Rare earth high-strength heat treatment steel rail thermit welding flux and welding method

Abstract

The invention discloses a rare earth high-strength heat treatment steel rail thermit welding flux and a welding method thereof, and belongs to the technical field of steel rail welding. The core components of the hot welding flux comprise, by mass, 16-20% of aluminum powder with the purity being larger than or equal to 99.0% and the proportion being 16-20%; ferric oxide, which accounts for 50-70%; the proportion of the iron pellets is 10 to 20 percent; ferromanganese, the ratio of which is 0.8 to 1.2 percent; ferrosilicon, which accounts for 0.7 to 1.2%; carbon, which accounts for 0.5 to 1.5%; the proportion of the ferrochrome is 0.50 to 0.90 percent; ferrovanadium, the proportion of which is 0.10 to 0.25 percent; la iron, Ce iron or La and Ce mixed rare earth iron alloy: the content of rare earth elements in the rare earth alloy is greater than or equal to 20%, the rare earth elements account for 0.010-0.050%, and the balance is inevitable impurities. By designing reasonable flux components and a welding process, the structure and grain size of a joint are improved, and the strength and toughness of the joint are further improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of rail welding, and particularly relates to a rare earth high-strength heat-treated rail aluminothermic flux and a welding method. BACKGROUND

[0002] Rail welding is the key and premise for the wide application of seamless lines, and the quality, performance and service state of the welded joint directly affect the application of the rail and the safety of the line. If the weld metal cannot be well fused with the parent rail, the performance such as the strength and hardness of the welded joint cannot meet the requirements, which brings potential safety hazards to the operation of the train. At present, the main analysis of rail welding is flash welding, aluminothermic welding and pressure welding. Aluminothermic welding relies on the aluminothermic reaction of aluminum and iron oxide to generate a large amount of heat, generate iron and aluminum oxide, obtain molten steel, and cast the weld. Aluminothermic welding has the characteristics of simple equipment, low cost, short process, high efficiency and stable quality, and is suitable for on-site mobile operation, on-line repair of broken rails and turnout welding. Aluminothermic welding can realize simultaneous operation and occupies small operation space, and has been widely applied in seamless rail welding.

[0003] The selection of aluminothermic flux and the selection of welding process are the main reasons affecting the quality of the rail welded joint. The composition and microstructure of the weld metal obtained under different welding materials and welding process conditions are different, and the macroscopic performance is the difference of the mechanical properties of the weld. If the joint performance obtained by aluminothermic welding is greatly different from the parent material, uneven wear and joint damage will occur at the joint, which seriously affects the service of the joint and the safety of the seamless line. Therefore, the ideal weld should have similar chemical composition, similar microstructure and similar mechanical properties to the parent material.

[0004] The rare earth high-strength heat-treated rail takes C, Si, Mn and Cr as the main elements, increases V, RE and other micro-alloying elements, and goes through production processes such as controlled rolling and online heat treatment, so as to have the characteristics of high strength and high hardness, and can meet the application of heavy haul railway. Due to the high carbon content and carbon equivalent of the rare earth high-strength heat-treated rail, its weldability is poor, and at present there is no specific flux for the rare earth high-strength heat-treated rail, so a new flux and welding method need to be developed to meet the application requirements of the rare earth high-strength heat-treated rail. At the same time, the problems of low hardness and toughness of the joint of the rare earth high-strength heat-treated rail are solved, so that the performance of the aluminothermic welded joint meets the requirements of TBT 1632.3-2019 Steel Rail Welding Part 3: Aluminothermic Welding. SUMMARY

[0005] The purpose of the present application is to provide a rare earth high-strength heat-treated rail aluminothermic flux and a welding method, which improves the joint organization and grain size by designing reasonable flux composition and welding process, so as to further improve the strength and toughness of the joint.

[0006] To solve the above technical problems, the application adopts the following technical solutions:

[0007] The rare earth high-strength heat-treated steel rail aluminum heat flux agent has the following core component composition by mass percentage:

[0008] Aluminum powder: purity ≥ 99.0%, accounting for 16-20%, which provides main heat as a reducing agent;

[0009] Iron oxide: total iron content ≥ 70%, accounting for 50-70%, which is used to react with aluminum powder to generate liquid iron;

[0010] Iron ball: carbon content ≤ 0.05%, accounting for 10-20%, used to adjust the temperature of molten steel and increase the amount of deposited metal;

[0011] Manganese iron: manganese content ≥ 75%, accounting for 0.8-1.2%, used to improve the strength and toughness of the weld;

[0012] Silicon iron: silicon content ≥ 75%, accounting for 0.7-1.2%, used for deoxidization and improving fluidity;

[0013] Carbon: C ≥ 98%, accounting for 0.5-1.5%, used to adjust the carbon content of the weld;

[0014] Chromium iron: chromium content ≥ 70%, accounting for 0.50-0.90%, used to strengthen the weld and improve the hardenability of the joint;

[0015] Vanadium iron: vanadium content ≥ 80%, accounting for 0.10-0.25%, used for weld strengthening, improving joint strength and hardness;

[0016] La iron, Ce iron or La, Ce mixed rare earth iron alloy: rare earth element content in rare earth alloy ≥ 20%, accounting for 0.010-0.050%, used to improve joint toughness, refine joint structure and purify steel;

[0017] The rest is inevitable impurities.

[0018] Further, the core component of the heat flux agent has the following composition by mass percentage:

[0019] Aluminum powder: purity ≥ 99.0%, accounting for 17%;

[0020] Iron oxide: total iron content ≥ 70%, accounting for 66%;

[0021] Iron ball: carbon content ≤ 0.05%, accounting for 13%;

[0022] Manganese iron: manganese content ≥ 75%, accounting for 1.2%;

[0023] Silicon iron: silicon content ≥ 75%, accounting for 0.95%;

[0024] Carbon: C≥98%, 1.06% by weight;

[0025] Chromite: Cr content≥70%, 0.65% by weight;

[0026] Vanadium iron: V content≥80%, 0.12% by weight;

[0027] La iron, Ce iron or La, Ce mixed rare earth iron alloy: rare earth element content in rare earth alloy≥20%, 0.02% by weight.

[0028] The application also provides a welding method of the rare earth high-strength heat-treated steel rail aluminothermic welding agent, which comprises the following steps: preparation, rail end drying, rail end rust and dirt removal, rail clamping, sand mold installation, clamp installation, box sealing, preheating, crucible installation, ignition, reaction, mold removal, bulge pushing and polishing.

[0029] Further, the rail gap distance is 28mm.

[0030] Further, the preheating time is 7.5min.

[0031] Further, the preheating temperature is 1000℃.

[0032] Further, the normalizing treatment temperature is 930℃.

[0033] Compared with the prior art, the application has the beneficial technical effects that:

[0034] The application focuses on the composition and structure transformation characteristics of the rare earth high-strength heat-treated steel rail, and improves the joint structure and grain size by designing reasonable welding agent composition and welding process, so as to further improve the joint strength and toughness.

[0035] The obtained rare earth high-strength heat-treated steel rail aluminothermic welded joint has the characteristics of high strength, high hardness and high toughness, wherein the joint tensile strength is≥900MPa, the weld hardness is≥350HB, and the room temperature impact is≥20J. DETAILED DESCRIPTION

[0036] The rare earth high-strength heat-treated rail welded by the application is mainly composed of C, Si, Mn and Cr, and increases V, RE and other micro-alloying elements, and is produced through controlled rolling, on-line heat treatment and other processes, so that the rail has the characteristics of high strength, high hardness and high toughness. The chemical composition of the rail is as follows: C: 0.71-0.81%, Si: 0.50-0.80%, Mn: 0.80-1.20%, Cr: 0.25-0.40%, V: 0.04-0.08%, RE: 0.0005-0.0020%, P≤0.025%, S≤0.025%, Al: ≤0.010%, and the rest is Fe.

[0037] The core composition of the aluminum thermit flux for the rare earth high-strength heat-treated rail is as follows: aluminum powder: purity≥99.0%, about 16-20%, which provides main heat as a reducing agent; iron oxide: total iron content≥70%, about 50-70%, which reacts with aluminum powder to generate liquid iron; iron ball: carbon content≤0.05%, about 10-20%, which is used for adjusting the temperature of molten steel and increasing the amount of deposited metal; manganese iron: manganese content≥75%, about 0.8-1.2%, which improves the strength and toughness of the weld; silicon iron: silicon content≥75%, about 0.7-1.2%, which deoxidizes and improves fluidity; carbon: C≥98%, about 0.5-1.5%, which adjusts the carbon content of the weld; chromium iron: chromium content≥70%, about 0.50-0.90%, which is used for strengthening the weld and improving the hardenability of the joint; vanadium iron: vanadium content≥80%, about 0.10-0.25%, which is an essential element for weld strengthening and can improve the strength and hardness of the joint; La iron, Ce iron or La, Ce mixed rare earth iron alloy: rare earth element content in the rare earth alloy≥20%, about 0.010-0.050%, which is used for improving the toughness of the joint, refining the joint structure and purifying steel; and the rest is inevitable impurities.

[0038] The aluminum thermit welding method for the rare earth high-strength heat-treated rail includes the following steps: preparation work→rail end drying→rail end rust removal and decontamination→rail alignment→sand mold installation→clamp installation→box sealing→preheating→crucible installation→ignition→reaction→mold removal→pushing→polishing. The rail gap is controlled to be between 25-30mm during the rail alignment; the rail preheating process is as follows: propane and oxygen are used for heating treatment, the preheating time is controlled to be between 5-8min, and the preheating temperature is controlled to be between 950-1050℃; the sand box is removed and the rail is pushed 8-13min after the aluminum thermit reaction is completed; the joint is polished and then normalized, the normalizing heating temperature is controlled to be between 900-950℃, the temperature is kept for 10min, and then the joint is naturally cooled.

[0039] Based on the above invention, the rare earth high-strength heat-treated rail aluminum thermite welded joint has the characteristics of strength, high hardness and high toughness, wherein the joint tensile strength is ≥900 MPa, the weld hardness is ≥350 HB, and the room temperature impact is ≥20 J. The present application focuses on the composition and microstructure transformation characteristics of rare earth high-strength heat-treated rail, and improves the joint microstructure and grain size by designing reasonable flux composition and welding process, thereby further improving the strength and toughness of the joint.

[0040] 4. Process comparison during implementation:

[0041] Table 1 Comparison of different flux compositions during implementation

[0042]

[0043]

[0044] The rest are unavoidable impurities.

[0045] Table 2 Comparison of different welding processes during implementation

[0046]

[0047] As can be seen from Table 1 and Table 2, the comparative examples and the examples are different rare earth high-strength heat-treated rail aluminum thermite flux and welding method implementation process, Table 1 mainly compares different chemical composition ratio in the flux, the amount of rare earth alloy; Table 2 mainly compares the preheating time, preheating temperature and post-welding heat treatment temperature during the implementation process. As can be seen from Table 1, compared with Comparative Example 1 and Comparative Example 2, in order to improve the performance indicators such as joint strength, hardness and toughness, considering the refinement of grain size and the improvement of hardenability, Example 3 increases the proportion of strengthening element alloy, and at the same time increases the content of rare earth alloy to 0.02%, further plays the role of inclusions dispersion and micro-alloy strengthening and toughening of rare earth alloy. The joint mechanical properties of the comparative examples and the examples are compared and analyzed, as shown in Table 2.

[0048] Table 3 Comparison of joint properties under different processes during implementation

[0049]

[0050] As can be seen from Table 3, compared with Comparative Example 1 and Comparative Example 2, the joint tensile strength, tread hardness and room temperature impact value of Example 3 are the highest, and the joint has excellent strength and toughness. The tensile strength of the aluminum thermite welded joint is ≥900 MPa, the joint hardness is ≥350 HB, and the room temperature impact is ≥20 J. The strength and toughness of the joint of Example 3 are closest to the base material, thereby better playing the characteristics of high strength and toughness of rare earth high-strength heat-treated rail and weld.

[0051] The above described embodiments are only to illustrate the preferred modes of the present application, and are not intended to limit the scope of the present application. Any modification and improvement made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application as defined by the claims.

Claims

1. A rare earth high-strength heat-treated rail thermite flux, characterized by: The core components of the thermal flux by mass percentage are: Aluminum powder: purity ≥99.0%, accounting for 16-20%, which acts as a reducing agent to provide the main heat; Iron oxide: total iron content ≥70%, accounting for 50-70%, which is used to react with aluminum powder to generate liquid iron; Iron balls: Carbon content ≤ 0.05%, accounting for 10-20%, used to adjust the temperature of molten steel and increase the amount of deposited metal; Ferromanganese: Manganese content ≥75%, accounting for 0.8-1.2%, used to improve weld strength and toughness; Ferrosilicon: silicon content ≥75%, accounting for 0.7-1.2%, used for deoxidation and improving fluidity; Carbon: C ≥ 98%, accounting for 0.5-1.5%, used to adjust the carbon content of the weld; Ferrochrome: Chromium content ≥70%, accounting for 0.50-0.90%, used to strengthen welds and improve joint hardening; Ferrovanadium: Vanadium content ≥80%, accounting for 0.10-0.25%, used for weld strengthening, improving joint strength and hardness; La iron, Ce iron or La, Ce mixed rare earth iron alloy: the rare earth element content in the rare earth alloy is ≥20%, accounting for 0.010-0.050%, used to improve joint toughness, refine joint structure and purify steel quality; The rest are inevitable impurities.

2. The rare earth high-strength heat-treated rail thermite flux according to claim 1, characterized in that: The core components of the thermal flux by mass percentage are: Aluminum powder: purity ≥99.0%, accounting for 17%; Iron oxide: total iron content ≥70%, accounting for 66%; Iron balls: carbon content ≤ 0.05%, accounting for 13%; Ferromanganese: manganese content ≥75%, accounting for 1.2%; Ferrosilicon: silicon content ≥75%, accounting for 0.95%; Carbon: C ≥ 98%, accounting for 1.06%; Ferrochrome: chromium content ≥ 70%, accounting for 0.65%; Ferrovanadium: vanadium content ≥80%, accounting for 0.12%; La iron, Ce iron or La, Ce mixed rare earth iron alloy: the rare earth element content in the rare earth alloy is ≥20%, accounting for 0.02%.

3. The welding method of rare earth high-strength heat-treated rail thermite flux according to claim 1 or 2, characterized in that: The welding process includes: preparation → rail end drying → rail end rust and dirt removal → rail alignment → sand mold installation → fixture installation → box sealing → preheating → crucible installation → ignition → reaction → mold removal → nodule removal → grinding; among which, the rail gap of the aligned rails is controlled between 25-30mm; the rail preheating process is: propane and oxygen are used for heating treatment, the preheating time is controlled between 5-8 minutes, and the preheating temperature is controlled between 950-1050℃; 8-13 minutes after the thermite reaction is completed, the sand box is removed and the nodule is pushed; after the joint is polished, the joint is normalized, the normalizing heating temperature is controlled between 900-950℃, the heat preservation is carried out for 10 minutes, and then it is cooled naturally.

4. The welding method of rare earth high-strength heat-treated rail with thermite flux according to claim 3, characterized in that: The rail gap spacing is 28mm.

5. The welding method of rare earth high-strength heat-treated rail thermite flux according to claim 3, characterized in that: Preheating time: 7.5 minutes.

6. The welding method of rare earth high-strength heat-treated rail with thermite flux according to claim 3, characterized in that: Preheating temperature 1000℃.

7. The welding method of rare earth high-strength heat-treated rail thermite flux according to claim 3, characterized in that: Normalizing temperature is 930℃.

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