Search

CN-121988932-A - U75V steel rail thermite welding agent for railway in low-pressure area and welding method

CN121988932ACN 121988932 ACN121988932 ACN 121988932ACN-121988932-A

Abstract

The invention discloses a U75V steel rail thermite welding agent for a plateau railway and a welding method, wherein the thermite welding agent is prepared by newly designing a composite oxygen supply-purification-crack resistance integrated alloy system, introducing a barium peroxide-cerium oxide composite oxygen supply agent, a lanthanum cerium alloy rare earth purifying agent and a molybdenum vanadium composite crack resistance synergistic agent, precisely matching the chemical components of the U75V steel rail, and realizing the high-quality welding of the U75V steel rail by matching with a dedicated welding process of a plateau of gas heat preservation-two-stage oxygen enrichment preheating-speed control pouring-gradient slow cooling-windproof protection. Through environmental verification of an altitude of 3000-5000 m, the tensile strength of the welding joint is greater than or equal to 980MPa, the impact energy is greater than or equal to 32J, the degree of matching between the hardness and the base metal is greater than or equal to 0.95, the grain size is greater than or equal to 8 levels, the defects of air holes, cracks and the like are avoided, and all indexes meet special technical requirements and are suitable for on-site welding operation of 60kg/m U V steel rails with an altitude of more than 3000 m.

Inventors

  • ZHENG RUI
  • ZHOU KE
  • BIAN YING
  • XUE HUDONG
  • DONG JIE
  • WANG HUIJUN
  • YAN LEI

Assignees

  • 内蒙古包钢钢联股份有限公司

Dates

Publication Date
20260508
Application Date
20260324

Claims (10)

  1. 1. The U75V steel rail thermite welding agent for the railway in the low-pressure area is characterized by comprising, by mass, 19.5-20.5% of high-purity Al powder, 62.0-63.5% of composite iron oxide, 0.8-1.0% of Si iron powder, 1.3-1.5% of Mn iron powder, 0.08-0.12% of V iron powder, 6.5-7.5% of cast iron balls, 1.2-1.8% of composite oxygen supply agent, 0.3-0.5% of rare earth purifying agent, 0.6-0.9% of cracking resistance synergist and 1.5-2.0% of slag former.
  2. 2. The U75V steel rail thermite welding agent for low pressure areas according to claim 1, wherein the total weight of the thermite welding agent is 15.8+/-0.2 kg.
  3. 3. The U75V steel rail thermite welding agent for the railway in the low-pressure area, which is disclosed in claim 1, is characterized in that the composite oxygen supply agent is formed by compounding barium peroxide and cerium oxide according to a mass ratio of 2:1, has a granularity of 100-150 meshes, and is used for supplementing oxygen required by the reaction in a plateau low-pressure environment, so that the thermite reaction is ensured to be fully carried out.
  4. 4. The U75V steel rail thermite welding agent for the railway in the low-pressure area according to claim 1, wherein the rare earth purifying agent is lanthanum cerium alloy powder, wherein La accounts for 68-72%, ce accounts for 28-32%, the purity is more than or equal to 99.9%, and the granularity is 200-300 meshes, and the rare earth purifying agent is used for deoxidizing and dehydrogenating, refining grains and purifying weld joint tissues.
  5. 5. The U75V steel rail thermite welding agent for the railway in the low-pressure area, which is characterized in that the cracking resistance synergist is compounded by molybdenum powder and vanadium powder according to the mass ratio of 3:1, the purity is more than or equal to 99.9%, and the granularity is 150-200 meshes, and is used for improving the cracking resistance and the high-temperature stability of a welding line.
  6. 6. The U75V steel rail thermite for railways in low-pressure areas according to claim 1, wherein the composite iron oxide is formed by mixing FeO and Fe 2 O 3 、Fe 3 O 4 according to the mass ratio of 3:2:1, the purity is more than or equal to 99.5%, and the thermite reaction rate is ensured to be stable in a plateau environment by optimizing oxygen potential matching.
  7. 7. The U75V steel rail thermite welding agent for the railway in the low-pressure area, which is characterized in that the purity of the high-purity Al powder is more than or equal to 99.9 percent, the granularity is 50-100 meshes, and the high-content design compensates for the heat loss of the plateau environment; the Si iron powder contains 78-82% of Si, 18-22% of Fe and less than 0.5% of C, so that the fluidity of the molten metal is improved; The Mn iron powder has 65-70% of Mn and less than 0.5% of C, so that deoxidation and desulfurization are realized; the V content of the V iron powder is 0.80-0.85%, and the V content is accurately matched with the V content of the U75V steel rail base metal, so that the component segregation is reduced; the Fe content in the cast iron ball is more than or equal to 97%, the grain diameter is 3-5 mm, and the carbon content of a welding line is regulated; the slag former is prepared by compounding fluorite powder, zircon sand and siliconized copper powder according to a mass ratio of 3:1:0.5, has a granularity of 100-200 meshes, and has synergistic effects of slag formation, dehydrogenation and slag removal improvement.
  8. 8. A method for welding U75V rails on a plateau using the thermite welding agent of any one of claims 1 to 7, comprising the steps of: (1) The steel rail pretreatment comprises the steps of selecting a 60kg/m U V steel rail, cleaning oxide skin, greasy dirt and impurities within the range of 60mm on the welding end face and the two sides, ensuring the end face to be flat, ensuring the verticality deviation to be less than or equal to 0.5mm, and naturally airing after wiping the end face by adopting alcohol to avoid water residue; (2) The gas heat preservation and sand mold installation, namely preheating oxygen and acetylene gas for welding to 10-25 ℃ and preserving heat, so as to avoid the influence of low-temperature gas on combustion efficiency; (3) The two-stage oxygen-enriched preheating comprises the steps of primary preheating oxyacetylene flame, oxygen pressure of 0.40-0.45 MPa, acetylene pressure of 0.045-0.05 MPa, preheating for 300-320 s, and enabling the temperature of the end face of a steel rail to rise to 250-300 ℃, wherein the secondary preheating is switched into oxygen-enriched flame, the volume ratio of oxygen to acetylene is 1.2:1, preheating is carried out for 120-150 s, the temperature of the steel rail and a sand mold is raised to 450-500 ℃, the two sides of a steel rail to be welded are covered by a heat affected zone, the temperature of the steel rail is respectively more than or equal to 40mm, and the preheating uniformity deviation is less than or equal to +/-20 ℃; (4) Filling the thermite welding agent according to claim 1 into a flux bag, placing the flux bag above a sand mould, igniting the ignition agent to start thermite reaction, supplementing oxygen through a vent hole at the top of the sand mould, maintaining the oxygen concentration of a reaction area to be more than or equal to 20%, and controlling the casting speed to be 5-8 mm/s to ensure that molten liquid fully fills a welding line; (5) Standing for 480-520 s for tranquillization after casting, and adopting a process of 'rock wool heat preservation cover plus gradual cooling', wherein the heat preservation cover is covered for heat preservation for 240-300 s, then the heat preservation cover is uncovered for 1/3 for 120-150 s, and finally the heat preservation cover is completely uncovered; (6) And (3) joint post-treatment and detection, namely dismantling the sand mould, cleaning the weld seam surplus height, performing appearance inspection and ultrasonic flaw detection on the welded joint, and then intercepting a sample to perform mechanical property and metallographic structure detection so as to ensure that the defects of air holes, cracks and slag inclusion are avoided.
  9. 9. The welding method according to claim 7, wherein in the step (2), the gas insulation is realized by adopting a special insulation box, so that the temperature of oxygen and acetylene gas is maintained at 10-25 ℃ in the conveying and using processes, and the flame combustion sufficiency in the plateau environment is improved; in the step (5), the wind shield is made of high-temperature resistant flame-retardant materials, and the shielding range covers the welded joint and 50mm areas on two sides, so that the influence of strong wind on the cooling rate is effectively weakened.
  10. 10. The welding method according to claim 7, wherein the performance detection standard in the step (6) is that the tensile strength Rm is equal to or more than 980MPa, the elongation A is equal to or more than 12%, the impact power KU2 is equal to or more than 32J, the rail top surface hardness Hj/Hp is equal to or more than 0.95, the soft spot Hj1/Hp is equal to or more than 0.90, the grain size is equal to or more than 8 grades, and the microstructure is pearlite+a small amount of ferrite and has no martensite harmful structure.

Description

U75V steel rail thermite welding agent for railway in low-pressure area and welding method Technical Field The invention belongs to the technical field of steel rail welding, and particularly relates to U75V steel rail aluminum heat welding agent suitable for high and low air pressure, oxygen deficiency, strong wind and large temperature difference environments and a corresponding welding method, which are suitable for on-site welding operation of high-altitude railways with the altitude of more than 3000 m. Background The altitude of the altitude is reduced by about 10kPa per 1000m, the altitude is more than 3000m, the altitude is only about 70% of the plain, the altitude is 5000m, the altitude is less than 60%, the oxygen content is synchronously reduced by only 60-70%, the day-night temperature difference can reach 20-30 ℃, and the weather is strong wind all year round. The environmental factors bring technical pain points which are difficult to solve for thermite welding of 60kg/m U V steel rails, and the U75V steel rail is used as a high-strength heavy-load steel rail, the carbon content is 0.74-0.78%, the vanadium content is 0.06+/-0.02%, the strength is more than or equal to 980MPa, and the welding quality directly determines the operation safety of a plateau railway. In the prior art, steel rail thermite welding agents and welding processes are mostly designed based on plain environments, and are not subjected to adaptation optimization aiming at plateau extreme environments, so that a plurality of problems exist in practical application: The low air pressure and the oxygen deficiency cooperate to cause insufficient oxygen supply and insufficient combustion in the aluminothermic reaction, so that the exothermic strength of the reaction is reduced, the sufficient melting of welding seams can not be ensured, a large number of internal defects such as air holes, slag inclusion and the like are easily generated, and the compactness of the joint is seriously influenced; The existing welding flux lacks a targeted oxygen supply and purification system, so that a short plateau oxygen plate cannot be made up, harmful impurities such as hydrogen, oxygen and the like in a welding line are difficult to remove, and moreover, the cooling speed of a joint is too high due to strong plateau wind and large temperature difference, so that harmful tissues such as martensite and the like are extremely easy to generate, and cold cracks are initiated; The traditional welding process does not consider the problem of low combustion efficiency of the plateau gas, has uneven preheating temperature and poor control of a heat affected zone, lacks effective windproof measures, further aggravates the problems of coarse weld grains and reduced mechanical properties, and particularly has insufficient impact toughness, so that the service requirements of heavy load and high-speed operation of the plateau railway are difficult to meet; The existing plateau-adaptive steel rail welding technology focuses on an air pressure welding method, improves joint quality through means of air heat preservation, normalizing heat treatment and the like, but has complex air pressure welding equipment and low construction efficiency, is not suitable for on-site rapid welding and rush repair operation, and aiming at the plateau-adaptive technology of thermite welding, the existing welding flux is mostly a general formula, does not realize accurate matching with U75V steel rail components, lacks flux-process integrated optimization design, and cannot fundamentally solve core defects of plateau thermite welding. For example, patent publication No. CN 111283380A discloses a rail welding operation method at low temperature, the welding quality is ensured through preheating and cooling rate control, but the adaptive design of the low-pressure and anoxic environment of a plateau is not involved, the problems of insufficient aluminothermic reaction and low gas combustion efficiency in the environment cannot be solved, patent publication No. CN 20241101012981. X discloses a U63MnCrCuH rail plateau air pressure welding method, and although the heat preservation and windproof measures of the plateau air are considered, the adopted air pressure welding process is completely different from the aluminothermic welding principle, and the innovative optimization of a flux formula is not involved. Therefore, development of an integrated technical scheme of 'welding flux component innovation and process precision adaptation' is needed, the technical problem of U75V steel rail thermite welding under a plateau environment is specially solved, and the blank of the prior art is filled. Disclosure of Invention The invention aims to provide a U75V steel rail thermit welding agent for railways in low-pressure areas and a welding method, and aims to solve the technical problems that thermit welding of steel rails is easy to cause insufficient thermit reaction, weld seam air ho