JPS6361118B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a welding treatment method for eliminating welding micro-defects existing in a welded part by heat and pressure treatment after fusion welding. Generally, there are various types of welding defects that occur during welding of base metals, such as cracks, pores, poor fusion, and insufficient penetration, and the size of these defects also varies. When a welding defect exceeding the standard occurs, conventionally, the welded portion where the defect has occurred is completely removed and rewelded to repair the welding defect. However, in the above-mentioned repair, the work is complicated, and if the base material originally has poor weldability, there is a risk that welding defects will occur again even if we re-weld. For example, the turbine foil of a gas turbine is normally exposed to high temperatures of 500°C or higher and is a high-speed rotating body, so high strength is required.
In recent years, Ni-based heat-resistant alloys have been used as the metal material. However, when the disk of the gas turbine foil made of a Ni-based heat-resistant forged alloy and the blade made of a Ni-based heat-resistant cast alloy are joined by welding, the Ni-based heat-resistant cast alloy has poor weldability and weld metal solidification cracks. Otherwise, defects such as liquefaction cracking in the weld heat-affected zone occur, and it is difficult to obtain a good weld regardless of the fusion welding method. This is caused by carbides existing at grain boundaries during the rapid heating and cooling process.
Due to the reaction between the γ′ phase and the γ phase, Nb and
Al, Ti, S, O, and C segregate to form a low melting point phase, which melts and liquefies during welding, resulting in microcracks. These cracks are micro-cracks with a width of several microns to several hundred microns and a length of several tens of microns to several thousand microns. Moreover, it is very difficult to prevent the occurrence of welding defects during welding, and it is an uncertain method. Therefore, conventionally, the disc and the blade of the gas turbine foil have been mechanically connected by fitting, and the machining thereof requires a great deal of time and cost. Therefore, the present inventors took this into account, and without removing the welding defect occurring part inside the welded part,
By intensively researching methods to eliminate welding defects after welding and holding the workpieces mentioned above under high temperature and high pressure for several hours, it is possible to eliminate welding micro-defects and to homogenize the segregated elements near grain boundaries. We have confirmed that this is possible and have come up with the present invention. That is, in the present invention, after melt welding the base metal, a workpiece having micro defects such as cracks or pores inside the welded part is heated to a high temperature at which the base metal sufficiently causes plastic flow or creep behavior, and
A high pressure sufficient to promote plastic deformation of the base material is applied from uniaxial, biaxial, triaxial, or all directions using hydrostatic pressure, and the time period during which the defects are destroyed by a thermal processing process or metallurgical reaction at high temperatures. This is a welding processing method in which the welding micro-defects are eliminated by holding and heating and pressurizing, followed by unloading and cooling. Welding base materials to which the treatment method of the present invention can be applied include various steel materials, aluminum and its alloys, nickel and its alloys, copper and its alloys, titanium and its alloys, etc.
A specific example of the connection between a disk and a blade of a gas turbine foil using a Ni-based heat-resistant alloy will be described. The welding base materials used were Inconel 718, a Ni-based heat-resistant forging alloy, as the disk material, and Inconel 718 as the blade material.
Inconel713C is a Ni-based heat-resistant casting alloy. The chemical composition of both materials is shown in the table.

[Table] Electron beam welding was performed on the two types of materials (base metals) mentioned above for testing, as I-type butt joints as shown in FIG. 1, under the welding conditions shown in Table 2. In Fig. 1, 1 is the first base material for the disk material made of Inconel 718, 2 is the second base material for the blade material made of Inconel 713C, 3 is the welded part joined by electron beam welding, and 3a is the first base material for the blade material. 1
The welding heat affected zone 3b is the welding heat affected zone on the base material 1 side, and 3b is the welding heat affected zone on the second base material 2 side.

[Table] Next, the workpieces subjected to the above electron beam welding were subjected to heating and pressure treatment under the following conditions. Heating temperature: 1200°C Pressure: 1200 atm Holding time: 4 hours The processing method is to charge the workpiece to be welded into a pressure vessel, and inject high-pressure inert gas (Ar, He, etc.) into the pressure vessel.
is injected into the container to raise the pressure in the container to a predetermined level, applying hydrostatic pressure to the workpiece from all directions, applying pressure, and heating the workpiece to a predetermined temperature using a heater. After maintaining this state for a predetermined period of time, the pressure inside the container is lowered, the load is removed, and the container is cooled to complete the process. The above heating temperature is a temperature that sufficiently promotes plastic flow or creep behavior of the material (base material), and since creep behavior becomes noticeable at temperatures above approximately 2/3 of the melting point expressed in absolute temperature, The temperature is preferably from 1000°C to 1250°C in the case of the Ni-based heat-resistant alloy of this example. In addition, the above pressurizing pressure is for the material (base material)
The pressure is sufficiently high to promote plastic deformation, and in the case of the Ni-based heat-resistant alloy of this example, a load of 1000 atmospheres or more is required. Furthermore, the holding time of heating and pressurizing is the time required for welding micro defects to collapse due to the thermal processing process or metallurgical reaction,
In the case of the Ni-based heat-resistant alloy of this example, several hours are required. Table 3 shows the results of inspecting the welded parts subjected to the above heating and pressure treatment and the welded parts that had been subjected to electron beam welding for the occurrence of welding defects (mainly microcracks and pores) in the welded parts. Shown below. In this inspection, macro cross sections are taken from test pieces of both objects to be welded.
Measured by microscopic observation (100x magnification).

【table】

[Table] As shown in Table 3, micro-cracks were observed under all welding conditions (see Table 2) when electron beam welding was performed as is, but when the welding speed was slow in the case where heat and pressure treatment was applied. In specimens A and B, the microcracks were not completely eliminated, but in specimens C and D, where the welding speed was high, the microcracks were completely eliminated. Furthermore, a 100-hour creep rupture test was conducted to compare the high-temperature characteristics of the welded objects subjected to the above-mentioned heating and pressure treatment and the welded objects that had undergone electron beam welding as a high-temperature joint performance test. The results are shown in the graph of FIG. Incidentally, in this test, a rod-shaped test piece having a welded portion 3 in the middle was prepared from the object to be welded and used. As shown in Fig. 2, the as-welded specimens (broken lines) all had weld fractures, but the welded specimens (solid lines) that had been subjected to heat and pressure treatment after welding had fractures on the base metal side. It showed sufficient high temperature strength. In the above embodiment, the base metal is fused and welded by electron beam welding, but the same process can also be achieved by fusion welding by laser beam welding, TIG welding, or plasma welding. In addition, as for the pressurizing method, in addition to applying hydrostatic pressure from all directions as in the embodiment, a method of applying mechanical pressure from one, two, or three axes may also be adopted; The most effective method is to apply high pressure. In addition, if micro-defects such as cracks occur on the surface of the welded part, the above-mentioned heating and pressure treatment may be applied after the surface is ground to remove the defects, or the surface of the defect-generated part or The entire object to be welded is covered with a thin plate cover member having a melting point and high-temperature strength similar to that of the base metal, and then heated and pressurized. Therefore, according to the present invention as described above, after fusion welding, the workpiece to be welded is subjected to heating and pressure treatment at a high temperature and high pressure state where the base material exhibits plastic flow or creep behavior, thereby removing micro defects within the weld zone through thermal processing. In order to improve the welding strength by eliminating the welding micro-defects that have been destroyed by processes or metallurgical reactions, it is possible to reliably weld and join base materials that have conventionally been considered difficult to weld. Therefore, the disk and blade of the gas turbine foil, which had conventionally been forced to be joined mechanically, can be joined by fusion welding, which simplifies the machining of both parts and shortens the machining time. It has the advantage of being able to reduce costs.

[Brief explanation of drawings]

Figure 1 is a perspective view of the test piece, Figure 2 is a creep and
It is a graph showing the results of the Lapture test.

Claims (1)

[Claims] 1. A welded object that has micro-defects such as cracks or pores inside the welded part after fusion welding the base metal,
The base material is heated to a high temperature where it exhibits sufficient plastic flow or creep behavior, and
After applying a high pressure sufficient to promote plastic deformation of the base material from all directions, either axially or hydrostatically, and holding it for a period of time during which the defects are destroyed by a thermal processing process or metallurgical reaction at high temperature, and then subjected to heat and pressure treatment. ,
A welding processing method characterized by unloading and cooling to eliminate weld micro defects. 2 After melt welding Ni-based heat-resistant alloy as a base material,
The temperature of the object to be welded is 1000℃~1250℃ and the pressure is 1000℃.
2. The welding process according to claim 1, wherein the welding process is performed at a pressure above atmospheric pressure for several hours. 3. When joining a gas turbine foil disk made of a Ni-based heat-resistant forged alloy and a blade made of a Ni-based heat-resistant cast alloy, the disk and blade are butt-fused and welded by electron beam welding, laser beam welding, TIG welding, or plasma welding. After that, the gas turbine foil has a temperature of 1000℃
The welding processing method according to claim 2, characterized in that the heating and pressurizing treatment is performed for several hours in a hydrostatic inert gas at a temperature of ~1250°C and a pressure of 1000 atmospheres or more.