CN116043116A

CN116043116A - Hot rolled H-shaped steel with good Z-direction performance and yield strength of 450MPa and production method thereof

Info

Publication number: CN116043116A
Application number: CN202310047864.8A
Authority: CN
Inventors: 彭林; 吴湄庄; 沈千成; 单梅; 刘译泽; 赵旭
Original assignee: Maanshan Iron and Steel Co Ltd
Current assignee: Maanshan Iron and Steel Co Ltd
Priority date: 2023-01-31
Filing date: 2023-01-31
Publication date: 2023-05-02
Anticipated expiration: 2043-01-31
Also published as: CN116043116B

Abstract

The invention discloses a hot-rolled H-shaped steel with good Z-direction performance and yield strength of 450MPa grade and a production method thereof, wherein the hot-rolled H-shaped steel comprises the following chemical components in percentage by mass: c:0.15 to 0.18 percent, si:0.30 to 0.50 percent, mn:0.7 to 1.0 percent, P: less than or equal to 0.020%, S: less than or equal to 0.010 percent, nb:0.030 to 0.050 percent, ti:0.010 to 0.020%, ni: 0.10-0.30%, N less than or equal to 0.005%, and the balance Fe and unavoidable impurities, wherein the flange thickness range of the hot rolled H-shaped steel is 40-80 mm, the compression ratio of the blank to the flange thickness direction of the final product is 2-4, the section shrinkage rate in the thickness direction (Z direction) can meet the Z35 requirement specified in standard GB/T5313, and the hot rolled H-shaped steel has good low-temperature impact toughness at-20 ℃.

Description

Hot rolled H-shaped steel with good Z-direction performance and yield strength of 450MPa and production method thereof

Technical Field

The invention belongs to the technical field of H-shaped steel, and particularly relates to hot rolled H-shaped steel with good Z-direction performance and yield strength of 450MPa and a production method thereof.

Background

In recent years, high-rise building steel structures, offshore oil platforms, large-span bridges and similar important building (construction) steel structures in China are vigorously developed. The first heavy hot-rolled H-shaped steel production line in 2020 is formally put into production, and the heavy hot-rolled H-shaped steel is favored by the market because the welding joints are fewer when the heavy hot-rolled H-shaped steel is used as a component. In the production and welding of heavy hot rolled H-section steel, the member is liable to be torn in layers due to the quality of the steel, the welded structure, and the like, which is very disadvantageous for the joint which is pulled in the thickness direction.

Lamellar tearing, a weld defect, causes lamellar tearing failure of the component in the Z-direction, a hazard level well known. On the one hand, there is no sign on the appearance due to the concealment of the occurrence of Z-directed lamellar tearing; even if it is found that the repair is difficult, it is more critical that the lamellar tearing structure is mostly a large thick wall or thick plate structure, so that serious consequences are caused by insufficient Z-directional performance, and therefore, it is very necessary to study the Z-directional performance of the steel.

The most important reason for the insufficient Z-direction performance is that impurities and layering of the impurities are unavoidable in steel smelting, meanwhile, cracks are difficult to avoid in the welding process, and when the steel is subjected to constraint stress and load, the steel is expanded in the thickness direction to separate impurities from metal, so that brittle fracture is formed.

Chinese patent CN113564480a, publication No. 2021, 10 and 29, discloses a heavy hot-rolled H-section steel with Z-direction property and a production method thereof, and specifically discloses the hot-rolled H-section steel comprising the following chemical components: C. si, mn, nb, ti, N, B, als, the balance being iron and unavoidable impurities; the production method comprises the following steps: molten iron pretreatment, converter smelting, argon blowing refining, RH, special-shaped blank full-protection casting, stacking slow cooling, rolling and air cooling after rolling; according to the invention, through reasonable component proportion and process control and through the cogging rolling, universal rolling and air cooling process after rolling, the quantity of second-oriented particles precipitated is regulated and controlled by utilizing a phase change, precipitation and fine crystal combination strengthening mode, and the content of granular bainite after rolling is between 10 and 20 percent, so that the heavy hot rolled H-shaped steel with the flange thickness of less than 80mm has excellent toughness and Z-direction performance, and the Z-direction performance is 65 to 80 percent. The impact energy at-20 ℃ of the hot rolled H-section steel is not mentioned in the patent, and the flange thickness is limited to be below 80 mm.

Chinese patent CN113215495A with publication date of 2021, 5 month and 17 days discloses a method for improving the Z-direction performance of a 50-80mm thick Q390E plate, and specifically discloses the chemical components and weight percentage of the plate: c:0.07-0.10%; mn:1.4-1.50%; si:0.15-0.25%; s is less than or equal to 0.005%; p is less than or equal to 0.015 percent; als:0.020-0.04%; nb:0.025-0.035%; ti:0.035-0.045%; t [ O ] is less than or equal to 20PPM; n is less than or equal to 50PPM; h is less than or equal to 1.5PPM; the thickness range of the plate is 50-80mm; the whole process flow comprises the following steps: molten iron pre-desulfurization treatment, converter, LF+RH refining, slab thickness of 250mm, heating, rolling and cooling control, and cold piling; the converter tapping slag washing process is adopted, and high-alkalinity synthetic slag is used, wherein the synthetic slag comprises the following components: caO is more than or equal to 60% and less than or equal to 70%, baO is 15-20%, siO2 is more than or equal to 0 and less than or equal to 3.0%, al2O3 is more than or equal to 0 and less than or equal to 4.5%, na2O is more than or equal to 2.0 and less than or equal to 4.1%, caF2 is more than or equal to 7.5%, mgO is more than or equal to 4%; the specific chemical components of the covering slag used in the continuous casting process are as follows by weight percent: c4.1-6.5%, caO 25-30%; siO 227-32%; 5-10% of Na 2O; 7-10% of TiC; 23-6% of TiO; f5-8%; 37-15% of B2O; al2O3 is less than or equal to 3 percent; mgO 1-1.5%; mnO is less than or equal to 3 percent; fe2O3 is less than 3%; H2O is less than 0.5%. The invention relates to a thick plate, but hot-rolled H-shaped steel is not extracted, and the thickness is limited to be below 50-80 mm.

The Chinese patent CN111172465A with publication date of 2020, 5 and 19 discloses a steel plate for a low-carbon equivalent large-thickness Q390GJ building structure and a manufacturing method thereof, and specifically discloses the steel plate which comprises the following chemical components in percentage by weight: 0.10% -0.139%, si:0.20 to 0.39 percent of Mn:1.30 to 1.44 percent, P is less than or equal to 0.010 percent, S is less than or equal to 0.003 percent, and Nb:0.020% -0.039%, ti:0.006 to 0.016 percent, 0.01 to 0.04 percent of Al and Ceq:0.32 to 0.38, and the balance of iron and unavoidable impurities; the microstructure of the steel plate is mainly a fine polygonal ferrite and bainite structure, wherein the volume percentage of the polygonal ferrite is 25% -40%, the maximum thickness of the steel plate is 120mm, the yield strength is more than or equal to 390MPa, the tensile strength is 550MPa, the elongation after fracture is more than or equal to 28%, the yield ratio is less than or equal to 0.77, the Z-direction performance in the thickness direction is more than or equal to 60%, and the impact power at minus 40 ℃ is more than or equal to 200J. The steel plate of the product produced according to the chemical components and the production process requirements of the invention has the advantages of large thickness, high strength and toughness, high plasticity, low yield ratio, excellent welding performance and lamellar tearing resistance. The invention relates to a thick plate, and hot rolled H-shaped steel is not extracted.

The Chinese patent CN110983204B with publication date of 2020, 4 and 10 discloses a steel plate for engineering machinery and a preparation method thereof, and specifically discloses the steel plate comprising the following chemical components in percentage by weight: c:0.10% -0.17%, si:0.15% -0.40%, mn:1.10 to 1.70 percent, S is less than or equal to 0.015 percent, P is less than or equal to 0.025 percent, nb is less than or equal to 0.6 percent, V is less than or equal to 0.1 percent, ti:0.005-0.035%, ni:0.15-0.5%, cr:0.10% -0.5%, mo: 0.20-0.50%, B is less than or equal to 0.0025%, and the balance is Fe and trace impurities. According to the invention, through the composite addition of Nb, V, ti, cr, mo and other alloy elements and the reasonable design of Si and Mn contents, the steel plate for the large-thickness high-strength engineering machinery with the thickness of 100-110mm is obtained under the condition of low compression ratio through the implementation of 4300mm double-stand rolling, quenching and tempering and other process technologies. The tensile strength of the steel plate, the impact energy at the low temperature of minus 20 ℃ and the Z-direction performance are stable, and the requirement of mass production of large-thickness high-strength engineering machinery steel under the condition of low compression ratio is met. However, the invention adopts precious metals such as V, ni, increases the alloy cost, and the thickness is limited to 100-110mm, and the rolling of the plates is involved.

Compared with thick plates, the deformation of the hot rolled H-shaped steel is carried out in a hole type, the rolling temperature of the thick and heavy hot rolled H-shaped steel is high, the rolling temperature is influenced by the capability of blanks and rolling mills, the total compression ratio and the single pass compression ratio are limited, the deformation and permeation of the flange of the product in the thickness direction are difficult, the production process adjusting window is narrow, and particularly, the high-strength performance is also satisfied while the excellent low-temperature toughness and lamellar tearing resistance are satisfied.

Chinese patent CN110527915A with publication date of 2019, 12 month and 3 days discloses 460 MPa-grade hot-rolled H-shaped steel and a production method thereof, and specifically discloses the hot-rolled H-shaped steel which comprises the following chemical components in percentage by weight: 0.08 to 0.11 percent of C, 0.20 to 0.30 percent of Si, 0.50 to 0.70 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, 1.30 to 1.80 percent of Cr, 0.60 to 0.90 percent of Ni, 0.30 to 0.40 percent of Cu, 0.15 to 0.25 percent of Mo, 0.030 to 0.050 percent of Nb, 0.060 to 0.100 percent of V, 0.015 to 0.030 percent of Al, and the balance of Fe and unavoidable impurities. The production method comprises the steps of blank heating, cogging and rolling, first-stage and second-stage universal rolling and air cooling. The invention can obtain the hot rolled H-shaped steel with 460MPa grade yield strength and excellent toughness, Z-direction performance, fire resistance, corrosion resistance and earthquake resistance through reasonable component proportion and process control. The patent adds noble metals such as noble metal V, ni with higher content, has higher production cost, and the thickness of the hot rolled H-shaped steel is 20-50mm.

Disclosure of Invention

The invention aims to provide hot rolled H-shaped steel with good Z-direction performance and yield strength of 450MPa grade and a production method thereof, wherein the thickness range of a flange of the hot rolled H-shaped steel is 40mm-80mm, the compression ratio of a blank to the thickness direction of a flange of a final product is 2-4, the shrinkage rate of a cross section in the thickness direction (Z-direction) can meet the requirement of Z35 specified in standard GB/T5313, and meanwhile, the hot rolled H-shaped steel has good low-temperature impact toughness at-20 ℃.

In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:

a hot rolled H-shaped steel with good Z-direction performance and yield strength of 450MPa level comprises the following chemical components in percentage by mass: c:0.15 to 0.18 percent, si:0.30 to 0.50 percent, mn:0.7 to 1.0 percent, P: less than or equal to 0.020%, S: less than or equal to 0.010 percent, nb:0.030 to 0.050 percent, ti:0.010 to 0.020%, ni:0.10 to 0.30 percent, N is less than or equal to 0.005 percent, and the balance is Fe and unavoidable impurities.

The flange metallographic structure of the hot rolled H-shaped steel with good Z-direction performance and the yield strength of 450MPa grade is ferrite and bainite, the area ratio of the bainite is 20-30%, the grain size grade of the ferrite is more than grade 9, and the thickness of the bainite layer is more than or equal to 1/4 of the thickness of the flange.

The yield strength of the hot rolled H-shaped steel with the yield strength of 450MPa grade and good Z-direction performance is more than or equal to 4500MPa, the tensile strength is more than or equal to 550MPa, the elongation A is more than or equal to 21%, the longitudinal V-shaped impact energy KV2 at minus 20 ℃ is more than or equal to 100J, and Z is more than or equal to 52%.

The production method of the hot rolled H-shaped steel with the yield strength of 450MPa and good Z-direction performance comprises the following steps: molten iron pretreatment, converter smelting, argon blowing refining, LF refining, RH or VD vacuum treatment, special-shaped blank full-protection casting, blank heating, rolling and controlled cooling after rolling; the compression ratio of the blank to the flange thickness direction of the final product is 2-4.

In the LF refining step, the refining time is prolonged by 15-20 min so as to fully maintain white slag. The temperature before argon blowing is more than or equal to 1550 ℃, the time of argon blowing each time is more than or equal to 1min, and various inclusions in molten steel are promoted to fully float upwards. The N content is controlled below 0.005%, so that the concentration product of nitrogen and titanium is ensured below the equilibrium concentration product, and the precipitation of TiN is reduced. The solubility product of TiN is small, polygonal TiN particles which are precipitated in liquid state can be frequently seen in molten steel, the size is in a micron level, the precipitated TiN can remain in the subsequent heating and rolling processes, so that the performance of steel is adversely affected, and the precipitation fraction of the TiN particles is controlled to be below 0.01% by strictly controlling the N content to be below 0.005%. And at the same time, the content of each alloy element is further controlled at the stage so as to meet the requirements.

In the RH or VD vacuum treatment step, the volume fraction of hydrogen in molten steel after RH or VD is controlled to be less than or equal to 1.5X10 ^-6 The method comprises the steps of carrying out a first treatment on the surface of the Further, by pre-baking the dipleg for 2-10 min, the insertion depth of the immersion tube is more than or equal to 400mm, the vacuum degree is maintained below 100Pa, the holding time is controlled to be more than or equal to 10min, and the volume fraction of hydrogen in molten steel after RH or VD is controlled to be less than or equal to 1.5X10 ^-6 If the volume fraction of hydrogen exceeds this range, white spots appear in the steel during drawing, and the white spots have a diameter exceeding 0.5mm and an area ratio exceeding 0.25%, which seriously affect the lamellar tearing resistance of the steel. Meanwhile, calcification treatment is carried out at the stage, the mass percentage value of Ca/S is controlled to be 1.2-2.0, sulfide inclusions are ensured to be modified into spheres, and because the affinity of Ca and S is very strong, plastic MnS inclusions in steel can be converted into non-plastic spheres of CaS inclusions, or double-phase inclusions formed by high-calcium aluminate with high sulfur capacity and CaS are not easy to elongate during rolling, and the properties of steel are improved. The control of the calcium-sulfur ratio (Ca/S) is very important in the calcium treatment, when the Ca/S is too small, sulfide cannot be fully spheroidized, when the Ca/S is large, coarse spherical and community-shaped inclusions are formed, the cleanliness of molten steel is reduced, the Ca/S is optimally controlled to be 1.2-2.0 according to the actual production, the complete spheroidization rate of the sulfide in the steel reaches more than 98%, the precipitation fraction of the sulfide is controlled to be less than 0.015%, and the size is controlled to be less than 300 nm.

In the step of fully-protected casting of the special-shaped blank, a low-temperature fast casting process is adopted, the superheat degree of molten steel is controlled at 20-35 ℃, and the segregation can be effectively inhibited by low superheat degree casting. Argon seal protection is adopted between the steel tapping hole and the middle pouring pipe to prevent secondary oxidation, the blank pulling speed is 0.45-1.0 m/min, and the primary cooling crystallization water flow is 100-300 m ³ And/h, the specific water quantity of secondary cooling is 0.55-0.75L/kg, and the solidification speed of the casting blank is improved, so that excessive growth of niobium and titanium carbonitride precipitates and generation of large-particle inclusions can be effectively avoided. The aim of the stage is to ensure that the volume fraction of TiN, nbC, ti +Nb composite particles precipitated in the casting blank after the continuous casting is finished is 0.050-0.10%, and the average diameter of corresponding second phase particles is 50-100 nm.

In the blank heating step, a casting blank enters a heating furnace, is heated to 1200-1250 ℃ by the heating furnace, and is kept for 150-180 min, so that the alloy elements are ensured to be fully dissolved in solid, and meanwhile, over-burning and excessive coarsening of austenite grains are avoided.

In the rolling step, rolling comprises a rough rolling stage and a finish rolling stage; the total rolling reduction of the blank in the rough rolling stage is controlled to be 40% -50%; the finish rolling stage adopts two stages to control rolling, the pass reduction rate of the first stage is controlled to be 5% -10%, the stage is in the range of the recrystallization temperature of the austenite part, and larger deformation, uneven austenite grains and reduced performance of the final product are avoided as much as possible; the second stage has pass reduction rate controlled in 5-15%, and the second stage has pass reduction rate reduced with temperature decrease, and the second stage has great deformation in the non-re-crystallizing temperature range for forming ferrite grains with deformation zone and austenite grain boundary to form nuclei.

The initial rolling temperature in the rough rolling stage is controlled to 1150-1180 ℃ and the final rolling temperature is controlled to be more than 1000 ℃.

In the rough rolling stage, when the rolling temperature is less than or equal to 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled to be less than or equal to 20 percent and the rolling speed is controlled to be less than or equal to 1.5m/s and less than or equal to 2.0m/s;

when the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is less than or equal to 25% and the rolling speed is less than 1.0m/s and less than or equal to 1.5m/s;

when the rolling temperature is less than 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled to be less than or equal to 30 percent, and the rolling speed is controlled to be less than or equal to 0.5m/s and less than or equal to 1.0m/s.

The rough rolling stage is in the austenite recrystallization temperature range, the pass reduction rate and rolling speed in different temperature ranges are controlled to realize the high-temperature low-speed large-reduction process, ensure that deformation fully penetrates into the center part in the thickness direction, enable austenite grains to be uniform through repeated deformation recrystallization, ensure that the austenite recrystallization percentage of each pass reaches more than 50%, and enable austenite grains to be continuously refined through larger rolling deformation and repeated austenite recrystallization, so that the ferrite grain size of the final product reaches 9.0 grade or more, and meet the final comprehensive mechanical property requirement of the product.

In the finish rolling stage, the initial rolling temperature is controlled to 980-1000 ℃ and the final rolling temperature is controlled to over 960 ℃; the second stage is to control the initial rolling temperature to 930-950 deg.c and the final rolling temperature to 830-850 deg.c.

In the post-rolling cooling control step, an intercooling process is adopted, the cooling speed is controlled to be 6-10 ℃/s, and the rolled piece is ensured to be subjected to off-line air cooling within the range of 650-750 ℃. The aim of adopting the intercooling process is to reduce the residence time from the rolling to the phase transformation as much as possible, inhibit the growth of austenite grains before transformation, control the state of austenite grains after thermal deformation, fix dislocation caused by deformation, increase supercooling degree, reduce the phase transformation temperature, further refine ferrite and bainite tissues, and simultaneously ensure that the stress of the rolled piece is fully released during the slow cooling in the lower line. Because the product is thicker, the tissue uniformity in the thickness direction is difficult to control, the cooling speed cannot be too high, the performance difference in the thickness direction is too high easily caused by the excessive cooling speed, and the strength and the toughness of the product can be improved by adopting the cooling process under the condition that the tissue difference in the thickness direction of the product is not very high.

The design idea of the invention is as follows:

the chemical components of the invention adopt the design thought of Nb/Ti/Ni microalloying components, and the content of impurity elements such as P, S is strictly controlled, and the content of each component is controlled as follows:

c:0.15 to 0.18 percent, C is taken as a basic element in steel, plays a very important role in improving the strength of the steel, and in order to obtain higher strength and reduce the difficulty of steel-making and decrystallization, the lower limit value is set to 0.15 percent, the excessive C content seriously worsens the plasticity, the toughness and the weldability of the steel, and the upper limit is set to 0.18 percent.

Si:0.30 to 0.50 percent of Si with proper content can play a strong solid solution strengthening role, si is an important reduction and deoxidization element in the steelmaking process, the lower limit value is set to be 0.30 percent, but the Si content cannot be too high, researches show that the 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 influenced, and the upper limit value is set to be 0.50 percent.

Mn:0.7 to 1.0%, mn as a strengthening element in steel can improve the strength and hardenability of steel, and in order to ensure the strength of steel, the lower limit value is set to 0.7%, but the Mn content cannot be excessively high, which leads to a significant increase in the possibility of casting blank segregation, adversely affecting the formability of steel, and the upper limit value is set to 1.0%.

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 0.010 percent.

Nb: 0.030-0.050%, nb is a strong carbon and nitrogen compound forming element, strength of steel is mainly improved by refining grains, the solid-dissolved Nb plays a role in dragging a solute to the growth of austenite grains, austenite is organized to grow, meanwhile, undissolved Nb and C, N elements form Nb (C, N) compounds to be remarkably pinned at austenite grain boundaries, austenite grains are refined, and the structure of a final product is refined, in order to improve strength and plasticity of the steel, the lower limit value is set to 0.030%, but Nb content is too high, cracks are easily caused on the surface of a casting blank, surface quality of the final product is affected, and the upper limit value is set to 0.050%.

Ti: 0.010-0.020%. Ti is a main element for forming TiN, the TiN is a high-temperature stable compound, and austenite grains in a high-temperature area are pinned by the TiN to prevent the austenite grains from growing so as to refine the austenite grains in the heating and rolling processes. To achieve this effect, the lower line of Ti content was set to 0.010%; when the Ti content is too high, the Ti is combined with the redundant N element in the molten steel, so that the Ti rapidly grows, the TiN particles with coarse size cannot play a role in refining grains in the steel, but can become a source of cracks in the steel, and the upper limit of the Ti is set to be 0.020%.

Ni:0.10 to 0.30 percent, ni can be continuously dissolved in steel, dislocation movement resistance is reduced, plasticity and toughness of the steel can be obviously improved, compactness and stability of a rust layer on the surface of the steel can be improved, surface quality of a product can be effectively improved, in order to obtain good low-temperature toughness and product surface quality, the lower limit value is set to be 0.10 percent, and the upper limit value is set to be 0.30 percent in consideration of higher cost.

N: less than or equal to 0.005%, and trace N can form a compound with V to be separated out, so that the strength, the plasticity and the toughness of the steel can be obviously improved. N2 is formed in the steel grade when the content of N is too high, and pores are easily formed in the steel during solidification, and the pores are the cracking source of cracks. At the same time, too high N may precipitate in grain boundaries or crystals with Fe to form Fe4N, which may cause embrittlement of the metal, and adversely affect low-temperature toughness, and the upper limit is set to 0.005%.

When the specification and the size of the blank are fixed, compared with the hot rolled H-shaped steel with the thin flange thickness, the hot rolled H-shaped steel with the thick flange thickness has smaller rolling reduction rate in the flange thickness direction in the rolling process, is more difficult to deform and permeate, and is difficult to meet the requirement of the patent in the traditional smelting and rolling process. The design concept of the invention mainly adopts Nb/Ti/Ni microalloying, firstly reduces the precipitation of TiN through a standard smelting process, ensures sulfide inclusion to be modified into a sphere, refines an as-cast structure, inhibits the segregation, and avoids excessive growth of niobium and titanium carbonitride precipitates and generation of large-particle inclusions; ni is utilized to enlarge the austenitic region of steel, ferrite grains are thinned, and low-temperature toughness is improved; and secondly, a standard rolling and cooling control process is adopted to improve the internal structure of the steel ingot, promote the segregation of central carbon and manganese to be fully diffused, optimize the steel ingot heating system and ensure that most of precipitate particles are fully dissolved under the condition of high soaking temperature. Adopting two-stage controlled rolling, adopting a high-temperature low-speed high-pressure process in the austenite recrystallization stage to fully crush crystal grains at the core of the steel ingot, and welding the loose core of the steel ingot, thereby remarkably improving the density of internal tissues; the rolling reduction rate of austenite in the unrecrystallized stage is reasonably distributed so as to increase the deformation zone and the deformation-induced precipitation effect, so that fine grains are obtained, and the toughness of the steel is improved; after rolling, controlling weak cooling to fully refine ferrite grains and lighten banded tissues; and after rolling, the wire is taken off and slowly cooled to ensure that the stress is fully released. Finally, the product with the thickness direction (Z direction) section shrinkage rate reaching the Z35 requirement specified in the standard GB/T5313 is obtained, the flange thickness range of the product is 40 mm-80 mm, and the product meets the yield strength of 450MPa and has the characteristics of good low-temperature impact toughness at-20 ℃.

The flange thickness of the hot rolled H-shaped steel obtained by adopting the technical scheme is 40-80 mm, the microstructure is a ferrite and bainite complex phase structure, the ferrite grain size grade is more than 9 grades, and the bainite layer thickness is more than or equal to 1/4 of the flange thickness. The bainite area ratio is 20-30%, the yield strength of the product is more than or equal to 4500MPa, the tensile strength is more than or equal to 550MPa, the elongation A is more than or equal to 21%, the longitudinal V-shaped impact energy KV2 at minus 20 ℃ is more than or equal to 100J, and Z is more than or equal to 52%, and the product has higher strength, good plasticity, low-temperature toughness and good Z-direction performance.

Compared with the prior art, the invention provides the ultra-thick hot rolled H-shaped steel with good Z-direction performance under the condition of small compression ratio (the compression ratio of the blank to the flange thickness direction of the final product is 2-4) under the condition of comprehensively considering cost and quality, and the ultra-thick hot rolled H-shaped steel and the production method thereof are processed by corresponding smelting and rolling processes, so that the product with the thickness direction (Z-direction) section shrinkage rate reaching the Z35 requirement specified in the standard GB/T5313 is obtained, the flange thickness range of the product is 40-80 mm, and the product meets the yield strength of 450MPa and has the characteristic of good low-temperature impact toughness at-20 ℃.

Drawings

FIG. 1 is a metallographic structure diagram of a hot rolled H-shaped steel in example 1;

FIG. 2 is a schematic view of the internal precipitated phase of a hot rolled H-steel slab in example 1, wherein FIG. B is a partial enlarged view of FIG. A;

FIG. 3 is an EDS diagram of the internal precipitated phase of a hot rolled H-steel slab in example 1.

Detailed Description

The invention provides a hot rolled H-shaped steel with good Z-direction performance and yield strength of 450MPa, which comprises the following chemical components in percentage by mass: c:0.15 to 0.18 percent, si:0.30 to 0.50 percent, mn:0.7 to 1.0 percent, P: less than or equal to 0.020%, S: less than or equal to 0.010 percent, nb:0.030 to 0.050 percent, ti:0.010 to 0.020%, ni:0.10 to 0.30 percent, N is less than or equal to 0.005 percent, and the balance is Fe and unavoidable impurities.

In the LF refining step, the refining time is prolonged by 15-20 min; the temperature before argon blowing is more than or equal to 1550 ℃, and the time for each argon blowing is more than or equal to 1min; the N content is controlled below 0.005%.

In the RH or VD vacuum treatment step, the immersion tube is baked for 2-10 min in advance, the insertion depth of the immersion tube is more than or equal to 400mm, the vacuum degree is maintained below 100Pa, the holding time is controlled to be more than or equal to 10min, and the volume fraction of hydrogen in molten steel after RH or VD is ensured to be less than or equal to 1.5X10 ^-6 . And simultaneously calcification treatment is carried out at the stage, and Ca/S is controlled to be between 1.2 and 2.0.

In the special-shaped blank full-protection casting step, a low-temperature quick casting technology is adopted, the superheat degree of molten steel is controlled at 20-35 ℃, the blank pulling speed is 0.45-1.0 m/min, and the primary cooling crystallization water flow is 100-300 m ³ And/h, the specific water quantity of secondary cooling is 0.55-0.75L/kg.

In the blank heating step, a casting blank enters a heating furnace, and is heated to 1200-1250 ℃ through the heating furnace, and the heat preservation time is 150-180 min.

In the rolling step, rolling comprises a rough rolling stage and a finish rolling stage; the total rolling reduction of the blank in the rough rolling stage is controlled to be 40% -50%; the finish rolling stage adopts two stages of controlled rolling, and the pass reduction rate in the first stage is controlled to be 5% -10%; the pass reduction rate in the second stage is controlled to be 5% -15%.

In the rough rolling stage, when the rolling temperature is less than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled to be less than or equal to 20 percent and the rolling speed is controlled to be less than 1.5m/s and less than or equal to 2.0m/s;

In the post-rolling cooling control step, an intercooling process is adopted, the cooling speed is controlled to be 6-10 ℃/s, and the rolled piece is ensured to be subjected to off-line air cooling within the range of 650-750 ℃.

The present invention will be described in more detail with reference to examples.

Example 1

The high-strength hot-rolled H-shaped steel with good Z-direction performance comprises the following chemical components in percentage by mass: c:0.17%, si:0.36%, mn:0.85%, P:0.015%, S:0.008%, nb:0.038%, ti:0.015%, ni:0.23%, N:0.003% of Fe and the balance of unavoidable impurities.

The production method of the ultra-thick hot-rolled H-shaped steel with good Z-direction performance comprises the following steps: molten iron pretreatment, converter smelting, argon blowing refining, LF refining, RH or VD vacuum treatment, special-shaped blank full-protection casting, blank heating, rolling and controlled cooling after rolling, and the method specifically comprises the following steps:

Step one, preprocessing molten iron and smelting the molten iron in a converter;

blowing inert gas argon in the converter smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel;

refining in an LF furnace, wherein the refining time is prolonged by 16min, the temperature is 1565 ℃ before argon blowing, the time for blowing argon each time is 2min, and the TiN precipitation fraction is 0.0075%;

step four, RH or VD vacuum treatment, wherein the immersion tube is baked for 4min in advance, the insertion depth of the immersion tube is 432mm, the vacuum degree is maintained at 92Pa for 12min, and the volume fraction of hydrogen in molten steel is 1.41×10 ^-6 Ca/S was controlled at 1.28. At this time, the complete spheroidization rate of sulfide in the steel was 99.1%, the precipitation fraction of sulfide was 0.012%, and the average size was 246nm.

Fifthly, controlling the superheat degree of molten steel at 27 ℃, adopting argon seal protection between a tapping hole and a middle injection pipe, controlling the blank pulling speed at 0.52m/min, and controlling the flow of primary cooling crystallization waterAt 130m ³ And/h, controlling the specific water quantity of secondary cooling to be 0.65L/kg. At this time, the volume fraction of TiN, nbC, ti +Nb composite particles precipitated in the casting blank was 0.067%, and the average diameter of the corresponding second phase particles was 76nm.

And step six, the casting blank enters a heating furnace, and is heated to 1234 ℃ through the heating furnace, and the heat preservation time is 167min.

Step seven, in the rough rolling stage, the initial rolling temperature is controlled at 1167 ℃, the final rolling temperature is controlled at 1023 ℃, specifically, the rolling temperature is more than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled at 17%, the rolling speed is controlled at 1.6m/s, and the austenite recrystallization percentage is 52%; the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is controlled at 23%, the rolling speed is controlled at 1.3m/s, and the austenite recrystallization percentage is 54%; the rolling temperature is less than or equal to 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled at 26%, the rolling speed is controlled at 0.6m/s, the austenite recrystallization percentage is 52%, and the total reduction rate of the blank in the whole stage is controlled at 43%.

And step eight, a finish rolling stage, wherein the finish rolling adopts two stages to control rolling, the initial rolling temperature of the first stage is controlled at 991 ℃, the final rolling temperature is controlled at 972 ℃, and the pass reduction rate of the stage is controlled at 7%. The second stage is controlled at 942 deg.c, the final rolling temperature at 839 deg.c and the pass reduction rate at 11%.

Step nine, rapidly entering a cooling control device after rolling, controlling the cooling speed at 7.1 ℃/s, and controlling the temperature of the rolled piece at 694 ℃ after starting off-line slow cooling.

The structure of the final product was ferrite + bainite structure, the ferrite grain size was 9.5 grade, the bainite ratio was 26%, and the performance test results of the obtained hot rolled H-steel were shown in table 1.

Example 2

The high-strength hot-rolled H-shaped steel with good Z-direction performance comprises the following components in percentage by mass: c:0.16%, si:0.45%, mn:0.75%, P:0.018%, S:0.005%, nb:0.042%, ti:0.012%, ni:0.18%, N:0.003% of Fe and the balance of unavoidable impurities.

The production method of the ultra-thick hot-rolled H-shaped steel with good Z-direction performance comprises the following process flows: molten iron pretreatment, converter smelting, argon blowing refining, LF refining, RH or VD vacuum treatment, special-shaped blank full-protection casting, blank heating, rolling and controlled cooling after rolling; the method comprises the following steps:

step one, preprocessing molten iron and smelting the molten iron in a converter.

And step two, blowing inert gas argon in the converter smelting process, removing dissolved gas and suspended nonmetallic inclusion of the steel grade, and purifying molten steel.

And thirdly, refining in an LF furnace, wherein the refining time is prolonged by 18min, the temperature before argon is 1557 ℃, the time for blowing argon each time is 2min, and the TiN precipitation fraction is 0.008%.

Step four, RH or VD vacuum treatment, wherein the immersion tube is baked for 6min in advance, the immersion tube is inserted into the vacuum tube for 408mm, the vacuum degree is maintained at 84Pa for 13min, and the volume fraction of hydrogen in molten steel is 1.39X10 ^-6 Ca/S was controlled at 1.56, at which time the complete spheroidization rate of sulfide in the steel was 98.7%, the precipitation fraction of sulfide was 0.009%, and the average size was 232nm.

Fifthly, controlling the superheat degree of molten steel at 23 ℃, adopting argon seal protection between a tapping hole and a middle injection pipe, controlling the blank pulling speed at 0.65m/min, and controlling the flow rate of primary cooling crystallization water at 160m ³ And/h, controlling the specific water quantity of secondary cooling to be 0.58L/kg, wherein the volume fraction of TiN, nbC, ti +Nb composite particles precipitated in the casting blank is 0.083%, and the average diameter of corresponding second-phase particles is 58nm.

And step six, the casting blank enters a heating furnace, and is heated to 1210 ℃ through the heating furnace, and the heat preservation time is 154min.

Step seven, in the rough rolling stage, the initial rolling temperature is controlled to 1153 ℃, the final rolling temperature is controlled to 1008 ℃, specifically, the rolling temperature is more than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled to 16%, the rolling speed is controlled to 1.9m/s, and the austenite recrystallization percentage is 56%; the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is controlled to be 24%, the rolling speed is controlled to be 1.1m/s, and the austenite recrystallization percentage is 60%; the rolling temperature is less than or equal to 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled at 27%, the rolling speed is controlled at 0.7m/s, the austenite recrystallization percentage is 52%, and the total reduction rate of the blank in the whole stage is controlled at 48%.

And step eight, a finish rolling stage, wherein the finish rolling adopts two stages to control rolling, the initial rolling temperature of the first stage is controlled to be 985 ℃, the final rolling temperature is controlled to be 962 ℃, and the pass reduction rate of the first stage is controlled to be 6%. The second stage is controlled at 937 ℃, the final rolling temperature is controlled at 842 ℃, and the pass reduction is controlled at 8%.

And step nine, rapidly entering a cooling control device after rolling, wherein the cooling speed is controlled to be 6.6 ℃/s, and the rolling piece is started to be cooled off line and slowly to be controlled to be 7366 ℃.

The structure of the final product was ferrite + bainite structure, the ferrite grain size was 9.0 grade, the bainite ratio was 23%, and the performance test results of the obtained hot rolled H-steel were shown in table 1.

Example 3

The high-strength hot-rolled H-shaped steel with good Z-direction performance comprises the following components in percentage by mass: c:0.15%, si:0.32%, mn:0.9%, P:0.013%, S:0.007%, nb:0.040%, ti:0.016%, ni:0.25%, N:0.005% of Fe and the balance of unavoidable impurities.

And thirdly, refining in an LF furnace, wherein the refining time is prolonged by 15min, the temperature before argon is 1560 ℃, the time for blowing argon each time is 2min, and the TiN precipitation fraction is 0.006%.

Step four, RH or VD vacuum treatment, wherein the immersion tube is baked for 2min in advance, the immersion tube is inserted into the depth of 410mm, the vacuum degree is maintained at 67Pa for 11min, and the volume fraction of hydrogen in molten steel is 1.29×10 ^-6 Ca/S is controlled at 1.86, at which time the steel is sulfidedThe complete spheroidization rate was 99.3%, the precipitation fraction of sulfide was 0.012%, and the average size was 195nm.

Fifthly, controlling the superheat degree of molten steel at 33 ℃, adopting argon seal protection between a tapping hole and a middle injection pipe, controlling the blank pulling speed at 0.85m/min, and controlling the flow rate of primary cooling crystallization water at 270m ³ And/h, controlling the specific water quantity of secondary cooling to be 0.73L/kg, wherein the volume fraction of TiN, nbC, ti +Nb composite particles precipitated in the casting blank is 0.074%, and the average diameter of corresponding second-phase particles is 83nm.

Step six, the casting blank enters a heating furnace, and is heated to 1229 ℃ through the heating furnace, and the heat preservation time is 176min.

Step seven, in the rough rolling stage, the initial rolling temperature is controlled to 1176 ℃, the final rolling temperature is controlled to 1025 ℃, specifically, the rolling temperature is more than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled to 15%, the rolling speed is controlled to 1.5m/s, and the austenite recrystallization percentage is 53%; the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is controlled to 25%, the rolling speed is controlled to 1.5m/s, and the austenite recrystallization percentage is 51%; the rolling temperature is less than or equal to 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled to be 30%, the rolling speed is controlled to be 1.0m/s, the austenite recrystallization percentage is 57%, and the total reduction rate of the blank in the whole stage is controlled to be 47%.

And step eight, a finish rolling stage, wherein the finish rolling adopts two stages to control rolling, the initial rolling temperature of the first stage is controlled to be 986 ℃, the final rolling temperature is controlled to be 963 ℃, and the pass reduction rate of the stage is controlled to be 10%. The second stage is controlled at 938 ℃, the final rolling temperature is controlled at 837 ℃, and the pass reduction is controlled at 14%.

Step nine, rapidly entering a cooling control device after rolling, controlling the cooling speed at 8.8 ℃/s, and controlling the initial off-line slow cooling of the rolled piece at 663 ℃.

The structure of the final product was ferrite + bainite structure, the ferrite grain size was 10.0 grade, the bainite ratio was 29%, and the performance test results of the obtained hot rolled H-steel were shown in table 1.

Example 4

The high-strength hot-rolled H-shaped steel with good Z-direction performance comprises the following components in percentage by mass: c:0.17%, si:0.37%, mn:0.87%, P:0.009%, S:0.004%, nb:0.047%, ti:0.019%, ni:0.19%, N:0.004%, and the balance of Fe and unavoidable impurities.

And thirdly, refining in an LF furnace, wherein the refining time is prolonged by 20min, the temperature before argon is 1571 ℃, the time for blowing argon each time is 2min, and the TiN precipitation fraction is 0.0078%.

Step four, RH or VD vacuum treatment, wherein the immersion tube is baked for 7min in advance, the insertion depth of the immersion tube is 423mm, the vacuum degree is maintained at 50Pa for 10min, and the volume fraction of hydrogen in molten steel is 1.12X10 ^-6 Ca/S was controlled at 1.65, at which time the complete spheroidization rate of sulfide in the steel was 98.5%, the precipitation fraction of sulfide was 0.014%, and the average size was 213nm.

Fifthly, controlling the superheat degree of molten steel at 22 ℃, adopting argon seal protection between a steel tapping hole and a middle injection pipe, controlling the blank pulling speed at 0.72m/min, and controlling the flow rate of primary cooling crystallization water at 270m ³ And/h, controlling the specific water quantity of secondary cooling to be 0.69L/kg, wherein the volume fraction of TiN, nbC, ti +Nb composite particles precipitated in the casting blank is 0.089%, and the average diameter of corresponding second-phase particles is 92nm.

Step six, the casting blank enters a heating furnace, and is heated to 1218 ℃ through the heating furnace, and the heat preservation time is 173min.

Step seven, in the rough rolling stage, the initial rolling temperature is controlled to 1171 ℃, the final rolling temperature is controlled to 1008 ℃, specifically, the rolling temperature is more than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled to 19%, the rolling speed is controlled to 1.8m/s, and the austenite recrystallization percentage is 59%; the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is controlled at 21%, the rolling speed is controlled at 1.1m/s, and the austenite recrystallization percentage is 63%; the rolling temperature is less than or equal to 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled to 29%, the rolling speed is controlled to 0.7m/s, the austenite recrystallization percentage is 52%, and the total reduction rate of the blank in the whole stage is controlled to 46%.

And step eight, a finish rolling stage, wherein the finish rolling adopts two stages to control rolling, the initial rolling temperature of the first stage is controlled to be 987 ℃, the final rolling temperature is controlled to be 969 ℃, and the pass reduction rate of the stage is controlled to be 8%. The second stage is controlled to be 935 ℃, the final rolling temperature is controlled to be 836 ℃ and the pass reduction is controlled to be 6%.

Step nine, rapidly entering a cooling control device after rolling, controlling the cooling speed to be 10.0 ℃/s, and controlling the initial off-line slow cooling of the rolled piece to be 652 ℃.

The structure of the final product was ferrite + bainite structure, the ferrite grain size was 10.0 grade, the bainite ratio was 28%, and the performance test results of the obtained hot rolled H-steel were shown in table 1.

Example 5

The high-strength hot-rolled H-shaped steel with good Z-direction performance comprises the following components in percentage by mass: c:0.18%, si:0.43%, mn:0.72%, P:0.018%, S:0.009%, nb:0.046%, ti:0.013%, ni:0.13%, N:0.004%, and the balance of Fe and unavoidable impurities.

And thirdly, refining in an LF furnace, wherein the refining time is prolonged by 19min, the temperature before argon is 1562 ℃, the time for blowing argon each time is 2min, and the TiN precipitation fraction is 0.0092%.

Step four, RH or VD vacuum treatment, wherein the immersion tube is baked for 3min in advance, the immersion tube is inserted into the vacuum tube for 406mm, the vacuum degree is maintained at 93Pa for 11min, and the volume fraction of hydrogen in molten steel is 1.10X10 ^-6 Ca/S was controlled at 1.92, at which time the complete spheroidization rate of sulfide in the steel was 99.3%, the precipitation fraction of sulfide was 0.010%, and the average size was 230nm.

Fifthly, controlling the superheat degree of molten steel at 25 ℃, adopting argon seal protection between a tapping hole and a middle injection pipe, controlling the blank pulling speed at 0.76m/min, and controlling the flow rate of primary cooling crystallization water at 260m ³ And/h, controlling the specific water quantity of secondary cooling to be 0.73L/kg, wherein the volume fraction of TiN, nbC, ti +Nb composite particles precipitated in the casting blank is 0.068%, and the average diameter of corresponding second-phase particles is 88nm.

And step six, the casting blank enters a heating furnace, and is heated to 1240 ℃ through the heating furnace, and the heat preservation time is 160min.

Step seven, in the rough rolling stage, the initial rolling temperature is controlled at 1170 ℃, the final rolling temperature is controlled at 1011 ℃, specifically, the rolling temperature is more than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled at 18%, the rolling speed is controlled at 1.8m/s, and the austenite recrystallization percentage is 55%; the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is controlled at 23%, the rolling speed is controlled at 1.3m/s, and the austenite recrystallization percentage is 53%; the rolling temperature is less than or equal to 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled at 27%, the rolling speed is controlled at 0.8m/s, the austenite recrystallization percentage is 51%, and the total reduction rate of the blank in the whole stage is controlled at 44%.

And step eight, a finish rolling stage, wherein the finish rolling adopts two stages to control rolling, the initial rolling temperature of the first stage is controlled to 996 ℃, the final rolling temperature is controlled to 970 ℃, and the pass reduction rate of the first stage is controlled to 7%. The second stage is controlled at 942 deg.c, the final rolling temperature at 839 deg.c and the pass reduction rate at 8%.

And step nine, rapidly entering a cooling control device after rolling, wherein the cooling speed is controlled at 7.6 ℃/s, and the rolling piece is controlled at 702 ℃ after beginning to be off-line and slowly cooled.

The structure of the final product was ferrite + bainite structure, the ferrite grain size was 9.0 grade, the bainite ratio was 22%, and the performance test results of the obtained hot rolled H-steel were shown in table 1.

Comparative example 1

The high-strength hot-rolled H-shaped steel with good Z-direction performance comprises the following components in percentage by mass: c:0.08%, si:0.43%, mn:1.36%, P:0.017%, S:0.025%, nb:0.012%, ti:0.014%, ni:0.01%, N:0.035%, and the balance of Fe and unavoidable impurities.

And thirdly, refining in an LF furnace, wherein the refining time is prolonged by 19min, the temperature before argon is 1558 ℃, the time for blowing argon each time is 2min, and the TiN precipitation fraction is 0.10%.

Step four, RH or VD vacuum treatment, wherein the immersion tube is baked for 3min in advance, the immersion tube is inserted into the vacuum tube for 406mm, the vacuum degree is maintained at 93Pa for 11min, and the volume fraction of hydrogen in molten steel is 1.11X10 ^-6 Ca/S was controlled at 1.92, at which time the complete spheroidization rate of sulfide in the steel was 99.1%, the precipitation fraction of sulfide was 0.023%, and the average size was 386nm.

Fifthly, controlling the superheat degree of molten steel at 25 ℃, adopting argon seal protection between a tapping hole and a middle injection pipe, controlling the blank pulling speed at 0.76m/min, and controlling the flow rate of primary cooling crystallization water at 260m ³ And/h, controlling the specific water quantity of secondary cooling to be 0.73L/kg, wherein the volume fraction of TiN, nbC, ti +Nb composite particles precipitated in the casting blank is 0.196%, and the average diameter of corresponding second-phase particles is 102nm.

Step seven, in the rough rolling stage, the initial rolling temperature is controlled at 1170 ℃, the final rolling temperature is controlled at 1009 ℃, specifically, the rolling temperature is more than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction is controlled at 18%, the rolling speed is controlled at 1.8m/s, and the austenite recrystallization percentage is 54%; the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is controlled at 23%, the rolling speed is controlled at 1.3m/s, and the austenite recrystallization percentage is 53%; the rolling temperature is less than or equal to 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled at 27%, the rolling speed is controlled at 0.8m/s, the austenite recrystallization percentage is 52%, and the total reduction rate of the blank in the whole stage is controlled at 44%.

And step eight, a finish rolling stage, wherein the finish rolling adopts two stages of controlled rolling, the initial rolling temperature of the first stage is controlled at 990 ℃, the final rolling temperature is controlled at 968 ℃, and the pass reduction rate of the stage is controlled at 7%. The second stage is controlled at 938 ℃, the final rolling temperature is controlled at 835 ℃, and the pass reduction is controlled at 8%.

And step nine, rapidly entering a cooling control device after rolling, wherein the cooling speed is controlled at 7.6 ℃/s, and the rolling piece is controlled at 713 ℃ after beginning to be off-line and slowly cooled.

The structure of the final product was ferrite + bainite structure, the ferrite grain size was 8.5 grade, the bainite ratio was 10%, and the performance test results of the obtained hot rolled H-steel were shown in table 1.

Comparative example 2

The high-strength hot-rolled H-shaped steel with good Z-direction performance comprises the following components in percentage by mass: c:0.17%, si:0.45%, mn:0.81%, P:0.016%, S:0.007%, nb:0.042%, ti:0.012%, ni:0.23%, N:0.004%, and the balance of Fe and unavoidable impurities.

And thirdly, refining in an LF furnace, wherein the refining time is prolonged by 19min, the temperature before argon is 1553 ℃, the time for blowing argon each time is 2min, and the TiN precipitation fraction is 0.0089%.

Step four, RH or VD vacuum treatment, wherein the immersion tube is baked for 1min in advance, the immersion tube is inserted into the vacuum tube for 380mm, the vacuum degree is maintained at 120Pa for 4min, and the volume fraction of hydrogen in molten steel is 3.5X10 ^-6 Ca/S was controlled at 5, at which time the complete spheroidization rate of sulfide in the steel was 46%, the precipitation fraction of sulfide was 0.21%, and the average size was 800nm.

Controlling the superheat degree of molten steel at 25 ℃, adopting argon seal protection between a steel outlet and a middle injection pipe, controlling the blank pulling speed at 0.76m/min, controlling the flow rate of primary cooling crystallization water at 260m3/h, controlling the specific water quantity of secondary cooling at 0.73L/kg, and at the moment, the volume fraction of TiN, nbC, ti +Nb composite particles precipitated in the casting blank is 0.071 percent, and the average diameter of corresponding second phase particles is 91nm.

Step seven, in the rough rolling stage, the initial rolling temperature is controlled at 1170 ℃, the final rolling temperature is controlled at 1015 ℃, specifically, the rolling temperature is more than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled at 18%, the rolling speed is controlled at 1.8m/s, and the austenite recrystallization percentage is 54%; the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is controlled at 23%, the rolling speed is controlled at 1.3m/s, and the austenite recrystallization percentage is 54%; the rolling temperature is less than or equal to 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled at 27%, the rolling speed is controlled at 0.8m/s, the austenite recrystallization percentage is 53%, and the total reduction rate of the blank in the whole stage is controlled at 44%.

And step eight, a finish rolling stage, wherein the finish rolling adopts two stages to control rolling, the initial rolling temperature of the first stage is controlled at 995 ℃, the final rolling temperature is controlled at 972 ℃, and the pass reduction rate of the stage is controlled at 7%. The second stage is controlled at 940 deg.c, 841 deg.c and 8% pass reduction.

Step nine, rapidly entering a cooling control device after rolling, controlling the cooling speed at 7.6 ℃/s, and controlling the temperature of the rolled piece at 696 ℃ after starting off-line slow cooling.

The structure of the final product is ferrite and bainite structure, the ferrite grain size is 9.0 grade, the bainite accounts for 18%, white spots appear in the steel in the drawing process, the diameter of the white spots exceeds 0.5mm, and the area accounts for 0.75%. The results of the performance test of the obtained hot rolled H-steel are shown in Table 1.

Comparative example 3

The high-strength hot-rolled H-shaped steel with good Z-direction performance comprises the following components in percentage by mass: c:0.18%, si:0.47%, mn:0.91%, P:0.018%, S:0.008%, nb:0.038%, ti:0.014%, ni:0.18%, N:0.003% of Fe and the balance of unavoidable impurities.

And thirdly, refining in an LF furnace, wherein the refining time is prolonged by 19min, the temperature before argon is 1560 ℃, the time for blowing argon is 2min each time, and the TiN precipitation fraction is 0.0076%.

Step four, RH or VD vacuum treatment, wherein the immersion tube is baked for 3min in advance, the immersion tube is inserted into the vacuum tube for 406mm, the vacuum degree is maintained at 93Pa for 11min, and the volume fraction of hydrogen in molten steel is 1.09×10 ^-6 Ca/S was controlled at 1.92, at which time the complete spheroidization rate of sulfide in the steel was 99.5%, the precipitation fraction of sulfide was 0.011%, and the average size was 216nm.

Fifthly, controlling the superheat degree of molten steel at 45 ℃, and adopting a steel tapping hole to a middle pouring pipeArgon seal protection is carried out, the blank pulling speed is controlled to be 1.1m/min, and the primary cooling crystallization water flow is controlled to be 90m ³ And/h, controlling the specific water quantity of secondary cooling to be 0.50L/kg, wherein the volume fraction of TiN, nbC, ti +Nb composite particles precipitated in the casting blank is 0.095%, and the average diameter of corresponding second-phase particles is 360nm.

Step seven, in the rough rolling stage, the initial rolling temperature is controlled at 1170 ℃, the final rolling temperature is controlled at 1020 ℃, specifically, the rolling temperature is more than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled at 18%, the rolling speed is controlled at 1.8m/s, and the austenite recrystallization percentage is 52%; the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is controlled at 23%, the rolling speed is controlled at 1.3m/s, and the austenite recrystallization percentage is 51%; the rolling temperature is less than or equal to 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled at 27%, the rolling speed is controlled at 0.8m/s, the austenite recrystallization percentage is 54%, and the total reduction rate of the blank in the whole stage is controlled at 44%.

And step eight, a finish rolling stage, wherein the finish rolling adopts two stages to control rolling, the initial rolling temperature of the first stage is controlled to be 987 ℃, the final rolling temperature is controlled to be 963 ℃, and the pass reduction rate of the first stage is controlled to be 7%. The second stage is controlled at 937 ℃, the final rolling temperature is controlled at 836 ℃, and the pass reduction is controlled at 8%.

And step nine, rapidly entering a cooling control device after rolling, wherein the cooling speed is controlled at 7.6 ℃/s, and the rolling piece is controlled at 689 ℃ after beginning to be off-line and slowly cooled.

The structure of the final product was ferrite + bainite structure, the ferrite grain size was 9.0 grade, the bainite ratio was 20%, and the performance test results of the obtained hot rolled H-steel were shown in table 1.

Comparative example 4

The high-strength hot-rolled H-shaped steel with good Z-direction performance comprises the following components in percentage by mass: c:0.18%, si:0.43%, mn:0.72%, P:0.018%, S:0.009%, nb:0.046%, ti:0.013%, ni:0.13%, N:0.004%, and the balance of Fe and unavoidable impurities. The same ingredients as in example 5 were used.

The production method of the ultra-thick hot-rolled H-shaped steel with good Z-direction performance comprises the following process flows: molten iron pretreatment, converter smelting, argon blowing refining, LF refining, RH or VD vacuum treatment, special-shaped blank full-protection casting, blank heating, rolling and controlled cooling after rolling;

The processing steps adopt the process flow of the invention, wherein, the main steps and the process parameters for controlling the smelting and rolling of the H-shaped steel are as follows:

Step seven, in the rough rolling stage, the initial rolling temperature is controlled at 1170 ℃, the final rolling temperature is controlled at 1010 ℃, specifically, the rolling temperature is more than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction is controlled at 11%, the rolling speed is controlled at 2.5m/s, and the austenite recrystallization percentage is 25%; the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is controlled to 15%, the rolling speed is controlled to 2.5m/s, and the austenite recrystallization percentage is 23%; the rolling temperature is less than 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled at 18%, the rolling speed is controlled at 2.5m/s, the austenite recrystallization percentage is 26%, and the total reduction rate of the blank in the whole stage is controlled at 26%.

And step eight, a finish rolling stage, wherein the finish rolling adopts two stages to control rolling, the initial rolling temperature of the first stage is controlled at 997 ℃, the final rolling temperature is controlled at 972 ℃, and the pass reduction rate of the first stage is controlled at 7%. The second stage is controlled at 948 deg.C, the final rolling temperature is controlled at 845 deg.C, and the pass reduction is controlled at 8%.

Step nine, rapidly entering a cooling control device after rolling, controlling the cooling speed at 7.6 ℃/s, and controlling the temperature of the rolled piece at 693 ℃ after starting off-line slow cooling.

The structure of the final product was ferrite + bainite structure, the ferrite grain size was 8.0 grade, the bainite ratio was 16%, and the performance test results of the obtained hot rolled H-steel were shown in table 1.

Comparative example 5

Step four, RH or VD vacuum treatment, wherein the immersion tube is baked for 3min in advance, the immersion tube is inserted into the vacuum tube for 406mm, the vacuum degree is maintained at 93Pa for 11min, and the volume fraction of hydrogen in molten steel is 1.10X10 ^-6 Ca/S was controlled at 1.92, at which time the complete spheroidization rate of sulfide in the steel was 99.3%, the precipitation fraction of sulfide was 0.010%, and the size was 230nm.

Step seven, in the rough rolling stage, the initial rolling temperature is controlled at 1170 ℃, the final rolling temperature is controlled at 1008 ℃, specifically, the rolling temperature is more than 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled at 18%, the rolling speed is controlled at 1.8m/s, and the austenite recrystallization percentage is 55%; the rolling temperature is less than 1050 ℃ and less than or equal to 1100 ℃, the pass reduction rate is controlled at 23%, the rolling speed is controlled at 1.3m/s, and the austenite recrystallization percentage is 54%; the rolling temperature is less than or equal to 1000 ℃ and less than or equal to 1050 ℃, the pass reduction rate is controlled at 27%, the rolling speed is controlled at 0.8m/s, the austenite recrystallization percentage is 52%, and the total reduction rate of the blank in the whole stage is controlled at 44%.

And step eight, a finish rolling stage, wherein the finish rolling adopts two stages to control rolling, the initial rolling temperature of the first stage is controlled to be 989 ℃, the final rolling temperature is controlled to be 962 ℃, and the pass reduction rate of the first stage is controlled to be 7%. The second stage is controlled at 936 deg.c, 833 deg.c and 8% pass reduction.

Step nine, rapidly entering a cooling control device after rolling, controlling the cooling speed to be 3.5 ℃/s, and controlling the initial off-line slow cooling of the rolled piece to be 780 ℃.

The structure of the final product was ferrite + bainite structure, the ferrite grain size was 8.5 grade, the bainite ratio was 11%, and the performance test results of the obtained hot rolled H-steel were shown in table 1.

TABLE 1 list of performance test cases for inventive examples and comparative examples

The foregoing detailed description of a hot rolled H-section steel having a yield strength of 450MPa grade with good Z-direction performance and a method for producing the same, with reference to the examples, is illustrative and not limiting, and several examples can be listed according to the limits, therefore variations and modifications without departing from the general inventive concept shall fall within the scope of protection of the present invention.

Claims

1. The hot rolled H-shaped steel with good Z-direction performance and the yield strength of 450MPa grade is characterized by comprising the following chemical components in percentage by mass: c:0.15 to 0.18 percent, si:0.30 to 0.50 percent, mn:0.7 to 1.0 percent, P: less than or equal to 0.020%, S: less than or equal to 0.010 percent, nb:0.030 to 0.050 percent, ti:0.010 to 0.020%, ni:0.10 to 0.30 percent, N is less than or equal to 0.005 percent, and the balance is Fe and unavoidable impurities.

2. The hot rolled H-section steel with a yield strength of 450MPa grade having good Z-direction performance according to claim 1, wherein the metallographic structure of the hot rolled H-section steel with a yield strength of 450MPa grade having good Z-direction performance is ferrite + bainite, the area ratio of bainite is 20 to 30%, the grain size of ferrite is 9 grade or more, and the thickness of bainite layer is 1/4 or more of the thickness of flange.

3. The hot rolled H-section steel with the yield strength of 450MPa and good Z-direction performance according to claim 1, wherein the yield strength of the hot rolled H-section steel with the yield strength of 450MPa and good Z-direction performance is more than or equal to 4500MPa, the tensile strength is more than or equal to 550MPa, the elongation A is more than or equal to 21%, the longitudinal V-shaped impact power KV2 at-20 ℃ is more than or equal to 100J, and Z is more than or equal to 52%.

4. A method for producing a hot rolled H-section steel of 450MPa grade in yield strength with good Z-properties according to any one of claims 1-3, characterized in that it comprises the steps of: molten iron pretreatment, converter smelting, argon blowing refining, LF refining, RH or VD vacuum treatment, special-shaped blank full-protection casting, blank heating, rolling and controlled cooling after rolling; the compression ratio of the blank to the flange thickness direction of the final product is 2-4.

5. The production method according to claim 4, wherein in the LF refining step, refining time is prolonged by 15-20 min, the temperature before argon blowing is more than or equal to 1550 ℃, the time for each argon blowing is more than or equal to 1min, and the N content is controlled below 0.005%.

6. The method according to claim 4, wherein in the RH or VD vacuum treatment step, the volume fraction of hydrogen in the molten steel after RH or VD is controlled to be 1.5X10-6 or less; and simultaneously calcification treatment is carried out at the stage, and Ca/S is controlled to be between 1.2 and 2.0.

7. The method according to claim 4, wherein in the step of fully protecting and casting the special-shaped blank, the superheat degree of molten steel is controlled to be 20-35 ℃, argon seal protection is adopted between a steel outlet and a middle injection pipe, the blank pulling speed is 0.45-1.0 m/min, and the primary cooling crystallization water flow rate is 100-300 m ³ And/h, the specific water quantity of secondary cooling is 0.55-0.75L/kg.

8. The method according to claim 4, wherein in the step of heating the billet, the billet is fed into a heating furnace and heated to 1200 to 1250 ℃ by the heating furnace for 150 to 180 minutes.

9. The method according to claim 4, wherein in the rolling step, the rolling includes a rough rolling stage and a finish rolling stage; the total rolling reduction of the blank in the rough rolling stage is controlled to be 40% -50%; the finish rolling stage adopts two stages to control rolling, the rolling reduction rate of the first stage is controlled to be 5% -10%, and the rolling reduction rate of the second stage is controlled to be 5% -15%.

10. The production method according to claim 9, wherein the initial rolling temperature in the rough rolling stage is controlled to 1150-1180 ℃ and the final rolling temperature is controlled to be above 1000 ℃.

11. The production method according to claim 10, wherein in the rough rolling stage, when the rolling temperature is less than or equal to 1100 ℃ and less than or equal to 1150 ℃, the pass reduction rate is controlled to be less than or equal to 20% by 15% < and the rolling speed is controlled to be less than or equal to 2.0m/s by 1.5m/s;

12. The production method according to claim 9, wherein the finish rolling stage is performed at a start rolling temperature of 980-1000 ℃ and a finish rolling temperature of 960 ℃ or higher; the second stage is to control the initial rolling temperature to 930-950 deg.c and the final rolling temperature to 830-850 deg.c.

13. The method according to claim 4, wherein in the post-rolling cooling control step, an inter-cooling process is adopted, the cooling speed is controlled to be 6-10 ℃/s, and the rolled piece is ensured to be subjected to off-line air cooling within the range of 650-750 ℃.