JPH01262077A - Build-up welding method for titanium or titanium alloy - Google Patents

Abstract

PURPOSE:To form a sound build-up welding metal in the shape of an excellent welding bead by controlling the ratio of the positive electrode component time in a voltage waveform to the negative electrode component time in the specified range in case of the AC plasma arc build-up welding of Ti or Ti alloy. CONSTITUTION:The specified pilot current is fed from a pilot power source 5 between the inner cylinder 3a of a plasma arc torch 1 and W electrode, the specified welding current is fed from the main AC power source 6 fitted with the positive polarity and reverse polarity time ratio adjusting device 8 capable of adjusting the time ratio of the positive polarity and reverse polarity optionally between the W electrode 2 and Ti alloy sheet 11 to be processed and the high frequency generator 7 for igniting a plasma arc is fitted between the W electrode 2 and Ti alloy sheet 11. The powder build-up material 9 of a Co base super heat resistant alloy, etc. is fed from a pipe 4 into the plasma arc 10 generated between the W electrode 2 and Ti alloy sheet 11 and build-up welding is executed by electrifying with the time ratio satisfying an equation I between the positive electrode component time ta in the voltage waveform and negative electrode component time tb.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overlay welding method for performing overlay welding on the surface of titanium or a titanium alloy.

[Conventional technology]

The face surfaces of intake and exhaust engine valves in automobiles and the like are required to be overlaid to improve their wear resistance under high-temperature atmospheres. For this reason, a heat-resistant steel material, for example, martensitic heat-resistant steel 5U113 according to JIS G 4311, has been used as an engine valve material, and a Co-based super super heat-resistant alloy is overlay welded onto the face surface of the engine valve material.

Co-based super super heat-resistant alloy has high hardness and excellent heat resistance, so it is often used as a build-up material for engine valve faces.

Recently, efforts have been made to reduce the weight of valve materials in order to improve engine responsiveness and reduce fuel consumption, and the use of titanium alloys in place of conventional heat-resistant steel is being considered. However, although this titanium alloy has excellent heat resistance and corrosion resistance, it has poor wear resistance, and therefore requires hardfacing treatment when used as an engine valve material.

As another use for titanium and titanium alloy materials, recently titanium alloys have been used instead of steel for drill pipes and their couplings in order to reduce the weight of drilling materials when drilling oil wells etc. on land. An example of its use can be seen.

Ti-6Aj is generally used as the titanium alloy trill pipe and tool joint! -4V (6% to Ti
Titanium alloys containing Aβ, 4% Hardfacing treatment is required on the surface.

Conventionally, as a hardfacing welding method for such materials, Japanese Patent Application Laid-open No. 6
As described in Publication No. 1-23574, a plasma arc build-up welding method has been proposed that uses a mixed powder composed of titanium and metal carbide on an engine valve face made of a titanium-based alloy material. .

In this proposal, a commonly used positive polarity plasma arc build-up welding method is used as the plasma arc build-up welding method. It is well known that positive polarity plasma arc build-up welding involves greater dilution of the base metal than reverse polarity plasma arc welding. When hard overlay welding is performed using overlay material, intermetallic compounds are generated at the bonding interface between the base metal and overlay weld metal, forming a brittle joint. As the dilution into the base material increases, the width of formation of the brittle compound phase increases, which poses a practical problem. If positive plasma arc welding, which has no cleaning effect, is applied to welding materials such as titanium or titanium alloys, which form an oxide film with a high melting temperature on the surface of the base material,
There are problems such as inclusions being formed at the bonding interface, making it impossible to obtain a healthy bond.

Furthermore, JP-A-59-78774 discloses a welding process in which a hardening agent containing hardened metal carbide grains in pure titanium powder is deposited on the surface of titanium or titanium alloy by TIG welding or plasma arc welding. A method is proposed.

As the plasma arc build-up welding method in the above proposal, a reverse polarity soft plasma arc welding method is used. It is known that the reverse polarity soft plasma welding method causes less dilution of the base material and has a cleaning effect of removing the base +4 oxide film. This overlay welding method is especially effective when overlaying active metals and alloys, such as titanium or titanium alloys, whose base metal surface is covered with an oxide film with a high melting temperature. . However, in a reverse polarity connection where the base material is the cathode and the electrode is the anode, electrons generated from the base material are constantly generated.
A large diameter water-cooled copper electrode is generally used instead of the W electrode used in positive plasma arc welding because the electrode is heated and damaged by collision with the electrode. For this reason, reverse polarity plasma arc welding I/-CH is larger due to the positive polarity plasma arc welding torch, making it unsuitable for overlay welding of small items such as engine valve faces.
There is a problem with welding operability.

In addition, since both the reverse polarity plasma arc welding method and the positive polarity plasma arc welding method use direct current as the current used, they are affected by magnetic blowing, so there are problems such as difficulty in obtaining a good bead shape.

[Problem to be solved by the invention]

The present invention removes the strong oxide film with a high melting temperature that forms on the surface of titanium or titanium alloys, reduces dilution to the base material, eliminates the formation of brittle compound phases at the joint interface, and eliminates the effects of magnetic blowing. The object of the present invention is to provide a plasma arc build-up welding method that allows a good bead shape to be obtained.

[Means to solve the problem]

In order to achieve the above object, the plasma arc build-up welding method for titanium or titanium alloy according to the present invention uses an AC plasma arc build-up welding method in the build-up welding method for the surface of titanium or titanium alloy. If the positive polarity component time of the waveform is t8 and the negative polarity component time is also,
This method is characterized by overlay welding at a time ratio that satisfies the following formula.

t + [Function] Titanium or a titanium alloy can be used as the titanium material constituting the engine valve material or the excavation material, but titanium alloy materials are generally preferred. Ti-6A7 is a typical titanium alloy material. -4
V alloy (Ti alloy containing 6% Aβ and 4% ■) as well as Ti-6AI2-2Sn-4Zr-2M
o alloy (6% AI!, 2% Sn, 4% Zr and 2% M.

) and Fi-5An-2,5
Sn alloys (Ti alloys containing 5% L and 2.5% Sn) and the like are suitable as engine valve materials and drilling materials.

Stellite alloy (trade name) is a CO-based super super heat-resistant alloy used as a powder material for overlay. The typical name and main components are Stellite tooth 1 (30%Cr-2,5
%C-1%Si 1%Mn-1%Mo-3%F
e -3%Ni 12.5%W-Ba1-Co), Stellite m, 6 (28%Cr 1.1%C-1%S
i -1%Mn -1%Mo -3%Fe -3%Ni
-4%W-Ba1・CO), Stellai 141.12 (
29%Cr -1,4%C-1,4%Si ~1%
Mn -1%Mo -3%Fe -3%Ni
-8%W-Bal.Co), etc.

The present inventors have discovered that the deterioration of the joint that occurs when the Co-based super super heat-resistant alloy is overlaid on titanium or titanium alloy is due to the formation of inclusions at the joint interface due to oxides formed on the surface of the base material and the dilution of the base material. Considering that this is due to the formation of a compound phase at the joint interface due to an increase in

As a result, the reverse polarity plasma arc welding method (connection with the base metal as the cathode and the electrode as the anode) is recommended to suppress the deterioration of the joints mentioned above.
It was also found that an AC plasma arc welding method in which the time ratio between positive polarity and negative polarity is within a predetermined range is effective.

However, in the reverse polarity plasma arc welding method, as mentioned above, the heat shape and welding operability are poor due to the large size of the plasma welding 1-chi and the magnetic blowing by direct current.
This is not a sufficient method for overlay welding of titanium or titanium alloys.

It has been found that in the AC plasma arc welding method of the present invention, the time ratio of the positive polarity and reverse polarity components has a close relationship with the cleaning effect of removing the oxide film formed on the surface of the base material and the dilution rate of the base material. Ta. In the relationship between the two, the opposite polarity component cleans the oxide film formed on the base material, and the positive electrode component increases the dilution of the base material, but ensures cooling of the electrode. Therefore, as shown in FIG. 2, the positive polarity component time (t8
) and the reverse polarity component time (1b) within a predetermined range, damage to the electrode can be prevented, dilution of the base material can be suppressed, and an appropriate cleaning effect range width can be ensured.

FIG. 3 presents a graph showing the relationship between the time ratio of the positive polarity component and the reverse polarity component, the width of the cleaning effect range, and the dilution rate in AC plasma arc overlay welding according to the present invention.

When the time ratio of the positive polarity component is less than 60%, the amount of heat generated by the electrode is due to electrons generated from the base material colliding with the electrode during the reverse polarity component.
The amount of heat generated by the electrode increases rapidly, causing damage to the electrode.
Sound welding will no longer be possible.

In addition, when the time ratio of the positive polarity component exceeds the upper limit of 90%, the dilution rate to the base material increases rapidly, and the cleaning effect is no longer observed, and inclusions and compound phases are generated at the interface of the joint. Sexuality deteriorates.

For the above reasons, in order to prevent electrode damage, suppress the dilution rate of the base material to a predetermined value, and obtain a cleaning effect range, the bipolar component time (ta + ttb) L, l + tb applied to the electrode must be 60%. As mentioned above, a range of 90% or less is appropriate.

The present invention will be specifically described below based on Examples.

〔Example〕

Next, the overlay welding method of the present invention will be explained based on FIG.

FIG. 1 is an explanatory diagram showing an example of an AC plasma arc welding apparatus suitable for overlay welding a powder overlay material onto the surface of a titanium alloy plate using an AC power supply.

In FIG. 1, (1) shows the tip of a plasma arc torch, and the plasma arc torch (1) is equipped with a tungsten electrode (2) in the center, and outside of this electrode (2). is the torch inner cylinder (3a) and 1.-
Each outer cylinder (3b) is provided. A plasma gas passage (13) is provided between the tungsten electrode (2) and the torch inner cylinder (3a).
) and the torch outer cylinder (3b).
4) and a powder supply pipe (4) for supplying powder overlay material (9). The passageway (13) is configured to be supplied with an inert gas such as argon gas as a plasma gas. The shield gas passage (14) is supplied with an inert gas such as argon gas to shield the welding area from the atmosphere.

A titanium alloy plate (11) to be subjected to overlay welding is installed below the plasma arc torch (1) configured as described above. Then, the powder overlay material (9) is supplied into the plasma arc (10) through the powder feed pipe (4) using an inert gas such as argon gas as a supply gas, and the titanium alloy plate (11) is Overlay metal (12) is sequentially formed on the surface of.

Note that a predetermined pilot current is supplied from a pilot power source (5) between the tungsten electrode (2) and the torch inner cylinder (3a). In addition, between the tungsten electrode (2) and the titanium alloy plate (11), a main AC power supply ( 6)
From this, a predetermined welding current can be supplied.

Further, a high frequency generator (7) for igniting the plasma arc is disposed between the tungsten electrode (2) and the torch inner cylinder (3a).

Next, in order to confirm the effects based on the present invention, the powder overlay materials shown in Table 3 were combined with the titanium and titanium alloy plates shown in Table 2, and Overlay welding was carried out under the following welding conditions using the AC plasma arc overlay welding apparatus of the embodiment. Table 1 shows the results of examining the bondability and bead shape of the built-up portion.

(1) Welding conditions: Welding current 60A Welding speed 500mm/min Plasma gas flow rate (Ar) ], 5 j! /min
Shield gas flow rate (Ar) 20 j2 /min Powder carrier gas flow rate (Ar) 27! /min Test Nos. 1 to 6 in Table 1 were overlay welded using the AC plasma arc overlay welding apparatus shown in Fig. No. 9, No. 10 was a reverse polarity plasma arc welding method, and for comparison, overlay welding was performed using the reverse polarity plasma arc welding method.

Minami 1 to 4 satisfied the requirements of the present invention, and no inclusions or compound phases were observed at the bonding interface of the built-up part, and good bonding properties and bead-shaped built-up metals were obtained.

Moreover, it goes without saying that there was no damage to the electrodes and stable welding could be performed.

Folds 5 and 6 were performed by AC plasma arc welding, and are examples of positive polarity component time ratio: t + . In floor 5, the positive polarity component time ratio is lower than the lower limit,
The electrode was severely damaged and the arc became unstable during welding, so welding was stopped. In No. 6, the positive polarity component time ratio exceeded the upper limit, there was no cleaning effect, the dilution of the base metal increased, inclusions and compound phases were formed at the joint interface, and cracks were observed.

In the case of Room 7 and Floor 8, positive polarity plasma arc welding was used for comparison, but satisfactory bonding properties and bead shapes could not be obtained in either case.

In the case of floors 9 and 10, reverse polarity plasma arc welding was used, and although the bondability was good, a satisfactory bead shape could not be obtained.

Table 2 Table 3 [Effects of the Invention] As is clear from the above examples, if the method for overlay welding of titanium or titanium alloy of the present invention is used, (1G) overlay welding of titanium or titanium alloy can be achieved. It removes the oxide film on the surface of the base material that degrades bonding properties, prevents the formation of brittle compound phases and inclusions at the bond interface, and provides a good heat shape. In addition, it is possible to always perform stable overlay welding without damaging the electrodes, and to perform plasma overlay welding in which a sound overlay weld metal can be obtained, which is extremely effective industrially.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of an apparatus for carrying out the overlay welding method for titanium/titanium alloy of the present invention using an AC power source;
Fig. 2 is a diagram showing the voltage waveform applied to the electrode of the present invention, and Fig. 3 is a graph showing the relationship between the ratio of the positive polarity component time and the reverse polarity component time, the cleaning effect range width, and the dilution rate of the base material. It is. DESCRIPTION OF SYMBOLS 1...Tungsten electrode, 2...Plasma arc torch, 3a...Torch inner cylinder, 3b...1--Torch outer cylinder,
4...Powder supply pipe, 5...Pilot power supply,
6... Main AC power supply, 7... High frequency generator, 8
... Positive electrode reverse polarity time ratio adjustment circuit, 9... Powder overlay material, 10... Plasma arc, 11... Titanium alloy plate, 12... Overlay metal, 13... Plasma gas Passage, 14... Shield gas passage.

Claims (1)

[Claims] (1) In the overlay welding method for the surface of titanium or titanium alloy, an AC plasma arc overlay welding method is used, and the positive electrode component time of the voltage waveform is t_a, and the negative electrode component time is t_
In case of b, a method for overlay welding of titanium or titanium alloy, characterized in that overlay welding is performed at a time ratio that satisfies the following formula. 60%≦t_a/(t_a+t_b)×100≦90%
...(1)