CN115747631B - Q420-grade heavy hot-rolled H-shaped steel and tissue refining production method thereof - Google Patents
Q420-grade heavy hot-rolled H-shaped steel and tissue refining production method thereof Download PDFInfo
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Abstract
The invention discloses Q420-grade heavy hot-rolled H-shaped steel and a tissue refining production method thereof, belonging to the technical field of steel. The chemical components mainly comprise: C. si, mn, P, S, nb, ti, V, N, H, fe; wherein: the volume fraction of TiN second phase particles is more than 0.01%, the size of the TiN second phase particles is less than 20 nanometers, the volume fraction of NbC second phase particles is more than 0.03%, the size of the TiN second phase particles is less than 40 nanometers, the volume fraction of VC second phase particles is more than 0.02%, the size of the TiN second phase particles is less than 20 nanometers, the volume fraction of Nb-V-Ti composite second phase particles is more than 0.03%, and the size of the Nb-V-Ti composite second phase particles is less than 40 nanometers. The production method comprises the following steps: heating the blank, cogging and rolling, universal first-stage rolling, water spray cooling, universal second-stage rolling and cooling by a cooling bed, wherein the grain size of the final Q420-grade heavy hot rolled H-shaped steel reaches more than 10 grades.
Description
Technical Field
The invention belongs to the technical field of steel, and particularly relates to a heavy hot-rolled H-shaped steel tissue refining production method.
Background
The hot rolled H-shaped steel has an optimized cross-sectional shape, and is widely applied to the fields of rail transit, large bridges, oil platforms, large buildings and the like as an economic iron-based structural material. With the development of science and technology, the enlargement of engineering structures is a development trend, so that the requirements for the enlargement and the high performance of the hot rolled H-shaped steel are also raised. From the perspective of high performance, global oil gas resource exploitation is advanced to the severe high-cold region with severe climate conditions, international major engineering, oil gas pipelines and logistics traffic in the high-cold region are rapidly developed, and the characteristic of high performance requirements is not only reflected in improving the strength and plasticity used under the conventional conditions, but also particularly requires that the material has high low-temperature toughness so as to meet the special service conditions in the high-cold region. The product is large-sized, which can lead to the increase of the difficulty of high performance, at present, the development of hot rolled H-shaped steel with flange thickness of more than 50mm in the prior art still belongs to an exploration stage, a large amount of import is still needed, in addition, the hot rolled H-shaped steel can also be manufactured by adopting welding processing, but the welding can lead to a series of social and economic problems such as cost, environmental protection, quality and the like.
Because the rolling capacity of the steel plate rolling mill is large, the rolling compression ratio of blank to material is also large, the rolling at low temperature and high pressure can be realized, and the performance of the steel plate is improved by utilizing the traditional thermal mechanical processing (TMCP) technology of strain-induced phase transition and combining means such as water cooling after rolling, off-line heat treatment and the like. Compared with a steel plate, the hot-rolled H-shaped steel has a complicated section, so that the rolling conditions (rolling temperature and rolling compression ratio) are limited, and therefore, the ultra-thick hot-rolled H-shaped steel cannot be simply used for referencing the manufacturing process and chemical composition of the steel plate, and the heavy hot-rolled H-shaped steel meeting the GB/T1591 standard requirement is developed. The tissue refinement is a very effective technical means for improving the plasticity, particularly the low-temperature impact toughness, at the level of improving the strength. Currently, thermal mechanical processing (TMCP) technology is commonly used in research and practical applications, and its key point is low temperature and high pressure. The production of heavy hot rolled H-shaped steel is limited by the size of a blank and the tooling capacity, and the process requirements of low temperature and high pressure are difficult to realize, so that a technology for realizing the refinement of a structure by utilizing austenite grain boundary to promote phase transformation nucleation and utilizing induced austenite to dynamically recrystallize to obtain ultrafine austenite grains is proposed. In order to realize the requirement of austenite dynamic recrystallization refinement structure, a rolling mode suitable for heavy hot-rolled H-shaped steel structure refinement is researched and developed to adapt to the requirement of induced austenite dynamic recrystallization refinement structure.
At present, studies on structure refinement and hot rolling of H-steel have been conducted in a large amount. For example, in the case of large-sized steel products such as thick plates, japanese JFE iron and steel companies have used online accelerated cooling equipment for thick plate production in the world, developed a powerful cooling equipment Super-CR in close proximity to a rolling mill, and continued tempering process by using an online heating equipment HOP, thereby achieving high performance of thick plates. The new generation TMCP (NG-TMCP) technology based on ultra-fast cooling technology is developed in university of northeast, but the above research and development work is mainly performed for cooling after rolling, and the control focused on the rolling process is a completely different process stage from the invention, and the application of the fast cooling process after rolling has inherent defects in the production of hot rolled H-section steel: the main reason is that the cross section shape of the hot rolled H-shaped steel is complex, the cooling unevenness of each part can be aggravated by rapid cooling after rolling, the appearance of the hot rolled H-shaped steel is deformed, the subsequent straightening is difficult, and the hot rolled H-shaped steel becomes waste. Wu Baoqiao et al published in the journal of "thermal processing technology", which discloses an article of "influence of temperature-controlled rolling on mechanical properties of vanadium microalloy hot rolled H-section steel", which researches the rule of influence of V content on strength of thin gauge (50 mm thick) hot rolled H-section steel, and has no consideration of toughness of products, and the focus is on the relation between V microalloying and strength, which is completely different from the realization of heavy hot rolled H-section steel toughening through optimization of technological rules and coupling microalloy design. Guo Xiuhui et al, J.iron and steel research, disclose a "research for improving the impact properties of ultra-thick gauge Q275D hot rolled H-section steel", which researches on analyzing only the reasons for insufficient low-temperature impact toughness at-20 ℃ of thin gauge (26 mm thick) hot rolled H-section steel and gives countermeasures, and focused on the analysis of the reasons for unqualified low-temperature toughness, which is essentially different from the realization of toughening of heavy hot rolled H-section steel by optimizing coupling microalloying design through technical regulations.
China patent application No. 202011321554.3, 2 months and 12 days in 2021 discloses ultra-thick Q355 grade hot rolled H-shaped steel with good low temperature toughness and a production method thereof. The chemical composition of the alloy is C：0.12～0.18％、Si：0.10～0.50％、Mn：1.20～1.60％、Al：0.02～0.06％、Nb：0.02～0.06％、N：0.0040～0.0100％、P≤0.015％、S≤0.005％,, the balance of Fe and unavoidable impurities, the flange thickness t is 80-150 mm, CEV is less than or equal to 0.42%, and Pcm is less than or equal to 0.25%; the design scheme of Nb and Al microalloying low cost components is provided, and AlN and NbC are regulated and controlled to be distributed in a continuous casting blank and H-shaped steel by matching with a reasonable continuous casting process and a rolling process, so that the H-shaped steel structure is refined. However, the invention adopts a rapid cooling process after rolling, which is very easy to cause the deformation of the hot rolled H-shaped steel to be out of the standard requirement, and cannot realize batch production. The invention adopts the air cooling process after rolling, greatly improves the size and the shape of the product, and improves the rolling temperature and the rolling condition through the coupling optimization of the process and the components.
The Chinese patent application No. 202010833685. X discloses 420MPa grade hot rolled H-shaped steel with excellent low temperature toughness and a production method thereof on the 12 th month 4 of 2020, wherein the chemical components are C, si, mn, P, S, V, ni, N, and the balance of Fe and unavoidable impurities, and the 420MPa hot rolled H-shaped steel with excellent comprehensive performance is developed through reasonable V, ni and N component design and matching of a matched rolling and cooling control process. However, the invention adopts a rapid cooling process after rolling, which is very easy to cause the shape deformation of the hot rolled H-shaped steel to be out of the standard requirement and can not realize batch production, and the invention also utilizes the precious metal Ni microalloying, which causes higher product cost and waste of precious elements, in addition, the thickness of the product of the invention is thinner (30-50 mm thick), which is essentially different from the invention shown in the text. The invention adopts a post-rolling air cooling process, greatly improves the size and the shape of the product, and realizes the high performance of heavy hot-rolled H-shaped steel by adopting common microalloy elements through the coupling optimization of the process and the components.
The Chinese patent application number is 202011243695.8, 26 days of 2021 and 2 months discloses a low-cost heavy Q355E hot rolled H-shaped steel and a manufacturing method thereof, the components are C, si, mn, nb, ti, N, the balance is iron and other impurities, the product range of Ti and N is 0.00004% -0.0007%, and the hot rolled H-shaped steel with high strength and high-low temperature toughness is obtained by controlling the reduction and deformation temperature of the 5 th-3 th pass of the universal reciprocal and controlling the austenite grain size after rough rolling in a matched manner.
The Chinese patent application number is 202011243693.9, and 2 months and 26 days in 2021 disclose a low-cost 460 MPa-grade hot-rolled H-shaped steel with excellent low-temperature toughness and a production method thereof, wherein the components of the hot-rolled H-shaped steel are C, si, mn, P, S, V, ni, C r and N, the balance of Fe and unavoidable impurities, the content ratio of V to N is 8:1-10:1, and the 460 MPa-grade hot-rolled H-shaped steel with high strength, high-low-temperature toughness, excellent weldability and thickness direction performance is developed through reasonable component proportion and TMCP technology of the whole process based on the production practice of the hot-rolled H-shaped steel.
The Chinese patent application number is 201380039137.1, and the H-shaped steel and the manufacturing method thereof are disclosed in the year 2015, 4 and 1, wherein the mass percentage of the chemical components of the material comprises ：C：0.05～0.16％、Si：0.01～0.50％、Mn：0.80～2.00％、Ni：0.05～0.50％、V：0.01～0.20％、Al：0.005～0.100％、Ti：0.005～0.030％、N：0.0010～0.0200％、O：0.0001～0.0100％、Ca：0.0003～0.0040％、Cr：0～0.50％、Cu：0～0.50％、Mo：0～0.20％、Nb：0～0.05％. flange thickness of 100-150 mm. The focus is to form "oxide particles containing 100 to 5000 oxide particles per unit area per mm 2 and having an equivalent circle diameter of 0.005 to 2.0 μm" by means of oxide metallurgy.
The H-shaped steel disclosed in China patent application No. 201780057895.4, 12 and 21 in 2017 and a manufacturing method thereof have the chemical components that the thickness of a ：C：0.050～0.160％、Si：0.01～0.60％、Mn：0.80～1.70％、Nb：0.005～0.050％、V：0.05～0.120％、Ti：0.001～0.025％、N：0.0001～0.0120％、Cr：0～0.30％、Mo：0～0.20％、Ni：0～0.50％、Cu：0～0.35％、W：0～0.50％、Ca：0～0.0050％、Zr：0～0.0050％. flange is 20-140 mm, the tensile yield stress is 385-530 MPa, and the Charpy impact absorption energy at-20 ℃ is more than 100J. In the invention, the low-temperature toughness is realized mainly by microalloying elements.
Under the condition of investigation of current patents and documents, aiming at heavy hot-rolled H-shaped steel with flange thickness exceeding 50mm, the defect of insufficient compression ratio of the heavy hot-rolled H-shaped steel is solved by optimizing a rolling process; by adopting water spray cooling among universal areas, researches on overcoming the problems that the conventional heavy hot rolled H-shaped steel is rolled for a long time and the production efficiency is improved and the like have not been reported yet.
Disclosure of Invention
1. Problems to be solved
The invention provides Q420-grade heavy hot-rolled H-shaped steel, which aims to take the Q420-grade heavy hot-rolled H-shaped steel with flange thickness more than or equal to 50mm as a product target by regulating and controlling the chemical components of the H-shaped steel and the parameters of second phase particles, wherein the grain size of the final product reaches more than 10 grades, and the low-temperature impact absorption energy of 0 ℃, -20 ℃, -40 ℃ and-60 ℃ is not less than 120J.
The invention also provides the Q420 grade heavy hot rolled H-shaped steel structure refinement production method, which is based on induced austenite dynamic recrystallization refinement structure, optimizes the rolling process, reduces the rolling reduction of the flange of the cogging area, increases the rolling reduction of the universal area, decomposes the existing universal rolling process into two-section rolling, rolls the first section at higher temperature, and refines the austenite structure through dynamic/static recrystallization; the thickness of the H-shaped steel rolled piece is reduced, water spray cooling is carried out between channels to quickly reduce the temperature waiting time; the second section is rolled at a lower temperature to realize dynamic recrystallization of induced austenite, so that ultra-fine austenite grains are obtained, ferrite transformation nucleation is promoted through the grain boundary of the ultra-fine austenite, and product tissue refinement is realized.
2. Technical proposal
In order to solve the problems, the invention adopts the following technical scheme.
The Q420 grade heavy hot rolled H-shaped steel mainly comprises the following chemical components: C. si, mn, P, S, nb, ti, V, N, H, fe; meanwhile, the contained alloy compound particles are TiN second phase particles, nbC second phase particles, VC second phase particles and Nb-V-Ti composite second phase particles, wherein: according to the national GB/T11263 standard, the performance samples of hot rolled H-section steel must be sampled at 1/6 of the flange width B, the H-section steel of the present invention is sampled at flange end B/6 and flange 1/4 thickness:
the volume fraction of TiN second phase particles is more than 0.01 percent, the size is less than 20 nanometers,
The volume fraction of the NbC second phase particles is more than 0.03 percent, the size of the NbC second phase particles is less than 40 nanometers,
The volume fraction of VC second phase particles is more than 0.02 percent, the size of the VC second phase particles is less than 20 nanometers,
The volume fraction of the Nb-V-Ti composite second phase particles is more than 0.03 percent, and the size of the Nb-V-Ti composite second phase particles is less than 40 nanometers.
Further, the volume fraction of second phase particles having a size of less than 15 nm is required to satisfy the formula (a):
VTiN+VVC+VNbC+VNb-V-Ti≥0.05％(a)，
Wherein: v TiN is the volume fraction of TiN, V VC is the volume fraction of VC, V NbC is the volume fraction of NbC, and V Nb-V-Ti is the volume fraction of Nb-V-Ti composite second phase particles.
Further, the chemical components of the alloy are ：C:0.06～0.14％,Si:0.10～0.60％,Mn:1.00～1.60％,P：≤0.015％,S：≤0.007％,Nb:0.01～0.06％,Ti：0.010～0.030％,V：0.010～0.040％,N：0.0040～0.0100％,H:≤0.0002％, percent by mass and the balance is iron and impurities, wherein the mass percent of C, mn satisfies the following relational expression (b):
C+Mn/6＝0.28-0.38％(b)。
further, the flange thickness of the H-shaped steel is t, and t is more than or equal to 50mm.
Further, the mass percent and t between Nb, ti, V, N satisfy formula (c):
1.7≤F＝[(Nb+Ti×N×1000+V)/t]×1000≤3.4(c)。
Further, the structure of the final product is ferrite and pearlite, and the grain size reaches more than 10 grades.
Wherein:
The content of C is set to be 0.06-0.14%. C (carbon) is an element effective for strengthening steel. Therefore, the lower limit of the C content is set to 0.06%. On the other hand, when the C content is more than 0.14%, the carbon equivalent CEV and the welding crack sensitivity index Pcm of the H-shaped steel can be remarkably improved, the weldability of the H-shaped steel is reduced, and meanwhile, the low-temperature toughness of the H-shaped steel is also reduced. Therefore, the upper limit of the C content is set to 0.12%.
The Si content is set to 0.10 to 0.60%. Si (silicon) is a deoxidizing element and contributes to improvement of strength. Therefore, the lower limit of the Si content is set to 0.10%. On the other hand, if the Si content is more than 0.60%, the Gao Wenbao layers are accelerated, the toughness and lamellar tearing properties are deteriorated, and the surface quality of the steel is adversely affected. Therefore, the upper limit of the Si content is set to 0.60%.
The Mn content is set to 1.00-1.60%. Mn (manganese) is in a certain range and improves the toughness and strength of the steel. Therefore, the lower limit of the Mn content is set to 1.00%. On the other hand, if the Mn content is more than 1.60%, macrosegregation is liable to occur, resulting in remarkable decrease in toughness of the steel and even occurrence of delamination phenomenon, deteriorating lamellar tearing resistance. Therefore, the upper limit of the Mn content is set to 1.60%.
The P content is less than or equal to 0.015 percent. Since P (phosphorus) is a cause of weld cracking and reduction in toughness due to solidification segregation, the amount of P should be reduced as much as possible, and P is limited to 0.015% or less in consideration of the total cost of P removal.
The S content is set to be less than or equal to 0.007 percent. S (sulfur) forms MnS inclusions in the central portion of the cast slab due to solidification segregation, and therefore, not only weld cracks and toughness are reduced, but also lamellar tearing resistance is deteriorated, and therefore, S content is limited to 0.007% or less in consideration of total S removal cost as much as possible.
The Nb content is set to 0.01-0.06%. Nb (niobium) is used to precipitate sufficient NbC to form a barrier to austenite grain growth by the pinning effect to achieve the effect of refining the austenite grains. Therefore, the lower limit of the Nb content is set to 0.01%; on the other hand, if the Nb content exceeds 0.06%, the fillets of the continuous casting special-shaped blank are easy to crack, the surface quality of the final product is affected, and the cost control is not facilitated. Therefore, the upper limit of the Nb content is set to 0.06%.
The Ti content is set to 0.010-0.030%. Ti (titanium) is a main element for forming TiN, wherein 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 realize the effect of refining the austenite grains; meanwhile, the refined TiN can promote NbC precipitation and refine the size of the second phase precipitation particles. Therefore, the lower limit of the Ti content is set to 0.010%. On the other hand, if the Ti content is too high, excessive Ti is dissolved in the steel material to cause alloy waste, which causes an increase in cost, and the upper limit is set to 0.030%.
The V content is set to 0.010-0.040%. V (vanadium) is an effective element for refining ferrite grains, and precipitates in grains to effectively improve the strength of steel. Therefore, the lower limit of the V content is set to 0.010%. On the other hand, if the V content exceeds 0.040%, the steel strength becomes excessive. Therefore, the upper limit of the V content is set to 0.040%.
The N content is set to 0.0040-0.0100%. N (nitrogen) is a main element for forming TiN, and contributes to refinement and precipitation strengthening of the structure, and is also a key element for controlling the size of TiN precipitation. Therefore, the lower limit of the N content is set to 0.0040%. If the N content is more than 0.0100%, tiN particles are caused to be coarse, and low-temperature toughness, continuous casting surface quality and strain aging property of the steel material are deteriorated. Therefore, the upper limit of the N content is set to 0.0100%.
The H content is less than or equal to 0.0002 percent. H (hydrogen) is a main cause of hydrogen induced cracks in steel, belongs to harmful elements, and can cause steel fracture if the H content of steel types exceeds the limit. Therefore, the upper limit of the H content is set to 0.0002%.
In the conventional heavy hot rolling H-shaped steel rolling process, rolled pieces are heated and bloomed for rolling and then enter a universal rolling mill for universal zone rolling. The cogging rolling temperature is about 1100 ℃ to 1150 ℃, and the cogging rolling is carried out and then enters a universal rolling mill for universal rolling after the temperature is 930 ℃ to 960 ℃. Because the total compression ratio of heavy hot rolling H-shaped steel is smaller, the total compression ratio is smaller when the flange is distributed in the thickness direction in the cogging rolling process according to the design of the traditional rolling process, the internal defects of the rolled piece and the refined austenite grain size cannot be effectively improved, so that the internal quality of the rolled piece is poor, the dynamic recrystallization of austenite is difficult to induce in the universal rolling process, the tissue refinement cannot be realized, and the grains of the final product are larger. Meanwhile, the rolled piece is larger in size after cogging and rolling, and the traditional process does not have the design of a water spray cooling process, so that the temperature waiting time of the rolled piece is longer, and the production efficiency is greatly influenced.
The heavy hot rolling H-shaped steel rolling consists of two parts, wherein the first part is cogging (rough rolling) rolling and the second part is universal (finish rolling) rolling. The first partial cogging rolling is two-roller grooved rolling, and is mainly used for expanding or shrinking to adjust the height or width dimension of a rolled piece to be suitable for universal rolling, and simultaneously, the rolling piece is compressed and rolled in the thickness direction to weld internal defects of the rolled piece. The second part of universal rolling is a universal rolling mill consisting of four rollers, and the second part of universal rolling is used for carrying out compression rolling on the flange and the web plate of the H-shaped steel in the thickness direction, so that the main effect is to improve the structure of the H-shaped steel and reduce the thickness of the H-shaped steel so as to obtain an ideal H-shaped steel product.
Therefore, the structure refinement production method of the Q420-grade heavy hot-rolled H-shaped steel comprises the following steps: blank heating, cogging rolling, universal first-stage rolling, water spray cooling, universal second-stage rolling, cooling bed air cooling, and the method specifically comprises the following steps:
(1) Heating the blank: the chemical components of the blank mainly comprise: C. si, mn, P, S, nb, ti, V, N, H, fe, wherein the mass percentage of the V element is 0.010-0.040%; the heating temperature is 1200-1250 ℃, the heat preservation is carried out for 120-160 min, and partial undissolved TiN second phase particles can be reserved for inhibiting the growth of austenite grains in the heating process; but also can ensure the complete dissolution of NbC particles and provide ingredient assurance for subsequent epitaxial precipitation; meanwhile, the whole section of the thick hot-rolled H-shaped steel can be uniformly heated, and the subsequent rolling is facilitated;
(2) Cogging and rolling: reducing the inclination of the special-shaped Kong Tuibu and enlarging the thickness of the special-shaped Kong Tuibu in the special-shaped hole of the cogging roller, thereby realizing the thickness reduction of the flange less than or equal to 5 percent, increasing the thickness of the rolled piece in the universal rolling stage, obtaining a larger universal rolling compression ratio and further increasing the strain accumulation of the universal rolling;
(3) Universal first stage rolling: the compression ratio is controlled to be more than 1.23, which is favorable for welding internal defects of a rolled piece and accumulating enough strain to promote austenite to fully recrystallize and refine austenite grains;
(4) And (3) water spray cooling: adopting a universal inter-rolling-channel full-section water spray cooling process to quickly reduce the temperature of rolled pieces to 925-930 ℃;
(5) Universal second stage rolling: the compression ratio is controlled to be 1.50-1.55, the coupled rolling temperature (925-930 ℃) promotes austenite to generate dynamic recrystallization refinement structure, the austenite enters the universal second-stage rolling, the Ti/Nb microalloying component design is matched, a large amount of precipitated NbC, VC and Nb, ti and V composite second-phase particles are utilized for strain induction to inhibit austenite static recrystallization among rolling passes of the universal second-stage rolling, strain accumulation is realized, and thus the austenite dynamic recrystallization refinement structure is induced;
(6) And (5) cooling by a cooling bed.
Further, in the step (1), the component system of the blank is ：C:0.06～0.14％;Si:0.10～0.60％,Mn:1.00～1.60％;P：≤0.015％;S：≤0.007％;Nb:0.01～0.06％;Ti：0.010～0.030％;V：0.010～0.040,N：0.0040～0.0100％;H:≤0.0002％;, and the balance is iron and other impurities, wherein:
In order to ensure the strength of the steel, the mass percentage between C, mn satisfies the following relation (b):
C+Mn/6＝0.28％～0.38％ (b)；
Considering the product thickness effect F, the mass percent between Nb, ti, V, N and the flange thickness t of the H-section steel satisfy the formula (c):
1.7≤F＝[(Nb+Ti×N×1000+V)/t]×1000≤3.4(c)。
Further, in the step (2), the cogging rolling pass is reduced to 5-7 passes, the cogging rolling speed and the roller conveying speed are improved to 3-5 m/s, the temperature loss of the rolled piece in the cogging rolling stage and the roller conveying process is reduced, the rolling temperature of the universal first stage is improved to 1050-1100 ℃, internal defects (loose, air holes, cracks and the like) of the rolled piece are welded, the sufficient recrystallization of austenite is ensured, the micro-alloying design of Ti/N is matched, the growth of austenite grains in the high-temperature stage is restrained by utilizing TiN second phase particles, and the austenite grain size is thinned, so that the austenite grains in the universal first stage are thinned.
Further, in the step (3), the universal first-stage rolling temperature is 1050-1100 ℃.
Further, in the step (4), the cooling speed of water spray cooling is 30 ℃/s to 50 ℃/s.
Further, in the step (4), the cooling speed of the cooling bed air cooling is 0.05 ℃/s to 0.5 ℃/s.
Under the condition that the Ti/N microalloying design is coupled with the rolling process, the volume fraction of TiN second phase particles is more than 0.01%, and the size of the second phase particles is less than 20 nanometers. The microalloying design of Nb is coupled with the rolling process conditions, so that the volume fraction of NbC precipitation is ensured to be more than 0.03%, and the size of NbC particles is less than 40 nanometers. The micro-alloying design of V ensures that the volume fraction of VC precipitation reaches more than 0.02 percent, and the size of VC particles is less than 20 nanometers. The volume fraction of the Nb-V-Ti composite second phase particles is more than 0.03 percent, and the size of the Nb-V-Ti composite second phase particles is less than 40 nanometers. Wherein the volume fraction of the second phase particles smaller than 15 nm is required to satisfy: v TiN+VNbC+VNb-V-Ti is more than or equal to 0.04%, wherein: v TiN: volume fraction of TiN; v NbC: volume fraction of NbC; v Nb-V-Ti: volume fraction of Nb-V-Ti composite particles.
The thick hot rolled H-shaped steel obtained by the method has the flange thickness of more than or equal to 50mm, the yield strength of more than 420MPa, the tensile strength of 520-680 MPa, the elongation after fracture of more than 19%, the thickness direction performance of more than 35%, the impact toughness of 0 ℃, -20 ℃, -40 ℃ and-60 ℃ of more than 120J.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
(1) The invention improves the traditional hot rolling H-shaped steel rolling process, reduces the rolling reduction of a cogging area, realizes universal two-stage rolling, promotes the welding and structure refinement of the defects of the universal stage rolling, solves the problem of insufficient compression ratio of heavy hot rolling H-shaped steel, and realizes induced austenite dynamic recrystallization by matching with the microalloying component design of Ti/Nb+low V, thereby refining the product structure, namely, the volume fraction of second phase particles of fine grain strengthening and precipitation strengthening, and realizing the strengthening and toughening of the product.
(2) The invention optimally thins the thickness of the universal second stage rolled piece, adopts water spray cooling between universal areas, overcomes the long-time waiting-temperature rolling of the traditional heavy hot rolled H-shaped steel, and greatly improves the production efficiency.
(3) The invention develops Q420 grade heavy hot rolled H-shaped steel with flange thickness more than or equal to 50mm, the grain size of the product reaches 10 grade, and the low temperature impact absorption energy at 0 ℃, -20 ℃, -40 ℃ and-60 ℃ is not less than 120J.
(4) The rolling time for controlling rolling temperature of the rolled piece is reduced by rolling the thinned rolled piece and water spray cooling between channels, so that the production efficiency of heavy hot rolled H-shaped steel is improved; optimizing the rolling process, providing a method for reducing the rolling reduction of the flange of the cogging area, increasing the rolling reduction of the universal area, decomposing the conventional universal rolling process into two-section rolling, realizing internal defect welding and refining austenite structure in the high-temperature rolling stage, and inducing austenite dynamic recrystallization in the low-temperature rolling stage to refine the product structure. The grain size of the product reaches more than 10 levels, the strength reaches Q420 level, and the low-temperature impact absorption energy at 0 ℃, -20 ℃, -40 ℃ and-60 ℃ is not less than 120J.
Drawings
FIG. 1 is a schematic view of the sampling position of the H-section steel of the present invention;
FIG. 2 is a microstructure of the H-shaped steel of example 1;
FIG. 3 is a microstructure of the H-shaped steel of example 3;
FIG. 4 is a microstructure of the H-shaped steel of example 5;
FIG. 5 is a microstructure of the H-shaped steel of comparative example 11;
FIG. 6 is a microstructure of the H-shaped steel of comparative example 28;
FIG. 7 shows the microstructure of the H-steel in comparative example 43.
Detailed Description
The invention is further described below in connection with specific embodiments and the accompanying drawings.
Example 1 to example 6
A Q420MPa grade heavy hot-rolled H-shaped steel tissue refinement production method comprises the following steps:
A. heating the blank: the temperature of the heating section of the special-shaped blank in the heating furnace is 1213-1246 ℃ and the heating time is 128-156 min.
B. Cogging and rolling: the cogging rolling passes are 5-7, the cogging rolling speed is 3-5 m/s, the flange thinning ratio is less than or equal to 5%, and the conveying roller way speed is 3-5 m/s.
C. The universal first stage rolling is carried out at the final rolling temperature of 1052-1069 ℃ and the rolling compression ratio of 1.236-2.831.
D. And (3) water spray cooling: and after the universal first-stage rolling, immediately spraying water for cooling, wherein the cooling speed is 32-48 ℃ per second, and the water spraying cooling time is 3-4 s.
E. Universal second stage rolling: the initial rolling temperature is 926-929 ℃, and the rolling compression ratio is 1.51-1.53.
F. And (5) air cooling after rolling.
The main specific process parameters related to the Q420 MPa-level heavy hot-rolled H-shaped steel structure refinement production method in the embodiment 1-the embodiment 6 are shown in the table 1; as shown in table 2 below, examples 1-6 include the following chemical components in weight percent: the balance not listed in table 2 being Fe and unavoidable impurities.
Comparative example 7-comparative example 46 the hot rolled H-section steel was produced in the same manner as in example 1-example 6 except that the process parameters were as shown in table 1. As shown in Table 2 below, a hot rolled H-shaped steel as described in comparative examples 7 to 46 comprises the following chemical components in weight percent, with the balance being Fe and unavoidable impurities not listed in Table 2.
As can be seen from tables 1 to 3, the present invention can efficiently produce Q420 MPa-grade hot rolled H-shaped steel having a flange thickness of 50mm to 115mm, high strength, high low temperature toughness, excellent weldability and thickness direction properties.
Table 1 production process parameters of examples 1-6 and comparative examples 7-46
TABLE 2 chemical composition (wt%) and thickness of examples 1-6 and comparative examples 7-46
The results of the volume fraction of the second phase particles, the structure grain size, the room temperature elongation, the low temperature impact property and the thickness direction property test of the Q420MPa grade heavy-duty hot-rolled H-steel described in example 1-example 6 and the hot-rolled H-steel described in comparative example 7-comparative example 46 are shown in Table 3, FIG. 1 is a schematic view of the sampling position of the H-steel, and FIGS. 2 to 7 are the microstructures of the H-steels in examples 1, 3 and 5, and comparative examples 11, 20 and 33, respectively.
TABLE 3 volume fractions and mechanical Properties of the second phase particles of examples 1-6 and comparative examples 7-46
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As can be seen from tables 1 to 3 above:
As can be seen from comparative examples 7, 20 and 33, the control of the cogging rolling process parameters can ensure that the finish rolling temperature in the first stage of the universal mill is not too low, otherwise, the grain size grade of the product structure is reduced, and the impact toughness cannot meet the requirement;
as is clear from comparative example 45, after the thinning ratio of the cogged flange is more than 5%, the yield strength, the thickness direction performance and the impact toughness of the product are all insufficient;
As can be seen from comparative examples 8, 9, 11, 21, 22, 24, 34, 35 and 37, the volume fraction of NbC second phase particles can be more than or equal to 0.03% only by controlling the starting rolling temperature of the universal second stage within 925-930, and the strength and impact toughness performance of the product can meet the requirements of the invention;
as can be seen from comparative examples 19, 32 and 46, when the temperature waiting time between the first stage and the second stage is long, the water spray cooling rate needs to be controlled to be lower so as to obtain H-shaped steel with expected performance, and in order to improve the production efficiency, the invention obtains the highest cost performance of 30-50 ℃/s of water spray cooling;
as can be seen from comparative examples 10, 23 and 36, when the universal second stage compression ratio is less than 1.5, the volume fraction of NbC second phase particles is less than 0.03%, and the strength and impact toughness of the product can not meet the requirements of the invention;
as can be seen from comparative examples 12, 13, 25, 26, 38, 39, C+Mn/6 is outside the range of 0.26 to 0.34, and the strength of the product is insufficient;
As can be seen from comparative examples 15, 17, 27, 28, 29, 30, 31, 40, 41 and 42, the element content Nb, ti, V, N is strictly regulated, otherwise, the thickness effect F of the product is not in the range of 1.7-3.4, the grain size of the product is less than 10 grade, and the thickness direction performance and the impact toughness are insufficient.
As is clear from comparative examples 14, 16, 18, 43 and 44, the strength and impact toughness of the H-shaped steel were low when the volume fraction of the second phase particles was out of the range defined in the present invention.
The examples of the present invention are merely for describing the preferred embodiments of the present invention, and are not intended to limit the spirit and scope of the present invention, and those skilled in the art should make various changes and modifications to the technical solution of the present invention without departing from the spirit of the present invention.
Claims (9)
1. The Q420-grade heavy hot rolled H-shaped steel is characterized in that: the chemical components mainly comprise: C. si, mn, P, S, nb, ti, V, N, H, fe; meanwhile, the contained alloy compound particles are TiN second phase particles, nbC second phase particles, VC second phase particles and Nb-V-Ti composite second phase particles, wherein:
the volume fraction of TiN second phase particles is more than 0.01 percent, the size is less than 20 nanometers,
The volume fraction of the NbC second phase particles is more than 0.03 percent, the size of the NbC second phase particles is less than 40 nanometers,
The volume fraction of VC second phase particles is more than 0.02 percent, the size of the VC second phase particles is less than 20 nanometers,
The volume fraction of the Nb-V-Ti composite second phase particles is more than 0.03 percent, and the size of the Nb-V-Ti composite second phase particles is less than 40 nanometers;
The volume fraction of second phase particles having a size of less than 15 nm is required to satisfy the formula (a):
VTiN+VVC+VNbC+VNb-V-Ti≥0.05％(a)，
Wherein: v TiN is the volume fraction of TiN, V VC is the volume fraction of VC, V NbC is the volume fraction of NbC, and V Nb-V-Ti is the volume fraction of Nb-V-Ti composite second phase particles.
2. The Q420 grade heavy duty hot rolled H-section steel of claim 1 wherein: the chemical components of the iron-containing alloy are ：C:0.06～0.14％,Si:0.10～0.60％,Mn:1.00～1.60％,P：≤0.015％,S：≤0.007％,Nb:0.01～0.06％,Ti：0.010～0.030％,V：0.010～0.040％,N：0.0040～0.0100％,H:≤0.0002％, percent by mass and the balance is iron and impurities, wherein the mass percent of C, mn satisfies the following relational expression (b):
C+Mn/6＝0.28-0.38％(b)。
3. The Q420 grade heavy duty hot rolled H-section steel according to claim 2, wherein: the flange thickness of the H-shaped steel is t, and t is more than or equal to 50mm.
4. A Q420 grade heavy duty hot rolled H-section steel according to claim 3 wherein: the mass percentage and t between Nb, ti, V, N satisfy the formula (c):
1.7≤F＝[(Nb+Ti×N×1000+V)/t]×1000≤3.4(c)。
5. A tissue refinement production method of Q420-grade heavy hot-rolled H-shaped steel is characterized by comprising the following steps of: the method comprises the following steps:
(1) Heating the blank: the heating temperature is 1200-1250 ℃, and the temperature is kept for 120-160 min; the chemical components of the blank mainly comprise: C. si, mn, P, S, nb, ti, V, N, H, fe, wherein the mass percentage of the V element is 0.010-0.040%;
(2) Cogging and rolling: the thickness reduction of the flange is less than or equal to 5 percent;
(3) Universal first stage rolling: the compression ratio is controlled to be more than 1.23;
(4) And (3) water spray cooling: reducing the temperature of the rolled piece to 925-930 ℃;
(5) Universal second stage rolling: the compression ratio is controlled to be 1.50-1.55;
(6) And (5) cooling by a cooling bed.
6. The method for producing the Q420 grade heavy hot rolled H-shaped steel by refining the structure, which is characterized by comprising the following steps of: in the step (2), the cogging rolling pass is 5-7 passes, and the cogging rolling speed and the roller conveying speed are 3-5 m/s.
7. The method for producing the Q420 grade heavy hot rolled H-shaped steel by refining the structure, which is characterized by comprising the following steps of: in the step (3), the universal first stage rolling temperature is 1050-1100 ℃.
8. The method for producing the Q420 grade heavy hot rolled H-shaped steel by refining the structure, which is characterized by comprising the following steps of: in the step (4), the cooling speed of water spray cooling is 30-50 ℃/s.
9. The tissue refining production method of the Q420 grade heavy hot rolled H-shaped steel according to any one of claims 5 to 8, which is characterized in that: in the step (4), the cooling speed of the cooling bed air cooling is 0.05-0.5 ℃/s.
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| CN114369764A (en) * | 2022-01-17 | 2022-04-19 | 马鞍山钢铁股份有限公司 | High-performance thick hot-rolled H-shaped steel with yield strength of 460MPa and production method thereof |
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| JP2016117932A (en) * | 2014-12-22 | 2016-06-30 | 新日鐵住金株式会社 | Rolling h-shaped steel and manufacturing method therefor |
| CN112410665A (en) * | 2020-11-10 | 2021-02-26 | 马鞍山钢铁股份有限公司 | Thick hot-rolled H-shaped steel for inhibiting grain growth and production method thereof |
| CN112359289A (en) * | 2020-11-23 | 2021-02-12 | 马鞍山钢铁股份有限公司 | Super-thick Q355-grade hot-rolled H-shaped steel with good low-temperature toughness and production method thereof |
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