High-strength bridge steel and production method thereof

Abstract

The present invention discloses a high-strength bridge steel and a production method thereof. The chemical composition of the steel is as follows: C: 0.08-0.11%, Si: 0.11-0.18%, Mn: 1.39-1.47%, Ni: 0.07-0.13%, Nb: 0.021-0.029%, Ti: 0.009-0.017%, Al: 0.026-0.046%, Cr: 0.07-0.13%, and the remainder is iron and impurities. In the method, the steel plate is first rolled to a thickness of 4t to 6.8t at a rolling temperature of T3 to T3+40°C, then rolled to a thickness of 1.8t to 3.2t at a rolling temperature of T4-50°C to T4+20°C, and finally rolled to a thickness of t at a rolling temperature of T5-40°C to T5; then the steel plate is air-cooled to a thickness of T6 to T6+20°C at a cooling rate of 1-10°C / s, and then water-cooled to a thickness of T7-30°C to T7+10°C at a cooling rate of 8-30°C / s, thereby obtaining a finished steel plate.

Description

Technical Field

[0001] The invention belongs to the technical field of steel alloy materials and relates to high-strength bridge steel and a production method thereof. Background Art

[0002] Structural steel for bridges is primarily used in key projects such as railway, highway, and sea and river bridge construction. Due to the unique nature of its operating environment, it places stringent requirements on comprehensive performance. The strength of the steel matrix, in particular, is crucial for bridge applications. Furthermore, other properties (such as weldability and yield strength ratio) are crucial for bridge steel.

[0003] In the existing manufacturing of bridge steel plates, how to obtain high strength while ensuring welding performance and yield strength ratio is an important point in production. Summary of the Invention

[0004] The object of the present invention is to provide a high-strength bridge steel and a production method thereof.

[0005] To achieve the above-mentioned purpose, one embodiment of the present invention provides a method for producing high-strength bridge steel. The chemical composition of the steel, in percentage by mass, includes: C: 0.08-0.11%, Si: 0.11-0.18%, Mn: 1.39-1.47%, Ni: 0.07-0.13%, Nb: 0.021-0.029%, Ti: 0.009-0.017%, Al: 0.026-0.046%, Cr: 0.07-0.13%, P ≤ 0.02%, S ≤ 0.0080%, N ≤ 0.0045%, and the remainder is iron and unavoidable impurities.

[0006] The production method comprises the following steps:

[0007] Heat the steel billet in the heating furnace to a temperature above T1+10℃ and below T2, where T1 is T NbC 、T NbN and T TiC The maximum value of T2 is T1+50℃, T TiN -150℃, the larger value; where T NbC 、T NbN 、T TiC and T TiN are the complete solution temperatures of NbC, NbN, TiC and TiN respectively;

[0008] After leaving the heating furnace, the billet is first rolled at a rolling temperature of T3 or higher and T3+40℃ or lower to a thickness of 4 to 6.8 times that of the finished product to obtain the first intermediate plate; then rolled at a rolling temperature of T4-50℃ or higher and T4+20℃ or lower to a thickness of 1.8 to 3.2 times that of the finished product to obtain the second intermediate plate; finally rolled at a rolling temperature of T5-40℃ or higher and T5 or lower to the thickness of the finished product; T3≥T4≥T5, +890[Ti]+363[Al]-357[Si], T5=910-310[C]-80[Mn]-15[Cr],

[0009] The rolled steel plate is air-cooled at a cooling rate of 1 to 10°C / s to a temperature between T6 and T6+20°C, then water-cooled at a cooling rate of 8 to 30°C / s to a temperature between T7-30°C and T7+10°C, and then naturally cooled to room temperature to obtain a finished steel plate; T5 ≥ T6 ≥ T7, T7 = 539-423[C]-17.7[Ni]-12.1[Cr]-11[Si]-30.4[Mn], T6 = 830-270[C]-90[Mn]-37[Ni]-70[Cr];

[0010] Among them, [C], [Nb], [Ti], [Al], [Si], [Ni], [Mn], and [Cr] are the mass percentages of C, Nb, Ti, Al, Si, Ni, Mn, and Cr in the steel billet, respectively.

[0011] As a further improvement of one embodiment, the chemical composition of the steel billet includes, by mass percentage: P: 0.0101-0.0151%, S: 0.0020-0.0080%, N: 0.0025-0.0045%.

[0012] As a further improvement of one embodiment, the carbon equivalent CEV of the chemical composition of the steel billet satisfies 0.333 to 0.380.

[0013] As a further improvement of one embodiment, the steel billet stays at a temperature above T1+10°C and below T2 for 0.07-0.13 min / mm, and the total time in the heating furnace is 1.15-1.35 min / mm.

[0014] As a further improvement of one embodiment, the steel billet adopts a five-stage process in the heating furnace, including a heat recovery section, a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the first heating section is 1120±15°C, the temperature of the second heating section is above T1+10°C and below T2, the temperature of the soaking section is lower than the temperature of the second heating section, and the temperature of the soaking section is 20-40°C lower than the temperature of the second heating section.

[0015] Alternatively, the steel billet adopts a three-stage process in the heating furnace, including a preheating section, a heating section and a soaking section. The temperature of the heating section is above T1+10°C and below T2, the temperature of the soaking section is lower than the temperature of the heating section, and the temperature of the soaking section is 20 to 40°C lower than the temperature of the heating section.

[0016] As a further improvement of one embodiment, when rolling to obtain the first intermediate plate, the starting rolling temperature is above T3+20°C and below T3+40°C, and the finishing rolling temperature is above T3 and below T3+20°C.

[0017] As a further improvement of one embodiment, when rolling to obtain the second intermediate plate, the starting rolling temperature is above T4 and below T4+20°C, and the finishing rolling temperature is above T4-50°C and below T4-30°C.

[0018] As a further improvement of one embodiment, when the second intermediate plate is rolled to the finished thickness, the starting rolling temperature is above T5-15°C and below T5, and the finishing rolling temperature is above T5-40°C and below T5-25°C.

[0019] To achieve the above-mentioned purpose, one embodiment of the present invention provides a high-strength bridge steel. The chemical composition of the steel, in percentage by mass, includes: C: 0.08-0.11%, Si: 0.11-0.18%, Mn: 1.39-1.47%, Ni: 0.07-0.13%, Nb: 0.021-0.029%, Ti: 0.009-0.017%, Al: 0.026-0.046%, Cr: 0.07-0.13%, P ≤ 0.0151%, S ≤ 0.0080%, N ≤ 0.0045%, and the remainder is iron and unavoidable impurities.

[0020] The thickness of the steel is 6-64 mm, the yield strength is ≥500 MPa, the tensile strength is ≥670 MPa, the elongation is ≥25%, and the yield strength ratio is ≤0.75.

[0021] As a further improvement of one embodiment, the steel has an impact energy KV2 of ≥260J at -20°C, an impact energy KV2 of ≥240J at -40°C, an impact energy KV2 of ≥200J at -60°C, and a steel plate unevenness of ≤1mm / m.

[0022] Compared with the prior art, the beneficial effects of one embodiment are:

[0023] (1) On the one hand, by designing the chemical composition and using a low alloy content, the high strength of the steel is achieved while also ensuring the yield strength ratio, toughness, and weldability of the steel, thereby achieving excellent overall performance of the steel; in addition, the production difficulty of the steel is low;

[0024] (2) On the basis of chemical composition, combined with specific process control of heating, rolling and cooling, precise control of microstructure is achieved. Under the condition of low alloy content, a huge improvement in strength is achieved (that is, the mechanical properties brought about by these elements are not reduced due to the low element content as commonly known). At the same time, other properties such as toughness, welding performance, and yield strength ratio are guaranteed. Under the condition of low alloy content, low production difficulty and short production process, comprehensive improvements in steel plates in terms of low yield strength ratio, easy welding, high strength and toughness, and good plate shape are achieved. The resulting steel plates are suitable for bridge engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 FIG. 4 is a metallographic structure diagram of a steel plate according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] One embodiment of the present invention provides a high-strength bridge steel, the chemical composition of which, in percentage by mass, includes: C: 0.08-0.11%, Si: 0.11-0.18%, Mn: 1.39-1.47%, Ni: 0.07-0.13%, Nb: 0.021-0.029%, Ti: 0.009-0.017%, Al: 0.026-0.046%, Cr: 0.07-0.13%, P≤0.02%, S≤0.0080%, N≤0.0045%, and the rest is iron and unavoidable impurities.

[0027] The role and control of each chemical component are described in detail below.

[0028] C: Carbon is the most economical strengthening element in steel. It has a significant solid solution strengthening effect and can effectively reduce the yield strength ratio. At the same time, it forms carbides with Nb, Ti, Cr, Mo, etc., which has a precipitation strengthening effect. When the carbon content is lower than 0.08%, the effect of increasing strength and reducing the yield strength ratio is not obvious. When the carbon content is higher than 0.11%, it will lead to deterioration of toughness and welding performance.

[0029] Si: Silicon has a solid solution strengthening effect in steel. When the Si content is lower than 0.11%, the solid solution strengthening effect is not obvious; when the Si content exceeds 0.18%, Fe2SiO4 is easily generated on the surface of the continuous casting billet, which is difficult to remove during descaling and is detrimental to the surface quality of the steel plate.

[0030] Mn: Manganese plays a role in solid solution strengthening in steel and is the most economical strengthening element besides carbon. When the Mn content is lower than 1.39%, the solid solution strengthening effect is not obvious; when the Mn content exceeds 1.47%, it is easy to form segregation in the center of the slab, reducing the low-temperature toughness of the steel plate and at the same time being detrimental to the welding performance.

[0031] Nb: Niobium is an important grain-refining element in steel. When the Nb content exceeds 0.021%, niobium carbonitride precipitates are formed during the rolling process, refining the recrystallized grains. During the cooling process, niobium can continue to precipitate in the form of carbonitrides, refining the microstructure after phase transformation and improving strength and toughness. However, when the Nb content is greater than 0.029%, the alloy cost will increase, and precipitation strengthening will be detrimental to the yield strength ratio.

[0032] Ti: Titanium is a nitrogen-fixing element in steel. It can form dispersed titanium nitride particles, which inhibit the coarsening of austenite grains during billet heating and rolling. However, when the Ti content is less than 0.009%, Ti cannot fully play its role. When the Ti content is greater than 0.017%, titanium carbonitride precipitation is easily formed in the core of the ingot, affecting the low-temperature toughness of the steel plate core.

[0033] Al: Aluminum is a deoxidizing element in steel. When the content is lower than 0.026%, Al cannot effectively achieve its deoxidation effect. When the content is higher than 0.046%, the Al2O3 inclusions in the steel increase, affecting the low-temperature toughness of the steel.

[0034] P, S, and N: impurity elements. However, S can also form MnS inclusions with Mn, reducing the low-temperature toughness of the steel. In this application, P ≤ 0.02%, S ≤ 0.0080%, and N ≤ 0.0045%. In some embodiments, the P content is preferably 0.0101-0.0151%, the N content is preferably 0.0025-0.0045%, and the S content is preferably 0.0020-0.0080%.

[0035] Ni: Nickel plays a role in solid solution strengthening in steel and is beneficial to low-temperature toughness. Therefore, in the present invention, Ni can be selectively omitted or added in a certain amount. For example, when the Ni content is 0.07-0.13%, the low-temperature toughness can be greatly improved.

[0036] Cr: Chromium acts as a solid solution strengthener in steel and also delays pearlite transformation. Therefore, in the present invention, adding a certain amount of Cr, for example, a Cr content of 0.07% or greater, can significantly improve low-temperature toughness. However, a Cr content exceeding 0.13% can negatively impact weldability. Therefore, the Cr content is preferably between 0.07% and 0.13%.

[0037] Thus, the present invention achieves high strength of steel with low alloy content through the design of chemical composition, while also ensuring the yield ratio, toughness and welding performance of the steel, thereby achieving excellent comprehensive performance of the steel; in addition, the production difficulty of the steel is low.

[0038] Specifically, the metallographic structure of the steel is a complex structure of deformation-induced ferrite + polygonal ferrite + acicular ferrite + bainite. Here, the metallographic structure of the steel can be obtained by conducting a structure test according to GB / T 15125-2009 "Specimens and test methods for metallographic examination of metallic materials".

[0039] The steel is a plate with a thickness of 6-64 mm, a yield strength ≥ 360 MPa, a tensile strength ≥ 510 MPa, an elongation ≥ 25%, and a yield strength ratio ≤ 0.75. Mechanical property testing can be performed in accordance with GB / T 228.1-2021 "Tensile Tests on Metallic Materials Part 1: Room Temperature Test Methods."

[0040] Furthermore, the steel has an impact energy KV2 of ≥260 J at -20°C and an impact energy KV2 of ≥240 J at -40°C. Here, the low-temperature toughness test can be performed according to GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method".

[0041] Furthermore, in terms of chemical composition, the carbon equivalent (CEV) of the steel satisfies 0.333 to 0.380.

[0042] Among them, carbon equivalent CEV = [C] + [Mn] / 6 + ([Cr] + [Mo] + [V]) / 5 + ([Cu] + [Ni]) / 15, where [C], [Mn], [Cr], [Mo], [V], [Cu], and [Ni] represent the mass percentages of elements such as C, Mn, Cr, Mo, V, Cu, and Ni in the steel. For example, when the mass percentage of C in the steel is 0.09%, the mass percentage of C is 0.09, and this value is substituted into the CEV formula.

[0043] The steel has excellent welding performance and excellent plate shape, with unevenness ≤1 mm / m, where the unit mm / m refers to mm per unit length of the steel plate, and the unit length is calculated in m.

[0044] Furthermore, an embodiment of the present invention also provides a method for producing the steel, which includes the steps of heating-controlled rolling-controlled cooling and the like.

[0045] Specifically, in the heating process, the continuous casting billet having the chemical composition consistent with the above-mentioned chemical composition of the steel is heated in a heating furnace.

[0046] The continuous casting billet can be prepared using known technologies in the industry, generally using KR desulfurization, converter smelting, RH refining, LF refining, and continuous casting technologies.

[0047] During the heating process, the maximum temperature of the heating furnace is set to be greater than T1+10°C and less than T2. ​​In other words, the billet is heated in the heating furnace to a temperature greater than T1+10°C and less than T2. ​​Generally, the set temperature of the heating furnace is considered to represent the temperature reached by the billet within the heating furnace. It is not necessary to directly contact or measure the billet with a temperature measuring element to determine the billet's temperature.

[0048] T1 is T NbC 、T NbN and T TiC The maximum value in .

[0049] Among them, T NbC 、T NbN 、T TiC and T TiN are the complete solution temperatures of NbC, NbN, TiC and TiN respectively.

[0050] In an optional embodiment, the method can be implemented by lg([Nb]×[N])=3.70-10800 / (T NbN +273.15), lg([Nb]×[C])=2.26-6770 / (T NbC +273.15), lg([Ti]×[C])=5.33-10475 / (T TiC +273.15), lg([Ti]×[N])=0.32-8000 / (T TiN +273.15) and calculate T NbC 、T NbN 、T TiC and T TiN , [Nb], [N]), [C], and [Ti] are the mass percentages of Nb, N, C, and Ti in the steel billet, respectively.

[0051] Of course, in a variant embodiment, T NbC 、T NbN 、T TiC and T TiN It can also be obtained using methods known in the art, such as industry experience values.

[0052] T2 is T1+50℃, T TiN -150℃, the larger value.

[0053] In this way, by controlling the temperature in the heating furnace to be above T1+10℃ and below T2, it can be ensured that the Nb precipitates in the steel are completely dissolved, the Ti carbides are completely dissolved, and the Ti nitrides are retained, thereby preventing the abnormal growth of austenite grains and ultimately ensuring the comprehensive performance of the finished steel plate.

[0054] In the controlled rolling process, the steel billet after leaving the heating furnace is first rolled at a rolling temperature of not less than T3 and not more than T3+40°C to a thickness of 4 to 6.8 times that of the finished product to obtain a first intermediate plate; then, the steel billet is rolled at a rolling temperature of not less than T4-50°C and not more than T4+20°C to a thickness of 1.8 to 3.2 times that of the finished product to obtain a second intermediate plate; and finally, the steel billet is rolled at a rolling temperature of not less than T5-40°C and not more than T5 to the thickness of the finished product.

[0055] Among them, T3≥T4≥T5, T5=910-310[C]-80[Mn]-15[Cr], [C], [Nb], [Ti], [Al], [Si], and [Ni] are the mass percentages of C, Nb, Ti, Al, Si, and Ni in the steel billet, respectively.

[0056] That is to say, one embodiment of the present invention controls the temperature of the steel billet during rolling to 4 to 6.8 times the thickness of the finished product, the temperature during rolling from 4 to 6.8 times the thickness of the finished product to 1.8 to 3.2 times the thickness of the finished product, and the temperature during rolling from 1.8 to 3.2 times the thickness of the finished product to completion. In this way, on the one hand, sufficient recrystallization and refinement of the recrystallized grains can be ensured first, and on the other hand, the recrystallized equiaxed grains can be deformed and flattened. On the other hand, rolling deformation can be used to induce ferrite phase transformation, and ferrite phase transformation occurs on the deformation band or in the grain boundary to obtain fine ferrite grains, thereby ensuring the yield strength and good toughness of the steel plate.

[0057] In the controlled cooling process, the rolled steel plate is air-cooled at a cooling rate of 1 to 10°C / s to a temperature between T6 and T6+20°C, then water-cooled at a cooling rate of 8 to 30°C / s to a temperature between T7-30°C and T7+10°C, and then naturally cooled to room temperature to obtain a finished steel plate.

[0058] Among them, T5≥T6≥T7, T7=539-423[C]-17.7[Ni]-12.1[Cr]-11[Si]-30.4[Mn], T6=830-270[C]-90[Mn]-37[Ni]-70[Cr], [C], [Si], [Ni], [Mn], [Cr] are the mass percentages of C, Si, Ni, Mn, and Cr in the steel billet, respectively.

[0059] That is, in one embodiment of the present invention, the cooling of a hot-rolled steel plate is divided into three stages with different cooling rates and cooling methods. Thus, in the first cooling stage, a ferrite phase transformation occurs, and the presence of ferrite ensures the low yield strength of the steel plate. Furthermore, in the second stage, the carbon-rich, supercooled austenite phase in the steel plate is rapidly cooled, causing it to transform into an acicular ferrite / bainite structure. The acicular ferrite / bainite phase transformation is completed by controlling the final cooling temperature. Furthermore, controlling the cooling rate effectively avoids the formation of martensite or pearlite phases. Furthermore, the above temperature control can also improve the shape of the finished steel plate. Taking all of the above aspects into consideration, the steel plate ultimately achieves high tensile strength, low yield ratio, excellent low-temperature toughness, excellent shape, and good weldability.

[0060] In this way, the production method described in the present invention, based on the chemical composition, combines the specific process control of heating, rolling and cooling to achieve precise control of the microstructure, and achieves a huge improvement in strength under low alloy content (that is, the mechanical properties brought about by these elements are not reduced due to the low element content as commonly known), while also ensuring other properties, such as toughness, welding performance, yield strength ratio, etc., so that under the conditions of low alloy content, low production difficulty and short production process, comprehensive improvements in steel plates in terms of low yield strength ratio, easy welding, high strength and toughness, good plate shape, etc. are achieved, and the resulting steel plates are suitable for bridge engineering.

[0061] Preferably, during the heating process, the steel slab remains in the heating furnace at a temperature of at least T1 + 10°C and not more than T2 for a time period of 0.07 to 0.13 min / mm, and the total time in the heating furnace is 1.15 to 1.35 min / mm. Here, "min / mm" refers to one minute per unit thickness of the steel slab, with unit thickness measured in mm.

[0062] More specifically, in an optional embodiment, the steel billet may be heated in the heating furnace using a five-stage process comprising a heat recovery stage, a preheating stage, a first heating stage, a second heating stage, and a soaking stage.

[0063] In this five-stage process, the temperature of the heat recovery section is ≤900℃, the temperature of the preheating section is ≤1000℃, the temperature of the first heating section is 1120±15℃, and the temperature of the second heating section limits the maximum temperature of the steel billet, that is, the temperature of the second heating section is set to above T1+10℃ and below T2, and the residence time of the steel billet in the second heating section is 0.07~0.13min / mm.

[0064] Preferably, in the five-stage process, the temperature of the soaking stage is lower than that of the second heating stage, and the temperature of the soaking stage is 20-40° C. lower than that of the second heating stage. This arrangement can further improve the toughness of the finished steel plate.

[0065] In an optional variation, the steel billet is heated in the heating furnace using a three-stage process comprising a preheating section, a heating section, and a soaking section.

[0066] Among them, in this three-stage process, the temperature of the preheating section is ≤1000℃, and the temperature of the heating section limits the maximum temperature of the steel billet, that is, the temperature of the heating section is set to above T1+10℃ and below T2, and the residence time of the steel billet in the heating section is 0.07~0.13min / mm.

[0067] Preferably, in the three-stage process, the temperature of the soaking section is lower than that of the heating section, and the temperature of the soaking section is 20-40° C. lower than that of the heating section. This arrangement can further improve the toughness of the finished steel plate.

[0068] Furthermore, in the controlled rolling process, during the rolling of the steel billet into the first intermediate plate, the reduction in each pass is ≥20 mm; during the rolling of the first intermediate plate into the second intermediate plate, the reduction in each pass is ≥12 mm; during the rolling of the second intermediate plate into the finished thickness, the reduction in each pass is ≥4 mm.

[0069] Preferably, during rolling the steel billet into the first intermediate plate, the start rolling temperature is greater than T3+20°C and less than T3+40°C, and the finish rolling temperature is greater than T3 and less than T3+20°C.

[0070] Furthermore, preferably, during rolling the first intermediate plate into the second intermediate plate, the start rolling temperature is greater than T4 and less than T4+20°C, and the finish rolling temperature is greater than T4-50°C and less than T4-30°C.

[0071] When the second intermediate plate is rolled into the finished plate thickness, the starting rolling temperature is higher than T5-15°C and lower than T5, and the finishing rolling temperature is higher than T5-40°C and lower than T5-25°C.

[0072] Preferably, the finished plate thickness is approximately 6 to 64 mm.

[0073] Furthermore, in the controlled cooling process, cooling can be carried out in an ultra-fast cooling system. For example, the cooling water manifolds in the front section of the system can be closed and the roller speed can be 0.5 to 2.2 m / s, so as to cool at a low cooling rate; while in the rear section of the system, 5 to 24 groups of cooling water manifolds can be opened and the roller speed can be 0.6 to 2.3 m / s, so as to achieve rapid cooling.

[0074] The final steel plate product has excellent structure and performance.

[0075] For example, the microstructure of the obtained steel plate product is a complex phase structure of deformation-induced ferrite + polygonal ferrite + acicular ferrite + bainite, wherein the area of ​​the deformation-induced ferrite in the metallographic sampling surface accounts for approximately 5% to 10%, the area of ​​the polygonal ferrite in the metallographic sampling surface accounts for approximately 5% to 10%, the area of ​​the acicular ferrite in the metallographic sampling surface accounts for approximately 5% to 10%, and the area of ​​the bainite in the metallographic sampling surface accounts for approximately 70% to 85%.

[0076] The finished steel plate has a yield strength ≥500MPa, a tensile strength ≥670MPa, an elongation ≥25%, a yield strength ratio ≤0.75, an impact energy KV2 at -20°C ≥260J, an impact energy KV2 at -40°C ≥240J, an impact energy KV2 at -60°C ≥200J, a steel plate unevenness ≤1mm / m, and excellent welding performance.

[0077] In summary, the beneficial effects of the present invention are:

[0078] (1) On the one hand, by designing the chemical composition and using a low alloy content, the high strength of the steel is achieved while also ensuring the yield strength ratio, toughness, and weldability of the steel, thereby achieving excellent overall performance of the steel; in addition, the production difficulty of the steel is low;

[0079] (2) On the basis of chemical composition, combined with specific process control of heating, rolling and cooling, precise control of microstructure is achieved. Under the condition of low alloy content, a huge improvement in strength is achieved (that is, the mechanical properties brought about by these elements are not reduced due to the low element content as commonly known). At the same time, other properties such as toughness, welding performance, and yield strength ratio are guaranteed. Under the condition of low alloy content, low production difficulty and short production process, comprehensive improvements in steel plates in terms of low yield strength ratio, easy welding, high strength and toughness, and good plate shape are achieved. The resulting steel plates are suitable for bridge engineering.

[0080] Some specific embodiments are described below. In these embodiments, the chemical composition of the steel is shown in Table 1.

[0081] [Table 1]

[0082]

[0083] The metallographic structure of the steel in each example is a duplex structure of deformation-induced ferrite+polygonal ferrite+acicular ferrite+bainite.

[0084] Furthermore, the thickness and properties of the steel of each embodiment are shown in Table 2. In addition, the steel plate roughness of each embodiment is ≤1 mm / m, and the welding performance is excellent.

[0085] [Table 2]

[0086]

[0087] The preparation process of each of the above embodiments is as follows: preparing a continuous casting billet through steelmaking and continuous casting; preparing a finished steel plate by adopting a five-stage heating, controlled rolling, and controlled cooling process route for the obtained continuous casting billet; wherein, during the controlled cooling process, first air cooling to a first cooling temperature at a cooling rate of 1 to 10°C / s, then water cooling to a second cooling temperature at a cooling rate of 5 to 30°C / s, and then naturally cooling to room temperature.

[0088] Among them, the important process parameters of each embodiment are shown in Table 3 and Table 4.

[0089] [Table 3]

[0090]

[0091] [Table 4]

[0092]

Claims

1. A method for producing high-strength bridge steel, characterized in that: The chemical composition of the steel includes, by mass percentage, C: 0.08-0.11%, Si: 0.11-0.18%, Mn: 1.39-1.47%, Ni: 0.07-0.13%, Nb: 0.021-0.029%, Ti: 0.009-0.017%, Al: 0.026-0.046%, Cr: 0.07-0.13%, P≤0.02%, S≤0.0080%, N≤0.0045%, and the remainder is iron and unavoidable impurities; The production method comprises: Heat the steel billet in the heating furnace to a temperature above T1+10℃ and below T2, where T1 is T NbC 、T NbN and T TiC The maximum value of T2 is T1+50℃, T TiN -150℃, the larger value; where T NbC 、T NbN 、T TiC and T TiN are the complete solution temperatures of NbC, NbN, TiC and TiN respectively; After leaving the heating furnace, the billet is first rolled at a rolling temperature of T3 or higher and T3+40℃ or lower to a thickness of 4 to 6.8 times the finished product thickness to obtain the first intermediate plate; then rolled at a rolling temperature of T4-50℃ or higher and T4+20℃ or lower to a thickness of 1.8 to 3.2 times the finished product thickness to obtain the second intermediate plate; finally rolled at a rolling temperature of T5-40℃ or higher and T5 or lower to the finished product thickness; T3≥T4≥T5, T3=887+464[C]+6445[Nb]-644 +890[Ti]+363[Al]-357[Si], T5=910-310[C]-80[Mn]-15[Cr], T4=910-203 -15.2[Ni]+44.7[Si]; The rolled steel plate is air-cooled at a cooling rate of 1-10°C / s to a temperature between T6 and T6+20°C, then water-cooled at a cooling rate of 8-30°C / s to a temperature between T7-30°C and T7+10°C, and then naturally cooled to room temperature to obtain a finished steel plate; T5 ≥ T6 ≥ T7, T7 = 539-423[C]-17.7[Ni]-12.1[Cr]-11[Si]-30.4[Mn], T6 = 830-270[C]-90[Mn]-37[Ni]-70[Cr]; Among them, [C], [Nb], [Ti], [Al], [Si], [Ni], [Mn], and [Cr] are the mass percentages of C, Nb, Ti, Al, Si, Ni, Mn, and Cr in the steel billet, respectively.

2. The method for producing high-strength bridge steel according to claim 1, characterized in that: The chemical composition of the steel billet includes, by mass percentage, P: 0.0101-0.0151%, S: 0.0020-0.0080%, and N: 0.0025-0.0045%.

3. The method for producing high-strength bridge steel according to claim 1, characterized in that: The carbon equivalent CEV of the chemical composition of the steel billet satisfies 0.333-0.

380.

4. The method for producing high-strength bridge steel according to claim 1, characterized in that: The residence time of the steel billet at a temperature above T1+10℃ and below T2 is 0.07~0.13min / mm, and the total time in the heating furnace is 1.15~1.35min / mm.

5. The method for producing high-strength bridge steel according to claim 1, characterized in that: The steel billet adopts a five-stage process in the heating furnace, including a heat recovery section, a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the first heating section is 1120±15℃, the temperature of the second heating section is above T1+10℃ and below T2, the temperature of the soaking section is lower than that of the second heating section, and the temperature of the soaking section is 20~40℃ lower than that of the second heating section. Alternatively, the steel billet adopts a three-stage process in the heating furnace, including a preheating section, a heating section and a soaking section. The temperature of the heating section is above T1+10°C and below T2, the temperature of the soaking section is lower than the temperature of the heating section, and the temperature of the soaking section is 20~40°C lower than the temperature of the heating section.

6. The method for producing high-strength bridge steel according to claim 1, characterized in that: When rolling to obtain the first intermediate plate, the starting rolling temperature is higher than T3+20°C and lower than T3+40°C, and the finishing rolling temperature is higher than T3 and lower than T3+20°C.

7. The method for producing high-strength bridge steel according to claim 1, characterized in that: When rolling to obtain the second intermediate plate, the starting rolling temperature is greater than T4 and less than T4+20°C, and the finishing rolling temperature is greater than T4-50°C and less than T4-30°C.

8. The method for producing high-strength bridge steel according to claim 1, characterized in that: When the second intermediate plate is rolled to the finished thickness, the starting rolling temperature is higher than T5-15°C and lower than T5, and the finishing rolling temperature is higher than T5-40°C and lower than T5-25°C.

9. A high-strength bridge steel, characterized in that: The chemical composition of the steel includes, by mass percentage, C: 0.08-0.11%, Si: 0.11-0.18%, Mn: 1.39-1.47%, Ni: 0.07-0.13%, Nb: 0.021-0.029%, Ti: 0.009-0.017%, Al: 0.026-0.046%, Cr: 0.07-0.13%, P≤0.0151%, S≤0.0080%, N≤0.0045%, and the remainder is iron and unavoidable impurities; The steel is produced by the production method of high-strength bridge steel according to claim 1; The steel has a thickness of 6-64 mm, a yield strength of ≥500 MPa, a tensile strength of ≥670 MPa, an elongation of ≥25%, and a yield strength ratio of ≤0.

75.

10. The high-strength bridge steel according to claim 9, characterized in that: The steel has an impact energy KV2 of ≥260J at -20°C, an impact energy KV2 of ≥240J at -40°C, an impact energy KV2 of ≥200J at -60°C, and a steel plate unevenness of ≤1mm / m.

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