Novel composite steel plate for railway freight car and preparation method of novel composite steel plate

Abstract

The invention discloses a preparation method of a clad steel plate, the clad steel plate prepared by the preparation method and application of the clad steel plate. The composite steel plate comprises a base plate layer and a covering layer, a single face of the covering layer is composited on the base plate layer, the base plate layer is made of weathering resistant steel, and the covering layer is made of stainless steel. The preparation method comprises the first step of pretreatment, the second step of assembly, the third step of seal welding, the fourth step of hot rolling, the fifth step of cooling and coiling treatment and the sixth step of heat treatment, vacuum electron beam welding is adopted in the third step, and differential multi-pass rough rolling and multi-pass finish rolling are adopted in the fourth step. The interface bonding rate of the composite steel plate provided by the invention reaches 100%, and the strength, the elongation, the impact property and the bending property are uniform and stable and are all higher than the standard requirements of steel for the truck body.

Description

Technical Field

[0001] The invention belongs to the technical field of metal composites, and particularly relates to a method for preparing a layered composite steel plate formed by single-sided composite and rolling of heterogeneous steel materials and the composite steel plate prepared thereby. Background Art

[0002] Railway freight has a large volume, high speed, and low cost. It is generally not restricted by climatic conditions and is suitable for long-distance transportation of bulky and heavy goods. Although the Q450NQR1 steel commonly used in railway vehicles has high strength and certain weather resistance, its resistance to corrosion from media such as sulfate ions is limited. The open car body made of this steel plate requires a lot of maintenance and replacement after 8 to 10 years of use, and the labor and material costs are extremely high. Ferritic stainless steel has good corrosion resistance and wear resistance, but the manufacturing cost is high and the strength performance is low. Combining the two steels together can make the composite steel have the advantages of both cladding metal and base metal, thereby providing a high-strength, corrosion-resistant composite steel plate for railway freight vehicles.

[0003] The preparation methods of composite steel plates mainly include explosive bonding, diffusion welding and rolling bonding, among which the first two have the limitations of poor interface bonding quality, uncontrollable bonding ratio and inability to produce large-size plates. The rolling bonding process generally includes assembly, edge sealing, welding and rolling of the cladding steel billet and the base steel billet, which can achieve mass production with high production efficiency. The edge sealing welding and rolling processes have an important influence on the performance of the composite steel plate. The prior art mostly controls the rolling process after assembly. For example, the Chinese invention patent application "Composite Steel Plate and Its Manufacturing Method" with publication number CN118418539A discloses a method for manufacturing a composite steel plate with a cladding layer of stainless steel and a base layer of carbon steel, wherein the rolling is performed twice, the carbon steel layer is on the upper part in the first rolling, and the steel plate needs to be turned over during the second rolling. For example, the Chinese invention patent application with publication number 114891989A, "A rolling process for wear-resistant and corrosion-resistant composite steel plate", discloses that the rolling process of the composite steel plate includes rough rolling and finish rolling; the starting rolling temperature of the rough rolling is 1060-1120℃, the rolling passes are 9-12 passes, and the single pass reduction rate is ≤20%; the starting rolling temperature of the finish rolling is 900-950℃, the cooling water flow of the rolling mill rolls is set to 1 / 2 of the maximum flow, and the final rolling temperature is 820-850℃; after rolling, the composite steel plate is also slowly cooled and quenched. However, when the billet is directly welded, a certain amount of air exists at the interface, which is easy to form oxides and affect the interface bonding quality. In this regard, the invention patent application with publication number CN09835013A, "A high-strength wear-resistant composite steel plate and its manufacturing method", discloses that when two steel billets are welded and connected after bonding, a vacuum channel is left at the edge, and then vacuum treatment is carried out; and the composite is carbon steel and medium manganese steel with a specific chemical composition. The invention patent application with publication number CN113522972A, "A production process for a surface corrosion-resistant stainless steel composite plate", relies on a method of vacuuming with a mechanical pump after submerged arc welding and welding after billet assembly. On the one hand, the welding process consumes a large amount of welding wire and flux, which increases the cost. On the other hand, the vacuum degree of the mechanical pump is not enough, and the air between the plates remains during the high-temperature rolling process, which will cause the billet to burst. The finished product often has unbonded areas and has large quality fluctuations, which does not meet the requirements of reliable quality and high cost-effectiveness of steel for railway freight car bodies.

[0004] Therefore, it is necessary to develop a method for preparing a composite steel plate with the existing Q450NQR1 or Q550NQR1 weathering steel as the base layer and T4003 ferritic stainless steel or S32001 duplex stainless steel as the cladding, so as to provide railway freight vehicles with cost-effective, corrosion-resistant and good mechanical properties body steel plates. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a method for preparing a composite steel plate with Q450NQR1 or Q550NQR1 weathering steel as a base layer and T4003 ferritic stainless steel or S32001 duplex stainless steel as a cladding layer. The method adopts a vacuum electron beam welding blank making process combined with an optimized rolling process to improve the interface recombination rate of heterogeneous steels, so that the composite steel plate can give full play to the advantages of the two base materials.

[0006] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0007] A method for preparing a composite steel plate, the composite steel plate comprising a substrate layer and a covering layer composited on one side of the substrate layer, the substrate layer is weathering steel, and the covering layer is stainless steel; the preparation method comprises the following steps:

[0008] I. Pretreatment

[0009] The surfaces to be bonded of the weathering steel ingot and the stainless steel ingot are respectively milled as a whole until the oxide scale is completely removed, and then ground to make the roughness of the surfaces to be bonded Ra ≤ 1.6 μm;

[0010] II. Assembly

[0011] The pretreated stainless steel billet is stacked on the weathering steel billet so that the two pretreated surfaces to be bonded are in contact with each other and the edges of the stainless steel billet and the weathering steel billet are strictly aligned, and the weathering steel billet and the stainless steel billet are fixed by a fixture positioning device to obtain a combined billet;

[0012] III. Sealing

[0013] The combined blank obtained in step II is transferred to a vacuum electron beam welding chamber and evacuated to a vacuum degree of ≤1.0×10 - 2 Pa, edge-sealing welding of the bonded weathering steel ingot and stainless steel ingot is performed under the conditions of acceleration 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° to the side of the weathering steel ingot; after welding, the combined ingot is cooled to room temperature at a rate of 50±10°C / hour in a vacuum environment;

[0014] IV. Hot rolling

[0015] The sealed and welded combined 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 on the bottom, 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 combined billet is firstly subjected to multiple rough rolling and then to multiple finish rolling until the composite plate reaches the target thickness;

[0016] Among them, the roll speed ratio between the lower roll and the upper roll of the roughing mill and the finishing mill is 1.03 to 1.05:1;

[0017] The first pass reduction rate of the rough rolling is 8% to 15%, and the total reduction rate is 75% to 85%; the rolling speed of the finishing rolling is 4 to 6 m / s, the reduction rate of each pass is 20% to 25%, and the final rolling temperature is 850 to 950°C;

[0018] V.Cooling and coiling process

[0019] The composite plate steel strip obtained in step IV is naturally cooled to 600-670° C., and the composite plate is coiled 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 speed of 5-10° C. / min, kept warm for 10-20 minutes, then flattened into a steel plate, and cooled to room temperature along with the furnace to obtain a composite steel plate.

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

[0023] Further preferably, the weathering steel ingot is a weathering steel ingot with a grade of Q450NQR1 or Q550NQR1.

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

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

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

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

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

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

[0030] Preferably, the step III also includes post-weld non-destructive testing, including using ultrasound or radiation to inspect the weld; if the weld is defective and the penetration reaches the specified depth, proceed to step IV; if the weld is defective or the penetration does not meet the standard, the composite steel billet is cut and separated and steps I to III are repeated until the post-weld non-destructive testing is qualified.

[0031] Preferably, in step IV, when the assembled blank is heated after sealing, the time in the furnace is 1 min / mm.

[0032] Preferably, in step IV, the target thickness of the composite plate after rolling is 5 to 10 mm.

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

[0034] Preferably, the thickness ratio of the weathering steel substrate layer to the stainless steel covering layer is 11:1.

[0035] Preferably, the weathering steel substrate layer is formed by hot rolling weathering steel ingots with a grade of Q450NQR1 or Q550NQR1.

[0036] Preferably, the stainless steel cladding layer is formed by hot rolling a ferritic stainless steel billet with a grade of T4003 or a duplex stainless steel billet with a grade of S32001.

[0037] Another object of the present invention is to provide an application of the above-mentioned composite steel plate in the body of a railway freight open car; wherein the weathering steel base layer of the composite steel plate is hot-rolled from a weathering steel ingot with a grade of Q450NQR1 or Q550NQR1, and the stainless steel covering layer is hot-rolled from a ferritic stainless steel ingot with a grade of T4003 or a duplex stainless steel ingot with a grade of S32001.

[0038] The present invention optimizes the process conditions of billet assembly and vacuum electron beam welding to achieve a heterogeneous interface bonding rate of the composite steel plate of 100%; further, combined with the optimized rolling and post-rolling heat treatment process conditions, it is ultimately ensured that the strength, elongation, impact performance and bending performance of the composite steel plate are uniform and stable, all of which are higher than the standard requirements for truck body steel.

[0039] The composite steel plate provided by the present invention has a thickness ratio of 10.8 to 11.2:1 between the weathering steel substrate layer and the stainless steel covering layer, preferably 11:1, which is the best ratio under current service conditions. At this ratio, the thinning rate of the stainless steel covering layer due to corrosion and wear meets the design life requirements of truck body steel; and the stress concentration between the weathering steel substrate layer and the stainless steel covering layer is small, and the composite steel plate has good strength and toughness. Therefore, at the above ratio, the composite steel plate of the present invention has the best comprehensive performance of corrosion resistance and strength and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0041] Figure 1 The photograph shows a cross section of the weld of the assembled blank after sealing welding in Comparative Example 1 along the thickness direction.

[0042] Figure 2 The photograph shows a cross section of the weld of the assembled blank after sealing welding in Comparative Example 2 along the thickness direction.

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

[0044] Figure 4 It shows Figure 3 The photo shows a scanning electron microscope photo of the rolled composite interface of the composite steel plate cross section (magnified 3000 times).

[0045] Figure 5 The photo shows the composite steel plate prepared in Comparative Example 3 after the cold bending performance test. The photo shows that micro cracks appear on the stainless steel cladding surface of the composite steel plate. DETAILED DESCRIPTION

[0046] The present invention is described below with reference to specific examples. It will be appreciated by those skilled in the art that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention in any way.

[0047] The experimental methods in the following examples are conventional methods unless otherwise specified. The raw materials, reagents, etc. used in the following examples are commercially available products unless otherwise specified.

[0048] Example 1 Preparation of a composite steel plate

[0049] I. Pretreatment

[0050] Q450NQR1 weathering steel ingot was selected as the base material with a thickness of 210 mm. Ferritic stainless steel ingot T4003 was selected as the covering material with a thickness of 25 mm. The surfaces to be bonded of the weathering steel ingot and the stainless steel ingot were milled as a whole until the oxide scale was removed, and then ground to make the roughness Ra of the surfaces to be bonded 0.8 μm and the surface exposed metallic luster.

[0051] II. Assembly

[0052] The pretreated stainless steel billet is stacked on the weathering steel ingot so that the two pretreated surfaces to be joined fit together, and the edges of the stainless steel billet and the weathering steel ingot are strictly aligned. The weathering steel ingot and the stainless steel billet are fixed using a fixture positioning device to ensure that the two do not move during the welding process to obtain a combined billet.

[0053] III. Sealing

[0054] The assembled blank obtained in step II is transferred to a vacuum electron beam welding chamber and evacuated to a vacuum level below 1.0×10 -2 Welding starts after Pa, and the welding depth is controlled to be ≥35mm. The welding process conditions are:

[0055] The acceleration voltage is 140 kV, the beam current is 90 mA, the welding speed is 5 mm / s, and the electron beam is offset 2° to the side of the weathering steel ingot.

[0056] After welding, the combined blank is cooled to room temperature at a rate of 50±10℃ / hour in a vacuum environment. The weld is then inspected using ultrasound. Inspection results: There are no obvious welding defects in the welded joint, and the welding penetration reaches 38mm; Inspection conclusion: The sealing weld meets the standard.

[0057] IV. Hot rolling

[0058] The sealed and welded combined billet obtained in step III is heated at a set temperature of 1150°C, with the stainless steel billet on top and the weathering steel billet on the bottom; the furnace time is 1min / mm, until the surface absorptive temperature of the stainless steel billet reaches the set heating temperature, and the surface absorptive temperature of the weathering steel billet is 1130°C; the heated combined billet is first subjected to multiple rough rolling and then to multiple fine rolling using the lower and upper roller differential speed process, until the composite plate reaches the target thickness of 6mm; the elongation of the base weathering carbon steel and the cladding stainless steel remains basically the same, without warping or buckling. Among them:

[0059] The roller speed ratio between the lower roller and the upper roller is 1.05:1;

[0060] The first pass reduction rate of rough rolling is 14%, and the total reduction rate is 78%;

[0061] The rolling speed of the finishing rolling is 5.5m / s, the reduction rate of the first pass is 23%, and the reduction rate of the 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 reached; the final rolling temperature is 910℃.

[0062] V.Cooling and coiling process

[0063] After the composite plate steel strip obtained in step IV is naturally cooled to 630° C., the composite plate 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 kept warm for 20 minutes; then it is flattened into a steel plate, and cooled to room temperature along with the furnace to obtain a composite steel plate.

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

[0067] Example 2 Preparation of a composite steel plate

[0068] I. Pretreatment

[0069] Same as step I in Example 1.

[0070] II. Assembly

[0071] Same as step II of Example 1.

[0072] III. Sealing

[0073] The assembled blank obtained in step II is transferred to a vacuum electron beam welding chamber and evacuated to a vacuum level below 1.0×10 -2 Welding starts after Pa, and the welding depth is controlled to be ≥35mm. The welding process conditions are:

[0074] The acceleration voltage is 150 kV, the beam current is 95 mA, the welding speed is 5.5 mm / s, and the electron beam is offset 3° to the side of the weathering steel ingot.

[0075] After welding, the combined blank is cooled to room temperature at a rate of 50±10℃ / hour in a vacuum environment. The weld is then inspected using ultrasound. Inspection results: There are no obvious welding defects in the welded joint, and the welding penetration reaches 41mm; Inspection conclusion: The sealing weld meets the standard.

[0076] IV. Hot rolling

[0077] The combined billet after sealing and welding obtained in step III is heated at a set temperature of 1250°C, with the stainless steel billet on top and the weathering steel billet on the bottom; the furnace time is 1min / mm, until the surface absorptive temperature of the stainless steel billet reaches the set heating temperature, and the surface absorptive temperature of the weathering steel billet is 1230°C; the heated combined billet is first subjected to multiple rough rolling and then to multiple fine rolling by using the lower and upper roller differential speed process, until the composite plate reaches the target thickness of 7mm; the elongation of the base weathering carbon steel and the cladding stainless steel remains basically the same, without warping or buckling. Among them:

[0078] The roller speed ratio between the lower roller and the upper roller is 1.03:1;

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

[0080] The rolling speed of the finishing rolling is 5.5 m / s, the reduction rate of the first pass is 23%, the reduction rate of each subsequent pass is 20-23%, and the final rolling temperature is 910°C.

[0081] V.Cooling and coiling process

[0082] After the composite plate steel strip obtained in step IV is naturally cooled to 625° C., the composite plate 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 kept warm for 15 minutes; then it is flattened into a steel plate, and cooled to room temperature along with the furnace to obtain a composite steel plate.

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

[0086] Example 3 Preparation of a composite steel plate

[0087] I. Pretreatment

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

[0089] II. Assembly

[0090] Same as step II of Example 1.

[0091] III. Sealing

[0092] The assembled blank obtained in step II is transferred to a vacuum electron beam welding chamber and evacuated to a vacuum level below 1.0×10-2 Welding starts after Pa, and the welding depth is controlled to be ≥35mm. The welding process conditions are:

[0093] The acceleration voltage is 145 kV, the beam current is 93 mA, the welding speed is 4.5 mm / s, and the electron beam is offset by 2.5° to the side of the weathering steel ingot.

[0094] After welding, the combined blank is cooled to room temperature at a rate of 50±10℃ / hour in a vacuum environment. The weld is then inspected using ultrasound. Inspection results: There are no obvious welding defects in the welded joint, and the welding penetration reaches 39mm; Inspection conclusion: The sealing weld meets the standard.

[0095] IV. Hot rolling

[0096] The sealed and welded combined billet obtained in step III is heated at a set temperature of 1200°C, with the stainless steel billet on top and the weathering steel billet on the bottom; the furnace time is 1min / mm, until the surface absorptive temperature of the stainless steel billet reaches the set heating temperature, and the surface absorptive temperature of the weathering steel billet is 1180°C; the heated combined billet is first subjected to multiple rough rolling and then to multiple fine rolling using the lower and upper roller differential speed process, 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 the same, without warping or buckling. Among them:

[0097] The roller speed ratio between the lower roller and the upper roller is 1.04:1;

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

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

[0100] V.Cooling and coiling process

[0101] After the composite plate steel strip obtained in step IV is naturally cooled to 650° C., the composite plate 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 kept warm for 15 minutes; then it is flattened into a steel plate, and cooled to room temperature along with the furnace to obtain a composite steel plate.

[0104] The composite steel plate prepared in this embodiment has a total thickness of 8 mm, wherein the weathering steel Q550NQR1 substrate layer has a thickness of 7.33 mm, and the stainless steel T4003 covering layer has a thickness of 0.67 mm, and the thickness ratio between the two is 10.9:1.

[0105] Comparative Example 1

[0106] I. Pretreatment

[0107] Same as step I in Example 1.

[0108] II. Assembly

[0109] Same as step II of Example 1.

[0110] III. Sealing

[0111] The assembled blank obtained in step II is transferred to a vacuum electron beam welding chamber and evacuated to a vacuum level below 1.0×10 -2 Welding starts after Pa, and the welding depth is controlled to be ≥35mm. The welding process conditions are:

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

[0113] After welding, the combined billet is cooled to room temperature at a rate of 50±10℃ / hour in a vacuum environment. The cross-sectional morphology of the weld is shown in the following figure. Figure 1 As shown in the figure, the welds of stainless steel and weathering steel have obviously deflected toward the stainless steel side, resulting in a fusion zone of only 25 mm, which cannot meet the requirements of the subsequent continuous rolling process.

[0114] Comparative Example 2

[0115] I. Pretreatment

[0116] Same as step I in Example 1.

[0117] II. Assembly

[0118] Same as step II of Example 1.

[0119] III. Sealing

[0120] The assembled blank obtained in step II is transferred to a vacuum electron beam welding chamber and evacuated to a vacuum level below 1.0×10 -2 Welding starts after Pa, and the welding depth is controlled to be ≥35mm. The welding process conditions are:

[0121] The acceleration voltage is 150 kV, the beam current is 120 mA, the welding speed is 4 mm / s, and the electron beam is offset by 2.5° to the weathering steel ingot side.

[0122] After welding, the combined billet is cooled to room temperature at a rate of 50±10℃ / hour in a vacuum environment. The cross-sectional morphology of the weld is shown in the following figure. Figure 2As shown in the figure, the weld is located at the center of the joint surface, the formation is good, and the penetration depth is about 50mm. However, there is a more obvious deformation gap in the unwelded area of ​​the combined billet, and the parent materials on both sides are not fitted, resulting in the inability to meet the billet assembly requirements of the subsequent continuous rolling process. Analysis of the reasons may be that the beam current is too large, the welding speed is too low, and the heat input is too large, which causes the parent materials on both sides to warp and deform.

[0123] Comparative Example 3 Preparation of a composite steel plate

[0124] I. Pretreatment

[0125] The process is basically the same as step I of Example 1, but the thickness of the substrate is 205 mm and the thickness of the covering material is 30 mm.

[0126] II. Assembly

[0127] Same as step II of Example 1.

[0128] III. Sealing

[0129] The assembled blank obtained in step II is transferred to a vacuum electron beam welding chamber and evacuated to a vacuum level below 1.0×10 -2 Welding starts after Pa, and the welding depth is controlled to be ≥35mm. The welding process conditions are:

[0130] The acceleration voltage is 150 kV, the beam current is 92 mA, the welding speed is 5 mm / s, and the electron beam is offset by 2.5° to the side of the weathering steel ingot.

[0131] After welding, the combined blank is cooled to room temperature at a rate of 50±10℃ / hour in a vacuum environment. The weld is then inspected using ultrasound. Inspection results: There are no obvious welding defects in the welded joint, and the welding penetration reaches 40mm; Inspection conclusion: The sealing weld meets the standard.

[0132] IV. Hot rolling

[0133] The sealed and welded combined billet obtained in step III is heated at a set temperature of 1150°C, with the stainless steel billet on top and the weathering steel billet on the bottom; the furnace time is 1min / mm, until the surface absorptive temperature of the stainless steel billet reaches the set heating temperature, and the surface absorptive temperature of the weathering steel billet is 1130°C; the heated combined billet is first subjected to multiple rough rolling and then to multiple fine rolling using the lower and upper roller differential speed process, until the composite plate reaches the target thickness of 6mm; the elongation of the base weathering carbon steel and the cladding stainless steel remains basically the same, without warping or buckling. Among them:

[0134] The roller speed ratio between the lower roller and the upper roller is 1.05:1;

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

[0136] The rolling speed of the finishing rolling is 5.5 m / s, the reduction rate of the first pass is 28%, the reduction rate of each subsequent pass is 20% to 28%, and the final rolling temperature is 910°C.

[0137] V.Cooling and coiling process

[0138] After the composite plate steel strip obtained in step IV is naturally cooled to 630° C., the composite plate 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 kept warm for 20 minutes; then it is flattened into a steel plate, and cooled to room temperature along with the furnace to obtain a composite steel plate.

[0141] The composite steel plate prepared in this comparative example has a total thickness of 6 mm, wherein the weathering steel Q450NQR1 substrate layer has a thickness of 5.4 mm, and the stainless steel T4003 covering layer has a thickness of 0.6 mm, and the thickness ratio of the two is 9:1. Test Example Performance Determination of Composite Steel Plates Prepared in Examples 1 to 3 and Comparative Example 3

[0142] 1. Heterogeneous interface bonding condition of composite steel plate

[0143] Take the composite steel plate prepared in Example 1, randomly take cross-section samples along the thickness direction at different positions, and take metallographic photos (magnified 500 times). Observe the metallographic photos of each sample and find that the interface bonding rate of each sample reaches 100%. The metallographic photo of the cross section of the composite steel plate at the 1 / 2 width position along the thickness direction and perpendicular to the rolling direction (magnified 500 times) is as follows: Figure 3 The microscopic morphology of the cross section was observed using a scanning electron microscope (magnification 3000 times), and the scanning electron microscope photo of the rolled composite interface is shown in Figure 4 shown.

[0144] Figure 3 It is shown that, for the composite steel plate prepared in Example 1, the interface bonding rate of heterogeneous steels reaches 100%. Figure 4 It shows that the bonding interface has 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° inner bending and outer bending), shear properties (interface shear strength), impact properties (-40°C KV2 impact absorption energy) and non-metallic inclusions of the composite steel plates prepared in Examples 1 to 3 and Comparative Example 3 were tested with reference to GB / T 228.1-2021, GB / T 232-2010, GB / T 6396-2008, GB / T 229-2020 and GB / T10561-2023. The results of Examples 1, 2 and Comparative Example 3 are shown in Table 1, the results of Example 3 are shown in Table 2, and the photos of the composite steel plates of Comparative Example 3 after the cold bending performance test are shown in Table 2. Figure 5 .

[0147] The data in Table 1 and Table 2 show that the properties of the composite steel plates prepared in the embodiments of the present invention all exceed the technical standards. However, the composite steel plate prepared in Comparative Example 3 does not meet the technical standards in terms of elongation after fracture and cold bending performance (180° inner bending).

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

[0149]

[0150]

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

[0152]

[0153] 3. Determination of surface corrosion resistance

[0154] The corrosion performance of the composite steel plates prepared in Examples 1 to 3 was tested with reference to TB / T 2375 "Cyclic Immersion Corrosion Test Method for Weathering Steel for Railways". The results showed that the corrosion resistance of the surface layer of the composite steel plates prepared in each example was equivalent to that of T4003.

[0155] The above performance measurement results show that the composite steel plate prepared by the present invention not only has the performance of both the base layer steel and the covering layer steel, but also the two steels are tightly combined and defect-free, and as a whole it exhibits good mechanical properties and corrosion resistance, and is particularly suitable for manufacturing railway freight open car bodies.

Claims

1. A method for preparing a composite steel plate, the composite steel plate comprising a substrate layer and a covering layer composited on one side of the substrate layer, the substrate layer being weathering steel and the covering layer being stainless steel; the preparation method comprising the following steps: I. Pretreatment The surfaces to be bonded of the weathering steel ingot and the stainless steel ingot are respectively milled as a whole until the oxide scale is completely removed, and then ground to make the roughness of the surfaces to be bonded 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 bonded are in contact with each other and the edges of the stainless steel billet and the weathering steel billet are strictly aligned, and the weathering steel billet and the stainless steel billet are fixed by a fixture positioning device to obtain a combined billet; III. Sealing The combined blank obtained in step II is transferred to a vacuum electron beam welding chamber and evacuated to a vacuum degree of ≤1.0×10 -2 Pa, edge-sealing welding of the bonded weathering steel ingot and stainless steel ingot is performed under the conditions of acceleration 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° to the side of the weathering steel ingot; after welding, the combined ingot is cooled to room temperature at a rate of 50±10°C / hour in a vacuum environment; IV. Hot rolling The sealed and welded combined 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 on the bottom, 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 combined billet is firstly subjected to multiple rough rolling and then to multiple finish rolling until the composite plate reaches the target thickness; Among them, the roll speed ratio between the lower roll and the upper roll of the roughing mill and the finishing mill is 1.03 to 1.05:1; The first pass reduction rate of the rough rolling is 8% to 15%, and the total reduction rate is 75% to 85%; the rolling speed of the finishing rolling is 4 to 6 m / s, the reduction rate of each pass is 20% to 25%, and the final rolling temperature is 850 to 950°C; V.Cooling and coiling process The composite plate steel strip obtained in step IV is naturally cooled to 600-670° C., and the composite plate is coiled 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 speed of 5-10° C. / min, kept warm for 10-20 minutes, then flattened into a steel plate, and cooled to room temperature along with the furnace to obtain a composite steel plate.

2. The preparation method according to claim 1, characterized in that: The thickness of the weathering steel ingot is 200-240 mm; Preferably, the weathering steel ingot is a weathering steel ingot with a grade of Q450NQR1 or Q550NQR1.

3. The preparation method according to claim 1 or 2, characterized in that: The thickness of the stainless steel billet is 10 to 30 mm; Preferably, the stainless steel billet is a ferritic stainless steel billet with a grade of T4003 or a duplex stainless steel billet with a grade of S32001.

4. The preparation method according to any one of claims 1 to 3, characterized in that In the step I, the roughness Ra of the surface to be bonded is 0.8-1.6 μm.

5. The preparation method according to claim 1, characterized in that: In the step III, a three-stage vacuum pump is used to evacuate the air; Preferably, in step III, the process conditions of vacuum electron beam welding are: acceleration voltage of 150 kV, beam current of 90-95 mA, and welding speed of 5 mm / s; Preferably, in step III, the vacuum electron beam welding penetration is ≥35 mm.

6. The preparation method according to claim 1 or 5, characterized in that: The step III also includes post-weld non-destructive testing, including using ultrasound or radiation to inspect the weld; if the weld has no defects and the penetration reaches the specified depth, then proceed to step IV; if the weld has defects or the penetration does not meet the standard, the composite steel billet is cut and separated and steps I to III are repeated until the post-weld non-destructive testing is qualified.

7. The preparation method according to claim 1, characterized in that: In step IV, when the assembled blank after sealing welding is heated, the time in the furnace is 1 min / mm; Preferably, in step IV, the target thickness of the composite plate after rolling is 5 to 10 mm.

8. A composite steel plate prepared by the preparation method according to any one of claims 1 to 7, comprising a weathering steel substrate layer and a stainless steel covering 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 covering layer is 10.8 to 11.2:1; preferably 11:

1.

9. The composite steel plate according to claim 8, characterized in that: The weathering steel substrate layer is formed by hot rolling weathering steel ingots with a grade of Q450NQR1 or Q550NQR1; Preferably, the stainless steel cladding layer is formed by hot rolling a ferritic stainless steel billet with a grade of T4003 or a duplex stainless steel billet with a grade of S32001.

10. Application of the composite steel plate according to claim 8 or 9 in railway freight open car bodies; wherein: The weathering steel substrate layer of the composite steel plate is formed by hot rolling weathering steel ingots with the grade of Q450NQR1 or Q550NQR1, and the stainless steel covering layer is formed by hot rolling ferritic stainless steel ingots with the grade of T4003 or duplex stainless steel ingots with the grade of S32001.

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