JPH0420705B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a butt covered arc welding method for rails used in railways and the like. (Prior Art) Conventional methods for joining rails include flash butt welding, gas pressure welding, thermite welding, and enclosed arc welding. Among these welding methods, the enclosed arc welding method, as introduced in Japanese Patent Publication No. 56-4350, has the advantage that it is possible to weld rails that are in a restrained state and that the reliability of the joint is high. Therefore, it is often used as an on-site welding method. Due to its intended use, rails are required to have high wear resistance, fatigue damage resistance, and static strength, and the same applies to welded joints, and there are no welding defects such as weld cracks, or there is no practical It must be kept as low as possible. As shown in Fig. 2, the conventional rail butt welding method is to perform multi-layer welding on the rising section 12 from the rail foot 11 to the abdomen, and then continuous welding from the abdomen to the head 13 without removing slag. Perform enclosed arc welding to
Finally, multi-layer welding was performed on the top of the head to complete the butt welding. At this time, in the rising portion 12,
This is a welding method in which the welding end crater portion 15 is kept within the cross section of the rail so that excess buildup is not created. In addition, coated arc welding rods are as shown in Table 1.
JIS Z3213 coated arc welding rods for low-alloy high-strength steel are used. The weld metal formed when such a welding rod is applied to the rail has a carbon content of 0.3%.
Therefore, the difference in pseudo-solidification temperature resulting from the difference in C content between the weld metal rail and the weld metal rail, that is, the solidification temperature of the weld metal is about 1530℃, and that of the rail is about 1530℃.
Due to the temperature being 1470℃, hot cracks occur near the melt boundary (HAZ) of the rail base material. Furthermore, a large amount of martensitic structure is generated in the HAZ even after welding, which also contributes to a decrease in fatigue strength. On the other hand, there have been many studies on the performance of rails in use, and it is clear that pearlite structures are the best in terms of wear resistance and fatigue damage resistance, and that pearlite structures with the same hardness and higher C content are better. is being used. Furthermore, in a weld metal having a C content equivalent to that of the rail, the above-mentioned hot cracking of the HAZ of the rail base material does not occur. For this reason, coated arc welding rods with a high C content, for example 0.4 to 1.0% C, have come to be used. By applying such high C-based coated arc welding rods to enclosed arc welding of rails,
It became possible to suppress the occurrence of hot cracking in the HAZ and the formation of martensite, significantly improving static strength and fatigue strength. Furthermore, the weld metal structure became a pearlite structure, and wear resistance and fatigue damage resistance were improved. (Problems to be Solved by the Invention) However, with high C components, solidification cracking (crater cracking) peculiar to austenite solidification is likely to occur at the weld end crater portion, similar to the case with austenitic stainless steel components. Crater cracking is a solidification crack that occurs in the molten pool at the end of welding with a single covered arc welding rod, and in some cases, this crack propagates and spreads. The size of this crater crack depends on the size of the molten pool in the crater area and the external tensile stress, and the larger these factors, the larger the crack, which will lead to a decrease in the static strength and fatigue strength of the welded joint. It can also be a cause. In particular, when welding is performed with a relatively large welding current value and in a narrow vertical gap, such as in enclosed arc welding, the size of the weld pool and external tensile stress tend to increase, and the occurrence of crater cracking cannot be overlooked. Particularly in rail welding, due to the shape of the multi-layer weld that extends over the abdomen of the upper part of the foot, the welding speed is extremely slow and craters occur due to the need to increase the thickness relative to the length of the bead. This increases in size, and the constraint of the already solidified lower layer causes a large shrinkage strain to be applied to the final solidified portion, making crater cracks more likely to occur. Furthermore, since the enclosed arc welding section from the rail abdomen to the head is continuous welding, it is not possible to remove the slag covering the weld bead unlike in multilayer welding. Therefore, welding is continued while the slag is remelted using a welding arc. Therefore, the welding current is relatively high, typically 250-280A. Therefore, the size of the crater increases, and the size of the crater crack also increases to the extent that it becomes a practical problem. The present invention solves the problems in using the above-mentioned coated arc welding rod and provides a method for welding rails used in railways, etc., which can stably ensure good joint performance. (Means for Solving the Problems) The gist of the present invention is that in butt welding of rails using a coated arc welding rod containing 0.4 to 1.0% C; At the rising part of the upper part of the leg, the end of the upper layer weld bead is overlapped with the end of the lower weld bead to form a surplus, and after the multilayer welding of the leg is completed, enclosed arc welding is performed from the abdomen of the rail to the head. When performing, the welding current value
Start at 240-280A and immediately increase the current value to 190-240A
This is a rail welding method in which the rail is welded continuously to the middle of the head, and then at least one pass or more of multi-layer welding is performed at low current to weld up to the top of the head, completing butt welding. The present invention will be explained in detail below with reference to FIG. FIG. 1 is a drawing showing the welding method of the present invention. First, the rail foot 1 is multi-layer welded in the same way as in the conventional method, and then the craters 3 at the end of the multi-layer weld on the rising part 2 that spans the abdomen of the upper part of the foot are overlapped with the lower layer 4 and are added to the outside of the rail cross section as extra material. put out. At this time, the bead has a downward slope with respect to the traveling direction, and the slope is large at a position where the bead is short.
If the arc is stopped at this point, the crater will flow downwards and take on a wide-spread shape (large ellipticity), resulting in crater cracking, which tends to propagate to the bead in the cross section of the rail. Therefore, in the stacking of the rising part, all the beads are extended as excess layers to the part of the lower layer of the rail cross section with a small slope to stop the arc. As a result, it is possible to form a clean bead without cracks within the cross section of the rail. Furthermore, in the enclosed arc welding section 5 from the rail belly to the head, the welding current at the start is set to 240 to 280 A.
After fully welding the four corners of the final layer of the foot, immediately lower the current value to 190-240A and perform continuous welding. As a result, the size of the bar joint or the final crater can be reduced, and crater cracking can be suppressed. At this time, the welding current value at the start was set to 240 to 280 A because if it is less than 240 A, it is difficult to form a bead that is sufficiently compatible with the already completed lower layer bead, and poor fusion is likely to occur. or,
The reason why we set it to 280A is because if it exceeds that, it becomes too much current and welding work cannot be sustained stably. Immediately after welding starts, that is, once a bead that has sufficiently blended with the lower layer bead is formed, immediately switch the current value to 190 to 240A. The current value in this case is
The reason for setting the current value to 190A or more and 240A or less is that if the current value is smaller than 190A, it will be difficult to remelt the slag, making enclosed arc welding itself impossible.
Also, if the current is larger than 240A, it will be difficult to suppress crater cracking as in the conventional method, and the problem will not be solved. After completing continuous welding from the abdomen to the head 5 in this manner, low current multi-layer welding may be performed only on the top 6 of the head, as the case may be. The reason for this low current is to reduce the size of the crater and suppress crater cracking to a level that does not pose a practical problem. The welding current in this case is
130-160A is desirable. The rail welding method according to the present invention does not cause high liquefaction cracking in the HAZ, the entire layer structure of all welded layers exhibits pearlite, and in addition to improving wear resistance, static strength, and fatigue strength, the high C-based coated arc It also suppresses the occurrence of crater cracking, which is a concern with welding rods, and makes it possible to manufacture high-performance rail welded joints. (Example) The effects of the present invention will be explained in more detail below using Examples. Using an arc welding rod coated with the flux adjusted as shown in Table 3 on the welding core wire shown in Table 2,
Enclosed arc welding was performed on the high C steel and low alloy steel rails shown in Table 4. Welding is carried out after preheating to 500℃ using an I-shaped groove.
The legs were welded in multiple layers facing downward, and an enclosure pad was applied from the abdomen to the head and continuously welded. When welding the head, replace only the welding rod that is most suitable for the head.
Two cases were used: continuous welding to complete the build-up welding to the top of the head, and cases in which continuous welding was stopped midway and multi-layer welding was then performed to the top of the head to complete the welding. At this time, at least one pass or more of the welding end (crater) is overlapped with the lower layer in the rising part of the upper part of the foot to form a surplus, and furthermore, in the enclosed arc welding from the rail abdomen to the head, welding current is 240～
Start at 260A (260→240A) and immediately increase to 190-240A
Low current welding was performed. For comparison, welding was also carried out under conventional conditions. After welding, the rail was heated to 900°C using a multi-hole nozzle burner that evenly heats the entire circumference of the rail cross section, and then allowed to cool. Furthermore, we used a multi-hole nozzle burner to heat only the top of the head to 700℃.
The top of the head was quenched by heating and forced air cooling.

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[Table] Table 5 shows welding conditions, presence or absence of defects by ultrasonic flaw detection, static bending and fatigue strength values. (Effects of the Invention) As explained above, according to the welding method of the present invention, welding defects are eliminated, static bending strength and fatigue strength are improved, and the joint performance of the rail can be stabilized.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a rail welding method according to the present invention and FIG. 2 is a conventional method. 1...Rail foot part, 2...Rising part, 3...Crater, 4...Lower layer, 5...Enclosed arc welding part, 6...Rail top part.

Claims (1)

[Claims] In butt welding of rails using a coated arc welding rod containing 1C; 0.4 to 1.0%, when the legs of opposing rails are multi-layer welded, the upper layer is welded at the rising part of the upper part of the leg. After the end of the weld bead is overlapped with the end of the weld bead on the lower layer to form a reinforcement, and the multi-layer welding of the legs is completed, when performing enclosed arc welding from the abdomen of the rail to the head, the welding current value is set to 240. Starting at ~280A,
A rail welding method characterized by immediately switching the current value from 190 to 240A and continuous welding to the top of the head to complete butt welding. 2C: In butt welding of rails using a coated arc welding rod containing 0.4 to 1.0%, when multi-layer welding the legs of opposing rails, weld the terminal end of the upper layer weld bead at the rising part of the upper part of the leg to the lower layer. When carrying out enclosed arc welding from the abdomen of the rail to the head after completing the multi-layer welding of the legs by overlapping the end of the weld bead, start the welding current at 240 to 280A and immediately A rail welding method characterized by continuous welding to the middle of the head at a current value of 190 to 240A, and then low-current multi-layer welding to the top of the head to complete butt welding.