JP2024060331A - Buried Arc Welding Method - Google Patents

Abstract

[Problem] To provide a buried arc welding method capable of suppressing the emission of manganese to the outside of the weld metal. [Solution] A consumable electrode buried arc welding method using a welding wire containing manganese, in which the tip of the welding wire is inserted into a space surrounded by a concave molten portion formed in the base metal by the arc, to weld the base metal. [Selected Figure] Figure 3

Description

The present invention relates to a buried arc welding method.

Gas Metal Arc (GMA) welding is used under high current conditions to weld thick plates, and the welding wire, which is a consumable electrode, contains manganese (Mn), which improves the strength and toughness of the weld metal (see, for example, Patent Document 1).

JP 2007-075833 A

However, in welding under high current conditions, the mechanical properties of the welded joints deteriorate, and one of the causes is the decrease in the manganese concentration in the weld metal.
In steel materials, manganese is known as an element that improves tensile strength. For example, SN490B steel in JIS G 3136 contains a maximum of 1.65% manganese.
In addition, manganese also plays a role as a deoxidizing element in welding. It is known that the inclusion of oxygen in the weld metal deteriorates the mechanical properties. In response to this, manganese combines with oxygen to form slag or fumes, which are then discharged outside the weld metal, thereby reducing the amount of oxygen in the weld metal. Therefore, in welding wires, the manganese concentration is often higher than that of the base metal in order to ensure the tensile strength of the weld metal while taking into account the consumption of manganese as a deoxidizing agent.
The greater the welding current or welding heat input, the greater the amount of manganese emitted as slag or fumes. This is because the molten metal is held at high temperatures for a long period of time, making it more susceptible to oxidation. Therefore, in high-current welding, the manganese concentration in the weld metal is likely to decrease, and the tensile strength is likely to decrease accordingly. In addition, in recent years, it has been pointed out that manganese in slag or fumes may cause health damage, and regulations have been strengthened, so that manganese emissions in slag or fumes are also undesirable from this perspective.
Based on the above, it is necessary to suppress the emission of manganese outside the weld metal from two perspectives: to prevent a decrease in the tensile strength of the weld metal and to reduce the risk of health damage.

The objective of this disclosure is to provide a buried arc welding method that can suppress the emission of manganese outside the weld metal.

The buried arc welding method disclosed herein is a consumable electrode buried arc welding method using a welding wire containing manganese, in which the tip of the welding wire is inserted into a space surrounded by a concave molten portion formed in the base metal by the arc, thereby welding the base metal.

According to the present disclosure, it is possible to suppress the emission of manganese outside the weld metal.

1 is a schematic diagram showing one configuration of a consumable electrode type arc welding device according to an embodiment of the present invention; FIG. 2 is a schematic diagram showing buried arc welding conditions. 1 is a bar graph showing the manganese concentration in the weld metal, comparing buried arc welding according to the present embodiment with general DC welding. 1 is a bar graph showing the tensile strength of the weld metal in comparison between buried arc welding according to the present embodiment and general DC welding.

A buried arc welding method according to an embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is intended to include all modifications within the scope of the claims and meaning equivalent to the claims. In addition, at least some of the embodiments described below may be combined in any combination.

The present invention will be described in detail below with reference to the drawings showing an embodiment of the present invention. The welding method according to this embodiment uses buried arc welding to suppress the emission of manganese outside the weld metal.

<Arc welding equipment>
1 is a schematic diagram showing one configuration of a consumable electrode type arc welding device according to the present embodiment. The arc welding device according to the present embodiment is a welding machine that performs GMA (Gas Metal Arc), and includes a welding power source 1, a torch 2, and a wire feeder 3.

The torch 2 is made of a conductive material such as a copper alloy, and has a cylindrical contact tip that guides the welding wire 5 to the part to be welded of the base material 4 and supplies the welding current Iw required to generate an arc. The contact tip comes into contact with the welding wire 5 that passes through it, and supplies the welding current Iw to the welding wire 5. The torch 2 also has a hollow cylindrical nozzle surrounding the contact tip that sprays shielding gas to the part to be welded. The shielding gas is, for example, carbon dioxide gas, a mixture of carbon dioxide gas and argon gas, an inert gas such as argon, etc.

The base material 4 to be welded is a steel material, for example a steel material for building construction, and contains manganese as an element to improve tensile strength.

The welding wire 5 is, for example, a solid wire, and contains manganese. The manganese content of the welding wire 5 is lower than the manganese content of the base material 4, and is less than 1.4 wt%. The diameter of the welding wire 5 is 0.9 mm or more and 1.6 mm or less, and functions as a consumable electrode. The welding wire 5 is, for example, a packed wire that is wound in a spiral shape and stored in a pail pack, or a reel wire that is wound on a wire reel.

The wire feeder 3 has a feed roller that feeds the welding wire 5 to the torch 2, and a motor that rotates the feed roller. The wire feeder 3 pulls out the welding wire 5 from the wire reel by rotating the feed roller, and supplies the pulled out welding wire 5 to the torch 2. Note that this method of feeding the welding wire 5 is one example, and is not particularly limited.

The welding power source 1 is connected to the contact tip of the torch 2 and the base material 4 via a power supply cable, and includes a power source unit 11 that supplies the welding current Iw, and a feed speed control unit 12 that controls the feed speed of the welding wire 5. The power source unit 11 and the feed speed control unit 12 may be configured separately. The power source unit 11 includes a power source circuit 11a that outputs a PWM-controlled direct current, a control circuit 11b, a voltage detection unit 11c, and a current detection unit 11d.

The voltage detection unit 11c is a sensor that detects the welding voltage Vw and outputs a voltage value signal Vd indicating the detected voltage value to the control circuit 11b.

The current detection unit 11d is, for example, a sensor that detects the welding current Iw that is supplied from the welding power source 1 to the welding wire 5 via the torch 2 and flows through the arc, and outputs a current value signal Id indicating the detected current value to the control circuit 11b.

The power supply circuit 11a includes an AC-DC converter that converts commercial AC to DC, an inverter circuit that converts the converted DC to the required AC by switching, and a rectifier circuit that rectifies the converted AC. The control circuit 11b PWM controls the inverter circuit of the power supply circuit 11a based on the set welding conditions and the detected welding current Iw and welding voltage Vw. The required welding voltage Vw is applied between the base material 4 and the welding wire 5, and the welding current Iw flows.

When a hand-operated switch provided on the torch 2 side is operated, the torch 2 outputs an output instruction signal to the welding power source 1. The output instruction signal is input to the welding power source 1 via a control communication line (not shown), and the control circuit 11b uses the output instruction signal as a trigger to start outputting the welding voltage Vw and welding current Iw from the power source circuit 11a.

<Welding method and conditions>
In the present embodiment, buried arc welding is used as a welding method for suppressing the emission of manganese to the outside of the contact metals. Hereinafter, buried arc welding for suppressing the emission of manganese to the outside of the contact metals and welding conditions will be described.

Figure 2 is a schematic diagram showing the welding conditions for buried arc. When a large current is supplied to the welding wire 5, as shown in Figure 2, a concave molten portion 4a is formed in the base material 4, and the tip of the welding wire 5 enters the space surrounded by the molten portion 4a. Hereinafter, the space surrounded by the concave molten portion 4a will be referred to as the buried space, and the arc generated between the welding wire 5 that has entered the buried space and the base material 4 or the molten portion 4a will be referred to as the buried arc, as appropriate.

In buried arc welding, the amount of manganese fumes generated is smaller than in conventional DC welding. This is because, as shown in Figure 2, in buried arc welding, most of the area around the high-temperature droplet and the arc is covered by molten metal (concave molten portion 4a).

The droplet transfer mode is a globule transfer including a drop transfer, a spray transfer including a pendulum-like transfer or a rotating transfer, or a combination of these. If the welding conditions of the buried arc welding are satisfied, the droplet transfer mode is as described above.
In droplet transfer modes other than these, such as short circuit transfer, fumes are likely to be generated when the arc is re-ignited after a short circuit, and this occurs frequently, resulting in a large amount of fume and a large amount of manganese emission into the fumes.

The horizontal axis of the graph shown in Figure 2 indicates the welding current Iw, and the vertical axis indicates the welding voltage Vw. The welding conditions for achieving buried arc welding are an average current of the welding current Iw of 300 A or more, preferably 300 A or more and 650 A or less. If the welding current Iw is less than 300 A, the arc pressure becomes weak and the molten metal cannot be pushed down, making it impossible to maintain buried arc welding. If the welding current Iw exceeds 650 A, the amount of slag and fumes generated increases due to the increased heat input, and therefore even with buried arc welding, the effect of suppressing the emission of manganese into the slag or fumes becomes smaller.

More preferably, the welding current Iw is 300 A or more, and current amplitude control or current waveform control is preferably applied. When current amplitude control or current waveform control is applied to buried arc welding of 300 A or more, irregular short circuits that occur unintentionally due to disturbances and the like are reduced, and fume generation during re-arcing can be suppressed. Specifically, the welding current Iw is periodically varied under the conditions of an average welding current of 300 A or more, a frequency of 10 Hz to 1000 Hz, and a current amplitude of 50 A or more. The frequency is preferably 50 Hz to 300 Hz, more preferably 80 Hz to 200 Hz. The current amplitude is preferably 100 A to 500 A, more preferably 200 A to 400 A.

The welding voltage Vw (arc voltage) has an upper limit voltage that varies depending on the welding conditions, etc. The upper limit voltage is the maximum voltage at which a buried arc can be maintained, and is the critical voltage above which buried arc welding does not occur but normal DC welding occurs. The upper limit voltage is an increasing function of the welding current Iw, and the higher the welding current Iw, the higher it becomes. The lower limit voltage is a voltage approximately 4V lower than this upper limit voltage. At a voltage lower than the lower limit voltage, as the tip position of the welding wire 5 descends, short circuits between the welding wire 5 and the molten pool occur frequently, increasing the amount of fumes generated when the arc is re-ignited and reducing welding stability.

The upper and lower limit voltages vary depending on various factors such as the type of welding wire 5, wire diameter, welding current Iw, wire extension length, groove shape, welding speed, and load condition on the secondary side of the welding power source, but the relationship between the welding current Iw and the welding voltage Vw is generally as shown in Figure 2.

The welding heat input is 25 kJ/cm or more and 65 kJ/cm or less. The welding current Iw or welding speed is adjusted so that the welding heat input is within this range. If the welding heat input is below 25 kJ/cm, the heat input is small, so even with normal DC welding, the manganese emission is small and does not pose a problem. If the welding heat input exceeds 65 kJ/cm, as described above, the amount of slag and fumes generated increases due to the increase in heat input, so even with buried arc welding, the effect of suppressing the emission of manganese into the slag or fumes is reduced. In addition, the upper limit of the welding heat input is more preferably 40 kJ/cm. This is one of the general heat input limiting indexes in GMA welding, and it is more desirable to keep the welding heat input at 40 kJ/cm or less from the viewpoint of ensuring sufficient toughness of the welded joint, including the weld metal and the heat-affected zone.

By using buried arc welding that satisfies the above welding conditions, it is possible to reduce manganese emissions into the slag or fumes. The buried arc welding method, which suppresses manganese emissions outside the weld metal, is a new discovery.

Comparative Example
A solid wire (YGW18) with a wire diameter of 1.4 mm is used as the welding wire 5, carbon dioxide gas is used as the shielding gas, and welding heat input is 38 kJ/cm. General DC welding (non-buried arc welding) and buried arc welding are performed under the conditions of the welding current Iw being 400 A in the case of general DC welding and 430 A in the case of buried arc welding. The arc voltage is 41 V in the case of general DC welding and 38 V in the case of buried arc welding. The welding speed is 26 cm/min. For stabilization, the above-mentioned current amplitude control or current waveform control is applied to the buried arc welding. The base material 4 is SN490B, and a butt weld joint with a plate thickness of 25 mm and a groove angle of 35° is welded. The backing is SN490B with a plate thickness of 9 mm.

Figure 3 is a bar graph showing the manganese concentration in the weld metal, comparing buried arc welding according to this embodiment with general DC welding. In general DC welding (non-buried arc welding), the manganese concentration in the weld metal is about 1.1%, whereas in buried arc welding according to this embodiment, the manganese concentration in the weld metal is high at about 1.3%. In other words, in buried arc welding according to this embodiment, manganese emissions from slag or fumes are suppressed. Note that a difference in manganese concentration of the order of 0.1% is very large.

Figure 4 is a bar graph showing the tensile strength of the weld metal, comparing buried arc welding according to this embodiment with general DC welding. The tensile strength of general DC welding (non-buried arc welding) is about 525 MPa, whereas the tensile strength of buried arc welding according to this embodiment is high at just under 600 MPa. This is because the manganese concentration in the weld metal is high.

As described above, the buried arc welding method according to this embodiment can suppress the emission of manganese to the outside of the weld metal. In other words, the yield of manganese in the weld metal can be improved. This can suppress the decrease in the tensile strength of the weld metal. At the same time, the emission of manganese into the slag and fumes can be suppressed, reducing the risk of health damage to the welding worker.

In addition, the manganese concentration of the welding wire 5 used when welding the base metal 4 of the steel material can be kept lower than the manganese concentration of the base metal 4. At least, the manganese concentration of the welding wire 5 can be kept below 1.4 wt %.
In response to the strengthening of manganese regulations, it is expected that the development and market distribution of low manganese wire will become even more active in the future. Although there is a risk that the tensile strength of the weld metal of low manganese wire may decrease, the decrease in tensile strength can be suppressed by combining it with buried arc welding.

1: Welding power source, 2: Torch, 3: Wire feeder, 4: Base material, 5: Welding wire, 11: Power source, 11a: Power circuit, 11b: Control circuit, 11c: Voltage detector, 11d: Current detector, 12: Feed speed controller

Claims (4)

A consumable electrode type buried arc welding method using a welding wire containing manganese, comprising:
A buried arc welding method in which a tip of the welding wire is inserted into a space surrounded by a concave molten portion formed in a base material by an arc, thereby welding the base material. The method of claim 1 , wherein the manganese content of the welding wire is lower than the manganese content of the base metal. The method of claim 2 , wherein the manganese content of the welding wire is less than 1.4% by weight. The buried arc welding method according to any one of claims 1 to 3, wherein an average welding current of 300 A or more and 650 A or less is supplied to the welding wire, and the base material is welded with a welding heat input of 25 kJ/cm or more and 65 kJ/cm or less.

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