Bridge steel plate and manufacturing method thereof

Abstract

The invention discloses a bridge steel plate and a manufacturing method thereof, and belongs to the technical field of steel, the bridge steel plate comprises the following chemical components in percentage by weight: 0.08-0.11% of C, 0.30-0.50% of Si, 1.50-1.70% of Mn, 0.030-0.060% of Nb, 0.040-0.070% of V, 0.010-0.040% of Ti and 0.015-0.050% of Als, a Mn-Nb-V-Ti component system is adopted, a low yield ratio control technology of a TMCP + T state bridge steel plate is developed, and by optimizing controlled cooling after rolling, the yield ratio of the steel plate is controlled to be smaller than that of the steel plate. The volume fraction of ferrite and bainite in a steel plate structure is effectively controlled, the high-performance requirement for the low yield ratio of the high-strength bridge steel plate is met, and stable batch economical production of the bridge steel plate with the thickness of 6-64 mm is achieved.

Description

Technical Field

[0001] This invention belongs to the field of steel technology, specifically relating to a bridge steel plate and its manufacturing method. Background Technology

[0002] Bridges are a crucial component of transportation infrastructure. Increased national investment in transportation has spurred bridge construction and driven market demand for high-performance bridge steel. Currently, my country's bridge construction meets various needs, including crossing mountains, seas, and urban areas, with engineering scale and technological levels reaching world-leading levels. The industry currently primarily adjusts the yield strength ratio by adding precious metals or employing complex heat treatment processes, but this significantly increases production costs and does not meet the economic requirements of large-scale infrastructure construction. Domestic and international research indicates that by optimizing composition design combined with TMCP (Thermomechanical Control Process), ideal low yield strength ratio characteristics can be obtained through fine-grain strengthening and phase transformation control without adding expensive alloys. Therefore, developing an economical low yield strength ratio Q420q bridge steel plate based on a conventional composition system and employing an efficient manufacturing process is of great value for improving the safety and economy of bridge construction in my country. It can meet the requirements of the GB / T 714-2015 standard while significantly reducing the construction costs of major projects.

[0003] Chinese patent CN120608243A discloses a method for preparing hot-rolled Q420qE bridge steel plates. The Q420qE bridge steel is composed of the following components by mass percentage: C: 0.07–0.09%, Si: 0.30–0.40%, Mn: 1.40–1.50%, Als: 0.015–0.030%, Cr: 0.15–0.25%, Nb: 0.015–0.025%, Ni: 0.10–0.15%, with the balance being Fe. The method for preparing 8–12 mm thick Q420qE bridge steel plates using these cast billets involves preparing continuously cast billets, segmented heating, hot rolling to the target thickness, post-rolling air cooling, and online shearing sampling. This method improves production efficiency, produces plates with good shape, and exhibits excellent comprehensive performance, with all mechanical properties meeting the requirements of GB / T714. Its drawback lies in the addition of expensive alloying elements such as Cr and Ni, which not only impairs welding performance but also results in excessively high production costs.

[0004] Chinese patent CN119194210A discloses a method for producing thin-gauge Q420qD bridge steel with a thickness of less than 12mm. The chemical composition, by weight percentage, is: C: 0.09~0.11%, Si: 0.22~0.32%, Mn: 1.55~1.68%, P: ≤0.015%, S: ≤0.005%, Nb: 0.036~0.0046%, V: 0.031~0.041%, Ti: 0.010~0.020%, Cr: 0.05~0.15%, Als: 0.020~0.035%, with the balance being Fe and unavoidable impurities. The method also discloses the main steps and process parameters. While ensuring mechanical and impact properties, it employs natural cooling to avoid the uneven cooling and shape problems caused by accelerated cooling of thin-gauge steel plates, effectively solving the challenge of matching high strength with thin specifications and plate shape. Its drawback is that it is only suitable for the production of thin-gauge Q420qD bridge steel with a thickness of less than 12mm.

[0005] Chinese patent CN119020702A discloses a novel low yield strength ratio Q420qE steel plate, whose chemical composition by mass percentage includes: C: 0.04~0.06%, Si: 0.2~0.3%, Mn: 1.48~1.56%, Nb: 0.030~0.045%, Ti: 0.011~0.017%, Cr: 0.05~0.13%, P: ≤0.015%, S≤0.002%, with the remainder being Fe and unavoidable impurities. The patent also provides a method for manufacturing the steel plate. This invention uses an alloy with low cost and has the advantage of large-scale production. Furthermore, it can effectively control the strength of the steel plate, achieving a qualified yield strength ratio, stable performance, and good plate shape through low final cooling. It also improves the temperature uniformity of the steel plate, eliminating the need for heat treatment tempering to adjust the strength, thus achieving a low-cost, high-efficiency production method. Its drawback is that it contains a small amount of precious alloy Cr and is only suitable for the production of Q420qE bridge steel plates with a thickness of 10mm to 30mm. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a bridge steel plate and its manufacturing method. Employing a Mn-Nb-V-Ti composition system, a low yield strength ratio control technology for TMCP+T-state bridge steel plates was developed. By optimizing post-rolling controlled cooling, the volume fractions of ferrite and bainite in the steel plate microstructure were effectively controlled, ensuring the high-performance requirement of a low yield strength ratio for the bridge steel plate and achieving stable, economical mass production of Q420qD / E steel plates with thicknesses ranging from 6 to 64 mm.

[0007] The technical solution adopted in this invention is as follows:

[0008] This invention provides a bridge steel plate comprising the following chemical composition by weight percentage: C: 0.08~0.11%, Si: 0.20~0.50%, Mn: 1.50~1.70%, S: ≤0.003%, P: ≤0.020%, Nb: 0.030~0.060%, V: 0.030~0.070%, Ti: 0.010~0.040%, Als: 0.015~0.050%, with the balance being Fe and unavoidable impurities.

[0009] Furthermore, the bridge steel plate also contains 0.10~0.20% Mo.

[0010] The metallographic structure of the bridge steel plate consists of granular bainite and ferrite, wherein the volume fraction of granular bainite is 45-65%.

[0011] The bridge steel plate has a yield strength of 450~500 MPa, a tensile strength of 550~610 MPa, a yield-to-tensile ratio of ≤0.85, an elongation of ≥26%, a longitudinal impact energy of 200~350J at -20℃, and a longitudinal impact energy of 140~280J at -40℃.

[0012] The present invention also provides a method for manufacturing the bridge steel plate, the method comprising the following steps: steelmaking, billet heating, rolling and heat treatment.

[0013] Furthermore, the steelmaking process includes the following steps: converter smelting, LF refining, RH vacuum refining, continuous casting, and billet cleaning.

[0014] In the converter smelting process, a sliding plate and slag-blocking plug are used to prevent slag from being discharged during steel tapping; the temperature of the molten iron entering the furnace is ≥1270℃, and the molten steel discharged from the furnace has C≤0.06%, P≤0.016%, and S≤0.030%.

[0015] In the LF refining process, alloys are added to fine-tune the composition and precisely control the alloy composition.

[0016] In the RH vacuum treatment step, the vacuum time is ≥12 min, the limit time is ≥8 min, and the vacuum degree is ≤133 Pa. For seamless calcium wire 100~150 m, the soft blowing argon time is ≥10 min.

[0017] In the slab continuous casting process, dynamic light reduction, protective pouring, and constant casting speed are adopted to produce a continuously cast slab with a thickness of 230mm. The low-magnification center segregation of the slab must be controlled below Class C, grade 1.5, and the center porosity must be controlled below grade 1.0. The slab can be either cold-charged or hot-charged.

[0018] In the billet heating step, the slab is heated in a walking beam furnace. When the slab is cold-charged: the preheating section temperature is 700~900℃, the first heating section temperature is 1100~1200℃, the second heating section temperature is 1200~1260℃, and the soaking section temperature is 1200~1270℃. When the slab is hot-charged, the heating temperature of each section is reduced by 20℃ based on the cold-charged requirements. The cold-charged slab is stored in the furnace for 240~310 minutes, and the hot-charged slab is stored in the furnace for 220~290 minutes.

[0019] In the rolling process, a 3800mm rolling mill is used for two-stage controlled rolling. The roughing rolling start temperature is ≥1000℃, the finishing rolling start temperature is ≤900℃, the cumulative deformation rate in the finishing rolling stage is not less than 50%, and the final rolling temperature is 810~850℃.

[0020] In the rolling process, the cooling rate after rolling is controlled at 5~10℃ / s, and the reheating temperature is controlled at 670~710℃. This ensures that the volume fraction of granular bainite in the microstructure of the steel plate reaches 45%~65% after tempering, thereby achieving the high-performance requirements of good plasticity-toughness matching and low yield strength ratio.

[0021] During the rolling process, the roll speed is controlled at 0.95~1.5m / s and the acceleration is controlled at 0.002~0.005m / s during post-rolling cooling. This effectively avoids excessively low head steel temperature and ensures uniformity of the overall plate performance.

[0022] The heat treatment is tempering, with a tempering temperature of 520~540℃ and a furnace time of 1.5H+60min, where H is the thickness of the steel plate in mm.

[0023] The functions and controls of each component in the bridge steel plate provided by this invention are as follows:

[0024] Carbon: C is the cheapest and most effective strengthening element in steel. When dissolved in the matrix, it provides solid solution strengthening and forms cementite, further increasing the steel's strength. However, excessive carbon content not only reduces the steel's ductility and toughness but also deteriorates its weldability. Therefore, the carbon content in steel must be reasonably controlled. This invention controls the carbon content to be 0.08~0.11%.

[0025] Manganese (Mn) is a weak carbide-forming element. In smelting, it plays a role in deoxidation and eliminating the effects of sulfur. It can also lower the austenite transformation temperature, refine ferrite grains, and improve the strength and toughness of steel plates. Simultaneously, it can strengthen ferrite through solid solution. As the Mn content increases, the strength of the steel also increases. However, excessive Mn will reduce the toughness and weldability of the steel. Furthermore, excessive Mn can easily cause segregation in the core of the cast billet, resulting in uneven composition in the thickness direction. This invention controls the Mn content to be 1.50~1.70%.

[0026] Silicon: In steel, silicon (Si) is primarily used as a deoxidizer, effectively removing oxygen and improving purity. Appropriate amounts of silicon can also increase the strength, hardness, and elastic limit of steel, as well as its wear resistance and oxidation resistance. However, excessive silicon content reduces the plasticity and toughness of the steel, affecting its machinability. Furthermore, excessive Si can increase the viscosity of the iron oxide scale on the surface of the steel billet after heating, easily causing surface problems such as pitting on the steel plate. This invention controls the Si content to be 0.20~0.50%.

[0027] Phosphorus: P is a harmful element in steel. The presence of P will increase the brittleness of steel, especially at low temperatures. P will significantly reduce the ductility and toughness of steel, that is, the "cold brittleness" of steel. High P steel is prone to welding cracks and cold cracks during the welding process, reducing the strength and reliability of the welded joint. This invention controls it.

[0028] Sulfur: S is a harmful element in steel, and its presence significantly reduces the toughness of the steel. Sulfur usually forms sulfides (such as FeS), which are distributed within the grains or at grain boundaries of the steel, forming a brittle phase. When heated to 1000~1200℃, the eutectic melts, causing the steel to crack at high temperatures; this phenomenon is called "hot brittleness," and it can lead to hot cracking during welding. Sulfides in steel tend to cause segregation, reducing the welded structure's resistance to lamellar tearing and the steel's toughness. This invention controls P ≤ 0.020%.

[0029] Niobium (Nb) exists in steel primarily in two forms: niobium carbonitride precipitates and niobium carbonitride in solid solution within the iron matrix. The niobium carbonitride second phase can refine grains and provide precipitation strengthening. Niobium can dissolve in the iron matrix, and because niobium atoms are larger than iron atoms, they easily aggregate along dislocation lines, resulting in a relatively high concentration of agglomerates. Therefore, dislocations experience significant drag from Nb atoms during climb, strongly inhibiting recrystallization nucleation and thus suppressing recrystallization. This invention controls the Nb content to be 0.030~0.060%.

[0030] Titanium (Ti): Ti is chemically highly reactive, capable of combining with carbon, sulfur, oxygen, and nitrogen in steel to form compounds. Therefore, Ti exists primarily in steel in a combined state rather than a solid solution state. Ti has the strongest affinity for oxygen; therefore, molten steel must be thoroughly deoxidized before adding ferrotitanium (TIG). Otherwise, Ti will combine with oxygen to form Ti₂O₃, reducing the effective Ti content of the steel. Ti combines with C and N to form carbonitrides, playing a role in grain refinement and precipitation strengthening. After solidification, molten steel precipitates tiny, dispersed TiN particles, which exist stably in the steel. If TiN particles are distributed on austenite grain boundaries, they strongly hinder the migration of austenite grain boundaries, thereby refining the austenite grains. This invention controls the content to be 0.010~0.040%.

[0031] Vanadium (V) has a strong affinity for carbon, ammonia, and oxygen, forming corresponding stable compounds. In steel, vanadium mainly exists as carbides. Its primary function is to refine the microstructure and grain size of steel, reducing its strength and toughness. When dissolved in solid solution at high temperatures, it increases hardenability; conversely, when existing as carbides, it reduces hardenability. Vanadium increases the tempering stability of quenched steel and produces a secondary hardening effect. In ordinary low-carbon alloy steel, vanadium refines grain size, improves the strength and yield ratio after normalizing, and enhances low-temperature properties, thus improving the weldability of the steel. Simultaneously, V can fix nitrogen in steel, improving its aging properties. Furthermore, V can fix nitrogen in welds, significantly improving the weldability of steel. However, V increases the ductile-brittle transition temperature of steel; therefore, this invention controls V to be 0.030~0.070%.

[0032] Aluminum (Al): Al is a major deoxidizing element that refines the grain size of steel and increases its grain coarsening temperature. Steel with an aluminum content greater than 0.015% is considered fine-grained. This is because aluminum forms fine, dispersed refractory compounds with other elements in steel, hindering the formation of these compounds, primarily due to the influence of AlN. However, excessively high Al content will result in a large amount of AlN in the steel, reducing the content of VN. Furthermore, excessively high aluminum content will worsen the weldability of the steel. This invention controls Al content to 0.015~0.050%.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The bridge steel plate provided by this invention does not contain expensive alloying elements such as Cr and Ni. Based on the Mn-Nb-V-Ti composition system, a TMCP+T state Q420q bridge steel plate with a low yield strength ratio has been developed. Controlled cooling after rolling effectively controls the volume fraction of ferrite and bainite in the steel plate microstructure, ensuring the high-performance requirements of high-strength Q420q steel plate with a low yield strength ratio. This enables stable, economical mass production of Q420q D / E bridge steel plates with thicknesses ranging from 6 to 64 mm. Attached Figure Description

[0035] Figure 1 The image shows the metallographic structure of the economical Q420q bridge steel plate in Example 1.

[0036] Figure 2 The image shows the metallographic structure of the economical Q420q bridge steel plate in Example 2.

[0037] Figure 3 The dynamic CCT curve of the economical Q420q bridge steel plate in Example 1 is shown. Detailed Implementation

[0038] This invention provides a bridge steel plate comprising the following chemical composition by weight percentage: C: 0.08~0.11%, Si: 0.20~0.50%, Mn: 1.50~1.70%, S≤0.003%, P≤0.020%, Nb: 0.030~0.060%, V: 0.030~0.070%, Ti: 0.010~0.040%, Als: 0.015~0.050%, with the balance being Fe and unavoidable impurities.

[0039] The manufacturing method of the bridge steel plate includes the following steps: converter smelting, LF refining, RH vacuum refining, continuous casting, billet cleaning, billet heating, rolling and heat treatment, wherein:

[0040] In the converter smelting process, a sliding plate and slag-blocking plug are used to prevent slag from being discharged during steel tapping; the temperature of the molten iron entering the furnace is ≥1270℃, and the molten steel discharged from the furnace has C≤0.06%, P≤0.016%, and S≤0.030%.

[0041] In the LF refining process, alloys are added to fine-tune the composition and precisely control the alloy composition.

[0042] In the RH vacuum treatment step, the vacuum time is ≥12 min, the limit time is ≥8 min, and the vacuum degree is ≤133 Pa. For seamless calcium wire 100~150 m, the soft blowing argon time is ≥10 min.

[0043] In the slab continuous casting process, dynamic light reduction, protective pouring, and constant casting speed are adopted to produce a continuously cast slab with a thickness of 230mm. The low-magnification center segregation of the slab must be controlled below Class C, grade 1.5, and the center porosity must be controlled below grade 1.0. The slab can be either cold-charged or hot-charged.

[0044] In the billet heating step, the slab is heated in a walking beam furnace. When the slab is cold-charged: the preheating section temperature is 700~900℃, the first heating section temperature is 1100~1200℃, the second heating section temperature is 1200~1260℃, and the soaking section temperature is 1200~1270℃. When the slab is hot-charged, the heating temperature of each section is reduced by 20℃ based on the cold-charged requirements. The cold-charged slab is stored in the furnace for 240~310 minutes, and the hot-charged slab is stored in the furnace for 220~290 minutes.

[0045] In the rolling process, a 3800mm rolling mill is used for two-stage controlled rolling. The roughing rolling start temperature is ≥1000℃, the finishing rolling start temperature is ≤900℃, the cumulative deformation rate in the finishing rolling stage is not less than 50%, and the final rolling temperature is 810~850℃.

[0046] In the rolling process, the cooling rate after rolling is controlled at 5℃ / s to 10℃ / s, and the reheating temperature is controlled at 670℃ to 710℃. This ensures that the volume fraction of granular bainite in the microstructure of the steel plate reaches 45% to 65% after tempering, thereby achieving the high-performance requirements of good plasticity-toughness matching and low yield strength ratio.

[0047] During the rolling process, the roll speed is controlled at 0.95~1.5m / s and the acceleration is controlled at 0.002~0.005m / s during post-rolling cooling. This effectively avoids excessively low head steel temperature and ensures uniformity of the overall plate performance.

[0048] The heat treatment is tempering, with a tempering temperature of 520~540℃ and a furnace time of 1.5H+60min, where H is the thickness of the steel plate in mm.

[0049] The present invention will now be described in detail with reference to the embodiments.

[0050] Example 1

[0051] An economical Q420q bridge steel plate, the chemical composition and weight percentage of which are shown in Table 1, with the balance being iron and unavoidable impurities.

[0052] Table 1

[0053]

[0054] The manufacturing method of the economical Q420q bridge steel plate is as follows:

[0055] 1) Converter smelting and LF refining: The temperature of the molten iron entering the furnace is 1281℃. Slag is blocked by a sliding plate and a slag stopper when tapping the steel. The C content of the steel tapped from the converter is 0.03%, P content is 0.012%, and S content is 0.010%.

[0056] 2) RH vacuum treatment: vacuum time 14 min, limit time 11 min, vacuum degree 128 Pa, seamless calcium wire 120 m, soft blowing argon time 15 min, the final smelting composition is shown in Table 1.

[0057] 3) Slab continuous casting: Dynamic light reduction, protective pouring, and constant casting speed process are adopted to produce a continuous casting slab with a thickness of 230mm. The slab has low magnification center segregation of Class C 1.0 grade and center porosity of 0.5 grade. The slab is cold-charged into the heating furnace.

[0058] 4) Heating: The slab is heated in a walking beam furnace. Cold charging furnace temperature control: preheating section about 820℃, first heating section about 1152℃, second heating section about 1237℃, soaking section about 1250℃, total furnace time 260min, to ensure that alloying elements are fully dissolved and the slab temperature is uniform.

[0059] 5) Rolling: Rolling adopts two-stage controlled rolling. The roughing rolling start temperature is 1026℃, the finishing rolling start temperature is 865℃, the cumulative deformation rate of the finishing rolling stage is ≥50%, the finishing rolling end temperature is 841℃, the cooling rate after rolling is controlled at 5℃ / s, the roll speed is controlled at 1.0m / s, the acceleration is controlled at 0.002m / s, the reddening temperature is 698℃, and the rolling thickness is 24mm.

[0060] 6) Tempering treatment: Tempering treatment is carried out in a roller hearth radiant tube heat treatment furnace. The set temperature is 530℃, the temperature fluctuation range is ±10℃, and the heat treatment time in the furnace is 96min.

[0061] The Q420q steel plate manufactured in this embodiment fully meets the performance requirements of the national standard GB / T 714, as shown in Table 2.

[0062] Table 2

[0063]

[0064] Figure 1 The image shows the metallographic structure of the economical Q420q steel plate in Example 1. As can be seen from the image, its metallographic structure consists of granular bainite and ferrite, with the volume fraction of granular bainite being 53%.

[0065] Example 2

[0066] An economical Q420q bridge steel plate, the chemical composition and weight percentage of which are shown in Table 3, with the balance being iron and unavoidable impurities.

[0067] Table 3

[0068]

[0069] The manufacturing method of the economical Q420q steel plate is as follows:

[0070] 1) Converter smelting and LF refining: The process flow is converter smelting - LF refining - continuous casting; the C content of the steel tapped from the converter is 0.03%, P is 0.012%, S is 0.010%, and the temperature of the molten iron entering the furnace is 1281℃.

[0071] 2) RH vacuum treatment: vacuum time 13 min, limit time 10 min, vacuum degree 127 Pa. Seamless calcium wire 125 m, soft blowing argon time 12 min. The final smelting composition is shown in Table 3.

[0072] 3) Slab continuous casting: Dynamic light reduction, protective pouring, and constant casting speed process are adopted to produce a continuous casting slab with a thickness of 230mm. The low magnification center segregation of the slab is Class C 1.0 grade, and the center porosity is 0.5 grade. The slab is hot-charged into the heating furnace.

[0073] 4) Heating: The slab is heated in a walking beam furnace. The furnace temperature control for hot charging is as follows: preheating section approximately 798℃, first charging section approximately 1133℃, second charging section approximately 1222℃, and soaking section 1248℃. The hot-charged slab is put into the furnace and stored for 240 minutes.

[0074] 5) Rolling: A 3800mm rolling mill is used for two-stage controlled rolling. The roughing rolling start temperature is 1050℃, the finishing rolling start temperature is 863℃, the cumulative deformation rate of the finishing rolling stage is ≥50%, the finishing rolling end temperature is 838℃, the cooling rate after rolling is controlled at 8℃ / s, the roll speed is controlled at 1.2m / s, the acceleration is controlled at 0.003m / s, the reddening temperature is 705℃, and the rolling thickness is 50mm.

[0075] 6) Tempering treatment: Tempering treatment is carried out in a roller hearth radiant tube heat treatment furnace. The set temperature is 530℃, the temperature fluctuation range is ±10℃, and the heat treatment time in the furnace is 135min.

[0076] The Q420q steel plate manufactured in this embodiment fully meets the performance requirements of the national standard GB / T 714, as shown in Table 4.

[0077] Table 4

[0078]

[0079] Figure 2 The image shows the metallographic structure of the economical Q420q steel plate in Example 2. As can be seen from the image, its metallographic structure consists of granular bainite and ferrite, with the volume fraction of granular bainite being 59%.

[0080] Example 3

[0081] A type of Q420q bridge steel plate, the chemical composition and weight percentage of which are shown in Table 5, with the balance being iron and unavoidable impurities.

[0082] Table 5

[0083]

[0084] The manufacturing method of the Q420q bridge steel plate is as follows:

[0085] 1) Converter smelting and LF refining: The process flow is converter smelting - LF refining - continuous casting; the C content of the steel tapped from the converter is 0.04%, P is 0.011%, S is 0.015%, and the temperature of the molten iron entering the furnace is 1281℃.

[0086] 2) RH vacuum treatment: vacuum time 14 min, limit time 10 min, vacuum degree 128 Pa. Seamless calcium wire 132 m, soft blowing argon time 11 min. The final smelting composition is shown in Table 5.

[0087] 3) Slab continuous casting: Dynamic light reduction, protective pouring, and constant casting speed process are adopted to produce a continuous casting slab with a thickness of 230mm. The low magnification center segregation of the slab is Class C 1.0 grade, and the center porosity is 0.5 grade. The slab is hot-charged into the heating furnace.

[0088] 4) Heating: The slab is heated in a walking beam furnace. The furnace temperature control for hot charging is as follows: preheating section 798℃, first heating section approximately 1132℃, second heating section 1224℃, and soaking section 1249℃. The hot-charged slab is placed in the furnace and stored for 243 minutes.

[0089] 5) Rolling: A two-stage controlled rolling process is carried out using a 3800mm rolling mill. The roughing rolling start temperature is 1100℃, the finishing rolling start temperature is 867℃, the cumulative deformation rate of the finishing rolling stage is ≥50%, the finishing rolling finish temperature is 832℃, the post-rolling cooling rate is controlled at 10℃ / s, the roll speed is controlled at 1.5m / s, the acceleration is controlled at 0.002m / s, the reddening temperature is 698℃, and the rolling thickness is 30mm.

[0090] 6) Tempering treatment: Tempering treatment is carried out in a roller hearth radiant tube heat treatment furnace. The set temperature is 530℃, the temperature fluctuation range is ±10℃, and the heat treatment time in the furnace is 105min.

[0091] The Q420q steel plate manufactured in this embodiment fully meets the performance requirements of the national standard GB / T 714, as shown in Table 6.

[0092] Table 6

[0093]

[0094] As can be seen from Table 6, the addition of Mo to this embodiment does not significantly improve the performance of Q420q steel plate compared to the previous embodiment, so the addition of the precious alloy Mo can be omitted.

[0095] Comparative Example 1

[0096] A type of Q420q bridge steel plate, the chemical composition and weight percentage of which are shown in Table 7, with the balance being iron and unavoidable impurities.

[0097] Table 7

[0098]

[0099] The manufacturing method of the Q420q bridge steel plate is as follows:

[0100] 1) Converter smelting and LF refining: The process flow is converter smelting - LF refining - continuous casting; the C content of the steel tapped from the converter is 0.03%, P is 0.012%, S is 0.016%, and the temperature of the molten iron entering the furnace is 1283℃.

[0101] 2) RH vacuum treatment: vacuum time 13min, limit time 10min, vacuum degree 129Pa.

[0102] 129m of seamless calcium wire was used, and the soft blowing argon time was 12min. The final smelting composition is shown in Table 7.

[0103] 3) Slab continuous casting: Dynamic light reduction, protective pouring, and constant casting speed process are adopted to produce a continuous casting slab with a thickness of 230mm. The low magnification center segregation of the slab is Class C 1.0 grade, and the center porosity is 0.5 grade. The slab is hot-charged into the heating furnace.

[0104] 4) Heating: The slab is heated in a walking beam furnace. The furnace temperature control is as follows: preheating section approximately 797°C, first heating section approximately 1134°C, second heating section 1227°C, soaking section 1251°C, and furnace storage time 248 minutes.

[0105] 5) Rolling: A 3800mm rolling mill is used for two-stage controlled rolling. The roughing rolling start temperature is ≥1050℃, the finishing rolling start temperature is 872℃, the cumulative deformation rate of the finishing rolling stage is ≥50%, the finishing rolling finish temperature is 842℃, the cooling rate after rolling is controlled at 8℃ / s, the roll speed is controlled at 1.0m / s, the acceleration is controlled at 0.002m / s, the reddening temperature is 701℃, and the rolling thickness is 55mm.

[0106] 6) Tempering treatment: Tempering treatment is carried out in a roller hearth radiant tube heat treatment furnace. The set temperature is 530℃, the temperature fluctuation range is ±10℃, and the heat treatment time in the furnace is 143min.

[0107] In this comparative example, because the steel composition lacked V and had low C and Mn content, the tensile strength and -40℃ impact strength of the manufactured Q420q steel plate did not meet the performance requirements of the national standard GB / T 714. Other properties met the national standard requirements, as shown in Table 8.

[0108] Table 8

[0109]

[0110] The above detailed description of a bridge steel plate and its manufacturing method with reference to the embodiments is illustrative rather than limiting. Several embodiments can be listed according to the defined scope. Therefore, changes and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A bridge steel plate, characterized in that, The bridge steel plate comprises the following chemical composition by weight percentage: C: 0.08~0.11%, Si: 0.20~0.50%, Mn: 1.50~1.70%, S≤0.003%, P≤0.020%, Nb: 0.030~0.060%, V: 0.030~0.070%, Ti: 0.010~0.040%, Als: 0.015~0.050%, with the balance being Fe and unavoidable impurities.

2. The bridge steel plate according to claim 1, characterized in that, The bridge steel plate also contains Mo: 0.10~0.20%.

3. The bridge steel plate according to claim 1, characterized in that, The metallographic structure of the bridge steel plate consists of granular bainite and ferrite, wherein the volume fraction of granular bainite is 45-65%.

4. The bridge steel plate according to claim 1, characterized in that, The bridge steel plate has a yield strength of 450~500MPa, a tensile strength of 550~610 MPa, a yield-to-tensile ratio of ≤0.85, an elongation of ≥26%, a longitudinal impact energy of 200~350J at -20℃, and a longitudinal impact energy of 140~280J at -40℃.

5. The method for manufacturing bridge steel plates as described in any one of claims 1-4, characterized in that, The manufacturing method includes the following steps: steelmaking, billet heating, rolling, and heat treatment.

6. The manufacturing method according to claim 5, characterized in that, In the billet heating step, the slab is heated in a walking beam furnace. When the slab is cold-charged: the preheating section temperature is 700~900℃, the first heating section temperature is 1100~1200℃, the second heating section temperature is 1200~1260℃, and the soaking section temperature is 1200~1270℃. When the slab is hot-charged, the heating temperature of each section is reduced by 20℃ based on the cold-charged requirements. The cold-charged slab is stored in the furnace for 240~310 minutes, and the hot-charged slab is stored in the furnace for 220~290 minutes.

7. The manufacturing method according to claim 5, characterized in that, In the rolling process, the roughing rolling start temperature is ≥1000℃, the finishing rolling start temperature is ≤900℃, the cumulative deformation rate in the finishing rolling stage is not less than 50%, and the final rolling temperature is 810~850℃.

8. The manufacturing method according to claim 5, characterized in that, In the rolling process, the cooling rate after rolling is controlled at 5℃ / s to 10℃ / s, and the reddening temperature is controlled at 670 to 710℃.

9. The manufacturing method according to claim 5, characterized in that, During the rolling process, the roll speed is controlled at 0.95~1.5m / s and the acceleration is controlled at 0.002~0.005m / s during post-rolling cooling.

10. The manufacturing method according to claim 5, characterized in that, The heat treatment is tempering, with a tempering temperature of 520~540℃ and a furnace time of 1.5H+60min, where H is the thickness of the steel plate in mm.

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