CN109252094B - High-strength bridge steel prepared by ultra-fast cooling process and production method thereof - Google Patents
High-strength bridge steel prepared by ultra-fast cooling process and production method thereof Download PDFInfo
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Abstract
The high-strength bridge steel prepared by the ultra-fast cooling process is characterized by comprising the following steps of: the alloy comprises 0.065-0.068% of C, 0.05-0.08% of Si, 1.5-1.55% of Mn, less than or equal to 0.01% of P, less than or equal to 0.004% of S, 0.13-0.2% of Nb + Ti + V, less than or equal to 0.050% of Al, at least 2 of 5 of Cr, Mo, Ni, Cu and rare earth, and the balance of Fe and inevitable impurity elements.
Description
Technical Field
The invention belongs to the technical field of metal materials, and particularly relates to high-strength bridge steel prepared by an ultra-fast cooling process and a production method thereof.
Background
The low-alloy structural steel with atmospheric corrosion resistance is widely applied to the field of manufacturing of outdoor steel structures such as buildings, bridges, containers, vehicles and the like. The low-carbon manganese steel is used as a base, and a small amount of low-alloy corrosion-resistant elements such as Cr, Cu, Ni and the like are added, so that the rust layer structure of the steel is promoted to change, the atmospheric corrosion speed is favorably slowed down, and the atmospheric corrosion resistance of the steel is remarkably improved.
CN 101135029A describes atmospheric corrosion resistant steel with yield strength of 700MPa and a manufacturing method thereof, and the strength is low, so that the high strength requirement of different occasions cannot be met. CN 103114253A describes a method for producing an ultra-thin steel plate with a thickness of 3-10 mm, although yield strength Rp0.2 can reach 950-1300MPa, tensile strength Rm: 1000-1500MPa, elongation at break A: 12-20%, impact absorption energy KV2 at-40 deg.C: 80-270J, but the hot rolled substrate is subjected to two quenching and tempering heat treatment processes, so that the production efficiency is obviously influenced. CN 103302255A describes a method for manufacturing a strip-cast 700 MPa-grade high-strength atmospheric corrosion resistant steel, which has a steel strip with a yield strength of at least 700MPa, a tensile strength of at least 780MPa and an elongation of at least 18%, and is difficult to adapt to new requirements of comprehensive properties such as high strength, high elongation and impact resistance.
In addition, at present, research on the ultra-fast cooling process is mainly focused on the fields of automobile steel plates and X70 and X80 pipeline steels, and research on the comprehensive properties of improving high strength, high elongation, impact resistance and the like by using the ultra-fast cooling process in the high-strength bridge steel field is less.
Disclosure of Invention
The invention aims to provide a novel high-strength high-elongation high-impact-resistance high-strength high-elongation high-impact-resistance high-elongation high-impact-resistance high. In order to achieve the above object, the present invention provides a composition of a high-strength bridge steel, and a method for producing the high-strength bridge steel.
The technical scheme is as follows:
the high-strength bridge steel prepared by the ultra-fast cooling process is characterized by comprising the following steps of: the alloy comprises 0.065-0.068% of C, 0.05-0.08% of Si, 1.5-1.55% of Mn, less than or equal to 0.01% of P, less than or equal to 0.004% of S, 0.13-0.2% of Nb + Ti + V, less than or equal to 0.050% of Al, at least 2 of 5 of Cr, Mo, Ni, Cu and rare earth, and the balance of Fe and inevitable impurity elements.
The high-strength bridge steel prepared by the ultra-fast cooling process is characterized by comprising the following steps of: the components are C0.065-0.068%, Si 0.05-0.08%, Mn 1.5-1.55%, P less than or equal to 0.01%, S less than or equal to 0.004%, Nb 0.065-0.07%, Ti 0.02-0.025%, V0.03-0.035%, Al less than or equal to 0.050%, Cr 0.45-0.48%, Mo 0.35-0.38%, Ni 0.12-0.15%, Cu 0.05-0.09%, rare earth 0.0001-0.001%, N0.001-0.005%, and the balance of Fe and inevitable impurity elements; the ultra-fast cooling process is that the steel is cooled to 350-355 ℃ from the finish rolling temperature of 840-845 ℃ at the cooling speed of 80-90 ℃/s, and is coiled at 345-350 ℃; through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 800MPa, the tensile strength is more than or equal to 1000MPa, the elongation after fracture is more than or equal to 24 percent, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
The high-strength bridge steel prepared by the ultra-fast cooling process is characterized by comprising the following steps of: the components are C0.065%, Si 0.05%, Mn 1.5%, P less than or equal to 0.01%, S less than or equal to 0.004%, Nb 0.065%, Ti 0.02%, V0.03%, Al less than or equal to 0.050%, Cr 0.45%, Mo 0.35%, Ni 0.12%, Cu 0.05%, rare earth 0.0001%, N0.001%, and the balance of Fe and inevitable impurity elements; the ultra-fast cooling process is that the steel is cooled to 350-355 ℃ from the finish rolling temperature of 840-845 ℃ at the cooling speed of 80-90 ℃/s, and is coiled at 345-350 ℃; through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 820MPa, the tensile strength is more than or equal to 1030MPa, the elongation after fracture is more than or equal to 24 percent, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
The high-strength bridge steel prepared by the ultra-fast cooling process is characterized by comprising the following steps of: the components are C0.066%, Si 0.06%, Mn 1.52%, P less than or equal to 0.01%, S less than or equal to 0.004%, Nb 0.067%, Ti 0.023%, V0.033%, Al less than or equal to 0.050%, Cr 0.46%, Mo 0.36%, Ni 0.14%, Cu 0.06%, rare earth 0.0005%, N0.003%, and the balance of Fe and inevitable impurity elements; the ultra-fast cooling process is that the steel is cooled to 350-355 ℃ from the finish rolling temperature of 840-845 ℃ at the cooling speed of 80-90 ℃/s, and is coiled at 345-350 ℃; through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is not less than 850MPa, the tensile strength is not less than 1050MPa, the elongation after fracture is not less than 24%, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
The high-strength bridge steel prepared by the ultra-fast cooling process is characterized by comprising the following steps of: the components are C0.068%, Si 0.08%, Mn 1.55%, P less than or equal to 0.01%, S less than or equal to 0.004%, Nb 0.07%, Ti 0.025%, V0.035%, Al less than or equal to 0.050%, Cr0.48%, Mo 0.38%, Ni 0.15%, Cu 0.09%, rare earth 0.001%, N0.005%, and the balance of Fe and inevitable impurity elements; the ultra-fast cooling process is that the steel is cooled to 350-355 ℃ from the finish rolling temperature of 840-845 ℃ at the cooling speed of 80-90 ℃/s, and is coiled at 345-350 ℃; through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 900MPa, the tensile strength is more than or equal to 1100MPa, the elongation after fracture is more than or equal to 24 percent, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
A production method of high-strength bridge steel prepared by an ultra-fast cooling process comprises the following process routes: molten iron pretreatment → molten steel smelting → external refining → continuous casting → heating and rolling → ultra-fast cooling process and coiling; the core steps are as follows:
(1) pretreating and desulfurizing molten iron;
(2) smelting in a converter: adopting double-slag operation, bottom blowing in a converter, wherein the carbon content target is less than or equal to 0.055%, the phosphorus content is less than or equal to 0.015%, and the tapping temperature is 1600-; carrying out double slag-blocking tapping by adopting a slag-blocking plug and a slag-blocking rod;
(3) LF + RH refining process or RH or VD vacuum degassing;
(4) the continuous casting process comprises the following steps: protective gas is blown in the whole process to avoid oxidation and nitrogen increase;
(5) heating and rolling; the method comprises the following steps of putting a steel billet into a heating furnace, heating at 1180-1220 ℃, wherein the total in-furnace time is more than or equal to 200min, the first rough rolling stage is austenite recrystallization zone rolling, the initial rolling temperature is 1050-1080 ℃, the single-pass reduction rate is more than 10%, the last-pass reduction rate is more than or equal to 25%, the second rough rolling stage is austenite non-recrystallization zone rolling, the initial rolling temperature of finish rolling is less than or equal to 890 ℃, the final rolling temperature is 840-845 ℃, the accumulated reduction rate is more than or equal to 80%, and the product thickness is 10-13mm after rolling is finished;
(6) ultra-fast cooling process and coiling; the ultra-fast cooling process is to cool the steel from the finish rolling temperature of 840-845 ℃ to 350-355 ℃ at the cooling speed of 80-90 ℃/s and to perform coiling at 345-350 ℃.
A production method of high-strength bridge steel prepared by an ultra-fast cooling process is characterized by comprising the ultra-fast cooling process and coiling in the step (6); the ultra-fast cooling process is to cool the steel from the finish rolling temperature of 840-845 ℃ to 350-355 ℃ at the cooling speed of 83-88 ℃/s and to perform coiling at 345-350 ℃.
A production method of high-strength bridge steel prepared by an ultra-fast cooling process is characterized by comprising the ultra-fast cooling process and coiling in the step (6); the ultra-fast cooling process is to cool from the finishing temperature of 843 ℃ to 353 ℃ at the cooling speed of 87 ℃/s and to perform coiling at 347 ℃.
A production method of high-strength bridge steel prepared by an ultra-fast cooling process is characterized by comprising the following steps of (5) heating and rolling; the method comprises the following steps of putting a steel billet into a heating furnace, heating at 1180-1200 ℃, wherein the total in-furnace time is more than or equal to 200min, the first stage of rough rolling is rolling in an austenite recrystallization region, the initial rolling temperature is 1050-1070 ℃, the single-pass reduction rate is more than 10%, the last-pass reduction rate is more than or equal to 25%, the second stage of rough rolling is rolling in an austenite non-recrystallization region, the initial rolling temperature of finish rolling is less than or equal to 890 ℃, the final rolling temperature is 840-845 ℃, the accumulated reduction rate is more than or equal to 80%, and the thickness of a product after rolling is finished is 10-13;
compared with the prior art, the invention has the technical effects that:
1. the invention controls the components and the production process accurately. Has the comprehensive properties of high strength, high elongation, impact resistance and the like.
2. The composite material has good comprehensive mechanical properties, avoids the increase of process conditions such as tempering, quenching and the like, saves the production process, does not need to rely on the production cost to obtain the properties, saves the production cost and has good adaptability.
Next, the reason for limiting the chemical components of the present invention will be described. Here, the% of the component means mass%.
C: the steel is beneficial to obtaining the required strength index; the stability of austenite is increased, the thermal stability and mechanical stability of the retained austenite can be controlled by the distribution of carbon element, but too high C causes component segregation during casting, resulting in poor welding performance. Therefore, the amount of C added is 0.065 to 0.068%.
Si has an effect of suppressing precipitation of carbide serving as a fracture origin. The heat stability of austenite is increased, the strength of the steel can be improved, and the requirements of the strength and the low cost of the invention steel are favorably realized. Si element can improve the hardenability and tempering resistance of the steel, is favorable for the comprehensive mechanical properties of the steel, particularly the elastic limit, and can also improve the yield strength and the like. Therefore, the amount of the additive is 0.05% or more. However, if the content exceeds 0.08%, the field weldability deteriorates. From the viewpoint of field weldability, Si is 0.05 to 0.08%.
Mn is a solid-solution strengthening element and can stabilize austenite. The phase transformation temperature of austenite is reduced, the crystal grain of steel is refined, the hardenability and the heat strength are improved, and enough strength and creep resistance are kept at high temperature. In addition, in the cooling after the rolling to increase the temperature of the austenite region to the low temperature side, there is an effect that the continuous cooling transformation structure, which is one of the constituent elements of the microstructure of the present invention, can be easily obtained. To obtain these effects, Mn is added in an amount of 1.5% or more. However, even if Mn is added in excess of 1.6%, the effect is saturated, so the upper limit is 1.55%. Further, Mn promotes center segregation of the continuously cast slab to form a hard phase serving as a fracture origin, so Mn is 1.5 to 1.55%.
P is an impurity, and is preferably 0.02% or less, as the content is lower, and if it exceeds 0.02%, P segregates in the central portion of the continuously cast steel sheet, causes grain boundary fracture, and significantly lowers the low-temperature toughness. Further, P is preferably 0.01% or less in view of the above problem because it adversely affects weldability.
S is an impurity, and not only causes cracking during hot rolling, but also if it is excessive, it deteriorates low-temperature toughness. Therefore, it is set to 0.004% or less. Further, S segregates near the center of the continuously cast steel sheet, and forms elongated MnS after rolling, which may not only become the starting point of hydrogen induced cracking but also cause plate cracking. Sulphur is usually present in the steel in the form of FeS. FeS has poor plasticity and low melting point. FeS is distributed around the grain boundary when the molten steel is crystallized. Therefore, S is less than or equal to 0.004%.
Nb and Ti are one of the important elements in the present invention. Nb has the following effects: the steel suppresses recovery, recrystallization and grain growth of austenite during or after rolling by a dragging effect in a solid solution state and/or a pinning effect as a carbonitride precipitate, and improves low-temperature toughness by making the effective crystal grain size fine and reducing crack propagation of brittle fracture. Further, fine carbides are generated in a coiling step, which is a characteristic of a hot-rolled steel sheet manufacturing step, and contribute to improvement in strength due to precipitation strengthening. Nb also has the following effects: the phase transition of gamma/alpha is delayed, and the phase transition temperature is lowered, whereby the microstructure after phase transition is stably changed to a continuously cooled phase transition structure even at a relatively slow cooling rate. However, in order to obtain these effects, at least 0.065% or more must be added. On the other hand, if the amount exceeds 0.075%, not only the effect is saturated, but also it is difficult to form a solid solution in the heating step before hot rolling, and coarse carbonitrides are formed as starting points of the fracture, which may deteriorate low-temperature toughness and acid resistance. Considering that the production cost and the strengthening effect are optimal, 0.065-0.07% of Nb is selected.
Ti begins to precipitate as nitrides at high temperatures immediately after solidification of an ingot obtained by continuous casting or ingot casting. The precipitates containing the Ti nitrides are stable at high temperatures, do not completely dissolve in the subsequent slab reheating, exhibit a pinning effect, suppress coarsening of austenite grains during slab reheating, refine the microstructure, and improve low-temperature toughness. Further, the generation of ferrite nuclei is suppressed in the γ/α transformation, and the generation of the continuous cooling transformation structure, which is a requirement of the present invention, is promoted. In order to obtain the above effects, at least 0.02% or more of Ti must be added. On the other hand, even if the amount exceeds 0.012%, the effect is saturated. The strength of the product is generally improved by fully utilizing the fact that N and Ti form TiN and TiC which are distributed in a fine dispersion mode. Since precipitates containing Ti nitrides are crystallized or precipitated finely with these fine oxides as nuclei, the average equivalent circle diameter of precipitates containing Ti nitrides and carbides is made small, and not only the recovery and recrystallization of austenite during or after rolling but also grain growth of ferrite after coiling are suppressed due to the effect of dense dispersion. Therefore, Ti is 0.02-0.025%.
V is also a common alloying element, V strengthens a steel matrix through precipitation strengthening and grain refinement, 0.1% of V can increase the strength of 60-100 MPa, and V is a ferrite stabilizing element, so that transformation of bainite and pearlite is inhibited, and the amount of residual austenite is increased. However, the selection of V has certain particularity in the invention, and is mainly reflected in that VC or V (C, N) can be completely dissolved in austenite at the temperature of more than 900 ℃, so that the V is mainly precipitated among phases in the austenite-ferrite phase transformation process and precipitation strengthening in ferrite. In the application, the selection of the finish rolling temperature is determined by fully considering the precipitation rule of VC or V (C, N), V is not wasted due to transitional addition, and the influence of V on the performances of strengthening, grain refining and the like is also considered, so that V is 0.03-0.035%.
Al is an element necessary for dispersing a large number of fine oxides in the molten steel during deoxidation. When the amount is excessively added, the effect is lost, so that the upper limit thereof is set to 0.05%.
N contains Ti, V, Nb nitrides and carbonitrides as described above, suppresses coarsening of austenite grains during slab reheating, and makes fine austenite grains related to effective crystal grain size in subsequent controlled rolling, thereby improving low-temperature toughness by making the microstructure into a continuous cooling transformation structure. However, if the content is less than 0.001%, the effect cannot be obtained. On the other hand, if the content exceeds 0.005%, the ductility decreases with time, and the formability during tube production decreases.
Cr is an element contributing to the improvement of the strength of the steel by precipitation strengthening, and is preferably added in an amount of 0.45% or more. On the other hand, if Cr is added in an amount exceeding 0.5%, hardenability may be increased, a bainite structure may be formed, and toughness may be impaired, so that the upper limit is preferably set to 0.48%. Therefore, Cr is 0.45-0.48%.
Mo has an effect of improving hardenability and increasing strength. In addition, Mo and Nb coexist, and have the effect of strongly suppressing recrystallization of austenite during controlled rolling, refining the austenite structure, and improving low-temperature toughness. However, even if the amount of the additive exceeds 0.35%, the effect is saturated, and therefore, the amount is 0.4% or less. Further, when 0.4% or more is added, ductility may be reduced, and formability during tube production may be reduced. Therefore, Mo is 0.35 to 0.38%.
Ni is less likely to form a hardened structure harmful to low-temperature toughness and acid resistance in a rolled structure (particularly, a center segregation zone of a slab) than Mn, Cr, and Mo, and therefore has an effect of improving strength without deteriorating low-temperature toughness and field weldability. However, even if the amount of Ni added exceeds 0.15%, the effect is saturated, so Ni is 0.12 to 0.15%.
Cu has the effect of improving corrosion resistance and hydrogen induced cracking resistance. At least 0.05% or more should be added, but even if the amount exceeds 0.09%, the effect is saturated. Therefore, Cu is 0.05 to 0.09%.
RE is an element which is commonly used for modifying nonmetallic inclusions, and can also refine grains, improve the pinning effect or lamellar tearing resistance of oxides, and improve the strength and toughness. However, even if less than 0.0001% is added, this effect is not obtained; when the amount of the additive exceeds 0.001%, the cost increases.
Detailed Description
The technical solution of the present invention will be described in detail with reference to the specific embodiments.
Example 1
The steel for the high-strength bridge prepared by the ultra-fast cooling process is characterized in that: the components are C0.065%, Si 0.05%, Mn1.5%, P less than or equal to 0.01%, S less than or equal to 0.004%, Nb 0.065%, Ti0.02%, V0.03%, Al less than or equal to 0.050%, Cr 0.45%, Mo 0.35%, Ni 0.12%, Cu 0.05%, rare earth 0.0001%, N0.001%, and the balance of Fe and inevitable impurity elements; the production process comprises the following steps:
(1) pretreating and desulfurizing molten iron;
(2) smelting in a converter: adopting double-slag operation, bottom blowing in a converter, wherein the carbon content target is less than or equal to 0.055%, the phosphorus content is less than or equal to 0.015%, and the tapping temperature is 1600-; carrying out double slag-blocking tapping by adopting a slag-blocking plug and a slag-blocking rod;
(3) LF + RH refining process or RH or VD vacuum degassing;
(4) the continuous casting process comprises the following steps: protective gas is blown in the whole process to avoid oxidation and nitrogen increase;
(5) heating and rolling; the method comprises the following steps of putting a steel billet into a heating furnace, heating at 1180-1220 ℃, wherein the total in-furnace time is more than or equal to 200min, the first rough rolling stage is austenite recrystallization zone rolling, the initial rolling temperature is 1050-1080 ℃, the single-pass reduction rate is more than 10%, the last-pass reduction rate is more than or equal to 25%, the second rough rolling stage is austenite non-recrystallization zone rolling, the initial rolling temperature of finish rolling is less than or equal to 890 ℃, the final rolling temperature is 840-845 ℃, the accumulated reduction rate is more than or equal to 80%, and the product thickness is 10-13mm after rolling is finished;
(6) ultra-fast cooling process and coiling; the ultra-fast cooling process is to cool the steel from the finish rolling temperature of 840-845 ℃ to 350-355 ℃ at the cooling speed of 80-90 ℃/s and to perform coiling at 345-350 ℃.
Example 1 through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 820MPa, the tensile strength is more than or equal to 1030MPa, the elongation after fracture is more than or equal to 24 percent, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
Example 2
The steel for the high-strength bridge prepared by the ultra-fast cooling process is characterized in that: the components are C0.066%, Si 0.06%, Mn1.52%, P less than or equal to 0.01%, S less than or equal to 0.004%, Nb 0.067%, Ti 0.023%, V0.033%, Al less than or equal to 0.050%, Cr 0.46%, Mo 0.36%, Ni 0.14%, Cu 0.06%, rare earth 0.0005%, N0.003%, and the balance of Fe and inevitable impurity elements; the production process comprises the following steps:
(1) pretreating and desulfurizing molten iron;
(2) smelting in a converter: adopting double-slag operation, bottom blowing in a converter, wherein the carbon content target is less than or equal to 0.055%, the phosphorus content is less than or equal to 0.015%, and the tapping temperature is 1600-; carrying out double slag-blocking tapping by adopting a slag-blocking plug and a slag-blocking rod;
(3) LF + RH refining process or RH or VD vacuum degassing;
(4) the continuous casting process comprises the following steps: protective gas is blown in the whole process to avoid oxidation and nitrogen increase;
(5) heating and rolling; the method comprises the following steps of putting a steel billet into a heating furnace, heating at 1180-1220 ℃, wherein the total in-furnace time is more than or equal to 200min, the first rough rolling stage is austenite recrystallization zone rolling, the initial rolling temperature is 1050-1080 ℃, the single-pass reduction rate is more than 10%, the last-pass reduction rate is more than or equal to 25%, the second rough rolling stage is austenite non-recrystallization zone rolling, the initial rolling temperature of finish rolling is less than or equal to 890 ℃, the final rolling temperature is 840-845 ℃, the accumulated reduction rate is more than or equal to 80%, and the product thickness is 10-13mm after rolling is finished;
(6) ultra-fast cooling process and coiling; the ultra-fast cooling process is to cool the steel from the finish rolling temperature of 840-845 ℃ to 350-355 ℃ at the cooling speed of 80-90 ℃/s and to perform coiling at 345-350 ℃.
Example 2 through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is not less than 850MPa, the tensile strength is not less than 1050MPa, the elongation after fracture is not less than 24%, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
Example 3
The steel for the high-strength bridge prepared by the ultra-fast cooling process is characterized in that: the components are C0.068%, Si 0.08%, Mn 1.55%, P less than or equal to 0.01%, S less than or equal to 0.004%, Nb 0.07%, Ti0.025%, V0.035%, Al less than or equal to 0.050%, Cr0.48%, Mo 0.38%, Ni 0.15%, Cu 0.09%, rare earth 0.001%, N0.005%, and the balance of Fe and inevitable impurity elements; the production process comprises the following steps:
(1) pretreating and desulfurizing molten iron;
(2) smelting in a converter: adopting double-slag operation, bottom blowing in a converter, wherein the carbon content target is less than or equal to 0.055%, the phosphorus content is less than or equal to 0.015%, and the tapping temperature is 1600-; carrying out double slag-blocking tapping by adopting a slag-blocking plug and a slag-blocking rod;
(3) LF + RH refining process or RH or VD vacuum degassing;
(4) the continuous casting process comprises the following steps: protective gas is blown in the whole process to avoid oxidation and nitrogen increase;
(5) heating and rolling; the method comprises the following steps of putting a steel billet into a heating furnace, heating at 1180-1220 ℃, wherein the total in-furnace time is more than or equal to 200min, the first rough rolling stage is austenite recrystallization zone rolling, the initial rolling temperature is 1050-1080 ℃, the single-pass reduction rate is more than 10%, the last-pass reduction rate is more than or equal to 25%, the second rough rolling stage is austenite non-recrystallization zone rolling, the initial rolling temperature of finish rolling is less than or equal to 890 ℃, the final rolling temperature is 840-845 ℃, the accumulated reduction rate is more than or equal to 80%, and the product thickness is 10-13mm after rolling is finished;
(6) ultra-fast cooling process and coiling; the ultra-fast cooling process is to cool the steel from the finish rolling temperature of 840-845 ℃ to 350-355 ℃ at the cooling speed of 80-90 ℃/s and to perform coiling at 345-350 ℃.
Example 3 through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, the other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 900MPa, the tensile strength is more than or equal to 1100MPa, the elongation after fracture is more than or equal to 24 percent, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
Comparative example 1
The product composition and production process steps (1) - (5) are the same as example 1, except that the cooling process in step (6) is to cool from the finish rolling temperature of 840-845 ℃ to 350-355 ℃ at the cooling rate of 5-15 ℃/s, and to perform coiling at 345-350 ℃. Through metallographic structure analysis, the final structure is 70-80% of acicular ferrite and 10-13% of bainitic ferrite counted by area ratio, other structures are martensite austenite, and the average width range of the formed acicular ferrite is 1.5-1.8 microns; through mechanical property analysis, the yield strength is more than or equal to 600MPa, the tensile strength is more than or equal to 750MPa, the elongation after fracture is more than or equal to 18 percent, and the impact energy at minus 40 ℃ is 250-270J.
Comparative example 2
The product components and the production process steps (1) to (5) are the same as the example 2, and the difference is that the ultra-fast cooling process and the coiling are carried out in the step (6); the ultra-fast cooling process is to cool the steel from the finish rolling temperature of 840-845 ℃ to 360-365 ℃ at the cooling speed of 80-90 ℃/s and to perform coiling at 355-360 ℃.
Through metallographic structure analysis, the final structure is that the area ratio is counted as 90-91% of acicular ferrite and 3.5-4.5% of lath martensite, other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.65-0.8 micron, and the average range of the width of the lath martensite is 0.4-0.5 micron; through mechanical property analysis, the yield strength is more than or equal to 770MPa, the tensile strength is more than or equal to 950MPa, the elongation after fracture is more than or equal to 20 percent, and the impact energy at minus 40 ℃ is 220-260J.
Comparative example 3
The product components and the production process steps (1) to (5) are the same as the example 3, and the difference is that the ultra-fast cooling process and the coiling are carried out in the step (6); the ultra-fast cooling process is to cool the steel from the finish rolling temperature of 840-845 ℃ to 350-355 ℃ at the cooling speed of 95-100 ℃/s and to perform coiling at 345-350 ℃.
Through metallographic structure analysis, the final structure is statistically 95-96% of acicular ferrite and 3-3.5% of lath martensite by area ratio, the other structures are granular bainite, the average width range of the formed acicular ferrite is 0.6-0.75 micrometer, and the average width range of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 820MPa, the tensile strength is more than or equal to 970MPa, the elongation after fracture is more than or equal to 22 percent, and the impact energy at minus 40 ℃ is 210-230J.
Comparative example 4
The production process is the same as that of example 1, but the components are C0.05%, Si 0.05%, Mn 1.3%, P0.01% or less, S0.004% or less, Nb 0.06%, Ti0.01%, V0.02%, Al 0.050% or less, Cr 0.45%, Mo 0.35%, Ni0.12%, Cu 0.05%, rare earth 0.0001%, N0.001%, and the balance of Fe and inevitable impurity elements;
through metallographic structure analysis, the final structure is statistically 85-88% of acicular ferrite and 5-7% of lath martensite by area ratio, other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.7-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 680MPa, the tensile strength is more than or equal to 830MPa, the elongation after fracture is more than or equal to 18.5 percent, and the impact energy at minus 40 ℃ is 250-260J.
Comparative example 5
The product had the same composition as in example 1, except that the composition was C0.065%, Si 0.05%, Mn 1.5%, P.ltoreq.0.01%, S.ltoreq.0.004%, Nb 0.065%, Ti 0.02%, V0.03%, Al.ltoreq.0.050%, Cr 0.2%, Mo 0.15%, Ni 0.1%, rare earth 0.0001%, N0.001%, and the balance being Fe and inevitable impurity elements;
through metallographic structure analysis, the final structure is 88-92% of acicular ferrite and 6-7% of lath martensite based on the area ratio, other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.85 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 740MPa, the tensile strength is more than or equal to 930MPa, the elongation after fracture is more than or equal to 18 percent, and the impact energy at minus 40 ℃ is 240-260J.
Comparative example 6
The product has the same components as example 1, but the components are C0.065%, Si 0.05%, Mn 1.5%, P less than or equal to 0.01%, S less than or equal to 0.004%, Nb 0.065%, Ti 0.05%, Al less than or equal to 0.050%, Cr 0.45%, Mo 0.35%, Ni 0.12%, Cu 0.05%, rare earth 0.0001%, N0.001%, and the balance of Fe and inevitable impurity elements;
through metallographic structure analysis, the final structure is statistically 93-95% of acicular ferrite and 3.5-5.5% of lath martensite by area ratio, other structures are bainitic ferrite and/or martensite austenite, the average range of the width of the formed acicular ferrite is 0.7-0.85 micrometer, and the average range of the width of the lath martensite is 0.48-0.55 micrometer; through mechanical property analysis, the yield strength is more than or equal to 760MPa, the tensile strength is more than or equal to 960MPa, the elongation after fracture is more than or equal to 22 percent, and the impact energy at minus 40 ℃ is 250-270J.
The terminology used herein is for the purpose of description and illustration, rather than of limitation. As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.
Claims (7)
1. The high-strength bridge steel prepared by the ultra-fast cooling process is characterized by comprising the following steps of: 0.065-0.068% of C, 0.05-0.08% of Si, 1.5-1.55% of Mn, less than or equal to 0.01% of P, less than or equal to 0.004% of S, 0.065-0.07% of Nb, 0.02-0.025% of Ti, 0.03-0.035% of V, less than or equal to 0.050% of Al, 0.45-0.48% of Cr, 0.35-0.38% of Mo, 0.12-0.15% of Ni, 0.05-0.09% of Cu, 0.0001-0.001% of rare earth, 0.001-0.005% of N, and the balance of Fe and inevitable impurity elements; the ultra-fast cooling process is that the steel is cooled to 350-355 ℃ from the finish rolling temperature of 840-845 ℃ at the cooling speed of 80-90 ℃/s, and is coiled at 345-350 ℃; through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, other structures are bainitic ferrite and martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 800MPa, the tensile strength is more than or equal to 1000MPa, the elongation after fracture is more than or equal to 24 percent, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
2. A high strength bridge steel prepared by the ultra-rapid cooling process according to claim 1, wherein: the alloy comprises, by mass%, 0.065% of C, 0.05% of Si, 1.5% of Mn, less than or equal to 0.01% of P, less than or equal to 0.004% of S, 0.065% of Nb, 0.02% of Ti, 0.03% of V, less than or equal to 0.050% of Al, 0.45% of Cr, 0.35% of Mo, 0.12% of Ni, 0.05% of Cu, 0.0001% of rare earth, 0.001% of N, and the balance of Fe and inevitable impurity elements; the ultra-fast cooling process is that the steel is cooled to 350-355 ℃ from the finish rolling temperature of 840-845 ℃ at the cooling speed of 80-90 ℃/s, and is coiled at 345-350 ℃; through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, other structures are bainitic ferrite and martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 820MPa, the tensile strength is more than or equal to 1030MPa, the elongation after fracture is more than or equal to 24 percent, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
3. A high strength bridge steel prepared by the ultra-rapid cooling process according to claim 1, wherein: the alloy comprises, by mass%, 0.066% of C, 0.06% of Si, 1.52% of Mn, 0.01% or less of P, 0.004% or less of S, 0.067% of Nb, 0.023% of Ti, 0.033% of V, 0.050% or less of Al, 0.46% of Cr, 0.36% of Mo, 0.14% of Ni, 0.06% of Cu, 0.0005% of rare earth, 0.003% of N, and the balance of Fe and inevitable impurity elements; the ultra-fast cooling process is that the steel is cooled to 350-355 ℃ from the finish rolling temperature of 840-845 ℃ at the cooling speed of 80-90 ℃/s, and is coiled at 345-350 ℃; through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, other structures are bainitic ferrite and martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is not less than 850MPa, the tensile strength is not less than 1050MPa, the elongation after fracture is not less than 24%, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
4. A high strength bridge steel prepared by the ultra-rapid cooling process according to claim 1, wherein: the alloy comprises, by mass, 0.068% of C, 0.08% of Si, 1.55% of Mn, less than or equal to 0.01% of P, less than or equal to 0.004% of S, 0.07% of Nb, 0.025% of Ti, 0.035% of V, less than or equal to 0.050% of Al, 0.48% of Cr0.48%, 0.38% of Mo, 0.15% of Ni, 0.09% of Cu, 0.001% of rare earth, 0.005% of N, and the balance of Fe and inevitable impurity elements; the ultra-fast cooling process is that the steel is cooled to 350-355 ℃ from the finish rolling temperature of 840-845 ℃ at the cooling speed of 80-90 ℃/s, and is coiled at 345-350 ℃; through metallographic structure analysis, the final structure is counted by area ratio to be 95.5-96.5% of acicular ferrite and 1.5-2.5% of lath martensite, other structures are bainitic ferrite and martensite austenite, the average range of the width of the formed acicular ferrite is 0.6-0.75 micrometer, and the average range of the width of the lath martensite is 0.4-0.5 micrometer; through mechanical property analysis, the yield strength is more than or equal to 900MPa, the tensile strength is more than or equal to 1100MPa, the elongation after fracture is more than or equal to 24 percent, the yield ratio is 0.79-0.81, and the impact energy at-40 ℃ is 200-230J.
5. A method for producing a high strength steel for bridges, prepared by the ultra-rapid cooling process according to any one of claims 1 to 4, the process route comprising: molten iron pretreatment → molten steel smelting → external refining → continuous casting → heating and rolling → ultra-fast cooling process and coiling; the method comprises the following steps:
(1) pretreating and desulfurizing molten iron;
(2) smelting in a converter: adopting double-slag operation, bottom blowing in a converter, wherein the carbon content target is less than or equal to 0.055%, the phosphorus content is less than or equal to 0.015%, and the tapping temperature is 1600-; carrying out double slag-blocking tapping by adopting a slag-blocking plug and a slag-blocking rod;
(3) LF + RH refining process or RH or VD vacuum degassing;
(4) the continuous casting process comprises the following steps: protective gas is blown in the whole process to avoid oxidation and nitrogen increase;
(5) heating and rolling; the method comprises the following steps of putting a steel billet into a heating furnace, heating at 1180-1220 ℃, wherein the total in-furnace time is more than or equal to 200min, the first rough rolling stage is austenite recrystallization zone rolling, the initial rolling temperature is 1050-1080 ℃, the single-pass reduction rate is more than 10%, the last-pass reduction rate is more than or equal to 25%, the second rough rolling stage is austenite non-recrystallization zone rolling, the initial rolling temperature of finish rolling is less than or equal to 890 ℃, the final rolling temperature is 840-845 ℃, the accumulated reduction rate is more than or equal to 80%, and the product thickness is 10-13mm after rolling is finished;
(6) ultra-fast cooling process and coiling; the ultra-fast cooling process is to cool the steel from the finish rolling temperature of 840-845 ℃ to 350-355 ℃ at the cooling speed of 80-90 ℃/s and to perform coiling at 345-350 ℃.
6. A method for producing a high-strength steel for bridges, which is manufactured by the ultra-rapid cooling process according to claim 5, wherein the ultra-rapid cooling process and the coiling in the step (6): the ultra-fast cooling process is to cool the steel from the finish rolling temperature of 840-845 ℃ to 350-355 ℃ at the cooling speed of 83-88 ℃/s and to perform coiling at 345-350 ℃.
7. A method for producing a high-strength steel for bridges, which is manufactured by the ultra-rapid cooling process according to claim 5, wherein the ultra-rapid cooling process and the coiling in the step (6): the ultra-fast cooling process is to cool from the finishing temperature of 843 ℃ to 353 ℃ at the cooling speed of 87 ℃/s and to perform coiling at 347 ℃.
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