CN109136773B - Heat treatment production process of continuous casting square billet of low-alloy high-strength bridge cable steel - Google Patents
Heat treatment production process of continuous casting square billet of low-alloy high-strength bridge cable steel Download PDFInfo
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
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- B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
- B22D11/225—Controlling or regulating processes or operations for cooling cast stock or mould for secondary cooling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/34—Methods of heating
- C21D1/42—Induction heating
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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Abstract
The invention discloses a heat treatment production process of a low-alloy high-strength bridge cable steel continuous casting square billet, which comprises, by weight, 0.90-1.20% of C, 0.90-1.10% of Si, 0.60-0.90% of Mn0.90, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 0.20-0.40% of Cr0.20, 0.60-0.80% of Nb + V, 0.010-0.015% of Ti0.005-0.015% of N, and 0.0005-0.0015% of B. According to the invention, titanium nitride particles precipitated in the solidification process of the continuous casting billet are used as nucleation points of new austenite in the austenitizing process of heating of the electromagnetic induction coil, and the titanium nitride particles and acicular ferrite are used as nucleation points of new austenite, and the austenite is refined under the action of the austenite boundary pinning of the particles, so that coarse columnar crystal structures in the continuous casting billet are reduced or eliminated, refined structures are provided for the production of the subsequent process, and the structures and the performances of final products can be further improved.
Description
Technical Field
The invention relates to the technical field of high-strength steel heat treatment, in particular to a heat treatment production process of a low-alloy high-strength bridge cable steel continuous casting square billet.
Background
The macrostructure in the continuous casting billet consists of three crystal bands from outside to inside: fine equiaxed zone (chill layer), columnar zone, central equiaxed zone (see figure 1). The plasticity of a steel cast slab is poor for general steel products because the grain boundaries of adjacent columnar crystals are relatively flat, the crystal grains are not as firm as equiaxed crystals bonded to each other, and particularly, the junctions of the columnar crystals extending in different directions tend to have fragile interfaces, so that the steel cast slab is easy to crack during rolling. The columnar crystals are also liable to cause internal cracks in the cast slab, and the coarse columnar crystals continue to affect the structure and properties of the product. With the development of national large bridge construction, the strength grade of the bridge cable steel wire is developed from the past grades of 1670MPa, 1770MPa and 1860MPa to the grades of 1960MPa and 2000MPa, and the development of the bridge cable steel wire with the grade of 2500MPa is carried out. Because the bridge cable steel wire is required to have high strength and high toughness (the twisting and bending times of the steel wire are more than 14 times), the bridge cable steel wire has higher requirements on chemical components, metallographic structures and mechanical properties of bridge cable steel wire products. In order to meet the requirement of users on high strength and high toughness, at present, iron and steel enterprises at home and abroad such as Japan Shenhu, New day iron, Chinese Bao steel, saddle steel, Xingchen and the like adopt bloom continuous casting (the edge size of the cross section of a casting blank is in the range of 200 mm-600 mm), and after cogging and rolling are carried out to form a small square blank (the edge size of the cross section of the casting blank is in the range of 100 mm-200 mm), bridge cable steel wire rods are rolled, so that the component segregation in the casting blank can be improved, the cast structure (fine isometric crystal, columnar crystal and isometric crystal) of the continuous casting blank can be converted into a rolled structure, the influence of the columnar crystal on the structure and the performance of the subsequent process is reduced, the grain size is refined, and the quality indexes of the bridge cable steel wire rod performance and the like are improved.
At present, the cogging and rolling process of continuous casting bloom is adopted when various steel mills produce bridge cable steel wires: molten steel in a ladle enters a crystallizer through a tundish to be solidified into a continuous casting bloom, the bloom is pulled out of the crystallizer by a straightening and withdrawal roller, and after passing through a secondary cooling area of a fan-shaped section of the continuous casting machine, a casting blank is cut according to a fixed size. Before cogging, a continuously cast bloom is charged into a heating furnace, heated until the structure in the steel becomes austenitic, and then rolled into the size of a small bloom. The production process has the advantages that the process of cooling the bloom and then putting the bloom into the heating furnace again for heating is adopted, the production time is prolonged (the heating time is at least more than 100 min), and the energy consumption is increased. At present, the wire market competition is becoming white and daily, and the product homogenization is serious, so how to better meet the user requirements, improve the user efficiency and reduce the user cost is a problem which iron and steel production enterprises have to face.
In order to reduce the energy consumption of reheating the blank between the continuous casting and the high-speed wire drawing process, at present, hot-feeding hot charging and direct rolling technologies are adopted in some steel mills at home and abroad, so that the production efficiency is improved, and the energy is saved and the consumption is reduced. However, in the production process of heating continuous casting billet austenitization by adopting a hot-feeding and hot-charging technology or a direct rolling technology, coal, gas, oil and electricity are used as power supplies in the traditional method, and heat is transferred to the continuous casting billet by radiation, convection, conduction and the like. The heating device includes a pit furnace, a through-type continuous furnace of a bell-type furnace, and the like, and is generally called an external heating furnace. There are three main disadvantages to externally heated heating: (1) the heating time is long, the continuous casting billet heating time is more than 100min for a continuous heating furnace, the time of periodic heating furnaces such as a pit furnace, a bell-type furnace and the like is several hours, the production efficiency is low, and the phenomena of surface oxidation and decarburization occur; (2) the efficiency of the external heating furnace is low, the efficiency of the fuel furnace is lower than 40-50%, the efficiency of the resistance furnace is about 70%, and the external heating furnace has large thermal inertia and needs longer start preheating time. (3) Longer heating time causes the depth of a decarburized layer to be increased, the size of austenite grains to be abnormally increased, and an abnormal structure (such as widmanstatten) of overburning to be generated. Therefore, the production efficiency, energy conservation and consumption reduction of the external heating type heating furnace and the heating process can be further improved.
Since the second half of the 20 th century, the development and progress of semiconductor technology, computer control and metal rapid heating phase change theory greatly improve the energy conversion efficiency of induction heating, increase the reliability and realize the automatic control of the whole production process. Induction heating is the generation of eddy currents by the alternating magnetic field of an inductor, and the eddy currents convert electromagnetic energy into joule heat in metal, thereby becoming an ideal choice for heat treatment heating. However, due to the skin effect of induction heating (the temperature rise is concentrated on the surface of the metal), induction heating techniques are often used for heating thin slabs or partially compensating the surface of a continuously cast slab to obtain temperature uniformity. For the continuous casting square billet with small length-width ratio of the edge part of the cross section, how to adopt the induction heating technology to improve the integral temperature of the continuous casting billet is a problem with great practical significance to be solved.
On the other hand, the addition of alloy elements such as niobium, vanadium, titanium and the like to the steel helps to improve the strength of the high-strength bridge cable steel to a certain extent. Wherein a small amount of titanium can form a large amount of nano-scale titanium nitride particles with small sizes and dispersed distribution, and the dispersed particles can pin austenite grain boundaries to move in the austenite transformation process, thereby effectively inhibiting the austenite grain growth in the coarse grain region of a heat affected zone. However, the temperature of molten steel during steel making and continuous casting is 1500 ℃ or higher, titanium nitride particles are dissolved in the molten steel, and the titanium nitride particles are not formed during cooling of a strand, and thus the formation of coarse columnar crystals cannot be prevented. Therefore, how to reduce the coarse columnar crystals by utilizing the "pinning" effect of the titanium nitride particles is also a problem to be solved.
In the aspect of titanium nitride particle refined structure, Chinese invention patent (application No. CN200610026267.3, application No. 2006.04.29) discloses a Fe-Ti-N grain refiner of steel in the technical field of metal materials and a preparation method thereof, wherein the grain refiner comprises the following components in percentage by weight: 35-99.4% of Fe, 0.5-50% of Ti and 0.1-15% of N, and the grain refiner contains TiN particles which are dispersed and distributed. The method comprises the following steps: putting 40-99.5% of pure iron and 0.5-60% of Ti into a crucible of a vacuum medium-frequency induction furnace, heating and melting, and keeping the temperature of a melt at 1550-1650 ℃; introducing nitrogen into the vacuum intermediate frequency induction furnace to keep the nitrogen partial pressure in the furnace at 0.01-0.1 MPa; the vent pipe is inserted into the alloy melt and nitrogen is blown, the vent pipe is drawn out after the preset time is reached, power is cut off and casting is carried out, and after a small amount of Fe-Ti-N grain refiner obtained by adopting the method is added into the steel melt, the size of cast structure equiaxial grains is greatly reduced, the proportion of equiaxial zones is improved to more than 60 percent, and the refining effect of the grain refiner is obvious.
In the aspect of continuous casting billet induction heating, the Chinese patent application (application No. CN201710240071.2, application No. 2017.4.13) discloses a continuous casting billet induction heating fast self-adaptive temperature control method based on mechanism model simplification setting, namely, the mechanism model refers to a finite element induction heating grid modeling method, electromagnetic coupling, eddy current heat generation, heat conduction, heat radiation and other evolution in the whole process of electromagnetic induction heating are inspected, and the mechanism model is abstractly simplified into mapping state equations of an initial state and a final state. The patent application mainly establishes an induction heating grid model, and improves the repeatability precision of the model through data checking.
However, how to reasonably arrange the induction heater and the continuous casting billet and reduce or eliminate the coarse columnar crystal structure in the continuous casting billet is a technical problem to be solved urgently.
Disclosure of Invention
The invention aims to provide a heat treatment production process of a low-alloy high-strength bridge cable steel continuous casting square billet, which can improve the efficiency and reduce or eliminate the influence of coarse as-cast crystal grains so as to improve the structural uniformity of a product, aiming at the defects of the technology.
In order to realize the aim, the heat treatment production process of the low-alloy high-strength bridge cable steel continuous casting square billet comprises the following steps:
1) smelting the molten steel according to preset components, and continuously casting to form a continuous casting square billet;
2) continuously casting the square billet through a secondary cooling area of a fan-shaped section of a continuous casting machine, controlling the surface temperature of the continuously cast square billet to be cooled to 500-800 ℃, wherein the cooling rate is not more than 200 ℃/m;
3) heating the continuous casting square billet subjected to the step 2) to 1000-1450 ℃ sequentially through a plurality of electromagnetic induction coils, so that the structure of the continuous casting square billet is completely converted into an austenite structure;
4) cooling the continuous casting square billet obtained in the step 3) to 500-800 ℃, and then, hot-conveying the continuous casting square billet to a rolling production line, or cooling the continuous casting square billet obtained in the step 3) to room temperature and then storing the continuous casting square billet;
wherein, the chemical components of the low-alloy high-strength bridge cable steel comprise the following components in percentage by weight:
c: 0.90-1.20 wt%, Si: 0.90-1.10 wt%, Mn: 0.60-0.90 wt%, P is less than or equal to 0.01 wt%, S is less than or equal to 0.01 wt%, Cr: 0.20-0.40 wt%, Nb + V: 0.60-0.80 wt%, Ti: 0.010-0.015 wt%, N: 0.005-0.015 wt%, B: 0.0005 to 0.0015 wt%, the balance being Fe and unavoidable impurities.
Separating out TiN particles in the process that the continuous casting square billet passes through a fan-shaped section secondary cooling area of a continuous casting machine, cutting the continuous casting square billet according to the sizing requirement, heating by adopting an electromagnetic induction coil when the surface temperature of the continuous casting square billet is cooled to 500-800 ℃, heating to 1000-1450 ℃, and completely converting the structure in the continuous casting square billet steel into an austenite structure; in the process of reconverting the as-cast structure into austenite, new austenite forms nuclei at TiN particles and acicular ferrite, the TiN particles pin new austenite grain boundaries (see figure 2 as a grain boundary diagram of the austenite structure of the high-strength bridge steel at 1000 ℃, titanium nitride particles at white arrows, and titanium nitride particles at black arrows), the austenite growth is prevented (see figure 3 as a grain boundary diagram of the austenite structure of the high-strength bridge steel with titanium nitride particles pinned at 1200 ℃ and titanium nitride particles at black arrows), and the nucleation sites at the TiN particles (see figure 4 as a titanium nitride grain diagram in the high-strength bridge steel at 583 ℃, and titanium nitride particles at white arrows), the acicular ferrite growth is promoted (see figure 5 as a growth diagram of the acicular ferrite at the titanium nitride particles observed at 582 ℃, and titanium nitride particles at white arrows), so that the size of the new austenite (see figure 6 as a refined austenite structure diagram after induction heating) is smaller than the original austenite (see figure 7) An austenite diagram before induction heating) to reduce the influence of coarse columnar crystals in the continuous casting billet on the structure and the performance of a product in a subsequent process; and then, the continuous casting blank cooled to 500-800 ℃ can be sent to a rolling production line in a hot mode, and can also be stored after being cooled to room temperature.
The above alloy composition design is explained in detail below:
c: steel is iron-carbon alloy, carbon is the most important constituent element in steel, and the carbon content directly determines the strength and plasticity of the steel. In the cold-drawn state, the tensile strength is continuously improved along with the increase of the carbon content, the tensile strength is continuously improved along with the increase of the total compression ratio, the carbon content is improved faster, and the plasticity is reduced along with the increase of the carbon content. Thus, invention C: 0.90 to 1.20 wt%.
Si: silicon is an important strengthening element in steel, can obviously improve the elastic limit of the drawn steel wire, can effectively reduce the strength reduction caused by heat treatment, and simultaneously can slow down the breakage of cementite in the drawing process and improve the comprehensive mechanical property of the steel wire. Therefore, in order to make up for the strength gap caused by the reduction of the carbon content and improve the performance of the drawn steel wire, the silicon content of the invention is obviously higher than that of the traditional bridge cable steel. Thus, the Si: 0.90 to 1.10 wt%.
Mn: the affinity of manganese with sulfur and oxygen is greater than that of iron, it is a good deoxidizer for steel-making, the manganese sulfide and manganese oxide produced in smelting reaction do not produce harmful effect on cold-drawing property of wire rod, and the manganese and manganese sulfide are combined to produce MnS, and can reduce harmful action of sulfur. Manganese also increases the relative amount of pearlite and makes pearlite fine. Therefore, the increase of the manganese content increases the strength and hardness of the steel wire, and the yield limit and the reduction of area are also increased. Therefore, the Mn: 0.60 to 0.90 wt%.
P, S: phosphorus and sulfur are harmful elements in the steel, phosphorus is easy to produce cold brittleness, sulfur is easy to produce hot brittleness, and further the processing conditions of steel wire drawing and heat treatment are deteriorated, so the content of the phosphorus and the sulfur needs to be reduced as much as possible. The invention has P less than or equal to 0.01 wt% and S less than or equal to 0.01 wt%.
Cr: the chromium can refine pearlite lamella and improve the strength of finished steel wires, but the excessively high chromium can improve the hardenability of wire rods, so that abnormal structures such as martensite appear in the hot rolling process, and meanwhile, the excessively small lamella can reduce the toughness of wire rods, so that the torsion performance which is the most key index of the steel wires is deteriorated, therefore, the Cr: 0.20 to 0.40 wt%.
Nb + V: vanadium has a high solubility in niobium and vanadium nitrides compared to other microalloys, allowing it to dissolve at normal heating temperatures, whether rolling or forging. The normal heating temperature is 900 to 1150 c, which is sufficient to dissolve all vanadium carbo-nitrides throughout the process to obtain the alloy composition. The linear relationship between niobium and vanadium additions and strength is very helpful in estimating the amount of alloy addition required to meet the minimum strength. The invention Nb + V: 0.60 to 0.80 wt%.
Ti: a small amount of titanium is added into the steel to form a large amount of nano titanium nitride particles with small sizes and fine dispersion distribution, and the dispersion distribution particles can pin austenite grain boundaries to move in the austenite transformation process, so that the growth of austenite grains in a coarse grain region of a heat affected zone is effectively inhibited. Meanwhile, TiN can be used as an effective nucleation particle to promote acicular ferrite nucleation in the cooling process. However, excessive Ti causes the TiN particles to grow and remelt at high temperature, thereby losing the effect of inhibiting the growth of austenite grains. Thus, the Ti: 0.010-0.015 wt%.
N: like carbon, nitrogen is dissolved in iron as a solid solution to form an interstitial solid solution, which plays roles of solid solution strengthening and time-efficient precipitation strengthening in steel, and it expands the gamma phase region to form and stabilize the austenite structure. When the nitrogen content exceeds a certain limit, the nitrogen is easy to form fine particles with elements such as titanium, niobium and the like in the steel, and the nitrogen plays a role in precipitation strengthening. Thus, the present invention N: 0.005-0.015 wt%.
B: trace boron in the high-carbon steel can inhibit the enrichment of P in grain boundaries and improve the form of inclusions, so that the cold processing performance of the wire rod can be improved, but excessive boron can weaken the bonding force of the grain boundaries and deteriorate the mechanical performance of the wire rod. Thus, invention B: 0.0005 to 0.0015 wt%.
Further, in the step 1), the specification of the continuous casting billet is as follows: the size of the edge of the cross section of the continuous casting square billet is 100-200 mm.
Further, in the step 3), the number of the electromagnetic induction coils is 1-3, the length of each electromagnetic induction coil is 2000-5000 mm, and the distance between each electromagnetic induction coil and the surface of the continuous casting square billet is 10-300 mm.
Further, in the step 3), in order to improve the heating efficiency of the continuous casting square billet, the current intensity of each electromagnetic induction coil is 5000-10000A, the heating frequency is 50-2000 Hz, the speed of the continuous casting square billet passing through each electromagnetic induction coil is 0.1-1.0 m/min, the continuous casting square billet has enough time to be heated to 1000-1450 ℃, the continuous casting square billet is ensured to be completely austenitized, and TiN particles are controlled not to be re-dissolved into austenite.
The principle of separating out titanium nitride particles and refining an austenite structure is as follows:
in the invention, titanium element in the high-strength bridge cable steel is precipitated into titanium nitride particles at the solidification later stage of the continuous casting billet, and the solubility product of TiN in an austenite phase along with the temperature change is shown as a formula (1):
Lg[w(Ti)d·w(N)d]γ＝4.35－14890/T (1)
in the formula, w (Ti)dAnd w (N)dThe mass fractions of Ti and N dissolved in austenite are respectively: t is the temperature at that time, K. It is also important to control the ratio of Ti to N content. Since undissolved Ti and N were matched with each other at a mass ratio of 3.42, as shown below:
[w(Ti)t－w(Ti)d]/[w(N)t－w(N)d]＝3.42 (2)
wherein w (Ti) t and w (N) t are the total mass fraction of Ti and N in the steel respectively. The temperature at which the titanium nitride particles in the sample began to precipitate was calculated to be 1453 ℃ from the simultaneous equation (1) and the equation (2). The solidification temperature of the steel was calculated to be 1521 ℃ by Thermo-calc calculation software and SSOL4 database. Therefore, in the present invention, in order to obtain a large amount of fine dispersion of TiN particles in the steel, it is necessary to control the heating temperature not to exceed 1450 ℃. And the Ti and N contents of the material are reasonably controlled, and titanium nitride particles which are small in quantity, large in size and uneven in distribution are prevented from being formed in molten steel. Therefore, the temperature at which TiN particles start to precipitate must be controlled to be lower than the solidification temperature of molten steel in accordance with the requirements of Ti and N contents.
TiN particles are precipitated in the cooling process after the continuous casting billet is solidified, so that a large number of fine dispersed nano-scale particles with the average size of about 30nm are formed. The dispersion-distributed particles are relatively stable at high temperature, and can promote the nucleation of TiN particles during induction heating to generate a large amount of austenite. And moreover, the movement of the austenite grain boundary is pinned in the austenite transformation process of the continuous casting billet, so that the growth of the austenite grains in a coarse columnar grain region is effectively inhibited. The more evenly and dispersedly the TiN particles are distributed, the smaller the size is, and the more the TiN particles are distributed, the more obvious the inhibiting effect on the growth of the austenite grains is.
The formation and refinement principle of needle-shaped ferrite:
MnS is precipitated in the steel, so that a manganese element lean area is formed around the inclusion, the existence of the lean area causes the stability of austenite around the inclusion to be reduced, the transformed Ae3 temperature is improved, the driving force of ferrite nucleation is increased, and the acicular ferrite nucleation is facilitated; in addition, the TiN particles and the acicular ferrite are in a body-centered cubic structure, the lattice constants are 0.423nm and 0.287nm respectively, and the TiN particles and the acicular ferrite have good coherent relation, can effectively reduce the interface energy and promote the acicular ferrite to nucleate. The change of solute element composition around the inclusion in the nucleation mechanism and the promotion of ferrite nucleation by the low-energy interface of the precipitate and acicular ferrite play a decisive role. Therefore, the adhered TiN particles have a strong ability to promote the nucleation of the acicular ferrite.
The austenite grain size is very fine due to the formation of acicular ferrite, which then maintains a fixed orientation with the prior austenite and grows in different directions with a large angle therebetween, and these acicular ferrite can also be nucleation sites of new austenite, refining the columnar grain structure during the phase transformation of austenite → ferrite → austenite (γ → α → γ) upon cooling and then induction heating of the continuously cast billet.
The principle of controlling thick columnar crystals in a continuous casting billet is as follows:
the macrostructure in the continuous casting billet consists of three crystal bands from outside to inside: the small equiaxed crystal bands, the columnar crystal bands and the central equiaxed crystal bands have poor plasticity of steel casting blanks for general steel products, because the grain boundaries of adjacent columnar crystals are relatively flat, the crystals are not as firm as equiaxed crystals bonded with each other, and particularly, a fragile interface is often formed at the joint of the columnar crystals extending along different directions. Therefore, cracking is likely to occur during rolling. The columnar crystals are easy to generate internal cracks in the casting blank, and the equiaxed crystal area has no obvious weak surface, so that the inter-grain hasp is firm, and the columnar crystals are not easy to crack during hot processing.
Columnar crystals in the continuous casting billet are gradually formed in the process that the casting billet is discharged from the crystallizer and enters a secondary cooling area. The method for reducing or eliminating the coarse as-cast structure in the continuous casting billet is to separate out TiN particles to form acicular ferrite after the molten steel in the continuous casting billet is completely solidified. Heating to 1000-1450 ℃ within the range of 500-800 ℃ by electromagnetic induction heating, and austenitizing all tissues in the continuous casting square billet. The new austenite forms nuclei in titanium nitride particles and acicular ferrite, grows across the prior austenite grain boundary, and refines the austenite through the pinning effect of the titanium nitride particles, and the size of the new austenite is smaller than that of the prior austenite, thereby reducing the influence of coarse columnar crystals.
Principle of electromagnetic induction heating
Electromagnetic induction heating is an induced current generated in a high-frequency magnetic field by using self-heating and heating a conductor. The principle of magnetic field induced eddy current is that the current passing through the coil generates a magnetic field, the magnetic field in the magnetic metal material can make the metal body generate countless small eddy currents (a plurality of closed rotating current objects are generated by the action of the alternating magnetic field of the induction coil in the metal body in the electromagnetic field), and because the current has the thermal effect, the current can generate a large amount of internal heat, so that the metal material is heated at high temperature.
For a continuous casting bloom, induction heating belongs to an electromagnetic-thermal coupling process, an electromagnetic field and a temperature field influence each other, electromagnetic laws all follow a Maxwell differential equation set and can be expressed as an equation set of a formula (3):
in the formula:is Laplace operator; d is the electric flux density, C/m2(ii) a Rho is the charge density, C/m3(ii) a E is the electric field intensity, V/m; b is magnetic induction, Wb/m2(ii) a H is the magnetic field intensity, A/m; j is the current density vector, A/m2(ii) a t is time, s.
The method is beneficial to solving the electromagnetic field by a complex vector magnetic potential method in ANSYS software, and a vector magnetic vector A is introduced, wherein the vector magnetic vector is defined as:
substituting the equation set of equation (3), a finite element equation for solving the alternating magnetic field can be obtained as follows:
[K+jωC]{A}＝{F} (5)
in the induction heating process of the continuous casting billet, the change of the temperature field is a typical three-dimensional unsteady heat conduction process with an internal heat source. The thermal conductivity differential equation can be expressed as equation (6).
The casting blank runs in the inductor, and belongs to an unsteady heat conduction process with an uneven internal heat source, wherein the heat source is derived from eddy current, namely the power loss of an electromagnetic field in the casting blank is neglected, and the unsteady heat conduction process with the uneven internal heat source is realized by neglecting the axial heat conduction of the casting blank:
in the formula: t is temperature, K; k is the thermal conductivity, W (/ m.K); q. q.svIs the intensity of an internal heat source, W/m3；ρdIs density, kg/m3(ii) a c is the specific heat capacity, J (/ kg. K).
Before the casting blank enters the inductor and runs between the inductors, the casting blank belongs to an unsteady heat conduction process without an internal heat source, wherein the internal heat source item is as follows: q. q.svIn the temperature field solving process, the heat loss of the workpiece is mainly caused by thermal convection and thermal radiation. The boundary condition analysis of the temperature field can be expressed as equation (7).
In the formula: k is a radical ofx、ky、kzThe thermal conductivity in the x, y and z directions, W (/ m.K); n isx、ny、nzRespectively are three-dimensional direction vectors of a space domain; alpha is alphacW (/ m) as convective heat transfer coefficient2·K)；αrW (/ m) is emissivity2·K)；Tα、TsThe temperature of the workpiece periphery environment and the workpiece surface temperature, K, respectively.
Compared with the prior art, the invention has the following beneficial effects:
1) the mechanical property of the bridge cable steel wire is improved by low alloy elements, and simultaneously, the titanium nitride particles precipitated in the continuous casting billet solidification process are facilitated, the titanium nitride particles and acicular ferrite serve as nucleation points of new austenite in the austenitizing process heated by the electromagnetic induction coil, and austenite is refined under the action of the 'pinning' austenite boundary of the particles, so that thick columnar crystal structures in the continuous casting billet are reduced or eliminated, refined structures are provided for the production of the subsequent process, and the structures and the performance of final products can be further improved
2) The heating speed of the electromagnetic induction coil is high, the thick cast structure is prevented from further growing up in the post process, the heating time is shortened, and compared with external heating type heating, the energy consumed by the blank in the heating process is saved by using the high-temperature waste heat of the continuous casting blank;
3) the process flow that the high-strength bridge cable steel continuous casting billet must be subjected to secondary fire cogging is broken through, the process flow is simplified for iron and steel enterprises, energy is saved, emission is reduced, the production cost of the enterprises is reduced, and the market competitiveness is improved.
Drawings
FIG. 1 is a schematic diagram of a cross-sectional structure of a continuous casting slab;
FIG. 2 is a diagram of austenite structure grain boundaries of high-strength bridge cable steel at 1000 ℃;
FIG. 3 is a diagram of austenite structure grain boundary of high-strength bridge cable steel pinned by titanium nitride particles when the temperature is raised to 1200 ℃;
FIG. 4 is a graph of titanium nitride particles observed in high-strength bridge cable steel at 583 ℃;
FIG. 5 is a graph showing growth of acicular ferrite at titanium nitride particles observed at 582 ℃;
FIG. 6 is a view of a refined austenite structure after induction heating;
fig. 7 is an austenite diagram before induction heating.
Detailed Description
By controlling the chemical components of the low-alloy high-strength bridge cable steel and controlling the heat treatment process parameters, a more refined and uniform structure can be obtained. The present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, specific examples and comparative examples, which are not intended to limit the invention.
Table 1 is a list of chemical compositions for each example and comparative example of the present invention, with the balance being iron;
table 2 is a list of process parameters of the heating process of the electromagnetic induction coils of each example and comparative example of the present invention;
table 3 is a table listing the experiments of the examples and comparative examples of the present invention.
TABLE 1 (wt%)
| Item | C | Si | Mn | P | S | Cr | Nb+V | Ti | N | B |
| Example 1 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.010 | 0.010 | 0.0010 |
| Example 2 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.012 | 0.010 | 0.0010 |
| Example 3 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.015 | 0.010 | 0.0010 |
| Comparative example 1 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.009 | 0.010 | 0.0010 |
| Comparative example 2 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.016 | 0.010 | 0.0010 |
| Comparative example 3 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.012 | 0.010 | 0.0010 |
| Comparative example 4 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.012 | 0.010 | 0.0010 |
TABLE 2
TABLE 3
Claims (2)
1. A heat treatment production process of a low-alloy high-strength bridge cable steel continuous casting square billet is characterized by comprising the following steps of: the continuous casting square billet heat treatment production process comprises the following steps:
1) smelting the molten steel according to preset components, and continuously casting to form a continuous casting square billet;
2) continuously casting the square billet through a secondary cooling area of a fan-shaped section of a continuous casting machine, controlling the surface temperature of the continuously cast square billet to be cooled to 500-800 ℃, wherein the cooling rate is not more than 200 ℃/m;
3) heating the continuous casting square billet subjected to the step 2) to 1000-1450 ℃ sequentially through a plurality of electromagnetic induction coils; the number of the electromagnetic induction coils is 1-3, the length of each electromagnetic induction coil is 2000-5000 mm, and the distance between each electromagnetic induction coil and the surface of the continuous casting square billet is 10-300 mm; the current intensity of each electromagnetic induction coil is 5000-10000A, the heating frequency is 50-2000 Hz, and the speed of the continuous casting billet passing through each electromagnetic induction coil is 0.1-1.0 m/min;
4) cooling the continuous casting square billet obtained in the step 3) to 500-800 ℃, and then, hot-conveying the continuous casting square billet to a rolling production line, or cooling the continuous casting square billet obtained in the step 3) to room temperature and then storing the continuous casting square billet;
wherein, the chemical components of the low-alloy high-strength bridge cable steel comprise the following components in percentage by weight:
c: 0.90-1.20 wt%, Si: 0.90-1.10 wt%, Mn: 0.60-0.90 wt%, P is less than or equal to 0.01 wt%, S is less than or equal to 0.01 wt%, Cr: 0.20-0.40 wt%, Nb + V: 0.60-0.80 wt%, Ti: 0.010-0.015 wt%, N: 0.005-0.015 wt%, B: 0.0005 to 0.0015 wt%, the balance being Fe and unavoidable impurities.
2. The continuous casting square billet heat treatment production process of the low-alloy high-strength bridge cable steel as claimed in claim 1, which is characterized in that: in the step 1), the specification of the continuous casting square billet is as follows: the size of the edge of the cross section of the continuous casting square billet is 100-200 mm.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2003328077A (en) * | 2002-05-16 | 2003-11-19 | Nippon Steel Corp | High-strength rolled and plated pc steel bar, and manufacturing method therefor |
| CN1743491A (en) * | 2004-08-30 | 2006-03-08 | 宝山钢铁股份有限公司 | Manufacture method for obtaining superfine crystal grain steel |
| CN102181786A (en) * | 2011-04-25 | 2011-09-14 | 江苏省沙钢钢铁研究院有限公司 | Coil rod used for 1670MPa level bridge cable zinc-coated wire and preparation method of coil rod |
| CN105112807A (en) * | 2015-10-08 | 2015-12-02 | 武汉钢铁(集团)公司 | High-strength bridge cable steel with pearlite inter-lamellar spacing smaller than 150nm and production method |
| CN106694834A (en) * | 2016-11-16 | 2017-05-24 | 北京科技大学 | Microalloyed steel continuous casting cooling control method based on steel grade solidification characteristic and evolution of microstructures |
-
2018
- 2018-10-30 CN CN201811280975.9A patent/CN109136773B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2003328077A (en) * | 2002-05-16 | 2003-11-19 | Nippon Steel Corp | High-strength rolled and plated pc steel bar, and manufacturing method therefor |
| CN1743491A (en) * | 2004-08-30 | 2006-03-08 | 宝山钢铁股份有限公司 | Manufacture method for obtaining superfine crystal grain steel |
| CN102181786A (en) * | 2011-04-25 | 2011-09-14 | 江苏省沙钢钢铁研究院有限公司 | Coil rod used for 1670MPa level bridge cable zinc-coated wire and preparation method of coil rod |
| CN105112807A (en) * | 2015-10-08 | 2015-12-02 | 武汉钢铁(集团)公司 | High-strength bridge cable steel with pearlite inter-lamellar spacing smaller than 150nm and production method |
| CN106694834A (en) * | 2016-11-16 | 2017-05-24 | 北京科技大学 | Microalloyed steel continuous casting cooling control method based on steel grade solidification characteristic and evolution of microstructures |
Non-Patent Citations (1)
| Title |
|---|
| 大跨度桥梁缆索用钢的发展及制造技术;任安超等;《天津冶金》;20171015(第05期);第33页第2节 * |
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