CN115679181B - Hot rolled angle steel with yield strength of 420MPa and minus 20 ℃ resistance and production method thereof - Google Patents
Hot rolled angle steel with yield strength of 420MPa and minus 20 ℃ resistance and production method thereof Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention discloses a hot rolled angle steel with yield strength of 420MPa and minus 20 ℃ resistance and a production method thereof. The hot rolled angle steel comprises the following elements in percentage by mass: c:0.08% -0.15%, si:0.25% -0.50%, mn:1.20% -1.55%, P: less than or equal to 0.020%, S: less than or equal to 0.015 percent, V:0.020% -0.065%, nb:0.020% -0.050%, als:0.010 to 0.025 percent, H is less than or equal to 0.0002 percent, N is less than or equal to 0.015 percent, and the balance is Fe and unavoidable impurities; the production method comprises the following steps: molten iron pretreatment, converter smelting, argon blowing refining, LF refining, VD refining, rectangular blank or square blank full-protection casting, rolling process and air cooling after rolling; by adopting chemical components and a rolling process and utilizing fine grain strengthening, precipitation strengthening, phase change strengthening and solid solution strengthening mechanisms, the hot rolled angle steel with excellent mechanical properties is obtained.
Description
Technical Field
The invention belongs to the technical field of steel rolling production, and particularly relates to hot rolled angle steel with yield strength of 420MPa and minus 20 ℃ resistance and a production method thereof.
Background
Along with the rapid development of economy, the bridge foundation engineering construction of China also gets the rapid development. In particular, in recent decades, bridge construction in China increases in the number of 3 ten thousand seats per year, the total length of the bridge increases at the speed of 5 ten thousand kilometers, a large number of world-level bridge projects are constructed, and China becomes a world bridge country. The section steel product has wide application in bridge construction due to the advantages of green energy conservation, simple section, convenient use and the like.
At present, the bridge steel products in the domestic market mainly comprise H-shaped steel, but in a steel girder structure, a truss girder generally needs to be a hot rolled angle steel product with high strength and high toughness. The traditional angle steel for the bridge can meet the requirement of using steel beam members at 345MPa level, but along with the change of bridge engineering environment, especially in low-temperature areas, the market of the angle steel for the bridge structure begins to develop in the main directions of high strength and high-low-temperature toughness. Research shows that the steel consumption can be greatly reduced along with the improvement of the steel strength, so that the dead weight of the whole bridge steel structure and the construction difficulty of bridge construction are reduced, and the bridge safety is improved. Therefore, development of hot rolled angle steel products with high strength and high-low temperature toughness can greatly promote development of bridge engineering in low-temperature areas. The D level of the steel for the bridge structure is required to be more than or equal to 120J (-20 ℃ C. Longitudinal V-shaped low-temperature impact energy).
Through searching, the publication number is CN105543677A, the publication date is 2016, 5 and 4 days, and the patent of 345MPa grade No. 14 hot rolled angle steel for a power communication tower in a plateau mountain area and a preparation method thereof is named as' C:0.14-0.20%, si:0.20-0.30%, mn:0.85-1.05%, V:0.016-0.030%, ti:0.015-0.030%, mo:0.015-0.025%, P is less than or equal to 0.020%, S is less than or equal to 0.015%, and the balance is Fe and unavoidable impurities. The method mainly adopts a large amount of V+Ti+Mo composite alloy elements, the production process is complex, the requirements on the steelmaking process are strict, meanwhile, the production cost is increased due to the large amount of alloy content, the yield strength of the angle steel product produced by the method is 345MPa, and the strength index does not meet the requirements of angle steel for bridge structures.
The publication number is CN105734418A, the publication date is 2016, 7 and 6, and the patent is named as low-temperature-resistant low-temperature-rolled angle steel and a preparation method thereof. The angle steel comprises the following chemical components in percentage by mass: c:0.10-0.15%, si:0.20-0.50%, mn:1.3-1.7%, V:0.04-0.06%, al:0.005-0.015%, N less than or equal to 0.01%, O less than or equal to 0.006%, P less than or equal to 0.020%, S less than or equal to 0.010%, and the balance of Fe and unavoidable impurities. The production method comprises the working procedures of molten iron pre-desulfurization, converter smelting, LF refining, continuous casting by a billet continuous casting machine and rolling, and the sulfur content in the molten iron is ensured to be less than or equal to 0.005wt% after desulfurization. The method has higher impact toughness, but the whole production process has extremely high requirements on steelmaking technology, the content of O, N, S and other elements is strictly controlled, the steelmaking cost is greatly increased, in addition, the heating temperature is too high in the rolling process, the soaking section 1220-1260 ℃ is higher in energy consumption, and the yield strength of the product produced by the method is more than 345MPa, but still does not meet the requirement on high strength of the bridge structural steel.
The method mainly comprises the steps of adopting a converter (content of end point control C, P, ti) -LF refining (temperature 1565-1575 ℃ after normal heat soft blowing) -continuous casting (full-process protection pouring) -rolling mill (initial rolling temperature 1050-1200 ℃, high-pressure water for descaling, billet rolling is not allowed, rolling groove number is ordered from a transmission side to an operation side, synchronous adjustment of guides is paid attention to after rolling piece adjustment, and simultaneously, the left side and the right side of each guide are squeezed by wood or other objects). The method has the advantages of complex control process, strict requirements on the field operation process, narrow process window and increased field tooling equipment investment, and the product can only finally meet the requirements of C-level (0 ℃) electric angle steel on low-temperature impact toughness and cannot realize service conditions with lower temperature (-20 ℃).
The publication number is CN106906411A, the publication date is 2017, 6 months and 30 days, the name is 'Q345 FRD fireproof anti-seismic hot rolled angle steel for public steel structure building and preparation method thereof', and the composition is C:0.16-0.21wt%, si:0.23-0.33wt%, mn:0.85-1.05wt%, V:0.017 to 0.032wt%, ti:0.015-0.030wt%, mo:0.080 to 0.100 weight percent, less than or equal to 0.015 weight percent of S, less than or equal to 0.020 weight percent of P, and the balance of Fe and unavoidable impurities, wherein the production process comprises the following steps: A. pretreating and desulfurizing molten iron; B. smelting molten steel; C. deoxidizing and alloying; D. refining molten steel in an LF furnace; E. casting molten steel; F. heating a steel billet; G. descaling a billet by using a high-pressure water tank; H. preforming by a cogging mill; I. tandem rolling by a universal rolling mill; J. detecting the online external dimension of angle steel; K. and (5) finishing. The method has strict requirements on the molten iron treatment process (molten iron pretreatment, converter smelting, deoxidization alloying, LF furnace refining and bloom whole-course protection continuous casting), increases the production procedures and production cost, and the yield strength of the final angle steel product is 345MPa, and the strength index does not meet the requirements of angle steel for bridge structures.
The patent with publication number CN107513665A and publication date 2017, 12 months and 26 days is named as 'Q345-level hot-rolled weather-resistant large-sized angle steel for iron towers and a preparation method thereof', and discloses that the Q345-level hot-rolled weather-resistant large-sized angle steel for iron towers comprises the following components: c:0.03-0.10wt%, si:0.15wt% to 0.50wt%, mn: 0.30-0.90 wt%, P is less than or equal to 0.020wt%, S is less than or equal to 0.015wt%, cr:0.40wt% to 0.80wt% of Ni:0.10wt% to 0.30wt%, cu: 0.20-0.50 wt%, als is more than or equal to 0.015wt%, ti:0.01wt% to 0.05wt%, V: 0.03-0.10wt% and the balance of Fe. Adopts the component design scheme of low C, V and Ti composite addition and proper amount of corrosion resistant elements. However, the composition process has strict control on the continuous casting special-shaped blank, particularly adopts Ti microalloy to increase refining energy consumption, and the final strength of the product can only reach 345MPa level, so that the requirement of the bridge structural steel on strength can not be met.
The publication number is CN103695772A, the publication date is 2014, 4 and 2, the name is 'fire-resistant weather-resistant earthquake-resistant building steel with yield strength of 550MPa level' and a production method thereof, and the steel comprises the following chemical components in percentage by weight: c:0.041-0.125, si:0.31-0.62, mn:1.81-2.40, P: less than or equal to 0.008, S: less than or equal to 0.002, nb:0.041-0.065, ti:0.007-0.020, mo:0.41-0.63, W:0.07-0.10, mg:0.0071-0.0098, O: less than or equal to 0.0012. The invention has higher Mn content, and the noble metals Nb and Mo with higher content are added, so the production cost is higher.
The patent with publication number CN110699598A and publication date 2020-1-27 is named as 'a niobium microalloyed high-strength high-weather-resistant angle steel and production process thereof', and the chemical components of the patent are as follows in percentage by mass: c:0.05-0.12%, si:0.20-0.75%, mn less than or equal to 1.00%, cu:0.20-0.55%, P:0.07-0.10%, cr:0.30-1.25%, ni:0.12-0.65%, nb:0.015-0.060%, S is less than or equal to 0.020%, ceq is less than or equal to 0.44, I is more than or equal to 6, and the balance is Fe and unavoidable impurities; the production process comprises continuous casting blank production, angle steel rolling and angle steel straightening. The method mainly adopts a large amount of Cr+Ni+Nb+Cu composite alloy elements, has complex production procedures and strict requirements on steel making technology, and the low-temperature (-20 ℃) impact energy of the product by adopting the method is only more than 34J and is far less than the requirements of angle steel for bridge structures on low-temperature impact values.
The publication number is CN109127724A, the publication date is 2020, 4 months and 10 days, the patent is named as a production process method of high-toughness angle steel, and the production process method comprises the following steps: the double heat-storage walking beam type heating furnace and the two-roller reversible rolling mill of the I frame 750 roll 5-7 times (rough rolling) +the two-roller reversible rolling mill of the II frame 750 roll 3 times (middle rolling) +stop for 0.5-3 minutes on a transition roller way between the finishing mill and the II frame 750 rolling mill, ensure that the temperature of the finishing mill is 800-900 ℃, and then enter the finishing mill for rolling. However, this method is subject to special rolling mill equipment arrangements, with rolling temperatures limited to 800-900 ℃, which increases the intermediate waiting time for a typical tandem rolling stand, slows down the rolling cadence, and is difficult to achieve in practical rolling production. Moreover, the strength grade of the product produced by the technical scheme is C grade, and the requirement of the D grade of the steel for the general bridge structure is not met.
The steel angle is disclosed as CN112011737A and 18 days in 2020, and is named as 390 MPa-grade hot rolled angle steel with minus 20 ℃ resistance for bridge structures and a production method thereof, and the steel angle steel comprises the following chemical components in percentage by weight: c:0.15-0.18%, si:0.20-0.45%, mn:1.35-1.45%, P: less than or equal to 0.025 percent, S: less than or equal to 0.025 percent, cr:0.020-0.060%, V:0.030-0.080%, als:0.010-0.025%, and the balance of Fe and unavoidable impurities. Through reasonable component proportion and production process control, the BD cogging rolling, finish rolling and controlled cooling process after rolling is utilized, and the hot rolled angle steel for bridge structures with the yield strength of 390MPa level, low finish rolling compression ratio, low yield ratio and low-temperature impact energy of minus 20 ℃ of not less than 65J is realized. However, the yield strength is only 390MPa, the high strength requirement cannot be met, the low-temperature impact energy at minus 20 ℃ is only more than 65J, and the requirement that the longitudinal V-shaped low-temperature impact energy at minus 20 ℃ of the bridge steel is more than 120J cannot be met.
Disclosure of Invention
1. Problems to be solved
Aiming at the problems that the yield strength of hot rolled angle steel for bridges is lower than 420MPa and the longitudinal V-shaped low-temperature impact energy at minus 20 ℃ is lower than 120J and cannot meet the requirements of bridge structures in the prior art, the invention provides the hot rolled angle steel with the yield strength of 420MPa and minus 20 ℃ and the production method thereof, which improve the yield strength and the low-temperature impact energy at minus 20 ℃ and meet the requirements of the strength for bridge structures and the impact energy at minus 20 ℃.
2. Technical proposal
In order to solve the problems, the technical scheme adopted by the invention is as follows:
the invention relates to a hot rolled angle steel with yield strength of 420MPa and minus 20 ℃, which comprises the following elements in percentage by mass: c:0.08% -0.15%, si:0.25% -0.50%, mn:1.20% -1.55%, P: less than or equal to 0.020%, S: less than or equal to 0.015 percent, V:0.020% -0.065%, nb:0.020% -0.050%, als:0.010% -0.025%, H is less than or equal to 0.0002%, N is less than or equal to 0.015%, and the balance is Fe and unavoidable impurities.
The production method of the hot rolled angle steel with the yield strength of 420MPa and the temperature resistance of minus 20 ℃ comprises the following steps: molten iron pretreatment, converter smelting, argon blowing refining, LF refining, VD refining, rectangular billet or square billet full-protection casting, rolling process and air cooling after rolling.
The rolling process of the hot rolled angle steel comprises the following steps:
1) Heating the blank: the rectangular blank or square blank enters a heating furnace, is heated to 1190-1230 ℃ by the heating furnace, and is heated for 90-130 min in the furnace for ensuring the sufficient solid solution of alloy elements, and simultaneously avoiding overburning and excessive coarsening of austenite grains;
2) Rough rolling: controlling the pass reduction rate to be 15% -25% in the temperature range of 1100-1150 ℃; controlling the pass reduction rate to be 25% -30% in the temperature range of 1050 ℃ -1100 ℃; controlling the pass rolling reduction to 15% -25% and controlling the total rolling reduction of the blank to 50% -70% in the temperature range of 1050-1000 ℃;
3) Finish rolling: after rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled below 900 ℃. The selective control cooling device between the middle and finish rolling mill frames can accurately control the temperature change of rolled pieces, and gives the set deformation amount to the angle steel in the corresponding temperature range by combining the rolling reduction designed in the rolling procedure so as to ensure the performance of the final product.
The thickness of the hot rolled angle steel obtained by adopting the technical scheme is less than or equal to 26mm, the structure is a ferrite 75-85% + pearlite 15-25% complex phase structure, and the ferrite grain size grade is more than or equal to 9.0 grade; the yield strength of the product is more than or equal to 420MPa, the tensile strength is more than or equal to 540MPa, the elongation A is more than or equal to 19%, the longitudinal V-shaped impact power KV2 at minus 20 ℃ is more than or equal to 120J, the yield ratio is less than or equal to 0.85, and the product has higher strength, good plasticity and higher low-temperature toughness.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
according to the production method of the hot rolled angle steel with the yield strength of 420MPa and the temperature resistance of minus 20 ℃, reasonable chemical components and rolling procedures are adopted, so that the performance uniformity of the whole section of a rolled piece is improved, and the influence of the temperature waiting on the rolling rhythm is avoided; the hot rolled angle steel with excellent comprehensive mechanical properties, thickness less than or equal to 26mm and yield strength greater than 420MPa and resisting-20 ℃ is obtained by utilizing fine grain strengthening, precipitation strengthening, phase change strengthening and solid solution strengthening mechanisms.
Drawings
The technical solution of the present invention will be described in further detail below with reference to the accompanying drawings and examples, but it should be understood that these drawings are designed for the purpose of illustration only and thus are not limiting the scope of the present invention. Moreover, unless specifically indicated otherwise, the drawings are intended to conceptually illustrate the structural configurations described herein and are not necessarily drawn to scale.
FIG. 1 shows a microstructure of steel angles obtained in example 1, wherein the microstructure is a ferrite+pearlite complex phase structure, and the grain size grade is 11.0 grade;
FIG. 2 shows the microstructure of the angle steel obtained in example 2, wherein the microstructure is a ferrite+pearlite complex phase structure, and the grain size grade is 10.5 grade;
FIG. 3 shows the microstructure of the angle steel obtained in example 3, wherein the microstructure is a ferrite+pearlite complex phase structure, and the grain size grade is 10.5 grade;
fig. 4 shows a complex phase structure of ferrite and pearlite, which is a grain size grade of 10.0, as the angle steel microstructure obtained in example 4.
Note that: white in the figure is ferrite, and black and gray brown are pearlite.
Detailed Description
The following detailed description of exemplary embodiments of the invention refers to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration exemplary embodiments in which the invention may be practiced. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it is to be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the invention. The following more detailed description of the embodiments of the invention is not intended to limit the scope of the invention, as claimed, but is merely illustrative and not limiting of the invention's features and characteristics in order to set forth the best mode of carrying out the invention and to sufficiently enable those skilled in the art to practice the invention. Accordingly, the scope of the invention is limited only by the attached claims.
The invention relates to a hot rolled angle steel with yield strength of 420MPa and minus 20 ℃, which comprises the following elements in percentage by mass: c:0.08% -0.15%, si:0.25% -0.50%, mn:1.20% -1.55%, P: less than or equal to 0.020%, S: less than or equal to 0.015 percent, V:0.020% -0.065%, nb:0.020% -0.050%, als:0.010% -0.025%, H is less than or equal to 0.0002%, N is less than or equal to 0.015%, and the balance is Fe and unavoidable impurities.
The invention adopts the design thought of Nb-V composite microalloying components, considers the production cost, aims to obtain sufficient V (C, N) precipitation to highlight the precipitation strengthening effect at low temperature and good low-temperature impact value, and considers the economy (the price of V-N is higher than that of V-Fe), the V element is added by adopting V-N:V-Fe=4:6 alloy, because nitrogen and carbon can be dissolved in iron in a solid way to form an intermittent solid solution, and can be synthesized into extremely stable nitride with the V element, thereby improving the impact toughness. However, the residual nitrogen content in the steel is too high, so that macroscopic tissue is loose or air holes are formed, the content N is less than or equal to 0.015%, and the content of impurity elements such as P, S and the like is strictly controlled. The content of each component is controlled as follows:
c:0.08% -0.15%, C is taken as a basic element in steel, plays an important role in improving the strength of the steel, and in order to obtain higher strength and reduce the difficulty of steel-making and dec, the lower limit value is set to 0.08%, but the excessive C content seriously deteriorates the plasticity, toughness and weldability of the steel, so the upper limit value is set to 0.15%.
Si:0.25% -0.50%, si with proper content can play a strong solid solution strengthening role, si is an important reduction and deoxidization element in the steelmaking process, in order to obtain higher strength, the lower limit value is set to 0.25%, but the Si content cannot be too high, researches show that too high Si content accelerates Gao Wenbao layers, reduces toughness and lamellar tearing resistance, red oxide scale is easily generated on the surface of steel, the surface quality of a product is affected, and the upper limit value is set to 0.50%.
Mn:1.20% -1.55%, mn is used as a strengthening element in steel, the strength and hardenability of the steel can be improved, the lower limit value is set to be 1.20% in order to ensure the strength of the steel, but the Mn content cannot be too high, the possibility of casting blank segregation is obviously increased due to too high Mn content, the forming performance of the steel is adversely affected, and the upper limit value is set to be 1.55%.
P, S as an impurity element adversely affects the plasticity, toughness and weldability of steel, and is strictly controlled in consideration of the difficulty of steelmaking control, and P is controlled in actual production: less than or equal to 0.020%, S: less than or equal to 0.015 percent.
V:0.020% -0.065%, V is taken as a strong carbide forming element, a V (C, N) dispersion compound formed by the V and C, N element is distributed in a steel matrix to play a role of precipitation strengthening, the precipitation strengthening is mainly realized by precipitation in and after the phase transformation from austenite to ferrite, in order to improve strength, the lower limit value is set to 0.020%, the production cost factor is considered while the comprehensive mechanical property index of the product is ensured, the upper limit value is set to 0.065%, and the V element is added according to the proportion of 70% V-N and 30% V-Fe.
Nb: the strengthening effect of Nb on steel is mainly fine crystal strengthening and dispersion strengthening, and Nb can form stable carbide and carbonitride with C, N in the steel. Nb can also realize the dispersion distribution of precipitates by inducing precipitation and controlling the cooling speed, and the toughness level of the steel is adjusted in a wider range. Therefore, adding Nb can not only improve the strength of the steel, but also improve the toughness, high-temperature oxidation resistance and corrosion resistance of the steel, reduce the brittle transition temperature of the steel and obtain good welding performance and forming performance. In order to improve the strength, the lower limit value is set to 0.020%, and the production cost factor is considered at the same time under the condition of ensuring the comprehensive mechanical property index of the product, and the upper limit value is set to 0.050%.
Als:0.010% -0.025%. Als has the advantages of reducing the ductile-brittle transition temperature of steel and improving the toughness of the steel at low temperature. Als is a good deoxidizer, refines essential grains of steel, increases the coarsening temperature of steel, and sets the lower limit to 0.010% in order to ensure the performance of steel, but when the content of solid solution gold-aluminum in steel exceeds a certain value, austenite grains grow and coarsen instead, so the upper limit should be controlled to 0.025%.
The production method of the hot rolled angle steel with the yield strength of 420MPa and the temperature resistance of minus 20 ℃ comprises the following steps: molten iron pretreatment, converter smelting, argon blowing refining, LF refining, VD refining, rectangular billet or square billet full-protection casting, rolling process and air cooling after rolling. The rolling process comprises a rough rolling stage and a medium finish rolling stage, and the rolling process of the hot rolled angle steel comprises the following steps:
1) Heating the blank: the rectangular blank or square blank enters a heating furnace, is heated to 1190-1230 ℃ by the heating furnace, and is heated for 90-130 min in the furnace for ensuring the sufficient solid solution of alloy elements, and simultaneously avoiding overburning and excessive coarsening of austenite grains;
2) Rough rolling: controlling the pass reduction rate to be 15% -25% in the temperature range of 1100-1150 ℃; controlling the pass reduction rate to be 25% -30% in the temperature range of 1050 ℃ -1100 ℃; controlling the pass rolling reduction to 15% -25% and controlling the total rolling reduction of the blank to 50% -70% in the temperature range of 1050-1000 ℃; the stage is in the austenite recrystallization temperature range, the pass deformation is required to be larger than the upper limit of the recrystallization critical deformation so as to ensure complete recrystallization, the pass reduction rate in different temperature ranges is controlled so as to ensure that the austenite recrystallization percentage of each pass reaches more than 50%, and austenite grains are continuously refined through larger rolling deformation and repeated recrystallization of austenite, so that the ferrite grain size of the final product reaches more than 9.5 levels, and the final comprehensive mechanical property requirement of the product is met;
3) Finish rolling: after rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled below 900 ℃.
Furthermore, in the temperature range of 1000-950 ℃, the pass reduction rate is controlled to be 10-15%, the stage is two-phase zone rolling, the deformation amount of more than 10% can improve the strength, and weak crystal textures are formed and the separation phenomenon is not obvious; controlling the pass reduction rate to be 25% -30% in the temperature range of 950 ℃ -900 ℃; the pass reduction rate is controlled to be 15% -20% in the temperature range below 900 ℃, and the blank reduction rate is controlled to be more than 50% in the stage.
The phase is in the range of austenite unrecrystallized temperature, austenite recrystallization does not occur in the temperature range, austenite grains can be elongated by accumulated deformation formed under low temperature and high pressure, a large number of deformation bands and dislocation are formed in the grains, the nucleation density of austenite is improved by increasing the area of grain boundaries, the grain size is further refined, the strength of steel is improved, and the toughness of the steel is improved. The large number of crystallographic defects generated within the deformed austenite provides nucleation sites for ferrite transformation, resulting in ferrite grain refinement. The elongated austenite and a large number of deformation bands and dislocation positions also provide a large number of landing points for precipitation of the second phase particles of the carbonitride, and the storage energy formed at low temperature and high pressure also provides enough kinetic energy for precipitation of the second phase particles of the carbonitride. Since Nb is added to the steel and the recrystallization temperature is increased in the steel containing these trace alloying elements, the austenite non-recrystallized region is enlarged, and thus rolling in the non-recrystallized region is advantageously achieved. The strength of the steel is improved by refining grains at a high temperature, the solid-solution Nb plays a role in dragging a solute to the growth of austenite grains to prevent the austenite grains from growing, and meanwhile, undissolved Nb and C, N elements form Nb (C, N) compounds which can be remarkably pinned at the austenite grain boundaries to refine the austenite grains and refine the structure of a final product. V is used as a strong carbide forming element, and with the addition of 0.06-0.12% of V alloy element, a large amount of V (C, N) dispersoids are formed and distributed in a matrix at the stage, so that the strength and toughness of the steel are further improved.
The Nb (C, N) and V (C, N) dispersoids are prepared by a physical and chemical phase analysis test method: i.e., the way the iron matrix is electrolytically dissolved, the micro-nano particles of interest (e.g., cementite M3C phase and MC particles) are extracted; all the second phase particles are extracted and subjected to separation treatment, X-ray structural analysis is carried out, the precipitated phases in the samples under different processes are qualitatively analyzed, and diffraction peak spectrums are obtained by analysis through XRD.
4) The selective control cooling device between the middle and finish rolling mill frames can accurately control the temperature change of rolled pieces, and gives the set deformation amount to the angle steel in the corresponding temperature range by combining the rolling reduction designed in the rolling procedure so as to ensure the performance of the final product. The selective control cooling device is used for controlling whether temperature data fed back by a roller way side plate and a nozzle at the bottom of the rack are opened or closed for a set temperature value or not, so that the temperature change of a rolled piece can be accurately controlled, and the set deformation of angle steel is given in a corresponding temperature interval by combining the reduction designed in a rolling procedure so as to ensure the performance of a final product.
The thickness of the hot rolled angle steel obtained by adopting the technical scheme is less than or equal to 26mm, the crystal phase structure of the hot rolled angle steel is a ferrite 75% -85% + pearlite 15% -25% complex phase structure, and the ferrite grain size grade is more than 9.0 grade; the yield strength of the product is more than or equal to 420MPa, the tensile strength is more than or equal to 540MPa, the yield ratio is less than or equal to 0.85, the elongation A is more than or equal to 19%, the longitudinal V-shaped impact power KV2 at-20 ℃ is more than or equal to 120J, and the product has higher strength, good plasticity and higher low-temperature toughness.
Example 1
The hot rolled angle steel with the yield strength of 420MPa and the temperature resistance of minus 20 ℃ comprises the following elements in percentage by mass: c:0.09%, si:0.28%, mn:1.25%, P:0.0160%, S:0.010%, V:0.020%, nb:0.020%, als:0.011%, H:0.00012%, N:0.0057%, and the balance of Fe and unavoidable impurity elements, wherein V-N is adopted for adding the V element: v-fe=4: alloy 6 was formulated as specified in table 1 below.
The production method of the hot rolled angle steel with the yield strength of 420MPa grade and the temperature resistance of minus 20 ℃ comprises the following steps: pretreatment of water, converter smelting, argon blowing refining, LF refining, VD refining, full-protection casting of rectangular billets or square billets, rolling process and air cooling after rolling. The rolling process comprises a rough rolling stage and a medium finish rolling stage, and is specifically produced according to the following steps:
1) Pretreating molten iron and smelting the molten iron in a converter;
2) Blowing inert gas argon in the smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel;
3) Refining in an LF furnace, and then continuously casting into billets;
4) The casting blank enters a heating furnace, is heated to 1200 ℃ by the heating furnace, and the furnace duration is 105;
5) The initial rolling temperature in the rough rolling stage is controlled at 1140 ℃, and the final rolling temperature is controlled at 1005 ℃. Further, in the temperature range of 1100-1150 ℃, the pass reduction rate is controlled at 19%; controlling the pass reduction rate at 27% in the temperature range of 1050-1100 ℃; the pass reduction rate is controlled to be 17% and the total reduction rate of the blank is controlled to be 54% in the temperature range of 1050-1000 ℃.
6) After rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled at 885 ℃.
Further, in the temperature range of 1000-950 ℃, the pass reduction rate is controlled at 13%; controlling the pass reduction rate at 27% in the temperature range of 950-900 ℃; the pass reduction rate is controlled to 18% in the temperature range below 900 ℃, and the total reduction rate of the blank at the stage is controlled to 55%.
7) And (5) air cooling the rolled angle steel on a cooling bed.
The process parameters in the production process of the hot rolled angle steel of this example are controlled as shown in table 2 below, and the structure is 75% ferrite and 25% pearlite.
Example 2
The hot rolled angle steel with the yield strength of 420MPa and the temperature resistance of minus 20 ℃ comprises the following elements in percentage by mass: see in particular table 1 below; the balance of Fe and unavoidable impurity elements, and V element is added by adopting V-N:V-Fe=4:6 alloy.
The production method of the hot rolled angle steel with the yield strength of 420MPa grade and the temperature resistance of minus 20 ℃ comprises the following steps: pretreatment of water, converter smelting, argon blowing refining, LF refining, VD refining, full-protection casting of rectangular billets or square billets, rolling process and air cooling after rolling. The rolling process comprises a rough rolling stage and a medium finish rolling stage.
The method comprises the following steps:
1) Pretreating molten iron and smelting the molten iron in a converter;
2) Blowing inert gas argon in the smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel;
3) Refining in an LF furnace, and then continuously casting into billets;
4) The casting blank enters a heating furnace, is heated to 1205 ℃ by the heating furnace, and the furnace time is 109min;
5) The initial rolling temperature in the rough rolling stage is controlled at 1150 ℃ and the final rolling temperature is controlled at 1010 ℃. Further, in the temperature range of 1100-1150 ℃, the pass reduction rate is controlled at 18%; controlling the pass reduction rate at 26% in the temperature range of 1050-1100 ℃; the pass reduction rate is controlled to be 16% in the temperature range of 1050-1000 ℃, and the total reduction rate of the blank is controlled to be 53%.
6) After rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled at 890 ℃. Further, in the temperature range of 1000-950 ℃, the pass reduction rate is controlled to be 12%; controlling the pass reduction rate at 26% in the temperature range of 950-900 ℃; the pass reduction rate is controlled to be 17% in the temperature range below 900 ℃, and the total reduction rate of the blank at the stage is controlled to be 53%.
7) And (5) air cooling the rolled angle steel on a cooling bed.
The process parameters in the production process of the hot rolled angle steel of this example are controlled as shown in table 2 below, and the structure thereof is 79% ferrite and 21% pearlite.
Example 3
The hot rolled angle steel with the yield strength of 420MPa and the temperature resistance of minus 20 ℃ comprises the following elements in percentage by mass: see in particular table 1 below; the balance of Fe and unavoidable impurity elements, and V element is added by adopting V-N:V-Fe=4:6 alloy.
The production method of the hot rolled angle steel with the yield strength of 420MPa grade and the temperature resistance of minus 20 ℃ comprises the following steps: pretreatment of water, converter smelting, argon blowing refining, LF refining, VD refining, full-protection casting of rectangular billets or square billets, rolling process and air cooling after rolling. The rolling process comprises a rough rolling stage and a medium finish rolling stage.
The method comprises the following steps:
1) Pretreating molten iron and smelting the molten iron in a converter;
2) Blowing inert gas argon in the smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel;
3) Refining in an LF furnace, and then continuously casting into billets;
4) The casting blank enters a heating furnace, is heated to 1222 ℃ by the heating furnace, and the furnace time is 110min;
5) The initial rolling temperature in the rough rolling stage is controlled at 1160 ℃, and the final rolling temperature is controlled at 1012 ℃. Further, in the temperature range of 1100-1150 ℃, the pass reduction rate is controlled at 21%; controlling the pass reduction rate at 28% in the temperature range of 1050-1100 ℃; the pass reduction rate is controlled to 22% and the total reduction rate of the blank is controlled to 56% in the temperature range of 1050-1000 ℃.
6) After rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled at 895 ℃. Further, in the temperature range of 1000-950 ℃, the pass reduction rate is controlled at 14%; controlling the pass reduction rate at 28% in the temperature range of 950-900 ℃; the pass reduction rate is controlled to be 19% in the temperature range below 900 ℃, and the total reduction rate of the blank at the stage is controlled to be 56%.
7) And (5) air cooling the rolled angle steel on a cooling bed.
The process parameters in the production process of the hot rolled angle steel of this example are controlled as shown in table 2 below, and the structure thereof is ferrite 81%, pearlite 19%.
Example 4
The hot rolled angle steel with the yield strength of 420MPa and the temperature resistance of minus 20 ℃ comprises the following elements in percentage by mass: see in particular table 1 below; the balance of Fe and unavoidable impurity elements, and V element is added by adopting V-N:V-Fe=4:6 alloy.
The production method of the hot rolled angle steel with the yield strength of 420MPa grade and the temperature resistance of minus 20 ℃ comprises the following steps: pretreatment of water, converter smelting, argon blowing refining, LF refining, VD refining, full-protection casting of rectangular billets or square billets, rolling process and air cooling after rolling. The rolling process comprises a rough rolling stage and a medium finish rolling stage.
The method comprises the following steps:
1) Pretreating molten iron and smelting the molten iron in a converter;
2) Blowing inert gas argon in the smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel;
3) Refining in an LF furnace, and then continuously casting into billets;
4) The casting blank enters a heating furnace, is heated to 1225 ℃ by the heating furnace, and the furnace time is 120min;
5) The initial rolling temperature is controlled at 1170 ℃ and the final rolling temperature is controlled at 1018 ℃. Further, in the temperature range of 1100-1150 ℃, the pass reduction rate is controlled at 20%; controlling the pass reduction rate at 26% in the temperature range of 1050-1100 ℃; the pass reduction rate is controlled to be 20% in the temperature range of 1050-1000 ℃, and the total reduction rate of the blank is controlled to be 53%.
6) After rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled at 897 ℃. Further, in the temperature range of 1000-950 ℃, the pass reduction rate is controlled at 13%; controlling the pass reduction rate at 26% in the temperature range of 950-900 ℃; the pass reduction rate is controlled to 18% in the temperature range below 900 ℃, and the total reduction rate of the blank at the stage is controlled to 53%.
7) And (5) air cooling the rolled angle steel on a cooling bed.
The process parameters in the production process of the hot rolled angle steel of this example are controlled as shown in table 2 below, and the structure thereof is ferrite 83% and pearlite 17%.
Comparative example 1
The hot rolled angle steel of the comparative example comprises the following elements in percentage by mass: see in particular table 1 below; the balance of Fe and unavoidable impurity elements.
The production method of the hot rolled angle steel of the comparative example comprises the following steps: pretreatment of water, converter smelting, argon blowing refining, LF refining, VD refining, full-protection casting of rectangular billets or square billets, rolling process and air cooling after rolling. The rolling process comprises a rough rolling stage and a medium finish rolling stage.
The method comprises the following steps:
1) Pretreating molten iron and smelting the molten iron in a converter;
2) Blowing inert gas argon in the smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel;
3) Refining in an LF furnace, and then continuously casting into billets;
4) The casting blank enters a heating furnace, is heated to 1200 ℃ by the heating furnace, and is heated for 105 minutes in the furnace;
5) The initial rolling temperature in the rough rolling stage is controlled to 1175 ℃, and the final rolling temperature is controlled to 1021 ℃. Further, in the temperature range of 1100-1150 ℃, the pass reduction rate is controlled at 14%; controlling the pass reduction rate at 24% in the temperature range of 1050-1100 ℃; the pass reduction rate is controlled to be 14% and the total reduction rate of the blank is controlled to be 48% in the temperature range of 1050-1000 ℃.
6) After rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled at 978 ℃. Further, in the temperature range of 1000-950 ℃, the pass reduction rate is controlled at 23%; controlling the pass reduction rate at 20% in the temperature range of 950-900 ℃; the pass reduction rate is controlled to 11% in the temperature range below 900 ℃, and the total reduction rate of the blank at the stage is controlled to 42%.
7) And (5) air cooling the rolled angle steel on a cooling bed.
The process parameters in the production process of the hot rolled angle steel of this comparative example are controlled as shown in table 2 below.
Comparative example 2
The hot rolled angle steel of the comparative example comprises the following elements in percentage by mass: see in particular table 1 below; the balance of Fe and unavoidable impurity elements.
The production method of the hot rolled angle steel of the comparative example comprises the following steps: pretreatment of water, converter smelting, argon blowing refining, LF refining, VD refining, full-protection casting of rectangular billets or square billets, rolling process and air cooling after rolling. The rolling process comprises a rough rolling stage and a medium finish rolling stage.
The method comprises the following steps:
1) Pretreating molten iron and smelting the molten iron in a converter;
2) Blowing inert gas argon in the smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel;
3) Refining in an LF furnace, and then continuously casting into billets;
4) The casting blank enters a heating furnace, is heated to 1210 ℃ by the heating furnace, and the duration of the heating furnace is 105min;
5) The initial rolling temperature in the rough rolling stage is controlled to 1183 ℃, and the final rolling temperature is controlled to 1026 ℃. Further, in the temperature range of 1100-1150 ℃, the pass reduction rate is controlled at 13%; controlling the pass reduction rate at 23% in the temperature range of 1050-1100 ℃; the pass reduction rate is controlled to 13% and the total reduction rate of the blank is controlled to 47% in the temperature range of 1050-1000 ℃.
6) After rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled at 981 ℃. Further, the pass reduction rate is controlled at 22% in the temperature range of 1000-950 ℃; controlling the pass reduction rate at 18% in the temperature range of 950-900 ℃; the pass reduction rate is controlled to be 10% in the temperature range below 900 ℃, and the total reduction rate of the blank at the stage is controlled to be 40%.
7) And (5) air cooling the rolled angle steel on a cooling bed.
The process parameters in the production process of the hot rolled angle steel of this comparative example are controlled as shown in table 2 below.
Comparative example 3
The hot rolled angle steel of the comparative example comprises the following elements in percentage by mass: see in particular table 1 below; the balance of Fe and unavoidable impurity elements.
The production method of the hot rolled angle steel of the comparative example comprises the following steps: pretreatment of water, converter smelting, argon blowing refining, LF refining, VD refining, full-protection casting of rectangular billets or square billets, rolling process and air cooling after rolling. The rolling process comprises a rough rolling stage and a medium finish rolling stage.
The method comprises the following steps:
1) Pretreating molten iron and smelting the molten iron in a converter;
2) Blowing inert gas argon in the smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel;
3) Refining in an LF furnace, and then continuously casting into billets;
4) The casting blank enters a heating furnace, is heated to 1220 ℃ by the heating furnace, and the duration of the heating furnace is 115min;
5) The initial rolling temperature in the rough rolling stage is controlled to 1161 ℃, and the final rolling temperature is controlled to 1014 ℃. Further, in the temperature range of 1100-1150 ℃, the pass reduction rate is controlled at 22%; controlling the pass reduction rate at 27% in the temperature range of 1050-1100 ℃; the pass reduction rate is controlled at 23% in the temperature range of 1050-1000 ℃, and the total reduction rate of the blank is controlled at 57%.
6) After rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled at 896 ℃. Further, in the temperature range of 1000-950 ℃, the pass reduction rate is controlled at 13%; controlling the pass reduction rate at 28% in the temperature range of 950-900 ℃; the pass reduction rate is controlled to 18% in the temperature range below 900 ℃, and the total reduction rate of the blank at the stage is controlled to 55%.
7) And (5) air cooling the rolled angle steel on a cooling bed.
The process parameters in the production process of the hot rolled angle steel of this comparative example are controlled as shown in table 2 below.
Comparative example 4
The hot rolled angle steel of the comparative example comprises the following elements in percentage by mass: see in particular table 1 below; the balance of Fe and unavoidable impurity elements.
The production method of the hot rolled angle steel of the comparative example comprises the following steps: pretreatment of water, converter smelting, argon blowing refining, LF refining, VD refining, full-protection casting of rectangular billets or square billets, rolling process and air cooling after rolling. The rolling process comprises a rough rolling stage and a medium finish rolling stage.
The method comprises the following steps:
1) Pretreating molten iron and smelting the molten iron in a converter;
2) Blowing inert gas argon in the smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel;
3) Refining in an LF furnace, and then continuously casting into billets;
4) The casting blank enters a heating furnace, is heated to 1220 ℃ by the heating furnace, and the duration of the heating furnace is 115min;
5) The initial rolling temperature is controlled at 1163 ℃ and the final rolling temperature is controlled at 1015 ℃ in the rough rolling stage. Further, in the temperature range of 1100-1150 ℃, the pass reduction rate is controlled at 21%; controlling the pass reduction rate at 28% in the temperature range of 1050-1100 ℃; the pass reduction rate is controlled at 23% and the total reduction rate of the blank is controlled at 55% in the temperature range of 1050-1000 ℃.
6) After rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled at 897 ℃. Further, in the temperature range of 1000-950 ℃, the pass reduction rate is controlled at 14%; controlling the pass reduction rate at 27% in the temperature range of 950-900 ℃; the pass reduction rate is controlled to be 17% in the temperature range below 900 ℃, and the total reduction rate of the blank at the stage is controlled to be 54%.
7) And (5) air cooling the rolled angle steel on a cooling bed.
The process parameters in the production process of the hot rolled angle steel of this comparative example are controlled as shown in table 2 below.
Comparative example 5
The hot rolled angle steel of the comparative example comprises the following elements in percentage by mass: see in particular table 1 below; the balance of Fe and unavoidable impurity elements.
The production method of the hot rolled angle steel of the comparative example comprises the following steps: pretreatment of water, converter smelting, argon blowing refining, LF refining, VD refining, full-protection casting of rectangular billets or square billets, rolling process and air cooling after rolling. The rolling process comprises a rough rolling stage and a medium finish rolling stage.
The method comprises the following steps:
1) Pretreating molten iron and smelting the molten iron in a converter;
2) Blowing inert gas argon in the smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel;
3) Refining in an LF furnace, and then continuously casting into billets;
4) The casting blank enters a heating furnace, is heated to 1225 ℃ by the heating furnace, and is heated for 125min in the furnace;
5) The initial rolling temperature in the rough rolling stage is controlled to 1171 ℃, and the final rolling temperature is controlled to 1020 ℃. Further, in the temperature range of 1100-1150 ℃, the pass reduction rate is controlled at 21%; controlling the pass reduction rate at 26% in the temperature range of 1050-1100 ℃; the pass reduction rate is controlled to 21% and the total reduction rate of the blank is controlled to 55% in the temperature range of 1050-1000 ℃.
6) After rough rolling, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank directly enters the middle and finish continuous rolling stage, the rest deformation of the blank is completed in the stage, and the final rolling temperature is controlled at 898 ℃. Further, in the temperature range of 1000-950 ℃, the pass reduction rate is controlled at 14%; controlling the pass reduction rate at 27% in the temperature range of 950-900 ℃; the pass reduction rate is controlled to 18% in the temperature range below 900 ℃, and the total reduction rate of the blank at the stage is controlled to 54%.
7) And (5) air cooling the rolled angle steel on a cooling bed.
The process parameters in the production process of the hot rolled angle steel of this comparative example are controlled as shown in table 2 below.
TABLE 1 list of values (mass%) of chemical components of examples 1-4 and comparative examples 1-5 of the present invention
| Angle steel specification | Numbering device | C | Si | Mn | P | S | V | Nb | Als | H | N |
| ∠100*8 | Example 1 | 0.09 | 0.28 | 1.25 | 0.016 | 0.010 | 0.020 | 0.020 | 0.011 | 0.00012 | 0.0057 |
| ∠140*12 | Example 2 | 0.10 | 0.30 | 1.30 | 0.016 | 0.011 | 0.028 | 0.025 | 0.013 | 0.00013 | 0.0060 |
| ∠180*16 | Example 3 | 0.12 | 0.33 | 1.38 | 0.017 | 0.012 | 0.032 | 0.030 | 0.017 | 0.00012 | 0.0055 |
| ∠200*24 | Example 4 | 0.13 | 0.36 | 1.45 | 0.015 | 0.011 | 0.038 | 0.035 | 0.019 | 0.00012 | 0.0053 |
| ∠100*8 | Comparative example 1 | 0.09 | 0.29 | 1.26 | 0.017 | 0.011 | 0.021 | 0.021 | 0.011 | 0.00012 | 0.0066 |
| ∠140*12 | Comparative example 2 | 0.11 | 0.31 | 1.30 | 0.015 | 0.011 | 0.028 | 0.026 | 0.012 | 0.00013 | 0.0058 |
| ∠180*16 | Comparative example 3 | 0.12 | 0.35 | 1.45 | 0.017 | 0.011 | 0.100 | - | 0.015 | 0.00013 | - |
| ∠180*16 | Comparative example 4 | 0.11 | 0.36 | 1.45 | 0.016 | 0.012 | 0.070 | 0.015 | 0.014 | 0.00012 | - |
| ∠200*24 | Comparative example 5 | 0.13 | 0.38 | 1.50 | 0.016 | 0.010 | 0.015 | 0.060 | 0.018 | 0.00012 | - |
The process steps for producing hot rolled angle steels described in comparative examples 1 to 5 are basically the same as the process of the present application, except that the parameters of each step are controlled, and the specific process parameters are shown in table 2 below.
TABLE 2 list of the main process parameters for inventive examples 1-4 and comparative examples 1-5
The performance of the hot rolled angle steels produced in examples 1 to 4 and comparative examples 1 to 5 was examined as shown in Table 3.
TABLE 3 list of Performance test cases for inventive examples 1-4 and comparative examples 1-5
It should be noted that comparative examples 1-2 are chemical components using the present invention and take values within the defined ranges, and the process uses the prior art; comparative examples 3-5 are chemical compositions of the prior art and the process of the present invention is employed.
From the above analysis of the data, it is difficult for the conventional rolling process to meet the requirements of the present invention when the billet size is fixed. The design concept of the invention is mainly that the production of hot rolled angle steel with excellent comprehensive mechanical properties, thickness less than or equal to 26mm and yield strength of 420MPa grade and minus 20 ℃ resistance is realized by reasonable and economic chemical component proportion, large-reduction crushing of columnar structure of casting blank and dynamic recrystallization behavior of a cogging section, and reasonable inter-pass reduction distribution of a middle finishing section. In particular, two stages of cogging rolling and medium finish rolling are adopted, deformation in the austenite partial recrystallization temperature range is avoided through reasonable reduction distribution of each pass, and the deformation in the austenite recrystallization temperature range is enlarged to further refine the grain size. In addition, the middle finish rolling section realizes temperature control by selective cooling and temperature control rolling, avoids deformation in the austenite partial recrystallization temperature range, and further refines the grain size by enlarging the deformation in the austenite recrystallization temperature range.
Claims (2)
1. A production method of hot rolled angle steel with yield strength of 420MPa and minus 20 ℃ is characterized by comprising the following elements in percentage by mass: c:0.08% -0.15%, si:0.25% -0.50%, mn:1.20% -1.55%, P: less than or equal to 0.020%, S: less than or equal to 0.015 percent, V:0.020% -0.065%, nb:0.020% -0.050%, als:0.010 to 0.025 percent, H is less than or equal to 0.0002 percent, N is less than or equal to 0.015 percent, the balance is Fe and unavoidable impurities, the hot rolled angle steel structure is a ferrite 75 to 85 percent+pearlite 15 to 25 percent complex phase structure, and the ferrite grain size grade is more than or equal to 9.0 grade; the yield strength of the product is more than or equal to 420MPa, the tensile strength is more than or equal to 540MPa, the yield ratio is less than or equal to 0.85, the elongation A is more than or equal to 19 percent, and the longitudinal V-shaped impact energy KV2 at minus 20 ℃ is more than or equal to 120J; the production method comprises the following steps: molten iron pretreatment, converter smelting, argon blowing refining, LF refining, VD refining, rectangular blank or square blank full-protection casting, rolling process and air cooling after rolling;
wherein the rolling process comprises the following steps:
1) Heating the blank: the blank enters a heating furnace, is heated to 1190-1230 ℃ by the heating furnace, and is heated for 90-130 min in the furnace;
2) Rough rolling: the initial rolling temperature is controlled to 1100-1180 ℃, and the final rolling temperature is controlled to be more than 1000 ℃;
the rough rolling process comprises the following steps: controlling the pass reduction rate to be 15% -25% in the temperature range of 1100-1150 ℃; controlling the pass reduction rate to be 25% -30% in the temperature range of 1050 ℃ -1100 ℃; controlling the pass rolling reduction to 15% -25% and controlling the total rolling reduction of the blank to 50% -70% in the temperature range of 1050-1000 ℃;
3) Finish rolling: after rough rolling is finished, the selective control cooling between the middle and finish rolling frames is started without waiting for temperature, the blank is directly subjected to the middle and finish continuous rolling stages, the rest deformation of the blank is finished, and the final rolling temperature is controlled below 900 ℃;
the finish rolling process comprises the following steps: controlling the pass reduction rate to be 10% -15% in the temperature range of 1000-950 ℃; controlling the pass reduction rate to be 25% -30% in the temperature range of 950 ℃ -900 ℃; the pass rolling reduction is controlled to be 15% -20% in the temperature range below 900 ℃ and the total rolling reduction of the blank is controlled to be more than 50%.
2. The method for producing the hot rolled angle steel with the yield strength of 420MPa grade and the temperature resistance of minus 20 ℃ according to claim 1, wherein the selective control cooling between the middle and finish rolling mill frames is that whether temperature data fed back by a nozzle combined with a thermometer at the side plate and the bottom of a roller way between the mill frames is a set temperature value or not is opened or closed, the temperature change of a rolled piece is accurately controlled, and the set deformation amount of the angle steel is given in a corresponding temperature range by combining the designed pressing in a rolling procedure.
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