A new type of composite steel plate for railway freight car and a method for manufacturing the same

Abstract

This invention discloses a method for preparing a composite steel plate, the prepared composite steel plate, and its applications. The composite steel plate includes a base layer and a cladding layer laminated on one side of the base layer. The base layer is weather-resistant steel, and the cladding layer is stainless steel. The preparation method includes: I. pretreatment, II. billet assembly, III. sealing welding, IV. hot rolling, V. cooling and coiling, and VI. heat treatment. Step III employs vacuum electron beam welding, and step IV employs differential speed multi-pass roughing and multi-pass finishing rolling. The composite steel plate provided by this invention achieves 100% interfacial bonding, and exhibits uniform and stable strength, elongation, impact resistance, and bending performance, all exceeding the standard requirements for steel used in truck bodies.

Description

Technical Field

[0001] This invention belongs to the field of metal composite technology, specifically relating to a method for preparing a layered composite steel plate made by single-sided composite and rolling of non-homogeneous steel materials, and the composite steel plate prepared therefrom. Background Technology

[0002] Railway freight transport boasts large capacity, high speed, and relatively low cost, and is generally unaffected by weather conditions, making it suitable for long-distance transport of bulk and heavy goods. While the Q450NQR1 steel commonly used in railway vehicles possesses high strength and some weather resistance, its resistance to corrosion from media such as sulfate ions is limited. Open wagon bodies made from this steel require extensive maintenance and replacement after 8 to 10 years of use, resulting in extremely high labor and material costs. Ferritic stainless steel, on the other hand, offers better corrosion and wear resistance, but its manufacturing cost is high and its strength is relatively low. Combining these two steels allows the composite steel to possess the advantages of both the cladding and base metals, thus providing a high-strength, corrosion-resistant composite steel plate for railway freight cars.

[0003] The main methods for preparing composite steel plates include explosive bonding, diffusion welding, and rolling bonding. The first two methods suffer from limitations such as poor interfacial bonding quality, uncontrollable bonding ratios, and inability to produce large-size plates. Rolling bonding generally involves assembling and sealing the cladding and base steel billets, followed by welding and rolling. This process enables mass production with high efficiency. The welding and rolling processes significantly impact the performance of the composite steel plate. Existing technologies primarily control the rolling process after billet assembly. For example, Chinese invention patent application CN118418539A, "Composite Steel Plate and Manufacturing Method Thereof," discloses a method for manufacturing a composite steel plate with a stainless steel cladding and a carbon steel base. This method involves two rolling processes: the first rolling is performed with the carbon steel layer on top, and the second rolling requires flipping the steel plate. For example, Chinese invention patent application No. 114891989A, "A Rolling Process for Wear-Resistant and Corrosion-Resistant Composite Steel Plate," discloses that the rolling process of the composite steel plate includes roughing and finishing rolling. The roughing rolling temperature is 1060-1120℃, with 9-12 rolling passes and a single-pass reduction rate ≤20%. The finishing rolling temperature is 900-950℃, the mill roll cooling water flow rate is set to 1 / 2 of the maximum flow rate, and the finishing rolling temperature is 820-850℃. After rolling, the composite steel plate is also subjected to slow cooling and quenching. However, when the billets are directly welded, there is a certain amount of air at the interface, which easily forms oxides and affects the interface bonding quality. In response, invention patent application No. CN09835013A, "A High-Strength Wear-Resistant Composite Steel Plate and Its Manufacturing Method," discloses that when the two steel billets are bonded together and welded to a closed connection, a vacuum channel is left at the edge, and then a vacuum treatment is performed. The composite steel is carbon steel and medium manganese steel with specific chemical compositions. The invention patent application CN113522972A, entitled "A Production Process for Corrosion-Resistant Stainless Steel Composite Plates," relies on submerged arc welding followed by vacuuming with a mechanical pump after billet assembly. On the one hand, the welding process consumes a large amount of welding wire and flux, increasing costs. On the other hand, the vacuum level provided by the mechanical pump is insufficient, and residual air between the plates can cause the billets to crack during high-temperature rolling. This results in numerous unbonded areas in the finished product, leading to significant quality fluctuations, which does not meet the requirements for reliable quality and high cost-effectiveness in railway freight car body steel.

[0004] Therefore, it is necessary to develop a method for preparing composite steel plates that use existing Q450NQR1 or Q550NQR1 weathering steel as the base layer and T4003 ferritic stainless steel or S32001 duplex stainless steel as the cladding layer, so as to provide cost-effective, corrosion-resistant and mechanically sound car body steel plates for railway freight cars. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing a composite steel plate with Q450NQR1 or Q550NQR1 weathering steel as the base layer and T4003 ferritic stainless steel or S32001 duplex stainless steel as the cladding. This method employs a vacuum electron beam welding billet-making process, combined with an optimized rolling process, which improves the interface composite rate of dissimilar steels, allowing the composite steel plate to leverage the advantages of both base materials.

[0006] To achieve the above-mentioned technical effects, the present invention adopts the following technical solution:

[0007] A method for preparing a composite steel plate, the composite steel plate comprising a base layer and a facing layer laminated on one side of the base layer, wherein the base layer is weather-resistant steel and the facing layer is stainless steel; the preparation method includes the following steps:

[0008] I. Preprocessing

[0009] The mating surfaces of the weathering steel billet and the stainless steel billet are milled as a whole until the oxide scale is completely removed, and then ground to make the surface roughness Ra≤1.6μm.

[0010] II. Assembly

[0011] The pretreated stainless steel billet is stacked on the weathering steel billet, so that the two pretreated surfaces to be joined are in contact, and the edges of the stainless steel billet and the weathering steel billet are strictly aligned. The weathering steel billet and the stainless steel billet are fixed by a clamp positioning device to obtain a combined billet.

[0012] III. Sealing

[0013] The composite billet obtained in step II is transferred to a vacuum electron beam welding chamber and evacuated to a vacuum level ≤1.0×10⁻⁶. - 2 Under the conditions of accelerating voltage of 140-150kV, beam current of 90-95mA, welding speed of 4.5-5.5mm / s, and electron beam offset of 2°-3° towards the weathering steel billet side, edge sealing welding is performed on the bonded weathering steel billet and stainless steel billet; after welding, the combined billet is cooled to room temperature in a vacuum environment at a rate of 50±10℃ / hour.

[0014] IV. Hot-rolled

[0015] The welded composite billet obtained in step III is heated at a set temperature of 1100-1250°C, with the stainless steel billet on top and the weathering steel billet below, until the surface uniform heating temperature of the stainless steel billet reaches the set heating temperature, and the surface uniform heating temperature of the weathering steel billet is 10-20°C lower than the set heating temperature; the heated composite billet is first subjected to multiple passes of rough rolling, and then multiple passes of finish rolling, until the composite plate reaches the target thickness.

[0016] The speed ratio of the lower roll to the upper roll in the roughing mill and finishing mill is 1.03 to 1.05:1.

[0017] The roughing rolling has a first pass reduction rate of 8% to 15% and a total reduction rate of 75% to 85%; the finishing rolling has a rolling speed of 4 to 6 m / s, a reduction rate of 20% to 25% per pass, and a final rolling temperature of 850 to 950℃.

[0018] V. Cooling and winding process

[0019] The composite steel strip obtained in step IV is naturally cooled to 600-670°C, and then the composite steel is wound up by a coiler to obtain a composite steel coil.

[0020] VI. Heat Treatment

[0021] The composite steel coil obtained in step V is heated to 650-750°C at a rate of 5-10°C / min, held for 10-20 minutes, then flattened into a steel plate and cooled to room temperature in the furnace to obtain the composite steel plate.

[0022] Preferably, the thickness of the weathering steel billet is 200-240 mm.

[0023] More preferably, the weathering steel billet is a weathering steel billet with the grade Q450NQR1 or Q550NQR1.

[0024] Preferably, the thickness of the stainless steel billet is 10-30 mm.

[0025] More preferably, the stainless steel billet is a ferritic stainless steel billet with grade T4003 or a duplex stainless steel billet with grade S32001.

[0026] Preferably, in step I, the roughness Ra of the surfaces to be bonded is 0.8 to 1.6 μm.

[0027] Preferably, in step III, a three-stage vacuum pump is used to create a vacuum.

[0028] Preferably, in step III, the process conditions for vacuum electron beam welding are: accelerating voltage of 150kV, beam current of 90-95mA, and welding speed of 5mm / s.

[0029] Preferably, in step III, the vacuum electron beam welding penetration depth is ≥35mm.

[0030] Preferably, step III further includes post-weld non-destructive testing, including inspecting the weld using ultrasound or radiography; if the weld is free of defects and the penetration depth reaches the specified depth, then proceed to step IV; if the weld is defective or the penetration depth is insufficient, then cut and separate the composite steel billet and repeat steps I to III until the post-weld non-destructive testing is qualified.

[0031] Preferably, in step IV, the furnace time for heating the welded composite billet is 1 min / mm.

[0032] Preferably, in step IV, the target thickness of the rolled composite plate is 5-10 mm.

[0033] Another objective of this invention is to provide a composite steel plate prepared by the above-described preparation method, comprising a weathering steel substrate layer and a stainless steel cladding layer tightly bonded together, with a total thickness of 5-10 mm, wherein the thickness ratio of the weathering steel substrate layer to the stainless steel cladding layer is 10.8-11.2:1.

[0034] Preferably, the thickness ratio of the weather-resistant steel substrate layer to the stainless steel cladding layer is 11:1.

[0035] Preferably, the weathering steel substrate layer is hot-rolled from a weathering steel billet of grade Q450NQR1 or Q550NQR1.

[0036] Preferably, the stainless steel cladding layer is hot-rolled from a ferritic stainless steel billet of grade T4003 or a duplex stainless steel billet of grade S32001.

[0037] Another objective of this invention is to provide the application of the aforementioned composite steel plate in the body of railway freight open wagons; wherein, the weathering steel base layer of the composite steel plate is hot-rolled from a weathering steel billet of grade Q450NQR1 or Q550NQR1, and the stainless steel cladding layer is hot-rolled from a ferritic stainless steel billet of grade T4003 or a duplex stainless steel billet of grade S32001.

[0038] This invention optimizes the billet assembly and vacuum electron beam welding process conditions to achieve a 100% heterogeneous interface bonding rate for the composite steel plate. Furthermore, by combining optimized rolling and post-rolling heat treatment process conditions, the strength, elongation, impact performance, and bending performance of the composite steel plate are ultimately guaranteed to be uniform and stable, all exceeding the standard requirements for steel used in truck bodies.

[0039] The composite steel plate provided by this invention has a thickness ratio of 10.8 to 11.2:1 for the weathering steel base layer and the stainless steel cladding layer, more preferably 11:1, which is the optimal ratio under current service conditions. At this ratio, the thinning rate of the stainless steel cladding layer due to corrosion and wear meets the design life requirements for truck body steel; moreover, the stress concentration between the weathering steel base layer and the stainless steel cladding layer is relatively small, resulting in good strength and toughness in the composite steel plate. Therefore, at the above ratio, the composite steel plate of this invention exhibits the best overall performance in terms of corrosion resistance and toughness. Attached Figure Description

[0040] The present invention will be further described below with reference to the accompanying drawings.

[0041] Figure 1 The photograph shows a cross-section along the thickness direction of the weld seam of the composite billet after sealing in Comparative Example 1.

[0042] Figure 2 The photograph shows a cross-section along the thickness direction of the weld seam of the composite billet after sealing in Comparative Example 2.

[0043] Figure 3 The photograph shows a metallographic image (500x magnification) of the composite steel plate prepared in Example 1 at a 1 / 2 width position along the thickness direction and perpendicular to the rolling direction.

[0044] Figure 4 What is shown is Figure 3 The photograph shows a scanning electron microscope image (3000x magnification) of the rolled composite interface of the composite steel plate cross section.

[0045] Figure 5 The photograph shows the composite steel plate prepared in Comparative Example 3 after cold bending performance testing. Microcracks are visible in the stainless steel cladding layer of the composite steel plate in the photograph. Detailed Implementation

[0046] The present invention will be described below with reference to specific embodiments. Those skilled in the art will understand that these embodiments are for illustrative purposes only and do not limit the scope of the invention in any way.

[0047] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available products.

[0048] Example 1: Preparation of a composite steel plate

[0049] I. Preprocessing

[0050] A Q450NQR1 weathering steel billet with a thickness of 210 mm was selected as the base material. A ferritic stainless steel billet of T4003 with a thickness of 25 mm was used as the cladding material. The mating surfaces of the weathering steel billet and the stainless steel billet were milled to remove the oxide scale completely, and then ground to achieve a surface roughness Ra of 0.8 μm, exposing a metallic luster.

[0051] II. Assembly

[0052] The pretreated stainless steel billet is stacked on the weathering steel billet, so that the two pretreated surfaces to be joined are in contact, and the edges of the stainless steel billet and the weathering steel billet are strictly aligned. The weathering steel billet and the stainless steel billet are fixed by a clamp positioning device to ensure that the two do not shift during the welding process, thus obtaining the combined billet.

[0053] III. Sealing

[0054] The composite billet obtained in step II is transferred to a vacuum electron beam welding chamber, and a three-stage vacuum pump is used to evacuate the vacuum to below 1.0 × 10⁻⁶. -2 Welding begins after Pa, with the weld depth controlled to ≥35mm. Welding process conditions are as follows:

[0055] The accelerating voltage was 140kV, the beam current was 90mA, the welding speed was 5mm / s, and the electron beam was offset by 2° towards the weathering steel billet.

[0056] After welding, the assembled billet was cooled to room temperature in a vacuum environment at a rate of 50±10℃ / hour. The weld was then inspected using ultrasound. Inspection results: No obvious welding defects were found in the welded joint; the weld penetration reached 38mm. Inspection conclusion: The seal weld met the standards.

[0057] IV. Hot-rolled

[0058] The welded composite billet obtained in step III was heated at a set temperature of 1150℃, with the stainless steel billet on top and the weathering steel casting billet below; the furnace time was 1 min / mm, until the surface uniform heating temperature of the stainless steel billet reached the set heating temperature, and the surface uniform heating temperature of the weathering steel casting billet was 1130℃; the heated composite billet was first subjected to multiple passes of rough rolling and then multiple passes of finish rolling using a differential speed process with lower and upper rolls, until the composite plate reached the target thickness of 6mm; the elongation of the base weathering carbon steel and the cladding stainless steel remained basically consistent, without any warping or buckling. Among these:

[0059] The speed ratio of the lower roller to the upper roller is 1.05:1;

[0060] The first pass reduction rate in rough rolling was 14%, and the total reduction rate was 78%.

[0061] The rolling speed of the finishing mill is 5.5 m / s, the first pass reduction rate is 23%, and the reduction rate of subsequent passes is adjusted within the range of 20% to 23% according to the actual pressing thickness of the previous pass until the target plate thickness is achieved; the final rolling temperature is 910℃.

[0062] V. Cooling and winding process

[0063] After the composite steel strip obtained in step IV is naturally cooled to 630°C, it is coiled by a coiler to obtain a composite steel coil.

[0064] VI. Heat Treatment

[0065] The composite steel coil obtained in step V is heated to 680°C at a rate of 10°C / min and held for 20 min; then it is flattened into a steel plate and cooled to room temperature in the furnace to obtain the composite steel plate.

[0066] The composite steel plate prepared in this embodiment has a total thickness of 6 mm, of which the thickness of the weathering steel Q450NQR1 substrate layer is 5.5 mm and the thickness of the stainless steel T4003 cladding layer is 0.5 mm, with a thickness ratio of 11:1.

[0067] Example 2: Preparation of a composite steel plate

[0068] I. Preprocessing

[0069] The same as step I in Example 1.

[0070] II. Assembly

[0071] The procedure is the same as step II in Example 1.

[0072] III. Sealing

[0073] The composite billet obtained in step II is transferred to a vacuum electron beam welding chamber, and a three-stage vacuum pump is used to evacuate the vacuum to below 1.0 × 10⁻⁶. -2 Welding begins after Pa, with the weld depth controlled to ≥35mm. Welding process conditions are as follows:

[0074] The accelerating voltage was 150kV, the beam current was 95mA, the welding speed was 5.5mm / s, and the electron beam was offset by 3° towards the weathering steel billet.

[0075] After welding, the assembled billet was cooled to room temperature in a vacuum environment at a rate of 50±10℃ / hour. The weld was then inspected using ultrasound. Inspection results: No obvious welding defects were found in the welded joint; the weld penetration reached 41mm. Inspection conclusion: The seal weld met the standards.

[0076] IV. Hot-rolled

[0077] The welded composite billet obtained in step III was heated at a set temperature of 1250℃, with the stainless steel billet on top and the weathering steel casting billet below; the furnace time was 1 min / mm, until the surface uniform heating temperature of the stainless steel billet reached the set heating temperature, and the surface uniform heating temperature of the weathering steel casting billet was 1230℃; the heated composite billet was first subjected to multiple passes of rough rolling and then multiple passes of finish rolling using a differential speed process with lower and upper rolls, until the composite plate reached the target thickness of 7mm; the elongation of the base weathering carbon steel and the cladding stainless steel remained basically consistent, without any warping or buckling. Among these:

[0078] The speed ratio of the lower roller to the upper roller is 1.03:1;

[0079] The first pass reduction rate in rough rolling is 12%, and the total reduction rate is 78%.

[0080] The finishing rolling speed is 5.5 m / s, the first pass has a reduction rate of 23%, and the subsequent passes have a reduction rate of 20-23%. The final rolling temperature is 910℃.

[0081] V. Cooling and winding process

[0082] After the composite steel strip obtained in step IV is naturally cooled to 625°C, it is coiled by a coiler to obtain a composite steel coil.

[0083] VI. Heat Treatment

[0084] The composite steel coil obtained in step V is heated to 650°C at a rate of 5°C / min and held for 15 min; then it is flattened into a steel plate and cooled to room temperature in the furnace to obtain the composite steel plate.

[0085] The composite steel plate prepared in this embodiment has a total thickness of 7 mm, of which the thickness of the weathering steel Q450NQR1 substrate layer is 6.42 mm and the thickness of the stainless steel T4003 cladding layer is 0.58 mm, with a thickness ratio of 11.1:1.

[0086] Example 3: Preparation of a composite steel plate

[0087] I. Preprocessing

[0088] The process is basically the same as step I in Example 1, except that Q550NQR1 weathering steel billet is used as the base material with a thickness of 210mm.

[0089] II. Assembly

[0090] The procedure is the same as step II in Example 1.

[0091] III. Sealing

[0092] The composite billet obtained in step II is transferred to a vacuum electron beam welding chamber, and a three-stage vacuum pump is used to evacuate the vacuum to below 1.0 × 10⁻⁶.-2 Welding begins after Pa, with the weld depth controlled to ≥35mm. Welding process conditions are as follows:

[0093] The accelerating voltage was 145kV, the beam current was 93mA, the welding speed was 4.5mm / s, and the electron beam was offset by 2.5° towards the weathering steel billet.

[0094] After welding, the assembled billet was cooled to room temperature in a vacuum environment at a rate of 50±10℃ / hour. The weld was then inspected using ultrasound. Inspection results: No obvious welding defects were found in the welded joint; the weld penetration reached 39mm. Inspection conclusion: The seal weld met the standards.

[0095] IV. Hot-rolled

[0096] The welded composite billet obtained in step III is heated at a set temperature of 1200℃, with the stainless steel billet on top and the weathering steel casting billet below; the furnace time is 1 min / mm, until the surface uniform heating temperature of the stainless steel billet reaches the set heating temperature, and the surface uniform heating temperature of the weathering steel casting billet is 1180℃; the heated composite billet is first subjected to multiple passes of rough rolling and then multiple passes of finish rolling using a differential speed process with lower and upper rolls, until the composite plate reaches the target thickness of 8mm; the elongation of the base weathering carbon steel and the cladding stainless steel remains basically consistent, without any warping or buckling. Among these:

[0097] The speed ratio of the lower roller to the upper roller is 1.04:1;

[0098] The first pass reduction rate in rough rolling is 15%, and the total reduction rate is 75%.

[0099] The finishing rolling speed is 4.5 m / s, the reduction rate per pass is 20%, and the final rolling temperature is 900℃.

[0100] V. Cooling and winding process

[0101] After the composite steel strip obtained in step IV is naturally cooled to 650°C, it is coiled by a coiler to obtain a composite steel coil.

[0102] VI. Heat Treatment

[0103] The composite steel coil obtained in step V is heated to 680°C at a rate of 8°C / min and held for 15 min; then it is flattened into a steel plate and cooled to room temperature in the furnace to obtain the composite steel plate.

[0104] The composite steel plate prepared in this embodiment has a total thickness of 8 mm, of which the thickness of the weathering steel Q550NQR1 base layer is 7.33 mm and the thickness of the stainless steel T4003 cladding layer is 0.67 mm, with a thickness ratio of 10.9:1.

[0105] Comparative Example 1

[0106] I. Preprocessing

[0107] The same as step I in Example 1.

[0108] II. Assembly

[0109] The procedure is the same as step II in Example 1.

[0110] III. Sealing

[0111] The composite billet obtained in step II is transferred to a vacuum electron beam welding chamber, and a three-stage vacuum pump is used to evacuate the vacuum to below 1.0 × 10⁻⁶. -2 Welding begins after Pa, with the weld depth controlled to ≥35mm. Welding process conditions are as follows:

[0112] The accelerating voltage is 150kV, the beam current is 120mA, the welding speed is 4mm / s, and the electron beam focus is located at the center of the joint surface.

[0113] After welding, the composite billet was cooled to room temperature in a vacuum environment at a rate of 50±10℃ / hour. The weld cross-section morphology was then observed when the composite billet was cut along its thickness direction. Figure 1 As shown in the figure, the weld seams of stainless steel and weathering steel show a significant deflection towards the stainless steel side, resulting in a fusion zone of only 25mm, which cannot meet the billet assembly requirements of the subsequent continuous rolling process.

[0114] Comparative Example 2

[0115] I. Preprocessing

[0116] The same as step I in Example 1.

[0117] II. Assembly

[0118] The procedure is the same as step II in Example 1.

[0119] III. Sealing

[0120] The composite billet obtained in step II is transferred to a vacuum electron beam welding chamber, and a three-stage vacuum pump is used to evacuate the vacuum to below 1.0 × 10⁻⁶. -2 Welding begins after Pa, with the weld depth controlled to ≥35mm. Welding process conditions are as follows:

[0121] The accelerating voltage was 150kV, the beam current was 120mA, the welding speed was 4mm / s, and the electron beam was offset by 2.5° towards the weathering steel billet.

[0122] After welding, the composite billet was cooled to room temperature in a vacuum environment at a rate of 50±10℃ / hour. The weld cross-section morphology was then observed when the composite billet was cut along its thickness direction. Figure 2As shown in the figure, the weld is located at the center of the mating surface, has good formation, and a penetration depth of approximately 50 mm. However, significant deformation gaps appear in the unwelded area of ​​the assembled billet, and the base materials on both sides are not properly bonded, failing to meet the assembly requirements of subsequent continuous rolling processes. The possible cause is an excessively high beam current, insufficient welding speed, and excessive heat input, leading to warping and deformation of the base materials on both sides.

[0123] Comparative Example 3: Preparation of a Composite Steel Plate

[0124] I. Preprocessing

[0125] The steps are basically the same as in Example 1, except that the substrate thickness is 205 mm and the cladding thickness is 30 mm.

[0126] II. Assembly

[0127] The procedure is the same as step II in Example 1.

[0128] III. Sealing

[0129] The composite billet obtained in step II is transferred to a vacuum electron beam welding chamber, and a three-stage vacuum pump is used to evacuate the vacuum to below 1.0 × 10⁻⁶. -2 Welding begins after Pa, with the weld depth controlled to ≥35mm. Welding process conditions are as follows:

[0130] The accelerating voltage was 150kV, the beam current was 92mA, the welding speed was 5mm / s, and the electron beam was offset by 2.5° towards the weathering steel billet.

[0131] After welding, the assembled billet was cooled to room temperature in a vacuum environment at a rate of 50±10℃ / hour. The weld was then inspected using ultrasound. Inspection results: No obvious welding defects were found in the welded joint, and the weld penetration reached 40mm; Inspection conclusion: The seal weld met the standards.

[0132] IV. Hot-rolled

[0133] The welded composite billet obtained in step III was heated at a set temperature of 1150℃, with the stainless steel billet on top and the weathering steel casting billet below; the furnace time was 1 min / mm, until the surface uniform heating temperature of the stainless steel billet reached the set heating temperature, and the surface uniform heating temperature of the weathering steel casting billet was 1130℃; the heated composite billet was first subjected to multiple passes of rough rolling and then multiple passes of finish rolling using a differential speed process with lower and upper rolls, until the composite plate reached the target thickness of 6mm; the elongation of the base weathering carbon steel and the cladding stainless steel remained basically consistent, without any warping or buckling. Among these:

[0134] The speed ratio of the lower roller to the upper roller is 1.05:1;

[0135] The first pass reduction rate in rough rolling is 15%, and the total reduction rate is 78%.

[0136] The finishing rolling speed is 5.5 m / s, the first pass has a reduction rate of 28%, and the subsequent passes have a reduction rate of 20% to 28%. The final rolling temperature is 910℃.

[0137] V. Cooling and winding process

[0138] After the composite steel strip obtained in step IV is naturally cooled to 630°C, it is coiled by a coiler to obtain a composite steel coil.

[0139] VI. Heat Treatment

[0140] The composite steel coil obtained in step V is heated to 680°C at a rate of 10°C / min and held for 20 min; then it is flattened into a steel plate and cooled to room temperature in the furnace to obtain the composite steel plate.

[0141] The composite steel plate prepared in this comparative example has a total thickness of 6 mm, of which the base layer of weathering steel Q450NQR1 is 5.4 mm thick and the cladding layer of stainless steel T4003 is 0.6 mm thick, with a thickness ratio of 9:1. Performance determination of the composite steel plates prepared in Examples 1-3 and Comparative Example 3 was conducted.

[0142] 1. Bonding status of heterogeneous interfaces in composite steel plates

[0143] Take the composite steel plate prepared in Example 1, and randomly take cross-sectional samples at different locations along the thickness direction. Metallographic photographs (magnified 500x) are then taken. Observation of the metallographic photographs of each sample reveals that the interfacial bonding rate of each sample reaches 100%. The metallographic photograph (magnified 500x) of the composite steel plate at the 1 / 2 width position along the thickness direction and perpendicular to the rolling direction is shown below. Figure 3 As shown. The microstructure of this cross-section was then observed using a scanning electron microscope (3000x magnification), with the following SEM image showing the rolling composite interface: Figure 4 As shown.

[0144] Figure 3 As shown, the composite steel plate prepared in Example 1 has a 100% bonding rate at the heterogeneous steel interface. Figure 4 The interface shows no defects, and the bonding quality is good.

[0145] 2. Determination of main properties of composite steel plates

[0146] The tensile properties (lower yield strength (Rel), tensile strength (Rm), and elongation after fracture (A)), cold bending properties (180° inward and outward bending), shear properties (interfacial shear strength), impact properties (-40℃ KV2 impact absorption energy), and non-metallic inclusions of the composite steel plates prepared in Examples 1-3 and Comparative Example 3 were tested according to GB / T 228.1-2021, GB / T 232-2010, GB / T 6396-2008, GB / T 229-2020, and GB / T10561-2023, respectively. The results for Examples 1, 2, and Comparative Example 3 are shown in Table 1, and the results for Example 3 are shown in Table 2. A photograph of the composite steel plate of Comparative Example 3 after the cold bending performance test is shown in [Table 1]. Figure 5 .

[0147] The data in Tables 1 and 2 show that the composite steel plates prepared in each embodiment of the present invention exceed the technical standards in all aspects. However, the composite steel plate prepared in Comparative Example 3 fails to meet the technical standards in both elongation after fracture and cold bending performance (180° internal bending).

[0148] Table 1. Performance test results of the composite steel plates prepared in Examples 1, 2 and Comparative Example 3.

[0149]

[0150]

[0151] Table 2. Performance test results of the composite steel plate prepared in Example 3

[0152]

[0153] 3. Surface corrosion resistance test

[0154] The corrosion performance of the composite steel plates prepared in Examples 1-3 was tested according to TB / T 2375 "Test Method for Cyclic Immersion Corrosion of Weathering Steel for Railway". The results show that the corrosion resistance of the cladding layer of the composite steel plates prepared in each example is comparable to that of T4003.

[0155] The above performance test results show that the composite steel plate prepared by the present invention not only has the properties of both the base layer steel and the cladding layer steel, but also the two steels are tightly bonded and without defects. As a whole, it exhibits good mechanical properties and corrosion resistance, and is particularly suitable for manufacturing railway freight open wagon bodies.

Claims

1. A method for preparing a composite steel plate, the composite steel plate comprising a base layer and a facing layer laminated on one side of the base layer, wherein the base layer is weather-resistant steel and the facing layer is stainless steel; the preparation method comprises the following steps: I. Preprocessing The mating surfaces of the weathering steel billet and the stainless steel billet are milled as a whole until the oxide scale is completely removed, and then ground to make the surface roughness Ra≤1.6 μm. II. Assembly The pretreated stainless steel billet is stacked on the weathering steel billet, so that the two pretreated surfaces to be joined are in contact, and the edges of the stainless steel billet and the weathering steel billet are strictly aligned. The weathering steel billet and the stainless steel billet are fixed by a clamp positioning device to obtain a combined billet. III. Sealing The composite billet obtained in step II is transferred to a vacuum electron beam welding chamber and evacuated to a vacuum level ≤1.0×10⁻⁶. -2 The edge sealing welding of the bonded weathering steel billet and stainless steel billet was carried out under the conditions of accelerating voltage of 140~150 kV, beam current of 90~95 mA, welding speed of 4.5~5.5 mm / s, and electron beam offset of 2°~3° towards the weathering steel billet side; after welding, the combined billet was cooled to room temperature in a vacuum environment at a rate of 50±10℃ / hour. IV. Hot-rolled The welded composite billet obtained in step III is heated at a set temperature of 1100-1250°C, with the stainless steel billet on top and the weathering steel billet below, until the surface uniform heating temperature of the stainless steel billet reaches the set heating temperature, and the surface uniform heating temperature of the weathering steel billet is 10-20°C lower than the set heating temperature; the heated composite billet is first subjected to multiple passes of rough rolling, and then multiple passes of finish rolling, until the composite plate reaches the target thickness. The speed ratio of the lower roll to the upper roll in the roughing mill and finishing mill is 1.03~1.05∶1; The roughing mill has a first pass reduction rate of 8% to 15% and a total reduction rate of 75% to 85%; the finishing mill has a rolling speed of 4 to 6 m / s, a reduction rate of 20% to 25% per pass, and a final rolling temperature of 850 to 950°C. V. Cooling and winding process The composite steel strip obtained in step IV is naturally cooled to 600~670℃, and then the composite steel is wound up by a coiler to obtain a composite steel coil. VI. Heat Treatment The composite steel coil obtained in step V is heated to 650-750°C at a rate of 5-10°C / min, held for 10-20 minutes, then flattened into a steel plate and cooled to room temperature in the furnace to obtain the composite steel plate.

2. The preparation method according to claim 1, characterized in that, The thickness of the weathering steel billet is 200~240mm.

3. The preparation method according to claim 2, characterized in that, The weathering steel billet is a weathering steel billet with the grade Q450NQR1 or Q550NQR1.

4. The preparation method according to claim 1, characterized in that, The thickness of the stainless steel billet is 10~30mm.

5. The preparation method according to claim 4, characterized in that, The stainless steel billet is a ferritic stainless steel billet with grade T4003 or a duplex stainless steel billet with grade S32001.

6. The preparation method according to claim 1, characterized in that, In step I, the roughness Ra of the surfaces to be bonded is 0.8~1.6μm.

7. The preparation method according to claim 1, characterized in that, In step III, a three-stage vacuum pump is used to create a vacuum.

8. The preparation method according to claim 1, characterized in that, In step III, the process conditions for vacuum electron beam welding are: accelerating voltage of 150 kV, beam current of 90~95 mA, and welding speed of 5 mm / s.

9. The preparation method according to claim 1 or 8, characterized in that, In step III, the vacuum electron beam welding penetration depth is ≥35mm.

10. The preparation method according to claim 1, characterized in that, Step III also includes post-weld non-destructive testing, including using ultrasound or radiography to inspect the weld; if the weld is free of defects and the penetration depth reaches the specified depth, proceed to step IV; if the weld is defective or the penetration depth is insufficient, cut and separate the composite steel billet and repeat steps I to III until the post-weld non-destructive testing is qualified.

11. The preparation method according to claim 1, characterized in that, In step IV, the furnace time for heating the welded composite billet is 1 min / mm.

12. The preparation method according to claim 1, characterized in that, In step IV, the target thickness of the rolled composite plate is 5~10mm.

13. A composite steel plate, prepared by any one of claims 1 to 12, comprising a weathering steel substrate layer and a stainless steel cladding layer tightly bonded together, with a thickness of 5 to 10 mm, wherein the thickness ratio of the weathering steel substrate layer to the stainless steel cladding layer is 10.8 to 11.2:

1.

14. The composite steel plate according to claim 13, characterized in that, The thickness ratio of the weathering steel substrate layer to the stainless steel cladding layer is 11:

1.

15. The composite steel plate according to claim 13 or 14, characterized in that, The weathering steel substrate layer is hot-rolled from a weathering steel billet of grade Q450NQR1 or Q550NQR1.

16. The composite steel plate according to claim 13 or 14, characterized in that, The stainless steel cladding layer is hot-rolled from a ferritic stainless steel billet of grade T4003 or a duplex stainless steel billet of grade S32001.

17. The application of the composite steel plate according to any one of claims 13 to 16 in the body of a railway freight open wagon; wherein, The weathering steel base layer of the composite steel plate is hot-rolled from weathering steel billets of grade Q450NQR1 or Q550NQR1, and the stainless steel cladding layer is hot-rolled from ferritic stainless steel billets of grade T4003 or duplex stainless steel billets of grade S32001.

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