JPS588950B2 - How to weld heat-resistant cast steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding method for heat-resistant cast steel, and aims to improve welding quality and welding efficiency.

The shape of the groove 2 between the base materials 1 and 1 conventionally employed in TIG welding is shown in FIG. 1, for example.

Recently, groove angle α and root radius β have been developed to improve welding efficiency.
The groove shape has been changed by making the root face smaller and the root face larger, but with the current TIG welding method, welding work,
There are problems with the quality of the weld (poor fusion, hot cracking), and there is a limit to narrowing the groove area.

Furthermore, cracks 3 were recently observed in the welded parts of reaction tubes used in the petrochemical industry, and an investigation into the cause revealed that a thin bead was welded over i, but at this time the upper layer of the bead was welded. When the beads in the lower layer remelt and become integrated with the beads in the upper layer, a large molten layer is formed, and when this large molten layer resolidifies, the solidification progresses from the base material 1 side toward the center and Impurities were segregated, resulting in a macrostructure as shown in FIG. 2 with a crack 3 in the center, and improvement of this structure was desired.

In order to solve the above-mentioned problems, the present invention adopts a welding construction method in which the first layer is TIG welded using back wave welding, and the second and subsequent layers are distributed welded using MIG welding to increase the layer thickness. The present invention will be explained in detail below with reference to Examples.

The macrostructure shown in Figure 2 has directionality and segregation of impurities in the center.The purpose of the present invention is to create a macrostructure without directionality in which cracks 3 do not occur from the center of the molten metal. It is.

When multilayer welding with a thin bead thickness is performed, the macrostructure of the weld metal becomes as shown in FIG. 2, so distribution welding was used in the present invention.

Furthermore, as a welding method, MIG welding was used in which the thickness of the bead 5 can be relatively easily controlled by changing the position of the torch 4.

In order to eliminate the directionality of the macrostructure, it is better to have a thicker bead 5 per layer, and the results of experiments have shown that if the bead is 5 mm or more, the influence of the lower layer is eliminated.

In other words, if the thickness of the bead 5 is set to 5 mm or more using MIG welding, which has an arc with excellent heat concentration, when the upper layer bead 5 is welded, the lower layer bead 5 will not remelt and only the upper layer bead 5 will solidify. However, at this time, the upper layer bead 5 solidifies upward from the lower layer bead 5 side, and segregation of impurities occurs in the upper part of each bead 5.

In this way, since each bead 5 is not remelted and integrated, segregation occurs only in each bead 5 and becomes discontinuous, and as a result, a macrostructure with directionality as shown in Fig. 2 is not formed. Therefore, cracks 3 do not occur.

Therefore, in order to increase the layer thickness, the position of the torch 4 was shifted somewhat toward the rotation direction from the top surface as shown in FIG. 3 (if the torch position was reversed, the layer thickness would be thinner).

As shown in FIG. 4, the first layer was TIG welded to form the Uranami bead 6, and the second and subsequent layers were distributed and welded by MIG welding to form a bead 5 having a layer thickness of 5 mm or more.

Table 1 shows an example of welding conditions for the welding method of the present invention.

Table 2 shows the results of the ASTM A567 HK-40 rupture test under the conditions shown in Table 1.

However, the conventional method breaks after about 80 hours.In the present invention, as mentioned above, the Uranami bead is formed by TIG welding of the first layer, so the Uranami bead becomes smooth and the quality of the Uranami bead is good. Since the second and subsequent layers are welded by MIG welding, the welding speed for the second and subsequent layers is fast, and since a bead of 5 mm or more is formed, as mentioned above, when the upper layer bead is welded, the lower layer is welded. The beads do not remelt, and only the upper beads solidify upward from the lower bead side, resulting in segregation of impurities at the top of each bead.

As a result, there is an advantage that the segregation of impurities in each bead becomes discontinuous, does not lack directionality, and no cracking is observed.

Therefore, the present invention can improve welding quality and welding efficiency.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing a conventional groove shape, Fig. 2 is a cross-sectional view showing a conventional welded part, Fig. 3 is a side view showing the welding method of the present invention, and Fig. 4 is a cross-sectional view showing a conventional welded part. In the cross-sectional view, 5 is a bead and 6 is a uranami bead.

Claims (1)

[Claims] 1 Form a Uranami bead by TIG welding the first layer, and M
A method for welding heat-resistant cast steel, characterized by forming a bead with a layer thickness of 5 mm or more by IG welding.