A rolling method for easily welded U71Mn high-speed rail

Abstract

The invention discloses a rolling method for an easy-to-weld U71Mn high-speed rail, and belongs to the technical field of metallurgical materials. The rolling method for an easy-to-weld U71Mn high-speed rail provided by the invention can ensure that the obtained high-speed rail has good welding performance by adopting a larger cooling bed step in the rolling process, and the high-speed rail welding drop hammer qualified rate is significantly improved, and the average gray spot area of ​​the fracture is significantly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a rolling method for an easy-to-weld U71Mn high-speed rail. Background Art

[0002] Rail welding is the foundation of seamless lines. Welded joints are the concentrated areas where stress is generated and are also the weakest parts of rail welding. Welding quality is the key to ensuring the normal operation of seamless lines. The commonly used rail welding methods at home and abroad are flash welding, gas pressure welding, aluminothermic welding and arc welding. According to statistics, flash welded joints account for about 90% of the total number of joints in my country's seamless lines. my country's railway rail factory welding uses flash welding and requires post-weld heat treatment. Rail welded joints are the weak link in the line. Therefore, one of the keys to improving rail performance is to improve the performance of welded joints and ensure the quality of rail welding, which is of great significance to the safe operation of railways. Rails with poor weldability reduce the running speed, running stability and running safety of trains, and damage the running quality of trains.

[0003] At present, my country's high-speed railway rails are mainly U71MnG and U75VG. U71MnG has the advantages of high strength, toughness and fatigue resistance, and is widely used in my country's high-speed railways. However, with the increase in usage, many problems have gradually been found: U71Mn has poor weldability and is not easy to weld. For example, due to the high Mn element in U71Mn rails and the presence of many MnS inclusions in the parent material, stress concentration will occur around the inclusions when the rail is under load, and cracks will occur when the stress exceeds the adjacent stress peak; U71Mn rails have a higher frequency of gray spots and drop hammer test failures in welded joints compared to U75V, which reduces the mechanical properties of welded joints; when gray spots appear at the bottom corner edge of the rail, the strength and toughness of the weld will be greatly reduced, and the rail is prone to fatigue fracture under the action of alternating stress; therefore, the welding quality of U71Mn high-speed rails is seriously affected, and segregation is prone to occur. Summary of the invention

[0004] In view of the above problems, the present invention provides a rolling method for an easily weldable U71Mn high-speed rail, which can ensure that the obtained easily weldable high-speed rail has good welding performance by adopting a larger cooling bed step in the rolling process.

[0005] In one aspect of the present invention, a rolling method for an easy-to-weld U71Mn high-speed rail is provided, which comprises the following processes: continuous casting billet heating - universal rolling mill rolling - cooling bed cooling pre-bending - straightening; wherein:

[0006] In the continuous casting billet heating process, the total heating time is ≥3 hours, the soaking temperature is 1120-1280°C, the heating stage II temperature is 1220-1290°C, the heating stage I temperature is ≤1200°C, and the preheating stage temperature is ≤800°C;

[0007] In the universal rolling mill rolling process, the starting rolling temperature is controlled at 1020°C to 1120°C, and the final rolling temperature is ≤915°C;

[0008] In the cooling bed cooling pre-bending process, the cooling bed step distance is increased from 350mm to 500mm;

[0009] In the straightening process, the straightening temperature shall not exceed 60°C;

[0010] The continuous casting billet comprises the following chemical components in terms of mass percentage: C 0.65-0.73; Si 0.35-0.55; Mn 0.80-0.90; P≤0.020; S≤0.006, and the rest are Fe and unavoidable impurities.

[0011] In the above rolling method, the continuous casting billet includes the following chemical components in terms of mass percentage: C 0.67-0.70; Si 0.37-0.45; Mn 0.85-0.88; P≤0.014; S≤0.005, and the rest is Fe and unavoidable impurities.

[0012] Another aspect of the present invention provides an easily weldable U71Mn high-speed rail, which is obtained by rolling using the above-mentioned rolling method.

[0013] The weld drop hammer pass rate of the above-mentioned easy-to-weld U71Mn high-speed rail is over 97%, and the gray spot area of ​​the rail fracture is 4.16 / mm 2 the following.

[0014] The rolling method of the easy-to-weld U71Mn high-speed rail provided by the above technical solution can ensure that the obtained high-speed rail has good mechanical properties such as strength and hardness while having good welding performance by adopting a larger cooling bed step in the rolling process, so that the welding drop hammer qualification rate of the high-speed rail is increased from 92% to more than 97%, and the gray spot area of ​​the rail fracture is small, and the average gray spot area of ​​the fracture is reduced from 13.35 / mm 2 Reduced to 4.16 / mm 2 The following improves the welding performance of high-speed rails (such as U71Mn) as a whole, is suitable for large-scale production, and has good promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the location of gray spots on rail fracture. DETAILED DESCRIPTION

[0016] The present invention aims to provide a rolling method for an easily weldable U71Mn high-speed steel rail, and thereby provides an easily weldable U71Mn high-speed steel rail.

[0017] The rolling method of the easy-to-weld U71Mn high-speed rail provided by the present invention comprises the following processes: continuous casting billet heating - universal rolling mill rolling - cooling bed cooling pre-bending - straightening; wherein:

[0018] In the continuous casting billet heating process, the total heating time is ≥3 hours, the soaking temperature is 1120-1280°C, the heating stage II temperature is 1220-1290°C, the heating stage I temperature is ≤1200°C, and the preheating stage temperature is ≤800°C;

[0019] In the universal rolling mill rolling process, the starting rolling temperature is controlled at 1020°C to 1120°C, and the final rolling temperature is ≤915°C;

[0020] In the cooling bed cooling pre-bending process, the cooling bed step distance is increased from 350mm to 500mm;

[0021] In the straightening process, the straightening temperature shall not exceed 60°C;

[0022] The continuous casting billet includes the following chemical components by mass percentage: C 0.65-0.73; Si 0.35-0.55; Mn 0.80-0.90; P≤0.020; S≤0.006, and the rest is Fe and inevitable impurities. The continuous casting billet can be obtained according to the production process of the traditional U71Mn rail, which includes: molten iron pretreatment → converter smelting → LF refining → VD vacuum degassing → continuous casting.

[0023] Based on the above rolling method, an easy-to-weld U71Mn high-speed rail can be obtained, which may include the following chemical components in terms of mass percentage: C 0.65-0.73; Si 0.35-0.55; Mn 0.80-0.90; P≤0.020; S≤0.006, with the remainder being Fe and inevitable impurities; preferably, it may include the following chemical components: C 0.67-0.70; Si 0.37-0.45; Mn0.85-0.88; P≤0.014; S≤0.005, with the remainder being Fe and inevitable impurities. The weld drop hammer qualified rate of the easy-to-weld U71Mn high-speed rail reaches more than 97%, the gray spot area of ​​the rail fracture is small, and the average gray spot area of ​​the fracture can reach 4.16 / mm 2 the following.

[0024] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0025] Example 1

[0026] The following steps are followed in sequence: molten iron pretreatment - converter smelting - LF refining - VD vacuum degassing - continuous casting (wherein the converter smelting adopts aluminum-free deoxidation alloying, and the whole process is hydrogen blowing according to normal refining; vacuum degree ≤ 0.10 KPa, deep vacuum time ≥ 15 min, superheat △ T ≤ 30 ° C), to produce a continuous casting billet of U71Mn rail. The chemical composition and content of the continuous casting billet are shown in Table 1 below.

[0027] The continuous casting billet produced is rolled according to the following process to obtain U71Mn rails: continuous casting billet heating - high-pressure water descaling - universal rolling mill rolling - cooling bed cooling pre-bending - straightening - flaw detection - processing - inspection and storage; wherein:

[0028] In the continuous casting billet heating process, the total heating time is ≥3 hours, the soaking temperature is 1120-1280°C, the heating stage II temperature is 1220-1290°C, the heating stage I temperature is ≤1200°C, and the preheating stage temperature is ≤800°C;

[0029] In the universal rolling mill rolling process, the starting rolling temperature is controlled at 1120°C and the final rolling temperature is 915°C;

[0030] In the cooling bed cooling pre-bending process, the cooling bed step distance is 500mm;

[0031] In the straightening process, the straightening temperature shall not exceed 60°C.

[0032] The mechanical properties of the U71Mn rail obtained by rolling were tested, and the results are shown in Table 2 below.

[0033] Example 2-3

[0034] Example 2-3 is carried out according to the operation of Example 1, except that: 1) the chemical composition content of the continuous casting billet of Example 2-3 is different from that of Example 1, as shown in Table 1 below; 2) the start rolling temperature and the final rolling temperature in the rolling process of the universal rolling mill are different, specifically: the start rolling temperature in Example 2 is controlled at 1060°C and the final rolling temperature is 900°C; the start rolling temperature in Example 3 is controlled at 1000°C and the final rolling temperature is 885°C. The mechanical properties of the U71Mn rail obtained by rolling in Example 2-3 are tested, and the results are shown in Table 2 below.

[0035] The non-metallic inclusions of the steel rails obtained by rolling in Examples 1-3 were inspected, and the results are shown in Table 3 below; the steel rails obtained by rolling in Examples 1-3 were subjected to a fixed flash welding test using a GAAS80 welding machine, and static bending (static bending requirements: maximum static bending force ≥ 1300KN, 1 time without interruption), drop hammer performance test (wherein the 467 steel rails subjected to the drop hammer performance test include: 155 rails rolled in Example 1, 155 rails rolled in Example 2, and 157 rails rolled in Example 3), and statistical analysis of the gray spot area at the rail port was performed, wherein Figure 1 The positions of the gray spots on the fracture are shown, and the results are shown in Tables 4, 5 and 6 below respectively.

[0036] Comparative Example 1

[0037] Comparative Example 1 was carried out in accordance with the operation of Example 1, except that in the cooling bed cooling pre-bending process of Comparative Example 1, the cooling bed step was 350 mm. The rails obtained by rolling in Comparative Example 1 were subjected to a drop weight performance test, and the gray spot area at the end thereof was statistically analyzed, and the results are shown in Tables 5 and 6 below, respectively.

[0038] Table 1: Chemical composition and content (%) of each embodiment and comparative example

[0039]

[0040] Table 2: Mechanical properties of the rails obtained by rolling in Examples 1-3

[0041]

[0042] Table 3: Test results of non-metallic inclusions in the rails produced in Examples 1-3

[0043]

[0044] Table 4: Static bending test results of the rails produced in Examples 1-3

[0045]

[0046] Table 5: Drop weight performance test results of the rails produced in the examples and comparative examples

[0047]

[0048] Table 6: Gray spot area of ​​the rail fracture of each embodiment and comparative example

[0049]

[0050]

[0051] It can be seen from the results recorded in Tables 2-5 above that the rails produced in each embodiment have good strength and hardness mechanical properties, and the static bending performance fully meets the standard. Compared with Comparative Example 1, the welding drop hammer qualified rate of the high-speed rails produced in the embodiment is higher, from 92% to more than 97%, and the gray spot area of ​​the rail fracture is smaller, and the average gray spot area of ​​the fracture is increased from 13.35 / mm 2 Reduced to 4.16 / mm 2 Compared with the original, it is reduced by about 69%, and the metallographic structure of the rail is normal without abnormal structures such as martensite. The welding performance is significantly improved, which has good promotion value.

[0052] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A rolling method for an easy-to-weld U71Mn high-speed rail, comprising the following processes: continuous casting billet heating - universal rolling mill rolling - cooling bed cooling pre-bending - straightening; wherein: In the continuous casting billet heating process, the total heating time is ≥3 hours, the soaking temperature is 1120-1280°C, the heating stage II temperature is 1220-1290°C, the heating stage I temperature is ≤1200°C, and the preheating stage temperature is ≤800°C; In the universal rolling mill rolling process, the starting rolling temperature is controlled at 1020°C to 1120°C, and the final rolling temperature is ≤915°C; In the cooling bed cooling pre-bending process, the cooling bed step distance is increased from 350mm to 500mm; In the straightening process, the straightening temperature shall not exceed 60°C; The continuous casting billet comprises the following chemical components in terms of mass percentage: C 0.65-0.73; Si 0.35-0.55; Mn 0.80-0.90; P≤0.020; S≤0.006, and the rest are Fe and unavoidable impurities.

2. The rolling method according to claim 1, wherein the continuous casting billet comprises the following chemical components in terms of mass percentage: C 0.67-0.70; Si 0.37-0.45; Mn 0.85-0.88; P≤0.014; S≤0.005, and the rest is Fe and unavoidable impurities.

3. An easily weldable U71Mn high-speed rail, obtained by rolling by the rolling method according to claim 1 or 2.

4. The easy-to-weld U71Mn high-speed rail according to claim 3 has a welding drop hammer pass rate of more than 97% and a gray spot area of ​​4.16 / mm2 on the rail fracture. 2 the following.

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