CN112359289B - Super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness and production method thereof - Google Patents

Super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness and production method thereof Download PDF

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CN112359289B
CN112359289B CN202011321554.3A CN202011321554A CN112359289B CN 112359289 B CN112359289 B CN 112359289B CN 202011321554 A CN202011321554 A CN 202011321554A CN 112359289 B CN112359289 B CN 112359289B
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shaped steel
temperature
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CN112359289A (en
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邢军
吴保桥
张建
夏勐
汪杰
黄琦
吴湄庄
彭林
彦井成
丁朝晖
何军委
陈辉
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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
    • B21B37/74—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
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
    • 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
    • C22C38/04—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

Abstract

The invention discloses super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness and a production method thereof; the H-shaped steel comprises the following chemical components in percentage by mass: 0.12 to 0.18%, Si: 0.10 to 0.50%, Mn: 1.20-1.60%, Al: 0.02 to 0.06%, Nb: 0.02-0.06%, N: 0.0040-0.0100%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, and the balance is Fe and inevitable impurities, wherein the flange thickness t is 80-150mm, CEV is less than or equal to 0.42%, and Pcm is less than or equal to 0.25%; the invention provides a low-cost component design scheme for Nb and Al microalloying, and regulates and controls the distribution of AlN and NbC in continuous casting billets and H-shaped steel by matching with a reasonable continuous casting process and a rolling process, thereby improving the structure of special-shaped billets, refining the structure of the H-shaped steel, and having good mechanical property and economic benefit.

Description

Super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness and production method thereof
Technical Field
The invention relates to the technical field of steel production, in particular to super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness and a production method thereof.
Background
Hot-rolled H-section steel is one of the steels for main structures, and plays an important role in the development of socioeconomic performance. With the economic development and scientific and technological progress, the construction of a series of large engineering structures such as high-rise buildings, ocean platforms, large all-weather railway traffic, large bridges and the like puts forward performance requirements such as large scale, high performance, greenization and the like on the hot-rolled H-shaped steel. Generally, the thicker the steel material product is, the more difficult it is to ensure the strength and toughness. At present, China still has a blank for ultra-thick hot-rolled H-shaped steel products with flanges of 80-150mm, and the H-shaped steel is usually formed by welding thick plates, so that the manufacturing process is complex, the environmental pollution is great, and the economic benefit is poor.
Compared with a steel plate, due to the complex section of the hot-rolled H-shaped steel, the rolling conditions (rolling temperature and rolling compression ratio) are limited, 1) the rolling compression ratio is difficult to adjust, especially the super-thick H-shaped steel, the deformation between each pass is difficult to adjust, and the total compression ratio is small (the minimum is only 1.5); 2) the cooling speed of each part of the flange, the web and the transition arc of the H-shaped steel in the rolling process is different, so that the rolling temperature difference of each part is large, and the rolling temperature is uneven. Therefore, the ultra-thick hot-rolled H-shaped steel cannot simply refer to the manufacturing process and chemical composition of the steel plate, the strength and toughness are difficult to guarantee, the GB/T1591 standard requirements cannot be met, and the difficulty in developing the ultra-thick Q355-grade good low-temperature toughness hot-rolled H-shaped steel is high.
Patent document 1: the invention patent with the publication number of CN104487604B and the name of 'H-shaped steel and manufacturing method thereof' discloses an H-shaped steel with the flange thickness of 100-150mm and a manufacturing method thereof, which properly controls Al and Ca oxides in the steel to be dispersed and distributed, refines austenite grains through the pinning effect of the oxides to realize the structure refinement of the H-shaped steel, and properly adds Si, Mn, V, Ni and other components to improve the hardenability of the H-shaped steel so as to improve the strength and the toughness of the H-shaped steel.
Patent document 2: the invention patent with the publication number of CN103987866B and the name of 'high-strength extremely-thick H-shaped steel' also discloses an H-shaped steel with the flange thickness of 100-150mm and a manufacturing method thereof, wherein the H-shaped steel mainly comprises C, Si, Mn, Cu, Ni, V, Al, Ti, B, N and O by reasonably controlling the composition of the components of the H-shaped steel, Ceq is ensured to be 0.37-0.50, at least one of Mo and Nb is added, the hardenability of the steel is improved, the generation of ferrite is inhibited, a large amount of bainite tissues are obtained by regulating the area rate of bainite at the depth of 1/4 outside the flange to be more than 60%, the H-shaped steel can be manufactured under the conditions of not adding a large amount of alloy and carrying out extremely-low carbonization with large steel manufacturing load, the extremely-thick high-strength H-shaped steel is obtained, the manufacturing cost can be reduced, the construction period can be shortened, and the cost can be greatly reduced.
Patent document 3: the invention patent with the publication number of CN109715842B and the name of 'H-shaped steel and a manufacturing method thereof' discloses H-shaped steel with the flange thickness of 20-140mm and a manufacturing method thereof, which comprises the steps of C, Si, Mn, Nb, V, Ti, N, Cr, Mo, Ni, Cu, W, Ca, Zr, Al, B and other elements, controlling Ceq to be 0.30-0.48, adopting Mn, Nb and V micro-alloying design, matching with controlled rolling and natural cooling to obtain a mixed structure MA of ferrite, martensite and austenite with the concentration of more than 60% and less than 100%, wherein the MA of the mixed structure is less than 3.0%, and other structures are less than 37%, wherein the average grain diameter of the ferrite is 1-30 mu m, and the product performance is realized.
Patent document 4: the invention application with the publication number of CN110291218A and the name of 'H-shaped steel and a manufacturing method thereof' discloses H-shaped steel with the flange thickness of 25-140mm and a manufacturing method thereof, which comprises elements such as C, Mn, Cu, Ni, Cr, Nb, V, Al, Ti, B, N and the like, and can be added with Si, Mo, W, Ca, Zr, Mg, REM and the like, Ceq is controlled to be 0.30-0.48, a metal structure with the average crystal grain diameter of below 38 mu m and the surface integral rate of a martensite-austenite mixed structure (MA) of below 1.2% is obtained by reasonable controlled rolling and cooling, and the patent adopts low Si, Cu, Ni, Nb and V microalloying design to be matched with controlled rolling and cooling to obtain the product performance with the average grain diameter of below 38 mu m of ferrite.
Disclosure of Invention
Compared with steel plates or H-shaped steel with ordinary thickness, any process details are more important when the ultra-thick H-shaped steel with 80-150mm is rolled, otherwise, products with satisfactory mechanical strength are difficult to obtain.
In the above patent documents 1 and 2, a large amount of bainite is used as a main metallographic phase, and in the patent documents 3 and 4, a large amount of alloy is added, and noble metals such as Ni are used, so that the production cost is high, and the economical efficiency of the product is not facilitated; in addition, the prior art does not have stricter control on the production process, which causes the inventor to encounter many obstacles in actual production, so the inventor proposes the scheme in the application.
The present application was made in view of the above circumstances, and an object thereof is to provide a super thick Q355 grade hot-rolled H-section steel with good low-temperature toughness and a production method thereof.
In order to achieve the purpose, the invention provides the following technical scheme: the super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness has a flange thickness t of 80-150mm, and comprises the following chemical components in percentage by mass: 0.12 to 0.18%, Si: 0.10 to 0.50%, Mn: 1.20-1.60%, Al: 0.02 to 0.06%, Nb: 0.02-0.06%, N: 0.0040 to 0.0100%, P < 0.015%, S < 0.005%, and the balance Fe and inevitable impurities, CEV < 0.42% is determined by the formula CEV ═ C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15, and Pcm < 0.25% is determined by the formula Pcm ═ C + Si/30+ (Mn + Cu + Cr)/20+ Ni/60+ Mo/15+ V/10+ 5B.
Preferably, the H-shaped steel contains 500-2000 pieces/mm by number densitometer per unit area at b/6 part from flange end part in width direction of flange and t/4 part from flange outer surface in thickness direction of flange2AlN particles having a diameter of 10 to 300nm in terms of equivalent circle diameter and 500 to 2000 particles/mm2The NbC particles having a diameter of 10 to 400nm in terms of equivalent circle diameter.
Preferably, the structure of the flange of the H-shaped steel at a position b/6 away from the flange end part in the width direction and at a position t/4 away from the flange outer surface in the thickness direction is ferrite and pearlite, the size of ferrite grains in the structure is less than 30um, ferrite grains of 8-15 um account for more than 80% of the total volume of the ferrite, and the total volume of the ferrite accounts for 70-75% of the total volume of the structure.
Preferably, the yield strength R is at a position b/6 away from the flange end part in the width direction of the flange of the H-shaped steel and at a position t/4 away from the outer surface of the flange in the thickness direction of the flangeeHGreater than 355 MPa; the tensile strength Rm is 450-590 MPa, the elongation A is more than 23%, and the low-temperature impact toughness KV2 at the temperature of minus 20 ℃ is more than or equal to 120J.
The invention also provides another technical scheme, and the production method of the super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness comprises the following process flows of heating a blank, cogging and rolling, universal finish rolling and cooling;
heating the blank: in the step, the temperature of a heating section of the beam blank in a heating furnace is 1200-1230 ℃, the heating time is 30-40 min, the temperature of a soaking section is 1210-1225 ℃, the soaking time is 50-60min, and the time in the heating furnace is 110-130 min;
cogging and rolling: the step is carried out in two stages, wherein the rolling temperature of the cogging rolling stage 1 is 1100-1150 ℃, and the accumulated deformation of the flange is 8-10%; the rolling temperature of the cogging rolling 2 stage is 1000-1100 ℃, and the accumulated deformation of the flange is 10-20%;
universal finish rolling: the step is carried out in two stages, the rolling temperature of the high-temperature rolling stage is 930-980 ℃, and the accumulated deformation of the flange is more than 40%; in the low-temperature rolling stage, the rolled piece is heated to below 900 ℃, the deformation is finished, the residual compression is completed, and the accumulated deformation of the flange is more than 20%;
and (3) cooling: two-stage cooling is adopted, wherein the first stage is rapid cooling, the cooling speed is 15-30 ℃/s, and the final cooling temperature of the surface of a rolled piece is 600-650 ℃; and air cooling in the second stage, wherein the rolled piece enters a cooling bed for air cooling to room temperature.
Preferably, the method also comprises a step of continuous casting of the special-shaped blank before the blank is heated, wherein in the step, the pressure of cooling water of the crystallizer is 0.7-2.0 MPa, the pressure of secondary cooling water is 1.0-3.0 MPa, and the pulling speed is 0.20-0.60 m/min.
Preferably, the process flow comprises molten iron pretreatment → converter smelting → LF refining → RH refining → beam blank continuous casting → blank heating → cogging rolling 1 → cogging rolling 2 → universal finish rolling → rapid cooling → cooling bed → straightening → sizing → inspection → packaging and warehousing.
Preferably, the yield strength R is at a position b/6 away from the flange end part in the width direction of the flange of the H-shaped steel and at a position t/4 away from the outer surface of the flange in the thickness direction of the flangeeH375 to 445 MPa; the tensile strength Rm is 468-590 MPa, the elongation A is 24-32%, and the low-temperature impact toughness KV2 at-20 ℃ is 128-180J.
Compared with the prior art, the invention has the beneficial effects that:
1. the super-thick Q355-grade good low-temperature toughness hot-rolled H-shaped steel and the production method thereof use Q335D hot-rolled H-shaped steel with the flange thickness of 80-150mm as a product target, provide a design scheme of Nb and Al microalloying, regulate and control the distribution of AlN and NbC in a continuous casting billet and the H-shaped steel by matching with a reasonable continuous casting process and a rolling process, improve the structure of a beam blank, refine the structure of the H-shaped steel, and develop Q355D hot-rolled H-shaped steel with the flange thickness of 80-150 mm; the structure is ferrite and pearlite, the grain size is less than 30um, the yield strength is greater than 355MPa, the tensile strength is 450-590 MPa, the elongation after fracture is greater than 23%, and the impact toughness at-20 ℃ is greater than 120J.
2. The production method of the super-thick Q355-grade good low-temperature toughness hot-rolled H-shaped steel reasonably controls the cooling speed and the drawing speed of the continuous casting billet, promotes the continuous casting billet to greatly precipitate fine AlN pinning austenite grain boundaries in a high-temperature region to refine austenite grains, and greatly precipitates fine NbC second-phase grains in a composite low-temperature region to jointly refine austenite grains and subsequent continuous casting billet tissues.
3. According to the production method of the super-thick Q355-grade good low-temperature toughness hot-rolled H-shaped steel, blank heating is controlled, components and structures are homogenized, rolling deformation resistance is reduced, the situation that an austenite reheating process is abnormally large is prevented, a large number of dispersed AlN second-phase particles are reserved, and the austenite particles are refined by utilizing the pinning grain boundary effect in the heating process.
4. According to the production method of the super-thick Q355-grade good low-temperature toughness hot-rolled H-shaped steel, the cogging rolling is carried out in stages, the internal defects of a casting blank can be better welded, the external dimension of the blank is adjusted, the rolling of a universal finishing mill is convenient, meanwhile, the AlN second-phase particles separated out in the rolling process can be used for inhibiting static recrystallization in the rolling process to promote dynamic recrystallization, and austenite grains are refined.
5. According to the production method of the super-thick Q355-grade good low-temperature toughness hot-rolled H-shaped steel, the rolling temperature and the deformation of a high-temperature section promote the precipitation of a large amount of fine NbC second-phase particles and the AlN coupling effect precipitated before to inhibit the static recrystallization among rolling passes, the strain accumulation in the composite rolling process promotes the repeated austenite dynamic recrystallization, and austenite grains are fully refined; the rolling temperature and the deformation amount of the low-temperature section can avoid the recrystallization of austenite, promote the austenite to generate larger deformation, obtain more defect positions, and are beneficial to ferrite nucleation and ferrite structure refinement.
6. The ultra-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness and the production method adopt a design scheme of Nb and Al microalloying, and have the advantages of low production cost, excellent mechanical properties of products and good economic and social benefits.
Drawings
FIG. 1 is a schematic structural diagram of H-shaped steel, wherein A is a standard strength detection point, namely a position b/6 away from the end of a flange in the width direction of the flange of the H-shaped steel and a position t/4 away from the outer surface of the flange in the thickness direction of the flange.
Detailed Description
The super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness has a flange thickness t of 80-150mm, and comprises the following chemical components in percentage by mass: 0.12 to 0.18%, Si: 0.10 to 0.50%, Mn: 1.20-1.60%, Al: 0.02 to 0.06%, Nb: 0.02-0.06%, N: 0.0040-0.0100%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, and the balance is Fe and inevitable impurities; CEV is less than or equal to 0.42 percent, Pcm is less than or equal to 0.25 percent,
wherein CEV is obtained by the formula CEV ═ C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15,
pcm is obtained by the formula Pcm, namely C + Si/30+ (Mn + Cu + Cr)/20+ Ni/60+ Mo/15+ V/10+ 5B;
the component design considerations are as follows:
the C content is set to 0.12-0.18%. C (carbon) is an element effective for strengthening steel and also an element that significantly deteriorates weldability of steel. Therefore, the lower limit of the C content is set to 0.12%. When the C content is more than 0.18 percent, the reaction is carried outObviously improving the carbon equivalent CEV and the welding crack sensitivity index P of the H-shaped steelcmThe weldability of the H-shaped steel is reduced, and simultaneously, the low-temperature toughness of the H-shaped steel is also reduced. Therefore, the upper limit of the C content is set to 0.18%.
The Si content is set to 0.10 to 0.50%. Si (silicon) is an element that is a deoxidizing element and also contributes to improvement of strength. Therefore, the lower limit of the Si content is set to 0.10%. When the Si content is more than 0.50%, high-temperature delamination is accelerated, toughness and lamellar tearing performance are deteriorated, and the surface quality of steel is also adversely affected. Therefore, the upper limit of the Si content is set to 0.50%.
The Mn content is set to 1.20 to 1.60%. Mn (manganese) improves the toughness and the strength of the steel within a certain range. Therefore, the lower limit of the Mn content is set to 1.20%. When the Mn content is more than 1.60%, macro segregation is easy to generate, so that the toughness of the steel is obviously reduced, even the phenomenon of delamination occurs, and the lamellar tearing resistance is deteriorated. Therefore, the upper limit of the Mn content is set to 1.60%.
The content of P is less than or equal to 0.015 percent. P (phosphorus) is a cause of weld cracking due to solidification segregation and a reduction in toughness, and therefore, it is desirable to reduce P as much as possible, and the total cost for removing P is limited to 0.015% or less.
The S content is set to be less than or equal to 0.005 percent. Since S (sulfur) forms MnS in a central segregation portion formed by solidification segregation, not only causes weld cracking and a reduction in toughness, but also causes lamellar tearing resistance, the amount of S should be limited to 0.005% or less in consideration of the total cost for S removal, while minimizing the amount of S.
The Al content is set to 0.02-0.06%. Al (aluminum) is not only a deoxidizer in steel but also an important element for forming nitride particles that granulate austenite grains by a pinning effect. In order to obtain the effect of refining grains, the lower limit of the Al content is set to 0.02%. When the Al content becomes excessive, coarse oxides are generated, resulting in a significant decrease in toughness. Therefore, the upper limit of the Al content is set to 0.06%.
The Nb content is set to 0.02 to 0.06%. Nb (niobium) is an important element for forming carbide particles that granulate austenite grains by a pinning effect. In order to obtain this effect, the lower limit of the Nb content is set to 0.02%. When the Nb content is too high, the internal fillet of the continuous casting beam blank is easy to crack, the surface quality of a final product is influenced, the cost control is not facilitated, and the upper limit is set to be 0.06%.
The content of N is set to 0.0040 to 0.0100%. N (nitrogen) is one of the main elements forming AlN, and contributes to granulation and precipitation strengthening of the structure. Therefore, the lower limit of the N content is set to 0.0040%. If the N content is more than 0.0100%, 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 0.0100%.
Furthermore, the flange width direction of the H-shaped steel is b/6 away from the flange end part and the thickness direction of the flange is t/4 away from the outer surface of the flange (A part in figure 1), and the number density meter per unit area contains 500-2000 pieces/mm2AlN particles having a diameter of 10 to 300nm in terms of equivalent circle diameter and 500 to 2000 particles/mm2The NbC particles having a diameter of 10 to 400nm in terms of equivalent circle diameter.
Furthermore, the structure of the flange of the H-shaped steel at the position b/6 away from the flange end part in the width direction and at the position t/4 away from the flange outer surface in the thickness direction (A position in figure 1) is ferrite and pearlite, the size of ferrite grains in the structure is less than 30um, the ferrite grains of 8-15 um account for more than 80% of the total volume of the ferrite, and the total volume of the ferrite accounts for 70-75% of the total volume of the structure.
According to the regulation of the standard GB/T2975, the yield strength R of the H-shaped steel is at a position b/6 away from the end part of the flange in the width direction of the flange and at a position T/4 away from the outer surface of the flange in the thickness direction of the flange (A position in figure 1)eHGreater than 355 MPa; the tensile strength Rm is 450-590 MPa, the elongation A is more than 23%, and the low-temperature impact toughness KV2 at the temperature of minus 20 ℃ is more than or equal to 120J.
Based on the same invention concept, the production method of the super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness comprises the steps of heating a blank, cogging and rolling, universal finish rolling and cooling, and more specifically comprises the steps of hot metal pretreatment → converter smelting → LF refining → RH refining → beam blank continuous casting → heating of the blank → cogging and rolling 1 → cogging and rolling 2 → universal finish rolling → rapid cooling → cooling bed → straightening → cutting and sizing → inspection → packaging and warehousing;
heating the blank: in the step, the temperature of a heating section of the beam blank in a heating furnace is 1200-1230 ℃, the heating time is 30-40 min, the temperature of a soaking section is 1210-1225 ℃, the soaking time is 50-60min, and the time in the heating furnace is 110-130 min; heating is mainly for homogenization of components and structure, and rolling deformation resistance is reduced, and abnormal coarsening in the austenite reheating process is prevented. The design of the heating temperature can retain a large amount of dispersed and precipitated AlN second phase particles, and the crystal boundary function of the AlN second phase particles is utilized to refine austenite grains in the heating process.
Cogging and rolling: the step is carried out in two stages, wherein the rolling temperature of the cogging rolling stage 1 is 1100-1150 ℃, and the accumulated deformation of the flange is 8-10%; the rolling temperature of the cogging rolling 2 stage is 1000-1100 ℃, and the accumulated deformation of the flange is 10-20%; the rolling in the cogging stage is mainly used for welding internal defects of a casting blank and adjusting the external dimension of the blank so as to facilitate the rolling of a universal finishing mill, and meanwhile, AlN second-phase particles separated out in the rolling process can be used for inhibiting static recrystallization in the rolling process to promote dynamic recrystallization and refining austenite grains.
Universal finish rolling: the step is carried out in two stages, the rolling temperature of the high-temperature rolling stage is 930-980 ℃, and the accumulated deformation of the flange is more than 40%; under the rolling temperature and the deformation, the coupling effect of a large amount of fine NbC second-phase particles and the AlN precipitated before the second-phase particles can be promoted to inhibit static recrystallization among rolling passes, the strain accumulation in the composite rolling process can promote repeated austenite dynamic recrystallization, austenite grains can be fully refined, meanwhile, the rolling temperature is improved as much as possible, the load of a rolling mill is reduced, and the consumption and the energy consumption of the rolling mill are reduced; in the low-temperature rolling stage, the rolled piece is heated to below 900 ℃, the deformation is finished, the residual compression is completed, and the accumulated deformation of the flange is more than 20%; the recrystallization of austenite is avoided, the austenite is promoted to generate larger deformation, more defect positions are obtained, and ferrite nucleation and ferrite structure refinement are facilitated.
And (3) cooling: two-stage cooling is adopted, wherein the first stage is rapid cooling, the cooling speed is 15-30 ℃/s, and the final cooling temperature of the surface of a rolled piece is 600-650 ℃; air cooling is carried out in the second stage, and the rolled piece enters a cooling bed to be air cooled to room temperature; the rapid cooling is utilized, the temperature drop time is shortened, the distortion caused by the rolling deformation in the H-shaped steel is reserved, the supercooling degree of the phase change is enlarged, the phase change nucleation speed is promoted to be larger than the phase change crystal grain growth speed, the structure of the H-shaped steel after the phase change is refined, and the structure change is promoted.
In the above-mentioned beam blank continuous casting process, preferably, the cooling water pressure of the crystallizer is set to 0.7-2.0 MPa, the secondary cooling water pressure is set to 1.0-3.0 MPa, and the pulling speed is controlled to 0.20-0.60 m/min; reasonably controlling the cooling speed and the drawing speed of the continuous casting billet, and promoting the continuous casting billet to separate out a large amount of fine AlN pinning austenite grain boundary refined austenite grains in a high-temperature region and separate out a large amount of fine NbC second phase grains in a composite low-temperature region to jointly refine the austenite grains and the subsequent continuous casting billet structure.
The chemical composition, process parameters, second phase particles, microstructure and mechanical properties of examples 1 to 6 are as follows:
table 1 chemical composition of examples 1 to 6
Examples of the invention Product thickness mm C％ Si％ Mn％ P％ S％ Nb％ Al％ N％ CEV Pcm
1 80 0.13 0.24 1.40 0.010 0.005 0.03 0.03 0.0068 0.36 0.21
2 90 0.12 0.50 1.60 0.006 0.004 0.02 0.06 0.0100 0.39 0.22
3 100 0.15 0.28 1.42 0.009 0.004 0.04 0.03 0.0078 0.39 0.23
4 120 0.16 0.30 1.40 0.008 0.005 0.05 0.04 0.0075 0.39 0.24
5 140 0.18 0.10 1.20 0.008 0.005 0.06 0.02 0.0040 0.41 0.25
6 150 0.16 0.29 1.38 0.007 0.004 0.05 0.04 0.0089 0.39 0.24
Table 2 continuous casting and heating process parameters of examples 1 to 6
Figure BDA0002793084850000091
Figure BDA0002793084850000101
TABLE 3 controlled Rolling Process parameters for examples 1 to 6
Figure BDA0002793084850000102
Table 4 controlled cooling process parameters for examples 1 to 6
Figure BDA0002793084850000103
TABLE 5 second item particles and microstructures (detected at A in FIG. 1) of examples 1 to 6
Figure BDA0002793084850000104
TABLE 6 Properties of examples 1 to 6 (measured at A in FIG. 1)
Figure BDA0002793084850000111
According to the invention, the low-cost microalloying component design of Nb and Al is adopted, the second-phase particle precipitation of AlN and NbC is regulated and controlled, the structure of a beam blank is improved, the austenite grains of H-shaped steel are refined by matching with reasonable controlled rolling and controlled cooling process and the like, a uniform and fine ferrite and pearlite composite structure is obtained, Q355D hot-rolled H-shaped steel with the flange thickness of 80-150mm is developed, and as can be seen from Table 6, the yield strength R of the H-shaped steel is at a position b/6 away from the end part of the flange in the flange width direction and at a position t/4 away from the outer surface of the flange in the flange thickness direction (position A in figure 1) in the flange thickness directioneH375 to 445 MPa; the tensile strength Rm is 468-590 MPa, the elongation A is 24-32%, and the low-temperature impact toughness KV2 at the temperature of minus 20 ℃ is 128-180J; the invention has low production cost and excellent mechanical property.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope defined by the claims.
The present invention is not described in detail, but is known to those skilled in the art.

Claims (6)

1. The super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness is characterized in that the flange thickness t of the H-shaped steel is 80-150mm, and the hot-rolled H-shaped steel comprises the following chemical components in percentage by mass: 0.12 to 0.18%, Si: 0.10 to 0.50%, Mn: 1.20-1.60%, Al: 0.02 to 0.06%, Nb: 0.02-0.06%, N: 0.0040-0.0100%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, and the balance is Fe and inevitable impurities, wherein CEV is less than or equal to 0.42% as determined by a formula CEV = C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15, and Pcm is less than or equal to 0.25% as determined by a formula Pcm = C + Si/30+ (Mn + Cu + Cr)/20+ Ni/60+ Mo/15+ V/10+ 5B;
b/6 part from the flange end part in the width direction of the flange of the H-shaped steel and t & ltSUB & gt & lt/SUB & gt from the outer surface of the flange in the thickness direction of the flange4, 500 to 2000 pieces/mm in terms of number density per unit area2AlN particles having a diameter of 10 to 300nm in terms of equivalent circle diameter and 500 to 2000 particles/mm210 to 400nm NbC particles in terms of equivalent circle diameter;
the structure of the flange of the H-shaped steel, which is located b/6 away from the end of the flange in the width direction of the flange and t/4 away from the outer surface of the flange in the thickness direction of the flange, is ferrite and pearlite, the size of ferrite grains in the structure is below 30um, ferrite grains of 8-15 um account for more than 80% of the total volume of the ferrite, and the total volume of the ferrite accounts for 70-75% of the total volume of the structure.
2. The super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness of claim 1, wherein the steel is characterized in that: the yield strength R is at a position b/6 away from the end part of the flange in the width direction of the flange of the H-shaped steel and at a position t/4 away from the outer surface of the flange in the thickness direction of the flangeeHGreater than 355 MPa; tensile strength Rm450-590 MPa, the elongation A is more than 23%, and the low-temperature impact toughness KV2 at-20 ℃ is more than or equal to 120J.
3. The method for producing the ultra-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness as claimed in claim 1 or 2, wherein the method comprises the following steps: the process flow comprises blank heating, cogging rolling, universal finish rolling and cooling;
heating the blank: in the step, the temperature of a heating section of the beam blank in a heating furnace is 1200-1230 ℃, the heating time is 30-40 min, the temperature of a soaking section is 1210-1225 ℃, the soaking time is 50-60min, and the time in the heating furnace is 110-130 min;
cogging and rolling: the step is carried out in two stages, wherein the rolling temperature of the cogging rolling stage 1 is 1100-1150 ℃, and the accumulated deformation of the flange is 8-10%; the rolling temperature of the cogging rolling 2 stage is 1000-1100 ℃, and the accumulated deformation of the flange is 10-20%;
universal finish rolling: the step is carried out in two stages, the rolling temperature of the high-temperature rolling stage is 930-980 ℃, and the accumulated deformation of the flange is more than 40%; in the low-temperature rolling stage, the rolled piece is heated to below 900 ℃, the deformation is finished, the residual compression is completed, and the accumulated deformation of the flange is more than 20%;
and (3) cooling: two-stage cooling is adopted, wherein the first stage is rapid cooling, the cooling speed is 15-30 ℃/s, and the final cooling temperature of the surface of a rolled piece is 600-650 ℃; and air cooling in the second stage, wherein the rolled piece enters a cooling bed for air cooling to room temperature.
4. The production method of the super-thick Q355-grade good low-temperature-toughness hot-rolled H-shaped steel according to claim 3, characterized by comprising the following steps of: the process flow also comprises a step of continuous casting of the special-shaped blank before the blank is heated, wherein in the step, the pressure of cooling water of a crystallizer is 0.7-2.0 MPa, the pressure of secondary cooling water is 1.0-3.0 MPa, and the pulling speed is 0.20-0.60 m/min.
5. The method for producing the ultra-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness as claimed in claim 3 or 4, wherein the method comprises the following steps: the process flow comprises molten iron pretreatment → converter smelting → LF refining → RH refining → beam blank continuous casting → blank heating → cogging rolling 1 → cogging rolling 2 → universal finishing rolling → rapid cooling → cold bed → straightening → cutting and sizing → inspection → packaging and warehousing.
6. The method for producing the super-thick Q355-grade good low-temperature-toughness hot-rolled H-shaped steel according to claim 5, wherein the method comprises the following steps: the yield strength R is at a position b/6 away from the end part of the flange in the width direction of the flange of the H-shaped steel and at a position t/4 away from the outer surface of the flange in the thickness direction of the flangeeH375 to 445 MPa; the tensile strength Rm is 468-590 MPa, the elongation A is 24-32%, and the low-temperature impact toughness KV2 at-20 ℃ is 128-180J.
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