rolling mill 13; the temperature of the casting belt 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, a hot rolled strip with the thickness of 0.8-2.5mm is formed after hot rolling, and the rolled strip steel is cooled by adopting a gas atomization cooling mode, so that the temperature uniformity of the strip steel is improved; after the head of the hot rolled strip is cut by the flying shear device 16, the cut head falls into a flying shear pit 18 along a flying shear guide plate 17, and the hot rolled strip after the head is cut enters a coiler 19 for coiling; taking the steel coil down from the coiling machine, and naturally cooling the steel coil 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 steels of the examples of the present invention are shown in table 1, and the balance of the compositions is Fe and other unavoidable impurities. The manufacturing method and the process parameters of the invention are 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 fire-resistant weather-resistant steel plate/strip produced by the thin strip continuous casting process has the room-temperature yield strength of more than or equal to 345MPa, the tensile strength of more than or equal to 490MPa 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 232MPa 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 is less than or equal to 60 percent, the steel meets and exceeds the performance requirement of the fire-resistant weathering steel, and meanwhile, the supply of thin hot-rolled products can be realized, the production cost is also greatly reduced, the yield ratio of the material is low, the anti-seismic performance is excellent, the fire resistance is excellent, and the steel is an ideal material in the field of anti-seismic and fire-resistant steel.

Claims

1. A production method of a fire-resistant weather-resistant steel plate/belt 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 is less than or equal to 0.03%, S is less than or equal to 0.007%, cr:0.30-0.80%, cu:0.10-0.60%, mo:0.20-0.60%, 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 satisfying:

Mn/S>250；

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

the microstructure of the fire-resistant weather-resistant steel plate/belt 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 fire-resistant weather-resistant steel plate/belt reaches: the yield strength at room temperature is more than or equal to 345MPa, the tensile strength is more than or equal to 490MPa, 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 232MPa 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:

a) 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 the molten steel composition, mn/S>250；

b) 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 position with the minimum 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; a two-stage steel water distribution system is adopted for continuous casting flow distribution, namely a tundish and a flow distributor;

c) Lower enclosed chamber protection

d) In-line hot rolling

e) Strip steel cooling after rolling

f) Strip steel coiling

2. The method for producing fire and weather resistant steel plate/strip as claimed in claim 1, further comprising the step g) of using the coil formed after the strip is wound as a hot rolled plate/strip directly or as a finished plate/strip after trimming and flattening.

3. The method for producing fire and weather resistant steel sheet/strip as claimed in claim 1, wherein the non-oxidizing gas in step c) comprises: n is a radical of hydrogen ₂ CO obtained by sublimation of Ar or dry ice ₂ A gas.

4. The method for producing fire and weather resistant steel sheet/strip as claimed in claim 1, wherein the hot rolling reduction in the step d) is in the range of 30 to 50% and the thickness of the strip is 0.8 to 2.5mm or 1.2 to 2.0mm.

5. The method for producing fire and weather resistant steel plate/strip as claimed in claim 1, wherein in the step e), the gas-water ratio of the gas-atomized 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.

6. The method for producing fire and weather resistant steel sheet/strip as claimed in claim 1, wherein the coiling in step f) is in a twin coiler form or a carrousel coiler form.

7. The method for producing fire and weather resistant steel plate/strip as claimed in claim 1, wherein in step f), mnO-SiO having a low melting point is obtained in the molten steel 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 fire and weather resistant steel plate/strip as claimed in claim 1, wherein the diameter of the crystallization roll in step f) is 800mm.