Method for straightening a composite steel plate for a bridge

Abstract

The bridge composite steel plate correcting method provided by the application sets different heating temperatures according to bending directions and unevenness, realizes correction by heating the carbon steel side of the bridge composite steel plate, and according to different bending directions, the steel plate is heated and then heat preserved or not heat preserved, so that the bending position is corrected on the basis of not wasting resources, and the mechanical properties of the bending position are not affected.

Description

Technical Field

[0001] This invention relates to the field of steel smelting and manufacturing technology, and in particular to a method for straightening composite steel plates for bridges. Background Technology

[0002] Bridge composite steel plates combine the corrosion resistance of stainless steel with the superior mechanical properties and price advantages of bridge steel, representing an important development direction for steel materials. However, bridge composite steel plates are prone to warping during processing such as hoisting, cutting, and welding.

[0003] Currently, the straightening methods for bridge composite steel plates generally involve straightening with straightening machines and flattening machines. However, these methods require equipment with high straightening capabilities, which not all steel mills possess. Furthermore, in situations where equipment is limited at the construction site or where some composite plates have already been fabricated into structural components, straightening equipment alone is insufficient for proper plate shape correction. Additionally, due to the significant internal stress in the composite plate, it is prone to rebound after straightening, severely impacting its on-site usability. Summary of the Invention

[0004] The purpose of this invention is to provide a method for straightening bridge composite steel plates. This method involves heating and straightening the carbon steel side of the steel plate to address unevenness in the bending direction and position of the steel plate. This solves the problem of high equipment and site requirements associated with straightening machines or flattening machines in the prior art.

[0005] To achieve one of the aforementioned objectives, one embodiment of the present invention provides a method for straightening a bridge composite steel plate, wherein the bridge composite steel plate is a double-layer composite plate of carbon steel and stainless steel, and the straightening method involves heating the bent portion on the carbon steel side, wherein:

[0006] When the bending direction is on the stainless steel side: if the unevenness D ≤ 10 mm / m, then the heating temperature T1 must satisfy: 650-100°C. 1 / 2 -100[Mn]-250[Si]-170[Cr]-170[Ni]+5D-30≤T1≤650-100[C] 1 / 2 -100[Mn]-250[Si]-170[Cr]-170[Ni]+5D+30, holding time is t1=50d / (T1-350), then air cooling; if the unevenness D>10mm / m, then the heating temperature T2 satisfies: 200[C] 1 / 2 +200[Mn]+500[Si]+340[Cr]+340[Ni]+5D-30≤T2≤200[C] 1 / 2+200[Mn]+500[Si]+340[Cr]+340[Ni]+5D+30, holding time is t2=50d / (T2-450), then air cooling;

[0007] When the bending direction is towards the carbon steel side, the heating temperature T3 should meet the following requirements: 750-200°C. 1 / 2 +450[Si]-150[Ni]+310[Mo]-100[Mn]+110[Cr]+200[Cu]-700[P]-400[Ti]+5D-30≤T3≤750-200[C] 1 / 2 +450[Si]-150[Ni]+310[Mo]-100[Mn]+110[Cr]+200[Cu]-700[P]-400[Ti]+5D+30, no insulation, direct air cooling;

[0008] Wherein, the heat preservation time is in seconds, d is the thickness of the steel plate in mm, and [C], [Si], [Mn], [Cr], [Ni], [Mo], [Cu], [P], and [Ti] represent 100 times the weight percentage of the corresponding elements in the carbon steel.

[0009] As a further improvement to one embodiment of the present invention, before heating, the bending position is divided into heating zones and the shape and area of ​​the heating zones are determined:

[0010] When the bending position is uneven in one direction, either laterally or longitudinally, N1 strip-shaped heating zones are divided at intervals along the vertical direction of the unevenness at the bending position. The area of ​​each strip-shaped heating zone is B×L=A / [N1×(4.0~6.0)], where B is the width of the heating zone, L is the length of the heating zone, and A is the area of ​​the bending position.

[0011] As a further improvement of one embodiment of the present invention, when the bending position is bidirectionally uneven in both the transverse and longitudinal directions, N2 point-shaped heating zones are divided at the bending position, and the area of ​​each point-shaped heating zone is π×R. 2 =A / [N2×(5.0~10.0)], the radius R of the point heating zone is 50~150mm.

[0012] As a further improvement of one embodiment of the present invention, when the bending position is uneven in one direction along the transverse or longitudinal direction, the width of the strip heating zone B = (3~7)d.

[0013] As a further improvement of one embodiment of the present invention, the bending position of the steel plate is preheated before heating, the preheating temperature is 100-150°C, the total preheating area A0 = (1.0-3.0)A, and the preheating position completely includes the bending position.

[0014] As a further improvement of one embodiment of the present invention, when the bending method of the steel plate includes longitudinal unidirectional unevenness and transverse unidirectional unevenness, the intersection of longitudinal unidirectional unevenness and transverse unidirectional unevenness is the bending position with bidirectional unevenness in both the transverse and longitudinal directions; if the diameter of the intersection of longitudinal unidirectional unevenness and transverse unidirectional unevenness is greater than 150mm, then with the intersection of longitudinal unidirectional unevenness and transverse unidirectional unevenness as the center, the point heating area is evenly distributed on the circumference of the concentric circle formed with the center.

[0015] As a further improvement of one embodiment of the present invention, when the bending position is bidirectionally uneven along the transverse and longitudinal directions, the unevenness when calculating the heating temperature is taken as the maximum value of the unevenness between the unidirectional unevenness along the transverse direction and the unidirectional unevenness along the longitudinal direction.

[0016] As a further improvement of one embodiment of the present invention, the gas used for flame straightening is a mixture of oxygen and propane, the flame type is a neutral flame, the flame core height is 3-8 mm from the steel plate, and the angle between the flame and the steel plate is 80-90°.

[0017] As a further improvement of one embodiment of the present invention, the corrected steel plate satisfies the flatness D≤5mm / m.

[0018] As a further improvement of one embodiment of the present invention, the corrected steel plate meets the following requirements: flatness D≤5mm / m, tensile strength≥510MPa, yield strength≥370MPa, elongation≥20%, shear strength≥300MPa, impact strength at -40℃≥120J, no cracks in intergranular corrosion detected by E method, and no cracks in internal and external bending during 180° cold bending.

[0019] One or more technical solutions provided by this invention have at least the following technical effects or advantages:

[0020] The bridge composite steel plate straightening method provided by the present invention sets different heating temperatures according to the bending direction and unevenness, and achieves straightening by heating the carbon steel side of the bridge composite steel plate, so as to straighten the bending position without wasting resources and without affecting the mechanical properties of the bending position. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of longitudinal unidirectional unevenness in an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of unidirectional unevenness along the transverse direction in an embodiment of the present invention.

[0023] Figure 3 This is a schematic diagram of longitudinal unidirectional unevenness and transverse unidirectional unevenness in an embodiment of the present invention.

[0024] Figure 4This is a schematic diagram of a strip-shaped heating zone with longitudinal unidirectional unevenness in an embodiment of the present invention.

[0025] Figure 5 This is a schematic diagram of a strip-shaped heating zone in a transversely uneven area according to an embodiment of the present invention.

[0026] Figure 6 This is a schematic diagram of point heating under longitudinal and transverse unidirectional unevenness in an embodiment of the present invention. Detailed Implementation

[0027] The present invention will be described in detail below with reference to specific embodiments, but these embodiments do not limit the present invention. Any changes in reaction conditions, reactants or raw material amounts made by those skilled in the art based on these embodiments are included within the protection scope of the present invention.

[0028] This invention provides a method for straightening a bridge composite steel plate, wherein the bridge composite steel plate is a double-layer composite plate of carbon steel and stainless steel, and the straightening method involves heating the bent area on the carbon steel side, wherein:

[0029] When the bending direction is on the stainless steel side: if the unevenness D ≤ 10 mm / m, then the heating temperature T1 must satisfy: 650-100°C. 1 / 2 -100[Mn]-250[Si]-170[Cr]-170[Ni]+5D-30≤T1≤650-100[C] 1 / 2 -100[Mn]-250[Si]-170[Cr]-170[Ni]+5D+30, holding time is t1=50d / (T1-350), then air cooling; if the unevenness D>10mm / m, then the heating temperature T2 satisfies: 200[C] 1 / 2 +200[Mn]+500[Si]+340[Cr]+340[Ni]+5D-30≤T2≤200[C] 1 / 2 +200[Mn]+500[Si]+340[Cr]+340[Ni]+5D+30, holding time is t2=50d / (T2-450), then air cooling;

[0030] When the bending direction is towards the carbon steel side, the heating temperature T3 should meet the following requirements: 750-200°C. 1 / 2 +450[Si]-150[Ni]+310[Mo]-100[Mn]+110[Cr]+200[Cu]-700[P]-400[Ti]+5D-30≤T3≤750-200[C] 1 / 2+450[Si]-150[Ni]+310[Mo]-100[Mn]+110[Cr]+200[Cu]-700[P]-400[Ti]+5D+30, no insulation, direct air cooling;

[0031] Wherein, the heat preservation time is in seconds, d is the thickness of the steel plate in mm, and [C], [Si], [Mn], [Cr], [Ni], [Mo], [Cu], [P], and [Ti] represent 100 times the weight percentage of the corresponding elements in the carbon steel.

[0032] Preferably, when heating the bent area, a flame straightening technique is used. The flame straightening technique uses a mixture of oxygen and propane, a neutral flame, a flame core height of 3-8 mm from the steel plate, and an angle of 80-90° between the flame and the steel plate.

[0033] Based on the chemical composition of carbon steel in bridge composite steel plates, calculations from practical applications show that temperatures T1 and T2 are lower than T3, and T1 is lower than T2. ​​When the bending direction is on the stainless steel side, the stress on the stainless steel side is relatively large, while the stress on the carbon steel side is relatively small. Heating the carbon steel side at a lower temperature (T1, T2) can restore the steel plate's shape; however, the greater the unevenness, the higher the required heating temperature (T2). Insulation after heating does not affect the corrosion resistance of the stainless steel side and prevents over-straightening of the steel plate. When the bending direction is on the carbon steel side, the stress on the carbon steel side is relatively large, while the stress on the stainless steel side is relatively small. A higher heating temperature (T3) is required on the carbon steel side to restore the plate's shape. However, due to the high heating temperature, insulation is not necessary after heating to avoid affecting the mechanical properties of the steel plate.

[0034] Furthermore, before heating, the bending area is divided into heating zones, and the shape and area of ​​the heating zones are determined:

[0035] When the bending position is uneven in one direction, either laterally or longitudinally, N1 strip-shaped heating zones are divided at intervals along the vertical direction of the unevenness at the bending position. The area of ​​each strip-shaped heating zone is B×L=A / [N1×(4.0~6.0)], where B is the width of the heating zone, L is the length of the heating zone, and A is the area of ​​the bending position.

[0036] When bending steel plates, the area of ​​the bending position is usually large, so it is necessary to heat in sections to prevent the problem of uneven heating temperature caused by the large heating area.

[0037] The bending position is uneven in one direction along the longitudinal direction (e.g.) Figure 1 The unevenness of the cut surface when slicing along the longitudinal direction of the steel plate, with the bending point being uneven in one direction only (e.g.) Figure 2 The cut surface is uneven and bent when the steel plate is cut along its width.

[0038] When the bending method at the bending location is either longitudinal unidirectional unevenness or transverse unidirectional unevenness, the bending method is singular. The bending location is heated in strips, and the length direction of the strip heating zone is parallel to the direction of cutting the steel plate when the unevenness direction is confirmed. Multiple heating zones are spaced apart along the direction perpendicular to the cutting of the steel plate (e.g., ...). Figure 4 , 5 This allows the heat from a single heating zone to radiate to areas near the heating zone, and the steel plate in the heating zone can also cause the position between every two spaced heating zones to recover its deformation during the recovery process.

[0039] Preferably, when the bending position is uneven in one direction along the transverse or longitudinal direction, the width of the strip heating zone B = (3~7)d. If the width of the strip heating zone is too narrow, it is difficult to achieve; if it is too wide, it is difficult to ensure the uniformity of the heating temperature, which can easily reduce the strength of the steel plate.

[0040] Furthermore, when the bending position is bidirectionally uneven along both the transverse and longitudinal directions, N2 point heating zones are divided at the bending position, with the area of ​​each point heating zone being π×R. 2 =A / [N2×(5.0~10.0)], the radius R of the point heating zone is 50~150mm.

[0041] Preferably, when the bending position is bidirectionally uneven along both the transverse and longitudinal directions, in order to ensure that the steel plate can be corrected to the allowable unevenness range, the unevenness calculated when heating temperature is taken as the maximum value of the unevenness in the unidirectional unevenness along the transverse direction and the unidirectional unevenness along the longitudinal direction.

[0042] Bidirectional unevenness along both the transverse and longitudinal directions at the bending location means that the cut surface is uneven when the steel plate is cut along both the longitudinal and width directions. This bidirectional unevenness means that the bending location includes both longitudinal and transverse unidirectional unevenness (e.g.,...). Figure 3 (The intersection of longitudinal and transverse unidirectional unevenness). The bending pattern at this bend is relatively complex, and the length, width, and distribution of the strip heating zone are difficult to determine. Therefore, point heating is used, with the point heating zones spaced at intervals at the bend with longitudinal and transverse unidirectional unevenness.

[0043] Preferably, the heating temperature is the average heating temperature of the heating zone, and the temperature difference of the strip heating zone does not exceed 50°C, and the temperature difference of the point heating zone does not exceed 30°C.

[0044] During the heating process, it is impossible to guarantee that the temperature of every point in the heating zone is the same, so a temperature difference is allowed. However, the strip heating zone is longer and the temperature is more difficult to control precisely, so the temperature difference is allowed to be greater.

[0045] The bending location, bending type, and bending degree mentioned above are determined according to the national standard GB / T 709-2019 "Dimensions, Shape, Weight and Permissible Deviations of Hot-Rolled Steel Plates and Strips", thereby obtaining the length, width, diameter, etc. of the bending location, and thus obtaining the area of ​​the bending location. The national standard uses "flatness" to represent bending deformation.

[0046] The length of the strip heating zone is the width of the bending position. The width of the strip heating zone is determined according to the strip heating zone width B = (3~7)d as described above. Before heating, draw the rectangular range of the strip heating zone on the steel plate, and then use a flame gun to heat within the drawn rectangular frame.

[0047] Similarly, for the point heating area, draw a circle with a radius of 50 to 150 mm at the curved position, and then use a flame gun to heat within the drawn circular frame.

[0048] In some embodiments, the bending position of the steel plate is preheated before heating, with a preheating temperature of 100-150°C and a total preheating area A0 = (1.0-3.0)A, and the preheating position completely includes the bending position.

[0049] Preheating the bent area to 100-150℃ can prevent cracks from appearing in the steel plate during the heat straightening process. Also, since there is a certain range of heat-affected zone around the heated area during heat straightening, the preheated area needs to be no less than the bent area, and the preheated area should completely include the bent area.

[0050] In some embodiments, when the bending method of the steel plate includes longitudinal unidirectional unevenness and transverse unidirectional unevenness, the intersection of longitudinal unidirectional unevenness and transverse unidirectional unevenness is the bending position with bidirectional unevenness in both the transverse and longitudinal directions; if the diameter of the intersection of longitudinal unidirectional unevenness and transverse unidirectional unevenness is greater than 150mm, then with the intersection of longitudinal unidirectional unevenness and transverse unidirectional unevenness as the center, the point heating area is evenly distributed on the circumference of the concentric circle formed with the center.

[0051] When steel plates are bent in one direction (longitudinal or transverse), there are three types of bending locations: unidirectional transverse bending, unidirectional longitudinal bending, and bidirectional bending (both transverse and longitudinal). The intersection of longitudinal and transverse unidirectional unevenness presents both transverse and longitudinal unevenness, thus constituting a bidirectional bending location, and its heating zone is a point-like heating zone. Bending locations other than the intersection of longitudinal and transverse unidirectional unevenness may exhibit either transverse or longitudinal unidirectional unevenness, therefore their heating zone is a strip-like heating zone.

[0052] When a steel plate is bent, any unidirectional unevenness, whether longitudinal or transverse, has a straight line where the maximum unevenness occurs, such as... Figure 6 The straight line at the very top of the longitudinal and transverse unidirectional unevenness. When a steel plate is bent in a manner that includes both transverse and longitudinal unevenness, if the diameter of the intersection of the longitudinal and transverse unidirectional unevenness is greater than 150mm, the area of ​​this bending location is relatively large. Using the aforementioned intersection point as the center, draw concentric circles around this center, and evenly distribute the point-heating zones on these concentric circles. Figure 6 As shown, it can achieve a good correction effect and ensure the uniformity of steel plate recovery.

[0053] The aforementioned bending methods include bidirectional unevenness along both the transverse and longitudinal directions. This is not only the intersection of unidirectional unevenness along the longitudinal direction and unidirectional unevenness along the transverse direction on the steel plate, but may also be spherical deformation occurring on the steel plate. That is, the bending position is a curved surface similar to a sphere, rather than being caused by the intersection of transverse and longitudinal unevenness.

[0054] The heating temperatures T1, T2, and T3 shall not exceed T, where T = 723 - 10.7[Mn] + 29.1[Si] + 16.9[Cr] - 16.9[Ni]. When straightening bridge composite steel plates by heating, the heating temperature should not be too high; if it exceeds T, it will affect the mechanical properties of the steel plate at the bending position.

[0055] Furthermore, the corrected steel plate meets the requirement that the unevenness D ≤ 5 mm / m.

[0056] Furthermore, the tensile strength is ≥510MPa, yield strength is ≥370MPa, elongation is ≥20%, shear strength is ≥300MPa, impact strength at -40℃ is ≥120J, no cracks are found in the intergranular corrosion test using the E method, and no cracks are found in the internal and external bending tests at 180°. The E method test conforms to GB / T4334, and the cold bending method conforms to GB / T6396.

[0057] The technical solution of this application will be further described below with reference to some specific embodiments.

[0058] The bridge composite steel plate used in all the following embodiments is grade 316L+Q370qE, with a total thickness of 19mm, a width of 2200mm, and a length of 13000mm. The chemical composition of Q370qE, by weight percentage, includes: C: 0.10%, Si: 0.19%, Mn: 1.47%, Cr: 0.11%, Ni: 0.12%, Ti: 0.013%, and P: 0.01%.

[0059] Example 1

[0060] The bridge composite steel plate is bent along the stainless steel side, with a unidirectional unevenness along the longitudinal direction. The unevenness D is 8 mm / m, and the bending area is 2.2 × 10⁻⁶. 6 mm 2.

[0061] The bridge composite steel plate was preheated at a temperature of 150℃, with a preheating area of ​​3×10. 6 mm 2 The flame straightening gas is a mixture of oxygen and propane, the flame type is a neutral flame, the flame core height is 5mm from the plate surface, and the angle between the flame and the steel plate is 90°.

[0062] Heating is performed on the carbon steel side. The heating zone is strip-shaped, 100mm wide and 500mm long, with 8 heating zones in total, for a total heating area of ​​4×10. 5 mm 2 The heating zone is evenly distributed along the width direction, the heating temperature is 400℃, and the holding time after reaching the temperature is 19s.

[0063] After the above-mentioned process correction, the unevenness of the bridge composite steel plate is 3mm / m, the tensile strength is 562MPa, the yield strength is 462MPa, the elongation is 21%, the shear strength is 473MPa, the impact strength at -40℃ is 330J, the E-method test shows no cracks in intergranular corrosion, and the cold bending test shows no cracks in the inner and outer bending.

[0064] Example 2

[0065] The steel plate used was similar to that in Example 1, except for the bending direction (the bending direction was the carbon steel side). The preheating and heating zone size were the same as in Example 1. The heating temperature was 630℃, without heat preservation. The resulting steel plate had a flatness of 3mm / m, a tensile strength of 542MPa, a yield strength of 432MPa, an elongation of 27%, a shear strength of 413MPa, an impact strength of 310J at -40℃, no cracks in the intergranular corrosion detected by the E method, and no cracks in the cold bending inside and outside.

[0066] Example 3

[0067] The bridge composite steel plate is bent along the stainless steel side, and the bending method is unidirectional unevenness in the transverse direction, with an unevenness D of 15mm / m and a bending area of ​​5×10. 6 mm 2 .

[0068] The bridge composite steel plate was preheated at 150℃, with a preheating area of ​​5×10. 6 mm 2 The flame straightening gas is a mixture of oxygen and propane, the flame type is a neutral flame, the flame core height is 5mm from the plate surface, and the angle between the flame and the steel plate is 90°.

[0069] Heating is performed on the carbon steel side. The heating zone is strip-shaped, 100mm wide and 1000mm long, with 10 heating zones in total, for a total heating area of ​​1×10⁻⁶.6 mm 2 The heating zone is evenly distributed along the length direction, the heating temperature is 600℃, and the holding time after reaching the temperature is 6.3s.

[0070] After the above-mentioned process correction, the unevenness of the bridge composite steel plate is 4mm / m, the tensile strength is 571MPa, the yield strength is 452MPa, the elongation is 24%, the shear strength is 453MPa, the impact strength at -40℃ is 315J, the E-method test shows no cracks in intergranular corrosion, and the cold bending test shows no cracks in the inner and outer bending.

[0071] Example 4

[0072] The steel plate used was the same as that in Example 3, except that the bending direction was different (the bending direction was the carbon steel side). The preheating and heating zone size were the same as in Example 3. The heating temperature was 660℃, and no heat preservation was performed. The resulting steel plate had a flatness of 3mm / m, a tensile strength of 539MPa, a yield strength of 430MPa, an elongation of 28%, a shear strength of 415MPa, an impact strength of 305J at -40℃, no cracks were found in the intergranular corrosion detected by the E method, and no cracks were found in the internal and external bending during cold bending.

[0073] Example 5

[0074] The bridge composite steel plate is bent along the stainless steel side, with bidirectional unevenness in both the transverse and longitudinal directions. The transverse unevenness D is 8 mm / m, and the longitudinal unevenness is 10 mm / m. The bending area is 4 × 10 mm. 6 mm 2 .

[0075] The bridge composite steel plate was preheated at 150℃, with a preheating area of ​​5×10. 6 mm 2 The flame straightening gas is a mixture of oxygen and propane, the flame type is a neutral flame, the flame core height is 5mm from the plate surface, and the angle between the flame and the steel plate is 90°.

[0076] Heating is performed on the carbon steel side, with the heating zone being dot-shaped and having an area of ​​5×10. 4 mm 2 There are 10 heating zones, with a total heating area of ​​5×10. 5 mm 2 The heating zone is evenly distributed at the bending position with the intersection of the horizontal and vertical unevenness as the center. The heating temperature is 450℃, and the holding time after reaching the temperature is 9.5s.

[0077] After the above-mentioned process correction, the flatness of the bridge composite steel plate is 5mm / m, the tensile strength is 575MPa, the yield strength is 455MPa, the elongation is 23%, the shear strength is 443MPa, the impact strength at -40℃ is 329J, the E-method test shows no cracks in intergranular corrosion, and the cold bending test shows no cracks in the inner and outer bending.

[0078] Example 6

[0079] The steel plate used was the same as that in Example 5, except that the bending direction was different (the bending direction was the carbon steel side). The preheating and heating zone size were the same as in Example 5. The heating temperature was 650℃, and no heat preservation was performed. The resulting steel plate had a flatness of 4mm / m, a tensile strength of 555MPa, a yield strength of 451MPa, an elongation of 26%, a shear strength of 435MPa, an impact strength of 295J at -40℃, no cracks were found in the intergranular corrosion detected by the E method, and no cracks were found in the internal and external bending during cold bending.

[0080] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0081] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for correcting composite steel plates for bridges, characterized in that, The bridge composite steel plate is a double-layer composite plate of carbon steel and stainless steel. The straightening method involves heating the bent area on the carbon steel side, wherein: When the bending direction is on the stainless steel side: if the unevenness D ≤ 10 mm / m, then the heating temperature T1 must satisfy: 650-100°C. 1 / 2 -100[Mn]-250[Si]-170[Cr]-170[Ni]+5D-30≤T1≤650-100[C] 1 / 2 -100[Mn]-250[Si]-170[Cr]-170[Ni]+5D+30, holding time is t1=50d / (T1-350), then air cooling; if the unevenness D>10mm / m, then the heating temperature T2 satisfies: 200[C] 1 / 2 +200[Mn]+500[Si]+340[Cr]+340[Ni]+5D-30≤T2≤200[C] 1 / 2 +200[Mn]+500[Si]+340[Cr]+340[Ni]+5D+30, the holding time is t2=50d / (T2-450), then air cooling; When the bending direction is towards the carbon steel side, the heating temperature T3 should meet the following requirements: 750-200°C. 1 / 2 +450[Si]-150[Ni]+310[Mo]-100[Mn]+110[Cr]+200[Cu]-700[P]-400[Ti]+5D-30≤T3≤750-200[C] 1 / 2 +450[Si]-150[Ni]+310[Mo]-100[Mn]+110[Cr]+200[Cu]-700[P]-400[Ti]+5D+30, no insulation, direct air cooling; Wherein, the heat preservation time is in seconds, d is the thickness of the steel plate in mm, and [C], [Si], [Mn], [Cr], [Ni], [Mo], [Cu], [P], and [Ti] represent 100 times the weight percentage of the corresponding elements in the carbon steel.

2. The method for correcting bridge composite steel plates according to claim 1, characterized in that, Before heating, the bending area is divided into heating zones, and the shape and area of ​​the heating zones are determined: When the bending position is uneven in one direction, either horizontally or vertically, N1 strip-shaped heating zones are divided at intervals along the vertical direction of the unevenness at the bending position. The area of ​​each strip-shaped heating zone is B×L=A / [N1×(4.0~6.0)], where B is the width of the heating zone, L is the length of the heating zone, and A is the area of ​​the bending position.

3. The method for correcting bridge composite steel plates according to claim 2, characterized in that, When the bending point is bidirectionally uneven in both the transverse and longitudinal directions, N2 point heating zones are defined at the bending point, with the area of ​​each point heating zone being π×R. 2 =A / [N2×(5.0~10.0)], the radius of the point heating zone R=50~150mm.

4. The method for correcting bridge composite steel plates according to claim 2, characterized in that, When the bending position is uneven in one direction, either laterally or longitudinally, the width of the strip heating zone B = (3~7)d.

5. The method for correcting bridge composite steel plates according to claim 2, characterized in that, Before heating, the bent part of the steel plate is preheated at a temperature of 100~150℃, and the total preheated area A0 = (1.0~3.0)A, and the preheated area completely includes the bent part.

6. The method for correcting bridge composite steel plates according to claim 3, characterized in that, When the bending method of the steel plate includes longitudinal unidirectional unevenness and transverse unidirectional unevenness, the intersection of longitudinal unidirectional unevenness and transverse unidirectional unevenness is the bending position with bidirectional unevenness in both the transverse and longitudinal directions; if the diameter of the intersection of longitudinal unidirectional unevenness and transverse unidirectional unevenness is greater than 150mm, then with the intersection of longitudinal unidirectional unevenness and transverse unidirectional unevenness as the center, the point heating area is evenly distributed on the circumference of the concentric circle formed with this center.

7. The method for correcting bridge composite steel plates according to claim 3, characterized in that, When the bending position is bidirectionally uneven along both the transverse and longitudinal directions, the unevenness calculated when heating temperature is taken as the maximum value of the unevenness in the unidirectional transverse and longitudinal directions.

8. The method for correcting bridge composite steel plates according to claim 1, characterized in that, When heating the bent area, flame straightening technology is used. The gas used in flame straightening technology is a mixture of oxygen and propane. The flame type is a neutral flame, the flame core height is 3~8mm from the steel plate, and the angle between the flame and the steel plate is 80~90°.

9. The method for correcting bridge composite steel plates according to any one of claims 1 to 8, wherein the corrected steel plate satisfies the flatness D≤5mm / m.

10. The method for correcting bridge composite steel plates according to claim 9, characterized in that, Tensile strength ≥510MPa, yield strength ≥370MPa, elongation ≥20%, shear strength ≥300MPa, impact strength at -40℃ ≥120J, no cracks detected by E-method for intergranular corrosion, no cracks detected by 180° cold bending (both internal and external).

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