Semi-coated bimetal composite steel rail and preparation method thereof

Abstract

The invention discloses a semi-coated bimetal composite steel rail and a preparation method thereof. A tread of the composite steel rail is made of a steel rail raw material, and a rail body and a rail bottom are coated with stainless steel; the composite steel rail is composed of a covering layer and an inner core. The coating layer is made of 304 stainless steel; the inner core is made of common steel rail materials. The tread is exposed by carbon steel, so that the hardness index of the steel rail tread can be ensured in the service process; normal abrasion of the steel rail tread is guaranteed, and the problem of rail head nuclear damage is avoided; repeated abrasion of the tread and wheels does not need corrosion resistance, and cost is reduced. The preparation method comprises the steps of bimetal raw material assembly, bimetal composite rolling, plasma cutting, composite hot rolling forming and the like, metallurgical compounding of stainless steel and carbon steel is achieved, the stainless steel coating can solve the problem of corrosion of the rail web and the rail bottom in transportation and use, and a good foundation can be laid for deep development of the bimetal composite steel rail in the future.

Description

Technical Field

[0001] The present invention belongs to the field of railway rail products, and relates to the preparation technology of bimetallic composite rails, specifically a semi-clad bimetallic composite rail and a preparation method thereof. Background Art

[0002] With the rapid development of the Chinese railway, the demand for rails is huge. During the process of transporting a large number of rails to all over the world by sea and long-term service, the corrosion problems of the rail waist and bottom have attracted people's attention. The corrosion of the rails not only affects the appearance but also seriously affects the service life of the rails. Therefore, a large number of researchers have carried out research on corrosion-resistant rails. However, while meeting the service performance of the rails, the corrosion-resistant effect achieved by simply adjusting the composition of the rails is very limited. Therefore, some researchers and production units have focused their research on the development of bimetallic composite rails.

[0003] The most critical problems in the research and development of bimetallic composite rails are as follows: In terms of the composite rolling process, at present, except for composite plates, large-scale trial production of composite materials has not been realized, especially for complex-section profiles with rails as the leading ones, and the preparation is difficult. The original single-metal material rolling process cannot meet the coordinated deformation of the bimetal, not only cannot achieve a good composite effect, but also generates ears during the BD1 rolling process, causing a series of problems such as shelling and steel jamming; solving this problem requires accumulating a large amount of bimetal rolling experience and designing a suitable rolling process and pass. In terms of the practicality of the product, the generally defined fully clad material products do not conform to the use characteristics of rail products. The characteristics of the stainless steel tread cannot guarantee the application requirements of the rails, and the application technology has not been developed maturely. Therefore, the feasibility of the generally defined fully clad bimetallic composite rail products is relatively low.

[0004] At present, there is little research on the development of composite steel rails, and there are many technical problems. For example, Patent CN117161702A, "A Bimetallic Composite Steel Rail and Its Preparation Method", designs a bimetallic composite rolling method of round billet + rolled square billet, using the composite square billet to roll the steel rail, which solves the influence of multi-directional stress in the profile rolling process on bimetallic rolling. However, the product preparation cost is relatively high, and the stainless steel cladding has inferior service performance compared to the original composition of the steel rail during use, so its practicability is poor. Patent CN202164509U, "Epoxy Resin Composite Steel Rail", prevents the steel rail from corrosion by coating an epoxy resin coating on the outer periphery of the steel rail, with low cost, but it is not environmentally friendly. Moreover, the intermittent vibration during the use of the steel rail will cause the epoxy resin to crack and fall off, and it needs to be peeled off and re-coated in time, so its practicability is not high. Patent CN112275799A, "Steel-Aluminum Bimetallic Rolling Composite Method with Inlaid Groove Interlocking", uses the interlocking principle to ingeniously design and process the steel plate to be rolled to obtain inlaid grooves, and uses the aluminum plate as the inlay to achieve the interlocking effect for rolling. However, this invention has high requirements for the processing accuracy of materials, and this method is only suitable for rolling composite plate materials with simple structures and is not applicable to the rolling of composite steel rails. Patent CN100553811C, "Semi-Solid Copper-Lead Bearing Alloy / Steel Bimetallic Rolling Composite Process", provides a method of casting a semi-solid alloy on a preheated steel plate and sending it into a rolling mill for rolling and compounding. This method is relatively complex in operation and is only applicable to the rolling of composite plates. Summary of the Invention

[0005] In order to overcome the defects existing in the above-mentioned prior art, the purpose of the present invention is to provide a semi-clad bimetallic composite steel rail and its preparation method that conforms to the use characteristics of steel rails. According to the use characteristics of steel rails, its lower jaw, web, and bottom are covered with stainless steel cladding, and the tread is exposed to the original material of the steel rail. The production process of the composite steel rail is designed, and combined with a suitable rolling process and pass design, the bimetallic is coordinated to deform to an intermediate billet, and the finished product is rolled using this intermediate billet. This technical solution is of great significance for the development and subsequent research of composite steel rails. By combining the existing production line equipment to prepare bimetallic composite steel rails, composite steel rail products with lower production costs and better composite effects can be obtained, which can lay a good foundation for the development and preparation of bimetallic composite steel rails in the future.

[0006] To achieve the above-mentioned invention purpose, the present invention provides a semi-clad bimetallic composite steel rail. The tread of the composite steel rail is the original material of the steel rail, and the rail body and the rail bottom are covered with stainless steel. The composite steel rail consists of a cladding and a core.

[0007] Furthermore, the material of the tread of the composite steel rail is the exposed core material, and the cladding is a stainless steel layer coated on the outside of the core at the rail body and the rail bottom.

[0008] Furthermore, the material of the cladding is stainless steel, preferably 304 stainless steel; the inner core is made of ordinary rail material, preferably rail grades such as U71Mn and U75V.

[0009] A preparation method of the above semi-clad bimetallic composite rail, the method comprising the following steps:

[0010] ① Bimetallic raw material blanking: The inner core rail steel round blank and the cladding stainless steel seamless steel pipe are used to obtain a composite large round blank through a vacuum welding process.

[0011] Furthermore, in the vacuum welding process, the welding is sealed in an environment with a vacuum degree less than 1×10 -2 Pa. The diameter range of the composite large round blank is φ500 - φ550mm, and the cladding thickness range is 20 - 25mm.

[0012] ② Bimetallic composite rolling: The bimetallic composite large round blank welded in step ① is sent into a heating furnace and heated in the range of 1220°C - 1260°C for 7 - 9 hours. Among them, the preheating temperature is 800°C - 900°C, the preheating time is 1 - 2.5 hours, the starting rolling temperature is controlled at 1200°C - 1240°C, and square blank rolling is carried out until a (200 - 240)mm*(460 - 500)mm composite square blank is obtained, and the final rolling temperature is 900°C - 950°C.

[0013] In the above technical solution, furthermore, during the bloom rolling process, a rolling method of 2 passes without pass + 12 passes of box pass is adopted, and the box pass parameters are as follows:

[0014] The bottom width of the groove bk = B + (-3 - 5);

[0015] The width of the groove opening Bk = Δh*β + B + (8 - 12);

[0016] The slope of the side wall of the pass tanψ = [Δh*β + (3 - 15)] / 2hp;

[0017] The height of the pass h = H - Δh;

[0018] The roll gap s = (0.02 - 0.05)D0;

[0019] The depth of the rolling groove hp = (h - s) / 2;

[0020] The radius of the bottom fillet of the groove r1 = (0.15 - 0.3)B;

[0021] The radius of the groove opening fillet r2 = (0.1 - 0.2)B;

[0022] In the above formula: B - incoming material width / mm; H - incoming material height / mm; Δh - reduction per pass / mm; β - spread coefficient / mm; D0 - nominal roll diameter / mm.

[0023] Furthermore, the pass rolling is divided into 14 passes; to ensure the smooth biting of the billet, it is necessary to ensure that h / b < 1.4; the first pass is skipped, and the reduction in the second pass is controlled within 3% - 5%; the reduction in the third and fourth passes is 5% - 6%; the reduction starts to increase from the fifth pass, with the reduction being 7% - 10%; the reduction after the sixth pass is 10% - 15%, and the reduction in the last pass is adjusted according to different process parameter designs. The steel is flipped every 2 passes, and the number of flipping times is 4 - 6 times. There is no further flipping until the desired specification is rolled.

[0024] ③ Plasma cutting: Using plasma cutting on the slow cooling bed, the composite billet (such as 220mm * 480mm) obtained in step ② is evenly cut into 2 composite billets (i.e., 220mm * 240mm), and directly hot charged and hot sent to the heating furnace for heating for 0.5 - 1.5h in the temperature range of 1160℃ - 1200℃.

[0025] ④ Composite hot rolling forming: The discharged composite billet directly enters BD2 rolling, with the carbon steel side being the rail head side for rolling, and finally a composite rail with a carbon steel rail head tread and a stainless steel cladding on the rail web and bottom is obtained; after rolling, it is air - cooled.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] ① The present invention designs a semi - clad bimetallic composite rail, with the tread being exposed carbon steel. First, during service, it can ensure the hardness index of the rail tread; second, it can ensure the normal wear of the rail tread to avoid the problem of head nuclear damage; third, since the tread does not need corrosion resistance during repeated wear with the wheels, the cost is reduced.

[0028] ② Since the heating time of the carbon steel exposed side in the second stage is reduced, the decarburization of the tread will be significantly reduced, and the tread hardness will be further improved compared to ordinary rails.

[0029] ③ Through reasonable process and process design, this technical solution combines the existing production line equipment to prepare bimetallic composite rails, obtaining composite rail products with lower production costs and better composite effects, realizing the metallurgical composite of stainless steel and carbon steel. The stainless steel cladding can solve the corrosion problems of the rail web and bottom during transportation and use, laying a good foundation for the further development of bimetallic composite rails in the future. Brief Description of the Drawings

[0030] Figure 1 It is a schematic diagram of the bimetallic semi - clad composite rail of the present invention;

[0031] Figure 2Microstructure diagram of the semi-coated bimetallic composite rail obtained in Example 1. Detailed implementation manners

[0032] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way. To avoid redundancy, in the following embodiments, the raw materials are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0033] A semi-coated bimetallic composite rail, the tread of the composite rail is the original material of the rail, and the rail body and the rail bottom are coated with stainless steel; the composite rail is composed of a cladding layer and a core; the tread material of the composite rail is the exposed core material, and the cladding layer is a stainless steel layer coated on the outside of the core at the rail body and the rail bottom; as shown in the attached Figure 1 figure. The material of the cladding layer is 304 stainless steel; the core is ordinary rail material, and the rail grades are U71Mn and U75V.

[0034] A preparation method for the above-mentioned semi-coated bimetallic composite rail, the method comprises the following steps:

[0035] ① Billet assembling of bimetallic raw materials: Obtain a composite large billet by vacuum welding a steel round billet for the core rail and a seamless stainless steel pipe for the cladding;

[0036] ② Bimetallic composite rolling: Heat the bimetallic composite large billet welded in step ① in the range of 1220 °C to 1260 °C for 7 to 9 hours; then perform bloom rolling to roll it into a composite bloom of (200 - 240) mm * (460 - 500) mm; during the bloom rolling process, adopt the rolling method of no pass in the first 2 passes + box pass in 3 - 9 passes;

[0037] ③ Plasma cutting: Cut the composite bloom obtained in step ② (such as 220 mm * 480 mm) into 2 pieces of composite blooms (i.e., 220 mm * 240 mm) on average, directly hot charge and hot transfer them to a heating furnace, and heat them in the temperature range of 1160 °C to 1200 °C for 0.5 to 1.5 hours;

[0038] ④ Composite hot rolling forming: The composite bloom taken out of the furnace directly enters BD2 rolling, and the carbon steel side is the rail head side for rolling, and finally a composite rail with a carbon steel rail head tread and a stainless steel cladding layer on the rail waist and the bottom is obtained; air cooling after rolling.

[0039] For the parts not described in the following embodiments, they are the same as the description content of the above detailed implementation manners.

[0040] Embodiment

[0041] A semi-clad bimetallic composite steel rail. The composite steel rail consists of a clad layer and a core. The tread material of the composite steel rail is the exposed core material, and the clad layer is a stainless steel layer wrapped around the outside of the core at the rail body and rail base. Taking the 50 kg / m type steel rail as an example for design, the core is made of ordinary steel rail materials of grades U71Mn and U75V, and the clad layer material is 304 stainless steel; the schematic diagram of this bimetallic semi-clad composite steel rail is as shown in Figure 1 shown below.

[0042] A preparation method for a semi-clad bimetallic composite steel rail, the method comprising the following steps:

[0043] ① Billet assembly of bimetallic raw materials: Obtain a composite large billet by vacuum welding a steel round billet for the core steel rail and a seamless stainless steel tube for the clad layer; the vacuum welding process is to weld and seal in an environment with a vacuum degree less than 1×10 -2 Pa. The diameter range of the composite large billet is φ500 - φ550 mm, and the clad layer thickness range is 20 - 25 mm.

[0044] ② Bimetallic composite rolling: Heat the bimetallic composite large billet welded in step ① in the range of 1220°C - 1260°C for 7 - 9 hours; then perform square billet rolling, and the starting rolling temperature of the rolling is controlled at 1200°C - 1240°C, and the final rolling temperature is controlled at 900°C - 950°C; roll it into a 220 mm * 480 mm composite square billet; during the bloom rolling process, adopt the rolling method of the first 2 passes without pass + 12 passes of box pass.

[0045] The calculation of the box pass parameters is as follows:

[0046] The bottom width of the groove bk = B + (-3 to 5);

[0047] The width of the groove opening Bk = Δh * β + B + (8 to 12);

[0048] The slope of the side wall of the pass tanψ = [Δh * β + (3 to 15)] / 2hp;

[0049] The height of the pass h = H - Δh;

[0050] The roll gap s = (0.02 to 0.05)D0;

[0051] The depth of the rolling groove hp = (h - s) / 2;

[0052] The radius of the bottom fillet of the groove r1 = (0.15 to 0.3)B;

[0053] The radius of the groove opening fillet r2 = (0.1 to 0.2)B;

[0054] In the above formula: B - incoming material width; H - incoming material height; Δh - reduction per pass; β - spread coefficient; D0 - nominal roll diameter. When the double-metal large round billet is φ510mm, the reduction is taken as 40mm. After the first two passes of rolling and turning the billet over, the width B = 475mm, the height H = 550mm, and D0 = 7000mm; then the bottom width of the groove bk = B + (-3 to 5) = 475mm + (-3 to 5), taking 480mm; the width of the groove opening Bk = Δh * β + B + (8 to 12) = 40 * 0.5 + 475 + (8 to 12), taking 505mm; the height of the pass h = H - Δh = 550mm - 40mm = 510mm; the roll gap s = (0.02 to 0.05), taking D0 as 350mm, the depth of the rolling groove hp = (h - s) / 2 = (510mm - 350mm) / 2 = 80mm; the slope of the pass sidewall tanψ = [Δh * β + (3 to 15)] / 2hp = [40 * 0.5 + (3 to 15)] / 160, taking 3 / 16; the radius of the bottom fillet of the groove r1 = (0.15 to 0.3)B, taking 100mm; the radius of the fillet at the groove opening r2 = (0.1 to 0.2)B = 90mm.

[0055] The rolling described in step ② is divided into 9 passes, and it is ensured that h / b < 1.4; the first pass is skipped, the reduction in the second pass is 3% to 5%, the reduction in the third and fourth passes is 5% to 6%, the reduction in the fifth pass is 7% to 10%, the reduction after the sixth pass is 10% to 15%, and the reduction in the last pass is adjusted according to different process parameter designs; the billet is turned over once every 2 passes, and the number of times of turning the billet over is 5 times.

[0056] ③ Plasma cutting: Cut the 220mm * 480mm composite billet into 2 pieces of 220mm * 240mm composite billets, and directly hot charge and hot transfer them into the heating furnace, and heat them in the temperature range of 1160°C to 1200°C for 1h;

[0057] ④ Composite hot rolling forming: The composite billet out of the furnace directly enters BD2 rolling, and the carbon steel side is the rail head side for rolling, and finally a composite rail with the rail head tread being carbon steel and the rail web and bottom being stainless steel cladding is obtained; after rolling, it is air-cooled.

[0058] The microstructural diagram of the semi-clad double-metal composite rail prepared in Example 1 is as Figure 2 shown, and it can be seen from Figure 2 that the composite situation is good.

[0059] Table 1 Reduction data of blooming rolling %

[0060]

[0061] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible variations and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or it can be modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A semi-clad bimetallic composite rail, characterized in that: The composite rail is composed of an inner core and a cladding; the tread material of the composite rail is the exposed inner core material, and the cladding is a stainless steel layer covering the outer side of the inner core at the rail body and the rail bottom.

2. The composite rail according to claim 1, characterized in that: The material of the cladding is 304 stainless steel; the inner core is made of U71Mn and U75V grade rail material.

3. A method for preparing a semi-clad bimetallic composite rail as claimed in claim 1, characterized in that: The method comprises the following steps: ① Bimetallic raw material assembly: The inner core rail steel round billet and the cladding stainless steel seamless steel pipe are vacuum welded to obtain a composite large round billet; ② Bimetallic composite rolling: The bimetallic composite round billet welded in step ① is heated in the range of 1220℃~1260℃ for 7~9h; then the billet is rolled to a composite square billet of (200~240)mm*(460~500)mm; during the billet rolling process, the first 2 passes of non-hole type + 12 passes of box-type hole rolling are adopted; ③ Plasma cutting: the composite billet obtained in step ② is evenly cut into 2 composite billets, which are directly hot-charged and hot-sent to a heating furnace, and heated at a temperature range of 1160° C. to 1200° C. for 0.5 to 1.5 h; ④ Composite hot rolling forming: The composite billet is directly rolled into BD2, and the carbon steel side is rolled as the rail head side. Finally, a composite rail with carbon steel rail head tread and stainless steel cladding on rail waist and bottom is obtained; air cooling after rolling.

4. The preparation method according to claim 3, characterized in that: Step ① The vacuum welding process is carried out at a vacuum degree of less than 1×10 -2 Pa environment welding seal.

5. The preparation method according to claim 3, characterized in that: In step ①, the diameter of the composite large round billet is in the range of φ500 to φ550 mm, and the thickness of the coating is in the range of 20 to 25 mm.

6. The preparation method according to claim 3, characterized in that: In step ②, the starting rolling temperature is controlled at 1200°C to 1240°C, and the final rolling temperature is controlled at 900°C to 950°C.

7. The preparation method according to claim 3, characterized in that: Step ② The box hole parameters are as follows: Groove bottom width bk = B + (-3 ~ 5); Notch width Bk = Δh*β+B+(8-12); The slope of the hole side wall is tanψ = [Δh*β+(3-15)] / 2hp; Hole height h = H-Δh; Roll gap s = (0.02 ~ 0.05) D0; Groove depth hp = (hs) / 2; Groove bottom fillet radius r1 = (0.15 ~ 0.3) B; The radius of the notch corner r2 = (0.1-0.2) B; In the above formula: B is the width of the incoming material; H is the height of the incoming material; Δh is the amount of reduction per pass; β is the expansion coefficient; D0 is the nominal diameter of the roll.

8. The preparation method according to claim 3, characterized in that: The rolling in step ② is divided into 9 passes, and it is ensured that h / b<1.4; the first pass is empty, the second pass has a reduction of 3% to 5%, the third and fourth passes have a reduction of 5% to 6%, the fifth pass has a reduction of 5% to 10%, and the reduction of the passes after the sixth pass is controlled at 10% to 15%, and the reduction of the last pass is adjusted according to the different process parameter designs; the steel is turned once every 2 passes, and the number of steel turnings is 4 to 6 times.

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