CN111187980B - Rare earth microalloyed high-strength construction steel bar and production method thereof - Google Patents
Rare earth microalloyed high-strength construction steel bar and production method thereof Download PDFInfo
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- CN111187980B CN111187980B CN202010088297.7A CN202010088297A CN111187980B CN 111187980 B CN111187980 B CN 111187980B CN 202010088297 A CN202010088297 A CN 202010088297A CN 111187980 B CN111187980 B CN 111187980B
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/108—Feeding additives, powders, or the like
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/116—Refining the metal
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/08—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires for concrete reinforcement
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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Abstract
The invention discloses a rare earth microalloyed high-strength construction steel bar and a production method thereof, belongs to the technical field of steel for building structures, provides a novel high-strength construction steel bar, develops a rare earth alloy cored wire aiming at rare earth microalloyed high-strength steel bar varieties, obtains qualified steel bars meeting the national standard requirements in the production of the high-strength steel bars, and solves the problem of higher cost caused by commonly used expensive elements such as V and the like in the prior art. The construction steel bar comprises the following chemical components in percentage by weight: c: 0.20-0.25%, Si: 0.40-0.80%, Mn: 1.1% -1.60%, RE > 0.025%, P: < 0.045%, S: < 0.045%, O, Ca + Mg satisfy the following mass percentages: O/S is less than 0.2, and RE/(Ca + Mg) is controlled to be between 10 and 100; the balance of Fe and inevitable impurities. The construction steel bar meets the national standard requirements and reduces the cost.
Description
Technical Field
The invention belongs to the technical field of steel for building structures, and particularly relates to a rare earth microalloyed high-strength building steel bar and a production method thereof.
Background
The development of rare earth steel has been in history for decades, China is a large rare earth producing country, and the rare earth production and application technology in steel are at the leading level in the world. The application of rare earth in steel includes rare earth treatment technology and rare earth microalloying technology. The role of rare earths in steel includes: purifying molten steel, improving the form of inclusions, improving solidification structure and microalloying. The effects of the rare earth microalloying which play an obvious role at present comprise: has obvious effects on the aspects of wear resistance, corrosion resistance, heat resistance, low temperature resistance, fatigue resistance, oxidation resistance, high temperature durability, electromagnetic property improvement and the like of steel. The steel types treated with rare earth include engineering structural steel, gear steel, ultra-high strength structural steel, spring steel, bearing steel, tool steel, weathering steel, stainless acid-resistant steel, heat-resistant steel and electrothermal alloy, high manganese steel, cast steel, and the like. It is not deep enough in rare earth microalloying, and it is thought that because the atomic radius of rare earth elements is much larger than that of iron, in order to reduce distortion energy caused in a matrix, solid-dissolved rare earth atoms tend to interact with crystal defects such as dislocations, grain boundaries and the like, and grain boundary segregation and solute gas clusters of solute atoms are formed. Grain boundary segregation of rare earth elements is grain boundary equilibrium segregation. Meanwhile, because the large atom size of the rare earth has limited solid solution amount in steel and the particle size of the rare earth oxysulfide is large, the research on the basic functions of microalloying, such as solid solution strengthening, precipitation strengthening and fine grain strengthening, needs to be deeply researched, and the contribution effect of the rare earth on the strength of steel is not widely recognized.
According to the regular mechanism of solid solution formation by Hume-Rothery, the difference in atomic sizes between solute and solvent is no more than 15% and has greater solubility. The atomic diameters of rare earth elements (e.g., yttrium, rhenium, cerium) and iron differ by more than 42% as shown in table 1. The difference in atomic diameter between iron and these rare earth elements is much greater than 15%. The resulting lattice distortion is quite high when rare earth metal atoms replace iron atoms in the crystal lattice. It is believed that the atomic arrangement of the grain boundaries is looser, with more voids providing the large rare earth atoms. If a rare earth metal atom moves from the crystal interior to the grain boundary, the distortion energy is necessarily reduced. Therefore, the rare earth metal atom meta-particle grain boundary is a spontaneous process, the solid solution strengthening effect of the rare earth element is poor, and the rare earth element is generally considered to be not easy to apply in steel production in the industry, so the rare earth element is rarely used in steel production, especially in the production of construction steel bars.
TABLE 1 rare earth element/iron atomic diameter
| Element(s) | α-Fe | Y | β-La | β-Ce |
| Crystal structure | BCC | HCP | DHCP | FCC |
| Atomic radius, nm | 0.127 | 0.1803 | 0.1877 | 0.1824 |
| A difference in size% | 0 | 42 | 47.4 | 43.2 |
Disclosure of Invention
In view of the above analysis, the invention aims to provide a rare earth microalloyed high-strength construction steel bar and a production method thereof, the invention adopts rare earth as microalloyed element addition, provides a new high-strength construction steel bar, develops a special rare earth alloy cored wire and a continuous casting production wire feeding process technology thereof aiming at rare earth microalloyed high-strength steel bar varieties, obtains qualified steel bars meeting the national standard requirements in the production of high-strength steel bars, and solves the problem of higher cost caused by commonly used expensive elements such as V and the like in the prior art.
The purpose of the invention is mainly realized by the following technical scheme:
on one hand, the invention discloses a rare earth microalloyed high-strength construction steel bar, which comprises the following chemical components in percentage by weight: c: 0.20-0.25%, Si: 0.40-0.80%, Mn: 1.1% -1.60%, RE > 0.025%, P: < 0.045%, S: < 0.045%, O, Ca + Mg satisfy the following mass percentages: O/S is less than 0.2, and RE/(Ca + Mg) is controlled to be between 10 and 100; the balance of Fe and inevitable impurities.
Furthermore, RE is one or more of La, Ce and Y, and RE/S is controlled to be between 1.6 and 2.2.
Further, RE is added in the form of a rare earth core-spun yarn, and the rare earth core-spun yarn is fed into a crystallizer.
Furthermore, the diameter phi of the rare earth core-spun wire is 3-15 mm.
Further, the cross-sectional dimension is 170mm2The following continuous casting billet is a rare earth core-spun wire with the diameter of less than 9mm, and the section size is 170mm2The core-spun wire with the diameter of more than 9mm is selected for the continuous casting billet.
Further, the rare earth core-spun yarn comprises a sheath and a wire core, wherein the wire core is prepared from the following components in percentage by weight: RE: 10% -50%, Si: 10-20%, and the ratio of RE/(Ca + Mg) is 10-100.
Furthermore, the thickness of the outer skin is 0.3-0.5 mm.
Furthermore, the yield strength ReL of the steel bar is more than or equal to 400MPa, the tensile strength Rm is more than or equal to 580MPa, the elongation after fracture is more than or equal to 24 percent, and the maximum total force elongation is more than or equal to 14 percent.
On the other hand, the invention also discloses a production method of the rare earth microalloying high-strength construction steel bar, the rare earth addition adopts a mode of feeding the rare earth core-spun yarn, a stepless speed change yarn feeder is adopted to feed the rare earth core-spun yarn into the crystallizer, and the fluctuation of the temperature difference of inlet and outlet water of the crystallizer is controlled within 2 ℃ in the process of feeding the rare earth core-spun yarn into the crystallizer.
Furthermore, the heating temperature of the steel billet produced by steel rolling of the steel bar is controlled between 1100 ℃ and 1200 ℃, a weak water penetration process is adopted after rolling, and the weak water penetration process is controlled within 50 ℃ above the austenite-ferrite phase transition temperature.
Compared with the prior art, the invention can at least realize one of the following technical effects:
1) based on the spontaneous process of rare earth metal atom partion crystal boundary, the solid solution strengthening effect of rare earth elements is poor, and the rare earth elements are not easy to be applied in the production of steel, the invention innovatively applies the rare earth elements to the production of high-strength steel bars. In research and development, the technical problem of the current rare earth adding process in steel production is a great obstacle to the application of rare earth in steel. Due to rare earth oxides in the rare earth-containing steel, a phenomenon of water gap blockage often occurs in the casting process or the production is not smooth. The invention further researches the adding mode of rare earth, feeds the rare earth core-spun yarn through a continuous casting crystallizer, and solves the technical problems that during continuous casting, a liquid level protective slag layer reacts with the fed rare earth yarn, so that the performance of the liquid level protective slag layer is degraded, the viscosity is increased, even the rare earth yarn is crystallized, during continuous casting and steel casting, molten steel is likely to be coiled with slag, the quality of finished steel billets is affected, the probability of crack generation in the steel billets is increased, and finally the slag surface crusting and steel leakage accidents are directly caused seriously.
2) According to the invention, through the rare earth microalloying high-strength steel bar alloy component control, the rare earth calcium magnesium alloy core-spun yarn and the crystallizer wire feeding production control technology, the crystallizer rare earth feeding yield is high, the required rare earth alloy elements are accurately fed in matching with the continuous casting speed, and the multi-furnace continuous casting stabilization production of the rare earth microalloying high-strength steel bar is successfully realized.
3) In the invention, aiming at the characteristic that small-sized rare earth inclusions with independent nucleation lengths are combined into large-sized inclusions in molten steel due to the higher surface activity of rare earth elements in rare earth microalloyed steel, the sizes of the inclusions exceed the standard, the quality of steel is influenced, the grain refining effect and the effect of blocking grain boundary migration are weakened, a certain amount of Ca and Mg alloy is added into a rare earth alloy cored wire, the discretization and the miniaturization of the rare earth inclusions are realized by utilizing the characteristic that precipitated particles of calcium and magnesium elements have small polymerization tendency and dispersion tendency, the fine-grain rare earth microalloyed high-strength steel bar is produced, and meanwhile, because the magnesium alloy elements are added into rare earth alloy wires, the rare earth inclusions have small aggregation tendency and the power of small-grain inclusions floating is insufficient, the content of rare earth oxides in the protective slag can not be rapidly increased, and the increase of the viscosity of the protective slag, meanwhile, MgO and other components in the covering slag form melilite, olivine, magnesium rosalite and the like with low melting point, so that the melting temperature of the covering slag is reduced, and the viscosity of the covering slag is reduced.
4) Rare earth RE (lanthanum, cerium, yttrium) in the cored wire mixed alloy: the addition of RE in steel can make the steel have good corrosion resistance, and meanwhile, RE purifies the molten steel quality, so that the O, S content in the molten steel is greatly reduced, and the total amount of impurities in the steel is reduced; rare earth oxysulfide is precipitated in a liquid state, and is used as nucleation particles to refine dendritic crystals and inhibit the growth of columnar crystals in the process of casting blank solidification, so that segregation is reduced, a columnar crystal area is shortened, and equiaxed grains are refined; the rare earth elements are partially aggregated at austenite grain boundaries, so that grain boundary nucleation during transformation of a supercooled austenite structure is inhibited, the incubation period is prolonged, the transformation C curve of proeutectoid ferrite and pearlite is shifted to the right, and the hardenability of the steel is improved. The grain boundary segregation of the rare earth elements hinders the grain boundary migration and inhibits the grain growth. Rare earths can refine carbides in the pearlite transformation. The result of refining the columnar crystal structure or the ferrite pearlite structure by improving the equiaxed crystal rate of the casting blank has the effect of improving the strength and the toughness of the steel, particularly refining pearlite lamella, obviously improving the tensile strength of the steel bar, effectively improving the yield ratio of the steel bar and ensuring the anti-seismic performance index.
5) The rare earth core-spun yarn for continuous casting has the advantages that the core-spun yarn can prevent the crystallizer casting powder from deteriorating in the continuous casting, improve the utilization rate of rare earth, ensure the production of high-quality steel, improve the productivity, reduce the unit cost of per ton steel, reduce the probability of generating cracks in steel billets, improve the steel quality and avoid the occurrence of steel leakage accidents of a casting machine caused by the deterioration of the crystallizer casting powder.
6) Heating the billet produced by rolling the rare earth steel bar at 1100-1200 ℃ to prevent austenite grains from growing abnormally and cause the property of the steel bar to fluctuate; the weak water penetration process is adopted after rolling, and the water penetration process after rolling is controlled within 50 ℃ above the austenite-ferrite phase transition temperature, namely the water penetration temperature after rolling is Ar3-Ar3Within +50 ℃. The purpose is to further narrow the performance fluctuation range of the steel bar on the basis of homogenizing and thinning the grain size and ensuring the anti-seismic performance of the steel bar.
7) The room temperature performance of the steel bar rolled according to the technical scheme reaches: the yield strength ReL is more than or equal to 400 MPa. The tensile strength Rm is more than or equal to 580MPa, the elongation after fracture is more than or equal to 24 percent, the yield ratio is more than or equal to 1.40, and the maximum force total elongation is more than or equal to 14 percent. The traditional research considers that the atom size of the rare earth element is larger, the solid solution strengthening effect of the solid solution in steel is poorer, the particle size of the rare earth oxysulfide is larger, and the contribution effect of the rare earth to the strength of steel is not widely recognized. The rare earth microalloyed high-strength steel bar prepared by rare earth elements has high comprehensive performance, and overcomes the technical prejudice of the prior art.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention.
Detailed Description
A rare earth microalloyed high strength construction steel bar and a method for manufacturing the same will be described in further detail with reference to specific examples, which are provided for purposes of comparison and explanation only and to which the present invention is not limited.
A rare earth microalloyed high strength construction steel bar comprises the following chemical components in percentage by weight: c: 0.20-0.25%, Si: 0.40-0.80%, Mn: 1.1% -1.60%, RE > 0.025%, P: < 0.045%, S: < 0.045%, O, Ca + Mg satisfy the following mass percentages: O/S is less than 0.2, and RE/(Ca + Mg) is controlled to be between 10 and 100; the balance of Fe and inevitable impurities.
The action and the proportion of each element of the invention are as follows:
carbon: can directly influence the mechanical properties of the steel, such as strength, toughness and the like. Has obvious solid solution strengthening effect and improves the hardenability of the steel. However, when the content is high, the weldability, corrosion resistance and the like of the steel are deteriorated. The carbon content range of the invention is 0.20-0.25%.
Silicon: important reduction and deoxidation elements, and simultaneously has stronger solid solution strengthening effect, thereby being beneficial to high-temperature strengthening. However, excessive Si lowers the toughness and weldability of the steel. The content of silicon in the steel is 0.40-0.80%, preferably 0.60-0.80%.
Manganese: the deoxidizer and the desulfurizer are good deoxidizers and desulfurizers, play a role in solid solution strengthening in steel, improve the strength and hardness of the steel, improve the quenching performance of the steel and improve the hot workability of the steel, but the plasticity and weldability of the steel can be reduced by increasing the Mn content. The manganese content in the steel of the invention ranges from 1.1% to 1.60%, preferably from 1.45% to 1.60%.
Phosphorus and sulfur: the content of impurity elements in the steel is controlled to be less than 0.045%, preferably within 0.02% and 0.01% respectively, the lower the content is, the better the ductility and the welding performance are, without increasing the cost obviously.
Rare earth RE: the addition of RE in steel can make the steel have good corrosion resistance, and meanwhile, RE purifies the molten steel quality, so that the O, S content in the molten steel is greatly reduced, and the total amount of impurities in the steel is reduced; rare earth oxysulfide is precipitated in a liquid state, and is used as nucleation particles to refine dendritic crystals and inhibit the growth of columnar crystals in the process of casting blank solidification, so that segregation is reduced, a columnar crystal area is shortened, and equiaxed grains are refined; the rare earth elements are partially aggregated at austenite grain boundaries, so that grain boundary nucleation during transformation of a supercooled austenite structure is inhibited, the incubation period is prolonged, the transformation C curve of proeutectoid ferrite and pearlite is shifted to the right, and the hardenability of the steel is improved. The grain boundary segregation of the rare earth elements hinders the grain boundary migration and inhibits the grain growth. Rare earths can refine carbides in the pearlite transformation. The result of refining the columnar crystal structure or the ferrite pearlite structure by improving the equiaxed crystal rate of the casting blank has the effect of improving the strength and the toughness of the steel, particularly refining pearlite lamella, obviously improving the tensile strength of the steel bar, effectively improving the yield ratio of the steel bar and ensuring the anti-seismic performance index. Because the rare earth elements have high surface activity, all small inclusions are mutually attracted, drawn together and combined. On one hand, the method for obtaining the fine rare earth inclusions needs to ensure that the lower the oxygen content and the sulfur content in the molten steel is, the better the oxygen content and the sulfur content in the molten steel is, and in addition, the rare earth content has a proper interval, once the steel is impure or the rare earth addition amount is excessive, the generated composite compounds are gathered into larger particles, string-shaped inclusions are formed after rolling, and meanwhile, RE-Fe brittle intermetallic compounds are generated, so that the performance of the steel is deteriorated. Therefore, the invention adopts the alloy optimization measures and the continuous casting production process optimization measures to effectively control the aggregation and growth of the rare earth inclusions. The rare earth elements RE in the steel can be added jointly or respectively, and the adding amount is controlled between 1.6 and 2.2 according to the ratio of O/S <0.20 and RE/S, so as to determine the content of the rare earth.
Preferably, RE is one or more of La, Ce and Y, and RE/S is controlled to be between 1.6 and 2.2.
RE is added into the rare earth core-spun yarn, and the rare earth core-spun yarn is fed into a crystallizer. The diameter phi of the rare earth core-spun wire is 3-15 mm.
The cross-sectional dimension is 170mm2The following continuous casting billet is a rare earth core-spun wire with the diameter of less than 9mm, and the section size is 170mm2The core-spun wire with the diameter of more than 9mm is selected for the continuous casting billet.
The rare earth core-spun yarn comprises a sheath and a yarn core, wherein the yarn core is prepared from the following components in percentage by weight: RE: 10% -50%, Si: 10-20%, and the ratio of RE/(Ca + Mg) is 10-100. The thickness of the outer skin is 0.3-0.5 mm.
The yield strength ReL of the steel bar is more than or equal to 400 MPa. The tensile strength Rm is more than or equal to 580MPa, the elongation after fracture is more than or equal to 24 percent, and the maximum force total elongation is more than or equal to 14 percent.
A method for producing rare earth microalloyed high-strength construction reinforcing steel bar is characterized in that rare earth is added in a mode of feeding rare earth core-spun yarns by a crystallizer, and the rare earth core-spun yarns are fed into the crystallizer by a stepless speed change yarn feeder.
The rare earth core-spun yarn comprises a sheath and a yarn core, wherein the yarn core is prepared from the following components in percentage by weight: RE: 10% -50%, Si: 10-20%, the addition principle of Mg and Ca is adjusted within the range of 10-100 times according to the ratio of RE/(Ca + Mg), and the balance of Fe.
Specifically, the rare earth core-spun yarn adopts powdery rare earth alloy as a wire core, low-carbon cold-rolled strip steel is wrapped outside the wire core to be used as a sheath, and the rare earth core-spun yarn is produced by a core-spun yarn machine set, wherein the thickness of the sheath is 0.3-0.5 mm. The steel sheath outside the core-spun yarn can prevent the core-spun yarn from being melted once entering molten steel, so that the rare earth alloy in the core-spun yarn does not react with the protective slag layer of the crystallizer.
The rare earth is a mixture mainly containing cerium, lanthanum, yttrium and the like, and can be singly mixed or mixed into the rare earth wire core alloy.
The calcium element and the magnesium element in the core-spun wire mixed alloy, the strong deoxidizing element, the Ca element and the Mg element are used as a strong deoxidizing agent, so that the dissolved oxygen in steel is very low, the growth rate of deoxidized inclusions is reduced, a large amount of fine deoxidized inclusions are obtained, meanwhile, oxides of the calcium and the magnesium are not easy to polymerize in molten steel, the aggregation polymerization growth rate and the upward floating of rare earth oxides are reduced, and the phenomenon that the performance of crystallizer casting powder is deteriorated by the rare earth oxides is delayed and prevented.
In order to prevent the phenomenon of slag turning caused by the fact that the wire feeding speed is too high and the fluctuation amplitude range of the liquid level of the crystallizer is enlarged, different diameters of the rare earth core-spun wires are adopted according to different cross-sectional sizes of continuous casting billets, and the diameter phi of the rare earth core-spun wires is 3-15 mm. The cross-sectional dimension is 170mm2The following continuous casting billets are fed by rare earth core-spun yarns with the diameter of less than 9mm and the section size of 170mm2The continuous casting billet is fed with rare earth core-spun yarns with the diameter of more than 9 mm. The feed rate can be set according to the following formula: vFeeding speed＝VPulling device×M×G/g
In the formula: vFeeding speedThe feeding speed of the rare earth core-spun yarn is m.min-1；VPulling deviceIs casting blank drawing speed, and the unit is m.min-1(ii) a M is the casting blank unit weight and the unit is t/M-1(ii) a G is the addition of the rare earth core-spun yarn and the unit is g.t-1(ii) a g is the single weight of the rare earth core-spun yarn and the unit is g.t-1. Considering that the rare earth yield is higher in the feeding process of the rare earth core-spun yarn, the feeding amount of the rare earth can be properly increased according to the yield of 80-90 percent.
The principle of rare earth addition is that the quantity basis of rare earth addition, in order to improve the utilization ratio of rare earth, the O/S ratio in the smelting molten steel is less than 0.20, and the addition amount of rare earth micro-alloy elements is determined according to the S content in the molten steel before the furnace and is controlled as follows: the ratio RE/S is between 1.6 and 2.2.
Because the rare earth inclusion is precipitated in the molten steel, in order to refine the size growth of the rare earth inclusion and prevent the polymerization of the rare earth inclusion, the continuous casting temperature with lower superheat degree is required, the superheat degree is less than 40 ℃, and the superheat degree is preferably controlled within 30 ℃.
Under normal conditions, the temperature difference of inlet and outlet water of the crystallizer is controlled to be 6-7 ℃, the temperature difference of inlet and outlet water fluctuates in the wire feeding process of the continuous casting crystallizer, and the fluctuation value is controlled to be within 2 ℃. As the rare earth alloy core-spun yarn is fed from the crystallizer, the rare earth oxidation reaction generates heat release phenomenon, and meanwhile, the covering slag continuously absorbs rare earth oxide impurities floating from molten steel in the using process to form high-melting-point impurities. The alkalinity is increased to greatly improve the crystallization of the casting powder, thereby increasing the cooling thermal resistance of the crystallizer, improving the temperature of the casting powder and increasing the viscosity, leading to the thinning of casting blank shells, increasing the water temperature difference of a cooling water inlet and outlet of the crystallizer, leading to the change of the temperature field of the crystallizer, easily causing the aggregation phenomenon of massive rare earth inclusions, reducing the yield of rare earth oxides, stabilizing the yield of rare earth and inhibiting the growth of the rare earth inclusions, therefore, measures such as optimizing the casting powder of the crystallizer, adjusting the alloy component proportion in a rare earth cored wire and the like are needed, leading the temperature difference of inlet and outlet water of the crystallizer to be controlled within a stable set value range, leading the temperature difference control principle to be that on the basis of the original temperature difference of inlet and outlet water, the fluctuation value of the water temperature difference is controlled within 2 ℃, leading the casting powder to be replaced when exceeding the fluctuation range, and leading, the temperature difference between the inlet water and the outlet water of the crystallizer exceeds 9 ℃, and the covering slag needs to be replaced.
Heating a steel billet produced by steel rolling of the steel bar is controlled between 1100 ℃ and 1200 ℃, so that abnormal growth of austenite grains is prevented, and the performance of the steel bar fluctuates; the weak water penetration process is adopted after rolling, and the water penetration process after rolling is controlled within 50 ℃ above the austenite-ferrite phase transition temperature, namely the water penetration temperature after rolling is Ar3-Ar3Within +50 ℃. The purpose is to further narrow the performance fluctuation range of the steel bar on the basis of homogenizing and thinning the grain size and ensuring the anti-seismic performance of the steel bar.
The room temperature performance of the steel bar rolled according to the components and the technical scheme of the steel of the invention reaches: the yield strength ReL is more than or equal to 400MPa, the tensile strength Rm is more than or equal to 580MPa, the elongation after fracture is more than or equal to 24 percent, and the maximum force total elongation is more than or equal to 14 percent.
The casting powder of the common crystallizer can be used for the continuous casting of the rare earth steel, but when the number of casting furnaces is 3 and 4, the performance of the casting powder can be deteriorated, so that the casting nozzle is blocked and needs to be replaced.
In order to further increase the number of continuous casting molten steel furnaces, slow down the performance deterioration of the casting powder in the process of feeding rare earth alloy wires into the crystallizer, ensure the production of high-quality steel, improve the productivity, reduce the unit cost of steel per ton and avoid the problem of slag contaminationThe occurrence of the steel leakage accident of the casting machine caused by the deterioration of the mold powder is avoided, and preferably, the low-reaction mold powder of the rare earth steel continuous casting mold for continuous casting comprises the following components in percentage by mass: CaO: 16% -20% of SiO2：30％-38％、Al2O3<4％、Na2O<4％、K2O：5％-7％、F：4％-5％、MgO：4％-6％、B2O3: 8% -11%, C: 16% -20%; alkalinity R (CaO%/SiO)2Percent) of (B) 0.5 to 0.6, melting point<The viscosity of the mold flux at 910 ℃ and 1300 ℃ is 0.4-0.6 pas.
According to the requirements of the invention, 4 furnaces of steel are smelted by an electric furnace, wherein examples 1-3 and comparative example 1 are products in four furnace numbers respectively, and the specific chemical components are produced as shown in table 2. The actual production process of the cast slab rolling is shown in table 3.
TABLE 2 examples of the invention with the balance Fe
TABLE 3 concrete production process system for continuous casting and rolling
TABLE 4 mechanical Properties of inventive and comparative examples
Table 4 shows the mechanical properties of the embodiment and the comparative example of the present invention, and it can be seen from table 4 that the properties of the lower yield strength, the elongation after fracture, and the maximum total elongation of the rare earth microalloyed high strength construction steel bar of the present invention are equivalent to those of the steel bar added with V, and the strength ratio of the tensile strength region is also improved by a small amount. And V is several times of rare earth, the application adopts lower production cost to achieve the same or even better technical effect.
From the properties of the high-strength steel bar obtained in the examples 1 to 3, the rare earth microalloyed high-strength construction steel bar prepared by the steel components and the method reaches the 2 nd part of steel for reinforced concrete in GB/T1499.2-2018 in China: hot rolled ribbed bar standard HRB400 MPa.
The rare earth core-spun yarn for continuous casting has the advantages that the core-spun yarn can prevent the crystallizer casting powder from deteriorating in the continuous casting, improve the utilization rate of rare earth, ensure the production of high-quality steel, improve the productivity, reduce the unit cost of per ton steel, reduce the probability of generating cracks in steel billets, improve the steel quality and avoid the occurrence of steel leakage accidents of a casting machine caused by the deterioration of the crystallizer casting powder.
In addition, at present, no rare earth is adopted as a microalloy element to be added to HRB400 and HRB500 steel bars in high-strength steel bars GB/T1499.2-2018 for building concrete. Therefore, the invention develops the special rare earth alloy core-spun yarn and the continuous casting production wire feeding process technology aiming at the rare earth microalloyed high-strength steel bar variety, and the qualified steel bar meeting the national standard requirement is obtained in the high-strength steel bar production.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (9)
1. A rare earth microalloyed high strength construction steel bar is characterized in that the chemical components by weight percentage are as follows: c: 0.20-0.25%, Si: 0.40-0.80%, Mn: 1.1% -1.60%, RE > 0.025%, P: < 0.045%, S: < 0.045%, O, Ca + Mg satisfy the following mass percentages: O/S is less than 0.2, RE/(Ca + Mg) is controlled to be between 10 and 100, and RE/S is controlled to be between 1.6 and 2.2; the balance of Fe and inevitable impurities;
the RE is added in the form of a rare earth core-spun yarn, and the rare earth core-spun yarn is fed into a crystallizer.
2. The rare earth microalloyed high strength construction steel bar as claimed in claim 1, wherein RE is one or more of La, Ce and Y.
3. The rare earth microalloyed high strength construction steel bar as claimed in claim 1, wherein the rare earth cored wire has a diameter Φ of 3-15 mm.
4. The rare earth microalloyed high strength construction steel bar as in claim 3, wherein the cross-sectional dimension is 170mm2The following continuous casting billet is a rare earth core-spun wire with the diameter of less than 9mm, and the section size is 170mm2The core-spun wire with the diameter of more than 9mm is selected for the continuous casting billet.
5. The rare earth microalloyed high strength construction steel bar as claimed in claim 1, wherein the rare earth cored wire comprises a sheath and a core, and the core ratio is as follows by weight percent: RE: 10% -50%, Si: 10-20%, and the ratio of RE/(Ca + Mg) is 10-100.
6. The rare earth microalloyed high strength construction steel bar as set forth in claim 5, wherein the thickness of the outer skin is 0.3 to 0.5 mm.
7. The rare earth microalloyed high strength construction steel bar as claimed in any one of claims 1 to 6, wherein the steel bar has a yield strength ReL of not less than 400MPa, a tensile strength Rm of not less than 580MPa, a post-fracture elongation of not less than 24% and a maximum total elongation of not less than 14%.
8. The method for producing rare earth microalloyed high strength construction steel bar as claimed in any one of claims 1 to 7, wherein the rare earth is added by feeding a rare earth cored wire, the rare earth cored wire is fed into a crystallizer by a stepless speed change wire feeder, and the fluctuation of the temperature difference between inlet and outlet water of the crystallizer is controlled within 2 ℃ during the process of feeding the rare earth cored wire into the crystallizer.
9. The method for producing a rare earth microalloyed high strength construction steel bar as claimed in claim 8, wherein the heating temperature of the steel billet produced by rolling the steel bar is controlled between 1100 ℃ and 1200 ℃, and the weak water penetration process is adopted after rolling and is controlled in the range of 50 ℃ above the austenite-ferrite transformation temperature.
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| CN111500933A (en) * | 2020-06-05 | 2020-08-07 | 江苏联峰实业有限公司 | Rare earth element microalloyed high-strength steel bar and production process thereof |
| CN112122567B (en) * | 2020-09-07 | 2021-07-09 | 东北大学 | Method for improving solidification quality of casting blank by feeding stainless steel ladle core wire into crystallizer |
| CN113481440B (en) * | 2021-09-08 | 2021-11-30 | 北京科技大学 | Corrosion-resistant and anti-seismic steel, steel bar and preparation method thereof |
| CN114672728B (en) * | 2022-03-11 | 2022-10-11 | 钢铁研究总院有限公司 | Rare earth-containing corrosion-resistant steel and method for controlling content and existing form of rare earth |
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