JPS5993837A - Improvement of fatigue failure resistance of weld zone of rail - Google Patents

Abstract

PURPOSE:To improve the fatigue failure resistance of the weld zone of a rail and to prolong the endurance life of the rail by rapidly cooling the whole of the weld zone or the rail head and belly of the zone when the zone is kept at a specified temp. after finishing welding. CONSTITUTION:The whole of the weld zone 4 of a rail or the rail head 1 and belly 2 of the zone 4 are rapidly cooled when the zone 4 is kept at 400 deg.C- a temp. just below the A1 transformation point by its potential heat or external heating after finishing welding. By the rapid cooling the weld zone 4 is provided with large compressive residual stress, and since compressive residual stress acts as average stress, the fatigue limit is extended. As a result, the fatigue failure resistance of the weld zone of the rail is improved, and the endurance life of the rail is prolonged.

Description

[Detailed description of the invention] It is related to

Rail joints are susceptible to shocks and vibrations caused by passing trains, which can easily cause damage to the rails and joint plates, which poses problems in maintenance and management, as well as poor riding comfort.Recently, long rails have been made by welding. has been measured. As a result, rail damage has been decreasing, and it has become possible to obtain a more comfortable ride. However, due to the heat effect during welding, it is inevitable that the welded part will have uneven hardness (heat affected) on the head of the gill rail, and unevenness will occur due to wear after installation. Furthermore, welding deformation, etc., overlap, and impact loads are applied to the gaps and welded areas where trains pass. As a result, fatigue failure such as rolling damage from the top surface of the rail welds or phantom (rail bottom force) has become a problem.As a result, recent efforts have been made to improve the hardness of the rail head at the welds. In order to improve the uniformity and create a finer pearlite matrix for higher strength, a technology has been developed in which the rail head is heat treated after welding. This improves the unevenness of the hardness of the rail head and reduces the unevenness of the welded part due to wear, reducing the impact load when a train passes, and also improves the fracture characteristics of the welded part due to its high strength. As a result, the number of accidents resulting in injury has decreased considerably.

However, this time, a completely unexpected fracture from the rail welded part 4 has become a problem. An example of this damage is shown in Figure 1 (b). A crack 6 is generated from the starting point 5, propagates in the longitudinal direction of the rail and in the thickness direction of the abdominal plate, and finally leads to a transverse crack.Cracks occur on straight lines 5, curves, and small rails. It can be seen on both the field side and the gauge corner side.

The cause of this kind of damage was initially thought to be due to welding defects or bending (tensile) stress acting on the abdomen due to uneven loads on the wheels. .

However, even if there are no welding defects, cracks are observed to occur even on the gauge corner side of the rail where only compressive bending stress is applied.The true cause has not been clarified, and of course there are no countermeasures. There was one lesson that was not taught at all.

Therefore, in order to take effective measures against the above-mentioned damage, the inventors conducted on-site experiments and conducted various inspections to determine the cause of this damage. As a result, the cause of this damage was shown in Figure 2.
As shown in the example, it was found that this was due to a very large vertical tensile residual stress occurring at the center of the abdomen of the rail weld.

However, it has been found that damage can be significantly prevented by changing the force to remove this tensile residual stress or compression. In addition, Figure 2 shows the hard head (fine Tsuku-light treatment).
The vertical residual stress distribution of the flash welded part of the rail is shown.
・) indicates the distribution at the bottom position.

The present invention has been made based on this knowledge, and its gist is that the entire rail or the rail at the rail welded portion is heated to a temperature of 400°C to A just below the transformation point using self-retained heat after welding or external heating. This is intended to improve the plane 1 fatigue fracture characteristics of the rail weld by rapidly cooling the head and abdomen to impart a large compressive residual stress to the core.

The present invention will be explained in detail below. For convenience of explanation, the names of each part will be described in Figure 1(a) from VC. Part 1 is the rail head, part 2 is the abdomen, and part 3 is the bottom.

The present invention rapidly cools the entire rail or the rail head and abdomen at the rail welding part, which is at a temperature of 400°C to A, just below the transformation point, using self-retained heat after welding or external heating. There are two methods for improving the fatigue fracture resistance of rail welds.

In the present invention, it is possible to easily apply a large compressive residual stress to the rapid cooling start temperature of 400°C to a temperature just below the A1 transformation point without causing interstitial fluid failure in the rail, thereby improving fatigue strength. l・Required temperature range, 40
At cold temperatures below 0°C, there is no sufficient compressive residual stress to improve fatigue strength; on the other hand, at temperatures higher than the transformation point, the martensitic structure is formed by rapid cooling. tend to increase crack susceptibility.

In this case, the cooling rate is ray/l, and the higher the cooling rate, such as water cooling, the better, since it increases the compressive residual stress of the welding sound. Furthermore, from the perspective of fatigue resistance in the rail welding sound t force n heat and quenching range), the entire rail at the rail weld is desirable, but the damage intended by the present invention can be prevented even if the rail welding part is welded. can. In order to obtain the above temperature range, the first pair 5 may be used after welding is completed, or flame or high frequency induction may also be used.

The rail welding sound produced by the above-mentioned uninvented method is given a large compressive residual stress, and the compressive residual stress acts as an average stress, increasing the fatigue limit. As a result, the welding noise and fatigue fracture characteristics are improved and the service life is extended.

Next, examples of the present invention will be described.

One rail used in the experiment was an AI (hard head (fine barlite treated) rail with an EΔ136 lb.), a flash no. Thereafter, the entire rail at the rail welded portion, including the heat-engraved section, was heated with gas (heated to 600° C.), and the entire rail was immediately cooled with water to room temperature.

As a result, as shown in Table 1, l [, a large compressive residual stress E As (-1) was given to the rail welded part of the rail of the present invention, and abdominal crack reproduction experiment (repetitive load J) ma25
t+ P ##+5 t+ 3-point bending fatigue test at 4 million repetitions, Sunokun 11η) results show that cracks occur in conventional welded rails, but No cracks were observed in the rails, indicating that they have very good fatigue and fracture resistance.

[Brief explanation of the drawing]

FIG. 1(a) is a front view of the rail, FIG. 1(b) is an explanatory diagram of the occurrence of cracks in the id rail, and FIG. 2 is a vertical residual stress distribution diagram of the rail weld. 1...Rail head, 2...Abdomen, 3...Bottom, 4
...Welded part, 5... Starting point of cracking, 6... Crack. Patent applicant Representative patent attorney Tomoyuki Yafuki (and 1 other person) Figure 1 (a)

Claims (1)

[Claims] It is characterized by rapid cooling of the entire rail or the rail head and abdomen at the rail welding part, which is at a temperature of 400 ° C to A, just below the transformation point, by heating by self-retained heat after welding is completed or by external force. Method for improving fatigue fracture resistance of rail welds.