JPS6213111B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for joining α+β type titanium alloys. Titanium is lightweight due to its low specific gravity, has high strength due to its hexagonal crystal structure, and has excellent heat resistance and corrosion resistance, which makes it comparable to ordinary stainless steel. ,
It has come to be used in a wide range of fields including chemical industrial equipment. In particular, strong titanium alloys, which have been made even stronger by adding alloying elements such as aluminum, have a fairly high specific strength (strength/density) and have excellent properties, so they are used in aerospace and aviation applications. It has come to be widely used in fields such as aircraft outer panels and rocket motor cases, and research in these areas is also actively progressing. When joining titanium alloys to manufacture such strong titanium alloy structures,
For example, welding may be performed by electron beam welding (EBW) with the welded parts of titanium alloys being butted together. However, according to this welding, the weld metal part (referring to the part that has been melted and solidified by welding) has a solidified structure that has grown from a liquid phase to a solid phase with a sharp temperature gradient. α affects the toughness and ductility of weld metal parts
Because it is difficult to control grain refinement, the toughness of the weld metal part tends to decrease compared to other base metal parts, and post-weld heat treatment also improves the mechanical properties of the weld metal part. However, depending on the type of titanium alloy, heat treatment may actually cause the weld metal to become brittle. In addition, regular TIG welding, which is an inert gas-shielded arc welding method using non-consumable electrodes, is also used and a pure titanium rod is used as the filler metal. This has caused a problem in that the strength may be lower than that of other base metal parts. The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to ensure that the weld metal part is well alloyed after welding titanium alloys and that no welding defects occur. The object of the present invention is to provide a method for joining α+β type titanium alloys having excellent strength and toughness and good mechanical properties in a welded joint. That is, the present invention focuses on the fact that the Al element in the α+β type titanium alloy is an α-phase stable element, and that a certain relationship is established between the concentration of the Al element in the alloy and the strength of the alloy. When joining α + β type titanium alloys, the α + β type titanium alloys are interposed with pure titanium or an insert material containing 3.0% by weight or less of aluminum, with the remainder being substantially titanium. In this state, the abutted portions are welded by high energy density welding and then heat treated. Titanium alloys to which the present invention can be applied include α
A few percent of Al, which is a stable element, is added to strengthen the titanium as a solid solution, and V, V, and V as third elements are added.
For example, an α+β type titanium alloy with solid solution strengthening of the β base by adding β-stable elements such as Cr or Mo.
Ti-6%Al-4%V and Ti-6%Al-6%V-2
%Sn etc. Next, as the insert material interposed in the abutting portion of the α+β type titanium alloys, pure titanium or a material containing 3.0% by weight or less of aluminum with the remainder substantially made of titanium is used. As the pure titanium, pure titanium having a chemical composition conforming to the first to third types specified in JIS H 4650 can be used. In this case, the manufacturing method is
Sponge titanium is the main raw material, and ingots produced in a vacuum or inert gas using a consumable electrode arc furnace or plasma beam furnace are used for forging, extrusion,
Although it is possible to use methods such as rolling to form insert materials into predetermined shapes, it is also possible to form pure titanium raw materials into rod-shaped ingots in a plasma melting furnace, and then use the rod-shaped bodies as consumable electrodes to re-melt in vacuum. However, it is also desirable to carry out a two-stage melting process in which an insert material of a predetermined shape is then obtained by appropriate processing means. In addition, as pure titanium, we have reduced the amount of interstitial impurity elements that greatly affect properties such as titanium's strength and toughness.
ELI (Extra Low Interstitial) titanium with C<0.01 to 0.015% and C<0.02 to 0.03% can also be used. In addition, in order to further improve the strength such as tensile strength and yield strength in the weld metal part, we added 3.0% by weight.
It is also possible to use the following insert materials containing aluminum, with the balance essentially consisting of titanium. In this case, the aluminum content is 3.0% by weight
The reason for the following is to ensure that the aluminum content in the weld metal after welding does not exceed approximately 6%, which is the solid solubility limit of aluminum in titanium, which may reduce the elongation and toughness of the weld metal. This is to prevent An insert material containing pure titanium or 3.0% by weight or less of aluminum with the remainder substantially made of titanium is inserted into the abutting portion of the α+β type titanium alloys to be welded, and the abutting portion is in this state. Welding is performed by high energy density welding, and welding methods in this case include electron beam welding using an electron beam as a heat source, laser beam welding using a laser beam as a heat source, plasma welding using a plasma arc as a heat source, tungsten, etc. It is possible to apply TIG welding, which is arc welding by superimposing pulses, using a non-consumable electrode, preferably under an inert gas shield with He added as a working gas. Among these, those that use an electron beam or laser beam as a heat source have a higher energy density than those that use an arc as a heat source, and
It is particularly advantageous because it has the characteristic that the heat source can be easily controlled, and it enables highly accurate and highly efficient welding. In the case of high-density energy welding such as the above-mentioned electron beam welding, the energy required per unit length of the weld line is very small, and the area of the fusion zone and the heat-affected zone near it becomes considerably narrower and remains. Since the strain and stress are small and such deterioration areas are localized, it shows excellent mechanical properties even in the as-welded state without heat treatment, and the mechanical properties can be improved by heat treatment. Further improvements can be made. In addition, when such high-density energy welding is performed, a significant boiling phenomenon occurs in the irradiated area of the beam (arc), and a molten pool with moderate stirring is formed, so inserts made of pure titanium etc. The material does not remain in the welded metal part with its original composition, and alloying is performed well in the welded metal part, resulting in excellent mechanical properties. Next, the posture during welding can be roughly divided into downward welding using a vertical beam (arc) and horizontal welding using a horizontal beam (arc).
There is. Among the above, when performing penetration welding in downward welding, depending on the thickness of the alloy (thickness of the welded part), the surface tension of the back bead alone cannot support the molten pool (the part that melts during welding). In this case, it is sometimes necessary to use a backing metal to prevent the molten pool from falling to a state where it is partially penetrated. On the other hand, in the case of horizontal welding, the influence of the weight of the molten pool is smaller than in the case of downward welding, the stability of the beam hole etc. is excellent, and penetration welding can be easily performed, so horizontal welding is more suitable. In addition, horizontal welding can be roughly divided into upward welding, downward welding,
There are horizontal welding, circumferential welding, etc., and it is desirable to select and carry out the method appropriately depending on the object to be welded, welding conditions, etc. In addition, in the case of high-energy density beam welding such as electron beam welding, in both penetrating and non-penetrating welding, as the beam output increases, the width of the molten pool increases and the inside of the molten pool is violently agitated. Since molten metal may flow out and cause welding defects such as recesses in the welded metal part, the frequency, amplitude, vibration direction, etc. of the beam vibration related to the molten pool movement during welding should be selected.
In addition, it is desirable to appropriately select beam penetration rate, beam current, etc. In some cases, it may also be preferable to use a local vacuum welding method in which only the vicinity of the weld line is evacuated. In addition, in the case of TIG welding, by performing welding with pulses, alloying in the weld metal part can be further improved, and a welded joint with excellent mechanical properties can be obtained. Next, the ratio of the insert material to be interposed is preferably 5 to 85% per unit volume of the molten metal part. That is, in the cases shown in FIGS. 1 and 2, the ratio t ₁ /t ₂ of the thickness t ₁ of the insert material to the thickness t ₂ of the weld metal part is in the range of 5 to 85%. It is desirable to do so. This is because if the percentage of insert material is less than 5%, the toughness of the weld metal part may be lower than that of other base metal parts, and 85%
For example, if the thickness of the insert material exceeds the beam width of electron beam welding, and even if the insert material is melted, stirring will not be sufficient, and the components of the insert material will remain unevenly distributed in the weld metal, which will deteriorate the mechanical properties. This is to reduce the Next, as the heat treatment after welding, stress strain relief treatment (SR treatment), diffusion treatment (D treatment), solid solution treatment + aging treatment (STA treatment), etc. are appropriately selected and performed. Among these, when stress and strain relief treatment is performed, it is preferable to perform a treatment of heating at a temperature of approximately 450 to 950° C. for approximately 15 minutes to 15 hours, followed by air cooling or water cooling. Also, when performing diffusion processing, approximately
It is best to heat the product at a temperature of 800°C or higher for about 15 minutes to 15 hours and then cool it with water or air. Furthermore, when performing solid solution treatment + aging treatment, approximately 800 to 1000
It is best to heat the material at a temperature of approximately 400 to 680 degrees Celsius for approximately 15 minutes to 6 hours, followed by water cooling, oil cooling, or air cooling. good. In addition, in the prescription processing, it is also possible to do this in multiple times.
It is also possible to perform a treatment that involves overaging. In addition, in titanium alloys, α-type alloys are stable at low temperatures, so heat treatability cannot be expected. Therefore, the solid solution treatment + aging treatment described above is targeted at α+β-type alloys, and in α+β-type alloys, the metal is affected by αβ transformation. Adjust the microstructure to improve and stabilize mechanical properties. In this way, when welding α+β type titanium alloys, we butt them together with the above-mentioned insert material interposed, weld this butt part by high energy density welding, and then heat treat it. By controlling the concentration of Al element in the alpha grains of the weld metal to an appropriate value, it is possible to improve the toughness and ductility of the weld metal, although the strength of the weld metal may decrease slightly. This makes it possible to obtain welded joints with excellent physical properties. Example 1 As shown in FIG. 1, titanium alloy plates having a thickness T=40 mm and chemical compositions shown in Table 1 were prepared as welding base materials 1 and 2. Further, as the insert material 3, two types of pure titanium plates having thicknesses t ₁ =0.6 mm and t ₁ =1.2 mm and chemical components shown in Table 2 were prepared.

【table】

[Table] Next, the two types of insert materials 3 were individually interposed between the welding base materials 1 and 2 and butted, and in this state, the abutted portions were electron beam welded. At this time, horizontal penetration welding was performed in which the electron beam was directed substantially horizontally in the direction of arrow A and moved laterally in the direction of arrow B. Table 3 shows the welding conditions at this time.

[Table] In addition, when welding, the frequency, amplitude, vibration direction, etc. of the beam vibration should be appropriately adjusted to eliminate the occurrence of welding defects, and the weld metal part 4 after welding shown in Fig. 2 should be adjusted as appropriate. Thickness t ₂ is 4.5
It was set to mm. Next, samples with a thickness of 5 mm, a width of 12.5 mm, and a length of 300 mm are cut out from the welded base metals 1 and 2 after the welding described above, centering on the weld metal part 4. Next, each sample is subjected to heat treatment, and then the above-mentioned A test piece 5 shown in FIG. 3 was cut out from the sample in the direction of the weld line, and a tensile test was conducted in the direction of the weld line. The above heat treatment was performed by heating at 933° C. for 30 minutes as a solid solution treatment, followed by water cooling, and then heating at 545° C. for 6 hours as an aging treatment, followed by air cooling. In addition, the dimensions of the test piece 5 are: total length L _T = 100 mm, parallel part length P
=45mm, gauge length L=35mm, diameter D=4±0.05
mm, shoulder radius R = 10mm, thread S = M10 x 1.5
It is. The results of this tensile test are also shown in Table 4.

【table】

[Table] As is clear from Table 4, it was confirmed that the toughness of the welded specimens with insert material 3 was significantly improved compared to the welded specimens welded with no insert material. It was done. This is achieved by controlling the concentration of Al element in the α grains of the weld metal to an appropriate level when welding with the insert material 3 interposed.
This was due to the ability to improve ductility, and it was confirmed that the strength was further improved in all cases where heat treatment was performed after welding. Example 2 As welding base materials 1 and 2, α+β type titanium alloy plates having a plate thickness T=40 mm and chemical compositions shown in Table 1 above were prepared. In addition, as insert material 3, plate thickness
Two types of Ti-1.5% by weight Al plates with t ₁ =0.6 mm and t ₁ =1.2 mm, both of which had chemical components shown in Table 5, were prepared.

[Table] Next, the two types of insert materials 3 are interposed separately between the welding base materials 1 and 2 and butted, and in this state, the electron beam is directed approximately horizontally in the direction of arrow A. Welding was carried out under the conditions shown in Table 3. Next, samples having the same dimensions as in Example 1 were cut out from the base metals 1 and 2 after welding, centering around the weld metal part 4, and then each sample was solid solutionized under the same conditions as in Example 1. After treatment and aging treatment, a test piece 5 shown in FIG. 3 was cut out from the sample in the direction of the weld line and subjected to a tensile test. The results are shown in Table 6.

【table】

[Table] As is clear from Table 6, welding with insert material 3 interposed and then heat-treated results in a lower welding rate than those in which welded with no insert material and heat-treated after welding. It was observed that the toughness was significantly improved. Example 3 Welding base materials 1 and 2 (see Fig. 1) having the same chemical composition as shown in Table 1 as in Example 1 and having a plate thickness T = 40 mm,
Prepare insert materials 3 (see Fig. 1) having the chemical composition shown in Table 2 and having a plate thickness t ₁ = 0.6 mm,
Next, the insert material 3 was interposed between the welding base materials 1 and 2 and they were butted together, and in this state, electron beam welding was performed under the conditions shown in Table 3. Next, a sample of 5 mm in thickness, 12.5 mm in width, and 300 mm in length was cut out from the base metals 1 and 2 after welding, centering on the weld metal part 4, and then heated at a temperature of 948°C for 10 hours. After water cooling and diffusion treatment, the distribution of chemical components was examined using an X-ray microanalyzer at equal intervals in the thickness direction of the weld metal part 4. The results are shown in Table 7.

[Table] As shown in Table 7, since the molten metal part is well stirred during welding, alloying is sufficiently carried out in the weld metal part 4, and no pure titanium remains. It was confirmed that very good results were obtained. Example 4 Weld base materials 1 and 2 with the same chemical composition shown in Table 1 as Example 1 and plate thickness T = 2.5 mm (see Figure 1)
and the chemical composition shown in Table 2 and the plate thickness t ₁ = 0.5 mm
Pure titanium insert material 3 (see Figure 1) of Superimposed TIG welding was performed.

[Table] Next, after welding, heat treatment was performed in a vacuum furnace at 933°C for 20 minutes as a solid solution treatment, followed by oil cooling, and then as an aging treatment, heat treatment was performed at 545°C for 5 hours and then air cooled. When a test piece was cut out from the welded metal part 4 in the direction of the weld metal part 4 and tested for mechanical properties, good results were obtained for both strength and toughness. Also, in the thickness direction of the weld metal part 4,
When component analysis was carried out at regular intervals using a line microanalyzer, it was confirmed that the structure was sufficiently dispersed and alloyed. As detailed above, according to the present invention, titanium alloys can be welded together very well, no weld defects are observed in the weld metal part, and dispersion alloying in the weld metal part is achieved quite well. It is possible to improve the strength by applying heat treatment, and it has the remarkable effect of being able to join titanium alloys through welded joints with excellent mechanical properties.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams of slopes before and after welding, respectively, in the welding situation according to an embodiment of the present invention, and FIG. 3 is an explanatory diagram of a tensile test piece used for testing mechanical properties. 1, 2... Welding base material, 3... Insert material, 4... Welding metal part.

Claims (1)

[Claims] 1 When joining α + β type titanium alloys, the α + β type titanium alloys are butted together with an insert material containing pure titanium or 3.0% by weight or less of aluminum, with the remainder being substantially titanium, and in this state. A method for joining titanium alloys, characterized in that the abutted portions are welded by high energy density welding and then heat treated.