JP2022064169A - Manufacturing method of welding jointed body and manufacturing method of ceramic heater - Google Patents

Abstract

To provide a manufacturing method of providing a welding joined body of preferable welding quality according to a method of manufacturing the welding joined body by performing laser welding of two metal members by setting a coated film-remaining portion in which a coated film remains on the surface as a welding portion, without removing the coated film, with respect to a cold-forged article as the cold-forged article formed by forging forging-raw material formed of the coated film as a lubricant on the surface of at least one metal member of two metal members.SOLUTION: A cold forged article is forged from forging raw material in which a fluorine resin coated film is formed as a lubricant on the surface. When the coated film remaining on the cold forged article is the fluorine resin coated film, a low-melting point component to be contained in the coated film has small amounts and, therefore, the occurrence of blow hole or else can be extremely reduced even when the coated film receives thermal energy due to laser welding. When mother material of one side which is to be laser welded is the cold forged article, the fluorine resin coated film is effectively used for the lubricant of forging.SELECTED DRAWING: None

Description

The present invention relates to a method for manufacturing a welded joint, and more particularly to a method in which at least one of two metal members is a cold forged product and the two metal members are laser welded to manufacture a welded joint.

In cold forging, the metal material before forging (working material made of steel material, etc., hereinafter also referred to as "forging material" or simply "material") is subjected to frictional resistance and processing with the mold surface for forging. Lubricants are used to reduce pressure, improve the dimensional accuracy and surface condition of cold forged products, and prevent seizure during forging. This lubricant is usually formed by applying (coating) to a material, immersing the material in a lubricant (liquid), and then undergoing a drying treatment step to bring the material into close contact with the surface of the material as a film. Conventionally, various such coatings (lubricants) have been used, such as a water-soluble oxalate coating, an inorganic coating, and a lime coating that dissolves in an acid. This film undergoes deformation such as thinning according to the process (usually multiple forging processes) until the material becomes a cold forged product, following the deformation (plastic deformation) of the material, the expansion of the surface area, and the like. However, it remains on the surface of the cold forged product after the final plastic deformation.

Conventionally, it is possible to perform laser welding (hereinafter, also simply referred to as “welding”) as it is between metal members (base materials) that are cold forged products in which such a coating remains. When welding is performed at a portion having the coating film, blow holes and spatters (hereinafter referred to as blow holes, etc.) are generated in the welded portion. For this reason, it is easy to cause deterioration of welding quality and welding defects, so that it is not suitable for manufacturing welded joints that require high precision in welded parts, especially small welded joints, and there is a problem that it cannot be applied. there were. The cause of the occurrence of blowholes and the like is that the film (lubricant) remaining on the surface of the cold forged product contains a low melting point component as an impurity, and therefore heat is generated by high-density energy caused by laser irradiation. It is considered that the impurities generate gas at the welded parts (melted and solidified parts). And, such a problem is not limited to cold forged products, but if one is a cold forged product with a residual coating, the other (metal member of the other party of laser welding) is a machined product (member, product). ) Also occurs.

Therefore, when a cold forged product is laser-welded to a metal member of the other party to manufacture a welded joint, the film remaining on the surface of the cold forged product is applied to at least the planned welding location (welded portion) and the welded portion. In the vicinity thereof, a step of removing the coating film before welding by cutting, pickling, or the like is required. Welding after the film removal process (finishing process) by cutting or the like is impaired the merit of precision forging by cold forging. Further, by any means of cutting or cleaning, removing such a film means that the manufacturing process of the welded joint is increased and the manufacturing efficiency is lowered. Therefore, as a result, it becomes a factor that causes an increase in the manufacturing cost of the welded joint.

Under these circumstances, a zinc phosphate film (bonde film) is formed on the surface of the material and cold forged, and in the cold forged product before welding, at least the desired welded portion (welded portion) is 100 ° C. to 500 ° C. Blow holes, etc. are generated by performing heat treatment (heat treatment) to heat to ℃, dissociating and releasing low melting point components (crystal water, etc.) in the zinc phosphate coating (bonde coating), and then performing laser welding. A technique has been proposed in which the above-mentioned problem of deterioration of welding quality is solved (see Patent Document 1).

Japanese Unexamined Patent Publication No. 10-235482

According to the technique described in Document 1, a cutting process and a cleaning process are not required, but a heat treatment process is required. Therefore, although it is a relatively simple processing process, the coating film is required. In terms of requiring a removal process, there is no change in the number of processes. Moreover, the bonde coating has a problem that it cannot be applied to stainless steel whose material is one of the main materials to be processed for cold forging, and there is a problem that the range of metals to which cold forging is applied is narrow. there were.

Under these circumstances, the inventor of the present application has applied various lubricants to various metal materials (forged material test pieces) including stainless steel in order to obtain good laser welding for cold forged products without requiring a film removing step. A cold forged product (test piece) was manufactured by forming a coating film, and a test laser welding was performed. That is, for the cold forged product (test piece), the test piece after the film is removed and the film residual test piece without the film removal are combined with other members (for example, a machined product without a film). Hereinafter, test welding of laser welding was repeatedly performed on each of the "other members"). As a result, for cold forged products (test pieces) whose starting material is a material in which a film is formed using a specific lubricant, the occurrence of blow holes and the like can be significantly reduced even in the film residual test piece. I learned that a welded joint with good welding quality (required passing quality) can be obtained.

In the present invention, cold forging is performed by using a specific lubricant as a film in laser welding between cold forged products or between a cold forged product and a metal member other than the cold forged products in view of the above problems. Based on the knowledge obtained from the above test welding that good welding quality can be obtained even if the product is laser welded without removing the coating film, and it can be used even if the material is stainless steel. It is made and an object thereof is to provide a suitable method for manufacturing a welded joint including a cold forged product.

The invention according to claim 1 is a cold forged product in which at least one of the two metal members is forged from a forged material having a coating film forming a lubricant on the surface thereof. For cold forged products, a welded joint is manufactured by laser welding the two metal members with the film remaining on the surface as the welded site with the film remaining. In the method
It is a method for manufacturing a welded joint, characterized in that the cold forged product is forged from a forged material having a fluororesin film formed on the surface as a lubricant.
The invention according to claim 2 is the method for manufacturing a welded joint according to claim 1, wherein the cold forged product is made of stainless steel.

In the invention according to claim 3, one metal member is a shaft member, the other metal member is a tubular body, and the welded joint is formed inside one end of the tubular body. It is a shaft-shaped member manufactured by fitting one end of the metal member and laser welding two metal members with the outer peripheral edge of the joint formed by the fitting as the welded portion. The method for manufacturing a welded joint according to any one of claims 1 and 2.

The invention according to claim 4 is the ceramic so as to maintain continuity between a rod-shaped ceramic heater element whose tip generates heat when energized and one of the electrode terminals formed on the ceramic heater element. The cylinder is provided with a tubular body which is a metal member fixed to the rear end portion of the heater element, and a shaft member which is a metal member whose tip is fitted into the rear end portion of the tubular body by press fitting. The shape and the shaft are laser-welded with the outer peripheral edge of the joint formed by the fitting as a welded portion, so that the electrode terminal and the shaft are connected to each other via the tubular body. In a method of manufacturing a ceramic heater provided with a holding terminal shaft structure,
At least one of the tubular body and the shaft material is cold forged from a forged material having a fluororesin film formed on the surface as a lubricant, and the fluororesin film remains in the cold forged product. This is a method for manufacturing a ceramic heater, which comprises laser welding with the outer peripheral edge of the joint as a welded portion.

In the case of laser welding a cold forged product, the inventor of the present application forges using a lubricant made of various materials as described above in order to enable laser welding without removing the film remaining on the surface. A film was formed on the material to make a cold forged product (test piece), and test welding was repeated. As a result, in the case of laser welding with the remaining film portion as the weld site, a film was formed with various well-known lubricants (water-soluble oxalate film, inorganic film, lime film soluble in acid, etc.) as described above. Compared to cold forged products forged from forged materials, cold forged products forged from materials with a film formed of fluororesin can significantly reduce the occurrence of blow holes at welded parts, resulting in better welding quality ( It was found that a welded joint of the required acceptable quality) could be obtained. The inventor of the present application focused on the fact that the fluororesin has a high degree of lubricity, low friction, heat resistance, and adhesion, tried this as a coating, and laser welded the remaining coating portion as a welding portion. As a result of this, it was obtained. Moreover, unlike the bonde coating, the fluororesin coating has no problem in being applied to stainless steel.

As described above, the fluororesin can be applied as a coating film in cold forging of stainless steel and other metal materials, and even if it remains without being removed, there is no problem in welding quality in laser welding. Therefore, in the case of a cold forged product and then laser welding to produce a welded joint, it is extremely effective to use a fluororesin coating as a lubricant. That is, according to the present invention, since the fluororesin film is formed as a lubricant in cold forging, a welded joint having good laser welding quality can be obtained without requiring a step of removing the film. As a result, it is possible to obtain a peculiar effect that the manufacturing efficiency in the manufacturing of the welded joint is improved and the cost is reduced.

The factors for obtaining the above effects are considered as follows. Conventionally, when a cold forged product having a residual film is laser-welded, blow holes and the like occur in the components of the cold forged material, for example, when the material is stainless steel (Fe—Cr alloy). It is considered that the components having a lower melting point (low melting point component) than the main base material (Fe) form impurities, which causes the generation of gas due to the heat generated by the laser irradiation. On the other hand, when a fluororesin film was used as the film, the above effect was obtained. From this result, when a fluororesin film is used as the film, among the components contained in the film remaining on the surface of the cold forged product, the component having a melting point lower than that of the base material (Fe) (hereinafter referred to as the component). , Also referred to as "low melting point component") is significantly less than that of conventional cold forged products using a coating film that forms a lubricant, and therefore the amount of gas generated due to heat generation due to laser irradiation is suppressed. Conceivable. For example, in a cold forged product made of SUS430, the occurrence rate of blow holes and the like, which is a defect judgment when welding using a conventional Ka-containing inorganic film or the like, was 7 to 9%, whereas the fluororesin The rate of occurrence of blow holes and the like, which is a defect judgment when using the above, was 1% or less, which is much lower than those. The effect of the present invention is demonstrated from such test welding results.

In addition, the inventor of the present application inspected the low melting point component in the vicinity of the welded portion after welding with respect to the above example, and tried to verify the above reasoning. As a result, after laser welding, a component having a melting point lower than Fe (low melting point component) in SUS430 contained in the film in the vicinity of the welded portion in the cold forged product was inspected, and as a result, the film formed on the forged material was obtained. When the Ka-containing inorganic film was used, the total low melting point component (mass) was about 20% when Fe was 100%. On the other hand, when the fluororesin film was used for the film formed on the forged material, the total low melting point components (mass) when Fe was 100% was 5% or less. From this verification result, it is considered that the small amount of the low melting point component causes the reduction of gasification due to laser irradiation (heat generation) and greatly contributes to the reduction of the occurrence of blow holes and spatter.

In the present application, the above-mentioned "cold forged product" in which the coating residual portion is a welded portion may be one or both of the two metal members (welded base materials) to be welded. The "cold forged product" includes a product in which a part or most of the material is formed by cold forging, and is not limited to a product in which the entire material is formed by cold forging. Further, in the case where only a part of the forged material is formed by cold forging, a case where a film is formed only on the surface of a part of the material is included. In such a cold forged product, for example, the surface portion of the molded portion corresponding to a part thereof becomes the coating residual portion and becomes the welded portion. The metal member (base material) of the other party of the above-mentioned "cold forged product" whose welded portion is the remaining film portion is not only a machined product but also a cold forged product, such as cutting, cleaning, and heat treatment. The film is also removed by the method. In the present invention, the fluororesin used for the coating film refers to a resin containing a fluororesin as a main component, and examples thereof include tetrafluororesin, trifluororesin, and 4-6 fluororesin. In such a fluororesin film, the forging material is dipped in a liquid obtained by mixing and stirring the raw materials containing these resins as the main component (fine powder) with appropriate water, or the same liquid is applied to the forging material. It is formed by processing such as drying.

In the present invention, the cold forged product to be laser-welded without removing the fluororesin film (remaining) is not limited to the material of the material. The cold forged product is suitable for cold forging (plastic working) such as steel materials including stainless steel (SUS430, SUS630, etc.) and alloy steel, as well as non-ferrous metal materials such as aluminum and copper, and lasers. Widely applicable to things that can be welded. Further, the metal member and the welded joint according to the present invention are suitable for small items that require high precision, but are not limited thereto. In addition, depending on the application of the metal member, the welded joint, etc., it can be made into various shapes such as a tubular body (tube), a plate, a rod, etc., and the welded part (butting part, fitting part, etc.). It can be widely applied regardless of the shape and structure, and the welded joint can be embodied as a desired shape and structure in addition to the above-mentioned shaft-shaped member.

It is a schematic diagram explaining Embodiment-1 which embodied the manufacturing method of the welded joint of this invention, and A is the explanatory drawing of two metal members (shaft material and a tubular body) before welding. B is a cross-sectional view after welding. A vertical cross-sectional view of a glow plug having a welded joint of FIG. 1 as a terminal shaft structure for energization with an electrode terminal of a ceramic heater element, and an enlarged view illustrating a terminal shaft structure portion thereof. It is a schematic diagram explaining the form example-2 of the welded joint, A is the explanatory view of two metal members before welding, and B is the figure after welding.

The first embodiment, which embodies the method for manufacturing a welded joint of the present invention, will be described in detail with reference to FIG. As shown in the left figure (A) of FIG. 1, the two metal members forming the welded joint of the present invention, for example, one of them (upper figure) is a shaft made of SUS430 and having a circular cross section with a different diameter. The material 51 is the material 51, and the other (see the figure below) is a cylindrical body (pipe) 61 made of SUS630 and having a cylindrical shape (a tubular body having a circular cross section). Of these, in this example, the shaft member 51 is a cold forged product manufactured from a forged material having a fluororesin film formed on its surface through a multi-step cold forging process, and after cold forging, the fluororesin film (fluororesin film). (4 Fluororesin) has not been removed, and therefore a fluororesin film remains on the surface thereof. “Shading” in FIG. 1 (A) indicates the same coating. Although the tubular body 61 is a cold forged product, it is assumed that the coating film on the surface thereof has been removed by heat treatment or the like. The shaft member 51 has a shaft in which one end (shown, lower end) is fitted, for example, by press fitting to the inside (inner peripheral surface) of one end (shown, upper end) 63 of the tubular body 61. A large-diameter flange (large-diameter portion) 55 forming a portion 54, facing the other end side (illustrated, upper end side) following the portion 54, and having the same diameter as the outer diameter of the tubular body 61 in the fitted state thereof. A slender shaft portion 58 having an outer diameter smaller than that of the shaft portion 54 extends toward the other end side of the flange 55.

In this example, as shown in FIG. 1-B, in the welded joint 100, one end portion (shaft portion 54) of the shaft member 51 is press-fitted into the inside of one end 63 of the tubular body 61 by press fitting. , One end (annular surface) 63 of the tubular body 61 is brought into contact with one end facing surface (annular surface) 57 of the large-diameter flange 55 of the shaft member 51, and a joint portion (two) formed by the fitting thereof. The outer peripheral edge W of the abutment portion of the torus joint surfaces 57 and 63) is used as the welded portion. In laser welding, the outer peripheral edge W is irradiated with laser La under the condition that a predetermined melting depth can be obtained, and both members are made to circulate around the axis thereof, and two metal members (cylindrical body 61, shaft member 51). ) Is laser welded on the outer peripheral edge W so as to obtain a predetermined weld bead. As a result, a shaft-shaped member which is a welded joint 100 is manufactured. The shaft portion 54, which is one end of the shaft member 51, has a portion near the tip 53 that serves as a guide portion 54a for fitting with a tapered taper, and is outside the portion of the shaft portion 54 that is press-fitted into the inner peripheral surface of the tubular body 61. The diameter is set to be slightly larger (for the press-fitting allowance) than the inner diameter of the tubular body 61.

The structure of the welded joint (shaft member) 100 manufactured in this example is used, for example, in a ceramic heater having a known structure shown in FIG. 2 (for example, a glow plug used to promote the start of a diesel engine). A tubular body 61 fixed to the rear end of the element 11 so as to maintain continuity with one of the electrode terminals 16 formed on the rod-shaped ceramic heater element 11. This can be applied to a terminal shaft structure that maintains continuity between the electrode terminal 16 and the shaft member 51 via the tubular body 61. Details will be described later.

In the welded joint 100 manufactured in this example, a tetrafluoride resin coating remains on the surface of the shaft member 51, which is a cold forged product, as shown in FIG. However, neither blow holes whose welding quality was judged to be defective were found in the weld beads (welded parts) generated in the laser welding process, and spatters such as welding defects were not found in the vicinity thereof. In this way, when the tetrafluororesin coating is used for cold forging, there is no problem in the welding quality even if laser welding is performed in the state where it remains without removing it. A welded joint with high joint strength can be obtained. Further, in the production of the welded joint 100, the film removing step as in the conventional case is not required, so that the production efficiency can be improved and the cost can be reduced accordingly.

As a comparative example, a cold forged product obtained by cold forging by changing only the point where a film was formed on the same material with the above-mentioned conventional film material (inorganic film, etc.) as a lubricant was used as described above. In the same manner as above, laser welding was performed to manufacture a welded joint, and the weld quality of the welded joint was inspected. As a result, in the generated weld bead, the welding quality was judged to be defective and many blow holes were generated, and in the vicinity of the weld bead, the welding quality was judged to be defective and spatter was also frequently generated. .. From this comparative test, in the case of using an inorganic film, which is a conventional film, the removal step is indispensable before welding, but in the above example, it is not necessary, and as described above, welding is extremely efficient. Welds can be manufactured. The same effect was obtained when a trifluoride resin film or a 4-6 fluoride resin film was used instead of the tetrafluoride resin film.

As described above, the welded joint (shaft member) 100 of the above example is a terminal for connecting to one electrode 16 of the ceramic heater element 11 constituting the ceramic heater (glow plug) 201 shown in FIG. Applicable to shaft structure. That is, the cylindrical body 61 constituting the welded joint (shaft member) 100 in the above example has a resistance heating element 14 that generates heat by energizing the inside of the other end (lower end in FIG. 2). Of the pair of electrodes 16 and 17 formed behind the outer peripheral surface of the ceramic heater element 11 by fitting the rear end 13 of the round bar-shaped ceramic heater element 11 inside the tip portion 10 by press fitting. It is an energization holding pipe that holds energization with the electrode 16 located relatively on the rear end side (the upper end of the element 11 in FIG. 2). On the other hand, in the shaft member 51 constituting the shaft-shaped member which is a welded joint, one end portion 53 of the shaft member 51 is fitted inside one end 63 of the tubular body 61, and the side opposite to the one end portion 53. It is a current-carrying relay shaft material having the other end 52 side as a terminal. In the case where the shaft member 51 is press-fitted and fitted like such a tubular body 61, it is a cold forged product in which a fluororesin film is formed on the forged material. However, in order to ensure continuity with the electrode 16 of the element 11 and to form a plating layer, it is preferable to remove the coating film on the surface by heat treatment after forging.

As described above, the structure of the welded joint 100 composed of the tubular body 61 and the shaft member 51 shown in FIG. 1 is suitable as a terminal shaft structure for the ceramic heater element 11. This is because the application to the terminal shaft structure does not require a coating removal step, so that the rod-shaped ceramic heater element 11 is inside the other end (lower end of FIG. 2) of the energization holding pipe which is the tubular body 61. Manufacture of a heater element assembly formed by fitting the rear end portion (rear end 13), and by extension, the shaft member 51 is fitted into the tubular body 61 in the heater element assembly as described above. This is because it is possible to improve the efficiency of laser welding and manufacturing a ceramic heater as a glow plug. Moreover, in recent years, there has been a strong demand for glow plugs to be smaller (smaller diameter), lighter, and longer reach, and the current-carrying relay shaft material, which is the shaft material 51, is also smaller in diameter and longer (slender). There is a demand for conversion. In such a glow plug, a gap (gap) between the outer peripheral surface of the terminal shaft structure composed of the ceramic heater element 11, the tubular body 61 and the shaft member 51, and the inner peripheral surface of the tubular main body 31 surrounding them. Is getting smaller. Therefore, in the case of laser welding the welded portion as described above, if blow holes or spatter occur, the risk of short circuit increases. On the other hand, by using the present invention, it is possible to eliminate the occurrence of the film without removing the film, and therefore, it is expected that the cost of the glow plug that can meet the demand for such miniaturization (smaller diameter) can be reduced. To.

The configuration (structure) of the ceramic heater (glow plug) 201 shown in FIG. 2 will be described as follows. The glow plug is a stainless steel metal cylinder (different diameter cylinder) formed by fixing (fixing) the front end (lower end in the figure) 10 and the rear end 13 of the ceramic heater element 11 so as to protrude inward in a tightly fitted state. Body) 21 and a cylindrical metal body 31 made of stainless steel that is coaxially arranged, fitted, and welded to the different diameter and large diameter portion 22 of the rear end portion (upper end in the drawing) of the metal cylinder 21. From the above, it is configured as follows.

That is, the ceramic heater element 11 is formed in the shape of a round bar having the same diameter in the axis G direction, and the electrode terminals 16 connected to both ends of the resistance heating element 14 provided in the insulating substrate (for example, silicon nitride ceramic). , 17 are exposed on the outer peripheral surface (side surface) at a position shifted from the front to the back at the portion near the rear end of the ceramic heater element 11. Of these, one (tip side) electrode terminal (ground side electrode terminal) 17 is pressed against the inner peripheral surface of the metal cylinder 21 and is electrically connected. Then, as described above, the tubular body 61 is press-fitted into the rear end 13 of the element 11, and the conduction between the inner peripheral surface thereof and the other electrode terminal 16 is maintained. Further, the shaft member 51 is coaxially inserted and arranged in the metal main body 31 while being insulated, and the rear end 52 is projected from the rear end of the main body 31. Is fixed to an external terminal 71 to which a lead wire for power supply is connected. However, this external terminal 71 has a mounting hole that opens in the center on the tip side, and after inserting a portion near the rear end 52 of the shaft member 51 into this mounting hole, the outer circumference corresponding to the mounting hole is inserted. It is fixed to the shaft member 51 by crimping the surface. A diameter-expanded portion is provided on the inner peripheral surface of the rear end portion of the main body 31, and a ring-shaped packing 81 is provided between the inner peripheral surface of the enlarged diameter portion and the outer peripheral surface of the shaft member 51. A cylindrical insulating member 91 is arranged, and the shaft member 51 is configured to hold and fix the insulating member at the rear end of the main body 31. A screw portion 37 for attaching the glow plug 201 to the engine by a screwing method is formed on the outer peripheral surface of the portion near the rear end of the metal main body 31, and the screwed portion 37 is formed on the outer peripheral surface of the portion near the rear end. It is provided with a polygonal portion (for example, a head-shaped portion of a hexagon bolt) 39 for use.

In the above example, the welded joint has a terminal shaft structure suitable for a ceramic heater, and the two metal members are a tubular body and a shaft material, which are fitted as a fitting structure as described above. An example of a shaft-shaped member manufactured by laser welding two metal members with the outer peripheral edge of the joint surface in the state as a welded portion has been illustrated, but the present invention has a welded joint and the shape and structure of the two metal members. And, the welded portion is not limited, and it can be embodied as an appropriate one depending on the use of the welded joint as described above. For example, as in the welded joint 102 shown in FIG. 3 as the second embodiment, the metal member is made up of two cylindrical bodies (disk 51 or cylindrical member 61), and the metal members are thrust at the end faces 57 and 63 of both. It can be widely applied regardless of the shape and structure of the metal member and the welded joint, such as when laser welding La is performed around the outer peripheral edge W of the butt surface as a welded portion.

That is, the present invention is a cold forged product in which at least one of the two metal members is forged from a forged material having a coating film forming a lubricant on the surface thereof, and the cold forging is performed. As for the product, the cold method is used in a method of manufacturing a welded joint by laser welding two metal members with the film remaining portion on the surface as the welded portion without removing the film. To the extent that the forged product is forged from a forged material having a fluororesin film formed on the surface as a lubricant, to the extent that it does not deviate from the gist of the present invention, the shape and structure of metal members, welded parts, and welded joints Can be widely applied without limitation.

11 Ceramic heater elements 16, 17 Electrodes of heater elements 51 Metal members (cold forged products)
61 Metal members 100, 102 Welded joint 201 Ceramic heater (glow plug)

Claims (4)

At least one of the two metal members is a cold forged product formed by forging from a forged material having a coating film forming a lubricant on the surface, and the cold forged product has a coating film. In a method of manufacturing a welded joint by laser welding the two metal members with the film remaining portion on the surface as the welded portion in the state where the film remains.
A method for manufacturing a welded joint, characterized in that the cold forged product is forged from a forged material having a fluororesin film formed on the surface as a lubricant. The method for manufacturing a welded joint according to claim 1, wherein the cold forged product is made of stainless steel. One metal member is a shaft member, the other metal member is a tubular body, and the welded joint has one end of the shaft member fitted inside one end of the tubular body. One of claims 1 or 2, wherein the axial member is manufactured by laser welding two metal members with the outer peripheral edge of the joint formed by fitting as the welded portion. The method for manufacturing a welded joint according to the section. It is fixed to the rear end of the ceramic heater element so that the continuity between the rod-shaped ceramic heater element whose tip generates heat when energized and one of the electrode terminals formed on the ceramic heater element is maintained. A tubular body that is a metal member and a shaft member that is a metal member whose tip is fitted into the rear end portion of the tubular body by press fitting are provided, and the tubular body and the shaft member are formed. By laser welding the outer peripheral edge of the joint formed by the fitting as a welded portion, the terminal shaft structure for maintaining the continuity between the electrode terminal and the shaft member via the tubular body is provided. In the method of manufacturing ceramic heaters
At least one of the tubular body and the shaft material is cold forged from a forged material having a fluororesin film formed on the surface as a lubricant, and the fluororesin film remains in the cold forged product. A method for manufacturing a ceramic heater, which comprises laser welding with the outer peripheral edge of the joint as a welded portion.

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