JPS61232068A - Arc welding - Google Patents

Abstract

PURPOSE:To suppress the increase in local hardness and to perform good welding with less residual stress by swinging an arc in the welding line direction in the magnetic field and by-eliminating local over-heating and thermal inclination after building up the metal virtually including carbon powders on the arc surface of a cast iron member. CONSTITUTION:A buildup welding 1a is performed with the electrode 2 made of the metal virtually including no carbon and of Ni or Ni based alloy on the welding surface of a cast iron made member 1. In case of magnets 4, 5 being approached to this welding zone, an arc 3 is moved before and behind in the welding line direction in case of the welding current being AC and to the built-up zone in case of DC. The local overheating of the weld zone is prevented and the thermal gradient with the peripheral side is eliminated. The generation of martensite layers is controlled by the fact that there is no generation of the high hardness ledeburite due to the overheating and rapid cooling and that there is less temp. gradient. A good welding without any deformation is therefore performed because of no welding cracks and less residual stress.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an arc welding method, and particularly to an arc welding method suitable for welding cast iron.

[Prior Art] Gas welding using cast iron welding rods and arc welding using special alloy (Ni-based, Ni-Fe-based, etc.) welding rods have been used for a long time to repair cast products. This is a well-known method.

However, these conventional methods do not have sufficient mechanical properties (welding defects are likely to occur and joint strength is low), and as a result, they have rarely been applied to structural materials that require strength. .

In contrast, the cast iron welding rod or cast iron welding method proposed by the present applicant (Japanese Patent Publication No. 56-35993,
6-77093 and 57-9904), reliable welding that can withstand use as a strength member can be performed.

Here, we will briefly explain why it is difficult to weld cast iron.

As is well known, cast iron has a large amount of carbon, and most of the carbon is crystallized in flaky or spherical shapes.

When the cast iron is melted by the heat applied during welding, the graphite crystallized in the cast iron rapidly dissolves and crystallizes in the molten metal.

On the other hand, recrystallization of graphite from the molten metal during cooling and solidification occurs very slowly, so when the metal is rapidly cooled, such as during welding, a highly hard carbide-containing structure such as ledebrite is generated. Due to the formation of such a highly hard structure, cracks are extremely likely to occur, making sound welding difficult.

According to the above-mentioned three inventions already published by the present applicant (hereinafter referred to as the three inventions of the earlier application), the above-mentioned problems in welding cast iron can be solved.

That is, in the three inventions of the prior application, the composition and structure of the welding rod or various aspects during welding are changed so that the carbon contained in the molten metal in the molten state becomes spherical or flaky graphite and crystallizes in the weld metal. This is for selecting conditions. By doing so, the generation of highly hard carbide structures in the weld metal or in the base metal near the weld boundary is suppressed, and it is possible to perform sound welding.

[Problems to be solved by the invention] However, even with the three inventions of the earlier applications, if the temperature during welding is increased excessively, the carbon content in the molten metal will completely dissolve and the carbon content will melt during cooling. It crystallized as a highly hard carbide, and there was a risk that the integrity of the weld structure would be impaired.

In particular, in conventional arc welding methods, the welding rod, droplets and molten pool are heated to extremely high temperatures by the arc. (For example, when a droplet is falling from a welding rod, the arc around it is constricted by thermal and magnetic pinch effects and becomes a high-temperature semi-plasma state, so the droplet with a large specific surface area is rapidly This high temperature droplet is then continuously supplied and the molten pool, which is itself exposed to the arc, is heated to extremely high temperatures of about 1800°C or more.) The molten metal is rapidly cooled after the arc has passed, and the carbon that has melted therein crystallizes out as a highly hard carbide-containing structure, causing the crystallized structure to lose its integrity.

In order to avoid such problems, in the three inventions of the earlier applications, the temperature of the molten metal during welding is lowered by the gas welding method, but even the arc welding method, which has good workability, can It is hoped that improvements will be made to enable sound welding.

[Means for Solving the Problems] In order to solve the above problems, the present invention includes overlaying a metal that does not substantially contain carbon on the surface to be welded when welding cast iron members by arc welding. At the same time, a magnetic field is applied to the arc to cause the arc to swing in the direction of the welding line or mainly in the direction of the welding line, thereby preventing excessive temperature rise of droplets and molten pool during welding. It is.

The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 is a perspective view illustrating an embodiment of the method of the present invention.

Reference numeral 1 denotes a plate-shaped welding member, and the plate surface is overlaid with metal 1a that does not substantially contain carbon. and,
A welding rod 2 is arranged to face this plate surface.

The rear end of the welding rod 2 is connected to a welding machine (not shown). An arc 3 is generated between the tip of the welding rod 2 and the welding member 1, and an electromagnet 4.5 is arranged so as to apply a magnetic field to the arc 3. In the figure, 4 indicates the north pole of the magnet, and 5 indicates the south pole of the magnet. 6 indicates a bead caused by welding.

By applying a voltage between the welding member 1 and the welding rod 2 to generate an arc 3, and applying a magnetic field to the arc 3 by the magnet 4.5, the arc 3 follows the magnetic lines of force according to Fleming's law. It swings in the direction of the welding line perpendicular to (in the direction of arrow 7 or 8). This prevents excessive heating of the droplets falling from the tip of the welding rod 2 and the molten pool 9 formed on the welding member l directly below the welding rod 2.

Note that there is an alternating current between the welding rod 2 and the welding member l.

Current with any waveform, such as direct current or pulsed current, may be applied.

Figure 2 is a diagram explaining the arc deflection when a sinusoidal alternating current is applied as the welding current.
(a) is a plan view, (b) is a side sectional view, and (c) is a current waveform diagram. When alternating current is used as the welding current as shown in FIG. 2, the arc oscillates around the molten pool 9 as shown in FIG. 2(b). The period of this contact matches the frequency of the welding current. In addition, in the illustrated example.

When the arc moves to the position directly below the welding rod, the moving speed of the arc is extremely fast, so the thermal energy added to the molten pool 9 per unit time is small, and the excessive temperature of the droplet 10 and the molten pool 9 is prevented. rising is prevented.

FIG. 3 shows the arc deflection state when the direct current shown in FIG. 3(c) is used as the welding current. In this state shown in FIG. 3, the arc is shifted backward in the direction of movement of the welding rod 2. In the example shown in FIG. 3, an excessive rise in temperature of the droplet 10 and the molten pool 9 is more reliably prevented.

In FIG. 4, a pulsed current or a double-wave rectified current is applied as the welding current. In this case, the arc 3 swings back and forth between the direction directly below the welding rod 2 and the rear direction in the direction of movement of the welding rod.

FIG. 5 shows an example in which an electromagnet 11 is installed to apply a magnetic field in a direction perpendicular to the direction of the magnetic field formed by the magnet 4.5. In FIG. 5, a direct current shown in FIG. 5(C) is applied as a welding current, and an alternating current is applied to the electromagnet 11. Then, the arc 3 is shifted backward in the welding rod movement direction by the magnetic field formed by the magnet 4.5, and is also reciprocated in the direction connecting the magnets 4.5 by the magnetic field formed by the electromagnet 11. (In other words, the arc is swung in a direction that includes the welding line.The range in which the arc is swung is not particularly limited, but
For example, as shown in the diagram, approximately 45 mm on each side across the weld line.
It can be expanded to a range of about 90° to 60a (total degree of 90° to 120'). ), in this case, the amount of thermal energy applied to the droplet and the molten pool per unit time is further reduced compared to the embodiments shown in FIGS. 2 to 4.

Although the members to be welded by the method of the present invention are made of cast iron, only one member to be joined by welding may be made of cast iron.

As is well known, there are various types of cast iron such as gray cast iron, white cast iron, cold and hard cast iron, malleable cast iron, spotted iron, etc., and the present invention can be applied to any cast iron.

In the present invention, the metal to be overlaid may be overlaid on only one member, or on both members to be welded. However, since there is no difference in the actual effect, there is no difference in cost. From this point of view, it is preferable to build up only on one member.

In this case, if the other member is not made of cast iron, it is preferable to build up the other member.

This overlay metal is a metal that does not substantially contain metal (
Although either a single substance or an alloy may be used, Nt or Ni-based alloys are particularly suitable.

In this way, by interposing a fleshy metal that does not substantially contain carbon, the tsuba wipes the hard material at the welding interface. Toughness can be achieved.

In the present invention, as the welding rod, the cast iron welding rod disclosed in the three inventions of the prior application is suitable, but other cast iron welding rods may also be used.

In the above illustrations and explanations, sinusoidal alternating current, direct current, double-wave rectified current, and pulsed current are shown as the welding current, but it is clear that current with other waveforms may be applied in the present invention. be.

Furthermore, during welding after build-up in the present invention, in short, it is sufficient to apply a magnetic field to cause the arc to oscillate. The magnetic field is not limited to acting only on the welding rod, but may be applied in a direction diagonal to the moving direction of the welding rod, for example.

[Function] Generally, the liquidus temperature of hypereutectic cast iron is much higher than the eutectic temperature, and if the temperature during welding is lower than this liquidus line, the graphite in the cast iron will not completely melt into crystals. It remains in the molten metal without being released. If graphite remains in the molten metal,
With this as a nucleus, graphite grows rapidly, and hardened structures such as ledebrite are less likely to occur even in the case of rapid cooling as in arc welding.

In the conventional arc welding method, the temperature during welding is 1800℃ or higher, so the graphite in the molten metal is almost completely melted and crystallized, and a hardened structure is formed during cooling. Put it away.

On the other hand, according to the method of the present invention, the temperature of the droplets and molten pool during arc welding can be lowered below the liquidus line, thereby preventing the melting and crystallization of graphite and causing no or almost no hardened structure. It is possible to obtain weld metal that does not produce any weld metal.

In particular, in the present invention, since a metal layer substantially free of carbon is interposed at the weld boundary, crystallization of a hard carbide structure in the weld heat affected zone is avoided, and the weld area is further strengthened. High toughness can be achieved.

Further, in the present invention, since the arc is oscillated, a wide range can be heated with a low current density, and the following effects are also achieved.

■ Since there is less heat input into the base metal where the droplets fall, the width of the weld heat affected zone becomes significantly smaller.

■ Even after welding, it is possible to heat the parts by the swung arc (however, in this case, the arc needs to be swung backwards in the direction of rejoining movement).
By reducing the cooling temperature in the aOO~500°C region,
It is possible to make martensitic phase less likely to occur.

According to the present invention, the heat input to the base metal is distributed over a wide range, the temperature gradient of the base metal is reduced, and welding deformation is also reduced.

[Examples] Examples will be described below, but the present invention is not limited to the following examples unless the gist of the invention is exceeded.

Example 1 (a) Using a cast iron welding rod having the composition shown in Table 81, Ni was deposited on the surface of the base metal (FC25) to a thickness of approximately 1 mm, and then the welding process was performed as shown in Figure 1. A bead was then formed by arc welding. At this time, the magnetic flux was set perpendicular to the traveling direction of the welding rod, the strength of the magnetic field was varied in the range of 0 to 140 Gauss, and the temperature of the molten pool was measured.

Table 1 The temperature of the molten pool is measured by stopping the arc momentarily and measuring the surface temperature of the molten pool at that moment using a radiation thermometer. As shown in Figure 6,
According to Figure 6, the stronger the magnetic field acting on the arc, the more
It is observed that the temperature of the molten pool decreases. In addition, it was clearly observed by naked eye observation through a filter that the arc amplitude also increased.

(b) Next, using the hypereutectic cast iron welding rod of (a) above,
Condition 0, in which the strength of the magnetic field acting on the arc was adjusted so that the molten pool temperature was 1300°C and a weld bead was formed, was the same as in (a) except that the strength of the magnetic field was adjusted in this way. It is.

After the bead formation was completed, the bead and base metal were cut vertically and the cut surfaces were polished to determine the distribution of Vickers hardness Hv of the welded portion. The results are shown in FIG. 7. Discussion of the measurement results shown in FIG. 7 will be described after Comparative Example 1 below.

Comparative Example 1 A weld bead was formed and the Vickers hardness Hv distribution of the weld was measured in the same manner as in Example 1 (b) except that Ni was not built up on the surface of the base metal. The results are shown in FIG. 7 by broken lines.

From FIG. 7, in the example of the present invention in which Ni is built up, the local increase in hardness near the boundary between the weld metal and the base metal is eliminated, and the hardness of the entire weld metal is also reduced. It is recognized that there are On the other hand, in the comparative example without Ni overlay, it is recognized that a significant increase in hardness occurs near the boundary between the weld metal and the base metal.

When the metal structure of the weld was observed under a microscope, it was found that in the example of the present invention, spherical or flaky graphite was precipitated almost uniformly except for the built-up layer, but in the comparative example, it was found that graphite was precipitated almost uniformly at the weld boundary. In the vicinity, the number of spherical or flaky graphite deposits decreased.

[effect] As detailed above, the arc welding method of the present invention is as follows.

When welding cast iron parts, the surface of the base material is coated with Ni, which does not contain substantially carbon, and the arc is swung by the action of a magnetic field. Thermal and magnetic pinch hardening is prevented, and the following excellent effects are achieved.

(b) It is possible to prevent excessive temperature rise of molten metal during welding, so even when welding cast iron, it is possible to prevent the generation of highly hard weld metal and obtain a healthy weld structure. It is.

(b) Local increase in hardness at the weld boundary is avoided, resulting in significantly high toughness.

(c) It is possible to make the weld heat affected zone extremely small.

(d) By adjusting the swing direction of the arc,
It is possible to reduce the cooling rate and suppress the formation of a martensite layer.

(e) The heat input to the base metal can be distributed over a wide range, and the temperature gradient can be reduced to reduce welding deformation.

[Brief explanation of the drawing]

FIG. 1 is a perspective view illustrating an embodiment of the method of the present invention. Each of the figures in FIGS. 2 to 5 is a diagram explaining the details of the embodiment method, in which (a) is a plan view, (b) is a longitudinal cross-sectional view, and (C) is a current waveform. It is a diagram. Moreover, FIG. 6 and FIG. 7 are graphs showing measurement results in Examples. 1... Base material, la... Overlay metal, 2...
・Welding rod, 3... Arc, 4.5... Magnet,
6... Bead. Agent Patent Attorney Tsuyoshi Shigeno Figure 2 Figure 3 (C) (C) Figure 4 Figure 5 (a) (a) (b) (b) (c) (C) Figure 6 Magnetic flux density ( (Glass) Figure 7 Distance from welding boundary (mml

Claims (1)

[Claims] (1) In the method of arc welding cast iron members, after overlaying the surface to be welded with a metal that does not substantially contain carbon,
An arc welding method characterized by applying a magnetic field to the arc and performing welding while swinging the arc in the welding line direction or mainly in the welding line direction.