JP2006088257A - Method of welding and repairing gear box of rolling stock - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of welding and repairing a gear box of a rolling stock, which eliminates a fear of cracking at the time of welding, achieves uniform hardness at a welding portion, and is free from degradation of strength of a base metal. <P>SOLUTION: There is provided the method of welding and repairing the gear box of the rolling stock, which is formed of spheroidal graphite cast iron. According to the method, a defective cast portion of the gear box is subjected to gas welding by using a welding rod formed of a common material, and heated to a temperature of 890 °C or more, followed by holding the same state over a predetermined period. Then the gear box is furnace-cooled down to 750 to 820°C, and held at the same temperature over one hour or more, followed by air-cooling the same. According to the method, the gear box for the rolling stock can be formed of the spheroidal graphite cast iron of which a large vibration damping effect can be expected compared with a gear box formed of cast steel. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for welding repair of a portion where a casting defect has occurred when a gear box used for a railway vehicle is manufactured from spheroidal graphite cast iron.

  The railway vehicle gear box is generally manufactured by casting, but is relatively thin, so that it is generally thin due to the demand for weight reduction. Moreover, since the shape is complicated, the change in the cross-sectional thickness is large. Therefore, the gear box for a railway vehicle has been conventionally manufactured mainly from cast steel in consideration of mechanical properties such as required hardness and tensile strength.

  By the way, in recent railway vehicles, suppression of vibration has become a major issue as the speed increases, but this requirement for suppression of vibration is no exception in the gearbox.

  Under such circumstances, it has been studied to use spheroidal graphite cast iron, which can be expected to have a vibration damping effect as compared with conventionally used cast steel, as the material of the gear box.

  However, since the gear box is thin and has a large change in cross-sectional thickness as described above, casting defects are likely to occur, and welding repair may be required. On the other hand, since spheroidal graphite cast iron is generally difficult to weld, in order to produce a gear box using spheroidal graphite cast iron, it is necessary to solve this welding repair problem.

  Usually, Ni-based alloy rods or cast iron co-material rods are used for welding spheroidal graphite cast iron. When a Ni-based alloy rod is used, the welded portion is different from the base material. Further, since arc welding is generally used, the temperature at the time of welding rises too much and the heat-affected zone becomes too hard, so that there is a problem that toughness is reduced and weld cracking is likely to occur.

  In order to soften the part hardened by such welding and make the hardness uniform, it is effective to perform heat treatment at a temperature equal to or higher than the transformation point after welding. There is a problem of lowering.

On the other hand, when the common bar is used, a portion different from the base material is not formed in the welded portion. However, the welded portion and its periphery are hardened as compared with the base material portion, and the toughness is reduced as compared with the base material.
Thus, it was practically difficult to weld spheroidal graphite cast iron.

  The results of investigating the hardness after welding in the case of welding using these Ni-based alloy bars and common bar are shown in Table 1 below. Table 1 below shows the results of experiments using the base material and the common bar of chemical components shown in Table 2 below and the Ni rod of chemical components shown in Table 3 below.

Therefore, it has been disclosed to use a common metal welding material that can be welded at a relatively low preheating temperature of about 250 ° C. as a means for welding spheroidal graphite cast iron without cracking. However, in this case, it is described that it is desirable to perform welding by a TIG welding (arc welding) method having a high energy input density.
JP-A-7-185880

  However, the technique disclosed in Patent Document 1 has a problem that the hardness becomes non-uniform due to preheating at a low temperature and the use of arc welding, and the toughness is reduced. It is expected that the mechanical properties of spheroidal graphite cast iron are not satisfied.

  The problem to be solved by the present invention is that the conventional spheroidal graphite cast iron welding repair method has non-uniform hardness, and the toughness of the welded part and its vicinity is reduced, so that the machine inherently possessed by spheroidal graphite cast iron In this case, the railway vehicle gearbox was not made of spheroidal graphite cast iron.

The method for welding repair of a railway vehicle gear box according to the present invention,
In order to prevent cracks due to welding, to make the hardness of the welded portion uniform, and to prevent the strength of the base material from being reduced,
A method for welding and repairing a railway vehicle gearbox made of spheroidal graphite cast iron,
After gas welding the casting defect portion of the gear box using a joint material welding rod,
After heating to a temperature of 890 ° C. or higher and holding for a certain time, the furnace is cooled to 750 ° C. to 820 ° C. and held at that temperature for 1 hour or longer,
After that, air cooling is the main feature.

  In the welding repair method for a railway vehicle gear box according to the present invention, welding of a repaired portion of a railway vehicle gear box made of spheroidal graphite cast iron is used without using a Ni-based alloy rod. When using a Ni-based welding rod, arc welding is generally used as described above, so the temperature during welding becomes too high, the welded part and its surroundings become too hard, and the welded part This is because a portion different from the base material is formed.

  Further, in the welding repair method for a railway vehicle gearbox according to the present invention, the two-stage heat treatment performs both the uniformization of the welded portion and the strength reduction of the base material only by the conventional one-stage heat treatment. This is because the welded portion can be made uniform, but in the case of furnace cooling, the strength of the base material is inevitably reduced, while in the case of air cooling, the welded portion and its surroundings become too hard. .

  The first heat treatment of the two stages of heat treatment is performed at a temperature of 890 ° C. or higher because the chill structure cannot be decomposed when the heat treatment temperature is lower than 890 ° C. This is because the hardness cannot be made uniform. Needless to say, the upper limit of the first heat treatment temperature is a temperature at which the base material becomes ferritic and the strength of the base material does not decrease.

  Moreover, the reason why the second heat treatment is performed at a temperature of 750 ° C. to 820 ° C. is that if the temperature is lower than 750 ° C., the strength reduction of the base material cannot be suppressed, and if it exceeds 820 ° C., the welded part and its surroundings become too hard. It is.

The reason why the holding time in the second heat treatment is set to 1 hour or longer is that, according to the experiments by the inventors, if the time is less than 1 hour, the effect of performing the second heat treatment cannot be obtained.
The reason for air cooling after the second heat treatment is that the strength of the base material is not improved when the furnace is cooled.

  According to the present invention, spheroidal graphite cast iron can be welded without causing a decrease in the strength of the base material while making the hardness of the welded portion uniform, so that the gear box used for railway vehicles can be compared with cast steel. Thus, it has an advantage that it can be made of spheroidal graphite cast iron which can be expected to have a vibration damping effect.

BEST MODE FOR CARRYING OUT THE INVENTION The best embodiment of the welding repair method for a railway vehicle gearbox according to the present invention will be described below.
The railway vehicle gearbox welding repair method according to the present invention is, for example, a repair in which a casting defect is produced in a spheroidal graphite cast iron gearbox produced by casting a base material having the chemical composition shown in Table 2 above. The part is gas-welded with, for example, oxygen acetylene gas using a welding rod having the same chemical composition as shown in Table 2.

  Then, as shown in FIG. 1, the gear box in which the repaired portion is gas-welded is heated to a temperature of, for example, 900 ° C. and held for 2 hours, and then cooled in a furnace, resulting in a temperature of 750 ° C. to 820 ° C. By the way, after holding at that temperature for 1 hour, it is air-cooled.

  In order to confirm the effect of the welding repair method for a railway vehicle gear box according to the present invention, the material (height) of spheroidal graphite cast iron having the chemical composition shown in Table 2 has the dimensions shown in FIG. A test piece having an inner diameter of φ10 mm and a depth of 6 mm in the center of one side surface (30 mm × width 40 mm × length 170 mm) was produced.

  Then, after preheating the test piece at 700 ° C., by using a joint rod of the chemical composition shown in Table 2 (outer diameter: 5 mm) in the hole of the test piece, oxygen acetylene gas welding is performed. Overlaying was performed. Then, after holding at a temperature of 900 ° C. for 2 hours, the furnace was cooled, and the mechanical properties when the second heat treatment temperature was changed variously and held for 1 hour and then cooled by air were investigated.

  The results are shown in Table 4 below. Table 4 below shows the mechanical properties of two types of spheroidal graphite cast iron (FCD450) and, as a comparison, the case before heat treatment (No. 1) and the case where only the first heat treatment was performed (No. 2, 3). The mechanical properties of are also shown. In addition, the sample material which obtained the result of Table 4 was extract | collected from the Y-type test piece. Moreover, the tensile test was done using the JIS4 test piece.

  As is clear from Table 4, when the conventional one-stage heat treatment was performed, when the cooling was furnace cooling (No. 2), the hardness and tensile strength were lower than before the heat treatment (No. 1). However, the standard FCD450 standard for spheroidal graphite cast iron was not satisfied.

Further, among the cases where the conventional one-step heat treatment was performed, when the cooling was air cooling (No. 3), the hardness increased so much that the upper limit of the standard was not satisfied.
When two-stage heat treatment is performed on these (No. 4 to No. 8), when the second heat treatment is performed at 850 ° C. (No. 4), the hardness satisfies the upper limit of the standard. However, when it was performed at 750 ° C. to 820 ° C. (No. 5 to No. 8), all the items of the standard were satisfied.

  As described above, according to the welding repair method for a railway vehicle gear box of the present invention, cracks due to welding do not occur, the hardness of the welded portion can be made uniform, and the strength of the base material is not reduced. It was confirmed that spheroidal graphite cast iron could be welded.

  The present invention is not limited to the above example, and it goes without saying that the embodiments may be changed as appropriate within the scope of the technical idea described in the claims.

It is a figure explaining the heat processing pattern of the welding method of the gear box for rail vehicles of this invention. It is explanatory drawing of the test piece used for the experiment conducted in order to confirm the effect of the welding method of the gear box for railway vehicles of this invention.

Claims (1)

A method for welding and repairing a railway vehicle gearbox made of spheroidal graphite cast iron,
After gas welding the casting defect portion of the gear box using a joint material welding rod,
After heating to a temperature of 890 ° C. or higher and holding for a certain time, the furnace is cooled to 750 ° C. to 820 ° C. and held at that temperature for 1 hour or longer,
Thereafter, the method for welding repair of a gear box for a railway vehicle is characterized by air cooling.

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