Production method of special steel with extreme specification, high strength and high corrosion resistance

Abstract

The present invention discloses a production method of extreme specification high-strength and high-corrosion-resistant special steel. Niobium and titanium are used in the composition design to ensure strength, chromium and copper are added to ensure corrosion resistance, and rare earth wire is fed into the crystallizer to improve corrosion resistance; nickel is not added, so that the steel is pure and cost is saved; higher heating temperature, coiling temperature and other measures are adopted to ensure excellent plate shape, high strength, excellent corrosion resistance and good formability; performance indicators all meet the requirements; rough rolling and fine rolling have good rolling stability and low scrap rate. The extreme specification high-strength and high-corrosion-resistant special steel produced by the present invention has good atmospheric environment exposure test and salt spray corrosion test of atmospheric corrosion-resistant steel; the finished product has excellent quality and high finished product rate, without defects such as broken edges and warping; the process is simple and feasible, which greatly improves the rolling stability and yield rate of extreme specification high-strength and high-corrosion-resistant special steel, promotes the development of the corrosion-resistant industry, and reduces environmental pollution and energy consumption caused by non-ferrous metal metallurgy.

Description

Technical Field

[0001] The invention belongs to the technical field of steel rolling production, and specifically relates to a method for producing extreme specification high-strength and high-corrosion-resistant special steel. Background Art

[0002] The corrosion of metals under natural environmental conditions is called atmospheric corrosion, so steel that can resist corrosion under natural atmospheric environmental conditions is called atmospheric corrosion resistant steel. The so-called atmospheric corrosion resistant steel refers to low-alloy steel that has better corrosion resistance than ordinary carbon steel in the atmosphere and only needs to contain a few percent of a small amount of alloying elements (Cu, P, Cr, Ni, Nb, RE, etc.) and is inexpensive. Boilers, exterior wall frames, containers, railway vehicles, bridges, and ships are exposed to the atmosphere for operation. Atmospheric corrosion is one of the main reasons for the damage of the above components. Components made of ordinary carbon steel have poor atmospheric corrosion resistance and short service life. They need to be repaired after two and a half years of operation and overhauled after five years. The use of atmospheric corrosion resistant steel is an effective measure to extend the service life of components.

[0003] With the increasing loading volume, from the perspective of reducing dead weight and reducing the frequency of welds, atmospheric corrosion-resistant steel is developing towards high-strength, thin and wide extreme specifications, thus generating a market demand for a series of high-strength, thin and wide extreme specifications of hot-rolled coils (steel grade: Q800, specification 1.2mm×2000mm). For the production of this extreme specification of high-strength and high-corrosion-resistant steel, it is extremely difficult for major domestic steel mills to produce it in batches and stably.

[0004] Compared with rolling of general specifications, the difficulty lies in: poor rolling stability, high scrap rate, poor plate convexity control ability, easy occurrence of edge breakage, warping and other defects, which greatly reduce the production efficiency and yield rate of extreme specification steel plates. The current solution is to increase the thickness of the steel plate, reduce the width of the steel plate, and increase the welding frequency. The disadvantage is that it increases the procurement cost and process cost for customers.

[0005] The Chinese patent "A method for producing a fatigue-resistant low-yield ratio steel plate with a limit specification" with a publication number of CN114875297 does not add elements such as Cr, Ni and Cu in the composition design, and is not corrosion-resistant. In addition, the refining adopts a double-station process, which takes a long time and has a high cost. Patent CN105463317A discloses "A low-yield ratio hot-rolled pipeline steel uncoiling or uncoiling and its preparation method", which adds micro-alloy elements such as Nb, Cr, and Ti on the basis of low-carbon and low-manganese components; optimizes the TMCP production process, and finally obtains low-yield ratio hot-rolled pipeline steel produced by online quenching; the invention adopts an online quenching process, and its online quenching steel plate has a high internal stress, and no stress relief treatment is performed after uncoiling. The steel plate produced by the invention has no internal stress requirements, and the unevenness of the steel plate is not greater than 5 / 1000 mm, and the requirements for the shape of the steel plate are relatively low. Chinese patent CN112458360A discloses "A method for producing hot-rolled steel plates for bridge U-ribs with low residual stress", which includes the following steps: smelting, heating of continuous casting billets, rough rolling, finish rolling, cooling, coiling, slow cooling, leveling, unrolling, cross-cutting, and heat treatment; each bundle of steel coils is packaged into a continuous heat treatment furnace for stress relief treatment and longitudinal slitting; the residual stress of the 345~370MPa grade hot-rolled steel plates for bridge U-ribs obtained by this method is within -15~+15MPa; the heat treatment process of the invention is 450~530℃, and the tensile strength of the steel plate is 345~370MPa, which is relatively low in strength and has no requirement for the yield strength ratio.

[0006] The patent with publication number CN103114253B discloses "A method for producing ultra-thin ultra-high strength steel plates", which uses pure steel smelting, hot rolling forming, coiling, hot rolling base plate quenching and tempering, and controls the heating temperature of the ingot, uses large reduction during rolling, taps the heat treatment potential, and uses process means to ensure ultra-fine organization, and produces ultra-thin specifications with a finished thickness of 3-10 mm and a tensile strength of 1000-1500MPa ultra-high strength steel plates, which have excellent low-temperature toughness indicators, carbon equivalent (CEN) ≤0.4%, and good welding performance. The invention uses a double quenching + tempering process for heat treatment, and the double quenching has high energy consumption and a high yield strength ratio of the steel plate. Summary of the invention

[0007] In view of the problems in the original production of atmospheric corrosion-resistant steel, such as poor stability of rough rolling and finishing rolling, high scrap rate, poor plate convexity control ability, broken edges and warping of finished products, the purpose of the present invention is to provide a method for producing special high-strength and high-corrosion-resistant steel with extreme specifications. The present invention aims to combine the hot rolling unit with special process control means and optimized production organization control, which well solves the difficulties faced by the production of high-strength and high-corrosion-resistant steel with extreme specifications, can greatly reduce process costs, improve the stability of rough rolling and finishing rolling, and enhance market competitiveness.

[0008] In order to achieve the above-mentioned invention object, the present invention provides a production method for a special steel with extreme specifications, high strength and high corrosion resistance. The chemical composition of the special steel is as follows by mass percentage (wt%): C: ≤0.12%, Si: ≤0.50%, Mn: ≤1.60%, S: ≤0.005%, P: ≤0.015%, Cu: 0.20 - 0.60%, Al: 0.015 - 0.06%, Cr: 0.30 - 0.70%, Ca: 0.0010 - 0.0050%, N: 0.0010 - 0.0060%, Nb: 0.015 - 0.09%, Ti: 0.10 - 0.15%. In particular, in order to improve the corrosion resistance, rare earth RE: 0.05 - 0.10% is added to the steel, and the rest is Fe and inevitable impurities.

[0009] In the high-strength and high-corrosion-resistant special steel, niobium and titanium are added to ensure the strength; chromium and copper are added to ensure the corrosion resistance. In particular, in order to further improve the corrosion resistance, rare earth wires are fed into the mold. The special steel for atmospheric corrosion resistance has good corrosion resistance, and the alloying elements play a decisive role, including: reducing the conductivity of the rust layer, precipitating and covering the steel surface by itself; affecting the phase structure and types in the rust layer, hindering the growth of the rust layer; delaying the crystallization of rust; accelerating the uniform dissolution of the steel; blocking cracks and defects by alloying elements and their compounds.

[0010] A production method for the above-mentioned special steel with extreme specifications, high strength and high corrosion resistance. The production process flow of the method is: continuous casting billet heating → rough descaling → width sizing press → rough rolling → flying shear → finish rolling → laminar cooling → coiling → sampling → functional inspection → packaging and warehousing;

[0011] The extreme specifications of the high-strength and high-corrosion-resistant special steel are 1.2 mm × 2000 mm.

[0012] The addition method of the rare earth is to feed rare earth wires into the mold; by feeding rare earth wires on the basis of adding Cu and Cr elements to the steel, the high corrosion resistance of the special steel is further achieved. Adding rare earth to the steel can reduce the conductivity of the rust layer, precipitate and cover the steel surface by itself; affect the phase structure and types in the rust layer, hinder the growth of the rust layer; delay the crystallization of rust; accelerate the uniform dissolution of the steel; block cracks and defects by alloying elements and their compounds.

[0013] The continuous casting billet is hot delivered and hot charged;

[0014] The heating process of the continuous casting billet includes: high-temperature preheating section, heating section 1, heating section 2, soaking section;

[0015] The rough rolling adopts an R1 three-pass and R2 three-pass rolling scheme, and controls the thickness of the intermediate billet to be 25 mm - 35 mm;

[0016] The finish rolling uses a 7-stand hot continuous rolling process, and the temperature of the steel entering the finish rolling is 1040°C to 1080°C.

[0017] Since the steel contains easily oxidizable elements such as titanium and copper, which are likely to cause defects such as edge breakage and copper cracking in the finished product, the following are achieved in the heating system: the hot charging process for continuous casting billets; the high-temperature short-time rapid processing technology to fully ensure the diffusion of enriched titanium and copper (>1130°C) in the heating process into the steel matrix and the interior of the scale, effectively inhibiting the diffusion of titanium and copper to the austenite grain boundaries during rough rolling and finish rolling deformation; to reduce the load of the finish rolling mill and improve the controllability of the finish rolling process, the rough rolling reduction is increased as much as possible, the thickness of the intermediate billet is reduced, and the temperature of the steel entering the finish rolling is increased, etc. In addition, the spare parts in the rough rolling and finish rolling areas are inspected and replaced in a timely manner to ensure the equipment accuracy.

[0018] In the above technical solution, further, the heating process includes a high-temperature preheating section where the continuous casting billet is preheated at a temperature of 800°C to 900°C; a heating section 1 where the residence time of the continuous casting billet at 900°C to 1130°C is reduced to 25 - 30 min, effectively inhibiting the aggregation of titanium and copper on the surface of the steel matrix and the scale; a heating section 2 where, to reduce the enrichment of titanium and copper on the scale and the steel matrix, a weakly reducing atmosphere is used for heating, and the temperature is increased at a heating rate of 20 - 30°C / min in the range of 1130°C to 1230°C; a soaking section where a weakly reducing atmosphere is used for heat preservation, and the heat preservation time is 25 min to 35 min, reducing the diffusion of titanium and copper on the surface of the scale and the steel matrix to the scale and the steel matrix, effectively preventing defects such as edge breakage and warping caused by titanium and copper.

[0019] Further, in the rough rolling area: the rough rolling adopts a 3+3 rolling scheme (three passes for R1 and three passes for R2 rolling), ensuring that the camber of the intermediate billet is controlled within ±10 mm, and the thickness of the intermediate billet is in the range of 25 mm to 35 mm, creating favorable conditions for the stability control of the finish rolling mill and good strip shape.

[0020] Further, in the finish rolling area: a 7-stand hot continuous rolling is adopted. To effectively reduce the temperature drop of the intermediate billet and ensure temperature uniformity, a hot coil box is used; the temperature of the steel entering the finish rolling mill is increased as much as possible to ensure that it is in the range of 1040°C to 1080°C; the reduction distribution in the finish rolling is adjusted to increase the load on F1 - F3, the target crown of the strip coil is set to 35 µm, the strip shape of the strip coil is controlled well, and the rolling stability is improved. Preferably, the reduction of F1 and F2 is 20% each, the reduction of F7 is 8 - 10%, and the remaining reduction is distributed among the F4 - F6 stands.

[0021] Further, in the laminar cooling process: to improve the strength and toughness of the steel plate, the laminar cooling adopts an intermittent cooling mode; the coiling temperature is in the range of 600°C to 650°C to obtain a ferrite + bainite structure, meeting the performance requirements.

[0022] Furthermore, the rollers and spare parts are checked and replaced in time before rolling. By checking and replacing the spare parts of the rolling mill, the stability of the spare parts during the rolling process is ensured, thus preparing for precise rolling.

[0023] Furthermore, when rolling the 1.2mm×2000mm extreme specification special steel, a good rolling cycle is selected, and 5 to 6 pieces of transition materials of the same material are used. Through the reasonable arrangement of the plan, defects such as edge breakage and warping caused by titanium and copper can be effectively prevented.

[0024] The present invention adopts low-cost alloy component design to produce significant composite strengthening effects (including precipitation strengthening, fine grain strengthening and precipitation strengthening) and corrosion resistance in steel; the "extreme specification high-strength and high-corrosion-resistant special steel" produced based on the above method is a special steel developed for the production of boilers, exterior wall frames, containers, railway vehicles, bridges, ships and other corrosion-resistant structural parts; this steel is in contact with the atmosphere for a long time, and the salt spray accelerated corrosion test (relative to Q345B) is ≤60%, the yield strength of the material reaches more than 800MPa, and the anti-atmospheric corrosion passivation coating on the surface of the material is slightly damaged, a new type of material.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] In terms of chemical composition design, no precious alloys such as nickel and molybdenum are added, and the steel is pure, which saves costs while ensuring excellent performance; it has high strength and excellent atmospheric corrosion resistance, meeting user requirements; it has good forming performance; various indicators of mechanical properties meet the requirements, and the surplus is sufficient; in terms of plate shape control, reasonable higher heating temperature, higher coiling temperature and other measures are adopted to ensure excellent plate shape; the rough rolling and finish rolling have good rolling stability and low scrap rate.

[0027] The extreme specification high strength and high corrosion resistant special steel (1.2mm×2000mm) produced by the present invention fully meets the user's usage requirements with its excellent performance and good plate quality. The manufacturing cost of extreme specification high strength and high corrosion resistant special steel produced by this technology is much lower than the original atmospheric corrosion resistant steel (containing nickel corrosion resistant steel), which reduces the cost of the enterprise, reflects a higher quality of finished products and yield, and has good economic benefits; the atmospheric environment exposure test and salt spray corrosion test of atmospheric corrosion resistant steel are good, meeting the requirements of technical specifications; the finished product quality is excellent, without defects such as broken edges and warping; the process is simple and feasible to implement, which greatly improves the rolling stability and yield rate of extreme specification high strength and high corrosion resistant special steel; at the same time, it can save the amount of expensive metal nickel and save a lot of costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a microstructure photograph of the extreme specification high-strength and high-corrosion-resistant special steel prepared in the example. Detailed implementation manners

[0029] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way. To avoid repetition, in the following embodiments, raw materials are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0030] A production method of a special steel with extreme specifications, high strength and high corrosion resistance. The mass percentage of the chemical components of the special steel satisfies C: ≤0.12%, Si: ≤0.50%, Mn: ≤1.60%, S: ≤0.005%, P: ≤0.015%, Cu: 0.20 - 0.60%, Al: 0.015 - 0.06%, Cr: 0.30 - 0.70%, Ca: 0.0010 - 0.0050%, N: 0.0010 - 0.0060%, Nb: 0.015 - 0.09%, Ti: 0.10 - 0.15%. In particular, to further improve the corrosion resistance, rare earth RE: 0.05 - 0.10% is added to the steel, and the rest is Fe and inevitable impurities.

[0031] The technological process of the production method: continuous casting billet heating → rough descaling → width press → rough rolling → flying shear → finish rolling → laminar cooling → coiling → sampling → functional inspection → packaging and warehousing → delivery.

[0032] Embodiment

[0033] This embodiment provides a hot rolling production method of a special steel with extreme specifications, high strength and high corrosion resistance, which is widely used in manufacturing boilers, exterior wall frames, containers, railway vehicles, bridges, ships and other corrosion-resistant structural parts, etc.

[0034] The method and control means involved in the present invention are used to roll Q800 on a 2300mm hot tandem rolling mill. The rolling specification is 1.2mm×2000mm, and this specification is a typical representative of the extreme specifications of the special steel with high corrosion resistance.

[0035] Production is carried out on site according to the technical solution of the present invention. The specific heating process on site is shown in Table 1, the rolling process is shown in Table 2, the reduction distribution plan of the rough rolling mill is shown in Table 3, and the reduction distribution plan of the finish rolling mill is shown in Table 4. The specific results are as follows:

[0036] Table 1 Heating furnace heating process

[0037]

[0038] Table 2 Rolling process

[0039]

[0040] Table 3 Reduction rate distribution of rough rolling / mm

[0041]

[0042] Table 4 Finishing Reduction Rate Allocation / %

[0043]

[0044] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or it can be modified into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A production method of a special steel with high strength and high corrosion resistance for extreme specifications, characterized in that, The mass percentage of the chemical components of the special steel is C ≤ 0.12%, Si ≤ 0.50%, Mn ≤ 1.60%, S ≤ 0.005%, P ≤ 0.015%, Cu: 0.20% - 0.60%, Al: 0.015% - 0.06%, Cr: 0.30% - 0.70%, Ca: 0.0010% - 0.0050%, N: 0.0010% - 0.0060%, Nb: 0.015% - 0.09%, Ti: 0.10% - 0.15%, RE: 0.05% - 0.10%, and the rest is Fe and inevitable impurities; The limit specification of the high-strength and high-corrosion-resistant special steel is 1.2 mm × 2000 mm; the yield strength of the special steel reaches over 800 MPa; The technological process of the production method is: continuous casting billet heating → rough descaling → width-sizing press → rough rolling → flying shear → finish rolling → laminar cooling → coiling → sampling → functional inspection → packaging and warehousing; among which, The addition method of rare earth is to feed rare earth wire into the mold; hot charging and hot sending of continuous casting billets; The continuous casting billet heating process includes: high-temperature preheating section, heating section 1, heating section 2, soaking section; in the high-temperature preheating section, the continuous casting billet is preheated at a temperature of 800°C - 900°C; in heating section 1, the residence time of the continuous casting billet at 900°C - 1130°C is reduced to 25 - 30 min; in heating section 2, under a weakly oxidizing atmosphere, at a temperature in the range of 1130°C - 1230°C, it is heated at a heating rate of 20 - 30°C / min; in the soaking section, it is kept warm under a weakly reducing atmosphere, and the soaking time is 25 - 35 min; The rough rolling adopts a 3 + 3 rolling scheme, that is, three passes for R1 and three passes for R2, ensuring that the thickness of the intermediate billet is 25 - 35 mm; in the rough rolling area, the camber of the intermediate billet is ensured to be controlled within ±10 mm; The finish rolling adopts 7-stand hot continuous rolling, and the temperature of the billet entering the finish rolling mill is 1040°C - 1080°C; The laminar cooling adopts an intermittent cooling mode, and the coiling temperature is 620°C - 650°C, obtaining a ferrite + bainite structure.

2. The production method of the special steel according to claim 1, characterized in that, Before rolling, the rolls and spare parts in the rough rolling and finish rolling areas are inspected and replaced.

3. The production method of the special steel according to claim 1, characterized in that, When rolling the 1.2 mm × 2000 mm limit specification, a rolling cycle is formulated, and 5 - 6 transition materials of the same material are used.

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