CN113528970B - Low-compression-ratio yield strength 355 MPa-grade heavy hot-rolled H-shaped steel and production method and application thereof - Google Patents

Low-compression-ratio yield strength 355 MPa-grade heavy hot-rolled H-shaped steel and production method and application thereof Download PDF

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CN113528970B
CN113528970B CN202110818912.XA CN202110818912A CN113528970B CN 113528970 B CN113528970 B CN 113528970B CN 202110818912 A CN202110818912 A CN 202110818912A CN 113528970 B CN113528970 B CN 113528970B
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temperature
shaped steel
rolling
flange
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CN113528970A (en
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沈千成
吴保桥
吴湄庄
孙晓明
邢军
陈辉
夏勐
何军委
彭林
丁朝晖
彦井成
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Maanshan Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/08—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling structural sections, i.e. work of special cross-section, e.g. angle steel
    • B21B1/088—H- or I-sections
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/56—Elongation control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • B21B37/76—Cooling control on the run-out table
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The invention provides a thick and heavy hot-rolled H-shaped steel with low compression ratio yield strength of 355MPa and a production method thereof, wherein the thick and heavy hot-rolled H-shaped steel comprises the following components of 0.13-0.20% of C, 0.15-0.40% of Si, 1.10-1.50% of Mn, less than or equal to 0.035% of P, less than or equal to 0.035% of S, 0.030-0.060% of V, 0.0008-0.0015% of B, and Nb: 0.02-0.05%, N: 0.015-0.020%, more than or equal to 3.5 (Nb + V)/less than or equal to 5.5%, less than or equal to 0.005% of Als, and the balance of Fe and inevitable impurities. The thickness of the flange of the finished product is 50-100mm, the core part is a ferrite + pearlite complex phase structure, and the surface layer is a tempered sorbite structure. The thick and heavy hot-rolled H-shaped steel with excellent performance is obtained and is used in the field of high-rise buildings or large-span bridges.

Description

Low-compression-ratio yield strength 355 MPa-grade heavy hot-rolled H-shaped steel and production method and application thereof
Technical Field
The invention belongs to the technical field of hot-rolled H-shaped steel production, and particularly relates to thick and heavy hot-rolled H-shaped steel with low compression ratio yield strength of 355MPa and flange thickness within the range of 50-100mm, and a production method and application thereof.
Background
The hot rolling H-shaped steel is usually rolled by a special-shaped blank, and because the cross section size is complex, the temperature difference of different areas is large during continuous casting, cracks are easy to appear on the surface of the continuous casting blank, and the surface quality of a product is seriously influenced. Meanwhile, as the hot rolling of the H-shaped steel adopts pass rolling, the deformation unevenness is increased, the deformation distribution among passes is limited by the pass, and the material performance is difficult to ensure.
At present, only hot-rolled H-shaped steel with the flange thickness less than 50mm can be produced in China, and the comprehensive mechanical property of the H-shaped steel is improved by adding Nb, V and Ti microalloy elements. When the thickness exceeds 50mm abroad, slab cogging rolling is adopted, and the method has the advantages of long process flow, high requirement on continuous casting equipment and large investment. The special-shaped continuous casting billet is adopted for rolling, the limitation of the section size of the continuous casting billet is met, the compression ratio in the thickness direction of the flange is small, the mechanical property of a finished product is unstable, the yield is low, and how to ensure the comprehensive mechanical property becomes the key of process and component design. Therefore, the development of thick and heavy hot-rolled H-shaped steel with excellent comprehensive performance in the thickness range of 50-100mm and the 355MPa level is very difficult.
Patent document CN 108754327B with patent number CN 108754327B published in 11/6/2018 and named as 'high-toughness weather-resistant hot-rolled H-shaped steel for bridge structure with yield strength 460MPa and production method thereof', mainly discloses that through reasonable component design, reduction distribution and temperature control rolling, fine-grain strengthening, precipitation strengthening and phase change strengthening mechanisms are utilized, and direct air cooling is carried out after hot rolling, so that a complex phase structure of ferrite, bainite and pearlite can be obtained, the strength grade is not lower than 460MPa, and the corrosion speed is not higher than 50% compared with Q345B. The main production specification is concentrated below 35mm of the flange thickness of the H-shaped steel, and is lower than the specification of 50-100mm of the flange thickness produced by the patent.
Patent document CN 109161813A, entitled X70 steel plate of low compression ratio pipeline steel and production method thereof, published in 1, 8 and 2019, mainly discloses that a steel plate with the thickness of 21mm is produced by a continuous casting slab with the thickness of 150mm, the total compression ratio is less than 6, and the components and the process mainly comprise: c: 0.030-0.080%, Mn: 1.55-1.75%, Si: 0.10-0.40%, S is less than or equal to 0.0050%, P: less than or equal to 0.015 percent, Nb: 0.035 to 0.060%, Ti: 0.008-0.025%, V is less than or equal to 0.10%, Alt: 0.020 to 0.060%, Cr: less than or equal to 0.30 percent, Mo: less than or equal to 0.20 percent, the balance of Fe and inevitable impurities, and 60-70 percent of ferrite and 30-40 percent of bainite are obtained after two-stage controlled rolling and laminar flow sectional cooling after rolling. The obtained product has the yield strength of 490-550 MPa, the tensile strength of 590-640 MPa, the yield ratio of less than 0.85 and the proportion of the drop-weight shear area of more than 85% at-15 ℃. But the production process is mainly applied to the plate strip direction and is not suitable for the production of heavy hot-rolled H-shaped steel.
Disclosure of Invention
The invention aims to provide a thick and heavy hot-rolled H-shaped steel with low compression ratio yield strength of 355MPa and a production method thereof, wherein the thick and heavy hot-rolled H-shaped steel with finished Flange thickness within the range of 50-100mm is obtained by matching reasonable component proportion with a rolling process, particularly distribution of rolling reduction, temperature-controlled rolling and SFC (Selective Flange Coling) (chilling-deformation-reverse temperature deformation infiltration process) and QST (online Quenching and Self Tempering) (Quenching and Self Tempering) controlled Cooling process after rolling to obtain a core ferrite and pearlite complex phase structure and a surface tempered sorbite structure, so that the thick and heavy hot-rolled H-shaped steel with excellent performance is obtained.
The invention provides application of thick and heavy hot-rolled H-shaped steel with low compression ratio yield strength of 355MPa, which is applied to the field of high-rise buildings or large-span bridges.
The specific technical scheme of the invention is as follows:
the heavy hot-rolled H-shaped steel with the low compression ratio yield strength of 355MPa comprises the following components in percentage by mass: 0.13-0.20% of C, 0.15-0.40% of Si, 1.10-1.50% of Mn, less than or equal to 0.035% of P, less than or equal to 0.035% of S, 0.030-0.060% of V, 0.0008-0.0015% of B, Nb: 0.02-0.05%, N: 0.015-0.020%, more than or equal to 3.5 (Nb + V)/less than or equal to 5.5%, less than or equal to 0.005% of Als, and the balance of Fe and inevitable impurities.
In order to control the stability of the performance, the thick and heavy hot-rolled H-shaped steel with the low-compression ratio yield strength of 355MPa comprises the following components in percentage by mass: c: 0.15-0.19%, 0.18-0.32% of Si, 1.15-1.45% of Mn, less than or equal to 0.030% of P, less than or equal to 0.020% of S, 0.035-0.050% of V, 0.001-0.0013% of B, Nb: 0.03-0.05%, N: 0.015 to 0.020 percent, more than or equal to 3.5 and less than or equal to (Nb + V)/N is less than or equal to 4.5, less than or equal to 0.005 percent of Als, and the balance of Fe and inevitable impurities.
The chemical components of the invention adopt the design idea of C-Si-Mn-V-Nb components, the production cost is considered, in order to obtain sufficient carbonitride precipitation, the V element is added by adopting V-N alloy, 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: 0.13-0.20%, wherein C is used as a basic element in the 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 decarburization, the lower limit value is set to 0.13%, the excessively high content of C seriously deteriorates the plasticity, toughness and weld crack sensitivity index Pcm of the steel and reduces the weldability of the H-shaped steel, and the upper limit value is set to 0.20%.
Si: 0.15-0.40%, Si with proper content can play a strong solid solution strengthening role, Si is also an important reduction and deoxidation element in the steelmaking process, in order to obtain higher strength, the lower limit value is set to be 0.15%, but the Si content cannot be too high, researches show that the high Si content can accelerate high-temperature stripping, reduce toughness and lamellar tearing resistance, and red iron oxide scales are easily generated on the surface of steel to influence the surface quality of products, and the upper limit value is set to be 0.40%.
Mn: 1.10-1.50%, Mn is used as a strengthening element in the steel, the strength and the hardenability of the steel can be improved, in order to ensure the strength of the steel, the lower limit value is set to be 1.10%, but the Mn content cannot be too high, so that the feasibility of casting blank segregation is obviously increased, the forming performance of the steel is adversely affected, and the upper limit value is set to be 1.50%.
P, S as impurity elements adversely affect the plasticity, toughness and weldability of the steel. Wherein P is a solidification segregation element, which easily causes welding cracks and reduces the toughness; s can form MnS in the process of central segregation formed by solidification segregation, welding cracks are caused, the toughness is reduced, and lamellar tearing resistance can be caused, the control difficulty of steelmaking is considered, and the proportion of P: less than or equal to 0.035%, S: less than or equal to 0.035%.
V:0.030 to 0.060%, V is a strong carbide forming element, V (C, N) dispersed compound formed by the V and C, N elements is distributed in a steel matrix to play a role in precipitation strengthening, the V is mainly used as a ferrite phase transformation nucleation point in the phase transformation process from austenite to ferrite to play a role in refining ferrite grains and precipitating after phase transformation to play a role in precipitation strengthening, and in order to improve the strength, the lower limit value is set to be 0.030%; on the other hand, when the V content is more than 0.06%, precipitates are coarse and coarse to impair the toughness, and the upper limit is set to 0.060% in consideration of the production cost while ensuring the overall mechanical properties of the product.
0.020-0.050% of Nb, wherein Nb is used as a strong carbide forming element, and Nb (C, N) dispersed compound formed by Nb and C, N element is distributed in a matrix of the steel to play a role in precipitation strengthening and improve toughness. The addition of Nb can inhibit austenite recrystallization in the rolling process, enlarge the austenite non-recrystallization temperature range, and lead austenite grains to be elongated by accumulated deformation formed under the subsequent low temperature and high pressure, a large amount of deformation bands and dislocation are formed at grain boundaries, and a large amount of nucleation points are provided in the subsequent phase transformation process to refine the grains.
0.0008 to 0.0015 percent of B. B is used as an element for improving the hardenability of the steel, thereby saving a large amount of other expensive alloy elements and reducing the cost of the steel. The mechanism of action is that ferrite easily nucleates at grain boundaries during austenite transformation. Because B is adsorbed on the grain boundary, defects are filled, the energy position of the grain boundary is reduced, new phase nucleation is difficult, the stability of austenite is increased, and the hardenability is improved. The lower limit is set to 0.0008% for improving hardenability. Research shows that when the B content exceeds a certain value, the hardenability is reduced as compared with steel without B, so the upper limit of B is set to 0.0015%.
N: 0.015 to 0.020%. N (nitrogen) is an element which forms V, Nb carbide and contributes to grain refinement and precipitation strengthening of the structure. Therefore, the lower limit of the N content is set to 0.015%. However, if the N content is more than 0.020%, the low temperature toughness is lowered, the continuous casting surface cracks and the strain aging of the steel material are caused. Therefore, the upper limit of the N content is set to 0.020%. In addition, in order to promote the precipitation of a large amount of finely dispersed second phase particles such as VN, V (CN), Nb (C, N) and the like in the steel, the ratio of (Nb + V)/N is limited to 3.5-5.5.
Als is less than or equal to 0.005 percent. Al is a strong deoxidizing element and is commonly used in molten steel to reduce the oxygen content, thereby reducing the number and size of inclusions in the steel and obtaining pure steel. However, Al is also a strong nitride-forming element to form AlN, and a proper amount of AlN can refine grains and improve impact toughness. But AlN is easy to gather and grow in molten steel, the crack sensitivity of continuous casting special-shaped blanks is enhanced, and surface cracks are easy to appear. Meanwhile, excessive Al elements in the steel occupy the N elements, so that the precipitation quantity of second phase particles such as V (C, N), Nb (C, N) and the like in the steel is reduced, and the action of elements such as V, Nb and the like is weakened. Therefore, Als in the steel is less than or equal to 0.005 percent.
The total compression ratio of the thick and heavy hot-rolled H-shaped steel with the low-compression-ratio yield strength of 355MPa is less than 5, wherein the ratio of the blank to the final product in the thickness direction of the flange is less than 2.5.
The thickness range of the flange of the thick and heavy hot-rolled H-shaped steel with the low compression ratio yield strength of 355MPa is 50-100 mm.
The 1/2 position (core) of the flange of the thick and heavy hot-rolled H-shaped steel with the low compression ratio yield strength of 355MPa is a ferrite and pearlite complex phase structure, the ferrite grain size grade is more than 8.0 grade, and the pearlite area accounts for 25-45 percent; the surface layer in the thickness direction of the flange is a tempered sorbite structure, and the grain size of ferrite is more than 10.0 grade.
The invention provides a production method of thick and heavy hot-rolled H-shaped steel with low compression ratio yield strength of 355MPa, which comprises the following process flows of: molten iron pretreatment → converter smelting → argon blowing refining → beam blank full-protection pouring → rolling → QST after rolling controls cold.
The rolling comprises the following steps:
s1, heating;
s2 rough rolling;
and S3 finish rolling.
The step S1 of heating specifically includes: the heating temperature of the special-shaped blank in the heating furnace is 1200-1250 ℃, and the furnace time is not less than 240 min; wherein the temperature of the preheating section is 700-900 ℃, the temperature of the heating section is 1210-1260 ℃, the temperature of the soaking section is 1200-1250 ℃, the soaking time is 140min, and the air-fuel ratio is 2.1-2.4.
The rough rolling in the step S2 specifically comprises the following steps: the cogging rolling temperature in the rough rolling stage is 1100-1200 ℃, and the finish rolling temperature is above 1050 ℃. In the cogging rolling process, the compression ratio of the rough rolling stage accounts for 20-25% of the total compression ratio from the blank to the finished product.
The step S3 finish rolling specifically comprises the following steps: and (5) after the rough rolling is finished, entering a finish rolling stage, and finishing the rest deformation of the blank at the stage. The finish rolling cogging temperature is 980-1050 ℃, and the final rolling temperature is controlled at 930-950 ℃ because the product is added with appropriate elements such as Nb, the austenite non-recrystallization temperature range is expanded, and the rolling pressure condition of the last rolling mill is comprehensively considered. The total reduction rate of the web pass is controlled to be 25% -30% in a temperature range of 980-1050 ℃, and further, the pass reduction rate in the thickness direction of the flange needs to meet the requirement that eta web plus (0-5%) is equal to eta flange; namely, the pass reduction rate of the flange in the thickness direction is 0 to 5 percent greater than that of the web plate in the temperature range of 980 to 1050 ℃; in order to reduce the surface temperature of the flange and increase the surface hardness, so that the deformation of steel at high temperature permeates to the flange core part and the permeability of the deformation of the ultra-thick hot-rolled H-shaped steel flange is increased, the SFC process is started three times before the steel is fed into a finishing mill, the water pressure is controlled to be 0.8-1.0 MPa, and the opening degree of a water nozzle is 70-80%; in the last three passes, the temperature is controlled to be 930-950 ℃, the total reduction rate of the web plate passes is controlled to be 10-15%, the reduction rate of the web plate in the last pass is 0-5%, and the reduction rate is not 0%. In order to ensure that the deformation and infiltration effects of the core part and the temperature of the edge surface and the core part tend to be consistent, the uniformity of the structure on the flange section is ensured, the final rolling temperature is in a target range, the SFC process is started in the last 3 times, the water pressure is controlled to be 0.8-1.0 MPa, and the opening degree of the water nozzle is 60-70%. In the range of austenite non-recrystallization temperature at the stage, the Nb (C, N) second-term particles are utilized to inhibit inter-pass static recrystallization, accumulated strain is realized, accumulated deformation formed under high pressure can enable austenite grains to be elongated, a large number of deformation bands and dislocation are formed in the grains, the increase of grain boundary area improves the nucleation density of austenite, the grain size is further refined, the strength of steel is improved, and the toughness of the steel is improved. Meanwhile, elongated austenite and a large number of deformation zones and dislocation positions also provide a large number of landing points for the precipitation of second phase particles of carbonitride, and the stored energy formed at low temperature and high pressure also provides enough kinetic energy for the precipitation of the second phase particles of carbonitride. Nb and V are used as strong carbide forming elements, and a large amount of V (C, N) and Nb (C, N) dispersoids are formed and distributed in a matrix at the present stage, so that the strength and the toughness of the steel are further improved.
The production method also comprises water passing after rolling (QST controlled cooling): and (3) immediately performing controlled cooling after the H-shaped steel is finish rolled, cooling the H-shaped steel to below an Ms point, waiting for the temperature to return to 650-700 ℃, and then performing air cooling on a roller way and a cooling bed to room temperature.
In order to further achieve the effect of controlled cooling, the H-shaped steel immediately enters a QST controlled cooling device after finish rolling, the water pressure of penetrating water is set to be 1.0-1.4 MPa, the speed of a roller way is 0.6-1.2 m/s, and the red-reflecting time is set to be 200-250 s. Wherein in the water passing process, the opening degree of the baffles at the two sides is 800-1000 mm, and the angle of the nozzle is 10-53 degrees.
Preferably, the opening degree of the baffle plates at the two sides is 850-900 mm, and the angle of the nozzle is 15-20 degrees. Ensuring that the thickness of the tempered layer in the thickness direction of the flange after quenching and tempering reaches 1/4 of the thickness of the flange; if the cooling time is too long, the structure of the surface tempered layer of the product can become tempered martensite, and the structure is unfavorable for the toughness of the product.
According to the method, the austenite structure can be well refined, the core structure is converted to the pearlite structure, the surface layer structure is converted to the tempered sorbite structure, the growth of the core pearlite structure is inhibited, the grain structure refinement of the steel is greatly promoted, the grain size reaches 10 grades, and the structure of each section of the H-shaped steel is relatively uniform. The mechanical property reaches：ReHNot less than 355MPa, RmNot less than 570MPa, A not less than 20 percent and 0 ℃ longitudinal V-shaped impact energy KV2Not less than 85J; the performance Z in the thickness direction of the flange is more than or equal to 25 percent.
In the technical scheme of the invention, based on the pass rolling deformation characteristic of hot-rolled H-shaped steel, the limitation of blank heating and cogging rolling is taken into consideration, more deformation is distributed to the first few passes of the finish rolling stage, temperature control rolling and SFC (Small form factor correction) process starting are carried out in the finish rolling stage, the deformation permeability of a rolled piece at high temperature is increased, and the pinning effect of Nb and V elements is matched, so that the rolling effect of an austenite non-recrystallization region is maximized, and fine grain strengthening is realized; the chemical composition adopts higher V content to ensure the precipitation strengthening effect of secondary carbonitride; the thick specification adopts relatively low rolling temperature to obtain good deformation permeation, and the uniformity of a microstructure in the thickness direction of the flange is improved by matching with Mn element; the contents of Nb and V are controlled, so that the surface quality of a product is effectively controlled on the premise of not improving the sensitivity of surface cracks of the continuous casting special-shaped blank; through reasonable component proportion, pressing distribution and temperature control rolling, by utilizing a fine grain strengthening mechanism, a precipitation strengthening mechanism, a phase change strengthening mechanism, a deformation penetration control technology and a QST (stress induced plasticity) cooling control process after rolling, the temperature difference between the flange and the web is reduced as much as possible, and the uniform temperature of the section of the H-shaped steel is ensured. By increasing the cooling speed after rolling, the flange surface layer rapidly passes through an austenite region, so that more microalloy elements dissolved in austenite in the final rolling are kept in a low-temperature phase region for precipitation, meanwhile, the temperature of the steel surface layer is taken away by cooling water instantly, the temperature difference between the inner side and the outer side of the flange of the H-shaped steel is increased, the conduction speed of the core temperature to the outer surface is accelerated, the supercooling degree is increased, the core tissue is inhibited from growing, and the comprehensive mechanical property of the thick and heavy H-shaped steel is improved because the core tissue is ferrite plus pearlite and the surface layer is tempered sorbite.
Compared with the prior art, the thickness of the flange of the thick and heavy hot-rolled H-shaped steel finished product with the low compression ratio yield strength of 355MPa is 50-100mm, the core ferrite + pearlite complex phase structure is obtained by matching reasonable component proportion, controlling rolling and QST (stress induced cracking) controlled cooling technology after rolling, the ferrite grain size grade is more than 8.0 grade, and the pearlite accounts for 25-45 percent; surface temper SoxhletThe thickness of the body layer reaches 1/4 of the total thickness of the flange, wherein the area ratio of ferrite with the ferrite grain size of 12-20 mu m accounts for 70-85% of the total volume, and the ferrite with the ferrite grain size of 10-15 mu m accounts for 90-95% of the total ferrite. Meanwhile, through reasonable reduction distribution and temperature control rolling, fine grain strengthening, precipitation strengthening and phase change strengthening mechanisms and a temperature control-deformation coupling technology, the deformation permeation of the heavy hot-rolled H-shaped steel is increased, and the heavy hot-rolled H-shaped steel with excellent performance is obtained. Yield strength R of the producteHNot less than 355MPa, tensile strength RmNot less than 570MPa, elongation A not less than 20%, and 0 ℃ longitudinal V-shaped impact energy KV2The strength is not less than 85J, the performance Z of the flange in the thickness direction is not less than 25%, and the composite material has high strength, good plasticity, low-temperature toughness and good Z-direction performance and meets the application requirements in the field of high-rise buildings or large-span bridges.
Drawings
FIG. 1 is a metallographic structure of a penetrating layer of the product of example 1, wherein the penetrating layer is a surface tempered sorbite layer and is a tissue layer extending from the surface layer to the core in the thickness direction of the flange to a depth of 1/5 degrees which is at least the total thickness of the flange;
FIG. 2 is the metallographic structure of the transition zone of the product of example 1, which is the structure of the transition zone between the water-penetrating layer and the core part;
FIG. 3 shows the metallographic structure of the base of the product of example 1, which is a structure of a flange core and is a composite structure of ferrite and pearlite, wherein the pearlite content is 32%.
FIG. 4 shows a metallographic structure of a base material of a product according to example 2, which is a flange core structure and is a composite structure of ferrite and pearlite, wherein the proportion of pearlite is up to 30%.
FIG. 5 shows the metallographic structure of the base of the product of example 3, which is a flange core structure and is a composite structure of ferrite and pearlite, wherein the pearlite content is up to 28%.
FIG. 6 shows the metallographic structure of the base of the product of example 4, which is a structure of a flange core and is a composite structure of ferrite and pearlite, wherein the pearlite content is 29%.
FIG. 7 shows the metallographic structure of the base of the product of comparative example 1, which is a flange core structure and has a pearlite ratio of 22% in a ferrite + pearlite composite structure.
FIG. 8 shows the metallographic structure of the base of the product of comparative example 2, which is a flange core structure and in which 23% pearlite is present as a ferrite-pearlite composite structure.
Detailed Description
The following description of the embodiments of the present invention provides a detailed description of the embodiments of the present invention:
example 1 to example 6
The heavy hot-rolled H-shaped steel with the low compression ratio yield strength of 355MPa comprises the following elements in percentage by mass, and specifically shown in the following table 1; the balance of Fe and inevitable impurity elements.
The production process flow of the thick and heavy hot-rolled H-shaped steel with the yield strength of 355MPa, which is disclosed by the embodiments 1-6 of the invention, is as follows: molten iron pretreatment → converter smelting → argon blowing refining → LF refining → shaped blank full-protection casting → blank heating → temperature control rolling → QST cooling after rolling.
The rolling comprises a heating stage, a rough rolling stage and a finish rolling stage.
The method comprises the following specific steps:
1) the special-shaped blank enters a heating furnace and is heated to 1200-1250 ℃ by the heating furnace, the furnace time is 240min, wherein the temperature of the preheating section is 700-900 ℃, the temperature of the heating section is 1210-1260 ℃, the temperature of the soaking section is 1200-1250 ℃, the soaking time is 100-140min, and the air-fuel ratio is 2.1-2.4.
2) The initial rolling temperature of the cogging rolling in the rough rolling stage is 1100-1200 ℃, the final rolling temperature is above 1050 ℃, and the compression ratio from the initial rolling to the final rolling is 20-25% of the total compression ratio of the blank to the finished product.
3) And after the rough rolling is finished, entering a finish rolling stage, and performing the rest deformation of the blank at the stage. The initial rolling temperature is 980-1050 ℃, and because the product is added with appropriate elements such as Nb, the non-recrystallization temperature of austenite is improved, and the rolling pressure condition of the last rolling mill is comprehensively considered, the final rolling temperature is controlled at 930-950 ℃. The total reduction rate of the web plate pass is controlled to be 25-30% in the temperature range of 980-1050 ℃, the reduction rate of the web plate in the thickness direction is coordinated with the flange, namely the reduction rate of the flange in the thickness direction needs to meet etaWeb plate+(0～5％)＝ηFlange of wing. Starting the SFC process three times before entering a finishing mill, controlling the water pressure to be 0.8-1.0 MPa, and controlling the opening degree of a water nozzle to be 70-80%; in the last three passes, the total reduction rate of the inter-pass web plates is controlled to be 10% -15%, the reduction rate of the web plates in the last pass is 0-5%, and the reduction rate is not 0%. Simultaneously starting the SFC process, controlling the water pressure to be 0.8-1.0 MPa, and controlling the opening degree of a water nozzle to be 60-70%; meanwhile, the SFC process mainly reduces the surface temperature of the flange and increases the surface hardness for three times before finish rolling, so that the deformation of the steel at high temperature permeates to the flange core part, and the permeability of the deformation of the flange of the ultra-thick hot-rolled H-shaped steel is increased; and starting the SFC process in the last three times of finish rolling, adjusting the temperature of the flange surface of the H-shaped steel to be consistent with that of the core part while ensuring the deformation and infiltration of the core part, ensuring the uniformity of the structure on the section of the flange, and simultaneously ensuring that the final rolling temperature is in a target range.
4) After finishing finish rolling, enabling the rolled piece to enter a QST water passing stage, controlling the speed of a roller way to be 0.6-1.2 m/s, controlling the water pressure to be 1.0-1.4 MPa, setting the anti-red time to be 200-250 s, setting the opening degree of baffles at two sides to be 850-900 mm, and setting the angle of a nozzle to be 15-20 degrees so as to cool the rolled piece to be below an Ms point in the water passing process after rolling, waiting for the temperature to return to 650-700 ℃, and then performing air cooling on the roller way and a cooling bed to room temperature.
Examples 1-6 process parameters during the production of hot rolled H-section steel are controlled as in table 2 below.
Table 1 tabulates (wt%) values of chemical compositions of inventive examples 1-6, with the balance being Fe and unavoidable impurities.
Figure BDA0003171299850000131
The production processes of the hot-rolled H-shaped steel described in examples 1 to 6 and comparative examples 1 to 3 were carried out according to the above-mentioned methods, and the specific process parameters are as shown in the following tables 2 to 1, 2 to 2 and 2 to 3.
TABLE 2-1 heating and roughing parameters for inventive and comparative examples
Figure BDA0003171299850000132
TABLE 2-2 finish Rolling parameters for inventive and comparative examples
Figure BDA0003171299850000141
Tables 2-3 QST stage parameters for various examples of the invention and comparative examples
Figure BDA0003171299850000142
The dimensions and properties of the H-shaped steel products produced in the respective examples and comparative examples were measured as shown in tables 3-1 and 3-2.
TABLE 3-1 List of the dimensional measurements of inventive and comparative examples
Blank form Blank type specification and size (mm) Product size (mm) Total compression ratio Compression ratio of flange in thickness direction
Example 1 BB5 900*510*165 H498*432*45*70 3.2 2.4
Example 2 BB6 1030*440*112.5 W21*275 4.0 2.0
Example 3 BB5 900*510*165 W14*500 3.6 2.4
Example 4 BB7 1300*510*215 W14*550 3.3 2.2
Example 5 BB6 1030*440*112.5 W40*503 4.2 1.9
Example 6 BB7 1300*510*215 W36*723 2.5 2.2
Comparative example 1 BB7 1300*510*215 W14*550 3.3 2.2
Comparative example 2 BB6 1030*440*112.5 W40*503 4.2 1.9
Comparative example 3 BB7 1300*510*215 W36*723 2.5 2.2
Tables 3-2 List of Performance test cases of inventive and comparative examples
Figure BDA0003171299850000151
The above detailed description of a low compression ratio yield strength 355MPa grade ultra-thick hot rolled H-section steel and the method for producing the same with reference to the examples is illustrative and not restrictive, and several examples can be cited within the limits thereof, so that variations and modifications without departing from the general concept of the present invention shall fall within the scope of the present invention.

Claims (3)

1. The low-compression-ratio yield strength 355 MPa-grade heavy hot-rolled H-shaped steel is characterized by comprising the following components, by mass, 0.13-0.20% of C, 0.15-0.40% of Si, 1.10-1.50% of Mn, less than or equal to 0.035% of P, less than or equal to 0.035% of S, 0.030-0.060% of V, 0.0008-0.0015% of B and Nb: 0.02-0.05%, N: 0.015-0.020%, more than or equal to 3.5 (Nb + V)/less than or equal to 5.5% of N, less than or equal to 0.005% of Als, and the balance of Fe and inevitable impurities;
the production method of the thick and heavy hot-rolled H-shaped steel with the low compression ratio yield strength of 355MPa comprises the following steps of heating a blank, wherein the heating process comprises the following steps: the heating temperature of the special-shaped blank in the heating furnace is 1200-1250 ℃, and the furnace time is not less than 240 min;
the production method comprises rough rolling, wherein the cogging rolling temperature in the rough rolling stage is 1100-1200 ℃, and the finish rolling temperature is above 1050 ℃; the compression ratio of the rough rolling stage accounts for 20-25% of the total compression ratio from the blank to the finished product;
the production method also comprises finish rolling, wherein the finish rolling cogging temperature is 980-1050 ℃, and the finish rolling temperature is controlled at 930-950 ℃; the total reduction rate of the web plate is controlled to be 25-30% in a temperature range of 980-1050 ℃; the reduction rate in the thickness direction of the flange needs to meet eta web + (0-5%) = eta flange; starting the SFC process in the first three times of the finishing mill, controlling the water pressure to be 0.8-1.0 MPa, and controlling the opening degree of a water nozzle to be 70-80%; in the finish rolling stage, in the last three passes, the temperature is controlled to be within the temperature range of 930-950 ℃, the total reduction rate of the web plate passes is controlled to be 10-15%, and the reduction rate of the web plate in the last pass is 0-5%; starting the SFC process for the last 3 times, controlling the water pressure to be 0.8-1.0 MPa, and controlling the opening degree of a water nozzle to be 60-70%;
the production method also comprises the step of water penetration after rolling, and specifically comprises the following steps: cooling the material below the Ms point, waiting for the temperature to return to 650-700 ℃, and then air-cooling the material on a roller way and a cooling bed to room temperature;
1/2 parts of the low-compression-ratio yield strength 355 MPa-level heavy hot-rolled H-shaped steel in the thickness direction of the flange are ferrite and pearlite complex phase structures, the ferrite grain size grade is above 8.0 grade, and the area of the pearlite accounts for 25% -45%; the surface layer in the thickness direction of the flange is a tempered sorbite structure, and the grain size of ferrite is more than 10.0 grade.
2. The thick and heavy hot-rolled H-section steel with a low specific compressive yield strength of 355MPa according to claim 1, wherein the thickness of the flange is in the range of 50-100 mm.
3. The application of the thick and heavy hot-rolled H-shaped steel with the low compression ratio yield strength of 355MPa according to claim 1 or 2 is characterized in that the thick and heavy hot-rolled H-shaped steel is used in the field of high-rise buildings or large-span bridges.
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