CN112522576B - Thin-gauge high-corrosion-resistance steel and production method thereof - Google Patents

Thin-gauge high-corrosion-resistance steel and production method thereof Download PDF

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CN112522576B
CN112522576B CN201910888777.9A CN201910888777A CN112522576B CN 112522576 B CN112522576 B CN 112522576B CN 201910888777 A CN201910888777 A CN 201910888777A CN 112522576 B CN112522576 B CN 112522576B
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吴建春
方园
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Baoshan Iron and Steel Co Ltd
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Abstract

A thin high corrosion-resistant steel and its production method, its chemical composition weight percent is: c:0.02 to 0.06%, si:0.1-0.5%, mn:0.4-1.7%, P is less than or equal to 0.02%, cr:4.0-6.0%, ni:1.0-3.0%, S is less than or equal to 0.007%, N:0.004-0.010% of Als<0.001%, B:0.001-0.006%; total oxygen [ O ]] T :0.007 to 0.020%, the balance being Fe and unavoidable impurities, and simultaneously satisfying: contains Cu:0.1-0.6% or Sn:0.005-0.04% of one or two elements; mn/S>250. The invention uses the residual Sn, cu and other elements in the scrap steel to smelt the molten steel, and selectively adds Cr, ni and B elements; controlling the alkalinity of slag, the type and melting point of inclusions in steel, the content of free oxygen in molten steel and the content of acid-soluble aluminum Als in the smelting process; then, adopting a double-roller thin strip for continuous casting and casting a cast strip, and entering an online rolling mill for hot rolling through a lower closed chamber; and the cooling after rolling adopts an air atomization cooling mode.

Description

Thin-gauge high-corrosion-resistance steel and production method thereof
Technical Field
The invention belongs to a high-corrosion-resistant steel product, and particularly relates to thin high-corrosion-resistant steel and a production method thereof.
Background
In recent years, due to continuous recycling of scrap, scrap resources are increasing, electricity prices are also continuously decreasing, domestic short-process electric furnace steel making based on scrap is rising day by day, so that the content of residual elements such as Sn and Cu in steel is gradually increased, sn and Cu in steel are easily segregated elements, and defects such as cracks caused by enrichment in grain boundaries occur, so that the content of Sn and Cu elements in the traditional process is strictly controlled, and in steel for common structure, clear requirements on the content of Sn and Cu are provided: sn (wt%) is less than or equal to 0.005%; cu (wt%) is less than or equal to 0.2%.
In the traditional steel production flow, tin (Sn) and copper (Cu) are typical residual elements or harmful elements in steel, the Sn and the Cu are difficult and expensive to remove fully in the steel making process, once the steel contains the Sn and the Cu, the Sn and the Cu cannot be completely eliminated basically, and the contents of the Sn and the Cu can be reduced only by diluting molten steel, which causes the increase of the smelting cost of steel products.
Therefore, if the residual elements such as Sn, cu and the like in steel (particularly scrap steel) can be reasonably utilized, the 'harm is turned into good', the positive influence on the whole metallurgical boundary is generated; the method can realize the effective utilization of the existing steel scrap or low-quality inferior ore resources (high tin ore and high copper ore), promote the recycling of steel, reduce the production cost and realize the sustainable development of the steel industry.
The traditional thin strip steel is produced by casting blanks with the thickness of 70-200mm through multi-pass continuous rolling, and the traditional hot rolling process flow is as follows: continuous casting, casting blank reheating and heat preservation, rough rolling, finish rolling, cooling and coiling, namely firstly, a casting blank with the thickness of about 200mm is obtained through continuous casting, the casting blank is reheated and heat preserved, then rough rolling and finish rolling are carried out to obtain a steel strip with the thickness generally larger than 2mm, and finally laminar cooling and coiling are carried out to the steel strip to complete the whole hot rolling production process. The difficulty is relatively great if steel strip with a thickness of less than 1.5mm inclusive is to be produced, which is usually done by subsequent cold rolling and annealing of the hot rolled strip. And the process flow is long, the energy consumption is high, the number of unit equipment is large, the capital construction cost is high, and the production cost is high.
The thin slab continuous casting and rolling process flow is as follows: continuous casting, heat preservation and soaking of a casting blank, hot continuous rolling, cooling and coiling. The main differences between the process and the traditional process are as follows: the thickness of a casting blank in the thin slab process is greatly reduced to 50-90mm, and because the casting blank is thin, the casting blank can be reduced to the required specification before finish rolling only by carrying out 1-2 times of rough rolling (when the thickness of the casting blank is 70-90 mm) or not carrying out the rough rolling (when the thickness of the casting blank is 50 mm) on the casting blank, while the casting blank in the traditional process can be repeatedly rolled for multiple times; and the casting blank of the thin slab process directly enters a soaking pit furnace for soaking and heat preservation without cooling or 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 rapid cooling rate of the continuous casting and rolling of the thin slab leads to the improvement of the strength of steel and the improvement of the yield ratio, thereby increasing the rolling load, so that the thickness specification of a hot rolled product which can be economically produced cannot be too thin, generally being equal to or larger than 1.5mm, see patents CN200610123458.1, CN200610035800.2 and CN200710031548.2, and the patents do not relate to elements Sn and Cu.
The ESP realizes the continuous casting of the slab continuously, cancels the slab flame cutting and the heating furnace with the functions of heat preservation, soaking and slab transition, and greatly shortens the length of the whole production line to about 190 meters. The thickness of a plate blank continuously cast by the continuous casting machine is 90-110mm, the width of the plate blank is 1100-1600mm, the plate blank continuously cast by the continuous casting machine plays a role in heat preservation and soaking through a section of induction heating roller way, and then the plate blank sequentially enters the working procedures of rough rolling, finish rolling, layer cooling and coiling to obtain a hot rolled plate. The process realizes endless rolling, can obtain the hot rolled plate with the thinnest thickness of 0.8mm, expands the specification range of the hot rolled plate, and has the output of a single production line reaching 220 kiloton per year. At present, the process is rapidly developed and popularized, and a plurality of ESP production lines are operated and produced in the world at present.
The process flow shorter than the thin slab continuous casting and rolling is a thin strip continuous casting and rolling process, the thin strip continuous casting technology is a leading-edge technology in the fields of metallurgy and material research, the emergence of the technology brings a revolution to the steel industry, the production process of steel strips in the traditional metallurgy industry is changed, continuous casting, rolling, even heat treatment and the like are integrated into a whole, the produced thin slab is subjected to online hot rolling once to form a thin steel strip, the production process is greatly simplified, the production period is shortened, and the length of the process line is only about 50 m; the equipment investment is correspondingly reduced, the product cost is obviously reduced, and the method is a low-carbon and environment-friendly hot-rolled thin strip production process. The twin-roll thin strip continuous casting process is a main form of thin strip continuous casting process and is also a thin strip continuous casting process which only realizes industrialization in the world.
The typical process flow of twin roll strip casting is shown in fig. 1, molten steel in a ladle 1 is directly poured into a molten pool 7 surrounded by two oppositely rotating and rapidly cooled crystallizing rolls 8a and 8b and side sealing devices 6a and 6b through a 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 on the circumferential surfaces of the rotating crystallizing rolls 8a and 8b and gradually grows, a cast strip 11 with the thickness of 1-5mm is formed at the minimum gap (nip point) between the two crystallizing rolls, the cast 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 is fed into a coiler 19 to be coiled.
Thin-gauge high-corrosion-resistance steel is increasingly applied to fields needing high corrosion resistance, such as the transformation of carriages of green cars in the train manufacturing industry, the market quantity of steel for the transformation of the carriages of the green cars is large, and the steel has severe requirements on the corrosion resistance of the steel, and the corrosion resistance of the steel is required to be doubled on the basis of the traditional atmospheric corrosion-resistance steel. And also has certain requirements on cost. Aiming at such a huge market demand, no ready-made steel grade can be directly corresponded and used, and a brand-new steel grade needs to be developed. Stainless steel is not suitable for cost reasons, and the product is required to have good bending and forming properties; the thickness specification of the product is as follows: 1.0-2.0mm. The invention provides that the thin-strip continuous casting process is adopted to produce the high-corrosion-resistant steel, has certain advantages, and the successful development of the thin-gauge high-corrosion-resistant steel product provides a wide prospect for the train manufacturing industry in the aspects of light weight, greenness, energy consumption reduction, high corrosion resistance, stainless steel comparable to the corrosion resistance and the like.
Thin-gauge high-corrosion-resistance steel is produced by adopting thin-strip continuous casting, and the thin-strip continuous casting process has strong manufacturing and cost advantages due to the thin thickness. The specification characteristic thickness of the product supplied after the high corrosion resistant steel is post-processed is 1.0, 1.1, 1.2, 1.25, 1.4mm, 1.5mm, 1.6mm, 1.8mm, 2.0mm and the like, and because the product thickness is thin, if the production is difficult by adopting the traditional continuous casting and hot continuous rolling production line, the production is generally carried out by adopting the first hot continuous rolling process and then the cold rolling mode, and the production cost of the thin high corrosion resistant steel is increased by the production flow.
When the hot-rolled strip steel is used as a thin hot-rolled plate or a product which is 'hot to cool', 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 is, the better the scale is, and it is required to control the scale formation in the subsequent stages of the strip casting, for example, in the twin roll strip casting process, the closed chamber means is used in the crystallizing roll up to the inlet of the rolling mill to prevent the oxidation of the strip, and the scale thickness on the surface of the strip can be controlled by adding hydrogen gas into the closed chamber means such as 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 (rusty spots) are formed on the surface of strip steel, and the surface quality is influenced; secondly, cooling water for laminar cooling or spray cooling easily causes uneven local cooling on the surface of the strip steel and uneven microstructure inside the strip steel, thereby causing uneven performance of the strip steel and influencing the product quality; thirdly, the local cooling of the surface of the strip steel is uneven, which causes the deterioration of the plate shape and influences the quality of the plate shape.
However, due to the self rapid solidification process characteristic of the strip continuous casting, 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 thin strip continuous casting production line for producing high corrosion-resistant steel products has certain difficulties and challenges, and needs to have breakthroughs in composition and process.
At present, a plurality of patents have been applied for corrosion-resistant steel and manufacturing methods thereof at home and abroad, wherein the corrosion-resistant steel with the strength level of 450MPa or above mostly adopts Nb, V, ti and Mo composite microalloying technology, and the comprehensive mechanical property of the corrosion-resistant steel is improved through fine grain strengthening and precipitation strengthening, and the specific patent components and properties are shown in Table 1.
TABLE 1 patented comparison of Corrosion resistant steels (wt%)
Figure BDA0002208096310000041
Figure BDA0002208096310000051
The high-strength corrosion-resistant steel adopts a micro-alloying route, all contains Nb, V, ti, mo and other alloy elements in a component system, and is produced by adopting the traditional hot rolling process. The traditional hot rolling process flow is as follows: continuous casting, casting blank reheating and heat preservation, rough rolling, finish rolling, cooling and coiling, namely firstly, a casting blank with the thickness of about 200mm is obtained through continuous casting, the casting blank is reheated and heat preserved, then rough rolling and finish rolling are carried out to obtain a steel strip with the thickness generally larger than 2mm, and finally laminar cooling and coiling are carried out to the steel strip to complete the whole hot rolling production process. If a strip having a thickness of less than 2mm is to be produced, the hot rolled strip is generally subjected to further cold rolling and subsequent annealing. The above patents also mention the addition of boron (B) element in steel, such as patents CN200610125125.2 and US6315946, but the disclosure of the invention does not relate to a specific process control method after the addition of boron (B) element, and the amount of boron (B) element added is relatively small.
The production of microalloy high-strength corrosion-resistant steel by using the traditional process has the main problems that:
(1) 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.
(2) The corrosion-resistant steel contains high-content elements which are easy to segregate, such as copper and the like and can improve the corrosion resistance of the steel strip, and the traditional process is low in casting blank solidification and cooling speed, so that macro segregation of the elements, such as copper and the like, can be easily caused, the anisotropy and the macro cracks of the casting blank are caused, and the yield is low.
(3) Because the corrosion-resistant steel has the characteristic of easy segregation in the traditional process, in the component design for producing the high-strength corrosion-resistant steel by utilizing the traditional process, the addition amount of copper is in the range of 0.2-0.55%, the lower limit is usually taken in the actual production, and the addition amount of chromium is in the range of 0.2-1.25, which is generally lower. As a result, the corrosion resistance of the steel strip is not high.
(4) The corrosion resistance of the corrosion-resistant steels cannot meet the requirement of the corrosion resistance of the steel, namely the corrosion resistance is doubled on the basis of the traditional corrosion-resistant steels.
(5) In the traditional process, because microalloy elements cannot be kept as solid solutions in the hot rolling process and are partially precipitated, the steel structure has fine grains, the yield ratio is improved, and the formability is poor, so that the rolling load is obviously increased, the energy consumption and the roller consumption are increased, and the equipment is greatly damaged, thereby limiting the thickness range of economically and practically producing high-strength corrosion-resistant steel hot rolled products, which is usually less than or equal to 2mm. The steel strip thickness can be further reduced by continuing the cold rolling of the conventional hot rolled product, but the high strength of the hot rolled steel strip also causes difficulty in the cold rolling. Firstly, high cold rolling load has high requirements on equipment and great damage; and second, a second phase precipitated by alloy elements in a hot rolled product obviously increases the recrystallization annealing temperature of the cold rolled steel strip.
If the thin slab continuous casting and rolling process is adopted to produce the microalloy high-strength corrosion-resistant steel, the defects of the traditional process can be overcome to a certain extent. The thin slab continuous casting and rolling process flow is as follows: continuous casting, heat preservation and soaking of a casting blank, hot continuous rolling, cooling and coiling. The main differences between the process and the traditional process are as follows: the thickness of a casting blank in the thin slab process is greatly reduced to 50-90mm, and the casting blank is thin, so that the casting blank can be reduced to the required specification before finish rolling only by carrying out 1-2 times of rough rolling (when the thickness of the casting blank is 70-90 mm) or not carrying out the rough rolling (when the thickness of the casting blank is 50 mm) on the casting blank in the traditional process through repeated multi-pass rolling; the casting blank of the thin slab process directly enters a soaking pit furnace for soaking and heat preservation without cooling, or a small amount of temperature supplement is carried out, so the thin slab process greatly shortens the process flow, reduces the energy consumption, reduces the investment and further reduces the production cost; in addition, the solidification and cooling speed of the casting blank in the thin slab process is accelerated, and the macrosegregation of elements can be reduced to a certain extent, so that the defects of products are reduced, and the yield is improved.
Chinese patent CN200610123458.1 discloses a method for producing 700MPa grade high-strength corrosion-resistant steel by Ti micro alloying process based on thin slab continuous casting and rolling process, the chemical components of the corrosion-resistant steel plate manufactured by the method are: c:0.03 to 0.07%, si:0.3-0.5%, mn:1.2-1.5, P: less than or equal to 0.04%, S: less than or equal to 0.008 percent, 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: less than or equal to 0.008 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 775MPa, and the elongation is more than or equal to 21 percent. In the patent, the phosphorus is controlled according to impurity elements, the content is less than or equal to 0.04 percent, and is less than or equal to 0.025 percent compared with the traditional process, which is relaxed.
Chinese patent CN200610035800.2 discloses a method for producing 700MPa grade V-N microalloying corrosion resistant steel based on thin slab continuous casting and rolling process, the chemical components of the method for manufacturing the corrosion resistant steel plate are: c: less than or equal to 0.08 percent, si:0.25 to 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 that improve corrosion 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.
Although the thin slab process has the above advantages in producing microalloyed high strength corrosion resistant steel, certain problems in the conventional process production still exist in the thin slab process, such as: the microalloy elements can not be kept as solid solutions in the hot rolling process, partial precipitation occurs, and the steel strength is improved, so that the rolling load is increased, the energy consumption and the roller consumption are increased, and the thickness specification of a high-strength corrosion-resistant steel hot-rolled product which can be economically and practically produced is not too thin and is more than or equal to 1.5mm, see Chinese patents CN200610123458.1, CN200610035800.2 and CN200710031548.2.
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. Compared with the invention, the trace element B is added in the components of the invention, the content of Cr is obviously increased, and the invention has obvious distinguishing characteristics, and simultaneously, the subsequent treatment processes are completely different.
The manufacturing method of the high-copper low-alloy thin strip mentioned in the US patent 2008264525/CN200580009354.1 is technically characterized in that the strip steel is cooled to be lower than 1080 ℃ in a non-oxidizing atmosphere before entering a rolling mill so as to prevent the strip steel from generating the phenomenon of hot brittleness. Compared with the invention, the trace element B is added, the content of Cr is obviously increased, and the subsequent treatment method of the strip steel after strip discharging is different.
International patents WO 2008137898, WO 2008137899 and WO 2008137900, and chinese patents CN200880023157.9, CN200880023167.2 and CN200880023586.6 disclose a method for producing microalloy steel strip with thickness of 0.3-3mm by using strip continuous casting and rolling process. The method adopts the following chemical components: less than or equal to 0.25 percent, mn:0.20 to 2.0%, si:0.05 to 0.50%, al: 0.01% or less, and further comprises Nb:0.01 to 0.20%, V:0.01 to 0.20%, mo: 0.05-0.50% of at least one. Under the technological conditions that the hot rolling reduction is 20-40% and the coiling temperature is less than or equal to 700 ℃, the microstructure of the hot rolled strip is bainite and acicular ferrite. The patent states that the alloying elements mainly present in the solid-solution state in the cast strip inhibit the recrystallization of austenite after hot rolling, and that the recrystallization of austenite is very limited even if the reduction rate reaches 40%. Since austenite is not recrystallized at the hot rolling reduction of 20 to 40%, hardenability of coarse austenite is maintained after hot rolling, and thus a room-temperature structure of bainite + acicular ferrite is obtained. The temperature ranges used for hot rolling are not given in the patents, but are in articles related to these patents (C.R. Killmore, etc. development of Ultra-Thin case Strip Products by the
Figure BDA0002208096310000081
Ais Tech, indianapolis, indiana, USA, may 7-10, 2007), and it is reported that the hot rolling temperature employed is 950 ℃.
The thin strip continuous casting low-carbon microalloyed steel product produced by the method has high strength, the yield strength can reach 650MPa and the tensile strength can reach 750MPa in the range of the component system, but the main problem is that the elongation percentage of the product is not high (less than or equal to 6 percent or less than or equal to 10 percent). The main reasons for the low elongation are: the cast strip obtained by the thin strip continuous casting process has uneven austenite grain size, which is as small as tens of microns and as large as seven-eight-hundred microns. Generally, the hot rolling reduction rate of the strip casting process is only 1-2 stand rolling mills, which is hardly more than 50%, the effect of refining grains through deformation is very small, if austenite grains are not refined through recrystallization, the inhomogeneous austenite structure is hardly improved effectively after hot rolling, and the bainite + acicular ferrite structure generated after transformation of the austenite with inhomogeneous size is also inhomogeneous, so the elongation is not high.
In order to improve the strong plasticity matching of the thin strip continuous casting microalloyed steel, chinese patent No. 02825466.X proposes another method for producing a microalloyed steel thin strip with the thickness of 1-6mm by utilizing a thin strip continuous casting and rolling process. The microalloyed steel component system adopted by the method is C:0.02 to 0.20%, mn:0.1 to 1.6%, si:0.02 to 2.0%, al: less than or equal to 0.05 percent, S: less than or equal to 0.03%, P: less than or equal to 0.1 percent, cr:0.01 to 1.5%, ni:0.01 to 0.5%, mo: less than or equal to 0.5 percent, N: 0.003-0.012%, and the rest is Fe and inevitable impurities. The hot rolling of the cast strip is carried out at 1150- (Ar 1-100) DEG C, and the hot rolling is carried out in a hot rolling reduction of 15-80% corresponding to an austenite region, an austenite ferrite two-phase region, or a ferrite region. According to the method, an online heating system is designed behind a thin strip continuous casting and rolling unit, the heating temperature range is 670-1150 ℃, and the purpose is to ensure that the cast strip is completely recrystallized after heat preservation for a period of time after hot rolling in different phase regions, so that the steel strip obtains better strong plasticity matching. When the method is used for production, an online heating system is required to be added during production line design, and the heating uniformity can be ensured only if the heating furnace has enough length due to the length of heating time and the dependence on the belt speed and the length of the heating furnace. The investment cost is increased, the occupied area of the thin strip continuous casting and rolling production line is obviously increased, and the advantages of the production line are reduced.
Disclosure of Invention
The invention aims to provide thin high-corrosion-resistance steel and a production method thereof, which fully utilize scrap steel as a raw material to reduce the cost of molten steel, and can further reduce the cost of production procedures and improve the product performance, particularly the corrosion resistance of the product, by thin-strip continuous casting. The yield strength of the high corrosion-resistant steel reaches more than 350MPa, the tensile strength reaches more than 480MPa, and the elongation rate reaches more than 26%; the relative corrosion rate is less than or equal to 25 percent.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the invention uses the residual Sn, cu and other elements in the scrap steel to smelt the molten steel, and selectively adds alloy elements such as Cr, ni and the like and B elements in the steel; controlling the alkalinity of slag, the type and melting point of inclusions in steel, the content of free oxygen in molten steel and the content of acid-soluble aluminum Als in the smelting process; then, performing double-roller thin-strip continuous casting to cast strip steel with the thickness of 1.5-3mm, directly entering a lower closed chamber with non-oxidizing atmosphere after the strip steel exits from a crystallization roller, and entering an online rolling mill for hot rolling under the closed condition; the rolled strip steel is cooled by adopting an air atomization cooling mode, and the air atomization cooling mode can effectively reduce the thickness of oxide skins on the surface of the strip steel, improve the temperature uniformity of the strip steel and improve the surface quality of the strip steel. The finally produced steel coil can be used after acid pickling-flattening and can also be used after acid pickling-hot galvanizing.
Specifically, the thin high-corrosion-resistance steel comprises the following chemical components in percentage by weight: c:0.02-0.06%, si:0.1-0.5%, mn:0.4-1.7%, P is less than or equal to 0.02%, cr:4.0-6.0%, ni:1.0-3.0%, S is less than or equal to 0.007%, N:0.004-0.010%, als<0.001%, B:0.001-0.006% of total oxygen [ O ]] T :0.007 to 0.020%, the balance being Fe and unavoidable impurities, and, simultaneously:
contains Cu:0.1-0.6% or Sn:0.005-0.04% of one or two elements;
Mn/S>250。
the yield strength of the high corrosion-resistant steel reaches more than 350MPa, the tensile strength reaches more than 480MPa, and the elongation rate reaches more than 26%; the relative corrosion rate is less than or equal to 25 percent.
The microstructure of the high corrosion-resistant steel is a mixed microstructure of acicular ferrite and pearlite.
In the chemical composition design of the high corrosion-resistant steel, 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 level of the steel is determined to a great extent by the content of C, namely, higher C content corresponds to higher strength level. However, since interstitial solid solution and precipitation of C are harmful to the plasticity and toughness of steel, and an excessively high C content is disadvantageous to welding performance, the C content cannot be excessively high, and the strength of steel is compensated by appropriate addition of alloying elements. Meanwhile, for conventional slab continuous casting, casting in a peritectic reaction region is easy to generate surface cracks of a casting blank, and 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, strip casting of Fe — C alloys also requires avoidance of the peritectic reaction zone. Therefore, the content range of C adopted by the invention is 0.02-0.06%.
Si: si acts as a solid solution strengthening in steel, and addition of Si to steel improves steel purity and deoxidation, but too high a Si content leads to deterioration of weldability and toughness in weld heat affected zone. Therefore, the Si content range adopted by the invention is 0.1-0.5%.
Mn: mn is one of the cheapest alloy elements, can improve the hardenability of steel, has considerable solid solubility in the steel, improves the strength of the steel through solid solution strengthening, basically has no damage to the plasticity and the toughness of the steel, is the most main strengthening element for improving the strength of the steel, and can play a role in deoxidizing in the steel. However, too high Mn content results in deterioration of weldability and toughness of weld heat-affected zone. Therefore, the Mn content range adopted by the invention is 0.4-1.7%.
P: high content of P is easy to be segregated in grain boundary, increases cold brittleness of steel, deteriorates welding performance, reduces plasticity and deteriorates cold bending performance. In the thin strip continuous casting process, the solidification and cooling rates of the cast strip are extremely high, and the segregation of P can be effectively inhibited, so that the disadvantages of P can be effectively avoided, and the advantages of P can be fully exerted. Therefore, in the invention, the P content is higher than that in the traditional process, the content of the P element is properly relaxed, the dephosphorization procedure is eliminated in the steelmaking procedure, in the actual operation, the dephosphorization procedure is not required to be carried out intentionally, and no extra phosphorus is required to be added, and the range of the P content is less than or equal to 0.02 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 (3) 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 C element, N element can improve the strength of steel through interstitial solid solution, and the invention needs to utilize the action of N and B in the steel to generate a BN precipitated phase, and needs to have certain N content in the steel. However, the interstitial solid solution of N has great harm to the plasticity and the toughness of the steel, and the existence of free N can improve the yield ratio of the steel, so the content of N cannot be too high. The content range of N adopted by the invention is 0.004-0.010%.
Cr: not only the element for improving the hardenability of the steel, but also Cr is the main alloy element in the stainless steel, the corrosion resistance of the steel can be obviously improved, the welding performance can be seriously deteriorated if the content of Cr is too high, and the content of Cr is limited to 4.0-6.0 percent in the invention.
Ni: the alloy can improve hardenability, remarkably improve the low-temperature toughness of steel, and is a favorable element for improving the corrosion resistance and the toughness of steel, meanwhile, ni can adversely affect the welding performance of Cr punching, and Ni can effectively prevent the hot brittleness of Cu. The present invention limits the Ni content to 1.0-3.0%.
Nb: in the strip casting process, the added alloying element Nb can be made to exist mainly in a solid solution state in the steel strip due to its unique rapid solidification and rapid cooling characteristics, and precipitation of Nb is hardly observed even if the steel strip is cooled to room temperature. The Nb element which is dissolved in the steel can play a role in solid solution strengthening. The content range of Nb designed by the invention is 0.01-0.08%.
V: in the strip casting process, V and Nb are similar but weaker than Nb and mainly exist in a solid solution state in the steel strip, and even if the steel strip is cooled to room temperature, precipitation of V is hardly observed, and V element dissolved in the steel can play a role of solid solution strengthening. The content range of V adopted by the invention is 0.01-0.08%.
Cu: the Cu is an easily segregated element, so that the Cu content is generally controlled strictly 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 realize the effective utilization of copper in scrap steel or inferior ore resources (high copper ores) in a certain sense, promote the recycling of steel, reduce the production cost and realize the purpose of sustainable development.
Sn: the Sn element is also one of main participating elements in scrap steel, and is generally recognized as a harmful element in steel, because Sn is an easily segregated element, a small amount of Sn can be enriched in grain boundaries, and defects such as cracks can be caused, so that the content of the Sn element is strictly controlled in the conventional process. Due to the characteristic of rapid solidification, segregation of elements among dendrites is greatly reduced, and the solid solution amount of the elements can be greatly improved, so that the range of Sn elements can be expanded under the condition of a strip continuous casting process, and the steelmaking cost can be greatly reduced. Fig. 2 is a relationship between Sn element and average heat flux density. As can be seen from fig. 2, when the Sn addition is less than 0.04%, the influence on the heat flux density is not great, i.e., the ribbon solidification process is not affected. FIG. 3 is a relationship between Sn content and surface roughness. Since cracks on the surface of the cast strip usually occur at the uneven folds on the surface of the cast strip, the surface roughness is used to characterize the occurrence of surface cracks. If the roughness is large, the probability of occurrence of cracks is high. As is clear from FIG. 3, the increase in Sn content does not adversely affect the surface quality of the cast strip under the rapid solidification conditions. From the results of fig. 2 and 3, it is understood that Sn does not adversely affect the solidification and surface quality of the cast strip. Therefore, in the present invention, the requirement for Sn content can be further relaxed, and the Sn content is designed to be in the range of 0.005-0.04%.
B: the significant role of B in steel is: the hardenability of the steel can be multiplied by trace boron, and B can preferentially precipitate coarse BN particles in high-temperature austenite so as to inhibit the precipitation of fine AlN, weaken the pinning effect of the fine AlN on grain boundaries, improve the growth capability of grains, coarsen and homogenize austenite grains, facilitate the recrystallization after rolling, and improve the yield ratio and the forming performance of products after the austenite grains are coarsened and homogenized; in addition, the combination of B and N can effectively prevent the grain boundary low melting point phase B 2 O 3 Is present.
B is an active segregation-prone element and is easy to segregate in a grain boundary, and the content of B is generally controlled to be very strict and is generally about 0.001-0.003% when B-containing steel is produced by a traditional process; in the thin-strip continuous casting process, the solidification and cooling rates are high, the segregation of B can be effectively inhibited, and more B content is dissolved, so that the content of B can be properly widened; coarse BN particles can be generated through reasonable process control, and the precipitation of fine AlN is inhibited, so that the nitrogen fixation effect is achieved. The research also shows that when B is added with Nb and V in a compounding way, better effect can be obtained, the segregation tendency of C atoms can be reduced, and grain boundary Fe is avoided 23 (C,B) 6 So that more B can be added. Therefore, in the present invention, a higher B content is used than in the conventional process, in the range of 0.001-0.006%.
The invention relates to a production method of thin-gauge high-corrosion-resistance steel, which comprises the following steps of:
a) Smelting
Smelting according to the chemical composition requirements, wherein the slagging alkalinity a = CaO/SiO in the steelmaking process 2 Is controlled at a<1.5, preferably a<1.2, or a =0.7-1.0; obtaining low melting point MnO-SiO in molten steel 2 -Al 2 O 3 MnO/SiO in ternary inclusions 2 Controlling the concentration to be 0.5-2, preferably 1-1.8; free oxygen [ O ] in molten steel] Free The contents are as follows: 0.0005-0.005%; among the components of the molten steel, the molten steel has the characteristics of high temperature,
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; the continuous casting flow distribution adopts a two-stage steel water distribution system, namely a tundish and a flow distributor;
c) Lower enclosed chamber protection
After the casting strip is taken out of the crystallization roller, the casting strip is directly fed into a lower closed chamber at the temperature of 1420-1480 ℃, non-oxidizing gas is introduced into the lower closed chamber, the oxygen concentration in the lower closed chamber is controlled to be less than 5 percent, and the temperature of the casting strip at the outlet of the lower closed chamber is 1150-1300 ℃;
d) In-line hot rolling
Conveying the cast strip to a rolling mill through pinch rolls in a lower closed chamber, and rolling the cast strip into strip steel with the thickness of 0.8-2.5mm, wherein the rolling temperature is 1100-1250 ℃, the hot rolling reduction is controlled to be 10-50%, preferably 30-50%, and the thickness of the rolled strip steel is 0.8-2.5mm, preferably 1.0-1.8mm;
e) Strip steel cooling after rolling
Cooling the rolled strip steel, and cooling the strip steel by adopting an air atomization cooling mode, wherein the cooling rate of 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 at the coiling temperature of 600-700 ℃.
Further, the method also comprises the step g) of subsequent treatment, wherein the steel coil is used as an acid flat coil after acid washing and flattening, or used as a galvanized sheet after acid washing and hot galvanizing.
Preferably, in the step a), 100% of all-waste steel can be selected as smelting raw materials, pre-screening is not needed, and electric furnace steelmaking is adopted for molten steel smelting; or, the smelting adopts a converter for steel making, the scrap steel is added into the converter according to the proportion of more than 20 percent of the smelting raw materials, and pre-screening is not needed; then refining in an LF furnace, a VD/VOD furnace or an RH furnace.
Preferably, in step c), the non-oxidizing gas is N 2 Ar, or CO obtained by sublimation of dry ice 2 A gas.
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, in the step f), the coiling is in a double coiler form, and also can be in a carrousel coiling form, so that the continuous production of the strip steel is ensured.
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. shaded area of FIG. 4, mnO-SiO 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.
In order to improve the castability of thin strip continuous casting molten steel, oxygen (O) in the steel is an essential element for forming oxide inclusions, and the present invention requires formation of MnO-SiO with a low melting point 2 -Al 2 O 3 The ternary inclusions of (2) require free oxygen [ O ] in molten steel] Free The range is as follows: 0.0005 to 0.005 percent.
In order to improve the castability of the thin strip continuous casting molten steel, the Mn and S of the above components should satisfy the following relation: mn/S >250.
The 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, the oxygen concentration in the lower closed chamber is controlled to be less than 5 percent, the lower closed chamber protects the anti-oxidation of the cast strip to the inlet of a rolling mill, and the temperature of the cast strip at the outlet of the lower closed chamber is 1150-1300 ℃.
The theoretical basis of BN precipitated phase involved in the lower sealing process of the cast strip is as follows:
the thermodynamic equation of boron with nitrogen, aluminum and nitrogen in gamma-Fe in steel is as follows:
BN＝B+N； Log[B][N]＝-13970/T+5.24 (1)
AlN＝Al+N； Log[Al][N]＝-6770/T+1.03 (2)
as shown in FIG. 5, the initial precipitation temperature of BN in the steel is about 1280 ℃ and the precipitation of BN at 980 ℃ is in equilibrium, but the precipitation of AlN is just started (the precipitation temperature of AlN is about 980 ℃), and the precipitation of BN is thermodynamically preferred to AlN. According to the invention, the combination of B and N is completed in the lower closed chamber, and coarse BN particles are generated, so that the precipitation of fine AlN is inhibited, the pinning effect of fine AlN on crystal boundaries is weakened, the growth capability of crystal grains is improved, and austenite crystal grains are coarsened, so that the austenite crystal grains are more uniform, the yield ratio of a product is effectively reduced, and the product performance is improved; in addition, the combination of B and N can effectively prevent the grain boundary low melting point phase B 2 O 3 Of the cell.
The raw materials can be selected from 100 percent of all-scrap steel without pre-screening, so that the production cost is greatly reduced:
in order to save investment cost and production cost, modern iron and steel production enterprises actively carry out technical innovation on the existing production process flow. Aiming at the problems of long process flow, more equipment and complexity of the existing hot strip steel production process, a plurality of manufacturers tightly combine the continuous casting and rolling technology with the traditional process so as to meet the requirements of the continuous casting and rolling process.
The converter steelmaking is adopted to provide molten steel, so that furniture of a production plant needs to be provided with conditions for providing molten iron, and generally, blast furnace ironmaking equipment or non-blast furnace ironmaking equipment is needed, and the converter steelmaking method belongs to the current long-flow steel production mode. However, nowadays, the steel scrap resource is increasingly abundant, the country advocates improving the steel scrap ratio of the converter so as to achieve the purposes of energy saving, consumption reduction and cost reduction, the average level of the steel scrap ratio of the converter is about 8 percent in the past, and the steel scrap ratio of the converter is 15-25 percent in the present and future. The converter scrap ratio of the invention can reach more than 20 percent.
Steel-smelting lifter by electric furnaceFor molten steel, the steel scrap is used as main raw material, and the solidification cooling speed of the conventional process such as die casting or thick plate continuous casting is only 10 -1 10 ℃/s, the residual elements in the steel scrap can generate grain boundary segregation during the solidification process, deteriorate the performance and quality of the steel, and directly generate cracking and fracture phenomena in severe cases, so that in the traditional process, the harmful elements need to be strictly controlled, in the selection of the steel scrap raw material, some pre-screening needs to be carried out, and in the steel-making process, some special treatment needs to be carried out, such as adding some concentrate for dilution, and the like, which undoubtedly increases the production operation cost. Because the components of steel need to be controlled, certain quality requirements are required for the adopted steel scrap raw materials, and the steel scrap needs to be pre-screened and classified under general conditions. In order to improve the production efficiency of some domestic electric furnace steel mills, concentrated materials such as outsourced sponge iron, iron carbide and the like are selectively added in the raw material composition to dilute harmful elements which are difficult to remove in the waste steel, so that the quality of the molten steel is improved. Some domestic steel mills with blast furnaces and electric furnaces simultaneously use self-produced molten iron to be added into the electric furnace as raw materials of the electric furnace to improve the production efficiency of the electric furnace, thereby greatly shortening the tapping time of the electric furnace, and the molten iron blending ratio in the electric furnace can reach 30-50%.
The adoption of twin-roll thin-strip casting technology is a typical sub-rapid solidification process, and the solidification cooling speed is as high as 10 2 -10 4 The residual harmful elements in the scrap steel, such as Cu, sn, P and the like, can be dissolved in the matrix of the steel to the maximum extent without generating grain boundary segregation, so that 100 percent of total scrap steel smelting can be realized, pre-screening is not needed, and the raw material cost is greatly reduced. These residual elements also act as solid solution strengthening to produce ultra-thin hot rolled strip with excellent properties. Realizes the comprehensive utilization of the production of inferior steel scrap resources, and has the effects of turning harmful into beneficial and utilizing waste on the harmful residual elements in the steel scrap.
The rolled strip steel adopts an air atomization cooling mode:
the strip steel after on-line hot rolling is cooled after rolling, 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 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. The cooling rate of the gas atomization cooling is in the range of 20-100 ℃/s.
The invention has the main advantages that:
the invention utilizes the thin strip continuous casting technology to produce the corrosion-resistant steel containing tin (Sn), copper (Cu)/tin (Sn), copper (Cu) and boron (B), and has no report so far and has the advantages as follows:
1. the invention omits the complex processes of slab heating, multi-pass repeated hot rolling and the like, and has the advantages of shorter production flow, higher efficiency and greatly reduced production line investment cost and production cost by adopting the working procedures of double-roller thin-strip continuous casting and one-pass online hot rolling.
2. The invention omits a plurality of complex intermediate steps in the traditional process for producing the corrosion-resistant steel, greatly reduces the production energy consumption and CO2 emission compared with the traditional production process, and is a green and environment-friendly product.
3. According to the invention, the hot-rolled thin corrosion-resistant steel is produced by adopting a thin strip continuous casting process, the corrosion resistance is greatly improved by improving the content of Cr without the segregation problem of Cr, the corrosion resistance can be comparable to that of stainless steel, and the corrosion resistance can be doubled on the basis of the traditional corrosion-resistant steel; meanwhile, the thickness of the cast strip is thin, and the thin-specification product is produced without cold rolling by hot rolling on line to the thickness of the expected product and is directly supplied to the market for use, so that the purposes of supplying thin-specification hot rolled plates and cooling in hot bands are achieved, and the cost performance of the plates and strips can be obviously improved.
4. According to the invention, trace boron is added, coarse BN particles are preferentially precipitated in high-temperature austenite, so that the precipitation of fine AlN is inhibited, the pinning effect of fine AlN on grain boundaries is weakened, the growth capability of grains is improved, austenite grains are coarsened and homogenized, and the yield ratio and the forming performance of a product are improved.
5. The smelting adopts the electric furnace for steelmaking, the smelting raw materials can realize 100 percent of all-scrap steel smelting in the true sense, pre-screening is not needed, and the raw material cost is greatly reduced; if the steel is smelted by the converter, the scrap steel is added into the converter according to the proportion of more than 20 percent of the smelting raw materials without pre-screening, so that the scrap steel ratio of the converter is improved to the maximum extent, and the smelting cost and the energy consumption are greatly reduced.
6. The invention utilizes the scrap steel containing Cu and Sn to turn the Cu and Sn in the steel into harmful and beneficial, realizes the full utilization of the existing scrap steel or low-quality inferior ore resources (high-tin ore and high-copper ore), promotes the recycling of the scrap steel, reduces the production cost and realizes the sustainable development of the steel industry.
7. 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, and achieves the effect of homogenizing the internal microstructure; meanwhile, the cooling is uniform, so that the shape quality and the performance stability of the strip steel can be improved; effectively reducing the thickness of oxide scale on the surface of the strip steel.
8. In the traditional process, the alloy elements are precipitated in the cooling process of the plate blank, and the utilization rate of the alloy elements is reduced because the re-dissolution of the alloy elements is insufficient when the plate blank is reheated. In the thin strip continuous casting process, the high-temperature cast strip is directly hot-rolled, and the added alloy elements mainly exist in a solid solution state, so that the alloy utilization rate can be improved.
9. According to the invention, a hot rolled steel strip carrousel coiler is selected, so that the length of a production line is effectively shortened; meanwhile, the control precision of the coiling temperature can be greatly improved by the co-position coiling, and the stability of the product performance is improved.
10. 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 diameter of the crystallization roller is 1500mm, the crystallization roller is large, the molten steel capacity of a molten pool is large, the distribution is easy, and the manufacturing, operation and maintenance costs of the crystallization roller are high. CASTIP technology is characterized in that the diameter of a crystallization roller is 500mm, the crystallization roller 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 to be larger, and in order to meet the temperature of the molten steel in a molten pool, the tapping temperature needs to be greatly improved. The increase of the tapping temperature causes problems such as increase of steel-making cost, increase of energy consumption, and shortening of the life of refractory.
11. The diameter of the crystallization roller is 500-1500mm, preferably the diameter of the 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 the two-stage flow distribution system is adopted, compared with a three-stage flow distribution system, the cost of refractory materials is greatly reduced; the flow path of the molten steel is shortened, so that the temperature drop of the molten steel is reduced, the tapping temperature can be reduced, and compared with a three-level flow distribution system, the tapping temperature can be reduced by 30-50 ℃. The steel tapping temperature is reduced, so that the steel making cost can be effectively reduced, the energy consumption is saved, and the service life of refractory materials is prolonged. The invention is matched with the crystallization roller with the optimal roller diameter of phi 800mm, and adopts a two-stage steel water distribution system, thereby not only realizing the requirement of stable distribution of molten steel, but also realizing the aims of simple structure, convenient operation and low processing cost.
Drawings
FIG. 1 is a schematic diagram of a process arrangement for a twin roll strip casting process;
FIG. 2 is a graph showing the relationship between Sn content and average heat flux density;
FIG. 3 is a schematic representation of the relationship between Sn content and surface roughness of a cast strip;
FIG. 4 shows MnO-SiO 2 -Al 2 O 3 Ternary phase diagram (shaded area: low melting point region);
FIG. 5 is a schematic view showing the thermodynamic curves of BN and AlN precipitates.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the invention in any way. Any variations in the practice of the invention that may occur to those skilled in the art and which are made in the light of the teachings of this specification are intended to be within the scope of the following claims.
Referring to fig. 1, molten steel designed according to the chemical composition of the present invention is directly poured into a molten pool 7 surrounded by two relatively rotating and rapidly-cooled crystallizing rollers 8a and 8b and side sealing plate devices 6a and 6b through a ladle 1, a tundish 2, a tundish 3, a submerged nozzle 4 and a distributor 5, the molten steel is solidified on the circumferential surfaces of the rotating crystallizing rollers 8a and 8b, and then a solidified shell is formed and gradually grows to form a casting strip 11 with a thickness of 1.5-3mm at the minimum gap (nip point) between the two crystallizing rollers; the diameter of the crystallization roller is 500-1500mm, and water is introduced into the crystallization roller for cooling. The casting speed of the casting machine ranges from 60 to 150m/min according to the thickness of the cast strip.
After the cast strip 11 comes out of the crystallization rollers 8a and 8b, the cast strip is at 1420-1480 deg.C and directly enters the lower closed chamber 10, the lower closed chamber 10 is filled with inert gas to protect the strip steel, so as to realize the oxidation-proof protection of the strip steel, and the atmosphere of the oxidation-proof 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. Lower enclosed chamber 10 protects against oxidation of cast strip 11 to the entrance of rolling mill 13. The temperature of the cast strip at the outlet of the lower closed chamber 10 is 1150-1300 ℃. Then the cast strip is sent to a hot rolling mill 13 through a swinging guide plate 9 and a pinch roll 12, a hot rolled strip with the thickness of 0.8-2.5mm is formed after hot rolling, and the rolled strip steel is cooled by adopting an air atomization cooling mode, so that the temperature uniformity of the strip steel is improved. After the head is cut by the flying shear device 16, the head falls into the flying shear pit 18 along the flying shear guide plate 17, and the hot rolled strip after the head is cut enters the coiler 19 for coiling. Taking down the steel coil from the coiling machine, and naturally cooling the steel coil to room temperature. The finally produced steel coil can be used after acid cleaning and flattening, and can also be used after acid cleaning and hot galvanizing.
The process of the invention is further illustrated by the examples. The chemical compositions of the examples of the present invention are shown in table 2, and the balance of the compositions is Fe and other unavoidable impurities. The manufacturing method of the invention has the process parameters shown in the table 3, and the mechanical properties of the finally obtained hot rolled strip are shown in the table 4.
The corrosion resistance of the example steels was tested: a common carbon steel Q345B and a traditional atmospheric corrosion resistant steel SPA-H are used as comparison samples, and a periodic infiltration cyclic corrosion test for 72 hours is carried out according to a corrosion resistant steel periodic infiltration corrosion test method (TB/T2375-93). 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 5.
In conclusion, the high corrosion-resistant steel produced by the strip continuous casting process technology according to the design range of the steel grade components provided by the invention has the advantages that the yield strength is more than or equal to 350MPa, the tensile strength is more than or equal to 480MPa, the elongation is more than or equal to 26%, the yield ratio is lower than 0.8, and the cold-working bending performance is qualified. The comparison result of the corrosion resistance also shows that the relative corrosion rate of the steel grade is less than or equal to 25.
Figure BDA0002208096310000201
Figure BDA0002208096310000211
Figure BDA0002208096310000221
Figure BDA0002208096310000231

Claims (11)

1. The thin-gauge high-corrosion-resistance steel comprises the following chemical components in percentage by weight: c:0.02-0.06％，Si：0.1-0.5％，Mn：0.4-1.7％，P≤0.02％，Cr：4.0-6.0％，Ni：1.0-3.0％，S≤0.007％，N：0.004-0.010％，Als<0.001%, B:0.001-0.006% of total oxygen [ O ]] T :0.007 to 0.020%, the balance being Fe and unavoidable impurities, and, simultaneously:
contains Cu:0.1-0.6% or Sn:0.005-0.04% of one or two elements;
Mn/S>250；
the microstructure of the high corrosion-resistant steel is a mixed microstructure of acicular ferrite and pearlite;
the yield strength of the high corrosion-resistant steel reaches more than 350MPa, the tensile strength reaches more than 480MPa, and the elongation reaches more than 26%; the relative corrosion rate is less than or equal to 25 percent; and is obtained by a process comprising the steps of:
a) Smelting
Smelting according to the chemical composition requirements, wherein the slagging alkalinity a = CaO/SiO in the steelmaking process 2 Controlling 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 minimum position of a gap between two crystallizing rollers; the diameter of the crystallization roller is 500-1500 mm; cooling the crystallization roller by introducing water, wherein the casting speed of the casting machine is 60-150m/min; a two-stage steel water distribution system is adopted for continuous casting flow distribution, namely a tundish and a flow distributor;
c) Lower sealed chamber protection
After the cast strip is taken out of the crystallization roller, the temperature of the cast strip is 1420-1480 ℃, the cast strip directly enters a lower closed chamber, non-oxidizing gas is introduced into the lower closed chamber, the oxygen concentration in the lower closed chamber is controlled to be less than 5 percent, and the temperature of the cast strip at an outlet of the lower closed chamber is 1150-1300 ℃;
d) In-line hot rolling
Conveying the cast strip to a rolling mill through a pinch roll in a lower closed chamber, and rolling the cast strip into strip steel with the thickness of 0.8-2.5mm, wherein the rolling temperature is 1100-1250 ℃, the hot rolling reduction rate is controlled to be 10-50%, and the thickness of the rolled strip steel is 0.8-2.5mm;
e) Strip steel cooling after rolling
Cooling the rolled strip steel, and cooling the strip steel by adopting an air atomization cooling mode, wherein the cooling rate of 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 at the coiling temperature of 600-700 ℃.
2. The production method of the thin-gauge high-corrosion-resistance steel is characterized by comprising the following steps of:
a) Smelting of
Smelting according to the following chemical composition requirements, wherein the basicity of slagging in the steelmaking process is a = CaO/SiO 2 Control at a =0.7-1.0; obtaining low melting point MnO-SiO in molten steel 2 -Al 2 O 3 MnO/SiO in ternary inclusions 2 Controlling the temperature to be 0.5-2; free oxygen [ O ] in molten steel] Free The contents are as follows: 0.0005-0.005%; in the molten steel composition, mn/S>250；
The thin-gauge high-corrosion-resistance steel comprises the following chemical components in percentage by weight: c:0.02 to 0.06%, si:0.1-0.5%, mn:0.4-1.7%, P is less than or equal to 0.02%, cr:4.0-6.0%, ni:1.0-3.0%, S is less than or equal to 0.007%, N:0.004-0.010%, als<0.001%, B:0.001-0.006% of total oxygen [ O ]] T :0.007-0.020%, the balance being Fe and unavoidable impurities, and, simultaneously: contains Cu:0.1-0.6% or Sn:0.005-0.04% of one or two elements;
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 minimum position of a gap between two crystallizing rollers; the diameter of the crystallization roller is 500-1500 mm; cooling the crystallization roller by introducing water, wherein the casting speed of the casting machine is 60-150m/min; a two-stage steel water distribution system is adopted for continuous casting flow distribution, namely a tundish and a flow distributor;
c) Lower sealed chamber protection
After the cast strip is taken out of the crystallization roller, the temperature of the cast strip is 1420-1480 ℃, the cast strip directly enters a lower closed chamber, non-oxidizing gas is introduced into the lower closed chamber, the oxygen concentration in the lower closed chamber is controlled to be less than 5 percent, and the temperature of the cast strip at an outlet of the lower closed chamber is 1150-1300 ℃;
d) In-line hot rolling
Conveying the cast strip to a rolling mill through pinch rolls in a lower closed chamber, and rolling the cast strip into strip steel with the thickness of 0.8-2.5mm, wherein the rolling temperature is 1100-1250 ℃, the hot rolling reduction is controlled to be 10-50%, and the thickness of the rolled strip steel is 0.8-2.5mm;
e) Cooling after rolling strip steel
Cooling the rolled strip steel by adopting an air atomization cooling mode, wherein the cooling rate of air atomization cooling is 20-100 ℃/s;
f) Strip steel coiling
And cutting the head of the cooled hot-rolled strip steel to remove the head with poor quality, and directly coiling the hot-rolled strip steel into coils at the coiling temperature of 600-700 ℃.
3. The method for producing thin gauge high corrosion resistant steel according to claim 2, further comprising the step of g) a subsequent treatment, wherein the steel coil is used as an acid flat coil after acid pickling-flattening, or as a galvanized sheet after acid pickling-hot galvanizing.
4. The method for producing thin gauge high corrosion resistant steel according to claim 2, wherein in step a), 100% of all scrap steel is selected as the raw material for smelting, and pre-screening is not required, and electric furnace steel making is adopted for smelting molten steel; or, the smelting adopts a converter for steelmaking, the scrap steel is added into the converter according to the proportion of more than 20 percent of the smelting raw materials, and pre-screening is not needed; then refining in an LF furnace, a VD/VOD furnace or an RH furnace.
5. The method for producing thin gauge high corrosion resistant steel according to claim 2 wherein in step c), the non-oxidizing gas is N 2 Ar, or CO obtained by sublimation of dry ice 2 A gas.
6. The method for producing thin gauge high corrosion resistant steel according to claim 2, wherein in 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.
7. The method for producing thin gauge highly corrosion resistant steel as claimed in claim 2, wherein in step f), the coiling is performed in a double coiler type or a carrousel coiling type, thereby ensuring continuous production of the strip.
8. The method for producing a thin gauge high corrosion resistant steel according to claim 2 wherein in step a), a low melting point MnO-SiO is obtained in said molten steel 2 -Al 2 O 3 MnO/SiO in ternary inclusions 2 The temperature is controlled to be 1-1.8.
9. The method for producing a thin gauge high corrosion resistant steel according to claim 2, wherein the diameter of the crystallization roll in step b) is 800mm.
10. The method for producing thin gauge high corrosion resistant steel according to claim 2, wherein the hot rolling reduction in step d) is 30 to 50%.
11. The method for producing thin gauge high corrosion resistant steel according to claim 2, wherein in step d), the thickness of the steel strip is 1.0 to 1.8mm.
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