Bimetallic composite rail and preparation method thereof

Abstract

The invention discloses a bimetallic composite rail and a preparation method thereof. The invention comprises the following steps: assembling a steel round billet for a rail and a stainless steel seamless steel pipe and vacuum welding the billets to form a bimetallic round billet; rolling the bimetallic round billet into a bimetallic composite square billet; heating the bimetallic composite square billet in a temperature range of 1200° C. to 1240° C. for 0.5 to 1 hour, and then rolling the bimetallic composite square billet into a bimetallic composite rail; the BD1 rolling mill hole type selected for the rolling is a box hole; 8-9 rolling passes are set; and under the premise of ensuring that the rail can be bitten without falling off, the reduction amount of the first two passes is controlled within 10%; and under the premise of ensuring that H / B is less than 1.5, the reduction amount of the last 6 passes is controlled within 10 to 30%; and the composition of the rail coating is designed at the same time; and the problem that the existing bimetallic composite rolling process is not suitable for the rolling of the bimetallic composite rail due to the complex rail hole type, which is prone to multi-directional force deformation, is effectively solved.

Description

Technical Field

[0001] The invention relates to the field of railway rail products, and in particular to a production method of a bimetallic composite rail. Background Art

[0002] Through long-term service monitoring, it is found that the corrosion of railway rails will seriously affect the service life of rails. Therefore, many researchers and production units have carried out the development of composite rails, designed the coating composition and the preparation and rolling technology of matching composite materials, and are committed to improving the corrosion resistance of rails and extending the service life of rails.

[0003] However, during the research process, it was found that the rolling process is one of the key factors in the development of bimetallic composite rails. The original single metal material rolling process used in the experiment cannot guarantee the coordinated deformation of the bimetal, and problems such as ears and shelling occur frequently during the rolling process.

[0004] Attempts have also been made to roll bimetallic composite rails using a rolling method for rolling a bimetallic composite round billet into a square billet disclosed in CN 113695399 B. However, due to the difference in the required billet sizes, the disclosed patent is more suitable for rolling equilateral composite billets, while rolling rails requires 280mm*380mm composite billets. In the first step of preparing the billet, there are serious problems of ears and inverted squares, such as Figure 1 As shown in the figure, due to the complexity of the cross-sectional shape of the rail, the processing process uses multi-directional force deformation, which brings great difficulties to the composite rolling. Problems such as ears, squareness, and steel jamming frequently occur during the rolling process, so the public patent method is even less suitable for the design of the product rolling process; and the production using the public patent method has the problems of numerous process steps and slow production rhythm, which will also hinder its application in subsequent production. Therefore, it is necessary to develop a composite rolling process technology that is more suitable for the uneven deformation of rails to cope with the situation of multi-directional uneven force deformation.

[0005] The difference in the deformation characteristics of bimetallic materials is the difficulty in developing composite products. Figure 2 This is a stress column diagram of the two materials at different temperatures in the experiment. It can be seen that there is a large gap in the deformation resistance of the two materials, and there are large differences in the deformation characteristics of the two metal materials. In addition, the rolling of steel rails is different from that of composite steel plates. The hole shape is complex and deformation occurs in multiple directions. The primary issue in developing composite rails is to solve the rolling process of bimetallic materials. Summary of the invention

[0006] In view of this, the present invention provides a method for preparing a bimetallic composite rail to solve the problem that the rail is prone to multi-directional force deformation due to its complex hole shape, and the existing bimetallic composite rolling process is not suitable for rolling bimetallic composite rails. The composition of the coating is also designed to improve the corrosion resistance of the material to meet the use requirements.

[0007] In addition, the present disclosure also provides a bimetallic composite rail prepared by the above method.

[0008] In a first aspect, the method for preparing the bimetallic composite rail comprises assembling a steel round billet for the rail and a stainless steel seamless steel pipe and vacuum welding them to form a bimetallic round billet, and rolling the bimetallic round billet into a bimetallic composite square billet; wherein:

[0009] After heating the bimetallic composite square billet in a temperature range of 1200° C. to 1240° C. for 0.5 to 1 h, the bimetallic composite square billet is rolled into a bimetallic composite rail. The BD1 rolling mill pass selected for the rolling is a box-shaped hole. The parameters of the box-shaped hole are as follows:

[0010] Groove bottom width bk = B + (-5 ~ 5);

[0011] Notch width Bk = Δh*β+B+(7-15);

[0012] The slope of the hole side wall is tanψ = [Δh*β+(2-20)] / (H-Δh-s);

[0013] Groove bottom fillet radius r1 = (0.15 ~ 0.25) B;

[0014] The radius of the notch corner r2 = (0.12-0.15) B;

[0015] Roll gap height s = (0.01-0.2) D0;

[0016] Hole height h = H-Δh;

[0017] Groove depth hp = (hs) / 2;

[0018] Groove bottom convexity f = 0.02 ~ 0.04) B;

[0019] In the formula: B-incoming material width; H-incoming material height; Δh-pass reduction; β-width expansion coefficient; D0-nominal diameter of the roll.

[0020] Wherein: the first groove bottom width bk≥B+(1~5);

[0021] The rolling is set to be rolled for 8-9 passes. Under the premise of ensuring that the steel can be bitten without falling off, the reduction in the first two passes is controlled within 10%; the reduction in the subsequent passes is controlled to be 10-30% under the premise of ensuring H / B < 1.5; and air cooling is performed after rolling.

[0022] In the present disclosure and possible embodiments, the steel round billet adopts the rail material grade U71Mn or U75V, the stainless steel seamless pipe grade 03Cr24Ni8Mo3Cu2NbN, and the composition of the stainless steel seamless pipe is: C: 0.03-0.04, Si: 0.9-1.3, Mn: 1.4-1.6, Ni: 6.5-8.5, Cr: 22-25, Mo: 2.9-3.9, Cu: 2-2.5, Nb: 1-1.2, N: 0.1-0.25.

[0023] In the present disclosure and possible embodiments, the billet assembly is to use the steel round billet as the core and the stainless steel seamless steel pipe as the cladding;

[0024] The vacuum welding is carried out at a vacuum degree of less than 3*10 -2 Pa environment, welding the seal of the blank.

[0025] In the present disclosure and possible embodiments, before the square billet is rolled, the bimetallic round billet is heated in a temperature range of 1240°C to 1270°C for 7-8h; the opening temperature of the square billet is controlled at 1200°C to 1240°C, and the square billet is rolled for 9 to 13 passes until the composite square billet has a set specification, and the bimetallic composite square billet is obtained by air cooling.

[0026] In the present disclosure and possible embodiments, during the rolling process of the open square billet, non-hole rolling and box-type hole rolling are adopted, and the box-type hole rolling is adopted in the last 6 passes, and the hole parameters are as follows:

[0027] Groove bottom width bk = B + (2 to 8);

[0028] Notch width Bk = Δh*β / 2 + B + (1-5);

[0029] The slope of the hole side wall is tanψ = [Δh*β / 2+(-7~3)] / (H-Δh);

[0030] Groove bottom fillet radius r1 = (0.1 ~ 0.3) B;

[0031] The radius of the notch corner r2 = (0.05-0.2) B;

[0032] Roll gap height s = (0.02-0.05) D0;

[0033] Hole height h≤H-Δh;

[0034] Groove depth hp = (hs) / 2;

[0035] In the formula: B-incoming material width; H-incoming material height; Δh-pass reduction; β-width expansion coefficient; D0-nominal diameter of the roll.

[0036] In the present disclosure and possible embodiments, the square billet is rolled for 11 or 13 passes; h / b is controlled to be less than 1.6, the reduction in the first and second passes is controlled to be between 0 and 7%; the reduction in the third and fourth passes is controlled to be between 5 and 10%; the reduction in the fifth and sixth passes is controlled to be between 10-15%; and the reduction in subsequent passes is controlled to be between 5 and 20%.

[0037] In a second aspect, the bimetallic composite rail is prepared by the method described in the first aspect.

[0038] Beneficial effects of the present invention:

[0039] The method for preparing a bimetallic composite rail of the present invention designs process parameters such as box-shaped hole formation parameters, rolling passes and reduction amount of each pass based on the complex characteristics of the rail hole type, so it can effectively solve the existing bimetallic composite large round billet square billet rolling method for the rolling process of the bimetallic composite rail. Due to the complexity of the cross-sectional shape of the rail, the processing process utilizes multi-directional force deformation, which brings great difficulties to the composite rolling, resulting in difficult forming during the rolling process, poor composite effect, and frequent occurrence of ears, square inversion, steel jamming and other problems, thereby obtaining a bimetallic composite rail with good composite effect. Therefore, the bimetallic composite rail rolled by the method of the present invention not only has excellent corrosion resistance equivalent to that of the cladding 03Cr24Ni8Mo3Cu2NbN stainless steel, so as to solve the corrosion problem in transportation and use; the mechanical properties of the bimetallic composite rail are further improved due to the increase in the total reduction; in addition, the method of the present invention realizes integrated rolling from the combined billet to the composite rail, takes into account the reduction of process quantity and the reduction of cost, and can fully guarantee the composite quality of the composite product, thus providing a practical method for the rolling of the bimetallic composite rail. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The inverted square phenomenon occurs when the bimetallic composite square billet is rolled using the rolling process of the patent described in the background technology of the present invention;

[0041] Figure 2 Stress-strain curves of alloy steels and stainless steels;

[0042] Figure 3 This is a metallographic inspection diagram of the bimetallic rail according to Example 1 of the present invention. DETAILED DESCRIPTION

[0043] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts that are not described in detail, those skilled in the art can also fully understand the present disclosure.

[0044] At the same time, unless the context clearly requires otherwise, the words "include", "comprises" and similar words throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0045] Taking the design of a 50kg / m model rail as an example, the following Examples 1-8 and Comparative Examples 1-2 illustrate the preparation method of the corrosion-resistant bimetallic composite rail for sea transportation and long-term outdoor service provided by the present invention and the corresponding product effect. The specific steps are as follows:

[0046] 1. Design The cladding materials used in comparative examples 1-2 and embodiments 1-8 are all 03Cr24Ni8Mo3Cu2NbN stainless steel, and the inner core material is ordinary rail material U71Mn or U75V; the inner core material is ordinary rail material U71Mn or U75V.

[0047] The main process routes adopted in the design embodiments 1-8 are: raw material assembly and vacuum welding - billet rolling - composite rail rolling.

[0048] 2. The operation steps are as follows:

[0049] 1. Assembly and vacuum welding:

[0050] The core is made of U71Mn, U75V and other rail steel round billets, and the cladding is made of 03Cr24Ni8Mo3Cu2NbN stainless steel seamless steel pipe.

[0051] Through vacuum welding process, the vacuum degree is less than 3*10 -2 Pa environment, welding and sealing, to obtain a φ480mm bimetallic composite round billet, the coating thickness range is 28-31mm, the coating thickness is shown in Table 1:

[0052] Table 1 Rail coating thickness data of each embodiment and comparative example

[0053]

[0054] 2. Billet rolling:

[0055] The welded bimetallic composite round billet is sent into a heating furnace and heated in the range of 1240°C to 1270°C for 7-8h. The rolling temperature is controlled at 1200°C to 1240°C. The billet is rolled for 9 to 13 passes, preferably 11 or 13 passes. The billet is rolled into a composite square billet of 280mm*380mm.

[0056] In the process of rolling the square billet, non-hole rolling + box-type hole rolling is adopted, and the last 6 passes are box-type hole rolling. The hole parameters are as follows:

[0057] Groove bottom width bk = B + (2 to 8);

[0058] Notch width Bk = Δh*β / 2 + B + (1-5);

[0059] The slope of the hole side wall is tanψ = [Δh*β / 2+(-7~3)] / (H-Δh);

[0060] Groove bottom fillet radius r1 = (0.1 ~ 0.3) B;

[0061] The radius of the notch corner r2 = (0.05-0.2) B;

[0062] Roll gap height s = (0.02-0.05) D0;

[0063] Hole height h≤H-Δh;

[0064] Groove depth hp = (hs) / 2.

[0065] In the formula: b-billet width; B-incoming material width; H-incoming material height; Δh-pass reduction; β-width expansion coefficient; D0-nominal diameter of the roll.

[0066] To ensure smooth biting of the blank, it is necessary to ensure that h / b<1.6, the first and second pass reduction Δh are controlled at 0-7%; the third and fourth pass reduction is controlled at 5-10%; the fifth and sixth pass reduction is controlled at 10-15%; the subsequent pass reduction is controlled at 5-20%.

[0067] The implementation of bimetallic round bloom to square bloom rolling is shown in Table 2:

[0068] Table 2 Data of rolling reduction of billets in various embodiments and comparative examples (%)

[0069]

[0070]

[0071] 3. Composite rail rolling:

[0072] The bimetallic composite square billet is directly sent to a heating furnace for short-time reheating, specifically, heated at 1200°C to 1240°C for 0.5h, and the bimetallic composite rail is rolled at a temperature between 1190°C and 1220°C.

[0073] The design of the rail hole is particularly critical. The BD1 rolling mill hole is a box hole. The design parameters of the box hole are as follows:

[0074] Groove bottom width bk = B + (-5 ~ 5);

[0075] Notch width Bk = Δh*β+B+(7-15);

[0076] The slope of the hole side wall is tanψ = [Δh*β+(2-20)] / (H-Δh-s);

[0077] Groove bottom fillet radius r1 = (0.15 ~ 0.25) B;

[0078] The radius of the notch corner r2 = (0.12-0.15) B;

[0079] Roll gap height s = (0.01-0.2) D0;

[0080] Hole height h = H-Δh;

[0081] Groove depth hp = (hs) / 2;

[0082] Groove bottom convexity f = (0.02 ~ 0.04) B;

[0083] In the formula: b-billet width; B-incoming material width; H-incoming material height; Δh-pass reduction; β-width expansion coefficient; D0-nominal diameter of the roll.

[0084] Among them: the width of the first groove bottom bk≥B+(1~5).

[0085] Because BD (rail BD hole type) is the concentrated stage of uneven deformation of rail rolling, and BD1 rolling mill hole type is the key stage of coordinated deformation of bimetal. The deformation of bimetallic composite rail is more complicated than the deformation process of general composite plate. In order to ensure the coordinated deformation of bimetallic composite billet, BD1 is designed to roll 8-9 times. Under the premise of ensuring that it can bite without falling off, the reduction of the first two times is controlled within 10%, that is, micro-tension rolling, so that the bimetallic composite billet can be stably deformed under the appropriate hole type; the reduction of the last 6 times is increased under the condition of ensuring H / B <1.5, and controlled within 10-30%; air cooling after rolling.

[0086] The specific implementation of the bimetallic composite rail rolling process used in each of Examples 1-8 and Comparative Examples 1-2 of the present disclosure is shown in Table 3:

[0087] Table 3 Compression data of each embodiment and comparative example BD1 (%)

[0088]

[0089] Figure 3 This is a metallographic detection diagram of the bimetallic rail of Example 1 of the present invention. From this metallographic detection diagram, it can be seen that the bimetallic composite effect of the rail rolled in Example 1 is good.

[0090] 3. Comparative test of coating hardness

[0091] The coating compositions of five 03Cr24Ni8Mo3Cu2NbN stainless steels and the comparison steel are shown in Table 4:

[0092] Table 4 Coating composition

[0093]

[0094] The hardness test results of the five 03Cr24Ni8Mo3Cu2NbN stainless steels and the comparison steel in Table 4 above are shown in Table 5:

[0095] Table 5 Steel hardness test results

[0096] Sample number test Hardness HBW Contrast steel 187 Example 1 228 Example 2 211 Example 3 216 Example 4 215 Example 5 234

[0097] As shown in Table 4, in the design of the coating stainless steel composition, the embodiment of the present invention selects stainless steel with N addition, which not only improves the material strength and plasticity but also improves the work hardening orientation of the steel, and is friendly to the service process of the rail head arc area; the combination of N and Nb has a composite effect on improving pitting corrosion, so that the composite rail is not afraid of sea transportation during transportation, and is beautiful and corrosion-resistant, so as to achieve the corrosion resistance of the bimetallic composite rail. As shown in Table 5, the hardness is greatly improved, which is more suitable for the application environment of the rail.

[0098] The above-described embodiments are only embodiments of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the present disclosure. It should be noted that, for a person of ordinary skill in the art, without departing from the concept of the present disclosure, several variations, equivalent substitutions, improvements, etc. may be made, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure shall be subject to the attached claims.

Claims

1. A method for preparing a bimetallic composite rail, characterized in that: include: Assembling rail steel round billets and stainless steel seamless steel pipes and vacuum welding them to form bimetallic round billets, and rolling the bimetallic round billets into bimetallic composite square billets; After heating the bimetallic composite square billet in a temperature range of 1200° C. to 1240° C. for 0.5 to 1 h, the bimetallic composite square billet is rolled into a bimetallic composite rail. The BD1 rolling mill pass selected for rolling the composite square billet is a box-shaped hole. The parameters of the box-shaped hole are as follows: Groove bottom width bk = B + (-5 ~ 5); Notch width Bk = Δh*β+B+(7-15); The slope of the hole side wall is tanψ = [Δh*β+(2-20)] / (H-Δh-s); Groove bottom fillet radius r1 = (0.15 ~ 0.25) B; The radius of the notch corner r2 = (0.12-0.15) B; Roll gap height s = (0.01-0.2) D0; Hole height h = H-Δh; Groove depth hp = (hs) / 2; Groove bottom convexity f = (0.02 ~ 0.04) B; In the formula: B-incoming material width; H-incoming material height; Δh-pass reduction; β-width expansion coefficient; D0-nominal roll diameter, Wherein: the first groove bottom width bk≥B+(1~5); The composite square billet is rolled for 8-9 passes. Under the premise of ensuring that the billet can be bitten without falling off, the reduction in the first two passes is controlled within 10%; the subsequent passes are controlled to have a reduction of 10-30% under the premise of ensuring H / B < 1.5; and air cooling is performed after rolling.

2. The method for preparing a bimetallic composite rail according to claim 1, characterized in that: The steel round billet adopts the rail material grade U71Mn or U75V, the grade of the stainless steel seamless pipe is 03Cr24Ni8Mo3Cu2NbN, and the composition of the stainless steel seamless pipe is: C: 0.03-0.04, Si: 0.9-1.3, Mn: 1.4-1.6, Ni: 6.5-8.5, Cr: 22-25, Mo: 2.9-3.9, Cu: 2-2.5, Nb: 1-1.2, N: 0.1-0.

25.

3. The method for preparing a bimetallic composite rail according to claim 2, characterized in that: The billet assembly is to use the steel round billet as the core and the stainless steel seamless steel pipe as the cladding; The vacuum welding is carried out at a vacuum degree of less than 3*10 -2 Pa environment, welding the seal of the blank.

4. The method for preparing a bimetallic composite rail according to claim 3, characterized in that: Before the square billet rolling, the bimetallic round billet is heated in a temperature range of 1240°C to 1270°C for 7-8h; the opening rolling temperature of the square billet rolling is controlled at 1200°C to 1240°C, and the square billet rolling is performed for 9 to 13 passes until the composite square billet has a set specification, and the bimetallic composite square billet is obtained by air cooling.

5. The method for preparing a bimetallic composite rail according to claim 3, characterized in that: In the process of rolling the square billet, non-hole rolling and box-type hole rolling are adopted, and the box-type hole rolling is adopted in the last 6 passes, and the hole parameters are as follows: Groove bottom width bk = B + (2 to 8); Notch width Bk = Δh*β / 2 + B + (1-5); The slope of the hole side wall is tanψ = [Δh*β / 2+(-7~3)] / (H-Δh); Groove bottom fillet radius r1 = (0.1 ~ 0.3) B; The radius of the notch corner r2 = (0.05-0.2) B; Roll gap height s = (0.02-0.05) D0; Hole height h≤H-Δh; Groove depth hp = (hs) / 2; In the formula: B-incoming material width; H-incoming material height; Δh-pass reduction; β-width expansion coefficient; D0-nominal diameter of the roll.

6. The method for preparing a bimetallic composite rail according to claim 5, characterized in that: The square billet is rolled for 11 or 13 passes; h / b is controlled to be less than 1.6, the reduction in the first and second passes is controlled to be 0-7%; the reduction in the third and fourth passes is controlled to be 5-10%; the reduction in the fifth and sixth passes is controlled to be 10-15%; and the reduction in subsequent passes is controlled to be 5-20%.

7. A bimetallic composite rail, characterized in that: The preparation method thereof is: The method is prepared by any one of claims 1 to 6.

Images