Hot mechanical rolled 420MPa-grade bridge steel plate

Abstract

The invention discloses a hot mechanical rolled 420 MPa bridge steel plate which comprises the following chemical components in percentage by mass: 0.085 to 0.105 percent of C, 0.20 to 0.30 percent of Si, 1.50 to 1.60 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.035 to 0.045 percent of Nb, 0.030 to 0.040 percent of V, 0.008 to 0.020 percent of Ti, 0.020 to 0.035 percent of Als and the balance of Fe and inevitable impurities. The invention further discloses specific preparation process steps and parameters. The steel plate produced by the invention has the following mechanical properties: the yield strength is greater than or equal to 420 MPa, the tensile strength is greater than or equal to 540 MPa, the percentage elongation after fracture is greater than or equal to 19%, the impact energy at-20 DEG C and-40 DEG C is greater than or equal to 120 J, and meanwhile, the steel plate has the characteristics of easiness in welding, low yield ratio, fatigue resistance and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of 420MPa bridge steel plate production, and in particular relates to a thermomechanically rolled 420MPa grade bridge steel plate. Background Art

[0002] Bridge steel is widely used in large-span, heavy-load bridges for highways, railways, and dual-use highway and railways. It is a special steel for bridge construction. It requires high strength and toughness, as well as the ability to withstand the load and impact of locomotives and vehicles, and good fatigue resistance, certain low-temperature toughness, and atmospheric corrosion resistance. Due to the advantages of Q420q-level bridge steel, such as higher strength, reduced use, and small installation workload, people are increasingly inclined to use Q420q-level bridge steel.

[0003] GB / T714-2015 "Structural Steel for Bridges" stipulates that Q420q can only be delivered by thermomechanical rolling, and has strict regulations on the chemical composition, especially the carbon content (carbon content ≤ 0.11%), which objectively increases the difficulty of producing 420MPa grade bridge steel plates.

[0004] Chinese patent CN 115094315 A discloses "an economical niobium-chromium reinforced 420MPa bridge steel plate and its production method", which adopts a low-carbon, Mn-Nb-Ti-Cr micro-alloying composition system, does not add precious alloy elements such as V, Mo, Ni, and Cu, and can produce bridge steel plates with a thickness of 8 to 50 mm, a yield strength of ≥420MPa, an impact energy of ≥160J at -40℃, and a yield strength ratio of ≤0.80 by heating the narrow continuous casting billet and controlling the rolling and cooling process. The disadvantage is that the steel plate needs to be slowly cooled for more than 24 hours after it comes off the line, which reduces production efficiency.

[0005] Chinese patent CN 106282789 B discloses "a low-carbon extra-thick TMCP type Q420qE bridge steel and its manufacturing method". The process flow is KR molten iron pretreatment - converter smelting - LF, RH refining - continuous casting - slow cooling of ingot - heating of continuous casting ingot - rolling - pre-straightening - controlled cooling - hot straightening - stacking slow cooling - cutting finishing. The production of low-carbon TMCP type Q420q E bridge steel with a thickness of 60mm-80mm is achieved, ensuring low-temperature impact and strength surplus, and improving welding performance. The disadvantage is that the present invention adds elements such as Ni and Cr for steel plates with a thickness of 60mm-80mm, which is more expensive and is not suitable for steel plates with a thickness of less than 50mm.

[0006] Chinese patent CN 108998726 B discloses "420MPa grade low yield ratio low temperature bridge steel and production method of thick specifications". By controlling the appropriate controlled rolling and controlled cooling and tempering heat treatment of 100mm thick steel plates to ensure the uniformity of steel plate structure and performance, a structural steel for bridges with excellent performance indicators is obtained. The disadvantage is that the present invention is aimed at 100mm thick steel plates, and elements such as Ni and Cr are added, which is costly and not suitable for steel plates with a thickness of less than 50mm. Summary of the invention

[0007] The purpose of the present invention is to provide a thermomechanically rolled 420MPa grade bridge steel plate, which has the following properties: yield strength ≥420MPa, tensile strength ≥540MPa, elongation after fracture ≥19%, impact energy at -20℃ and -40℃ ≥120J, and has the characteristics of easy welding, low yield strength ratio, fatigue resistance, etc.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The present invention discloses a thermomechanically rolled 420MPa grade bridge steel plate, wherein the chemical composition of the steel plate is C: 0.085-0.105%, Si: 0.20-0.30%, Mn: 1.50-1.60%, P: ≤0.015%, S: ≤0.005%, Nb: 0.035-0.045%, V: 0.030-0.040%, Ti: 0.008-0.020%, Als: 0.020-0.035%, and the balance is Fe and unavoidable impurities;

[0010] The preparation process of the thermomechanically rolled 420MPa grade bridge steel plate comprises the following steps:

[0011] S1 Hot metal pretreatment: After the hot metal is desulfurized and dephosphorized by KR stirring method, S≤0.005% and P≤0.015% are ensured;

[0012] S2 converter smelting: The converter smelting stage uses molten iron and scrap steel that have been pre-treated with desulfurization as raw materials. The molten iron temperature is greater than 1260°C. The phosphorus and carbon content are reduced through efficient top and bottom double blowing technology to ensure that the molten steel P≤0.010%, S≤0.004%;

[0013] S3 LF refining: In the LF stage, the composition of molten steel is precisely controlled, deoxidation and alloying are carried out to further reduce non-metallic inclusions and harmful impurities in the molten steel, S≤0.004%;

[0014] S4 RH vacuum treatment: This treatment mode is used to significantly reduce the hydrogen, oxygen and nitrogen gas content in molten steel, and reduce the adverse effects of harmful gases on steel quality; the vacuum time is maintained for more than 20 minutes, the pure degassing time is greater than 15 minutes, and the soft blowing time is greater than 15 minutes, ensuring that the hydrogen content of the molten steel is ≤1.6ppm, the oxygen content is ≤30ppm, and the nitrogen content is ≤50ppm;

[0015] S5 slab continuous casting: dynamic light pressure is used during continuous casting, with light pressure positions at 8, 9, and 10, and a total pressure reduction of 7-8mm; electromagnetic stirring is used, with electromagnetic stirring positions at 3-stage outlet and 4-stage inlet, electromagnetic stirring frequency is 5Hz, and current is 350A; water volume on the wide side of the crystallizer is 4500L / min, water volume on the narrow side is 370L / min, crystallizer inlet temperature is 36±2℃, crystallizer outlet temperature is 38±1℃, secondary cooling water temperature is 22~25℃, and water quality indicators must meet process requirements; protective casting is used, and the argon pressure of the long water inlet seal is greater than 0.3MP a. Flow rate 130~160L / min; argon gas pressure for sealing the tundish immersion nozzle is greater than 0.2Mpa, flow rate 15~20L / min; continuous casting superheat 20~30℃, tundish liquid level is not less than 30 tons when changing tundish; constant pulling speed is adopted, and the pulling speed is stable at 1.0m / min; the straightening temperature of the ingot is controlled at 950~1000℃, and the temperature difference of the ingot along the width direction shall not exceed 50℃, and finally a 250mm thick continuous casting ingot is produced, and the low-multiple center segregation of the ingot is controlled below Class C 3.0, and the ingot is pile-cooled or pit-cooled for more than 36 hours after it comes off the line;

[0016] S6 Heating: The slab is heated in a walking beam heating furnace. The atmosphere in the furnace is strictly controlled to ensure the heating temperature and heating time of the slab. The heating temperature is 1210℃~1240℃. The total time in the furnace is greater than 270min, of which the heating section time is greater than 120min and the soaking section time is greater than 30min, to ensure that the alloy elements are fully dissolved and the slab temperature is uniform.

[0017] S7 rolling: rolling adopts two-stage controlled rolling, usually called rough rolling stage and finishing rolling stage; rough rolling is carried out on a 3800mm rough rolling mill, the start rolling temperature is above 1170℃, and the relative reduction rate of a single pass is controlled at more than 15% for at least two passes; during finishing rolling, the deformation of each pass is strictly controlled, the start rolling temperature of finishing rolling is ≤900℃, and the final rolling temperature is 800±15℃;

[0018] S8 cooling: After rolling, the steel plate is subjected to laminar cooling, the water temperature is 17-20℃, the final cooling temperature is 630-660℃, the head is shielded by 0-2.0m, the tail is shielded by 0-2.5m, the edge is shielded by 0-2.0m, and the overall temperature difference of the steel plate after it returns to red is controlled to be ≤50℃; the steel plate is stacked and slowly cooled for 12 hours before sampling and inspection.

[0019] Furthermore, the chemical composition of the steel plate is C: 0.085%, Si: 0.25%, Mn: 1.52%, P: 0.013%, S: 0.003%, Nb: 0.040%, V: 0.035%, Ti: 0.010%, Als: 0.021% by weight, and the remainder is Fe and unavoidable impurities.

[0020] Furthermore, the chemical composition of the steel plate is C: 0.09%, Si: 0.25%, Mn: 1.53%, P: 0.012%, S: 0.002%, Nb: 0.039%, V: 0.035%, Ti: 0.011%, Als: 0.021% by weight, and the balance is Fe and inevitable impurities.

[0021] Furthermore, the chemical composition of the steel plate is C: 0.09%, Si: 0.26%, Mn: 1.54%, P: 0.011%, S: 0.002%, Nb: 0.041%, V: 0.036%, Ti: 0.010%, Als: 0.020% by weight, and the balance is Fe and unavoidable impurities.

[0022] Furthermore, the chemical composition of the steel plate is C: 0.09%, Si: 0.26%, Mn: 1.55%, P: 0.011%, S: 0.002%, Nb: 0.040%, V: 0.036%, Ti: 0.011%, Als: 0.022% by weight, and the remainder is Fe and inevitable impurities.

[0023] Furthermore, the chemical composition of the steel plate is C: 0.09%, Si: 0.24%, Mn: 1.56%, P: 0.012%, S: 0.002%, Nb: 0.041%, V: 0.037%, Ti: 0.010%, Als: 0.022% by weight, and the remainder is Fe and unavoidable impurities.

[0024] Furthermore, the chemical composition of the steel plate is C: 0.095%, Si: 0.26%, Mn: 1.58%, P: 0.012%, S: 0.003%, Nb: 0.041%, V: 0.036%, Ti: 0.011%, Als: 0.022% by weight, and the remainder is Fe and unavoidable impurities.

[0025] Compared with the prior art, the beneficial technical effects of the present invention are:

[0026] (1) The present invention adopts a low carbon-niobium-vanadium-titanium alloying composition design according to GB / T 714-2015, and adopts a thermomechanical rolling technology to produce a 14-50mm thick 420MPa grade bridge steel plate, the yield strength of the steel plate is ≥420MPa, the tensile strength is ≥540MPa, the elongation after fracture is ≥19%, and the impact energy at -20℃ and -40℃ is ≥120J. At the same time, it has the characteristics of easy welding, low yield strength ratio, fatigue resistance, etc.

[0027] (2) The present invention ensures the strength and low-temperature impact toughness of the steel plate by controlling the start rolling temperature and the final rolling temperature and coordinating the cooling process.

[0028] (3) The present invention obtains a microstructure of ferrite + pearlite + a small amount of bainite and a grain size of 11-12 by controlling the rolling temperature and cooling process.

[0029] (4) The present invention adopts a relatively high final cooling temperature and steel plate stack cooling, which effectively improves the shape of the steel plate and solves the problem of uneven stress in the high-strength steel plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below in conjunction with the accompanying drawings.

[0031] Figure 1 This is a low-magnification photograph of the ingot corresponding to the steel plate of the embodiment of the present invention.

[0032] Figure 2 This is the near-surface optical metallographic structure diagram of the steel plate in Example 4 of the present invention.

[0033] Figure 3 This is a low-power image of the impact fracture of the steel plate of Example 4 of the present invention.

[0034] Figure 4 This is a high-magnification image of the impact fracture of the steel plate of Example 4 of the present invention.

[0035] Figure 5 This is the cold-bending specimen of the steel plate according to Example 4 of the present invention. DETAILED DESCRIPTION

[0036] The present invention is described in more detail below with reference to the accompanying drawings using examples. These examples are merely descriptions of the best mode of carrying out the present invention and do not impose any limitation on the scope of the present invention.

[0037] A thermomechanically rolled 420MPa bridge steel plate, the chemical composition of the steel plate by weight percentage is C: 0.085-0.105%, Si: 0.20-0.30%, Mn: 1.50-1.60%, P: ≤0.015%, S: ≤0.005%, Nb: 0.035-0.045%, V: 0.030-0.040%, Ti: 0.008-0.020%, Als: 0.020-0.035%, and the balance is Fe and unavoidable impurities.

[0038] In addition, the present invention also provides a method for manufacturing a steel plate. The main steps and process parameters are as follows:

[0039] S1 Hot metal pretreatment: After the hot metal is desulfurized and dephosphorized by KR stirring method, S≤0.005% and P≤0.015% are ensured;

[0040] S2 converter smelting: The converter smelting stage uses molten iron and scrap steel that have been pre-treated with desulfurization as raw materials. The molten iron temperature is greater than 1260°C. The phosphorus and carbon content are reduced through efficient top and bottom blowing technology to ensure that the molten steel P≤0.010%, S≤0.004%.

[0041] S3 LF refining: In the LF stage, the composition of molten steel is precisely controlled, deoxidation and alloying are carried out to further reduce non-metallic inclusions and harmful impurities in the molten steel, S≤0.004%.

[0042] S4 RH vacuum treatment: This treatment mode is used to significantly reduce the hydrogen, oxygen and nitrogen gas content in molten steel, and reduce the adverse effects of harmful gases on steel quality. The vacuum time is maintained for more than 20 minutes, the pure degassing time is greater than 15 minutes, and the soft blowing time is greater than 15 minutes, ensuring that the hydrogen content of the molten steel is ≤1.6ppm, the oxygen content is ≤30ppm, and the nitrogen content is ≤50ppm.

[0043] S5 slab continuous casting: dynamic light pressure is used during continuous casting, with light pressure positions at 8, 9, and 10, and a total pressure reduction of 7-8mm; electromagnetic stirring is used, with electromagnetic stirring positions at 3-stage outlet and 4-stage inlet, electromagnetic stirring frequency of 5Hz, and current of 350A; water volume on the wide side of the crystallizer is 4500L / min, water volume on the narrow side is 370L / min, crystallizer inlet temperature is 36±2℃, crystallizer outlet temperature is 38±1℃, secondary cooling water temperature is 22~25℃, and water quality indicators must meet the process requirements Requirements: Use protective pouring, the argon pressure of the long nozzle seal is greater than 0.3MPa, and the flow rate is 130-160L / min; the argon pressure of the tundish immersion nozzle seal is greater than 0.2Mpa, and the flow rate is 15-20L / min; the continuous casting superheat is 20-30℃, and the tundish liquid level is not less than 30 tons when changing tundishes; use a constant pulling speed, and the pulling speed is stable at 1.0m / min; the straightening temperature of the billet is controlled at 950-1000℃, and the temperature difference of the billet along the width direction shall not exceed 50℃. Finally, a 250mm thick continuous casting billet is produced, the low-multiple center segregation of the billet is controlled below Class C 3.0, and the billet is pile-cooled or pit-cooled for more than 36 hours after it comes off the line.

[0044] S6 Heating: The slab is heated in a walking beam heating furnace, and the atmosphere in the furnace is strictly controlled to ensure the heating temperature and heating time of the slab, which is 1210℃~1240℃. The total time in the furnace is greater than 270min, of which the heating section time is greater than 120min and the soaking section time is greater than 30min, to ensure that the alloy elements are fully dissolved and the slab temperature is uniform.

[0045] S7 rolling: The rolling adopts two-stage controlled rolling, usually called rough rolling stage and finishing rolling stage. Rough rolling is carried out in a 3800mm rough rolling mill, the start rolling temperature is above 1170℃, and the single pass relative reduction rate is controlled at more than 15% for at least two passes. During finishing rolling, the deformation of each pass is strictly controlled, the start rolling temperature of finishing rolling is ≤900℃, and the final rolling temperature is 800±15℃.

[0046] S8 cooling: After rolling, the steel plate is cooled in laminar flow, the water temperature is 17-20℃, the final cooling temperature is 630-660℃, the head is shielded by 0-2.0m, the tail is shielded by 0-2.5m, and the edge is shielded by 0-2.0m. The overall temperature difference of the steel plate after returning to red is controlled to be ≤50℃. After the steel plate is stacked and slowly cooled for 12 hours, samples are taken for inspection.

[0047] The present invention is described in detail below in conjunction with practical embodiments.

[0048] Table 1 lists the chemical composition of the examples, and Table 2 lists the rolling process parameters of the examples.

[0049] Table 1 Chemical composition of the present invention (wt%)

[0050]

[0051]

[0052] Table 2 Rolling process parameters of the embodiment of the present invention

[0053]

[0054] The mechanical properties, low temperature impact properties and cold bending properties of the steel plate of the embodiment of the present invention were tested, and the results are shown in Table 3.

[0055] Table 3 Mechanical properties of steel plates according to the present invention

[0056]

[0057] The present invention adopts low carbon-niobium-vanadium-titanium chemical composition combined with a specific process flow to produce a 14-50mm thick thermomechanical controlled rolling 420MPa bridge steel plate, the steel plate has a yield strength of ≥420MPa, a tensile strength of ≥540MPa, an elongation after fracture of ≥19%, and an impact energy of ≥120J at -20℃ and -40℃. It also has the characteristics of easy welding, low yield strength ratio, fatigue resistance, etc. It can be used to manufacture large-scale highway and railway large-span and heavy-load bridges.

[0058] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A thermomechanically rolled 420MPa grade bridge steel plate, characterized in that: The chemical composition of the steel plate is C: 0.085-0.105%, Si: 0.20-0.30%, Mn: 1.50-1.60%, P: ≤0.015%, S: ≤0.005%, Nb: 0.035-0.045%, V: 0.030-0.040%, Ti: 0.008-0.020%, Als: 0.020-0.035%, and the balance is Fe and unavoidable impurities. The preparation process of the thermomechanically rolled 420MPa grade bridge steel plate comprises the following steps: S1 Hot metal pretreatment: After the hot metal is desulfurized and dephosphorized by KR stirring method, S≤0.005% and P≤0.015% are ensured; S2 converter smelting: The converter smelting stage uses molten iron and scrap steel that have been pre-treated with desulfurization as raw materials. The molten iron temperature is greater than 1260°C. The phosphorus and carbon content are reduced through efficient top and bottom double blowing technology to ensure that the molten steel P≤0.010%, S≤0.004%; S3 LF refining: In the LF stage, the composition of molten steel is precisely controlled, deoxidation and alloying are carried out to further reduce non-metallic inclusions and harmful impurities in the molten steel, S≤0.004%; S4 RH vacuum treatment: This treatment mode is used to significantly reduce the hydrogen, oxygen and nitrogen gas content in molten steel, and reduce the adverse effects of harmful gases on steel quality; the vacuum time is maintained for more than 20 minutes, the pure degassing time is greater than 15 minutes, and the soft blowing time is greater than 15 minutes, ensuring that the hydrogen content of the molten steel is ≤1.6ppm, the oxygen content is ≤30ppm, and the nitrogen content is ≤50ppm; S5 slab continuous casting: dynamic light pressure is used during continuous casting, with light pressure positions at 8, 9, and 10, and a total pressure reduction of 7-8mm; electromagnetic stirring is used, with electromagnetic stirring positions at 3-stage outlet and 4-stage inlet, electromagnetic stirring frequency is 5Hz, and current is 350A; water volume on the wide side of the crystallizer is 4500L / min, water volume on the narrow side is 370L / min, crystallizer inlet temperature is 36±2℃, crystallizer outlet temperature is 38±1℃, secondary cooling water temperature is 22~25℃, and water quality indicators must meet process requirements; protective casting is used, and the argon pressure of the long water inlet seal is greater than 0.3MP a. Flow rate 130~160L / min; argon gas pressure for sealing the tundish immersion nozzle is greater than 0.2Mpa, flow rate 15~20L / min; continuous casting superheat 20~30℃, tundish liquid level is not less than 30 tons when changing tundish; constant pulling speed is adopted, and the pulling speed is stable at 1.0m / min; the straightening temperature of the ingot is controlled at 950~1000℃, and the temperature difference of the ingot along the width direction shall not exceed 50℃, and finally a 250mm thick continuous casting ingot is produced, and the low-multiple center segregation of the ingot is controlled below Class C 3.0, and the ingot is pile-cooled or pit-cooled for more than 36 hours after it comes off the line; S6 Heating: The slab is heated in a walking beam heating furnace. The atmosphere in the furnace is strictly controlled to ensure the heating temperature and heating time of the slab. The heating temperature is 1210℃~1240℃. The total time in the furnace is greater than 270min, of which the heating section time is greater than 120min and the soaking section time is greater than 30min, to ensure that the alloy elements are fully dissolved and the slab temperature is uniform. S7 rolling: rolling adopts two-stage controlled rolling, usually called rough rolling stage and finishing rolling stage; rough rolling is carried out on a 3800mm rough rolling mill, the start rolling temperature is above 1170℃, and the relative reduction rate of a single pass is controlled at more than 15% for at least two passes; during finishing rolling, the deformation of each pass is strictly controlled, the start rolling temperature of finishing rolling is ≤900℃, and the final rolling temperature is 800±15℃; S8 cooling: After rolling, the steel plate is subjected to laminar cooling, the water temperature is 17-20℃, the final cooling temperature is 630-660℃, the head is shielded by 0-2.0m, the tail is shielded by 0-2.5m, the edge is shielded by 0-2.0m, and the overall temperature difference of the steel plate after it returns to red is controlled to be ≤50℃; the steel plate is stacked and slowly cooled for 12 hours before sampling and inspection.

2. The thermomechanically rolled 420MPa grade bridge steel plate according to claim 1, characterized in that: The chemical composition of the steel plate is C: 0.085%, Si: 0.25%, Mn: 1.52%, P: 0.013%, S: 0.003%, Nb: 0.040%, V: 0.035%, Ti: 0.010%, Als: 0.021% by weight, and the balance is Fe and inevitable impurities.

3. The thermomechanically rolled 420MPa grade bridge steel plate according to claim 1, characterized in that: The chemical composition of the steel plate is C: 0.09%, Si: 0.25%, Mn: 1.53%, P: 0.012%, S: 0.002%, Nb: 0.039%, V: 0.035%, Ti: 0.011%, Als: 0.021% by weight, and the remainder is Fe and inevitable impurities.

4. The thermomechanically rolled 420MPa grade bridge steel plate according to claim 1, characterized in that: The chemical composition of the steel plate is C: 0.09%, Si: 0.26%, Mn: 1.54%, P: 0.011%, S: 0.002%, Nb: 0.041%, V: 0.036%, Ti: 0.010%, Als: 0.020% by weight, and the remainder is Fe and inevitable impurities.

5. The thermomechanically rolled 420MPa grade bridge steel plate according to claim 1, characterized in that: The chemical composition of the steel plate is C: 0.09%, Si: 0.26%, Mn: 1.55%, P: 0.011%, S: 0.002%, Nb: 0.040%, V: 0.036%, Ti: 0.011%, Als: 0.022% by weight, and the remainder is Fe and inevitable impurities.

6. The thermomechanically rolled 420MPa grade bridge steel plate according to claim 1, characterized in that: The chemical composition of the steel plate is C: 0.09%, Si: 0.24%, Mn: 1.56%, P: 0.012%, S: 0.002%, Nb: 0.041%, V: 0.037%, Ti: 0.010%, Als: 0.022% by weight, and the remainder is Fe and inevitable impurities.

7. The thermomechanically rolled 420MPa grade bridge steel plate according to claim 1, characterized in that: The chemical composition of the steel plate is C: 0.095%, Si: 0.26%, Mn: 1.58%, P: 0.012%, S: 0.003%, Nb: 0.041%, V: 0.036%, Ti: 0.011%, Als: 0.022% by weight, and the remainder is Fe and inevitable impurities.

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