RU2822600C1 - Fire-resistant steel strip, resistant to atmospheric effects, and method of manufacturing thereof - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to fire-resistant steel strip resistant to atmospheric effects. Fire-resistant steel strip has the following chemical composition, wt.%: C 0.02–0.06, Si 0.1–0.55, Mn 0.4–1.7, P ≤ 0.03, S ≤ 0.007, Cr 0.3–0.8, Mo 0.20–0.60, N 0.004–0.010, Als < 0.001, B 0.001–0.006, one or both of Cu 0.1–0.6 and Sn 0.005–0.04, optionally Nb 0.01–0.08, total oxygen [O]_T 0.007–0.020, Fe and unavoidable impurities are the rest, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.%, where Pcm=C+Si/30+Mn/20+Cu/20+Cr/20+Mo/15+5B.

EFFECT: providing a high level of strength at high temperature, as well as high resistance to seismic effects.

16 cl, 7 dwg, 8 tbl

Description

Technical field

The present invention relates to a fire-resistant steel strip in the form of a tape or strip, resistant to atmospheric influences, and a method for its production by continuous casting using a twin-roll machine.

Prior Art

In the traditional steelmaking process, typical residual or harmful elements in steel are tin (Sn) and copper (Cu). It is very difficult and expensive to completely remove Sn and Cu during steelmaking. If the steel contains Sn and/or Cu elements, they usually cannot be eliminated completely. The content of Sn and Cu can only be reduced by diluting the molten steel, which leads to an increase in the cost of smelting iron and steel.

In recent years, due to the continuous recycling of scrap steel, scrap steel resources are becoming more and more abundant, and the price of electricity continues to decline. The country is increasingly developing short-process electric steelmaking based on steel scrap, which leads to a gradual increase in the content of residual elements such as Sn and Cu in steel. Sn and Cu in steel are easily segregated elements that easily accumulate in grain boundaries and cause defects such as cracks. Therefore, the content of Sn and Cu elements in the traditional process is strictly controlled. There are clear requirements for the Sn and Cu content for conventional structural steel: Sn ≤ 0.005 wt.%; Cu ≤ 0.2 wt.%.

Therefore, if residual elements in steel (especially in steel scrap), such as Sn and Cu, can be put to good use and “turn the bad around,” it will have a positive impact on the entire metallurgical industry. Efficient utilization of available steel scrap or low-grade and low-quality mineral resources (e.g. high tin ore, high copper ore) can be realized, thereby promoting steel recycling, reducing production costs and achieving sustainable development of the steel industry.

The production of traditional thin strip steel is carried out mainly by multi-pass continuous rolling of cast slabs with a thickness of 70 - 200 mm. The traditional hot rolling process consists of the following sequence of operations: continuous casting + reheating of the cast slab and isothermal holding + rough rolling + finish rolling + cooling + winding. In particular, a cast slab with a thickness of about 200 mm is initially produced by continuous casting; the cast slab is heated and held; then rough and finishing rolling is carried out to obtain a steel strip with a thickness, as a rule, more than 2 mm; and finally, to complete the hot rolling process, laminar cooling and winding of the steel strip are carried out. Producing steel strip with a thickness of 1.5 mm or thinner is a relatively difficult task, since it usually requires subsequent cold rolling and annealing of the hot-rolled steel strip. In addition, a long technological process, high energy consumption, a large number of equipment and the high cost of capital construction lead to high production costs.

The technological process of continuous casting and rolling of thin slabs is as follows: continuous casting + isothermal holding and simmering of the cast slab + hot continuous rolling + cooling + winding. The main differences between this process and the traditional one are as follows: the thickness of the cast slab in the process of casting thin slabs is significantly reduced - to 50 - 90 mm. Since the cast slab is thin, it only needs to undergo 1 - 2 rough rolling passes (for a cast slab thickness of 70 - 90 mm) or not to undergo rough rolling at all (for a cast slab thickness of 50 mm). Unlike a cast slab, a continuously cast slab in a traditional process must be rolled multiple times in multiple passes before it can be thinned to the required gauge before finishing rolling. In addition, the cast slab in the process of casting thin slabs is not subjected to cooling, but goes directly into the simmer furnace for simmering and isothermal holding, or a small amount of heat is added to it. Thus, thin slab casting technology significantly shortens the technological process, reduces energy consumption, reduces investment costs and, consequently, production costs. However, due to the high cooling rate, the technology of continuous casting and rolling of thin slabs increases the strength of steel and the yield strength to tensile strength ratio, thereby increasing the rolling pressure, so taking into account the economic feasibility of production, the thickness of hot-rolled steel cannot be too small (usually it is ≥ 1.5 mm), see CN 200610123458.1, CN 200610035800.2 and CN 200710031548.2. None of these patents mention the element Sn or Cu.

The continuous casting and rolling process of continuous thin slabs, known as casting and rolling complex (ESP), which has become widespread in recent years, is an advanced technology developed from the above-mentioned continuous casting and rolling technology of semi-infinite thin slabs. Within the casting and rolling complex, endless rolling is implemented for continuous casting of the slab, while autogenous cutting of the slab and the use of a heating furnace, which is used for isothermal holding, simmering and conversion of slabs, are eliminated. The total length of the production line is significantly reduced to approximately 190 meters. The slab produced by continuous casting on a continuous casting machine has a thickness of 90 - 110 mm and a width of 1100 - 1600 mm. The slab produced by the continuous casting method passes through an induction heated roller table for isothermal holding and simmering of the slab. The slab is then rough-rolled, finished-rolled, laminar-cooled and coiled to produce hot-rolled strip. Since this technology implements continuous rolling, it is possible to obtain hot-rolled sheets with a minimum thickness of 0.8 mm, which expands the range of calibers of hot-rolled sheets. In addition, the productivity of one production line can reach 2.2 million tons/year. Nowadays, this technology is rapidly developing and advancing, and there are many ESP production lines operating around the world.

The technological process of continuous casting and rolling of thin strips is characterized by a shorter duration in comparison with the process of continuous casting and rolling of thin slabs. Thin strip continuous casting technology is an advanced technology in the field of metallurgy and materials research. Its appearance revolutionized the steel industry. It involves changing the steel strip manufacturing process in the traditional steel industry by combining continuous casting, rolling and even heat treatment, so that the resulting thin strip blank can be formed into thin steel strip at a time after one hot rolling pass on the line. Accordingly, investment costs for equipment are reduced, and the cost of production is significantly reduced. It is a low carbon, environmentally friendly process for producing hot rolled thin strip. The double roll thin strip continuous casting process is the basic form of thin strip continuous casting process, and in addition, it is the only thin strip continuous casting process industrialized in the world.

A typical thin strip twin-roll continuous casting process is shown in FIG. 1. The molten steel passes through the steel ladle 1, the steel ladle guard pipe 2, the tundish 3, the submersible nozzle 4 and the distributor 5, and then is poured directly into the melt bath 7 formed by the side sealing plates 6a, 6b and two counter-rotating crystallization rollers 8a, 8b, capable of rapid cooling. The molten steel solidifies on the circumferential surfaces of the rotating crystallization rolls 8a, 8b, forming a solidified shell, which gradually increases and ultimately forms a strip 11 with a thickness of 1 - 5 mm in the minimum gap (clamping point) between the two crystallization rolls. The steel strip is guided by the guide plate 9 to the pressure rolls 12 and sent to the rolling mill 13 for rolling into a thin strip of 0.7 - 2.5 mm, and then cooled by the cooling device 14. After cutting off the head part with the flying shears 16, it is sent to the coiler 19 for rolling into a roll.

In recent years, with the constant emergence of domestic and foreign large-scale buildings and high-rise structures, in the event of a fire, the strength of building steel will be sharply reduced due to heating, resulting in the collapse of the building, causing enormous damage to the lives and property of residents. Process design for fire resistance of structural steel has received widespread attention in the international arena. Technological design regarding the fire resistance of building steel has become one of the necessary measures to ensure the safety of a building. When ordinary structural steel heats up, its strength and load-bearing capacity quickly decline, which cannot meet fire safety requirements. To improve the fire resistance of buildings constructed from conventional structural steel, measures such as spraying fire-resistant coatings or cladding with fire-resistant boards were often used in the past. Nowadays, the widespread use of fire-resistant steel reduces or eliminates the need for fire-resistant coatings or fire-resistant boards, and also ensures that the steel maintains a high level of strength at high temperatures. The use of fire-resistant steel can also reduce construction time, improve building quality, improve building safety, and reduce construction costs, which has significant economic and social benefits. At the same time, most steel used in construction is exposed to air and must have a long service life. Therefore, by taking the characteristics of fire resistance and weather resistance as a basis, a completely new steel product can be obtained that is resistant to fire and weather conditions. In the context of the above applications, fire-resistant and weather-resistant steel strips are increasingly used in several industries and applications such as structural steel, tower masts, construction machinery and industrial structures requiring fire resistance. Especially in high-rise buildings, large public buildings and luxury residential buildings with high fire safety requirements, fire-resistant and weather-resistant steel strips are widely used.

Fire-resistant and weather-resistant steel must have good high-temperature properties, but it is different from heat-resistant steel, which is required to be able to operate for long periods of time at high temperatures. Heat-resistant steel must have good high-temperature strength and high-temperature stability, so high-alloy steel is usually used. In contrast, fire-resistant and weather-resistant steel is loaded at room temperature, but is required to maintain a high yield strength under high temperature conditions for a short time (typically 1 - 3 hours) in the event of a fire, which can help buy valuable time for the safe evacuation of personnel. Therefore, fire-resistant and weather-resistant steel belongs to the category of low-alloy structural steels, and too many expensive alloying elements should not be added to its composition.

The Japanese design regulations for safe steel structures stipulate that 2/3 of the yield strength of steel at room temperature is equivalent to the long-term allowable stress of the material. In the event of a fire, if the yield strength of fire-resistant and weather-resistant steel remains at this level, the building will not collapse. Therefore, it is necessary that the yield strength of fire-resistant and weather-resistant steel at high temperature is at least 2/3 of the yield strength at room temperature. To improve the seismic resistance of steel structures, it is always desirable to maximize the seismic energy absorption capacity of steel. If the ratio of the yield strength to the ultimate strength (σ _s /σ _b ) of the steel is high, then during an earthquake there will be a local stress concentration and local plastic deformation. At this time, the steel structure can only absorb less energy. Therefore, a low value of the yield strength to ultimate strength ratio is beneficial to improve the energy absorption of a building structure during an earthquake. Generally, the yield strength to tensile strength ratio of earthquake-resistant, fire-resistant and weather-resistant steel should be ≤ 0.8.

One of the key considerations in developing fire-resistant and weather-resistant steel is determining the required fire-resistant temperature to achieve high-temperature strength. At the Creusot-Loire steel mill in Europe, research was carried out on Mo-containing steel with high heat resistance of 900 - 1000°C, but it was not widely used due to high cost. To determine the fire resistance temperature that provides the best match between manufacturing cost reduction and material fire resistance reduction, Nippon Steel conducted high-temperature tensile tests on several typical steels with tensile strengths ranging from 400 to 780 MPa. The tests showed the following: the yield strength ( _σs ) of all tested steels decreases sharply in the range of 500 - 600°C, and _σs drops below 50 MPa at temperatures of 700°C and above. If the strength temperature is set at 700°C, a large amount of alloying elements must be added, which makes it difficult to achieve good weldability and significantly increases the cost. If the temperature for strength is set at a lower level of 500°C, the thickness of the fire-resistant coating can be reduced only slightly, which defeats the original intention of using fire-resistant and weather-resistant steel. Therefore, the fire resistance temperature of fire-resistant and weather-resistant steel is set at 600°C.

In general and in accordance with the general requirements for structural steel, the indicators of fire-resistant and weather-resistant steel are determined as follows:

(1) Fire resistance: σ _{s, 600°C} ≥ (2/3) σ _{s, 20°C} ;

(2) The mechanical properties and other quality indicators at room temperature meet the requirements of the standards for ordinary construction steel;

(3) Seismic resistance: σ _s /σ _b ≤ 0.8 at room temperature, and the fluctuation range of yield strength is as small as possible;

(4) Good weldability, equal to or better than that of ordinary structural steel;

(5) Weather resistance: Compared with Q345B, measured by TB/T 2375-1993 standard, the relative corrosion rate is ≤ 60%.

A continuous thin strip casting process is used to produce this high strength, fire resistant and weather resistant steel strip tape/strip. Due to the sub-rapid solidification inherent in the thin strip continuous casting process, a fine-grained layer of a certain thickness is naturally formed on the surface of the steel strip, so the produced steel is weather-resistant; at the same time, it has certain production and cost advantages when used in thin sheet form. The characteristic thickness of high-strength, fire-resistant and weather-resistant sheet steel is 1.2 - 2.0 mm. Due to the thin thickness of the product, it is difficult to produce using the traditional continuous casting + hot continuous rolling production line. Even if it is produced by continuous casting and rolling of thin slabs, the consumption of rolls is relatively high. This manufacturing process increases the cost of producing high-strength, fire-resistant and weather-resistant sheet/strip steel.

When using hot-rolled steel strip as hot-rolled thin sheet, high surface quality is required. It is generally required that the thickness of the oxide layer on the surface of the steel strip be as thin as possible. To do this, it is necessary to control the formation of oxide scale on the cast strip at subsequent stages. For example, in the continuous casting process of thin sheet steel, a closed chamber device is used to prevent oxidation of the cast strip from the solidification rolls to the entrance to the rolling mill. Adding hydrogen to the closed chamber device, as described in US Pat. No. 6,920,912, and controlling the oxygen content of the closed chamber device to less than 5%, as described in US 20060182989, can help control the thickness of the oxide layer on the surface of the cast strip. . However, there are few patents related to the issue of how to control the thickness of oxide scale during the transportation process from the rolling mill to the coiler, especially in the process of cooling the steel strip by laminar cooling or spray cooling. When the high temperature steel strip is in contact with cooling water, the thickness of the oxide scale on the surface of the cast strip increases rapidly. At the same time, the contact of high-temperature steel strip with cooling water may also cause many problems: firstly, water stains (rust stains) may form on the surface of the steel strip, which will affect the surface quality; Secondly, the cooling water for laminar or spray cooling tends to cause local uneven cooling on the surface of the steel strip, resulting in a heterogeneous microstructure inside the steel strip, so that its properties are not uniform and product quality is deteriorated; thirdly, local uneven cooling on the surface of the steel strip can cause deterioration in the shape of the strip, that is, negatively affect the quality of the shape.

However, since the thin strip continuous casting process itself is characterized by rapid solidification, the steel produced by this method usually has problems such as non-uniform structure, low elongation to failure, high yield strength ratio and poor formability. At the same time, the austenite grains in the cast strip are clearly not homogeneous, so the structure of the final product obtained after austenite transformation is also not homogeneous. Consequently, the properties of the product, especially the ability to deform, are not stable. Therefore, producing high-strength, fire-resistant and weather-resistant steel products using thin strip continuous casting process is also somewhat difficult and problematic. A breakthrough is needed in both the composition and the technological process. The present invention effectively improves the uniformity of the structure by adding an appropriate amount of element B and taking appropriate cooling measures after rolling, and achieves the object of reducing the yield strength to tensile strength ratio.

Application CN 200610123458.1 discloses a method for producing high-strength weather-resistant steel of 700 MPa class using Ti micro-alloying technology based on a continuous casting and thin slab rolling process. The chemical composition of weather-resistant sheet steel produced using this method includes the following elements, wt.%: C 0.03 - 0.07, Si 0.3 - 0.5, Mn 1.2 - 1.5, P ≤ 0.04, S ≤ 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 - 0.14, N ≤ 0.008, as well as the remainder consisting of Fe and inevitable impurities. Such steel sheet has a yield strength ≥ 700 MPa, a tensile strength ≥ 775 MPa and an elongation to failure ≥ 21%. In this patent application, phosphorus is controlled as an impurity element, and its content is ≤ 0.04 mass%, which is higher than ≤ 0.025 mass% in the conventional process.

Application CN 200610035800.2 discloses a method for producing micro-alloyed weathering steel of 700 MPa class based on a process of continuous casting and rolling of thin slabs with the addition of vanadium and nitrogen. The chemical composition of weather-resistant sheet steel produced by this method includes the following elements, wt.%: C ≤ 0.08, Si 0.25 - 0.75, Mn 0.8 - 2, P 0.07 - 0.15, S ≤ 0.04, Cr 0.3 - 1.25, Ni ≤ 0.65, Cu 0.25 - 0.6, V 0.05 - 0.2, N 0.015 - 0.03, as well as the remainder consisting of Fe and inevitable impurities. Such steel sheet has a yield strength of ≥ 700 MPa, a tensile strength of ≥ 785 MPa and an elongation to failure of ≥ 21%. In this patent application, phosphorus is controlled as an element that improves weather resistance, and its content is 0.07 - 0.15 wt.%. The copper content is 0.25 - 0.6 wt%, with the lower and upper limits being higher than 0.2 wt% and 0.55 wt% copper, respectively, in the conventional process.

Application CN 1633509A mentions a method for producing a copper-containing carbon steel product by continuous thin strip casting. This patent application emphasizes that such steel strip must be subjected to heat treatment (annealing, tempering, etc.) in the temperature range of 400 - 700°C to ensure precipitation or recrystallization of the copper element in the steel strip. The method for producing high-copper low-alloy thin strip mentioned in the application US 2008264525 / CN 200580009354.1 is characterized in that the steel strip is cooled to a temperature below 1080°C in a non-oxidizing atmosphere before entering the rolling mill to prevent the phenomenon of “hot brittleness” of the steel strip.

All of the above patents relate to weathering steel, but none of the inventions in them have the effect of fire resistance. The present invention is a type of steel specifically designed to provide fire and weather resistance properties.

Disclosure of the Invention

One of the objectives of the present invention is to obtain a fire-resistant steel tape/strip that is resistant to weathering, maintains a high level of strength at high temperatures, can reduce the weight of a building and increase its safety level, while reducing the cost of construction, as well as the method of manufacturing such steel. At the same time, due to the nature of the thin strip continuous casting process, a fine-grained layer of a certain thickness is naturally formed on the surface of the steel strip, so the produced steel is weather-resistant. The product has excellent seismic resistance, fire resistance and weather resistance characteristics, and is an ideal seismic and fire-resistant steel material. Such products can be widely used in some industries and fields, such as construction steel, railings for tower-like masts, construction machinery and industrial structures, etc., where there are requirements for fire resistance and earthquake resistance of materials, especially in the construction of high-rise buildings, large public buildings, luxury residential buildings and other facilities with high fire safety requirements. The technical solution of the present invention aimed at solving the above problem is as follows:

According to the present invention, residual elements in steel scrap such as Sn and/or Cu are used to smelt molten steel, and Mo/Nb/Cr and other micro-alloy elements and element B are selectively added to the steel. During the smelting process, the basicity of the slag, the type and melting temperature of inclusions in the steel, the content of free oxygen in the molten steel, as well as the content of acid-soluble aluminates are controlled. Then the thin strip is continuously cast on a twin-roll machine for casting steel strip with a thickness of 1.5 - 3 mm. After the steel strip leaves the solidification rolls, it directly enters the lower closed chamber with a non-oxidizing atmosphere and enters the rolling mill for hot rolling under closed conditions. The rolled steel strip is cooled by gas spraying. Gas atomization cooling can effectively reduce the thickness of oxide scale on the surface of the steel strip, increase the temperature uniformity of the steel strip, and improve the surface quality of the steel strip. Finally, the resulting steel coil can be used directly as hot-rolled steel strip/strip or can be cut and flattened into finished steel strip/strip. The material of the present invention has a low yield strength ratio, excellent seismic performance and excellent fire resistance, which makes it an ideal earthquake-resistant and fire-resistant steel material.

Fire-resistant steel strip tape/strip, resistant to atmospheric influences, in accordance with the present invention, has the following chemical composition, wt.%: C 0.02 - 0.06, Si 0.1 - 0.55, Mn 0.4 - 1.7, P ≤ 0.03, S ≤ 0.007, Cr 0.3 - 0.8, Mo 0.20 - 0.60, N 0.004 - 0.010, Als < 0.001, B 0.001 - 0.006, optional Nb 0.01 - 0.08, total oxygen [O] _T 0.007 - 0.020, Fe and inevitable impurities - the rest, and also including one or both of the following components, wt.%: Cu 0.1 - 0.6 and Sn 0.005 - 0.04, with Mn /S ≥ 250, and Pcm ≤ 0.27 wt.%, where: Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B. Preferably, the steel strip has a thickness of 0.8 - 2.5 mm, preferably 1.2 - 2.0 mm; Pcm ≤ 0.25 wt.%, in some embodiments, 0.14 wt.% ≤ Pcm ≤ 0.25 wt.%; yield strength (σ _s ) at room temperature ≥ 345 MPa, tensile strength ≥ 490 MPa, elongation to failure ≥ 17%, ratio of yield strength to tensile strength at room temperature σ _s /σ _b ≤ 0.8, preferably ≤ 0.75, yield strength (σs _,600°C ) at 600°C ≥ 232 MPa, ratio of yield strength at 600°C to yield strength at room temperature (σs _,600°C /σs _,20°C ) ≥ 0.67 and relative corrosion rate ≤ 60%.

In another embodiment of the invention, the steel strip has the following chemical composition, wt.%: C 0.02 - 0.06, Si 0.1 - 0.55, Mn 0.4 - 1.7, P ≤ 0.03, S ≤ 0.007 , Cr 0.30 - 0.80, Mo 0.20 - 0.60, N 0.004 - 0.010, Als < 0.001, B 0.001 - 0.006, total oxygen [O]_T 0.007 - 0.020, Fe and inevitable impurities - the rest, and also including one or both of the following components, wt.%: Cu 0.1 - 0.6 and Sn 0.005 - 0.04, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.%, where: Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B. Preferably, the steel strip has a thickness of 0.8 - 2.5 mm, preferably 1.2 - 2.0 mm; Pcm ≤ 0.25 wt.%, in some embodiments, 0.14 wt.% ≤ Pcm ≤ 0.25 wt.%; yield strength (σ_s) at room temperature ≥ 345 MPa, tensile strength ≥ 490 MPa, elongation to failure ≥ 17%, ratio of yield strength to ultimate strength at room temperature σ_s/σ_b≤ 0.8, preferably ≤ 0.75, yield strength (σ_s,600°C) at 600°C ≥ 232 MPa, the ratio of the yield strength at 600°C to the yield strength at room temperature (σ_s,600°C/σ_s,20°C) ≥ 0.67 and relative corrosion rate ≤ 60%. Preferably, in some embodiments of the invention, the steel strip has a tensile strength (σ) of 345 - 370 MPa_b) tensile 490 - 530 MPa, relative elongation to failure 19 - 27%, ratio of yield strength to ultimate strength at room temperature σ_s/σ_b0.66 - 0.72, yield strength (σ_s,600°C) at 600°C 235 - 260 MPa, the ratio of the yield strength at 600°C to the yield strength at room temperature (σ_s,600°C/σ_s,20°C) 0.68-0.74 and relative corrosion rate ≤ 60%.

In some embodiments of the invention, the steel strip has the following chemical composition, wt.%: C 0.02 - 0.06, Si 0.1 - 0.55, Mn 0.4 - 1.7, P ≤ 0.03, S ≤ 0.007 , Cr 0.3 - 0.8, Mo 0.20 - 0.60, N 0.004 - 0.010, Als < 0.001, B 0.001 - 0.006, Cu 0.10 - 0.60, optional Sn 0.005 - 0.04, total oxygen [O ]_T 0.007 - 0.020, Fe and inevitable impurities - the rest, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.%, where: Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B. Preferably, in these embodiments, the steel strip has a yield strength ≥ 345 MPa, a tensile strength (σ_b) tensile ≥ 490 MPa, elongation to failure ≥ 17%, ratio of yield strength to ultimate strength at room temperature σ_s/σ_b≥ 0.8, preferably 0.75, yield strength (σ_s,600°C) at 600°C ≥ 232 MPa, the ratio of the yield strength at 600°C to the yield strength at room temperature (σ_s,600°C/σ_s,20°C) ≥0.67 and relative corrosion rate ≤ 60%. In some embodiments of the invention, the steel strip has a yield strength at room temperature of 345 - 370 MPa, tensile strength of 490 - 530 MPa, elongation to failure of 19 - 27%, ratio of yield strength to tensile strength at room temperature σ_s/σ_b 0.66 - 0.72, yield strength at 600ºС 235 - 260 MPa, ratio of the yield strength at 600°C to the yield strength at room temperature (σ_s,600°C/σ_s,20°C) 0.68 - 0.74 and relative corrosion rate ≤ 60%.

In some embodiments, the steel strip has the following chemical composition, wt.%: C 0.02 - 0.06, Si 0.1 - 0.55, Mn 0.4 - 1.7, P ≤ 0.03, S ≤ 0.007, Cr 0.30 - 0.80, Cu 0.10 - 0.60, Mo 0.20 - 0.60, Nb 0.01 - 0.08, N 0.004 - 0.010, Als < 0.001, B 0.001 - 0.006, total oxygen [O] _T 0.007 - 0.020, Fe and inevitable impurities - the rest, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.%, where: Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo /15 + 5B.

Preferably, in these embodiments, the steel strip has a room temperature yield strength of ≥ 410 MPa, a tensile strength of ≥ 590 MPa, an elongation to failure of ≥ 17%, a yield strength to room temperature strength ratio of σ _s /σ _b ≤ 0.8, preferably ≤ 0.75, yield strength at 600ºC ≥ 275 MPa, ratio of yield strength at 600°C to yield strength at room temperature (σs _,600°C /σs _,20°C ) ≥ 0, 67 and relative corrosion rate ≤ 60%. In some embodiments of the invention, the steel strip has a yield strength at room temperature of 410 - 450 MPa, tensile strength of 590 - 630 MPa, elongation to failure of 18 - 28%, ratio of yield strength to tensile strength at room temperature σ _s /σ _b 0.67-0.73, yield strength at 600°C 275 - 310 MPa, ratio of yield strength at 600°C to yield strength at room temperature (σs _,600°C /σs _,20°C ) 0.67 - 0.72 and relative corrosion rate ≤ 60%.

In some embodiments, the steel strip has the following chemical composition, wt.%: C 0.02 - 0.06, Si 0.1 - 0.55, Mn 0.4 - 1.7, P ≤ 0.03, S ≤ 0.007, Cr 0.30 - 0.80, Mo 0.20 - 0.60, N 0.004 - 0.010, Cu 0.10 - 0.60, Als < 0.001%, B 0.001 - 0.006, total oxygen [O] _T 0.007 - 0.020, Fe and inevitable impurities - the rest, and the steel strip contains Nb 0.01 - 0.08 or does not contain Nb, but includes Sn 0.005 - 0.04, or contains neither Nb nor Sn, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.%, where: Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B. In these embodiments, the steel strip has a room temperature yield strength of ≥ 345 MPa, a tensile strength of ≥ 490 MPa, an elongation to failure of ≥ 17%, a yield strength to room temperature strength ratio of σ _s /σ _b ≤ 0, 8, preferably ≤ 0.75, yield strength at 600°C ≥ 232 MPa, ratio of yield strength at 600°C to yield strength at room temperature (σs _,600°C /σs _,20°C ) ≥ 0.67 and relative corrosion rate ≤ 60%. In some embodiments of the invention, the steel strip has a yield strength at room temperature of 345 - 370 MPa, tensile strength of 490 - 530 MPa, elongation to failure of 19 - 27%; ratio of yield strength to ultimate strength at room temperature σ _s /σ _b 0.66 - 0.72, yield strength at 600°C 235 - 260 MPa, ratio of yield strength at 600°C to yield strength at room temperature (σ _{s, 600°C} /σ _s,20°C ) 0.68 - 0.74; and relative corrosion rate ≤ 60%. In some embodiments of the invention, the steel strip has a yield strength at room temperature of 410 - 450 MPa, tensile strength of 590 - 630 MPa, elongation to failure of 18 - 28%; ratio of yield strength to ultimate strength at room temperature σ _s /σ _b 0.67 - 0.73, yield strength at 600°C 275 - 310 MPa, ratio of yield strength at 600°C to yield strength at room temperature (σ _{s, 600°C} /σ _s,20°C ) 0.67 - 0.72; and relative corrosion rate ≤ 60%.

It is preferable that in any of the above embodiments, the inequality Mn/S>250 is satisfied.

It is preferable that the average corrosion rate of the steel strip be ≤ 0.3000 mg/cm ² h.

The microstructure of the steel strip is a mixed microstructure of solid ferrite + pearlite + acular ferrite, or a mixed microstructure of solid ferrite + pearlite + lower bainite.

The compositional chemistry of the fire resistant weather resistant steel tape/strip according to the present invention is as follows.

Carbon (C): C is the most economical and primary strengthening element in steel. It increases the strength of steel through solid solution strengthening and precipitation strengthening. C is a necessary element for cementite precipitation during austenite transformation. Therefore, the level of C content largely determines the strength level of the steel. That is, a higher C content leads to a higher level of strength. However, since intergranular solid solution and C precipitation cause great harm to the ductility and toughness of steel, and excessively high C content adversely affects welding quality, the C content cannot be too high. The strength of steel is compensated by the addition of an alloying element (elements) in an appropriate amount. At the same time, when continuously casting slabs using traditional technology, casting in the peritectic reaction zone is fraught with the formation of cracks on the surface of the cast slab, and in severe cases, breakthrough incidents may occur. The same is true for continuous casting of thin strips, i.e. Casting in a peritectic reaction zone can lead to the formation of cracks on the surface of the cast strip billet, and in severe cases, to destruction of the strip. Therefore, when continuously casting a thin strip of Fe-C alloy, it is also necessary to bypass the peritectic reaction zone. In this regard, the value of the C content used in accordance with the present invention is in the range of 0.02 - 0.06 wt.%.

Silicon (Si): Si plays an important role in the solid solution strengthening process of steel and the addition of Si to steel can improve its purity and deoxygenate it. However, excessively high Si content degrades weldability and welding heat-affected zone toughness. In this regard, the Si content value used in accordance with the present invention is in the range of 0.1 to 0.55 mass%.

Manganese (Mn): Mn is one of the cheapest alloying elements. It can improve the hardening ability of steel. It has significant solid solubility in steel and increases the strength of steel through solid solution strengthening without compromising the ductility or toughness of the steel. It is the most important strengthening element for increasing the strength of steel and can also play a role in deoxygenation of steel. However, excessively high Mn content degrades the weldability and toughness of the welding heat-affected zone. In this regard, the Mn content value used in accordance with the present invention is in the range of 0.4 - 1.7 wt.%.

P: When the P content is high, it tends to segregate at the grain boundary, so that the cold brittleness of the steel will be increased, thereby deteriorating the weldability, and the ductility of the steel will be reduced, thereby deteriorating the cold bendability. In the thin strip continuous casting process, the solidification and cooling speed of the cast strip is very high, so the segregation of P can be effectively suppressed. As a result, the disadvantages of P can be effectively avoided and the advantages of P can be fully utilized. Therefore, according to the present invention, the P content is higher than in the conventional production process, and the limitation on the P element content is relaxed accordingly. The dephosphorization process is eliminated from the steel making process. In practice, there is no need to carry out a dephosphorization process or specially add phosphorus, and the P content is in the range of ≤ 0.03 wt%.

Sulfur (S): In general, S in steel is a harmful element. In particular, it imparts hot brittleness to steel, reduces the ductility and toughness of steel, and causes cracks during rolling. S also reduces weldability and corrosion resistance. Therefore, according to the present invention, the S content is also controlled by the principle of impurity element and maintained at ≤ 0.007 mass%. In some embodiments, the S content is ≤0.0067 wt.%. Additionally, Mn/S ≥ 250. In some embodiments, Mn/S > 250.

Aluminum (Als): In order to limit aluminum inclusions in steels, Al cannot be used for deoxygenation, which is required by the present invention. When using refractory materials, additional addition of Al should also be avoided whenever possible, and the content of acid-soluble aluminum Als should be strictly controlled and maintained at < 0.001 wt.%.

N: Similar to the element carbon (C), the element N is capable of increasing the strength of steel through interstitial solid solution. According to the present invention, a certain amount of N must be present in the steel since the interaction of N and B in the steel is necessary for the formation of the BN precipitation phase. However, the N interstitial solid solution deteriorates the ductility and toughness of steel relatively significantly, and the presence of free N can increase the yield strength to tensile strength ratio of steel. Therefore, the N content should not be too high. In this regard, the value of N content used in accordance with the present invention is in the range of 0.004 - 0.010 wt.%.

Chromium (Cr): Cr not only improves the hardenability of steel, but also can significantly improve the oxidation and creep resistance of steel. The addition of Cr to the composition of fireproof and weathering steel is used to improve its high temperature strength and creep resistance, and is also mainly used to improve the weathering resistance of steel, which can greatly improve its corrosion resistance. If its content is too high, the weldability of steel is seriously deteriorated. In accordance with the present invention, the Cr content is limited to the range of 0.30 to 0.80 mass%.

Niobium (Nb): In fire-resistant steel, Nb is primarily used to increase high temperature strength by precipitation strengthening of NbC in ferrite. Meanwhile, in the thin strip continuous casting process, due to the unique characteristics of fast solidification and fast cooling, the added Nb alloy element can exist in the steel strip mainly in a solid solution state. The element Nb, which is present in steel in a solid dissolved state, can play a role in the solid-solution strengthening process. According to the present invention, when Nb is added, the content of this element is in the range of 0.01 - 0.08 wt.%.

Molybdenum (Mo): Dissolves in ferrite and strengthens the ferrite matrix. Mo is slowly dissipated into ferrite at high temperature, so it can greatly improve the high temperature strength and creep resistance of steel. Research has shown that solid dissolved Mo is easily eliminated at the grain boundary, which can improve the high-temperature strength of steel. Mo is also able to improve the stability of supercooled austenite, and the volume fraction of bainite in steel increases after the addition of Mo. The bainitic structure with a high dislocation density allows fire-resistant and weather-resistant steel to acquire good high-temperature properties. Mo can precipitate in the steel to form carbides, improving the high temperature strength of the steel. Research has shown that adding Nb and Mo together can give better deposition enhancement effect: The first opinion is that in addition to the strengthening effect of adding Nb or Mo separately, when adding Mo combined with Nb, molybdenum can also be enriched at the NbC interface /matrix, which prevents the coarsening of NbC particles, thereby further improving the high-temperature strength of steel; The second opinion is that Mo reduces the driving force of NbC precipitation, inhibits the diffusion and nucleation process of NbC, and thus delays the precipitation of NbC. Mo in the steel composition promotes bainite transformation, which leads to an increase in dislocation density, which in turn increases the number of NbC nucleation sites. All this leads to better dispersion strengthening, which, in turn, increases the high-temperature strength of steel. Too high a Mo content will increase the cost of making steel from raw materials. Therefore, according to the present invention, the Mo content is limited to the range of 0.20 to 0.60 mass%.

Copper (Cu): Cu in steel mainly affects solid solution and precipitation strengthening. Cu also improves weather resistance. Since Cu is an element prone to segregation, the Cu content is usually strictly controlled in conventional technology. Considering the rapid solidification effect of continuous casting of thin strip, according to the present invention, the upper limit of Cu content is increased to 0.60 mass%. In a certain sense, the increased Cu content can ensure the efficient use of scrap steel, and no selection is required in the preparation of scrap steel. This can improve smelting productivity and reduce costs, promote steel recycling and achieve the goal of sustainable development, and can ensure the efficient use of copper in scarce mineral resources (such as high-copper ore).

Tin (Sn): The element Sn is also one of the main impurity elements in steel scrap. It is recognized as a harmful element in steel. Since Sn is a segregation-prone element, even small amounts of Sn can be enriched at grain boundaries, resulting in defects such as cracks. Therefore, within the framework of traditional technology, the content of the Sn element is strictly controlled. Since continuous casting of thin strip has the property of rapid solidification, the interdendritic segregation of the element is significantly reduced. As a result, the solubility of the element in the solid state can be significantly increased. Therefore, under the conditions of thin strip continuous casting process, the range of Sn element content can be expanded and thus the steelmaking cost can be significantly reduced. In Fig. Figure 2 shows the relationship between the Sn element content and the average heat flux. From Fig. 2 shows that when the amount of Sn added is less than 0.04 mass%, the effect on the heat flow is negligible. That is, there is no influence on the solidification process of the thin strip. In FIG. Figure 3 shows the relationship between Sn content and surface roughness. Since cracks on the surface of cast strip usually occur at uneven folds, surface roughness is used to characterize the occurrence of surface cracks. If the roughness is large, then the likelihood of cracks is high. From Fig. 2 it can be seen that an increase in the Sn content does not have a negative effect on the surface quality of the cast strip under the condition of rapid solidification. As can be seen from the results in Fig. 2 and Fig. 3, Sn does not have a negative effect on the solidification and surface quality of the cast strip. Therefore, according to the present invention, the limitation on the Sn content can be further relaxed, and the estimated Sn content is in the range of 0.005 to 0.04 mass%.

Boron (B): The significant role of B in steel is that a small amount of boron can double the hardenability of steel. B is able to preferentially precipitate large BN particles in high-temperature austenite, inhibiting the precipitation of AlN fines, weakening the pinning effect of AlN fines at grain boundaries, and improving the grain growth ability, thereby coarsening and homogenizing austenite grains, which promotes recrystallization after rolling. After enlargement and homogenization of austenite grains, it is advantageous to reduce the ratio of the yield strength to the ultimate strength σ _s /σ _b of the product, reduce the range of fluctuations in tensile strength and improve seismic characteristics. In addition, the combination of B and N can effectively prevent the appearance of the low melting point phase B ₂ O ₃ at the grain boundary.

B is an active element prone to segregation at grain boundaries. When producing boron-containing steel in the traditional way, the B content is usually very strictly controlled, typically in the range of about 0.001 - 0.003 wt.%. In the thin strip continuous casting process, the solidification and cooling rate is high. Therefore, the segregation of B can be effectively suppressed, and more B can be dissolved in the solid state. Therefore, the restriction on B content can be relaxed accordingly. Large BN particles can also be produced by appropriate process control to suppress precipitation of fine AlN. Thus, B plays a role in nitrogen fixation. Other studies have shown that adding B in combination with Nb and Mo can achieve better results. In particular, the probability of segregation of C atoms is reduced and the deposition of Fe ₂₃ (C,B) ₆ at the grain boundary can be avoided. Therefore, more B can be added. Therefore, according to the present invention, a higher B content than conventional process is used, and its range is 0.001 to 0.006 wt%.

To ensure the welding characteristics of the steel according to the present invention, the following relational expressions must be satisfied when planning the above-mentioned elements:

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

The method for producing fire-resistant, weather-resistant steel sheet/strip according to the present invention includes the following steps:

a) Smelting:

at this stage, smelting is carried out with the above chemical composition; in this case, the basicity a = CaO/SiO ₂ (mass ratio) for the slag during the steelmaking process is maintained at the level of a < 1.5, preferably a < 1.2, or a = 0.7 - 1.0; in this case, the MnO/SiO ₂ ratio (mass ratio) in the molten steel to obtain a ternary inclusion of MnO - SiO ₂ - Al ₂ O ₃ with a low melting point is maintained at the level of 0.5 - 2, preferably 1 - 1.8; in this case, the content of free oxygen [O] _Free in molten steel is 0.0005 - 0.005%; and the content of Mn and S in the molten steel should be controlled and maintained in accordance with the following ratio: Mn/S ≥ 250;

b) Continuous casting:

at this stage, two-roll continuous casting of a thin strip is used, in which a cast strip with a thickness of 1.5 - 3 mm is formed in the smallest gap between two crystallization rolls, while the crystallization rolls have a diameter of 500 - 1500 mm, preferably 800 mm, and for cooling inward crystallization rolls supply water, while the casting machine has a casting speed of 60 - 150 m/min, and to supply molten steel during continuous casting, a two-stage system for dosing and distributing molten steel is used, i.e. tundish + distributor;

c) Protection of the lower closed chamber:

at this stage, after leaving the continuously cast strip from under the crystallization rollers, it has a temperature of 1420 - 1480 ° C and enters directly into the lower closed chamber, into which non-oxidizing gas is supplied, and the oxygen concentration in the lower closed chamber is maintained at a level of < 5%, while the cast strip at the exit from the lower closed chamber has a temperature of 1150 - 1300°C;

d) On-line hot rolling:

at this stage, the cast strip is fed through rollers in the lower closed chamber to the rolling mill, where it is rolled into a thin steel strip with a thickness of 0.8 - 2.5 mm at a rolling temperature of 1100 - 1250 ° C and a reduction degree of 10 - 50%, preferably 30 - 50%, while the thickness of the steel strip is 0.8 - 2.5 mm, preferably 1.2 - 2.0 mm;

e) Cooling after rolling:

at this stage, the rolled steel strip is cooled by gas spraying, and the cooling rate is 20 - 100°C/s;

f) Steel strip winding: After cooling, the poor-quality hot-rolled steel strip head is cut off using shears and then rolled into a roll at a winding temperature of 500 - 680°C.

In addition, this method also includes step g): post-processing, in which the steel coil is used directly as a hot-rolled strip/strip or is cut and flattened and then used as a finished strip/strip.

It is preferable that in step a) an electric furnace is used to smelt molten steel, where 100% steel scrap is selected as the raw material for smelting without pre-sorting, or a converter is used for smelting to produce molten steel, where scrap steel is added to the converter in an amount of 20% from raw materials for smelting without pre-sorting, while the molten steel then enters the furnace of a complex steel processing unit, the furnace of a vacuum degassing / vacuum - oxygen decarburization installation or a circulation evacuation furnace for subsequent refining.

Preferably, in step c) N ₂ , Ar or CO ₂ obtained by sublimation of dry ice is used as the non-oxidizing gas.

It is preferable that in step e) when cooling by gas atomization, a gas to water flow ratio of 15:1 - 10:1, a gas pressure of 0.5 - 0.8 MPa and a water pressure of 1.0 - 1.5 MPa are used, while flow rate has a unit of measurement m ³ / h. The gas to water ratio used is tied to the compressed air to water flow ratio.

In particular, fire-resistant steel strip tape/strip, resistant to atmospheric influences, has the following chemical composition, wt.%: C 0.02 - 0.06, Si 0.1 - 0.55, Mn 0.4 - 1.7 , P ≤ 0.03, S ≤ 0.007, Cr 0.3 - 0.8, Mo 0.20 - 0.60, N 0.004 - 0.010, Als < 0.001, B 0.001 - 0.006, total oxygen [O] _T 0.007 - 0.020, Fe and inevitable impurities - the rest, and also including one or both of the following components, wt.%: Cu 0.1 - 0.6 and Sn 0.005 - 0.04, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.% , where Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B, and at stage f) the winding temperature is 580 - 680°C.

In particular, the steel strip has the following chemical composition, wt.%: C 0.02 - 0.06, Si 0.1 - 0.55, Mn 0.4 - 1.7, P ≤ 0.03, S ≤ 0.007 , Cr 0.30 - 0.80, Cu 0.10 - 0.60, Mo 0.20 - 0.60, Nb 0.01 - 0.08, N 0.004 - 0.010, Als < 0.001, B 0.001 - 0.006 , total oxygen [O] _T 0.007 - 0.020, Fe and inevitable impurities - the rest, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.%, where Pcm = C + Si/30 + Mn/20 + Cu/ 20 + Cr/20 + Mo/15 + 5B, and in step f) the winding temperature is 500 - 600°C.

It is preferable that in step f) the winding is carried out using a two-reel installation or a carousel winding method.

Within the framework of the manufacturing method in accordance with the present invention.

In order to improve the casting properties of molten steel for continuous casting of thin strip, the basicity a = CaO/SiO ₂ for the slag in the steelmaking process is maintained at a < 1.5, preferably a < 1.2, or a = 0.7 - 1.0.

In order to improve the casting properties of molten steel for continuous casting of thin strip, it is necessary to obtain a ternary inclusion of MnO - SiO ₂ - Al ₂ O ₃ with a low melting point, as shown in the shaded area in FIG. 4. The MnO/SiO ₂ ratio in the ternary inclusion of MnO - SiO ₂ -Al ₂ O ₃ is maintained at the level of 0.5 - 2, preferably 1 - 1.8.

To improve the casting properties of molten steel for thin strip continuous casting, oxygen (O) is a necessary element to ensure the formation of oxide inclusion in the steel. Since in accordance with the present invention it is necessary to form a ternary inclusion of MnO - SiO ₂ - Al ₂ O ₃ with a low melting point, the free oxygen content [O] _Free in the molten steel should be in the range of 0.0005 - 0.005 wt.%.

In order to improve the casting properties of molten steel for thin strip continuous casting, in addition to the above components, it is necessary to control the Mn and S content to satisfy the following condition: Mn/S ≥ 250.

In order to save investment costs and production costs, modern steel manufacturing enterprises are actively introducing technological innovations into existing production processes. In an effort to solve the problems of long process times and high number of complex devices within the current hot-rolled steel technology, many manufacturers are combining continuous casting and rolling technology with traditional processes to meet the demand for continuous casting and rolling technology.

The use of a converter to enable steelmaking to produce molten steel requires the manufacturer to have the conditions in place to produce molten pig iron. As a rule, equipment is required for blast furnace or non-blast furnace production of cast iron. This applies to the current regime of long-term steel production. However, as the availability of scrap steel is now increasing, the government is advocating for an increase in the proportion of scrap steel supplied to converters to achieve the goals of energy conservation, consumption reduction and cost reduction. In the past, the average scrap steel supply to converters was around 8%. Currently and in the foreseeable future, the target share of steel scrap supplied to converters is in the range of 15 - 25%. The proportion of scrap steel supplied to the converter according to the present invention can reach 20% or higher.

When using an electric furnace to produce molten steel for steelmaking, scrap steel is used as the main raw material. In traditional processes such as injection molding or continuous casting of thick slabs, the cooling rate during solidification is only 10 ^-1 -10°C/s. During the solidification process, intergranular segregation of residual elements in steel scrap occurs, which deteriorates the properties and quality of the steel, and in severe cases even causes direct cracking and destruction. Therefore, within the framework of traditional technology, the content of these harmful elements must be strictly controlled. When selecting raw materials from scrap steel, pre-sorting is required, and in the process of steel smelting, some special processing operations are required, such as adding concentrate for dilution, etc., which undoubtedly increases the production cost. Due to the need to control the composition of steel, there are certain requirements for the quality of the raw materials used - steel scrap. As a rule, scrap steel must be pre-selected and sorted. To improve production efficiency, some Chinese electric furnace steel mills prefer to add concentrates such as purchased sponge iron, iron carbide, etc. to the raw material to dilute harmful elements that are difficult to remove from scrap steel, thereby improving the quality of the molten material. become. Some Chinese steel mills that have both a blast furnace and an electric furnace add self-made molten iron to the electric furnace as electric furnace raw material to improve the production efficiency of the electric furnace, thereby greatly reducing the production time of the electric furnace. The mixing ratio of molten iron in an electric furnace can reach 30 - 50%.

The twin roll thin strip continuous casting technology used in accordance with the present invention is a typical sub-rate solidification process in which the solidification cooling rate is 10 ² - 10 ⁴ °C/s. Some harmful residual elements in steel scrap, such as Cu, Sn, P, etc., can be dissolved to the maximum extent in the steel matrix without causing intergranular segregation, so that the use of 100% steel scrap for smelting can be achieved without pre-sorting, which significantly reduces the cost of raw materials. These residual elements can also play a role in solid solution strengthening, helping to produce ultra-thin hot-rolled steel strip with excellent properties. For these harmful residual elements in steel scrap, the comprehensive use of low-quality steel scrap resources in the production has the effect of “turning harm into good” and “recycling waste”.

After the cast strip leaves the crystallization rollers, its temperature is 1420 - 1480°C, and it enters directly into the lower closed chamber 10. Non-oxidizing gas is supplied to the lower closed chamber to protect the steel strip from oxidation. The protective antioxidant atmosphere may be N ₂ or Ar, or another non-oxidizing gas, such as CO 2 gas obtained by sublimation of dry ice. The oxygen concentration in the lower closed chamber is maintained at <5%. The protection of the cast strip from oxidation provided by the lower closed chamber extends to the entrance of the rolling mill. The temperature of the cast strip at the exit from the lower closed chamber is 1150 - 1300°C.

Theoretical basis for the deposition of the BN phase in the cast strip, which occurs during the process of bottom circuit.

The thermodynamic equations between boron and nitrogen, and between aluminum and nitrogen in γ-Fe in steel are as follows:

As shown in FIG. 5, the start temperature of BN deposition in steel is about 1280°C, the deposition of BN stops at 980°C, while the deposition of AlN just begins (the start temperature of AlN deposition is about 980°C). The deposition of BN thermodynamically precedes the deposition of AlN. According to the present invention, the combination of B and N is completed in the lower closed chamber to form large BN particles. This prevents the precipitation of AlN fines and thus weakens the pinning effect of AlN fines at the grain boundary, so that the grain growth ability is improved and the austenite grains become coarser. As a result, austenite grains become more homogeneous, which has a beneficial effect on reducing the ratio of the yield strength to the ultimate strength σ _s /σ _b of the product, reducing the range of fluctuations of the yield strength and improving seismic characteristics. In addition, the combination of B and N can effectively prevent the appearance of the low melting point phase B ₂ O ₃ at the grain boundary.

After hot rolling in online mode, the steel strip is subjected to post-roll cooling. In particular, the steel strip is cooled using gas spray cooling. Gas atomization cooling can effectively reduce the thickness of oxide scale on the surface of the steel strip, increase the temperature uniformity of the steel strip, and improve the surface quality of the steel strip. When cooling by gas atomization, a gas and water ratio of 15: 1 - 10: 1 is used, gas pressure is 0.5 - 0.8 MPa and water pressure is 1.0 - 1.5 MPa. After atomizing the gas, a high-pressure water mist is formed, which is sprayed onto the surface of the steel strip. On the one hand, it plays a role in reducing the temperature of the steel strip. On the other hand, water mist forms a dense gas film that covers the surface of the steel strip, protecting it from oxidation, thereby effectively suppressing the growth of oxide scale on the surface of the hot-rolled steel strip. By using this cooling technology, the problems associated with traditional spray or laminar cooling can be avoided, and the surface temperature of the steel strip can be reduced evenly, which can improve the temperature uniformity of the steel strip, achieve the homogenization effect of the internal microstructure, and improve the yield strength-tensile strength ratio of the material. At the same time, uniform cooling improves the shape quality and stability of the steel strip. In addition, it is possible to effectively reduce the thickness of oxide scale on the surface of the steel strip. The cooling rate for gas atomization cooling is in the range of 20 - 100°C/s.

After cooling, the poor-quality steel strip head is cut off by shearing, and then the hot-rolled steel strip is directly coiled, and the rewinding temperature of the hot-rolled strip is kept at 500 - 680°C, so that the high-temperature austenitic structure after rolling is transformed into a mixed microstructure of solid ferrite+pearlite+angular ferrite or mixed microstructure of bulk ferrite+pearlite+low bainite as shown in Fig. 6. To ensure the continuous production of steel strip, a double bobbin machine or Carrousel coiler is used as a coiler.

Main advantages of the present invention.

The use of thin strip continuous casting technology to produce fire-resistant steel tape/strip that is weather resistant has not yet been described. Its advantages are as follows.

1. Complex processes such as slab heating, multi-pass repeated hot rolling and the like are eliminated. By using the continuous casting process of thin steel strip using double-roll machine + single-pass hot rolling, the production process is shorter, the efficiency is higher, and the investment cost of the production line and production cost are greatly reduced.

2. A large number of complex intermediate steps inherent in the traditional production process are eliminated. Compared with the traditional production process of thin corrugated steel strip, energy consumption and CO ₂ emissions when manufactured according to the present invention are significantly reduced, and the product is environmentally friendly.

3. Thin strip continuous casting process is used to produce thin steel strip. Due to the sub-rapid solidification characteristics of the thin strip continuous casting process itself, a fine-grain layer of a certain thickness is naturally formed on the surface of the strip steel, so that the resulting steel is weather-resistant. At the same time, the thickness of the cast strip itself is relatively small. By hot rolling on-line to the desired product thickness, thin sheet products can be directly supplied to the market for the supply of thin sheet hot rolled sheet, which can significantly improve the profitability of sheets and strips.

4. By adding a trace amount of boron element to preferentially precipitate large BN particles in high-temperature austenite and inhibit the precipitation of fine AlN, the pinning effect of fine AlN fractions at the grain boundary is weakened, and the grain growth ability is enhanced. As a result, austenite grains become larger and homogenized. This helps to improve the profiling characteristics of the product and reduce the ratio of the yield strength to the ultimate strength of the material. A low value of the ratio of yield strength to ultimate strength contributes to better energy absorption by the building structure during earthquakes and improves the seismic characteristics of the material.

5. When using an electric furnace for smelting, the proportion of steel scrap without pre-sorting in the total volume of raw materials for smelting can actually reach 100%, which significantly reduces the cost of raw materials. When smelting uses a converter to produce molten steel, scrap steel is added to the converter in an amount ≥ 20% of the total smelting raw material without pre-sorting, which maximizes the proportion of scrap steel fed to the converter and significantly reduces production costs and energy consumption.

6. Steel scrap containing Cu and Sn is used. Cu and Sn in steel “transform from harm to benefit.” Full utilization of existing steel scrap or low-grade and low-grade mineral resources (high tin ore, high copper ore) is made, which is conducive to recycling steel scrap, reducing production costs and achieving sustainable development of the steel industry.

7. Adopting gas atomization cooling technology, it avoids the problems associated with traditional atomization or laminar cooling, and the surface temperature of the steel strip is reduced evenly, which can improve the temperature uniformity of the steel strip and achieve the homogenization effect of the internal microstructure. At the same time, uniform cooling improves the shape quality and stability of the steel strip. In addition, it is possible to effectively reduce the thickness of oxide scale on the surface of the steel strip.

8. In the traditional slab cooling process, alloy elements are deposited, and when the slab is reheated, the re-dissolution of alloy elements is not enough, so the utilization rate of alloy elements is low. In the thin strip continuous casting process of the present invention, the high-temperature cast strip is directly hot rolled, and the added alloy elements are essentially in a solid solution state. In this way, the utilization rate of alloy elements can be increased.

9. Carrousel coiler is used for hot rolled steel strip, which can effectively shorten the length of the production line. At the same time, winding directly on the production site can greatly improve the accuracy of winding temperature control and improve the stability of product properties.

10. The most significant features that distinguish the present invention from existing thin strip continuous casting technology include the diameter of the crystallization rollers and the corresponding mode of distribution of molten steel. A technical feature of the EUROSTRIP technology is crystallization rollers with a large diameter of ∅1500 mm. Due to the large crystallization rollers together with the large melt pool capacity, it is easy to distribute the molten steel, but the manufacturing cost of the crystallization rollers as well as the operation and maintenance cost are high. A technical feature of the CASTRIP technology is crystallization rollers with a small diameter of ∅500 mm. Due to the small crystallization rollers together with the small capacity of the melt pool, it is very difficult to distribute molten steel, but the manufacturing cost of the crystallization rollers and the operation and maintenance cost are low. To solve the problem of uniformly distributing molten steel in a small molten pool, CASTRIP technology uses a three-stage molten steel dosing and distribution system (tundish + adapter + distributor). The use of a three-stage molten steel distribution system results in a direct increase in the cost of refractory materials. Moreover, the three-stage molten steel distribution system makes the molten steel flow path longer, and the temperature drop of the molten steel is also larger. To achieve the required temperature of molten steel in the melt bath, it is necessary to significantly increase the outlet temperature. Increasing tapping temperatures leads to problems such as increased steelmaking costs, increased energy consumption, and reduced service life of refractory materials.

11. The crystallization rolls according to the present invention have a diameter of 500 - 1500 mm, preferably a diameter of ∅800 mm. A two-stage system for dosing and distributing molten steel is used (tundish + distributor). The molten steel flowing from the distributor forms different distribution patterns along the surfaces of the rolls and the two side surfaces, and flows along two paths that do not interfere with each other. Thanks to the use of a two-stage distribution system, as opposed to a three-stage one, the cost of refractory materials is significantly reduced; The flow path of the molten steel is shortened, so that the temperature drop of the molten steel is reduced, and the outlet temperature can be lowered. Compared to a three-stage distribution system, the outlet temperature can be reduced by 30 - 50°C. Reducing the tapping temperature can effectively reduce the cost of steel smelting, save energy, and extend the service life of refractory materials. The combined use of crystallization rollers with a preferred roll diameter of ∅800mm and a two-stage molten steel dosing and distribution system according to the present invention not only meets the requirement of stable distribution of molten steel, but also achieves the goals of simple structure, convenient operation and low processing cost.

Description of drawings

Fig. 1 is a schematic view showing a flow chart of a thin strip continuous casting process with two rolls.

Fig. 2 is a schematic diagram showing the relationship between Sn content and average heat flux.

Fig. 3 is a schematic diagram showing the relationship between Sn content and surface roughness of cast strip.

Fig. 4 is a ternary phase diagram of MnO - SiO ₂ - Al ₂ O ₃ (shaded area: low melting point region).

Fig. 5 is a schematic diagram showing the thermodynamic deposition curves of BN and AlN.

In FIG. 6 is a photograph of the microstructure of steel from Example 1 of the present invention.

In FIG. 7 is a photograph of the microstructure of steel from Example 15 of the present invention.

Detailed description

The present invention will now be described with reference to the following examples and the accompanying drawings.

In FIG. 1: Molten steel corresponding to the compositional chemistry of the present invention passes through the steel ladle 1, the guard tube 2 of the steel ladle 1, the tundish 3, the dip nozzle 4 and the distributor 5, and then is poured directly into the melt bath 7 formed by the side sealing plates 6a, 6b and two counter-rotating crystallization rollers 8a, 8b capable of rapid cooling. The molten steel solidifies on the circumferential surfaces of the rotating crystallization rolls 8a, 8b, forming a solidified shell, which gradually increases and ultimately forms a strip 11 with a thickness of 1.5 - 3 mm in the minimum gap (clamping point) between the two crystallization rolls. The diameter of the crystallization rolls is 500 - 1500 mm; water is supplied inside the rolls for cooling. Depending on the thickness of the cast strip, the casting speed on the casting machine is in the range of 60 - 150 m/min.

After the cast strip 11 leaves the crystallization rolls 8a and 8b, its temperature is 1420 - 1480°C, and the strip enters directly into the lower closed chamber 10. Non-oxidizing gas is supplied to the lower closed chamber 10 to protect the steel strip from oxidation. The protective antioxidant atmosphere may be N ₂ or Ar, or another non-oxidizing gas, such as CO 2 gas obtained by sublimation of dry ice. The oxygen concentration in the lower closed chamber 10 is maintained at <5%. The protection of the cast strip 11 from oxidation, provided by the lower closed chamber 10, extends to the inlet of the rolling mill 13. The temperature of the cast strip at the outlet of the lower closed chamber 10 is 1150 - 1300°C. Then the cast strip enters the hot rolling mill 13 through a rotary wire plate 9, pressure rolls 12 and a rolling table 15. After hot rolling, a hot-rolled strip with a thickness of 0.8 - 2.5 mm is formed. The rolled steel strip is cooled by gas atomization using the gas atomization rapid cooling device 14 to improve the temperature uniformity of the steel strip. After cutting off the head part of the steel strip with flying shears 16, the cut off head part falls into the pit 18 along the wire plate 17, and the hot-rolled strip with the cut off head part enters the winder 19 for winding. After removing the steel coil from the coiler, it is cooled in air to room temperature. Finally, the resulting steel coil can be used directly as hot-rolled steel strip/strip or can be cut and flattened into finished steel strip/strip.

The method presented in the present invention is further illustrated by examples. The chemical compositions of Examples 1 - 14 are shown in Table 1; the remainder is Fe and other inevitable impurities. The technological parameters of the manufacturing method in examples 1 - 14 are shown in Table 2, and the properties of the resulting hot-rolled strips in examples 1 - 14 are shown in Table 3.

Corrosion Resistance Tests on Example Steels: 72-hour periodic infiltration and cyclic corrosion experiments were conducted in accordance with the Test Method for Periodic Infiltration and Cyclic Corrosion of Corrosion Resistant Steel (TB/T2375-1993) using ordinary grade carbon steel as comparative samples. Q345B. The average corrosion rate was obtained by calculating the corrosion mass loss per unit area of the sample, and then the relative corrosion rate of the steel was obtained. The test results in examples 1 - 14 are shown in table 4.

As shown in Table 3, the fire-resistant steel strip/tape/strip, weather-resistant, manufactured using the developed composite composition using the thin strip continuous casting process, has a room temperature yield strength ≥ 345 MPa, a tensile strength ≥ 490 MPa, relative elongation to failure ≥17%, ratio of yield strength to ultimate strength at room temperature σ _s /σ _b ≤ 0. 8; yield strength at 600°C ≥ 232 MPa, and the ratio of the yield strength at 600°C to the yield strength at room temperature (σs _,600°C /σs _,20°C ) ≥ 0.67; at the same time, the cold bendability meets the requirements. The corrosion resistance comparison results shown in Table 4 also show that the relative corrosion rate of steel is ≤ 60%. These results meet and even exceed the performance requirements of fire-resistant and weather-resistant steel. In addition, the supply of hot-rolled thin sheets can be realized, and the manufacturing cost can be significantly reduced. The material has a low yield strength ratio, excellent seismic performance and excellent fire resistance. It is an ideal material in the category of earthquake-resistant and fire-resistant steel.

Chemical composition of steel, wt.%. Examples 1 - 14

Table 1 No.
at-
measure C Si Mn P S N O Als Cr Mo Cu Sn B Pcm, wt.% 1 0.028 0.25 1.35 0.008 0.005 0.0077 0.0093 0.0009 0.35 0.50 0.37 - 0.003 0.19 2 0.044 0.10 0.90 0.013 0.003 0.0063 0.0110 0.0006 0.51 0.20 0.24 0.005 0.001 0.15 3 0.055 0.37 1.28 0.015 0.004 0.0056 0.0150 0.0004 0.52 0.48 0.10 0.023 0.004 0.21 4 0.022 0.28 1.10 0.013 0.004 0.0085 0.0130 0.0008 0.63 0.37 0.22 0.040 0.006 0.17 5 0.020 0.47 0.65 0.009 0.002 0.0054 0.0120 0.0007 0.30 0.27 0.45 - 0.003 0.14 6 0.036 0.45 0.67 0.012 0.002 0.0048 0.0070 0.0008 0.55 0.54 0.57 - 0.005 0.20 7 0.045 0.18 0.85 0.015 0.003 0.0040 0.0100 0.0005 0.60 0.60 0.16 0.035 0.003 0.19 8 0.047 0.37 1.00 0.024 0.004 0.0100 0.0085 0.0006 0.45 0.44 0.60 - 0.002 0.20 9 0.038 0.36 0.84 0.018 0.003 0.0058 0.0200 0.0003 0.74 0.37 0.33 0.028 0.004 0.17 10 0.056 0.47 0.40 0.030 0.001 0.0075 0.0125 0.0004 0.53 0.44 0.55 0.015 0.006 0.21 eleven 0.060 0.55 0.65 0.010 0.002 0.0093 0.0090 0.0005 0.44 0.55 0.43 - 0.003 0.21 12 0.043 0.26 1.70 0.012 0.0067 0.0088 0.0118 0.0003 0.80 0.26 0.33 0.013 0.002 0.22 13 0.038 0.44 1.37 0.008 0.004 0.0047 0.0132 0.0006 0.48 0.45 0.35 0.037 0.005 0.20 14 0.027 0.26 1.40 0.017 0.003 0.0066 0.0075 0.0005 0.54 0.38 0.25 - 0.004 0.19

Technological parameters of the manufacturing method. Examples 1 - 14

table 2 Example No. Thickness of the cast strip,
mm Atmosphere in the lower closed chamber Oxygen concentration in the lower closed chamber, % Hot rolling temperature,
°C The degree of compression during hot rolling is
ke, %. Thickness of hot rolled strip,
mm Cooling rate after rolling, °C/s Winding temperature
°C 1 2.10 N ₂ 3.6 1190 24 1.60 88 670 2 2.40 Ar 4.3 1240 31 1.65 72 620 3 2.20 N ₂ 2.6 1200 32 1.50 56 660 4 2.00 _CO2 2.7 1160 38 1.25 50 630 5 2.30 Ar 3.3 1165 22 1.80 92 670 6 2.70 Ar 2.8 1100 26 2.00 82 650 7 2.50 N ₂ 1.5 1180 50 1.25 20 600 8 2.00 _CO2 0.8 1230 40 1.20 40 580 9 1.80 Ar 1.5 1250 33 1.20 22 650 10 2.10 N ₂ 1.9 1170 33 1.40 75 660 eleven 2.40 Ar 1.3 1240 25 1.80 100 585 12 2.20 N ₂ 2.6 1160 36 1.40 70 675 13 2.10 _CO2 2.5 1190 29 1.50 thirty 680 14 2.00 Ar 2.5 1160 35 1.30 25 660

Mechanical properties of hot-rolled steel strips. Examples 1 - 14

Table 3 Example No. Thickness of the cast strip,
mm Thickness of the final product
mm Yield strength
MPa Ultimate tensile strength,
MPa Relative elongation to failure,
% Ratio of yield strength to tensile strength
(σ _s /σ _b) Bending diameter at an angle of 180 ^o d=a (a - strip thickness) Yield strength at temperature 600 ^o C,
MPa Ratio of yield stress at 600°C to yield stress at room temperature (σ _s,600°C /σ _s,20°C ) 1 2.10 1.60 350 503 23 0.70 Satisfactorily 238 0.68 2 2.40 1.65 351 510 26 0.69 Satisfied 241 0.69 3 2.20 1.50 366 515 21 0.71 Satisfied 245 0.67 4 2.00 1.25 348 512 19 0.68 Satisfied 246 0.71 5 2.30 1.80 360 523 22 0.69 Satisfied 245 0.68 6 2.70 2.00 347 498 23 0.70 Satisfied 256 0.74 7 2.50 1.25 354 515 25 0.69 Satisfied 248 0.70 8 2.00 1.20 365 505 24 0.72 Satisfied 250 0.68 9 1.80 1.20 360 514 27 0.70 Satisfied 254 0.71 10 2.10 1.40 354 523 25 0.68 Satisfied 250 0.71 eleven 2.40 1.80 357 496 23 0.72 Satisfied 244 0.68 12 2.20 1.40 366 508 22 0.72 Satisfied 253 0.69 13 2.10 1.50 356 527 23 0.68 Satisfied 242 0.68 14 2.00 1.30 348 530 22 0.66 Satisfied 241 0.69

Results of tests for corrosion resistance of steel. Examples 1 - 1 4

Table 4 Example No. Average corrosion rate, mg/ ^cm2.h Relative corrosion rate, % Q345B 0.4902 100 1 0.2506 51.12 2 0.2758 56.26 3 0.2848 58.10 4 0.2766 56.43 5 0.2668 54.43 6 0.2724 55.57 7 0.2905 59.26 8 0.2876 58.67 9 0.2862 58.38 10 0.2797 57.06 eleven 0.2657 54.20 12 0.2558 52.18 13 0.2908 59.32 14 0.2839 57.92

The chemical compositions of Examples 15-28 with Nb inclusion are shown in Table 5; the remainder is Fe and other inevitable impurities. The technological parameters of the manufacturing method in examples 15-28 are shown in Table 6, and the mechanical properties of the resulting hot-rolled strips in examples 15-28 are shown in Table 7.

Corrosion Resistance Tests on Example Steels: 72-hour periodic infiltration and cyclic corrosion experiments were conducted in accordance with the Test Method for Periodic Infiltration and Cyclic Corrosion of Corrosion Resistant Steels (TB/T2375-1993) using ordinary grade carbon steel as comparative samples. Q345B. The average corrosion rate was obtained by calculating the corrosion mass loss per unit area of the sample, and then the relative corrosion rate of the steel was obtained. The test results in examples 15-28 are shown in table 8.

As shown in Table 7, the fire-resistant steel strip/tape/strip, weather-resistant, manufactured using the developed composite composition using the thin strip continuous casting process, has a room temperature yield strength ≥ 410 MPa, a tensile strength ≥ 590 MPa, relative elongation to failure ≥ 17%, ratio of yield strength to ultimate strength at room temperature σ _s /σ _b ≤ 0.8; yield strength at 600°C ≥ 275 MPa, and the ratio of the yield strength at 600°C to the yield strength at room temperature (σ _s,600°C /σ _s,20°C ) ≥ 0.67; at the same time, the cold bendability meets the requirements.

The corrosion resistance comparison results shown in Table 8 also show that the relative corrosion rate of steel is ≤ 60%. These results meet and even exceed the performance requirements of fire-resistant and weather-resistant steel. In addition, the supply of hot-rolled thin sheets can be realized, and the manufacturing cost can be significantly reduced. The material has a low yield strength ratio, excellent seismic performance and excellent fire resistance. It is an ideal material in the category of earthquake-resistant and fire-resistant steel.

Chemical composition of steel, wt.%. Examples 15 - 28

Table 5 No.
example C Si Mn P S N O Als Cr Nb Mo Cu B Pcm, wt.% 15 0.028 0.26 1.36 0.008 0.005 0.0074 0.0093 0.0009 0.37 0.03 0.53 0.36 0.003 0.19 16 0.045 0.10 0.90 0.013 0.003 0.0061 0.0110 0.0006 0.52 0.02 0.20 0.23 0.001 0.15 17 0.056 0.33 1.27 0.015 0.004 0.0058 0.0150 0.0004 0.55 0.04 0.45 0.10 0.004 0.21 18 0.020 0.28 1.11 0.013 0.004 0.0087 0.0130 0.0008 0.63 0.02 0.34 0.35 0.006 0.19 19 0.023 0.45 0.66 0.009 0.002 0.0052 0.0120 0.0007 0.30 0.04 0.25 0.48 0.003 0.14 20 0.038 0.47 0.68 0.012 0.002 0.0046 0.0070 0.0008 0.54 0.06 0.57 0.55 0.005 0.21 21 0.046 0.18 0.86 0.015 0.003 0.0040 0.0100 0.0005 0.60 0.07 0.60 0.18 0.003 0.19 22 0.047 0.37 1.00 0.024 0.004 0.0100 0.0085 0.0006 0.32 0.01 0.44 0.60 0.002 0.19 23 0.038 0.33 0.86 0.018 0.0033 0.0078 0.0200 0.0003 0.78 0.04 0.36 0.45 0.004 0.20 24 0.060 0.47 0.40 0.030 0.001 0.0055 0.0125 0.0004 0.56 0.05 0.46 0.51 0.006 0.21 25 0.054 0.55 0.68 0.010 0.002 0.0090 0.0090 0.0005 0.47 0.04 0.58 0.43 0.003 0.21 26 0.035 0.23 1.70 0.012 0.0067 0.0085 0.0118 0.0003 0.80 0.08 0.29 0.36 0.002 0.22 27 0.048 0.49 1.38 0.008 0.004 0.0045 0.0132 0.0006 0.46 0.05 0.44 0.53 0.005 0.24 28 0.027 0.26 1.43 0.017 0.003 0.0064 0.0075 0.0005 0.56 0.04 0.36 0.28 0.004 0.19

Technological parameters of the manufacturing method. Examples 15 - 28

Table 6 Example No. Thickness of the cast strip,
mm Atmosphere in the lower closed chamber Oxygen concentration in the lower closed chamber, % Hot rolling temperature,
°C Reduction rate during hot rolling, %. Thickness of hot rolled strip,
mm Cooling rate after rolling, °C/s Winding temperature
°C 15 2.10 N ₂ 3.4 1190 26 1.55 88 570 16 2.60 Ar 4.2 1240 35 1.70 72 600 17 2.00 N ₂ 2.4 1200 28 1.45 56 580 18 2.10 _CO2 2.8 1160 43 1.20 50 540 19 2.40 Ar 3.4 1165 50 1.20 92 570 20 2.60 Ar 2.6 1100 23 2.00 82 550 21 2.20 N ₂ 1.4 1180 25 1.65 20 600 22 2.10 _CO2 0.8 1230 31 1.45 40 580 23 1.90 Ar 1.5 1250 37 1.20 22 500 24 2.00 N ₂ 1.9 1170 28 1.45 75 560 25 2.40 Ar 1.7 1240 25 1.80 100 580 26 2.20 N ₂ 2.6 1160 43 1.25 70 575 27 2.00 _CO2 2.5 1190 thirty 1.40 thirty 580 28 2.10 Ar 2.2 1160 36 1.35 25 520

Mechanical properties of hot-rolled steel strips. Examples 15 - 28

Table 7 Example No. Thickness of the cast strip,
mm Thickness of the final product
mm Yield strength
MPa Ultimate tensile strength,
MPa Relative elongation to failure,
% Ratio of tensile strength to tensile strength
(σ _s /σ _b) Bend diameter at an angle of 180° d=a (a - strip thickness) Yield strength at temperature 600 ^o C,
MPa Ratio of yield stress at 600°C to yield stress at room temperature (σ _s,600°C /σ _s,20°C ) 15 2.10 1.55 413 615 21 0.67 Satisfactorily 275 0.67 16 2.60 1.70 425 608 20 0.70 Satisfied 289 0.68 17 2.00 1.45 432 612 28 0.71 Satisfied 293 0.68 18 2.10 1.20 433 621 23 0.70 Satisfied 302 0.70 19 2.40 1.20 428 603 19 0.71 Satisfied 293 0.68 20 2.60 2.00 426 622 22 0.68 Satisfied 305 0.72 21 2.20 1.65 419 597 18 0.70 Satisfied 286 0.68 22 2.10 1.45 432 625 22 0.69 Satisfied 302 0.70 23 1.90 1.20 442 628 23 0.70 Satisfied 297 0.67 24 2.00 1.45 423 618 25 0.68 Satisfied 295 0.70 25 2.40 1.80 446 610 24 0.73 Satisfied 305 0.68 26 2.20 1.25 427 612 25 0.70 Satisfied 302 0.71 27 2.00 1.40 425 608 23 0.70 Satisfied 288 0.68 28 2.10 1.35 429 615 21 0.70 Satisfied 296 0.69

Results of tests for corrosion resistance of steel. Examples 15 - 28

Table 8 Example No. Average corrosion rate, mg/ ^cm2.h Relative corrosion rate, % Q345B 0.4902 100 15 0.2938 59.93 16 0.2764 56.39 17 0.2833 57.79 18 0.2793 56.98 19 0.2843 58.00 20 0.2916 59.49 21 0.2783 56.77 22 0.2776 56.63 23 0.2852 58.18 24 0.2797 57.06 25 0.2869 58.53 26 0.2747 56.04 27 0.2838 57.89 28 0.2793 56.98

Claims (26)

1. Fire-resistant steel strip, resistant to atmospheric influences, having the following chemical composition, wt.%: C 0.02-0.06, Si 0.1-0.55, Mn 0.4-1.7, P ≤ 0 .03, S ≤ 0.007, Cr 0.3-0.8, Mo 0.20-0.60, N 0.004-0.010, Als < 0.001, B 0.001-0.006, optional Nb 0.01-0.08, total oxygen [O] _T 0.007-0.020, Fe and inevitable impurities - the rest, and also including one or both of the following components, wt.%: Cu 0.1-0.6 and Sn 0.005-0.04, while Mn/S ≥ 250, and Pcm ≤ 0.27 wt.%, where: Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B. 2. Steel strip according to claim 1, having the following chemical composition, wt.%: C 0.02-0.06, Si 0.1-0.55, Mn 0.4-1.7, P ≤ 0.03 , S ≤ 0.007, Cr 0.3-0.8, Mo 0.20-0.60, N 0.004-0.010, Als < 0.001, B 0.001-0.006, total oxygen [O] _T 0.007-0.020, Fe and inevitable impurities - the rest, and also including one or both of the following components, wt.%: Cu 0.1-0.6 and Sn 0.005-0.04, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.%, where: Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B. 3. Steel strip according to claim 1, having the following chemical composition, wt.%: C 0.02-0.06, Si 0.1-0.55, Mn 0.4-1.7, P ≤ 0.03 , S ≤ 0.007, Cr 0.3-0.8, Mo 0.20-0.60, N 0.004-0.010, Als < 0.001, B 0.001-0.006, Cu 0.10-0.60, optional Sn 0.005- 0.04, total oxygen [O] _T 0.007-0.020, Fe and inevitable impurities - the rest, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.%, where: Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B. 4. Steel strip according to claim 1, having the following chemical composition, wt.%: C 0.02-0.06, Si 0.1-0.55, Mn 0.4-1.7, P ≤ 0.03 , S ≤ 0.007, Cr 0.3-0.8, Cu 0.10-0.60, Mo 0.20-0.60, Nb 0.01-0.08, N 0.004-0.010, Als < 0.001, B 0.001-0.006, total oxygen [O] _T 0.007-0.020, Fe and inevitable impurities - the rest, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.%, where: Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B. 5. The steel strip according to claim 1, the microstructure of which is a mixed microstructure of quasi-polygonal ferrite + pearlite + acicular ferrite or a mixed microstructure of quasi-polygonal ferrite + pearlite + lower bainite. 6. Steel strip according to any one of claims 1 to 3, having a yield strength (σ _s ) at room temperature ≥ 345 MPa, tensile strength (σ _b ) ≥ 490 MPa, elongation to failure ≥ 17%, yield strength ratio to the tensile strength at room temperature σ _s /σ _b ≤ 0.8, yield strength at 600°C (σ _s,600°C ) ≥ 232 MPa, ratio of the yield strength at 600°C to the yield strength at room temperature (σ _{s ,600°C} /σ _s,20°C ) ≥ 0.67 and relative corrosion rate ≤ 60%. 7. Steel strip according to claim 2 or 3, having a yield strength (σ _s ) at room temperature of 345-370 MPa, tensile strength (σ _b ) of 490-530 MPa, elongation to failure of 19-27%, limit ratio yield strength to tensile strength at room temperature σ _s /σ _b 0.66-0.72, yield strength at 600°C (σ _s,600°C ) 235-260 MPa, ratio of yield strength at 600°C to yield strength at room temperature (σ _s,600°C /σ _s,20°C ) 0.68-0.74 and relative corrosion rate ≤ 60%. 8. Steel strip according to claim 4, having a yield strength (σ _s ) at room temperature ≥ 410 MPa, tensile strength (σ _b ) ≥ 590 MPa, elongation to failure ≥ 17%, ratio of yield strength to tensile strength at room temperature temperature σ _s /σ _b ≤ 0.8, preferably ≤ 0.75, yield strength at 600°C (σ _s,600°C ) ≥ 275 MPa, ratio of yield strength at 600°C to yield strength at room temperature (σ _s,600°C /σ _s,20°C ) ≥ 0.67 and relative corrosion rate ≤ 60%, preferably, the steel strip has a yield strength (σ _s ) at room temperature of 410-450 MPa, tensile strength (σ _b ) tensile strength 590-630 MPa, relative elongation to failure 18-28%, ratio of yield strength to ultimate strength at room temperature σ _s /σ _b 0.67-0.73, yield strength at 600°C (σ _{s,600° C} ) 275-310 MPa, the ratio of the yield stress at 600°C to the yield stress at room temperature (σs _,600°C /σs _,20°C ) 0.67-0.72 and the relative corrosion rate ≤ 60%. 9. A method for producing a fire-resistant steel strip, resistant to weathering, according to any one of claims 1 to 8, including the following steps: a) smelting: control the basicity a = CaO/SiO ₂ of the slag at a < 1.5, preferably a < 1.2 or a = 0.7-1.0, while the ratio of MnO/SiO ₂ in the molten steel to obtain a triple MnO-SiO ₂ -Al ₂ O ₃ inclusions are maintained at a level of 0.5-2, preferably 1-1.8, while the content of free oxygen [O] _Free in the molten steel is 0.0005-0.005 wt.% and at the same time in molten steel Mn/S ≥ 250; c) continuous casting: two-roll continuous casting of a thin strip is used, in which a cast strip with a thickness of 1.5-3 mm is formed in the smallest gap between two crystallization rolls, while the crystallization rolls have a diameter of 500-1500 mm, preferably 800 mm, and for cooling Water is supplied inside the crystallization rolls, while the casting machine has a casting speed of 60-150 m/min, and to supply molten steel during continuous casting, a two-stage system for dosing and distributing molten steel is used, i.e. tundish + distributor; c) protection of the lower closed chamber: after the continuously cast strip leaves the crystallization rollers, it has a temperature of 1420-1480 ° C and enters directly into the lower closed chamber, into which non-oxidizing gas is supplied, and the oxygen concentration in the lower closed chamber is maintained at a level of < 5%, while the cast strip at the exit from the lower closed chamber has a temperature of 1150-1300°C; d) online hot rolling: the cast strip is fed through rolls in the lower closed chamber to the rolling mill, where it is rolled into a steel strip with a thickness of 0.8-2.5 mm at a rolling temperature of 1100-1250°C and a reduction degree of 10-50 %, preferably 30-50%, while the thickness of the steel strip is 0.8-2.5 mm, preferably 1.0-1.8 mm; f) post-rolling cooling of the steel strip: the rolled steel strip is cooled by gas spraying, and the cooling rate is 20-100°C/s; f) Steel strip winding: After cooling, the poor-quality head of the hot-rolled steel strip is cut off using shears and then rolled into a roll at a winding temperature of 500-680°C. 10. The method according to claim 9, including step g): post-processing, in which the steel coil is used directly as a hot-rolled strip or is cut and flattened and then used as a finished strip. 11. The method according to claim 9, in which at step a) an electric furnace is used to smelt molten steel, where 100% steel scrap is selected as the raw material for smelting without pre-sorting, or a converter is used for smelting to produce molten steel, where steel scrap added to the converter in an amount of 20% of the raw material for smelting without pre-sorting, while the molten steel then enters the furnace of the complex steel processing unit, the furnace of the vacuum degassing / vacuum-oxygen decarburization unit or the circulation evacuation furnace for subsequent refining. 12. The method according to claim 9, in which in step c) N ₂ , Ar or CO ₂ obtained by sublimation of dry ice is used as the non-oxidizing gas. 13. The method according to claim 9, in which at stage e) when cooling by gas atomization, a gas and water flow ratio of 15:1-10:1, gas pressure of 0.5-0.8 MPa and water pressure of 1.0- 1.5 MPa, while the flow rate has the unit of measurement m ³ / h. 14. The method according to claim 9, in which at step f) a two-reel installation is used for winding, or winding is carried out using the carousel method. 15. The method according to claim 9, in which the manufactured fire-resistant steel strip, resistant to atmospheric influences, has the following chemical composition, wt.%: C 0.02-0.06, Si 0.1-0.55, Mn 0, 4-1.7, P ≤ 0.03, S ≤ 0.007, Cr 0.3-0.8, Mo 0.20-0.60, N 0.004-0.010, Als < 0.001, B 0.001-0.006, total oxygen [O] _T 0.007-0.020, Fe and inevitable impurities - the rest, and also including one or both of the following components, wt.%: Cu 0.1-0.6 and Sn 0.005-0.04, with Mn /S ≥ 250, and Pcm ≤ 0.27 wt.%, where Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B, and at stage f) the winding temperature is 580-680°C. 16. The method according to claim 9, in which the manufactured fire-resistant steel strip, resistant to atmospheric influences, has the following chemical composition, wt.%: C 0.02-0.06, Si 0.1-0.55, Mn 0, 4-1.7, P ≤ 0.03, S ≤ 0.007, Cr 0.30-0.80, Cu 0.10-0.60, Mo 0.20-0.60, Nb 0.01-0, 08, N 0.004-0.010, Als < 0.001, B 0.001-0.006, total oxygen [O] _T 0.007-0.020, Fe and inevitable impurities - the rest, with Mn/S ≥ 250, and Pcm ≤ 0.27 wt.% , where Pcm = C + Si/30 + Mn/20 + Cu/20 + Cr/20 + Mo/15 + 5B, and at stage f) the winding temperature is 500-600°C.