JPH1177339A - Thermit welding method for rail - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the toughness of weld metal for improving the reliability of a thermit welded joint in a railway in a cold district. SOLUTION: This welding method is the one that, at the time of pouring molten metal formed by thermit reaction into a mold and leaving it standing, deoxidizing elements are inserted into the pouring flow of the molten metal and/or, simultaneously with the start of its leaving to stand, deoxidizing elements are inserted into the molten metal to allow secondary deoxidation to occur. In this way, fine oxide particles produced by the secondary deoxidation are dispersed into the weld metal to refine the cast structure, and furthermore, these fine particles are made the nuclei of transformation and refine the final structure to improve the toughness of the weld metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for thermite welding of rails for improving the toughness of a weld metal.

[0002]

2. Description of the Related Art In recent years, noise at a joint portion of a rail,
Long rails are being rapidly welded to reduce vibration and reduce track maintenance. For long rails, 25 or 50 m standard length rails generally shipped from a rail factory are welded to a length of 150 to 200 m by flash butt welding or gas pressure welding at a rail welding factory or a temporary base, and then transported to the laying site. Here, the thickness becomes several hundred to several thousand m by thermite welding or the enclosed arc welding.

[0003] Enclosed arc welding requires skilled welding skills and has the disadvantage of requiring a long time in a welding place, but the reliability of welded joints is high. On the other hand, thermite welding is widely used because it has advantages such as a simple apparatus, a short time for a welding place, and a high level of skill is not required. However, there was a problem that the reliability of the welded joint was low.

[0004] There are many well-known documents concerning thermite welding of rails, and as an example, there is a description of "Progress of thermite welding method" in Journal of the Japan Welding Society, Vol. 54, No. 1 (1985), pages 43-49. . In thermite welding, high-temperature molten steel is generated by a redox reaction between iron oxide and aluminum in a crucible, and the molten steel is injected into a rail welded part equipped with a refractory mold to weld a rail. A concave portion is provided in a portion of the inner surface of the mold where the weld metal is in contact, and is a space into which high-temperature molten steel can flow. The injected molten steel fills the recesses, and forms an excess according to the shape of the recesses. Further, Japanese Patent Application Laid-Open No. 5-261596 discloses a thermite welding mold for rail welding using a split mold.

[0005] In such a thermite welding method, the base material rail is melted by the erosion effect due to the flow of the molten steel at the time of pouring and the sensible heat of the molten steel. Therefore, in order to obtain a normal welded joint, (1) supply a sufficient amount of molten steel into the mold to promote the erosion effect of the molten steel, and (2) promote melting of the base metal by the sensible heat of the molten steel (3) to provide a concave space for holding molten steel on the inner surface of the mold, (3) to preheat prior to welding, to raise the initial temperature of the base metal, and to promote the melting of the base metal during injection, (4) It is necessary to press and sharpen the extra head as hot as possible. The conventional thermite welding process also takes these points into consideration.

[0006] In the welding of rails, the time required for the welding place is emphasized because it is necessary to complete the welding within a limited time together with the joint strength of the welded portion. In recent thermite welding, a welding method as disclosed in JP-B-53-29649, in which the amount of heat is increased from the molten steel by increasing the amount of solvent to limit the preheating time to 1.5 to 2 minutes. Is the mainstream. Also,
Japanese Patent Application No. 29650 discloses a shape of a margin.

[0007] As described above, although there is much knowledge about the thermite welding from the viewpoints of jointability and joint strength, it relates to the formation of the weld metal after solidification, which is a factor affecting toughness which is one of the joint performances. Little is known.

[0008]

Since the weld metal in thermite welding is used as it is solidified, it is affected by a so-called cast structure and has a coarse grain size. For this reason, there is a concern that the toughness of the weld metal portion is lowered, and particularly in a region where the temperature is low, brittle fracture from minute weld defects or fatigue cracks is easily caused. An object of the present invention is to solve such a problem and improve the toughness of a thermite weld metal.

[0009]

In order to achieve the above object, the present invention has the following constitution. That is, (1)
The rails to be welded are placed facing each other with their groove end faces opened with a groove gap, a mold is mounted surrounding the groove gap, and in a mold space formed between the groove gap and the mold, Thermit welding of rails for injecting the melt generated by the thermite reaction, statically solidifying the melt, and performing butt welding. A thermite welding method for a rail, comprising performing one or both of inserting an acid element into a molten metal and performing secondary deoxidation of the molten metal. And (2) the rails to be welded are installed facing each other with a groove gap therebetween, and a mold is mounted around the groove gap to be formed between the groove gap and the mold. The molten metal generated by the thermite reaction is poured into a mold space, and the molten metal is allowed to stand and solidify, and thermite welding of the rail for performing butt welding, wherein one or two of Mg and Ti are used as deoxidizing elements, Inserting the deoxidizing element in the injection flow of the molten metal, inserting the deoxidizing element into the molten metal at the same time as the start of standing, or both, to perform secondary deoxidation of the molten metal. (3) The rails to be welded are opposed to each other with a gap between the end faces of the rails,
A mold is mounted around the groove gap, a molten metal generated by a thermite reaction is poured into a mold space formed between the groove gap and the mold, the molten metal is allowed to stand and solidify, and butt welding is performed. Thermite welding of the rail to be performed, wherein one or two of Mg and Ti are used as deoxidizing elements,
Inserting the deoxidizing element in the injection flow of the molten metal, or performing one or both of inserting the deoxidizing element into the molten metal at the same time as the start of standing, to perform secondary deoxidation of the molten metal, Mg in the weld metal after deoxidation: 0.0005 to 0.010
A thermit welding method for rails, characterized in that one or two kinds of 0% and Ti: 0.0010 to 0.0150% are contained in a total of 0.0150% or less when two kinds are contained.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. Thermite molten steel contains Al and dissolved oxygen remaining after the thermite reaction, and after solidification, Al ₂ O ₃ is present as an inclusion in the weld metal. Furthermore, there are MnS inclusions, which are independently dispersed.

On the other hand, the inventor of the present invention added Mg or Ti, which is a strong deoxidizing agent, to the molten steel containing dissolved Al and oxygen, alone or in combination, to obtain MgO, Ti ₂ O ₃ during the subsequent solidification.
And spinel-type MgO.Al ₂ O ₃ are generated and finely dispersed in the weld metal, dendrite becomes fine, and TiN and MnS are easily precipitated on these oxides. It was found that these finely dispersed precipitates act as transformation nuclei for ferrite and pearlite.

As a result, in the past, in order to reduce the grain size, post-heat treatment such as normalization was required. On the other hand, in the as-solidified weld metal structure, bainite containing ferrite and acicular ferrite was used. Each metal structure of pearlite can be made fine, and the toughness value can be improved.

Here, the types of desirable deoxidizing elements and the limitation of the amount thereof will be described. As described above, in the thermite reaction, most oxygen is removed by Al, which is a strongly deoxidizing element, but oxygen is still dissolved in the molten steel. In order to fix this oxygen and leave it finely in the steel without agglomeration and floating, deoxidation by a strong deoxidizing element is required. Mg and Ti have such a strong property, and Mg and Ti are most suitable for deoxidizing residual oxygen.

The optimum amount of Mg is as follows:
When the content is less than 0.0005%, the amount of deoxidized products is small, and the above-described effects of miniaturization of the dendrite and its subsequent function as a transformation nucleus are small. On the other hand, if it exceeds 0.0100%, the deoxidized product becomes coarse and the fine dispersion effect is reduced, so that the above effect is reduced. Also, regarding Ti, 0.00
If it is less than 10%, the effect is small like Mg,
If it exceeds 0.0150%, the effect is reduced. Even in the case of adding both of them, if the addition exceeds 0.0150%, the deoxidized product becomes coarse and the effect is reduced.

[0015]

The present invention will be described in detail with reference to the following examples.
The end faces of the rails are installed facing each other with a groove gap therebetween, a mold is mounted around the groove gap, and the molten metal generated by thermit reaction from the crucible provided on the upper part of the mold is filled between the mold and the groove gap. Was injected into the mold space formed in the mold. At this time, or into the molten metal after the injection is completed, or both, insert at least one of the magnesium alloy wire and the titanium wire from the injection port of the mold,
Secondary deoxidation, standing, and coagulation. As a comparative example, a conventional thermite welding method without inserting the wire was also performed.

Table 1 shows the weld metal components and the Charpy impact test values. In Table 1, the weld metal components of steels A, B, C and F correspond to claim 3 of the present invention, and D, F,
G and H correspond to claims 1 and 2. The Charpy impact test value was determined according to the Charpy impact test method specified in JIS Z 2242, using a No. 3 U-notch Charpy test piece specified in JIS Z 2202.

[0017]

[Table 1]

[0018]

The secondary deoxidization after the thermite reaction causes transformation nuclei of ferrite and pearlite to be generated, thereby making the weld metal structure finer and improving the toughness value. As a result, U-notch Charpy test value of 25 J / cm stipulated in the ghost standard for railroads in cold regions such as the Russian Railways
Including toughness that satisfies ^2, toughness is obtained satisfies at least 20 J / cm ^2, can greatly improve the reliability of the thermite welded joints.

Claims (3)

[Claims] 1. A rail, which is an object to be welded, is installed facing each other with a groove gap formed therebetween, and a mold is mounted around the groove gap. The rail is formed between the groove gap and the mold. The molten metal generated by the thermite reaction is injected into a mold space, and the molten metal is allowed to stand and solidify, and thermit welding of a rail for performing butt welding is performed. A thermite welding method for a rail, characterized in that one or both of a deoxidizing element and a deoxidizing element are inserted into a molten metal at the same time as the start of the placement to perform secondary deoxidizing of the molten metal. 2. A rail, which is an object to be welded, is installed opposite to each other with an end gap formed between the end faces thereof, and a mold is mounted so as to surround the groove gap. The rail is formed between the groove gap and the mold. The molten metal generated by the thermite reaction is poured into a mold space, and the molten metal is allowed to stand and solidify, and thermit welding of a rail for performing butt welding, wherein one or two of Mg and Ti are used as deoxidizing elements, Inserting the deoxidizing element in the injection flow of the molten metal, performing one or both of inserting the deoxidizing element into the molten metal at the same time as the start of standing,
A method for thermite welding of rails, wherein the molten metal is subjected to secondary deoxidation. 3. A rail, which is an object to be welded, is installed facing each other with a groove gap formed between the end faces thereof, a mold is mounted surrounding the groove gap, and the rail is formed between the groove gap and the mold. The molten metal generated by the thermite reaction is poured into a mold space, and the molten metal is allowed to stand and solidify, and thermit welding of a rail for performing butt welding, wherein one or two of Mg and Ti are used as deoxidizing elements, Inserting the deoxidizing element in the injection flow of the molten metal, performing one or both of inserting the deoxidizing element into the molten metal at the same time as the start of standing,
Secondary deoxidation of the molten metal is performed, and M
g: 0.0005-0.0100%, Ti: 0.001
A thermite welding method for rails, characterized in that when two or more kinds of 0 to 0.0150% are contained, a total of 0.0150% or less is contained.