A Nb-V-Ti-B Q500qENHW weathering bridge steel resistant to high heat input welding

Abstract

The invention discloses a Nb-V-Ti-B series Q500qENHW weather-resistant bridge steel resistant to large heat input welding, wherein the chemical components are as follows by weight percentage: C 0.035-0.055, Si 0.20-0.40, Mn 1.45-1.55, Cr 0.42-0.60, Ni 0.35-0.45, Cu 0.30-0.55, Mo 0.17-0.20, Nb 0.032-0.058, V 0.030-0.060, Ti 0.018-0.025, B 0.0004-0.0008, Al 0.015-0.034, N 0.0040-0.0080, O 0.0015-0.0025, La 0.0015-0.0025 0.0070-0.0090, P≤0.015, S≤0.005, the balance is Fe and unavoidable impurities. The weather-resistant bridge steel of the present invention has high strength, high heat input welding resistance and excellent matching with weather resistance, the scheme is easy to implement, the production process is easy to control, and low-cost stable batch industrial production can be achieved, and it can be widely used in large-span, all-welded structure, and paint-free bridge construction.

Description

Technical Field

[0001] The present invention belongs to the technical field of weathering steel materials, and in particular relates to a Nb-V-Ti-B series Q500qENHW weathering bridge steel resistant to high heat input welding, which not only has excellent strength-toughness matching, but also has excellent -40°C low-temperature toughness in the welding heat affected zone under high heat input welding conditions. Background Art

[0002] At present, my country is vigorously promoting the construction of national key railway projects such as the Sichuan-Tibet Railway and the Yunnan-Tibet Railway. Many of the lines pass through high mountains and canyons, and nearly 100 thousand-meter-level super-large span unpainted weathering steel bridges are planned to be built. The bridges are located in harsh geological conditions such as high cold hypoxia, frozen soil landslides, and frequent earthquakes. The ecological environment is fragile, but the climatic conditions are relatively suitable for the construction of weathering bridge steel. In addition, the bridge manufacturing period is tight, and high-strength steel and thick-gauge steel plates (maximum thickness can reach 80mm) are mostly used for welding. For this reason, the materials must meet the design requirements of high load, anti-brittle fracture, efficient manufacturing and green environmental protection.

[0003] The existing mature 345-420MPa grade weather-resistant bridge steel strength skewness cannot meet the high-load use requirements of key load-bearing components in super-long span bridge structures. Domestic related teams have also done a lot of research on 500MPa grade high-strength weather-resistant bridge steel. Although the strength, toughness, weather resistance and weldability of the steel plate have reached the relevant standard requirements of 500MPa grade weather-resistant steel, it can only meet the conventional single-wire gas shielded welding and submerged arc automatic welding forms of welding manufacturing, and cannot meet the double-wire high heat input submerged arc automatic welding manufacturing. The welding efficiency is low, the construction period is long, and it cannot meet the engineering technical requirements. In addition, the domestic bridge steel manufactured by heat-resistant input welding is only suitable for ordinary non-weather-resistant bridge steel and cannot be used without coating. Therefore, it is extremely urgent to develop high-performance Q500qENHW weather-resistant bridge steel with high strength and toughness, high weather resistance and resistance to high heat input welding. However, there is a matching contradiction between the high strength, weather resistance and weldability of 500MPa grade weather-resistant bridge steel in this environment. How to achieve an excellent match of high strength and toughness, high weather resistance and resistance to high heat input welding is a key technical issue that urgently needs to be broken through in the field of design and manufacturing technology of this type of weather-resistant steel.

[0004] In order to solve the above problems, many scholars have conducted the following useful explorations in the comprehensive performance regulation of this type of steel.

[0005] The invention patent with authorization announcement number CN101876032A, "A high-strength steel plate for weather-resistant bridge steel and its production method", uses low-carbon equivalent, Mn-Ni-Cr-Cu-Nb-V-Ti tempered bainite steel. Through low-carbon equivalent design and controlled rolling and controlled cooling + tempering process, the weather-resistant bridge steel produced has the characteristics of high strength, good weldability, and resistance to lamellar tearing. However, its impact temperature requirement is -23°C, which cannot meet the low-temperature toughness requirement of -40°C.

[0006] The invention patent with the authorization announcement number CN108342662A, "A high-strength weathering steel with a yield strength of 550MPa", reduces production costs by optimizing the composition design, does not add niobium and vanadium, strictly controls the N content in the steel, and adopts controlled rolling and controlled cooling technology to produce high-strength weathering steel with stable mechanical properties and good cold bending performance. However, the -40℃ impact absorption energy Akv of weathering steel is only not less than 38J, and the low-temperature toughness surplus is insufficient.

[0007] The invention patent with the authorization announcement number CN103451537A, "A low-temperature weathering steel plate with high welding performance and its production method", controls the lower Si, Mn, and Cr content (<0.15%, 0.40-0.80%, not added), which is expected to reduce the brittle structure of the MA component, so that the steel plate and the heat-affected zone of the weld under high heat input have excellent low-temperature toughness, but it also leads to insufficient strength of this steel, not reaching the 500MPa level, and insufficient resistance to typical atmospheric corrosion. In addition, the addition of harmful elements Sn (0.001-0.004%), although it can make up for the lack of weather resistance, it is easy to cause the tendency of weld cracks and deteriorate the welding performance of the steel plate.

[0008] The invention patent with publication number CN107326304A, "A TMCP type yield 500MPa grade bridge steel plate and production method", refines the structure through low carbon and Nb-V microalloying control technology, thereby improving the yield strength of the steel plate and the strength and toughness of the steel plate. In addition, the Mn and Cr content (1.45-1.55%, 0.20-0.25%) in the steel plate is low, which reduces the brittle structure of the MA component and improves the low-temperature toughness of the welding heat affected zone. However, the amount of corrosion-resistant elements added to the steel is seriously insufficient, and it does not have the performance of resisting typical atmospheric corrosion.

[0009] The invention patent with publication number CN109609845A, "A 500MPa weather-resistant bridge steel and its manufacturing method", controls the relatively high Si and Cr contents (0.10-0.50%, 0.30-1.25%), and obtains good atmospheric corrosion resistance (I≥6.5), but it also easily leads to an increase in the brittle structure of the MA component and insufficient low-temperature toughness of the welding heat-affected zone. In addition, the Mn content (0.80-1.20%) is relatively low, resulting in low tensile strength of the steel plate (≤640MPa), and thus a high yield strength ratio (0.85-0.89), which is not conducive to structural safety.

[0010] The invention patent with the authorization announcement number CN103451561B, "A weathering steel plate capable of being welded with large heat input and its production method", adopts low-carbon, low-silicon, low-manganese C, Si, Mn (0.02-0.06, <0.10%, 0.40-0.80%) composition design, controls the oxygen content in the steel, performs thermomechanical controlled rolling and controlled cooling, reduces the brittle structure of the MA component in the steel plate, and improves the low-temperature toughness of the welding heat-affected zone, but also leads to a low yield strength that does not reach the 500MPa level. At the same time, the invention only provides the -20 ℃ impact value of the welding heat-affected zone, and it is not certain whether the -40 ℃ impact performance requirements are met. And the atmospheric corrosion resistance index I is only 6.10, and the weather resistance is also insufficient. Therefore, this steel still needs to be improved in terms of comprehensive performance regulation.

[0011] The invention patent with authorization announcement number CN103451561B, "A weathering steel plate capable of being welded with large heat input and its production method", controls Si and Mn (<0.10%, 0.40-0.80%) at a relatively low level, which can also reduce the brittle structure of the MA component, which is beneficial to improving the low-temperature toughness of the welding heat affected zone, but also leads to a low yield strength, which does not reach the 500MPa level. At the same time, the invention only provides the -20 ℃ impact value of the welding heat affected zone, and it is not yet certain whether the -40 ℃ impact performance requirements are met. In addition, the atmospheric corrosion resistance index I is only 6.10, and the weather resistance is also insufficient. Therefore, this steel still needs to be improved in terms of comprehensive performance regulation.

[0012] It can be seen from this that the current existing 500MPa-grade weather-resistant bridge steel and similar material technologies have not yet conducted in-depth research on the design and regulation of alloying components, and have failed to achieve comprehensive control of the high strength and toughness, high weather resistance and high heat input welding resistance of 500MPa-grade high-strength weather-resistant bridge steel. Summary of the invention

[0013] The problem to be solved by the present invention is to provide a Nb-V-Ti-B series Q500qENHW weather-resistant bridge steel resistant to large heat input welding, with a thickness range of 32-80mm and a yield strength of 500MPa. It has both high strength and toughness and high weather resistance. Under the conditions of single / double-wire submerged arc automatic welding with a large heat input range of 15-75kJ / cm, the impact energy of the welding heat affected zone at -40°C is not less than 60J, and it can be used in the construction of ultra-large span unpainted weather-resistant steel bridges.

[0014] In order to solve the above technical problems, the technical solution adopted by the present invention is: a Nb-V-Ti-B series Q500qENHW weathering bridge steel resistant to large heat input welding, whose chemical composition is calculated by weight percentage: C 0.035-0.055, Si 0.20-0.40, Mn 1.45-1.55, Cr0.42-0.60, Ni 0.35-0.45, Cu 0.30-0.55, Mo 0.17-0.20, Nb0.032-0.058, V 0.030-0.060, Ti0.018-0.025, B 0.0004-0.0008, Al 0.015-0.034, N0.0040-0.0080, O 0.0015-0.0025, La 0.0070-0.0090, P ≤0.015, S ≤0.005, the balance is Fe and unavoidable impurities;

[0015] The above chemical composition satisfies the following conditions by weight percentage: 570≤Ta≤590, 0.47≤Dp≤0.68, and atmospheric corrosion resistance index I≥6.5.

[0016] in,

[0017] Ta =729-394C-68.3Mn+24.5Si-36.1Ni-24.8Cr-20.5Cu,

[0018] Dp = 15.32Ti+5.79V+0.08B+0.18C+0.15N,

[0019] I=26.01Cu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29Cu*Ni-9.10Ni*P-33.39Cu 2 .

[0020] Furthermore, the number of (Ti, B, V) (C, N) composite precipitated particles with a size of 20-80 nm that have an inhibitory effect on the growth of austenite grains in the welding heat affected zone of the weathering bridge steel accounts for 85-95%, and the number density is 9.10×10 5 / mm3~9.75×10 5 Pieces / mm3 between.

[0021] Furthermore, in the welding heat affected zone of the weathering bridge steel, the (Ti, B, V) (C, N) precipitated particles with a size of 0.5-1.5 μm that can promote the heterogeneous nucleation of intragranular ferrite account for 90-95%, and the number density is 8.14×10 4 Pieces / mm 3 ~8.95×10 4 Pieces / mm 3 .

[0022] Furthermore, when single / double-wire submerged arc automatic welding with a large heat input range of 15-75 kJ / cm is used, the welding heat affected zone meets -40°C KV2≥60J.

[0023] Furthermore, the yield strength ReL of the weather-resistant bridge steel is ≥500MPa, and the tensile strength Rm is ≥630MPa.

[0024] Furthermore, the microstructure of the heat affected zone of the weather-resistant bridge steel welding is composed of acicular ferrite, granular bainitic ferrite and MA components, wherein the area of ​​acicular ferrite accounts for no less than 30%, and the area of ​​MA components accounts for no more than 10%.

[0025] Furthermore, the preparation method of the weather-resistant bridge steel comprises the following steps:

[0026] 1) Smelting: Steel billets are loaded into a furnace, heated until melted, and cast into ingots.

[0027] The chemical composition of the steel billet is calculated by mass percentage: C 0.035-0.055, Si 0.20-0.40, Mn1.45-1.55, Cr 0.42-0.60, Ni 0.35-0.45, Cu0.30-0.55, Mo 0.17-0.20, Nb 0.032-0.058, V0.030-0.060, Ti 0.018-0.025, B 0.0004-0.0008, Al0.015-0.034, N 0.0040-0.0080, O0.0015-0.0025, La 0.0070-0.0090, P ≤0.015, S ≤0.005, and the balance is Fe and unavoidable impurities;

[0028] 2) Thermomechanical rolling: heat the steel billet to a temperature of 1200-1280°C; the starting temperature of rough rolling is 1100-1190°C, and the final rolling temperature of rough rolling is 1020-1080°C; the starting temperature of finishing rolling is 900-960°C, and the final rolling temperature of finishing rolling is 730-850°C; the starting temperature of the cooling stage is controlled to be 720-780°C, and the final cooling temperature is 500-580°C;

[0029] 3) Steel plate tempering treatment: tempering temperature 550~660℃, tempering time 2.0~3.0min / mm × plate thickness (mm).

[0030] The technical solution of the present invention is to achieve the above-mentioned purpose through the following principles and methods.

[0031] 1) The weather-resistant bridge steel of the present invention needs to reasonably design and control the following chemical compositions (by weight percentage) based on an accurate understanding of the principles of multi-element alloying of high-strength and easy-to-weld weather-resistant steel C, Si-Mn, Cr-Ni-Cu, Nb-V-Ti-B-La and the control of the content of N and O gas elements.

[0032] C: An appropriate amount of C can significantly improve the strength of steel, which is beneficial for the steel of the present invention to ensure higher strength and lower yield strength ratio. However, too high C will increase the sensitivity of welding cracks, increase the brittle phase content of the MA component in the welding heat affected zone, and deteriorate the welding performance. Therefore, the C content in the steel of the present invention is controlled at 0.035-0.055%.

[0033] Si: A proper amount of Si can improve the strength and corrosion resistance of weathering steel. However, when the Si content is too high, the content of hard phase MA components in the welding heat affected zone will increase and the low temperature toughness will deteriorate. For this reason, the Si content of the steel of the present invention is controlled at 0.20-0.40%.

[0034] Mn: Mn is a solid solution strengthening element, which can significantly improve the strength through solid solution strengthening. However, too high a Mn content will increase the welding crack sensitivity of the base material. Therefore, the Mn content of the steel of the present invention is controlled between 1.45-1.55%.

[0035] Cu, Cr, Ni: Cu, Cr, and Ni are added in combination to ensure the weather resistance of the steel. However, if too much is added, the low-temperature toughness of the heat-affected zone of the weld will be deteriorated. Therefore, the steel of the present invention controls the Cu content to 0.30-0.55%, the Cr content to 0.42-0.60%, and the Ni content to 0.35-0.45%.

[0036] Mo: An appropriate amount of Mo can significantly improve the weather resistance and the toughness of the base material and the heat affected zone of the weld. However, too much Mo will increase the production cost and damage the low temperature toughness of the heat affected zone of the weld. Therefore, the Mo content of the steel of the present invention is controlled at 0.17-0.20%.

[0037] Nb: An appropriate amount of Nb can induce precipitation through rolling deformation, refine grains, and thus improve the strength and toughness of the base material. However, too much Nb increases the cost and is not conducive to the formation of (Ti, B, V) (C, N) precipitated particles, affecting welding performance. Therefore, the steel of the present invention controls Nb: 0.032-0.058%.

[0038] V-Ti-B: V, Ti, and B are added in combination. They can form (Ti, B, V) (C, N) particles to pin austenite grain boundaries and inhibit austenite grain growth during high heat input welding thermal cycles. They can also promote heterogeneous nucleation of intragranular ferrite, refine ferrite grains, and subsequently generate brittle and hard phase M / A components. Therefore, the steel of the present invention controls Nb: 0.032-0.058%, V: 0.030-0.060%, Ti: 0.018-0.025%, and B: 0.0004-0.0008%.

[0039] N: Appropriate addition of N can promote the precipitation of (Ti, B, V) (C, N) particles. However, too much N is prone to strain aging embrittlement. Therefore, the N content of the steel of the present invention is controlled at 0.0040-0.0080%.

[0040] La: Adding a proper amount of rare earth element La can enrich (Ti, B, V) (C, N) particles and improve the nucleation rate of the precipitated particles. However, too high La will increase the cost, increase the size of the precipitated particles, and reduce the nucleation effect. Therefore, the La content is controlled to be 0.0070-0.0090%.

[0041] Al: Al is the main deoxidizer and plays a deoxidizing role in the steelmaking process. Too much Al will promote the formation of harmful chain B-type inclusions, which is not conducive to the role of titanium nitride and vanadium nitride. Therefore, the Al content of the steel of the present invention is controlled at 0.015-0.034%.

[0042] P: P has a serious tendency to segregate in steel. If added too much, the mechanical properties and welding properties of the steel will deteriorate. Therefore, the P content in the steel of the present invention is limited to below 0.015%.

[0043] S: S is an inevitable element mixed in as an impurity. If the S content is too high, coarse inclusions will be generated, which will reduce the mechanical properties and welding properties of the steel plate. Therefore, the S content of the steel of the present invention is controlled to be less than 0.005%.

[0044] 2) Accurately control the relative addition amounts of some key elements to give full play to the key regulating role of these elements on the comprehensive properties of the steel of the present invention, such as high heat input welding resistance, mechanical properties and weather resistance.

[0045] (1) By adjusting the relationship 570≤Ta≤590, it is required that the double-wire submerged arc welding, gas-electric vertical welding and other welding methods determined by the six main components of C, Mn, Si, Ni, Cr, and Cu according to Ta =729-394C-68.3Mn+24.5Si-36.1Ni-24.8Cr-20.5Cu should be used to control the starting temperature Ar3 of the transformation from austenite to ferrite in the heat-affected zone of 75KJ / cm to 570-590℃, so as to inhibit the nucleation and growth of coarse granular bainite and side lath ferrite at the original austenite grain boundary, and create kinetic conditions for the transformation of fine intracrystalline acicular ferrite and improvement of toughness; too high Ta value will result in more side lath ferrite structure, and too low Ta value will result in more coarse granular bainite or widmanstatten structure, which are not conducive to the refinement of the heat-affected zone structure and low-temperature toughness.

[0046] (2) By adjusting the relationship 0.47≤Dp≤0.68, it is required that the five key microalloying elements, Ti, V, B, N, and C, be controlled between 0.47 and 0.68 according to the relationship Dp=15.32Ti+5.79V+0.08B+0.18C+0.15N, so that the number of nanoscale (Ti, B, V) (C, N) composite precipitated particles with a size of 20 to 80 nm in the heat affected zone of welding accounts for 85% to 95%, and the number density is 9.10×10 5 Pieces / mm 3 ~9.75×10 5 Pieces / mm 3 The formation of micron-scale (Ti, B, V) (C, N) precipitated particles with a size of 0.5-1.5 μm accounts for 90-95%, and the number density is 8.14×10 4 Pieces / mm 3 ~8.95×10 4 Pieces / mm 3 . The micron-scale (Ti, B, V) (C, N) precipitated particles formed can inhibit the growth and coarsening of austenite grains in the weld heat affected zone during the welding thermal cycle, while the nanoscale (Ti, B, V) (C, N) precipitated particles formed can promote the formation of acicular ferrite in the weld heat affected zone during the welding thermal cycle. The two work together to effectively refine the weld heat affected zone structure and improve the low-temperature toughness. Too high a Dp value makes the (V, Ti, B) (C, N) particle size too small, and it cannot play a role in inhibiting the growth and coarsening of austenite grains. Too low a Dp value makes the number of (V, Ti, B) (C, N) submicron particles too small, and the ability to promote the heterogeneous nucleation of acicular ferrite is insufficient, which is not conducive to refining the weld heat affected zone structure and improving the low-temperature toughness of the weld heat affected zone.

[0047] (3) By adjusting the relationship I≥6.5, it is required that the four main components of Cu, Ni, Cr and Si (excluding the brittle element P) be adjusted according to I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39 (%Cu) 2 The lower limit of the determined weathering resistance index is controlled within the range of ≥6.5 to ensure that the corrosion thinning of the steel of the present invention does not exceed 1 mm in a 100-year life cycle under typical atmospheric conditions of mild climate. Too low I value leads to insufficient weathering resistance, while too high I value damages the overall performance and increases the cost.

[0048] 3) The key process parameters of thermomechanical rolling and tempering are defined, including appropriate steel billet heating temperature, rough rolling temperature, finishing rolling temperature, initial cooling temperature, final cooling temperature, tempering temperature and time. The purpose is, firstly, to form a moderately refined multiphase composite structure in the base material to obtain high plasticity and toughness mechanical properties; secondly, to form nano-scale particles and submicron-scale particles with a moderate size and quantity distribution in the base material, so that they can play a role in refining the structure and improving toughness in the welding heat affected zone.

[0049] The beneficial effects of the present invention are:

[0050] 1. Under the welding condition of heat input of 75KJ / cm, the microstructure of the welding heat affected zone of the steel of the present invention is composed of acicular ferrite, granular bainitic ferrite and MA components, wherein the area of ​​acicular ferrite accounts for not less than 30%, and the area of ​​MA components accounts for not more than 10%, thereby making the -40°C impact energy of the welding heat affected zone not less than 60J;

[0051] 2. The structure is mainly acicular ferrite and granular bainite, with yield strength ≥532MPa, tensile strength ≥657MPa, yield strength ratio 0.80-0.82, and Charpy V-notch impact energy at -40℃ ≥250J;

[0052] 3. Atmospheric corrosion resistance index I≥6.5. After five cycles (216h) of cyclic immersion accelerated corrosion test, the corrosion rate tends to be stable, and the corrosion rate is 1.25g / m 3 •h, which is about twice that of ordinary C-Mn steel;

[0053] 4. It achieves an excellent match between high strength, high heat input welding resistance and weather resistance of 500MPa grade high-strength weathering steel. The solution is easy to implement and the production process is easy to control. It can achieve low-cost and stable mass industrial production and can be widely used in large-span, all-welded structure and painting-free bridge construction.

[0054] The present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a microstructure diagram of the parent material of steel embodiment 1 of the present invention;

[0056] Figure 2 The microstructure of the heat affected zone of the steel example 1 of the present invention at a welding heat input of 75 KJ / cm;

[0057] Figure 3 This is the microstructure of the heat affected zone of comparison steel 1 at a welding heat input of 75KJ / cm. DETAILED DESCRIPTION

[0058] The invention discloses a Nb-V-Ti-B series Q500qENHW weather-resistant bridge steel resistant to large heat input welding, wherein the chemical components are as follows by weight percentage: C 0.035-0.055, Si 0.20-0.40, Mn 1.45-1.55, Cr 0.42-0.60, Ni 0.35-0.45, Cu 0.30-0.55, Mo 0.17-0.20, Nb0.032-0.058, V 0.030-0.060, Ti 0.018-0.025, B0.0004-0.0008, Al 0.015-0.034, N 0.0040-0.0080, O0.0015-0.0025, La 0.0070-0.0090, P ≤0.015, S ≤0.005, the balance is Fe and unavoidable impurities.

[0059] The above chemical composition satisfies the following conditions by weight percentage: 570≤Ta≤590, 0.47≤Dp≤0.68, and atmospheric corrosion resistance index I≥6.5.

[0060] Among them, Ta =729-394C-68.3Mn+24.5Si-36.1Ni-24.8Cr-20.5Cu,

[0061] Dp = 15.32Ti+5.79V+0.08B+0.18C+0.15N,

[0062] I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)- 7.29(%Cu)(%Ni)-9.10(%Ni)(%P) -33.39 (%Cu) 2 .

[0063] The above-mentioned weather-resistant bridge steel plate manufacturing method comprises the following steps: preparing steel billet-rolling-cooling-tempering treatment. The required heating temperature in the hot rolling stage is 1200-1240°C, the rough rolling final rolling temperature is controlled at 1020-1080°C in the rough rolling stage, the start rolling temperature is controlled at 900-960°C in the finishing rolling stage, and the finishing rolling final rolling temperature is controlled at 730-850°C. After finishing rolling, the steel plate is cooled by laminar water, the start cooling temperature is controlled at 720-780°C, the cooling is stopped at 500-580°C, and the steel plate is air-cooled to room temperature, and then tempered, the tempering temperature is controlled at 550-660°C, and the tempering time is 2.0-3.0t (t is the plate thickness) to obtain the finished steel plate.

[0064] The ingredients of the examples and comparative examples are shown in Table 1.

[0065] Table 1 Composition of steel in the examples and comparative examples

[0066] .

[0067] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific implementation methods.

[0068] A 75kg vacuum furnace was used to refine 6 batches of test steel according to the components of Examples 1-4 and Comparative Examples 1-2, and a weather-resistant bridge steel plate was prepared according to the method for manufacturing a weather-resistant bridge steel plate of the present invention. The specific steps are as follows:

[0069] 1) Smelting: Prepare steel billets, and prepare steel billets in each furnace according to the composition shown in Table 1. Load the steel billets into the furnace, evacuate to 1 Pascal, heat the molten steel until it is melted, refine the molten steel at high temperature and high vacuum for 10 minutes, fill with protective gas argon, add alloy, adjust the temperature, and cast into profiles respectively. The profiles in the present invention are square steel ingots.

[0070] 2) Thermomechanical rolling: First, the square ingot is heated to the complete austenitization temperature of 1200-1280℃ at a speed of 10℃ / s, and kept warm for more than 3 hours, and then rough rolling and finish rolling are carried out in sequence, that is, the two-stage rolling process of the austenite recrystallization zone and the austenite non-recrystallization zone, and a large reduction is used for rolling. The rough rolling control final rolling temperature is shown in Table 2, and the total rough rolling reduction rate is not less than 50%; the start rolling temperature in the finish rolling stage is controlled to be 900-960℃, and the final rolling temperature is 730-850℃; see Table 2 respectively, and a steel plate with a thickness of 50mm is produced after finish rolling.

[0071] 3) Then enter the rapid cooling device for cooling. The starting temperature, cooling rate and final cooling temperature are shown in Table 2.

[0072] 4) Finally, tempering treatment is performed. The tempering process (time and temperature) is shown in Table 2 to obtain a finished weather-resistant bridge steel plate.

[0073] Table 2 Rolling process of weather-resistant bridge steel plate

[0074] .

[0075] The steel plates prepared by the above method were tested for mechanical properties. The results are shown in Table 3. The yield strength is greater than 500MPa, the tensile strength is greater than 630MPa, the elongation is greater than 20%, the yield strength ratio is less than 0.85, and the impact energy at -40℃ is above 254J.

[0076] Table 3 Mechanical properties of weather-resistant bridge steel plates

[0077] .

[0078] A 10.5*10.5*80mm Gleeble thermal simulation test specimen was cut from a 50mm thick steel plate after finishing, heated to 1350℃ at a heating rate of 100℃ / s, and then cooled for 150s at t8 / 5 to simulate the typical heat input of 75KJ / cm for submerged arc welding. The thermal simulation test specimen was then processed into a 10*10*55mm standard impact specimen and tested for -40℃ impact performance on a 500kJ impact tester.

[0079] The metallographic structure of the steel plate parent material in Example 1 is as shown in the attached Figure 1 As shown in the figure, it is a refined granular bainite + acicular ferrite complex phase structure, which is conducive to obtaining excellent strength and toughness. When the simulated welding heat input is 75KJ / cm, the metallographic structure of the heat affected zone is shown in the attached figure. Figure 2 , Comparative Example 1 When the simulated welding heat input is 75KJ / cm, the heat affected zone structure is shown in the attached Figure 3 . It can be seen that the heat-affected zone of the weather-resistant bridge steel plate of the present invention is mainly composed of a multiphase composite structure of acicular ferrite (AF) + granular bainitic ferrite (GB) + M / A components, in which the proportion of acicular ferrite is about 50%, the proportion of acicular ferrite is relatively high, and the proportion of MA components is 8%, which is relatively small in size. This structure makes its heat-affected steel have good low-temperature toughness. In contrast, the chemical composition content and proportion of comparative steel 2 are not within the scope of the innovative design technology defined in the present invention. The obtained structure is coarse granular bainite + lath bainite, without refined acicular ferrite structure, and the proportion of brittle and hard M / A components is about 30%. This coarse hard phase MA component is prone to microcracks when subjected to impact loads, resulting in brittle fracture, which makes the low-temperature toughness of its welding heat-affected zone poor. The results of the low-temperature impact toughness test are shown in Table 4.

[0080] Table 4 Impact energy of heat affected zone of steel plate under typical heat input

[0081] .

[0082] The above results show that the impact energy of the heat affected zone at -40°C of each embodiment of the present invention under typical heat input conditions is greater than 100 J, and the low-temperature toughness is excellent. However, the impact energy of the heat affected zone at -40°C of the comparative steel 1-2 is less than 60 J, and the low-temperature toughness is poor.

[0083] As can be seen from Table 1, the atmospheric corrosion resistance index I of the weathering steel embodiments 1-8 of the present invention is greater than 6.5. 40*60*4mm corrosion samples were cut from the finished steel plates of embodiment 1 and comparative example 1, and a simulated industrial atmospheric environment periodic immersion accelerated corrosion test was carried out for 5 cycles totaling 216h. Samples were taken for each cycle and weighed to measure the weight loss. The average corrosion weight loss rate of the steel of the present invention was calculated to be 1.25g·(m2·h) -1 , while the average corrosion weight loss rate of the comparative steel 1 was 2.51 g·(m2·h) -1 The weather resistance of the steel plate of the present invention is about twice that of the comparative steel, and has good atmospheric corrosion resistance.

[0084] In summary, within the composition range and preparation process conditions of the present invention, the mechanical properties, corrosion properties and high heat input resistance welding properties of the obtained steel plate are significantly better than those of the control steel.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. A Nb-V-Ti-B Q500qENHW weathering bridge steel resistant to high heat input welding, characterized in that: The chemical composition is calculated by weight percentage: C 0.035-0.055, Si 0.20-0.40, Mn 1.45-1.55, Cr 0.42-0.60, Ni0.35-0.45, Cu 0.30-0.55, Mo 0.17-0.20, Nb 0.032-0.058, V 0.030-0.060, Ti 0.018-0.025, B 0.0004-0.0008, Al 0.015-0.034, N 0.0040-0.0080, O 0.0015-0.0025, La0.0070-0.0090, P ≤0.015, S ≤0.005, the balance is Fe and unavoidable impurities; The above chemical composition satisfies the following conditions by weight percentage: 570≤Ta≤590, 0.47≤Dp≤0.68, and atmospheric corrosion resistance index I≥6.

5. in, Ta =729-394C-68.3Mn+24.5Si-36.1Ni-24.8Cr-20.5Cu, Dp = 15.32Ti+5.79V+0.08B+0.18C+0.15N, I=26.01Cu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29Cu*Ni-9.10Ni*P-33.39Cu 2 .

2. The weather-resistant bridge steel according to claim 1, characterized in that: In the heat affected zone of the weathering bridge steel, among the particles with a size of 20-80 nm, the number of (Ti, B, V) (C, N) composite precipitated particles that have an inhibitory effect on the growth of austenite grains accounts for 85-95%, and the number density is 9.10×10 5 / mm3~9.75×10 5 Pieces / mm 3 between.

3. The weather-resistant bridge steel according to claim 1, characterized in that: The number of (Ti, B, V) (C, N) precipitated particles in the heat affected zone of the weathering bridge steel that can promote the heterogeneous nucleation of intragranular ferrite is 90-95%, and the number density is 8.14×10 4 Pieces / mm 3 ~8.95×10 4 Pieces / mm 3 .

4. The weather-resistant bridge steel according to claim 1, characterized in that: When single / double wire submerged arc automatic welding with a maximum heat input range of 15-75kJ / cm, the welding heat affected zone meets the requirement of -40℃KV2≥60J.

5. The weather-resistant bridge steel according to claim 1, characterized in that: The yield strength ReL of the weather-resistant bridge steel is ≥500MPa, and the tensile strength Rm is ≥630MPa.

6. The weather-resistant bridge steel according to claim 1, characterized in that: The microstructure of the heat affected zone of the weather-resistant bridge steel welding is composed of acicular ferrite, granular bainitic ferrite and MA components, among which the area proportion of acicular ferrite is not less than 30%, and the area proportion of MA components is not more than 10%.

7. The weather-resistant bridge steel according to any one of claims 1 to 6, characterized in that: The preparation method of the weather-resistant bridge steel comprises the following steps: 1) Smelting: The steel billet is loaded into the furnace, heated until it melts, and poured into steel ingots. The chemical composition of the steel billet is calculated by mass percentage: C 0.035-0.055, Si 0.20-0.40, Mn 1.45-1.55, Cr 0.42-0.60, Ni 0.35-0.45, Cu 0.30-0.55, Mo 0.17-0.20, Nb 0.032-0.058, V0.030-0.060, Ti 0.018-0.025, B 0.0004-0.0008, Al 0.015-0.034, N 0.0040-0.0080, O0.0015-0.0025, La 0.0070-0.0090, P ≤0.015, S ≤0.005, and the balance is Fe and unavoidable impurities; 2) Thermomechanical rolling: heat the steel billet to a temperature of 1200-1280°C; the starting temperature of rough rolling is 1100-1190°C, and the final rolling temperature of rough rolling is 1020-1080°C; the starting temperature of finishing rolling is 900-960°C, and the final rolling temperature of finishing rolling is 730-850°C; the starting temperature of the cooling stage is controlled to be 720-780°C, and the final cooling temperature is 500-580°C; 3) Steel plate tempering treatment: tempering temperature 550~660℃, tempering time 2.0~3.0min / mm × plate thickness (mm).

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